[Federal Register Volume 81, Number 164 (Wednesday, August 24, 2016)]
[Rules and Regulations]
[Pages 58009-58162]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2016-18768]



[[Page 58009]]

Vol. 81

Wednesday,

No. 164

August 24, 2016

Part II





Environmental Protection Agency





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40 CFR Parts 50, 51, and 93





 Fine Particulate Matter National Ambient Air Quality Standards: State 
Implementation Plan Requirements; Final Rule

Federal Register / Vol. 81 , No. 164 / Wednesday, August 24, 2016 / 
Rules and Regulations

[[Page 58010]]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 50, 51, and 93

[EPA-HQ-OAR-2013-0691; FRL-9946-36-OAR]
RIN 2060-AQ48


Fine Particulate Matter National Ambient Air Quality Standards: 
State Implementation Plan Requirements

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: The Environmental Protection Agency (EPA) is finalizing 
requirements that state, local and tribal air agencies would have to 
meet as they implement the current and future national ambient air 
quality standards (NAAQS) for fine particulate matter 
(PM2.5). Specifically, this document provides details on 
meeting the statutory state implementation plan (SIP) requirements that 
apply to areas designated nonattainment for any PM2.5 NAAQS, 
such as: General requirements for attainment plan due dates and 
attainment dates; emissions inventories; attainment demonstrations; 
provisions for demonstrating reasonable further progress; quantitative 
milestones; contingency measures; and nonattainment New Source Review 
(NNSR) permitting programs, among other things. This rule clarifies the 
specific attainment planning requirements that apply to 
PM2.5 NAAQS nonattainment areas based on their 
classification (either Moderate or Serious), and the process for 
reclassifying Moderate areas to Serious. Additionally, in this document 
the EPA is revoking the 1997 primary annual standard for areas 
designated as attainment for that standard because the EPA revised the 
primary annual standard in 2012. The EPA first established the 
PM2.5 NAAQS in 1997, completed a review and revision of 
those standards in 2006, and most recently completed a review and 
revision of the PM2.5 NAAQS on December 14, 2012.

DATES: This final rule is effective on October 24, 2016.

ADDRESSES: The EPA has established a docket for this action, identified 
by Docket ID No. EPA-HQ-OAR-2013-0691. All documents in the docket are 
listed in the http://www.regulations.gov Web site. Although listed in 
the index, some information is not publicly available, e.g., 
Confidential Business Information or other information whose disclosure 
is restricted by statute. Certain other material, such as copyrighted 
material, is not placed on the Internet and will be publicly available 
only in hard copy. Publicly available docket materials are available 
either electronically in http://www.regulations.gov.

FOR FURTHER INFORMATION CONTACT: For general information on this rule, 
contact Mr. Rich Damberg, Office of Air Quality Planning and Standards, 
U.S. EPA, by phone at (919) 541-5592 or by email at 
[email protected]; or Mr. Patrick Lessard, Office of Air Quality 
Planning and Standards, U.S. EPA, by phone at (919) 541-5383 or by 
email at [email protected]. For information on the Information 
Collection Request (ICR), contact Mr. Butch Stackhouse, Office of Air 
Quality Planning and Standards, U.S. EPA, by phone at (919) 541-5208 or 
by email at [email protected].

SUPPLEMENTARY INFORMATION: 

I. General Information

A. Preamble Glossary of Terms and Acronyms

    The following are abbreviations of terms used in the preamble.

AERR Air Emissions Reporting Requirements
BACM Best Available Control Measures
BACT Best Available Control Technology
BART Best Available Retrofit Technology
BC Black Carbon
CAA Clean Air Act
CAIR Clean Air Interstate Rule
CAMx Comprehensive Air Quality Model with Extensions
CBI Confidential Business Information
CBSA Core-based Statistical Area
CDD Clean Data Determination
CFR Code of Federal Regulations
CMAQ Community Multi-Scale Air Quality Model
CSAPR Cross-State Air Pollution Rule
CSN Chemical Speciation Network
DOD Department of Defense
DOT Department of Transportation
EC Elemental Carbon
EGU Electric Generating Unit
EPA Environmental Protection Agency
Fe Iron
FEM Federal Equivalent Method
FIP Federal Implementation Plan
FRM Federal Reference Method
HCl Hydrogen Chloride
ICR Information Collection Request
LAER Lowest Achievable Emission Rate
MACT Maximum Achievable Control Technology
MATS Mercury and Air Toxics Standards
MSM Most Stringent Measures
MPO Metropolitan Planning Organization
NAAQS National Ambient Air Quality Standards
NAICS North American Industry Classification System
NAPAP National Acid Precipitation Assessment Program
NEI National Emissions Inventory
NESHAP National Emissions Standard for Hazardous Air Pollutants
NH3 Ammonia
NH4 Ammonium
NH4NO3 Ammonium Nitrate
NH4HSO4 Ammonium Bi-Sulfate
(NH4)2SO4 Ammonium Sulfate
NNSR Nonattainment New Source Review
NOX Nitrogen Oxides
NO3 Nitrate
NSPS New Source Performance Standards
O3 Ozone
OM Organic Mass
OMB Office of Management and Budget
PM Particulate Matter
PM2.5 Particulate Matter Equal to or Less than 2.5 
Microns in Diameter (Fine Particulate Matter)
PM10 Particulate Matter Equal to or Less than 10 Microns 
in Diameter
PRA Paperwork Reduction Act
PSD Prevention of Significant Deterioration
RACM Reasonably Available Control Measures
RACT Reasonably Available Control Technology
RFP Reasonable Further Progress
RICE Reciprocating Internal Combustion Engines
SIP State Implementation Plan
SOA Secondary Organic Aerosols
SO2 Sulfur Dioxide
SO4 Sulfate
TAR Tribal Authority Rule
TIP Tribal Implementation Plan
TIP Transportation Improvement Program
TSP Total Suspended Particles
[mu]m Micrometer (Micron)
VMT Vehicle Miles Traveled
VOC Volatile Organic Compounds

B. Entities Affected by This Rule

    Entities potentially affected directly by this final rule include 
state, local and tribal governments and air pollution control agencies 
responsible for attainment and maintenance of the NAAQS. Entities 
potentially affected indirectly by this final rule as regulated sources 
include owners and operators of sources that emit PM2.5, 
sulfur dioxide (SO2), oxides of nitrogen (NOX), 
volatile organic compounds (VOC) and/or ammonia (NH3). 
Parties affected by the conformity-related elements include state and 
local transportation and air quality agencies, metropolitan planning 
organizations (MPOs), and all federal agencies including the U.S. 
Department of Transportation, the U.S. Department of Defense, the U.S. 
Department of Interior and the U.S. Department of Agriculture. Others 
potentially affected indirectly by this final rule include members of 
the general public who live, work, or recreate in areas affected by 
elevated ambient PM2.5 levels in areas designated 
nonattainment for a PM2.5 NAAQS.

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C. Obtaining a Copy of This Document and Other Related Information

    In addition to being available in the docket, an electronic copy of 
this Federal Register document will be posted at http://www3.epa.gov/airquality/particlepollution/actions.html.

D. Organization of This Federal Register Document

    The information presented in this document is organized as follows:

I. General Information
    A. Preamble Glossary of Terms and Acronyms
    B. Entities Affected by This Rule
    C. Obtaining a Copy of This Document and Other Related 
Information
    D. Organization of This Federal Register Document
II. Background
    A. Introduction
    B. Overview of PM2.5 NAAQS and Implementation
    C. Atmospheric Chemistry of PM2.5 and Its Precursors
III. Requirements With Respect to the Treatment of PM2.5 
Precursors in Attainment Plans and the NNSR Program
    A. Background
    B. Summary of Proposal
    C. Final Rule
IV. Requirements for PM2.5 Moderate Nonattainment Area 
Plans
    A. Plan Due Dates
    B. Emissions Inventory Requirements
    C. Pollutants To Be Addressed in the Plan
    D. Attainment Plan Control Strategy
    E. Modeling for Attainment Demonstrations
    F. RFP Requirements
    G. Quantitative Milestones
    H. Contingency Measures
    I. Attainment Dates
    J. Attainment Date Extensions
V. Reclassification of a PM2.5 Moderate Nonattainment 
Area to Serious
    A. Discretionary Authority
    B. Mandatory Duty
VI. Requirements for PM2.5 Serious Nonattainment Area 
Plans
    A. Plan Due Dates
    B. Emissions Inventory Requirements
    C. Pollutants To Be Addressed in the Plan
    D. Attainment Plan Control Strategy
    E. Modeling for Attainment Demonstrations
    F. RFP Requirements
    G. Quantitative Milestones
    H. Contingency Measures
    I. Attainment Dates
    J. Attainment Date Extensions
VII. Requirements Under CAA Section 189(d) for PM2.5 
Serious Areas That Fail To Attain the NAAQS by the Applicable 
Attainment Date
    A. Plan Due Dates
    B. Emissions Inventory Requirements
    C. Pollutants To Be Addressed in the Plan
    D. Attainment Plan Control Strategy
    E. Modeling for Attainment Demonstrations
    F. RFP Requirements
    G. Quantitative Milestones
    H. Contingency Measures
    I. Attainment Dates
VIII. NNSR Requirements for PM2.5 Nonattainment Areas
    A. Background
    B. What are the final NNSR requirements for PM2.5?
    C. Transition Provisions for Major Source Permitting in 
PM2.5 Nonattainment Areas
IX. Other Requirements and Considerations for PM2.5 
Nonattainment Areas
    A. Waivers Under Section 188(f)
    B. Conformity Requirements
    C. Clean Data Policy
    D. Section 179B/International Border Areas
    E. Enforcement and Compliance
    F. Multi-Pollutant Considerations
    G. Measures To Ensure Appropriate Protections for Overburdened 
Populations
    H. Tribal Issues
    I. Voluntary Programs for Reducing Ambient PM2.5
    J. Improved Stationary Source Emissions Monitoring
    K. Stationary Source Test Methods for Emissions of Condensable 
PM2.5
X. Revocation of the 1997 Primary Annual PM2.5 NAAQS
    A. Background
    B. History of Revocation of Other NAAQS
    C. Requirements for Revocation and Related Anti-Backsliding 
Requirements for the 1997 Primary Annual PM2.5 NAAQS
XI. Environmental Justice Considerations
XII. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and 
Executive Order 13563: Improving Regulation and Regulatory Review
    B. Paperwork Reduction Act (PRA)
    C. Regulatory Flexibility Act (RFA)
    D. Unfunded Mandates Reform Act (UMRA)
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From 
Environmental Health and Safety Risks
    H. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution, or Use
    I. National Technology Transfer and Advancement Act
    J. Executive Order 12898: Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations
    K. Congressional Review Act (CRA)
    L. Determination Under Section 307(d)
    M. Judicial Review
XIII. Statutory Authority

II. Background

A. Introduction

    Ambient, or outdoor, air can contain a variety of pollutants, 
including particulate matter (PM). Airborne PM can be comprised of 
either solid or liquid particles, and can be a complex mixture of 
particles in both solid and liquid form. The most common constituents 
of airborne PM include the following: Sulfate (SO4); nitrate 
(NO3); ammonium (NH4); elemental carbon (EC); 
organic mass (OM); and inorganic material, generally referred to as 
``crustal'' material, which can include metals, dust, sea salt and 
other trace elements. Airborne PM can be of different sizes, commonly 
referred to as ``coarse'' and ``fine'' particles. Fine particles, in 
general terms, are PM with an aerodynamic diameter less than or equal 
to a nominal 2.5 micrometers ([micro]m). For this reason, particles of 
this size are referred to as PM2.5. PM2.5 
particles commonly include ``primary'' particles and ``secondary'' 
particles. Primary particles, or direct PM2.5, are emitted 
by sources directly into the air as solid or liquid particles (e.g., 
elemental carbon from diesel engines or wildfires, or condensable 
organic particles from gasoline engines). Secondary particles are 
formed in the atmosphere as a result of chemical reactions between 
specific pollutants known as PM2.5 precursors (e.g., 
reactions between NOX and SO2 emissions from 
mobile and stationary sources combined with ammonia to form ammonium 
nitrate and ammonium sulfate).
    The human health effects associated with long or short-term 
exposure to PM2.5 are significant and include premature 
mortality, aggravation of respiratory and cardiovascular disease (as 
indicated by increased hospital admissions and emergency room visits) 
and development of chronic respiratory disease. In addition, welfare 
effects associated with elevated PM2.5 levels include 
visibility impairment as well as effects on sensitive ecosystems, 
materials damage and soiling and climatic and radiative processes.\1\
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    \1\ For a complete discussion of the human health and welfare 
effects associated with exposure to elevated concentrations of 
particulate matter, see generally ``Integrated Science Assessment 
for Particulate Matter.'' U.S. Environmental Protection Agency, 
Office of Research and Development, National Center for 
Environmental Assessment--RTP Division, February 10, 2010. EPA/600/
R-08/139F. Available at: http://www3.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_isa.html. See Chapter 2.
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    On December 14, 2012, the EPA made revisions to the suite of the 
NAAQS for PM to provide requisite protection of public health and 
welfare with an adequate margin of safety. The EPA also made 
corresponding revisions to the data handling conventions for PM and the 
ambient air monitoring, reporting and network design requirements for 
PM. Specifically, the agency revised the primary annual 
PM2.5 standard by lowering the level from 15.0 to 12.0 
[mu]g/

[[Page 58012]]

m\3\ to provide increased protection against health effects associated 
with long- and short-term PM2.5 exposures. The EPA did not 
revise the secondary annual PM2.5 standard, which remains at 
15.0 [mu]g/m\3\.\2\ The EPA eliminated spatial averaging as part of the 
form of the PM2.5 annual standards to avoid potential 
disproportionate impacts on at-risk populations. In addition, the EPA 
retained the level and form of the primary and secondary 24-hour 
PM2.5 standards to continue to provide supplemental 
protection against health effects associated with short-term 
PM2.5 exposures. Although not directly relevant to this 
rulemaking with respect to implementation of the PM2.5 
NAAQS, it should be noted that in December 2012, the EPA also did not 
revise the level or form of the primary and secondary 24-hour 
PM10 NAAQS, which remain at 150 [mu]g/m\3\.\3\
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    \2\ 78 FR 3086 (January 15, 2013).
    \3\ This final rulemaking applies to implementation of the 
PM2.5 NAAQS. For the PM10 NAAQS, states and 
the EPA will continue to implement those NAAQS in accordance with 
the applicable statutory requirements of the CAA and the EPA's 
existing guidance in the ``The General Preamble for Implementation 
of Title I of the Clean Air Act (CAA) Amendments,'' 57 FR 13498 
(April 16, 1992); and ``State Implementation Plans for Serious PM-10 
Nonattainment Areas: Addendum to the General Preamble for the 
Implementation of Title I of the Clean Air Act (CAA) Amendments,'' 
59 FR 41998 (August 16, 1994). Throughout this preamble, these 
documents will be referred to as the ``General Preamble'' and the 
``Addendum,'' respectively.
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    Estimates show that attainment of the primary PM2.5 
standards will result in hundreds fewer premature deaths each year, 
prevent tens of thousands of hospital admissions each year and prevent 
hundreds of thousands of doctor visits, absences from work and school 
and respiratory illnesses in children annually.\4\ Attainment of the 
primary PM2.5 standards will have welfare co-benefits in 
addition to direct human health benefits. The term ``welfare co-
benefits'' covers both environmental and societal benefits of reducing 
pollution, such as reductions in visibility impairment, materials 
damage and ecosystem damage.\5\
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    \4\ ``Regulatory Impact Analysis for the Final Revisions to the 
National Ambient Air Quality Standards for Particulate Matter.'' 
U.S. Environmental Protection Agency, Office of Air Quality and 
Planning Standards, Health and Environmental Impacts Division, 
February 28, 2013. EPA-452/R-12-005. See http://www3.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_ria.html.
    \5\ Ibid.
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B. Overview of PM2.5 NAAQS and Implementation

1. General Background
    Sections 108 and 109 of the Clean Air Act (CAA or Act) govern the 
establishment, review and revision, as appropriate, of the NAAQS for 
widespread pollutants emitted from numerous and diverse sources 
considered harmful to public health and the environment. The CAA 
requires two types of NAAQS: (i) Primary standards, which set limits to 
protect public health, including the health of at-risk populations; and 
(ii) secondary standards, which set limits to protect public welfare, 
including protection against visibility impairment, damage to animals, 
crops, vegetation and buildings.
    The CAA also establishes important roles both for state and tribal 
governments and for the EPA in implementing the NAAQS. In accordance 
with the principle of cooperative federalism, both state and tribal 
governments and the EPA have respective authorities and 
responsibilities under the CAA. At the outset, the EPA has the 
authority and responsibility to promulgate the NAAQS. In turn, state, 
local and tribal air pollution control agencies (``air agencies'') have 
the authority and primary responsibility for developing and 
implementing attainment plans that contain emission control measures 
needed to achieve the air quality standards in a timely manner in each 
nonattainment area, consistent with the requirements of the CAA. The 
EPA often assists states by promulgating regulations or providing 
guidance for meeting implementation requirements and by providing 
technical tools, including information on control 
measures.6 7
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    \6\ It is important to note that the EPA does not have a 
mandatory duty to promulgate an implementation rule for the 
PM2.5 NAAQS, and the obligations of state and tribal air 
agencies to develop and submit an attainment plan are independent 
obligations and not conditioned upon the EPA promulgating an 
implementation rule for the PM2.5 NAAQS.
    \7\ When the term ``state'' is used hereafter, it will refer 
generically to states, local air agencies, and tribal governments 
electing to be treated as states for the purposes of implementing 
the CAA. Of additional note is that the 1998 Tribal Authority Rule 
(TAR), which is found in 40 CFR part 49, which implements section 
301(d) of the CAA, provides that tribes be treated in the same 
manner as a state when implementing certain sections of the CAA. It 
gives tribes the option of developing tribal implementation plans 
(TIPs), but unlike states, tribes are not required to develop 
implementation plans. Section IX.I of this preamble provides further 
discussion of tribal issues.
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    The EPA also promulgates nationally applicable control requirements 
and emission limits for many sources such as new motor vehicles, 
certain categories of new and modified major stationary sources and 
existing stationary sources of toxic air pollutants. These federal 
actions assist states by achieving emissions reductions from certain 
categories of sources nationwide, which can help with local attainment 
needs in a given nonattainment area. The EPA also has authority to 
provide funding, technical assistance, and guidance to states to 
support implementation of the NAAQS. In addition, the EPA has authority 
to address interstate transport of pollutants, in the event that states 
fail to do so. Through this authority, the EPA has addressed regional 
transport of pollutants from upwind states to downwind states, and has 
previously done so for purposes of the PM2.5 NAAQS.\8\ In 
addition, the EPA has the authority and responsibility to review and 
take action to approve or disapprove attainment plans submitted by 
states based upon whether they meet applicable statutory and regulatory 
requirements and to initiate the process for imposition of sanctions 
and/or issue federal implementation plans (FIPs) when states fail to 
fulfill their CAA obligations.
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    \8\ See 76 FR 48208 (August 8, 2011).
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2. History of PM2.5 NAAQS Implementation
    The EPA first promulgated annual and 24-hour NAAQS for 
PM2.5 in July 1997.\9\ Prior to that time, the EPA had 
addressed ambient PM through other means, first by regulating ``total 
suspended particles'' (TSP) and then later by regulating 
PM10. After protracted litigation, the 1997 NAAQS for 
PM2.5 were upheld by the U.S. Court of Appeals for the 
District of Columbia Circuit in March 2002.\10\ The EPA subsequently 
promulgated designations for the 1997 PM2.5 NAAQS 
nationwide, designating a number of areas as nonattainment for the 1997 
PM2.5 NAAQS, effective April 2005.\11\ In April 2007, the 
EPA issued a detailed implementation rule to assist states with the 
development of SIP submissions to meet attainment plan requirements for 
the 1997 NAAQS (the ``2007 PM2.5 Implementation Rule'').\12\ 
In May 2008, the EPA issued another rule to assist states with SIP 
submissions to meet the specific requirements for permitting programs 
for NNSR purposes in designated nonattainment areas (the ``2008 
PM2.5 NSR Rule'').\13\ The EPA premised both the 2007 
PM2.5 Implementation Rule and the 2008 PM2.5 NSR 
Rule on the EPA's interpretation of the statute that

[[Page 58013]]

nonattainment areas for the PM2.5 NAAQS were subject solely 
to the general attainment plan requirements of subpart 1, part D of 
title I of the CAA (``subpart 1'').
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    \9\ 62 FR 38652 (July 18, 1997).
    \10\ For a complete summary of legal challenges and related 
court decisions on the PM NAAQS, see generally 78 FR 3086 (January 
15, 2013).
    \11\ 70 FR 944 (January 5, 2005).
    \12\ 72 FR 20583 (April 25, 2007).
    \13\ 73 FR 28231 (May 16, 2008).
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    Section 109(d)(1) of the CAA requires the EPA periodically to 
review the science upon which the standards are based and the standards 
themselves, and to revise the standards as may be appropriate. In 
October 2006, the EPA promulgated revisions to the suite of the NAAQS 
for PM, and in particular the EPA revised the 24-hour PM2.5 
standards.\14\ In accordance with section 107(d), the EPA subsequently 
designated a number of areas as nonattainment for the revised 2006 24-
hour PM2.5 standards, effective December 2009.\15\ In March 
2012, the EPA issued a guidance document specifically to aid states in 
preparing their SIP submissions to meet attainment plan requirements 
for the 2006 24-hour PM2.5 NAAQS in designated nonattainment 
areas.\16\ The EPA's guidance for the 2006 PM2.5 NAAQS was 
based, in large part, on the requirements finalized in the 2007 
PM2.5 Implementation Rule, which the EPA based solely upon 
the statutory requirements of subpart 1.
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    \14\ 71 FR 61144 (October 17, 2006).
    \15\ 74 FR 58688 (November 13, 2009).
    \16\ Memorandum of March 2, 2012 (withdrawn June 6, 2013), from 
Stephen D. Page, Director, Office of Air Quality Planning and 
Standards, to the EPA Regional Air Directors, Regions I-X, 
``Implementation Guidance for the 2006 24-Hour Fine Particle 
(PM2.5) National Ambient Air Quality Standards (NAAQS).'' 
Available at: http://www3.epa.gov/ttn/naaqs/aqmguide/collection/cp2/20120302_page_implement_guidance_2006-24-hr_pm2.5_naaqs.pdf.
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    The EPA initiated a review of the PM2.5 NAAQS in June 
2007, proposing revisions to the primary and secondary PM2.5 
NAAQS on June 29, 2012.\17\ The EPA issued its final rule on December 
14, 2012, in which it lowered the primary annual PM2.5 
standard from 15.0 [mu]g/m\3\ to 12.0 [mu]g/m\3\ to provide increased 
protection against health effects associated with long- and short-term 
fine particle exposures.\18\ The EPA also eliminated spatial averaging 
as part of the form of the annual standard to avoid potential 
disproportionate impacts on at-risk populations.\19\ The EPA retained 
the level (35 [mu]g/m\3\) and form (98th percentile, averaged over 3 
years) of the primary 24-hour PM2.5 standard, as revised in 
2006, to provide supplemental protection against health effects 
associated with short-term PM2.5 exposures, especially in 
areas with high peak PM2.5 concentrations.\20\ This suite of 
primary PM2.5 standards provides increased public health 
protection, including the health of at-risk populations which include 
children, older adults, persons with pre-existing health and lung 
disease and persons of lower socioeconomic status, against a broad 
range of PM2.5-related effects that include premature 
mortality, increased hospital admissions and emergency department 
visits and development of chronic respiratory disease.\21\ With regard 
to the secondary (welfare-based) standards, the EPA retained the 
existing annual PM2.5 standard of 15.0 [mu]g/m\3\ and the 
existing 24-hour PM2.5 standard of 35 [mu]g/m\3\ to protect 
against PM-related non-visibility welfare effects including ecological 
effects, effects on materials and climate impacts. In addition, the 
secondary 24-hour PM2.5 standard provides protection for PM-
related visibility impairment.
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    \17\ 77 FR 38890 (June 29, 2012).
    \18\ 78 FR 3086 (January 15, 2013).
    \19\ Spatial averaging of monitored ambient air quality data was 
a feature of the prior PM2.5 NAAQS monitoring regulations 
which had the potential for masking particularly high 
PM2.5 concentrations at certain monitored locations 
within nonattainment areas.
    \20\ 71 FR 61144 (October 17, 2006).
    \21\ General information regarding the health effects associated 
with PM2.5 exposures is available at: http://www3.epa.gov/airquality/particlepollution/health.html. Additional 
information, such as the EPA's technical documents supporting the 
latest review of the standards, is available at: http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_index.html.
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    On January 4, 2013, shortly after the EPA promulgated the 2012 
revisions to the suite of PM NAAQS, the D.C. Circuit issued its 
decision in a challenge to the 2007 PM2.5 Implementation 
Rule and the 2008 PM2.5 NSR Rule. In NRDC v. EPA, the court 
held that the EPA erred in implementing the 1997 PM2.5 NAAQS 
pursuant only to the general implementation requirements of subpart 1, 
rather than also to the implementation requirements specific to 
particulate matter (PM10) in subpart 4, part D of title I of 
the CAA (``subpart 4'').\22\ The court reasoned that the plain meaning 
of the CAA requires implementation of the 1997 PM2.5 NAAQS 
under subpart 4 because PM2.5 particles fall within the 
statutory definition of PM10 and thus implementation of the 
PM2.5 NAAQS is subject to the same statutory requirements as 
the PM10 NAAQS. In addition, although the court stated that 
its decision that the EPA must implement the PM2.5 NAAQS 
pursuant to subpart 4 requirements meant that it did not have to reach 
decisions on other issues concerning the regulation of precursors to 
PM2.5, the court nonetheless noted that subpart 4 has 
specific requirements with respect to regulation of such precursors. As 
a result, the court remanded to the EPA both the 2007 PM2.5 
Implementation Rule and the 2008 PM2.5 NSR Rule, both of 
which were premised on the EPA's interpretation of the statute that 
subpart 1 was the only applicable subpart for the implementation of the 
1997 PM2.5 NAAQS in nonattainment areas. The court 
instructed the EPA ``to repromulgate these rules pursuant to subpart 4 
consistent with this opinion.'' Given the D.C. Circuit's opinion in 
NRDC v. EPA, the EPA withdrew its 2012 guidance document for the 2006 
24-hour PM2.5 NAAQS in June 2013. Because the court had 
concluded that the EPA and states must implement the PM2.5 
NAAQS consistent with the statutory requirements of subpart 4, the 
EPA's 2012 guidance for attainment plans for the 2006 PM2.5 
NAAQS premised solely upon subpart 1 requirements was no longer 
appropriate.
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    \22\ NRDC v. EPA, 706 F.3d 428 (D.C. Cir. 2013).
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    The EPA issued a notice of proposed rulemaking (NPRM) on March 23, 
2015 (80 FR 15340) titled, ``Fine Particulate Matter National Ambient 
Air Quality Standards: State Implementation Plan Requirements'' 
(PM2.5 SIP Requirements Rule) to meet a number of 
objectives. This final rule accomplishes those objectives. It clarifies 
how states should meet the statutory SIP requirements that apply to 
areas designated nonattainment for any PM2.5 NAAQS under 
subparts 1 and 4. It does so by establishing regulatory requirements 
and providing guidance that will be applicable to attainment plans for 
the 2012 PM2.5 NAAQS and any future revisions of the 
PM2.5 NAAQS, subject to revisions that may be necessary for 
implementation purposes in the future. In addition, this action 
responds to the D.C. Circuit's remand of the 2007 PM2.5 
Implementation Rule and the 2008 PM2.5 NSR Rule. As a 
result, the requirements of the rule will also govern future actions 
associated with states' ongoing implementation efforts for the 1997 and 
2006 PM2.5 NAAQS.
    The public comment period for the proposed PM2.5 SIP 
Requirements Rule closed on May 29, 2015, and the EPA received 56 
comments during that period. The preamble to this final rule includes 
discussion of the most significant comments received on the proposal 
and how the EPA considered them in developing the agency's final action 
concerning the specific nonattainment planning requirements. The 
Response to Comments document that accompanies this final rule provides 
more detailed responses to the significant comments received. The 
public comments received on the NPRM and the EPA's Response to Comment

[[Page 58014]]

document are posted in the docket at http://www.regulations.gov (Docket 
ID No. EPA-HQ-OAR-2013-0691).

C. Atmospheric Chemistry of PM2.5 and Its Precursors

1. Overview
    In order to determine how to regulate sources of direct 
PM2.5 and PM2.5 precursors to attain the 
PM2.5 NAAQS in a given nonattainment area, it is necessary 
to understand the basic chemical processes that cause or contribute to 
the formation of ambient PM2.5. Accordingly, an 
understanding of these processes is necessary to design appropriate 
regulations for implementation of the PM2.5 NAAQS.
    As noted earlier, the term PM2.5 refers to particles of 
solid and liquid material less than 2.5 microns in aerodynamic 
diameter.\23\ ``Primary'' PM2.5 is emitted directly from 
emissions sources or activities, such as from diesel fuel combustion, 
wood burning, construction activities, and unpaved roads, and it 
includes both filterable and condensable particles.\24\ ``Secondary'' 
PM2.5 is formed as a result of emissions of certain 
precursor gases that undergo chemical reactions in the atmosphere. The 
principal precursor gases that contribute to secondary PM2.5 
formation are SO2, from the combustion of coal or other high 
sulfur fuels; NOX, from many types of fossil fuel 
combustion; VOC, from certain fuels, solvents and industrial processes; 
and ammonia, from sources such as animal feeding operations, wastewater 
treatment and fertilizer. To illustrate the types of sources that emit 
relevant pollutants, Table 1 provides National Emissions Inventory 
(NEI) data for 2011 that represent nonattainment area anthropogenic and 
wildfire emissions estimates for direct PM2.5 and the four 
main PM2.5 precursor gases from major source sectors.
---------------------------------------------------------------------------

    \23\ The regulatory definition of PM2.5 includes 
particles with an upper 50 percent cut-point of 2.5[mu]m aerodynamic 
diameter (the 50 percent cut-point diameter is the diameter at which 
the sample collects 50 percent of the particles and rejects 50 
percent of the particles). PM2.5 particles have a 
penetration curve as measured by a reference method based on 
Appendix L of 40 CFR part 50 and designated in accordance with 40 
CFR part 53, by an equivalent method designed in accordance with 40 
CFR part 53, or by an approved regional method designated in 
accordance with Appendix C of 40 CFR part 58.
    \24\ Certain commercial or industrial activities involving high 
temperature processes (e.g., fuel combustion, metal processing, 
cooking operations) emit gaseous pollutants into the ambient air 
that rapidly condense into particle form. These ``condensable'' PM 
emissions exist almost entirely in the 2.5 or less micron range and 
can consist of organic material, sulfuric acid and metals.

       Table 1--Total Emissions of PM2.5 and Precursors for Major Sectors in PM2.5 Nonattainment Areas \a\
                                                 [In tons/year]
                            Source: 2011 National Emissions Inventory (Version 2) \b\
----------------------------------------------------------------------------------------------------------------
            Category               Direct PM2.5         SO2             NOX             VOC             NH3
----------------------------------------------------------------------------------------------------------------
Fuel combustion, electric                 11,339         324,658          82,509           3,001           3,572
 generating utilities (EGUs)....
Fuel combustion, industrial.....          10,286          23,762          57,690           6,251             892
Fuel combustion, other..........          29,582           8,224          60,636          32,320           8,819
Chemical and allied products....           1,504           1,329           1,056           2,828             685
Metals processing...............           4,037          19,490           4,543           4,586             130
Petroleum and related industries           1,534           7,273           3,775          18,830             215
Other industrial processes......          24,168           8,466          22,599          24,928           1,094
Solvent utilization.............           1,089              39              56         242,022              68
Storage and transport...........           3,420             628           7,067          55,410           3,684
Waste disposal and recycling....           4,143             830           4,130          16,492          19,389
Onroad mobile...................          21,073           2,598         540,800         234,136          17,525
Offroad mobile..................          13,660           5,874         239,169         152,504             150
Miscellaneous (includes                  158,565           7,368          13,734         248,835         236,577
 emissions from fire,\c\ dust
 and some agricultural
 operations)....................
                                 -------------------------------------------------------------------------------
    Total.......................         284,401         410,540       1,037,764       1,042,144         292,800
----------------------------------------------------------------------------------------------------------------
\a\ There were 33 areas designated as nonattainment for the 1997, 2006, or 2012 PM2.5 NAAQS as of June 6, 2016.
  These areas were comprised of 67 whole or partial counties. The emissions data in this table represents whole
  county emissions for the 67 counties because such data is readily available in EPA databases. Actual emissions
  totals for the 33 nonattainment areas in aggregate would be somewhat lower because some nonattainment areas
  include partial counties.
\b\ For more details on the definitions of the emission categories listed in Table 1, see Sector/Tier crosswalk
  table for the 2011 NEI, available at: ftp://ftp.epa.gov/EmisInventory/2011/doc/scc_eis_crosswalk_2011neiv1.xlsx.
\c\ Emissions from fire include wildfire, prescribed fire, and agricultural burning.

2. Composition and Sources of PM2.5 Constituents
    PM2.5 is a complex and highly variable mixture of 
particles, but the majority of PM2.5 by mass is often 
comprised of five constituents: (i) OM; (ii) EC; (iii) crustal 
material; (iv) ammonium sulfate 
((NH4)2SO4); and (v) ammonium nitrate 
(NH4NO3).\25\ The discussion that follows 
provides an overview of each of the five major components of 
PM2.5, all of which are known to contribute to ambient 
PM2.5 levels in areas throughout the U.S.\26\ Section 
II.C.3.d of this preamble provides more details on the atmospheric 
chemistry involved in the formation of sulfate, nitrate and OM, to 
illustrate the importance of controlling emissions of PM2.5 
precursors as part of any comprehensive strategy to reduce ambient 
PM2.5 levels in excess of the NAAQS. Section II.C.4 of this 
preamble presents a brief overview of PM2.5 composition by 
region of the U.S.
---------------------------------------------------------------------------

    \25\ Seinfeld J.H. and Pandis S.N., 2006. Atmospheric Chemistry 
and Physics: From Air Pollution to Climate Change. 2nd edition, J. 
Wiley, New York.
    \26\ U.S. Environmental Protection Agency, 2004. ``The Particle 
Pollution Report: Current Understanding of Air Quality and Emissions 
through 2003.'' Office of Air Quality Planning and Standards, 
Emissions, Monitoring, and Analysis Division, December 2004. 
Available at: http://www.epa.gov/airtrends/reports.html.
---------------------------------------------------------------------------

    OM is the fraction of ambient PM2.5 with the most 
diverse chemical composition, containing potentially thousands of 
different organic compounds (i.e., those compounds containing carbon) 
composed primarily of carbon, hydrogen, oxygen and nitrogen. Both 
primary particles and secondary particles contribute to ambient OM 
concentrations, with

[[Page 58015]]

combustion sources being the dominant type of emissions sources. 
Another portion of primary OM particles results from direct emissions 
of organic compounds from sources of incomplete combustion, such as gas 
and diesel engines. Secondary OM particle formation involves oxidation 
of both anthropogenic and biogenic (plant-derived) VOC, and can involve 
other, more complex chemical reactions. Further details of the 
chemistry behind the formation of secondary OM, known more commonly as 
secondary organic aerosols (SOA), are described in Section II.C of this 
preamble.
    EC refers to particulate carbon that has a graphitic molecular 
structure, and is sometimes referred to as ``black carbon'' (BC). It is 
emitted directly from emission sources and does not undergo any 
significant reactions with other gases in the atmosphere. EC particles 
result from primary emissions involving combustion, especially from 
diesel-fueled vehicles, but also from other processes involving the 
burning of fossil fuels. The latter include anthropogenic sources such 
as boilers and waste disposal. In addition, some EC particles originate 
from biomass combustion such as from prescribed fires, wildfires and 
residential wood combustion.
    Crustal PM is comprised of particles of soil and oxides of metals 
from some industrial processes. Compounds comprised of elements such as 
silicon, aluminum, iron, calcium, titanium, magnesium and potassium, as 
well as oxygen, are major components.\27\ Sources of crustal 
PM2.5 include windblown dust, dust from mechanical 
resuspension (e.g. dust from construction activities or vehicles 
driving on unpaved roads) and some forms of combustion, especially of 
coal. Crustal PM2.5 comprised of elements, like iron (Fe), 
and their oxides can also be emitted from industrial sources.
---------------------------------------------------------------------------

    \27\ Appel, K.W., Pouliot, G.A., Simon, H., Sarwar, G., Pye, 
H.O.T., Napelenok, S.L., Akhtar, F., and Roselle, S.J., 2013. 
Evaluation of dust and trace metal estimates from the Community 
Multiscale Air Quality (CMAQ) model version 5.0, Geoscientific Model 
Development Discussions 61859-1899; Sorooshian, A., Shingler, T., 
Harpold, A., Feagles, C.W., Meixner, T., and Brooks, P.D., 2013. 
Aerosol and precipitation chemistry in the southwestern United 
States: spatiotemporal trends and interrelationships, Atmospheric 
Chemistry and Physics 13, 7361-7379.
---------------------------------------------------------------------------

    The remaining portion of ambient PM2.5 is mostly 
composed of SO4, NO3 and NH4, which 
react in the ambient air to form ammonium sulfate 
((NH4)2SO4) and ammonium nitrate 
(NH4NO3). Another common PM2.5 
particle is ammonium bi-sulfate (NH4HSO4). In 
some areas, less common ions such as chloride are also found in 
PM2.5 samples in the form of particles that include sodium 
chloride and ammonium chloride. Particle-bound water is often also 
associated with this fraction of PM2.5. Sulfate, nitrate and 
ammonium particles originate through both primary and secondary 
mechanisms, although the vast majority of these PM2.5 
particles are formed through secondary formation, as described in the 
following section.
3. Secondary Formation of PM2.5 From Gaseous Precursors
    a. Overview. The composition of PM2.5 is complex and 
highly variable due in part to the large contribution of secondary 
PM2.5 to total fine particle mass in most locations, and to 
the complexity of secondary particle formation processes. A large 
number of possible chemical reactions, often non-linear in nature, can 
convert the gases SO2, NOX, VOC and ammonia to 
PM2.5. Thus, these gases are precursors to PM2.5. 
A brief discussion of SO4, NO3 and SOA formation, 
as well as the role of ammonia in their formation, follows.
    b. SO4 Formation. SO2 is emitted mostly from the 
combustion of fossil fuels in boilers operated by electric utilities 
and other industries, with less than 10 percent of SO2 
emissions nationwide currently coming from other industrial sources, 
such as oil refining and pulp and paper production.\28\ When 
SO2 oxidizes it forms sulfuric acid, a highly corrosive 
compound toxic to humans and to ecosystems that contributes to acid 
deposition (acid rain). In the presence of ammonia, however, sulfuric 
acid will react to form (NH4)2SO4, a 
less acidic compound and one of the five major components of 
PM2.5. If there is not enough ammonia present to fully 
neutralize the sulfuric acid, part of it may convert to 
NH4HSO4, which is more acidic than 
(NH4)2SO4, but less so than sulfuric 
acid. There is a large amount of emerging scientific evidence that 
SO2 may also contribute to the formation of SOA from 
biogenic VOC emissions (see section later on SOA). Sulfate levels in 
the ambient air peak in summer months due to increased SO2 
emissions, generally from electric generating units (EGUs), and from 
meteorological conditions that are conducive to sulfate formation.
---------------------------------------------------------------------------

    \28\ U.S. Environmental Protection Agency, 2013. ``2008 National 
Emissions Inventory: Review Analysis and Highlights.'' Office of Air 
Quality Planning and Standards, Air Quality Assessment Division, May 
2013. EPA-454/R-005. Available at: https://www.epa.gov/sites/production/files/2015-07/documents/2008report.pdf.
---------------------------------------------------------------------------

    c. NO3 Formation. The main sources of NOX emissions are 
combustion of fossil fuel in boilers and mobile sources, accounting for 
more than 80 percent of national anthropogenic NOX emissions 
(based on the 2011 NEI), with boilers and EGUs contributing about 27 
percent and mobile sources contributing 56 percent. Oxides of nitrogen 
react in the atmosphere to form nitric acid, another prime contributor 
to acid deposition in the environment. Nitric acid converts to ammonium 
nitrate, one of the five main components of PM2.5, in the 
presence of ammonia. Low temperatures and high relative humidity create 
ideal conditions for the formation of ammonium nitrate, typically 
leading to higher atmospheric levels in winter months and lower levels 
in summer months.\29\
---------------------------------------------------------------------------

    \29\ Carlton, A.G., Pinder, R.W., Bhave, P.B., Pouliout, G.A., 
2010. To What Extent Can Biogenic SOA Be Controlled, Environmental 
Science and Technology 44(9), 3376-80.
---------------------------------------------------------------------------

    d. SOA Formation. As discussed earlier, the OM component of ambient 
PM2.5 is a complex mixture of hundreds or even thousands of 
anthropogenic and biogenic organic compounds. These compounds are 
either emitted directly from sources (i.e., as ``primary'' 
PM2.5) or formed by reactions in the ambient air to make SOA 
(i.e., as ``secondary'' PM2.5).
    VOC (both anthropogenic and biogenic) are key precursors to the SOA 
component of PM2.5. The relative importance of these 
compounds in the formation of organic particles varies between 
geographic areas, depending upon local emission sources, atmospheric 
chemistry and season of the year. It should be further noted that not 
all inventoried VOC may be contributing to the formation of organic 
particles. For example, chemical reactions involving VOC are generally 
accelerated in warmer temperatures, and for this reason studies show 
that SOA typically comprises a higher percentage of PM2.5 in 
the summer than in the winter.\30\
---------------------------------------------------------------------------

    \30\ Pandis S.N., Harley R.A., Cass G.R., and Seinfeld J.H., 
1992. Secondary Organic Aerosol Formation and Transport, Atmospheric 
Environment, 26, 2266-82.
---------------------------------------------------------------------------

    Anthropogenic sources of VOC include mobile sources, petrochemical 
manufacturing, oil and gas emissions, fire emissions, and solvents.\31\ 
In addition, some biogenic VOC, emitted by vegetation such as trees, 
can also contribute significantly to SOA formation, especially in 
heavily forested areas, such as the southeastern U.S. It should be 
noted, however, that

[[Page 58016]]

anthropogenic contributions to SOA are likely highest in the wintertime 
when biogenic SOA levels are lower; conversely, in the summertime, 
biogenic contributions to SOA are likely higher. Despite significant 
progress that has been made in understanding the origins and properties 
of SOA, it remains the least understood component of PM2.5 
and continues to be a significant topic of research and investigation.
---------------------------------------------------------------------------

    \31\ Carlton, A.G., Bhave, P.B., Napelenok, S.L., Edney, E.O., 
Sarwar, G., Pinder, R.W., Pouliout, G.A., and Houyoux, M. (2010), 
Model Representation of Secondary Organic Aerosol in CMAQ4.7, 
Environmental Science and Technology 44(22), 8553-60.
---------------------------------------------------------------------------

    e. Role of Ammonia in Sulfate, Nitrate and SOA Formation. Ammonia 
is a gaseous pollutant emitted by natural and anthropogenic sources. 
The EPA's 2011 NEI shows that the two main sources of ammonia emissions 
are fertilizer application (27 percent) and livestock raising (54 
percent). It should be noted that the 2011 NEI indicates that mobile 
sources in the aggregate contribute about 3 percent of nationwide 
ammonia emissions. Catalytic converters installed on light-duty 
gasoline vehicles are designed to convert NOX to nitrogen 
(N2); however, some ammonia is formed as a secondary product 
and emitted during this process.
    As indicated earlier, ammonia plays an important role in 
neutralizing acids, such as sulfuric acid and nitric acid, in clouds, 
precipitation and particles. On the other hand, deposited ammonia can 
contribute to problems of eutrophication in water bodies due to its 
nutritive properties.\32\ Ammonia would not exist in particles if not 
for the presence of acidic species with which it can combine to form a 
particle. In the eastern U.S., sulfate, nitrate and the ammonium 
associated with them can together account for between roughly 30 
percent and 75 percent of the total PM2.5 mass in a given 
area. The ammonium portion by itself roughly accounts for between 5 
percent and 20 percent of the total PM2.5 mass in the 
East.\33\
---------------------------------------------------------------------------

    \32\ Seinfeld, J.H. and Pandis, S.N. (1998), Atmospheric 
Chemistry and Physics: From Air Pollution to Climate Change, 1st 
edition, J. Wiley, New York.
    \33\ NARSTO, 2003. Particulate Matter Science for Policy Makers. 
A NARSTO Assessment. Parts 1 and 2. NARSTO. Management Office 
(Envair), Pasco, Washington. Available at: http://narsto.org/pm_science_assessment.
---------------------------------------------------------------------------

    f. Role of NOX in Nitrate and SOA Formation. In addition to the 
contribution of NOX emissions to secondary particulate 
nitrate formation, NOX also reacts with anthropogenic and 
biogenic VOC to enhance the secondary formation of organic compounds 
that make up SOA. NOX is thus involved in all secondary PM 
chemistry, not just in particulate nitrate formation.\34\
---------------------------------------------------------------------------

    \34\ Carlton, A.G., Pinder, R.W., Bhave, P.B., and Pouliout, 
G.A., 2010. To what extent can Biogenic SOA be Controlled, 
Environmental Science and Technology 44(9), 3376-3380.
---------------------------------------------------------------------------

4. Fine Particulate Composition by Location.
    Table 2 shows regional 3-year mean concentrations (2009-2011) of 
PM2.5 and its main components at sites in the Chemical 
Speciation Network (CSN).\35\ In addition to the mean values for all 
sites in each region, the table includes the minimum and maximum 
observed PM2.5 and species concentrations for sites within 
each region. These data illustrate broad observed spatial patterns 
across the U.S. in PM2.5 concentrations and its composition. 
For example, PM2.5 concentrations are highest on average in 
the Central and West regions. Sulfate mass comprises a larger fraction 
of PM2.5 than nitrate mass in the northeastern U.S., whereas 
nitrate has a greater contribution than sulfate in the West. OM is the 
dominant component in all regions, with the highest concentrations of 
OM on average found in the West, Northwest and Southeast. On a 
percentage basis, the concentrations of EC and crustal material are 
relatively low throughout all regions of the U.S. compared to the other 
major PM2.5 components.
---------------------------------------------------------------------------

    \35\ The organic matter (OM) values in Table 2 were calculated 
by multiplying the measured organic carbon (OC) concentrations by 
1.6 (Turpin and Lim (2001), Aerosol Science and Technology, 35, 602-
610). PM2.5 concentrations come from measurements of the 
Federal Reference/Equivalance Methods (FRM/FEM) rather than from the 
CSN PM2.5 measurement.
---------------------------------------------------------------------------

    The composition of PM2.5 also varies between urban and 
rural areas. This is reflective of the distribution of urban and 
regional emission sources, atmospheric reactions and transport of fine 
particles. More details about the spatial distribution and origins of 
PM2.5 components can be found in the docket for this 
action.\36\
---------------------------------------------------------------------------

    \36\ Reff and Rao, Memo to the docket, 2013.

                                        Table 2--PM2.5 Chemical Composition Data at 2009-2011 Nonattainment Sites
                                                         [Source: EPA Speciation Trends Network]
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                     Concentration  ([mu]g/m\3\)
                   Region                              Statistic           -----------------------------------------------------------------------------
                                                                              Sulfate      Nitrate         OM           EC        Crustal       PM2.5
--------------------------------------------------------------------------------------------------------------------------------------------------------
Central....................................  Min ([mu]g/m\3\).............         1.46          0.3         2.73         0.31         0.01         8.92
                                             Mean ([mu]g/m\3\)............         2.69         1.49         3.57         0.68         0.26        11.63
                                             Max ([mu]g/m\3\).............         4.19         3.34         4.81          1.1          1.0        13.51
                                             N............................           61           61           50           50           61           42
East North Central.........................  Min ([mu]g/m\3\).............         0.83         0.38         1.97         0.19         0.01         6.03
                                             Mean ([mu]g/m\3\)............         1.68          1.8         2.84         0.48         0.19         9.86
                                             Max ([mu]g/m\3\).............         2.51         3.57         3.69         0.79         0.61        11.87
                                             N............................           29           28           20           20           28           23
North East.................................  Min ([mu]g/m\3\).............         0.58         0.12         1.74         0.14            0         4.42
                                             Mean ([mu]g/m\3\)............         2.06         0.97         3.14         0.69         0.17         9.33
                                             Max ([mu]g/m\3\).............         5.12         2.26         5.05         1.69         0.52        15.05
                                             N............................           59           59           39           39           59           46
North West.................................  Min ([mu]g/m\3\).............         0.24         0.05         2.91         0.42         0.01         6.06
                                             Mean ([mu]g/m\3\)............         0.54          0.4         5.02         0.81         0.15         8.33
                                             Max ([mu]g/m\3\).............         1.09         1.79         8.44         1.25         0.53        10.96
                                             N............................           33           33           13           13           33           14
South......................................  Min ([mu]g/m\3\).............         0.88         0.18         1.36         0.12         0.02         5.22
                                             Mean ([mu]g/m\3\)............         2.06          0.8         3.32         0.57          0.5        10.05
                                             Max ([mu]g/m\3\).............         3.08         1.67          5.1         1.48         2.38        14.27
                                             N............................           36           27           23           23           36           23
South East.................................  Min ([mu]g/m\3\).............          1.6          0.2         1.75         0.37         0.01         6.76
                                             Mean ([mu]g/m\3\)............         2.39         0.53         4.12         0.63         0.26        10.77

[[Page 58017]]

 
                                             Max ([mu]g/m\3\).............         4.33         1.51         5.71          1.2         0.85        13.38
                                             N............................           44           43           30           30           43           29
South West.................................  Min ([mu]g/m\3\).............         0.34         0.07         2.34         0.46         0.02          5.3
                                             Mean ([mu]g/m\3\)............         0.63         0.49         3.01          0.7          0.5         7.93
                                             Max ([mu]g/m\3\).............         1.13         2.65         4.39         1.04         1.96         9.73
                                             N............................           46           46           11           11           46           12
West.......................................  Min ([mu]g/m\3\).............         0.33         0.08         1.79         0.52         0.01         6.84
                                             Mean ([mu]g/m\3\)............          0.9          1.4         5.22         0.85         0.32        11.49
                                             Max ([mu]g/m\3\).............         2.08         5.14        10.27         1.56         1.05        16.57
                                             N............................           44           44           20           20           44           21
West North Central.........................  Min ([mu]g/m\3\).............         0.29         0.06         1.22         0.09            0         3.23
                                             Mean ([mu]g/m\3\)............         0.67         0.48         3.16         0.44         0.22         7.25
                                             Max ([mu]g/m\3\).............         1.79         2.02         8.28         1.21         0.53        13.72
                                             N............................           30           30            7            7           30           10
--------------------------------------------------------------------------------------------------------------------------------------------------------

III. Requirements With Respect to the Treatment of PM2.5 
Precursors in Attainment Plans and the NNSR Program

A. Background

    The EPA recognizes that the treatment of PM2.5 
precursors is an important issue in developing a PM2.5 
attainment plan \37\ or implementing the NNSR program in a 
nonattainment area. The EPA has long recognized the scientific basis 
for concluding that there are multiple scientific precursors to 
PM10\38\and PM2.5.\39\ Appropriate control of 
precursors is especially important for attaining the PM2.5 
NAAQS because secondarily formed particles (such as ammonium nitrate, 
ammonium sulfate, and some portion of organic carbon) comprise a large 
fraction of ambient PM2.5 concentrations in many 
nonattainment areas. However, in some PM2.5 nonattainment 
areas, a particular precursor or precursors may not contribute 
significantly to PM2.5 levels that exceed the relevant 
NAAQS. This section of the preamble describes optional precursor 
demonstrations that a state may choose to submit to the EPA in order to 
establish that sources of particular precursors need not be regulated 
for purposes of attainment planning or in the NNSR permitting program 
for a specific nonattainment area.
---------------------------------------------------------------------------

    \37\ Note that in this document the term ``attainment plan'' 
refers to a state's required SIP submittal elements other than those 
elements related to the NNSR program.
    \38\ See the General Preamble, 57 FR 13498, (April 16, 1992).
    \39\ See 2007 PM2.5 Implementation Rule, 72 FR 20586 
(April 25, 2007). The rule discussed the fact that emissions of 
SO2, NOX, VOC and ammonia are factual and 
scientific precursors to PM2.5.
---------------------------------------------------------------------------

    Section III.A of this preamble provides background on the January 
2013 NRDC v. EPA court decision, in which the court found that subpart 
4 of part D of the CAA presumptively requires regulation of all 
PM2.5 precursors, except under certain circumstances. 
Section III.A of this preamble also provides information on the 
requirements of the subpart 4 provisions applicable to attainment plans 
for PM NAAQS. Section III.B of this preamble provides a summary of the 
precursor demonstration options in the proposed rule and comments 
received. Section III.C of this preamble provides a discussion of the 
optional precursor demonstrations provided in the final rule.
    The final rule describes how in some cases a state may demonstrate 
that the adoption of additional emission reduction measures for a 
particular precursor is not needed for purposes of achieving 
expeditious attainment nor for advancing the attainment date by at 
least a year in a nonattainment area. (This is referred in the preamble 
as an ``expeditious attainment demonstration.'') The rule also 
describes three optional approaches for demonstrating that a particular 
precursor is not a significant contributor to ambient PM2.5 
levels that exceed the standard in a particular nonattainment area. 
These three precursor demonstrations are: (a) Comprehensive precursor 
demonstration; (b) major stationary source precursor demonstration; and 
(c) NNSR precursor demonstration. If a state chooses to submit a 
precursor demonstration, it must do so in accordance with provisions in 
the final rule. A state may use this type of demonstration to justify 
that sources of the given precursor may be excluded from certain 
PM2.5 attainment plan requirements and/or NNSR requirements, 
although the particular sources and requirements eligible for exclusion 
will depend on the type of demonstration submitted.
    Section III.C of this preamble also outlines certain technical 
issues, such as the appropriate geographic scope of a precursor 
demonstration, recommended significance thresholds, and recommended 
analytical approaches for evaluating precursor contributions to ambient 
PM2.5 levels and the sensitivity of PM2.5 levels 
in an area to decreases or increases of emissions.
    January 2013 court decision in NRDC v. EPA. As explained in the 
proposed rule, the EPA's approach to the evaluation and regulation of 
PM2.5 precursors pursuant to subpart 1 in both the 2007 
PM2.5 Implementation Rule and the 2008 PM2.5 NSR 
Rule was invalidated in the court's 2013 decision in NRDC v. EPA. As an 
example of the distinction between the divergent substantive 
requirements of subpart 1 and subpart 4 of part D of the CAA, the court 
noted that subpart 4 has specific provisions related to regulation of 
precursors not present in subpart 1. Although the court stated that it 
was not reaching a decision on the issue of regulation of precursors, 
the court's opinion specifically discussed the approach to precursors 
in both the 2007 PM2.5 Implementation Rule and the 2008 
PM2.5 NSR Rule and compared that approach to section 189(e) 
of the CAA, which contains the sole explicit reference to the 
regulation of precursors in subpart 4. The court decision included the 
following statements with regard to precursors:

    Ammonia is a precursor to fine particulate matter, making it a 
precursor to both PM2.5

[[Page 58018]]

and PM10. For a PM10 nonattainment area 
governed by subpart 4, a precursor is presumptively regulated. See 
42 U.S.C. 7513a(e) [CAA section 189(e)]. Under the PM rules 
challenged here, the EPA established a rebuttable presumption 
against regulating ammonia unless a state or the EPA ``provides an 
appropriate technical demonstration'' that shows emissions from 
ammonia ``significantly contribute to PM concentration in the 
nonattainment area.'' 40 CFR 51.1002(c)(4)(i). When Congress enacted 
subpart 4, it sought to end this administrative gamesmanship.\40\
---------------------------------------------------------------------------

    \40\ NRDC v. EPA, 706 F.3d 428, 437, n.7 (D.C. Cir. 2013).

    The court continued to hold that ``[i]n light of our disposition, 
we need not address the petitioners' challenge to the presumptions in 
40 CFR 51.1002(c)(3)-(4) that volatile organic compounds and ammonia 
are not PM2.5 precursors, as subpart 4 expressly governs 
precursor presumptions.'' \41\
---------------------------------------------------------------------------

    \41\ NRDC v. EPA, 706 F.3d 428, 437, n.10 (D.C. Cir. 2013).
---------------------------------------------------------------------------

    Section 189(e) of the CAA establishes requirements for precursors 
to PM10 (which the court concluded expressly includes 
PM2.5) and provides that: ``The control requirements 
applicable under plans in effect under this part for major stationary 
sources of PM10 shall also apply to major stationary sources 
of PM10 precursors, except where the Administrator 
determines that such sources do not contribute significantly to 
PM10 levels which exceed the standard in the area.'' The 
court reasoned that the EPA's approach to precursors in the 2007 
PM2.5 Implementation Rule and 2008 PM2.5 NSR Rule 
had the effect of reversing the presumption embodied within subpart 4 
that a state should address all PM10 precursors unless the 
state has made a specific showing why regulation of a particular 
precursor is not necessary.
    Subpart 4 of part D of the CAA. The provisions of subpart 4 (CAA 
sections 188-190) do not define the term ``precursor'' for purposes of 
PM10, nor do they explicitly require the control of any 
specifically identified PM precursor. However, the statutory definition 
of ``air pollutant'' provides that the term ``includes any precursors 
to the formation of any air pollutant, to the extent the Administrator 
has identified such precursor or precursors for the particular purpose 
for which the term `air pollutant' is used.'' See CAA section 302(g). 
The EPA has determined that SO2, NOX, VOC and 
ammonia are factual and scientific precursors to PM and, thus, the 
attainment plan requirements of subpart 4 apply equally to emissions of 
direct PM2.5 and these precursors in PM2.5 
nonattainment areas, except as otherwise provided in the statute. 
Section 189(e) of the CAA explicitly requires the control of precursors 
from all major stationary sources in PM2.5 nonattainment 
areas unless there is a demonstration to the satisfaction of the 
Administrator that such major stationary sources do not contribute 
significantly to PM levels that exceed the standards in the 
nonattainment area.\42\ Section 189(e) of the CAA contains the only 
express exception to control requirements for PM precursors under 
subpart 4.
---------------------------------------------------------------------------

    \42\ The EPA notes that it previously had addressed the 
requirements of subpart 4 for precursors, specifically within the 
context of the requirements of CAA section 189(e), in the General 
Preamble. See the Federal Register published on April 16, 1992 (57 
FR 13498, 13539, 13541 and 13542).
---------------------------------------------------------------------------

    When Congress adopted the 1990 CAA Amendments, the NAAQS for 
PM10 was in effect, but no standard for PM2.5 had 
yet been established. At that time, it was understood that the 
interaction of PM10 precursors in the atmosphere led to the 
formation of PM10 in many areas. However, in some of the 
PM10 nonattainment areas, air quality problems were caused 
primarily by area sources emitting direct PM emissions (e.g., a 
nonattainment area with numerous wood burning devices, or with 
substantial sources of windblown coarse particles from construction 
sites), and precursor emissions from major stationary sources were not 
considered to make a significant contribution to the local 
nonattainment problem. For cases such as these, CAA section 189(e) 
provided a possible exception to the requirement to control all 
PM10 precursors from major sources in a particular 
nonattainment area.
    Consistent with past practice for implementation of the 
PM10 NAAQS, the EPA proposed to interpret the control 
requirements addressed by CAA section 189(e) to include RACM/RACT (and 
additional reasonable measures) for Moderate nonattainment areas, BACM/
BACT (and additional feasible measures) for Serious nonattainment 
areas, most stringent measures (MSM) (for Serious areas as applicable) 
and NNSR on all major sources of precursors in the nonattainment areas. 
The General Preamble indicates that consideration of precursors is 
necessary for attainment plans, and it recognizes the specific 
applicability of CAA section 189(e) to both existing and new major 
stationary sources, including new and modified sources subject to NNSR 
permitting requirements. Even though CAA section 189(e) only explicitly 
contemplates exceptions to control requirements for PM2.5 
precursors from major stationary sources in nonattainment areas, the 
EPA believes that by analogy it has authority to promulgate regulations 
that allow states to determine that it is not necessary to regulate 
PM2.5 precursors from other sources in nonattainment areas 
as well, under appropriate circumstances.
    While CAA section 189(e) expressly requires control of precursors 
from major stationary sources, it is clear that subpart 4 and other CAA 
provisions collectively require the control of direct PM2.5 
and all PM2.5 precursors from all types of sources (i.e., 
stationary sources, area sources, and mobile sources) as may be needed 
for the purposes of demonstrating attainment as expeditiously as 
practicable in a given nonattainment area.\43\ Longstanding EPA 
guidance for RACM has indicated that the state should inventory all 
emissions of the relevant pollutants and precursors in the 
nonattainment area, evaluate the available control measures for the 
relevant pollutant and precursors to determine if such controls are 
economically and technologically feasible, and then adopt those 
measures that are deemed reasonably available and necessary in order to 
attain the NAAQS as expeditiously as practicable.\44\ The EPA guidance 
has also long indicated that the state must ensure that there is no 
other collection of available control measures that if adopted would 
advance the attainment date by at least 1 year.\45\ Section IV.D of 
this preamble provides additional discussion on the development of 
emissions inventories and the identification, adoption and 
implementation of reasonably available control measures for 
PM2.5 nonattainment areas, including a discussion particular 
to wildfire and wildland prescribed fire found in Section IV.D.3.b.\46\
---------------------------------------------------------------------------

    \43\ See CAA requirements for states to demonstrate attainment 
``as expeditiously as practicable'' (CAA section 188(c)(1); CAA 
section 172(a)(2)).
    \44\ 57 FR 13498 (April 16, 1992).
    \45\ In the context of the PM10 NAAQS, the EPA has 
concluded that ``advancement of the attainment date'' should mean an 
advancement of at least 1 calendar year. See State Implementation 
Plans; General Preamble for the Implementation of Title I of the CAA 
Amendments of 1990, 57 FR 13498 (April 16, 1992). See also Sierra 
Club v. EPA, 294 F.3d 155 (D.C. Cir. 2002).
    \46\ See Section IV of this preamble for a thorough discussion 
of past policy and guidance on reasonably available control measures 
(RACM) and reasonably available control technology (RACT). Section 
IV of this preamble discusses the EPA's final policy that under 
subpart 4, for Moderate areas that demonstrate that attainment by 
the statutory attainment date is impracticable, RACM and RACT would 
constitute all those technologically and economically feasible 
measures available for sources in the area that can be implemented 
within 4 years of designation, but they would not constitute the 
complete set of measures required to demonstrate attainment as 
expeditiously as practicable.

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[[Page 58019]]

    In light of the court's decision in NRDC v. EPA, the EPA considers 
it necessary to describe how states must address regulation of 
PM2.5 precursors in attainment plans and NNSR programs for 
the PM2.5 NAAQS. The court's decision made clear that 
appropriate regulation of all precursors in designated nonattainment 
areas is presumptively required under the CAA, and the regulation of 
precursors in general is a critical issue for attainment of the 
PM2.5 NAAQS because secondarily formed particles are a 
substantial component of PM2.5 concentrations in most 
nonattainment areas of the United States.
    For the purposes of this rule, the EPA considers that for all 
PM2.5 nonattainment areas, the PM2.5 precursors 
for regulatory purposes are the four scientific precursors that the EPA 
has previously identified: SO2, NOX, VOC and 
ammonia. This rule does not include any national presumption that would 
allow a state to exclude, without a demonstration, sources of emissions 
of a particular precursor from further analysis for attainment plan or 
NNSR control requirements in a PM2.5 nonattainment area. 
However, the EPA's interpretation of subpart 4 requirements with 
respect to precursors in attainment plans for PM10, as set 
out in the General Preamble, contemplates that the state may develop an 
attainment plan that regulates only those precursors that are necessary 
to control for purposes of timely attainment in the nonattainment area, 
i.e., states may determine that only certain precursors need to be 
regulated in a particular PM2.5 nonattainment area for 
attainment purposes.\47\ Courts have upheld this approach to the 
requirements of subpart 4 for PM10.\48\ The EPA believes 
that application of a similar approach to PM2.5 precursors 
under subpart 4 is appropriate and reasonable.
---------------------------------------------------------------------------

    \47\ See the Federal Register published on April 16, 1992 (57 FR 
13498, 13540 and 13541).
    \48\ See, e.g., Assoc. of Irritated Residents v. EPA, et al., 
423 F.3d 989 (9th Cir. 2005).
---------------------------------------------------------------------------

    The EPA interprets the CAA to require states to inventory emissions 
and adopt control measures as appropriate for direct PM2.5 
and all PM2.5 precursors. This interpretation is based on 
CAA section 302(g), which defines an air pollutant as including 
precursors contributing to the formation of that pollutant; the EPA's 
identification of the four main scientific PM2.5 precursors; 
and the CAA provisions requiring adoption of all control measures 
(i.e., RACM and RACT) needed in order to attain the standard as 
expeditiously as practicable. CAA section 189(e) explicitly requires 
that the control requirements applicable for major stationary sources 
of direct PM2.5 emissions must also apply to major 
stationary sources of PM2.5 precursors, unless the state 
provides a showing that emissions of a particular precursor from major 
stationary sources do not contribute significantly to levels that 
exceed the standard in the nonattainment area of concern. Thus, the 
statute generally requires control of all PM2.5 precursors 
in a nonattainment area, but it provides an express exception 
applicable to major stationary sources in such areas if an appropriate 
demonstration is made.
    The EPA also notes that CAA section 189(e) contains certain 
ambiguities that require interpretation. For example, CAA section 
189(e) does not specify the precise method by which a state or the EPA 
should determine whether precursor emissions from major stationary 
sources do not ``contribute significantly'' to levels which exceed the 
standard in a given nonattainment area. Subpart 4 also does not 
explicitly address whether it would be appropriate to include a 
potential exemption from precursor controls for all source categories 
under certain circumstances, because a specific exemption from 
precursor controls is expressly made available in the statute only for 
major stationary sources. These issues are addressed in this final 
rule.

B. Summary of Proposal

    In the proposal, the EPA sought comment on how states could focus 
regulatory efforts on the appropriate PM2.5 precursors in 
each area. Rather than simply requiring each state to regulate direct 
PM2.5 and all PM2.5 precursors without regard to 
whether that would be appropriate and necessary for expeditious 
attainment of the NAAQS, EPA took comment on different approaches for 
states to focus regulatory efforts on the appropriate pollutants. Thus, 
in the proposal, the EPA sought comment on three options by which a 
state could demonstrate that emission control requirements for a 
particular PM2.5 precursor or precursors would not be 
required for sources in a particular nonattainment area.\49\ The 
proposed ``precursor demonstration'' options outlined procedures and 
technical analyses a state could elect to perform to demonstrate that 
control requirements for sources of a particular precursor are not 
needed for expeditious attainment, or that a particular 
PM2.5 precursor does not significantly contribute to 
PM2.5 concentrations in the area. The proposal indicated 
that if the EPA were to approve such a precursor demonstration, then it 
would not be necessary for the state to adopt control requirements for 
sources of the precursor or precursors in the PM2.5 
attainment planning process generally and/or in the NNSR permitting 
process for that particular area. The EPA requested comment on whether 
the final rule should include one or more precursor demonstration 
approaches, and whether it would be appropriate to combine specific 
elements from different options.
---------------------------------------------------------------------------

    \49\ The three proposed options were: (1) Option 1--two 
independent analyses consisting of an attainment planning analysis 
showing that control measures for a particular precursor are not 
needed for expeditious attainment and an optional NNSR analysis 
showing that major stationary sources of a particular precursor do 
not contribute significantly to levels that exceed the 
PM2.5 standard, (2) Option 2--a single analysis (for 
purposes of attainment planning and NNSR) showing that all emissions 
of a particular precursor do not contribute significantly to levels 
that exceed the PM2.5 standard, and (3) Option 3--a 
single analysis (for purposes of attainment planning and NNSR) 
showing that control measures for all sources for a particular 
precursor are not needed for expeditious attainment.
---------------------------------------------------------------------------

    The EPA also described three technical issues associated with any 
such precursor demonstration and sought comment on the following: (1) 
The appropriate geographic scope of the analysis; (2) whether specific 
types of technical analyses (such as evaluating the contribution of the 
precursor to total PM2.5 concentrations, or evaluating the 
sensitivity of the area to decreases or increases of the precursor) 
should be required for a precursor demonstration; and (3) whether the 
EPA should establish a bright-line ambient air quality threshold (e.g., 
3 percent of the level of the relevant NAAQS in the area) to define an 
air quality change below which a precursor contribution should not be 
considered to be significant, thereby establishing that control of 
sources of the precursor is unnecessary in the area.
    Lastly, the EPA indicated in the proposal that if a state had an 
approved precursor demonstration for a particular precursor in a 
Moderate area and the EPA later reclassifies the area to Serious, then 
the state would be required to develop an updated precursor 
demonstration if the state were again interested in having the 
precursor treated as insignificant for purposes of the Serious area 
plan. An updated precursor demonstration is necessary because many 
factors (e.g., emissions, air quality and fine particle concentrations) 
could have changed substantially since the original

[[Page 58020]]

demonstration for the Moderate area attainment plan.\50\
---------------------------------------------------------------------------

    \50\ For more information on the proposed precursor 
demonstration options, see 80 FR 15340, at 15350-15362.
---------------------------------------------------------------------------

C. Final Rule

    The EPA received many comments on the three proposed precursor 
demonstration approaches. Most commenters supported the inclusion of 
some kind of optional precursor demonstration in the final rule. Some 
commenters suggested that states should have the flexibility to develop 
any of the types of demonstrations that the EPA described in the three 
proposed options. One group of commenters opposed any option that would 
exempt a particular precursor from control measures even if the state 
could demonstrate it could expeditiously attain the standard by the 
attainment date without controls on sources of the precursor. Another 
group of commenters suggested that if only one option is finalized, it 
should allow a state to rely on a sensitivity analysis to show that 
changes in emissions of a particular precursor would not have a 
substantial contribution to PM2.5 concentrations in the 
area.
    The EPA agrees with commenters who suggested that states should 
have the flexibility to conduct different types of precursor 
demonstrations appropriate to the area in question. Regardless of the 
type of precursor demonstration, the state will still need to provide 
adequate technical support and that demonstration will be subject to 
EPA approval. Thus, the EPA concludes that the specific form of the 
demonstration is not as crucial as its content and adequacy, in light 
of the facts and circumstances in the area. The EPA disagrees with 
commenters who argued that a state should not be able to determine 
insignificance for a precursor based on an attainment planning analysis 
showing expeditious attainment in the area without adopting new 
emissions reduction measures for the precursor in question. This 
approach has been upheld under subpart 4 with respect to implementation 
of the PM10 NAAQS, and the EPA finds that it is reasonable 
to allow for a similar policy when implementing the PM2.5 
NAAQS.\51\
---------------------------------------------------------------------------

    \51\ See, e.g., Assoc. of Irritated Residents v. EPA, et al., 
423 F.3d 989 (9th Cir. 2005).
---------------------------------------------------------------------------

    After consideration of the numerous comments received on this 
issue, the EPA has decided to adopt a final approach that allows 
exclusion of certain precursor sources from certain SIP requirements, 
provided that states make the appropriate demonstrations. However, the 
EPA has revised the details of the specific types of demonstrations 
based on further evaluation of the comments received. Section III.C.1 
of this preamble describes the expeditious attainment demonstration, in 
which a state shows that control requirements for a particular 
precursor are not needed for expeditious attainment by the Moderate 
area attainment date. Section III.C.2 of this preamble describes the 
three types of optional precursor demonstrations a state may submit to 
the EPA to establish that emissions of a precursor do not contribute 
significantly to PM2.5 levels in a particular nonattainment 
area: (a) Comprehensive precursor demonstration; (b) major stationary 
source precursor demonstration; and (c) NNSR precursor demonstration. 
Each option is described in detail in the following subsections.
    Section III.C.3 of this preamble highlights various technical 
issues associated with precursor demonstrations, including the 
appropriate geographic scope of the analyses, thresholds for 
characterizing an insignificant air quality change, and different 
analytical methods for assessing precursor contributions. Section 
III.C.4 of this preamble discusses certain procedural issues associated 
with precursor demonstrations. Section III.C.5 of this preamble 
addresses other relevant comments and responses.
1. Expeditious Attainment Demonstration
    As noted earlier, the EPA's interpretation of subpart 1 and 4 
requirements with respect to precursors in attainment plans for 
PM10 has been that a state may develop an attainment plan 
that regulates only those precursors that are necessary to control for 
purposes of timely attainment in the area. The EPA believes that a 
similar policy approach for PM2.5 precursors is also 
appropriate.
    Under the expeditious attainment demonstration, a state may be able 
to determine through its identification of RACM/RACT for existing 
sources in an area whether expeditious attainment could be achieved 
without new control measures for a particular PM2.5 
precursor. It is important to note that this approach is available to a 
state only if the demonstration for the area (1) ensures attainment by 
the Moderate area attainment date (i.e., the end of the sixth calendar 
year after designation), and (2) ensures that the area could not 
advance the attainment date by at least 1 year if it were to adopt 
reasonable control measures for the precursor in question. If the state 
determines that the area cannot practicably attain by the relevant 
Moderate area attainment date, then the state still would have the 
option of developing one of the precursor demonstrations described in 
Sections III.C.2.a-c of this preamble for showing that the precursor 
contribution is not significant. The expeditious attainment option is 
not available for Serious nonattainment areas because BACM/BACT 
measures for Serious areas are not solely limited to those measures 
needed for expeditious attainment under this final rule. (See further 
discussion of this issue in Section VI.D of this preamble, Serious Area 
Attainment Plan Control Strategies.)
    For the expeditious attainment demonstration, the required analysis 
is what is already needed for a Moderate area attainment demonstration: 
The identification of reasonably available control measures that 
provide for expeditious attainment by the attainment date, and a 
determination that attainment cannot be advanced through the imposition 
of other reasonable measures (i.e. RACM/RACT and other reasonable 
measures that are identified for the area but not necessary for the 
area to attain within 6 years). See 40 CFR 51.1006(a). After a 
comprehensive emissions inventory has been developed, the state should 
then identify potential control measures and assess factors related to 
technological feasibility, economic feasibility, and time needed for 
implementation for all types of sources in the area (i.e., stationary, 
area, mobile) and all precursors emitted by such sources as included in 
the emissions inventory.
    After identifying the set of control measures that are economically 
and technologically feasible for all precursors, the state may be able 
to show (using best available information on emissions, control 
options, technologies, and costs, along with appropriate air quality 
modeling) that those measures that could be identified as RACM/RACT and 
additional reasonable measures would not need to include new control 
measures for sources of a given precursor.\52\ The state could show 
this by demonstrating that one set of control measures to be adopted 
into the plan would provide for attainment by the statutory attainment 
date; and that an additional set of potential control measures 
(including measures for the precursor in question, and remaining 
measures for all other contributing pollutants) collectively

[[Page 58021]]

would not advance the attainment date by at least 1 year (i.e., enable 
the area to attain 1 year earlier). Under these circumstances, the 
state would not need to adopt the second set of measures (including 
measures for the particular precursor) because they would not expedite 
attainment of the NAAQS in the area.
---------------------------------------------------------------------------

    \52\ See Section IV.D.1 of this preamble, Background for 
Attainment Plan Control Strategy, for further discussion of 
``additional reasonable measures.''
---------------------------------------------------------------------------

    If the attainment planning demonstration shows that the area can 
attain the NAAQS expeditiously without new emission reduction measures 
for a particular precursor, the state would be required to adopt 
control measures for only a subset of the four PM2.5 
precursors as part of the attainment plan for the area, and existing 
sources in the nonattainment area would not be required to adopt new 
control measures for the particular precursor. Accordingly, the state 
would not need to address the precursor in the reasonable further 
progress plan, in quantitative milestones and associated reports, or be 
required to adopt contingency measures to reduce the precursor. See 40 
CFR 51.1009(a)(4)(i). (Note that for purposes of meeting the 
contingency measure requirement, however, the state would still have 
the discretion to adopt control measures as contingency measures for a 
precursor that would otherwise not be subject to RACM/RACT 
requirements.)
    It also should be noted that development of an approvable 
attainment plan that does not include new control measures for a 
particular precursor would not exempt the state from the requirements 
to address the same precursor with respect to the NNSR program, nor 
would it excuse the state from reconsidering the significance of the 
precursor to the PM nonattainment problem in any subsequent Serious 
area SIPs that could be required for the nonattainment area.
2. Optional Precursor Demonstrations
    a. Comprehensive Precursor Demonstration. In line with the EPA's 
proposal for precursor insignificance demonstrations, the EPA is 
finalizing an option whereby a state may submit a comprehensive 
precursor demonstration as part of any Moderate or Serious area 
attainment plan. The use of the term ``comprehensive'' here refers to 
the fact that the demonstration covers all existing stationary, area, 
and mobile sources, rather than major sources alone. Note, however, 
that the comprehensive precursor demonstration does not affect 
precursor requirements for future new sources. Under this comprehensive 
precursor demonstration, the state would need to show that emissions of 
a particular precursor from all existing stationary, area, and mobile 
sources located in the nonattainment area do not contribute 
significantly to PM2.5 levels that exceed the standard in 
the area. The state would first need to evaluate the contribution of 
all existing source emissions of the particular precursor to 
PM2.5 concentrations that exceed the PM2.5 
standard (described in Section III.C.2 of this preamble). If the state 
cannot demonstrate via the concentration-based precursor demonstration 
that sources of a particular precursor have an insignificant 
contribution to PM2.5 levels in an area,, then the state 
could still demonstrate that the precursor's contribution is 
insignificant by conducting a sensitivity analysis to evaluate the 
sensitivity of ambient PM2.5 concentrations in the 
nonattainment area to decreases in the precursor emissions in the area 
(e.g., whether a given decrease is insignificant) as discussed further 
in Section III.C.2.c of this preamble.
    If a comprehensive precursor demonstration for a precursor is 
approved, the state would not establish a motor vehicle emissions 
budget for the relevant precursor, and regional emissions analyses for 
the precursor would not be required to be included in transportation 
conformity determinations. This is consistent with the transportation 
conformity rule's provisions concerning PM2.5 precursors. 
(See 40 CFR 93.102(b)(2)(iv) and (v)). Separately, states may continue 
to determine that on-road emissions of PM2.5 precursors are 
insignificant even if emissions of a given precursor from other sources 
are significant. (See 40 CFR 93.102(b)(2)(iv) and (v) and 93.109(f)). 
With regard to general conformity, if a state precursor demonstration 
is approved for one or more precursors, federal agencies would not be 
required to address the affected precursor(s) in general conformity 
determinations.
    If a comprehensive precursor demonstration is approved by the EPA, 
then in developing the attainment plan for the area, the state would 
not be required to adopt control measures (e.g., RACM/RACT) for the 
precursor for any existing stationary, area, or mobile sources in the 
nonattainment area. The attainment plan also would not be required to 
address the relevant precursor in meeting the RFP or quantitative 
milestone requirements, or in adopting contingency measures because 
these requirements commonly apply to pollutants that are the subject of 
emission reduction measures in the attainment plan. (Note that for 
purposes of meeting the contingency measure requirement, however, the 
state would still have the discretion to adopt emission reduction 
requirements on the precursor in question, in conjunction with emission 
reduction requirements on other pollutants.) The state would still need 
to include the precursor in all nonattainment area emission inventory 
submissions.
    It also should be noted that development of an approvable 
attainment plan that does not include new control measures for a 
particular precursor would not exempt the state from the requirements 
to address that precursor with respect to the NNSR program, nor would 
it excuse the state from reevaluating the significance of the precursor 
to the PM nonattainment problem in any subsequent Serious area SIPs 
that could be required for the nonattainment area.
    b. Major Stationary Source Precursor Demonstration. The state has 
the option of submitting a major stationary source precursor 
demonstration as part of any Moderate or Serious area plan, consistent 
with CAA section 189(e). This demonstration differs from the 
comprehensive demonstration in that it only evaluates existing major 
sources, and therefore may only be used to justify the exclusion of 
existing major sources from the control requirements for the applicable 
precursor. Although the EPA expects that most states making precursor 
demonstrations will opt for comprehensive demonstrations, this option 
is provided to offer additional flexibility. The requirements for a 
stationary source precursor demonstration are nearly identical to those 
of the comprehensive precursor demonstration, except the state would 
only need to show that a particular precursor from all existing major 
stationary sources located in the nonattainment area do not contribute 
significantly to PM2.5 levels that exceed the standard in 
the area. Similar to the comprehensive demonstration, the state must 
first evaluate the contribution of major stationary source emissions of 
the particular precursor to PM2.5 levels that exceed the 
PM2.5 standard (pursuant to section III.C.3.c of this 
preamble). If the state cannot demonstrate via the concentration-based 
precursor demonstration that sources of a particular precursor have an 
insignificant contribution to PM2.5 levels in an area, then 
the state could still try to demonstrate that the precursor is 
insignificant by conducting a sensitivity analysis to evaluate the 
sensitivity of PM2.5 levels in the nonattainment area to a 
reduction in major stationary source

[[Page 58022]]

emissions in the area (pursuant to Section III.C.3.d of this preamble).
    If such a demonstration is approved by the EPA, then in developing 
the attainment plan for the area, the state would not be required to 
adopt control measures for the precursor for existing major stationary 
sources in the nonattainment area. The attainment plan also would not 
be required to address the emissions of the relevant precursor from 
major stationary sources in meeting the RFP or quantitative milestone 
requirements, or in adopting contingency measures. (Note that for 
purposes of meeting the contingency measure requirement, however, the 
state would still have the discretion to adopt emission reduction 
requirements on the precursor in question, in conjunction with emission 
reduction requirements on other pollutants.) The state would still need 
to include stationary source emissions of the precursor in all 
nonattainment area emission inventory submissions.
    Note that a state might consider developing a major stationary 
source demonstration to avoid the requirement to adopt nonattainment 
planning control measures for a particular precursor emitted from 
existing major stationary sources in the area if the state does not 
believe that it could comprehensively demonstrate that the precursor 
does not have a significant contribution, and if major stationary 
source emissions of the precursor do not make up a very large 
percentage of the emissions inventory in the area. For example, it 
might be possible that in a particular area the overwhelming amount of 
emissions of a certain precursor could originate from mobile or area 
sources, or both, but not from existing major stationary sources. If 
the EPA approves a major stationary source precursor demonstration, the 
attainment plan would still need to evaluate and potentially impose 
control requirements for the relevant precursor for existing non-major 
stationary sources, area sources and mobile sources in order to 
demonstrate expeditious attainment.
    It also should be noted that development of an approvable 
attainment plan that does not include new control measures for a 
particular precursor would not exempt the state from the requirements 
to address that precursor with respect to the NNSR program, nor would 
it excuse the state from the requirement to evaluate and adopt control 
measures for the precursor in any subsequent Serious area SIPs that 
could be required for the nonattainment area.
    c. NNSR Precursor Demonstration. The state also has the option of 
submitting a NNSR precursor demonstration as part of any Moderate or 
Serious area plan. This specific type of precursor demonstration is the 
only one of the three demonstrations described in this section that if 
approved would exempt new and modified major stationary sources of a 
precursor from regulation under the NNSR permitting program.
    Under the NNSR precursor demonstration, the state would need to 
conduct an analysis to evaluate the sensitivity of PM2.5 
levels in the nonattainment area to an increase in emissions of a 
particular precursor in the area, simulating the response of the 
atmosphere (and associated PM2.5 concentrations) to the 
addition of one or more new or modified stationary sources in the 
nonattainment area (see Section III.C.3.d of this preamble). Section 
III.C.3 of this preamble addresses additional issues related to 
technical analyses for precursor demonstrations.
    The EPA believes that this approach to interpreting CAA section 
189(e) of the statute as it applies to control requirements for the 
NNSR program is appropriate because (1) an analysis that evaluates the 
sensitivity of the atmosphere in an area to increases in emissions 
would most closely replicate the scenario of concern, where precursor 
emissions from new major stationary sources or major modifications are 
added to the existing inventory for the area; and (2) this approach 
would take into consideration the specific atmospheric chemistry and 
emissions profile that varies from area to area. For example, one 
nonattainment area may have low emissions of a particular precursor 
from all existing sources (and corresponding low current ambient 
contributions from the precursor), but the introduction of a new major 
stationary source of emissions of that particular precursor could in 
some cases significantly contribute to the ambient PM2.5 
levels in the area because other pollutants with which the precursor 
reacts in the atmosphere could be relatively abundant.
    For purposes of the NNSR precursor demonstration, the state is not 
required to first evaluate the contribution of existing major sources 
to PM2.5 levels that exceed the standard in the area, as 
would be required by the comprehensive and major stationary source 
demonstrations. Since NNSR permitting requirements do not apply to 
existing sources (unless such sources engage in a major modification), 
the EPA does not believe it is necessary or reasonable to require 
evaluation of current emissions from existing major stationary sources 
as it would not inform the question of whether increases in emissions 
would significantly contribute to PM2.5 levels in the area. 
Note, however, that the NNSR precursor demonstration is used only to 
justify an exclusion of sources of the precursor from the NNSR control 
requirements in the area. A state would need to pair the NNSR precursor 
demonstration with another type of precursor demonstration to address 
control requirements beyond NNSR, as described previously for each type 
of demonstration.
3. Technical Issues Associated With Precursor Demonstrations
    a. Geographic Area. The proposal indicated that the emissions 
inventory to be used as the starting point for the comprehensive, major 
stationary source, and NNSR precursor demonstrations should represent 
emissions from sources located in the nonattainment area, and the final 
rule remains unchanged. The EPA believes that limiting the emissions 
inventory for these analyses to sources in the nonattainment area is 
appropriate based on the statutory construction of CAA section 189(e), 
in which the relevant test is whether ``such sources contribute 
significantly to [PM2.5] levels which exceed the standard in 
the area.'' The EPA believes that a reasonable interpretation is that 
this provision applies to sources in the nonattainment area.
    b. Significance Threshold. The proposal described the concept of 
including a bright-line threshold of 3 percent of the relevant NAAQS in 
the rule for precursor demonstrations other than the expeditious 
attainment approach, such that if an air quality contribution was found 
not to exceed the threshold amount, then it would not be considered 
significant. The proposal also included an option for no bright-line 
threshold in the final rule, based on the recognition that all 
nonattainment area situations are different.
    Some commenters supported the bright-line threshold concept, but 
they suggested thresholds across a broad range, from less than 1 
percent of the relevant NAAQS, to up to 5 percent. Some commenters 
stated that inclusion of a bright-line threshold of 3 percent of the 
relevant NAAQS was preferred because without such a threshold, states 
would be unsure about whether their proposed precursor assessment would 
be acceptable. Other commenters supported having no bright line 
threshold because the circumstances of each area are unique, and for 
that reason

[[Page 58023]]

each area should be considered on a case-by-case basis.
    The EPA found merit in comments supporting both proposed options. 
The EPA agrees that an insignificance threshold can help avoid 
situations where lack of clarity may lead to delays in the EPA 
assessment of precursor demonstrations. At the same time, the EPA 
understands that PM2.5 nonattainment problems are complex 
and vary greatly based on the facts and circumstances of each area.
    After considering the range of comments on this issue and the 
complexity of the types of analyses that may be conducted for precursor 
demonstrations, the EPA has decided that the best approach is for the 
final rule to codify the availability and basic requirements for 
precursor demonstrations, but to provide technical details (such as a 
recommended approach for assessing whether a particular air quality 
concentration threshold can be considered to be insignificant in a 
given area) in guidance supporting this final rule.
    c. Concentration-based Contribution Analysis. The first type of 
analysis required for the comprehensive precursor demonstration (or, 
less commonly, the major stationary source precursor demonstration) is 
an existing source contribution analysis that would demonstrate whether 
emissions of a particular precursor from all existing sources (or, for 
a major source precursor demonstration, emissions from existing major 
sources) in the nonattainment area do not significantly contribute to 
PM2.5 concentrations that exceed the standard in the area. 
The state should use technically credible approaches for estimating the 
ambient contribution of emissions of a particular precursor to total 
PM2.5 concentration in the nonattainment area. The EPA 
anticipates that the forthcoming technical guidance will discuss the 
possible use of advanced air quality modeling tools to estimate 
precursor contributions to total PM2.5 concentrations in an 
area. For example, several photochemical air quality models (e.g., 
Community Multi-Scale Air Quality Model (CMAQ) and the Comprehensive 
Air Quality Model with Extensions (CAMx)) can be used to quantify the 
contributions of precursor emissions to PM2.5 concentrations 
in the area.\53\
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    \53\ For more information on CMAQ, see http://www.epa.gov/air-research/community-multi-scale-air-quality-cmaq-modeling-system-air-quality-management. For more information on CAMx, see http://www.camx.com/.
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    Other techniques such as the analysis of chemical speciation data 
and emissions inventories also may be appropriate for determining the 
contribution of a particular precursor to PM2.5 
concentrations. For example, SO2 emissions and measured 
sulfate concentrations (in the form of ammonium sulfate or other forms) 
may be small in a particular nonattainment area. A simple analysis of 
measured species concentrations (attributable to a particular 
precursor) combined with nonattainment area emissions and other 
relevant data analyses may be sufficient to show that a precursor does 
not contribute significantly to PM2.5 concentrations in the 
area.
    d. Sensitivity-based Contribution Analysis. A second type of 
analysis may also be used in developing comprehensive precursor 
demonstrations (or, less commonly, major source precursor 
demonstrations). This type of analysis is a sensitivity-based 
contribution analysis that would demonstrate the degree to which 
concentrations in the nonattainment area are sensitive to decreases of 
a precursor. Changes in PM2.5 concentrations at a particular 
location often will not be linear with respect to changes in 
PM2.5 precursor emissions; therefore, sensitivity analyses 
are useful for better understanding the complexity and variability of 
the atmospheric chemistry affecting PM2.5 concentrations in 
different areas across the country. A sensitivity-based contribution 
analysis evaluating the effect of precursor emissions reductions could 
be used in the event the state cannot demonstrate via the 
concentration-based analysis that sources of a particular precursor 
have an insignificant contribution to PM2.5 levels in an 
area.
    The EPA also requires a sensitivity-based analysis as the means for 
conducting the NNSR precursor demonstration. In this case, in contrast 
to the assessment of decreases described for the comprehensive (or 
major source) precursor demonstration for existing sources, the 
appropriate sensitivity analysis is one that evaluates the impact of 
precursor emissions increases--without the need for a separate 
evaluation of existing source contribution to PM2.5 
concentrations. This analysis is clearly most appropriate for NNSR, 
which is a program that governs emissions increases. Thus, the final 
rule requires that such an analysis must be used if a state chooses to 
submit a NNSR precursor demonstration.
    The EPA states in the final rule that a sensitivity-based analysis 
is an appropriate approach for understanding whether emissions of a 
precursor make an insignificant contribution to PM2.5 levels 
in an area. Several main components of PM2.5 are secondarily 
formed in the atmosphere and are the result of chemical reactions 
between various PM2.5 precursors. In some areas, one 
precursor may be abundant while a second precursor, with which it 
primarily reacts, may be less abundant. In such cases, a sensitivity 
analysis may find that reducing emissions of the second, less abundant 
precursor (the ``limiting'' precursor) may be generally more effective 
for reducing PM2.5 concentrations. It may also find that 
increasing emissions of the less abundant precursor may be more 
effective at increasing PM2.5 concentrations than a 
comparable tonnage increase of a more abundant precursor.
    In another type of area, the PM2.5 concentrations that 
exceed the standard may be commonly dominated by primary 
PM2.5 emissions rather than by secondarily formed 
PM2.5. In such an area, a sensitivity analysis may be able 
to demonstrate that sources of a particular precursor in the 
nonattainment area do not contribute significantly to PM2.5 
levels that exceed the standard, and that the potential air quality 
improvement from reducing emissions of the precursor in the area may be 
limited.
    Thus, the most effective precursor strategies for reducing 
PM2.5 concentrations as part of attainment planning will 
vary from area to area, depending upon which specific precursors play a 
role in forming or limiting PM2.5 formation in the 
particular area. The EPA therefore believes that it is a reasonable 
interpretation of the statute to allow a precursor to be excluded from 
control requirements if the PM2.5 concentration in the area 
is insensitive to decreases of that precursor.
    For states that choose to develop an optional precursor 
demonstration, the final rule provides that in addition to the basic 
requirement to do a concentration-based contribution analysis, the 
state may choose to develop a sensitivity-based contribution analysis 
evaluating potential emissions reductions for either a comprehensive 
precursor demonstration or a major stationary source demonstration 
intended to show that emissions reductions of the particular precursor 
are not effective in reducing PM2.5 levels that exceed the 
standard in the area. As noted previously, the EPA expects to recommend 
approaches for assessing whether a particular air quality concentration 
threshold can be considered to be insignificant in a given area. If a 
concentration-based contribution analysis conducted for

[[Page 58024]]

either a comprehensive precursor demonstration or a major stationary 
source precursor demonstration shows that the contribution from a 
precursor is less than a particular threshold which may be considered 
insignificant at each PM2.5 monitor in the area, then the 
EPA could approve the concentration-based contribution analysis. 
However, if a concentration-based contribution analysis cannot be 
approved (e.g., shows that the contribution of a precursor to 
PM2.5 levels in the area is not less than such a threshold 
at one or more monitors), then the overall precursor demonstration 
still could be approved, but only if the state also provides an 
appropriate sensitivity-based contribution analysis. If the 
sensitivity-based contribution analysis shows that the reduction in 
PM2.5 concentration at each PM2.5 monitor 
resulting from an emission reduction level that would not exceed such a 
threshold, then the EPA could approve the overall precursor 
demonstration, and the state would not be required to adopt control 
requirements for the precursor or address the precursor for attainment 
planning purposes.
    In evaluating whether it would be appropriate to exclude sources of 
any precursors from NNSR regulation in a nonattainment area, it is 
important to understand the sensitivity of the atmosphere to potential 
increases in precursor emissions that could result from major source 
growth (from both new sources and major modifications at existing major 
sources) in the nonattainment area. For example, in some circumstances, 
adding a few hundred tons of a ``less abundant'' precursor to an area 
could result in a significant increase in PM2.5 
concentrations even if there are currently very few existing major 
sources of the precursor in the area. In contrast to the emissions 
reduction analyses described for attainment planning purposes, 
sensitivity analyses that consider the effect of potential emissions 
increases of a particular precursor in the nonattainment area will help 
the state and the EPA to understand the potential response of 
PM2.5 concentrations to increased emissions in the area in 
order to assess whether the contribution from such increases is not 
significant under CAA section 189(e). In assessing whether a state 
precursor demonstration (i.e., for attainment planning or for NNSR) can 
be approved, the EPA will consider the air quality changes estimated in 
the state's technical sensitivity analyses, their relationship to 
thresholds developed under any EPA-recommended approaches (including 
any thresholds that EPA may recommend), and any other information 
presented by the state.
4. Procedural Considerations
    a. Consultation and Public Review. The EPA anticipates that a 
state's development of an approvable PM2.5 precursor 
demonstration will require a substantial level of effort and 
consultation with the EPA. Such a demonstration by the state would 
likely involve technically rigorous and complex analyses, such as air 
quality modeling and ambient data analyses. Accordingly, the EPA 
strongly recommends that any state that is considering limiting the 
applicability and associated control strategy decisions only to 
specific precursors, either for the attainment plan, for the NNSR 
permitting program, or for both, should develop a precursor 
demonstration early in the attainment plan development process. The EPA 
is committed to consulting with states on designing technically 
appropriate precursor demonstrations consistent with EPA technical 
guidance. If a state chooses to develop a precursor demonstration, it 
must be submitted to the appropriate EPA regional office no later than 
the date of submission of the relevant attainment plan or NNSR program 
revision; an earlier submission is preferable. For example, if a state 
submits the Moderate area plan elements no later than 18 months from 
the date of designation (as discussed in Section IV.A of the preamble), 
it should submit any precursor demonstration no later than this same 
date. In its review of any precursor demonstration provided by a state, 
the EPA will consider all relevant information.
    The critical first step in any precursor analysis is the 
development of a comprehensive inventory of all precursor emissions in 
the nonattainment area. A state will not be able to reasonably 
determine whether reductions of a given PM2.5 precursor are 
needed for expeditious attainment, or whether sources of such precursor 
are insignificant contributors to PM2.5 levels above the 
standard in an area, unless the state has adequately accounted for all 
nonattainment area emissions in its emissions inventory. (See section 
IV.B of this preamble for more details on emission inventory 
requirements.)
    In the preamble to proposed rule, we indicated that if a state 
developed a precursor demonstration as part of its draft attainment 
plan or NNSR program submission, then in accordance with the state 
rulemaking process, the demonstration would be subject to public review 
at the state level. We also stated that, as required under any 
rulemaking process, the state had to consider and provide a response in 
the rulemaking record to any information or evidence brought forward by 
commenters during the state's SIP planning, development and review 
process. By ensuring that this important issue was explicitly addressed 
and supported in any attainment plan or NNSR program revision submitted 
to the EPA, the EPA could better evaluate the precursor demonstration 
in accordance with its obligations under the CAA. The EPA believes 
these are sound procedural steps for a state rulemaking process, and 
the final rule includes similar language requiring public review of any 
proposed precursor demonstration.
    If a state chooses to develop a comprehensive precursor 
demonstration or major stationary source precursor demonstration for a 
nonattainment area, it must submit a concentration-based contribution 
analysis and, if applicable, a sensitivity-based contribution analysis 
conducted for the area. In cases where a sensitivity-based analysis was 
developed the concentration-based analysis must also still be 
submitted. Although the rule clearly provides that the precursor 
demonstration requirement may still be satisfied in such cases, the 
information in the concentration-based analysis will help inform review 
of the overall demonstration by the EPA. Similarly, the data from the 
concentration-based analysis should be available in the public record 
because it will help inform the review of the overall precursor 
demonstration by the public. See 40 CFR 51.1006(b).
    b. Precursor Demonstration to be Reevaluated for Each New State 
Implementation Plan. There may be situations where the EPA approved a 
Moderate area plan that excluded a precursor from regulation from one 
or more requirements based on an approvable precursor demonstration, 
and then the area is reclassified as a Serious area, triggering an 
additional plan submission requirement. (Section V of this preamble 
provides additional detail on reclassification of areas from Moderate 
to Serious under subpart 4.) In addition, an area that had been 
reclassified as Serious later may be required to submit one or more 
additional SIPs if it obtains an extension of the Serious area 
attainment date, or if it fails to attain the standard by the end of 
the tenth year after designation. For a state seeking to continue a 
precursor exclusion in a subsequent attainment plan or NNSR program

[[Page 58025]]

submission, the final rule requires the state to assess the 
appropriateness of continuing the exclusion by providing a new 
precursor demonstration updated to reflect the type of plan and the 
conditions in effect when the new plan is submitted.
    When an area is reclassified to Serious, existing sources of all 
PM2.5 precursors in the area are again presumptively subject 
to evaluation for BACM/BACT control measures and potential future 
control requirements, unless a new precursor demonstration is developed 
and approved as part of the Serious area plan. As noted in the 
discussion of the provisions for excluding sources of precursors from 
certain Moderate area requirements based on an expeditious attainment 
demonstration, this option is not available for Serious areas. 
Accordingly, if the state seeks to submit an updated precursor 
demonstration for a Serious area, at this stage it must submit a 
comprehensive, major stationary source, or NNSR precursor 
demonstration. Regardless of the type of demonstration(s) provided in 
the Moderate area plan, the final rule requires that the state must 
submit a reevaluated and updated precursor demonstration for the 
Serious area plan. The reason for this is that the Serious area plan 
would be due several years after the submission of a state's original 
precursor demonstration, and over that period, substantial emissions 
changes could have occurred that might call into question the basis of 
the previous precursor demonstration. In addition, because the area 
failed to attain by the Moderate area attainment date, it is reasonable 
and appropriate to require the state to reconsider and update its prior 
precursor demonstration. The final rule also requires similar updates 
for each successive plan beyond the initial Serious area plan (such as 
a revised Serious area plan for an area that fails to attain by the end 
of the tenth calendar year after designation). The EPA recommends that 
in developing a revised precursor demonstration, the state should 
consider changes in a number of factors, including: Changes in 
emissions inventory levels due to implementation of control programs, 
growth in emissions, and changes in emission estimation methodologies; 
recent ambient air quality concentrations; fine particle composition 
and the sensitivity of the atmosphere to increases and decreases of 
different precursors; advances in technical tools and modeling 
techniques to assess the effectiveness of precursor reductions; and 
advances in control technologies and emission reduction programs.
5. Comments and Responses.
    Comment: With regard to whether the existing source contribution 
analysis or the sensitivity-based contribution analyses should be 
required if a state opts to submit a precursor demonstration, a number 
of commenters supported only the sensitivity analysis because they 
believed the analysis would help identify the control measures that are 
most effective at reducing PM2.5 concentrations. Some 
commenters noted that conducting a ``zero-out'' analysis (i.e., 
simulating the change in atmospheric chemistry and PM2.5 
concentrations due to a hypothetical removal of 100 percent of the 
emissions of a precursor from the inventory) is not appropriate for a 
sensitivity analysis because the response of the photochemical grid 
model is highly non-linear under such circumstances.
    Another group of commenters supported requiring only the 
concentration-based existing source contribution analysis because only 
that analysis would address the question alluded to in the statute, 
which is whether sources of the precursor contribute significantly to 
levels which exceed the standard in the area. These commenters stated 
that sensitivity-based analyses reflect localized conditions and do not 
represent a consistent effect across an air basin. The commenters 
suggested that sensitivity analyses might be considered to inform what 
pollutants are most cost-effective to control, but believed that this 
is dubious because the fact that certain pollutants are very abundant 
is likely the result of a history of under-regulation. They suggested 
that it actually may be cheaper to control the more abundant pollutant 
than the less abundant pollutant in order to achieve an equal amount of 
air quality improvement.
    Response: The EPA agrees with commenters who suggested that the 
rule should closely align with the statutory language in CAA section 
189(e) of subpart 4 and include provisions for evaluating the 
contribution of existing sources to PM2.5 levels which 
exceed the standard in the area. For this reason, the final rule states 
that the existing source contribution analysis should be required for 
any comprehensive precursor demonstration or major stationary source 
precursor demonstration seeking to exempt a precursor from attainment 
planning requirements.
    The EPA also believes that a sensitivity-based contribution 
analysis is consistent with the language and intent of CAA section 
189(e). As applied to attainment plans, CAA section 189(e) allows 
states to evaluate whether PM2.5 precursors significantly 
contribute to levels which exceed the standard in the area. The intent 
of CAA section 189(e) in applying control requirements to 
PM2.5 precursors is to ensure expeditious attainment of the 
standard. However, if conditions in a particular area are such that 
control of sources of one or more precursors does not reduce 
PM2.5 concentrations in the area, then those controls will 
not help the area attain (expeditiously or otherwise). Therefore, the 
EPA disagrees with commenters who argue that sensitivity-based 
contribution analyses are not appropriate for determining if precursors 
do not significantly contribute to PM2.5 levels in the area. 
The EPA believes that sensitivity-based contribution analyses can be 
useful for determining whether adoption of control requirements for 
sources of a particular precursor would be effective in reducing 
PM2.5 concentrations, and can be useful for determining 
whether potential emissions increases under the NNSR program would lead 
to insignificant air quality changes. For this reason, the final rule 
allows states to conduct sensitivity-based contribution analyses for 
the comprehensive, major stationary source, and NNSR precursor 
demonstrations.
    Comment: Some commenters expressed support for the precursor option 
from the proposal (i.e., Option 3) that would have allowed for an 
expeditious attainment precursor demonstration to be deemed to 
demonstrate under CAA section 189(e) that emissions of the precursor do 
not need to be addressed for all major stationary source requirements, 
such as the NNSR program.
    Response: Upon further consideration of this potential approach, 
the EPA decided that it would not be appropriate to include such an 
approach in the final rule. The reason for this is that an expeditious 
attainment planning analysis on its own would determine that the area 
could attain the standard by the Moderate area attainment date without 
new control requirements for sources of a particular precursor, but it 
would not address the potential impact of increased emissions of the 
precursor in the area due to new or modified sources, as is reasonably 
needed under the NNSR precursor demonstration. The evaluation of 
controls required for expeditious attainment does not consider what 
happens if new sources move into an area. Thus, while a state might be 
able to show that controlling existing sources of a precursor does not

[[Page 58026]]

advance attainment, the analysis would not determine whether a new 
major source of that precursor might have a significant contribution to 
air quality. The EPA believes it is important for purposes of CAA 
section 189(e) and our overall environmental goal under the NNSR 
program to evaluate emissions increases. Consequently, the EPA has 
revised the details of the specific types of demonstrations to include 
a specific stand-alone demonstration for purposes of exempting new 
major stationary sources and major modifications of a precursor from 
regulation under the NNSR permitting program.

IV. Requirements for PM2.5 Moderate Nonattainment Area Plans

    Sections 189(a), (c), and (e) of the CAA require that Moderate area 
attainment plans contain the following: (i) An approved permit program 
for construction of new and modified major stationary sources (CAA 
section 189(a)(1)(A)); (ii) a demonstration that the plan provides for 
attainment by no later than the applicable Moderate area attainment 
date or a demonstration that attainment by that date is impracticable 
CAA (section 189(a)(1)(B)); (iii) provisions for the implementation of 
RACM and RACT no later than 4 years after designation (CAA section 
189(a)(1)(C)); (iv) quantitative milestones that will be used to 
evaluate compliance with the requirement to demonstrate reasonable 
further progress (RFP) (CAA section 189(c)); and, (v) evaluation and 
regulation of PM2.5 precursors (in general to meet RACM and 
RACT and other attainment planning requirements, and as specifically 
provided for major stationary sources under CAA section 189(e)). In 
addition, subpart 1 requirements for attainment plans continue to apply 
to PM2.5 nonattainment areas unless they are superseded by 
subpart 4 provisions and include the following: (i) A description of 
the expected annual incremental reductions in emissions that will 
demonstrate RFP (CAA section 172(c)(2)); (ii) emissions inventories, as 
necessary (CAA section 172(c)(3)); (iii) other control measures 
(besides RACM and RACT) needed for attainment (CAA section 172(c)(6)); 
and, (iv) contingency measures (CAA section 172(c)(9)). The EPA notes 
that its longstanding guidance on interpreting these statutory 
requirements is embodied in the General Preamble and the Addendum.\54\ 
The preamble for the proposed rule presented several interpretations of 
these provisions, and further explained where its proposal varies from 
past EPA guidance and the reasons for the variance. The following 
sections of this preamble explain the EPA's final approach and, where 
different from the proposal, also explain EPA's reasons for finalizing 
an amended approach. This final rule reflects our careful consideration 
of the numerous thoughtful comments we received from air agencies, who 
are responsible under the CAA for these implementation activities, and 
a variety of other stakeholders.
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    \54\ See 57 FR 13498, 13536, 13537, 13538, 13539, 13540, 13541, 
13542, 13543, 13544 and 13545 (April 16, 1992); and 59 FR 41988 
(August 16, 1994).
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A. Plan Due Dates

1. Summary of Proposal
    The EPA proposed to require that all Moderate area plan elements 
for a nonattainment area be submitted by the state no later than 18 
months from the effective date of designation. The attainment plan 
submission would thus include all necessary plan elements required 
under CAA subparts 1 and 4.
2. Final Rule
    The final regulations at 51.1003(a) require all Moderate 
nonattainment area elements to be submitted by no later than 18 months 
from the date of designation, as proposed. Section 189 of the CAA 
specifies the schedule by which states must submit attainment plans for 
the PM2.5 NAAQS. Specifically, CAA section 189(a)(2)(B) 
requires states to submit an attainment plan that meets Moderate area 
attainment plan requirements no later than 18 months from the date of 
nonattainment designation.\55\ While subpart 1 of the CAA could 
potentially be interpreted to authorize the EPA to provide up to 3 
years after designation for states to submit certain attainment plan 
elements, the EPA believes that such an interpretation would be 
inconsistent with the specific deadlines that Congress imposed in 
subpart 4. The EPA concludes that all subpart 1 and subpart 4 
nonattainment area requirements should be considered together in order 
to facilitate state development, and EPA review, of a comprehensive 
plan to attain the PM2.5 NAAQS in a given nonattainment 
area. In fact, the EPA finds that meeting key subpart 1 requirements 
within the 18-month timeframe of subpart 4 is fundamentally necessary 
for the state to develop an approvable plan. For example, the state 
must develop an emissions inventory (or inventories) either before or 
at the same time as the other attainment plan elements due under 
subpart 4 because the information contained in the emissions inventory 
is critical for development of other elements of the Moderate area 
attainment plan, such as its precursor analysis, analysis of RACM and 
RACT and additional reasonable measures, and attainment demonstration 
modeling. The EPA's ability to evaluate the submitted attainment plan 
therefore will be impaired if the state does not submit all the 
required plan elements at the same time.
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    \55\ The EPA notes that Congress provided different statutory 
deadlines for submission of attainment plans under subpart 1 and 
subpart 4. Under section 172(b) of the CAA, the EPA is directed to 
establish the date for the attainment plan submission, but it can 
extend no later than 3 years from the date of a nonattainment 
designation. By contrast, under CAA section 189(a)(2)(B), the 
statute provides that states must make the attainment plan 
submissions within 18 months after designation. Due to the December 
2013 court decision in NRDC v. EPA, however, the EPA promulgated an 
alternative submission date of December 31, 2014, for attainment 
plans for the 1997 PM2.5 and 2006 PM2.5 NAAQS 
in order to provide a reasonable, prospective due date for 
attainment plans that must comply with subpart 4 requirements and to 
clarify the requirements that a state must meet prior to 
redesignation of a PM2.5 nonattainment area. See 79 FR 
31566 (June 2, 2014).
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3. Comments and Responses
    Comment: Commenters suggested that the EPA should interpret the 
statute to allow more time for states to develop and submit contingency 
measures.
    Response: As discussed earlier in this section, the EPA believes 
that it would be inconsistent with the specific deadlines that Congress 
imposed in subpart 4 to allow contingency measures to be submitted 
later than the other elements of the attainment plan. Contingency 
measures need to be adopted and ready for rapid and timely 
implementation in the event a nonattainment area fails to meet RFP 
requirements or fails to attain the PM2.5 NAAQS by the 
applicable attainment date. The state's evaluation of what emissions 
controls are appropriate to meet the contingency measure requirement is 
closely related to other aspects of the attainment plan, such as the 
pollutants and sources to be addressed in meeting the RACM/RACT 
requirements, and the amount of emissions reductions that the 
contingency measures should achieve, based upon the facts and 
circumstances of the attainment plan for the area. The same types of 
facts and analyses that are necessary for the other elements of an 
attainment plan are directly relevant to the development of contingency 
measures.
    Although nothing in the CAA prohibits states from making separate 
attainment plan submissions to meet the

[[Page 58027]]

individual required elements for attainment plans in advance of the 
required date, the EPA presumes that development and submission of all 
of the attainment plan elements simultaneously will be most efficient, 
both for the state and for the EPA in reviewing the state's submission. 
A Moderate area implementation plan with a single SIP submission due 
date will be less administratively burdensome than a program with two 
SIP submission due dates. Under an approach with two submissions, the 
state would likely need to issue two sets of proposed regulations, hold 
two sets of public hearings, and respond to two sets of public 
comments, rather than dealing with all of these requirements in one 
comprehensive action. Likewise, the EPA would have two separate 
submissions to review and two sets of proposed and final actions to 
publish in the Federal Register for every Moderate nonattainment area. 
Thus, for the reasons outlined earlier, the final rule includes a 
single Moderate area attainment plan submission deadline of 18 months 
after designation. Accordingly, the areas designated as nonattainment 
for the 2012 PM2.5 NAAQS (with an effective date of April 
15, 2015) are required to submit Moderate area attainment plans to the 
EPA no later than October 15, 2016. See 40 CFR 51.1003(a).

B. Emissions Inventory Requirements

1. Summary of Proposal
    In the proposal, the EPA proposed for both Moderate and Serious 
areas to require both a ``base year inventory for the nonattainment 
area'' and an ``attainment projected inventory for the nonattainment 
area.'' The proposal spelled out a list of requirements for each of 
these inventories. The proposal also specified, based on the timing 
requirements of CAA section 172(b), that the emissions inventories 
required for a Moderate area must be submitted within 18 months after 
the effective date of the designation of the nonattainment area.
    The EPA proposed that the base year inventory for the nonattainment 
area: (a) Be required to represent one of the 3 years used for 
designations or another technically appropriate year; (b) include 
actual emissions of all sources within the nonattainment area; (c) be 
annual total or average-season-day emissions in accordance with the 
NAAQS violation(s) (annual and/or 24-hour); (d) include direct 
PM2.5 (filterable and condensable) as well as all scientific 
PM2.5 precursors; (e) follow the Air Emissions Reporting 
Requirements (AERR), 40 CFR part 51, subpart A for the emissions 
thresholds for point sources; (f) use the level of detail as prescribed 
by the AERR; and (g) still meet the public review requirements even if 
submitted as a separate plan.
    The EPA further proposed that the attainment projected inventory 
for the nonattainment area (a) be required to represent projected 
emissions in the first year for which attainment is demonstrated by the 
modeled attainment demonstration; (b) include projected emissions of 
the same sources included in the base year inventory for the 
nonattainment area; (c) use the same temporal period as the base year 
inventory (annual or average-season-day); (d) include the same 
pollutants as the base year inventory; (e) report as point sources the 
same sources treated as point sources in the base year inventory; (f) 
be consistent in inventory detail with the base year inventory; and (g) 
still meet the public review requirements even if submitted as a 
separate plan.
2. Final Rule
    The final regulations at 51.1008 provide the inventory requirements 
for Moderate areas. The EPA received a number of comments on the 
emissions inventory requirements for Moderate areas. Commenters both 
supported the provisions of the proposed rule and objected to some 
aspects of the inventory requirements. The EPA is finalizing all of the 
proposed Moderate area requirements with some modifications based on 
comments. Specifically, the definition of what can constitute a 
seasonal inventory has been made more flexible to accommodate certain 
cases, as explained in Section IV.B.2.c of this preamble.
    Pursuant to its authority under section 110 of title I of the CAA, 
the EPA has long required states to submit inventories of the emissions 
of criteria pollutants and their precursors. The EPA codified these 
requirements in 40 CFR part 51, subpart Q in 1979 and amended them in 
1987. Additionally, the 1990 CAA Amendments revised many of the 
provisions of the CAA related to attainment of the NAAQS and the 
protection of visibility in mandatory Class I federal areas (certain 
national parks and wilderness areas). These revisions established new 
emissions inventory requirements applicable to areas that were 
designated nonattainment for certain pollutants. In the case of PM, 
Congress did not create a specific emissions inventory requirement in 
subpart 4 that would supersede the emissions inventory requirement 
under subpart 1. Thus, the CAA section 172 (c)(3) emissions inventory 
requirements continue to apply, and that provision explicitly requires 
``a comprehensive, accurate, and current inventory of actual emissions 
of the relevant pollutants'' in the nonattainment area. In addition, 
the specific attainment plan requirements for the PM2.5 
NAAQS set forth in CAA section 189(a) and associated modeling 
requirements make an accurate and up-to-date emissions inventory a 
critical element of any viable attainment plan. Because of the nature 
of PM2.5, the EPA concludes that the statutory requirements 
for emissions inventories need further elaboration through additional 
regulatory requirements as described later.
    Emissions inventory data serve as the foundation for various types 
of analyses performed by states and by the EPA. For example, these data 
enable states to evaluate the degree to which different emissions 
sources contribute to the nonattainment problem in a given 
nonattainment area and enable states to estimate the air quality 
improvement that can be achieved through different control measures. 
States should use the best available, current emissions inventory 
information for attainment plan development, because high quality 
emissions inventory data are essential for the development of an 
effective control strategy. To assist states in preparing complete, 
high quality inventories, the EPA provides guidance for developing 
emissions inventories called ``Emissions Inventory Guidance for 
Implementation of Ozone and Particulate Matter National Ambient Air 
Quality Standards (NAAQS) and Regional Haze,'' which is available from 
https://www.epa.gov/air-emissions-inventories/emissions-inventory-guidance-documents. This guidance is commonly called the ``SIP 
Emissions Inventory Guidance.'' The EPA recommends that states consult 
this guidance while developing the emissions inventories to meet 
statutory and regulatory requirements.
    a. Inventory Requirements. As explained in the proposed rule, CAA 
section 172(c)(3) requires states to submit an emissions inventory and 
periodic revisions thereof with an attainment plan. 80 FR at 15363. In 
addition, pursuant to CAA section 301, the EPA has authority to 
promulgate regulations as necessary for the implementation of the 
PM2.5 NAAQS, including requirements pertaining to emissions 
inventories. In this final action, the EPA is establishing several 
different inventory requirements that the agency has determined are 
necessary

[[Page 58028]]

for the proper implementation of the PM2.5 NAAQS in 
attainment plans.
    There are three key facets of the emissions inventory requirements, 
as described later: (i) The type of inventories required; (ii) the 
timing of submission of these inventories; and (iii) the content of 
these inventories. These content requirements are described in this 
section; however, the EPA's rationale for these content requirements is 
in some cases further described in subsequent sections of this 
document.
    First, states must submit at least two separate and distinct 
nonattainment area emissions inventories as elements of an attainment 
plan. The first emissions inventory is relevant for assessing the 
current or base year emissions from sources located in the 
nonattainment area; the second emissions inventory is a projected 
inventory relevant for assessing emissions in the target attainment 
year in the nonattainment area. The first type of inventory is called 
the ``base year inventory for the nonattainment area,'' and the second 
type of inventory is called the ``attainment projected inventory for 
the nonattainment area.'' See 40 CFR 51.1000. The base year inventory 
for the nonattainment area is necessary for development and evaluation 
of various elements of the attainment plan, such as the determination 
of appropriate pollutants, sources, and emission controls addressed in 
other elements of the attainment plan for the nonattainment area. The 
attainment projected inventory is necessary to implement the attainment 
demonstration requirement of CAA section 189(a)(1)(B), and it also may 
be used as part of meeting the RFP requirement (see Section IV.F of 
this preamble). The need for the attainment projected inventory also 
stems from the need for both the EPA and the public to be able to 
compare, during their reviews of the attainment plan, the base year 
inventory against the attainment projected inventory for the 
nonattainment area. For these reasons, this rule establishes a 
regulatory requirement at 51.1008 that Moderate area attainment plans 
must include a base year inventory for the nonattainment area and an 
attainment projected inventory for the nonattainment area.
    Second, as noted in Section IV.A of this preamble, to meet the 
statutory requirements for submission of certain attainment plan 
elements required under subpart 4, the EPA believes that states must 
meet the same submission schedule for emissions inventories as for the 
other elements of an attainment plan, i.e., within 18 months after the 
effective date of the designation of the nonattainment area. This 
schedule must apply to both of these emissions inventories because they 
are necessary for effective evaluation of the attainment plan as a 
whole. Consequently, under the authority of CAA section 172(b), this 
rule establishes a regulatory requirement for Moderate areas that 
states must submit the required base and projected emissions 
inventories by 18 months after designation.
    Third, the EPA is establishing specific requirements for both the 
base year inventory for the nonattainment area and for the attainment 
projected inventory for the nonattainment area in order to implement 
the PM2.5 NAAQS most effectively. Accordingly, this final 
rule requires that the base year inventory for Moderate nonattainment 
areas must meet the following minimum criteria 1 through 7:
    (1) The inventory year must be one of the 3 years used for 
designations for the relevant PM2.5 NAAQS or another 
technically appropriate inventory year. Another inventory year may be 
chosen under specific circumstances (e.g., to account for a change in 
sources in the nonattainment area, changes in nonattainment area 
boundaries, to allow the base year to be consistent with the base year 
needed for the conformity rule, or significant time lag between 
designations and preparation of the inventory) with consultation from 
the appropriate EPA Regional Office. This requirement is intended to 
ensure that the inventory will adequately represent the emissions 
sources that contributed to the nonattainment designation for the area. 
See 40 CFR 51.1008(a)(1)(i).
    (2) The inventory must include actual emissions of all sources 
within the nonattainment area. This requirement stems directly from the 
language in CAA section 172(c)(3). Sources outside of the nonattainment 
area are explicitly not included in the section 172(c)(3) requirement 
with the words ``in such area.'' Furthermore, the EPA interprets the 
Act requirement for ``actual emissions from all sources'' in CAA 
section 172(c)(3) as intending to include all emissions that may 
contribute to the formation of PM2.5 within the 
nonattainment area. This means that the inventory must include point 
sources, stationary nonpoint sources,\56\ mobile sources, prescribed 
fires and wildfires. The EPA encourages states and tribes to work 
together to ensure that the information used in developing the base 
year inventory for the nonattainment area is inclusive of all emissions 
from the designated nonattainment area, including emissions from 
sources in tribal areas located therein. See 40 CFR 51.1008(a)(1)(ii).
---------------------------------------------------------------------------

    \56\ Point sources are the same as major stationary sources, and 
the term indicates sources that must be reported at an individual 
facility with process-level details. Nonpoint sources are all other 
stationary sources, and the term indicates sources that are reported 
as a county total. The definitions for this rule (see 51.1000) refer 
to the definitions in the AERR (40 CFR part 51, subpart A). Nonpoint 
sources include minor sources, synthetic minor sources, and area 
sources such as residential heating and other sources where it is 
not realistic to estimate emissions from each emissions point.
---------------------------------------------------------------------------

    (3) The emissions must be reported as annual total emissions, 
average-season-day emissions, or both, as appropriate for the relevant 
PM2.5 NAAQS. The rationale for the type(s) of emissions 
provided must be included as part of the attainment plan. When seasonal 
emissions are included, the rationale for the seasonal period must also 
be included as part of the attainment plan. A discussion of the EPA's 
rationale for including the option of seasonal or annual inventories is 
provided in Section IV.B.2.c of this preamble. See 40 CFR 
51.1008(a)(1)(iii).
    (4) As discussed earlier and consistent with past implementation 
rule requirements, the inventory must include emissions of direct 
PM2.5 (both filterable PM2.5 and condensable 
PM2.5, provided as separate components), as well as all 
scientific PM2.5 precursors (SO2, NOX, 
VOC and ammonia). A discussion of the EPA's rationale for including 
this requirement is provided in Section IV.B.2.d of this preamble. See 
40 CFR 51.1008(a)(1)(iv).
    (5) States must follow the Air Emissions Reporting Requirements 
(AERR), 40 CFR part 51, subpart A criteria for emissions thresholds for 
states to use to determine which emissions sources must be reported as 
point sources. This requirement is consistent with past implementation 
rules and is needed to specify whether emissions must be submitted as 
specific major source stationary facilities with detailed emissions 
processes or whether emissions can be provided as county totals (i.e., 
area sources, also called nonpoint sources). A discussion of the use of 
40 CFR part 51, subpart A for the emissions thresholds is provided in 
Section IV.B.2.e of this preamble. See 40 CFR 51.1008(a)(1)(v).
    (6) The level of detail of the emissions included in the inventory 
must be consistent with the detail required by 40 CFR part 51, subpart 
A. For example, all emissions must be subdivided to individual 
emissions processes within a facility or county. While these details 
should underlie the emissions

[[Page 58029]]

inventory, this information can be summarized for other elements of the 
attainment plan. This requirement is consistent with the remanded 2007 
PM2.5 Implementation Rule and is needed to define the data 
reporting elements (i.e., how they are reported) as opposed to the 
emissions values (i.e., how much emissions derive from each source or 
source category) of the emissions inventories submitted to the EPA. See 
40 CFR 51.1008(a)(1)(vi).
    (7) If the base year inventory for the nonattainment area is 
submitted to the EPA as a separate plan submission (i.e., severed from 
the overall attainment plan and provided separately), the inventory 
must still meet the notice and public hearing requirements of CAA 
sections 110(a)(1) and 110(a)(2).
    For the attainment projected inventory for Moderate nonattainment 
areas, this final rule also establishes specific requirements necessary 
to implement the PM2.5 NAAQS effectively. Accordingly, the 
attainment projected inventory must meet the following minimum criteria 
1 through 7:
    (1) The year of the projected inventory must be the most 
expeditious year for which projected emissions show modeled 
PM2.5 concentrations below the level of the NAAQS, 
consistent with the requirement for expeditious attainment by no later 
than the applicable deadlines provided in the statute. See 40 CFR 
51.1008(a)(2)(i).
    (2) The emissions must be projected emissions from the same sources 
included in the base year inventory for the nonattainment area and any 
new sources projected to locate within the boundaries of the 
nonattainment area. The projected emissions should be the best 
available representation of expected emissions, and thus should take 
into account emissions growth and contraction, facility closures, new 
facilities, new controls and other changes in emissions forecast to 
occur between the base year and the attainment year. In deciding what 
factors are relevant, states should consider factors affecting 
projected emissions that could significantly alter the conclusions of 
the modeled attainment demonstration. See 40 CFR 51.1008(a)(2)(ii). For 
prescribed and wildfire emissions, Section IV.D.3.b of this preamble 
describes in more detail the appropriate way to handle these sources in 
the attainment projected inventory.
    (3) The temporal period of emissions must be the same temporal 
period (annual, average-season-day, or both) as the base year inventory 
for the nonattainment area. See 40 CFR 51.1008(a)(2)(iii).
    (4) Consistent with the base year inventory for the nonattainment 
area, the inventory must include all emissions of direct 
PM2.5 (both filterable and condensable PM2.5 
provided as separate components), as well as all emissions of the 
scientific precursors (SO2, NOX, VOC and 
ammonia). See 40 CFR 51.1008(a)(2)(iv).
    (5) The same sources reported as point sources in the base year 
inventory for the nonattainment area must also be provided as point 
sources in the attainment projected inventory for the nonattainment 
area. Likewise, nonpoint and mobile source projected emissions must 
also be provided using the same delineations as the base year 
inventory. See 40 CFR 51.1008(a)(2)(v).
    (6) The detail of the emissions included must be consistent with 
the level of detail in the base year inventory (i.e., as required by 40 
CFR part 41, subpart A). See 40 CFR 51.1008(a)(2)(vi).
    (7) If the attainment projected inventory for the nonattainment 
area is submitted to the EPA as a separate plan submission (e.g., 
severed from the overall attainment plan and provided separately), then 
the inventory must still meet all the notice and public hearing 
requirements of CAA sections 110(a)(1) and 110(a)(2).
    b. Comparison to Inventory Requirements from Earlier 
PM2.5 Implementation Rules. The 2007 PM2.5 
Implementation Rule required states to submit specific emissions 
inventories in connection with the RFP requirements of CAA section 
172(c)(2) under subpart 1. In this rule, no specific RFP related 
inventory is required, but the attainment projected inventory for the 
nonattainment area also may serve a purpose for evaluation of RFP. Past 
EPA guidance with respect to RFP requirements under subpart 4 has not 
explicitly required a separate emissions inventory for this purpose for 
PM10 NAAQS. Through evaluation of the RFP requirement in 
connection with this rulemaking, however, EPA has determined that there 
may be circumstances in which such an approach may be appropriate. For 
this reason, the EPA describes this issue more fully in Section IV.F of 
this preamble.
    The 2007 PM2.5 Implementation Rule also required states 
to submit a statewide base year emissions inventory as part of the 
attainment plan. The EPA included the statewide emissions inventory 
requirement because it was relevant to evaluation of emissions 
reductions from sources outside of the designated nonattainment area 
for purposes of RFP. The EPA no longer interprets the CAA to allow such 
reductions for purposes of RFP, so this particular form of emissions 
inventory is not needed for attainment plan for the PM2.5 
NAAQS. Furthermore, statewide inventories are already required as part 
of the AERR (40 CFR part 51, subpart A) on a triennial basis. While 
these inventories do not receive the same level of scrutiny as 
inventories associated with attainment plans, the EPA believes that 
this existing statewide inventory requirement is sufficient for 
understanding the PM2.5 nonattainment contributions from 
areas outside of the nonattainment area, which is a necessary component 
of modeled attainment demonstrations described in Section IV.E of this 
preamble.
    c. Seasonal Inventories. The statute does not explicitly address 
whether the emissions inventory required under CAA section 172(c)(3) 
should include emissions throughout an entire calendar year or 
emissions during some shorter portion of the year that may be 
appropriate for implementation of a particular NAAQS. In the case of 
the PM2.5 NAAQS, the standards currently include both annual 
NAAQS and 24-hour NAAQS. With respect to the annual NAAQS, the form of 
the NAAQS includes monitored ambient PM2.5 values at all 
times throughout the course of the year, and thus an annual emissions 
inventory is necessarily required for development of an appropriate 
attainment plan for a given area. In the case of the 24-hour NAAQS, 
however, the form of the NAAQS is based upon monitored values on 
particular days with high levels of ambient PM2.5, and in 
some nonattainment areas those days may occur only during a distinct 
and definable season of the year. The EPA considers it appropriate to 
interpret the emissions inventory requirements of the CAA in light of 
the specific inventory needs that are relevant for the NAAQS in 
question. For the PM2.5 NAAQS, states can meet the inventory 
requirement with different combinations of temporal resolutions for the 
emissions. For the annual standard, annual emissions must be submitted. 
For the 24-hour standard, states must submit either an annual or an 
average-season-day inventory and optionally may submit both. For a 
nonattainment area for both the annual and 24-hour standard, states can 
meet the inventory requirement with only an annual inventory or with 
both an annual and average-season-day inventory.
    In contrast with the annual PM2.5 NAAQS, the 24-hour 
PM2.5 NAAQS are designed to protect against peak exposures. 
Thus, for the 24-hour PM2.5

[[Page 58030]]

NAAQS, there are circumstances in which the EPA believes that only 
seasonal emissions inventories may be useful for attainment planning 
purposes. This rule at 40 CFR 51.1008(a)(1)(iii) allows states to use 
seasonal inventories for attainment plan development for attaining the 
24-hour PM2.5 standard in areas that are designated 
nonattainment for only the 24-hour standard. Use of a seasonal 
emissions inventory will also be appropriate only if the monitored 
violations of the 24-hour PM2.5 NAAQS in the area occur 
during an identifiable season. In the event that it is appropriate to 
rely on a seasonal emissions inventory, the state should confer with 
the EPA concerning the exact length of the season and the start and 
stop dates of the season. The duration and start and stop dates of the 
season will be an important component of the attainment plan and must 
be approved by the EPA along with other elements of the attainment plan 
for a given nonattainment area. Further, this rule requires that 
seasonal inventories must use average-season-day emissions values for 
this purpose, defined by 40 CFR 51.1000. The nature of some seasonal 
PM2.5 emissions sources (e.g., residential wood combustion) 
does not allow for only weekday emissions to be included in the 
inventory, therefore all days must be included. The state would need to 
explain the rationale for the duration of the season used for the 
inventory as part of the attainment plan submission. To justify the use 
of a seasonal emissions inventory, the state must demonstrate why a 
seasonal emissions inventory is appropriate for the particular 
PM2.5 nonattainment area in question.
    Commenters recommended that the EPA should allow episode-specific 
inventories, in lieu of seasonal inventories. As a result, the EPA 
acknowledges in this final rule that, for some source categories, it 
may be advisable to limit the ``season'' considered in calculating 
emissions to an episodic period to reflect periods of higher emissions 
during periods of high ambient PM2.5. Such an approach could 
help to ensure the nonattainment area inventory reflects the emissions 
conditions that led to an initial nonattainment area designation. For 
example, if nonattainment conditions are associated only with periods 
of peak emissions from residential wood combustion, then an episodic 
average for residential wood combustion may be more appropriate than a 
seasonal average. The resulting seasonal emissions inventory would then 
have a mix of the seasonal averages as defined by 40 CFR 51.1000 for 
most categories, but using a shorter period for the emissions 
categories that can be justified and an improvement. In such cases, in 
addition to the requirement to justify the seasonal period, the state 
must additionally justify the factual basis for the period used to 
calculate emissions from such categories, and this would be subject to 
EPA approval. While the EPA encourages using the same averaging period 
for all sectors for purposes of simplicity, an episodic averaging 
period may only be needed for a select group of sources or even for a 
single category of sources. Those special cases must be explained in 
the emissions inventory part of the state implementation plan [see 40 
CFR 51.1008(a)(1)(iii)]. For the purposes of the definitions included 
in this final rule, all non-annual emissions (whether seasonal or 
episodic) will be referred to as ``seasonal'' in this rule.
    d. Pollutant Requirements. This rule requires that states must 
submit emissions inventories that include all emissions of direct 
PM2.5 and all emissions of scientific PM2.5 
precursors: SO2, NOX, VOC and ammonia. 
Furthermore, the inventories must differentiate between the condensable 
and filterable portions of direct PM2.5 emissions, and 
states must provide this information in the emissions inventories as 
separate components. As described in Section IV.B.3 of this preamble, 
commenters disagreed with the EPA's proposal to require inclusion of 
ammonia emissions and to require separate reporting of condensable and 
filterable emissions. The approach being finalized in this rule does 
not differ from the EPA's proposal despite these adverse comments.
    Section II.B of this preamble describes the background needed to 
understand the importance of including these precursors in emissions 
inventories for attainment plan purposes for the PM2.5 
NAAQS. Emissions information about PM2.5 and its precursors 
is a necessary precondition to meeting other core attainment plan 
requirements, such as effective evaluation of control measures and 
adequate demonstration of projected future attainment of the NAAQS 
through modeling. The EPA notes that, with respect to requiring states 
to include emissions of direct PM2.5 and PM2.5 
precursors in emissions inventories, the agency is following the 
requirements it established for the 2007 PM2.5 NAAQS 
Implementation Rule in the past.\57\ Section 172(c)(3) of the CAA 
explicitly requires states to submit a ``comprehensive, accurate, 
current inventory of actual emissions of the relevant pollutants'' and 
the EPA continues to believe that to meet these basic statutory 
requirements for the PM2.5 NAAQS, states must address 
PM2.5 and all PM2.5 precursors in their emissions 
inventories.
---------------------------------------------------------------------------

    \57\ 72 FR 20647 (April 25, 2007).
---------------------------------------------------------------------------

    The EPA requires states to use the best available methodologies for 
estimating emissions of PM2.5 and its precursors.
    e. The AERR Defines the Thresholds, Data Elements and Data Methods. 
Because the provisions of the CAA do not specify the form of the 
emissions information to be reported to the EPA for meeting the 
attainment plan inventory requirement under CAA section 172(c)(3), it 
is necessary for the EPA to prescribe specifically the data elements of 
that emissions inventory and the attainment projected inventory. The 
EPA uses the AERR to define basic requirements/parameters of reporting 
emissions for all pollutants. This approach creates consistency and 
eases the burden for the states, because states have one basic set of 
rules that apply to all emissions they have to report to the EPA.
    Distinct from the emissions values (i.e., how much emissions derive 
from each source or source category), the emissions elements (i.e., how 
they are reported) refer to the reporting definitions, data codes and 
required data fields. Under this final rule, states must use the 
emissions elements from 40 CFR part 51, subpart A in preparing their 
inventories to be submitted to the EPA for implementing the 
PM2.5 NAAQS. It also requires that states use point source 
thresholds from Appendix A of the same subpart. This is consistent with 
past requirements for the form of emissions inventories.
    In addition to defining the point source thresholds and data 
elements, 40 CFR part 51, subpart A also requires states to submit 
emissions information to the EPA. The EPA is not referring to those 
emissions submission requirements here, but rather to the emissions 
elements--the definitions, data codes and required data fields. Later, 
the EPA addresses the issue of whether the emissions values submitted 
through the AERR are relevant to the inventory requirements of this 
final rule (see Section IV.B.2.g of this preamble).
    As noted earlier, the EPA recommends that states consult the SIP 
Emissions Inventory Guidance in preparing the inventories required by 
this rule. In addition to the AERR, this guidance includes definitions 
for data fields that are not required by the AERR, such as seasonal 
emissions values and

[[Page 58031]]

other fields that are optional in the AERR data collection system. The 
EPA is updating the SIP Emissions Inventory Guidance in coordination 
with this final rule. It provides specific guidance to states on how to 
develop base year inventories for the nonattainment area and attainment 
projected inventories for 8-hour ozone, PM2.5, and regional 
haze SIPs. While the AERR sets forth requirements for data elements and 
definitions, the guidance complements these requirements, defines all 
data elements (even those that are voluntary AERR elements), and 
indicates how states should prepare and document the data for 
attainment plan submissions.
    In the case of prescribed fires and wildfires, the AERR no longer 
requires those categories to be submitted, but rather the emissions 
data can be optionally provided as an ``Event'' source, which is a day-
specific source at a point location. For this rule as described 
earlier, states are required to include prescribed fires and wildfires 
for the base year inventory for the nonattainment area and the 
attainment projected inventory for the nonattainment area. For this 
rule, states are not expected to use the ``Event'' detail to meet their 
inventory reporting requirements. Instead, states can report these fire 
emissions by county as nonpoint sources are reported.
    f. Emissions Inventories for Support of Modeled Attainment 
Demonstrations. This section clarifies the difference between the 
inventories required to be a part of a state's Moderate area attainment 
plan submission (as described earlier) and other modeling inventories 
that are also relevant for attainment planning. While the EPA is not 
establishing additional modeling inventory requirements in this rule 
(i.e., for which a state must submit an emissions inventory to the 
EPA), to meet the attainment demonstration requirements of CAA sections 
189(a)(1) and 189(b)(1), states are required to submit either an 
attainment demonstration (which includes air quality modeling) to show 
how the area will attain the NAAQS by the applicable attainment date or 
a demonstration that the area cannot attain by the attainment date. The 
modeled attainment demonstration requirements for Moderate areas are 
described fully in Section IV.E of this preamble.
    As part of the modeled attainment demonstration, the EPA presumes 
that states will need to prepare attainment demonstration modeling 
inventories for both a modeled base year and projected attainment year. 
Respectively, these are called the ``base year (baseline) inventory for 
modeling'' and the ``attainment projected inventory for modeling.'' 
These inventories contain emissions for all regions (i.e., not just 
from sources in the nonattainment area) within the modeling domain 
being used for the attainment plan modeling demonstration, which 
typically includes counties and even states outside of the 
nonattainment area. They include detailed spatial and temporal elements 
needed to support air quality modeling. States should follow the 
requirements laid out in Section IV.E of this preamble and the 
procedures described in the SIP Emissions Inventory Guidance and the 
Air Quality Modeling Guidance to meet the minimum requirements for 
documentation and emissions summaries supporting modeling 
demonstrations.
    The base year inventory and projected attainment year inventory 
include emissions from only within the nonattainment area. The EPA 
expects that modeling inventories will be consistent with those 
nonattainment area inventories; however, some exceptions may exist. 
Where possible, the nonattainment area base year and projected 
attainment year inventories can be a sum (for annual data) or average 
(for PM2.5 season-day data) of day-specific or hour-specific 
data used for modeling. In some cases, however, annual or season-day 
data may not be sufficient for modeling purposes. For example, greater 
spatial detail (gridded rather than county total) and temporal detail 
(hourly rather than annual) are needed for on-road mobile modeling 
inventories as compared to the base year inventory for the 
nonattainment area. Rather, for the nonattainment area base year 
inventory, one goal is to allow for the repeatability of the approach 
in order to create average-season-day or annual inventories to help 
meet other attainment plan requirements, such as RFP or motor vehicle 
emissions budgets established for transportation conformity purposes. 
That goal is not necessarily compatible with the modeling need for 
greater spatial and temporal detail, which requires much greater effort 
and expense than is practical for RFP or establishing motor vehicle 
emissions budgets. In cases where some differences are unavoidable, 
states should attempt to promote consistency where feasible.
    g. Using AERR (40 CFR part 51, subpart A) Inventory Submission to 
Meet the Requirement for the Base Year Inventory for the Nonattainment 
Area. The AERR includes both triennial and annual statewide reporting 
requirements, with more extensive reporting requirements for triennial 
inventory years. All AERR submissions are required to be made 
electronically. For the interim annual inventories, reporting is 
limited to emissions data from only the larger point sources (Type 
``A'' sources), as defined by Appendix A of 40 CFR part 51, subpart A. 
For the triennial inventories, lower point source thresholds are given 
in Appendix A, consistent with the definition of major sources in 40 
CFR part 70, and data from all other sources of emissions must be 
reported as from either nonpoint or mobile sources on a county basis.
    In the past, some states have incorrectly asserted that their AERR 
submission meets the requirements for base year inventories required by 
other implementation rules. To avoid confusion, the EPA explains here 
the limited circumstances under which the AERR emissions inventories 
will be considered to meet the base year inventory requirement for 
Moderate nonattainment areas. The following conditions must be met to 
use AERR inventories for attainment planning:
    (1) The AERR emissions inventory must have gone through the notice 
and public hearing requirements of CAA sections 110(a)(1) and 
110(a)(2).
    (2) The AERR emissions inventory includes all sources of emissions 
and all pollutants required for the base year inventory for the 
nonattainment area. This is only possible if the year for the base year 
inventory for the nonattainment area aligns with a triennial AERR year, 
because the data system implementing the AERR only accepts emissions 
from point sources and not other source categories in non-triennial 
years.
    (3) The EPA's inventory data system must be accepting data for the 
inventory year being submitted. Inventories are allowed to be submitted 
to the AERR for a given year for only a limited time during the 
development cycle of the National Emissions Inventory.
    (4) The AERR submission must include emissions from all sources 
required for the base year inventory for the nonattainment area 
consistent with 40 CFR 51.1008(a)(1), and must include mobile source 
emissions in nonattainment areas (instead of simply providing inputs or 
other data that is allowed under the AERR). In some cases, the AERR 
requirement can be met without actually ``submitting'' emissions; for 
example, states may elect to accept the EPA estimates for some nonpoint 
emissions sectors. Accepting EPA emissions does not meet the 
requirements of CAA section 172(c)(3) or this rule. In addition, the 
AERR revision finalized in February 2015 (80 FR 8787) replaces the 
prior requirement of reporting onroad mobile and nonroad

[[Page 58032]]

mobile source emissions with a requirement for reporting the input 
parameters that can be used to run the EPA models to generate the 
emissions. If choosing to use an AERR submission to meet the base year 
inventory for the nonattainment area requirement, the state should 
submit the nonattainment area emissions, irrespective of the options 
provided to meet the AERR requirements. Because the ``statewide'' 
emissions are actually provided for individual point sources and 
counties, the EPA believes that the AERR submission can be sufficient 
for most PM2.5 nonattainment areas.
    h. Mobile Source Emissions Models. A key part of emissions 
inventory development includes estimating mobile source emissions. For 
all of the mobile source inventories used for PM2.5 NAAQS 
implementation, states should use the latest emissions models available 
at the time that the attainment plan inventory is developed.\58\ In 
general, for states other than California that choose to fulfill 
various modeling requirements by using the latest EPA emissions model, 
the latest approved version of the MOVES model should be used to 
estimate emissions from onroad transportation sources. States should 
use the latest available planning emission inputs including, but not 
limited to, vehicle miles traveled (VMT), speeds, fleet mix, SIP 
control measures and fuels. The current version of MOVES is available 
at http://www.epa.gov/otaq/models/moves/index.htm. The appropriate EPA-
approved model(s) should similarly be used for California onroad source 
emissions.\59\
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    \58\ Section 172(c)(3) of the CAA requires that emission 
inventories be based on the most comprehensive, accurate and current 
information available. To do so, air agencies should use the most up 
to date method for estimating emissions.
    \59\ At this time, the California onroad mobile model is called 
EMFAC2014.
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    When using MOVES, states should follow the most current version of 
the MOVES Technical Guidance, available at http://www.epa.gov/otaq/models/moves/index.htm. MOVES includes multiple options for estimating 
and processing emissions that could result in different emissions 
inventories. The EPA recommends that states use the same approach in 
any analysis that compares two or more emissions cases (e.g., different 
control scenarios, different years). If different approaches are taken 
for inventories that serve different purposes (for example, between 
inventories developed for air quality modeling, which may require 
greater temporal and spatial detail, and inventories used as the motor 
vehicle emissions budget), states should seek to understand and 
minimize any differences in results. For example, an approach may be 
used for the modeled attainment demonstration that uses gridded 
temperatures and other meteorological data, but this approach could be 
too burdensome for use in the base year inventory for the nonattainment 
area. If a state chooses to use MOVES to create emissions inventories 
for purposes of RFP and establishing motor vehicle emissions budgets 
for transportation conformity purposes, it must use the same MOVES 
approach in the base year inventory for the nonattainment area, and 
using a straightforward MOVES approach without gridded meteorology is 
more reasonable for that purpose.
    Likewise, if states choose to fulfill various inventory 
requirements by using the latest EPA emissions model, the most current 
version of the NONROAD model or its successor must be used for 
estimates of nonroad mobile source emissions, preferably with state-
supplied model input data. States can alternatively develop 
technologically equivalent or superior state-specific nonroad emissions 
estimates, but should explain why their approach gives a better 
estimate than the EPA model. For nonroad sources not estimated by the 
NONROAD model, the best available methods should be used, and the EPA 
recommends that states refer to the SIP Emissions Inventory Guidance 
for more information on emissions from these sources. Links to Federal 
Register documents and policy guidance memos on the latest approved 
versions of MOVES and NONROAD can be found at http://www3.epa.gov/otaq/models.htm.
3. Comments and Responses
    Comment: Several commenters pointed out the uncertainties 
associated with ammonia emissions and organic matter emissions from 
livestock and fertilizer application sources, including in data 
developed by the EPA such as the National Emissions Inventory. 
Commenters pointed to the data available through the National Air 
Emissions Monitoring Study (NAEMS) for use in developing improved 
ammonia estimation approaches from livestock activities, and asserted 
that the EPA cannot move forward with SIP implementation requirements 
that implicate livestock and poultry farmers without using the NAEMS 
data. The commenters stated that not only is this technically unsound, 
but that the idea of moving forward on regulating livestock operations 
without the most critical tool for establishing requirements is a 
violation of the spirit of the consent agreements \60\ and the NAEMS.
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    \60\ In 2005, the EPA offered animal feeding operations (AFOs) 
an opportunity to participate in a voluntary consent agreement 
referred to as the Air Compliance Agreement. Under the Agreement, 
participating AFOs provided the funding for the National Air 
Emissions Monitoring Study (NAEMS)--a 2 year, nationwide emissions 
monitoring study of the animal confinement structures and manure 
storage and treatment units in the broiler, egg-layer, swine, and 
dairy industries (see 70 FR 4958).
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    Response: The EPA acknowledges that there is some uncertainty in 
quantifying ammonia emissions and other PM2.5 precursors 
from source categories such as livestock and fertilizer application. 
This uncertainty extends to the emissions and chemical composition of 
VOC and PM2.5, which also have an impact on ambient 
PM2.5. These uncertainties have an impact on attainment 
demonstrations because they cause uncertainty in the modeling done to 
demonstrate future attainment of the PM2.5 standard. 
However, the EPA disagrees with the assertion that these uncertainties 
should eliminate certain pollutants from consideration for control 
measures or should slow progress on attainment planning.
    Emissions uncertainty is a fact of air quality planning and cannot 
be avoided. Despite uncertainties in inventories of all kinds 
throughout the NAAQS program, great progress in improving air quality 
has been made through the attainment planning process and the 
implementation of control measures selected in part based on modeled 
attainment demonstrations. While emissions uncertainties remain, enough 
information is available for PM2.5 implementation planning 
purposes. The requirements contained in this final rule may drive 
further improvements in our understanding of emissions, and while the 
EPA strives to provide approaches for estimating emissions from a 
variety of source categories, the CAA places the burden for developing 
accurate emissions inventories on the states. The CAA does not allow 
for implementation of the NAAQS to be put on hold until all emissions 
uncertainties are eliminated. In fact, in spite of numerous 
uncertainties, states have developed emissions inventories for 
PM2.5 and PM2.5 precursors and performed modeling 
for PM2.5 attainment demonstrations for the previous 1997 
and 2006 NAAQS over the last 10 or more years.
    Updated emissions estimating methodologies for animal feeding 
operations are under development using data collected during the period 
2007-2009 from representative operations pursuant to the National Air 
Emissions

[[Page 58033]]

Monitoring Study.\61\ For the 2008 and 2011 national emission 
inventories, the EPA compiled state and county-level ammonia emissions 
estimates using information from state and local governments, the USDA 
Census of Agriculture and National Agriculture Statistical Service, and 
from existing ammonia emissions models. A new approach in development 
for use in the 2014 NEI uses the NAEMS data to improve the EPA's 
approach for estimating county-total emissions. The EPA expects that 
this update and other uses of the NAEMS data will help to reduce 
uncertainties in current ammonia inventories and will improve the 
quality of future emissions inventories needed for implementing the 
PM2.5 NAAQS. The EPA disagrees that implementation planning 
should wait until NAEMS results are fully available. The EPA continues 
to make progress in using these data; however, the full use and 
implementation of new methods based on these data is not a prerequisite 
for progress on considering ammonia as a PM2.5 precursor for 
the NAAQS implementation purposes. Moreover, in order for a state to 
demonstrate a precursor's insignificance (as necessary under this rule 
before excluding it from certain control or planning requirements), in 
some cases it may need to move forward without waiting until the NAEMS 
results are fully available. The EPA and USDA are continuing to work 
collaboratively to better understand agricultural ammonia related 
emissions in order to more accurately represent the emissions and 
impacts of ammonia in relation to PM2.5.
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    \61\ For more information on the NAEMS study, see: http://www3.epa.gov/airquality/agmonitoring/.
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    Comment: Commenters supported the EPA's proposed approach to 
require distinct emissions for filterable and condensable 
PM2.5. Commenters asserted that this proposed requirement 
created an additional inventory requirement beyond what is already 
required in the AERR. Commenters also asserted that this requirement 
places an unnecessary burden on states and industry.
    Response: The EPA disagrees with the assertion that an additional 
inventory requirement has been imposed by this rule. Within the AERR, 
40 CFR 51.15(a)(1)(vi) states (with regard to what must be reported): 
``Primary PM2.5. As applicable, also report filterable and 
condensable components.'' The term ``also'' implies ``in addition to 
total primary PM2.5,'' and the phrase ``as applicable'' is 
intended to mean when such emissions are emitted from the source. This 
requirement has been in place since 2008, providing ample time for 
states to ensure compliance with this reporting requirement in advance 
of this final rule. Furthermore, the EPA points out that it would be 
much more difficult for the EPA to assess (as part of evaluating an 
attainment plan) whether states have met the requirement to include 
condensable emissions, and thus a complete PM2.5 inventory, 
without the states providing condensable emissions as something 
separate and distinct from filterable and total PM2.5. In 
addition, having a complete emission inventory of filterable and 
condensable PM2.5 emissions will enable a state to better 
identify contributing sources and develop a more effective plan.
    The EPA also notes that new electric generating units that are 
subject to (40 CFR part 60, subpart Da) without PM continuous emissions 
monitors (CEMs) have to conduct annual testing for condensable PM using 
Method 202 of appendix M of part 51.
    Comment: Some commenters supported the EPA's proposed approach to 
require an attainment projected inventory for the nonattainment area. 
Other commenters asserted that such an inventory should not be required 
because it has not been required before and because the attainment 
demonstration is sufficient.
    Response: The EPA disagrees with the latter commenters, noting that 
the rationale that such inventories have not been required before is 
not in and of itself a reasonable basis on which to exclude such a 
requirement now. The purpose of these inventories is well justified by 
the need for both the EPA and the public to be able to compare, during 
their reviews of the attainment plan, the base year inventory to the 
attainment projected inventory. Without such information, it is 
extremely difficult for the EPA to assess the projected emissions 
changes in the nonattainment area that the state asserts contribute to 
attainment. The attainment projected inventory may also play a role in 
meeting the RFP requirements of this rule. Furthermore, while the EPA 
has not explicitly required submittal of an attainment projected 
inventory in regulation, many states have developed such future year 
inventories as part of attainment demonstrations and have submitted 
them as part of PM2.5 attainment plans in the past, thus 
demonstrating their viability and utility.
    Comment: Commenters supported the EPA's proposed approach to allow 
seasonal inventories. Some commenters requested the use of clear 
language stating an allowance for episode-specific inventories in lieu 
of seasonal inventories.
    Response: The EPA agrees with the commenters that for some source 
categories, seasonally averaged winter conditions would not be 
sufficient to represent the conditions leading to violations of the 24-
hour PM2.5 standard. As described in Section IV.B.2.c of 
this preamble, some modifications have been made to the explanation of 
seasonal inventories to clarify that it would be reasonable to use an 
episodic average from the modeled attainment demonstration in some 
cases.

C. Pollutants To Be Addressed in the Plan

    Under subpart 4 of the CAA, states are presumptively required to 
analyze and evaluate emissions reduction measures for all sources of 
direct PM2.5 and PM2.5 precursors (i.e., 
SO2, NOX, VOC and ammonia) in developing 
PM2.5 attainment plans. Direct PM2.5 emissions 
include both filterable and condensable PM2.5 emissions. See 
further discussion of filterable and condensable PM2.5 
emissions in the background section (Section II of this preamble) and 
in the emissions inventory requirements for Moderate area attainment 
plans (Section IV.B of this preamble). Thus, a state must evaluate 
control measures for sources of filterable and condensable 
PM2.5 emissions as part of an approvable control strategy 
for a Moderate PM2.5 nonattainment area.
    With regard to PM2.5 precursors, Section III of the 
preamble describes that the rule provides for the possibility that the 
state may demonstrate that nonattainment area emissions of a particular 
precursor may not make a significant contribution to PM2.5 
levels that exceed the standard in the area, or that emissions 
reductions of the precursor may not be needed for expeditious 
attainment. Thus, the rule presumptively requires the state to evaluate 
potential control measures for all four precursors, but the state may 
not need to address one or more requirements for a particular precursor 
with an approvable precursor demonstration.

D. Attainment Plan Control Strategy

1. Background on Attainment Planning and the Evaluation of Control 
Measures
    a. Summary of Proposal. The proposal included an overview of the 
statutory requirements and general guidance associated with attainment 
planning and evaluation of control measures.
    b. Final Rule. The following overview of statutory requirements and 
general

[[Page 58034]]

guidance remains unchanged except as discussed in this final rule.
    The attainment planning requirements of subparts 1 and 4 were 
established to ensure that two important CAA goals are met: (i) That 
states implement measures that provide for attainment of the 
PM2.5 NAAQS as expeditiously as practicable, but not later 
than the statutory attainment date; and (ii) that states adopt 
effective emissions reduction strategies in nonattainment areas. The 
Moderate nonattainment area attainment date is as expeditiously as 
practicable, but not later than the end of the sixth calendar year 
after designation.
    CAA section 172(c) of subpart 1 of the CAA describes the general 
attainment plan requirement for RACM and RACT, requiring that 
attainment plan submissions ``provide for the implementation of all 
reasonably available control measures as expeditiously as practicable 
(including such reductions in emissions from existing sources in the 
area as may be obtained through the adoption, at a minimum, of 
reasonably available control technology) and shall provide for 
attainment'' of the NAAQS.\62\ The attainment planning requirements in 
subpart 4 that are specific to PM10 (including 
PM2.5) likewise impose upon states an obligation to develop 
attainment plans that require RACM and RACT for sources of direct 
PM2.5 and PM2.5 precursors within a Moderate 
nonattainment area. CAA section 189(a)(1)(C) requires that states with 
areas classified as Moderate have attainment plan provisions to assure 
that RACM/RACT are implemented by no later than 4 years after 
designation of the area.\63\ The EPA reads CAA sections 172(c)(1) and 
189(a)(1)(C) together to require that attainment plans for Moderate 
nonattainment areas must provide for the implementation of RACM and 
RACT for existing sources of PM2.5 and PM2.5 
precursors in the nonattainment area as expeditiously as practicable 
but no later than 4 years after designation.\64\ The terms RACM and 
RACT are not defined within subpart 4, nor do the provisions of subpart 
4 specify how states are to meet the RACM and RACT requirements. 
However, the EPA's longstanding guidance in the 1992 General Preamble 
helps inform our interpretation of RACM and RACT for the purpose of 
implementing the PM2.5 NAAQS.
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    \62\ Because in CAA section 172(c) the term ``reasonably 
available control measures,'' or RACM, also includes ``reasonably 
available control technology,'' or RACT, this document uses the 
abbreviation ``RACM/RACT'' to represent these requirements 
collectively, where appropriate.
    \63\ States with areas later reclassified as ``Serious'' 
nonattainment areas under subpart 4 must also develop and submit 
later plans to meet additional requirements for Serious areas. See 
40 CFR 51.1003(b).
    \64\ This interpretation is consistent with guidance described 
in the General Preamble. See 57 FR 13498 (April 16, 1992), at page 
13540.
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    The EPA's guidance on RACM for sources of PM10 and 
PM10 precursors under subpart 4 in the General Preamble and 
Serious area Addendum includes the following: (i) A recommended list of 
potential measures to reduce PM10 for states to consider; 
\65\ (ii) an emphasis on state evaluation of the technological and 
economic feasibility of potential control measures to determine whether 
such measures are reasonably available for implementation; (iii) an 
expectation that the state will provide a reasoned explanation for a 
decision not to adopt a particular control measure, including those 
measures recommended to the state in public comments or at a public 
hearing; and (iv) a discussion that in some cases partial 
implementation of an emissions reduction program may be considered RACM 
when full implementation would be infeasible within the given Moderate 
area timeframe.\66\ Thus, the RACM requirement under subpart 4 applies 
to all types of sources and is not focused only on forms of control 
that are technology-based.
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    \65\ The appendices to the General Preamble, 57 FR 18070 (April 
28, 1992), included sections on available fugitive dust control 
measures, available residential wood combustion measures, and 
available prescribed burning control measures.
    \66\ See 57 FR 13498 (April 16, 1992), at pages 13540-41. See 
also the Addendum.
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    With respect to RACT requirements, the EPA's guidance in the 
General Preamble includes the following: (i) RACT has historically been 
defined as ``the lowest emission limit that a source is capable of 
meeting by the application of control technology that is reasonably 
available considering technological and economic feasibility''; (ii) 
RACT generally applies to stationary sources, both stack and fugitive 
emissions; (iii) major stationary sources (i.e., sources with potential 
to emit 100 tons per year or more of direct PM2.5 or any 
PM2.5 precursor) should be the minimum starting point for a 
state's RACT analysis, but states are recommended to evaluate RACT for 
smaller stationary sources as needed for attainment and considering the 
feasibility of controls; \67\ and (iv) it is possible that a State 
could demonstrate that an existing source in an area should not be 
subject to a control technology especially where such technology is 
unreasonable in light of the area's attainment needs, or such 
technology is infeasible. In such a case, it could be concluded that no 
control technology is ``reasonably available,'' and RACT for the source 
could be considered to be no additional control.\68\ Thus, the RACT 
requirement under subpart 4 is primarily focused on stationary sources 
and forms of emissions control that are technology-based.
---------------------------------------------------------------------------

    \67\ Ibid.
    \68\ Ibid.
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    The appendices to the General Preamble noted that reducing air 
emissions may not justify adversely affecting other resources, for 
example, by increasing pollution in bodies of water, creating 
additional solid waste disposal problems or creating excessive energy 
demands. An otherwise available control technology may not be 
reasonable if these other environmental impacts are sufficiently 
adverse and cannot reasonably be mitigated. A state may consider a 
control measure for direct PM2.5 or a PM2.5 
precursor not reasonable if, considering the availability of mitigating 
adverse impacts of that control on pollution of other media, the 
control would not, in the state's reasoned judgment, provide a net 
benefit to public health and the environment. It should be noted that, 
in many past situations, states and owners of existing sources have 
adopted control technologies for direct PM2.5 and/or 
PM2.5 precursors with known energy penalties and some 
adverse effects on other media, based on the reasoned judgment that 
installation of such technology would result in a net benefit to public 
health and the environment. States should consider this before 
determining that a control technology is not reasonable because it may 
have other, negative environmental impacts that are on balance 
marginal.
    This final rule specifies the basic requirements that states must 
meet in identifying and selecting the complete suite of measures needed 
for an attainment plan submission for a Moderate PM2.5 
nonattainment area. This preamble, together with the General Preamble, 
provides further description of the recommended process for states to 
follow in meeting these requirements. Under this process, the specific 
determination of RACM and RACT is to be made within the broader context 
of assessing control measures for all stationary, area and mobile 
sources of direct PM2.5 and PM2.5 precursors that 
would collectively contribute to meeting the Moderate area attainment 
date as expeditiously as practicable.\69\
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    \69\ In Sierra Club v. EPA, 294 F.3d 155 (D.C. Cir. 2002), the 
court stated, in upholding the EPA's statutory interpretation of 
RACM, that the CAA does not compel a state to consider a measure 
without regard to whether it would expedite attainment.

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[[Page 58035]]

    The final rule requires that all moderate area plans contain RACM, 
which is defined as any technologically and economically feasible 
measure that can be implemented in whole or in part within 4 years 
after the effective date of designation of a PM2.5 
nonattainment area and that achieves permanent and enforceable 
reductions in direct PM2.5 emissions and/or PM2.5 
precursor emissions from sources in the area. RACM includes reasonably 
available control technology (RACT). The EPA recommends that to meet 
this definition, the state should follow a process by which it first 
identifies all sources of emissions of direct PM2.5 
(including filterable and condensable PM2.5) and all 
PM2.5 precursors in the nonattainment area, and all 
potential control measures to reduce emissions from those source 
categories.\70\ The state next determines if any of the identified 
potential control measures are not technologically feasible and whether 
any of the identified technologically feasible control measures are not 
economically feasible. Measures that are not necessary for attainment 
need not be considered as RACM/RACT.\71\
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    \70\ The proposal described situations where some control 
measures could be exempted from consideration at the beginning of 
the analytical process. For example, control measures for a 
particular precursor would not need to be evaluated if the air 
agency submits an acceptable precursor demonstration as described in 
Section III of the preamble.
    \71\ This has been the EPA's longstanding interpretation of 
RACM/RACT in CAA sections 172(c)(1) and 189(a)(1)(C), which were 
enacted as part of the amendments to the Act in 1990. Even prior to 
the 1990 amendments, the EPA interpreted the statutory term RACM to 
encompass only those measures ``necessary to assure reasonable 
further progress and attainment by the required date.'' 44 FR 20375 
(Apr. 4, 1979); see 40 CFR 51.1(o) (1972) (defining RACT in similar 
terms); 42 U.S.C. 7502(b)(2) (1988) (requiring RACM in the precursor 
to current CAA section 172(c)(1)). In the 1990 amendments to the 
Act, Congress enacted a ``[g]eneral savings clause'' stating that 
``[e]ach regulation, standard, rule, notice, order and guidance 
promulgated or issued by [EPA] under this chapter, as in effect 
[before the 1990 Amendments], shall remain in effect according to 
its terms.'' 42 U.S.C. 7415. Since the passage of the 1990 
amendments, the EPA's interpretation of RACM and RACT as 
encompassing only those measures necessary to advance attainment has 
been upheld in multiple U.S. Circuit Courts of Appeals. See NRDC v. 
EPA, 571 F.3d 1245, 1251-1253 (D.C. Cir. 2009); Sierra Club v. EPA, 
314 F.3d 735, 743-744 (5th Cir. 2002); Sierra Club v. EPA, 294 F.3d 
155, 162 (D.C. Cir. 2002). But cf. Sierra Club v. EPA, 793 F.3d 656 
(6th Cir. 2015) (holding that an area must have subpart 1 RACM/RACT 
approved into its SIP prior to redesignation, regardless of whether 
the area is attaining the NAAQS).
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    Measures that can only be implemented after the 4-year deadline for 
RACM and RACT, but before the end of the sixth calendar year following 
designation, are defined in the final rule as ``additional reasonable 
measures.'' \72\ The EPA has created this new definition based on the 
recognition that in some areas there could be emission reduction 
strategies that still could be implemented beginning 4 years after 
designation through the attainment date that could help to improve air 
quality and attain the standard expeditiously in the area. Note also 
that the state has discretion to require reductions from any source 
inside or outside of a PM2.5 nonattainment area (but within 
the state's boundaries) in order to fulfill its obligation to 
demonstrate attainment in a PM2.5 nonattainment area as 
expeditiously as practicable, and it may need to require emissions 
reductions on sources located outside of a PM2.5 
nonattainment area if such reductions are needed in order to provide 
for expeditious attainment of the PM2.5 NAAQS.
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    \72\ In addition to the statutory requirements under CAA 
sections 172(c)(1) and 189(a)(1)(C) for RACM and RACT, CAA section 
172(c)(6) requires that a state's attainment plan for a 
nonattainment area ``include enforceable emission limitations, and 
such other control measures, means or techniques (including economic 
incentives such as fees, marketable permits, and auctions of 
emission rights), as well as schedules and timetables for 
compliance, as may be necessary or appropriate to provide for 
attainment of such standard in such area by the applicable 
attainment date specified in this part.'' The EPA interprets this 
statutory provision to require a state to identify, select and 
implement additional measures to those identified as RACM and RACT 
for the area if needed to provide for timely attainment of the area. 
In the EPA's proposed approach, the EPA describes criteria for 
identifying and selecting ``additional reasonable measures'' for 
sources of direct PM2.5 and PM2.5 precursors 
in a Moderate nonattainment area which may be necessary in order to 
bring the area into expeditious attainment.
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    Lastly, the final rule requires the state to perform an analysis 
(typically an air quality modeling analysis) to determine the earliest 
practicable attainment date for the area. This analysis should take 
into account projected emissions reductions associated with existing 
federal and state regulations, plus any additional reductions that 
would be achieved due to new control measures that would be needed for 
expeditious attainment.
    In the case of a Moderate area that can demonstrate it can attain 
by the statutory attainment date without implementing all reasonably 
available control measures (i.e. RACM/RACT and additional reasonable 
measures), the state would not be required to adopt certain otherwise 
reasonable measures if the state demonstrates that collectively such 
measures would not enable the area to attain the standard at least 1 
year earlier (i.e., ``advance the attainment date'' by 1 year). The EPA 
has long applied this particular test to satisfy the statutory 
provision related to an area demonstrating attainment ``as 
expeditiously as practicable.'' \73\ The EPA continues to believe that 
this approach provides an appropriate degree of flexibility to a state 
to tailor its attainment plan control strategy to the actual attainment 
needs of a particular PM2.5 nonattainment area. In the case 
of a Moderate area that cannot demonstrate that it will practicably 
attain by the statutory attainment date, the state would be required to 
evaluate potential control measures for sources in the nonattainment 
area and adopt all reasonable measures (i.e., RACM and RACT, and any 
``additional reasonable measures'').
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    \73\ The term ``expeditious attainment'' is used throughout this 
proposal to describe the ability of a nonattainment area to attain 
``as expeditiously as practicable'' based on the test described 
here.
---------------------------------------------------------------------------

    The following sections of the preamble describe the steps of the 
control measure evaluation process in more detail, and include 
discussion of the consideration of public comments as appropriate.
2. Step 1: Identify Sources of Emissions
a. Summary of Proposal
    The proposal stated that the identification of all sources of 
emissions of direct PM2.5 (including filterable and 
condensable PM2.5) and all four PM2.5 precursors 
in the nonattainment area is the starting point for the state's 
analysis of potential control measures. It was noted that an exception 
to this comprehensive review requirement might be possible if the final 
rule includes a policy that would allow a state to demonstrate that one 
or more precursors in a nonattainment area do not significantly 
contribute to PM2.5 levels that exceed the standard. If such 
a demonstration were approved by EPA, then the state would not be 
required to adopt control measures for the precursor.
    The proposal also included discussion of a possible de minimis 
source category exemption concept for Moderate areas. Under the 
approach, the analysis and identification of ``de minimis source 
categories'' for Moderate areas would occur early in the planning 
process, before potential control measures are identified or attainment 
modeling is conducted. The proposal recognized the challenges 
associated with defining ``source categories.'' The proposal also 
included potential options on how source categories could be defined, 
and requested comment on using the North American Industry

[[Page 58036]]

Classification System (NAICS) (which provides a detailed hierarchy of 
numeric codes for different industries and process types) at the two, 
four, or six digit levels.
    The proposal also presented the concept of a possible bright line 
ambient impact threshold for determining whether a source category 
should be considered de minimis (in the event a de minimis concept is 
adopted). Comments were requested on two options: (1) No bright line 
threshold; and (2) a threshold in the range of 1-3 percent of the 
relevant PM2.5 NAAQS. This range was selected because it was 
similar to the de minimis source category threshold range (2.0-3.3 
percent of the PM10 NAAQS) included in the 1994 Serious Area 
Addendum.
b. Final Rule
    Section 172(c)(3) of the CAA requires that attainment plans for 
PM2.5 nonattainment areas include a ``comprehensive, 
accurate, current inventory of actual emissions from all sources of the 
relevant pollutant or pollutants.'' Consistent with the proposal, the 
final rule maintains the policy that the state must begin the control 
consideration process by identifying potential control measures for all 
the sources included in the most recently available emissions inventory 
for the nonattainment area. The inventory must include emissions 
information for all existing major stationary sources as point sources, 
nonpoint sources (as defined by 40 CFR 51.50) including non-major point 
sources, and mobile sources of direct PM2.5 (including 
filterable and condensable PM2.5) and PM2.5 
precursors in the nonattainment area. Section IV.B of this preamble 
provides a detailed discussion of emission inventory requirements.
    The rule requires that a state must identify all of the sources 
reflected in the nonattainment area's base year inventory as the 
initial step in developing reasonable control measures for the area, as 
each of these sources may play a role in the area's PM2.5 
problem. A state would need to consider all inventoried sources of 
direct PM2.5 emissions (including filterable and condensable 
PM2.5) and sources of all four scientific PM2.5 
precursors as it conducts its determination of reasonable control 
measures for an area.
    Some commenters suggested that subpart 4 only provides authority to 
regulate precursors from major stationary sources and not from other 
types of sources, such as area or mobile sources. However, EPA 
disagrees with these commenters, given that the CAA provides an 
overarching requirement to attain the standard as expeditiously as 
practicable, PM2.5 precursor emissions play a very 
significant role in fine particle concentrations nationally, non-major 
sources are important sources of precursor emissions, and nothing in 
the statutory requirements for RACM and BACM limits these requirements 
only to major stationary sources.
    As discussed in the previous section, the final rule provides that 
states may develop a precursor demonstration showing that a particular 
PM2.5 precursor does not contribute significantly to 
PM2.5 levels that exceed the standard. If such a 
demonstration is approved by the EPA, then the state would not be 
required to adopt control measures for the precursor. Note that the 
state would still be obligated to evaluate and adopt control measures 
from a source if the source has emissions of direct PM2.5 
and/or the remaining PM2.5 precursors that must be 
controlled in the plan.
    The EPA received a diverse set of comments on whether to include a 
de minimis source category exemption policy. Some commenters questioned 
why an up-front (i.e., before analysis of potential control measures) 
source category by source category exemption should be included in the 
final rule in the first place, when the traditional RACT/RACM policy 
approach for the NAAQS implementation has enabled states not to adopt 
otherwise reasonable control measures if after analyzing potential 
control measures it is determined that such measures are not needed for 
expeditious attainment. These commenters also suggested that a de 
minimis source category approach would undermine any RACM/RACT analysis 
to evaluate whether a collection of measures could advance the 
attainment date by a year, because a de minimis exemption policy would 
potentially allow for an area to exempt many categories which together 
could have a substantial ambient impact. Other commenters noted that 
providing a source category exemption in one nonattainment area would 
give those companies a competitive advantage over the same types of 
sources in other areas.
    A number of commenters supported the de minimis source category 
concept because they believed it could result in a reduced burden in 
the control measure evaluation stage and help avoid regulating sources 
with limited impact on PM2.5 levels. However, a number of 
commenters also expressed concern about the analytical resources that 
might be needed to conduct air quality modeling for a de minimis source 
category analysis. To address this analytical concern, some commenters 
suggested that the EPA include an emissions-based threshold (e.g., tons 
per day) rather than an air quality based threshold, and allow for its 
use only if controls on the source are not needed for expeditious 
attainment. However, the commenters did not address the fact that the 
air quality impact of a specific tons per day rate could vary widely 
from one pollutant to another within a particular nonattainment area. 
Other commenters noted that the NAICS system does not provide 
categories for nonpoint sources, and that this issue would need to be 
addressed if the NAICS approach were to be included in the final rule. 
Other commenters suggested that the rule not have a de minimis 
threshold at all but include the ability for the state to propose de 
minimis source categories to the EPA on a case-by-case basis.
    After taking the range of comments on the de minimis source 
category concept into consideration, the EPA has decided to not 
finalize a de minimis source category approach for Moderate areas. The 
EPA is persuaded by commenters who argued it is not necessary, and 
believes that without this concept, the final rule will nevertheless 
provide sufficient flexibility in the Moderate area control measure 
analysis and attainment demonstration process due to the availability 
of precursor demonstrations, considerations of case-specific factors in 
determining technical and economic feasibility, and the longstanding 
ability for the state not to adopt certain otherwise reasonable 
measures if they are not needed for expeditious attainment. The EPA 
also finds that from a technical perspective, it would be very 
challenging to implement a de minimis source category process in a 
consistent manner nationally without clear guidelines describing how 
narrowly or how broadly a de minimis exemption could apply, or how the 
technical analysis would need to be performed. The EPA agrees with 
commenters that NAICS codes do not provide an appropriately 
comprehensive approach for defining source categories for this purpose. 
We note that a de minimis source category exemption process has been 
available in PM10 NAAQS implementation guidance (the 
Addendum) since 1994, and remains available. In many PM10 
areas, it is relatively straightforward to identify the predominant 
source categories contributing to the NAAQS violations (such as direct 
PM emissions from dust or wood smoke), and therefore to be able to 
identify what categories might be considered de

[[Page 58037]]

minimis. However, implementation of the PM2.5 NAAQS presents 
more complex challenges. Precursors and their contribution to 
secondarily formed PM play a much greater role in PM2.5 
nonattainment areas than in PM10 nonattainment areas. In 
addition, the relative impact of each precursor to local 
PM2.5 concentrations varies from area to area. For these 
reasons, a de minimis source category concept for PM2.5 is 
not included in this final rule.
c. Comments and Responses
    Any additional comments received on this section are addressed in 
the Response to Comments document found in the docket for this action.
3. Step 2: Identify Existing and Potential Control Measures
a. General Guidance
i. Summary of Proposal
    The proposal preamble described general guidance for identifying 
existing and potential control measures.
ii. Final Rule
    The guidance remains largely unchanged from the proposal. The 
state's compilation of existing and potential control measures \74\ 
should be sufficiently broad to provide a basis for identifying all 
technologically and economically feasible controls that may be RACM or 
RACT for sources of direct PM2.5 (including filterable and 
condensable PM2.5) and PM2.5 precursor emissions 
in the nonattainment area at issue. Because RACM applies to area and 
mobile sources as well as stationary sources, states should identify 
and consider control measures for all types of sources.\75\
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    \74\ Note that the term ``control measures'' as used in this 
preamble broadly represents a range of enforceable approaches for 
reducing emissions. These enforceable approaches include, but are 
not limited to, installation of control technology, process changes, 
a change in fuel use, limitations on use or operation of a 
particular pollutant-emitting device, equipment replacement, dust 
minimization practices, and road paving.
    \75\ Additional guidance on evaluating potential control 
measures is provided in the previous Section III.D.1 of this 
preamble, Background.
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    It is important to note that the emission inventory provisions of 
this rule require states with sources of direct PM2.5 to 
include emissions data for both filterable PM2.5 and 
condensable PM2.5 in the base year inventory for the 
nonattainment area. For some types of sources, condensable emissions 
can be much larger than filterable emissions, in some cases by ten 
times or more. Because the availability of condensable PM2.5 
emissions data has been limited to date but more data will become 
available through nonattainment planning efforts, the EPA recommends 
that states pay particular attention to identifying potential control 
measures for source categories with substantial condensable emissions. 
If measures are found to be technically and economically feasible for 
reducing condensable PM2.5 emissions as well as filterable 
PM2.5 emissions from a source, the state will need to adopt 
a new emissions limit for the source that accounts for both the 
filterable and condensable portions, and includes requirements for 
ensuring compliance using source test methods updated in 2011.\76\
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    \76\ See 75 FR 80118 (December 21, 2010), revisions to test 
methods for measuring condensable PM emissions from stationary 
sources (Method 202).
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    The control measure evaluation process described in this section 
generally allows states to apply reasoned judgment as they identify 
potential control measures for sources of direct PM2.5 and 
PM2.5 precursors in their respective nonattainment areas. In 
section 51.1009(a)(3)(iii) of the final rule, the state is required to 
include a complete and reasoned explanation to support its selection 
and rejection of control measures as part of the attainment plan 
submission for any Moderate nonattainment area.
    Existing control measures. As a starting point when identifying 
candidate control measures, a state should include an initial list of 
control measures that are being implemented or will be implemented due 
to promulgated and/or adopted (i.e., ``on the books'') regulations for 
sources of direct PM2.5 and PM2.5 precursors in 
its Moderate PM2.5 nonattainment area. The EPA expects that 
the state will incorporate anticipated emissions reductions from these 
``existing'' control measures (such as expected SO2 
reductions from the MATS; reductions of NOX and direct 
PM2.5 from engine and fuel standards to reduce emissions 
from on-road and nonroad mobile sources) into its attainment 
demonstration modeling for the nonattainment area, and therefore the 
EPA believes it is appropriate for the state to clearly indicate the 
existence of such measures in the attainment plan for the area.
    The EPA recognizes that for some sources located in a Moderate 
PM2.5 nonattainment area, a state may have previously 
conducted control technology analyses to address emissions for previous 
RACM/RACT analyses or for other statutory purposes. Some of these 
determinations may have been done relatively recently, while other 
determinations may be several years old. A state may not simply rely on 
a previous RACM or RACT determination or other control technology 
analysis for a particular source or source category, regardless of how 
recently it was performed, when developing the attainment plan for a 
PM2.5 NAAQS. Past experience has shown that due to ongoing 
innovation, cost-effective control technologies and process 
alternatives for many sectors continue to be developed, and new 
reasonable opportunities to reduce emissions in the future are expected 
to be available for existing sources, particularly those with 
technology determinations made several years ago. For this reason, the 
state must determine whether the existing controls or emissions 
reduction approach at the source can be updated or improved with 
reasonably available controls or strategies to achieve increased levels 
of emission reduction. In cases where a stationary source has installed 
new state-of-the-art emissions controls fairly recently (e.g., within 
the last 3 years), the state technically would still need to provide a 
RACT analysis for the source, but in such cases it may be appropriate 
to find that existing controls satisfy the RACT requirement. Based on 
this policy, the state's updated RACM and RACT analyses will represent 
the most thorough, up-to-date review of control measures for its 
PM2.5 nonattainment area. The collection of existing control 
measures, any updated RACT/RACM determinations, and potential new 
control measures can then be considered together by the state as part 
of a comprehensive analysis to ensure the area will attain 
expeditiously. The EPA notes, however, that the more recently this 
analysis has been done, the less effort is expected to be needed to 
verify that it is up to date.
    Potential control measures. In addition to identifying and 
reviewing existing control measures for sources in a Moderate 
PM2.5 nonattainment area, a state must develop a 
comprehensive list of potential new control measures. This process 
should involve close coordination between the state, source owners, 
municipalities, and other interested stakeholders. The potential 
measures should also have a strong technical basis. Analysis of 
emission inventory data summaries, fine particle speciation monitoring 
data and source apportionment air quality modeling data can help 
identify key sectors contributing to the PM2.5 problem in an 
area. Other analyses to characterize the seasonal variation of 
PM2.5

[[Page 58038]]

concentrations and associated meteorology may help inform the state in 
identifying contributing sources and potential control measures.
    Information about potential control measures and control 
technologies is available from a number of sources. One important 
source of information is the combined regulatory experience of other 
states. A compilation of existing control regulations that are on the 
books in other states can be a useful starting point for identifying 
potential control measures. Another source of information is the EPA's 
Office of Air Quality Planning and Standards (OAQPS) ``Menu of Control 
Measures'' document, available online at http://www3.epa.gov/ttn/naaqs/pdfs/MenuOfControlMeasures.pdf. This document was developed to provide 
information useful in the development of local emissions reduction and 
the NAAQS SIP scenarios, and identifying and evaluating potential 
control measures. It provides a broad, though not comprehensive, 
listing of potential emissions reduction measures for direct 
PM2.5 and precursors of ozone and PM2.5 from 
stationary, area and mobile sources. More complete information on 
mobile source control measures can be found on the EPA's Office of 
Transportation and Air Quality Web site at http://www.epa.gov/otaq.
    The RACT/BACT/LAER Clearinghouse (RBLC) provides a central database 
of air pollution technology information (including past RACT, BACT and 
LAER decisions contained in NSR permits) to promote the sharing of 
information among permitting agencies and to aid in future case-by-case 
control measure determinations. The RBLC permit database contains over 
5,000 determinations that can help a state identify appropriate 
technologies to mitigate most air pollutant emission streams. The RBLC 
includes data submitted by several U.S. territories and all 50 states 
on over 200 different air pollutants and 1,000 industrial processes, 
and can be searched for control approaches that address specific 
pollutants. The RBLC can be found at: http://cfpub.epa.gov/rblc.
    Additionally, the EPA maintains a Web site with links to other 
online sources of information on control measures for states to 
consider.\77\ Again, the EPA recognizes that control technology 
guidance for certain source categories has not been updated for many 
years, and, for this reason, the agency expects states to identify and 
consider new and updated information in their RACM and RACT 
determinations as it becomes available.
---------------------------------------------------------------------------

    \77\ Links are provided to a number of national, state and local 
air quality agency sites from the EPA's PM2.5 Web site: 
http://www3.epa.gov/pm/measures.html.
---------------------------------------------------------------------------

iii. Comments and Responses
    Any additional comments received on this section are addressed in 
the Response to Comments document found in the docket for this action.
b. Managing Emissions From Wildfire and Wildland Prescribed Fire.
i. Proposed Rule
    The EPA proposed to recommend as guidance but not as a requirement 
of the final rule that, if wildfire impacts are significant, 
contributing to exceedances of the standard, then states should 
consider RACM for wildfires (which RACM could include a required 
program of prescribed fires). The EPA also proposed to recommend that 
states should consider RACM for managing emissions from prescribed 
fires (including those prescribed fires conducted to reduce future 
wildfire emissions). The proposal noted that information is available 
from the DOI and the USDA Forest Service on smoke management programs 
and basic smoke management practices (BSMP). The EPA requested comment 
on the concept of, and practical considerations associated with RACM 
for wildfire and RACM for prescribed fire, including such issues as how 
such measures can be characterized in the emissions inventory and 
attainment demonstration and made federally enforceable for adoption in 
a SIP.
ii. Final Rule
    Wildfire can make a large contribution to air pollution (including 
PM2.5), and wildfire events can threaten public safety. 
These effects can be mitigated through management of wildland 
vegetation, including through prescribed fire. Such mitigation can help 
manage the contribution of fires to PM2.5 levels in 
nonattainment areas. Prescribed fire (and some wildfires) can mimic the 
natural processes necessary to maintain fire dependent ecosystems, 
minimizing catastrophic wildfires and the risks they pose to safety, 
property and air quality.
    Upon consideration of public comments and further consultation with 
other federal agencies, the EPA recommends, as guidance for states as 
they implement the final rule, that states follow a different approach 
to addressing RACM for wildland fire than the approach that the EPA 
proposed to recommend. Before explaining this recommendation further, 
the EPA wishes to clarify that the recommendation is focused on 
wildland fire management. There are other uses of prescribed fire and 
other types of burning that occur in nonattainment areas, or that 
affect downwind nonattainment areas, such as burning of land clearing 
debris, agricultural burning, and burning of logging slash on land 
where the primary purpose of the logging is for commercial timber 
sale.\78\ The challenges with applying the traditional nonattainment 
planning framework that are raised in this discussion are particular to 
wildland fire, and the EPA believes that addressing these other uses of 
prescribed fire does not present nearly the same level of challenge, 
and thereby can still be accommodated within the nonattainment planning 
framework. For example, where these other types of burning currently 
contribute to PM2.5 levels in a nonattainment area, states 
may, with an adequate technical demonstration, be able to take credit 
for reductions resulting from improvement in smoke management 
techniques for these types of prescribed fire where the improvement 
results in a demonstrated reduction in impacts in the nonattainment 
area. The remainder of this discussion is not meant to address these 
categories, and is instead focused on prescribed fire on wildlands.
---------------------------------------------------------------------------

    \78\ The EPA notes that some wildland logging operations are 
conducted for the same purposes as prescribed fire (e.g., reducing 
fuel load, ecosystem benefits, etc.). The fact that some of the 
removed trees may be sold as timber does not make commercial timber 
sale the primary purpose of such operations.
---------------------------------------------------------------------------

    The EPA also wants to clarify that it is not the intention to in 
any way discourage federal, state, local or tribal agencies or private 
land owners from taking situation-appropriate steps to minimize impacts 
from prescribed fire emissions on wildland. The EPA encourages all land 
owners and managers to apply appropriate basic smoke management 
practices to reduce emissions from prescribed fires, especially where a 
state has determined that prescribed fires are a significant source 
affecting air quality. The EPA understands that the federal land 
managers (FLMs) apply these measures routinely and will be available to 
consult with other agencies and private parties interested in doing the 
same.
    However, for several reasons, the EPA does not believe it would be 
effective policy or technically appropriate to recommend that control 
measures for wildland fire be adopted into the SIP as enforceable 
measures and credited for emissions reductions (of PM2.5 and 
precursors) that would help the area

[[Page 58039]]

attain the standard.\79\ Instead, EPA recommends that PM2.5 
nonattainment plans (and in particular the attainment demonstrations) 
not expressly account for expected air quality changes over the 
planning period resulting from changes in the use of wildland 
prescribed fire to reduce future wildfires, or air quality changes over 
the planning period resulting from changes in wildland fire emissions 
due to a program of prescribed fire or due to any other cause including 
climate change. In most cases, state attainment demonstration modeling 
should assume that wildland prescribed fire and wildfire emissions in 
the attainment year will be equal to, and have the same temporal and 
geographic pattern as, those assumed in the baseline inventory year.
---------------------------------------------------------------------------

    \79\ These reasons include concerns raised by commenters about 
the difficulties associated with requiring or even encouraging 
states to incorporate wildland fire emissions into existing 
nonattainment planning procedures and practices under the CAA; high 
year-to-year variability and unpredictability with emissions from 
wildland fires; uncertainty in the amount of credit to give for 
reduced wildfire within the planning period and in the amount of 
benefit that exists after accounting for increases in prescribed 
fires within the planning period; and finally, the fact that air 
quality data actually influenced by fire events may ultimately be 
excluded under the provisions of the Exceptional Events Rule.
---------------------------------------------------------------------------

    The EPA acknowledges that some temporal and spatial patterns of 
fire emissions must still be assumed in the attainment demonstration in 
order to ensure that the required air quality modeling results in a 
realistic physical and chemical environment and a correspondingly 
realistic model response against which to analyze the changes from 
categories where express accounting of changes is still being done. 
This rule is not intended to constrain the options for states regarding 
the appropriate assumptions to make for fire emissions. Rather, it 
simply recommends that once this base level is established, 
PM2.5 plans should not attempt to expressly project changes 
over the planning period in emissions from wildfires or prescribed 
fires on wildland within the nonattainment area, or in upwind areas 
included in the modeling domain, that are due to variability in 
wildfire occurrence or changes in the use of prescribed fire or other 
wildland fire management practices. Moreover, the EPA anticipates that 
changes in spatial and temporal patterns of wildfire will likewise be 
too uncertain for them to be allowed to have the effect of reducing or 
increasing the control requirement on conventional anthropogenic 
sources. The EPA therefore recommends that baseline wildland fire 
emissions should generally be held constant over the planning period, 
regardless of whether wildland fire management practices by land 
managers are expected, and possibly encouraged, to change.
    States still have flexibility in determining how best to represent 
baseline wildland fire emissions. As noted earlier, base year emission 
inventories for the nonattainment areas should represent the conditions 
leading to nonattainment and be consistent with inventories used for 
modeling. For fires, the EPA additionally encourages states to use a 
representative mix of prescribed fire and wildfire in their 
inventories. In the past, some plans under previous PM2.5 
NAAQS have estimated the actual fire emissions and temporal and spatial 
patterns from a given year and used this estimate as the assumed future 
baseline for planning, while others have used average emissions over 
multiple years. Other approaches may be appropriate as well. Moreover, 
regardless of the approach used, the EPA still encourages states to 
submit actual wildfire and prescribed fire activity data that are 
critical to developing emissions estimates to the NEI as suggested in 
the AERR.
    A consequence of the recommendation of not expressly accounting for 
changes in wildland fires in attainment demonstrations is that measures 
to reduce emissions from wildland fires, such as prescribed fire for 
wildland wildfire prevention and mitigation purposes or smoke 
management programs and BSMP for prescribed fires in wildland, need not 
be included as RACM for the respective fire types. This is because the 
changes in emissions due to such measures would not be accounted for in 
determining what is necessary for attainment and/or what would advance 
the attainment date, which is how the EPA is recommending that RACM be 
determined. So, for example, in an area that can attain in 6 years with 
measures that do not address wildland fire, the EPA does not recommend 
that states attempt to quantify whether increased prescribed fire could 
advance the attainment date by 1 year, due to aforementioned 
difficulties associated with such quantification.
    To be clear, nothing about this policy regarding RACM is intended 
to suggest that fires should be ignited in wildland (or elsewhere) 
without regard to the air quality or public health consequences. As 
noted earlier, the EPA believes these consequences are important to 
address, and intends to engage in dialogue with the FLMs, air agencies, 
tribes, state and private land owners and other stakeholders at 
appropriate times, such as during the process for the development of 
land management plans, about how land managers determine when and where 
prescribed fire is appropriate for particular wildlands and how to 
identify and implement appropriate mitigation measures. The policy 
simply makes clear the EPA's view regarding its recommendation for RACM 
for wildland fires.
    The EPA notes that this recommendation regarding RACM differs 
somewhat from the recommendation that was offered in the preamble as 
guidance to states as they implement the EPA's recent SIP Requirements 
Rule for the 1997 and 2008 ozone NAAQS. The reasons for the strategy 
outlined earlier apply equally well to attainment demonstrations for 
the ozone NAAQS, and so EPA hereby makes the same recommendation for 
implementation of these ozone NAAQS as well. This recommendation, 
offered here in the same manner as the prior recommendation, supersedes 
the prior recommendation on RACM for wildfire in the preamble to the 
final SIP Requirements Rule for the 1997 and 2008 ozone NAAQS. The EPA 
will convey this revised recommendation to the air agencies that are 
working to prepare these ozone SIPs. The EPA also anticipates making 
this recommendation as part of our planned rulemaking on implementation 
of the 2015 ozone NAAQS. Note that this discussion pertains only to the 
RACM policy, and that other aspects of the fire discussions in the 
ozone SIP Requirements Rule remain applicable.
    Finally, the EPA notes that, because a significant element of the 
rationale for this policy is the uncertainty in the timing of 
wildfires, we may reconsider this recommendation in the future, if 
adequate tools emerge that allow for predicting fire emissions with 
sufficient specificity. However, even if such tools emerge, due to 
inherent uncertainties it may be impossible to satisfactorily 
incorporate the use of such information into an attainment 
demonstration framework.
iii. Comments and Responses
    The EPA received many comments expressing agreement with EPA's 
recognition of the importance of wildland prescribed fire, and 
welcoming continued dialogue among states, the EPA, and other federal 
agencies on how best to ensure that land managers have adequate 
management tools available, including prescribed fire and some 
wildfire, but also to ensure that use of these tools does not result in 
unhealthy air. The EPA intends to engage in such dialogue.

[[Page 58040]]

    Some commenters also took positions on how specifically to define 
RACM for wildfires, ranging from required smoke management plans to 
simply stating that fires themselves are RACM with no further measures 
required. In light of the fact that EPA did not propose specific 
guidance on defining RACM for wildfires and typically does not define 
RACM for specific categories, and the fact that EPA is not recommending 
that states include RACM as proposed, we are not providing further 
guidance in response to those comments. Similarly, regarding baseline 
fire emissions, some commenters provided detailed suggestions regarding 
approaches to calculating baselines based not on actual fires (which 
may include periods when fires were suppressed) but on science-based 
fire regimes, fire return intervals and ecosystem types, including 
characteristics of wildland vegetation. The EPA notes that this 
guidance is not establishing or recommending any particular approach to 
calculating baseline fire emissions.
c. RACT for EGUs
i. Summary of Proposal
    Through guidance in the preamble to the 2007 PM2.5 
Implementation Rule, the EPA established a rebuttable presumption that 
compliance with the CAIR would satisfy RACM and RACT requirements for 
SO2 and NOX emissions from EGUs in states 
participating in the CAIR cap-and-trade program for such emissions.\80\ 
The EPA indicated that states could presume that EGUs located within a 
given nonattainment area were meeting the RACM and RACT requirements, 
based solely upon a regional program that imposed controls for 
SO2 and NOX emissions from sources both within 
and outside designated nonattainment areas.
---------------------------------------------------------------------------

    \80\ See the Federal Register published on April 25, 2007 (72 FR 
20586, 20623, 20624 and 20625).
---------------------------------------------------------------------------

    In June 2007, the EPA received a petition for reconsideration 
questioning the legality of this presumption, which the D.C. Circuit 
later found to be unlawful in the context of a similar presumption in 
the Phase 2 Ozone (NAAQS) Implementation Rule.\81\ The agency granted 
the petition for reconsideration in 2011 and proposed to withdraw from 
the 2007 PM2.5 Implementation Rule any presumption that 
compliance with the CAIR automatically satisfies RACM and RACT 
requirements for SO2 and NOX emissions from EGUs 
located in nonattainment areas for the 1997 PM2.5 
NAAQS.82 83 In that proposal, the EPA explained that given 
the explicit wording of CAA section 172(c)(1) that sources ``in the 
area'' (i.e., in the nonattainment area) must at a minimum adopt RACT 
controls for that area, the agency believes that it is no longer 
appropriate to presume that this requirement is satisfied merely based 
upon the participation of a source in a regional cap-and-trade program. 
Indeed, implicit in a regional cap-and-trade program is that some 
sources, including those located within nonattainment areas, may elect 
to buy allowances in lieu of controlling emissions in order to meet the 
regional emissions reductions requirements.
---------------------------------------------------------------------------

    \81\ See ``Petition for Reconsideration,'' filed by Paul Cort, 
Earthjustice, on behalf of the American Lung Association, Medical 
Advocates for Healthy Air, Natural Resources Defense Council, and 
the Sierra Club (June 25, 2007). A copy of the petition is in the 
docket for this action. The EPA's decision to grant the petition for 
reconsideration on the issue of the CAIR being presumptively equal 
to RACT for EGUs was in part based on a D.C. Circuit decision 
related to a similar issue. Specifically, the Court decided that the 
provisions in the Phase 2 Ozone Implementation Rule indicating that 
a state need not perform (or submit) a NOX RACM/RACT 
analysis for EGU sources subject to a cap-and-trade program that 
meets the requirements of the NOX SIP Call are 
inconsistent with the statutory requirements of CAA section 
172(c)(1). The Court concluded that the phrase ``in the area'' means 
that reductions must occur from sources within the area and 
``reductions from outside the nonattainment area do not satisfy the 
requirement.'' See NRDC v. EPA, 571 F.3d 1245 (D.C. Cir. 2009).
    \82\ Letter dated April 25, 2011, from former Administrator Lisa 
Jackson to Paul Cort, Earthjustice. A copy of this letter is located 
in the docket for this action.
    \83\ 79 FR 32892 (June 9, 2013).
---------------------------------------------------------------------------

    Accordingly, in the proposal the EPA stated that it did not intend 
to include any rebuttable presumption that the CAIR or any other 
regional control strategy constitutes RACM or RACT for EGUs or any 
other source category. Instead, the EPA stated that it is clarifying 
that in order to meet the RACM and RACT requirements for the 
PM2.5 NAAQS, states should evaluate EGU sources for RACM and 
RACT level controls just like any other source category, and not merely 
presume for EGUs located in a nonattainment area that compliance with a 
cap-and-trade program, including the CAIR or any other program, would 
satisfy their obligation to implement RACM and RACT. As required by the 
CAA, states are required to analyze what constitutes RACM and RACT for 
EGUs in each nonattainment area.
ii. Final Rule
    The final rule maintains the proposed policy approach as described 
earlier. As required by the CAA, states are required to analyze what 
constitutes RACM and RACT for EGUs in each nonattainment area, just as 
they are required to do for all other types of sources.
iii. Comments and Responses
    Any additional comments received on this section are addressed in 
the Response to Comments document found in the docket for this action.
4. Step 3: Determine Whether an Available Control Measure or Technology 
Is Technologically Feasible
a. Summary of Proposal
    The proposal cited longstanding guidance from the General Preamble 
regarding factors to consider when determining the technological 
feasibility of a potential control measure or control technology, and 
it requested comment on the factors. These factors included a source's 
processes and operating procedures, raw materials, physical plant 
layout, and potential environmental impacts such as increased water 
pollution, waste disposal, and energy requirements. One sentence in the 
proposal stated: ``With respect to determining whether a given control 
measure might not be technologically feasible for an area or mobile 
source, the EPA also proposes to retain its longstanding practice that 
a state may consider relevant factors in conducting its analysis, such 
as the social acceptability of the measure . . .'' \84\
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    \84\ See the proposed PM2.5 SIP requirements rule (80 
FR 15340, 15373)
---------------------------------------------------------------------------

b. Final Rule
    Several comments addressed the EPA's inclusion of the social 
acceptability factor in the proposal. In reviewing this issue, the EPA 
determined that this factor actually has not been identified as a 
factor in the EPA's longstanding guidance, and thus was 
mischaracterized in the proposal. Nevertheless, some commenters 
supported inclusion of the factor because no other factor is presented 
to help limit or eliminate a potential measure with strong public 
opposition. Other commenters that opposed use of such a factor 
suggested that including it in the final rule could allow a state to 
reject almost any control measures that is otherwise found to be 
technically and economically feasible.
    When the EPA issued a proposed PM2.5 NAAQS 
implementation rule in 2005, it requested comment on the same social 
acceptability factor, and ultimately did not include social 
acceptability as a factor for determining RACM in the final 2007 
PM2.5 implementation rule. In the 2007 final rule, however, 
the EPA stated:

[[Page 58041]]

``Therefore, given the concerns raised by commenters that establishment 
of `social acceptability' as a factor in the RACM analysis is without 
basis in the CAA and might result in inappropriate skewing of control 
strategies, we have removed this term from the final rule. We 
reiterate, however, that capability of effective implementation and 
enforcement are relevant considerations in the RACM analysis, even 
though public `unpopularity' is not. Moreover, in assessing the 
efficacy of measures and the credit they should be given in the context 
of attainment demonstrations or RFP calculations, EPA believes that 
such considerations are important.'' For the same reason it was not 
included in the previous implementation rule, the EPA has decided to 
not include the social acceptability factor in this final rule as well. 
See 40 CFR 51.1009(a)(3)(i).
    The following guidance is similar to what was presented in the 
proposal but has been updated to exclude the social acceptability 
factor:
    Once a state has identified existing and potential control measures 
and technologies for sources of direct PM2.5 and 
PM2.5 precursors in the nonattainment area(s), it must 
evaluate these controls to determine if any of those controls would be 
technologically infeasible in the particular nonattainment area.
    With respect to the technological feasibility of control 
technologies for stationary sources, the EPA has a longstanding 
approach to evaluating facts relevant to this criterion under subpart 
4.\85\ The EPA interprets the term technological feasibility to include 
consideration of factors such as a source's processes and operating 
procedures, raw materials, physical plant layout, and potential 
environmental impacts such as increased water pollution, waste disposal 
and energy requirements. For example, the EPA recognizes that the 
process, operating procedures and raw materials used by a source can 
affect the feasibility of implementing process changes that reduce 
emissions and can also affect the selection of add-on emissions control 
equipment. The feasibility of modifying processes or applying control 
equipment also can be influenced by the physical layout of the 
particular plant, if the physical space available in which to implement 
such changes limits the choices. A state may consider such factors in 
determining whether a control measure is or is not technologically 
feasible to implement.\86\
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    \85\ See the Federal Register published on April 16, 1992 (57 FR 
13498, 13540 and 13541).
    \86\ Addendum to the General Preamble, 59 FR 41998 (August 16, 
1994), at page 42013. Guidance is provided in the context of Serious 
area BACM determination, but the EPA is applying it here for 
Moderate area RACM determinations.
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    In addition, with respect to determining whether a given control 
measure might not be technologically feasible for an area or mobile 
source, the EPA also retains its longstanding practice that a state may 
consider relevant factors in conducting its analysis, such as the 
condition and extent of needed infrastructure, population size, or 
workforce type and habits, which may prohibit certain potential control 
measures from being implementable.
c. Comments and Responses
    Comment: Some commenters stated that the EPA should make clearer in 
its rule and guidance that some categories of sources, particularly 
those such as animal and crop production, do not lend themselves to 
national determinations of best control practices; instead, these types 
of sources should be evaluated on nonattainment area specific 
conditions in determining the appropriate level of control measures.
    Response: The EPA agrees that nonattainment area-specific 
conditions are important factors when considering emission reduction 
options. States need to consider the feasibility of all identified 
options that have been demonstrated to reduce PM2.5 and 
PM2.5 precursors to determine whether such measures are 
appropriate for use in a particular PM2.5 nonattainment 
area.
    The EPA believes the determination of best control practices for 
any operation, particularly for animal production or crop production 
operations, should be a case-specific process. The process should start 
with the identification of PM2.5 and PM2.5 
precursor emissions from the operation. Then it should consider which 
of the measures for reducing PM2.5 and PM2.5 
precursors in a particular PM2.5 nonattainment area are 
technically and economically feasible for a particular operation. The 
EPA recognizes that there are a number of factors specific to each 
operation that could determine whether a potential emission reduction 
measure is technically and economically feasible for implementation.
    Although the EPA is not making any national determinations of best 
control practices for animal production and crop production operations, 
we do note that there are many relevant references on potential 
emissions reduction options, including the Agricultural Air Quality 
Conservation Measures Reference Guide for Cropping Systems and Land 
Management.\87\ The EPA and USDA jointly developed this document to 
identify measures that have been demonstrated to reduce emissions and 
describe factors related to the applicability of each measure. A 
companion document is under development by the EPA and USDA that will 
identify potential emission reduction approaches for livestock 
operations. Additionally, USDA's Natural Resources Conservation Service 
(NRCS) provides a list of approved practices in managing air emissions 
of concern for particulate matter, ozone, greenhouse gas, and odor-
related issues.\88\ A number of regulatory and non-regulatory programs 
are already being implemented (in nonattainment and attainment areas 
alike) to reduce emissions of PM2.5 and PM2.5 
precursors from agricultural operations. Finally, a large body of 
information is available on topics such as feed management, livestock 
housing, conservation tillage, road use and other topics from federal 
agencies, states, industry groups, academic institutions, and 
international organizations.
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    \87\ See the EPA Web site at https://www3.epa.gov/airquality/agriculture/.
    \88\ See the USDA NRCS Air Quality Technical Resources at http://www.nrcs.usda.gov/wps/portal/nrcs/main/national/air/quality/.
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5. Step 4: Determine Whether an Available Control Measure or Technology 
Is Economically Feasible
a. Summary of Proposal
    The proposal described that in the 1992 General Preamble, EPA's 
longstanding interpretation of the term ``economic feasibility'' in the 
context of evaluating potential RACM and RACT has included a 
presumption that it is reasonable for similar sources to bear similar 
costs of emissions reductions, even if they are in different 
nonattainment areas or different states. The proposal indicated that 
this presumption was not included in the 2007 implementation rule for 
the PM2.5 NAAQS that the EPA had received a petition for 
reconsideration with respect to this issue, and that EPA had granted 
this petition in 2011.89 90 The March

[[Page 58042]]

2015 proposed PM2.5 SIP requirements rule indicated the 
EPA's intention to not adopt the economic feasibility factors as 
described in the 2007 rule, but to return to the original 
interpretation from the 1992 General Preamble, including the 
presumption that it is reasonable for similar sources to bear similar 
costs of emissions reductions.
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    \89\ ``Petition for Reconsideration,'' filed by Paul Cort, 
Earthjustice, on behalf of the American Lung Association, Medical 
Advocates for Healthy Air, Natural Resources Defense Council, and 
the Sierra Club (June 25, 2007). A copy of the petition is in the 
docket for this action.
    \90\ Letter dated April 25, 2011, from former Administrator Lisa 
Jackson to Paul Cort, Earthjustice. A copy of this letter is located 
in the docket for this action.
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    The proposal also characterized past guidance from the 1992 General 
Preamble as stating that if a state contends that a source-specific 
control level should not be established because the source(s) cannot 
afford the control measure that is demonstrated to be economically 
feasible for other sources in its source category, then the state must 
support the claim with information regarding the impact of imposing the 
identified control measure or technology on the several financial 
indicators. The proposal also recommended that cost effectiveness 
should generally be evaluated by assessing the cost per ton of 
emissions reduced associated with a control measure, but the proposal 
also requested comment on an alternative metric to assess cost 
effectiveness in terms of the cost per unit of air quality improvement 
(i.e., ``cost per microgram'').
b. Final Rule
    Based on a consideration of the comments received, the EPA has 
determined that economic feasibility considerations should generally 
align with the interpretation in the 1992 General Preamble. Note that 
the proposal indicated that if it is claimed that a control approach is 
not economically feasible for a specific source, the state needs to 
provide information related to several financial indicators to support 
the claim. We note that the original policy in the 1992 General 
Preamble suggests that if a source desires to make such a claim, it 
should provide such information to the state for its consideration. 
This final rule characterizes the policy in a similar manner, where the 
source would have the option of providing this financial information to 
the state for its review. This approach should address the concerns of 
some commenters that such financial information may not be readily 
available to the state. Thus, the final policy for considering economic 
feasibility of control measures is described in the following 
paragraphs.
    The EPA has a longstanding interpretation of the term ``economic 
feasibility'' in the context of evaluating potential RACM and RACT 
which involves considering the cost of reducing emissions and the 
difference between the cost of an emissions reduction measure at a 
particular source and the cost of emissions reduction measures that 
have been implemented at other similar sources in the same or other 
areas.\91\ Absent other indications, the EPA presumes that it is 
reasonable for similar sources to bear similar costs of emissions 
reductions. Economic feasibility of RACM and RACT is thus largely 
informed by evidence that other similar sources have implemented the 
control technology, process change or measure in question.
---------------------------------------------------------------------------

    \91\ See the Federal Register published on April 16, 1992 (57 FR 
13498, 13540 and 13541).
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    For each technologically feasible control measure, a state should 
evaluate the economic feasibility of the measure or control, through 
consideration of factors such as the capital costs, operating and 
maintenance costs, and cost effectiveness (i.e., cost per ton of 
pollutant reduced by that measure or technology) associated with such 
measure or control. A state should not reject a technologically 
feasible control measure or technology as being economically infeasible 
if such a measure or technology has been implemented at other similar 
sources (i.e., at sources that would be included in the same source 
category in the emissions inventory data collection process), unless 
the state provides an adequate justification that clearly explains the 
specific circumstances of the source or sources in the nonattainment 
area that make such a measure or technology economically infeasible for 
sources in the nonattainment area. See 40 CFR 51.1009(a)(3).
    The EPA believes that it is appropriate for states to give 
substantial weight to cost effectiveness in evaluating the economic 
feasibility of an emission reduction measure or technology. The cost 
effectiveness of a measure is its annualized cost ($/year) divided by 
the emissions reduced (tons/year) which yields a cost per amount of 
emission reduction ($/ton). Cost effectiveness provides a relative 
value for each emissions reduction option that is comparable with other 
options and, in the case of control technologies, other facilities. In 
considering what level of control is reasonable, the EPA does not 
recommend a specific fixed dollar per ton cost threshold for economic 
feasibility of controls identified as potential RACM and RACT.
    If a source contends that a source-specific control-level should 
not be established because the source cannot afford the control measure 
or technology that is demonstrated to be economically feasible for 
other sources in its source category, the source should make its claim 
known to the state and support the claim with information regarding the 
impact of imposing the identified control measure or technology on the 
following financial indicators, to the extent applicable:
    (1) Fixed and variable production costs ($/unit)
    (2) Product supply and demand elasticity
    (3) Product prices (cost absorption vs. cost pass-through)
    (4) Expected costs incurred by competitors
    (5) Company profits
    (6) Employment costs
    (7) Other costs (e.g., for RACM implemented by public sector 
entities).\92\
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    \92\ These longstanding factors were established in the EPA 
guidance in 1992 and are applicable to implementation programs for 
all the NAAQS pollutants. See the appendices to the General 
Preamble, 57 FR 18070 (April 28, 1992).
---------------------------------------------------------------------------

c. Comments and Responses
    Comment: With regard to the presumption that it is reasonable for 
similar sources to bear similar costs of emissions reductions, some 
commenters supported returning to the approach described in the General 
Preamble as EPA proposed, while other commenters suggested that based 
on its experience with industry the EPA knows that just because a 
technology will work at one source does not mean that it will 
necessarily work at a similar source due to source configuration and 
non-RACT reasons (e.g., enforcement proceedings) for the installation 
of different technology at ``similar'' sources.
    Response: The latter commenters appear concerned that the rule 
would require the imposition of all controls on similar sources without 
allowing for consideration of whether such controls are technologically 
and economically feasible. This is not what EPA proposed. Instead, the 
EPA proposed, and is now finalizing, a requirement that the state first 
identify potential control measures for sources in a nonattainment 
area. The state should then identify which control measures are 
economically and technologically feasible based on its review of 
various factors. If the state determines that certain controls are not 
reasonably available based on its review of these factors, it must 
provide a written justification to the EPA explaining its rationale. 
This review should at least evaluate the feasibility of all the 
identified controls on similar sources to determine whether 
implementation of such controls in the nonattainment area at issue is

[[Page 58043]]

reasonable. The EPA recognizes that there are a number of source-
specific factors that the state can take into account in making these 
determinations. Factors such as the physical onsite configuration of a 
facility may determine whether a particular control device or operation 
can be feasibly implemented. Likewise, a state should take into account 
information provided by the source on particular economic factors such 
as those described earlier in making a case-by-case determination of 
the economic feasibility of a control measure.
    Comment: Two commenters supported the EPA's proposal that cost-
effectiveness should consider capital costs, operating costs and 
maintenance costs at the particular source in question.
    Some commenters supported using an alternative cost effectiveness 
metric such as cost per microgram of air quality improvement where 
appropriate air quality modeling has been developed for the area and 
can reasonably characterize the relative importance of various 
precursors. Some commenters opposed the proposal's alternative cost-
effectiveness metric because the approach is overly complex and the 
impacts are rarely uniform across an area.
    Response: The EPA has decided to maintain its traditional 
recommendation to use a cost per ton approach for evaluating the cost 
effectiveness of particular control options. The EPA does not recommend 
the cost per microgram alternative approach because there are a number 
of technical and resource challenges associated with implementing it in 
a technically rigorous manner based on detailed air quality modeling 
information. The EPA believes that this policy approach would 
unnecessarily add complication and extra burden to the state's process 
for determining economic feasibility for subject sources in a 
nonattainment area. Moreover, the EPA believes that the flexibility 
described here to consider cost-effectiveness in assessing economic 
feasibility, when coupled with the upcoming discussion of Step 6, and 
with the major stationary source and comprehensive precursor 
demonstrations previously described will ensure that unreasonable 
application of measures (e.g., those that are not effective in reducing 
PM2.5 concentrations) will not occur.
6. Step 5: Determine the Earliest Date by Which a Control Measure or 
Technology Can be Implemented in Whole or in Part
a. Summary of Proposal
    In this section, the proposal discussed two main issues related to 
the date by which control measures can be implemented. First, it 
proposed that when a state is determining RACM/RACT, it must consider 
whether a control measure can be implemented in part when full 
implementation of the measure within 4 years of designation is not 
feasible. The proposal also introduced the concept of ``additional 
reasonable measures,'' meaning those measures that can only be 
implemented after the fourth year but prior to the Moderate area 6-year 
attainment date. It was proposed that a state must identify additional 
reasonable measures and adopt those measures as needed for expeditious 
attainment.
b. Final Rule
    This section remains relatively unchanged from the proposal. CAA 
section 189(a)(1)(C) requires that the attainment plan for a Moderate 
PM2.5 nonattainment area provide for the implementation of 
RACM and RACT no later than 4 years after designation. The agency has 
long interpreted the term ``implemented'' to mean that a control 
measure or technology has not only been submitted to the EPA for 
approval as part of a SIP but has also been built, installed and/or 
otherwise physically manifested, and is achieving the intended 
emissions reductions, and the EPA retains this definition in this rule. 
See 40 CFR 51.1000.
    The EPA recognizes that a state may be able to implement a given 
control measure only partially within 4 years after designation. The 
EPA addressed this situation in the General Preamble, stating: ``It is 
important to note that a State should consider the feasibility of 
implementing measures in part when full implementation would be 
infeasible.'' \93\ The EPA continues to interpret the RACM/RACT 
definition to mean that a state should not reject an otherwise 
technologically and economically feasible control measure or technology 
as RACM or RACT even if it can be only partially implemented within the 
statutory 4-year timeframe following designation of the area. Instead, 
a state must adopt as RACM and RACT that portion of a control measure 
or technology that can feasibly be implemented within 4 years of the 
effective date of designation. See 40 CFR 51.1009(a)(4)(i)(A). For 
instance, if paving unpaved roads is a control measure that is 
technologically and economically feasible in a nonattainment area but a 
state cannot pave all candidate roads within 4 years of designation, 
the state must adopt as RACM a measure that requires paving of that 
portion of roads that the state could feasibly accomplish within 4 
years if such a measure is needed for timely attainment of the 
PM2.5 NAAQS in the area.
---------------------------------------------------------------------------

    \93\ 57 FR 13498 (April 16, 1992), at page 13541.
---------------------------------------------------------------------------

    Therefore, for the purposes of meeting the RACM/RACT requirement, a 
state must identify those technologically and economically feasible 
control measures and technologies that it can implement fully or 
partially within 4 years of designation of its Moderate 
PM2.5 nonattainment area. Depending on the severity of the 
PM2.5 nonattainment problem in the area, some or all of 
these measures identified as implementable within 4 years may be needed 
in order to bring the area into attainment as expeditiously as 
practicable. These candidate measures may constitute RACM and RACT if 
the state determines, through its attainment demonstration that it 
needs to implement them to achieve timely attainment for the area.
    In addition, a state must separately identify those technologically 
and economically feasible control measures that can only be implemented 
after the statutory window for implementing RACM and RACT, but before 
the attainment date. The statutory 4-year timing requirement for 
implementing RACM and RACT under CAA section 189(a)(1)(C) limits the 
control measures and technologies that can qualify as RACM and RACT for 
a Moderate PM2.5 nonattainment area. However, the statutory 
requirement of CAA 172(c)(6) also requires states to implement ``other 
measures'' necessary to provide for timely attainment in an area. The 
EPA interprets this provision to include ``additional reasonable 
measures,'' which are those measures and technologies that can be 
applied at sources in the nonattainment area that are otherwise 
technologically and economically feasible but can only be implemented 
in whole or in part later than 4 years after designation.\94\
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    \94\ With respect to ``partial measures'' under this proposed 
approach, the EPA would require that a state implement as RACM that 
portion of any control measure determined to be technologically and 
economically feasible and implementable within 4 years after 
designation of a nonattainment area. The state would then be 
required to implement as an additional reasonable measure that 
portion of the same control measure that can be implemented starting 
4 years from designation through the sixth calendar year following 
designation.

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[[Page 58044]]

7. Step 6: Evaluate the Collective Impact of Potential Control Measures 
To Determine Whether the Area Can Attain Expeditiously or Whether it is 
Impracticable to Attain by the Attainment Date, and Adopt the 
Appropriate Set of Control Measures
a. Summary of Proposal
    The proposal described the control measure requirements for two 
situations: The case where the state can demonstrate attainment by the 
attainment date; and the case where the state demonstrates the area 
cannot practicably attain by the attainment date. If a state determines 
that a Moderate nonattainment area can attain the PM2.5 
NAAQS by the statutory attainment date, the state must adopt and 
implement any technologically and economically feasible control 
measures that are necessary to ensure that the area will attain the 
NAAQS as expeditiously as practicable. Those technologically and 
economically feasible measures needed for attainment that can be 
implemented within 4 years of the date of designation would be 
considered to be RACM/RACT. Those measures needed for attainment that 
cannot be implemented within 4 years but can be implemented no later 
than the attainment date would be considered to be ``additional 
reasonable measures.'' The proposal stated that, consistent with 
longstanding policy, this means that the state may choose to not adopt 
certain measures if collectively they would not advance the attainment 
date by 1 year.\95\
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    \95\ In the context of the PM10 NAAQS, the EPA has 
concluded that ``advancement of the attainment date'' should mean an 
advancement of at least 1 calendar year. See ``State Implementation 
Plans; General Preamble for the Implementation of Title I of the CAA 
Amendments of 1990,'' 57 FR 13498 (April 16, 1992). See also Sierra 
Club v. EPA, 294 F.3d 155 (D.C. Cir. 2002).
---------------------------------------------------------------------------

    For the situation where a state determines that it is impracticable 
to attain by the Moderate area attainment date, the proposal included 
two policy options for describing what control measures must be adopted 
and implemented. One option would have required the state to adopt all 
technologically and economically feasible control measures, as stated 
in past guidance in the General Preamble. The other option would have 
required adoption of technologically and economically feasible control 
measures with an explicit exception for those measures that 
collectively are determined to be ``ineffective in reducing ambient 
PM2.5 levels.'' The proposal also reviewed the proposed 
options for demonstrating that a precursor does not make a significant 
contribution to PM2.5 levels that exceed the standard, and 
discussed how the final precursor policy may be an important 
consideration in deciding upon a control measure policy approach for 
Moderate areas that demonstrate they cannot practicably attain.
b. Final Rule (General)
    For an area that can demonstrate that it will attain by the 
attainment date, the final rule maintains the same approach as 
described in the proposal regarding the collective evaluation of 
potential control measures to determine whether the area can advance 
the attainment date by 1 year. For an area that demonstrates that it 
would be impracticable to attain by the attainment date, the final rule 
does not include an explicit exception for those measures that 
collectively are determined to be ``ineffective in reducing ambient 
PM2.5 levels.'' More details are provided in sections (c) 
and (d) that follow.
    Section 189(a)(1) of the CAA establishes a requirement that the 
attainment plan for a Moderate PM2.5 nonattainment area must 
demonstrate either that an area can attain the relevant NAAQS by the 
applicable attainment date, or that it is impracticable for the area to 
do so. As noted previously, for Moderate PM2.5 nonattainment 
areas, the ``applicable attainment date'' is as expeditious as 
practicable, but no later than the end of the sixth calendar year after 
designation as nonattainment. A complete discussion of the requirements 
for attainment demonstration modeling is presented in Section IV.E of 
this preamble. However, one of the key features of attainment 
demonstration modeling and related analysis is that they provide a 
means of synthesizing the effects of emissions reductions from all 
existing and potential new control measures identified for sources in a 
given nonattainment area on overall air quality in that area. States 
will use the results of their analyses to identify the appropriate 
combination of reasonable control measures for sources in their 
Moderate PM2.5 nonattainment area and any other control 
measures needed on sources outside the nonattainment area to ensure 
expeditious attainment of the relevant NAAQS in the area and to meet 
the statutory requirements of CAA sections 189(a)(1)(B) and 172(c)(6) 
as explained later.\96\
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    \96\ Note that under section 110(l) of the CAA, after a state 
has adopted a control measure into the SIP for an attainment 
demonstration, it may remove or modify a measure if the state 
demonstrates to the satisfaction of the EPA that such removal or 
modification will not interfere with any applicable requirement of 
the CAA, such as attainment of the PM2.5 NAAQS or meeting 
RFP requirements.
---------------------------------------------------------------------------

    Section 188 establishes the attainment dates for Moderate and 
Serious PM10 nonattainment areas, and this rule also applies 
such dates to Moderate and Serious PM2.5 nonattainment 
areas. As described in Sections IV.D and IV.E of this preamble, in the 
case of a Moderate PM2.5 nonattainment area for which a 
state can demonstrate attainment by the end of the sixth calendar year 
following designation, the state must follow a two-step process for 
determining the appropriate attainment date for the area. First, the 
state must demonstrate through air quality modeling that the area can 
attain the relevant NAAQS by the latest statutory attainment date and 
determine which control measures and technologies are needed for the 
area to attain by that date. Second, the state must determine whether 
implementing other reasonable controls (i.e., those not needed for 
attainment by the latest possible date but that are technologically and 
economically feasible) can cumulatively advance the attainment date for 
the area by at least 1 year. In the event that a state determines that 
the area can attain the relevant NAAQS earlier through the application 
of other measures, the state must propose the earlier date as part of 
the attainment plan submission for the area. When the EPA takes action 
to approve the different elements of the attainment plan for the area, 
one of the elements that the agency will take action on will be the 
state's proposed attainment date for the area. If the EPA approves an 
attainment date for the area that is earlier than the latest date 
allowed by statute, then the applicable attainment date for the area 
will be the approved date. See 40 CFR 51.1004(a)(1)(i). If the area 
ultimately needs additional time to attain the relevant NAAQS, the 
state may request an attainment date extension for the Moderate 
nonattainment area under section 188 as long as certain conditions are 
met, as described in Section IV.J of this preamble.
c. Final Rule--Step 6 (Attainment Case): If the State Can Demonstrate 
Attainment in the Area by the Statutory Attainment Date for a Moderate 
Area, Then the State Must Implement Those Control Measures Needed for 
Expeditious Attainment of the NAAQS in the Area
    If a state determines that a Moderate nonattainment area can attain 
the PM2.5 NAAQS by the statutory attainment date, the state 
must adopt and

[[Page 58045]]

implement any technologically and economically feasible control 
measures that are necessary to ensure that the area will attain the 
NAAQS as expeditiously as practicable. The EPA will consider any such 
measures that can be implemented within 4 years of designation of the 
area to fulfill the RACM and RACT requirements for the area. In 
addition, the EPA will consider any such measures that can only be 
implemented between 4 years and the sixth calendar year after 
designation to meet the requirements of CAA section 172(c)(6) as 
``additional reasonable measures'' for the area and necessary to 
demonstrate timely attainment under CAA section 189(a)(1)(B).
    For this type of situation, the state may reject any otherwise 
technologically or economically feasible measures that are not needed 
to demonstrate attainment or that will not advance the attainment date 
by at least 1 year. That is, for a Moderate area that can demonstrate 
attainment by the statutory Moderate area attainment date, the EPA 
defines as ``reasonable'' only those technologically and economically 
feasible measures that are necessary for expeditious attainment of the 
NAAQS, as the CAA does not require a state to adopt measures that are 
not needed for expeditious attainment in a Moderate PM2.5 
nonattainment area. Thus, a state may exclude those otherwise 
reasonably available measures that, if adopted and considered 
collectively, would not advance the attainment date for the area by at 
least 1 year, so long as the state can demonstrate attainment as 
expeditiously as practicable and no later than the statutory Moderate 
area attainment date. The EPA maintains that identifying a complete set 
of measures that qualify as RACM/RACT and additional reasonable 
measures but that are not necessary for attainment within 6 years is 
imperative to adequately demonstrate that such measures will not 
collectively advance the attainment date for a Moderate area by at 
least 1 year. The EPA will require a robust analysis and explanation by 
the state when such determinations are made. See 40 CFR 
51.1009(a)(4)(i).
d. Final Rule--Step 6 (Impracticability Case): If the State Cannot 
Demonstrate Attainment by the Statutory Attainment Date for a Moderate 
Area, Then the State Must Adopt All Reasonably Available Control 
Measures
    Section 189(a)(1)(B) of the CAA anticipates that not all Moderate 
nonattainment areas will be able to demonstrate attainment by the 
attainment date, and it incorporates the concept of an 
``impracticability demonstration'' for such areas.\97\ Commenters on 
this issue stated that nowhere in the statute is there an explicit 
exception for those measures that collectively are determined to be 
``ineffective in reducing ambient PM2.5 levels.'' Further, 
they suggested that such an approach would enable the most polluted 
areas to exempt sources that individually are small by some arbitrary 
test when in other cleaner areas such sources would be required to 
reduce emissions because they collectively would advance attainment. 
Other commenters emphasized that sources located in such Moderate areas 
should still be subject to the regular review process for determining 
whether potential control measures are not technologically or 
economically feasible.
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    \97\ The concept of an ``impracticability demonstration'' is 
established in CAA section 188(b), which addresses reclassifying 
Moderate PM2.5 areas to Serious. Section 188(b)(1) of the 
CAA describes the EPA's discretionary authority to reclassify an 
area upon a determination that an area cannot practicably attain by 
the Moderate area attainment date. More relevant to this 
determination, however, CAA section 189(a)(1)(B) specifically 
provides for submission of a demonstration addressing this concept 
in the case of Moderate areas that cannot attain the NAAQS by the 
applicable attainment date.
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    After considering comments on the two options described in the 
proposal, the EPA has decided to keep the policy in this final rule 
consistent with past guidance in the General Preamble. This guidance 
stated that ``the EPA believes it is reasonable for all available 
control measures that are technologically and economically feasible to 
be adopted for areas that do not demonstrate attainment [by the 
applicable attainment date].'' \98\ The EPA believes that this 
interpretation is compelled by the language of CAA section 
189(a)(1)(C), which separately requires a state to submit a Moderate 
area attainment plan and meet the RACM and RACT requirement, even if 
the state submits a demonstration showing that with those measures it 
cannot attain the NAAQS by the applicable attainment date.
---------------------------------------------------------------------------

    \98\ 57 FR 13498 (April 16, 1992), at page 13544.
---------------------------------------------------------------------------

    Under this approach, if the state had an approved precursor 
demonstration (as described in Section III of this preamble) showing 
that a particular precursor does not have a significant contribution on 
PM2.5 levels that exceed the standard, then it would not 
need to adopt control measures for that particular precursor. The state 
then would be required to identify potential control measures for 
sources in the area that emit direct PM2.5 and any remaining 
significant precursors. Of these potential measures, the state would 
determine which would be technologically feasible to implement. Then 
the state would identify which of the technologically feasible measures 
are economically feasible to implement.
    Subpart 4 requires that Moderate areas that cannot or do not meet 
the Moderate area attainment date be reclassified as Serious 
nonattainment areas, in which case sources in the areas are then 
subject to BACM and BACT requirements. In the General Preamble, the EPA 
indicated that ``it may be reasonable, in some limited circumstances, 
for states to consider the compatibility of RACM and RACT with the BACM 
and BACT that will ultimately be implemented under the Serious area 
plans for those areas.'' \99\ Furthermore, for such areas that do not 
meet the Moderate area attainment date, the EPA indicated that ``in the 
case of RACM for area sources, EPA anticipates that any future 
implementation of BACM for these sources will be additive to, and hence 
compatible with, RACM. This is because BACM will generally consist of a 
more extensive implementation of the RACM measures . . . Since EPA 
anticipates that RACM and BACM for these sources will be compatible, 
the SIP's (sic) for these areas should reflect the application of 
available control measures to existing sources in moderate 
nonattainment areas as determined by the analysis described . . . for 
RACM.'' \100\ Thus, the state should assess the remaining set of 
technologically and economically feasible measures with regard to the 
compatibility of implementing RACM/RACT in the near term in a way that 
supports addressing BACM/BACT for such sources when the area is 
reclassified to Serious.
---------------------------------------------------------------------------

    \99\ Ibid. at 13544.
    \100\ Ibid.
---------------------------------------------------------------------------

    The General Preamble also provided guidance for stationary source 
controls in this situation: ``In many instances, the installation of 
pollution controls representing RACT may involve substantial capital 
expenditures. In the event that BACT is later required for those 
sources, this may require controls significantly incompatible with 
those recently installed as RACT, largely wasting those recent 
expenditures. Under such circumstances, the installation of controls in 
the first round of SIP planning would be unreasonable.'' Accordingly, 
SIPs for the Moderate areas that cannot practicably attain need not 
require major changes to the control systems for specific stack and 
process sources where a State reasonably demonstrates that such changes 
will be significantly

[[Page 58046]]

incompatible with the application of BACT-level control systems. A 
State's demonstration should include, for example, showing what the 
State believes are RACT and BACT for the source, and why they are 
significantly incompatible.
    The EPA believes that in such cases, a state should consider 
selecting and implementing controls that may qualify as BACM or BACT in 
a Moderate nonattainment area as part of their RACM and RACT analysis. 
Early adoption of controls that would constitute BACM or BACT could be 
more efficient and could further the objectives of attaining the NAAQS 
expeditiously to protect public health and the environment.
e. Comments and Responses
    Any additional comments received on this section are addressed in 
the Response to Comments document found in the docket for this action.
8. RACM and RACT and Additional Reasonable Measures Submission 
Requirements
a. Summary of Proposal
    The proposal described a set of submission requirements for RACM/
RACT and additional reasonable measures.
b. Final Rule
    The requirements in the final rule remain very similar to those 
that were included in the proposal. To ensure that attainment plan 
submissions contain the necessary supporting information to enable the 
EPA to review and approve a state's evaluation and selection of 
measures that constitute RACM and RACT in a given nonattainment area, 
the EPA requires under the authority of section 301(a) of the CAA that 
a state must submit the following information as part of its 
submission:
    (1) A list of all sources and activities in the nonattainment area 
that emit direct PM2.5 or any PM2.5 precursor 
(for multi-state nonattainment areas, this would include source 
categories, sources and activities from all states which make up the 
area). See 40 CFR 51.1008(a)(1).
    (2) For each source or activity in the nonattainment area, an 
inventory of direct PM2.5 emissions and emissions of all 
PM2.5 precursors, and a comprehensive list of potential 
control measures considered by the state for the nonattainment area. 
See 40 CFR 51.1009(a)(2). If the state submitted a precursor 
demonstration that was approved by the EPA, the state would not be 
required to submit a list of sources and potential measures to control 
emissions of the relevant precursor from the stationary sources 
addressed by the demonstration (i.e., all sources for a comprehensive 
precursor demonstration, or major sources for a major source precursor 
demonstration). See 40 CFR 51.1006(a)(1) and (2). Note that the 
emissions inventory would still need to include all sources of the 
relevant precursor. See 40 CFR 51.1008(a)(1).
    (3) For each potential control measure considered by the state but 
eliminated from further consideration due to a determination by the 
state that the control measure or technology was not technologically 
feasible, a narrative explanation and quantitative or qualitative 
supporting documentation to justify the state's conclusion. See 40 CFR 
51.1009(a)(3).
    (4) For each technologically feasible emission control measure or 
technology, a determination of whether the measure is economically 
feasible must be included, with narrative explanation and quantitative 
supporting documentation to justify the state's conclusion. See 40 CFR 
51.1009(a)(3). The following additional information relevant to 
economic feasibility should be included as necessary to justify the 
determination: (a) The control efficiency by pollutant; (b) the 
possible emissions reductions by pollutant; and, (c) the estimated cost 
per ton of pollutant reduced.
    (5) For each technologically and economically feasible emission 
control measure or technology, the date by which the technology or 
measure could reasonably be implemented, in whole or in part. See 40 
CFR 51.1009(a)(4)(i)-(ii).
    Each of these elements will provide information needed by the EPA 
to evaluate whether the state is meeting the statutory requirements for 
an attainment plan, and in particular meeting the statutory requirement 
for states to implement RACM and RACT on sources within the 
nonattainment area. The EPA recognizes that the base year emissions 
inventory for the area that the state submits in conjunction with its 
attainment plan will likely contain some of the information proposed to 
be required under the first two items in this list. However, the EPA is 
finalizing a requirement for emissions inventory information 
specifically relevant to the RACM and RACT element of the state's 
attainment plan in order to ensure that the EPA or any other party can 
appropriately evaluate the state's RACM and RACT analysis.
c. Comments and Responses
    Comment: Some commenters supported the general submission 
requirements because in some cases RACM/RACT demonstrations fail to 
provide the information necessary for the EPA to reasonably conclude 
that these requirements have been met and are supported by a systematic 
analysis.
    Response: The EPA agrees with the commenters and the final rule 
generally tracks the proposal.
9. Criteria for Effective Regulations to Implement RACM and RACT and 
Additional Reasonable Measures
a. Summary of Proposal
    The preamble to the proposed rule described the four main criteria 
for effective control measure regulations: Such regulations must be 
quantifiable, enforceable, replicable and accountable.
b. Final Rule
    The guidance in this preamble to the final rule remains very 
similar to what was proposed. After a state has identified a particular 
control measure as RACM or RACT or additional reasonable measure for a 
particular nonattainment area, it must then implement that measure 
through a legally enforceable mechanism that will be included in the 
SIP (e.g., a state rule that the EPA will approve as a part of the 
federally enforceable SIP for the state). The EPA is proposing that in 
order for the EPA to be able to approve any such measure as part of the 
SIP, the state would have to provide information to meet the following 
four criteria. These criteria are similar to the criteria finalized as 
part of the remanded 2007 PM2.5 Implementation Rule.
    First, the base year emissions from the source or group of sources 
to which the control measure applies and the future year projected 
emissions from those sources once controlled must be quantifiable so 
that the projected emissions reductions from the sources can be 
attributed to the specific measures being implemented. It is important 
that the emissions from the source category in question are accurately 
represented in the base year inventory so that emissions reductions are 
properly calculated. In particular, it is especially important to 
ensure that both the filterable and condensable components of direct 
PM2.5 emissions are accurately represented in the base year.
    Second, the control measures must be enforceable. This means that 
they must specify clear, unambiguous and measurable requirements. The 
measurable requirements for larger emitting facilities must include 
periodic source testing, monitoring or other viable means to establish 
whether the

[[Page 58047]]

affected source meets the applicable emission limit. Additionally, to 
verify the continued performance of the control measure, specific 
emissions monitoring programs appropriate for the type of control 
measure employed and the level of emissions must be included to verify 
the continued performance of the control measure. The control measures 
and monitoring program must also have been adopted according to proper 
legal procedures. Note that if measures are found to be technically and 
economically feasible for reducing condensable PM2.5 
emissions as well as filterable PM2.5 emissions from a 
source, the state will need to adopt a new emission limit for the 
source that accounts for both the filterable and condensable portions, 
and includes requirements for ensuring compliance using condensable 
PM2.5 source test methods updated in 2011.\101\
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    \101\ See 75 FR 80118 (December 21, 2010), revisions to test 
methods for measuring condensable PM emissions from stationary 
sources (Method 202).
---------------------------------------------------------------------------

    In response to a comment on this criterion, the EPA clarifies that 
an enforceable regulation for a CAA program must be enforceable by the 
EPA, the state, and citizens. By taking action to approve emissions 
limitations and related provisions into the SIP, the EPA thereby makes 
those emission limitations a federally enforceable component of the SIP 
that the state, the EPA, and citizens can enforce thereafter in the 
event of a violation. SIP provisions that effectively preclude 
enforcement of violations by the EPA or citizens, whether through 
impermissible exemptions or other SIP provisions that function to bar 
effective enforcement, are not acceptable.
    Third, the results of application of the control measures must be 
replicable. This means that where a rule contains procedures for 
interpreting, changing or determining compliance with the rule, the 
procedures are sufficiently specific and objective so that two 
independent entities applying the procedures would obtain the same 
result.
    Fourth, the control measures must be accountable. This means, for 
example, that source-specific emission limits must be permanent and 
must reflect the assumptions used in the attainment plan for the area, 
including the modeling conducted in conjunction with the attainment 
demonstration. It also means that the attainment plan must establish 
requirements to track emissions changes at sources and provide for 
corrective action if emissions reductions are not achieved according to 
the plan.
c. Comments and Responses
    Any additional comments received on this section are addressed in 
the Response to Comments document found in the docket for this action.
10. Determination of RACM and RACT and Additional Reasonable Measures 
in Multi-State Nonattainment Areas
a. Summary of Proposal
    The proposal included several proposed recommendations about the 
development of control measures by states with multi-state 
nonattainment areas.
b. Final Rule
    The guidance in the final preamble remains very similar to what was 
proposed. States in multi-state nonattainment areas will need to 
consult with each other on appropriate control measures for the shared 
nonattainment area. The agency anticipates that states could decide 
upon RACM and RACT and additional reasonable measures that differ from 
state to state in a shared nonattainment area, based upon each state's 
determination of the most effective strategies given the relevant 
mixture of sources and potential controls in the respective states' 
portions of a shared nonattainment area. As long as each state can 
adequately demonstrate that its chosen attainment strategy, including 
its selection and adoption of RACM and RACT and additional reasonable 
measures, will provide for meeting RFP requirements and for attainment 
of the NAAQS as expeditiously as practicable for the nonattainment area 
at issue, the EPA anticipates being able to approve individual state 
plans that may elect to control a different mix of sources or to 
implement different controls, under the proper circumstances. 
Nevertheless, in evaluating RACM and RACT and additional reasonable 
measures for a particular nonattainment area, states must consider 
potential reasonable control measures developed for other areas or 
other states, and particularly for other portions of an interstate 
nonattainment area. In addition, states in multi-state nonattainment 
areas must evaluate whether the reasonable measures each state may have 
identified as not being necessary for attainment could collectively 
advance the attainment date for the area by at least 1 year. The EPA 
may consider such measures in assessing the approvability of each 
state's individual attainment plan for a multistate nonattainment area.
c. Comments and Responses
    Any additional comments received on this section are addressed in 
the Response to Comments document found in the docket for this action.
11. Environmental Justice Considerations in Developing the Attainment 
Plan Control Strategy for a Moderate PM2.5 Nonattainment 
Area
a. Summary of Proposal
    The proposal provided guidance about environmental justice 
considerations in developing the attainment plan control strategy for a 
Moderate area.
b. Final Rule
    The guidance remains very similar to what was proposed. Current air 
quality data indicate that the more severe PM2.5 
nonattainment areas contain a high population of people with low socio-
economic status, who are among the most at-risk for adverse health 
effects from exposure to PM2.5. As part of its EJ2020 Action 
Agenda, the EPA is committed to making progress on improving air 
quality in communities with high particulate pollution. The EPA, 
therefore, strongly urges states to consider environmental justice 
concerns with respect to any control measures they have identified as 
potential RACM or RACT or additional reasonable measures in an area, 
particularly to the extent that control measures that a state may be 
considering are otherwise approximately equal (in terms of 
technological and economic feasibility) but unequal with respect to 
their direct or indirect impacts on overburdened populations.\102\ In 
such cases, the EPA encourages the state to prioritize imposition of 
the control measures that will result in the least possible burden and 
greatest degree of health protection for overburdened populations in 
the nonattainment area. Section XI of this preamble discusses possible 
approaches for states to address environmental justice concerns 
associated with implementation of the PM2.5 NAAQS in their 
SIP development process and attainment plans.
---------------------------------------------------------------------------

    \102\ The term ``overburdened populations'' is defined in the 
EPA's ``Plan EJ 2014'' to describe the minority, low-income, tribal, 
and indigenous populations or communities in the U.S. that 
potentially experience disproportionate environmental harms and 
risks as a result of greater vulnerability to environmental hazards. 
This increased vulnerability may be attributable to an accumulation 
of both negative and lack of positive environmental, health, 
economic or social conditions within these populations or 
communities. For more information on Plan EJ 2014, see https://www.epa.gov/environmentaljustice.

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[[Page 58048]]

c. Comments and Responses
    Any comments received on this section are addressed in the Response 
to Comments document found in the docket for this action.

E. Modeling for Attainment Demonstrations

1. Demonstrations for Moderate Areas
a. Summary of Proposal
    Section 189(a) of the CAA generally requires a state with a 
designated Moderate nonattainment area to submit an attainment plan for 
such area. Section 189(a)(1)(B) of the CAA requires the state to submit 
an attainment demonstration including air quality modeling to establish 
either: (i) That the area will attain the relevant NAAQS by the 
applicable attainment date; or (ii) that it is impracticable for the 
area to attain the relevant NAAQS by the applicable attainment date. 
For Moderate nonattainment areas, the attainment date is as 
expeditiously as practicable, but no later than the end of the sixth 
calendar year after designation as nonattainment. The EPA therefore 
proposed to require all Moderate nonattainment areas to submit either 
an attainment demonstration which includes air quality modeling which 
establishes that the area will attain the PM2.5 NAAQS by the 
applicable attainment date, or an impracticability demonstration which 
documents that the area will not attain the NAAQS by the applicable 
attainment date. The EPA proposed that the impracticability 
demonstration must also include air quality modeling, but also asked 
for comments on an alternative option that would not require air 
quality modeling as part of an impracticability demonstration. The EPA 
also proposed to allow states to fulfill the statutory modeling 
requirement through either locally generated photochemical and/or 
dispersion modeling or, with proper justification, appropriate regional 
or national modeling.
    An attainment demonstration is a plan that provides an explanation 
of how a state will attain the PM2.5 NAAQS by the applicable 
attainment date in a particular nonattainment area.\103\ The EPA 
proposed that the demonstration must contain: (i) Technical analyses 
such as base year and future year modeling of emissions which 
identifies sources and quantifies their emissions that are contributing 
to violations of the PM2.5 NAAQS; and (ii) analyses of 
future year emissions reductions and air quality improvement resulting 
from existing (i.e., already-adopted or ``on the books'') national, 
regional and local programs, and potential new local measures needed 
for attainment, including RACM and RACT controls for the area.
---------------------------------------------------------------------------

    \103\ An area is designated nonattainment for either the annual 
PM2.5 NAAQS or the 24-hr PM2.5 NAAQS or both. 
The attainment demonstration should show that the area is attaining 
the form of the NAAQS for which they have been designated 
nonattainment.
---------------------------------------------------------------------------

    The EPA further proposed that each state with a Moderate 
nonattainment area must submit an attainment plan with an attainment 
demonstration that includes analyses supporting the state's 
determination of its proposed attainment date. In all cases, the state 
must show that the area will attain the NAAQS as expeditiously as 
practicable, but not later than the sixth calendar year after 
designation. In order to establish that the attainment date is as 
expeditious as practicable, the state must explain why the control 
measures adopted in the attainment plan provide for the most 
expeditious attainment and, in particular, must explain why any 
cumulative group of reasonable and available control measures that the 
state elected not to adopt will not collectively advance the attainment 
date by at least 1 year.
    b. Final Rule. As required by CAA section 189(a)(1)(B), the EPA is 
finalizing a requirement for states with Moderate nonattainment areas 
to submit a demonstration to establish either: (i) That the area will 
attain the relevant NAAQS by the applicable attainment date; or (ii) 
that it is impracticable for the area to attain the relevant NAAQS by 
the applicable attainment date.
    As proposed, attainment demonstrations must include analyses 
(including air quality modeling) supporting the state's determination 
of its proposed attainment date. In all cases, the state must show that 
the area will attain the NAAQS as expeditiously as practicable, but not 
later than the sixth calendar year after designation. The demonstration 
must include implementation of all measures identified as RACT/RACM 
plus additional reasonable measures, as necessary, for expeditious 
attainment. In order to establish that the attainment date is as 
expeditious as practicable, the state must explain why the control 
measures adopted in the attainment plan provide for the most 
expeditious attainment and, in particular, must explain why the 
cumulative group of reasonable and available control measures that the 
state elected not to adopt will not collectively advance the attainment 
date by at least 1 year. See 40 CFR 51.1009(a)(4).
    The EPA is not finalizing a regulatory requirement for air quality 
modeling to be included as part of an impracticability demonstration. 
See 40 CFR 51.1009(a)(4). Since all nonattainment areas will have 
modeling requirements associated with their attainment demonstration, 
the EPA believes it is likely that modeling will be submitted in 
support of impracticability demonstrations. However, it may be possible 
in some cases to support an impracticability demonstration with ambient 
PM2.5 data and other relevant non-modeling information. For 
example, the ambient data in a nonattainment area may be so far above 
the NAAQS, and the reasonable and available controls (i.e. RACM/RACT 
and additional reasonable measures) so limited, that it is clearly 
impossible (and thus also impracticable) for the area to attain by the 
Moderate area attainment date.\104\ In order to support this type of 
demonstration, the state must show that, even if all reasonable 
controls (i.e. RACM or RACT and additional reasonable measures) were 
implemented, the state could not attain the NAAQS within the statutory 
timeframe for a Moderate area.
---------------------------------------------------------------------------

    \104\ Pursuant to CAA section 188(b)(1)(B), upon the EPA 
determination that attainment by the Moderate date is impracticable, 
the EPA shall reclassify the area as Serious within 18 months after 
the Moderate area SIP due date.
---------------------------------------------------------------------------

    The EPA continues to assume that in most cases photochemical grid 
modeling will be required to demonstrate attainment with the 
PM2.5 NAAQS. However, the EPA recognizes that more 
simplistic modeling techniques (such as dispersion, receptor, and/or 
box models) may suffice to demonstrate that an area will attain the 
NAAQS, especially in areas that are dominated by primary 
PM2.5 emissions (e.g. residential wood smoke).
    c. Comments and Responses. Comment: Some commenters supported the 
EPA's proposal to require modeling to demonstrate that attainment is 
not practicable. The commenters stated that such an interpretation 
flows logically from the Act's requirement in section 189(a)(1)(B) that 
attainment demonstrations be supported by modeling. One commenter 
supported the alternative approach described in the proposal in which 
air quality modeling would not be required for a Moderate area 
impracticability demonstration.
    Response: After further consideration of this issue, the EPA has 
determined that modeling need not be a regulatory requirement to 
support an impracticability demonstration. We note that CAA section 
189(a)(1)(B)(i) includes the parenthetical ``including air quality 
modeling'' which clearly

[[Page 58049]]

makes modeling a statutory requirement for moderate area attainment 
demonstrations. However, the same parenthetical statement is absent 
from CAA section 189(a)(1)(B)(ii), which addresses an impracticability 
demonstration. While we believe that most impracticability 
demonstrations will indeed be supported by air quality modeling, there 
are cases where a modeling demonstration may not be needed. In 
addition, the EPA believes the burden of proof for an impracticability 
demonstration is logically lower than for an attainment demonstration 
because submission of an impracticability demonstration also requires 
reclassification to a serious nonattainment area and the accompanying 
more stringent regulatory requirements (e.g. BACT/BACM). The area is 
still required to meet RACT/RACM requirements and will also be required 
to submit a serious area attainment demonstration, which will 
necessarily need to include air quality modeling.
    Comment: Some commenters agreed with the EPA that states should be 
afforded flexibility to fulfill the statutory modeling requirement 
through appropriate regional or national modeling.
    Response: The EPA agrees that, where appropriate, regional and/or 
national scale air quality modeling could be sufficient to fulfill the 
statutory modeling requirement for attainment demonstration modeling. 
However, as with any attainment demonstration, the modeling must be 
shown to be appropriate for the nonattainment area, including good 
model performance, appropriate emissions and meteorological inputs, and 
consideration of emissions control strategies. It should be noted, 
however, that it may be difficult to fulfill other CAA requirements 
(such as emissions inventory, RACM, RFP, establishing motor vehicle 
emissions budgets for transportation conformity purposes, etc.) using 
regional or national modeling data. In order to fulfill those 
requirements, states may need more detailed data for sources in their 
nonattainment area compared to what is available through regional or 
national modeling.
    Comment: Some commenters stated that, as the proposal stands, if 
states wish to preclude RACT/RACM for any sources in the nonattainment 
area, they must do modeling for the year preceding the attainment year 
to demonstrate early attainment; this would require modeling for 3 
years, rather than 2 years.
    Response: Although a RACM analysis is required, and eliminating 
potential control measures requires an assessment of whether the 
measures collectively could advance the attainment date by 1 year, EPA 
did not propose any specific modeling requirements for the RACM 
analysis. There are several components to the analysis. First, 
potential emissions reductions need to be assessed. Then, an assessment 
of whether those emissions reductions can advance attainment by at 
least a year needs to be completed. One way to minimize the number of 
future modeled years is to establish (through sensitivity modeling) a 
relationship between PM2.5 and PM2.5 precursor 
emissions reductions and PM2.5 concentrations in the 
nonattainment area. The established relationship can be used to 
estimate whether a particular set of emissions reductions will be able 
to advance the attainment date by at least a year. Also, in some cases, 
the emissions reductions identified through the RACM analysis may be 
relatively small (as a percentage of area-wide emissions) that a 
modeling analysis is not needed to show that the attainment date cannot 
be advanced.
2. Available Modeling Guidance for Demonstrating Attainment
    a. Summary of Proposal. The EPA proposed that attainment 
demonstrations should be consistent with the procedures for modeling 
PM2.5 as described in the EPA's ``Guidance on the Use of 
Models and Other Analyses for Demonstrating Attainment of Air Quality 
Goals for Ozone, PM2.5, and Regional Haze'' \105\ as well as 
the Guideline on Air Quality Models (40 CFR part 51, Appendix W).
---------------------------------------------------------------------------

    \105\ The PM2.5 attainment demonstration modeling 
guidance can be found at the following Web site: http://www3.epa.gov/ttn/scram/guidance_sip.htm.
---------------------------------------------------------------------------

    The PM2.5 attainment demonstration modeling guidance 
(hereafter referenced as the ``modeling guidance'') describes how 
states can apply air quality models to generate results needed to 
demonstrate attainment. Models are used to test whether control 
measures in an attainment plan to be adopted into a SIP are likely to 
result in attainment of the relevant standards. The attainment 
demonstration modeling guidance recommends a modeled attainment test 
for the annual and 24-hour PM2.5 NAAQS that uses a 
combination of ambient PM2.5 and PM2.5 species 
data and modeled PM2.5 concentrations to estimate future 
year air quality. In the recommended attainment test the state applies 
the test at each PM2.5 ambient monitor location within or 
near a designated nonattainment area. Models are used in a relative 
sense to estimate the response of measured air quality to future 
changes in emissions. Future air quality is estimated by multiplying 
recent monitored PM2.5 values by the modeled relative 
response (percent change) to projected future changes in emissions. If 
the future design value at all monitoring locations in the 
nonattainment area does not exceed the concentration of 
PM2.5 specified in the NAAQS, the area is projected to 
attain the NAAQS.
    b. Final Rule. In the final rule, EPA is continuing to recommend 
that attainment demonstrations should be consistent with the procedures 
for modeling PM2.5 as described in the PM2.5 
attainment demonstration modeling guidance and Appendix W. The modeling 
guidance describes how states can apply air quality models to generate 
results needed to demonstrate attainment. These recommendations include 
developing a conceptual description of the problem to be addressed; 
developing a modeling/analysis protocol; selecting an appropriate model 
to support the demonstration; selecting appropriate meteorological 
episodes or time periods to model; choosing an appropriate area to 
model with appropriate horizontal/vertical resolution; generating 
meteorological and air quality inputs to the air quality model; 
generating emissions inputs to the air quality model; and evaluating 
performance of the air quality model. After these steps are completed, 
the state can apply a model to simulate effects of future year 
emissions and candidate control strategies.
    The EPA has updated the 2007 PM2.5 modeling guidance to 
include additional information related to the 2012 PM2.5 
NAAQS and associated monitoring requirements.\106\ The main components 
of the modeling guidance and the modeled attainment test have not 
changed. Additional information has been added to address near-road 
monitoring sites and other information that was not available when the 
guidance was first released in 2007.
---------------------------------------------------------------------------

    \106\ See updated guidance at https://www3.epa.gov/ttn/scram/guidance/guide/Draft_O3-PM-RH_Modeling_Guidance-2014.pdf: ``Draft 
Modeling Guidance for Demonstrating Attainment of Air Quality Goals 
for Ozone, PM2.5, and Regional Haze,'' December 2014.
---------------------------------------------------------------------------

    The modeling guidance continues to recommend a relative attainment 
test for both the annual and 24-hour PM2.5 NAAQS. The EPA is 
not recommending a specific model for use in the attainment 
demonstration for the PM2.5 NAAQS. At present, there is no 
single model that has been extensively tested and shown to be clearly 
superior to other available models. The current

[[Page 58050]]

modeling guideline, 40 CFR part 51, appendix W, does not identify a 
preferred model for use in attainment demonstrations of the NAAQS for 
PM2.5. Thus, states may choose from several alternatives.
    The EPA has developed software to perform both the annual and 24-
hour PM2.5 attainment test (including interpolating PM 
species data where necessary). The current software is called the 
Software for the Modeled Attainment Test--Community Edition (SMAT-
CE).\107\ The software is provided as a way to make it relatively easy 
for states to apply the recommended modeled attainment test(s). 
However, states are not required to use SMAT-CE and can develop their 
own post-processing software as necessary.
---------------------------------------------------------------------------

    \107\ SMAT-CE replaced the Modeled Attainment Test Software 
(MATS) in January 2016. SMAT-CE performs the same functionality as 
MATS, but is open source, runs faster, and is more stable than its 
predecessor.
---------------------------------------------------------------------------

    The modeling guidance continues to describe the opportunity for 
states to supplement their modeling with a ``weight of evidence'' 
demonstration. States may use other information and analyses, in 
addition to the modeled attainment test to estimate whether future 
attainment of the NAAQS in an area is likely. Other analyses may 
include, but are not limited to, emissions trends, ambient data trends 
and analyses, other modeling analyses, and documentation of other non-
modeled emissions control strategies, including voluntary programs.
    The application of air quality models requires a substantial effort 
by state and local agencies. Therefore, states should work closely with 
their EPA regional office in executing each step of the modeling 
process. By doing so, it will increase the likelihood of the EPA's 
approval of the state demonstration submitted at the end of the 
modeling and overall attainment plan development process.
    c. Comments and Responses. Comment: Several commenters questioned 
the ability of the current most common photochemical models to 
accurately model how the PM2.5 precursors impact overall 
PM2.5 concentrations. They raise particular concerns about 
ammonia emissions and the ability of models to predict PM2.5 
formation from ammonia precursor emissions. The commenters stated that 
emissions inventories necessary for such modeling, as well as the tools 
used to measure those emissions, remain uncertain and are sometimes 
inaccurate; e.g., emission rates are too often based on unreliable 
data, due to either lack of representative information or technical 
issues associated with test methods. Some commenters stated that these 
concerns are particularly salient here because the PM2.5 SIP 
Requirements Proposal requires that states account for new precursors, 
including VOCs and ammonia.
    Response: The EPA disagrees with the commenters' assertion that 
emissions inventory and modeling tools are insufficient to estimate 
PM2.5 concentrations and the predicted change in 
PM2.5 due to changes in PM2.5 emissions and 
PM2.5 precursors. While there will always be uncertainty in 
emissions inventories and modeling, photochemical models of 
PM2.5 concentrations, including secondary formation through 
chemistry, have been used in the scientific and regulatory community 
for over 30 years. State attainment demonstration modeling has been 
performed by numerous states over the last 10+ years to support the 1st 
round of PM2.5 SIPs that were due in 2007. In addition, the 
EPA has used photochemical modeling of PM2.5 to support 
numerous regulatory rulemakings over the last decade.
    The technical tools to perform photochemical modeling are well 
established and have been improved almost continuously over many years. 
New versions of the CMAQ and CAMx models with numerous science updates 
are released every 1 to 2 years. National emissions inventories that 
include primary PM2.5 and all scientific precursors 
(SO2, NOX, VOC and ammonia) have existed since 
the NEI for 2002. The NEI is released every 3 years with methodological 
improvements with every release.
    In addition, the commenters refer to VOC and ammonia as ``new 
precursors,'' which is not accurate. VOC and ammonia have always been 
``scientific'' PM2.5 precursors, and as such have always 
been inventoried and modeled with chemistry in PM2.5 
photochemical models. The only thing ``new'' is that VOC and ammonia 
are now assumed to be presumptive PM2.5 precursors. However, 
even though the previous implementation rule did not assume that VOC 
and ammonia were default precursors, all photochemical modeling of 
PM2.5 has always included VOC and ammonia emissions and the 
resultant chemical formation of ammonium sulfate, ammonium nitrate, and 
secondary organic carbon.
    The commenters were concerned that model errors in the formation of 
PM2.5 from ammonia sources would impose an unreasonable 
regulatory burden on sources of ammonia such as animal agriculture. 
Even though there may be general uncertainty in ammonia inventories, it 
is not clear how those uncertainties would lead to an unreasonable 
regulatory burden on any emissions sources in particular. Every 
modeling application in support of an attainment demonstration must be 
shown to adequately represent the emissions, chemistry, and 
PM2.5 concentrations in the nonattainment area. Ambient 
measurements of PM2.5 and precursors are used in a model 
performance evaluation to demonstrate that the modeling system is 
appropriate to use to determine the sensitivity of PM2.5 
mass to emissions changes. In addition, all SIPs are required to 
undergo a public comment process where specific emissions and/or 
modeling concerns can be raised to the state. And then, after review of 
the SIP submission by EPA, all approvals or disapprovals of attainment 
SIPs go through a notice and comment rulemaking process. There are 
therefore numerous opportunities for both industry and the general 
public to participate in the SIP development process. States are 
expected to use the appropriate tools and the best information 
available to demonstrate how they will attain the PM2.5 
NAAQS by the attainment date. The EPA believes that the appropriate 
tools are available to perform the modeling needed for an attainment 
demonstration.
3. Demonstrating Attainment at Near-Road Monitors
    a. Summary of Proposal. The 2012 PM2.5 NAAQS final rule 
contains new requirements for operating near-road monitors in the 
largest metropolitan areas.\108\ The first set of monitors was required 
to be in place by January 1, 2015. Some of the near-road monitors began 
operation prior to 2015. However, none of the monitors will have the 
requisite 3 years of monitoring data that can be used to calculate a 
PM2.5 design value until 2017 at the earliest. Therefore, 
these data were not used for the initial designations for the 2012 
PM2.5 NAAQS (finalized in December 2014) and in most 
nonattainment areas, there will be less than 3 years' worth of data 
available when the initial attainment demonstrations for Moderate 
nonattainment areas are due in 2016. As a result of this timing, the 
EPA proposed that the initial set of Moderate area attainment 
demonstrations will not need to include projected design values for 
near-road monitors. But when 3 or more years' worth of complete ambient 
data are available at near-road monitors,

[[Page 58051]]

states will need to address those monitors in their attainment 
demonstrations and will need to include a demonstration that those 
monitors will attain the NAAQS by the applicable statutory attainment 
date.
---------------------------------------------------------------------------

    \108\ 78 FR 3283.
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    b. Final Rule. For the final rule, the EPA maintains the policy of 
not requiring the use of ambient air quality data in a modeled 
PM2.5 attainment demonstration unless there is at least one 
complete design value of data available (generally 3 complete years of 
data). This applies to both near-road and other PM2.5 
ambient monitoring data. Some states may have installed their monitors 
well before the January 1, 2015 deadline and may therefore have 
complete data before the SIP deadline. In addition, some attainment 
demonstrations may be submitted after the statutory deadline. Because 
of the varying monitor installation dates, the use of near-road 
monitoring data in attainment demonstrations depends on the timing of 
the attainment demonstration submission relative to the installation 
date of the monitor(s). Ambient data with sufficient completeness to 
calculate a design value may not be ignored in an attainment 
demonstration. Such data can be addressed either in the attainment 
demonstration analysis of ambient monitors or as part of an unmonitored 
area analysis (see the next section), as appropriate.
    The revised PM2.5 modeling guidance document includes 
procedures for applying a dispersion model or a combination of 
photochemical grid models and dispersion modeling to demonstrate 
attainment at monitors with large primary PM2.5 
concentration gradients. Depending on the nature of the ambient data in 
a particular area, it may be appropriate to treat near-road monitors as 
high concentration gradient locations. However, in other cases, near-
road monitors may have little or no gradient compared to other nearby 
monitors. Therefore, the appropriate treatment of near-road monitors in 
attainment demonstrations should be evaluated on a case-by-case, 
depending on the facts and circumstances in each nonattainment area.
    c. Comments and Responses. Comment: Some commenters stated the 
EPA's proposal to excuse areas from having to include projected design 
values for near-road monitoring locations promises to undermine the 
likelihood of success for attainment demonstrations. The commenters 
stated the EPA's blanket waiver for near-road data has no rational 
basis and that just because such monitors were not required before 
January 1, 2015, does not mean that areas did not have them in place 
before then. The commenters stated the EPA should at least clarify that 
if an area has 3 years of near-road monitoring data, it should use such 
data in its attainment modeling. The commenters stated this would be 
particularly important, for example, if an area is late in preparing 
its demonstration.
    Response: The EPA agrees there should not be a ``blanket waiver'' 
for the use of near-road monitoring data in attainment demonstrations 
that are due in 2016 or thereafter. The statements in the proposal 
referenced the fact that the near-road monitors were not required to be 
in place before January 1, 2015. This makes it unlikely that sufficient 
data from these monitors will be available to be considered in 
attainment demonstrations that are due in 2016. However, if complete 
data are available at near-road monitors during the development of the 
attainment demonstration, the data should be considered as appropriate 
(similar to any other PM2.5 monitoring data). Since the 
near-road PM2.5 monitoring network is relatively new, there 
may not be 3 years of complete data in time to be considered in the 
upcoming attainment demonstrations. In addition, the base modeling year 
of the attainment demonstration may predate the startup date of the 
near-road monitor(s). In this case, it may be possible to consider the 
near-road data in the attainment demonstration, but the recommended 
default projection methodology may not be applicable (since the time 
period of the near-road data may not correspond to the 5 year time 
period centered about the base modeling year, as recommended in the 
modeling guidance). Additionally, near-road PM2.5 monitors 
are only required in the 27 largest metropolitan areas of the country. 
Some PM2.5 nonattainment areas may not have any near-road 
monitoring sites. States should consult with the appropriate EPA 
regional office to determine the best way to treat near-road data in 
their attainment demonstration.
4. Demonstrating Attainment in Unmonitored Areas
    a. Summary of Proposal. The 2007 PM2.5 modeling guidance 
describes a recommended ``relative'' attainment test that is based on 
showing attainment at ambient monitoring locations. The guidance also 
recommends that states conduct further analyses based on modeling 
results to determine whether there are unmonitored areas that merit 
additional analysis or investigation. In order to clarify the statutory 
and rule requirements of a modeled attainment demonstration, the EPA 
proposed four options for demonstrating attainment in unmonitored areas 
in an attainment demonstration.
    Option 1 would require the attainment demonstration modeling to 
demonstrate attainment at ambient monitoring locations. There would be 
no requirement to specifically examine attainment in unmonitored areas. 
Option 2 would require modeling to demonstrate attainment at ambient 
monitoring locations and in unmonitored areas within the nonattainment 
area. Enforceable emissions reductions would be required to eliminate 
any potential future year NAAQS violations in all locations within the 
nonattainment area (including unmonitored areas). Option 3 would 
require modeling to demonstrate attainment at ambient monitoring 
locations and in unmonitored areas within the nonattainment area. 
However, rather than requiring states to impose additional enforceable 
emissions reductions in the SIP to address potential violations in 
unmonitored areas, states would be required to use the unmonitored area 
analysis results to develop an assessment of the likelihood of 
violations in unmonitored areas. The assessment would be used to 
evaluate the need for additional controls and/or could be used to 
inform the ambient monitoring plan (the need to add additional monitors 
or move existing monitors). Option 4 would require modeling to 
demonstrate attainment at ambient monitoring locations and recommend 
the analysis of unmonitored areas within the nonattainment area. This 
differs from Option 3 in that there would be no rule requirement to 
perform an unmonitored area analysis. But the submission of an 
unmonitored area analysis would still be recommended, especially in 
areas with a relatively sparse PM2.5 monitoring network or 
in locations where information such as modeling data, emissions 
inventories or non-FEM monitoring data (such as from special purpose 
monitors or saturation monitoring studies) may indicate potential high 
PM2.5 concentrations in areas that are currently 
unmonitored.
    b. Final Rule. The EPA is finalizing proposed Option 4. This option 
requires states to show attainment at all current and recent monitoring 
locations. States will not be required to provide an unmonitored area 
analysis as a mandatory element of each attainment demonstration. 
However, an unmonitored area analysis can provide useful information 
about PM2.5

[[Page 58052]]

concentrations and gradients in the nonattainment area and therefore 
the EPA recommends that all attainment demonstrations should contain an 
unmonitored area analysis. The EPA encourages states to use information 
available to them to consider what, if any, impacts may be occurring in 
unmonitored areas. States can evaluate the need to perform an 
unmonitored area analysis by using available information such as 
modeling data, emissions inventories, or non-FEM monitoring data (such 
as from special purpose monitors or saturation monitoring studies) to 
indicate the potential high PM2.5 concentrations in areas 
that are currently unmonitored. An unmonitored area analysis is 
strongly recommended where the state and/or the EPA has reason to 
believe that potential violations may be occurring in unmonitored 
areas, or other available information indicates that further analysis 
is warranted. The EPA will consider whether the state has adequately 
addressed all available information about potential exceedances of the 
NAAQS in unmonitored areas when determining whether the plan can be 
approved.
    The EPA is requiring an attainment demonstration approach that 
relies primarily on existing monitoring sites and modeling to project 
attainment in future years. This approach to evaluating monitored and 
unmonitored areas is consistent with how EPA determines whether an area 
meets the PM2.5 NAAQS for purposes of designations and 
redesignations. As discussed in Section II of this preamble, the EPA 
promulgates designations for PM2.5 NAAQS nonattainment areas 
based primarily on ambient data measured at FRM and FEM monitors.\109\ 
Although the EPA considers other information for purposes of evaluating 
areas with sources that contribute to those monitored violations for 
inclusion within the nonattainment area boundaries, the fundamental 
basis for designating an area as nonattainment for a PM2.5 
NAAQS is the presence of one or more FRM or FEM monitors with data 
showing violations of the NAAQS. Similarly, determinations of 
attainment of the PM2.5 NAAQS for purposes of redesignation 
actions are based primarily on monitored data. When all FRM and FEM 
monitors in a nonattainment area measure attainment of the 
PM2.5 NAAQS, the state is eligible to submit a redesignation 
request for the area, assuming that it has complied with all other 
applicable requirements for purposes of redesignation. Specifically, 
the EPA's approval of a redesignation request is subject to meeting the 
requirements of CAA section 107(d)(3)(E). Among those requirements is 
that the area has attained the NAAQS. For the PM2.5 NAAQS, 
this determination is based on ambient data measured at the FRM and FEM 
monitors in the area in question.
---------------------------------------------------------------------------

    \109\ A monitor must have 3 years of quality assured ambient 
data available to be used to calculate a PM2.5 design 
value and determine compliance with the NAAQS.
---------------------------------------------------------------------------

    In addition, the ``relative'' attainment test for PM2.5 
attainment demonstrations uses FRM or FEM ambient monitoring data, 
combined with future year modeled percentage changes in 
PM2.5 concentrations to project future year design values. 
Since the attainment test relies on ambient monitoring data, an 
analysis of future year concentrations in unmonitored areas can only be 
accomplished by interpolating ambient data to a particular location 
where there is no existing monitor or recent monitoring data. 
Therefore, in the context of an attainment demonstration, the 
projection of future year PM2.5 concentrations in 
unmonitored locations is inherently more uncertain than projections in 
monitored locations due to the fact that the ambient concentrations 
from which these projections are developed are unknown in the 
unmonitored locations.
    While the unmonitored area analysis is not a regulatory 
requirement, and states are not required to identify enforceable 
emissions reductions to eliminate potential violations in unmonitored 
areas, an unmonitored area analysis has the potential to provide 
additional important information about PM2.5 levels and 
gradients in the nonattainment area. The results of the analysis can be 
used to provide information to inform future monitoring plans, to 
examine the need for potential emissions controls, to evaluate 
potential environmental justice concerns, and to provide additional 
information to the public. The EPA believes that Option 4 provides the 
best balance between the regulatory requirements of the attainment 
demonstration and additional analyses which could provide helpful 
information to inform future regulatory activities.
    Where information is available, states and the EPA have obligations 
to address potential violations in unmonitored areas, and, although we 
expect this to be relatively rare, attainment plans need to address air 
quality in unmonitored areas where information exists suggesting the 
potential for such violations. Where an unmonitored area analysis is 
performed, states should use model results and available ambient data 
to develop an assessment of the likelihood of violations in unmonitored 
areas. The nature of the assessment depends on the available 
information and the nature of the local PM2.5 problem, but 
could include, as appropriate, elements such as an evaluation of the 
emissions inventory (particularly for local direct PM2.5 
sources), the existing ambient data for the area, and meteorological 
model inputs to evaluate the accuracy of the modeled violations in 
unmonitored areas. If potential violations are determined to be likely, 
additional steps could include imposition of emissions reductions at 
nearby emission sources or a commitment to deploy special purpose 
monitors and/or saturation monitors in the area (in order to further 
evaluate the problem). The state should document the assessment, 
including analyses of emissions, meteorological inputs and ambient 
data.
    The PM2.5 modeling guidance recommends a default 
procedure for applying an unmonitored area analysis, which combines 
gridded model data with interpolated ambient data. States can apply the 
default recommended approach or develop their own analysis which may be 
more appropriate for the specific area or situation. States are 
expected to consult with the appropriate EPA Regional Office to 
evaluate available information to determine if an unmonitored area 
analysis is needed for a particular area and how the analysis should be 
performed.
    c. Comments and Responses. Comment: Some commenters stated that, of 
the options for addressing unmonitored areas, only Option 2 is 
technically and legally defensible (80 FR 15382). The commenters stated 
the Act requires that ambient concentrations in all areas meet the 
applicable NAAQS and cited 42 U.S.C. 7407(a) as requiring states to 
assure ``air quality within the entire geographic area comprising such 
State'' will achieve the national standards and requiring ``an 
implementation plan [to] . . . specify the manner in which national 
primary and secondary ambient air quality standards will be achieved 
and maintained''). The commenters also cited 42 U.S.C. 7410(a)(1) as 
requiring implementation plans to provide for implementation of the 
NAAQS ``in each air quality control region (or portion thereof) within 
such State''). The commenters stated it is insufficient to suggest that 
an area need only show attainment at monitored locations and need only 
adopt controls that will address those locations.
    Response: The EPA does not agree that Option 2 is the only 
technically and

[[Page 58053]]

legally defensible option. The CAA requires states with nonattainment 
areas to submit an attainment demonstration as part of their 
PM2.5 SIP. States must show that they will attain the NAAQS 
by their attainment date. The CAA also requires states to use air 
quality modeling in their attainment demonstration. But other than 
those general requirements, the EPA believes states have discretion to 
interpret how and where to show attainment of the NAAQS through 
modeling in support of an attainment demonstration.
    In addition, the EPA believes that a monitor based attainment 
demonstration satisfies the CAA requirement to show that ``the entire 
geographic area'' will attain the NAAQS. The EPA's monitoring 
requirements for PM2.5 are designed to ensure a robust 
nationwide monitoring network in both nonattainment and attainment 
areas. States have achieved this by maintaining their PM2.5 
networks in accordance with EPA's network design criteria. 
Historically, these criteria provided that CBSAs have at least one 
PM2.5 monitoring site located in an ``area-wide'' location 
of expected maximum concentration (within the CBSA).\110\ Thus, by 
assuring compliance with the NAAQS at the location of the expected 
highest area-wide concentration in the CBSA, air quality is protected 
throughout each CBSA. The EPA has identified recommended procedures for 
PM2.5 modeled attainment demonstrations. These 
recommendations are contained in modeling guidance. The recommended 
attainment test relies on the ambient monitors to provide the ``anchor 
point'' for future year air quality projections. This ensures that 
future year concentration predictions are grounded by ``real world'' 
measurements. Since the attainment test relies on ambient monitoring 
data, the projection of future year PM2.5 concentrations in 
unmonitored locations is inherently more uncertain than projections in 
monitored locations due to the fact that the ambient concentrations 
from which these projections are developed are unknown in the 
unmonitored locations. Therefore, the EPA continues to believe that for 
PM2.5 attainment demonstrations, modeling results in 
unmonitored areas are too uncertain to use in this manner. For the 
reasons stated earlier, in the final rule, the EPA does not believe 
that it is necessary to require states to submit an unmonitored area 
analysis and to show that any potential violations of the NAAQS in 
unmonitored areas have been eliminated through enforceable controls.
---------------------------------------------------------------------------

    \110\ See fine particulate (PM2.5) design criteria at 
40 CFR part 58-Appendix D to part 58.
---------------------------------------------------------------------------

    Comment: Several commenters supported Option 1 where only monitored 
grid cells are included in the attainment plan. Commenters stated that, 
due to their concerns related to the accuracy of air dispersion 
modeling tools and protocols, it is not appropriate to use air 
dispersion modeling to predict receptor impacts in unmonitored areas. 
Some commenters stated that Option 1 is the approach that most closely 
describes the current EPA rule.
    Response: The EPA agrees that the modeling results are too 
uncertain in unmonitored areas to require an unmonitored area analysis 
as part of the attainment demonstration (for the reasons enumerated 
earlier). However, the EPA disagrees that Option 1 is the approach that 
most closely describes the attainment demonstration requirements in the 
2007 PM2.5 implementation rule. An unmonitored area analysis 
has never been an implementation rule requirement, but was a 
recommended analysis in the PM2.5 modeling guidance. 
Therefore, the EPA believes that Option 4 is closer to the current 
status quo. This final rule clearly states the continued recommendation 
to perform an unmonitored area analysis and the benefits of doing so.
    Comment: Some commenters stated that an ``unmonitored area 
analysis'' is essential since speciation monitoring is conducted at a 
limited number of sites. The commenters stated that, however, given the 
inherent uncertainty from modeling analysis in unmonitored areas, 
results from such analysis should only be used to inform additional 
actions. The commenters stated that, while modeling analysis in 
unmonitored areas can be used as a reference for additional studies, it 
should not be used for the attainment demonstration in the SIP. The 
commenters stated that, under any of the options, the EPA should 
specify the recommended level of detail for an unmonitored area 
analysis, especially if it is required. The commenters recommended that 
the analysis need not require modeled results at finer spatial scales 
than those specified in the modeling protocol.
    Response: The EPA agrees that an unmonitored area analysis is 
important and continues to recommend development of unmonitored area 
analyses to support attainment demonstrations. The EPA also agrees that 
due to uncertainty, the results from such analysis should only be used 
to inform additional actions. As stated earlier, the PM2.5 
modeling guidance contains a default recommended unmonitored area 
analysis technique which combines gridded modeling data and 
interpolated ambient data (including PM2.5 speciation data). 
But the exact nature of the unmonitored area analysis can be considered 
based on the information relevant to each nonattainment area. The EPA 
also agrees that where an unmonitored area analysis is conducted, it 
should be at the same spatial scale (model resolution) as the modeled 
attainment demonstration at monitoring locations. For example, if the 
gridded modeling analysis is performed at 4km resolution (model grids 
that are 4km on a side), then the unmonitored areas should be examined 
at the same resolution. Similarly, if near road monitors are examined 
with a dispersion model at a finer resolution (compared to the other 
monitors) as part of the attainment demonstration, the unmonitored area 
analysis could also examine unmonitored near-road areas at a finer 
resolution.
    Comment: Several commenters disagreed with the proposal to require 
states to perform the attainment test at ``recent'' monitoring 
locations. Commenters stated that, within the EPA's description of 
Option 1, the proposal indicates that the attainment test required 
under Option 1 would also apply to locations that have ``recent'' FRM 
and/or FEM monitoring data. Commenters stated the current FRM/FEM 
monitoring data should be sufficient to demonstrate attainment.
    Response: States must demonstrate that they will attain the 
PM2.5 NAAQS in the nonattainment area as expeditiously as 
practicable, and no later than the moderate area attainment date. The 
recommended attainment test in the modeling guidance uses recent 
ambient data that encompass a 5-year period that is dependent on the 
base modeling year. For example, for a base modeling year of 2014, the 
guidance recommends using ambient PM2.5 data from the 2012-
2016 period. The guidance also recommends only using ambient data from 
a particular monitoring site if it has at least one complete design 
value period during the relevant 5-year period. With these 
recommendations in mind, there are numerous cases where a monitoring 
site may have only partial data from the relevant 5-year period or may 
be a new monitor that started collecting data after the 5-year period 
or may have been shut down before the 5-year period. The EPA agrees 
that it is generally not necessary to examine the modeling results 
where monitors were shut down before the base modeling period. These 
monitors will not be used to make future

[[Page 58054]]

decisions relating to attainment status of the area. However, monitors 
that are new or were operating during the base modeling period are 
still relevant and can be used to provide additional information in the 
attainment demonstration. The data from these monitors may serve as the 
basis for examining potential violations in the area as part of an 
unmonitored area analysis. This is especially the case for new 
monitors, which may not have enough data to provide a robust future 
year concentration estimate in the attainment demonstration. But the 
monitoring data, combined with modeled information, can provide 
information about the likelihood of future violations in the area 
surrounding the monitor location.
5. Future Year(s) To Be Modeled in Attainment Demonstrations
    a. Summary of Proposal. A state performing a modeling analysis for 
an attainment demonstration or impracticability analysis must select a 
future year for the analysis. For an attainment demonstration, a state 
should select the future modeling year such that all emissions control 
measures relied on for attainment will have been fully implemented by 
the beginning of that year. The EPA proposed that to demonstrate 
attainment, the modeling results for the nonattainment area must 
predict that emissions controls implemented no later than the beginning 
of the last calendar year preceding the attainment date will result in 
PM2.5 concentrations that meet the level of the 
standard.\111\ While states should choose the future modeling year 
based on a number of factors, the EPA proposed the last possible year 
permitted under the statute as a starting point for modeling.
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    \111\ Note that for purposes of the PM2.5 NAAQS, a 
determination of attainment (or failure to attain), which the EPA is 
required to make after the attainment date has passed, is based on 
an average of the most recent 3 years of ambient data prior to the 
area's attainment date.
---------------------------------------------------------------------------

    b. Final Rule. The EPA is finalizing the recommendation that the 
last possible year permitted under the statute is an appropriate 
starting point for modeling. See 40 CFR 51.1011(a)(6). For a state that 
is submitting an attainment demonstration, modeling the sixth calendar 
year is a logical starting point to determine if attainment by that 
year is likely. Even though attainment is determined by averaging 3 
years' worth of ambient data, states do not have to model 2 years 
before the attainment date to show modeled attainment. Since the design 
value is an average of 3 years' worth of data, attainment can still be 
shown even if concentrations exceed the NAAQS in one or more of the 3 
years used to determine attainment (as long as the 3 year average is 
less than the NAAQS). Therefore, it can be appropriate to model any of 
the 3 years used to determine attainment. In addition, if ambient data 
show attainment-level concentrations in the final statutory attainment 
year, a state may be eligible for up to two 1-year extensions of the 
attainment date, if the area meets the criteria for such extensions. 
Therefore, modeling attainment-level concentrations for the last year 
permitted by statute is acceptable.
    States with Moderate areas that submit an impracticability 
demonstration must show that the area cannot attain the NAAQS by the 
end of the sixth calendar year following designation of the area. 
Therefore, the appropriate future modeling year for such a 
demonstration is also the sixth calendar year after designation.
    For the reasons stated earlier, it is both acceptable, and will in 
fact be most efficient, for a state to begin the attainment 
demonstration process by modeling the last year permitted under the 
statute to determine future year modeled PM2.5 
concentrations in the sixth year after designations. For example, since 
designations for the 2012 PM2.5 NAAQS were effective in 
March 2015, it is appropriate for states to model air quality for 2021 
in the attainment demonstrations for designated nonattainment areas.
    Because an area must attain ``as expeditiously as practicable,'' 
additional considerations are necessary before an attainment date can 
be established. For purposes of determining the attainment date that is 
as expeditious as practicable, the state must conduct future year 
modeling which takes into account expected growth and known controls 
that are already in effect or that are adopted and will be in effect by 
January 1 of the future year. For example, for a Moderate nonattainment 
area for the 2012 PM2.5 NAAQS, a future base case scenario 
for the year 2021 would project future air quality given implementation 
of existing federal, state and local measures. If this future base case 
scenario demonstrates attainment, then the state must determine if 
attainment can be achieved in an earlier year through the application 
of additional measures. Therefore, the state must conduct an analysis 
of RACM and RACT and additional reasonable measures to determine if, 
collectively, all technologically and economically feasible measures 
identified by the state that can be implemented by the beginning of the 
sixth calendar year following designations can advance the attainment 
date by at least 1 year (note that RACM and RACT controls must be 
implemented within 4 years of an area being designated nonattainment, 
but additional reasonable measures for an area for which a state can 
demonstrate attainment by the end of the sixth calendar year following 
designation of the area are those technologically and economically 
feasible measures that can be implemented by the beginning of the last 
year prior to the projected attainment date). Results of this analysis 
may indicate attainment can be achieved earlier, through implementation 
of all reasonable control measures (i.e., RACM and RACT and additional 
reasonable measures).
    If, on the other hand, the future base case scenario does not 
demonstrate attainment, then a control case scenario is needed to 
examine whether the reasonable, technically and economically feasible 
measures identified by the state would result in attainment in the 
analysis year (i.e., in 2021 for purposes of this example based on the 
2012 PM2.5 NAAQS). The control case scenario would add 
potential control measures--e.g. RACM and RACT (which must be 
implemented in 4 years) and additional reasonable measures, plus any 
measures on sources outside of the nonattainment area that the state 
has identified as feasible to implement by the attainment date. This 
modeling, along with other relevant information, would inform a 
judgment as to whether attainment of the relevant NAAQS is practicable 
by the end of the sixth year after designation or earlier. In the case 
of areas designated for the 2012 PM2.5 NAAQS, if the 
analysis does not demonstrate attainment by December 31, 2021, then the 
analysis could serve as the technical basis for the state to submit a 
demonstration that attainment by the outermost statutory attainment 
date for Moderate areas is impracticable. This in turn could serve as a 
technical basis for the Administrator to reclassify the area to 
Serious.\112\ If the analysis does demonstrate attainment, then the 
remaining step is to assess whether the attainment date can be advanced 
by 1 year.
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    \112\ A demonstration that the area cannot attain by the 
moderate area attainment date would not be the only trigger for a 
reclassification to serious nonattainment. The Administrator 
maintains wide discretion in making a determination that an area 
cannot practicably attain the NAAQS by their attainment date.
---------------------------------------------------------------------------

    In conducting this assessment, the EPA believes that it is not 
reasonable to require states to model each and every calendar year to 
determine the

[[Page 58055]]

appropriate attainment date. Developing and modeling future year 
inventories is a time-consuming and resource intensive process. 
Multiple emissions models are needed in order to generate year specific 
emissions for the various emissions sectors (e.g. mobile, non-road, 
non-EGU point and EGU point). In some cases it may be reasonable to 
model one additional interim year before the maximum statutory 
attainment date.\113\ However, in most cases, the air quality benefits 
of an identified set of RACM and RACT and additional reasonable 
measures can be estimated through model sensitivity analyses and the 
development of sensitivity factors (i.e., factors to relate tons of 
emissions reductions in the area to PM2.5 concentration 
changes in the area). For example, states can model across the board 
percentage reductions in direct PM2.5 and/or precursor 
emissions (in separate model runs or using advanced modeling techniques 
such as DDM) to determine the impact of emissions reductions on 
PM2.5 concentrations in the area. This modeling can be 
performed with a single attainment year modeling platform, which is 
much less resource intensive than modeling additional future years. The 
identified potential emissions reductions available from RACT and RACM 
and additional reasonable measures can be compared to the magnitude of 
the modeled PM2.5 reductions from the sensitivity analyses 
to determine if all such controls will advance attainment by a year. 
The EPA strongly recommends that states discuss the selection of the 
future year(s) to model with their EPA Regional Office as part of the 
modeling protocol development process and before embarking on the 
modeling.
---------------------------------------------------------------------------

    \113\ If several future modeling years are available, it may in 
some cases be appropriate for states to interpolate PM2.5 
concentrations between years.
---------------------------------------------------------------------------

    c. Comments and Responses. Comment: Some commenters disagreed with 
the proposal that the future year should reflect when all control 
measures relied on have been fully implemented by the beginning of that 
year and it should be no later than the beginning of the last calendar 
year preceding the attainment date. The commenters stated the CAA 
provides attainment must be achieved as expeditiously as practicable 
but no later than the end of the sixth calendar year (except RACT/RACM 
are required within 4 years) and states should be given the full period 
to demonstrate attainment and to require control of emissions.
    Response: The proposal to require the modeling to reflect control 
measures that have been fully implemented no later than the beginning 
of the last calendar year preceding the attainment date does give 
nonattainment areas ``the full period'' to demonstrate attainment and 
to require control of emissions. Since the design value is an average 
of 3 years' worth of data, it could be argued that modeling and related 
emissions controls should be in place 3 years before the attainment 
date. However, if ambient data show attainment level concentrations in 
the final statutory attainment year, a state may be eligible for up to 
two 1-year extensions of the attainment date, if the area meets the 
criteria for such extensions. Therefore, modeling attainment level 
concentrations for the last year permitted by statute is acceptable. 
But in order to measure attainment level concentrations in the final 
year, controls must be in place for the full year (at the beginning of 
the year). Implementation of emissions controls at the end of the year 
would not be consistent with modeling attainment level or measuring 
attainment level concentrations during the year.
6. Attainment Year Motor Vehicle Emissions Budgets
    The transportation conformity rule requires that attainment plans 
establish motor vehicle emissions budgets for the area's attainment 
year. Therefore, once an area's attainment date has been established, 
the state would establish motor vehicle emissions budgets for direct 
PM2.5 and any relevant PM2.5 precursor for the 
attainment year.\114\ It should be noted that states that submit 
impracticability demonstrations for Moderate areas under CAA section 
189(a)(1)(B)(ii) are not required to submit motor vehicle emissions 
budgets for attainment purposes because the submitted SIP does not 
demonstrate attainment. A motor vehicle emissions budget for the 
purposes of a PM2.5 attainment plan is that portion of the 
total allowable emissions within the nonattainment area allocated to 
on-road sources as defined in the submitted attainment plan. Such motor 
vehicle emissions budgets would be calculated using the latest planning 
assumptions and the latest approved motor vehicle emissions model 
available at the time that the attainment plan is developed, unless EPA 
approves the state's use of an alternative model.\115\
---------------------------------------------------------------------------

    \114\ For more information on PM2.5 precursor 
requirements, see CAA section 93.102(b)(2)(iv) and (v) of the 
transportation conformity rule. See also the May 6, 2005, final 
transportation conformity rule that addressed requirements for 
PM2.5 precursors. (70 FR 24280).
    \115\ If an area includes re-entrained road dust in the motor 
vehicle emissions budget, the latest approved version of AP-42 
should be used unless the EPA has approved an alternative model for 
the area.
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F. RFP Requirements

1. Background on Statutory Requirements and Existing Guidance
    Reasonable further progress (RFP) is a concept included in the CAA 
under part D, title I to assure that states make steady, incremental 
progress toward attaining air quality standards in the years prior to 
the attainment date for a nonattainment area, rather than merely 
deferring implementation of control measures and therefore emissions 
reductions until the date by which the standards are to be attained. As 
discussed elsewhere in this preamble, section 172 of the CAA addresses 
attainment plan provisions in general. Section 172(c)(2) of the CAA 
requires attainment plans to provide for RFP, which is defined in CAA 
section 171(l) as ``such annual incremental reductions in emissions of 
the relevant air pollutant as are required by [part D of title I] or 
may reasonably be required by the Administrator for the purpose of 
ensuring attainment of the applicable national ambient air quality 
standard by the applicable date.'' Section 189(c) of the CAA requires 
that ``[P]lan revisions demonstrating attainment submitted to the 
Administrator for approval under this subpart shall contain 
quantitative milestones which are to be achieved every 3 years until 
the area is redesignated attainment and which demonstrate reasonable 
further progress, as defined in CAA section 171(1), toward attainment 
by the applicable date.'' Quantitative milestones are discussed later 
in Section IV.G of the preamble.
    Section 172(c)(3) of the CAA requires the state plan to include ``a 
comprehensive, accurate, current inventory of actual emissions from all 
sources of the relevant pollutant or pollutants in such area . . .'' 
Section 172(c)(1) of the CAA requires the state plan to include ``all 
reasonably available control measures as expeditiously as practicable 
(including such reductions in emissions from existing sources in the 
area as may be obtained through the adoption, at a minimum, of 
reasonably available control technology) . . .'' Section 172(c)(9) 
requires the state plan to ``provide for the implementation of specific 
measures to be undertaken if the area fails to make reasonable further 
progress . . . Such measures shall be

[[Page 58056]]

included in the plan revision as contingency measures to take effect in 
any such case without further action by the State or the 
Administrator.'' For additional background on statutory requirements 
and existing guidance, refer to preamble Section IV.F of the proposal 
for this rule.\116\
---------------------------------------------------------------------------

    \116\ 80 FR 15385.
---------------------------------------------------------------------------

2. General Approach to RFP
    a. Summary of Proposal. To satisfy the statutory requirements for 
RFP at CAA section 172(c)(2), the EPA proposed that a state must submit 
an RFP plan as part of its Moderate area attainment plan submission. 
The EPA proposed the following two options for developing an RFP plan.
    Under the first option, the EPA proposed that the RFP analysis for 
any Moderate PM2.5 nonattainment area that can demonstrate 
attainment by the statutory attainment date must demonstrate either: 
(i) Generally linear progress toward attainment; or (ii) stepwise 
progress toward attainment. Stepwise emissions reductions would be 
slower than ``generally linear'' reductions for certain periods, and 
then would decline sharply (due to implementation of a new emission 
reduction program, or new operation of control technology on one or 
more stationary sources). The EPA proposed that a state must follow one 
primary approach for conducting the RFP analysis, but that they also 
have an option to conduct a secondary analysis that will provide 
greater flexibility in setting RFP goals with alternative emissions 
reductions and air quality improvement scenarios. The primary approach 
would be to show that nonattainment area emissions of each pollutant 
decline from the base year to the attainment year, either in a 
generally linear manner or in a stepwise manner. In the optional 
secondary analysis, the state could show that emissions of the various 
pollutants would change in a manner that would provide a change in air 
quality during the attainment period that is equivalent or more 
expeditious than the air quality change that would be estimated to 
occur under the primary approach. This optional analysis was referred 
to as an equivalency determination.
    Under the second proposed option, the state would provide the 
control strategy implementation schedule and estimate the emissions 
reductions anticipated from the control measures (i.e., RACM/RACT and 
additional reasonable measures) for sources in the nonattainment area. 
The state then would employ modeling or another quantitative method to 
predict the overall PM2.5 concentrations in the 
nonattainment area for each milestone year. The milestone years would 
correspond to the years for which the state would be required to 
provide quantitative milestones pursuant to the requirement in section 
189(c) of the Act.
    b. Final Rule. The EPA is finalizing RFP requirements that allow 
the state flexibility to demonstrate RFP under CAA section 172(c)(2) 
using any of the general approaches included in the proposed rule. As 
part of its Moderate area attainment plan submission, the state must 
submit an RFP plan that includes three components: (1) An 
implementation schedule for control measures on sources in the 
nonattainment area, (2) RFP projected emissions for each applicable 
quantitative milestone year determined in Section IV.G of this 
preamble, based on the anticipated control measure implementation 
schedule; and (3) an analysis that demonstrates that this schedule of 
aggregate emissions reductions achieves sufficient progress toward 
attainment between the applicable baseline year to the attainment year. 
See 40 CFR 51.1012(a).
    The first component of the RFP plan is the implementation schedule 
for all required control measures contained in the control strategy. 
The schedule should describe which measures will be implemented within 
the first 4 years following designation (and therefore would meet the 
statutory requirement for RACM and RACT). It should also describe the 
implementation schedule of additional reasonable measures (to be 
implemented more than 4 years following designation but before the 
attainment date) that have been adopted to help provide for expeditious 
attainment of the standard. Any Moderate area that cannot demonstrate 
attainment by the statutory Moderate area attainment date is required 
to provide an implementation schedule for all of the control measures 
identified as RACM/RACT and additional reasonable measures, in the same 
manner as an area that can demonstrate attainment.
    The second component of the RFP plan is an analysis by the state 
identifying the RFP projected emissions by pollutant that are expected 
to be achieved by the control measures implemented within the 
nonattainment area according to the implementation schedule. The EPA 
requires the state to estimate these RFP projected emissions for each 
quantitative milestone year (i.e., for a Moderate area, at 4.5 years 
and 7.5 years after designation of the area) by sector on a pollutant-
by-pollutant basis. These milestone year projected emissions are 
discussed further in Section IV.F.3 of the preamble. This information 
will be used by the state to show that the area is complying with 
quantitative milestone and RFP requirements for the area (discussed in 
Section IV.G of this preamble).
    The final component of the RFP plan is an analysis demonstrating 
that the schedule of emissions changes achieves reasonable progress 
toward attainment between the applicable baseline year and the 
attainment year. This demonstration can be expressed in the form of 
emissions reductions only, or emissions reductions converted to air 
quality concentrations. This optional air quality RFP analysis is 
discussed later in this section.
    Because the statute does not clearly establish the applicable 
baseline year from which to begin calculating annual emissions 
reductions for purposes of demonstrating RFP, the EPA is finalizing a 
requirement that states use the same year as the base year inventory 
used for developing the control strategy and associated air quality 
modeling demonstrating that the area will attain expeditiously.
    A demonstration based on only emissions reductions must show that 
the implementation schedule achieves either: (i) Generally linear 
progress toward the projected attainment date; or (ii) stepwise 
progress toward the projected attainment date. For example, in one area 
new emission standards for mobile sources may achieve reductions in a 
generally linear manner over time, as a portion of the existing vehicle 
fleet is replaced each year with new vehicles meeting the more 
stringent standards. In another area, regulations to reduce emissions 
from certain stationary source sectors could have a single compliance 
date by which controls must be in place, which could result in a 
significant drop in emissions in a ``stepwise'' manner over a 
relatively short period.
    In the first case, the EPA expects that, so long as the attainment 
date is as expeditious as practicable, then generally linear progress 
toward attainment by that date would satisfy the RFP requirement. In 
the second case, where progress is slower than generally linear, the 
state is required to submit a clear rationale and supporting 
information to explain why generally linear progress is not appropriate 
(e.g., due to the nature of the nonattainment problem, the types of 
sources contributing to PM2.5 levels in the area and the 
implementation schedule for control requirements at such sources).
    Similarly, for areas that cannot demonstrate attainment within the

[[Page 58057]]

Moderate area statutory deadline in CAA section 188(c)(1), the state 
must demonstrate either generally linear or stepwise emissions 
reductions toward the full amount of reductions that will be achieved 
by that deadline, i.e., the amount that reflects implementation of all 
of the control measures identified as RACM and RACT and additional 
reasonable measures for the entire period of the applicable attainment 
plan. Generally linear progress toward this full amount would meet the 
RFP requirement, but progress that is slower than that would require 
further justification.
    In some circumstances, the EPA expects that a state could develop 
an approvable RFP plan even if emissions of one or more 
PM2.5 plan precursors are not decreasing. In this scenario, 
the state must demonstrate that the emissions reductions of direct 
PM2.5 combined with the aggregate emissions reductions of 
PM2.5 plan precursors support expeditious attainment of the 
applicable PM2.5 NAAQS. To accomplish this, the EPA expects 
that a state could use the relative air quality impacts of the 
different PM2.5 plan precursors identified in the attainment 
modeling to demonstrate that the emissions reductions of direct 
PM2.5 and aggregate PM2.5 plan precursors 
constitute an acceptable RFP plan. For example, the state could 
demonstrate that even if one or more PM2.5 plan precursor is 
not decreasing, the emissions reductions of direct PM2.5 and 
the remaining PM2.5 plan precursors are the dominant factors 
in reducing ambient PM2.5 levels and are therefore adequate 
to support expeditious attainment. In providing this flexibility, the 
EPA recognizes that control measures for certain pollutants may be more 
effective at reducing PM2.5 concentrations than others, and 
that states may be able to implement some measures more quickly than 
others while still achieving reasonable overall progress toward 
attainment.
    The EPA is also providing an additional optional RFP analysis that 
evaluates the collective changes in emissions of multiple pollutants 
during the attainment period in terms of changes in air quality 
concentration. Under this optional approach, a state would have to show 
that the air quality improvement that is anticipated by milestone dates 
due to the identified control measures in the implementation schedule 
supports expeditious attainment of the PM2.5 NAAQS. For an 
area that can demonstrate attainment within the Moderate area statutory 
deadline, a state using this option could rely upon attainment 
demonstration modeling results that link emissions reductions with air 
quality improvements. For areas that cannot demonstrate attainment 
within the Moderate area statutory deadline, the state may have to 
conduct modeling or employ another quantitative method to predict the 
overall PM2.5 concentrations in the nonattainment area in 
each milestone year. The state would compare these air quality target 
values to certified ambient air quality monitoring data as part of the 
quantitative milestone report due after the area reaches each 
quantitative milestone date. The EPA recommends that states estimate 
air quality targets by establishing the relationship between modeled 
emissions reductions and air quality changes in the attainment plan 
(for the attainment year) and interpolating to the intermediate year(s) 
based on the same relationship.
    The EPA recognizes that because atmospheric processes are complex, 
a specific percent change in emissions of PM2.5 precursors 
does not lead to an equivalent percent change in air quality, 
potentially creating uncertainty when determining air quality targets 
based upon predicted emissions reductions. Nevertheless, the EPA 
recognizes the importance of providing the flexibility to address 
different pollutants on different timetables so long as the plan can 
reasonably be expected to achieve the intended air quality benefits 
represented by the RFP analysis.
    As previously noted, submission of the air quality-based RFP plan 
is optional. However, in certain circumstances, the applicable Regional 
Administrator may strongly recommend that a state or local agency 
submit an RFP plan with air quality targets for milestone years in 
order to satisfy the statutory RFP requirement. This approach could be 
appropriate when one or more pollutants is not decreasing over the 
attainment planning period or for areas that have experienced 
longstanding and persistent PM2.5 pollution problems despite 
the prior implementation of required control measures. The EPA will 
review each RFP plan on a case-by-case basis to determine whether it 
provides for such annual incremental reductions in emissions of the 
relevant air pollutant(s) as are necessary for the purpose of ensuring 
attainment by the applicable attainment date. See 40 CFR 51.1012. An 
additional RFP analysis will be required as part of a Serious area 
attainment plan if EPA reclassifies the area to Serious.
    c. Comments and Responses. Comment: Some commenters generally 
supported the equivalency determination concept because they noted that 
different precursors are more or less effective in reducing atmospheric 
concentrations of PM2.5. Some commenters stated that, 
because the goal is timely attainment regardless of when controls are 
implemented for each precursor that is to be controlled, the EPA should 
allow both options, including the option for states to determine 
whether to approach the demonstration on a pollutant-by-pollutant 
basis, or overall.
    Response: The final rule allows for emissions from one or more 
PM2.5 plan precursors to increase over the attainment 
planning period, as long as the emissions of direct PM2.5 
and aggregate PM2.5 plan precursors decrease consistent with 
RFP and the state can demonstrate that the emissions increase does not 
delay expeditious attainment. This approach recognizes the fact that 
different precursors have different impacts on PM2.5 
concentrations depending upon the specific atmospheric chemistry of 
each area. As previously noted, submission of the air quality-based RFP 
plan is optional but may be strongly recommend by the applicable 
Regional Administrator depending upon the unique circumstances of the 
nonattainment area.
    Comment: One commenter suggested that the equivalency determination 
must be based on modeling of ambient concentrations, not simply on 
inter-pollutant equivalency ratios.
    Response: The EPA recognizes the importance of modeling and notes 
that there are potential benefits of using modeling when providing the 
optional air quality analysis. Additionally, in the preamble, the EPA 
described when these types of tools could be useful in the development 
the air quality targets. Because the development of air quality targets 
is optional and complements the emissions reductions analysis, the EPA 
does not require modeling of ambient conditions for this purpose.
    Comment: A few commenters supported the proposed Option 1 and the 
allowance for either generally linear or stepwise progress toward 
attainment. These commenters stated that allowing both methods is 
consistent with the pattern of many federal emissions reduction 
measures and it provides the most flexibility to states. Other 
commenters stated that existing guidance in the Addendum failed to 
recognize that, in many cases, more can be accomplished during one 
given year than in another. The commenters suggested the EPA provide 
states with the flexibility to manage their resources for rulemaking 
such that emissions reductions are obtained to attain

[[Page 58058]]

generally linear progress averaged over the 3-year period rather than 
in each individual year.
    Response: As stated earlier, this rule requires that the RFP 
analysis must demonstrate either generally linear or stepwise emissions 
reduction progress toward attainment. If there are significant 
differences between emissions reductions in different years, which make 
the emissions reductions no longer generally linear, then the state 
would have to provide a justification for the stepwise progress as 
discussed earlier. Therefore, the suggestion of averaging the emissions 
reductions to obtain generally linear progress over a 3-year period is 
not an acceptable way to demonstrate RFP. In this example, the state 
would have to submit a justification of why stepwise emissions 
reductions are more appropriate for their area. However, the EPA notes 
that if stepwise emissions reductions are achieved more rapidly than 
expected and consistent with the amount necessary to demonstrate RFP 
toward timely attainment, this would be in line with the overall 
principles of the CAA and would not require the aforementioned 
justification.
3. RFP Projected Emissions for RFP Analyses
    a. Summary of Proposal. The EPA proposed that a state with a 
Moderate PM2.5 nonattainment area must submit RFP projected 
emissions for sources within the nonattainment area as part of the RFP 
plan. The EPA also proposed that these RFP projected emissions would, 
at a minimum, include projected emissions of each pollutant by 
different source types corresponding to the quantitative milestone 
dates for the area.
    b. Final Rule. The EPA is finalizing that a state with a Moderate 
PM2.5 nonattainment area must submit RFP projected emissions 
for sources within the nonattainment area as part of the RFP plan. 
These RFP projected emissions shall, at a minimum, include projected 
emissions of each pollutant (i.e., direct PM2.5 and 
PM2.5 plan precursors) by different source types 
corresponding to the quantitative milestone dates for the area 
(quantitative milestone dates are described in greater detail in 
Section IV.G of this preamble). Specifically, the EPA requires that the 
RFP plan for any Moderate area must contain RFP projected emissions for 
each calendar year in which quantitative milestones for a Moderate 
nonattainment area must be met. As explained in Section IV.G of this 
preamble, a state must identify as part of the attainment plan 
submission for a Moderate nonattainment area quantitative milestones to 
be achieved every 3 years from the Moderate area attainment plan due 
date, or 4.5 years from the effective date of designation of the 
area.\117\ For example, the first round of designations for the 2012 
PM2.5 NAAQS became effective in April 2015; Moderate area 
attainment plans for these areas will thus be due 18 months later, or 
in October 2016. The first quantitative milestones for each of these 
areas will then have to be met in October 2019; the second quantitative 
milestones, in October 2022; and so on, until the area attains the 
NAAQS. Under this approach, the state will be required to submit such 
RFP projected emissions as part of the Moderate area attainment plan 
due in October 2016 that project emissions from sources in the 
nonattainment area for the same calendar years as those for which 
quantitative milestones will be due (i.e., 2019 and 2022 inventories in 
this example).
---------------------------------------------------------------------------

    \117\ According to CAA section 189(a)(2)(B), Moderate area 
attainment plans are due to the EPA 18 months after designation.
---------------------------------------------------------------------------

    The transportation conformity rule requires that RFP plans 
establish motor vehicle emissions budgets. RFP plans would therefore be 
required to establish motor vehicle emissions budgets for direct 
PM2.5 and any relevant PM2.5 precursor as 
determined under the transportation conformity rule.\118\ Precursors 
that are relevant for transportation conformity purposes would be 
limited to the PM2.5 plan precursors but may not include all 
of the PM2.5 plan precursors. For example, it is likely that 
many PM2.5 plans will include SO2 as a plan 
precursor. However, emissions of SO2 from on-road sources 
are usually low compared to stationary sources. The transportation 
conformity rule allows for the state to determine through its SIP 
development process if it is necessary to establish motor vehicle 
emissions budgets for SO2. See 40 CFR 93.102(b)(2)(v). On 
the other hand, if a state provides a precursor demonstration approved 
by the EPA which shows that VOCs do not have a significant contribution 
to PM2.5 levels in a particular nonattainment area, then a 
motor vehicle emissions budget for VOCs would not need to be 
established for the area for transportation conformity purposes. A 
motor vehicle emissions budget for the purposes of a PM2.5 
RFP plan is that portion of the total allowable emissions allocated to 
on-road sources as defined in the submitted RFP plan for the relevant 
years as described earlier.\119\ Such motor vehicle emissions budgets 
will be calculated using the latest planning assumptions and the latest 
approved motor vehicle emissions model available at the time that the 
attainment plan is developed, unless the EPA approves the state's use 
of an alternative model.\120\
---------------------------------------------------------------------------

    \118\ For more information on PM2.5 precursor 
requirements, see CAA section 93.102(b)(1) and (b)(2)(iv) and (v) of 
the transportation conformity rule. See also the May 6, 2005, final 
transportation conformity rule that addressed requirements for 
PM2.5 precursors. (70 FR 24280).
    \119\ A state would also establish motor vehicle emissions 
budgets for an area's attainment year. Those budgets would be the 
motor vehicle emissions that the SIP establishes as being necessary 
to attain the NAAQS.
    \120\ If an area includes re-entrained road dust in the motor 
vehicle emissions budget, the latest approved version of AP-42 
should be used unless the EPA has approved an alternative model for 
the area.
---------------------------------------------------------------------------

    c. Comments and Responses. Comment: Some commenters stated that 
since RFP is one of the general attainment plan provisions listed in 
CAA section 172(c), the EPA's proposal to require motor vehicle 
emissions budgets as part of RFP plans extends beyond just the 
implementation of the PM2.5 NAAQS and, as a result, this 
proposal should be presented within the context of a revision to the 
conformity rule itself and not just this PM2.5 
implementation rule.
    Response: The EPA disagrees with the commenters. The transportation 
conformity rule already states that motor vehicle emissions budgets 
come from control strategy SIPs.\121\ Additionally, the transportation 
conformity rule defines control strategy SIPs as RFP plans and 
attainment demonstrations. It goes further to say that control strategy 
SIPs include the SIPs required by CAA sections 172(c), 189(a)(1)(B) and 
189(b)(1)(A). The requirement in this PM2.5 SIP Requirements 
Rule does not amend the transportation conformity rule; it merely 
explains what is already required.
---------------------------------------------------------------------------

    \121\ 40 CFR 93.101.
---------------------------------------------------------------------------

4. Geographic Coverage of Emission Sources for RFP
    a. Summary of Proposal. The EPA proposed that the RFP demonstration 
to be included with a state's PM2.5 nonattainment area plan 
must include emissions only for sources located in the nonattainment 
area, and not from an area larger than the nonattainment area. This 
proposed policy approach differed from the remanded 2007 
PM2.5 implementation rule. As explained in the proposal, the 
difference was due to the evolution of policy on a similar RFP issue in 
the ozone NAAQS implementation program that stemmed in part from a 
petition for reconsideration and a DC Circuit

[[Page 58059]]

decision on the November 2005 Phase 2 Ozone Implementation Rule. The 
EPA received a similar petition for reconsideration of the 2007 
PM2.5 Implementation Rule, which dealt with the EPA's 
interpretation of the statutory RFP requirements to allow a state to 
take ``credit'' for emissions reductions from outside the nonattainment 
area when addressing RFP in its attainment plan.\122\ The EPA granted 
the petition for reconsideration on this issue in 2010, after the DC 
Circuit issued its decision on litigation on the Phase 2 Ozone 
Implementation Rule.123 124 In light of these developments, 
the proposal indicated that the EPA now believes the best reading of 
the statute is that the CAA does not allow for a state to include 
emissions reductions from sources outside a nonattainment area when 
developing the plan to meet the CAA section 172(c)(2) RFP requirements 
for a PM2.5 nonattainment area.
---------------------------------------------------------------------------

    \122\ This same petition raised concerns regarding the criteria 
used to determine the economic feasibility of controls being 
considered for RACT for the 1997 PM2.5 NAAQS. See 
``Petition for Reconsideration,'' filed by Paul Cort, Earthjustice, 
on behalf of the American Lung Association, Medical Advocates for 
Healthy Air, Natural Resources Defense Council, and the Sierra Club 
(June 25, 2007). A copy of the petition is in the docket for this 
action.
    \123\ Letter dated May 13, 2010, from Gina McCarthy to David S. 
Baron and Paul Cort, Earthjustice. A copy of the letter is located 
in the docket for this action.
    \124\ See NRDC v. EPA, 571 F.3d 1245 (D.C. Cir. 2009).
---------------------------------------------------------------------------

    b. Final Rule. The EPA is finalizing that the RFP demonstration to 
be included with a state's PM2.5 nonattainment area plan 
must include emissions only for sources located in the nonattainment 
area, and not from an area larger than the nonattainment area. 
Commenters disagreed with limiting the RFP demonstration to include 
emissions only for sources located in the nonattainment area stating 
that some areas are so dominated by upwind emissions and local sources 
over which they have no control, such as motor vehicles, that they 
cannot demonstrate RFP. One of these commenters noted they have 
provided extensive comments on this issue in connection with the EPA's 
proposal for the recent ozone implementation rule and incorporated by 
reference their prior comments. Other commenters agreed with the 
proposal and stated the EPA's conclusion is compelled by CAA sections 
172(c)(1), 172(c)(3) and 189(d), which all focus on emissions and 
reductions in the area.
    In the preamble to the remanded 2007 PM2.5 
Implementation Rule, the EPA allowed states to incorporate reductions 
of NOX and SO2 emissions up to 200 km from 
outside the nonattainment area (and potentially for reductions of VOC 
or ammonia) into their RFP plan when certain conditions were met. This 
policy was included in the 2007 PM2.5 Implementation Rule in 
part to be consistent with a similar RFP policy for NOX and 
VOC that was included in the November 2005 Phase 2 ozone NAAQS 
implementation rule, which provided guidance for states on implementing 
the 1997 ozone NAAQS.\125\ Under this policy, if a state intended to 
include emissions reductions from outside the nonattainment area in the 
RFP plan, the state would need to take on the additional accounting 
work associated with developing: (i) An expanded baseline emissions 
inventory for the entire geographic area and, (ii) a projected 
attainment year inventory for this expanded area outside the boundaries 
of the designated nonattainment area. Development of these more 
extensive inventories would likely have involved a substantial amount 
of additional time and resources. In addition, the state would have 
needed to provide information supporting its decision regarding how far 
outside the nonattainment area the RFP inventory should extend. While 
this ``outside the nonattainment area'' RFP approach was theoretically 
available to states in developing their PM2.5 attainment 
plans due in 2008, there were no states to the agency's knowledge that 
elected to follow this approach.
---------------------------------------------------------------------------

    \125\ See Phase 2 Ozone Implementation rule, 70 FR 71612 
(November 29, 2005).
---------------------------------------------------------------------------

    Both the Phase 2 ozone implementation rule and the 2007 
PM2.5 Implementation Rule were challenged on several issues. 
With regard to the Phase 2 ozone implementation rule, the EPA granted a 
petition for reconsideration and ultimately issued a final notice of 
reconsideration in June 2007. In November 2008, the U.S. Court of 
Appeals for the DC Circuit heard oral argument concerning multiple 
petitions for judicial review of the Phase 2 ozone rule and the notice 
of reconsideration. One of the issues in that case involved whether 
compliance by EGUs with a regional emissions trading program could be 
considered to meet the RACT requirement for those sources located in a 
nonattainment area. In its July 2009 decision, the court emphasized 
that: ``The RACT requirement calls for reductions in emissions from 
sources in the area; reductions from sources outside the nonattainment 
area do not satisfy the requirement. Accordingly, participation in the 
NOX SIP call would constitute RACT only if participation 
entailed at least RACT-level reductions in emissions from sources 
within the nonattainment area.''
    In light of this court decision, the EPA has determined that the 
best reading of the statute is that the term ``sources in the area'' 
should be interpreted in the same manner as ozone. The term appears in 
CAA section 182 (requirements for ozone nonattainment areas) with 
regard to RFP as well as RACT. The decision on the Phase 2 ozone rule 
found that CAA section 182(b)(2) requires that a SIP must provide for 
implementation of RACT (under CAA section 172(c)) for emissions sources 
``in the area,'' meaning in the nonattainment area. Similarly, the EPA 
position is that when CAA section 182(b)(1)(A)-(B) defines baseline 
emissions for RFP as ``the total amount of actual VOC or NOX 
emissions from all anthropogenic sources in the area,'' this also means 
sources in the nonattainment area.
    Turning to PM2.5, the EPA has determined that the DC 
Circuit's interpretation of the phrase ``sources in the area'' should 
apply to RACT and RFP requirements for both the ozone NAAQS and the 
PM2.5 NAAQS. In particular, for PM2.5, the 
statutory language at CAA section 171(1) defines RFP in terms of 
``reductions in emissions'' required in an attainment plan, which the 
EPA interprets as being directly linked to the baseline emissions 
inventory for sources located in a PM2.5 nonattainment area. 
The baseline emissions inventory is the foundation for the attainment 
plan. The emissions inventory requirement of CAA section 172(c)(3) 
explicitly requires that the attainment plan inventory include all 
sources of the relevant pollutants ``in such area,'' which is a clear 
reference to the designated nonattainment area. Given that the baseline 
inventory must reflect the emissions ``in such area,'' and that this 
inventory provides the starting point for a state's RFP analysis, in 
which the state must calculate generally linear progress in emissions 
reductions that will lead to attainment of the NAAQS in the area, the 
EPA believes it is appropriate that a state should consider only 
sources located within the nonattainment area when conducting its 
analysis to determine the annual emissions reductions necessary for 
demonstrating RFP.
    Beyond the Court's interpretation, the EPA believes that the most 
appropriate approach with regard to the geographic area required to be 
covered for demonstrating RFP in a PM2.5 attainment plan 
also should be limited to the nonattainment area for two other

[[Page 58060]]

reasons. First, the EPA believes that it makes policy sense for the 
PM2.5 implementation rule approach to be consistent with the 
approach finalized in the 2008 NAAQS for Ozone: SIP Requirements 
rule.\126\ Second, a policy allowing the geographic area of the RFP 
plan to be larger than the nonattainment area would conflict with a key 
provision of subpart 4 that requires annual incremental reductions in 
emissions from sources within the nonattainment area. Under subpart 4, 
an area that fails to attain the standard by the Serious area 
attainment date is then subject to the provisions of CAA section 
189(d). Section 189(d) of the CAA specifies that the state must submit 
a plan revision within 12 months which provides for ``an annual 
reduction in PM10 or PM10 precursor emissions 
within the area of not less than 5 percent of the amount of such 
emissions as reported in the most recent inventory prepared for such 
area'' (emphasis added). Therefore, the EPA is finalizing an RFP policy 
approach that is consistent with CAA section 189(d).
---------------------------------------------------------------------------

    \126\ See 80 FR 12264.
---------------------------------------------------------------------------

    c. Comments and Responses. Comment: Some commenters supported the 
EPA's general guidance for developing the RFP demonstration. In 
particular, these commenters agreed with the EPA's interpretation of 
the CAA to require that emissions reductions for purposes of meeting 
the RFP requirement must come from sources within the designated 
nonattainment area. Thus, the commenters supported the EPA's proposal 
that the RFP demonstration submitted by states as a part of the 
attainment plan cannot take credit for emissions reductions occurring 
outside the nonattainment area to meet the RFP requirement. These 
commenters asserted that the EPA's conclusion is compelled by sections 
172(c)(1), 172(c)(3) and 189(d), which all focus on emissions and 
reductions in the designated nonattainment area. The commenters further 
stated the EPA has not identified any rational way for states to pick 
and choose what sources and related emissions outside the designated 
nonattainment area would need to be included in inventories and 
attainment planning in order to rationally measure RFP.
    Other commenters disagreed with the EPA's interpretation of the CAA 
on this issue and advocated that the EPA should provide an option for 
states to meet the RFP requirement with emissions reductions from 
sources outside the designated nonattainment area in addition to 
reductions from sources inside the area. One commenter suggested the 
EPA should provide this option to states and also consider alternatives 
to simplify the ``overly complicated analysis'' needed to support this 
option in the now superseded 2007 PM2.5 implementation rule. 
The comment did not address the consistency of such an interpretation 
of the RFP requirements with the statute.
    Another commenter asserted that the EPA should interpret the 
statute to permit states to meet the RFP requirement through emissions 
reductions from sources outside the designated area based upon several 
practical arguments. The commenter stated that, as the PM2.5 
standards become lower and reductions from sources within a designated 
nonattainment area become more challenging to find, it may be necessary 
to obtain emissions reductions from sources beyond the designated area 
in order to attain the NAAQS. According to the commenters, some 
nonattainment areas are so dominated by emissions from outside the area 
and from local sources over which they have no control that they cannot 
demonstrate RFP, even though they could demonstrate timely attainment 
due to reductions from sources outside the nonattainment area. The 
commenters thus argued that the EPA should provide states with the 
option to meet the RFP requirement with emissions reductions from 
sources outside the nonattainment area in cases where they believe it 
would be unreasonable or impossible to do so only with emissions 
reductions from within the nonattainment area.
    In response to the EPA's request for comment on any potential legal 
basis for authorizing states to meet the RFP requirement with emissions 
reductions from outside the nonattainment area, the commenter suggested 
potential theories. The primary legal theory was that EPA should by 
regulation redefine the term ``area'' for purposes of the RFP 
requirement so that it would encompass geographic areas that are not 
part of the designated nonattainment area. Through this theory, the 
commenters suggested that the EPA could authorize states to meet the 
RFP requirement based on reductions from the ``total area'' affecting 
that nonattainment area, rather than from the actual designated 
nonattainment area. As an alternative theory, the commenter argued that 
the EPA could regulatorily redefine the emissions inventory requirement 
of section 172(c)(3). To support this theory, the commenter disagreed 
with the EPA's position that because the base year inventory required 
by section 172(c)(3) includes the emissions from sources within the 
designated nonattainment area, it supports the EPA's reading of the 
statute with respect to the RFP requirement. The commenter instead 
argued that because the emissions information used for modeling purpose 
includes emissions from a much broader region (not just within the 
nonattainment area or even just within the state), the EPA was wrong to 
say in the proposal that the base year inventory for sources in the 
area is the ``foundation for the attainment plan.'' Finally, the 
commenter argued more broadly for the EPA to alter its interpretation 
of the statutory language to allow for the commenter's preferred 
approach to RFP. In support of their preferred approach to the RFP 
requirement, the commenters noted that the EPA acknowledged in the 
proposal that ``a literal interpretation is illogical'' for other 
statutory requirements. To support this contention, the commenters 
point to the criteria in section 188(d) that provide the criteria for 
an extension of the Moderate area attainment date that require 
significant interpretation in order to make them appropriate for the 
statistical form of the current PM2.5 NAAQS rather than for 
the exceedance-based form of the PM10 NAAQS that existed 
when the CAA was amended in 1990.
    Response: The final rule requires that states demonstrate that they 
meet the RFP requirement through emissions reductions from sources in 
the nonattainment area. The EPA has decided to adopt this approach for 
two reasons. First, it is the most consistent with the statute. It 
aligns with RFP as defined in CAA section 171(1) and as required in CAA 
section 172(c)(2) and 189(c), and is also most consistent with other 
related requirements for attainment plans, such as the requirements for 
imposition of emission controls, e.g., RACM and RACT, and with the 
process for designations of nonattainment areas pursuant to section 
107(d). Second, this approach is more straightforward to administer 
because it retains a nonattainment area focus to the RFP requirement 
and, while the alternative approaches would require complex and 
potentially burdensome requirements to define the scope of the out-of-
area sources that must be inventoried and accounted for in the 
determination of what constitutes RFP. The EPA has concluded that such 
emissions reductions from sources outside the nonattainment area are 
more properly accounted for and reflected in other elements of the 
attainment plan, such as the attainment demonstration

[[Page 58061]]

modeling which will take into account the emissions reductions that 
occur outside the nonattainment area in a less burdensome fashion.
    The EPA does not agree with the statutory interpretation of the RFP 
requirement preferred by the commenters who suggested that the EPA 
allow credit for emissions reductions from outside the area. Pursuant 
to section 171(1), the statute defines the term ``reasonable further 
progress'' to mean ``such annual incremental reductions in emissions . 
. . as are required by this part or may reasonably be required by the 
Administrator for the purposes of ensuring attainment of the applicable 
[NAAQS] by the applicable date.'' This provision plainly provides EPA 
with discretion to interpret this term within certain statutory 
parameters, i.e., ``as are required by this part,'' and consistent with 
the EPA's determination of what will be the appropriate approach for 
timely attainment, i.e., ``for the purpose of ensuring attainment . . . 
by the applicable date.'' Thus, for example, the EPA has authority to 
interpret the RFP requirement to allow states to demonstrate generally 
linear reductions or stepwise reductions, rather than as a specific 
percentage of emissions reductions each year, as appropriate methods 
for meeting the RFP requirement for purposes of the subpart 1 and 
subpart 4 provisions applicable to the PM2.5 NAAQS. It does 
not follow, however, that EPA is obligated to interpret the term 
``reasonable further progress'' in other ways that the EPA considers 
inconsistent with other relevant statutory requirements for attainment 
plans or more broadly.
    To the contrary, the EPA believes that interpretation of the RFP 
requirement to reflect reductions in emissions ``as are required by 
this part,'' properly includes consideration of the context and 
structure of the statute with respect to the other attainment plan 
requirements. As explained in the proposal for this action, the EPA has 
concluded that several other related requirements for attainment plans 
support an interpretation of the RFP requirement for purposes of 
PM2.5 to be limited to emissions reductions from sources 
located within the nonattainment area. These requirements include the 
emissions inventory requirement of section 172(c)(3), the RACM/RACT 
requirement of section 172(c)(1) and section 189(a)(1)(C), and the not 
less than 5 percent emission reduction requirement of section 189(d).
    With respect to the inventory requirement of section 172(c)(3), the 
EPA explained in the proposal its view that because the emissions 
inventory requirement explicitly refers to a comprehensive, accurate, 
and current emissions inventory of emissions ``from all sources of the 
relevant pollutant or pollutants in such area,'' this statutory 
language supports the view that the primary focus of the attainment 
plan is reductions of emissions from the nonattainment area, not 
emissions reductions from sources elsewhere. Similarly, EPA explained 
in the proposal its views that the court's decision in NRDC v. EPA, 571 
F.3d 1245 (D.C. Cir. 2009) supports an interpretation of the RFP 
requirement to apply to emissions reductions from sources within the 
area. Although that decision focused on the RACT requirement for ozone 
in particular, the reasoning of the court's decision based upon the 
phrase ``in the area'' is consistent with the EPA's longstanding 
approach to both RACM and RACT (or BACM and BACT for serious areas) 
being required for emissions sources within the nonattainment area. 
Given that states typically elect to demonstrate that they meet the RFP 
requirement through emissions reductions that result from expeditious 
imposition of RACM/RACT or BACM/BACT emission controls applied to 
sources within the area, it is logical that the separate RFP 
requirement should likewise be based upon the expeditious progress 
towards attainment achieved through those emission controls. The EPA 
emphasizes that the RFP requirement and the requirements of section 
172(c)(6) are separate components of an attainment plan. In those 
unusual circumstances where a state needs to impose specific additional 
controls on sources outside the nonattainment area in accordance with 
section 172(c)(6) to reach attainment, the state is not required to 
alter the base year emissions inventory for sources within the area or 
to alter its RFP analysis. As with other emissions reductions from 
sources outside the area that the state may rely upon, emissions 
reductions from measures states may impose to meet section 172(c)(6) 
will be reflected in the modeled attainment demonstration and thus 
included and taken into account in that fashion. [See sections IV.D.1 
and VI.D.2 of the preamble for additional discussion of section 
172(c)(6).]
    The EPA also considers this interpretation of the RFP requirement 
to be consistent with the comparable requirements of CAA section 
189(d). Specifically, section 189(d) requires that states with 
nonattainment areas that fail to attain by the applicable attainment 
date must make a new attainment plan submission in order to achieve 
emissions reductions of not less than 5 percent of the most recent 
emissions inventory ``for such area.'' As discussed in Section VII.F of 
this rule, the EPA interprets the statute to require an area subject to 
section 189(d) to achieve not less than a 5 percent reduction of the 
most recent emissions inventory of direct PM2.5 or any 
PM2.5 plan precursor ``for such area'' (meaning from sources 
located within the nonattainment area). As a result, the EPA's 
interpretation of ``in such area'' and ``for such area'' are 
consistently applied for these related provisions of the CAA.
    As explained in the proposal, the EPA also sees no appropriate 
legal or policy basis for addressing the geographic area from which 
emissions reductions for RFP must be achieved for PM2.5 
differently than is required by CAA section 182 for ozone. Both 
pollutants typically result from emissions from numerous sources that 
mix in the atmosphere and can transport great distances. For both 
pollutants, the CAA provides different tools for states and the EPA to 
address both the regional and the local contributions to violations of 
the NAAQS in a given area. With respect to the local contribution, the 
CAA provides a specific set of requirements (including RFP) designed to 
assure that states are properly addressing the emissions from sources 
located within the nonattainment area, whereas other requirements of 
the CAA are designed to address contributions from greater distances, 
whether from within the state, from other states, or even 
internationally. Were EPA to interpret the RFP requirements to 
authorize states to meet the emissions reductions requirement from 
sources outside the area, this would be inconsistent with the 
requirements specifically designed to assure that states get necessary 
reductions from the local sources that contribute to the violations 
through the attainment plan.
    One commenter recommended a potential statutory interpretation in 
support of an outside-the-area approach. The EPA appreciates the 
suggestion, but has determined that it would be too inconsistent with 
the structure and purpose of the attainment plan requirements of the 
statute. The commenter specifically suggested that EPA should redefine 
the term ``area'' to encompass not just the designated nonattainment 
area, but also some larger geographic area with sources of emissions 
that cause or contribute to the ambient air quality; and that 
reductions from such sources should be allowed to count towards meeting 
the RFP requirement in addition to reductions

[[Page 58062]]

from sources in the designated nonattainment area. The EPA considers 
such an approach inappropriate for several reasons. First, such a 
reading would be inconsistent with the EPA's longstanding reading of 
this same term in many important places throughout the statute, 
including but not limited to explicit statutory references to the 
``area'' in section 107(d)(1) (relevant to designations), section 
107(d)(3) (relevant to redesignations), section 110(a)(2)(I) (relevant 
to the scope of all of the attainment plan requirements imposed by Part 
D), section 189(B)(2) (relevant to the schedule for submission of 
attainment plans under subpart 4), and section 189(e) (relevant to the 
statutory test for regulating precursors in a given ``area''). Creating 
a different and conflicting definition of the word ``area'' for RFP 
purposes is not appropriate for common sense reasons, and it would 
require that the same word to be interpreted in multiple ways. Second, 
the EPA considers the redefinition of the term ``area'' inappropriate 
because it could be perceived as an attempt to alter the meaning of the 
term as the D.C. Circuit has already interpreted it in the NRDC v. EPA 
decision concerning the plain meaning of the term ``in the area.'' 
Third, to the extent that there are situations in which the boundaries 
of the nonattainment area are incorrect because they fail to include 
the sources that contribute violations in an adjacent area to the 
extreme degree posited by the commenters, the statute already provides 
a straightforward solution to such a situation through the initial 
designation and redesignation provisions of section 107(d).
    Finally, the EPA acknowledges that in the prior 2007 
PM2.5 implementation rule, the EPA did adopt a different 
interpretation of the RFP requirement for the first time that would 
have authorized states to meet the RFP requirement with emissions 
reductions from sources outside the nonattainment area within certain 
narrow parameters for purposes of the 1997 PM2.5 NAAQS.\127\ 
The EPA received a petition for reconsideration on this specific issue 
and granted the petition to reexamine that aspect of the 2007 
PM2.5 implementation rule.\128\ Before the EPA proceeded 
with that reconsideration, however, the litigation over the 2007 
PM2.5 implementation rule and the 2008 NSR revisions 
(addressing the PM2.5 NAAQS) proceeded with challenges on 
other statutory authority issues while the petition for reconsideration 
was still under evaluation. This litigation resulted in the court's 
decision in NRDC v. EPA, 706 F.3d 428 (D.C. Cir. 2013). In that 
decision, the court remanded the entire 2007 PM2.5 
implementation rule, including the portions relevant to the RFP 
requirement, to the EPA for failure to comply with the statutory 
requirements of subpart 4. This rulemaking constitutes the EPA's 
response to that judicial remand and through this process the EPA is 
replacing the 2007 PM2.5 implementation rule, including the 
prior regulatory provisions and guidance related to states meeting the 
RFP requirements with emissions reductions from outside the designated 
nonattainment area. Accordingly, upon completion of this rulemaking the 
EPA will be interpreting the RFP requirement consistent with past 
practice. The EPA also notes, as a factual matter, that states have not 
been using this feature of the 2007 PM2.5 implementation 
rule.\129\ Aside from the lack of a legal basis for the commenter's 
preferred approach to RFP, thus far the EPA's interpretation of the 
requirements has not posed the practical difficulties that the 
commenter raised.
---------------------------------------------------------------------------

    \127\ See the discussion of this prior approach to RFP in the 
proposal for this action. 80 FR 15388-89. By its terms, the 2007 
PM2.5 Implementation Rule applied only to the 1997 
PM2.5 NAAQS. The EPA's guidance for the 2006 
PM2.5 NAAQS did not follow this approach with respect to 
the RFP requirement for purposes of the 2006 PM2.5 NAAQS. 
The EPA later withdrew the guidance for the 2006 PM2.5 
NAAQS as a result of the court decision in NRDC v. EPA, 706 F.3d 428 
(D.C. Cir. 2013).
    \128\ See, Letter to David S. Baron, EarthJustice, from Gina 
McCarthy, Assistant Administrator, dated May 13, 2010. A copy of 
this letter is in the docket for this action.
    \129\ See, e.g., ``Approval and Promulgation of Implementation 
Plans; California; 2007 South Coast PM2.5 Plan and 2007 
State Strategy; Proposed Rule,'' 76 FR 41567, 41577-78 (July 14, 
2011); Final Approval of Air Quality Implementation Plans; 
California; South Coast Attainment Plan for the 1997 
PM2.5 NAAQS Standards; Final Rule,'' 76 FR 69928 
(November 9, 2011).
---------------------------------------------------------------------------

5. Other RFP Considerations
    a. Summary of Proposal. The proposal outlined the statutory 
requirements and existing guidance for RFP. During this discussion, the 
following guidance from the Addendum was referenced, ``Additionally, 
the EPA believes that it is appropriate to require early implementation 
of the most cost-effective control measures . . . while phasing in the 
more expensive control measures.'' \130\ The proposal also discussed 
other RFP considerations, including PM2.5 nonattainment 
areas that are shared by more than one state or tribe.
---------------------------------------------------------------------------

    \130\ Ibid. at 42016.
---------------------------------------------------------------------------

    b. Final Rule. The EPA is finalizing that, although early 
implementation of the most cost-effective control measures is often 
appropriate, states should consider both cost-effectiveness and 
pollution reduction effectiveness when developing implementation 
schedules for their control measures and may implement measures that 
are more effective at reducing PM2.5 earlier to provide 
greater public health benefits. This increased flexibility enables 
states to develop a more effective implementation schedules for their 
control measures while efficiently using their resources.
    For a multi-state or multi-jurisdictional nonattainment area, the 
RFP plans for each state represented in the nonattainment area shall 
demonstrate RFP on the basis of common multi-state inventories. The 
states or jurisdictions within which the area is located must provide a 
coordinated RFP plan. Each state must ensure that the sources within 
its boundaries comply with enforceable emission levels and other 
requirements that in combination with the reductions planned in other 
states within the nonattainment area will provide for attainment as 
expeditiously as practicable and demonstrate RFP consistent with these 
regulations. In general, the EPA seeks to ensure that PM2.5 
nonattainment areas that are shared by more than one state or tribe 
meet RFP requirements as a whole. States and tribes that share a 
nonattainment area should therefore consult with one another to develop 
the RFP analysis and control strategy implementation schedule for the 
area as a whole. Such states and tribes should work with the EPA region 
or regions that oversee them to confirm that their collective approach 
is appropriate for RFP.
    The EPA's approach for states to meet the RFP requirement is 
designed to ensure emissions reductions will yield incremental 
improvements in air quality on the path to attainment, while being 
sufficiently flexible to accommodate the range of control strategies 
necessary to address the complex mixtures of pollutants comprising 
PM2.5 in different areas.
    c. Comments and Responses. Comment: Some commenters asserted that 
the EPA should not ``require'' implementing the most cost-effective 
measures first since states should have the flexibility to implement 
the more effective but less cost-effective measure earlier, thus 
providing earlier and greater public health benefits.
    Response: In this final rule, the EPA is providing states with the 
flexibility to

[[Page 58063]]

implement measures that are more effective at reducing PM2.5 
earlier to provide greater public health benefits, but is not requiring 
it. This increased flexibility is in keeping with the overall 
requirement of expeditious attainment of the NAAQS.

G. Quantitative Milestones

1. General Approach to Quantitative Milestones
    a. Summary of the Proposal. The proposal built from the statutory 
language of 189(c)(1), which requires quantitative milestones that (1) 
demonstrate RFP, and (2) must be achieved every 3 years until the area 
is redesignated attainment. The proposal first addressed the issue of 
the starting date for counting the 3-year periods. For a Moderate area 
that cannot practicably attain the relevant PM2.5 NAAQS 
within the statutory timeframe for a Moderate area, the EPA proposed 
that a state must submit two sets of quantitative milestones--the first 
set to be achieved at year 4.5 from designation and the second set to 
be achieved at year 7.5 from designation. The EPA also proposed that 
the quantitative milestones contained in the attainment plan for a 
Moderate nonattainment area must be constructed such that they can be 
tracked, quantified and/or measured adequately in order for the state 
to meet its milestone reporting obligations, which come due 90 days 
after a given milestone date. The EPA therefore proposed to require 
that states select the quantitative milestones that are appropriate and 
quantifiable and that will provide for objective evaluation of progress 
toward attainment in their Moderate PM2.5 nonattainment 
area, whether the area can practicably attain the PM2.5 
NAAQS by the statutory attainment date or not. In addition to this 
general proposed approach for selecting quantitative milestones for a 
Moderate nonattainment area, the EPA proposed a requirement that, at a 
minimum, states must include in all attainment plans for Moderate 
PM2.5 nonattainment areas a metric to confirm that all 
control measures identified and adopted as RACM and RACT for the area 
have been fully implemented within 4 years of designation.
    b. Final Rule. Section 189(c) of the Act explicitly requires that 
quantitative milestones must be achieved every 3 years, but does not 
specify the starting date for counting the 3 year periods. In the 
General Preamble and Addendum, the agency stated that quantitative 
milestones must be achieved every 3 years starting from the due date 
for the plan submission (i.e., because the Moderate area attainment 
plan is due no later than 18 months after designation of the area, the 
first set of milestones would need to be achieved 4.5 years after the 
area's designation) until the area is redesignated attainment.\131\ The 
EPA is finalizing this approach for the PM2.5 NAAQS. The EPA 
interprets this requirement to be the most appropriate reading of CAA 
section 189(c)(1) which requires ``quantitative milestones which are to 
be achieved every 3 years until the area is redesignated attainment.'' 
This approach is also consistent with the longstanding approach 
outlined in the General Preamble.\132\ These timeframes for the 
quantitative milestones apply to all areas designated nonattainment for 
a PM2.5 NAAQS on or after January 15, 2015, including all 
areas designated nonattainment effective April 15, 2015 for the 2012 
PM2.5 NAAQS.\133\ See 40 CFR 51.1013(a).
---------------------------------------------------------------------------

    \131\ General Preamble, 57 FR 13498 (April 16, 1992), at page 
13539.
    \132\ 57 FR 13539.
    \133\ 80 FR 2206, January 15, 2015.
---------------------------------------------------------------------------

    For all areas designated nonattainment for the 1997 and/or 2006 
PM2.5 NAAQS before January 15, 2015,\134\ the EPA is 
establishing December 31, 2014 as the starting point for the first 3 
year period for quantitative milestones under CAA section 189(c). This 
is because December 31, 2014, was the due date for states to submit 
additional SIP elements necessary to satisfy the subpart 4 Moderate 
area requirements for the 1997 and 2006 PM2.5 
standards.\135\ Establishing December 31, 2014 as the starting point 
for the first 3 year period under CAA section 189(c) for the 1997 and 
2006 PM2.5 standards is in keeping with the EPA's historical 
approach to quantitative milestone dates (i.e., using the due date for 
the Moderate area plan submission as the starting point for the first 3 
year milestone period). Thus, for any area designated nonattainment for 
the 1997 and/or 2006 PM2.5 NAAQS that has not yet attained 
these NAAQS and therefore continues to have attainment planning 
obligations for these NAAQS, the state must submit quantitative 
milestones to be achieved by December 31, 2017 (the first milestone 
date), at minimum. Additional milestone dates may also apply to such an 
area depending on the relevant attainment planning period. See 40 CFR 
51.1013(a)(4).
---------------------------------------------------------------------------

    \134\ The EPA promulgated nonattainment area designations for 
the 1997 PM2.5 NAAQS effective April 2005 (70 FR 944, 
January 5, 2005 and 70 FR 19844, April 14, 2005). The EPA 
promulgated nonattainment area designations for the 2006 
PM2.5 NAAQS effective December 2009 (74 FR 58688, 
November 13, 2009), March 2011 (76 FR 6056, February 3, 2011), and 
November 2012 (77 FR 65310, October 26, 2012).
    \135\ 79 FR 31566 (June 2, 2014) (final rule establishing 
subpart 4 moderate area classifications and deadline for related SIP 
submissions) (``Classification and Deadline Rule''). Although the 
Classification and Deadline Rule did not affect any action that the 
EPA had previously taken under CAA section 110(k) on a SIP for a 
PM2.5 nonattainment area, the EPA noted that states may 
need to submit additional SIP elements to fully satisfy the 
applicable requirements of subpart 4, even for areas with previously 
approved PM2.5 attainment plans, and that the deadline 
for any such additional plan submissions was December 31, 2014. Id. 
at 31569.
---------------------------------------------------------------------------

    Regardless of whether or not an attainment plan demonstrates 
attainment by the statutory attainment date, the EPA requires that all 
Moderate area PM2.5 attainment plans must define appropriate 
quantitative milestones to be achieved by 4.5 years and 7.5 years 
following designation of the area. Although it occurs after the 
Moderate area attainment date, the EPA is requiring Moderate area plans 
to contain this 7.5 year milestone, even where those plans demonstrate 
attainment before the milestone would arrive. Where the EPA uses its 
discretionary authority in CAA section 188(b)(1) to reclassify an area 
before the Moderate area attainment date applicable to the area, CAA 
section 189(b)(2) allows the state up to 4 years to submit the required 
Serious area attainment demonstration and related plan elements, such 
as quantitative milestones. For example, if the reclassification occurs 
4 years after designation, the state may be allowed to submit the 
Serious area quantitative milestones up to 8 years after designation, 
well after the second milestone date (7.5 years after designation) has 
passed. Without the 7.5 year milestone requirement, this circumstance 
would undermine the purpose of the quantitative milestone requirement, 
which is to ensure that states will report to EPA on each nonattainment 
area's progress toward attainment at regular intervals, even following 
reclassification.\136\
---------------------------------------------------------------------------

    \136\ See, e.g., Addendum at 42016, n. 43 (noting that the plain 
terms of CAA section 189(c) require that milestones be achieved 
every 3 years until the area is redesignated attainment and, 
therefore, do not contemplate any breaks in the milestones due to an 
area's reclassification).
---------------------------------------------------------------------------

    A similar issue would result in the event that a Moderate area that 
did demonstrate attainment in the original attainment plan fails to 
attain by the statutory attainment date. In this case, the area would 
have failed to meet the attainment date which is as expeditiously as 
practicable but no later than the end of the sixth calendar year after 
designation as required by CAA section 188(c)(1). Section 188(b)(2) of 
the Act allows the Administrator up to

[[Page 58064]]

6 months to determine that a Moderate failed to attain and reclassify 
that area to Serious, which would be at least 6.5 years after 
designation. As described in Section VI.A.1 of this preamble, the 
Serious area would have 18 months from reclassification due to a 
failure to attain (8 years after designation) in order to submit an 
attainment plan. The EPA has therefore determined that, in order to 
avoid gaps of greater than 3 years in the implementation of 
quantitative milestones, all Moderate area attainment plans must 
contain quantitative milestones to be achieved 4.5 years and 7.5 years 
after designation and which demonstrate continued progress toward 
timely attainment of the relevant PM2.5 NAAQS. In the event 
that the area fails to attain, this will provide the EPA with 
appropriate tools necessary to continue to monitor the area's continued 
progress toward attainment while the state develops the Serious area 
attainment plan.
    The quantitative milestones contained in the attainment plan for a 
Moderate nonattainment area should be constructed such that they can be 
tracked, quantified and/or measured adequately in order for the state 
to meet its milestone reporting obligations, which come due 90 days 
after a given milestone date. In the Addendum, the EPA suggested some 
possible metrics that ``support and demonstrate how the overall 
quantitative milestones identified for an area may be met,'' such as 
percent implementation of control strategies, percent compliance with 
implemented control measures, and adherence to a compliance schedule. 
This list was not exclusive or exhaustive but reflected the EPA's view 
that the purpose of the quantitative milestone requirement is to 
provide an objective way to determine whether the area is making the 
necessary progress towards attainment by the applicable attainment 
date.\137\ The EPA interprets Section 189(c) of the Act to allow states 
to identify milestones that are suitable for the specific facts and 
circumstances of the attainment plan for a particular area, so long as 
they provide an objective means to measure RFP.
---------------------------------------------------------------------------

    \137\ Addendum to the General Preamble, 59 FR 41998 (August 16, 
1994), at page 42016.
---------------------------------------------------------------------------

    This rule requires that each attainment plan for a Moderate 
PM2.5 nonattainment area contain quantitative milestones 
that provide for objective evaluation of RFP toward attainment in the 
PM2.5 nonattainment area, whether the plan provides for 
attainment of the PM2.5 NAAQS by the statutory attainment 
date or demonstrates that attainment by such date is impracticable. For 
this approach, the EPA does not require that such quantitative 
milestones take any particular form, merely that they provide a means 
to evaluate progress (i.e., demonstrate RFP) meaningfully. The EPA will 
review each attainment plan submission on a case-by-case basis to 
determine whether the quantitative milestones contained in the plan are 
specific enough to provide an objective means for evaluating the area's 
progress toward attainment, consistent with the statutory requirements 
of CAA section 189(c). The EPA recommends that states confer with their 
respective EPA regional office to develop appropriate quantitative 
milestones. See 40 CFR 51.1013(a).
    The Addendum stated that the Moderate area quantitative milestones 
``will be met by showing that emissions reductions scheduled to be made 
between the SIP due date and the attainment date for these moderate 
areas were actually achieved. Most of these emissions reductions will 
result from implementation of RACM (including RACT) as part of the 
moderate area SIP.'' However, this rule does not specify that 
quantitative milestones must be expressed in terms of emissions 
reductions. The EPA recognizes that it is impractical to expect that a 
state will always be able to quantify and compare real and projected 
emissions reductions, and submit a report to the EPA within 90 days of 
a given milestone as required under CAA section 189(c)(2). Therefore, 
the final rule requires that, at a minimum, states must include in all 
attainment plans for Moderate PM2.5 nonattainment areas a 
milestone that all control measures identified and adopted as RACM and 
RACT for the area have been fully implemented within 4 years of 
designation. This milestone specifically derives from section 
189(a)(1)(C) of the Act, that applies to all Moderate areas and thus 
represents a milestone that all Moderate areas must meet regardless of 
whether it is listed explicitly as an individual milestone. See 40 CFR 
51.1013(a)(1)(iii).
    For an area that submitted air quality targets with the RFP plan 
under the optional provision that was described in Section IV.F of this 
preamble, an air quality based milestone (i.e., one that is expressed 
in terms of an ambient PM2.5 level) is strongly recommended 
to be included in order to confirm that the air quality target has been 
met for the quantitative milestone year. If used, this milestone will 
be compared to the most recently certified monitored ambient air data 
as part of the milestone report due after the area reaches each 
quantitative milestone date. The EPA recognizes that certified 
monitored ambient air data are not available for some period after a 
calendar year ends. As a result, the EPA expects that this quantitative 
milestone may sometimes be satisfied with data that are over a year 
old. For example, for Moderate areas having an effective date of 
designations in April 2015, the first quantitative milestone date will 
be in October 2019 (3 years after the 18 month SIP due date), and the 
associated report will be due 90 days later, in January 2020. In this 
example, the state would likely have to rely upon certified air quality 
data for 2018 because data for the 2019 calendar year would not yet be 
fully certified. Additionally, this milestone should normally be 
reported in the same form as the applicable PM2.5 NAAQS. 
However, the EPA expects that in some circumstances, it may be 
appropriate to use annual averages instead of the 3 year average to 
help justify variations due to meteorological occurrences.
    c. Comments and Responses. Comment: Some commenters stated the Act 
may be read to conclude that the requirement to include any 
quantitative milestones in a Moderate area plan does not apply to a 
plan demonstrating the impracticability of attaining the NAAQS by the 
attainment date.
    Response: The EPA's longstanding interpretation of CAA section 
189(c) as a requirement that applies to all PM10 
nonattainment area plans, including those demonstrating that attainment 
by the applicable attainment date is impracticable, is consistent with 
the purpose and structure of subpart 4. The design of the CAA for PM 
nonattainment areas combines the requirements of subpart 1 and subpart 
4 to support expeditious attainment of the applicable NAAQS. RFP is the 
prescribed tool available to a state to plan their emission reduction 
progress toward expeditious attainment. Quantitative milestones are a 
critical aspect of the CAA and the attainment plan in order for the EPA 
to monitor the area's RFP toward expeditious attainment and trigger the 
appropriate response if RFP is not maintained. The EPA thus determined 
that allowing an area to simply not submit any quantitative milestones 
would not afford the EPA the necessary tools to monitor RFP toward 
expeditious attainment.
2. Milestone Report Submission
    a. Summary of the Proposal. Because the statute does not define the 
parameters of quantitative milestone demonstrations, the EPA has 
discretion to determine the components of the required demonstration 
and the form

[[Page 58065]]

and manner for submission. The proposal took comment on options for 
doing this. The EPA proposed to require that the milestone report 
submission must include the following four components: (i) A 
certification by the Governor or Governor's designee that the state's 
attainment plan control strategy is being implemented as described in 
the applicable attainment plan, (ii) technical support sufficient to 
document completion statistics for appropriate milestones and to 
demonstrate that the quantitative milestones have been satisfied and 
how the emissions reductions achieved to date compare to those required 
or scheduled to meet RFP, (iii) as applicable, an air quality screening 
analysis to determine if measured air quality progress is consistent 
with the expected air quality improvement target correlated with the 
RFP emissions reductions for the previous 3 year period, and (iv) an 
evaluation of whether the PM2.5 NAAQS will be attained by 
the projected attainment date for the area. In addition, the EPA 
proposed that the milestone report must include a description and 
schedule for any remedial actions the state has taken or will take to 
address any failure to meet a quantitative milestone, including the 
implementation status of contingency measures for failing to meet RFP 
in the area.
    The EPA also sought comment on how electronic reporting could 
facilitate a state's submission of the required milestone report, how 
it could accommodate the various narrative and data-dependent 
components that the EPA proposed be part of such a submission, and what 
particular system features might be desirable to accommodate milestone 
report submissions through the eSIP system.
    b. Final Rule. The final rule, mirroring section 189(c)(2) of the 
Act, requires that each state containing a PM2.5 
nonattainment area submit to EPA, within 90 days after each milestone 
date applicable to the area, a demonstration that all measures in the 
approved plan (including the RFP plan) for the area have been 
implemented and that the milestone has been met. This rule outlines the 
content required by the EPA for the quantitative milestone report. The 
EPA must then determine whether or not a state's demonstration is 
adequate within 90 days after receiving a demonstration which contains 
the required information and analysis. The EPA intends to promptly 
inform the relevant state of any determination that the state has 
failed to submit a timely quantitative milestone report and any 
determination that a submitted milestone report is not adequate.
    The EPA will work with a state to assist them in meeting the 
reporting deadline, and expects that, because the report is to be 
fairly low burden and may be submitted electronically through eSIP, in 
most cases the state will submit it on time, especially if they have 
implemented the programs required to meet their milestones. If, 
however, a state fails to submit a milestone demonstration report by 
the due date or the EPA determines that a milestone was not met, the 
final rule requires the state to submit a SIP revision within 9 months 
of either the missed reporting deadline or the EPA's determination of 
the state's failure to meet a milestone. According to the statutory 
requirements of CAA section 189(c)(3), the new SIP revision must assure 
``that the State will achieve the next milestone (or attain the 
national ambient air quality standard . . . , if there is no next 
milestone) by the applicable date.'' If a state fails to make a SIP 
submission to correct a failure to meet RFP expeditiously, sanctions 
under CAA sections 110(m) and 179(b) may apply. If a state is unable to 
correct a failure to meet RFP, this may be evidence that the state 
cannot practicably attain the NAAQS by the applicable attainment date 
and may serve as a basis for reclassification of the area to Serious 
under CAA section 188(b)(1).
    As previously noted, the EPA has offered guidance about what the 
milestone report should contain. The Addendum says, ``This report must 
contain technical support sufficient to document completion statistics 
for appropriate milestones. For example, the demonstration should 
graphically display RFP over the course of the relevant 3 years and 
indicate how the emissions reductions achieved to date compare to those 
required or scheduled to meet RFP and the required [quantitative] 
milestones. The calculations (and any assumptions made) necessary to 
determine the emissions reductions to date should also be submitted. 
The demonstration should also contain an evaluation of whether the 
PM10 NAAQS will be attained by the projected attainment 
date.'' \138\ This guidance is still appropriate for states 
demonstrating compliance with RFP and quantitative milestones for 
PM2.5 NAAQS. The EPA requires that the milestone report 
submission must include the following components. See 40 CFR 
51.1013(b).
---------------------------------------------------------------------------

    \138\ Ibid. at 42017.
---------------------------------------------------------------------------

    First, the report must include a certification by the Governor or 
Governor's designee that the SIP control strategy is being implemented 
consistent with the RFP plan, as described in the applicable attainment 
plan. Second, the report must contain technical support, including 
calculations, sufficient to document completion statistics for each 
quantitative milestone and to demonstrate that the quantitative 
milestones have been satisfied and how the emissions reductions 
achieved to date compare to those required or scheduled to meet RFP. 
Additionally, the report must include a discussion of whether the 
PM2.5 NAAQS will be attained by the projected attainment 
date for the area. See 40 CFR 51.1013(b). The EPA decided not to 
finalize the proposed requirements to include an air quality screening 
analysis or the description and schedule for remedial actions taken by 
the state to address a failure to meet a quantitative milestone. This 
decision was made because the remaining components of the quantitative 
milestone report are sufficient to enable the EPA to assess whether the 
nonattainment area is meeting RFP.
    As stated in the Addendum, the milestone report must be submitted 
from the Governor or Governor's designee to the Regional Administrator 
of the respective EPA Regional Office serving the submitting state. The 
EPA will notify the state of its determination (regarding whether or 
not the state's report is adequate) by sending a letter to the 
appropriate Governor or Governor's designee. The EPA encourages states 
to submit milestone reports, including supporting documents, through 
the agency's electronic SIP (eSIP) submission system in order to 
simplify the process and reduce resource burden on all sides.
    c. Comments and Responses. Comment: Some commenters did not support 
the proposal and stated that requiring this level of documentation is 
unnecessary and puts an excessive workload burden on states and local 
agencies.
    Response: The EPA recognizes that there is some level of resources 
required to address the requirements prescribed by every rule. However, 
the EPA concluded that the benefit offered to the public by reviewing 
quantitative milestone reports while assessing whether nonattainment 
areas are making reasonable further progress toward attaining the 
PM2.5 NAAQS and the associated public health benefits 
outweigh the anticipated workload burden for states.
    Comment: Some commenters stated that the first two components of 
the

[[Page 58066]]

quantitative milestone report described in the proposal are sufficient 
to comply with the requirements of CAA section 189(c)(2). The 
commenters stated that the proposed air quality screening analysis is 
not supported by the statute and is unnecessary if the second component 
is fulfilled. The commenters stated that the proposed description and 
schedule for remedial actions the state has taken or will take to 
address any failure to meet a quantitative milestone is more than what 
is necessary to demonstrate compliance with RFP milestones and could 
require revisions to the SIP.
    Response: After considering these comments and in an effort to 
simplify the rule, the EPA decided to eliminate the two proposed 
requirements for the quantitative milestone report as suggested by 
these commenters. As stated earlier, this decision was made because the 
EPA determined that the remaining components of the quantitative 
milestone report are sufficient to enable the EPA to assess whether the 
nonattainment area is meeting RFP.
    Comment: One commenter stated that, while they would not object to 
filing periodic reports, as part of their milestone report, the EPA 
should not insist on the state actually inspecting all covered 
facilities and indicating that RACT or RACM has not been implemented if 
a small subset of facilities is found in violation.
    Response: It is not the intent of the EPA to require states to 
physically inspect all covered sources to verify the implementation of 
required control measures. The intent is that, at the time of the 
milestone due date, all covered sources would be legally required to 
have implemented required control measures and the state has reasonably 
been assured that this occurred.

H. Contingency Measures

1. Summary of the Proposal
    The Act requires Moderate PM2.5 nonattainment area plans 
to contain contingency measures consistent with CAA section 172(c)(9). 
Contingency measures are additional control measures to be implemented 
in the event that the EPA determines that an area failed to meet RFP 
requirements (including associated quantitative milestones) or failed 
to attain the PM2.5 primary standard by the applicable 
attainment date. These measures must be fully adopted rules or control 
measures that are ready to be implemented quickly upon failure to meet 
RFP or failure of the area to meet the standard by its attainment date, 
and such measures are required to take effect without further action by 
the state or the EPA. The EPA proposed and sought comment on general 
requirements for contingency measures for Moderate PM2.5 
nonattainment areas. The EPA has longstanding interpretations of the 
statute with respect to the contingency measure requirement, both for 
PM and for other pollutants, in the General Preamble and Addendum. 
These documents provide guidance and recommendations for states to 
follow in submitting contingency measures, and the proposal did not 
contain any significant changes to the existing guidance and 
recommendations. However, the EPA sought comment on whether the 
guidance needed to be revised or expanded. Additionally, as discussed 
in the proposal, the EPA believes that the DC Circuit's decision in 
NRDC v. EPA does not affect the overall contingency measure 
requirements that were finalized in the remanded 2007 PM2.5 
Implementation Rule. The EPA determined this because CAA section 
172(c)(9) imposes the contingency measure requirement for attainment 
plans for the PM2.5 NAAQS and it is not superseded or 
subsumed by any specific contingency measure requirements under subpart 
4. As a result, the proposal for this rule remained very similar to the 
final 2007 PM2.5 Implementation Rule.
2. Final Rule
    Consistent with the proposal, the final rule codifies existing 
policies on contingency measures, but does not make significant changes 
to these policies. Although CAA section 172(c)(9) requires contingency 
measures, the provision does not specify exactly what parameters such 
measures must meet. The EPA is finalizing an approach to contingency 
measures for the PM2.5 NAAQS that is similar to the approach 
recommended in earlier EPA guidance. Specifically, in order for 
contingency measures to be approvable as part of a state's Moderate 
area attainment plan submission for the PM2.5 NAAQS, the 
state plan must meet the following general requirements (See 40 CFR 
51.1014):
    (1) Contingency measures must be fully adopted rules or control 
measures that are ready to be implemented quickly upon a determination 
by the Administrator of the nonattainment area's failure to meet RFP, 
failure to meet any quantitative milestone, failure to submit a 
quantitative milestone report or failure to attain the standard by the 
applicable attainment date.
    (2) The state's attainment plan submission must contain trigger 
mechanisms for the contingency measures, specify a schedule for 
implementation, and indicate that the measures will be implemented with 
minimal further action by the state or by the EPA.
    (3) The contingency measures shall consist of control measures that 
are not otherwise included in the control strategy or that achieve 
emissions reductions not otherwise relied upon in the control strategy 
for the area.
    (4) Contingency measures should provide for emissions reductions 
approximately equivalent to 1 year's worth of reductions needed for 
RFP, based on the overall level of reductions needed to demonstrate 
attainment divided by the number of years from the base year to the 
attainment year, or approximately equivalent to 1 year's worth of air 
quality improvement or emissions reductions proportional to the overall 
amount of air quality improvement or emissions reductions to be 
achieved by the area's attainment plan.
    Regarding the first two points, consistent with prior guidance, 
states must show that their contingency measures can be implemented 
with minimal further action on their part and with no additional 
rulemaking actions such as public hearings or legislative review. After 
the EPA determines that a moderate PM2.5 nonattainment area 
has failed to meet an RFP requirement or to attain the PM2.5 
NAAQS, the EPA generally expects all actions needed to effect full 
implementation of the contingency measures to occur within 60 days 
after the EPA notifies the state of the area's failure. The EPA intends 
to notify the state of a failure to meet RFP or to attain the NAAQS by 
publication of its determination in the Federal Register. The state 
should ensure that the contingency measures are fully implemented as 
expeditiously as practicable after such notice.\139\
---------------------------------------------------------------------------

    \139\ Ibid. at 42015.
---------------------------------------------------------------------------

    Regarding the third point, the EPA interprets the contingency 
measure requirement of CAA section 172(c)(9) to require control 
measures that are not otherwise included in the control strategy or 
that achieve emissions reductions not otherwise relied upon in the 
control strategy for the area. However, suitable contingency measures 
may be measures that were technologically and economically feasible for 
the area, but did not qualify as RACM or RACT or additional reasonable 
measures for one or more reasons. For example, a candidate contingency 
measure may have been deemed technologically and

[[Page 58067]]

economically feasible, but it was not needed to achieve expeditious 
attainment in a Moderate area for which the state could demonstrate 
attainment by the statutory attainment date and therefore was not 
included as part of the attainment demonstration for the area. It is 
important that states make decisions concerning contingency measures in 
conjunction with their determination of the overall control strategy 
for bringing the area into expeditious attainment, and that states 
first must identify those control measures needed in order to 
demonstrate expeditious attainment of the standards; any remaining 
measures should then be considered as candidates for contingency 
measures.
    As discussed in Section IV.D of this preamble, the RACM/RACT 
provisions in this rule require that, for Moderate areas that cannot 
practicably attain the NAAQS by the statutory attainment date, states 
must implement all control measures that they determine to be 
reasonable (i.e., all technologically and economically feasible 
measures) for sources in the area. In such cases, the contingency 
measures for such nonattainment areas would necessarily exceed the 
criteria for determining whether a measure is reasonable for purposes 
of RACM/RACT and additional reasonable measures. For example, 
contingency measures could consist of reasonable controls on sources 
outside the nonattainment area, early implementation of BACM/BACT on 
select sources inside the area, other measures identified by the state, 
or a combination thereof, that collectively provide approximately 
equivalent to 1 year's worth of emissions reductions/air quality 
improvement. Such contingency measures would only be triggered in the 
event the area fails to meet RFP; the EPA does not interpret the 
requirement for contingency measures for failing to attain the NAAQS by 
the applicable attainment date to apply to a Moderate area that a state 
demonstrates cannot practicably attain the NAAQS by the statutory 
attainment date. Rather, the EPA believes it is appropriate for the 
state to identify and adopt these measures in a timely way as part of 
the Serious area attainment plan that it will develop once the EPA 
reclassifies such an area. However, if a Moderate area that cannot 
practicably attain the NAAQS fails to meet RFP when reviewed as part of 
the quantitative milestone either 4.5 or 7.5 years after designation, 
the requirement to implement contingency measures would be triggered as 
required by CAA section 172(c)(9). For any Moderate PM2.5 
nonattainment area, contingency measures can include measures that 
achieve emissions reductions on sources located outside the 
nonattainment area as well as from sources within the nonattainment 
area, provided that the measures offer reasonable assurance that the 
appropriate air quality impact will result within the nonattainment 
area.
    The final rule continues to allow states to rely on federal 
measures (e.g. federal mobile source measures based on the incremental 
turnover of the motor vehicle fleet each year) and local measures 
already scheduled for implementation that provide emissions reductions 
in excess of those needed to provide for RFP or expeditious attainment. 
The key is that the statute requires that contingency measures provide 
for additional emissions reductions that are not relied on for RFP or 
attainment and that are not included in the RFP or attainment 
demonstrations as meeting part or all of the contingency measure 
requirements. The purpose is ``to provide a cushion while the plan is 
being revised to meet the missed milestone.'' Nothing in the statute 
precludes a State from implementing such measures before they are 
triggered. Additionally, the EPA determined that the court ruling 
upholding contingency measures that were previously required and 
implemented where they were in excess of the attainment demonstration 
and RFP for ozone attainment plans necessitates similar treatment for 
PM2.5 NAAQS.\140\ The EPA has approved numerous SIPs under 
this interpretation, i.e., SIPs that use as contingency measures one or 
more federal or local measures that are in place and provide reductions 
that are in excess of the reductions required by the attainment 
demonstration or RFP plan.\141\
---------------------------------------------------------------------------

    \140\ See LEAN v. EPA, 382 F.3d 575 (5th Cir., 2004).
    \141\ See, e.g., 62 FR 15844 (April 3, 1997); 62 FR 66279 
(December 18, 1997); 66 FR 30811 (June 8, 2001); 66 FR 586 and 66 FR 
634 (January 3, 2001); 78 FR 64402 (October 29, 2013).
---------------------------------------------------------------------------

    For these reasons, the EPA concluded that this approach is 
reasonable for Moderate PM2.5 nonattainment areas that can 
demonstrate attainment by the statutory attainment date, as the state 
would calculate the emissions reductions needed for RFP separately from 
the control strategy determination for such an area. However, crediting 
an area for ``excess'' emissions reductions to satisfy the contingency 
measure requirement is not allowable for Moderate areas that cannot 
practicably attain by the statutory attainment date. Under the EPA's 
approach for calculating RFP for such areas, RFP would be calculated 
directly from the projected emissions reductions from all control 
measures identified for the area (as RACM and RACT or additional 
reasonable measures), such that there should be no difference between 
emissions reductions estimated from control measures and those 
estimated for demonstrating RFP.
    Finally, consistent with the EPA's past approach for contingency 
measures for PM2.5 nonattainment areas, the EPA expects that 
the emissions reductions from contingency measures should be 
approximately equivalent to 1 year's worth of emissions reductions 
while the state is revising its attainment plan for the area. States 
should explain the amount of anticipated emissions reductions to be 
accomplished by the contingency measures outlined in the plan. In the 
rare event that an area is unable to identify contingency measures to 
account for approximately 1 year's worth of emissions reductions, the 
state should provide a reasoned justification why the smaller amount of 
emissions reductions is appropriate. As described in Section IV.F of 
this preamble, the EPA requires an approach for interpreting the 
statutory RFP requirement that would require demonstrating RFP based on 
reductions from sources located inside the nonattainment area. Keeping 
with the historic linkage between RFP and contingency measures, the EPA 
is also finalizing a similar approach for calculating 1 year's worth of 
emissions reductions for purposes of adopting appropriate contingency 
measures. That is, the EPA's approach for determining the level of 
emissions reductions for contingency measure purposes is to calculate 
the annual reductions in emissions of direct PM2.5 and 
PM2.5 plan precursors needed from sources located inside the 
nonattainment area. As explained earlier, however, some or all of the 
contingency measures reductions can come from outside the area if they 
are demonstrated to produce the appropriate air quality impact within 
the nonattainment area.
    This rule requires that states must implement contingency measures 
after the EPA determines that the area has either failed to meet RFP 
requirements, failed to meet any quantitative milestone, failed to 
submit a quantitative milestone report, or failed to attain the 
standards by the applicable attainment date. The purpose of the 
contingency measure provision is to ensure that corrective measures are 
put in place automatically at the time that the EPA makes its 
determination that an area has either failed to meet RFP or failed to 
meet the standard by its attainment date. The EPA is required to

[[Page 58068]]

determine within 90 days after receiving a state's quantitative 
milestone demonstration, and within 6 months after the attainment date 
for an area, whether these requirements have been met. The additional 
consequences for states with areas that fail to attain the NAAQS or to 
meet RFP are described in section 179(d) of the CAA and discussed in 
Section V of this preamble.
    See Section IV.A of this preamble for a discussion of the due dates 
for submission of contingency measures and other attainment plan 
elements.
3. Comments and Responses
    Comment: Commenters stated that requiring contingency measures in 
areas with mature air pollution control programs is very challenging 
because they already have developed aggressive control measures to meet 
CAA requirements and support expeditious attainment. Commenters 
asserted that it would be extremely difficult to develop further 
control measures to meet any contingency measure requirements. 
Commenters objected to the proposed requirement that contingency 
measures must be approximately equivalent to 1 year's worth of 
emissions reductions because it is a departure from existing guidance 
which states the contingency emissions reductions ``should be'' 
approximately equal and because sometimes identifying control measures 
for this level of reductions is just not possible. Commenters advocated 
that EPA should provide a more reasonable approach to the contingency 
measure requirement, but did not provide specific recommendations. 
Other commenters stated that contingency measures should provide 1 
year's worth of emissions reductions needed for RFP.
    Response: The EPA acknowledges that states containing areas with 
more longstanding and pervasive nonattainment problems may already have 
implemented many control measures for purposes of attaining the NAAQS, 
and there may be fewer sources and measures available to meet the 
contingency measure requirements of the statute. However, the EPA notes 
that section 172(c)(9) of the CAA explicitly requires states to adopt 
contingency measures to apply in the event of failure to meet RFP or 
failure to attain the NAAQS as a required component of all attainment 
plans. Typically, contingency measures will be comprised of measures 
that a state and the EPA have determined are not required to meet RACM/
RACT or other requirements, e.g., on the grounds that they are more 
technologically or economically challenging. As a result, such measures 
may not be required as RACM/RACT, but are nevertheless available for 
use as contingency measures. Another approach to contingency measures, 
if appropriate, would be to rely on control measures imposed on sources 
outside the boundaries of the designated nonattainment area. Such 
contingency measures require adequate support to establish that the 
reductions would have the intended impacts within the nonattainment 
area, but can be a source of additional measures for this purpose.
    Finally, the EPA notes that its longstanding guidance is that 
contingency measures should provide approximately 1 year's worth of 
RFP, but this amount may vary based upon appropriate facts and 
circumstances of each unique nonattainment area. As discussed, states 
should explain the amount of anticipated emissions reductions to be 
accomplished by the contingency measures outlined in the plan. In the 
rare event that an area is unable to identify contingency measures to 
account for approximately 1 year's worth of emissions reductions, the 
state should provide a reasoned justification why the smaller amount of 
emissions reductions is appropriate.
    Comment: Commenters stated that ``excess'' emissions reductions 
(i.e., emission reduction measures that are included in a modeled 
attainment demonstration indicating that the area will improve air 
quality to well below the standard) should not be used as contingency 
measures in the event an area actually fails to attain. Commenters 
asserted that the failure to attain should be considered a 
demonstration that excess emissions reductions do not exist. Further, 
the commenters stated that excess reductions do not provide the public 
health benefit intended by Congress. Other commenters stated that 
Moderate areas that cannot attain by the statutory attainment date 
could also have excess emissions reductions creditable as contingency 
measures.
    Response: In keeping with longstanding practice, the final rule 
allows excess emissions reductions to be credited as contingency 
measures in plans that demonstrate attainment but not for plans that 
demonstrate an impracticability to attain. This allows nonattainment 
areas to credit emissions reductions beyond those planned to satisfy 
attainment plan requirements as meeting part or all of the contingency 
measure requirements. This allowance is further supported by the 
court's ruling in LEAN v. EPA, which found that emissions reductions in 
excess of what were needed for the attainment demonstration and RFP in 
ozone attainment plans are creditable for contingency measures. Because 
the contingency measures requirement for both ozone and 
PM2.5 originates in CAA section 172(c)(9), it is applicable 
for all areas designated nonattainment for any NAAQS. Therefore, the 
EPA concluded that the same approach is appropriate for Moderate 
PM2.5 nonattainment areas that can demonstrate attainment by 
the statutory attainment date. Allowing ``excess'' emissions reductions 
affords proper credit for these areas as they continue to make progress 
toward attainment while the new SIP is developed for the area. 
Additionally, in support of the overarching goal of the CAA, public 
health will benefit from the excess emissions reductions. However, such 
an allowance for a Moderate area that cannot practicably attain is not 
acceptable because all emissions reductions anticipated from control 
measures while developing the attainment plan should be accounted for 
in the RFP plan. With all of these reductions accounted for in the RFP 
plan, there are no excess reductions beyond the attainment planning 
period to be credited as contingency measures.

I. Attainment Dates

1. Summary of Proposal
    The proposal described the CAA section 188(c)(1) requirement for 
Moderate areas to attain the standard as expeditiously as practicable, 
but no later than the end of the sixth calendar year after the ``area's 
designation as nonattainment.'' For purposes of clarity, the EPA 
proposed to interpret the term ``area's designation'' as meaning ``the 
area's effective date of designation,'' consistent with the agency's 
past approach for implementing the 1997 and 2006 PM2.5 
NAAQS, and with its approach for implementing the NAAQS for other 
criteria pollutants under part D, title I of the CAA. The EPA requested 
comment on this interpretation. The preamble to the proposal also 
described the process for determining whether an area has attained the 
NAAQS.
2. Final Rule
    The final rule maintains the requirement interpreting of CAA 
section 188(c)(1) to mean that the attainment date must be as 
expeditiously as practicable, but no later than the end of the sixth 
calendar after the effective date of an area's designation. See 
51.1004(a)(1). Thus, as an example, for areas designated nonattainment 
in the first round of designations for the 2012 PM2.5 NAAQS, 
the effective date of designation is April 15, 2015, and the Moderate 
area attainment date would be as expeditious as practicable, but no

[[Page 58069]]

later than December 31, 2021 (i.e., the end of the sixth calendar year 
after designation). Serious area attainment dates are discussed fully 
in Section VI.I of this preamble.
    The EPA's approach to approving an attainment date for a 
PM2.5 nonattainment area will be different for a Moderate 
area that cannot practicably attain the relevant PM2.5 NAAQS 
by the end of the sixth calendar year after designation. Given that the 
agency will reclassify any such area to Serious and thereby trigger 
additional Serious area requirements for the area, the EPA will approve 
an attainment date for the area when it takes action on the Serious 
area attainment plan submitted for the area. In the interim, before the 
EPA takes action to reclassify the area, the statutory Moderate area 
attainment date will continue to apply to such an area. See 40 CFR 
51.1000 and 51.1004(a)(1)(ii). As discussed more fully in Section VI.I 
of this preamble, when the EPA reclassifies the area, then the 
presumptive attainment date for the area will be as expeditious as 
practicable, but no later than the end of the tenth calendar year 
following designation.
    Once an area has an approved attainment date and has implemented 
its plan, the EPA has the responsibility for determining whether the 
nonattainment area has attained the standard by its applicable 
attainment date. Section 179(c)(1) of the CAA requires the EPA to make 
determinations of attainment no later than 6 months following the 
attainment date for the area. Under CAA section 179(c)(2), the EPA must 
publish a notice in the Federal Register identifying those areas that 
failed to attain by the applicable attainment date. The statute further 
provides that the EPA may revise or supplement its determination of 
attainment for the affected areas based upon more complete information 
or analysis concerning the air quality for the area as of the area's 
attainment date.
    Section 179(c)(1) of the CAA provides that the EPA is to base the 
attainment determination for an area upon an area's ``air quality data 
as of the attainment date.'' The EPA will make the determination of 
whether an area's air quality is meeting the PM2.5 NAAQS by 
the applicable attainment date based upon data gathered from the air 
quality monitoring sites that have been entered into the EPA's Air 
Quality System (AQS) database. The state is not required to make any 
special or additional submission in order for EPA to make a 
determination of attainment.
    A Moderate PM2.5 nonattainment area's air quality status 
is determined in accordance with Appendix N of 40 CFR part 50. To show 
attainment of the current 24-hour and annual standards for 
PM2.5, data from the most recent 3 consecutive years prior 
to the area's attainment date must show that PM2.5 
concentrations over the prior 3 year period are at or below the levels 
of the standards. A complete year of air quality data, as described in 
part 50, Appendix N, is comprised of all 4 calendar quarters with each 
quarter containing data from at least 75 percent of the scheduled 
sampling days.
    The EPA will begin processing and analyzing data related to the 
attainment of Moderate PM2.5 nonattainment areas after the 
applicable attainment date for the affected areas. Current EPA 
regulations, under 40 CFR part 58, set the deadline for the state to 
submit air quality data into the AQS database as no later than 90 days 
after the end of the calendar year.
    While the EPA may determine that an area's air quality data 
indicate that an area may be meeting the PM2.5 NAAQS for a 
specified period of time, this does not eliminate the state's 
responsibility under the Act to adopt and implement an approvable 
attainment plan unless the area also has been granted a clean data 
determination. If the EPA determines that an area has attained the 
standard as of its attainment date, the area will remain designated as 
nonattainment until the state has submitted an acceptable redesignation 
request and maintenance plan, and EPA has approved them.
    In order for an area to be redesignated as attainment, the state 
must comply with the five requirements listed under section 
107(d)(3)(E) of the CAA. Briefly, this section requires that:
    (1) The EPA has determined that the area has attained the 
PM2.5 NAAQS;
    (2) The EPA has fully approved the applicable state implementation 
plan;
    (3) The improvement in air quality is due to permanent and 
enforceable reductions in emissions;
    (4) The EPA has fully approved a maintenance plan for the area; and
    (5) The state(s) containing the area or portions of the area have 
met all applicable requirements under CAA section 110 and part D.\142\
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    \142\ See ``Procedures for Processing Requests to Redesignate 
Areas to Attainment,'' Memorandum from John Calcagni, USEPA Office 
of Air Quality Planning and Standards, Director, Air Quality 
Management Division, September 4, 1992.
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J. Attainment Date Extensions

1. Attainment Date Extension Criteria
    a. Summary of Proposal. Subpart 4 of title I of the CAA provides 
the EPA with authority to grant up to two 1-year extensions of the 
attainment date for a Moderate area that otherwise could be found to 
have failed to attain the relevant PM2.5 NAAQS, if the area 
can meet specific statutory criteria related to monitored air quality 
in the area and the implementation of measures in the attainment plan. 
Under CAA section 188(d), a state may apply to the EPA for an extension 
of a Moderate area's attainment date of 1 additional year (the 
``Extension Year'') if ``(1) the state has complied with all 
requirements and commitments pertaining to the area in the applicable 
implementation plan; and (2) no more than one exceedance of the 24-hour 
[NAAQS] level for PM10 has occurred in the area in the year 
preceding the Extension Year, and the annual mean concentration of 
PM10 in the area for such year is less than or equal to the 
standard level.'' Section 188(d) of the CAA also provides for the 
possibility that the EPA may grant a second 1-year extension if the 
Moderate area meets specific criteria. The proposal took comment on two 
ambiguous aspects of this language that warrant further interpretation 
through this rule.
    First, the proposal addressed the statutory language explicitly 
setting ambient air quality conditions for an attainment date extension 
in terms that relate factually to the 24-hour PM10 NAAQS 
that was in effect at the time of the 1990 Amendments of the CAA, which 
has a statistical form that is substantially different from the 24-hour 
PM2.5 NAAQS. The requirement in CAA section 188(d)(2) states 
that an extension may be granted if ``no more than one exceedance of 
the 24-hour national ambient air quality standard level for 
PM10 has occurred in the area in the year preceding the 
Extension Year, and the annual mean concentration of PM10 in 
the area for such year is less than or equal to the standard level.'' 
The proposal noted that the form of the 2006 24-hour PM2.5 
NAAQS is a percentile-based form and not a ``one expected exceedance'' 
form as is the PM10 NAAQS, and therefore the statutory 
language requires some interpretation with regard to how it applies to 
the PM2.5 NAAQS.
    The EPA included a proposed option and requested comment on two 
other alternatives. The preferred proposed approach would only require 
a state to demonstrate that in the year prior to the applicable 
attainment date for the area, a Moderate area did not exceed the level 
of (i.e., had clean data for) the specific PM2.5 NAAQS for 
which the area is designated nonattainment (the ``applicable NAAQS'') 
and for which the

[[Page 58070]]

state is seeking the extension of the attainment date. The second 
approach would require that a state demonstrate that in the year prior 
to the applicable attainment date for an area, the Moderate area did 
not exceed the level of the specific PM2.5 NAAQS for which 
the area is designated nonattainment (the applicable NAAQS), and did 
not exceed the most stringent level of any other PM2.5 NAAQS 
in effect nationally at the time the area was designated for the 
applicable NAAQS. The third approach would require that a state 
demonstrate that in the year prior to the applicable attainment date 
for an area, the Moderate area did not have more than one exceedance of 
the level of the 24-hour PM2.5 standard, and that the annual 
mean concentration of PM2.5 in the area for the attainment 
year was less than or equal to the annual standard, regardless of the 
NAAQS for which the state is seeking an attainment date extension.
    Second, the proposal addressed how the language of CAA section 
188(d)(2) should apply to the PM2.5 NAAQS to the extent that 
it does not specify whether the air quality criteria for an attainment 
date extension apply equally for a Moderate area designated 
nonattainment for both the 24-hour and annual standards, or for just 
one of the standards. In practice, most areas designated nonattainment 
for the PM10 NAAQS following passage of the 1990 CAA 
Amendments were designated nonattainment only for the 24-hour 
PM10 NAAQS, with a few designated for only the annual 
PM10 NAAQS or for both the 24-hour and the annual 
PM10 NAAQS. The 24-hour NAAQS has served as the 
``controlling'' (i.e., functionally more stringent) PM10 
standard, such that the agency's experience to date in granting 
PM10 Moderate area attainment date extension requests has 
been limited to extending the attainment date for the 24-hour 
PM10 NAAQS.\143\ The situation is distinctly different for 
PM2.5 nonattainment areas, as the specific facts and 
circumstances of a particular area may warrant a nonattainment 
designation for either the 24-hour standard or the annual standard, but 
often not both. In most cases, for instance, the current nonattainment 
areas for PM2.5 are designated either for the 1997 annual 
NAAQS or for the 2006 24-hour NAAQS, but not both.\144\ For example, 
the EPA recently promulgated designations for areas violating only the 
annual PM2.5 NAAQS revised in 2012, not the 24-hour NAAQS, 
which was retained at the level established during the 2006 p.m. NAAQS 
review. If a PM2.5 nonattainment area is designated only for 
the 24-hour or only for the annual PM2.5 NAAQS, this 
situation raises the question of how CAA section 188(d)(2) air quality 
criteria for both standards should apply to such a PM2.5 
NAAQS nonattainment area if the state seeks an extension of the 
applicable attainment date for such area.
---------------------------------------------------------------------------

    \143\ For examples of the EPA actions to extend attainment dates 
for Moderate PM10 areas, see 61 FR 20730 (May 8, 1996), 
61 FR 66602 (December 18, 1996), and 66 FR 32752 (June 18, 2001).
    \144\ Nonattainment areas designated for both the 24-hour and 
annual PM2.5 NAAQS are located in central and southern 
CA.
---------------------------------------------------------------------------

    Regarding the ``requirements and commitments'' criterion, the EPA 
proposed to interpret this provision to mean that the state has adopted 
and is implementing the control measures in the SIP submission it made 
to address the attainment plan requirements for the applicable 
PM2.5 NAAQS. The proposal also described a second potential 
interpretation, in which the state would not be eligible for an 
attainment date extension unless it has adopted and submitted its 
Moderate area SIP and has received full approval from the EPA.
    b. Final Rule. The EPA received a number of comments on the 
attainment date extension criteria. With respect to the criterion 
requiring compliance with all requirements and commitments in the 
applicable implementation plan, several commenters agreed with the 
EPA's proposed approach that the state must have adopted and submitted 
its Moderate area SIP but does not need to have full approval of the 
plan by the EPA in order to receive an extension. These commenters 
indicated that a state should not be penalized for a failure by the EPA 
to take timely action on the implementation plan. Some commenters 
opposed the proposed approach, stating that an area's attainment date 
is not predetermined as the end of the sixth calendar year after 
designation, but instead is to be ``as expeditiously as practicable,'' 
and no later than the end of the sixth calendar year. For this reason, 
the commenters stated that the actual attainment date to be extended 
would not be known until after approval of the SIP by the EPA.
    After considering the comments received on this issue, the EPA is 
finalizing an approach similar to the preferred option in the proposal. 
This interpretation is based on the plain language of CAA section 
188(d) that does not explicitly require that the state comply with all 
requirements pertaining to the area in the CAA, but merely requires 
that the state comply with all requirements in the applicable SIP.\145\ 
In other words, the EPA believes that CAA section 188(d)(1) should be 
interpreted to mean that so long as the state has submitted the 
necessary attainment plan for the area for the applicable 
PM2.5 NAAQs and is implementing the control measures in the 
submission, the fact that the EPA has not yet acted on such submission 
to make it an approved part of the applicable SIP should not be a 
barrier to the state obtaining an extension of the attainment date 
under CAA section 188(d)(1). See section 51.1005(a)(1) of the CAA. For 
the same reason, the EPA also proposes to read this provision not to 
bar an extension if all or part of an area's Moderate area plan is 
disapproved or has been promulgated by the EPA as a FIP. In the case 
that the ``applicable implementation plan'' is a FIP (or combination of 
SIP and FIP), then the EPA requires the state to have implemented the 
control measures contained therein in order to meet the statutory 
criteria at CAA section 188(d)(1) for a Moderate area attainment date 
extension.
---------------------------------------------------------------------------

    \145\ This interpretation as applied to CAA section 188(e) for 
Serious area attainment date extensions was upheld by the Ninth 
Circuit Court of Appeals in Vigil v. Leavitt, 366 F.3d 1025, amended 
at 381 F.3d 826 (9th Cir. 2004).
---------------------------------------------------------------------------

    With respect to the air quality criterion, several commenters 
supported the EPA's preferred option because it would require an area 
to show clean data only for the specific standard for which it is 
seeking an extension year. Some commenters acknowledged that a literal 
reading of the statute may seem to require a showing of clean data for 
both the annual and 24-hour PM2.5 standards in order to 
receive an extension, but suggested that this interpretation would not 
make sense under the circumstance where the two standards have 
different attainment dates. The commenter believed it would lead to 
absurd results if, in order to receive an extension for one standard, 
an area were required to show clean data for the other standard for 
which the attainment date had not yet passed. On the other hand, other 
commenters favored the option that would require clean data for both 
standards in order to obtain an extension for one standard because they 
believed that only requiring clean data for one standard would allow 
the area to avoid or delay achieving additional emissions reductions.
    After considering the comments on the air quality criterion, the 
EPA has decided to finalize the approach that would require an area to 
show clean data during the attainment year only for

[[Page 58071]]

the specific standard for which it is seeking an extension. See 40 CFR 
51.1005(a)(1). Under this approach, the EPA interprets the requirement 
to demonstrate that the area had ``no more than one exceedance'' of the 
24-hour PM2.5 NAAQS to mean that the state must simply 
demonstrate that the area had ``clean data'' in the attainment year. 
Thus, a state seeking an attainment date extension for a Moderate 
nonattainment area for a 24-hour PM2.5 NAAQS would be 
required to demonstrate that the area had clean data with respect to 
the statistical form of that particular standard (i.e., for the 2006 
PM2.5 NAAQS, the 98th percentile value did not exceed 35 
[mu]g/m\3\) in the calendar year prior to the applicable attainment 
date for the area. The state would not have to demonstrate that the 
area also had clean data for any other PM2.5 NAAQS, 
including any annual PM2.5 NAAQS or later revision of the 
24-hour PM2.5 NAAQS. Likewise, a state seeking an attainment 
date extension for an annual PM2.5 NAAQS would be required 
to demonstrate that the area had clean data for that particular 
standard (i.e., for the 2012 annual PM2.5 NAAQS, the annual 
mean value did not exceed 12.0 [mu]g/m\3\) in the calendar year prior 
to the applicable attainment date for the area, but would not have to 
demonstrate that the area had clean data for any other PM2.5 
NAAQS.
    The EPA believes this interpretation of CAA section 188(d)(2) is 
appropriate for two main reasons. First, while most PM10 
nonattainment areas were designated nonattainment for either just the 
24-hour PM10 NAAQS or for both the 24-hour and annual 
PM10 NAAQS, the majority of current PM2.5 
nonattainment areas are, in contrast, designated for either the 24-hour 
or the annual PM2.5 NAAQS, and should arguably only need to 
demonstrate clean data for the NAAQS for which the area is designated 
nonattainment. For those few PM2.5 nonattainment areas 
designated for both 24-hour and annual PM2.5 NAAQS, the EPA 
believes it also is appropriate that a state must only demonstrate 
clean data for the specific NAAQS for which the state is seeking an 
attainment date extension because such an approach is consistent with 
the statute's overall approach to designating nonattainment areas and 
implementing control strategies for each separate PM2.5 
NAAQS. Second, if an area is designated as nonattainment for both the 
24-hour and annual PM2.5 standards and receives an extension 
for one standard while still working toward a later attainment date for 
the other standard, public health protection would not be delayed 
because the state would still be subject to the ongoing mandate to 
adopt and implement measures to ensure expeditious attainment of the 
other standard.
    c. Comments and Responses. Any additional comments received on this 
section are addressed in the Response to Comments document found in the 
docket for this action.
2. Process for Attainment Date Extension Request Submissions
    a. Summary of Proposal. The proposal recognized that CAA section 
188(d) does not specify the process by which the state should submit a 
Moderate area attainment date extension request, nor how the EPA should 
evaluate and act upon such a request. The proposal described the 
elements that the state would be required to submit for the various 
options proposed regarding the CAA section 188(d) extension criteria 
for 1) compliance with requirements and commitments in the applicable 
SIP, and 2) air quality data. The proposal suggested that any Moderate 
area extension request should be submitted to the EPA by the attainment 
date for the area (i.e., by December 31 of the attainment year), and it 
proposed requiring the state to submit certified air quality data for 
the attainment year to the EPA by February 28 of the following year in 
order for the EPA to issue a determination within 6 months of the 
attainment date regarding whether the area attained or failed to 
attain. The proposal stated that an attainment date extension should be 
granted only after the agency provides notice in the Federal Register 
and an opportunity for the public to comment. Lastly, the proposal 
clarified that any 1-year extension would extend from January 1 to 
December 31 for the year following the year including the December 31 
attainment date.
    b. Final Rule. As discussed in the previous section, in order for 
the EPA to make a decision on whether to grant a 1-year attainment date 
extension, the state needs to submit sufficient information to 
demonstrate that it has both complied with applicable requirements and 
commitments in the applicable implementation plan, and that it has 
clean data for the attainment year. Under the final rule, a state would 
have to demonstrate that control measures have been submitted in the 
form of a SIP revision, and that RACM and RACT and additional 
reasonable measures for sources in the area have been implemented. The 
SIP revision would need to have been adopted and submitted by the 
state, but it would not need to have been approved by the EPA in order 
for the state to qualify for an extension. See 40 CFR 51.1005(a)(1)(i). 
The state also would need to have ``clean'' air quality data in the 
attainment year, as explained in the previous section. See 40 CFR 
51.1005(a)(1)(ii)-(iii). Any decision made by the EPA to extend the 
attainment date for an area would be based on facts specific to the 
nonattainment area at issue.
    Some commenters suggested that in some cases a state will not know 
if it should seek an extension request until after the attainment date 
has passed, particularly for areas that commonly have higher air 
quality levels in the cooler months at the end of the calendar year. 
The commenter recommended that states should have until February 28 of 
the following year to submit an extension request along with certified 
air quality data. Other commenters stated that there is no legal basis 
for requiring the certification of monitoring data by February 28th of 
the following year, and therefore it should not be a requirement that 
could potentially disqualify a state from having an extension request 
be approved.
    The EPA considered these comments in light of the EPA's obligation 
under the CAA to issue a determination of attainment or failure to 
attain within 6 months of the original attainment date. After 
considering these comments, the EPA strongly recommends that a state 
should submit a Moderate area 1-year extension request to the 
appropriate EPA Regional Office by February 28 of the following year. 
In addition, the EPA strongly recommends that the state provide 
certified air quality data for the previous calendar year by this date 
or as close to this date as possible. The EPA understands that there 
may be certain situations that prevent the full certification of 
filter-based PM2.5 monitoring data by this date. If air 
quality data for the previous full calendar year has not been fully 
certified by February 28, the extension request should include any 
available preliminary data the state can provide. Submission of the 
necessary air quality data must occur as soon as possible after the 
attainment date to enable the EPA to review the state's request 
expeditiously and take appropriate action on the request prior to the 
date by which the EPA is required to make a determination that the area 
failed to attain by its Moderate area attainment date, i.e., within 6 
months of the applicable attainment date (see the discussion of 
reclassification in Section V of this preamble).
    As indicated in the proposal, the EPA believes that an attainment 
date

[[Page 58072]]

extension should only be granted after the agency provides notice in 
the Federal Register and an opportunity for the public to comment. A 
notice-and-comment rulemaking allows for the EPA to adequately evaluate 
whether the area meets the air quality and program implementation 
criteria, and to consider other relevant facts and information 
presented by the state and the public in determining whether the 
extension request should be granted or denied. This process also is 
consistent with past practice by the EPA in granting attainment date 
extensions, most recently for ozone nonattainment areas.
    Regarding the extension period, the EPA interprets CAA section 
188(d) to authorize the EPA to stipulate that any extension would begin 
on January 1 and end on December 31 of the extension year, and these 
dates would not depend on when the state submitted its request for an 
extension or was granted the extension by the EPA. The EPA is 
finalizing this interpretation at 40 CFR 51.1005(a)(4). The EPA 
believes this is a reasonable approach, as the original attainment date 
for the area will either be the end of the sixth calendar year 
following designation of the area, or the end of an earlier calendar 
year if the state demonstrated that it could advance attainment by at 
least 1 year. In addition, compliance with the relevant NAAQS will be 
evaluated based on monitored data collected over a full calendar year 
(i.e., over the period beginning January 1 and ending December 31), so 
starting the extension year on January 1 is logical.
    As noted earlier in this discussion of Moderate area attainment 
date extensions, CAA section 188(d) provides that a state may seek up 
to two 1-year extensions of the Moderate area attainment date if it 
meets the applicable criteria of CAA sections 188(d)(1) and 188(d)(2). 
The statute makes no distinction between the criteria that must be met 
for the first 1-year extension and the criteria for the second 1-year 
extension. Therefore, for a second 1-year attainment date extension 
request, the EPA intends to apply the same interpretations of the 
statutory criteria as described earlier in this section, including the 
recommended deadlines for the state to submit the extension request and 
the certified air quality data.
    c. Comments and Responses. Comment: Some commenters described the 
situation where the EPA has approved a Moderate area attainment date 
that is earlier than the latest date allowed by the statute (for 
example, assume the approved attainment date is the end of the 5th 
calendar year after designation). The commenter suggested that if the 
area was unable to attain by its ``earlier'' approved attainment date, 
CAA section 188(d) should be interpreted in a way that would not 
require the state to submit a request for an attainment date extension. 
The commenter suggested that the state should only be required to meet 
the CAA section 188(d) requirements if the area is seeking an extension 
beyond the latest Moderate area attainment date allowed by statute 
(i.e. the end of the sixth calendar year after designations).
    Response: The EPA does not agree with the commenter because the 
statute appears to address this situation clearly. Section 188(c)(1) of 
the CAA states that the Moderate area attainment date is ``as 
expeditiously as practicable but no later than the end of the sixth 
calendar year after the area's designation as nonattainment.'' If the 
area had provided an attainment demonstration supporting the approval 
of an earlier attainment date by the EPA, then that approved attainment 
date is then regarded as the ``applicable attainment date'' for that 
area. Section 188(d)(1) of the CAA of the statute then enables the EPA 
to grant a 1-year extension for the ``date specified in paragraph 
(c)(1),'' which in this case would be the earlier attainment date.

V. Reclassification of a PM2.5 Moderate Nonattainment Area 
to Serious

    As discussed elsewhere in this preamble, subpart 4, part D of title 
I of the CAA establishes a two-tier classification system for areas 
designated nonattainment for the PM2.5 NAAQS. While all 
areas designated nonattainment are initially classified as Moderate, 
CAA section 188(b) describes two pathways by which the EPA has the 
authority and/or the duty to reclassify a Moderate nonattainment area 
to a Serious nonattainment area. Pursuant to CAA section 188(b)(1), the 
EPA has general discretionary authority to reclassify from Moderate to 
Serious any area that the Administrator determines cannot practicably 
attain the NAAQS by the applicable Moderate area attainment date. 
Pursuant to CAA section 188(b)(2), the EPA has a mandatory duty to 
reclassify from Moderate to Serious any area that fails to attain the 
NAAQS by the applicable Moderate area attainment date. Both of these 
pathways are more fully described in the following sections.\146\
---------------------------------------------------------------------------

    \146\ Note that a reclassification for a multi-state 
nonattainment area will be done in a single action by the EPA; 
separate actions are not needed to reclassify the portion of each 
state comprising the multi-state nonattainment area.
---------------------------------------------------------------------------

A. Discretionary Authority

1. Summary of Proposal
    The proposal provided background on the EPA's discretionary 
authority to reclassify a Moderate area to Serious. It proposed to 
interpret the statute to give EPA broad authority to reclassify based 
on available information, noting that the EPA could base this 
determination upon whatever factors are pertinent. The proposal sought 
comment on whether EPA should discretionarily reclassify an area 
without a request or submission from the affected state. The proposal 
also addressed the mandatory statutory timing for discretionary 
reclassification (i.e., within 18 months of the moderate area SIP due 
date), and took comment on the appropriateness of EPA acting to 
reclassify an area beyond 18 months after the Moderate area SIP due 
date, including right up to the Moderate area attainment date.
2. Final Rule
    The final rule remains largely unchanged with regard to this issue. 
The EPA's discretionary authority to reclassify a Moderate area to 
Serious derives from language in section 188(b)(1) of the CAA, which 
provides that: ``The Administrator may reclassify as a Serious 
PM10 nonattainment area . . . any area that the 
Administrator determines cannot practicably attain the [NAAQS] . . . by 
the attainment date . . . for Moderate Areas.'' The use of this 
discretionary authority thus would be triggered by the EPA making a 
determination that the Moderate area in question cannot practicably 
attain by its statutory attainment date.
    The CAA does not specify the basis on which the EPA may make a 
determination that the area cannot practicably attain by the applicable 
attainment date. In the General Preamble, the EPA explained that the 
agency could base this determination upon whatever facts are pertinent, 
and could do so whether or not the state in question has submitted a 
Moderate area attainment plan, and whether or not the state has made 
the demonstration contemplated in CAA section 189(a)(1)(B).\147\ The 
EPA may make such a determination based on evaluation of the attainment 
plan for the Moderate area in question, or based on other facts known 
to the agency. As discussed earlier in this preamble, the attainment 
plan that a state would submit for a Moderate nonattainment area must 
include either a demonstration that the area will attain the NAAQS by 
the

[[Page 58073]]

statutory Moderate area attainment date or a demonstration that 
attaining by the statutory Moderate area attainment date is 
impracticable. If the state makes and the EPA concurs with an 
impracticability demonstration submitted as part of the attainment 
plan, then the demonstration could serve as the basis for the EPA 
initiating a notice-and-comment rulemaking to reclassify the area to 
Serious.
---------------------------------------------------------------------------

    \147\ See the Federal Register published on April 16, 1994 (57 
FR 13498, 13537 and 13538).
---------------------------------------------------------------------------

    However, the CAA does not specify the basis for the EPA's exercise 
of its discretionary authority and does not require the EPA to make its 
determination based on a submission from the state. Indeed, such a 
prerequisite would be illogical in the case of a state that fails to 
make any attainment plan submission or fails to address the issue of 
the need for reclassification in such submission. The EPA believes that 
while a Moderate area impracticability demonstration as contemplated in 
CAA section 189(a)(1)(B) is desirable in order to help the agency make 
a determination that the area cannot practicably attain by its 
attainment date, such a demonstration is not necessary to trigger 
action by the EPA to reclassify a Moderate area to Serious. The statute 
does not prohibit the EPA from using the weight of available evidence, 
including information available in the public record of a state, to 
make such a determination, even in the absence of a complete attainment 
plan submission.
    Regarding the timing of discretionary reclassifications, CAA 
section 188(b)(1)(B) establishes timeframes by which EPA is to act if 
it intends to exercise its discretionary authority to reclassify areas 
as appropriate following the Moderate area attainment plan due date, 
stating that ``the Administrator shall reclassify appropriate areas 
within 18 months after the required date for the state's submission of 
a SIP for the Moderate Area.'' In the case of areas designated 
nonattainment for the 2012 PM2.5 NAAQS in the first round of 
designations, states will be required by statute to submit a Moderate 
area attainment plan within 18 months of the date of designation (April 
2015), or no later than October 2016. Pursuant to CAA section 
188(b)(1)(B), the EPA would then have until April 2018 (18 months 
following the Moderate area attainment plan submission deadline) to use 
its discretionary authority to reclassify any area that the EPA 
determines at that time cannot practicably attain by the Moderate area 
attainment date of December 2021.
    However, as noted earlier, there may be situations in which it may 
be appropriate to reclassify an area at a point in time more than 18 
months after the SIP due date. On this issue, the General Preamble 
stated that:

    ``. . . under the plain meaning of the terms of section 
188(b)(1), EPA has general discretion to reclassify at any time 
before the applicable attainment date any area EPA determines cannot 
practically attain the standards by such date. Accordingly, CAA 
section 188(b)(1) is a general expression of delegated rulemaking 
authority. In addition, subparagraphs (A) and (B) of CAA section 
188(b)(1) mandate that the EPA reclassify at specified timeframes 
any areas it determines appropriate for reclassification at those 
dates. These subparagraphs do not restrict the general authority but 
simply specify that, at a minimum, it must be exercised at certain 
times.'' \148\
---------------------------------------------------------------------------

    \148\ Ibid. at 13537.

    The EPA continues to consider this the correct interpretation of 
the statutory requirements concerning its authority to reclassify a 
Moderate nonattainment area to Serious at any time prior to the area's 
Moderate area attainment date, if the agency determines that the area 
cannot practicably attain the relevant PM2.5 NAAQS by that 
date. See Section VI.A.2 of this preamble for a discussion of the due 
dates for submission of attainment plan elements for areas that receive 
a discretionary reclassification.
    The EPA emphasizes that a state with an area designated as 
nonattainment for the PM2.5 NAAQS is required to meet all 
Moderate area attainment plan requirements, even after the EPA 
reclassifies the area to Serious. Section 189(b)(1) of the CAA states 
clearly that ``in addition to'' the Moderate area attainment plan 
requirements, states with areas reclassified to Serious must also meet 
Serious area attainment plan requirements, i.e., the reclassification 
does not eliminate the statutory obligation to meet Moderate area 
attainment plan requirements.\149\ Thus, the EPA believes that 
reclassifying Moderate areas to Serious at any time under its 
discretionary authority does not provide incentives to delay 
development and implementation of control measures by excusing states 
from meeting substantive Moderate area attainment plan requirements or 
by extending the applicable attainment date. The EPA articulated this 
position in the General Preamble, explaining that this interpretation:
---------------------------------------------------------------------------

    \149\ See, Vigil v. Leavitt, 366 F.3d 1025, amended at 381 F.3d 
826 (9th Cir. 2004).

    . . . creates an incentive for the timely submittal and 
effective implementation of moderate area SIP requirements and 
facilitates the PM10 attainment objective. For example, 
if an area that fails to submit a timely moderate area SIP is 
reclassified, this does not obviate the requirement that the area 
submit and implement RACM consistent with the moderate area 
schedule. Accordingly, the area could be subject to sanctions for 
its delay in submitting the RACM SIP requirement . . . Further, 
reclassification before the applicable attainment date will ensure 
that additional control measures (i.e., in addition to RACM, serious 
areas must implement best available control measures (BACM)), are 
implemented sooner and will expedite the application of more 
stringent new source review requirements to the area . . . 
Similarly, where an area submits a timely moderate area SIP, EPA may 
not discover that the area cannot practicably attain until sometime 
after it begins implementing its moderate area control measures. The 
EPA then may want to reclassify the area in order to facilitate the 
development and implementation of BACM.\150\
---------------------------------------------------------------------------

    \150\ 57 FR 13498 (April 16, 1992), at page 13537.

    The EPA considers this longstanding interpretation of CAA section 
188(b)(1) to be the correct interpretation of the statutory 
requirements governing the discretionary reclassification of Moderate 
areas. The EPA will reclassify any area it determines cannot 
practicably attain by the Moderate area attainment date through notice-
and-comment rulemaking. See 40 CFR 51.1002(b)(1).
3. Comments and Responses
    Comment: Some commenters stated that while it may be desirable for 
a state or local agency to provide an impracticability demonstration to 
the EPA, the EPA is not prohibited from using the weight of available 
evidence to reclassify an area to Serious even before the Moderate area 
plan is due if it has a particularly challenging air quality situation. 
Other commenters did not agree with the EPA's interpretation of the 
statute, and believed that the EPA's authority should be limited to 
reclassification of areas that submit an impracticability 
demonstration.
    Response: For the reasons described earlier, the EPA agrees with 
the first commenter and does not believe its authority is limited in 
the manner suggested by the second commenter.

B. Mandatory Duty

1. Summary of Proposal
    The proposal provided background on the EPA's mandatory duty 
pursuant to CAA section 188(b)(2) to reclassify a Moderate area to 
Serious when the area fails to attain the standard by the attainment 
date. The CAA directs the EPA to reclassify an area from Moderate to 
Serious if the area fails to attain the relevant NAAQS by the 
applicable Moderate area attainment date

[[Page 58074]]

(including any attainment date that had been extended by one or 2 years 
pursuant to CAA section 188(d)). Reclassification occurs by operation 
of law when the EPA determines that the area failed to attain the NAAQS 
by the applicable attainment date, in accordance with CAA section 
188(b)(2)(A). Section 188(b)(2) of the CAA requires that ``within six 
months following the applicable attainment date for a PM10 
nonattainment area, the Administrator shall determine whether the area 
attained the standard by that date'' and publish its determination in 
the Federal Register.
    The EPA proposed that the date of reclassification would be the 
effective date of the Federal Register notice issued by the EPA that 
determines the area failed to attain by the attainment date. Thus, for 
example in the case of the 2012 PM2.5 NAAQS, assuming a 
Moderate PM2.5 nonattainment area fails to attain the 
standard by its approved attainment date of December 31, 2021, the EPA 
would be required to publish in the Federal Register no later than June 
30, 2022 its determination that the area failed to attain the NAAQS and 
is therefore reclassified as Serious by operation of law. The actual 
date of reclassification for the area would be the effective date of 
the Federal Register document (e.g. in July or August 2022). To meet 
the requirements of CAA section 189(b)(2), the Serious area attainment 
plan for the area would be due within 18 months of the actual 
reclassification date (i.e., in early 2024).
    The proposal also discussed a possible alternative option, which 
would be to consider the date of reclassification to Serious to be the 
same as the Moderate area attainment date. Applying this approach in 
the example earlier would yield an earlier date of reclassification of 
December 31, 2021, and an earlier Serious area attainment plan due date 
of June 30, 2023.
2. Final Rule
    Several commenters supported the EPA's proposed approach to 
interpret the date of reclassification as the effective date of the 
Federal Register notice announcing the area had failed to attain the 
standard by the Moderate area attainment date because this approach 
would allow adequate time for the EPA to evaluate air quality data and 
any exceptional events claims before making the determination that the 
area failed to attain. Some commenters opposed the proposed approach 
and supported interpreting the date of reclassification as being the 
same as the missed attainment date for the Moderate area. This 
commenter suggested that the proposed approach could introduce 
additional delay because the EPA does not always issue determinations 
of failure to attain promptly. They also claimed that the term 
``reclassified by operation of law'' in CAA section 188(b)(2)(A) would 
have no meaning (i.e., surplusage) if the proposed approach was 
adopted.
    After taking the comments received under consideration, the EPA has 
decided to retain the proposed approach. The date of reclassification 
is the effective date of the Federal Register notice issued by the EPA 
that determines the area failed to attain by the attainment date. For 
practical reasons, the EPA does not believe that as a general matter it 
can be expected to make a determination on December 31 that an area 
failed to attain. Because the PM2.5 ambient monitoring 
method requires laboratory analysis of filters prior to determining the 
ambient mass for each day, adequate time is needed after December 31 to 
ensure that the filter-based measurements have been evaluated and 
quality-assured in an accurate manner.
    Although CAA section 188(b)(2) does not explicitly address this 
issue, the EPA believes that this approach is a reasonable 
interpretation of statutory ambiguity in CAA section 188(b)(2) and 
preferable over the alternative approach for two additional reasons. 
First, the statute at CAA section 189(b)(2) gives a state 18 months 
from the date of reclassification of an area to submit for the EPA's 
approval an attainment demonstration with air quality modeling and 
provisions to assure timely implementation of BACM and BACT on sources 
in the nonattainment area. The workload associated with developing a 
Serious area plan can be substantial, and the EPA believes that it is 
reasonable to resolve the statutory ambiguity in favor of providing the 
state with the full 18 months from the effective date of 
reclassification to develop and submit a thorough, complete and 
accurate Serious area attainment plan that will provide for expeditious 
attainment of the NAAQS.
    Second, the statutory attainment date for a Serious area 
reclassified under any circumstances is as expeditious as practicable 
but no later than the end of the tenth year following designation of 
the area, and is thus independent of the date of reclassification of 
the area. Allowing a state some additional amount of time beyond 18 
months from the missed attainment date to develop and submit a complete 
Serious area attainment plan, including adopting BACM and BACT, will 
not change the statutory obligation on the state for the area to attain 
the relevant NAAQS by the applicable attainment date. On the contrary, 
the EPA believes that the extra time may in fact help the area timely 
attain the relevant NAAQS by allowing the state to develop a more 
effective attainment plan for the area.
    Thus, the EPA interprets the CAA such that the date of 
reclassification for an area reclassified under the EPA's mandatory 
duty is to be considered the effective date of the Federal Register 
document announcing that the area had not attained the relevant 
PM2.5 NAAQS and is therefore reclassified by operation of 
law. The EPA intends to make determinations of whether an area attained 
the relevant NAAQS pursuant to CAA section 188(b)(2) by notice-and-
comment rulemaking. See 40 CFR 51.1002(b)(2). Accordingly, the final 
rule establishes a definition of ``date of reclassification'' to mean 
the effective date of a PM2.5 area reclassification from 
Moderate to Serious as promulgated by the Administrator. This 
definition is then used, for example, to establish the due date for the 
Serious area SIP. (See Section VI.A.1 of this preamble for more 
information on mandatory reclassification area SIP due dates.)
3. Comments and Responses
    Any additional comments received on this section are addressed in 
the Response to Comments document found in the docket for this action.

VI. Requirements for PM2.5 Serious Nonattainment Area Plans

    Sections 189(b) and (c) of the CAA include the following 
requirements for Serious area attainment plan submissions: (i) An 
attainment demonstration (CAA section 189(b)(1)(A)); (ii) provisions 
for the implementation of best available control measures (BACM) no 
later than 4 years after reclassification of the area to Serious (CAA 
section 189(b)(1)(B)); (iii) quantitative milestones that will be used 
to evaluate compliance with the requirement to demonstrate RFP (CAA 
section 189(c)); and (iv) regulation of PM2.5 precursors (in 
general to meet attainment and control strategy requirements, and as 
specifically required for major stationary sources by CAA section 
189(e)). Other subpart 1 requirements for attainment plans not 
otherwise superseded under subpart 4 also apply to Serious areas for 
the PM2.5 NAAQS, including: (i) a description of the 
expected annual incremental reductions in emissions that will 
demonstrate RFP (CAA section 172(c)(2)); (ii) emissions inventories 
(CAA section 172(c)(3)); (iii) other control measures (besides BACM and

[[Page 58075]]

BACT) needed for attainment (CAA section 172(c)(6)); and (iv) 
contingency measures (CAA section 172(c)(9)).
    Additionally, CAA section 189(b)(1) requires that ``in addition'' 
to the attainment plan requirements specific to Serious areas, states 
must also meet all Moderate area attainment plan requirements. The EPA 
interprets the statutory language of CAA section 189(b)(1) to require 
states with areas that are reclassified to Serious to meet Moderate 
area attainment plan requirements, including all areas that the EPA 
reclassifies through rulemaking under its discretionary authority, even 
if that occurs before the area has met all of its Moderate area 
attainment plan requirements.\151\ The following section describes the 
EPA's final actions in this rule regarding Serious area attainment plan 
requirements in greater detail.
---------------------------------------------------------------------------

    \151\ See Vigil v. Leavitt, 366 F.3d 1025, amended at 381 F.3d 
826 (9th Cir. 2004).
---------------------------------------------------------------------------

A. Plan Due Dates

    The proposal discussed the statutory provisions that informed the 
options for the submission due dates for the various components of 
Serious area attainment plans. The timing of Serious area attainment 
plan elements is dictated by two provisions of the CAA: CAA section 
189(b)(2) for certain subpart 4 elements and CAA section 172(b) for 
subpart 1 elements not superseded by subpart 4 requirements. Section 
189(b)(2) of the CAA addresses the due dates for Serious area 
attainment demonstrations due under CAA section 189(b)(1)(A) and 
provisions for BACM and BACT implementation under CAA section 
189(b)(1)(B). Specifically, section 189(b)(2) stipulates two 
alternative schedules for states to submit Serious area attainment 
demonstrations, depending upon the statutory authority governing the 
reclassification action. For an area reclassified to Serious by 
operation of law under CAA section 188(b)(2) upon a determination by 
the EPA that the area failed to attain the relevant NAAQS by the 
applicable Moderate area attainment date, a state must submit a new 
attainment demonstration for the area no later than 18 months after 
reclassification. For an area reclassified to Serious pursuant to the 
agency's discretionary authority provided under CAA section 188(b)(1), 
a state must submit a new attainment demonstration no later than 4 
years after reclassification of the area.\152\ For all Serious 
nonattainment areas, CAA section 189(b)(2) requires a state to submit 
within 18 months of an area's reclassification ``provisions to assure 
that the best available control measures [BACM] for the control of 
PM10 shall be implemented no later than 4 years after the 
date the area is classified (or reclassified) as a Serious Area.''
---------------------------------------------------------------------------

    \152\ Section V of this preamble provides a more detailed 
discussion of the process for reclassifying areas with severe 
nonattainment problems to Serious.
---------------------------------------------------------------------------

    When considering attainment plan due dates for areas that have been 
discretionarily reclassified, it is also important to keep in mind the 
requirements of CAA section 188(b)(1). Section 188(b)(1) of the CAA 
generally states that: ``The Administrator may reclassify as a Serious 
PM10 nonattainment area . . . any area that the 
Administrator determines cannot practicably attain the [NAAQS] . . . by 
the attainment date . . . for Moderate Areas.'' In addition, CAA 
section 188(b)(1)(B) provides that ``the Administrator shall reclassify 
appropriate areas within 18 months after the required date for the 
state's submission of a SIP for the Moderate Area.'' Since all Moderate 
area SIPs are due 18 months after designation, then this provision 
contemplates that EPA will typically exercise its discretionary 
reclassification authority within 3 years of the area's designation as 
nonattainment. Taken together with CAA section 189(b)(2), which for 
discretionary reclassifications requires the state to submit the 
attainment demonstration within 4 years of reclassification to Serious, 
subpart 4 contemplates that attainment plans for discretionary 
reclassifications will be submitted no later than 7 years after 
designation. However, as noted in the previous section, the EPA 
believes it can discretionarily reclassify an area more than 18 months 
after the Moderate area SIP due date under certain circumstances, 
meaning that the Serious area attainment demonstration for such a plan 
could be submitted to EPA more than 7 years after designation. (See 
more discussion in Section V.A of this preamble on the timing of 
discretionary reclassifications.)
    Lastly, because some of the Serious area plan requirements noted 
earlier are established in subpart 1 of the Act (CAA section 172), the 
proposal also noted that CAA section 172(b) provides the EPA discretion 
to set a due date for submission of these subpart 1 attainment plan 
elements that is no later than 3 years after designation of the area. 
In the Addendum, the EPA interpreted the date of reclassification of a 
Moderate area to Serious to be analogous to the date of designation of 
the area to nonattainment. Accordingly, some of the options presented 
in the proposal included 3 year SIP due dates for certain plan 
requirements that stem from subpart 1.\153\
---------------------------------------------------------------------------

    \153\ Addendum to the General Preamble, 59 FR 41998 (August 16, 
1994), at page 42015.
---------------------------------------------------------------------------

1. Area Reclassified to Serious After Failing To Attain the 
PM2.5 NAAQS
    a. Summary of Proposal. The proposal noted that for an area 
reclassified to Serious after failing to attain the PM2.5 
NAAQS by the Moderate area attainment date, CAA section 189(b)(2) 
requires the state to submit both the attainment demonstration for an 
area and provisions to ensure timely BACM and BACT implementation to 
the EPA within 18 months after reclassification. The EPA proposed a 
straightforward codification of this 18 month deadline. Assuming the 
effective date of the Federal Register reclassification notice is 
typically about 6 months after the end of the calendar year, this means 
that the attainment demonstration and BACM/BACT provisions would be 
required at about 8 years after designations. The notice also proposed 
that (1) in addition to BACM/BACT and the attainment demonstration, the 
emission inventory would also be required to be submitted within 18 
months of the effective date of reclassification because it is 
essential for the development of BACM/BACT determinations; and (2) 
additional feasible measures (i.e., control measures that may be able 
to help the area attain by the attainment date or advance the 
attainment date by a year, and that may be implemented later than BACM/
BACT but before the attainment date) would also be required to be 
submitted within 18 months of the effective date of reclassification 
because such measures would be identified as part of the overall 
control measures analysis. Regarding the SIP submission date for the 
remaining required plan elements (i.e., RFP, quantitative milestones 
and contingency measures), the proposal included two options: (1) no 
later than 18 months after reclassification (i.e., at about 8 years 
after designation, or 2 years prior to the Serious area attainment 
date; or (2) within 3 years after reclassification (i.e., at about 9.5 
years after designation, or 6 months prior to the Serious area 
attainment date).
    b. Final Rule. Some commenters opposed the proposed requirements 
for SIP elements other than BACM/BACT and the attainment demonstration 
to be due within 18 months of the effective date of reclassification 
because they favored providing states with as much time and flexibility 
as possible to provide their submissions. Other commenters suggested 
that having all

[[Page 58076]]

elements--including RFP, quantitative milestones, and contingency 
measures--be due at the same time would be more administratively 
efficient for states and would allow for EPA to conduct a single 
coordinated review of these plans, and should therefore all be due 
within 18 months of the effective date of reclassification. They also 
indicated that the alternative would not make sense because RFP, 
quantitative milestones, and contingency measures are all linked to the 
attainment demonstration.
    After taking these comments into consideration, the EPA has decided 
to require all Serious area plan elements to be due within 18 months of 
the effective date of reclassification for any area reclassified due to 
a failure to attain by the Moderate area attainment date. The EPA 
believes that the proposed alternative 3 year deadline, which would 
have allowed some elements to be submitted as late as 6 months prior to 
the attainment date, would mean that the state would be required to 
submit two different SIPs and would require greater state government 
resources to conduct the administrative and public procedures required 
to submit the separate plans to the EPA. This approach also would not 
provide the EPA with sufficient time to appropriately review and take 
action on the state's submission prior to the attainment date. It also 
is appropriate to have the RFP, quantitative milestones, and 
contingency measures elements be developed and submitted at the same 
time as the attainment demonstration because they build from the 
information in the attainment demonstration. The EPA also maintains 
that requiring states to submit all elements of an attainment plan by 
the same date is reasonable because it allows for a complete review of 
the state submission by the EPA, regulated entities, and the general 
public, and it also should prove to be most efficient for states and 
the EPA. The EPA further agrees with commenters that a program 
requiring two submissions rather than one can generally be expected to 
be less administratively efficient because it will involve separate 
public hearings and comment periods at the state level, and separate 
proposed and final approval actions in the Federal Register by the EPA. 
Thus, the final rule requires any area that has been reclassified to 
Serious as a result of a failure to attain the standard by the Moderate 
area attainment date to submit all the plan elements to the EPA within 
18 months of reclassification: updated base year emission inventory 
(described in more detail in the next section); BACM/BACT 
determinations and adopted regulations; analysis of additional feasible 
measures (i.e., control measures that may be able to help the area 
attain by the attainment date or advance the attainment date by a year, 
and that may be implemented later than BACM/BACT but before the 
attainment date) and adopted regulations, as appropriate; attainment 
demonstration; RFP; quantitative milestones; and contingency measures. 
See 40 CFR 51.1003(b)(2)(ii).
    c. Comments and Responses. Any additional comments received on this 
section are addressed in the Response to Comments document found in the 
docket for this action.
2. Area Reclassified to Serious Because the EPA Finds in Its Discretion 
That the Area Cannot Practicably Attain the NAAQS by the Statutory 
Moderate Area Attainment Date
    a. Summary of Proposal. The proposal noted that for an area 
reclassified to Serious because the area cannot practicably attain the 
standard by the Moderate area attainment date, CAA section 189(b)(2) 
requires the state to submit its BACM/BACT analyses and any adopted 
regulations to the EPA within 18 months; and to submit the attainment 
demonstration within 4 years of reclassification. Similar to the 
proposal for mandatory reclassification areas, the notice also proposed 
that an updated emission inventory (required under section 172(b) of 
the CAA) be required to be submitted within 18 months of 
reclassification because it is essential for the development of BACM/
BACT determinations.
    The notice also discussed a potential control measure option 
(described in Section VI.D. of the proposal, Attainment Plan Control 
Strategy, at page 15410) that would closely link the BACM/BACT 
determinations to the attainment demonstrations (rather than consider 
BACM/BACT as an independent requirement). Therefore, to facilitate this 
linked approach to BACM/BACT, an alternative option was proposed for 
submission of the attainment demonstration within 18 months of 
reclassification, instead of within 4 years.
    The proposal also addressed the remaining plan elements: additional 
feasible measures (i.e., control measures that may be able to help the 
area attain by the attainment date or advance the attainment date by a 
year, and that may be implemented later than BACM/BACT but before the 
attainment date); RFP; quantitative milestones; and contingency 
measures. Two SIP submission due date options were proposed for the 
remaining plan elements: (1) No later than 3 years after 
reclassification \154\; or (2) no later than 4 years after 
reclassification. The proposal requested comments on all of the 
proposed options for the various elements of a Serious area attainment 
plan.
---------------------------------------------------------------------------

    \154\ Under the EPA's prior interpretation as described in the 
Addendum at 42015, the EPA had suggested that states could submit 
contingency measures no later than 3 years after reclassification of 
an area to Serious because of the language of CAA section 172(b).
---------------------------------------------------------------------------

    b. Final Rule. Most commenters opposed the option requiring the 
attainment demonstration to be due within 18 months, at the same time 
as the BACM/BACT submission. Some of these commenters suggested that a 
4-year due date for the attainment demonstration and other elements 
would provide maximum flexibility to the states. While some commenters 
acknowledged the reasoning behind requiring submittal of the attainment 
demonstration and BACM/BACT at the same time if BACM/BACT is linked to 
the attainment demonstration, most commenters favored an approach that 
provided additional time for submittal of the attainment demonstration.
    Some commenters stated that for an area that is reclassified to 
Serious because it cannot practicably attain the NAAQS by the Moderate 
area attainment date, CAA section 188(b)(1)(B) requires the EPA to 
reclassify the area within 3 years of designation (i.e. within 18 
months of the Moderate area SIP due date), and then per CAA section 
189(b)(2) the attainment demonstration for such area would be due 4 
years later (i.e., 7 years from designation). The commenter stated 
that, if the EPA finalizes any discretionary reclassifications beyond 3 
years after designation, then it cannot allow the area to have the full 
4 years for development of the attainment demonstration because it 
would undermine the deadlines and schedules that Congress was plainly 
trying to impose.
    For discretionary reclassification areas, just as for mandatory 
reclassification areas, the EPA is finalizing the statutory due date of 
18 months for the BACT/BACM submission. However, after considering 
comments received on the timing options for submission of the 
attainment demonstration, the EPA has determined that the attainment 
demonstration should generally be due later than 18 months for areas 
subject to discretionary reclassifications. Because the statutory 
provision in CAA section 189(b)(2) provides up to 4 years, the EPA 
believes that an appropriate default due date for

[[Page 58077]]

the attainment demonstration should be 4 years after reclassification 
for areas reclassified within 3 years of initial designation. However, 
after further consideration of this issue, the EPA also believes that a 
due date of less than 4 years should be required for areas that are 
reclassified closer to the Moderate area attainment date (i.e., 
reclassified between 4 and 6 years after initial designation). In 
considering what would be a reasonable submission deadline for the 
attainment demonstration in this situation, the EPA considered the 
provisions applicable to areas that fail to attain by the attainment 
date. Specifically, CAA section 189(b)(2) requires the attainment 
demonstration (and the rest of the plan) to be submitted no later than 
8 years after designation. As explained further, the EPA believes this 
requirement provides a reasonable outer bound for submission of Serious 
area plans for any area that is discretionarily reclassified to 
Serious.
    The circumstance that one of the commenters identifies, where the 
EPA reclassifies an area to Serious at a point in time more than 3 
years after designation, raises an important timing issue that was not 
explicitly addressed in the proposal. The EPA was aware that it might 
need to reclassify an area to Serious beyond 3 years after designation 
(e.g., for an area that fails to submit a Moderate area attainment plan 
at all; or for an area that is discretionarily reclassified by the EPA 
because it has very high air quality values). However, the proposal did 
not address the issue of when the attainment demonstration and other 
elements should be required for submission when this circumstance 
occurs. The comment raises the question regarding whether, in the most 
extreme example, it would be reasonable for an area to be reclassified 
just before the Moderate area attainment date (end of the sixth 
calendar year after designation) and then to have until just before the 
Serious area attainment date (end of the tenth calendar year after 
designation) to submit the attainment demonstration. This situation 
would provide little meaningful time for the state and relevant 
emissions sources to implement measures to reach attainment by the 
attainment date, nor would it provide sufficient time for the EPA to 
review and take action on the plan.
    The EPA maintains that the statutory authority to ``reclassify as a 
Serious PM-10 nonattainment area . . . any area that the Administrator 
determines cannot practicably attain [the NAAQS] by the attainment date 
. . . for Moderate Areas'' includes the authority to make that 
determination and issue a discretionary reclassification any time 
before the Moderate area attainment date, as long as doing so does not 
otherwise unreasonably frustrate the primary goals of the statute. For 
example, the EPA must consider the timing for submission of Serious 
area SIP requirements to ensure the state has sufficient time to 
implement an effective plan and the agency has sufficient time to 
review and act on the plan in advance of the outermost Serious area 
attainment date (i.e., the end of the tenth calendar year after initial 
designation as nonattainment). See CAA section 188(c)(2).
    The EPA interprets the statute to provide authority to require 
submission of attainment plan requirements, including the attainment 
demonstration, by a date less than 4 years from reclassification to 
Serious when exercising its discretionary authority to reclassify an 
area to serious nonattainment pursuant to CAA section 188(b)(1). While 
the EPA generally prefers to give states as much time as possible to 
develop and submit plans, the agency concluded that allowing 4 years 
for submission of the attainment demonstration in all discretionary 
reclassification actions would potentially frustrate the goals of the 
statute.
    To resolve this issue, EPA is finalizing a specific schedule for 
submission of the attainment demonstration following discretionary 
reclassification. As discussed earlier, the terms of the statute 
provide some guidance as to the appropriate schedule because, as 
explained earlier, a state would have until the end of the 7th calendar 
year to submit the attainment demonstration after a discretionary 
reclassification that follows the timing in CAA section 188(b)(1)(B), 
and a state would have until the end of the 8th calendar year after a 
mandatory reclassification to submit the attainment demonstration. See 
generally CAA sections 188(b) and 189(b).
    While not dispositive, these provisions indicate that Congress 
believes that Serious area attainment plans should be submitted at 
least 2 years in advance of the outermost statutory attainment date for 
Serious areas to ensure expeditious attainment of the NAAQS. The EPA 
finds that a minimum of 2 years is appropriate because (1) it provides 
time for emission reduction measures adopted by the state to take 
effect and improve air quality; (2) it will allow the agency sufficient 
time to evaluate and act on the Serious area attainment demonstration; 
and (3) for every other NAAQS, the CAA SIP submission dates are 
generally 2 years or more prior to the attainment date. If for example 
the plan is not submitted until just before year 10, and the agency 
determines the plan will not lead to attainment, there will be no time 
to take corrective action before the attainment date to ensure 
attainment of the NAAQS. Such a result would not be reasonable.
    Therefore, the EPA believes that a reasonable attainment 
demonstration due date for any discretionary reclassification to 
Serious would be the earlier of (1) 4 years from the date of 
reclassification, or (2) the end of the eighth calendar year after 
designation. As an example, an area that is reclassified at the end of 
year 5 would have 3 years rather than four years to submit the 
attainment demonstration and other plan elements by the end of year 8. 
An area that is reclassified no later than the end of year 4 would have 
the full four years, and any area reclassified after this point would 
have less than 4 years. At the outer extreme, in the unlikely event 
that the EPA chooses to exercise its discretion to reclassify an area 
in the sixth calendar year after designation (i.e., within a year of 
the attainment date), the area would still have 2 years to submit the 
attainment demonstration, which is still no less than the timeframe 
Congress provided for a Moderate area that is reclassified because it 
fails to attain. See 40 CFR 51.1003(b)(2)(i).
    Lastly, this section addresses appropriate SIP submission dates for 
the other required plan elements. Regarding the base year emission 
inventory, the EPA believes it is appropriate to require the updated 
base year emissions inventory at the same time that the BACM/BACT 
submission is due (18 months) because the updated inventory will be a 
critical element relied on for making control measure determinations. 
Regarding the remaining planning elements (i.e., additional feasible 
measures, RFP, quantitative milestones, contingency measures, and 
attainment projected inventory), the proposed options allowed for the 
possibility of up to three separate submissions under certain policy 
combinations, and we believe having such an outcome would be very 
inefficient. Thus, the EPA has determined that the remaining elements 
must be submitted at the same time as the attainment demonstration 
(i.e., the earlier of 4 years from the date of reclassification, or the 
end of the eighth calendar year after designation). This approach will 
provide for the most efficient process and at the same time provide the 
states with the maximum reasonable time when they are reclassified 
pursuant to the EPA's

[[Page 58078]]

discretionary authority in CAA section 188(b)(2).
    With regard to the due date for submission of NNSR program 
revisions that may be required when an area is reclassified to Serious, 
such as revisions to meet nonattainment NSR program requirements to 
lower the ``major stationary source'' threshold from 100 tons per year 
(tpy) to 70 tpy (CAA section 189(b)(3)) and to address the control 
requirements for major stationary sources of PM2.5 
precursors [CAA section 189(e)], \155\ the Act does not specify a 
deadline for the State's submission following reclassification of a 
Moderate PM2.5 nonattainment area as Serious nonattainment 
under subpart 4. Pursuant to EPA's gap-filling authority in CAA section 
301(a) and to effectuate the statutory control requirements in section 
189 of the Act, the final rule requires the state to submit these 
nonattainment NSR SIP revisions no later than 18 months after the 
effective date of final reclassification. This due date is also 
consistent with the due date for submission of BACM and BACT provisions 
and the emission inventory; thus, at most, a state will have two 
required SIP submissions after being reclassified. See 40 CFR 
51.1003(b)(2)(i) and (ii).
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    \155\ Section 189(e) of the CAA requires that the control 
requirements applicable to major stationary sources of 
PM2.5 also apply to major stationary sources of 
PM2.5 precursors, except where the state demonstrates to 
the EPA's satisfaction that such sources do not contribute 
significantly to PM2.5 levels that exceed the standard in 
the area.
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    c. Comments and Responses. Any additional comments received on this 
section are addressed in the Response to Comments document found in the 
docket for this action.

B. Emissions Inventory Requirements

1. Summary of Proposal
    The EPA proposed that the inventory requirements for Serious areas 
were the same as those for Moderate areas with some additions. In 
addition to the Moderate area requirements, the EPA proposed that 
Serious area inventory requirements would include using a major source 
threshold of 70 tons/year for reporting sources as point sources for 
both the base year inventory for the nonattainment area and the 
attainment projected inventory for the nonattainment area.
    With regard to the due date for the attainment projected inventory 
for the nonattainment area, the EPA proposed two cases. In the case 
where the area is reclassified after failing to attain the NAAQS by the 
Moderate area attainment date, the attainment projected inventory for 
the nonattainment area was proposed to be submitted no later than 18 
months after reclassification. In the case where the area is 
reclassified by the EPA because the area cannot practicably attain the 
NAAQS by the statutory attainment date, the EPA proposed that the 
attainment projected inventory for the nonattainment area would be due 
no later than 4 years after reclassification.
2. Final Rule
    a. What Emissions Inventory Requirements Apply to Serious Area 
Attainment Plans? As with Moderate PM2.5 nonattainment 
areas, Congress did not create a specific emissions inventory 
requirement in subpart 4 that would supersede the emissions inventory 
requirement under subpart 1 for Serious areas. Thus, the statutory 
emissions inventory requirements that apply for Serious area attainment 
plans continue to be those of section 172(c)(3), which explicitly 
requires ``a comprehensive, accurate, current inventory of actual 
emissions of the relevant pollutants'' in the nonattainment area. In 
addition, the specific attainment plan requirements for the 
PM2.5 NAAQS set forth in section 189(a) and associated 
modeling requirements make an accurate and up-to-date emissions 
inventory a critical element of any viable attainment plan. Finally, 
the additional attainment plan requirements for the PM2.5 
NAAQS for Serious areas contained in subpart 4 at section 189(b) have 
additional requirements that affect the emissions inventory 
requirements for Serious areas.\156\
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    \156\ All definitions described in Section III.B of this 
preamble for areas classified as Moderate apply in this section.
---------------------------------------------------------------------------

    As noted earlier in this preamble, states must use the best 
available, current emissions inventory information for attainment plan 
development, because complete, high quality emissions inventory data 
are essential for the development of an effective control strategy. To 
assist states in preparing complete, high quality inventories, the EPA 
provides guidance for developing emissions inventories in its SIP 
Emissions Inventory Guidance, available at https://www.epa.gov/air-emissions-inventories/emissions-inventory-guidance-documents. The EPA 
recommends that states consult this guidance while developing emissions 
inventories to meet requirements for Serious area attainment plans.
    b. How do States Meet the Inventory Requirements for the 
PM2.5 NAAQS for Areas Classified as Serious? As with 
Moderate PM2.5 nonattainment areas, neither section 
172(c)(3) nor the provisions specifically applicable to attainment 
plans for the PM2.5 NAAQS in subpart 4 specify how states 
should meet statutory emissions inventory requirements for Serious 
PM2.5 nonattainment areas. Section 172(c)(3) requires that 
states submit ``a comprehensive, accurate, current inventory of actual 
emissions from all sources of the relevant pollutant or pollutants in 
such area, including such periodic revisions as the Administrator may 
determine necessary to assure that the requirements of this part are 
met'' (emphasis added). The EPA interprets this provision to authorize 
the agency to require states to revise their base year emissions 
inventories whenever the state is required to submit a new attainment 
plan because of a change in the nonattainment area's status (e.g. 
failure to attain by the applicable attainment date resulting in 
reclassification). In addition, pursuant to CAA section 301, the EPA 
has additional authority to promulgate regulations as necessary for the 
implementation of the PM2.5 NAAQS, including requirements 
pertaining to emissions inventories. Accordingly, this rule includes 
specific emissions inventory requirements that the EPA considers 
necessary to effectuate the attainment plan requirements of the CAA for 
the PM2.5 NAAQS.
    Like Moderate areas, there are three key facets of the emissions 
inventory requirements: (i) The types of inventories required; (ii) the 
content of these inventories; and, (iii) the timing of submission of 
these inventories. The three facets are addressed in the following 
paragraphs.
    First, the same two types of inventories required for Moderate 
areas are also required for Serious areas. While these inventories are 
the same types and names of inventories as for Moderate areas, they 
must be created specifically for Serious area attainment plans in 
accordance with the applicable Serious area requirements. The first 
type of inventory is called the ``base year inventory for the 
nonattainment area,'' and the second type of inventory is called the 
``attainment projected inventory for the nonattainment area.'' See 40 
CFR 51.1000. The attainment projected inventory is necessary to 
implement the attainment demonstration requirement of section 
189(a)(1)(B), and it also may be used as part of the RFP requirement 
(see Section VI.F). For these reasons, this rule establishes a 
regulatory requirement that Serious area attainment plans must include 
a base year inventory for the nonattainment area and an attainment

[[Page 58079]]

projected inventory for the nonattainment area.
    Second, the content of the inventories will follow the content 
requirements for Moderate area inventories, with two exceptions needed 
to meet the requirements of section 189(b)(3). The first exception for 
Serious areas stems from the Section 189(b)(3) definition of a separate 
emissions threshold for major sources in Serious nonattainment areas 
(70 tpy potential to emit of PM10). This threshold is lower 
than the 100 tpy potential to emit general requirement for major 
sources of PM10, PM2.5 or one of its precursors 
that is used for Moderate area emissions inventories. Inventories for 
Serious area attainment plans must include these smaller sources as 
major stationary sources (rather than the nonmajor stationary source 
category that would apply for these in Moderate area plans) using the 
lower threshold specified in the CAA. Also as described earlier and in 
40 CFR part 51, subpart A, this means that all other smaller stationary 
sources within the nonattainment area must be included in the base year 
inventory and projected attainment year inventory as nonpoint sources.
    As described previously for Moderate areas, Appendix A of Table 1 
of 40 CFR part 51, subpart A (the AERR) is required by this rule to 
define which sources must be reported as point sources for inventories 
associated with this rule (base year and projected attainment year 
inventories). To be consistent with the 70 tpy threshold finalized in 
this rule, this rule is also amending Table 1 of Appendix A of the AERR 
to include the 70 tpy threshold for PM2.5, SO2, 
NOX, VOC and ammonia for point sources within nonattainment 
areas.
    The second difference between the Serious area and Moderate area 
inventory requirements is a minor wording difference for the year that 
should be chosen for the base year inventory. The year should be one of 
the 3 years used for reclassification (rather than designation for 
Moderate areas) or another technically appropriate inventory year. 
Another inventory year may be chosen under specific circumstances 
(e.g., to account for a change in sources in the nonattainment area, 
changes in nonattainment area boundaries, or significant time lag 
between designations and preparation of the inventory) with 
consultation from the appropriate EPA Regional Office. This requirement 
is intended to ensure that the inventory will represent the emissions 
sources whose contributions resulted in a nonattainment designation for 
the area.
    The third facet of the Serious area inventory requirements is the 
timing, which is somewhat different than for Moderate areas. Section 
VI.A of this preamble describes the requirement that states submit the 
base year inventory for a Serious nonattainment area at the same time 
that it submits provisions to implement BACM and BACT on sources in the 
area (due no later than 18 months from reclassification of the area 
pursuant to section 189(b)(2)). This is because the base year inventory 
serves as the starting point for conducting a BACM and BACT 
determination. In contrast to the base year inventory, the attainment 
projected inventory is more closely related to the Serious area 
attainment demonstration. Thus, the attainment projected inventory is 
most appropriately submitted with the attainment demonstration for a 
given Serious area to allow effective evaluation of the attainment plan 
as a whole.
    Consequently, this rule requires that attainment projected 
emissions inventories be submitted at the same time as the Serious area 
attainment demonstration. This requirement gives rise to two possible 
deadlines for Serious areas to submit the attainment projected 
emissions inventory for the nonattainment area. For areas that are 
reclassified after failing to attain the NAAQS by the applicable 
Moderate area attainment date, the deadline is no later than 18 months 
after reclassification (same time period as for Moderate areas). For 
areas reclassified by the EPA because the area cannot practicably 
attain the NAAQS by the statutory Moderate area attainment date, the 
deadline is the earlier of 4 years from the date of reclassification, 
or the end of the eighth calendar year after designation.
3. Comments and Responses
    Comment: Some commenters noted that the proposal was unclear with 
regard to the inventory year for areas that are reclassified from 
Moderate to Serious, and whether the terms ``reclassification'' and 
``designation'' are interchangeable in this regard.
    Response: In the final rule, the EPA clarifies that for areas that 
are redesignated to Serious, the inventory year must be one of the 3 
years used for reclassification. Any additional comments received on 
this section are addressed in the Response to Comments document found 
in the docket for this action.

C. Pollutants To Be Addressed in the Plan

    All PM2.5 precursors are presumptively required to be 
addressed in any Serious area attainment plan. Section III of this 
preamble includes a detailed discussion about optional analyses that a 
state may provide to demonstrate that sources of a precursor do not 
significantly contribute to PM2.5 concentrations in a 
particular nonattainment area. These demonstrations may be conducted 
for all sources of a precursor in an area (i.e., comprehensive 
precursor demonstration), or just for major sources of the precursor 
(i.e., major source precursor demonstration). It also discussed a 
similar demonstration that may be conducted for NNSR (i.e., NNSR 
precursor demonstration). These demonstrations may be used to justify 
the exclusion of certain types of precursor sources from certain SIP 
requirements in Serious area plans, just as in Moderate area plans. 
However, the expeditious attainment demonstration is not available for 
Serious area plans.
    As noted in Section III of this preamble, if the EPA approves a 
state's precursor demonstration for the Moderate area plan, the state 
would need to re-evaluate whether the precursor contributes 
significantly to PM2.5 levels that exceed the standard for 
the Serious area plan. The reason for this is that precursor emissions 
and air quality concentrations will have changed since the submission 
of the demonstration for the Moderate area, and precursor emissions 
technical information and scientific understanding of precursor 
emissions and interactions in the area should be better understood 
several years later, and the Serious area plan needs to be based on the 
best available information to date. If the state reevaluates a 
precursor for potential exclusion from one or more of the Serious area 
plan requirements, it should take into account factors such as 
increases or decreases in emissions since the last precursor 
demonstration; new ambient monitoring data for fine particle 
composition and concentrations of important gases (such as ammonia); 
and improved air quality modeling programs that reflect improved 
understanding of the role of precursors in atmospheric transformation 
processes. To the extent appropriate, this precursor demonstration can 
build off the analyses conducted for the Moderate area precursor 
demonstration.
    If the EPA approves a comprehensive precursor demonstration for the 
Serious area plan, then the state would not be

[[Page 58080]]

obligated to evaluate BACM/BACT measures for reducing that precursor in 
the nonattainment area, nor would it need to account for that precursor 
in the RFP plan, quantitative milestones, and contingency measures. If 
a major stationary source precursor demonstration is approved, then the 
state would not be obligated to evaluate BACM/BACT measures for 
reducing that precursor from major sources in the nonattainment area, 
nor would it need to account for emissions of that precursor from major 
sources in the RFP plan, quantitative milestones, and contingency 
measures. If a NNSR precursor demonstration is approved, then the state 
would not be obligated to address LAER and emission offset requirements 
for that precursor in the NNSR program for that nonattainment area.

D. Attainment Plan Control Strategy

1. General Approach to Designing a Control Strategy for a Serious 
Nonattainment Area
    The statutory attainment planning requirements of subparts 1 and 4 
were established to ensure that states meet the following goals of the 
CAA: (i) Implement measures that provide for attainment of the 
PM2.5 NAAQS as expeditiously as practicable, and (ii) adopt 
emission reduction strategies that will be effective at reducing 
PM2.5 levels in nonattainment areas. A state has discretion 
to require reductions from any source inside or outside of a 
PM2.5 nonattainment area (but within the state's boundaries) 
in order to fulfill its obligation to demonstrate attainment in a 
PM2.5 nonattainment area as expeditiously as practicable, in 
addition to having an obligation to meet the statutory requirements for 
specific control measures on sources located within a nonattainment 
area (e.g., BACM and BACT). A state may need to require emissions 
reductions on sources located outside of a PM2.5 
nonattainment area if such reductions are needed in order to provide 
for expeditious attainment of the PM2.5 NAAQS.
    The following sections describe the recommended approach for a 
state to follow in order to identify and select the complete suite of 
measures needed for an approvable attainment plan submission for a 
Serious PM2.5 nonattainment area.
2. Identification and Selection of BACM/BACT and Additional Feasible 
Measures
    a. Summary of Proposal. The proposal provided background 
information on statutory requirements and existing guidance regarding 
Serious area control strategies, and then presented two broad 
approaches describing the steps for determining BACM/BACT and 
additional feasible measures (i.e. control measures that may be able to 
help the area attain by the attainment date or advance the attainment 
date by a year, and that may be implemented later than BACM/BACT but 
before the attainment date). The first approach is consistent with 
current guidance for PM10 NAAQS implementation in the 
Serious Area Addendum. Under the first approach, the emphasis of the 
analysis would be on the identification of feasible control measures. 
The analysis would be considered to be ``generally independent'' of 
whether such measures are needed for expeditious attainment of the 
relevant NAAQS. However, this approach also would allow the state to 
identify de minimis source categories before conducting any further 
analysis of technologically feasible or economically feasible control 
measures. The proposal requested comment on inclusion of an ambient 
impact threshold of 3 percent for determining whether a source category 
impact would be de minimis. This proposed threshold level was similar 
to the de minimis ambient levels included in the Serious Area Addendum 
for implementation of the PM10 NAAQS, and the state would 
likely need to conduct air quality modeling to demonstrate de minimis 
impacts below a particular threshold. The proposal noted the challenges 
associated with providing a nationally consistent definition of what 
would be a ``source category.'' For source categories found to be de 
minimis, the state would not be obligated to evaluate potential control 
measures. The basic analytical steps for proposed option 1 were 
presented as follows: (1) Update base year emissions inventory for the 
area; (2) evaluate source category impacts; (3) identify existing and 
potential control measures; (4) determine whether an available control 
measure or technology is technologically feasible; (5) determine 
whether an available control measure or technology is economically 
feasible; (6) determine the earliest date by which a control measure or 
technology can be implemented in whole or in part.
    Under the second proposed option, there would be a greater emphasis 
on linking the control strategy evaluation process with the attainment 
needs for the area. Accordingly, this option would not include a ``de 
minimis'' step 2 early in the process. However, at the end of the 
process, the state would be able to choose to not adopt certain 
measures that would otherwise meet the criteria for BACM/BACT if those 
measures collectively would not be necessary to bring the area into 
attainment or to advance the attainment date by 1 year (similar to the 
approach that EPA uses, and has historically used, for RACM/RACT). The 
EPA requested comment on all aspects of these options, and indicated 
the agency may finalize either approach or various elements of each 
approach after evaluating the comments that had been received.
    b. Final Rule. The EPA has considered the comments that were 
submitted on the two proposed options for determining BACM/BACT (and 
additional feasible measures), and has determined that the final rule 
should include aspects of each option. The following sections provide 
background information and guidance on the steps of the process for 
determining Serious area control measures for PM2.5 
nonattainment areas.
i. BACM and BACT
    A Serious area attainment plan must include provisions to implement 
BACM on sources in a Serious nonattainment area, as provided by section 
189(b)(1)(B), no later than 4 years after reclassification. Under 
section 189(b)(2), a state has 18 months following reclassification to 
submit these BACM provisions.
    Section 189(b)(1)(B) refers only to BACM, but the EPA has long 
interpreted this term to include BACT, just as the analogous term for 
RACM includes RACT for Moderate areas. For implementation of the 
PM2.5 NAAQS, the EPA finds it reasonable to maintain the 
same interpretation. The legislative history for the 1990 Amendments to 
the CAA supports this interpretation, as the EPA has explained in past 
guidance.\157\ Additionally, the requirement for BACT for existing 
sources in the context of PM2.5 NAAQS implementation in 
nonattainment areas is separate and distinct from the requirement for 
BACT for new and modified sources under the Prevention of Significant 
Deterioration (PSD) permitting program for new stationary sources in 
areas designated as attainment or unclassifiable for the 
PM2.5 NAAQS. As described later in this section, however, 
the process and criteria that states have historically used to 
determine BACT for new and modified sources under the PSD program have 
also been referenced and applied to the process for determining BACT 
for PM10 NAAQS implementation, but these requirements

[[Page 58081]]

are otherwise unrelated. Consistent with past policy, BACT 
determinations for PM2.5 NAAQS implementation are to follow 
the same process and criteria that are applied to the BACT 
determination process for the PSD program.
---------------------------------------------------------------------------

    \157\ Ibid. at 42008-09.
---------------------------------------------------------------------------

    Longstanding guidance in the General Preamble and Addendum, 
together with past practice associated with implementing the 
PM10 NAAQS under subpart 4, has helped to establish a 
general approach for states and the EPA to determine BACM and BACT for 
Serious PM10 nonattainment areas. This approach has served 
as the basis for developing a more stringent control strategy for a 
Serious PM10 nonattainment area than that developed for such 
area when it was classified as Moderate. Indeed, as BACM and BACT are 
required to be implemented when a Moderate nonattainment area is 
reclassified as Serious due to its actual or projected inability to 
attain the relevant NAAQS by the Moderate area attainment date through 
the implementation of ``reasonable'' measures, it is logical that 
``best'' control measures should represent a more stringent and 
potentially more costly level of control.\158\ The level of stringency 
generally refers to the overall level of emissions reductions of a 
control measure or technology, or of such measures and technologies 
combined.
---------------------------------------------------------------------------

    \158\ Ibid. at 42009.
---------------------------------------------------------------------------

    Congress first defined BACT in CAA section 169(3) for the PSD 
permitting program as: ``an emission limitation based on the maximum 
degree of reduction of each pollutant . . . which the permitting 
authority, on a case-by-case basis, taking into account energy, 
environmental, and economic impacts and other costs, determines is 
achievable for such facility through application of production 
processes and available methods, systems, and techniques . . .''
    In the Addendum, the EPA provided guidance concerning the 
requirements for BACM and BACT for Serious area attainment plan 
requirements for the PM10 NAAQS.\159\ The EPA discussed in 
the Addendum that when Congress amended the CAA, Congress selected the 
same ``best'' terminology for PM10 nonattainment areas as it 
did for the language selected for the PSD program in 1977. The EPA 
interpreted this word choice at the time to mean that PSD BACT and 
PM10 nonattainment area BACM should be generally analogous 
in definition and implementation, but with some differences due to 
different end policy goals between the PSD and nonattainment area 
programs.\160\ The EPA thus defined BACM for PM10 Serious 
nonattainment area planning to be the maximum degree of emission 
reduction achievable from a source or source category which is 
determined on a case-by-case basis, considering energy, economic and 
environmental impacts and other costs.\161\
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    \159\ Ibid. at 42009.
    \160\ Ibid. at 42010. ``EPA will interpret PSD BACT and PM-10 
BACM as generally similar because, despite the similarity in 
terminology, certain key differences exist between control measures 
applicable in the PSD and PM-10 serious nonattainment area programs. 
The BACT under the PSD program applies only in areas already meeting 
the NAAQS, while PM-10 BACM applies in areas which are seriously 
violating the NAAQS. The difference in policy goals, arguably, 
suggests that the PM-10 BACM control standard should be more 
stringent than that for PSD BACT . . . EPA considers it reasonable 
to use the approach adopted in the PSD BACT program as defined in 
section 169(3) of the Act as an analogue for determining appropriate 
PM-10 nonattainment control measures in serious areas, while at the 
same time retaining the discretion to depart from that approach on a 
case-by-case basis as particular circumstances warrant.''
    \161\ Ibid.
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ii. BACM/BACT ``Generally Independent'' of Attainment
    As noted earlier, the issue of whether BACM/BACT should be 
considered generally independent of attainment or more closely tied to 
attainment for purposes of implementing the PM2.5 NAAQS was 
a central issue distinguishing the two proposed options for determining 
BACM/BACT. Some commenters suggested that the overarching requirement 
of the CAA is to attain the standard expeditiously, and therefore the 
benefits of a ``generally independent'' BACM/BACT requirement are not 
clear. On the other hand, some other commenters supported maintaining 
the longstanding policy from the Serious Area Addendum that the BACM/
BACT requirement is generally independent of attainment, citing the 
emphasis on ``best'' control measures and the statutory provision 
requiring BACM/BACT well before the attainment demonstration for 
certain reclassified areas. For the reasons discussed later in this 
section, the EPA has decided to maintain the policy that BACM/BACT 
determinations are to be ``generally independent'' of attainment for 
purposes of implementing the PM2.5 NAAQS.
    In the Serious Area Addendum, the EPA described BACM as a generally 
independent requirement, to be determined without regard to the 
specific attainment analysis (i.e., attainment demonstration) for the 
area.\162\ The EPA established that such an interpretation is in 
accordance with the structural scheme of the CAA, which by its 
definition requires that when an area is classified as Serious, BACM 
are implemented in addition to RACM. Because of the two types of 
measures employed, the EPA found it reasonable to interpret the statute 
as requiring a different analysis for determining BACM, i.e., that 
while RACM emphasizes the attainment needs of the area, BACM has a 
greater emphasis on identifying measures that are feasible to 
implement. Keeping in mind that the overall objective of the 
implementation of BACM and BACT and additional feasible measures is to 
bring a Serious PM2.5 nonattainment area into attainment as 
expeditiously as practicable, the General Preamble noted that the test 
for BACM puts a ``greater emphasis on the merits of the measure or 
technology alone,'' rather than on ``flexibility in considering other 
factors,'' in contrast to the approach for determining RACM and 
RACT.\163\
---------------------------------------------------------------------------

    \162\ Ibid. at 42011.
    \163\ Ibid at 42011.
---------------------------------------------------------------------------

    The view that BACM and BACT measures are generally independent of 
the attainment needs of the area is also consistent with the 
statutorily specified submission date for BACM and BACT control 
measures, contrasted against the statutorily specified submission date 
for the attainment demonstration for Serious areas. Specifically, 
states with Serious nonattainment areas must submit BACM and BACT 
measures within 18 months of reclassification of areas to Serious, 
whereas they are given up to 4 years from reclassification (for areas 
where it is impracticable to attain by the attainment date) to submit 
the attainment demonstration for such areas.
    Additionally, the EPA believes that interpreting the Serious 
PM2.5 nonattainment area BACM/BACT requirements to be 
``generally independent'' of attainment is consistent with the 
structure and substance of the CAA control measure requirements for 
ground-level ozone nonattainment areas with more serious air quality 
problems. In the CAA ozone implementation requirements, an area that is 
reclassified to a more serious category because it failed to attain the 
standard or because it is impracticable to attain by the attainment 
date is then subject to additional specific control measure 
requirements that are considered to be generally independent of 
attainment (for example, see CAA section 182(b) through (e)). The 
statute includes these specific requirements in order to ensure 
continued progress toward attainment for these areas with

[[Page 58082]]

more difficult air quality problems. The EPA believes it is appropriate 
to have a similar interpretation of the PM2.5 Serious area 
control measure requirements. In a similar manner, interpreting BACM/
BACT to be generally independent of the attainment needs of a Serious 
PM2.5 area will ensure continued progress toward attainment 
for those areas with more difficult air quality problems. The EPA also 
believes this more rigorous ``independent control measure'' approach 
for implementing the PM2.5 standards in a manner similar to 
ozone is appropriate because the health effects of both standards are 
very significant (including premature mortality), and robust emission 
reduction programs are needed to bring about expeditious attainment and 
public health protection for citizens in these nonattainment areas.
iii. No de Minimis Source Category Analysis for PM2.5 NAAQS 
Implementation
    Another central issue distinguishing the two proposed options for 
how to determine BACM/BACT was the issue of whether, before analyzing 
any potential BACM/BACT, the state should conduct technical analyses to 
identify whether there are any source categories having a de minimis 
contribution to PM2.5 levels in the PM2.5 
nonattainment area. This de minimis analysis is part of the process 
described in the Serious Area Addendum for implementation of the 
PM10 standards. Under the proposal, for source categories 
found to be de minimis, the state would not be obligated to evaluate 
potential control measures.
    As noted previously, the proposal requested comment on inclusion of 
an ambient impact threshold of 3 percent for determining whether a 
source category impact would be de minimis. This proposed threshold 
level was similar to the de minimis ambient levels included in the 
Serious Area Addendum for implementation of the PM10 NAAQS, 
and the state would likely need to conduct air quality modeling to 
demonstrate de minimis impacts below a particular threshold. The 
proposal noted the challenges associated with providing a nationally 
consistent definition of what would be a ``source category.''
    The EPA also proposed a similar de minimis source category concept 
for the RACM/RACT process for Moderate area plans, and many of the 
comments received on the proposed Moderate area ``upfront'' de minimis 
source category analysis are also applicable when considering whether 
to include a de minimis source category analysis concept for Serious 
areas in the final rule. A number of commenters expressed concern about 
the analytical resources that might be needed to conduct air quality 
modeling to identify whether all the sources in a particular source 
category have an ambient air quality contribution exceeding an air 
quality threshold. Some commenters suggested that a de minimis source 
category approach for either Moderate or Serious areas would allow the 
state to ignore a set of control measures that later in the control 
measure evaluation process could be determined to provide for a more 
expeditious attainment date. They believe that allowing the exemption 
of de minimis source categories would undermine any analysis to 
evaluate whether a collection of measures could advance the attainment 
date by a year. For example, it would be possible for a state to 
identify multiple de minimis source categories at the beginning of the 
process, and then after all potential control measures are identified, 
the state and the EPA would be unable to determine whether the 
collective reductions and air quality impact of the exempted categories 
could actually be sufficient to advance the attainment date. Other 
commenters noted that providing a source category exemption in one 
nonattainment area would lead to inconsistent treatment within a state 
or across states because it would give the exempted companies a 
competitive advantage over the same types of sources in other areas.
    A number of commenters supported the de minimis source category 
concept because they believed it could result in a reduced burden in 
the control measure evaluation stage and help avoid regulating sources 
with limited impact on PM2.5 levels. Some commenters 
supported the de minimis concept only if controls on the source are not 
needed for expeditious attainment. Some commenters suggested that the 
EPA include an emissions-based threshold (e.g. tons per day) rather 
than an air quality based threshold to reduce potential analytical 
burden associated with de minimis source category analyses. However, in 
their comments they did not address the fact that the air quality 
impact of a specific tons per day rate could vary greatly from one 
pollutant to another within a particular nonattainment area, or across 
different nonattainment areas. One state commenter noted that the NAICS 
system does not provide categories for nonpoint sources, and that this 
issue would need to be addressed if the NAICS approach were to be 
included in the final rule. Other commenters suggested that the rule 
not have a de minimis threshold at all but include the ability for the 
state to propose de minimis source categories to the EPA on a case-by-
case basis.
    After taking the range of comments on the de minimis source 
category concept into consideration, the EPA has decided to not 
finalize a de minimis source category approach for the purposes of 
implementing the PM2.5 NAAQS. The EPA is persuaded by 
commenters who argued it is not necessary, and believes that without 
this concept the final rule will nevertheless provide sufficient 
flexibility in the Serious area control measure analysis and attainment 
demonstration process, due to the availability of provisions enabling 
states to identify sources that should not be subject to control 
measures, including the ability to develop precursor demonstrations to 
exclude certain precursors from control requirements, and to consider 
case-specific factors in determining technical and economic feasibility 
of potential control measures. If the final rule were to include an 
explicit step to conduct a de minimis source category analysis on the 
entire inventory early in the control measure identification process, 
the EPA believes that there is a risk that such an analysis may bring 
about investment of scarce time and analytical resources on analysis of 
categories to exclude rather than on the identification of the most 
beneficial control measures for reducing PM2.5 and its 
precursors to achieve expeditious attainment of the standard. In 
addition, the EPA finds merit in comments suggesting that an upfront 
exemption of multiple de minimis source categories in an area would 
undermine the ability of the state (or other interested parties) to 
evaluate, after the identification of potential control measures, 
whether the area could advance the attainment date in order to attain 
``as expeditiously as practicable.''
    Moreover, as noted in Section IV.D of this preamble on Moderate 
areas, the EPA also finds that from a technical perspective, it would 
be very challenging to implement a de minimis source category process 
in a consistent manner nationally without clear guidelines describing 
how narrowly or how broadly a de minimis exemption could apply to a 
``source category,'' or how the technical analysis would need to be 
performed. For example, should a source category consist of all 
industrial boilers? Or all industrial boilers that burn a particular 
fuel? Or all industrial boilers that burn a particular fuel and

[[Page 58083]]

are within a specific size range? The NAICS codes do not provide an 
appropriately comprehensive approach for defining source categories for 
all stationary, mobile, and area sources for this purpose. It has been 
noted that a de minimis source category exemption process is described 
in the 1994 PM10 NAAQS implementation guidance (the Serious 
Area Addendum). In PM10 areas, however, it may have been 
relatively straightforward to identify what were the predominant source 
categories contributing to the NAAQS violations (such as direct 
PM2.5 emissions from dust or wood smoke), and therefore to 
be able to identify what categories might be considered as not 
predominant contributors (or de minimis). However, implementation of 
the PM2.5 NAAQS presents much more complex challenges. 
Precursors and their contribution to secondarily formed PM play a much 
greater role in PM2.5 nonattainment areas than in 
PM10 nonattainment areas. In addition, the relative impact 
of each precursor to local PM2.5 concentrations varies from 
area to area, and even within sections of the same area. To 
appropriately implement an approach allowing for de minimis source 
category impacts, the EPA believes that a nationally consistent source 
category definition would be needed, along with sophisticated air 
quality modeling to evaluate the relative impacts of precursors emitted 
from different ``source categories.'' The resources needed to conduct 
such analyses could be substantial, and would ultimately not help 
identify what control measures would be needed to solve the air quality 
problem. For all of these reasons, a de minimis source category concept 
is not included in the final rule for Serious areas.
iv. Additional Feasible Measures
    While the proposed approaches and criteria for identifying 
appropriate control measures for a Serious area are necessarily 
different than for a Moderate area, it is important to note two 
similarities: First, that the EPA interprets the requirement under CAA 
section 172(c)(6) for a state to adopt ``other measures'' needed for 
attainment to apply to sources located inside and outside of any 
PM2.5 nonattainment area (but within the state's 
boundaries), whether the area is classified as Moderate or Serious; and 
second, similar to the RACM requirement for Moderate nonattainment 
areas under subpart 4, CAA section 189(b)(1)(B) requires that BACM must 
be implemented no later than 4 years after a Moderate area is 
reclassified to Serious.
    Taking these two statutory provisions together, the EPA proposed 
that the other measures required under CAA section 172(c)(6) must 
include ``additional feasible measures,'' which would be those measures 
and technologies that otherwise meet the criteria for BACM/BACT but 
that can only be implemented in whole or in part beginning 4 years 
after reclassification of an area, but no later than the statutory 
attainment date for the area. See proposed 40 CFR 51.1000.
    Some commenters agreed that an area must also consider adopting 
control measures that cannot be implemented within the 4-year deadline 
for implementation of BACM and BACT. Some commenters suggested that 
additional feasible measures should only be tied to expeditious 
attainment.
    In the final rule, additional feasible measures would necessarily 
be implemented by sources in the nonattainment area, and a state is 
required to implement them if they are needed in addition to BACM and 
BACT to bring the area into expeditious attainment. The state must also 
adopt other emission reduction measures for sources within the state 
but outside the nonattainment area if such measures in conjunction with 
other control measures would enable the area to attain the standard by 
the attainment date, or enable the area to advance the attainment date 
by at least 1 year.
    These ``additional feasible measures'' would be analogous to the 
``additional reasonable measures'' in the RACM and RACT analysis 
process, which are technologically and economically feasible measures 
that cannot qualify as RACM or RACT because they cannot be implemented 
within 4 years of designation of a Moderate nonattainment area. Under 
the approach for determining BACM and BACT for sources in a Serious 
nonattainment area described later in this section, a state would 
identify additional feasible measures as part of the BACM and BACT 
determination process, just as additional reasonable measures would be 
identified as part of the state's RACM and RACT determination process.
    The EPA recognizes that with regard to Serious areas, only a 
nonattainment area that is reclassified under the agency's 
discretionary authority might have sufficient time between the date for 
implementing BACM and BACT and the statutory Serious area attainment 
date to implement additional measures beyond BACM and BACT. BACM and 
BACT must be implemented no later than 4 years after reclassification 
of the area; areas reclassified to Serious because they cannot 
practicably attain the relevant NAAQS by the applicable attainment date 
could potentially have significantly more than 4 years between the date 
of reclassification and the statutory Serious area attainment date, 
during which time the area could continue to implement additional 
feasible measures to bring the area into attainment.
    By way of illustration, for areas designated in the first round of 
designations for the 2012 PM2.5 NAAQS, the statutory 
Moderate area attainment date will be no later than December 31, 2021. 
If a state submits a Moderate area attainment plan by the statutory 
attainment plan due date (18 months after designation, or in this 
example, October 2016) and the plan demonstrates that the area cannot 
practicably attain the NAAQS by December 31, 2021, then the EPA has a 
statutory duty to reclassify such an area within 18 months of the 
attainment plan due date (i.e., by April 2018). The statutory Serious 
area attainment date would be the end of the tenth year following 
designation, or December 31, 2025. In such a case, the state would need 
to implement BACM for the area within 4 years of reclassification, or 
by April 2022, leaving over 3.5 years between the statutory deadline 
for implementing BACM and the statutory attainment date for the area. 
The requirement for the state to identify and adopt additional feasible 
measures for the area would mean that the state would need to identify 
those control measures and technologies that are feasible (according to 
the proposed BACM and BACT criteria described later in this section) 
and that can be implemented between April 2022 and December 2025. The 
EPA expects that while such a long span of time may be available only 
to a very few Serious nonattainment areas, it would be appropriate to 
require such areas to implement measures in addition to BACM and BACT 
if, taken together, they can provide for attainment by the attainment 
date or advance the attainment date for the area by at least 1 year. 
Accordingly the EPA has codified a definition of ``additional feasible 
measures'' and specified the conditions under which such measures would 
need to be included in a serious area plan submission. See 40 CFR 
51.1000 and 40 CFR 51.1010(a)(4)(ii).
v. Steps of the BACM/BACT Selection Process
    In addition to the regulatory decisions earlier, the EPA summarized 
and sought comment on further guidance for states

[[Page 58084]]

to follow in selecting BACM/BACT. The guidance was primarily derived 
from the Addendum. This section reviews that guidance, clarifies and 
updates it for purposes of PM2.5, and responds to 
significant comments on the guidance discussion included in the 
proposal.
    The BACM/BACT selection process for implementation of the 
PM2.5 NAAQS is designed to take into account the local facts 
and circumstances and the nature of the air pollution problem in a 
given nonattainment area. The following sections describe the steps of 
the process, including: (i) Develop a comprehensive inventory of 
sources and source categories of directly emitted PM2.5 and 
PM2.5 precursors; (ii) identify existing and potential 
control measures for the sources in the inventory; (iii) evaluate the 
technological feasibility of potential control measures; (iv) evaluate 
the economic feasibility of potential control measures; and (v) 
determine the earliest date by which a control measure or technology 
can be implemented in whole or in part.\164\ These steps are described 
more fully in the following subsections.
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    \164\ For additional information, see ibid. at 42012-13.
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    Step 1: Develop a comprehensive inventory of sources and source 
categories of directly emitted PM2.5 and PM2.5 
precursors. As with any control strategy analysis for a nonattainment 
area, the EPA recommends that the state begin with a current detailed 
emissions inventory of the various sources that emit direct 
PM2.5 and PM2.5 precursors in the Serious area. 
The inventory should identify major stationary sources (i.e., sources 
with the potential to emit 70 tpy of direct PM2.5 or any 
precursor), nonmajor stationary sources, mobile sources, and area 
sources. The inventory also should identify both anthropogenic and 
nonanthropogenic emissions sources.\165\ The EPA expects the state to 
start with the base year emissions inventory submitted with the 
Moderate area attainment plan as required under CAA section 172(c)(3), 
and update it as necessary to reflect new source construction, facility 
shutdowns, growth in certain source categories, and any other relevant 
changes. This inventory should be the most comprehensive and accurate 
inventory available, and it should be consistent with the emissions 
inventory requirements for Serious area plans as described in Section 
VI.B of this preamble.
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    \165\ Addendum to the General Preamble, 59 FR 41998 (August 16, 
1994), at page 42012.
---------------------------------------------------------------------------

    Step 2: Identify potential control measures. The state should 
identify potential control measures for all sources and source 
categories in the latest base year emission inventory for the 
nonattainment area. The list of existing and potential control measures 
should include options not previously considered as RACM/RACT for the 
area, as well as additional measures not previously evaluated in the 
RACM/RACT analysis. For purposes of identifying new measures to 
consider in its BACM/BACT analysis, the EPA recommends that the state 
obtain and evaluate a wide range of sources of information on existing 
and potential control measures. Other nonattainment areas in the same 
state, and other states across the country are important sources of 
information about control measures that are currently being 
implemented. Regional planning organizations, and state and local air 
quality consortiums have in the past developed summaries of control 
measures that should provide useful information for this process.\166\
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    \166\ Add cite to 2006 STAPPA ALAPCO document and other control 
measure summaries. Add cite to menu of measures. Specific to 
potential control measures for mobile source emissions, the EPA's 
past guidance has indicated that where mobile sources contribute 
significantly to PM2.5 violations, ``the state must, at a 
minimum, address the transportation control measures listed in CAA 
section 108(f) to determine whether such measures are achievable in 
the area considering energy, environmental and economic impacts and 
other costs.''
---------------------------------------------------------------------------

    The EPA's RBLC provides a central data base of air pollution 
technology information that may be highly relevant to states seeking 
information on stationary source control technology that may qualify as 
BACT for PM2.5 NAAQS implementation, and is available online 
at http://cfpub.epa.gov/RBLC/. There are also other resources available 
to assist states in identifying other potential control measures and 
control technologies for their BACM and BACT determinations. The EPA 
encourages states with Serious PM2.5 nonattainment areas to 
visit the agency's Web site to find links to other online sources of 
information on potential control measures for states to consider.\167\
---------------------------------------------------------------------------

    \167\ Links are provided to a number of national, state and 
local air quality agency sites from the EPA's PM2.5 Web 
site: http://www3.epa.gov/pm/measures.html.
---------------------------------------------------------------------------

    The state must incorporate appropriate measures into the list of 
potential control measures for the source categories in the Serious 
nonattainment area. The EPA would expect the state to identify an array 
of existing and potential new measures at least as broad as the list 
identified for the same area as part of the RACM and RACT analysis, in 
order to ensure that the state has a sufficiently expansive and 
comprehensive set of potential measures to evaluate. The list of 
potential measures must include all measures identified as potential 
control measures for the nonattainment area when it was classified as 
Moderate or, for a given source category, one or more alternative 
control measures that would control emissions even more stringently 
than the measures included in the RACM/RACT analysis. In this way, the 
state will begin its BACM/BACT determination with a list of potential 
control options that is as complete and up-to-date as possible.
    Step 3: Determine whether an available control measure or 
technology is technologically feasible. After developing a list of 
existing and potential new measures to evaluate for BACM and BACT, the 
state would then need to determine the technological feasibility of 
each identified control measure in light of a number of considerations, 
including each measure's individual energy and environmental 
impacts.\168\
---------------------------------------------------------------------------

    \168\ Ibid. at 42012.
---------------------------------------------------------------------------

    (1) Stationary sources. As described under the technological 
feasibility criteria for the control measures analysis for Moderate 
area attainment plans in Section IV.D of this preamble, the EPA's prior 
guidance on factors to consider for judging whether a particular 
control technology is technologically feasible should include a 
source's processes and operating procedures, raw materials, physical 
plant layout and potential environmental impacts such as increased 
water pollution, waste disposal and energy requirements. For example, 
the EPA recognizes that the process, operating procedures and raw 
materials used by a source can affect the feasibility of implementing 
process changes that reduce emissions and can also affect the selection 
of add-on emission control equipment. The feasibility of modifying 
processes or applying control equipment also can be influenced by the 
physical layout of the particular plant, if the physical space 
available in which to implement such changes limits the choices.\169\
---------------------------------------------------------------------------

    \169\ Ibid. at 42013.
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    (2) Area and mobile sources. With respect to determining whether a 
given control measure might not be technologically feasible as BACM for 
an area or mobile source, a state may consider factors in conducting 
its analysis that are similar to factors the state may have considered 
during the RACM and RACT determination process, such as local 
circumstances, the condition and extent of needed infrastructure, or 
population size or workforce type and habits, which may

[[Page 58085]]

prohibit certain potential control measures from being implementable. 
However, in the instance where a given control measure has been applied 
in another NAAQS nonattainment area (for PM2.5 or other 
pollutant), the state will need to provide a detailed justification for 
rejecting any potential BACM measure as technologically infeasible. 
Furthermore, if the state identifies a certain control measure for area 
or mobile sources that has been implemented in another nonattainment 
area and may qualify as BACM or BACT, the state must provide a reasoned 
justification if it deems it technologically infeasible to implement 
the same control measure to the same extent or magnitude as it was 
applied in the other nonattainment area.
    Step 4: Determine whether an available control technology or 
measure is economically feasible. The fourth step of this process is to 
evaluate the costs of implementing each of the technologically feasible 
control measures and technologies in order to eliminate from further 
consideration any measures determined to be economically infeasible. In 
assessing ``best'' control measures and technologies, states with 
Serious PM2.5 nonattainment areas must identify a control 
strategy for the area that overall is more stringent than that 
identified for the area when the state considered only the 
``reasonableness'' of potential control measures for purposes of the 
RACM/RACT analysis. States need to consider emission reduction measures 
with higher costs per ton when assessing the economic feasibility of 
BACM and BACT controls (and, where applicable, additional feasible 
measures) as compared to the economic feasibility criteria applied in 
their RACM and RACT analysis (and analysis for additional reasonable 
measures) for the same nonattainment area.
    Indeed, consistent with prior guidance on evaluating costs of a 
potential BACM/BACT, the EPA maintains that while the economic 
feasibility of a control measure is as important as its technological 
feasibility under the RACM and RACT determination process, economic 
feasibility is a less significant factor in the BACM and BACT 
determination process. In other words, a state must apply a higher 
standard for eliminating a technologically feasible control measure 
from further consideration as BACM due to cost alone.
    In the Addendum, the EPA stated that ``for PM10 BACM 
purposes, it is reasonable for similar sources to bear similar costs of 
emission reduction.'' \170\ Additionally, the EPA indicated that 
``economic feasibility for PM10 BACM purposes should focus 
upon evidence that the control technology in question has previously 
been implemented at other sources in a similar source category without 
unreasonable economic impacts.'' \171\ Thus, a state may not eliminate 
a particular control measure from further consideration as potential 
BACM if similar sources have successfully implemented such a measure. 
That is, a state must at a minimum continue to consider as potential 
BACM any technologically feasible control measures or technologies 
implemented by similar sources.
---------------------------------------------------------------------------

    \170\ Ibid.
    \171\ Ibid.
---------------------------------------------------------------------------

    In addition, a state may not automatically eliminate a particular 
control measure merely because other sources have not implemented the 
measure. In other words, a state must continue to consider 
technologically feasible measures that have not been implemented by 
similar sources but that can nonetheless effectively reduce emissions 
from the source category in question at a cost that is not cost 
prohibitive.
    As with the EPA's approach for evaluating economic feasibility of 
potential reasonable measures for Moderate area attainment plans, for 
each technologically feasible control measure or technology, a state 
must evaluate the economic feasibility of the measure through 
consideration of the capital costs, operating and maintenance costs, 
and cost effectiveness (i.e., cost per ton of pollutant reduced by that 
measure or technology) associated with such measure or control. While 
the EPA is not establishing a fixed dollar per ton cost threshold for 
economic feasibility of controls identified as potential BACM and BACT, 
the cost per ton of an acceptable measure for the BACM and BACT 
analysis generally would be higher than it was for the RACM and RACT 
analysis for the same nonattainment area. In addition, if a source 
contends that a source-specific control level should not be established 
because the source cannot afford the control measure or technology that 
is demonstrated to be economically feasible for purposes of BACM for 
other sources in its source category, the source should make its claim 
known to the state and support the claim with information regarding the 
impact of imposing the identified control measure or technology on the 
following financial indicators,\172\ to the extent applicable:
---------------------------------------------------------------------------

    \172\ These longstanding factors were established in the EPA 
guidance in 1992 and are applicable to implementation programs for 
all of the NAAQS pollutants. See the appendices to the General 
Preamble, 57 FR 18070 (April 28, 1992).
---------------------------------------------------------------------------

    1. Fixed and variable production costs ($/unit);
    2. Product supply and demand elasticity;
    3. Product prices (cost absorption vs. cost pass-through);
    4. Expected costs incurred by competitors;
    5. Company profits;
    6. Employment costs;
    7. Other costs (e.g., for BACM implemented by public sector 
entities).

    Step 5: Determine the earliest date by which a control measure or 
technology can be implemented in whole or in part. Section 189(b)(1)(B) 
of the CAA requires that Serious area attainment plans provide for the 
implementation of BACM no later than 4 years after reclassification of 
the area to Serious. As with the EPA's proposed approach to RACM and 
RACT, the EPA proposes the term ``implement'' to mean that the control 
measure or technology has not only been adopted into the SIP for the 
area but has also been built, installed and/or otherwise physically 
manifested and the affected sources are required to comply. The EPA 
thus expects a state with a Serious nonattainment area to take timely 
action to implement BACM and BACT in the area.
    A state must identify those technologically and economically 
feasible control measures and technologies that it can implement fully 
or partially within 4 years of reclassification of its Serious 
PM2.5 nonattainment area. These measures will be considered 
BACM and BACT for the area. If a state evaluates a potential BACM or 
BACT measure and determines that it can be implemented only partially 
within 4 years after reclassification, the state must adopt the partial 
measure as BACM.
    Where the earliest date that a measure can be implemented is beyond 
the 4 year mark following reclassification to Serious, the measure may 
still be needed as an ``additional feasible measure'' if the 4 year 
mark occurs before the Serious area attainment date. ``Additional 
feasible measures'' would be ``best''-level, feasible measures that a 
state could implement in whole or in part on sources in the area 
sometime after the fourth year following reclassification and prior to 
the statutory attainment date for the area.
    c. Comments and Responses. Any additional comments received on this 
section are addressed in the Response to

[[Page 58086]]

Comments document found in the docket for this action.
3. BACM and BACT Submission Requirements
    a. Summary of Proposal. The proposal further specified the 
submission requirements once a state has determined the BACT/BACM 
requirements in its plan. The proposal required the state to submit a 
list of emissions sources, an emissions inventory for such sources, and 
several pieces of information regarding potential control measures for 
these sources.
    b. Final Rule. The final rule remains relatively unchanged from the 
proposal. To ensure that attainment plan submissions contain the 
necessary supporting information for EPA review and approval of the 
state's selected BACM and BACT and additional feasible measures as 
applicable, 40 CFR 51.1010(a)(1)-(5) require the state to submit the 
following information as part of its Serious area attainment plan 
submission:
    (1) A list of all emissions source categories, sources and 
activities in the nonattainment area that emit direct PM2.5 
or any PM2.5 precursor (for multi-state nonattainment areas, 
this would include source categories, sources and activities from all 
states which make up the area);
    (2) For each source category, source or activity in the 
nonattainment area, an inventory of direct PM2.5 and all 
PM2.5 precursor emissions;
    (3) For each source category, source or activity in the 
nonattainment area, a comprehensive list of potential control measures 
considered by the state for the nonattainment area; 173 174
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    \173\ The EPA believes that it is not necessary to identify 
every possible variation of every type of control measure, or all 
possible combinations of technologies and measures that would apply 
to a given source or activity, as long as the state has properly 
characterized the potentially available emissions reductions and 
their costs. For example, the EPA believes that the state can 
conduct a thorough analysis of VMT reduction measures without 
including every possible level or stringency of implementation of 
certain possible measures or combinations of measures for reducing 
VMT, so long as those measures would not affect the overall 
assessment of VMT reduction capabilities and the associated costs.
    \174\ The Menu of Control Measures document is available at: 
http://www3.epa.gov/ttn/naaqs/pdfs/MenuOfControlMeasures.pdf.
---------------------------------------------------------------------------

    (4) For each potential control measure considered by the state but 
eliminated from further consideration due to a determination by the 
state that the control measure or technology was not technologically 
feasible, a narrative explanation and quantitative or qualitative 
supporting documentation to justify the state's conclusion;
    (5) For each technologically feasible emission control measure or 
technology, the state must provide the following information relevant 
to economic feasibility: (i) The control efficiency by pollutant; (ii) 
the possible emissions reductions by pollutant; (iii) the estimated 
cost per ton of pollutant reduced; and, (iv) a determination of whether 
the measure is economically feasible, with narrative explanation and 
quantitative supporting documentation to justify the state's 
conclusion;
    (6) For each technologically and economically feasible emission 
control measure or technology, the date by which the technology or 
measure can be implemented.
    As with a Moderate area attainment plan submission, the EPA 
recognizes that the base year emissions inventory that the state 
submits for the area in conjunction with its Serious area attainment 
plan will likely contain the information required under the first two 
items in this list. However, the EPA believes that it is incumbent on 
the state to ensure that the information needed for the EPA to evaluate 
the state's BACM and BACT and additional feasible measures analysis is 
presented as part of that analysis and in a format that provides 
transparency, consistency and the ability for another party to evaluate 
the state's analysis effectively and to duplicate the state's results. 
For this reason, the EPA is requiring the state to include the base 
year emissions inventory information with the BACM and BACT submission 
and as one element of the state's attainment plan due 18 months after 
reclassification of the area to Serious.
    c. Comments and Responses. Any additional comments received on this 
section are addressed in the Response to Comments document found in the 
docket for this action.
4. Criteria for Effective Regulations to Implement BACM and BACT and 
Additional Feasible Measures
    a. Summary of Proposal. The proposal described the four main 
criteria for effective control measure regulations: such regulations 
must be quantifiable, enforceable, replicable, and accountable.
    b. Final Rule. Guidance on effective control measure regulations is 
provided in the control strategy discussion for Moderate areas. See 
section IV.D.9 of this preamble, criteria for effective regulations to 
implement RACM and RACT and additional reasonable measures.
5. Relevance of Prior BACT, LAER and BART Determinations
    a. Summary of Proposal. The preamble of the proposed rule stated 
that it should not be assumed that past control technology 
determinations would automatically be deemed to meet the Serious area 
control measure requirements (BACM, BACT, or additional feasible 
measures) for an area.
    b. Final Rule. The guidance on this issue in the preamble to the 
final rule remains largely unchanged. The EPA believes that BACT or 
lowest achievable emission rate (LAER) provisions for new sources (as 
distinct from BACT for existing sources), or best available retrofit 
technology (BART) for existing sources, could potentially qualify as 
BACM or BACT for purposes of meeting the Serious area attainment plan 
requirements. However, the EPA does not believe it is appropriate for a 
state to assume that just because a certain control technology was 
determined to meet BACT, LAER, or BART criteria for a new source 
sometime in the past, that such a control will also automatically meet 
the criteria for BACM or BACT or additional feasible measures for 
attainment planning purposes because the regulated pollutant or source 
applicability may differ and the analyses may be conducted many years 
apart. Thus, a state may not simply rely on prior BACT, LAER or BART 
analyses for the purposes of showing that a source has also met BACT 
for the relevant PM2.5 NAAQS. Rather, the EPA expects that 
in Step 2 of the BACM and BACT determination process, the state would 
identify such measures as ``existing measures'' that should be further 
evaluated as potential BACM or BACT or additional feasible measures. At 
the same time, the EPA notes that the presence of previously installed 
control technology, and the technical and economic considerations that 
would be associated with upgrading to a measure that achieves greater 
reductions, is something that should be considered in the assessments 
of technological and economic feasibility of the newer measure.
    c. Comments and Responses. Any additional comments received on this 
section are addressed in the Response to Comments document found in the 
docket for this action.
6. Multi-state Nonattainment Areas
    a. Summary of Proposal. The preamble to the proposed rule provided 
general guidance on coordination between states in multi-state 
nonattainment areas to ensure they

[[Page 58087]]

adopt sufficient BACM/BACT and additional feasible measures to ensure 
expeditious attainment of the standard.
    b. Final Rule. The guidance in the final rule remains largely 
unchanged. States that share a multi-state Serious PM2.5 
nonattainment area must consult with one another on BACM and BACT and 
additional feasible measures that will be required for the 
nonattainment area in the different states. This requirement would be 
consistent with the overall requirements for BACM and BACT and 
additional feasible measures determinations, as all states with Serious 
areas need to consider implementing BACM and BACT-level measures that 
have been implemented in other states, even if those measures incur 
higher costs. The EPA anticipates that states may potentially adopt 
controls that differ from state to state, based upon each state's 
determination of what qualifies as ``best'' given the mixture of 
sources and potential controls in the state portions of relevant 
nonattainment areas, subject to EPA approval. If the state can 
adequately demonstrate that its chosen BACM and BACT and additional 
feasible measures fully meet the EPA's proposed criteria for such 
measures, then the agency may consider approving individual state plans 
that differ in implementation of control measures.
    c. Comments and Responses. Any additional comments received on this 
section are addressed in the Response to Comments document found in the 
docket for this action.
7. Environmental Justice Considerations for Developing the Attainment 
Plan Control Strategy for a Serious PM2.5 Nonattainment Area
    a. Summary of Proposal. The proposal provided general guidance for 
ensuring that overburdened populations are appropriately protected.
    b. Final Rule. The guidance in the final rule remains largely 
unchanged. The EPA strongly urges states to consider the environmental 
justice aspects of any control measures they have identified as BACM 
and BACT or additional feasible measures in order to provide health 
protection for overburdened populations. Please see Section XI of this 
preamble, which discusses possible approaches for states to address 
environmental justice concerns associated with implementation of the 
PM2.5 NAAQS in their SIP development process and attainment 
plans.
    c. Comments and Responses. Any additional comments received on this 
section are addressed in the Response to Comments document found in the 
docket for this action.

E. Modeling for Attainment Demonstrations

1. Due Dates for Submission of Serious Area Attainment Demonstrations
    a. Summary of Proposal. Section IV.E of this preamble describes the 
EPA's attainment demonstration and modeling requirements for Moderate 
area plans. The EPA proposed that the same general attainment 
demonstration and modeling requirements for Moderate area plans should 
apply to Serious area attainment demonstrations. However, Serious area 
plans have additional statutory requirements.
    Attainment demonstrations are due 18 months after reclassification 
if the EPA reclassifies the area to Serious after failure of the area 
to attain the applicable Moderate area deadline. Alternatively, CAA 
section 189(b)(2) requires states with designated Serious nonattainment 
areas to submit attainment demonstrations no later than 4 years after 
reclassification of the area to Serious if the reclassification occurs 
before the Moderate area attainment deadline. The EPA proposed an 
approach for determining an appropriate attainment plan control 
strategy for a Serious PM2.5 nonattainment area that 
requires the state to submit the attainment demonstration for the area 
within 18 months after reclassification, regardless of when or the 
authority under which an area was reclassified to Serious.
    b. Final Rule. The statutory attainment demonstration provisions 
for Serious areas are as follows: Section 189(b) of the CAA requires a 
state with a designated Serious nonattainment area to submit an 
attainment plan for such area. As discussed earlier, CAA section 
189(b)(1)(A) more specifically requires the state to submit an 
attainment demonstration including air quality modeling to establish 
either: (i) That the area will attain the relevant NAAQS by the 
applicable attainment date, or (ii) if the state is seeking an 
extension of the attainment date, that it is impracticable for the area 
to attain the relevant NAAQS by the statutory Serious area attainment 
date. For Serious nonattainment areas, the attainment date is as 
expeditiously as practicable, but no later than the end of the tenth 
calendar year after designation as nonattainment. A demonstration that 
shows that it is impracticable for the area to attain within this 
timeframe must also provide for attainment of the NAAQS by the most 
expeditious alternative date practicable, but no later than 5 years 
after the maximum statutory Serious area attainment date (based on the 
criteria specified in CAA section 188(e)).
    The EPA is not finalizing the proposed approach of requiring all 
Serious area attainment demonstrations to be due 18 months after 
reclassification. If the EPA reclassifies the area to Serious after 
failure of the area to attain the applicable Moderate area deadline, 
the attainment demonstration will be due in 18 months. States with 
Serious nonattainment areas that were reclassified before the Moderate 
area attainment deadline must submit attainment demonstrations the 
earlier of 4 years after reclassification of the area to Serious or the 
end of the eighth calendar year after initial designation. However, 
these areas are still required to submit BACT/BACM measures within 18 
months of being reclassified as Serious. Sections VI.A and VI.D of this 
preamble describe more fully the EPA's approach for plan due dates and 
control strategy analyses for all elements of a Serious area attainment 
plan. Section VI.J of this preamble provides a complete discussion of 
the EPA's criteria for granting a Serious area attainment date 
extension.
    c. Comments and Responses. Any comments received on this section 
are addressed in the Response to Comments document found in the docket 
for this action.
2. Attainment Demonstration Requirements for Serious Areas
    a. Summary of Proposal. The proposal described the attainment 
demonstration and impracticability demonstration requirements for 
Serious nonattainment areas. The EPA proposed that a serious area plan 
must include an attainment demonstration that demonstrates how a state 
will attain the PM2.5 NAAQS by the applicable attainment 
date, must include analyses supporting the state's determination of its 
proposed attainment date, and must show that the area will attain the 
NAAQS as expeditiously as practicable, but not later than the tenth 
calendar year after designation. The proposal indicated that in order 
to establish that the attainment date is as expeditious as practicable, 
the state must explain why the control measures adopted in the 
attainment plan provide for the most expeditious attainment and must 
include all BACM and BACT controls in the analysis.
    b. Final Rule. The final rule requirements for Serious area 
attainment demonstrations are generally unchanged from the proposal. As 
described in Section IV.E of this

[[Page 58088]]

preamble, an attainment demonstration is a plan that demonstrates how a 
state will attain the PM2.5 NAAQS by the applicable 
attainment date. The EPA is finalizing a requirement that the 
demonstration for Serious areas must consist of: (i) Technical analyses 
such as base year and future year modeling of emissions which identify 
sources and quantify emissions that are contributing to violations of 
the PM2.5 NAAQS; and, (ii) analyses of future year projected 
emissions reductions and air quality improvement resulting from 
existing (i.e. already-adopted or ``on the books'') national, regional 
and local programs, and potential new local measures needed for 
attainment, including RACM and RACT and BACM and BACT controls for the 
area, as well as other measures either inside the nonattainment area or 
outside the nonattainment area but within the state that could 
potentially accelerate attainment. Each state with a Serious 
nonattainment area must submit an attainment plan with an attainment 
demonstration that includes analyses supporting the state's 
determination of its proposed attainment date. In all cases, the state 
must show that the area will attain the NAAQS as expeditiously as 
practicable, but not later than the tenth calendar year after 
designation. In order to establish that the attainment date is as 
expeditious as practicable, the state must explain why the control 
measures adopted in the attainment plan provide for the most 
expeditious attainment and must include all BACM and BACT controls in 
the analysis.
    A state with a Serious nonattainment area can also submit an 
impracticability demonstration (under CAA section 189(b)(1)(A)(ii)) as 
part of seeking an extension of the attainment date under CAA section 
188(e). The impracticability demonstration for a Serious area would be 
similar to an impracticability demonstration for Moderate areas because 
it must show that the area will not be able to attain the 
PM2.5 NAAQS by the latest possible statutory attainment 
date, which in this case is by the end of the tenth calendar year 
following designation.
    In order to support a Serious area impracticability demonstration, 
the state must show (through modeling) that attainment cannot be 
reached by the latest statutory Serious area attainment date, even if 
all RACM and RACT and BACM and BACT controls, as well as other measures 
either inside the nonattainment area or outside the nonattainment area 
but within the state (as may be necessary to meet the requirements of 
172(c)(6)), were implemented before the attainment date. Moreover, in 
addition to the Serious area impracticability demonstration, to support 
an extension of the attainment date, the Serious area plan must 
demonstrate (again, using air quality modeling) that it provides for 
attainment by the most expeditious alternative date practicable 
employing MSM, as specified in CAA section 188(e). (MSM are discussed 
in more detail in Section VI.J of this preamble). As a result, the 
required plan in the case of a Serious area that cannot attain by the 
statutory attainment date is both an impracticability demonstration (to 
justify an extension beyond the statutory attainment date) and an 
attainment demonstration that serves as the basis for proposing an 
appropriate alternative attainment date. Note that this is different 
from a Moderate area impracticability demonstration, which is not 
required to serve as the basis for proposing a new area attainment 
date.
    c. Comments and Responses. Any comments received on this section 
are addressed in the Response to Comments document found in the docket 
for this action.
3. Air Quality Modeling Required for Serious Area Attainment 
Demonstrations and Impracticability Demonstrations
    a. Summary of Proposal. The EPA proposed to require air quality 
modeling in support of both a Serious area attainment demonstration and 
a Serious area impracticability demonstration.
    b. Final Rule. The EPA is finalizing a requirement for states to 
submit air quality modeling in support of both attainment 
demonstrations and impracticability demonstrations for Serious 
PM2.5 nonattainment areas. Unlike the impracticability 
demonstration for Moderate areas described in CAA section 
189(a)(1)(B)(ii), the impracticability demonstration for Serious areas 
in CAA section 189(b)(1)(A)(ii) also requires air quality modeling 
establishing the most expeditious alternative attainment date 
practicable. Therefore, air quality modeling is a required element in 
all attainment demonstrations for Serious areas.
    Some commenters believed that both Moderate and Serious area 
impracticability demonstrations must include air quality modeling. The 
EPA does not agree and believes the statute only requires air quality 
modeling for Serious area impracticability demonstrations. This stems 
from the slightly different statutory construction in CAA section 
189(b)(1)(A) compared to CAA section 189(a)(1)(B). Section 189(b)(1)(A) 
of the CAA specifies an air quality modeling requirement as a 
parenthetical, which the EPA interprets to apply to both the 
requirements in CAA section 189(b)(1)(A)(i) [attainment demonstrations] 
and CAA section 189(b)(1)(A)(ii) [impracticability demonstrations]. 
Additionally, the fact that a Serious area impracticability 
demonstration must also include an attainment demonstration with an 
alternative attainment date logically supports the final rule 
conclusion that a Serious area impracticability demonstration must 
include air quality modeling. Modeling is needed to demonstrate 
attainment and to propose an alternative attainment date for the 
Serious area. This differs from a Moderate area impracticability 
demonstration, which only serves to demonstrate that attainment cannot 
be reached by the Moderate area attainment date. A Moderate area 
impracticability demonstration does not require a demonstration of 
attainment or setting of an alternative future attainment date. It 
merely starts the process of reclassifying an area to Serious and the 
eventual required submission of a Serious area implementation plan.
    Other than the timing of plan submissions and additional required 
elements of a Serious area plan (such as BACM and BACT), the relevant 
air quality modeling procedures and guidance for Moderate and Serious 
area plans are the same. See Section IV.E of this preamble for more 
details on the modeling requirements and guidance for all 
PM2.5 nonattainment areas.
    c. Comments and Responses. Any additional comments received on this 
section are addressed in the Response to Comments document found in the 
docket for this action.
4. Attainment Demonstrations Required To Be Submitted by an Area 
Reclassified to Serious
    a. Summary of Proposal. The proposal discussed the attainment 
demonstration requirements for Moderate nonattainment areas that 
subsequently are reclassified to Serious nonattainment. The EPA 
proposed that states with Moderate nonattainment areas that get 
reclassified to Serious nonattainment areas must first submit a 
Moderate area plan and then a separate Serious area plan.
    b. Final Rule. The EPA is finalizing requirements for states to 
submit a Moderate area attainment demonstration (or impracticability 
demonstration) and then if reclassified to Serious nonattainment, a 
separate Serious area attainment demonstration. Under CAA section 
189(a)(1)(B), a state with a

[[Page 58089]]

Moderate nonattainment area is required to submit a demonstration that 
the area either will attain or cannot practicably attain the NAAQS by 
the statutory attainment date. Regardless of whether the state submits 
an attainment demonstration or an impracticability demonstration for a 
Moderate area, if such an area is reclassified to Serious prior to or 
after failing to attain the applicable NAAQS, the state is required 
under CAA section 189(b)(1)(A) to submit a new attainment demonstration 
as part of an area's Serious area attainment plan. The separate 
statutory requirements for Moderate and Serious nonattainment areas 
anticipate two separate attainment plan submissions, and the EPA's 
existing guidance in the General Preamble and Addendum further support 
this expectation. While the state is required to submit a separate 
Serious area attainment plan, the EPA anticipates that certain control 
strategies may build upon those previously adopted and implemented as 
part of the Moderate area plan. For example, an area dominated by wood 
smoke emissions may not attain the standard by the statutory Moderate 
area attainment date because all necessary woodstove change-outs could 
not occur in that timeframe, but additional woodstove change-outs could 
occur by the statutory Serious area attainment date.
c. Comments and Responses
    Comment: Some commenters agreed with the EPA that areas seeking to 
be reclassified from moderate to serious must submit two separate 
attainment plan submissions. The commenter stated the Act promises that 
all areas, even the most polluted, will implement reasonably available 
controls and provide at least some interim health protections while 
preparing a serious area plan containing more protective requirements.
    Response: The EPA agrees with the comment. In the final rule, an 
area that is reclassified to Serious must submit both Moderate and 
Serious area plans, and all statutory requirements for a Moderate area 
(including RACT and RACM) must be met by the statutory deadline.
5. Future Year(s) To Be Modeled in Attainment Demonstrations
    a. Summary of proposal. A state performing a modeling analysis for 
an attainment demonstration or a Serious area impracticability analysis 
must select a future year for the analysis. The EPA proposed that for 
an attainment demonstration, a state should select the future modeling 
year such that all emissions control measures relied on for attainment 
will have been implemented by the beginning of that year. The EPA 
recommended the last year of the statutory attainment date as a 
starting point for Serious nonattainment area modeling demonstrations.
    b. Final Rule. The EPA is finalizing a requirement that all 
emissions control measures relied on for attainment must have been 
implemented by the beginning of the attainment year. See 40 CFR 
51.1011(b)(6). To demonstrate attainment, the modeling results for the 
nonattainment area must predict that emissions reductions implemented 
by the beginning of the last calendar year preceding the attainment 
date will result in PM2.5 concentrations that meet the level 
of the standard.\175\
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    \175\ Note that for purposes of the PM2.5 NAAQS, a 
determination of attainment (or failure to attain), which the EPA is 
required to make after the attainment date has passed, is based on 
ambient data from the most recent 3 years prior to the attainment 
date for the area.
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    While states should choose the future modeling year based on a 
number of factors, the EPA recommends the last year of the statutory 
attainment date as a starting point for modeling for two reasons. 
First, a state with a Serious area for which it submits an attainment 
date extension request under CAA section 188(e) must show that the area 
cannot practicably attain the NAAQS by the end of the tenth calendar 
year following designation of the area. Therefore, the appropriate 
future modeling year for making such a demonstration is the tenth year 
after designations. Even if a state does not submit (or does not intend 
to submit) a Serious area attainment date extension request, modeling 
the tenth year is a logical starting point to determine if attainment 
by year ten is likely. If attainment-level concentrations of 
PM2.5 are not expected in the tenth calendar year after 
designations, then the area must also, as a requirement to receive an 
extension of the Serious area attainment date, submit a demonstration 
(using air quality modeling) that provides for attainment by the most 
expeditious alternative date practicable, but no later than the end of 
the fifteenth year after designation, with the implementation of MSM 
(see Section VI.J of this preamble for details about MSM 
determinations).
    Second, even though attainment of any PM2.5 NAAQS is 
determined by averaging 3 years of ambient data, states do not have to 
model 2 years before the attainment date to show modeled attainment. 
Since the design value is an average of the annual or 98th percentile 
value for 3 consecutive years, attainment can still be shown even if 
concentrations exceed the NAAQS in one or more of the 3 years used to 
determine attainment (as long as the average of the three annual values 
is less than the NAAQS). Therefore, it is appropriate to model any of 
the 3 years used to determine attainment. For these reasons, it is 
acceptable, and may in fact be most efficient, for a state to begin the 
Serious area attainment demonstration process by modeling the final 
year of the statutory attainment date to determine future year modeled 
PM2.5 concentrations in the tenth year after designations.
    Because an area must attain ``as expeditiously as practicable,'' 
additional considerations are necessary before an attainment date can 
be established. Criteria for establishment of the Serious area 
attainment date are discussed in Section VI.I of this preamble. In 
evaluating such considerations, the question arises as to whether 
additional future modeling is required beyond the recommended final 
year modeling just discussed. For purposes of determining the 
attainment date that is as expeditious as practicable, the state must 
conduct future year modeling that takes into account growth and known 
controls (including any controls that were previously determined to be 
RACM and RACT for the area). For example, for an area designated 
nonattainment for the 2012 PM2.5 NAAQS in 2015 and 
subsequently reclassified to Serious in 2021, a future case scenario 
for the year 2025 (10 years after the initial nonattainment 
designation) would be needed to examine whether existing federal, 
state, and local measures (including previously identified and 
implemented RACT/RACM controls for the area) plus the BACM and BACT 
identified by the state would result in attainment. Since the EPA is 
finalizing the requirement that BACM and BACT must be determined 
independent of the attainment demonstration for the area, the future 
case scenario must include BACM and BACT controls in the analysis plus 
any additional measures on sources inside and outside of the 
nonattainment area (but within the state) that the state has identified 
as feasible to implement by the attainment date. Note that similar to 
RACM and RACT, BACM and BACT controls must be implemented within 4 
years after reclassification to Serious nonattainment. In order to 
justify an extension of the attainment date beyond the end of the tenth 
year after designation, the state must show that attainment by that 
date (including the anticipated emissions reductions from

[[Page 58090]]

RACM and RACT and additional reasonable measures, and BACM and BACT and 
additional feasible measures) would be impracticable. Any proposed 
attainment date after the 10 year period must include modeling of BACM 
and BACT controls plus the most stringent measures that are included in 
the implementation plan of any state and can be feasibly implemented in 
the area. The attainment date extension beyond 10 years can be for up 
to 5 additional years, but the proposed attainment date must also be 
shown to be as expeditious as practicable. Section VI.J of this 
preamble provides a complete discussion of the EPA's proposed 
interpretation of the statutory requirements for a Serious area 
attainment date extension under CAA section 188(e).
    As with Moderate area attainment demonstrations, the EPA believes 
that it is not necessary or reasonable to require states to model each 
and every year to determine the appropriate attainment date for a 
Serious PM2.5 nonattainment area given the resource demands 
associated with modeling.\176\ In some cases it may be reasonable to 
model one additional interim year before the maximum statutory 
attainment date. However, in most cases, the air quality benefits of an 
identified set of reasonable control measures, BACM and BACT and 
additional feasible control measures can be estimated through model 
sensitivity analyses and the development of sensitivity factors 
(factors to relate tons of emissions reductions in the area to 
PM2.5 concentration changes in the area). For example, 
states can model across the board percentage reductions in direct 
PM2.5 and/or precursor emissions (in separate model runs or 
using advanced modeling techniques such as DDM) to determine the impact 
of emissions reductions on PM2.5 concentrations in the area. 
This modeling can be performed with a single attainment year modeling 
platform, which is much less resource intensive than modeling multiple 
additional future years. The EPA strongly recommends that states 
discuss the selection of the future year(s) to model with their 
respective EPA Regional Office as part of the modeling protocol 
development process prior to embarking on the modeling.
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    \176\ States with Serious areas that request an attainment date 
extension beyond 10 years must model the tenth year after 
designation of the area as part of an impracticability 
demonstration, plus an additional year beyond that which represents 
the attainment date.
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    c. Comments and Responses. Any comments received on this section 
are addressed in the Response to Comments document found in the docket 
for this action.
6. Attainment Year Motor Vehicle Emissions Budgets
    As with Moderate areas, the transportation conformity rule requires 
that Serious area attainment plans establish motor vehicle emissions 
budgets for the area's attainment year. Therefore, once a Serious 
area's attainment date has been established, the state is required to 
establish motor vehicle emissions budgets for direct PM2.5 
and any relevant PM2.5 precursor for the attainment 
year.\177\ If a state's SIP submission demonstrates that a Serious area 
cannot attain by the end of the tenth calendar year after the area's 
designation, motor vehicle emissions budgets are not required for that 
tenth calendar year, but are required for the year that the state 
demonstrates to be the area's attainment year. A motor vehicle 
emissions budget for the purposes of a Serious area PM2.5 
attainment plan is that portion of the total allowable emissions within 
the nonattainment area allocated to on-road sources as defined in the 
submitted attainment plan.\178\ Such motor vehicle emissions budgets 
would be calculated using the latest planning assumptions and the 
latest approved motor vehicle emissions model available at the time 
that the attainment plan is developed, unless EPA approves the state's 
use of an alternative model.\179\
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    \177\ For more information on PM2.5 precursor 
requirements, see CAA section 93.102(b)(2)(iv) and (v) of the 
transportation conformity rule. See also the May 6, 2005, final 
transportation conformity rule that addressed requirements for 
PM2.5 precursors. (70 FR 24280).
    \178\ A state would also establish motor vehicle emissions 
budgets for an area's attainment year. Those budgets would be the 
motor vehicle emissions that the SIP establishes as being necessary 
to attain the NAAQS.
    \179\ If an area includes re-entrained road dust in the motor 
vehicle emissions budget, the latest approved version of AP-42 
should be used unless the EPA has approved an alternative model for 
the area.
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F. RFP Requirements

1. General Approach to RFP
    a. Summary of the Proposal. The EPA generally proposed that a state 
must submit an RFP plan as part of any attainment plan submission for a 
Serious nonattainment area in order to satisfy the statutory 
requirements for RFP, similar to a Moderate area attainment plan. The 
EPA proposed that the applicable baseline year must be the same year as 
that represented by the latest base year inventory for the Serious 
area. The EPA proposed that the state must include in its RFP analysis 
the anticipated emissions reductions expected to be achieved through 
the implementation of control measures required by the control strategy 
explained in Section VI.D of this preamble (BACM and BACT, additional 
feasible measures and MSM if applicable). As with RFP plans for 
Moderate areas, the EPA proposed that a state must submit RFP projected 
emissions as part of the RFP plan for any Serious PM2.5 
nonattainment area following the same guidance that applies to 
emissions inventories for attainment plans (see Section VI.B of this 
preamble for a complete discussion of emissions inventories for Serious 
area attainment plans). The EPA also proposed that motor vehicle 
emissions budgets must also be established for direct PM2.5 
and any PM2.5 plan precursor using the latest planning 
assumptions and the latest approved motor vehicle emissions model 
available at the time that the Serious area attainment plan is 
developed.\180\ It was not necessary to propose that RFP plans for 
Serious areas include motor vehicle emissions budgets for direct 
PM2.5 and any PM2.5 plan precursor because, as 
stated in the section of this rule that addresses RFP requirements for 
Moderate PM2.5 areas, the transportation conformity rule 
already requires that RFP plans establish motor vehicle emissions 
budgets. RFP plans would therefore be required to establish motor 
vehicle emissions budgets for direct PM2.5 and any relevant 
PM2.5 plan precursor. The EPA also proposed that guidance 
found in the Moderate nonattainment areas RFP section of the proposal 
should also apply to Serious nonattainment areas.
---------------------------------------------------------------------------

    \180\ Ibid.
---------------------------------------------------------------------------

    b. Final Rule. The EPA is finalizing rule provisions for Serious 
areas that essentially mirror the approach to Moderate areas found in 
Section IV.F of this preamble. The EPA is further clarifying 
application of those provisions by providing guidance that closely 
follows the Moderate area guidance regarding how to prepare an RFP 
plan, RFP projected emissions, geographic coverage of emission sources 
for RFP, and RFP requirements for multi-state nonattainment areas.
    As with a Moderate area attainment plan, the EPA is finalizing that 
a state must submit an RFP plan as part of any Serious area attainment 
plan in order to satisfy the statutory requirements for RFP. The plan 
must contain appropriate information to demonstrate that adequate 
emissions reductions will be achieved through control measures in the 
attainment plan in order to meet the

[[Page 58091]]

statutory definition of RFP. The plan must include three components: 
(1) An implementation schedule for control measures on sources in the 
nonattainment area, (2) RFP projected emissions for each applicable 
quantitative milestone year determined in Section VI.G of this 
preamble, based on the anticipated control measure implementation 
schedule; and (3) an analysis that demonstrates that this schedule of 
aggregate emissions reductions achieves sufficient progress toward 
attainment between the applicable baseline year to the attainment year. 
For additional discussion of each of the components of the RFP plan, 
refer to Section IV.F of this preamble. See 40 CFR 51.1012(a).
    The EPA requires that the applicable baseline year must be the same 
year as that represented by the latest base year inventory for the 
Serious area. The projected attainment year may be up to the end of the 
tenth year following designation for a Serious area that can 
demonstrate attainment pursuant to CAA section 189(b)(1)(A), or up to 
the end of the fifteenth year following designation for a Serious area 
that sought an extension of the statutory attainment date pursuant to 
CAA section 188(e).\181\ As with Moderate areas, the RFP analysis must 
clearly convey how the schedule for implementing the control strategy 
will provide for generally linear or stepwise progress towards 
attainment. If stepwise progress is more appropriate for the specific 
nonattainment area, the state is required to submit a clear rationale 
and supporting information to explain why generally linear progress 
towards attainment in the area is not appropriate (e.g., due to the 
nature of the nonattainment problem, the types of sources contributing 
to PM2.5 levels in the area, and the ability to perform 
timely implementation of control measures). For a Serious area, the EPA 
requires that the state must include in its RFP analysis the 
anticipated emissions reductions expected to be achieved through the 
implementation of control measures required by the control strategy 
described in Section VI.D of this preamble (BACM and BACT, additional 
feasible measures and MSM, if applicable). Similar to Moderate areas, 
the optional air quality analysis discussed in Section IV.F of this 
preamble is also available for use by a state preparing a Serious area 
RFP plan.
---------------------------------------------------------------------------

    \181\ As noted in Section V.B of this preamble, depending upon 
when the area is reclassified from Moderate to Serious, this base 
year inventory may need to be more recent than the inventory 
submitted with the Moderate area attainment plan.
---------------------------------------------------------------------------

    Additionally, the EPA requires that motor vehicle emissions budgets 
must also be established for direct PM2.5 and 
PM2.5 plan precursors using the latest planning assumptions 
and the latest approved motor vehicle emissions model available at the 
time that the Serious area attainment plan is developed.\182\ See 40 
CFR 51.1012(a).
---------------------------------------------------------------------------

    \182\ If an area includes re-entrained road dust in the motor 
vehicle emissions budget, the latest approved version of AP-42 
should be used unless the EPA has approved an alternative model for 
the area.
---------------------------------------------------------------------------

    Finally, similar to Moderate areas, Serious areas that are multi-
state or multi-jurisdictional shall provide RFP plans for each state 
represented in the nonattainment area that demonstrate RFP on the basis 
of common multi-state inventories. The states or jurisdictions within 
which the area is located must provide a coordinated RFP plan. For 
further information, see Section IV.F.5 of this preamble. See 40 CFR 
51.1012(b).
    c. Comments and Responses. Any additional comments received related 
to RFP are addressed Section IV.F of this preamble or in the Response 
to Comments document found in the docket for this action.

G. Quantitative Milestones

1. Summary of the Proposal
    The EPA proposed that a Serious area plan for an area that can 
demonstrate attainment by the statutory Serious area attainment date 
must also include quantitative milestones to be reached 7.5 and 10.5 
years from designation, to help assess the state's progress toward 
attaining the PM2.5 NAAQS in the event the area fails to 
attain by the applicable attainment date. For a Serious area that 
cannot demonstrate attainment by the statutory Serious area attainment 
date, the EPA proposed that the state must include in the Serious area 
attainment plan quantitative milestones to be achieved at 7.5, 10.5 and 
13.5 years from the area's date of designation.
    The EPA proposed that the general approach to selecting 
quantitative milestones outlined in the Moderate nonattainment area 
section of the proposal should apply to any attainment plan for a 
PM2.5 nonattainment area, independent of its classification. 
Specifically, the EPA proposed that states be allowed to select the 
quantitative milestones that they identify as appropriate and 
quantifiable and that will provide for objective evaluation of progress 
toward attainment in their Serious PM2.5 nonattainment area, 
and that the EPA, in its attainment plan approval process, will 
determine if they satisfy the statutory requirements of CAA section 
189(c). Additionally, the EPA proposed to require that, at a minimum, 
states must include in all attainment plans for Serious 
PM2.5 nonattainment areas a measure to confirm that some 
specific portion of BACM and BACT for the area has been implemented as 
appropriate in order to comply with the statutory requirement at CAA 
section 189(b)(1)(B).
2. Final Rule
    The final rule provisions for Serious area quantitative milestones 
are similar to such provisions for Moderate areas discussed in Section 
IV.G of this preamble. As required for Moderate areas, Serious area 
attainment plans must include quantitative milestones that demonstrate 
RFP towards attainment to be achieved every 3 years until the area is 
redesignated to attainment. To account for variations in the timing of 
possible additional plans that may be required beyond the Serious area 
attainment plan (such as a plan revision under CAA section 189(d) for a 
Serious area that fails to attain) the EPA is also clarifying, 
consistent with the requirements discussed in Section IV.G of this 
preamble for Moderate areas, that all Serious area attainment plans 
must contain one additional quantitative milestone to be met in the 3-
year period beyond the applicable Serious area attainment date. This 
will provide the EPA with appropriate tools necessary to continue to 
monitor the area's continued progress toward attainment in the event 
that the area fails to attain and develops a new attainment plan.
    For an area that is discretionarily reclassified to Serious under 
the provisions of CAA section 188(b)(1), the Serious area plan must 
contain quantitative milestones to be achieved by 7.5 years from the 
area's date of designation as nonattainment. In this case, the 7.5 year 
quantitative milestone that was submitted with the Moderate area plan 
may still be sufficient to demonstrate RFP or may have to be adjusted 
to reflect the difference in actual progress from the projections of 
the Moderate area plan. For an area that is reclassified to Serious 
under CAA section 188(b)(2) due to failure to attain, the 7.5 year 
quantitative milestones that were submitted with the Moderate area plan 
are still required and would be sufficient for the EPA to evaluate the 
area's progress toward attaining the NAAQS while the Serious area plan 
is being developed. All Serious area plans must also include 
quantitative milestones to be achieved 10.5 years from designation, to 
help assess the state's progress toward attaining the

[[Page 58092]]

PM2.5 NAAQS in the event the area fails to attain by the 
applicable attainment date. Finally, for a Serious area that cannot 
demonstrate attainment by the statutory Serious area attainment date, 
the state must include quantitative milestones to be achieved every 3 
years, such that the final milestone falls within the 3 years after the 
applicable Serious area attainment date. For example, if a state 
requests an attainment date extension to 14 years after designation 
pursuant to CAA section 188(e), the attainment plan should contain not 
only the 7.5 and 10.5 year milestones, but also milestones to be 
achieved 13.5 and 16.5 years from designation.
    The Addendum included guidance that recommended milestones ``should 
be addressed by quantifying and comparing the annual incremental 
emissions reductions which result from implementation of BACM and BACT 
(required within 4 years after the area is reclassified as serious) and 
from additional measures included in the final serious area SIP to 
those reductions which were identified in the SIP as quantitative 
milestones necessary to achieve the NAAQS by the applicable attainment 
date.'' \183\ The final rule does not specify that the milestones must 
be expressed in terms of emissions reductions. While the EPA notes that 
the Addendum contains this fundamental concept, it is impractical to 
expect that a state will always be able to quantify and compare real 
and projected emissions reductions, and submit a report to the EPA 
within 90 days of a given milestone, as required under CAA section 
189(c)(2). Therefore, the final rule requires that states selecting 
quantitative milestones for a Serious area plan should use the approach 
outlined for Moderate areas, as described in Section IV.G of this 
preamble. This approach applies to any attainment plan for a 
PM2.5 nonattainment area, independent of its classification. 
Specifically, the final rule requires that states be allowed to select 
the quantitative milestones that they identify as appropriate and 
quantifiable and that will provide for objective evaluation of progress 
toward attainment in their Serious PM2.5 nonattainment area, 
and that the EPA, in its attainment plan approval process, will 
determine if they satisfy the statutory requirements of CAA section 
189(c). See 40 CFR 51.1013(a)(2).
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    \183\ Addendum to the General Preamble, 59 FR 41998 (August 16, 
1994), at page 42016.
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    In addition to this general approach for selecting quantitative 
milestones and similar to what the final rule requires for Moderate 
area attainment plans, the final rule requires that, at a minimum, 
states must ensure that the quantitative milestones for Serious 
PM2.5 nonattainment areas assure RFP is being met by 
demonstrating that BACM and BACT have been implemented, as appropriate 
considering the timing of the milestone report, in order to comply with 
the statutory requirement at CAA section 189(b)(1)(B). The agency is 
further finalizing a corresponding requirement for Serious 
PM2.5 nonattainment areas that receive an attainment date 
extension. For these areas, the quantitative milestone should assure 
that RFP is being met by demonstrating that MSM for the area has been 
implemented as required pursuant to CAA section 188(e). This 
requirement was not specifically outlined in the proposal. However, 
while considering the requirements that were proposed for Serious 
areas, the EPA determined that including this additional provision 
within quantitative milestones would enable the agency to better 
evaluate progress toward attainment in areas that receive a Serious 
area extension. The EPA acknowledges that the precise quantifiable 
metric for a quantitative milestone (e.g., 50 percent of BACM and BACT 
measures implemented by milestone date 7.5 years from designation) 
would need to be determined on a case-by-case basis, as it would depend 
upon the date of reclassification of the area, which quantitative 
milestone (i.e., 7.5 or 10.5 years from designation), and the 
anticipated implementation timing and nature of the BACM and BACT 
controls themselves. Nonetheless, the EPA believes it is appropriate to 
include confirmation that such control measures and technologies are 
implemented as a metric that any state with a Serious nonattainment 
area must adopt as a quantitative milestone to demonstrate RFP (and 
thus must demonstrate compliance with when they submit their milestone 
report), as it derives from a statutory provision that applies to all 
Serious areas and thus represents a milestone that all Serious 
nonattainment areas must meet.
    Additional provisions discussed in the Moderate area quantitative 
milestones requirements in Section IV.G of the preamble also apply to 
Serious areas. Specifically, if a Serious area submitted the optional 
air quality targets with the RFP plan then an air quality based 
milestone (i.e., one that is expressed in terms of an ambient 
PM2.5 level) is strongly recommended to be included in order 
to confirm that the air quality target has been met for the 
quantitative milestone year. If used, this milestone will be compared 
to the most recently certified monitored ambient air data as part of 
the milestone report due after the area reaches each quantitative 
milestone date. For additional details on this optional provision, 
refer to Section IV.G of this preamble.
    Finally, the quantitative milestone report requirements outlined in 
Section IV.G of this preamble apply to Serious areas as well. 
Specifically, the requirements associated with the timing and contents 
of the quantitative milestone report submission for a Moderate area 
also requirements in a Serious area. For additional details on these 
requirements, refer to Section IV.G of this preamble. See 40 CFR 
51.1013(b).
3. Comments and Responses
    Any additional comments received on this section are addressed in 
Section IV.G of this preamble or in the Response to Comments document 
found in the docket for this action.

H. Contingency Measures

1. Summary of the Proposal
    In the proposal, the EPA proposed that the criteria for identifying 
and selecting contingency measures for a Serious area attainment plan 
should be the same as those for Moderate area plans. The EPA also 
proposed that, as with Moderate areas, a state may elect to rely on 
contingency measures that achieve emissions reductions not only from 
sources within the nonattainment area, but also from sources located 
outside the nonattainment area but within the state, provided that the 
measures on sources outside the designated nonattainment area are 
demonstrated to produce the appropriate air quality impact within the 
nonattainment area. As with contingency measures for Moderate area 
attainment plans, the EPA proposed that the emissions reductions 
associated with contingency measures for Serious area plans must be 
equal to approximately 1 year's worth of emissions reductions necessary 
to achieve RFP for the area, unless the state adequately demonstrates 
that some smaller amount of reductions is appropriate while the state 
is revising its attainment plan for the area. The agency also proposed 
options for submission deadlines for Serious area contingency measures.
2. Final Rule
    As noted in Section IV.G of this preamble, all PM2.5 
nonattainment areas must include in their attainment plans contingency 
measures consistent with

[[Page 58093]]

CAA section 172(c)(9). Contingency measures are additional control 
measures to be implemented in the event that an area fails to meet RFP 
requirements, fails to meet any quantitative milestone, fails to submit 
a quantitative milestone report or fails to attain the PM2.5 
standard by the applicable attainment date. These measures must be 
fully adopted rules or control measures that are ready to be 
implemented quickly upon a determination by the EPA that a failure 
occurred, and such measures are required to take effect without 
significant further action by the state or the EPA.
    The statutory contingency measure requirement at CAA section 
172(c)(9) is not superseded or subsumed by any requirement under 
subpart 4, nor does it apply only to Moderate area attainment plans. 
Thus, contingency measures are required for Serious PM2.5 
nonattainment areas as part of a state's Serious area attainment plan 
submission. Accordingly, the final rule requires the criteria for 
identifying and selecting contingency measures for a Serious area 
attainment plan that are the same as those for Moderate area plans. 
Specifically, the EPA is finalizing that the following requirements 
must be met in order for contingency measures to be approvable as part 
of a state's Serious area attainment plan submission:
    (1) Contingency measures must be fully adopted rules or control 
measures that are ready to be implemented quickly upon a determination 
by the Administrator of the nonattainment area's failure to meet RFP, 
failure to meet any quantitative milestone, failure to submit a 
quantitative milestone report or failure to meet the standard by the 
applicable attainment date.
    (2) The SIP must contain trigger mechanisms for the contingency 
measures, specify a schedule for implementation, and indicate that the 
measures will be implemented without significant further action by the 
state or by the EPA.
    (3) Contingency measures should consist of control measures that 
are not otherwise included in the control strategy for the SIP, or that 
achieve emissions reductions not otherwise relied upon in the control 
strategy for the area.
    (4) Contingency measures should provide for emissions reductions 
equivalent to 1 year's share of reductions needed to demonstrate 
attainment (i.e., the overall needed reductions divided by the number 
of years from the base year to the attainment year), or approximately 
equivalent to 1 year's worth of air quality improvement or emissions 
reductions proportional to the overall amount of air quality 
improvement or emissions reductions to be achieved by the area's 
attainment plan.
    The EPA is also finalizing its proposal to allow a state to rely on 
contingency measures that achieve emissions reductions on sources 
located outside the nonattainment area, but within the state provided 
that the measures on sources outside the designated nonattainment area 
are demonstrated to produce the appropriate air quality impact within 
the nonattainment area.
    As with contingency measures for Moderate nonattainment areas, the 
EPA allows a state under these circumstances to rely on additional 
reductions from federal or local measures already scheduled for 
implementation as part or all of their contingency measures. The EPA 
could consider such measures as meeting the contingency measure 
requirement as long as they produce emissions reductions in excess of 
those required to meet other statutory nonattainment provisions (such 
as to meet BACM/BACT requirements) and they can be relied on to achieve 
a sufficient portion of the actual emissions reductions necessary to 
reduce emissions in the area while the state develops a new plan to 
bring the area into attainment.\184\ As with contingency measures for 
Moderate area attainment plans, the EPA requires that the emissions 
reductions associated with contingency measures for Serious area plans 
should be approximately equivalent to 1 year's worth of emissions 
reductions necessary to achieve RFP for the area, unless the state 
adequately demonstrates that some smaller amount of reductions is 
appropriate while the state is revising its attainment plan for the 
area. See 40 CFR 51.1014(b)(2).
---------------------------------------------------------------------------

    \184\ See LEAN v. EPA, 382 F.3d 575 (5th Cir. 2004).
---------------------------------------------------------------------------

    The Addendum provided guidance related specifically to the 
selection and implementation of contingency measures for Serious 
nonattainment areas. First, the guidance indicated that ``for those 
moderate areas reclassified as serious, if all or part of the moderate 
area plan contingency measures become part of the required serious area 
control measures (i.e., BACM), then additional contingency measures 
must be submitted whether or not the previously submitted contingency 
measures had already been implemented. Further, the affected states 
must ensure that serious areas have adequate contingency measures 
considering, among other things, new information about the potential 
attainment shortfall for the newly reclassified serious area.'' \185\ 
The EPA continues to believe that this approach to the statutory 
contingency measure requirement is appropriate and is finalizing it for 
purposes of implementing the PM2.5 NAAQS in Serious 
nonattainment areas. See 40 CFR 51.1014.
---------------------------------------------------------------------------

    \185\ Addendum to General Preamble, 59 FR 41988 (August 16, 
1994), at 42015.
---------------------------------------------------------------------------

    With regard to the timing for implementing contingency measures, 
the EPA reiterates that the purpose of contingency measures is to 
ensure that corrective measures are put in place automatically at the 
time that the EPA makes a determination that an area has failed to meet 
RFP, failed to meet any quantitative milestone, failed to submit a 
quantitative milestone report or failed to meet the NAAQS by the 
applicable attainment date. For any nonattainment area, the EPA is 
required to determine within 90 days after receiving a state's RFP 
demonstration, and within 6 months after the attainment date for an 
area, whether the state has met their statutory obligations for 
demonstrating RFP or attaining the standard, as appropriate. As with 
Moderate areas, the EPA expects that contingency measures should become 
effective for Serious areas within 60 days of the EPA making its 
determination that the area failed to meet RFP or attain the NAAQS.
3. Comments and Responses
    Comment: One commenter supported the proposal that contingency 
measures may be approved if they will result in the equivalent air 
quality improvement as would be obtained by implementing measures 
obtaining 1 year's worth of emissions reductions needed to demonstrate 
attainment.
    Response: In the case where a state selected the optional RFP 
analysis that includes air quality targets, the EPA expects that an 
area contingency measures may be approved if they will result in 
approximately 1 year's worth of air quality improvement.

I. Attainment Dates

1. Summary of Proposal
    Section 188(c) of the CAA states that the attainment date for a 
Serious area is to be the end of the tenth calendar year after 
designation. The EPA proposed to interpret the reference to 
``designation'' in section 188(c) as meaning the ``effective date of 
designation.''
2. Final Rule
    As explained earlier, section 188 establishes the attainment dates 
for both Moderate and Serious areas. For a

[[Page 58094]]

Serious area, CAA section 188(c)(2) provides that ``the attainment date 
shall be as expeditiously as practicable but no later than the end of 
the tenth calendar year beginning after the area's designation as 
nonattainment.'' \186\ For example, for an area initially designated as 
a Moderate nonattainment area effective in April 2015 that is 
reclassified to Serious at some future date, the Serious area 
attainment date, absent any approved Serious area attainment date 
extension, would be no later than December 31, 2025 (the end of the 
tenth calendar year after designation). As discussed in Section IV.I of 
this preamble, the EPA interprets the references to ``designation'' in 
CAA section 188(c) as meaning ``effective date of designation,'' 
consistent with the agency's prior approach for implementing the 
previous PM2.5 NAAQS under subpart 1 and other NAAQS.
---------------------------------------------------------------------------

    \186\ The EPA believes that there is no real effect on 
attainment date determinations due to the small difference in 
statutory language in CAA section 188(c) basing the Moderate area 
attainment date on the ``sixth calendar year after the area's 
designation'' and the Serious area attainment date on the ``tenth 
calendar year beginning after the area's designation,'' (emphasis 
added).
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3. Comments and Responses
    Any additional comments received on this section are addressed in 
the Response to Comments document found in the docket for this action.

J. Attainment Date Extensions

    Background. Section 188(e) of the CAA provides that the EPA may 
grant a Serious area one attainment date extension of no more than 5 
years ``upon application by any state . . . if attainment by the 
[original Serious area attainment date] would be impracticable, the 
state has complied with all requirements and commitments pertaining to 
that area in the implementation plan, and the state demonstrates to the 
satisfaction of the Administrator that the plan for that area includes 
the most stringent measures that are included in the implementation 
plan of any state or are achieved in practice in any state, and can 
feasibly be implemented in the area.''
    The statute also includes factors that the EPA may consider in 
determining whether to grant the extension and the length of the 
extension, including ``the nature and extent of nonattainment, the 
types and numbers of sources or other emitting activities in the area 
(including the influence of uncontrollable natural sources and 
transboundary emissions from foreign countries), the population exposed 
to concentrations in excess of the standard, the presence and 
concentrations of potentially toxic substances in the mix of 
particulate emissions in the area, and the technological and economic 
feasibility of various control measures.'' \187\
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    \187\ Notably, these statutory criteria do not include specific 
ambient air quality criteria like the criteria that need to be met 
in the year prior to a Moderate area attainment date in order for 
the area to qualify for an attainment date extension under CAA 
section 188(d).
---------------------------------------------------------------------------

    The proposal described the four main elements the state must submit 
when requesting a Serious area attainment date extension: (1) A 
demonstration that attainment by the statutory Serious area attainment 
date is impracticable; (2) a demonstration that the area is complying 
with all requirements and commitments in the applicable attainment 
plan; (3) a demonstration that the plan includes the MSM that are 
included in the implementation plan of any state, or are achieved in 
practice in any state; and (4) a demonstration of attainment by the 
most expeditious alternative date practicable. The proposal also 
included a discussion about the timing of extension request 
submissions, and how to interpret the second element in cases where the 
extension request is submitted after the state has already submitted an 
initial Serious area attainment plan. These topics are addressed in the 
following sections.
1. Demonstration That Attainment by the Statutory Serious Area 
Attainment Date is Impracticable
    a. Summary of Proposal. The proposed rule discussed the 
requirements for a demonstration to show that it is impracticable for a 
Serious area to attain by the attainment date. This demonstration 
involves evaluating through air quality modeling whether all best 
available control measures will enable the area to attain the standard 
by the attainment date.
    b. Final Rule. This section remains relatively unchanged from the 
proposal. In order to demonstrate that it is impracticable for an area 
to attain by the attainment date, the state would have to show that the 
implementation of all BACM/BACT (and additional feasible measures) will 
not bring the area into attainment by the statutory Serious area 
attainment date (i.e., by no later than the end of the tenth calendar 
year after designation).\188\ The statutory provision for demonstrating 
that it is impracticable to attain by the Serious area attainment date 
requires that the demonstration be based on air quality modeling (see 
CAA section 189(b)(1)(A)). Additional guidance on this demonstration is 
provided in Section VI.E of this preamble.
---------------------------------------------------------------------------

    \188\ This proposed approach parallels the EPA's proposed 
approach, described earlier in this preamble, for the 
impracticability option for Moderate areas under CAA section 
189(a)(1)(B) in which all measures that qualify as RACM and RACT and 
all additional reasonable measures are required before a Moderate 
area plan could show impracticability of attainment by the statutory 
Moderate area attainment date (the end of the sixth calendar year 
after designation).
---------------------------------------------------------------------------

    c. Comments and Responses. Any additional comments received on this 
section are addressed in the Response to Comments document found in the 
docket for this action.
2. Demonstration That the Area is Complying With all Requirements and 
Commitments in the Applicable Implementation Plan
a. Extension Request Submitted at the Same Time as the Serious Area 
Attainment Plan
i. Summary of Proposal
    The EPA proposed to interpret the criterion under CAA section 
188(e) that requires a state to have ``complied with all requirements 
and commitments pertaining to that area in the implementation plan'' 
simply to mean that the state has implemented the control measures in 
the SIP revisions it has submitted to address the applicable 
requirements in CAA sections 172 and 189. For a Serious area attainment 
date extension request being submitted contemporaneously with the 
``original'' Serious area attainment plan for the area, the EPA 
proposed to read CAA section 188(e) not to require the area to have a 
fully approved attainment plan that meets the CAA's requirements for 
Moderate areas. The EPA also proposed to read this provision not to bar 
an extension if all or part of an area's Moderate area plan is 
disapproved or has been promulgated as a FIP, provided the area has 
complied with all of the requirements in the applicable FIP, or in the 
applicable SIP and FIP.\189\
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    \189\ In Vigil v. Leavitt, 366 F.3d 1025, amended at 381 F.3d 
826 (9th Cir. 2004), the court indicated that an area that had 
previously failed to meet a requirement of the CAA could still be 
eligible to receive an attainment date extension: ``Nowhere does the 
provision limit extensions to those states that never made a misstep 
in their efforts to comply with the Act.''
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ii. Final Rule
    Some commenters stated that an area should only be able to receive 
an extension if the Moderate area plan had been fully approved by the 
EPA. Other commenters agreed with the EPA's proposed approach. They 
suggested that if a part of the Moderate plan had been disapproved, but 
it was clear that the

[[Page 58095]]

area could not practicably attain by the Serious area attainment date, 
then the area should be able to receive an extension. Other commenters 
suggested that an area should not be deprived an extension if the 
approval of all or part of the Moderate area attainment plan is delayed 
due to logistical reasons or the EPA's inability to take final action 
in a timely manner.
    The final rule does not require the area to have a fully approved 
Moderate area plan when the attainment date extension request is 
submitted at the same time as the Serious area plan. An extension is 
allowed if the area is complying with all Moderate area requirements 
and commitments pertaining to that area in the state's submitted 
Moderate area implementation plan, but the plan does not need to be 
fully approved by EPA. The EPA considers this to be a reasonable 
interpretation of the statute because, as noted by commenters, there 
may be various reasons why an area may not have a fully approved 
Moderate area SIP by the time an extension request may be granted.
iii. Comments and Responses
    Any additional comments received on this section are addressed in 
the Response to Comments document found in the docket for this action.
b. Extension Request Submitted After Submission of an ``Original'' 
Serious Area Attainment Plan
i. Summary of Proposal
    For a Serious area extension request that was submitted after 
submission of an ``original'' Serious area attainment plan that 
contained an attainment demonstration meeting the requirements of CAA 
section 189(b)(1)(A)(i), the EPA proposed to read CAA section 188(e) 
not to require the area to have a fully approved attainment plan that 
meets the CAA's requirements for Serious areas, but to have a fully 
approved Moderate area attainment plan. The EPA stated that this 
proposed interpretation of this criterion would apply whether the area 
was reclassified to Serious under the EPA's discretionary authority 
(CAA section 188(b)(1)) or by operation of law upon failing to attain 
by the Moderate area attainment date (CAA section 188(b)(2)).
    The proposal also requested comment on an ``alternative 
interpretation'' that, as pointed out by some commenters, appears to 
also have mistakenly required the same thing as the first option: That 
the state would need to have a fully approved Moderate area attainment 
plan in order to receive an extension.
    The EPA notes that Section VI.C of this preamble, Timing of 
Extension Request Submission, also discusses this issue. It requested 
comment on whether, for areas that had already submitted Serious area 
attainment plans, it would be appropriate that the state must have 
complied with all requirements and commitments in the area's initial 
Serious area plan (the EPA's preferred option), or in the Moderate area 
plan.
ii. Final Rule
    After considering the comments received on this issue, the EPA is 
finalizing an approach that requires that, where a Serious area 
attainment date extension is being submitted after the initial Serious 
area attainment plan has been submitted, the state would need to 
demonstrate that it was complying with all Serious area requirements 
and commitments pertaining to the area in the plan it had initially 
submitted. However, it would not need a fully approved Serious area 
attainment plan. The EPA believes the state should not be prevented 
from obtaining an attainment date extension in the event the EPA is 
unable to take final action on a submitted plan in a timely manner. The 
original proposal did not specify Serious area provisions implementing 
this approach, but commenters noted the proposed analogous provisions 
for Moderate areas seeking 1-year extensions, and suggested that EPA 
should adopt a similar approach for Serious areas. Under this approach, 
the state would not need a fully approved Serious area plan; it would 
be able to receive an extension if it had already submitted the Serious 
area plan but had not received EPA approval yet, and if it was 
complying with all Serious area requirements and commitments pertaining 
to the area in the state's implementation plan. The EPA also considered 
an alternative option wherein the state would be able to receive an 
extension only if it had a fully approved Serious area attainment plan. 
The commenters did not favor this option, nor does the EPA.
iii. Comments and Responses
    Any additional comments received on this section are addressed in 
the Response to Comments document found in the docket for this action.
3. Demonstration That the Plan Includes the MSM That Are Included in 
the Implementation Plan of Any State, or Are Achieved in Practice in 
Any State
    To qualify for any extension of a Serious area attainment date, CAA 
section 188(e) requires a state to ``demonstrate to the satisfaction of 
the Administrator that the plan for the area includes the most 
stringent measures that are included in the implementation plan of any 
state, or are achieved in practice in any state, and can feasibly be 
implemented in the area.'' In its prior guidance in the Addendum, the 
EPA interpreted the term ``most stringent measures'' (MSM) to mean the 
maximum degree of emission reduction that has been required or achieved 
from a source or source category in any other attainment plans or in 
practice in any other states and that can feasibly be implemented in 
the area seeking the extension, such as what LAER represents for new or 
modified sources under the NNSR permit program.\190\
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    \190\ Addendum to the General Preamble, 59 FR 41998 (August 16, 
1994), at page 42010.
---------------------------------------------------------------------------

    a. Summary of Proposal. The proposal suggested that a state would 
need to follow a process for determining MSM for a Serious 
nonattainment area that is generally similar to proposed Option 2 for 
BACM/BACT described in Section VI.D of this preamble, which would 
include exemptions from MSM for sources in de minimis source categories 
if such measures did not collectively advance the attainment date for 
the area by at least 1 year. The EPA also proposed an alternative 
approach for determining MSM for a Serious nonattainment area that 
would provide for de minimis source category exemptions for MSM only 
for those source categories that do not contribute significantly to 
ambient PM2.5 concentrations in the Serious nonattainment 
area, an approach more closely aligned with proposed Option 1 for 
determining BACM/BACT.
    For each approach, the proposal described a five step process for 
determining MSM: (1) Update the emissions inventories for the 
nonattainment area; (2) identify de minimis source categories through 
modeling; (3) identify potential MSM; (4) compare MSM to control 
measures already adopted in the SIP for the nonattainment area; and (5) 
adopt and implement any MSM that are more stringent than any measures 
that are already approved into the SIP. The proposal requested comment 
on whether the two proposed approaches are sufficiently consistent with 
the agency's respective proposed

[[Page 58096]]

approaches to BACM/BACT determinations.
    b. Final Rule. Almost all comments received on this section 
involved the issue of whether the rule should allow for de minimis 
source categories to be exempted in the process of determining MSM. A 
few commenters supported the identification of de minimis source 
categories and their exemption from the MSM requirement. These 
commenters were split in terms of their preference for the two de 
minimis approaches that were presented. Some commenters suggested that 
under any approach, an area could still exclude a measure from MSM 
based on the inability to feasibly implement the measure in the area. 
Some commenters stated that it would be too burdensome to require a 
state to evaluate whether a particular source category had a 
``significant'' or de minimis impact on air quality, while others 
supported the approach. One group of commenters disagreed with the 
notion that a Serious area could exempt de minimis sources from the MSM 
requirement in the first place. They stated that de minimis exemptions 
would not be appropriate for MSM, for which the CAA has expansive 
language requiring the most stringent measures required in any SIP or 
achieved in practice in any state.
    After considering the comments received on the de minimis source 
category issue, the EPA is adopting a final rule that does not include 
an explicit de minimis source category exemption in determining MSM. 
The agency's reasons for not allowing a de minimis source category or 
de minimis impact concept, articulated in prior sections on determining 
RACM/RACT (Section IV.D) and BACM/BACT (Section VI.D), apply equally 
here. Moreover, the EPA believes it would be particularly inappropriate 
to allow for a de minimis source category approach for MSM. The statute 
requires MSM to be implemented because the area is unable to attain the 
standard within 10 years of designation and has a more severe air 
quality problem. Congress clearly intended for such areas to more 
widely explore potential control measure possibilities, and a de 
minimis source category exclusion would be contrary to that intent.
    The EPA believes the rule provides sufficient flexibility in the 
MSM area control measure analysis and attainment demonstration process 
enabling states to identify sources that should not be subject to 
control measures, including the ability to develop precursor 
demonstrations to exclude precursors from control requirements, and to 
consider case-specific factors in determining technological and 
economic feasibility of potential control measures. If the final rule 
were to include an explicit step to conduct a de minimis source 
category analysis on the entire inventory early in MSM process, the EPA 
also believes that there is a risk that such an analysis may bring 
about investment of scarce time and analytical resources on analysis of 
categories to exclude rather than on the identification of the most 
stringent control measures necessary to attain the standard. As noted 
in Section IV.D of this preamble on Moderate areas, and again in 
[serious area section] the EPA also finds that from a technical 
perspective, it would be very challenging to implement a de minimis 
source category process in a consistent manner nationally without clear 
guidelines describing how narrowly or how broadly a de minimis 
exemption could apply to a ``source category,'' or how the technical 
analysis would need to be performed. For all of these reasons, a de 
minimis source category concept is not included in the final rule for 
MSM.
    Process for determining MSM. The following sections describe the 
process for determining MSM that is finalized in this rule: (a) Update 
emissions inventories; (b) identify potential MSM; (c) compare MSM to 
control measures already adopted in the SIP for the nonattainment area; 
and (d) adopt and implement any MSM that are more stringent than any 
measures that are already approved into the SIP. (See 40 CFR 
51.1010(b)(1)-(4).)
i. Update Emissions Inventories
    The first step would be for the state to update as needed the 
emissions inventory of direct PM2.5 and PM2.5 
precursor sources and source categories in the Serious nonattainment 
area required under CAA section 172(c)(3) for any attainment plan 
submission. The EPA expects that the state would meet this inventory 
requirement as part of its Serious area attainment plan submission 
without any additional work if the state submits the Serious area 
attainment date extension request simultaneously with the plan itself. 
However, in the event the attainment date extension request is 
submitted after the ``original'' Serious area attainment plan for the 
area (i.e., toward the end of the Serious area attainment period), then 
the state must submit a more recent, complete and accurate emissions 
inventory that meets the same emissions inventory requirements for 
Moderate and Serious PM2.5 nonattainment areas pursuant to 
CAA section 172(c)(3), as well as an attainment projected inventory as 
part of the new Serious area attainment plan for the area. The 
inventories submitted to support a Serious area attainment plan must 
also include point sources meeting the lower major stationary source 
threshold in 40 CFR part 51, subpart A.
ii. Identify Potential MSM
    The second step in determining MSM involves identifying the 
potentially MSM in other state implementation plans for 
PM2.5 or other NAAQS, or that are used in practice in other 
states for controlling emissions from sources similar to those listed 
in the emissions inventory. This information can be obtained from a 
number of sources, including state regulations on the books, state 
summaries of control measures, state permitting databases, the RACT/
BACT/LAER Clearinghouse, and control measure compilations developed by 
regional or state/local organizations. Elsewhere in this preamble, the 
EPA recommends that a state identify potential measures for 
consideration as RACM/RACT or BACM/BACT by evaluating control measures 
implemented by other states to meet PM2.5 NAAQS or other 
NAAQS. Thus, a state seeking to identify MSM should be able to start 
its process using the work already undertaken for the nonattainment 
area's RACM and BACM determinations and to make updates to the list of 
potential control measures accordingly.
    For each measure, the state is required to determine its 
technological and economic feasibility for sources in the area. States 
should apply more stringent criteria for determining the feasibility of 
potential MSM than that described for BACM and BACT in Section VI.D of 
this preamble. In some situations, MSM could involve increasing the 
coverage of measures that were already adopted and implemented as BACM 
and BACT (for example, changing out an even greater percentage of 
woodstoves in an area, if such sources were major contributors to the 
air quality problem in the nonattainment area).
    However, because BACM and BACT represent the ``best'' level of 
control feasible for an area, in some cases it may be possible for the 
MSM requirement to result in no more controls and no more emissions 
reductions in an area than result from the implementation of BACM and 
BACT. Stated another way, there may be sources or categories for which 
no other feasible controls exist beyond what a state has already 
adopted as BACM or BACT. Given the strategy in the nonattainment 
provisions of the CAA to offset longer attainment timeframes with more 
stringent control requirements, the EPA therefore

[[Page 58097]]

interprets the MSM provision so as to increase the potential that it 
will result in additional controls beyond the set of measures adopted 
as BACM and BACT. In the MSM analysis, in addition to identifying 
additional candidate MSM, the state is required to reanalyze any 
measures that were rejected during the state's BACM and BACT analysis 
for the area to see if they are now feasible for the area given the 
potentially longer attainment date (up to 5 years after the statutory 
Serious area attainment date), or given the changes that have occurred 
in the interim that improve the feasibility of previously rejected 
measures.
iii. Compare MSM to Control Measures Already Adopted in the SIP for the 
Nonattainment Area
    The third step requires the state to compare the potential MSM that 
have been identified for each source type or source category against 
the measures, if any, already adopted into the Serious area SIP for 
that source category to determine if such MSM would provide any 
additional reductions. This comparison will be used in determining what 
measures to adopt in the next step.
iv. Adopt and Implement Any MSM That are More Stringent Than Any 
Measures That Are Already Approved Into the SIP
    The fourth step requires the adoption of any MSM that are more 
stringent than existing measures as a regulation, and requires 
submission of the regulation as part of the SIP, as well as expeditious 
implementation of the regulation. For any measures that the state 
determines cannot be feasibly implemented in the area, it should 
provide a reasoned justification for rejecting the potential MSM.
    The EPA notes that CAA section 188(e) does not identify a deadline 
for a state to implement MSM, whereas elsewhere the statute establishes 
a deadline for implementing RACM and RACT and BACM and BACT [see CAA 
sections 189(a)(1)(C) and 189(b)(1)(A)], respectively). However, 
because the clear intent of CAA section 188(e) is to minimize the 
length of a Serious area attainment date extension, the EPA requires 
that the implementation of MSM must be as expeditious as practicable 
but no later than 1 year prior to the alternate Serious area attainment 
date identified by the state in its extension request.
    c. Comments and Responses. Any additional comments received on this 
section are addressed in the Response to Comments document found in the 
docket for this action.
4. Demonstration of Attainment by the Most Expeditious Alternative Date 
Practicable
    Section 189(b)(1)(A) of the CAA requires that a Serious area plan 
demonstrate attainment, using air quality modeling, by the most 
expeditious date practicable after the statutory Serious area 
attainment date. This demonstration is the final criterion that must be 
met before the EPA may consider granting an extension. The agency's 
determination of whether the plan provides for attainment by the most 
expeditious date practicable would depend on whether the plan provides 
for implementation of BACM and BACT by the statutory implementation 
deadline and MSM as expeditiously as practicable. In no case would a 
state be able to seek an extension of a Serious area attainment date to 
a date more than 5 years past the statutory attainment date for Serious 
areas. Section VI.E of this preamble describes the EPA's proposed 
requirements for attainment demonstration modeling for Serious area 
attainment plans.
5. Apply for an Attainment Date Extension
    The state would have to apply to the EPA for any extension of a 
Serious area attainment date. The request would have to accompany an 
attainment plan submission containing an attainment demonstration 
showing attainment by the most expeditious alternative date 
practicable, and the state would need to submit modeling as part of the 
attainment demonstration in accordance with Section VI.E of this 
preamble. Furthermore, the state would have to provide the public 
reasonable notice and a public hearing on the attainment date extension 
request before submitting it to the EPA, as the EPA would consider it 
an integral part of the attainment demonstration and part of the 
revised SIP submission which is subject to the requirements of the CAA 
and federal regulations for public notice and hearing on SIP revisions.
6. Timing of Extension Request Submission
    The EPA has identified two potential Serious area attainment date 
extension scenarios: (1) The more straightforward scenario where the 
attainment date extension is included with the initial Serious area 
plan, and (2) the scenario where a state may prepare and fully 
implement a timely Serious area plan that includes a modeling analysis 
that demonstrates the area would attain no later than the statutory 
Serious area attainment date (the end of the tenth calendar year 
following designation), and yet the state may see as the attainment 
date nears that the Serious area will in fact fail to attain by its 
projected attainment date. While the statute provides a remedy to be 
instituted immediately upon failure of a Serious area to attain the 
standard (through contingency measures and other measures stipulated in 
CAA section 189(d)), the EPA also believes that the criteria of CAA 
section 188(e) could be applied after a state submits a Serious area 
attainment plan but prior to the area failing to attain (as long as the 
area had not already been granted a prior Serious area attainment date 
extension under CAA section 188(e)).
    In the first scenario, there is no need to specify any further 
timing requirements beyond those previously described for Serious area 
plan submission. However, for the second scenario the final rule needs 
to specify a due date for the request. The EPA believes that it would 
be acceptable for a state to submit a Serious area attainment date 
extension request (as described earlier) together with a new Serious 
area attainment plan meeting all of the statutory requirements that 
apply to such plans. The state should submit the extension request and 
new implementation plan to EPA as early as possible, but the final rule 
requires that it must be submitted no later than 60 days prior to the 
approved attainment date for the area or, in the absence of an approved 
attainment date, no later than 60 days prior to the applicable 
statutory attainment date for Serious areas (i.e., the end of the tenth 
year after designation). See 40 CFR 51.1005(b)(6). The EPA believes 
that this deadline is necessary due to its statutory obligation to 
determine whether the area attained by the attainment date. In order to 
preserve the possibility that EPA could review and take action on the 
new attainment plan for the area and the accompanying attainment date 
extension request prior to its deadline for making the attainment 
determination the EPA estimates that the 60-day deadline provides the 
minimum amount of necessary time. The EPA notes that during this time, 
it would have to ascertain the status of compliance with all 
requirements and commitments in the Moderate and initial Serious area 
attainment plans for the area, evaluate the state's justification for 
the selection of the alternate attainment date (including modeling), 
and review provisions for the implementation of MSM).

[[Page 58098]]

VII. Requirements Under CAA Section 189(d) for PM2.5 Serious 
Areas That Fail To Attain the NAAQS by the Applicable Attainment Date

    Background. In the event that a Serious area fails to attain the 
PM2.5 NAAQS by the applicable attainment date, CAA section 
189(d) requires that ``the state in which such area is located shall, 
after notice and opportunity for public comment, submit within 12 
months after the applicable attainment date, plan revisions which 
provide for attainment of the . . . standard and, from the date of such 
submission until attainment, for an annual reduction in PM10 
or PM10 precursor emissions within the area of not less than 
5 percent of the amount of such emissions as reported in the most 
recent inventory prepared for such area.''
    In addition to the requirement for the submission of control 
measures providing for a 5 percent reduction in emissions of certain 
pollutants on an annual basis, the EPA interprets CAA section 189(d) as 
requiring the State to submit an attainment plan that includes the same 
basic statutory plan elements that are required for other attainment 
plans. Because section 189(d) does not include a specific provision 
specifying a new attainment date, the EPA relies on sections 179(d)(3) 
and 172(a)(2) of the CAA to establish the attainment date for such 
plans to be as expeditiously as practicable, and no later than five 
years from the effective date of the EPA's determination that the area 
failed to attain. Pursuant to those provisions, the Administrator may 
also extend the attainment date to the extent the Administrator deems 
appropriate, for a period no greater than 10 years from the effective 
date of the EPA's determination that the area failed to attain, 
considering the severity of nonattainment and the availability and 
feasibility of pollution control measures. The state must submit as 
part of the new attainment plan a justification explaining that it 
represents an attainment date that is as expeditious as practicable.
    A state must submit to the EPA its plan to meet the requirements of 
CAA section 189(d) in the form of a complete attainment plan submission 
that includes the following elements: (i) Base year and attainment 
projection year emissions inventory requirements; (ii) additional 
attainment plan control strategy requirements, including control 
measures and a demonstration that each year the area will achieve at 
least a 5 percent reduction in emissions of direct PM2.5 or 
a 5 percent reduction in emissions of a PM2.5 plan precursor 
based on the most recent emissions inventory for the area; (iii) 
attainment demonstration and modeling; (iv) RFP plan and quantitative 
milestones; and (v) contingency measures. A state with a Serious 
PM2.5 nonattainment area that fails to attain the NAAQS by 
the applicable Serious area attainment date must also address any 
statutory requirements relevant to Moderate nonattainment areas and 
Serious nonattainment areas under CAA sections 172 and 189 of the CAA 
that have not already been satisfied. These elements are discussed in 
more detail in the following sections.

A. Plan Due Dates

1. Summary of Proposal
    The proposed rule indicated that under CAA section 189(d), the 
state would be required to submit the attainment plan for a Serious 
area that failed to attain the NAAQS by the Serious area attainment 
date within 12 months after the applicable attainment date.
2. Final Rule
    The final rule remains unchanged from the proposal. Section 189(d) 
of the CAA requires a state with a Serious PM10 
nonattainment area that failed to attain the NAAQS by the applicable 
Serious area attainment date to submit a new attainment plan submission 
for the area within 12 months after the missed ``applicable attainment 
date.'' The EPA finds that the most straightforward interpretation of 
the statutory language is that the state must submit a new attainment 
plan for the area--with all required elements--within 12 months after 
the missed applicable attainment date. Although the EPA may take up to 
6 months to make a determination that the area failed to attain, the 
text of the statute ties the 12-month SIP due date to the missed 
attainment date, not to the date that the EPA determines that the area 
failed to attain. Because all attainment dates for implementation of 
the PM2.5 NAAQS under subpart 4 are expressed in terms of 
the end of a calendar year, the new due date for a SIP required under 
CAA section 189(d) also would be due on December 31--of the year 
following the area's Serious area attainment date. This requirement is 
consistent with the manner in which the CAA section 189(d) SIP 
submission date has been interpreted for implementation of the 
PM10 NAAQS in the past. The EPA recognizes that this 
statutory timeline is shorter than for Moderate or Serious area 
attainment plans, but expects that, given the prior planning history 
for such areas, much of the analyses to support these new attainment 
plan submissions will be based on updates to previous analyses, which 
would require less time than generating new analyses. In any event, it 
is clear from the face of the statute that Congress intended that 
states with areas that fail to attain the NAAQS by the outermost 
statutory attainment date for Serious areas must proceed more quickly 
to revise their SIPs to provide for attainment of the NAAQS.
3. Comments and Responses
    Any comments received on this section are addressed in the Response 
to Comments document found in the docket for this action.

B. Emissions Inventory Requirements

1. Summary of Proposal
    The EPA also proposed that the inventory requirements under section 
189(d) for Serious areas that fail to attain by the attainment date 
should be the same as those for Moderate and Serious areas, but with a 
change to the appropriate year for the inventory. The EPA proposed that 
for these areas, the inventory year must be one of the 3 years from 
which monitored data was used to determine that the area failed to 
attain the PM2.5 NAAQS by the applicable Serious area 
attainment date. In addition, the EPA proposed an alternative approach 
that would allow the state to use an earlier year than one of the 3 
years used to determine that the area failed to attain. As proposed, 
this alternative approach would require written justification that 
included an explanation of how the inventory modifications adequately 
incorporate emissions reductions projected to be achieved through the 
implementation of BACM and BACT, and additional feasible control 
measures submitted with the original Serious area attainment plan for 
the area, and through implementation of MSM if appropriate.
2. Final Rule
    The statute requires states to use an emissions inventory that 
meets the requirements of section 172(c)(3). The final rule recommends 
using an inventory for one of the 3 years for which air quality data 
were used to determine that the area failed to attain in order to meet 
this requirement. However it also allows the state to use an earlier 
inventory year under certain circumstances.
    As with all other attainment plan submissions required for Moderate 
and Serious PM2.5 nonattainment areas, a

[[Page 58099]]

state must develop its submission to meet CAA section 189(d) based on 
``the most recent inventory prepared for such [nonattainment] area.'' 
This inventory must meet the same requirements that would apply to any 
other emissions inventory submitted for a PM2.5 
nonattainment area to meet the requirements of CAA section 172(c)(3), 
which requires ``a comprehensive, accurate, current inventory of actual 
emissions of the relevant pollutants'' in the nonattainment area. 
Therefore this rule requires that the inventory submitted with an 
attainment plan to meet CAA section 189(d) requirements must also meet 
the EPA's regulatory requirements for such emissions inventories as 
described earlier in this preamble under Section IV.B of this preamble 
(for Moderate area attainment plans) and Section VI.B of this preamble 
(for Serious area attainment plans).
    One important aspect of the emissions inventory required to be 
submitted with an attainment plan under CAA section 189(d) is its role 
as the basis for calculating the emissions reductions of direct 
PM2.5 or any PM2.5 plan precursor necessary to 
satisfy the 5 percent annual reduction criterion of CAA section 189(d). 
For this reason, the ``most recent inventory'' for the area must not 
only meet the criteria described for a base year inventory submitted 
pursuant to CAA section 172(c)(3) and in Section VI.B of this preamble, 
but it also must fully account for emissions reductions achieved to 
date through the implementation of all RACM and RACT, BACM and BACT, 
additional reasonable and feasible measures, and MSM (as applicable) 
submitted with the Moderate and original Serious area attainment plans 
for the area. In this way, the state will calculate the additional 
reductions that the nonattainment area will need beyond those already 
required in order to fulfill the requirements of CAA section 189(d) and 
bring the area into attainment as expeditiously as practicable.
    To ensure that the inventory is representative of the nonattainment 
problem in the area current at the time of the CAA section 189(d) 
submission, the EPA strongly recommends that the inventory year be one 
of the 3 years from which monitored air quality data were used to 
determine that the area failed to attain the PM2.5 NAAQS by 
the applicable Serious area attainment date. The EPA believes that 
associating the inventory with one of these 3 years is reasonable in 
light of the fact that some control measures (e.g., BACM and BACT 
controls and additional feasible measures) for sources in the area may 
not be implemented until the beginning of the attainment year. Thus, 
using an emissions inventory for one of those 3 years will help ensure 
that the inventory adequately captures the emissions reductions already 
achieved through the prior implementation of control measures for 
Moderate and Serious areas.
    The EPA recognizes that the timing and resource requirements for 
inventory preparation may make it challenging in some cases for a state 
to use an inventory for a year that is one of the 3 years from which 
monitored data were used to determine that the area failed to attain 
the NAAQS by the applicable attainment date. To address such cases, the 
final rule allows states to use an earlier inventory year in the plan, 
provided that (1) the year is selected in consultation with the 
appropriate EPA Regional Office, and (2) the state provides a written 
justification for selecting the earlier year in its SIP submission. See 
51.1008(c)(1). At a minimum, the inventory must adequately incorporate 
emissions reductions projected to be achieved through the 
implementation of BACM and BACT, and additional feasible control 
measures submitted with the original Serious area attainment plan for 
the area, and MSM if appropriate. Because these emissions reductions 
may have occurred after the inventory year the state intends to use, 
adjustments to the original inventory for that year would need to be 
made to reflect those reductions. The written justification must also 
include an explanation of how those reductions have been incorporated 
into the inventory. In considering use of an ``older'' inventory, the 
EPA recommends that states weigh the possible impact of using an older 
inventory that could have higher emissions than a more current 
inventory. The state may be obligated to achieve a larger annual 
emissions reduction to satisfy the 5 percent annual reduction criteria 
of CAA section 189(d) than would otherwise be required if a newer 
inventory were used with lower emissions.
3. Comments and Responses
    Any additional comments received on this section are addressed in 
the Response to Comments document found in the docket for this action.

C. Pollutants To Be Addressed in the Plan

1. Summary of Proposal
    The proposed rule indicated that to determine what pollutants need 
to be addressed in the attainment plan and 5 percent requirement in CAA 
section 189(d), the state could provide a demonstration to the EPA 
showing that a particular precursor does not significantly contribute 
to PM2.5 levels that exceed the standard. The proposal 
suggested that if the precursor demonstration is approved by the EPA, 
then the state would not be required to evaluate or adopt control 
measures for that precursor, nor would the state need to address the 
precursor in meeting the 5 percent annual emissions reduction 
requirement in section 189(d). The proposal indicated that Section III 
of the preamble further discussed options describing optional precursor 
demonstrations.
2. Final Rule
    The final rule remains relatively unchanged with respect to this 
issue. Section 189(d) of the CAA requires states to develop a new 
attainment plan for an area that failed to attain by the applicable 
Serious area attainment date that provides for ``an annual reduction in 
PM10 or PM10 precursor emissions within the area 
of not less than 5 percent of the amount of such emissions'' reported 
in the latest emissions inventory for the area. In Section III of this 
preamble, the EPA describes optional approaches by which a state could 
demonstrate that a PM2.5 precursor does not contribute 
significantly to PM2.5 levels that exceed the standard in 
the area, and thereby would not need to adopt control measures for that 
precursor in the area. The EPA also interprets the CAA generally to 
allow a state to provide such a ``precursor demonstration'' for the 
attainment plan required under section 189(d), even if the area has 
previously failed to attain the relevant NAAQS by the applicable 
Serious area attainment date. If the state has provided a demonstration 
with the previous Serious area attainment plan to establish that a 
precursor does not significantly contribute to PM2.5 levels 
for purposes of the attainment plan for the area, and it seeks to 
maintain the status of that precursor as not significantly contributing 
to PM2.5 levels in the area, the state would still need to 
provide an updated precursor demonstration for the new section 189(d) 
SIP because emissions and atmospheric conditions will have changed 
since the previous demonstration was submitted, and the conclusions 
from any previous precursor demonstration may no longer be appropriate. 
See Section III of this preamble for more information about potential 
precursor demonstrations that could be conducted to show that a 
particular precursor does not contribute

[[Page 58100]]

significantly to PM2.5 levels that exceed the standard.
3. Comments and Responses
    Any comments received on this section are addressed in the Response 
to Comments document found in the docket for this action.

D. Attainment Plan Control Strategy

1. Background
    As for other PM2.5 NAAQS attainment demonstrations, the 
overarching requirement for the CAA section 189(d) control strategy is 
that it needs to provide for attainment of the standard as 
expeditiously as practicable. The strategy must include any additional 
measures (beyond those already adopted in previous SIPs for the area as 
RACM/RACT, BACM/BACT, MSM (if applicable), for example) that are needed 
for the area to attain expeditiously. The plan must also demonstrate 
that the new attainment plan will at a minimum achieve an annual 5 
percent reduction in emissions of direct PM2.5 or any 
PM2.5 plan precursor from sources in the area, based on the 
most recent emissions inventory for the area. However, it is important 
to emphasize that a CAA section 189(d) plan must require other control 
measures (even if beyond those sufficient to meet the annual 5 percent 
reduction requirement) that are needed in order to meet the overarching 
goal of attaining the standard as expeditiously as practicable.
2. 5 Percent Annual Reduction in Direct PM2.5 or Any 
PM2.5 Plan Precursor
    a. Summary of Proposal. Section 189(d) of the CAA requires an 
``annual reduction in PM10 or PM10 precursor 
emissions within the area of not less than 5 percent of the amount of 
such emissions as reported in the most recent inventory prepared for 
such area.'' Because the statute is ambiguous with regard to how this 
language should apply for the PM2.5 NAAQS, the EPA proposed 
two options for interpreting this provision. One option interpreted 
this language to require a 5 percent annual reduction in all pollutants 
that contribute to PM2.5, meaning direct PM2.5 
and the four precursors (SO2, NOX, VOC, and 
ammonia), or those precursors that are necessary to control in the 
area. A second option interpreted the language more literally, meaning 
that it required a 5 percent annual reduction of either direct 
PM2.5 or PM2.5 precursor emissions on an annual 
basis, and that a state could elect to control either direct 
PM2.5 or PM2.5 precursor emissions in a given 
year. (Note that under either proposed option, a precursor still could 
be excluded from control requirements if the state submitted a new 
precursor demonstration as part of the revised CAA section 189(d) 
implementation plan showing that the precursor does not contribute 
significantly to levels that exceed the relevant PM2.5 
NAAQS, and such demonstration is approved by the EPA).
    b. Final Rule. One group of commenters supported the inclusion of 
direct PM2.5 and all precursors in the calculation of the 
annual emission reduction requirement because precursors typically play 
a significant role in PM2.5 formation, and they believed 
that allowing states to be able to pick and choose which pollutants to 
reduce would undermine efforts to attain most expeditiously. Other 
commenters supported the second option because they believe it follows 
a plain reading of the statute (i.e., it uses the word ``or''), and 
because it would allow a state to devote resources toward achieving 
emissions reductions in those pollutants that are most effective in 
reducing PM2.5 concentrations and thus in attaining the 
NAAQS most expeditiously.
    After considering comments on this issue, the EPA agrees that the 
second option is the more appropriate reading of the statute. When 
paired with the overarching requirement for the area to reach 
attainment of the NAAQS as expeditiously as practicable, and with 
provisions in the rule allowing a state to demonstrate that a precursor 
does not provide a significant contribution to PM2.5 levels, 
the EPA believes that such an interpretation is reasonable and would 
authorize states to focus emission reduction efforts on those 
pollutants that will be most effective for purposes of attainment in a 
given area. For example, interpreting the statutory provision to 
require emissions reductions in a specific precursor merely for 
purposes of meeting a 5 percent requirement, without regard to whether 
the reductions would be effective for purposes of attainment, could be 
counterproductive to reducing the emissions of other pollutants that 
could result in earlier attainment. This interpretation of CAA section 
189(d) is also consistent with past EPA actions for an area that failed 
to attain the PM10 Serious area attainment date.\191\
---------------------------------------------------------------------------

    \191\ For example, see 69 FR 30006 (May 26, 2004). Approval and 
Promulgation of Implementation Plans for California-San Joaquin 
Valley PM-10 Nonattainment Area; Serious Area Plan for Attainment of 
the 24-Hour and Annual PM-10 Standards.
---------------------------------------------------------------------------

    Thus, in applying the statutory language to implementation of the 
PM2.5 NAAQS in the final rule, the EPA interprets an 
``annual reduction in PM10 or PM10 precursor 
emissions within the area of not less than 5 percent of the amount of 
such emissions'' to mean that an attainment demonstration for a Serious 
area that failed to attain by the attainment date must include control 
measures providing for a 5 percent annual reduction in direct 
PM2.5 emissions or in the emissions of any PM2.5 
plan precursor. The EPA considered whether the statutory phrase 
``precursor emissions'' requires a 5 percent reduction of each 
individual plan precursor in each year, but determined that such an 
interpretation was unnecessarily restrictive in light of the 
overarching requirement for states to adopt the control measures that 
will result in attainment as expeditiously as practicable, and is not 
compelled by the wording of the 5 percent requirement in the statute. 
Accordingly, the final rule requires an annual reduction of either 
direct PM2.5 or any single PM2.5 precursor.
    Because this requirement is an annual one, the final rule also 
authorizes the state to meet the 5 percent requirement to vary between 
direct PM2.5 and PM2.5 precursors, or among 
precursors, from year to year throughout the duration of the section 
189(d) attainment plan, so long as the attainment plan provides for 
expeditious attainment and meets the other applicable attainment plan 
requirements. For example, in year 1 a state could provide for a 5 
percent reduction of direct PM2.5, and in year 2 could 
provide for a 5 percent reduction in a precursor, and so on.
    c. Comments and Responses. Comment: Some commenters suggested that 
a more appropriate approach would be to require a 5 percent annual 
reduction in PM2.5 ambient concentrations (rather than in 
pollutant emissions), and allow the state to meet this air quality 
target with any combination of emissions reductions.
    Response: The EPA does not find that this approach would be 
consistent with the statutory language in CAA section 189(d), which 
clearly expresses the requirement in terms of emissions reductions 
(i.e., ``annual reduction in PM10 or PM10 
precursor emissions within the area of not less than 5 percent of the 
amount of such emissions as reported in the most recent inventory 
prepared for such area.'') Moreover, the EPA is concerned that this 
approach would necessitate, on an annual basis, a complex modeling 
analysis or at the very least some other analytical approach to 
translate emissions to

[[Page 58101]]

ambient concentrations. The burdens of such analysis could be 
significant, and it is unclear what benefit would be realized from such 
an approach. States are already obligated to provide a modeled 
attainment demonstration as part of the new SIP submission to meet the 
requirements of section 189(d), and the 5 percent requirement is a 
separate requirement that the statute explicitly imposes in addition to 
that modeled attainment demonstration. For these reasons, the EPA is 
not adopting the commenter's suggested air quality approach in the 
final rule.
3. Calculating the 5 Percent Annual Reductions
    a. Summary of Proposal. The proposed rule provided an example of 
how annual reductions would be tracked under this provision, and it 
also provided another example describing how reductions in excess of 
the 5 percent requirement in 1 year could be ``carried forward'' to 
help meet the requirement in a future year.
    b. Final Rule. The previous section 2 explains that the EPA 
interprets the statute to require a 5 percent annual reduction in 
direct PM2.5 emissions or in the emissions of any one 
PM2.5 plan precursor in each year, until attainment. The 
requisite minimum 5 percent emissions reduction level for any pollutant 
must be calculated from the total emissions of the pollutant contained 
in the most recent inventory for the area, as described earlier in this 
section. The requirement for a 5 percent annual reduction in any one 
pollutant, calculated based on the emissions levels in the most recent 
inventory, must then be achieved every year between the CAA section 
189(d) plan submission date and the new projected attainment date for 
the area.
    For example, assume it is 2026, and based on monitoring data from 
years 2023-2025, a Serious area has failed to attain the 2012 
PM2.5 NAAQS within 10 years of designation. Assume also that 
the most recent inventory available for an area subject to CAA section 
189(d) is for the year 2023. This inventory would serve as the base 
inventory for determining the 5 percent emissions reduction requirement 
under CAA section 189(d). If the state elects to reduce direct 
PM2.5 emissions each year of the plan (i.e., instead of 
choosing to reduce a precursor), and the most recent inventory (``base 
inventory'') indicates that emissions of direct PM2.5 from 
all sources in the area are 10,000 tons/year, then the area at a 
minimum would need to reduce emissions of direct PM2.5 by 5 
percent of the 2023 base inventory, or 500 tons, each year until the 
area attains the NAAQS. Thus, in the first year following submission of 
the CAA section 189(d) plan for the area, emissions of direct 
PM2.5 could not exceed 9500 tons/year; in the second year, 
emissions could not exceed 9000 tons/year; and so forth. Note that if 
the area needs emissions reductions beyond this amount (i.e., in direct 
PM2.5 or in PM2.5 plan precursors) in order to 
meet the overarching requirement of attaining the standard as 
expeditiously as practicable, then it must adopt and implement such 
control measures.\192\
---------------------------------------------------------------------------

    \192\ See Section IV.D.3 of this preamble for a discussion on 
sources of information for control measures.
---------------------------------------------------------------------------

    Although CAA section 189(d) requires that a state develop measures 
that will obtain annual emissions reductions of ``not less than 5 
percent'' from the most recent inventory, the EPA interprets this 
language to authorize states to maximize emissions reductions in 
earlier years and still meet the 5 percent per year requirement for 
subsequent years. The EPA notes that interpreting the statute in this 
way will encourage states to implement measures earlier, where 
possible, rather than delay implementation of measures merely to assure 
that the 5 percent requirement can be met in later years. Thus, using 
the example described earlier, the annual reduction requirement for the 
area would be 500 tons/year from a base year emissions level of 10,000 
tons/year. The required level after year 1 would be 9500 tons/year, 
after year 2 the level would be 9000 tons/year, and so on. If the area 
reached a level of 8100 tons/year by the end of year 3, then by the end 
of year 4 it would only need to reduce emissions by 100 tons/year to 
yield an emissions level of 8000 tons/year. Thus, this approach will 
allow states to carry forward any emissions reductions beyond the 
required minimum 5 percent in a given year to the next year as a means 
to encourage states to achieve emissions reductions as quickly as 
possible, as long as those emissions reductions are realized after the 
Serious area attainment date.\193\
---------------------------------------------------------------------------

    \193\ 69 FR 30006 (May 26, 2004).
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    The previous example addresses a situation where the state chooses 
to reduce only direct PM2.5. In that example, the 5 percent 
annual reduction amount for any year would be 5 percent of the 2023 
PM2.5 emission inventory amount of 10,000 tons. The final 
rule allows the state to meet its 5 percent reduction each year in 
terms of reducing direct PM2.5 or any PM2.5 plan 
precursor. Thus, if the area had a 2023 emission inventory that 
included 5000 tons of each of the four PM2.5 precursors, and 
if the state chose to meet its ``5% reduction'' obligation in a 
particular year by reducing SO2, it would need to achieve 
emissions reductions of 250 tons of SO2 in that year.
    The EPA is also clarifying its interpretation of the statutory 
language under CAA section 189(d) that requires a state to submit a new 
attainment plan to achieve annual reductions ``from the date of such 
submission until attainment,'' to mean annual reductions beginning from 
the due date of such submission until the new projected attainment date 
for the area based on the new or additional control measures identified 
to achieve at least 5 percent emissions reductions annually. This 
clarification is intended to make clear that even if a state is late in 
submitting its CAA section 189(d) plan, the area must still achieve its 
annual 5 percent emissions reductions beginning from the date by which 
the state is required to make its CAA section 189(d) plan submission, 
not by some later date. Because attainment dates for PM2.5 
nonattainment areas established under subpart 4 occur at the end of the 
calendar year, any CAA section 189(d) plan, which is required within 12 
months of the missed attainment date for the area, would also be due by 
the end of the calendar year.
    c. Comments and Responses. Any additional comments received on this 
section are addressed in the Response to Comments document found in the 
docket for this action.
4. Additional Guidance on CAA Section 189(d) Control Measures
    The EPA believes that an appropriate starting point for a state to 
identify measures to provide for attainment and to meet the requisite 
minimum 5 percent annual emissions reductions of direct 
PM2.5 and PM2.5 precursors is the list of 
potential control measures initially required to be identified as part 
of the RACM and RACT determination process, the BACM and BACT 
determination process, or the MSM determination process (if 
appropriate) for the area. The EPA anticipates that a state should be 
able to rely on much of the work it previously undertook to develop 
this list of potential control measures and analyze their technological 
and economic feasibility, and the time required to implement them. 
Control measures that the state identified but did not previously adopt 
may be likely measures for inclusion in an attainment plan to meet the 
requirements of section 189(d). However, for purposes of meeting the 
requirements of CAA section 189(d), the

[[Page 58102]]

EPA recommends that the state first identify any additional potential 
measures not previously identified for the area, and then analyze any 
new or additional measures that the state has not already adopted in a 
previous attainment plan for the area.
    In addition, a state may include in the CAA section 189(d) plan 
control strategy for the area any control measures triggered as 
contingency measures after the area failed to attain the 
PM2.5 NAAQS by the applicable attainment date. In order to 
be included as control measures that will help the area meet its 
requisite minimum 5 percent reductions in direct PM2.5 
emissions or in emissions of any one PM2.5 plan precursor, 
such measures would have to meet the same requirements as all other 
approvable control measures for being quantifiable, enforceable, 
replicable and accountable. The EPA believes that reliance on triggered 
contingency measures may be appropriate given the short timeline 
provided for in the statute for states to revise and submit their SIP 
revisions (12 months from the missed attainment date) and the fact that 
the contingency measures included in the prior attainment plan for the 
area under CAA section 172(c)(9) must be activated once the EPA 
publishes its finding of the area's failure to attain the NAAQS by the 
applicable attainment date. As explained previously, however, the EPA 
interprets the statute to require that any new 189(d) submission must 
meet all the statutory requirements applicable to all submissions, 
including the requirement to identify contingency measures. Thus, if 
contingency measures from the Serious area attainment plan are relied 
on in the new attainment demonstration as part of the control strategy, 
then the state must submit additional contingency measures for the CAA 
section 189(d) attainment plan. See 40 CFR 51.1003(c)(1)(vii).
5. Control Strategy Submission Requirements
    To ensure that attainment plan submissions contain the necessary 
supporting information for the EPA to review and approve the state's 
new control strategy to achieve at least 5 percent annual reductions in 
emissions of direct PM2.5 or any PM2.5 plan 
precursor, the final rule requires that a state must submit information 
about the new control strategy for an area subject to section 189(d) in 
a manner consistent with the requirements described in section VI.D.3.
    As with other PM2.5 attainment plan submissions, the EPA 
believes that it is incumbent on the state to ensure that the 
information needed for the EPA to evaluate the state's analysis of new 
control measures--which in the case of 189(d) plans is also needed to 
achieve annual 5 percent reductions--is presented separately as part of 
the control strategy analysis, and in a format that provides 
transparency, consistency and the ability for another party to evaluate 
the state's analysis effectively and to duplicate the state's results. 
For this reason, the EPA is including the CAA section 189(d) plan base 
year emissions inventory information as a necessary part of the control 
strategy submission and as one element of the state's CAA section 
189(d) plan due 12 months after the missed attainment date for the 
area. In addition, the state must provide information as part of any 
attainment plan submitted to meet the requirements of CAA section 
189(d) consistent with the criteria described in Section VI.D.5 of this 
preamble to ensure that a state adopts effective regulations to 
implement the control measures identified as being needed to meet those 
requirements. Specifically, all control measures must be quantifiable, 
enforceable, replicable and accountable.

E. Modeling for Attainment Demonstrations

    Section 189(d) of the CAA requires a state with a Serious 
nonattainment area that failed to attain the relevant NAAQS by the 
applicable Serious area attainment date to submit a new attainment plan 
for such area within 12 months after the missed attainment date. The 
same general requirements for attainment demonstrations and modeling 
that apply to Moderate area plans and Serious area plans due under CAA 
sections 189(a) and 189(b) should also apply to CAA section 189(d) 
attainment plans. However, the EPA is including additional requirements 
in the final rule specific to plans submitted pursuant to CAA section 
189(d), as described in the following sections.
1. Attainment Demonstrations for Serious Areas That Fail To Attain the 
NAAQS by the Applicable Attainment Date
    a. Summary of Proposal. The EPA proposed attainment demonstration 
modeling requirements for Serious areas that fail to attain the NAAQS 
by the applicable attainment date. See Section VI.E of this preamble, 
for more details on Serious area attainment demonstrations.
    b. Final Rule. The final rule requirements are unchanged from the 
proposal with respect to this requirement. Attainment demonstrations 
for Serious areas subject to CAA section 189(d) requirements must 
consist of: (i) Technical analyses such as base year and future year 
modeling of emissions that identify sources and quantify their 
emissions that are contributing to violations of the PM2.5 
NAAQS; (ii) analyses of future year projected emissions reductions and 
air quality improvement resulting from national, regional and local 
programs already implemented as part of previous Moderate and/or 
Serious area attainment plans for the area (including reasonable 
control measures, BACM and BACT and additional feasible measures), and 
(iii) additional measures needed for expeditious attainment, including 
measures needed to achieve 5 percent emissions reductions on an annual 
basis. Each state with a nonattainment area subject to the requirements 
of CAA section 189(d) must submit an attainment plan with an attainment 
demonstration that includes analyses supporting the state's 
determination of its proposed new attainment date. In all cases, the 
state must show that the area will attain the NAAQS as expeditiously as 
practicable.
    c. Comments and Responses. Any comments received on this section 
are addressed in the Response to Comments document found in the docket 
for this action.
2. Air Quality Modeling Required for Serious Areas Subject to the 
Requirements of CAA Section 189(d)
    a. Summary of Proposal. The EPA proposed that states are required 
to submit air quality modeling in support of an attainment 
demonstration for a nonattainment area subject to the requirements of 
CAA section 189(d).
    b. Final Rule. The final rule requirements are unchanged from the 
proposal with respect to this issue. States are required to submit air 
quality modeling in support of an attainment demonstration for a 
Serious nonattainment area subject to the requirements of CAA section 
189(d). The modeling demonstration must show how and when the area will 
attain the NAAQS. Other than the timing of plan submissions and 
requirement to achieve 5 percent emissions reductions in direct 
PM2.5 or any PM2.5 plan precursor, the relevant 
air quality modeling procedures and guidance for all PM2.5 
nonattainment area plans are the same. See Sections IV.E. and VI.E of 
this preamble for more details on proposed modeling requirements and 
guidance for Moderate and Serious PM2.5 nonattainment areas, 
respectively.
    c. Comments and Responses. Any comments received on this section 
are

[[Page 58103]]

addressed in the Response to Comments document found in the docket for 
this action.
3. Future Year(s) To Be Modeled in Attainment Demonstrations
    a. Summary of Proposal. The EPA proposed that a state performing a 
modeling analysis for a plan submitted under CAA section 189(d) must 
select a future modeling year such that all emissions control measures 
relied on for attainment will have been implemented by the beginning of 
that calendar year. To demonstrate attainment, the modeling results for 
the nonattainment area must predict that emissions reductions 
implemented by the beginning of the last calendar year preceding the 
attainment date will result in PM2.5 concentrations that 
meet the level of the standard.
    b. Final Rule. As discussed more fully in Section VII.I of this 
preamble, the EPA must establish a new attainment date for a 
PM2.5 nonattainment area subject to CAA section 189(d) and 
must do so according to the provisions of CAA sections 179(d)(3) and 
172(a)(2), which require that the new attainment date must be as 
expeditious as practicable, but no later than 5 years from the date of 
publication in the Federal Register of the EPA's determination that the 
area failed to attain the relevant NAAQS. In addition, the EPA may 
extend the attainment date by up to 5 additional years (thus up to 10 
years from the date of publication of the notice of finding of failure 
to attain by the applicable attainment date for the area) if the EPA 
deems it appropriate ``considering the severity of nonattainment and 
the availability and feasibility of pollution control measures.''
    For purposes of determining the attainment date that is as 
expeditious as practicable, the state must conduct future year modeling 
that takes into account emissions growth, known controls (including any 
controls that were previously determined to be RACM and RACT, BACM and 
BACT, and MSM if appropriate, for the area), the 5 percent per year 
emissions reductions required by CAA section 189(d), plus any other 
emissions controls that are needed for expeditious attainment of the 
NAAQS. A state performing a modeling analysis for a plan submitted 
under CAA section 189(d) must select a future modeling year such that 
all emissions control measures relied on for attainment will have been 
implemented by the beginning of that year. To demonstrate attainment, 
the modeling results for the nonattainment area must predict that 
emissions reductions implemented by the beginning of the last calendar 
year preceding the attainment date will result in PM2.5 
concentrations that meet the level of the standard.\194\
---------------------------------------------------------------------------

    \194\ Note that for purposes of the PM2.5 NAAQS, a 
determination of attainment (or failure to attain), which the EPA is 
required to make after the attainment date has passed, is based on 
an average of the most recent 3 years of ambient data prior to the 
area's attainment date.
---------------------------------------------------------------------------

    For a PM2.5 nonattainment area subject to CAA section 
189(d), the state must adopt any control measures necessary to 
demonstrate expeditious attainment within 5 years of the area failing 
to attain the NAAQS by the applicable Serious area attainment date.
    c. Comments and Responses. Any comments received on this section 
are addressed in the Response to Comments document found in the docket 
for this action.
4. Attainment Year Motor Vehicle Emissions Budgets
    As with all other PM2.5 NAAQS attainment plans, the 
transportation conformity rule requires that attainment plans for areas 
subject to CAA section 189(d) establish motor vehicle emissions budgets 
for the area's attainment year. Therefore, for such an area, the state 
would first determine the new attainment date as described in Section 
VII.I of this preamble. Once an area's attainment date has been 
established, the state would establish motor vehicle emissions budgets 
for direct PM2.5 and any relevant PM2.5 precursor 
for the attainment year.\195\ A motor vehicle emissions budget for the 
purposes of a PM2.5 attainment plan is that portion of the 
total allowable emissions within the nonattainment area allocated to 
on-road sources as defined in the submitted attainment plan.\196\ Such 
motor vehicle emissions budgets would be calculated using the latest 
planning assumptions and the latest approved motor vehicle emissions 
model available at the time that the attainment plan is developed, 
unless the EPA approves the state's use of an alternative model.\197\
---------------------------------------------------------------------------

    \195\ For more information on PM2.5 precursor 
requirements, see CAA section 93.102(b)(2)(iv) and (v) of the 
transportation conformity rule. See also the May 6, 2005, final 
transportation conformity rule that addressed requirements for 
PM2.5 precursors. (70 FR 24280).
    \196\ A state would also establish motor vehicle emissions 
budgets for an area's attainment year. Those budgets would be the 
motor vehicle emissions that the SIP establishes as being necessary 
to attain the NAAQS.
    \197\ If an area includes re-entrained road dust in the motor 
vehicle emissions budget, the latest approved version of AP-42 
should be used unless the EPA has approved an alternative model for 
the area.
---------------------------------------------------------------------------

F. RFP Requirements

1. Specific Requirements
    a. Summary of the Proposal. The EPA proposed to determine that a 
state has satisfied the RFP requirement if the state submits an 
approvable control strategy under CAA section 189(d) that demonstrates 
that the state will achieve at least 5 percent reductions in direct 
PM2.5 or PM2.5 precursor emissions from sources 
in the area annually until attainment. Additionally, the EPA proposed 
that motor vehicle emissions budgets must also be established as part 
of any RFP plan for direct PM2.5 and for any relevant 
PM2.5 plan precursor using the latest planning assumptions 
and the latest approved motor vehicle emissions model available at the 
time that the plan is developed for a Serious area subject to 
189(d).\198\
---------------------------------------------------------------------------

    \198\ Ibid.
---------------------------------------------------------------------------

    b. Final Rule. The EPA is finalizing RFP requirements for 
attainment plans required pursuant to CAA section 189(d) that are 
similar to other Serious area RFP requirements discussed in section 
VI.F of this preamble. The EPA is providing similar guidance regarding 
how to prepare an RFP analysis, RFP projected emissions, geographic 
coverage of emission sources for RFP, and RFP requirements for multi-
state nonattainment areas.
    The RFP analysis must contain appropriate information to 
demonstrate that the state will achieve the emissions reductions from 
the control strategy necessary to result in generally linear reductions 
in emissions and provide for expeditious attainment as discussed in 
Section VII.D of this preamble. As with other Serious area RFP 
analyses, the state may consider PM2.5 plan precursor 
emissions reductions in the aggregate for RFP purposes in a 189(d) 
area.
    The state's RFP analysis must include three components: (1) An 
implementation schedule for control measures on sources in the 
nonattainment area, (2) RFP projected emissions for each applicable 
quantitative milestone year (discussed in Section VII.G of this 
preamble), based on the anticipated control measure implementation 
schedule; and (3) an analysis that demonstrates that this schedule of 
aggregate emissions reductions achieves sufficient progress toward 
attainment between the applicable baseline year to the attainment year. 
For additional discussion of each of the components of the RFP 
analysis, refer to Section IV.F of this preamble. See 40 CFR 
51.1012(a).
    In the proposal, the EPA proposed an option to require at least 5 
percent

[[Page 58104]]

emissions reductions in direct PM2.5 and all 
PM2.5 plan precursor from sources in the area annually until 
attainment to meet the separate RFP requirement for attainment plans. 
However, some commenters did not agree that EPA should consider an area 
meeting the 5 percent requirement under CAA section 189(d) to 
automatically have satisfied the RFP requirement. The EPA agrees with 
this comment and is therefore not finalizing an approach to the RFP 
requirement that is tied to the 5 percent requirement. Instead, the 
final RFP requirement will be tied to progress toward expeditious 
attainment (which the EPA recommends should be generally linear but may 
also be stepwise with appropriate justification), just as it is for all 
other types of Moderate and Serious area plans for PM2.5 as 
summarized in the previous paragraph. The emissions reductions that a 
state achieves for purposes of meeting the 5 percent requirement may 
also be counted towards meeting the separate RFP requirement, but the 
EPA does not believe that meeting the 5 percent requirement would 
automatically equate to meeting the RFP requirement. That determination 
requires the separate evaluations required for the RFP analysis.
    The EPA requires that the applicable baseline year for the RFP 
analysis must be the same year as that represented by the latest base 
year inventory for the Serious area. The projected attainment date 
should be as expeditiously as practicable and is discussed further in 
Section VII.I of this preamble. The RFP analysis must clearly convey 
how the schedule for implementing the control strategy will provide for 
generally linear or stepwise progress towards attainment. If stepwise 
progress is more appropriate for the specific nonattainment area, the 
state is required to submit a clear rationale and supporting 
information to explain why generally linear progress towards attainment 
in the area is not appropriate (e.g., due to the nature of the 
nonattainment problem, the types of sources contributing to 
PM2.5 levels in the area, and the ability to perform timely 
implementation of control measures). Further, if a stepwise approach is 
needed, this does not relieve the state of the requirements of CAA 
section 189(d). As stated earlier, the EPA requires that a section 
189(d) plan must include in its RFP analysis the anticipated emissions 
reductions expected to be achieved through the implementation of 
control measures required by the control strategy described in Section 
VII.D of this preamble. Further, the optional air quality analysis 
discussed in Section IV.F of this preamble is also available for use by 
a state preparing a section 189(d) plan.
    Additionally, the EPA requires states to establish motor vehicle 
emissions budgets for direct PM2.5 and PM2.5 plan 
precursors using the latest planning assumptions and the latest 
approved motor vehicle emissions model available at the time that the 
189(d) plan is developed.\199\ See 40 CFR 51.1012(a).It is also 
important to note that if a section 189(d) area is multi-state or 
multi-jurisdictional, the states or jurisdictions comprising the area 
must provide a coordinated approach to meeting the RFP requirement for 
the shared area. For further information, see Section IV.F.5 of this 
preamble. See 40 CFR 51.1012(b).
---------------------------------------------------------------------------

    \199\ If an area includes re-entrained road dust in the motor 
vehicle emissions budget, the latest approved version of AP-42 
should be used unless the EPA has approved an alternative model for 
the area.
---------------------------------------------------------------------------

    c. Comments and Responses. Any additional comments received on RFP 
are addressed in the Response to Comments document found in the docket 
for this action.

G. Quantitative Milestones

1. Specific Requirements
    a. Summary of the Proposal. The proposal indicated that 
quantitative milestones would need to be achieved every 3 years until 
the area attains the relevant NAAQS, similar to proposed requirements 
for Moderate area plans and other types of Serious area plans. In the 
proposal, the EPA stated that, at a minimum, quantitative milestones 
selected for an attainment plan submitted under CAA section 189(d) 
would need to demonstrate a reduction of at least 15 percent (i.e., 5 
percent for each year in the 3-year period) in emissions of direct 
PM2.5 and PM2.5 plan precursors below those 
emissions reported in the most recent inventory for the area. The 
proposal identified requirements for direct PM2.5 and 
precursors, to be consistent with the RFP proposal. The EPA proposed 
that attainment plans developed pursuant to CAA section 189(d) would 
have to contain quantitative milestones beginning at 13.5 years or 16.5 
years from designation (depending on whether the section 189(d) plan 
would be due before or after the 13.5 year mark), and every 3 years 
thereafter until the attainment date for the area.
    The EPA also proposed that the requirements for quantitative 
milestones, described in Section VI.G of this preamble, should also 
apply to quantitative milestones submitted with any revised Serious 
area attainment plan pursuant to CAA section 189(d).
    b. Final Rule. The revised attainment plan for any Serious 
nonattainment area that fails to attain the relevant PM2.5 
NAAQS by the applicable attainment date must include quantitative 
milestones pursuant to CAA section 189(c). These quantitative 
milestones should track the progress being made in the nonattainment 
area in the implementation of specific control measures in the SIP, and 
may potentially be in the form of metrics for tracking air quality 
improvement or emissions reductions over time. The EPA wishes to 
clarify that the quantitative milestones for a section 189(d) plan are 
designed to track RFP, not solely to track progress in achieving the 
minimum 5 percent annual emission reduction requirement in this section 
of the CAA. The RFP discussion in the previous section noted that in 
some cases, the state may need to adopt additional emission reduction 
measures (beyond those existing or new measures that will meet the 5 
percent emission reduction requirement) in order for the plan to meet 
the overarching requirement to attain the standard as expeditiously as 
practicable. Thus, the RFP plan and quantitative milestones must be 
designed to track progress based on the overall set of control measures 
needed for expeditious attainment.
    The quantitative milestones need to be achieved every 3 years until 
the area attains the relevant NAAQS. Therefore, at a minimum, the final 
rule requires that quantitative milestones selected for an attainment 
plan submitted under CAA section 189(d) need to track progress in the 
implementation of control measures required to achieve RFP in emissions 
reductions of direct PM2.5 and/or all PM2.5 plan 
precursors described in the previous section. The CAA section 189(d) 
plan must contain quantitative milestones to be achieved every 3 years, 
beginning with a milestone at either 13.5 years or 16.5 years from the 
area's date of designation. If the attainment plan is due prior to a 
date 13.5 years from designation of the area, then the plan shall 
contain milestones to be achieved by no later than a milestone date of 
13.5 years from the date of designation of the area, and every 3 years 
thereafter, with the final milestone being the first 3-year milestone 
date falling after the applicable attainment date. If the attainment 
plan is due later than a date 13.5 years from designation of the area, 
then the plan shall contain milestones to be achieved by no later than 
a

[[Page 58105]]

milestone date of 16.5 years from the date of designation of the area, 
and every 3 years thereafter, with the final milestone being the first 
3-year milestone date falling after the applicable attainment date. See 
40 CFR 51.1013(a)(3).
    The EPA is also finalizing that the requirements for quantitative 
milestones described in Section VI.G of this preamble shall also apply 
to quantitative milestones submitted with any revised attainment plan 
pursuant to CAA section 189(d), including but not limited to, the 
construction, content, reporting requirements and a quantitative 
milestone that specifically tracks implementation of control measures 
identified in the plan to attach the standard as expeditiously as 
practicable. See 40 CFR 51.1013(a)(3).
    c. Comments and Responses. Any additional comments received on 
quantitative milestones are addressed in the Response to Comments 
document found in the docket for this action.

H. Contingency Measures

1. Summary of the Proposal
    The EPA proposed that contingency measures for attainment plans 
under CAA section 189(d) for Serious areas that fail to attain the 
NAAQS by the applicable attainment date must meet the same criteria as 
contingency measures for a Serious area attainment plan outlined in 
Section VI.H of this preamble. The EPA also proposed that the 
contingency measures should achieve approximately 1 year's worth of 
emissions reductions.
2. Final Rule
    All PM2.5 attainment plans, including plans for areas 
subject to CAA section 189(d), must contain contingency measures that 
are consistent with CAA section 172(c)(9). Section VI.H of this 
preamble describes the EPA's criteria for contingency measures for a 
Serious area attainment plan, and contingency measures for a section 
189(d) plan must meet the same criteria. The final rule reiterates the 
EPA's longstanding policy that contingency measures should provide for 
emissions reductions approximately equivalent to 1 year's worth of 
reductions needed for RFP.
    The statutory contingency measure requirement at CAA section 
172(c)(9) is not superseded or subsumed by any requirement under 
subpart 4. Thus, contingency measures are required as part of a state's 
attainment plan submission under section 189(d). Accordingly, the final 
rule requires the criteria for identifying and selecting contingency 
measures for a section 189(d) submission that are the same as for 
Moderate or Serious area attainment plans.
    Specifically, the EPA is finalizing that the following requirements 
must be met in order for contingency measures to be approvable as part 
of a state's attainment plan submission for purposes of section 189(d):
    (1) Contingency measures must be fully adopted rules or control 
measures that are ready to be implemented quickly upon a determination 
by the Administrator of the nonattainment area's failure to meet RFP, 
failure to meet any quantitative milestone, failure to submit a 
quantitative milestone report or failure to meet the standard by the 
applicable attainment date.
    (2) The SIP must contain trigger mechanisms for the contingency 
measures, specify a schedule for implementation, and indicate that the 
measures will be implemented without significant further action by the 
state or by the EPA.
    (3) Contingency measures should consist of control measures that 
are not otherwise included in the control strategy for the SIP, or that 
achieve emissions reductions not otherwise relied upon in the control 
strategy for the area.
    (4) Contingency measures should provide for emissions reductions 
equivalent to 1 year's share of reductions needed to demonstrate 
attainment (i.e., the overall needed reductions divided by the number 
of years from the base year to the attainment year), or approximately 
equivalent to 1 year's worth of air quality improvement or emissions 
reductions proportional to the overall amount of air quality 
improvement or emissions reductions to be achieved by the area's 
attainment plan.
    The EPA is also finalizing its proposal to allow a state to rely on 
contingency measures that achieve emissions reductions on sources 
located outside the nonattainment area, but within the state provided 
that the measures on sources outside the designated nonattainment area 
are demonstrated to produce the appropriate air quality impact within 
the nonattainment area.
    As with contingency measures for Moderate or Serious areas, the EPA 
allows a state under these circumstances to rely on additional 
reductions from federal or local measures already scheduled for 
implementation as part or all of their contingency measures. The EPA 
could consider such measures as meeting the contingency measure 
requirement as long as they produce emissions reductions in excess of 
those required to meet other statutory nonattainment provisions (e.g., 
such as to meet BACM/BACT requirements) and they can be relied on to 
achieve a sufficient portion of the actual emissions reductions 
necessary to reduce emissions in the area while the state develops a 
new plan to bring the area into attainment.\200\ As with contingency 
measures for Moderate area or Serious area attainment plans, the EPA 
requires that the emissions reductions associated with contingency 
measures for attainment plans under section 189(d) should be 
approximately equivalent to 1 year's worth of emissions reductions 
necessary to achieve RFP for the area, unless the state adequately 
demonstrates that some smaller amount of reductions is appropriate 
while the state is revising its attainment plan for the area. See 40 
CFR 51.1014(b)(2).
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    \200\ See LEAN v. EPA, 382 F.3d 575 (5th Cir. 2004).
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    The EPA recognizes that identifying contingency measures for a 
Serious PM2.5 nonattainment area that failed to attain the 
relevant NAAQS by the applicable attainment date may be challenging for 
a state that should already have fully implemented all control measures 
identified as ``reasonable'' and ``best,'' and potentially ``most 
stringent,'' in addition to any new control measures to achieve the 
requisite minimum 5 percent reductions in direct PM2.5 or 
PM2.5 plan precursor emissions necessary for expeditious 
attainment. However, for an area that has not implemented MSM, states 
could identify potential contingency measures by reviewing attainment 
plans for other nonattainment areas. The state should also reevaluate 
control measures that were identified previously as technologically or 
economically infeasible for the area, or otherwise removed from 
consideration as part of the RACM/RACT or BACM/BACT process. 
Additionally, states can review other sources of control measure 
information, such as the RBLC (a central database of air pollution 
control technology information) and the EPA's Menu of Control Measures 
document available at http://www3.epa.gov/ttn/naaqs/pdfs/MenuOfControlMeasures.pdf. See 40 CFR 51.1014.
3. Comments and Responses
    Comment: Commenters stated that because 189(d) requires annual 
emissions reductions of not less than 5 percent, then the EPA cannot 
assume that 1 year's worth of emissions reductions will be no greater 
than 5

[[Page 58106]]

percent. The commenter stated that only if an area shows that the 5 
percent reduction requirement of CAA section 189(d) is greater than 
what would be necessary to demonstrate RFP annually may an area assume 
that contingency measures must achieve only the 5 percent target.
    Response: The EPA agrees with the commenters. As discussed earlier 
and in Sections IV.H and VI.H of this preamble, contingency measures 
should equal approximately 1 year's worth of emissions reductions 
necessary to achieve RFP for the area. The EPA notes that RFP might 
require more than the 5 percent emissions reductions required by CAA 
section 189(d). Therefore, if contingency measures should equal 
approximately 1 year's worth of emissions reductions necessary to 
achieve RFP, then those contingency measures should provide more than 5 
percent of emissions reductions in direct PM2.5 or aggregate 
PM2.5 plan precursors.
    Comment: Commenters suggested that, similar to the ozone program, 
the EPA should consider whether the contingency measures for an area 
that failed to attain by the deadline for Serious areas could 
anticipate the development of proven new technology, with a requirement 
to add further contingency measures if such technology does not develop 
as anticipated.
    Response: The EPA disagrees with the commenters, noting that CAA 
section 182(e)(5) provides this flexibility for Extreme areas that are 
nonattainment for the ozone NAAQS. That section of the Act falls within 
subpart 2 of part D, which identifies additional contingency measure 
provisions applicable only in ozone nonattainment areas. Subpart 4 does 
not contain a provision similar to that in subpart 2. Therefore, CAA 
section 172(c)(9) applies and, as explained earlier, that provision 
requires contingency measures be included in the attainment plan.
    Comment: Commenters requested the EPA to allow a state to 
demonstrate, in the alternative, that its contingency measures will 
achieve a 5 percent reduction in PM2.5 ambient 
concentrations, and that such reductions can be obtained by reducing 
direct PM2.5 emissions, emissions of one or more precursors, 
or both.
    Response: The EPA is finalizing the optional air quality analysis 
as an additional component of the RFP plan, as previously discussed in 
Section IV.F of the preamble. Therefore, although the state could 
demonstrate that its contingency measures will achieve a 5 percent 
reduction in PM2.5 ambient concentrations, the EPA notes 
that this optional analysis does not relieve the requirements of 
189(d). Specifically, the area remains required to achieve an emissions 
reduction of not less than 5 percent of direct PM2.5 or any 
PM2.5 plan precursor.

I. Attainment Dates

1. Summary of the Proposal
    The proposed rule indicated that the new attainment date for an 
area that failed to attain by the Serious area attainment date would be 
governed by sections 172(a)(2) and 179(d)(3) of the CAA. Under the 
proposal, the attainment date would be as expeditiously as practicable, 
but no later than 5 years from the date of publication in the Federal 
Register of the EPA's determination that the area failed to attain the 
relevant NAAQS. The EPA may extend the attainment date by up to 5 
additional years based on certain criteria.
2. Final Rule
    As described in the proposal, the final rule includes the 
overarching requirement for a Serious area that failed to attain by the 
previous attainment date to establish a new date for attaining the 
standard as expeditiously as practicable. However, neither CAA section 
189(d) nor other sections in subpart 4 explicitly establish or provide 
the authority to establish a new attainment date for the area. 
Therefore, once an area is beyond the attainment dates that Congress 
specified in subpart 4 for the PM10 NAAQS, the EPA must look 
to other provisions of part D of the CAA to provide authority for a new 
attainment date. Sections 179(d)(3) and 172(a)(2) of the CAA provide 
generally applicable attainment dates that fill the gap in the statute 
left for areas subject to the requirements of CAA section 189(d). Thus, 
for a PM2.5 nonattainment area subject to CAA section 189(d) 
requirements, the EPA must establish a new attainment date according to 
the provisions of CAA section 179(d)(3) and 172(a)(2). The EPA has 
followed this same approach in the past for PM10 
nonattainment areas governed by subpart 4 nonattainment 
requirements.\201\
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    \201\ For example, see the Federal Register notice from June 6, 
2007 (72 FR 31183) in which the EPA found that the Phoenix 
PM10 Serious nonattainment area failed to attain the 
standard by the 2006 attainment date.
---------------------------------------------------------------------------

    Applying these provisions, the final rule therefore provides that 
the new attainment date in a CAA section 189(d) plan must be as 
expeditious as practicable, but no later than 5 years from the date of 
publication in the Federal Register of the EPA's determination that the 
area failed to attain the relevant NAAQS. The EPA may extend the 
attainment date by up to 5 additional years (thus to 10 years from the 
date of publication of the notice of finding of failure to attain by 
the applicable attainment date for the area) if the agency deems it 
appropriate ``considering the severity of nonattainment and the 
availability and feasibility of pollution control measures.'' For a 
PM2.5 nonattainment area subject to CAA section 189(d), the 
EPA expects that the state will adopt any control measures necessary to 
demonstrate expeditious attainment within 5 years of the area failing 
to attain the NAAQS by the applicable Serious area attainment date. The 
EPA will consider the state's proposed attainment date for the area 
based on its revised attainment demonstration and modeling of its 
updated control strategy, and other relevant facts and circumstances 
for the area, in order to identify the most expeditious attainment date 
practicable for the area.
3. Comments and Responses
    Comment: Some commenters stated that the EPA should set a date that 
is as expeditious as practicable, but if it takes longer than 10 more 
years to attain, the EPA may approve such a plan, as long as the 
minimum 5 percent reduction requirement is met. The commenter stated 
that this is the plain meaning of CAA section 189(d)'s reference that 
the plan shall provide for at least 5 percent reductions ``from the 
date of such submission until attainment.''
    Response: The EPA does not agree with the commenter. As indicated 
earlier, the EPA's longstanding interpretation is that the statutory 
provisions of CAA sections 172(c)(2) and 179(d)(3) govern the 
attainment date for new plans required under CAA section 189(d) for 
Serious areas that previously fail to attain by the Serious area 
attainment date. Under certain circumstances, these provisions would 
allow for an attainment date up to 10 years from the effective date of 
a finding of failure to attain, but would not allow for an attainment 
date longer than that.

VIII. NNSR Requirements for PM2.5 Nonattainment Areas

A. Background

1. Statutory Requirements for NSR
    Section 110(a)(2)(C) of the CAA requires states to include in their 
SIPs a preconstruction review permitting program that regulates the 
construction and modification of stationary sources

[[Page 58107]]

as necessary to ensure that NAAQS are achieved. To address the 
regulation of the larger pollutant-emitting sources (defined as major 
stationary sources), Congress provided specific permitting requirements 
in the CAA in parts C and D of title I. The requirements for 
preconstruction permits under parts C and D of the CAA are commonly 
known collectively as the major NSR program because they apply 
specifically to the preconstruction review and permitting of new major 
stationary sources and major modifications at existing sources. As 
explained in Sections VIII.A.1.a and b of this preamble, the 
preconstruction review of each proposed new major stationary source and 
major modification generally is carried out on a pollutant-specific 
basis and the permitting requirements with regard to each pollutant 
apply based on whether the area in which the proposed major source or 
major modification would locate is designated attainment (or 
unclassifiable) or nonattainment for that pollutant at the time the 
permit is issued.
    a. Prevention of Significant Deterioration. Part C of title I of 
the CAA (hereafter referred to simply as part C) contains 
implementation plan requirements that apply to new major stationary 
sources and major modifications locating in areas designated attainment 
or unclassifiable for any NAAQS. These requirements constitute the 
Prevention of Significant Deterioration (PSD) program. Pursuant to part 
C, the EPA has adopted PSD regulations at 40 CFR 51.166 (minimum 
requirements for an approvable state PSD program in the SIP) and 40 CFR 
52.21 (the federal PSD program, applicable in areas where the state 
does not have an EPA-approved PSD program in its SIP).\202\ The EPA 
last amended the PSD regulations for PM2.5 on January 15, 
2013, in the final rule revising the PM2.5 NAAQS.\203\ This 
final rule does not relate to the PSD program, nor does it amend the 
PSD regulations.
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    \202\ The federal PSD program enables the EPA or a state that 
has been delegated authority by the EPA to issue PSD permits.
    \203\ More information on the PSD requirements for 
PM2.5 as well as the public comments and the EPA's 
responses to those comments is contained in the January 15, 2013 
Federal Register document (78 FR 3086, beginning at page 3251).
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    b. Nonattainment New Source Review. Part D of title I of the CAA 
(hereafter referred to as part D) contains implementation plan 
requirements for nonattainment areas, which include the requirements 
for permitting new major stationary sources and major modifications 
locating in designated nonattainment areas, referred to as the 
Nonattainment New Source Review (NNSR) program. As noted earlier, part 
D contains several subparts that include various requirements for 
addressing nonattainment areas. Subpart 1 addresses plan requirements 
for nonattainment areas generally, including CAA section 172(c)(5), 
which requires preconstruction and operating permits for new major 
stationary sources and major modifications locating in nonattainment 
areas. Section 173 of the CAA outlines the minimum statutory 
requirements for a state's NNSR permit program and serves as the basis 
for the EPA's NNSR regulations for PM2.5 as promulgated in 
the 2008 PM2.5 NSR Rule published at 73 FR 28321, May 16, 
2008. Subpart 4 was added to part D as part of the 1990 CAA Amendments 
and includes additional plan provisions for designated PM10 
nonattainment areas. Relevant here, CAA section 189(a)(1)(A) of subpart 
4 requires states to include in their implementation plan a permit 
program addressing major stationary sources of PM10 that 
meets the requirements under CAA section 173 of subpart 1. Subpart 4 
also includes some additional preconstruction review requirements, 
which, until the court's decision in NRDC v. EPA, the EPA has only 
applied to major sources of PM10 located in PM10 
nonattainment areas. The specific NNSR requirements contained in both 
subparts 1 and 4 are described later, including the changes that we are 
making in this final rule to the NNSR regulations to address these 
requirements with respect to PM2.5.
2. Federal NNSR Regulations
    The EPA has adopted numerous NNSR regulations in 40 CFR parts 51 
and 52, including Sec.  51.165; part 51 Appendix S; and Sec.  52.24. An 
approvable NNSR program in a state's implementation plan must, at a 
minimum, meet the applicable program requirements set forth in the 
federal NNSR provisions at 40 CFR 51.165, which for PM2.5 
have been based on changes to that section made by the 2008 
PM2.5 NSR Rule. States with designated nonattainment areas 
for a particular pollutant are required to adopt regulations consistent 
with those applicable plan requirements, including any subsequent rule 
changes that the EPA may make, and submit them to the EPA for approval 
as part of their SIP within a period of time consistent with the 
schedule prescribed by the CAA or the EPA, as appropriate.
    The EPA interprets the requirement established under section 
110(a)(2)(C) of the CAA that states regulate the construction and 
modification of sources to apply as of the effective date of an area's 
designation to nonattainment for a given pollutant.\204\ Although CAA 
section 110(a)(2)(C) does not contain specific requirements a state 
must follow for issuing major source permits during the interim period 
between effective date of designation and the date when the EPA 
approves a state's NNSR program to address a given pollutant, the EPA 
regulations at 40 CFR 52.24(k) authorize states to apply 40 CFR part 
51, Appendix S, known as the Emission Offset Interpretative Ruling or 
simply the Offset Ruling, during the interim period.205 206
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    \204\ See the EPA's final rule to implement certain aspects of 
the 1990 CAA Amendments relating to NSR and PSD, published in the 
Federal Register on November 29, 2005 (70 FR 71612, 71677 and 
71678).
    \205\ States with designated PM2.5 nonattainment 
areas for the 1997 and 2006 PM2.5 standards were required 
to submit SIPs, including a NNSR program satisfying the requirements 
of the 2008 PM2.5 NSR Rule, by May 16, 2011, 3 years from 
the date of publication of that 2008 rule. See 73 FR 28321 (May 16, 
2008), at page 28342. States must continue to implement those 
approved state programs to issue permits to new major stationary 
sources and major modifications until the state's revised program 
containing the subpart 4 NNSR provisions promulgated in this 
rulemaking is approved under the applicable SIP.
    \206\ Appendix S was originally promulgated in 1976 to address 
whether, and to what extent, new and modified sources would be 
allowed to construct in nonattainment areas whose attainment 
deadlines had already passed, in light of the regulatory requirement 
that applications for construction permits for new or modified 
sources be disapproved where the source would interfere with 
attainment of the NAAQS, see 41 FR 55524 (December 21, 1976). When 
Congress added the part D provisions in the 1977 CAA Amendments, it 
also added the requirement that SIPs contain NNSR provisions as set 
forth in Part D. Additionally, Congress provided that Appendix S 
would govern preconstruction permitting in nonattainment areas 
lacking approved part D SIPs before a construction ban went into 
effect. When Congress removed the construction ban via the 1990 CAA 
Amendments (except as provided for in CAA section 110(n)(3)), it 
left in place the use of the interim NNSR program under Appendix S.
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    Accordingly, states with newly designated nonattainment areas for 
the revised primary PM2.5 NAAQS have two possible means by 
which they can implement NNSR requirements for PM2.5 
following the effective date of designations and until the EPA approves 
a SIP submission meeting the NNSR requirements for PM2.5 
promulgated in this rule. First, any state that already has a SIP-
approved NNSR program for PM2.5 (e.g., where the state has 
had other PM2.5 nonattainment areas for which the EPA has 
approved an NNSR program) should continue to apply those permitting 
requirements in the interim. Second, any state that lacks an approved 
NNSR program for PM2.5 may rely upon the NNSR provisions in 
Appendix S until the EPA approves that

[[Page 58108]]

state's SIP submission in order to ensure that proposed new major 
stationary sources and major modifications for PM2.5 in 
newly designated PM2.5 nonattainment areas undergo the 
appropriate type of preconstruction review in the interim.
    a. General Applicability. Stationary sources are considered to be 
``major'' sources based on the amount of a given pollutant (or a 
precursor for that pollutant) the source emits or has the potential to 
emit, as defined by the statute. New major stationary sources are 
subject to the NNSR requirements when they are major for the pollutant 
(or a precursor for that pollutant) for which an area is designated 
nonattainment. See 40 CFR 51.165(a)(2)(i). With regard to major 
modifications, NNSR applies to proposed physical changes or changes in 
the method of operation of an existing stationary source that (1) is 
major for the nonattainment pollutant (or a precursor for that 
pollutant) and (2) results in both a significant emissions increase and 
a significant net emissions increase of that same nonattainment 
pollutant (or same precursor for that pollutant).\207\
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    \207\ See 40 CFR 51.165(a)(1)(v)(A), (a)(2)(ii)(A). As will be 
explained in ensuing discussions, the nonattainment pollutant and 
any applicable precursors for that pollutant are considered 
separately for NNSR applicability purposes.
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    For each proposed new major stationary source and major 
modification, the general NNSR requirements to be included in a state's 
SIP include the following: (i) The installation and continuous 
operation of pollution control technology that complies with the Lowest 
Achievable Emission Rate (LAER); (ii) the acquisition of creditable 
emissions reductions to adequately offset the proposed emissions 
increase of the nonattainment pollutant; and (iii) a certification that 
all other sources owned by the applicant are complying with all 
applicable requirements of the
    CAA.\208\ These NNSR requirements apply as of the effective date of 
the designation of an area as nonattainment for the pollutant and must 
be satisfied by a proposed major new source or major modification 
locating in such area as a prerequisite for obtaining a NNSR permit.
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    \208\ The basic NNSR requirements are set forth in CAA section 
173 of subpart 1. Subpart 4 adds a more stringent definition of 
``major source'' for PM10 sources locating in 
PM10 nonattainment areas classified as Serious and sets 
forth provisions for the regulation and potential exemption from 
regulation of major sources of PM10 precursors in 
PM10 nonattainment areas. Until the decision in NRDC v. 
EPA was issued, the additional subpart 4 requirements had not been 
directly applied to PM2.5.
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    b. Historical Overview of NNSR for PM10 and PM2.5 National Ambient 
Air Quality Standards (NAAQS). The EPA revised the PM NAAQS in 1997, 
establishing new annual and 24-hour NAAQS using PM2.5 
particles as a new indicator, while retaining the NAAQS for 
PM10.\209\ In 2006, the EPA again revised the suite of PM 
NAAQS by tightening the 24-hour PM2.5 standards and 
retaining the level of the annual PM2.5 standards.\210\ In 
2008, the EPA issued the PM2.5 NSR Rule that established 
various provisions ensuring that proposed new major stationary sources 
or major modifications of sources of direct PM2.5 emissions 
or emissions of applicable PM2.5 precursors would be 
required to undergo preconstruction review.\211\ The EPA included 
specific provisions in the 2008 PM2.5 NSR Rule that apply 
when such sources are located in a designated PM2.5 
nonattainment area. Unlike the NNSR requirements for PM10 
developed under subpart 4, the EPA determined that the applicable 
implementation requirements for the PM2.5 NAAQS were limited 
to the general nonattainment provisions under subpart 1.
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    \209\ See 62 FR 38652 (July 18, 1997).
    \210\ See 71 FR 61144 (October 17, 2006).
    \211\ See 73 FR 28321 (May 16, 2008).
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    With regard to NSR applicability for PM2.5 precursors in 
the 2008 PM2.5 NSR Rule, the EPA recognized that, under the 
appropriate conditions, NOX, SO2, VOC and ammonia 
could each contribute to the formation of PM2.5 in the 
ambient air. However, the EPA issued regulations that did not require 
states to subject all of these precursors to regulation as part of the 
attainment plan or NSR permitting requirements applicable in a given 
nonattainment area.\212\ Instead, the EPA established the initial 
presumptions for nonattainment areas that SO2 and 
NOX should be regulated precursors for PM2.5, but 
VOC and ammonia need not be regulated precursors.\213\
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    \212\ See 72 FR 20589.
    \213\ In the 2008 PM2.5 NSR Rule, the EPA concluded 
that SO2 should be regulated as a precursor for 
PM2.5 in all areas. In addition, the EPA or the states 
could rebut the initial presumptions regarding NOX, VOC 
or ammonia on an area-by-area basis with a demonstration approved by 
the Administrator and thus reverse any of those presumptions in the 
state's implementation plan for that area. See 73 FR 28327.
---------------------------------------------------------------------------

    As described in Section II.B of this preamble, in January 2013 the 
court's decision in NRDC v. EPA held that the EPA erred in implementing 
the PM2.5 NAAQS under the general implementation 
requirements in subpart 1, rather than relying on the implementation 
requirements specific to PM10 in subpart 4 of the CAA. 
Accordingly, the court directed the EPA to comply with the requirements 
of subpart 4 when developing implementing regulations for 
PM2.5 nonattainment areas.
    The NRDC decision has specific implications for implementing the 
NNSR program for PM2.5. Two provisions of subpart 4 impose 
additional requirements on NNSR plans developed to address sources 
locating in areas designated nonattainment for PM2.5. The 
first relates to the definition of ``major stationary source'' that 
applies to areas initially designated as Moderate nonattainment areas 
and subsequently reclassified as Serious. In such areas, section 
189(b)(3) of the CAA defines the major source threshold as 70 tpy of 
PM10. The second relevant subpart 4 provision governs the 
treatment of major sources of PM10 precursors. As previously 
described in Section III of this preamble, section 189(e) of the CAA 
requires that the control requirements applicable to major stationary 
sources of PM10 also apply to major stationary sources of 
PM10 precursors, unless the Administrator determines that 
such sources of PM10 precursors do not contribute 
significantly to PM10 levels that exceed the standard in 
that area. The EPA's proposed amendments to address the subpart 4 
requirements with respect to PM2.5 and the EPA's responses 
to comments received on its proposal are summarized in the relevant 
subsections later.
    It is worth noting that the 2008 PM2.5 NSR Rule 
promulgated new NSR requirements for implementation of PM2.5 
in both nonattainment areas (NNSR) and attainment/unclassifiable areas 
(PSD). As subpart 4 includes requirements only pertinent to 
nonattainment areas, the EPA does not consider the portions of the 2008 
PM2.5 NSR Rule that address requirements for 
PM2.5 attainment and unclassifiable areas to be affected by 
the court's opinion in NRDC v. EPA. Therefore, the EPA did not propose 
to revise any PSD requirements promulgated in the 2008 PM2.5 
NSR Rule in order to comply with the court's decision.

B. Final NNSR Requirements for PM2.5 Nonattainment Areas

    This section provides a description of the changes that the EPA is 
making to the NNSR requirements for PM2.5 that are contained 
in 40 CFR 51.165, which provides the minimum requirements for a NNSR 
program under an approved implementation plan, and in Appendix S, which 
serves as an interim NNSR permitting program pending approval of

[[Page 58109]]

a state's SIP to address NNSR requirements for a particular pollutant.
    For both sets of regulations, we will describe the changes that 
were proposed, the final requirements, the comments received, and the 
EPA's responses to them.
1. 40 CFR 51.165
    In this final rule, as explained in more detail later, the EPA is 
making the following revisions that affect the NNSR regulations for 
PM2.5 at 40 CFR 51.165: (a) Amending the definition of 
``regulated NSR pollutant'' with regard to PM2.5 precursors; 
(b) amending the definition of ``major stationary source'' with regard 
to major sources of direct PM2.5 emissions and 
PM2.5 precursors locating in PM2.5 nonattainment 
areas classified as Moderate and Serious; (c) amending the definition 
of ``significant'' with regard to emissions of PM2.5 
precursors; and (d) codifying the EPA's policy for determining whether 
a source is ``major'' for PM2.5 with regard to emissions of 
direct PM2.5 and its precursors.
    Also, the EPA explains in this section that it is codifying the 
schedule for states to submit NNSR SIP revisions for PM2.5 
that meet the requirements of 40 CFR 51.165. The schedules for 
submitting revised NNSR programs for PM2.5 for Moderate and 
Serious areas are not contained in 40 CFR 51.165 NNSR regulations but 
in new 40 CFR 51.1003(a) and (b), respectively.
a. Definition of ``regulated NSR pollutant''--PM2.5 
Precursors
i. Summary of Proposal
    CAA section 189(e) requires that the control requirements 
applicable to major stationary sources of PM10 also apply to 
major stationary sources of PM10 precursors, unless the 
Administrator determines that such sources of PM10 
precursors do not contribute significantly to PM10 levels 
that exceed the standard in that area. In order to align the NNSR 
regulations for PM2.5 with the requirements of CAA section 
189(e), the EPA proposed several amendments to certain definitions 
within 40 CFR 51.165, as explained in the subsections that follow, in 
order to regulate all four identified PM2.5 precursors 
consistent with the statute.\214\ The EPA proposed to revise the NNSR 
definition of ``regulated NSR pollutant'' to include SO2, 
NOX, VOC and ammonia as regulated PM2.5 
precursors.
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    \214\ The EPA explained earlier in this preamble that the 
court's 2013 decision in NRDC v. EPA reasoned that the EPA's 
approach to precursors in the 2007 and 2008 PM2.5 
regulations had the effect of reversing the presumption embodied 
with subpart 4 at CAA section 189(e) that a state should regulate 
major sources of all PM precursors unless the state has made a 
specific showing why regulation of sources of a particular precursor 
is not necessary.
---------------------------------------------------------------------------

    The EPA also proposed to add language to the definition of 
``regulated NSR pollutant'' to address the provision of CAA section 
189(e) that allows an exemption from the NNSR permit requirements for 
major stationary sources or major modifications of a particular 
precursor if the state demonstrates to the satisfaction of the EPA that 
major stationary sources of such precursor do not contribute 
significantly to PM2.5 levels that exceed the 
PM2.5 ambient standards in a particular nonattainment area. 
In Section III of the preamble of the proposal, the EPA proposed and 
sought comment on several policy approaches that a state could use to 
make the necessary demonstration that would enable the state to exempt 
sources of a particular precursor from being regulated under the 
attainment plan for a particular PM2.5 nonattainment area 
altogether or from individual components of that plan, including the 
NNSR permitting requirements. See 80 FR 15350-62.
ii. Final Rule
    The EPA is amending the definition of ``regulated NSR pollutant'' 
at 40 CFR 51.165 to include a new provision stating that 
SO2, NOX, VOC and ammonia are PM2.5 
precursors in any PM2.5 nonattainment area. See 40 CFR 
51.165(a)(1)(xxxvii)(C)(2). The EPA is also providing in this final 
rule that sources of a particular precursor may be exempted from the 
NNSR control requirements via a demonstration approved by the 
Administrator showing that new major stationary sources and major 
modifications of a particular precursor would not contribute 
significantly to levels of PM2.5 that exceed the standard in 
a particular nonattainment area. It is noted, however, that the 
exemption provision is not being codified within the definition of 
``regulated NSR pollutant'' as originally proposed. Instead, this 
exemption provision is contained in a new paragraph 51.165(a)(13), 
which is based on CAA section 189(e) and provides generally that the 
control requirements applicable to new major stationary sources and 
major modifications of PM2.5 are also applicable to new 
major stationary sources and major modifications of PM2.5 
precursors.
    In addition, the provision has also been revised to focus on the 
exemption of control requirements for sources of a particular precursor 
rather than the exemption of the precursor itself. The EPA believes 
that this shift in focus is more consistent with the statutory language 
at CAA section 189(e), which also focuses on the exemption of sources 
from the control requirements for that precursor. As explained in 
Section III of this preamble, the EPA has defined a precursor 
demonstration specifically for exempting major sources of a particular 
precursor from regulation under the NNSR program. This demonstration 
involves a sensitivity-based analysis that evaluates the sensitivity of 
ambient PM2.5 concentrations in a nonattainment area to 
increases of precursor emissions resulting from potential major source 
growth in the area. The EPA intends to issue a technical assistance 
document that provides additional information on conducting appropriate 
sensitivity-based analyses for this purpose. A more complete 
description of this and the other types of precursor demonstrations is 
contained in Section III of this preamble.
    The EPA recommends that the state consult with the appropriate EPA 
Regional Office as early as possible to discuss appropriate analyses 
for the NNSR precursor demonstration. If the appropriate precursor 
demonstration is submitted to and approved by the Administrator, the 
state would not be required to regulate new major stationary sources 
and major modifications of the insignificant precursor under the 
state's approved NNSR program in a particular nonattainment area. Such 
exemption from the NNSR control requirements would include an exemption 
from all of the prerequisite conditions set forth in 40 CFR 51.165 for 
PM2.5, including the requirements to implement LAER and to 
obtain emissions offsets for the precursor.
iii. Comments and Responses
    Comments: Some commenters supported revising the definition of 
``regulated NSR pollutant'' consistent with the NRDC decision and 
subpart 4 to establish SO2, NOX, VOC and ammonia 
as regulated PM2.5 precursors, unless a state demonstrates 
that major stationary sources of a particular precursor do not 
contribute significantly to PM2.5 levels that exceed the 
standard in the nonattainment area.
    On the other hand, several commenters urged the EPA not to begin 
regulating VOC and ammonia as PM2.5 precursors under the 
NNSR program at this time. Some of the commenters cited ongoing 
technical challenges related to evaluating the contribution of 
PM2.5 precursor gases to ambient PM2.5

[[Page 58110]]

concentrations, while some commenters stated that the EPA should 
provide an up-front rebuttable presumption that a state is not required 
to regulate VOC and ammonia as PM2.5 precursors under NNSR. 
A commenter stated that requiring NNSR to apply to sources of these 
precursors that would have an insignificant impact on the nonattainment 
issue is a waste of resources and will unnecessarily lead to burdensome 
over-regulation for affected sources.
    Response: We do not agree with the commenters who oppose the EPA's 
proposal to require regulation of all four technical and scientific 
precursors in PM2.5 nonattainment areas. Specifically, we do 
not agree that a delay in regulating VOC and ammonia under a state's 
NNSR permitting program is reasonable or permissible. Similarly, the 
EPA does not agree that it has the authority to provide a rebuttable 
presumption to exempt VOC and ammonia from NNSR permitting 
requirements. CAA section 189(e) explicitly requires the regulation of 
major sources of PM2.5 precursors unless the state 
demonstrates to the EPA's satisfaction that such regulation is 
unnecessary. Thus, CAA section 189(e) does not allow the EPA to 
unilaterally exempt an identified scientific and technical 
PM2.5 precursor from regulation, nor does it permit the EPA 
to establish a rebuttable presumption exempting any PM2.5 
precursor from regulation. The EPA's use of a rebuttable presumption 
exempting certain precursors from regulation in its prior 
PM2.5 implementation rules was directly at issue in NRDC v. 
EPA, wherein the court made it clear that it would be inappropriate for 
the EPA to establish such presumptions pursuant to the requirements of 
subpart 4.\215\
---------------------------------------------------------------------------

    \215\ See NRDC v. EPA, 706 F.3d at 437, n.7 & n.10.
---------------------------------------------------------------------------

    In some PM2.5 nonattainment areas, the minimization (and 
offsetting) of new precursor emissions from major source growth in the 
area could be an important component of a state's attainment plan for 
the PM2.5 NAAQS. Where it is not, CAA section 189(e) 
provides states with the opportunity to make an area-by-area 
demonstration that would enable the state to exempt sources of any 
PM2.5 precursor from regulation if it is shown that sources 
of the precursor does not contribute significantly to the PM levels 
that exceed the standard in a particular nonattainment area. 
Accordingly, consistent with CAA section 189(e), this final rule 
provides guidance to assist states in preparing a NNSR precursor 
demonstration, as described in Section III of this preamble, by which 
sources of VOC, ammonia or any other PM2.5 precursor may be 
exempted from the NNSR requirements for PM2.5 if the state 
shows that increased source emissions of the relevant precursor would 
not contribute significantly to PM2.5 concentrations in a 
PM2.5 nonattainment area.
    Moreover, as described in Section VIII.B.2 of this preamble, the 
EPA is not commencing with the regulation of VOC and ammonia (hence not 
requiring NNSR review of any new major stationary sources and major 
modifications of such precursors) for those states relying on Appendix 
S to issue NNSR permits during the interim SIP development period.\216\ 
This provides states with an opportunity to evaluate the contribution 
of VOC and ammonia emissions from potential major source growth to 
ambient PM2.5 concentrations and determine whether an 
exemption of new and modified sources of either of these precursors 
from the NNSR permitting requirements is justified before such sources 
will be subject to regulation.
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    \216\ States should use Appendix S to issue NNSR permits to new 
major stationary sources and major modifications with respect to a 
particular nonattainment pollutant if the state's implementation 
plan lacks a NNSR program for that pollutant. Where a state's 
existing NNSR program for a particular pollutant lacks certain 
provisions for which revision in required, the existing program--not 
Appendix S--is the applicable permit program for issuing NNSR 
permits until the necessary revisions are approved by the EPA.
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b. Definition of ``major stationary source'' in Moderate and Serious 
PM2.5 Nonattainment Areas--Direct PM2.5 Emissions 
and PM2.5 Precursors
i. Summary of Proposal
    Subpart 4, as described earlier in this document, contains 
provisions for the classifications of PM10 nonattainment 
areas as either Moderate or Serious areas. However, the NNSR 
regulations for PM2.5 set forth in the 2008 PM2.5 
NSR Rule were developed pursuant to subpart 1, which does not provide 
for the classification of designated nonattainment areas as Moderate 
and Serious areas. Accordingly, in the proposal for this final rule, 
the EPA proposed to amend its definition of ``major stationary source'' 
in the 40 CFR 51.165 NNSR regulations for PM2.5 to address 
subpart 4 requirements concerning the regulation of direct 
PM2.5 and PM2.5 precursors in both Moderate and 
Serious nonattainment areas for PM2.5. First, the EPA 
proposed to revise the definition of ``major stationary source'' by 
qualifying the term ``regulated NSR pollutant'' with the new phrase 
``(as defined in paragraph (a)(1)(xxxvii) of this section).'' The new 
phrase explicitly cross-references the definition of ``regulated NSR 
pollutant,'' which also defines each of the PM2.5 
precursors. Hence, sources of both direct PM2.5 emissions 
and emissions of each PM2.5 precursor would clearly be 
included in the definition of a ``major stationary source.''
    Second, the EPA proposed to amend the definition of ``major 
stationary source'' consistent with section 189(b)(3) of the CAA to 
establish a lower major source threshold for new major stationary 
sources and major modifications locating in PM2.5 
nonattainment areas classified as Serious. CAA section 302(j) generally 
defines a ``major stationary source'' as a source that emits or has the 
potential to emit 100 tpy or more of any air pollutant. The provision 
explicitly states that this definition applies for purposes of the CAA 
except as otherwise expressly provided in the statute. Thus, for 
sources locating in PM2.5 nonattainment areas classified as 
Moderate, where no CAA provision provides otherwise, the applicable 
major source threshold for direct PM2.5 emissions and for 
each PM2.5 precursor is 100 tpy. Subpart 4, meanwhile, 
establishes a major source threshold for PM10 nonattainment 
areas classified as Serious at 70 tpy in CAA section 189(b)(3). 
Therefore, the EPA proposed to set the major source threshold for 
direct PM2.5 emissions and for each PM2.5 
precursor at 70 tpy of direct PM2.5 emissions and each 
individual precursor. The alternative proposed for consideration was to 
promulgate a PM2.5 major source threshold lower than 70 tpy 
of direct PM2.5 emissions, recognizing that PM2.5 
is a subset of PM10. The EPA sought comment on possible ways 
in which a PM2.5 emissions rate different from the statutory 
70 tpy rate for PM10 emissions could be established, taking 
into account variations in the PM10/PM2.5 ratio 
for different source categories and activities. Nevertheless, the 
agency indicated that the proposed option (i.e., a major source 
threshold of 70 tpy of direct PM2.5 emissions for stationary 
sources proposing to construct or modify in PM2.5 
nonattainment areas classified as Serious) represented the preferred 
approach.
    In its effort to ensure that major sources of PM2.5 
precursors locating in Serious areas are regulated in the same manner 
as major sources of direct PM2.5 emissions locating in 
Serious areas, the EPA proposed major source thresholds for 
PM2.5 precursors would be consistent with the threshold 
already defined for

[[Page 58111]]

direct PM2.5 emissions in PM2.5 nonattainment 
areas reclassified as Serious. Consistent with the EPA's preferred 
approach for direct PM2.5 emissions, the EPA proposed to 
define ``major'' for each PM2.5 precursor as 70 tpy. 
However, the EPA also solicited comments on the appropriateness of 
setting the precursor major source thresholds at a different rate, 
particularly if, as alternatively proposed, the agency defined ``major 
stationary source'' for sources of direct PM2.5 emissions in 
Serious PM2.5 nonattainment areas at a rate lower than 70 
tpy of PM2.5 emissions. For example, if the agency had set 
the major source threshold at 60 tpy of direct PM2.5 
emissions in Serious PM2.5 nonattainment areas, the agency 
would have also considered setting the major source threshold for each 
PM2.5 precursor at 60 tpy of that particular precursor.
    Regardless of whether the major source threshold for direct 
PM2.5 emissions was set at 70 tpy or some lower rate, the 
EPA indicated in the proposal that it believed a reasonable technical 
argument could be made that the threshold set for direct 
PM2.5 emissions would be too low to be regarded as ``major'' 
for each precursor when considering the effects that any precursor 
sources could have on ambient PM2.5 concentrations. In 
support of higher emissions rates for defining ``major'' for 
PM2.5 precursors, the EPA cited a previous analysis that it 
had undertaken to examine the relationship between emissions of 
SO2 and NOX and the formation of secondary 
PM2.5 in the ambient air.\217\ However, the agency also 
identified potential legal impediments to setting a major source 
threshold for precursors at a rate higher than those statutorily 
prescribed for direct emissions of a pollutant. Accordingly, the agency 
solicited comments on the general appropriateness of setting higher 
major source thresholds for one or more PM2.5 precursors in 
PM2.5 nonattainment areas, and asked commenters to include 
legal and technical considerations that should be made part of the 
EPA's future analysis of NNSR requirements with respect to 
PM2.5 precursors.
---------------------------------------------------------------------------

    \217\ See 80 FR 15433. The technical assessment, with details on 
data and modeling inputs, was fully described in a technical memo 
titled ``Details on Technical Assessment to Develop Interpollutant 
Trading Ratios for PM2.5 Offsets,'' which was placed in 
the docket to the 2008 PM2.5 NSR Rule. See also 73 FR 
28321 (May 16, 2008), at page 28339.
---------------------------------------------------------------------------

ii. Final Rule
    In this final rule, the EPA has followed its preferred approach and 
has made the changes necessary to ensure that ``major'' is defined for 
direct PM2.5 emissions as well as all PM2.5 
precursors in Moderate and Serious PM2.5 nonattainment 
areas. For Moderate areas, the major source threshold of 100 tpy 
applies individually to direct PM2.5 emissions and to each 
PM2.5 precursor; in Serious areas, the major source 
thresholds for direct PM2.5 emissions and emissions of each 
PM2.5 precursor are individually defined as 70 tpy. As 
explained in Section VIII.B.1.d of this preamble, the determination of 
whether sources of direct PM2.5 emissions or each 
PM2.5 precursor are ``major'' is to be made separately for 
each pollutant. That is, emissions rates for individual precursors 
should not be added together to determine a source's major source 
status with regard to PM2.5. See 40 CFR 51.165(a)(2)(i).
iii. Comments and Responses
    Comment: Most commenters generally supported the preferred approach 
of setting a major source threshold at 70 tpy of direct 
PM2.5 emissions in Serious areas, agreeing with the EPA that 
establishing a PM2.5 equivalency to PM10 
emissions would be problematic. Some commenters specifically opposed 
any effort to set a threshold for PM2.5 that is lower than 
the threshold for PM10. A commenter stated that, if 
PM2.5 is legally subject to subpart 4 because it is a subset 
of PM10, and Congress meant to subject all sources of 
PM10 emissions to subpart 4, then Congress meant to have the 
major source threshold for PM10 apply to PM2.5 as 
well. No commenter advocated that the EPA set a major source threshold 
lower than 70 tpy for direct PM2.5 emissions.
    Response: The EPA agrees with the commenters that it is reasonable 
to set the major source threshold at 70 tpy of direct PM2.5 
emissions for sources locating in PM2.5 nonattainment areas 
classified as Serious. While CAA section 189(b)(3) does not explicitly 
define a ``major source'' and ``major stationary source'' as 70 tpy of 
PM2.5 for PM2.5 nonattainment areas reclassified 
as Serious (because it refers to PM10), the most 
straightforward and consistent application of the statutory provision 
is to establish the same numerical threshold for sources of 
PM2.5 in Serious PM2.5 nonattainment areas as the 
threshold for sources of PM10 emissions in Serious 
PM10 nonattainment areas. Sources locating in Moderate 
nonattainment areas are already subject to the same numerical major 
source threshold (100 tpy) under CAA section 302(j) for direct 
emissions of both PM10 and PM2.5, so the EPA 
believes that it is also reasonable to establish the threshold for 
PM2.5 in Serious areas at the same numerical rate as the 
threshold that applies to PM10 in Serious areas.
    We also agree that it would be difficult to establish a lower 
uniform major source threshold for PM2.5 that would 
represent a rate that is equivalent to 70 tpy of PM10 
emissions at all sources subject to NNSR permitting requirements. With 
regard to the commenter who stated that ``Congress meant to have the 
major source threshold for PM10 apply to PM2.5 as 
well,'' it is not clear whether the commenter advocates that proposed 
sources of PM2.5 be subjected to NNSR permitting using a 
major source threshold of 70 tpy of PM10 emissions or a 
major source threshold of 70 tpy of PM2.5 emissions for 
sources of PM2.5 locating in PM2.5 nonattainment 
areas. The former is not the EPA's interpretation of the CAA. While 
PM2.5 is a subset of PM10, to assume that a 
source emitting major amounts of PM10 will also emit a 
substantial amount of PM2.5 is not always reasonable. The 
relative amounts of PM10 and PM2.5 emitted by 
various source categories is known to vary significantly and we do not 
believe that it would be reasonable to subject sources to major source 
review for PM2.5 on the basis of the level of 
PM10 emissions as this could mean that sources are subject 
to NNSR based on different levels of PM2.5 emissions on an 
area-by-area basis. We do not believe that Congress intended such a 
lack of uniformity in the application of the major source threshold to 
sources of direct PM2.5. Moreover, even if it were 
permissible to interpret CAA section 189(b)(3) in this manner, we have 
determined that the most reasonable and straightforward approach is to 
establish a separate major source threshold for direct emissions of 
PM2.5 at 70 tpy for sources locating in PM2.5 
nonattainment areas classified as Serious.
    Comment: With regard to the definition of ``major stationary 
source'' for PM2.5 precursors in Moderate and Serious areas, 
several commenters supported using the same major source threshold 
value for direct PM2.5 emissions and PM2.5 
precursors. One of these commenters expressly opposed any alternative 
approach that would set a different threshold for PM2.5 
precursors than for direct PM2.5 emissions because the 
commenter asserted that it would be impossible to set a uniform 
national ratio reflecting the effect of the various precursors on 
ambient PM2.5 concentrations relative to direct 
PM2.5 emissions.
    On the other hand, some commenters wanted the EPA to include a 
provision

[[Page 58112]]

in the NNSR regulations allowing states to make a case-by-case 
demonstration to use higher major source thresholds for 
PM2.5 precursors for permit reviews. These commenters 
expressed concern that the 100 tpy major source threshold for Moderate 
areas, and the 70 tpy threshold for Serious, are both too low for the 
PM2.5 precursors and do not realistically reflect the effect 
that each precursor has on ambient PM2.5 concentrations. 
These commenters suggested the EPA should conduct further analyses to 
determine what higher quantity of emissions of each regulated precursor 
would be equivalent to 100 tpy (for Moderate areas) and 70 tpy (for 
Serious areas) of direct PM2.5 emissions in terms of 
contribution to PM2.5 concentrations in ambient air. These 
commenters recommended that the EPA use the information gained from the 
recommended analyses to determine appropriate thresholds and make its 
proposed thresholds available for public comment.
    Response: In setting the major source threshold for each 
PM2.5 precursor at 100 tpy for Moderate areas, the EPA is 
following the precedent established in the 2008 PM2.5 NSR 
Rule in which the agency set the same 100 tpy major source threshold 
for direct PM2.5 emissions and each of the regulated 
precursors (at that time SO2 and NOX).\218\ 
Setting the same 100 tpy major source thresholds for sources of 
PM2.5 emissions and regulated PM2.5 precursor 
emissions is also consistent with the way in which we have historically 
interpreted the requirements of CAA section 189(e) as they applied to 
emissions of PM10 and PM10 precursors.\219\
---------------------------------------------------------------------------

    \218\ Ibid.
    \219\ See 57 FR 13498 (April 16, 1992), at page 13538.
---------------------------------------------------------------------------

    Moreover, section 302(j) of the CAA contains a definition of 
``major emitting facility'' and ``major stationary source'' that 
applies to, among other things, programs implemented under subpart 1 
such as the general NNSR program requirements in CAA section 173.\220\ 
This definition also applies to programs implemented under subpart 4 to 
the extent that they regulate PM2.5 nonattainment areas 
classified as Moderate, as subpart 4 does not establish a different 
definition of major sources for such areas. That definition defines a 
source as ``major'' whenever a facility or source ``emits, or has the 
potential to emit, one hundred tons per year or more of any air 
pollutant.'' \221\ This provision does not clearly provide the EPA with 
the authority to set a major source threshold higher than 100 tpy for a 
pollutant merely because it is a precursor for another pollutant. 
Rather, CAA section 302(g) clearly defines the term ``air pollutant'' 
to ``include any precursors to the formation of any air pollutant.''
---------------------------------------------------------------------------

    \220\ Ibid. (emphasis added).
    \221\ 42 U.S.C. 7602(j).
---------------------------------------------------------------------------

    With regard to the setting of the major source thresholds for 
PM10 precursors in Serious areas, a House of Representatives 
Report accompanying the 1990 amendments to the CAA described the 
effects of adding CAA section 189(b)(3), defining ``major'' sources 
locating in PM nonattainment areas classified as Serious as those 
sources that emit or have the potential to emit 70 tpy of 
PM10. The report specifically notes that ``new or modified 
sources emitting 70 tons or more per year of VOC [a PM2.5 
precursor] will be subject to new source review requirements.'' \222\ 
Thus, Congress contemplated that the same major source threshold would 
apply to sources of direct PM10 emissions and 
PM10 precursors in Serious PM10 nonattainment 
areas. The same approach logically applies when applying the provision 
to sources locating in areas designated as Serious PM2.5 
nonattainment areas.
---------------------------------------------------------------------------

    \222\ H.R. Rep. 101-490.
---------------------------------------------------------------------------

    Since the EPA may not have the legal authority to establish major 
source thresholds for PM2.5 precursors at levels higher than 
the statutory threshold applied to sources of direct PM2.5 
emissions, it would be inappropriate to allow states discretion for 
setting major source thresholds for PM2.5 precursors that 
exceed the statutory thresholds. Moreover, while we acknowledge that 
PM2.5 precursors will not likely form ambient 
PM2.5 in the nonattainment area on a ton-per-ton basis, 
there is not currently sufficient technical basis that would enable the 
agency to propose uniform higher major source thresholds for any of the 
four PM2.5 precursors. As stated in the proposal, the EPA 
intends to continue its analysis of the relationship between each 
precursor and ambient PM2.5 concentrations.
    Comment: Some commenters questioned the EPA's interpretation of the 
2006 court decision in South Coast Air Quality Mgmt. Dist. v. EPA \223\ 
as precluding higher major source thresholds because the court 
determined that NSR provisions, including major source thresholds, were 
control requirements subject to anti-backsliding provisions of the 
statute. The commenter argued that the South Coast decision did not 
address setting a major source threshold for a precursor pollutant that 
is as stringent as, or more stringent than, the major source threshold 
for the pollutant when the pollutant is directly emitted. The commenter 
stated the statutory provision on which the court in South Coast relied 
[CAA section 172(e)] is applicable on its face only when the EPA 
relaxes the NAAQS, which the commenter claimed is not relevant to the 
current situation here, where the EPA has promulgated progressively 
more stringent NAAQS for PM.
---------------------------------------------------------------------------

    \223\ South Coast Air Quality Mgmt. Dist. v. EPA, 472 F.3d 882, 
900-902 (D.C. Cir. 2006) (South Coast decision).
---------------------------------------------------------------------------

    Response: CAA section 189(e) requires the control requirements that 
are applicable to major stationary sources of PM2.5 to also 
apply to major stationary sources of PM2.5 precursors. The 
court in South Coast held that the term ``controls'' under section 
172(e) of the CAA includes NSR requirements, and in particular includes 
major source thresholds specified by the statute.\224\ The commenter 
did not explain why the term ``control'' in CAA section 189(e) of the 
statute should be interpreted differently than the term ``control'' in 
other parts of the statute. Section 172(e) of the CAA is a provision in 
subpart 1 of part D of the statute concerning anti-backsliding 
requirements in designated nonattainment areas. It is reasonable for 
the EPA to conclude that the term ``control'' in one part of the 
statute pertaining to nonattainment area requirements should be 
interpreted consistent with the use of that term in other provisions of 
part D pertaining to nonattainment area requirements, particularly 
where both provisions apply to designated PM2.5 
nonattainment areas. Thus, consistent with the holding of South Coast 
regarding the definition of ``controls,'' the EPA interprets the use of 
the term ``control requirements'' in CAA section 189(e) to require the 
same major source threshold be applied to PM2.5 precursors 
as applies to direct PM2.5 emissions.
---------------------------------------------------------------------------

    \224\ See South Coast decision (holding that ``controls'' in CAA 
section 172(e) anti-backsliding provision include NSR requirements 
such as LAER, offset ratios, and major source thresholds).
---------------------------------------------------------------------------

    The commenter also did not explain, and it is not clear, how a 
relaxation versus a strengthening of the NAAQS would bear on whether 
the EPA has authority to set different control requirements (e.g., 
major source thresholds) for sources of direct emissions of a pollutant 
and sources of precursors of that pollutant. The EPA notes that 
Congress, in adding additional particulate matter requirements in 
subpart 4 of the CAA,

[[Page 58113]]

decided that more stringent requirements were required to address air 
quality in particulate matter nonattainment areas. Hence, it would be 
inconsistent with that intention for Congress to allow higher major 
source thresholds to apply to sources of precursors than apply to 
direct PM2.5 emissions.
    The EPA therefore believes that at this time the most reasonable 
approach for defining the major source threshold for PM2.5 
precursors in both Moderate and Serious areas is to use the same 
threshold that is being defined for direct PM2.5 emissions. 
As explained earlier, the EPA currently has studies underway to better 
understand the effects of emissions of each precursor on the secondary 
formation of ambient PM2.5 concentrations. However, even if 
such studies support the commenters' recommendation for higher 
precursor thresholds, the EPA must consider the potential legal 
restrictions on setting thresholds for precursors above the statutory 
requirements for direct emissions of an air pollutant.
c. Significant Emissions Rates (SERs) for PM2.5 Precursors
i. Summary of Proposal
    As noted earlier, stationary sources locating in nonattainment 
areas are subject to the NNSR permitting requirements to the extent 
construction at the source qualifies as a major modification with 
respect to a pollutant for which the area is designated nonattainment. 
A major modification of a stationary source is defined in the NNSR 
regulations at 40 CFR 51.165(a)(1)(v)(A) as ``any physical change in or 
change in the method of operation of a major stationary source'' that 
would result in (1) a significant emissions increase of a regulated NSR 
pollutant, and (2) a significant net emissions increase of that 
pollutant. The term ``significant'' is separately defined at 40 CFR 
51.165(a)(1)(x)(A) to mean a rate of emissions specified for each 
pollutant or precursor for that pollutant. This is known as a 
significant emissions rate (SER). In the 2008 PM2.5 NSR 
Rule, the EPA defined ``significant'' for SO2 and 
NOX as PM2.5 precursors with an emissions rate of 
40 tpy for each precursor.\225\ Also, in the preamble to the 2008 
PM2.5 NSR Rule, the EPA indicated that it would consider 40 
tpy of VOC emissions to be ``significant'' in any state regulating VOC 
as a PM2.5 precursor; however, that significant emissions 
rate was not codified in any of the NSR regulations because the 
regulations governing both NNSR and PSD permitting programs provided 
that VOC was generally presumed not to be a precursor to 
PM2.5. Instead, the agency explained that any state making a 
demonstration that VOC should be treated as a PM2.5 
precursor in a particular nonattainment area ``would be required to 
adopt the 40 tpy SER unless it demonstrated that a more stringent SER 
(lower rate) is more appropriate.''\226\
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    \225\ See the Federal Register published on May 16, 2008 (73 FR 
28321, 28333 and 28334); and existing 40 CFR 51.165(a)(1)(x)(A).
    \226\ See the Federal Register published on May 16, 2008 (73 FR 
28321 and 28333).
---------------------------------------------------------------------------

    The EPA did not include any changes to the existing SERs for 
SO2 and NOX as PM2.5 precursors in the 
proposal. Nor did we propose a SER for ammonia, citing a lack of 
adequate technical support. However, the EPA proposed to codify a SER 
of 40 tpy for VOC in the NNSR permitting regulations. See 55 FR 
15434.\227\ The EPA further stated that, as a result, only the ammonia 
SER would remain to be defined by each state that needs to control 
major stationary sources of ammonia as part of its NNSR program for 
PM2.5. While not proposing to revise the existing 40 tpy SER 
values for SO2 and NOX, the EPA indicated it 
believed that, when more data are available, such data might provide a 
reasonable basis for considering subsequent changes to the SER for each 
PM2.5 precursor for purposes of implementing the 
PM2.5 NAAQS. Moreover, the EPA indicated that a separate 
rulemaking might be used to propose a new SER for each PM2.5 
precursor. See 80 FR 15434.
---------------------------------------------------------------------------

    \227\ The EPA notes that the 2015 NPRM included some potentially 
conflicting statements concerning the development of a SER for VOC. 
First, the preamble indicated that the EPA intended to consider a 
separate rulemaking to consider proposing new SERs for 
SO2 and NOX, while also proposing individual 
significant emissions rates for VOC and ammonia. Later in the same 
preamble, the EPA indicated that it was proposing to add VOC as a 
precursor with a 40 tpy significant emissions rate, and included 
regulatory text to show that aspect of the proposal, i.e., proposed 
40 CFR 51.165(a)(1)(x)(A).
---------------------------------------------------------------------------

ii. Final Rule
    The EPA is finalizing its proposed approach with some changes to 
the final regulatory language. The final rule amends the definition of 
``significant'' in the NNSR regulations at 40 CFR 51.165(a)(1)(x)(A) to 
add a SER for VOC. Thus, the revised definition contains individual 
SERs for direct PM2.5 emissions (10 tpy), SO2 
emissions (40 tpy), NOX emissions (40 tpy), and VOC 
emissions (40 tpy). The revised definition does not contain a SER for 
ammonia emissions. Instead, a new subparagraph has been added to the 
definition of ``significant'' to require that an implementation plan 
defines the term for ammonia in cases where sources of ammonia are not 
otherwise exempted from NNSR control requirements. See 40 CFR 
51.165(a)(1)(x)(F). Such definition of ``significant'' for ammonia 
would need to be established by the state for a particular 
nonattainment area as part of its SIP submission for NNSR. The EPA's 
rationale for not establishing an ammonia SER in this action is 
provided in greater detail in the following section.
iii. Comments and Responses
    Comment: Several commenters generally recommended that the EPA 
establish higher SERs for the PM2.5 precursors. These 
commenters expressed the need for values that more accurately 
represented each precursor's relative effect on ambient 
PM2.5 concentrations. One of these commenters stated that in 
the absence of such higher SERs in the NNSR regulations, the EPA should 
allow states to demonstrate the appropriateness of a higher SER for a 
particular precursor on either a statewide or area-by-area basis in a 
SIP submission, or through the NNSR program on a case-by-case basis.
    Another of the commenters supporting higher significance thresholds 
for each precursor stated that the CAA's definitions of ``major 
source'' and ``major emitting facility'' trigger the statutory control 
requirements and its permit requirements for affected sources, but they 
do not define how much of a pollutant is regulated after the control or 
permit requirement is triggered by the CAA. The commenter stated that 
the EPA would appear to have ample authority to require that precursors 
be regulated based on different thresholds once a major source triggers 
a particular control or permit requirement, provided there is adequate 
technical basis for doing so.
    Response: The EPA did not propose to reconsider or revise the SERs 
for SO2 and NOX; therefore, revisions to these 
rates are outside the scope of this action. Even if the EPA were to 
consider such a revision, it would provide little relief to new or 
modified sources subject to NSR. Because SO2 and 
NO2 are pollutants for which the EPA has established NAAQS 
and because NOX and VOC are precursors for ozone, 
modifications with emissions increases above the current SERs for 
SO2, NOX or VOC would still be subject to some 
form of new source review (PSD if the area is attainment for the NAAQS 
pollutant or nonattainment NSR if the area is nonattainment) even if 
the SERs for these pollutants as PM2.5 precursors were 
revised to a higher value.

[[Page 58114]]

Moreover, we do not believe that the statute would permit the EPA or 
states to adopt a definition of ``significant'' for purposes of 
identifying modifications subject to NSR permitting with rates greater 
than the statutory and regulatory definitions of a major source in a 
nonattainment area, as defined in CAA section 302(j) for sources 
locating in PM2.5 nonattainment areas classified as Moderate 
(100 tpy) and as defined in CAA section 189(b)(3) for sources locating 
in PM2.5 nonattainment areas classified as Serious (70 tpy). 
Consequently, we do not believe that there would be substantial cost 
savings to many sources if we were to revise the SERs for these 
pollutants specifically as PM2.5 precursors.
    Comment: Some commenters directed specific attention to the 
definition of a SER for ammonia. These commenters urged the EPA to set 
a significance threshold for ammonia as soon as possible. These 
commenters stated that, without a SER, any significant emissions 
increase greater than zero tons per year would result in a major source 
review for NNSR.
    Some commenters stated that, while the EPA indicates that a SER for 
ammonia may be developed in a subsequent rulemaking, if that rulemaking 
is not timely, the state would need to develop a SER for ammonia to 
reduce the burden on permit applicants and avoid permit issuance delays 
related to major source applicability determinations and permit 
development for ammonia and PM2.5. Two of the commenters 
noted that ammonia is used in many industry and source types to control 
NOX emissions through the implementation of selective 
catalytic reduction (SCR) and selective non-catalytic reduction (SNCR) 
control devices. These commenters stated that, without a SER for 
ammonia, it's very possible that many NNSR reviews will be initiated 
simply because of any ammonia increase at a major source. To address 
this problem, some commenters stated that, until the EPA completes its 
analysis for ammonia, states need the ability to conduct case-by-case 
reviews for NNSR permits by requiring applicants to submit a technical 
demonstration showing that emissions of a particular precursor do not 
significantly contribute to PM2.5 levels that exceed the 
standard in an area, thus exempting the precursor from being controlled 
by that source.
    Some commenters recommended that the EPA propose a SER for ammonia 
before finalizing the March 23, 2015, proposal and suggested the EPA 
should also provide definitive guidance for state and local agencies on 
how to conduct permitting of major sources of ammonia until a SER is 
established. Other commenters stated that, at the time the EPA proposes 
new significant emission rates for precursors, the EPA should also 
establish the significant emission rate for ammonia. Yet another 
commenter stated that any precursor analyses conducted by the EPA 
should be done in close coordination with designated nonattainment 
areas to reduce duplication of efforts and conflicting outcomes that 
could in turn lead to more costly impacts on sources and on agencies' 
limited resources. Finally, some commenters stated that the EPA should 
at least provide guidance for states to develop a SER for ammonia as a 
PM2.5 precursor.
    Response: The EPA did not propose a SER for ammonia and, therefore, 
this rule does not finalize a SER for ammonia. The EPA's initial plan, 
as explained in the proposal, was to establish a SER for ammonia in a 
separate rulemaking, which was also intended to establish significant 
impact levels (SILs) for Ozone and PM2.5 in order to 
streamline the air quality impact analysis under the PSD permitting 
program. However, based on the imminent need for the SILs (especially 
for ozone) for PSD permitting, the agency has decided to issue guidance 
in lieu of a rulemaking for the PSD-based SILs. After due 
consideration, the EPA has also concluded that a separate rulemaking 
solely for the purpose of developing a SER for ammonia is not 
warranted. We anticipate that very few states will actually need to 
control source modifications of ammonia under their NNSR programs for 
PM2.5 since (1) stationary sources of ammonia generally are 
not one of the primary causes of ambient PM2.5 
concentrations in most PM2.5 nonattainment areas, and (2) 
according to information in the EPA's NEI database, most existing 
PM2.5 nonattainment areas do not have an existing major 
stationary source of ammonia to which the ammonia SER would be applied 
to determine whether a proposed modification of such major source would 
be ``major'' for ammonia.
    Unlike the EPA's PSD regulations, the definition of ``significant'' 
in the NNSR regulations at 40 CFR 51.165 does not include a provision 
stipulating that, for any pollutant that does not have a listed 
emissions rate, ``any increase'' must be considered significant.\228\ 
Therefore, contrary to the concerns of some commenters, the absence of 
an ammonia SER in the EPA's NNSR regulations at 40 CFR 51.165 does not 
result in a default ``any increase'' interpretation of ``significant'' 
that must be contained in state NNSR programs. Accordingly, for the 
above reasons and due to the time, resources and process investment 
associated with a national rulemaking, the EPA believes that a national 
rulemaking to develop a SER for ammonia is neither warranted nor 
effective. As explained above, the EPA is finalizing a provision that 
requires states that must regulate modified major stationary sources of 
ammonia to develop and submit a definition of ``significant,'' such as 
an appropriate SER, for ammonia to be included, subject to the EPA's 
approval in the state's SIP. See 40 CFR 51.165(a)(1)(x)(F). The EPA 
recommends that states consult with the appropriate EPA Regional Office 
to develop an ammonia SER as a means of defining ``significant'' for a 
particular nonattainment area. As a general rule, the EPA believes that 
the ammonia SER in a Moderate nonattainment area should be an emissions 
rate no greater than 100 tpy of ammonia. Any SER that exceeds 100 tpy 
could not be approved by the EPA because any higher emissions rate 
would exceed the major source threshold established in the CAA.\229\ In 
the event that a nonattainment area is classified Serious for 
PM2.5, the maximum acceptable ammonia SER would be a rate no 
greater than 70 tpy in accordance with the major source thresholds 
being finalized in this rule for major stationary sources of direct 
PM2.5 emissions and PM2.5 precursors locating in 
Serious PM2.5 nonattainment areas. States that regulate 
ammonia as a PM2.5 precursor should also include a technical 
justification for the ammonia SER for a nonattainment area that the 
state includes as a part of its NNSR SIP rules submission for EPA 
approval.
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    \228\ Compare the definitions of ``significant'' under the PSD 
regulations at 40 CFR 51.166(b)(23) and 52.21(b)(23), especially 
subparagraph (ii), with the NNSR definition at 40 CFR 51.165(a)(x).
    \229\ The NNSR definition of ``major stationary source'' 
includes a provision at 40 CFR 51.165(a)(iv)(A)(3) that requires any 
physical change at an existing source that would not otherwise 
qualify as a major stationary source if the change would constitute 
a major stationary source by itself.
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d. NNSR Applicability Determinations
i. Summary of Proposal
    In setting SERs and major source thresholds for emissions of direct 
PM2.5 and PM2.5 precursors, the EPA explained in 
the preamble to the proposal that it intended for direct 
PM2.5 emissions and each individual PM2.5 
precursor to be treated separately for determining the applicability of 
the

[[Page 58115]]

NNSR requirements to a proposed new source or modification. The EPA 
stated that such individual treatment of direct emissions and 
precursors was consistent with its policy as explained in previous 
rulemakings. In particular, the preamble to the 2008 PM2.5 
NSR Rule explained that this applicability interpretation applied to 
both PSD and NNSR. However, at that time, we did not codify this 
interpretation in any of the NSR regulations. See 73 FR 28231, May 16, 
2008, at page 28331. In the proposal, the EPA proposed language in the 
NNSR regulations at 40 CFR 51.165(a)(2)(i) to explicitly codify the 
policy.
ii. Final Action
    The EPA is revising the NNSR regulations at 40 CFR 51.165(a)(2)(i) 
to codify the EPA's policy that direct emissions of a pollutant and 
emissions of any applicable precursor are to be considered 
independently for purposes of determining the applicability of the NNSR 
requirements for PM2.5 sources. For example, in order for a 
source to be subject to the NNSR requirements for PM2.5 with 
respect to NOX as a PM2.5 precursor, the source 
must be either (1) a new stationary source that emits or has the 
potential to emit major amounts of NOX (new major source of 
NOX); or (2) an existing major source of NOX that 
proposes to increase its emissions of NOX by a significant 
amount and also results in a significant net emissions increase.
iii. Comments and Responses
    Comment: A commenter requested that the EPA clarify in its NSR 
rules how to evaluate major source applicability for NNSR and PSD with 
respect to PM2.5 precursors. The commenter agreed that major 
source applicability determinations should be based on individual 
precursor pollutant emissions, and that different pollutants, including 
individual precursors, should not be summed to determine applicability 
for NNSR major stationary source or major modification. The commenter 
also raised various questions pertaining to how the precursors would 
trigger major source applicability for other pollutants.
    Response: This final rule contains the following statement within 
the NNSR regulations at 40 CFR 51.165(a)(2)(i), ``Different pollutants, 
including individual precursors, are not summed to determine 
applicability of a major stationary source or major modification.'' The 
commenter's specific precursor-related applicability questions and the 
EPA's responses are included in the Response to Comment document 
contained in the Docket for this rulemaking.
e. NNSR Plan Due Dates
i. Summary of Proposal
    In the proposal, the EPA explained that CAA section 189(a)(2)(B) 
requires states to submit to the EPA an attainment plan satisfying the 
applicable requirements within 18 months of an area being designated 
nonattainment pursuant to a new or revised PM2.5 NAAQS. See 
80 FR 15437. Section 189(a)(1)(A) of the CAA specifically requires that 
such plans include the NNSR permitting requirements under CAA section 
173. Thus, the EPA indicated that states would be required to submit 
the applicable NNSR program requirements for PM2.5 within 18 
months from the effective date of area designations for the 2012 
PM2.5 NAAQS. See 80 FR 15437.
    The EPA also noted that the CAA does not specify a deadline for the 
states' submittal of NNSR program revisions in the event that a 
Moderate PM2.5 nonattainment area is subsequently 
reclassified as Serious like the CAA establishes a deadline for other 
plan provisions. Accordingly, the EPA used its gap-filling authority 
under CAA section 301(a) to propose a similar 18-month deadline, from 
the effective date of a final reclassification of the area as Serious, 
for states to submit a plan prescribing the more stringent NNSR 
requirements required by the statute for Serious areas. However, in 
light of the fact that such revisions would generally be 
straightforward to make, and to assure that new major sources and major 
modifications in the area would be subject to the more stringent NNSR 
requirements contained in subpart 4 for Serious areas, the EPA sought 
comments on an alternative 12-month timeframe for submittal of the NNSR 
plan revisions for Serious areas.
ii. Final Rule
    The EPA is finalizing an 18-month deadline for states to submit 
plan revisions for NNSR requirements for PM2.5 after an area 
is initially designated to nonattainment (Moderate area) or 
reclassified to Serious. See 40 CFR 51.1003(a) and (b), respectively. 
As explained elsewhere in this Section VIII of the preamble, plan 
revisions applicable to areas reclassified as Serious must address the 
more stringent major source thresholds for direct PM2.5 
emissions and each applicable PM2.5 precursor for Serious 
areas. With regard to the provisions for precursors, the EPA emphasizes 
that if the state seeks to continue to exempt a precursor from NNSR 
control requirements, the state will need to reevaluate any previous 
finding that resulted in the exclusion of a precursor from the NNSR 
control requirements on the grounds that the precursor did not 
significantly contribute to PM2.5 levels that exceed the 
NAAQS. The requirement at 40 CFR 51.1006(b) calling for a new NNSR 
precursor demonstration means that, even if the existing NNSR program 
already includes the necessary provisions for a Serious area 
classification under a prior approval, a plan revision pertaining to 
NNSR may still be required to add requirements for a precursor that had 
previously been exempted, if a new NNSR precursor demonstration does 
not support continued exemption of that precursor.
    The requirements for submitting plan revisions at 40 CFR 51.1003 
also provide for situations where an area classified as Serious is 
subject to CAA section 189(d) for failing to attain the 
PM2.5 NAAQS by the applicable Serious area attainment date. 
See 40 CFR 51.1003(c). The list at Sec.  51.1003(c), which contains 
attainment plan requirements that must be submitted as plan revisions, 
does not include the NNSR plan requirements contained at Sec.  51.165. 
This omission results from the fact that Serious area requirements 
should have already been included in the NNSR program when the area was 
originally reclassified as Serious. Hence, there is no explicit 
requirement to revise the NNSR plan requirements in such cases. 
However, in light of the fact that states have the opportunity to 
submit a new NNSR precursor demonstration for each required plan 
revision (40 CFR 51.1006(b)), there may indeed be a need to revise the 
NNSR requirements in the event that a previous exemption can no longer 
be supported by the new NNSR precursor demonstration. Therefore, to the 
extent that a state's plan previously exempted sources of a precursor 
from NNSR regulation, a plan revision for a Serious area that fails to 
attain the PM2.5 NAAQS by the applicable Serious area 
attainment date will need to include a re-evaluated NNSR precursor 
demonstration if the state wishes to continue to exempt sources of that 
precursor. Such a plan revision is required to be submitted no later 
than 12 months from the applicable Serious area attainment date that 
was previously missed, in accordance with 40 CFR 51.1003(c)(2). The 
NNSR regulations have also been amended at 40 CFR 51.165(a)(13) to 
address the need to re-evaluate such a demonstration to

[[Page 58116]]

exempt a particular precursor from the NNSR requirements for 
PM2.5.
iii. Comments and Responses
    Comment: Some commenters supported allowing states at least 18 
months to make the required SIP submission for NNSR. A commenter who 
supported the longer submission period stated that, although it is easy 
to write the rule language to make this change, it is likely to be 
quite difficult to perform the environmental and socio-economic 
analyses required by state law if the lowering of the threshold for a 
Serious area does indeed have a significant effect on the building of 
new or the repowering of existing power plants.
    Response: Although the types of revisions needed to an existing 
NNSR program to address the new subpart 4 requirements for 
PM2.5 are relatively straightforward, the EPA acknowledges 
that such changes nevertheless often involve related analyses as well 
as state legislative review and approval. In addition, some states will 
be submitting NNSR regulations for PM2.5 for the first time 
and, as such, could need more than 12 months to obtain the necessary 
legislative review and approval. Accordingly, the EPA believes that the 
most reasonable approach for establishing the plan due date for revised 
plans for PM2.5 is to establish an 18-month deadline for 
submission of plans both upon initial designation to nonattainment for 
a particular PM2.5 standard and upon any subsequent 
reclassification to Serious.
2. Offset Ruling at 40 CFR Part 51 Appendix S
    In this final rule, as explained later, the EPA is making the 
following revisions for PM2.5 in the Emission Offset 
Interpretive Ruling (40 CFR part 51, Appendix S): (a) Amending the 
definition of ``regulated NSR pollutant'' with regard to 
PM2.5 precursors; (b) amending the definition of ``major 
stationary source'' with regard to major sources of direct 
PM2.5 emissions and PM2.5 precursors in Serious 
areas; and (c) amending the definition of ``significant'' with regard 
to identifying major modifications of sources of PM2.5 
precursors.
a. Appendix S Definition of ``Regulated NSR Pollutant''--
PM2.5 Precursors
i. Summary of Proposal
    The definition of ``regulated NSR pollutant'' contained in Appendix 
S at section II.A.31(ii)(b)(2) has, to date, only required regulation 
of SO2 as a PM2.5 precursor for states relying on 
Appendix S to issue permits to sources locating in PM2.5 
nonattainment areas. The EPA proposed to revise the definition in 
Appendix S of ``regulated NSR pollutant'' to also require regulation of 
NOX as a PM2.5 precursor.\230\ The EPA noted that 
this proposed approach would ensure that states using the permitting 
requirements contained in Appendix S to issue permits to major new and 
modified sources in PM2.5 nonattainment areas will regulate 
the same precursors that have been subject to regulation in states that 
have already adopted NNSR requirements for PM2.5 based on 
the 2008 PM2.5 NSR Rule.
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    \230\ The EPA notes that in the preamble to the proposal, it was 
stated that the EPA proposed to add NOX as a 
PM2.5 precursor at section II.A.31.(iii)(b) of Appendix 
S. This was an incorrect reference, which should have read ``section 
II.A.31.(ii)(b).'' This final rule cites the correct section for the 
affected portion of the definition of ``regulated NSR pollutant,'' 
where NOX is being added as a PM2.5 precursor.
---------------------------------------------------------------------------

    The EPA also proposed an alternative approach based on similar 
logic that would initially require only SO2 and 
NOX to be regulated as PM2.5 precursors, while 
later phasing in VOC and ammonia after states have prepared and the EPA 
has had sufficient time to evaluate any pending precursor 
demonstrations. See 80 FR 15436-37. Finally, the EPA also sought 
comments on an alternative to require the immediate regulation of all 
four scientific PM2.5 precursors (SO2, 
NOX, VOC and ammonia) in Appendix S.
ii. Final Rule
    The EPA is amending Appendix S in this final rule to provide for 
the immediate regulation of SO2 and NOX as 
regulated NSR pollutants (specifically as PM2.5 precursors) 
and for the subsequent conditional phasing in of VOC and ammonia as 
regulated NSR pollutants (PM2.5 precursors) on the date 24 
months from the effective date of the nonattainment designation in each 
area. The EPA was persuaded by the comments received expressing 
concerns that states may delay NNSR SIP development to instead rely on 
a less-inclusive Appendix S for NNSR permitting if only SO2 
and NOX were regulated.
    The alternative proposal featuring the phase-in approach balances 
the opportunity for states to demonstrate in the short-term that 
certain precursors need not be regulated with the need to ensure that 
the appropriate precursors are controlled in a manner consistent with 
the CAA. NNSR is unique among the nonattainment area requirements in 
that sources seeking a construction permit must comply with NNSR 
requirements for a particular pollutant as soon as an area is 
designated nonattainment for that pollutant and not some months or 
years later, when the EPA formally approves a state plan and the 
sources comply with the remaining plan provisions. With respect to 
precursors in particular, this means that new and modified major 
sources of direct PM2.5 or a regulated PM2.5 
precursor would be subject to NNSR regulation upon the effective date 
of the area designation to nonattainment. If the EPA required the 
immediate regulation of all four scientific PM2.5 precursors 
in Appendix S, states issuing permits pursuant to those provisions 
during the interim SIP development period would need to require 
regulation of certain precursors that the state may later be able to 
demonstrate through a SIP submission do not significantly contribute to 
PM2.5 levels that exceed the standard in a particular area. 
As state plans making such a NNSR precursor demonstration are not due 
until 18 months after the effective date of the area designation, and 
as the statute allows the EPA up to 18 months to act on such 
submissions, sources seeking permits to locate in such areas during 
this interim period might for several years be subject to more 
stringent controls than necessary to address PM2.5 
nonattainment in that area.
    The EPA is also cognizant, however, that some states have relied on 
Appendix S to conduct NNSR permitting well beyond the statutory SIP 
development period. In such cases, it would be inequitable if states 
could indefinitely rely on Appendix S that requires little to no 
regulation of some of the scientific PM2.5 precursors when 
other states are fulfilling their statutory duty to submit a SIP 
revision addressing all PM2.5 precursors. In particular, 
states that have submitted NNSR SIPs addressing PM2.5 
requirements for the 1997 and 2006 standards have to date regulated 
SO2 and NOX as PM2.5 precursors. These 
SIP provisions will continue to apply with respect to any areas 
designated nonattainment as to the 2012 standard in those states until 
the states submit SIP revisions to address the 2012 NAAQS, including 
provisions necessary to comply with the precursor requirements in CAA 
section 189(e). States either continuing to rely on Appendix S by 
virtue of a nonattainment area designation under a prior 
PM2.5 standard or states newly relying on Appendix S by 
virtue of a nonattainment area designation under the 2012 standard have 
to date only been required to regulate SO2 as a

[[Page 58117]]

regulated NSR pollutant (specifically as a PM2.5 precursor).
    In order to balance these competing interests and concerns, the EPA 
has determined in this final rule to revise Appendix S in order to 
require that any state relying on Appendix S initially regulate both 
SO2 and NOX as regulated NSR pollutants 
(PM2.5 precursors) for NNSR permits, thereby aligning the 
requirements of Appendix S with the prevailing requirements of SIP-
approved NNSR permitting provisions for PM2.5 in other 
states. See Appendix S, section II.A.31.(ii)(b)(2). Further, the final 
rule provides that VOC and ammonia will be phased in as regulated NSR 
pollutants (PM2.5 precursors) according to a prescribed 
schedule based on existing and future nonattainment area designations 
for PM2.5, unless the EPA has determined, prior to the 
scheduled phase-in, that the state submitted a complete proposed NNSR 
program for PM2.5 that includes a NNSR precursor 
demonstration. The EPA believes it is reasonable not to require 
regulation of sources of VOC and ammonia in Appendix S during the 
interim SIP development period because we expect that, in many cases, 
states will submit SIPs that include as part of their proposed NNSR 
rules for PM2.5 a NNSR precursor demonstration indicating 
that they do not need to regulate new major stationary sources and 
major modifications of ammonia (and in some cases of VOC) under their 
NNSR programs in order to provide for attainment of the 
PM2.5 NAAQS.
    Under the phase-in schedules being finalized in Appendix S, permits 
issued by states under the requirements in Appendix S will not be 
required to address VOC and ammonia as regulated NSR pollutants 
(PM2.5 precursors) until the state has had an opportunity to 
show that, as part of a proposed NNSR program for PM2.5, 
sources of a particular precursor does not significantly contribute to 
PM2.5 concentrations that exceed the standard in a given 
nonattainment area. If a state submits such a NNSR precursor 
demonstration as to either VOC or ammonia as part of a complete SIP 
submission that includes the state's proposed NNSR program for 
PM2.5, the state would not be required to regulate the 
applicable precursor pursuant to the provisions of Appendix S, unless 
the EPA reviews that proposed NNSR program for PM2.5 and the 
NNSR precursor demonstration and either determines that the SIP 
submission is incomplete or disapproves both the NNSR program and the 
NNSR precursor demonstration. Thus, the regulation of VOC and ammonia 
as regulated NSR pollutants (PM2.5 precursors) pursuant to 
Appendix S will occur in three circumstances. First, in the absence of 
a plan submission that includes the appropriate NNSR precursor 
demonstration, VOC and ammonia will be phased in as regulated 
precursors pursuant to Appendix S 24 months after the effective date of 
area designations for PM2.5. This will prevent states that 
fail to make a complete plan submission from continuing to rely on 
Appendix S to regulate only SO2 and NOX as 
PM2.5 precursors indefinitely. Second, if the EPA determines 
that the portion of the SIP containing the NNSR precursor demonstration 
submitted by the state is incomplete within the time allowed under CAA 
section 110(k)(1)(B), all precursors must be regulated upon EPA's 
determination of incompleteness or by the prescribed phase-in date, 
whichever date is later. The EPA believes it is important to condition 
the phase-in of VOC and ammonia regulation on the completeness of the 
SIP submission in order to deter the submission of plans that do not 
meet certain minimum criteria simply to avoid the regulation of these 
additional precursors.\231\ Finally, if the EPA disapproves both the 
proposed NNSR program for PM2.5 and the accompanying NNSR 
precursor demonstration, the relevant precursors will be phased in to 
be regulated under Appendix S as of the effective date of the 
disapproval or by the prescribed phase-in date, whichever date is 
later.\232\
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    \231\ The minimum requirements for evaluating the completeness 
of such submissions can be found in 40 CFR part 51, Appendix V, 
Criteria for Determining the Completeness of Plan Submissions.
    \232\ If the EPA disapproves a state's NNSR precursor 
demonstration but the state's NNSR program is otherwise approvable, 
the EPA may partially disapprove the NNSR SIP provisions for failure 
to properly regulate sources of the relevant precursor and otherwise 
partially approve the program. Upon the partial approval of a 
state's NNSR program, Appendix S will no longer be the applicable 
set of requirements by which NNSR permits are to be issued by the 
state. Thus, the phase-in of the relevant precursor will only occur 
in the event that the EPA both disapproves the NNSR program for 
PM2.5 and the state's NNSR precursor demonstration. The 
partial disapproval of a state's NNSR program with respect to the 
regulation of a precursor will obligate the EPA to promulgate a 
federal implementation plan (FIP) pursuant to CAA section 110(c)(1) 
to address the regulation of that precursor within 2 years of the 
disapproval unless the Administrator approves a state plan or plan 
revision correcting the deficiency. The disapproval will also 
trigger the application of sanctions pursuant to CAA section 179(a) 
unless the state corrects the deficiency within 18 months.
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    The EPA chose this 24-month period for phase-in of VOC and ammonia 
as PM2.5 precursors in accordance with (1) the requirement 
under CAA section 189(a)(2)(B) of subpart 4 that plan revisions for 
PM2.5 attainment plans be submitted to the EPA within 18 
months of area designations, and (2) the requirement under CAA section 
110(k)(1)(B) that the EPA determine no later than six months after the 
date by which a state is required to submit a SIP whether a state has 
made a submission that meets the minimum completeness criteria 
established per CAA section 110(k)(1)(A).\233\ In order to provide an 
appropriate balance between the EPA's interests in providing states 
with the opportunity to develop precursor demonstrations prior to 
regulation of those precursors and in encouraging states to submit SIPs 
in a timely manner, the EPA believes it is reasonable to align the 
conditional phase-in of VOC and ammonia as regulated NSR pollutants 
(PM2.5 precursors)with the statutory timeframe for states to 
make SIP submissions addressing precursor regulation for NNSR and for 
the EPA to evaluate whether a state has made a complete submission. 
Thus, if by this 24-month deadline, a state has not submitted a 
precursor demonstration that VOC and/or ammonia need not be regulated, 
which has been determined to be complete by the EPA or deemed complete 
by the operation of law by this 24-month deadline, Appendix S will 
require regulation of these precursors going forward.
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    \233\ CAA section 110(k)(1)(B) specifically requires the 
Administrator to evaluate the completeness of a SIP submission 
within 60 days of receipt, but no later than 6 months after the date 
by which the SIPs were due. If the Administrator does not 
affirmatively evaluate the completeness of the SIP within that time 
period, the statute provides that the SIP shall be deemed complete 
by operation of law 6 months after receipt.
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    The EPA has specifically included the 6-month period for EPA's 
completeness review because we believe it is important to discourage 
states from submitting SIPs that do not meet the minimum completeness 
criteria found in 40 CFR part 51, Appendix V. Conditioning the phase-in 
on a completeness review will not only encourage states to make timely 
SIP submissions addressing the NNSR requirements, but also ensure that 
those submissions contain the minimum information necessary to enable 
the Administrator to determine whether the SIP complies with the 
statute. If a state with a designated PM2.5 nonattainment 
area that is currently relying on Appendix S makes a submission 
addressing NNSR program requirements, including a NNSR precursor 
demonstration, within 18 months of the designation (as required by CAA 
section 189(a)(2)(B)), either EPA

[[Page 58118]]

must evaluate the submission for completeness within 6 months or the 
SIP will become complete by operation of law, pursuant to CAA section 
110(k)(1)(B). The latest date that a timely-submitted implementation 
plan would be determined to be complete by the EPA or deemed complete 
by operation of law is 24 months from the effective date of the 
PM2.5 nonattainment area designation. In other words, in the 
absence of EPA action to evaluate completeness, a state that submits a 
timely SIP addressing NNSR and including a NNSR precursor demonstration 
can be confident the submission will become complete by operation of 
law by the 24-month conditional phase-in date, and such states will not 
be required to regulate the precursor addressed by its demonstration 
(VOC or ammonia) in the PM2.5 nonattainment area pursuant to 
Appendix S during the period of EPA's review of the SIP. States that 
submit untimely SIPs, after the 18-month SIP submission deadline, 
cannot rely on the SIP becoming complete by operation of law before the 
24-month conditional phase-in date. If the EPA has not acted to 
evaluate the completeness of the state's untimely SIP by the 24-month 
conditional phase-in, control of VOC and ammonia are automatically 
phased in for the PM2.5 nonattainment area under Appendix S, 
regardless of whether such SIP submission might later be determined 
complete, whether by EPA or by operation of law. Thus, if a state 
submits an untimely SIP addressing NNSR for a particular 
PM2.5 nonattainment area, including an NNSR precursor 
demonstration, such state can only avoid the conditional phase-in of 
VOC and ammonia control pursuant to Appendix S if the EPA affirmatively 
determines the submission to be complete by 24 months from the date of 
the area designation. In such circumstances, states are encouraged to 
coordinate with the appropriate EPA Regional Office.
    The timing of the phase-in for a particular area will depend upon 
the effective date of the designation to nonattainment for 
PM2.5. Because this rule establishes requirements that apply 
in both present and future nonattainment areas, the regulations address 
the timing of the precursor phase-in both for areas already designated 
nonattainment for PM2.5 and for areas that may be so 
designated in the future.
    For any existing nonattainment area that was first designated 
nonattainment for PM2.5 effective on or before April 15, 
2015 (which includes areas designated for the 1997, 2006 and 2012 
PM2.5 NAAQS), VOC and ammonia will be required to be 
controlled as PM2.5 precursors for any NNSR permit issued on 
or after April 15, 2017 (24 months from the date of area designations 
for the 2012 PM2.5 NAAQS), unless the state has submitted 
before the phase-in date a complete SIP revision that includes the 
state's proposed NNSR program for PM2.5 and a NNSR precursor 
demonstration showing that VOC, ammonia, or both do not contribute 
significantly to PM2.5 concentrations that exceed the 
standard in a given PM2.5 nonattainment area, consistent 
with the requirements of 51.1003, in which case the control of the 
precursors addressed by the submitted demonstration will not be 
required to be controlled at the 24-month mark. See Appendix S, section 
II.A.31.(ii)(b)(3). In order to satisfy this condition, such 
demonstration must be submitted in the form of a SIP revision and must 
either be determined to be complete by the EPA or deemed to be complete 
by operation of law pursuant to the provisions in CAA section 
110(k)(1)(B).
    Although areas were designated nonattainment for the 1997, 2006, 
and 2012 standards at different times, the EPA believes it is 
reasonable to apply the same phase-in date for all areas designated 
nonattainment as of the date of the designations for the 2012 standard. 
Area designations for the 2012 PM2.5 standards were 
finalized on April 15, 2015, and plans addressing the nonattainment 
area requirements as to that standard are due October 15, 2016. 
Therefore, states evaluating their NNSR programs in light of the 
subpart 4 requirements with respect to the 2012 standard will have 
some, if limited, opportunity to consider the requirements of this rule 
and EPA's technical guidance before submitting a plan revision 
addressing the statutory and regulatory requirements. By contrast, area 
designations for the 1997 standards were finalized many years ago. As 
to those areas, after the court's decision in NRDC v. EPA, the EPA 
promulgated a rule setting a deadline of December 31, 2014, for states 
to submit any attainment plan provisions that may be necessary to 
satisfy the subpart 4 requirements. 79 FR 31566 (June 2, 2014) at 
31570. This included any submissions necessary to address NNSR 
permitting such as the CAA section 189(e) requirement that states 
regulate all PM2.5 precursors absent a demonstration that 
such regulation is unnecessary. This deadline superseded previous SIP 
submission deadlines initially established by application of the 
subpart 1 requirements. As that deadline has passed, if the EPA were to 
apply the 24-month phase-in policy strictly, states relying upon 
Appendix S to issue NNSR permits in these areas would have had to 
commence regulating VOC and ammonia as PM2.5 precursors in 
June 2015--6 months after the SIP submission deadline. The EPA believes 
it is reasonable to provide states that have areas designated 
nonattainment with respect to the 1997 and 2006 PM2.5 
standards with at least some limited opportunity to consider the 
requirements of this rule and EPA's technical guidance and submit a 
plan revision addressing the statutory and regulatory requirements 
before the state will be required to regulate sources of VOC and 
ammonia in such areas. Accordingly, the EPA finds that it is reasonable 
to subject all areas designated nonattainment for any PM2.5 
standard as of April 15, 2015, to the same Appendix S requirements in 
this final rule.
    For any area that is first designated nonattainment for any 
PM2.5 NAAQS after April 15, 2015 (that is, the area was not 
already designated nonattainment with respect to another 
PM2.5 NAAQS immediately prior to such date), any state 
relying on Appendix S to issue a NNSR permit on or after the effective 
date of such area designation must require control of SO2 
and NOX as regulated NSR pollutants (PM2.5 
precursors). Beginning on the date 24 months from the effective date of 
such area designation, a state relying on Appendix S to issue a NNSR 
permit must also require control of VOC and ammonia as regulated NSR 
pollutants (PM2.5 precursors) in that area, unless by that 
date the state has submitted a complete SIP revision that includes the 
state's proposed NNSR program for PM2.5 and an accompanying 
NNSR precursor demonstration that sources of VOC, ammonia, or both 
ammonia do not contribute significantly to the PM2.5 
concentrations that exceed the standard in the PM2.5 
nonattainment area. See Appendix S, section II.A.31.(ii)(b)(4). As 
explained earlier, such demonstration must be submitted as part of a 
SIP revision that is determined to be complete by the EPA or deemed to 
be complete by operation of law by the conditional phase-in date.
    As noted earlier, the second phase-in provision applies to 
PM2.5 nonattainment areas that were not already designated 
as nonattainment for PM2.5 immediately prior to that date. 
If at the time of a new designation, an area was already designated 
nonattainment as to any prior PM2.5 NAAQS, and Appendix S 
applied and continues to apply for NNSR permitting with respect

[[Page 58119]]

to that existing nonattainment area, all PM2.5 precursors 
would likely already be required to be regulated in accordance with a 
prior phase-in schedule prescribed under Appendix S for that existing 
nonattainment designation. In such cases, all precursors would continue 
to be subject to regulation for NNSR permitting under Appendix S, even 
as to the new nonattainment designation. That is, once Appendix S 
definition of regulated NSR pollutant applies to all PM2.5 
precursors in a given nonattainment area, it is not possible to later 
defer regulation of any precursors so long as the state continues to 
rely on Appendix S for NNSR permitting in that area. Once the state 
submits a SIP including an NNSR program and any appropriate NNSR 
precursor demonstration, and the EPA approves the SIP, Appendix S will 
no longer apply for the issuance of NNSR permits for PM2.5.
iii. Comments and Responses
    Comment: Several commenters generally supported the EPA's preferred 
approach in the proposal that would require only SO2 and 
NOX as PM2.5 precursors for NNSR permits issued 
pursuant to Appendix S. One commenter supported the alternative 
approach to phase in VOC and ammonia as PM2.5 precursors, 
while another commenter expressly opposed the EPA's preferred approach 
and the phase-in alternative, claiming that any approach that does not 
regulate all four scientific precursors of PM2.5 is contrary 
to CAA subpart 4 and unlawful.
    Commenters supporting the preferred approach did not believe that 
it was appropriate to require NSR permitting during an interim period 
for sources that may be exempted from control requirements if a state 
can demonstrate that these sources do not contribute significantly to 
nonattainment in a particular area. These commenters stated that, since 
most, if not all, areas will not be able to demonstrate that 
SO2 and NOX do not contribute significantly to 
nonattainment levels of PM2.5, the EPA's approach to include 
these two precursors in the interim is reasonable.
    One commenter who supported the EPA's alternative approach to phase 
in VOC and ammonia as PM2.5 precursors stated that there are 
many unanswered questions and the science is not adequate to justify 
regulation of secondary formation precursors at this time. The 
commenter further stated that Appendix S should initially require 
sources issued a NNSR permit to control only SO2 and 
NOX as PM2.5 precursors, and only later, after a 
prescribed date (e.g., the date on which SIP revisions based on subpart 
4 requirements are due), require sources to control emissions of VOC 
and ammonia, if applicable.
    A commenter who opposed any approach that did not immediately 
require the control of all four scientific precursors of 
PM2.5 stated that such approaches are unlawful and must be 
rejected. The commenter stated that the EPA must require immediate 
regulation of all four precursors, as only that alternative follows the 
plain language of the CAA and the NRDC decision. The commenter objected 
to the presumptive exemption of VOC and ammonia emissions as being 
identical to the ``gamesmanship'' that both Congress intended to 
curtail with subpart 4, and that the DC circuit found illegal in the 
NRDC decision. The commenter stated that the scope of the statutory 
definition, and consequently the application of subpart 4, did not 
change when the EPA subdivided PM10 by regulation. The 
commenter stated that only this option would conform Appendix S to the 
requirements of subpart 4, and in so doing, align Appendix S with 
forthcoming state obligations to harmonize the PM2.5 
portions of their SIPs with the obligations of subpart 4. The commenter 
stated that this approach would encourage states to submit SIPs in a 
timely fashion, rather than to rely on Appendix S for an extended 
period of time. The commenter stated that, in contrast, were the EPA to 
adopt illegally lax provisions into Appendix S, states might delay 
submitting replacement SIPs, particularly in those parts of the country 
with high VOC or ammonia precursor emissions.
    Response: The EPA took each of these comments into consideration in 
concluding that the proposed phase-in alternative is a reasonable 
approach that balances competing factors regarding the regulation of 
PM2.5 precursors for NNSR permits issued pursuant to 
Appendix S. While CAA section 189(e) generally requires state plans to 
control all PM2.5 precursors, it also affords states an 
opportunity to demonstrate that a particular precursor does not 
contribute significantly to levels of PM2.5 that exceed the 
standard in a PM2.5 nonattainment area. Section 189(e) of 
the CAA clearly addresses how PM2.5 precursors must be 
regulated in the state's plan, but the statute does not address exactly 
when precursors are to be regulated pursuant to the NNSR requirements 
of Appendix S prior to the submission of the state's plan. As noted 
earlier, the NNSR provisions are unique among the nonattainment area 
requirements in that sources are required to address NNSR immediately 
upon the effective date of an area's designation to nonattainment, 
rather than upon the EPA's approval of the state's SIP, which could be 
as much as 3 years after the nonattainment area designation (e.g., 
states have 18 months to submit attainment plans and the EPA may have 
up to 18 months from the date of the SIP submission to finalize action 
on such plans). Given this ambiguity in the statute and the unique 
application of the NNSR requirements, we believe a reasonable and 
balanced approach to the Appendix S requirements would allow states a 
time-limited period to submit a NNSR program for PM2.5 that 
includes a NNSR precursor demonstration that sources of a precursor do 
not contribute significantly to PM2.5 levels in a 
PM2.5 nonattainment area. The time limit will discourage 
states from unreasonably delaying regulation of such precursors where 
otherwise required to do so.
    Moreover, the EPA believes it is reasonable to construct the 
Appendix S provisions regulating PM2.5 precursors in a 
manner that closely follows the way in which the precursors are being 
regulated in most state NSR programs based on EPA's 2008 NSR 
regulation. For areas that were designated attainment or unclassifiable 
prior to a new nonattainment designation, the PSD permit program was in 
effect and required that, at minimum, SO2 and NOX 
be regulated as PM2.5 precursors. It is therefore reasonable 
to ensure that those precursors continue to be regulated as part of the 
interim NNSR permit program via Appendix S. Moreover, in areas that 
were already designated nonattainment for a pre-existing 
PM2.5 NAAQS, and an approved plan containing NNSR permit 
requirements for PM2.5 is in effect, sources are required to 
control SO2 and NOX as PM2.5 
precursors, as required under the 2008 PM2.5 NSR rule, until 
the EPA approves a SIP revision conforming those NNSR programs to the 
requirements of CAA subpart 4. Similarly, the EPA believes it is 
reasonable to not require the regulation of VOC and ammonia immediately 
upon designation of an area to nonattainment because it result in more 
regulation in newly designated nonattainment areas relying on Appendix 
S than is required in most states with approved programs. All states 
will ultimately be required to address the regulation of ammonia and 
VOC at the time their state plans are due or, failing submission of 
such plan by states relying on Appendix S to issue NNSR permits, 
Appendix S will require such regulation.

[[Page 58120]]

    The phase-in schedule contained in this final rule requires that 
VOC and ammonia be phased in as PM2.5 precursors 24 months 
from the effective date of area designations for PM2.5; 
however, states will not be required to control VOC and ammonia as 
PM2.5 precursors as part of a NNSR permit issued under 
Appendix S so long as the state submits a plan revision that includes 
the state's NNSR program for PM2.5 and a NNSR precursor 
demonstration to show that sources of a precursor does not contribute 
significantly to PM2.5 levels that exceed the standard in a 
PM2.5 nonattainment area. See Appendix S, sections 
II.A.31.(ii)(b)(3) and (4).
    In initially requiring sources to control SO2 and 
NOX as regulated NSR pollutants (PM2.5 
precursors), states that rely on Appendix S to issue NNSR permits 
generally will implement NNSR consistent with those states that issue 
NNSR permits for PM2.5 under the NNSR program in their 
approved SIP. The EPA believes that it is reasonable and appropriate to 
assure this consistency in the issuance of NNSR permits during the 
interim period when all states must revise their plans to address the 
2012 PM2.5 NAAQS. Moreover, this final rule allows states to 
submit a SIP revision that contains a NNSR precursor demonstration 
showing that new major stationary sources and major modifications of 
either SO2 or NOX should be exempted where an 
analysis of increases in emissions of the particular precursor shows 
that sources of the precursor do not contribute significantly to 
PM2.5 levels that exceed the standard in the 
PM2.5 nonattainment area. In this case, the opportunity to 
exempt sources of either SO2 or NOX as 
PM2.5 precursors is addressed in the NNSR rules at 51.165. 
See 40 CFR 51.165(a)(13). Hence, when the EPA approves a state's plan 
revision containing the NNSR program for PM2.5 and a NNSR 
precursor demonstration showing an insignificant contribution, a new 
major stationary source or major modification of either SO2 
or NOX as PM2.5 precursors will not be required 
to be controlled going forward in a NNSR permit issued to address 
PM2.5, which permit would then be issued in accordance with 
the NNSR requirements in the approved plan, rather than the NNSR 
requirements in Appendix S.
    With regard to the commenter's concern that states might delay 
submitting NNSR programs as part of their PM2.5 SIPs if 
Appendix S regulates only SO2 and NOX, the phase-
in approach in this final rule will negate any incentive that a state 
may have to delay submitting an NNSR program for PM2.5 
addressing the CAA section 189(e) requirement to regulate all four 
precursors, absent a showing that such regulation is unnecessary. In 
fact, the phase-in requirement should actually encourage states to 
timely submit their NNSR programs for PM2.5. Given CAA 
section 189(e) does not directly speak to its application to the 
Appendix S requirements, the EPA believes this approach represents a 
reasonable and equitable application of the CAA section 189(e) 
requirements regarding regulation of PM2.5 precursors to 
states applying Appendix S.
b. Appendix S Definition of ``major stationary source'' in Serious 
PM2.5 Nonattainment Areas
i. Summary of Proposal
    The EPA proposed to amend Appendix S by revising the definition of 
``major stationary source'' to include a separate PM2.5 
major source threshold applicable to new major stationary sources and 
major modifications of direct PM2.5 and PM2.5 
emissions in PM2.5 nonattainment areas reclassified as 
Serious. This proposed amendment to Appendix S was similar to one that 
was proposed to the definition of ``major stationary source'' in 40 CFR 
51.165.\234\
---------------------------------------------------------------------------

    \234\ The preamble language did not explicitly state that it was 
our intent to revise the definition in Appendix S to add separate 
major source thresholds for direct PM2.5 emissions and 
PM2.5 precursors, in the same way that earlier we had 
proposed to revise the definition of ``major stationary source'' in 
the NNSR regulations at 40 CFR 51.165. Instead, the preamble 
referred only to a change to the definition of ``major stationary 
source'' at proposed section II.A.4(i)(a)(7) of Appendix S, where a 
70 tpy threshold for direct PM2.5 emissions is addressed. 
The proposed regulatory text did, however, also include new section 
II.A.4(i)(a)(8) of Appendix S, which adds a 70 tpy major source 
threshold for emissions of individual PM2.5 precursors. 
Despite this omission in the preamble discussion of the proposed 
changes to Appendix S, we believe that commenters had ample 
opportunity to comment on the actual changes being made to the 
definition of ``major stationary source'' in Appendix S because the 
intended change concerning emissions of PM2.5 and 
PM2.5 precursors was accurately provided in the 
regulatory text.
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ii. Final Rule
    In this final rule, the EPA is amending the definition of ``major 
stationary source'' in Appendix S to include 70 tpy major source 
thresholds for direct PM2.5 emissions and individual 
PM2.5 precursors, applicable in Serious PM2.5 
nonattainment areas.\235\ See Appendix S sections II.A.4(i)(a)(7) and 
(8), respectively. As described earlier, applicability of the NNSR 
requirements to a source will be determined individually for direct 
PM2.5 emissions and for emissions of individual 
PM2.5 precursors. For example, if a new source locating in a 
Serious PM2.5 nonattainment area would emit 70 tpy of the 
PM2.5 precursor SO2, it will be considered a 
major source of PM2.5 (with respect to the SO2 
precursor) and will be subject to the NNSR requirements for 
PM2.5 with regard to the SO2 emissions. However, 
if the same proposed source does not emit 70 tpy of direct 
PM2.5 emissions or another PM2.5 precursor, the 
emissions increase of direct PM2.5 or the other precursor 
will not be subject to control based on the NNSR requirements for 
PM2.5. It should also be noted that VOC and ammonia are 
subject to the phase-in schedule described in the definition of 
``regulated NSR pollutant'' in the NNSR regulations at Appendix S, 
section II.A.31.(ii)(b)(2).
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    \235\ The EPA also notes that the definition of ``major 
stationary source'' in Appendix S is being revised in this rule at 
section II.A.4(i)(a) of Appendix S, which currently ends with the 
phrase ``according to paragraphs II.A.4(i)(a)(1) through (6) of this 
ruling.'' By proposing to add new paragraphs (7) and (8), this 
phrase will be revised to read ``according to paragraphs 
II.A.4(i)(a)(1) through (8) of this ruling.'' The phrase is being 
modified accordingly in this final rule.
---------------------------------------------------------------------------

iii. Comments and Responses
    As explained in Section VIII.B.1.b of this preamble, commenters 
addressing the proposed major source threshold of 70 tpy for sources of 
PM2.5 and its precursors locating in Serious areas had mixed 
responses, particularly with regard to the appropriate thresholds for 
precursors. Most of the comments applied generally to the proposed 
thresholds in 40 CFR 51.165 and Appendix S. The EPA's responses to 
these comments are provided in that earlier section of the preamble.
    Comment: One commenter, however, recommended that during the SIP 
transition period (and while the EPA continues its analysis of the 
precursor relationships to PM2.5), the EPA should allow 
states to make a case-by-case permitting demonstration to use higher 
major source thresholds for precursors for NNSR permit reviews.
    Response: As explained previously, in light of the ongoing 
precursor impact studies as well as concerns about the legality of 
setting higher major source thresholds than those specified in the CAA, 
the EPA believes it is most reasonable to establish a 70 tpy major 
source threshold under Appendix S for sources of direct 
PM2.5 emissions and each PM2.5 precursor locating 
in Serious nonattainment areas.

[[Page 58121]]

c. Significant Emissions Rates (SERs) in Appendix S--PM2.5 
Precursors
i. Summary of Proposal
    As explained earlier, the EPA proposed as its preferred approach to 
add NOX as a PM2.5 precursor in the Appendix S 
definition of ``regulated NSR pollutant.'' Accordingly, the EPA also 
proposed to amend the definition of ``significant'' at section 
II.A.10(i) of Appendix S to establish a SER of 40 tpy for 
NOX as a PM2.5 precursor. The Appendix S 
definition already contains a SER for SO2 as a 
PM2.5 precursor at 40 tpy of SO2. The EPA did not 
explicitly propose to include SERs for VOC and ammonia in Appendix S as 
part of the preferred approach; however, the EPA's proposed alternative 
approach to phase in VOC and ammonia as PM2.5 precursors at 
a later date would inherently necessitate adding SERs for those two 
additional precursors in the event that an alternative approach was 
ultimately selected for the final rule.
ii. Final Action
    The EPA is revising the definition of ``significant'' in Appendix S 
at section II.A.31(ii)(b)(2) to provide SERs for NOX and VOC 
as PM2.5 precursors, consistent with its decision to 
conditionally phase in regulation of all four PM2.5 
precursors 24 months from the date of redesignation. The individual 
SERs for NOX and VOC as PM2.5 precursors, being 
added to the existing SER for SO2 as a PM2.5 
precursor, are each defined as 40 tpy of the respective precursor, 
consistent with the SERs provided in the revised definition of 
significant in 40 CFR 51.165.
    The EPA is not adding a SER for ammonia (as a PM2.5 
precursor) in the Appendix S definition of ``significant'' in this 
action. Consistent with the EPA's approach for allowing states to 
define ``significant'' for ammonia in their NNSR rules, and for the 
reasons explained in Section VIII.B.1.c of this preamble, the EPA will 
allow states that issue NNSR permits pursuant to the requirements in 
Appendix S to define ``significant'' with respect to ammonia in a 
particular area in each NNSR permit issued pursuant to Appendix S. The 
state should provide a technical justification to support the 
definition of ``significant'' for ammonia, including any SER developed 
by the state for a particular nonattainment area, and such 
justification should be included in the administrative record for each 
proposed permit. The state also has the discretion to define 
``significant'' with respect to ammonia as a PM2.5 precursor 
in those cases where it is determined that the proposed modification 
will result in insignificant increases of ammonia and the source will 
therefore not be required to obtain a major NNSR permit. In such cases, 
the state and the source should also document the technical 
justification for determining the source impacts will be insignificant, 
including any SER developed by the state for a particular nonattainment 
area, whether such documentation occurs in the administrative record 
for a minor source permit, a nonapplicability determination, or some 
other form in the state or source's records. The state should consult 
with the appropriate EPA Regional Office for assistance in developing 
an appropriate definition of ``significant'' for ammonia as a 
PM2.5 precursor in each permit or for each nonattainment 
area.
iii. Comments and Responses
    The comments regarding the proposed addition of SERs for 
NOX and VOC emissions as PM2.5 precursors in the 
NNSR definition of ``significant'' were summarized in Section 
VIII.B.1.c of this preamble. Those comments applied generally to the 
NNSR regulations at 40 CFR 51.165 and Appendix S. The reader is 
referred to that earlier section of the preamble to review the comments 
and the EPA's responses to them.
    Comment: Some commenters seemingly addressing NNSR under Appendix S 
recommended that the EPA include a provision allowing states to make 
case-by-case determinations to use higher SERs for precursors for NNSR 
permits issued before the SIP is effective. The commenter stated that 
the precursor SERs are too low and do not realistically reflect the 
effect that each precursor has on ambient PM2.5 
concentrations.
    Response: The EPA believes that the commenter's concern is 
partially addressed by the fact that, in using Appendix S to review 
NNSR permit applications, neither VOC nor ammonia will need to be 
controlled as PM2.5 precursors if the state has submitted to 
the EPA a complete SIP submission that includes the state's NNSR 
program for PM2.5 and a NNSR precursor demonstration showing 
that a particular precursor does not contribute significantly to 
ambient concentrations of PM2.5 in the nonattainment area, 
even though the plan revision containing such demonstration has not yet 
been formally approved. Until the SIP development period has passed and 
unless the state has failed to submit such a demonstration, the state 
issuing permits pursuant to Appendix S will not be required to regulate 
VOC or ammonia as PM2.5 precursors. If a state has not 
submitted a SIP including the state's NNSR program for PM2.5 
and a NNSR precursor demonstration for either VOC or ammonia, sources 
of these precursor emissions must be controlled as PM2.5 
precursors in any NNSR permit issued pursuant to Appendix S beginning 
on the prescribed phase-in date.

C. Transition Provisions for Major Source Permitting in 
PM2.5 Nonattainment Areas

    The EPA did not propose any transition provisions for NNSR permit 
applications in either 40 CFR 51.165 or Appendix S that would expressly 
grandfather pending PSD or NNSR permit applications for proposed new 
and modified major stationary sources from newly established NNSR 
permit requirements applicable to PM2.5 nonattainment areas. 
In the final 2012 PM NAAQS Rule, the EPA provided a grandfathering 
provision only for certain PSD permit applications with respect to the 
revised PM2.5 standard. Historically, the EPA has not 
provided for the grandfathering of any permit applications from new 
NNSR requirements or from application of existing NNSR requirements to 
new or revised standards. Nevertheless, in promulgating the 2012 PM 
NAAQS Rule, the EPA received unsolicited comments advocating for 
grandfathering of NNSR requirements for the revised standard. Thus, 
while explaining the reasons why it did not believe that NNSR 
grandfathering was appropriate, the EPA sought comments in the proposal 
on possible circumstances where grandfathering similar to the PSD 
grandfathering provision established for the 2012 PM2.5 
standard might be appropriate with respect to changes made regarding 
NNSR requirements for PM2.5 in this rulemaking.
    Several comments received during the 2012 p.m. NAAQS rulemaking 
recommended that the EPA establish a grandfathering provision for NNSR 
as was proposed for the PSD program. A subset of these commenters 
recommended that PSD permit applications be grandfathered from the NNSR 
requirements for the revised 2012 PM2.5 standard by 
establishing an effective date for designations 1 year after initial 
publication in the Federal Register. The commenters presumably believed 
that by delaying the effective date of any new nonattainment 
designations for the primary annual PM2.5 NAAQS, sources 
with pending PSD permit applications could continue to be reviewed and 
permits issued under the PSD requirements rather than the NNSR 
requirements for PM2.5.

[[Page 58122]]

    The EPA explained at the time that the obligation to adopt new 
provisions under a state's NNSR program will not apply with regard to 
the revised NAAQS until such time as an area is designated 
nonattainment, and beginning on the effective date of the new area 
designations for PM2.5, proposed new and modified major 
sources would be required to meet the applicable NNSR requirements for 
PM2.5.\236\ Also, the EPA does not agree with the 
commenters' recommendation that the effective date of the area 
designation be delayed by 1 year because this approach, similar to 
delaying the effective date of the NAAQS, would also delay the 
implementation of the attainment plan and defer the important health 
benefits associated with the revised NAAQS. In the same preamble, the 
EPA proposed a schedule for promulgating area designations for 
PM2.5 that involved the maximum allowable 2-year period from 
the signature date of the 2012 PM2.5 NAAQS, as provided in 
CAA section 107(d)(1)(B). The CAA allows for a 1-year extension for 
such designations, but only if there is insufficient information to 
enable such designations to be made.\237\
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    \236\ The applicable NNSR requirements would be either the NNSR 
requirements for PM2.5 in the state's existing approved 
SIP or the requirements found at 40 CFR part 51 Appendix S, when a 
state's approved SIP does not currently include NNSR requirements 
for PM2.5. States will be required to submit to the EPA 
for approval SIP revisions containing the amended NNSR program 
requirements for PM2.5 contained in the final 
PM2.5 NAAQS implementation, but those additional 
requirements will not apply in states with approved SIPs that 
include NNSR requirements for PM2.5 until the EPA 
approves the SIP revision. See 78 FR 3086 (January 15, 2013), at 
page 3263.
    \237\ See 78 FR 3249 at page 3250.
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    In response to the EPA's request for comments in the proposal, 
commenters recommended that the EPA clarify the PM2.5 NSR 
grandfather policy to explain that both PSD and NNSR permit 
applications are exempt from the precursor and planning requirements 
being finalized in this rulemaking. In particular, the commenters 
recommended that the EPA establish a PM2.5 NSR transition 
policy that delays regulation of the scientific precursors of 
PM2.5 under any NSR program until the EPA has a better 
understanding of how these precursors contribute to nonattainment and 
could deteriorate air quality. One of the commenters indicated that a 
transitional policy is especially important until the EPA completes a 
rulemaking on a SER for ammonia. One of the commenters recommended that 
the EPA should allow for the grandfathering of pending PSD permit 
applications, similar to the PSD grandfathering provision for the 2012 
PM2.5 NAAQS, for sources that will not be issued a permit 
until after the effective date of the nonattainment designation under 
certain conditions. This commenter stated that CAA section 165(c), 
which forms part of the EPA's basis for grandfathering in the PSD 
context, should also apply to NNSR permit decisions.
    The EPA does not find a compelling reason to grandfather pending 
NNSR permit applications for which a permit has not yet issued once the 
new NNSR requirements--primarily affecting the control of 
PM2.5 precursors--become effective. The EPA believes that it 
is reasonable to require that a new or modified major stationary source 
control emissions of PM2.5 precursors where such emissions 
contribute significantly to PM2.5 levels in the 
nonattainment area. If such precursor emissions are not effectively 
controlled, and offset by reductions in existing emissions, an 
increased burden could be placed on the overall attainment plan to 
address those emissions in order to attain the NAAQS in a timely 
manner.
    While the final rule contains no general grandfathering provision, 
this final rule does provide a phase-in process for states relying on 
Appendix S for purposes of issuing NNSR permits for PM2.5. 
Appendix S will require the immediate regulation of SO2 and 
NOX as PM2.5 precursors, the regulation of VOC 
and ammonia as PM2.5 precursors will only be required under 
certain conditions and on a delayed timetable. See Appendix S, revised 
section II.A.31.(ii)(b)(2)-(5). The precursor provisions in Appendix S 
should alleviate some of the commenter's concerns that the regulation 
of additional precursors will be required immediately upon the 
effective date of this final rule. Instead, the phase-in schedule for 
the regulation of VOC and ammonia will permit states the opportunity 
allowed by CAA section 189(e) to demonstrate that a particular 
precursor need not be subjected to control in a particular 
nonattainment area. Accordingly under the interim NNSR requirements in 
Appendix S, a state will not be required to begin immediate regulation 
of precursors for which sources will likely be exempted from the 
regulations upon review of a state's NNSR SIP submission. Similarly, 
where the state has a previously approved NNSR program for 
PM2.5, the existing requirements for controlling precursors 
would continue to apply until the new SIP revisions required by this 
rule, including new precursor control requirements, are approved. Thus, 
such states would not be required to immediately regulate any 
PM2.5 precursors not already required by the approved plan 
during the interim plan development period.
    With regard to grandfathering PSD permit applications, we do not 
interpret the CAA to allow for the issuance of a PSD permit in an area 
that is designated nonattainment. The CAA requires proposed major 
stationary sources and major modifications to meet major NSR permitting 
requirements that apply on the basis of the area's designation.\238\ 
Accordingly, the EPA's longstanding interpretation of the CAA is that a 
proposed new major stationary source or major modification must satisfy 
the appropriate major NSR requirements (PSD vs. NNSR) for a particular 
pollutant that are in effect in a given area on the date that a permit 
is issued to the source, rather than the requirements that may have 
been applicable when the permit application was submitted.\239\
---------------------------------------------------------------------------

    \238\ Compare CAA section 165(a) (permitting requirements for 
sources locating in attainment and unclassifiable areas) with CAA 
sections 172(c)(5) and 173 (permitting requirements for sources 
locating in nonattainment areas).
    \239\ See Memorandum from John S. Seitz, Director, EPA Office of 
Air Quality Planning and Standards, on March 11, 1991, titled ``New 
Source Review (NSR) Transitional Guidance,'' Attachment p. 6, sent 
to Regional Air Division Directors.
---------------------------------------------------------------------------

IX. Other Requirements and Considerations for PM2.5 
Nonattainment Areas

A. Waivers Under CAA Section 188(f)

1. Statutory Requirements and Existing Guidance
    a. Summary of Proposal. The proposal summarized the statutory 
requirements and existing guidance for CAA section 188(f), which 
provides that, ``the Administrator may, on a case-by-case basis, waive 
any requirement applicable to any Serious Area . . . where the 
Administrator determines that anthropogenic sources of PM10 
do not contribute significantly to the violation of the PM10 
standard in the area.'' In addition it provides that, ``the 
Administrator may also waive a specific date for attainment of the 
[PM10] standard where the Administrator determines that 
nonanthropogenic sources of PM10 contribute significantly to 
the violation of the PM10 standard in the area.'' The agency 
requested comment on whether the existing guidance in the Addendum is 
appropriate when implementing the current and any future 
PM2.5 NAAQS.
    b. Final Rule. The EPA is hereby affirming its reliance on the 
interpretation of CAA section 188(f) described in the Addendum for

[[Page 58123]]

purposes of implementing the PM2.5 NAAQS.\240\ For example, 
the Addendum lays out a series of questions that should be answered 
before the waiver provisions can be applied, including questions 
related to the types of sources that may be considered anthropogenic 
and nonanthropogenic, the specific conditions under which the 
attainment date for a Moderate area may be waived, and the time period 
that would apply to an attainment date waiver. The EPA believes that 
these questions, and the general guidance provided in the Addendum on 
how to evaluate the answers, provide adequate direction to the EPA and 
to states potentially interested in seeking waivers for certain 
PM2.5 NAAQS nonattainment areas. The EPA therefore refers 
interested states to the waiver guidance contained in the Addendum for 
more detail on how the agency interprets CAA section 188(f) for 
purposes of implementing the PM2.5 NAAQS.
---------------------------------------------------------------------------

    \240\ See 59 FR 42003-42008, August 16, 1994.
---------------------------------------------------------------------------

    c. Comments and Responses. The comments received on this section 
are addressed in the Response to Comments document found in the docket 
for this action.
2. Relationship Between the CAA Section 188(f) Waiver Provisions and 
the EPA's Exceptional Events Rule
    a. Summary of Proposal. The proposal summarized the relationship 
between the 188(f) waiver provisions and the EPA's Exceptional Events 
Rule. On March 22, 2007, the EPA promulgated the ``Treatment of Data 
Influenced by Exceptional Events; Final Rule'' (72 FR 13560), known as 
the Exceptional Events Rule, pursuant to the 2005 amendment of CAA 
section 319.\241\ The Exceptional Events Rule provides a mechanism by 
which the EPA can concur with a state's request to exclude from 
regulatory decisions air quality monitoring data determined by the EPA 
to have been affected by exceptional events.\242\ The Exceptional 
Events Rule applies to all the NAAQS pollutants, including 
PM2.5. CAA section 188(f) and the Exceptional Events Rule 
provide separate mechanisms by which states can seek to have event-
influenced monitoring data excluded from certain regulatory 
requirements or decisions associated with the PM NAAQS implementation 
process, under appropriate circumstances.
---------------------------------------------------------------------------

    \241\ Section 319 of the CAA, as amended by section 6013 of the 
Safe Accountable Flexible Efficient-Transportation Equity Act: A 
Legacy for Users (SAFE-TEA-LU) of 2005, required the EPA to propose 
and promulgate regulations governing the review and handling of air 
quality monitoring data influenced by exceptional events.
    \242\ References to ``air agencies'' are meant to include state, 
local and tribal air agencies responsible for implementing the 
Exceptional Events Rule.
---------------------------------------------------------------------------

    b. Final Rule. The EPA did not make any revisions to its 
interpretation of the relationship between the CAA section 188(f) 
waiver provisions and EPA's Exceptional Events Rule.
    The Exceptional Events Rule addresses elevated emissions from 
specific events that influence monitored air quality concentrations. 
The EPA's regulations at 40 CFR 50.1(j) define an ``exceptional event'' 
as one that ``affects air quality, is not reasonably controllable or 
preventable, is an event caused by human activity that is unlikely to 
recur at a particular location or a natural event, and is determined by 
the Administrator in accordance with 40 CFR 50.14 to be an exceptional 
event.'' Further, 40 CFR 50.1(j) explicitly provides that exceptional 
events do ``. . . not include stagnation of air masses or 
meteorological inversions, a meteorological event involving high 
temperatures or lack of precipitation, or air pollution relating to 
source noncompliance.'' At 40 CFR 50.1(k), the EPA's regulations define 
a ``natural event'' as an event in which human activity plays little or 
no direct causal role to the event in question.\243\
---------------------------------------------------------------------------

    \243\ The EPA will generally consider human activity to have 
played little or no direct role in causing emissions of the dust 
generated by high wind for purposes of the regulatory definition of 
``natural event'' if contributing anthropogenic sources of the dust 
are reasonably controlled at the time of the event, regardless of 
the amount of dust coming from these reasonably controlled 
anthropogenic sources, and thus the event could be considered a 
natural event. In such cases, the EPA believes that it would 
generally be a reasonable interpretation of its regulations to find 
that the anthropogenic source had ``little'' direct causal role. If 
anthropogenic sources of windblown dust that are reasonably 
controllable but that did not have those reasonable controls applied 
at the time of the high wind event have contributed significantly to 
a measured concentration, then the event would not be considered a 
natural event. See preamble to the Exceptional Events Rule at 72 FR 
13560 (March 22, 2007), footnote 11 on page 13566.
---------------------------------------------------------------------------

    Air quality monitoring data that the EPA determines to have been 
influenced by an exceptional event under the procedural steps, 
substantive criteria, and schedule specified in the Exceptional Events 
Rule may be excluded from regulatory decisions such as initial area 
designations decisions and decisions associated with implementing the 
PM2.5 NAAQS such as clean data determinations, evaluation of 
attainment demonstrations, and discretionary or mandatory 
reclassifications of nonattainment areas from Moderate to Serious. 
While the EPA may agree with a state's request to exclude event-
influenced air quality monitoring data from regulatory decisions, these 
regulatory actions require the EPA to provide an opportunity for public 
comment on the claimed exceptional event and all supporting data prior 
to the EPA taking final agency action.
    If wildfire is a potential contributor to exceedances of the NAAQS 
and exceptional events, the EPA urges state and local agencies to 
coordinate with the land management agencies, as appropriate, in 
developing plans and appropriate public communications regarding public 
safety and reducing exposure. This action can directly help states meet 
their Exceptional Events Rule obligation whereby ``states must provide 
public notice, public education, and must provide for implementation of 
reasonable measures to protect public health when an event occurs.'' 
When wildfire impacts are significant in a particular area, states and 
communities may be able to lessen the impacts of wildfires by working 
collaboratively with land managers and land owners to employ various 
mitigation measures including taking steps to minimize fuel loading in 
areas vulnerable to fire.
    The EPA notes that there could be some potential overlap between 
the application of the Exceptional Events Rule and CAA section 188(f) 
because the conditions necessary for the Administrator to make a 
determination under CAA section 188(f)--i.e., the lack of a significant 
anthropogenic contribution to a violation--may overlap with conditions 
that may be considered an exceptional event, particularly a natural 
event, which by definition represents a non-anthropogenic contribution. 
The EPA believes that this potential for overlap can best be addressed 
by considering the applicability of the Exceptional Events Rule and CAA 
section 188(f) in sequence. Thus, the EPA recommends that states first 
consider whether the monitored air quality data on specific days were 
influenced by an exceptional event. If the state requests and the EPA 
agrees with this request and determines that the monitored air quality 
data should be excluded from consideration in regulatory decisions, 
then using the provisions in the Exceptional Events Rule could address 
the situation adequately, and there would be no need for a CAA section 
188(f) waiver. If the state determines that, even with the exclusion of 
the event-influenced data, the waiver provisions of CAA section 188(f) 
may also be applicable, then the EPA can evaluate that question based 
on the remaining data that are representative for the area in question. 
Given that section 188(f) has rarely been invoked, a state wishing to 
pursue this

[[Page 58124]]

provision should work closely with its EPA Regional Office.
    c. Comments and Responses. Comments: Some commenters urged the EPA 
to clarify the two-step approach. Some commenters recommended that the 
EPA refrain from directing the sequence and allow states to decide 
which of these provisions should apply in the specific circumstances 
that they are addressing, consistent with the commenter's overall 
recommendation that the EPA give states the maximum flexibility in 
developing PM2.5 SIPs. Some commenters urged the EPA to 
provide guidance to the states on when this two-step approach would be 
appropriate, and when it would be inappropriate. Commenters did not 
want implementation planning to follow the EPA's exceptional events 
justification model in which there is great variability among the EPA 
regions. Commenter encouraged the EPA to work to ensure that 
PM2.5 implementation plan reviews are subject to similar 
requirements in all EPA regions with clarifying language in the final 
guidance to ensure some level of national consistency.
    Response: The EPA agrees with the first comment that, rather than 
the EPA ``directing the sequence,'' the affected state and the 
appropriate EPA regional office should discuss the scenario and the 
affected data to determine whether the Exceptional Events Rule or CAA 
section 188(f) is the most appropriate mechanism. This decision would 
be made on a case-by-case basis considering the specific, relevant 
facts. In most cases, if the monitored air quality data satisfy the 
requirements of the Exceptional Events Rule, then applying these 
provisions would likely provide additional regulatory flexibilities 
beyond those that CAA section 188(f) would provide. However, regardless 
of whether the data in question meet or do not meet the requirements of 
the Exceptional Events Rule (e.g., because the exceptional events 
definition is not met in that the data do not constitute an exceedance 
or violation of the NAAQS or because other Exceptional Events rule 
criteria are not met), the waiver provisions in CAA section 188(f) 
could apply.
    The EPA recognizes the implementation challenges associated with 
the 2007 Exceptional Events Rule and recently proposed revisions to 
this rule to address certain substantive issues raised by state, local 
and tribal co-regulators and other stakeholders since promulgation of 
the rule and to increase the administrative efficiency of the 
Exceptional Events Rule criteria and process (80 FR 72840, November 20, 
2015). The public comment period on this rule closed on February 3, 
2016. The EPA will consider timely comments provided to the Exceptional 
Events Rule docket as we finalize the revisions to this rule.

B. Conformity Requirements

1. Requirements That Apply to Both Transportation Conformity and 
General Conformity
    a. Background on Transportation and General Conformity. Conformity 
is required under CAA section 176(c) to ensure that federal actions are 
consistent with (``conform to'') the purpose of the SIP. Conformity to 
the purpose of the SIP means that federal activities will not cause new 
air quality violations, worsen existing violations, or delay timely 
attainment of the relevant NAAQS or interim reductions and milestones. 
Conformity applies to areas that are designated nonattainment, and 
those nonattainment areas redesignated to attainment with a CAA section 
175A maintenance plan after 1990 (``maintenance areas'').
    The EPA's Transportation Conformity Rule (40 CFR 51.390 and part 
93, subpart A) establishes the criteria and procedures for determining 
whether transportation activities conform to the SIP. These activities 
include adopting, funding or approving transportation plans, 
transportation improvement programs (TIPs) and federally supported 
highway and transit projects. The EPA first promulgated the 
Transportation Conformity Rule on November 24, 1993 (58 FR 62188), and 
subsequently published several amendments. For example, the EPA 
published a final rule on July 1, 2004 (69 FR 40004) that provided 
conformity procedures for state and local agencies under the 1997 
PM2.5 NAAQS, among other things. On May 6, 2005 (70 FR 
24280) the EPA published a final rule that addressed transportation 
conformity requirements for PM2.5 precursors.\244\ The EPA 
published another final rule on March 24, 2010 (75 FR 14260) that 
addressed additional requirements for the 2006 PM2.5 NAAQS. 
Finally, the EPA published a final rule on March 14, 2012 (77 FR 14979) 
that restructured portions of the transportation conformity rule so 
that they would clearly apply to nonattainment and maintenance areas 
for the new and revised NAAQS, including the 2012 PM2.5 
NAAQS. All of these rules apply to the current PM2.5 NAAQS 
including the 1997 PM2.5 NAAQS, the 2006 24-hour 
PM2.5 NAAQS and the 2012 primary annual PM2.5 
NAAQS and will apply to future PM2.5 NAAQS. For further 
information on transportation conformity rulemakings, policy guidance 
and outreach materials, see the EPA's Web site at http://www3.epa.gov/otaq/stateresources/transconf/index.htm. The EPA issued transportation 
conformity guidance related to the implementation of the 2012 primary 
annual PM2.5 NAAQS in November 2015. The guidance is 
available at http://www3.epa.gov/otaq/stateresources/transconf/documents/420b15091.pdf.
---------------------------------------------------------------------------

    \244\ This final rule was not challenged, nor was it affected by 
the January 2013 D.C. Circuit Court decision requiring the EPA to 
implement the PM2.5 NAAQS pursuant to subpart 4 of the 
CAA.
---------------------------------------------------------------------------

    With regard to general conformity, the EPA first promulgated 
general conformity regulations in November 1993 (40 CFR part 51, 
subpart W and 40 CFR part 93, subpart B). Subsequently, the EPA 
finalized revisions to the general conformity regulations on April 5, 
2010. (75 FR 17254-17279) The general conformity program ensures that 
federal actions not covered by the transportation conformity rule will 
not interfere with the SIP. General conformity also fosters 
communications between federal agencies and state/local air quality 
agencies, provides for public notification of and access to federal 
agency conformity determinations and allows for air quality review of 
individual federal actions. More information on the general conformity 
program is available at www.epa.gov/airquality/genconform/.
    b. Conformity in the Proposed Rule. The EPA did not propose any 
changes to the transportation conformity program as part of the current 
action. Nevertheless, to provide clarity in applying those regulations, 
the EPA is providing affected parties with information on when 
conformity must be implemented after nonattainment areas are designated 
for a new or revised PM2.5 NAAQS. At this time the EPA is 
using the 2012 PM2.5 NAAQS as an example. The agency is also 
discussing how it plans to make the transition from demonstrating 
conformity for the 1997 annual PM2.5 NAAQS to the 2012 
primary annual PM2.5 NAAQS because this transition is unique 
in that the 1997 annual PM2.5 NAAQS was retained as a 
secondary NAAQS. Finally, we proposed a change to the general 
conformity rule that addresses de minimis levels that apply to federal 
actions in PM2.5 areas. The information presented here is 
consistent with existing conformity regulations and statutory 
provisions that are not addressed by this PM2.5 
implementation rulemaking. Affected parties would include state and 
local transportation

[[Page 58125]]

and air quality agencies, metropolitan planning organizations (MPOs), 
and all federal agencies including the U.S. Department of 
Transportation, the U.S. Department of Defense, the U.S. Department of 
Interior and the U.S. Department of Agriculture.
    c. Applicability of Transportation and General Conformity to Areas 
Designated Nonattainment for the 2012 Primary Annual PM2.5 
NAAQS. Transportation and general conformity apply 1 year after the 
effective date of nonattainment designations for a new or revised 
PM2.5 NAAQS including the 2012 primary annual 
PM2.5 NAAQS, April 15, 2016. This is because CAA section 
176(c)(6) provides a 1-year grace period from the effective date of 
initial designations for any new NAAQS before transportation and 
general conformity apply in areas newly designated nonattainment for a 
specific pollutant and the NAAQS. With regard to general conformity, 
the EPA's April 2010 revisions to its general conformity regulations 
(see 75 FR 17277, April 5, 2010) apply the same 1-year grace period for 
the purposes of general conformity.
    With regard to transportation conformity, the conformity grace 
period applies to all areas designated nonattainment for a new or 
revised PM2.5 NAAQS including the 2012 primary annual 
PM2.5 NAAQS. The requirements differ depending on whether 
the nonattainment area includes any part of an MPO area designated 
under 23 U.S.C. 134 or is an isolated rural area. Within 1 year after 
the effective date of the initial nonattainment designation for a given 
pollutant and the NAAQS, the MPOs and DOT must make a transportation 
conformity determination with regard to that pollutant and standard for 
all of the metropolitan transportation plans and TIPs in the 
nonattainment area. The conformity requirements for surrounding ``donut 
areas,'' including the application of the 1-year conformity grace 
period, are generally the same as those for metropolitan areas.\245\ 
For the purposes of the implementation of the 2012 PM2.5 
NAAQS, MPOs and any adjacent donut areas in a 2012 PM2.5 
nonattainment area must continue to meet conformity requirements during 
the grace period for any other applicable NAAQS, including the 1997 
annual PM2.5 NAAQS and the 2006 24-hour PM2.5 
NAAQS. If, at the end of the grace period for the 2012 annual 
PM2.5 NAAQS, the MPO and DOT have not made a transportation 
plan and TIP conformity determination for that NAAQS, the area would be 
in a conformity ``lapse.'' During a conformity lapse, only certain 
projects can receive federal funding or approvals to proceed. The 
practical impact of a conformity lapse will vary from area to area. 
Finally, the 1-year conformity grace period also applies to project 
level conformity determinations.
---------------------------------------------------------------------------

    \245\ For the purposes of transportation conformity, a ``donut'' 
area is the geographic area outside a metropolitan planning area 
boundary, but inside a designated nonattainment or maintenance area 
boundary that includes an MPO (40 CFR 93.101).
---------------------------------------------------------------------------

    Isolated rural nonattainment and maintenance areas are areas that 
do not contain or are not part of an MPO (40 CFR 93.101). 
Transportation conformity requirements for isolated rural nonattainment 
and maintenance areas can be found at 40 CFR 93.109(g). The CAA section 
176(c)(6) 1-year grace period for newly designated nonattainment areas 
applies to isolated rural areas. Therefore, 1 year after the effective 
date of the initial nonattainment designation for a given pollutant and 
the NAAQS, conformity requirements with regard to that pollutant and 
standard would apply in any nonattainment areas that are isolated rural 
areas. Per the transportation conformity rule, an isolated rural area 
would be required to make a transportation conformity determination 
only at the point when an applicable transportation project needs 
funding or approval. This project level conformity determination may 
occur significantly after the 1-year grace period has ended. See the 
EPA's transportation conformity guidance related to the implementation 
of the 2012 primary annual PM2.5 NAAQS for further 
information on how the EPA has implemented this conformity grace period 
in metropolitan, donut and isolated rural areas. The guidance is 
available at http://www3.epa.gov/otaq/stateresources/transconf/documents/420b15091.pdf.
    d. Applicability of Transportation and General Conformity With 
Regard to the 1997 Annual PM2.5 NAAQS, Which was Retained as a 
Secondary NAAQS. In the December 2012 PM NAAQS final rule, the EPA 
established a new health-based primary annual PM2.5 NAAQS of 
12.0 [mu]g/m\3\. In that same action the EPA retained the 1997 annual 
PM2.5 NAAQS of 15.0 [mu]g/m\3\ as a secondary NAAQS to 
protect against certain welfare effects. In the 1997 PM2.5 
designations rule (70 FR 944), the EPA designated areas nonattainment 
for both the 1997 primary and secondary annual PM2.5 NAAQS 
(which have identical levels of 15.0 [mu]g/m\3\). Designations for the 
2012 primary annual PM2.5 NAAQS were made in January 2015 
(80 FR 2206) and were effective on April 15, 2015. This action did not 
make any changes to the designations that apply for the 1997 secondary 
annual PM2.5 standard. Therefore, at this time, all areas 
designated nonattainment in 2005 for the 1997 annual PM2.5 
standard are considered as having been designated nonattainment for 
both the 1997 primary annual PM2.5 NAAQS and for the 1997 
secondary annual PM2.5 NAAQS. Similarly, for any 1997 
PM2.5 nonattainment areas that have approved redesignation 
requests for attainment of the 1997 PM2.5 NAAQS, the 
redesignation applies to both the primary and secondary standards of 
the 1997 PM2.5 NAAQS. A discussion of how transportation and 
general conformity apply in this situation follows.
    CAA section 176(c)(5) requires compliance with transportation and 
general conformity only in: (1) Nonattainment areas and (2) areas that 
have been redesignated to attainment and are required to develop a 
maintenance plan under CAA section 175A.
    CAA section 175A(a), in turn, establishes the requirements that 
must be fulfilled by nonattainment areas in order to be redesignated to 
attainment. That section only requires that nonattainment areas for the 
primary standard submit a plan addressing maintenance of the primary 
NAAQS in order to be redesignated to attainment; it does not require 
nonattainment areas for secondary NAAQS to submit maintenance plans in 
order to be redesignated to attainment. See 42 U.S.C. 7505a(a) 
Therefore, since conformity does not apply in areas that have been 
redesignated without CAA section 175A maintenance plans, the EPA 
concludes that transportation and general conformity do not apply in 
areas that have been redesignated to attainment for any secondary 
NAAQS, such as the 1997 secondary annual PM2.5 NAAQS.
    Elsewhere in this final rule, the EPA is finalizing one of the 
proposed options for revoking the 1997 primary annual PM2.5 
NAAQS, which has been replaced by the more health protective 2012 
primary annual PM2.5 NAAQS. As discussed in detail in 
Section X of this preamble, the EPA is finalizing the option that calls 
for revoking the 1997 primary annual PM2.5 NAAQS in areas 
that have always been designated attainment for that NAAQS and in areas 
that have been redesignated to attainment for that NAAQS. As a result, 
after the effective date of the revocation, areas that have been 
redesignated to attainment for the 1997 annual PM2.5 NAAQS 
(i.e., maintenance areas for the 1997 annual PM2.5 NAAQS) 
will not be

[[Page 58126]]

required to make transportation or general conformity determinations 
for the 1997 annual PM2.5 NAAQS. The revocation would leave 
nonattainment designations in place for the 1997 annual NAAQS for areas 
that have not yet been redesignated to attainment for that NAAQS. The 
EPA will continue to redesignate areas to attainment as states submit 
redesignation requests for the remaining nonattainment areas. Any area 
that is designated as nonattainment for the 1997 annual NAAQS at the 
time of the initial revocation would have to continue to make 
transportation and general conformity determinations for that NAAQS 
until such time that they are redesignated to attainment for that 
NAAQS.
    For any area that has been redesignated to attainment for the 1997 
annual PM2.5 NAAQS (i.e., a maintenance area for the 1997 
annual PM2.5 NAAQS) and is not designated nonattainment for 
the 2012 primary annual PM2.5 NAAQS, the relevant planning 
organization will not have to make conformity determinations for any 
annual PM2.5 NAAQS after the effective date of the 
revocation of the 1997 primary annual PM2.5 NAAQS because, 
as discussed earlier, the CAA does not require maintenance areas for 
secondary NAAQS to make conformity determinations and the 1997 primary 
annual NAAQS will have been revoked. This means that, after the 
effective date of the revocation, areas redesignated to attainment for 
the 1997 annual PM2.5 NAAQS will no longer be required to 
make metropolitan transportation plan, TIP, or project-level 
transportation conformity determinations for that NAAQS. In addition, 
federal agencies will no longer be required to make conformity 
determinations for that NAAQS. Areas that remain designated 
nonattainment for the 1997 annual PM2.5 NAAQS will continue 
to make metropolitan transportation plan, TIP, and project-level 
conformity determinations for that NAAQS and federal agencies will be 
required to continue to make general conformity determinations for that 
NAAQS in these areas until such time as these areas attain that NAAQS 
and are redesignated to attainment (i.e., until the effective of the 
redesignation to attainment). Table 3 shows which types of areas are 
required to make conformity determinations for either the 1997 or 2012 
annual PM2.5 NAAQS after the revocation of the 1997 primary 
annual NAAQS is effective.

   Table 3--Where Is Conformity Required for the Various PM2.5 NAAQS After the Revocation of the 1997 Primary
                                               Annual PM2.5 NAAQS?
----------------------------------------------------------------------------------------------------------------
                                       1997 Primary and
          Attainment status            secondary annual     1997 24-Hour       2006 24-Hour       2012 Primary
                                            NAAQS              NAAQS              NAAQS           annual NAAQS
----------------------------------------------------------------------------------------------------------------
Nonattainment.......................                  X                  X                  X                  X
Redesignated to Attainment (i.e.,     .................                  X                  X                  X
 Maintenance).......................
----------------------------------------------------------------------------------------------------------------

    e. Impact of Implementation of a New or Revised PM2.5 
NAAQS (such as the 2012 PM2.5 NAAQS) on a State's 
Transportation and/or General Conformity SIP. As long as the EPA does 
not make specific changes to its transportation or general conformity 
regulations states should not need to revise their transportation and/
or general conformity SIPs. The EPA is not making any changes to its 
transportation conformity regulations and no transportation conformity 
SIP revisions are necessary. The only change that the EPA is making to 
its general conformity regulations is to change the de minimis levels 
in its general conformity regulations as discussed in Section IX.B.2.a 
of this preamble. States with a general conformity SIP should evaluate 
the need to revise those SIPs in light of this change. States with new 
nonattainment areas may also need to revise conformity SIPs in order to 
ensure the state regulations apply in any newly designated areas.
    In the event that a nonattainment designation causes transportation 
conformity to apply for the first time in a state,\246\ such a state is 
required by the statute and the EPA regulations to submit a SIP 
revision that addresses three specific transportation conformity 
requirements that address consultation procedures and written 
commitments to control or mitigation measures associated with 
conformity determinations for transportation plans, TIPs or projects. 
(40 CFR 51.390) Additional information and guidance can be found in the 
EPA's ``Guidance for Developing Transportation Conformity State 
Implementation Plans'' (http://www3.epa.gov/otaq/stateresources/transconf/policy/420b09001.pdf).
---------------------------------------------------------------------------

    \246\ This is not currently the case for the areas designated 
for the 2012 PM2.5 NAAQS, but the EPA is noting this in 
the event that future designations result in this situation.
---------------------------------------------------------------------------

2. Additional General Conformity Requirements for PM2.5 
Nonattainment Areas
    a. De minimis Emission Levels for Direct PM2.5 and its 
Precursors. Federal actions estimated to have an annual net emissions 
increase less than the de minimis levels established in the general 
conformity regulations are not required to demonstrate conformity under 
those regulations. For direct PM2.5 and its precursors 
(SO2, NOX, VOC and ammonia), the existing de 
minimis emission levels are set forth in the EPA's general conformity 
regulations at 40 CFR 93.153(b)(1). Those levels were based on the 
definition of a major stationary source for nonattainment NSR programs. 
The EPA believes it is appropriate to continue this practice for 
implementing the current and any future PM2.5 NAAQS. 
However, because the definition of precursors currently in the general 
conformity regulations at 40 CFR 93.153(b)(1) does not reflect the 
rebuttable presumptions for certain PM2.5 precursors, the 
EPA is finalizing changes to these conformity provisions to make them 
consistent with the agency's revised precursor requirements. 
Specifically, the current definition of precursors for PM2.5 
in the general conformity regulations does not reflect the rebuttable 
presumptions for VOC and ammonia. To address the lack of rebuttable 
presumptions for VOC and ammonia the EPA is revising the tables in 40 
CFR 93.153(b)(1) and (2) remove ``(if determined to be a significant 
precursor)'' from the entries in the tables that apply to VOC and 
ammonia emissions as PM2.5 precursors. It also does not 
reflect the subpart 4 definitions for ``major source'' and ``major 
stationary source'' that apply for Serious PM2.5 
nonattainment areas. Therefore, the EPA is finalizing changes to the 
PM2.5 precursor de minimis levels currently in 40 CFR 
93.153(b)(1) to make those levels consistent with the statutory 
requirements for major stationary source thresholds under subpart 4 and 
any relevant changes finalized in Section III of this preamble. 
Comments received on this proposed

[[Page 58127]]

change were supportive. The EPA is setting the de minimis levels that 
apply to direct PM2.5 and PM2.5 precursors for 
PM2.5 nonattainment areas for purposes of general conformity 
as identified in Table 4.

    Table 4--General Conformity De Minimis Emission Levels for PM2.5
                               Precursors
------------------------------------------------------------------------
                                      Tons/year  in
                                      moderate PM2.5     Tons/year  in
                                      nonattainment      serious PM2.5
         Type of emission             areas and all      nonattainment
                                    maintenance areas        areas
 
------------------------------------------------------------------------
Direct emissions..................                100                 70
SO2...............................                100                 70
NOX...............................                100                 70
VOC...............................                100                 70
Ammonia...........................                100                 70
------------------------------------------------------------------------

    b. Implementation Considerations for the General Conformity 
Program. The EPA did not propose any other revisions to the general 
conformity regulations and is not taking any additional final actions 
in this rule. However, as areas develop SIPs for the 2012 and future 
PM2.5 NAAQS, the agency recommends that state and local air 
quality agencies work with federal agencies with large facilities 
(e.g., commercial airports, ports and large military bases) that are 
subject to the general conformity regulations to establish an emissions 
budget for those facilities in order to facilitate future conformity 
determinations under the conformity regulations. Such a budget could be 
used by federal agencies in determining conformity or identifying 
mitigation measures if the budget level is included and identified in 
the SIP.
    In a few cases, tracts of land under federal management may also be 
included in nonattainment and maintenance area boundaries. The role of 
fire in these areas should be assessed and emissions budgets developed 
in concert with those federal land management agencies. In such areas 
the EPA encourages states to consider in any baseline, modeling and SIP 
attainment inventory used and/or submitted to include emissions 
expected from projects subject to general conformity, including 
emissions from wildland fire that may be reasonably expected in the 
area. Where appropriate, states may consider developing plans for 
addressing wildland fuels in collaboration with land managers and 
owners. Information is available from DOI and USDA Forest Service on 
the ecological role of fire and on smoke management programs and basic 
smoke management practices.\247\
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    \247\ USDA Forest Service and Natural Resources Conservation 
Service, Basic Smoke Management Practices Tech Note, October 2011, 
http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb1046311.pdf.
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C. Clean Data Policy

1. Summary of the Proposal
    In the proposed rule, the EPA described its longstanding clean data 
policy and proposed to codify the policy in regulatory text. A clean 
data determination (CDD) is a notice-and-comment rulemaking wherein the 
EPA determines that a specific nonattainment area has attained the 
relevant NAAQS based on 3 years of quality-assured certified air 
quality monitoring data. The CDD suspends the state's obligation to 
submit to the EPA the planning elements related to attaining the 
standard required of nonattainment areas under the Clean Air Act for as 
long as the area continues to attain the standard.\248\ The CDD does 
not suspend certain CAA requirements, such as an emissions inventory, 
nonattainment new source review requirements, and certain emission 
reduction requirements, that are considered independent of attainment 
needs.
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    \248\ In the context of CDDs, the EPA distinguishes between 
attainment planning requirements of the CAA, which relate to the 
attainment demonstration for an area and related control measures 
designed to bring an area into attainment for the given NAAQS as 
expeditiously as practicable, and other types of requirements, such 
as permitting requirements under the NNSR program, and any specific 
control requirements independent of those strictly needed to ensure 
timely attainment of the given NAAQS.
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    The proposal provided additional discussion about attainment 
demonstrations, control requirements for Moderate areas, RFP and 
quantitative milestones, and contingency measures. With regard to 
control requirements for Serious areas, the proposal included two 
options: one option would suspend BACT/BACM requirements under a CDD if 
elsewhere in the rule such requirements were considered necessary for 
expeditious attainment, and the other option would not suspend BACT/
BACM requirements if elsewhere in the rule such requirements were 
considered to be generally independent of attainment.
2. Final Rule
    The final rule codifies the clean data policy in rules governing 
the implementation of current and future PM2.5 NAAQS, and 
much of the guidance discussed in the proposal regarding which 
requirements are suspended remains the same. The EPA has already 
codified the clean data policy in a regulation implementing the 1997 8-
hour ozone NAAQS that was specifically challenged and upheld by the 
D.C. Circuit in NRDC v. EPA, 571 F.3d 1245 (D.C. Cir. 2009), and 
numerous United States Circuit Courts of Appeal have upheld the Clean 
Data Policy, including the EPA's application of this interpretation of 
the CAA with regard to implementation of the PM10 NAAQS 
under subpart 4. See Latino Issues Forum v. EPA, Nos. 06-75831 and 08-
71238 (9th Cir. March 2, 2009) (memorandum opinion). The EPA had also 
codified the clean data policy for PM2.5 in the now remanded 
2007 PM2.5 implementation rule. For a complete discussion of 
the Clean Data Policy's history and EPA's longstanding interpretation 
under the Clean Air Act, please refer to the proposal.
    The planning elements under subpart 1 and subpart 4 generally 
include reasonable further progress (RFP) requirements, attainment 
demonstrations, RACM and RACT, nonattainment area contingency measures, 
and other state planning requirements related to attaining the 
NAAQS.\249\ The suspension of the

[[Page 58128]]

obligation to submit such requirements applies regardless of when the 
plan submissions are due. The CDD does not suspend CAA requirements 
that are independent of helping the area achieve attainment, such as 
the requirements to submit an emissions inventory and nonattainment new 
source review requirements. The determination of attainment is not 
equivalent to a redesignation, and the state must still meet the 
statutory requirements for redesignation in order to be redesignated to 
attainment. A determination of attainment for purposes of the Clean 
Data Policy/regulations is also not linked to any particular attainment 
deadline, and is not necessarily equivalent to a determination that an 
area has attained the standard by its applicable attainment deadline, 
e.g., under CAA section 188(b). Note also that if the EPA determines 
that an area with a clean data determination subsequently is violating 
the standard prior to being redesignated to attainment, the area will 
be required to address the pertinent requirements when it submits the 
SIP to EPA. As has long been the EPA's policy, areas subject to a 
determination that a CDD is rescinded due to subsequent violation of 
the NAAQS would receive a reasonable amount of time to address the 
previously suspended requirements and submit revisions to their SIPs. 
The EPA would establish this SIP submittal date on a case-by-case 
basis, taking into account individual circumstances surrounding the 
particular SIP provisions at issue.\250\
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    \249\ See December 14, 2004 memorandum from Stephen D. Page, 
Director, EPA Office of Air Quality Planning and Standards, to Air 
Division Directors, EPA Regions I-X, titled ``Clean Data Policy for 
the Fine Particle National Ambient Air Quality Standards.'' 
Available at: http://www.epa.gov/airquality/urbanair/sipstatus/docs/pm25_clean_data_policy_14dec2004.pdf.
    \250\ Ibid.
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    This rule specifies that a determination that a nonattainment area 
is attaining the current and future PM2.5 NAAQS would 
suspend the following attainment planning related requirements under 
subpart 1 and subpart 4: (i) The part D, subpart 4 and subpart 1 
obligation to provide an attainment demonstration pursuant to CAA 
section 189(a)(1)(B); (ii) the RACM and RACT provisions of CAA section 
189(a)(1)(C); (iii) the RFP and quantitative milestones provisions of 
CAA section 189(c); and, (iv) related attainment demonstration, RACM 
and RACT, RFP and contingency measure provisions requirements of 
subpart 1, section 172. The following sections a-d provide additional 
detail on the PM2.5 NAAQS planning requirements that would 
be suspended by a CDD.
    a. Attainment Demonstrations. With respect to the attainment 
demonstration requirements of section 172(c) and section 189(a)(1)(B) 
of the CAA, the EPA finds that if an area already has air quality 
monitoring data demonstrating attainment of the standard, there is no 
need for an area to make a further submission containing additional 
measures to achieve attainment, nor is there a need for the area to 
perform future modeling to show how the area will achieve attainment. 
The plain language of CAA section 189(a)(1)(B) requires that the 
attainment plan provide for ``a demonstration (including air quality 
modeling) that the [SIP] will provide for attainment by the applicable 
attainment date.'' Where the area has attained the standard, such a 
demonstration no longer serves a purpose.
    b. Control Measure Requirements for Moderate Areas. Both CAA 
sections 172(c)(1) and 189(a)(1)(C) require ``provisions to assure that 
reasonably available control measures'' (i.e., RACM) are implemented in 
a nonattainment area. Reasonably available control technology (i.e., 
RACT) is a subset of RACM. The EPA has long interpreted ``reasonably 
available control measures'' under CAA sections 172(c)(1) and 
189(a)(1)(C) to mean only those measures that are necessary to help an 
area achieve attainment. Thus, where an area is already attaining the 
standard, no additional RACM are required, but all measures adopted 
into the SIP prior to attainment would remain. The EPA is interpreting 
CAA section 189(a)(1)(C) consistent with its interpretation of CAA 
section 172(c)(1).
    c. RFP and Quantitative Milestones. The EPA has long interpreted 
the provisions of part D, subpart 1 of the CAA (sections 171 and 172) 
as not requiring the submission of RFP for an area already attaining 
the PM10 NAAQS. For an area that is attaining, showing that 
the state will make RFP towards attainment ``will, therefore, have no 
meaning at that point.''
    d. Contingency Measures. Other SIP submission requirements are 
linked with these attainment demonstration and RFP requirements, and 
similar reasoning applies to them. These requirements include the 
contingency measure requirements of CAA sections 172(c)(9). The EPA has 
interpreted the obligation to submit contingency measure requirements 
of CAA sections 172(c)(9) as suspended when an area has attained the 
standard because those ``contingency measures are directed at ensuring 
RFP and attainment by the applicable date.'' 57 FR at 13564; see also 
Seitz memo at pgs. 5-6.
    e. Control Measure Requirements for Serious Areas. Section VII.D of 
the preamble explains the rationale of the EPA's decision to maintain 
its longstanding policy of considering the BACT/BACM requirement of CAA 
section 189(b)(1)(B) to be generally independent of attainment. 
Accordingly, this rule states that a clean data determination would not 
suspend the obligation for the state to submit any applicable 
outstanding BACM and BACT requirements.
    For a Serious area that failed to attain the relevant 
PM2.5 NAAQS by the applicable attainment date and that is 
therefore subject to the annual 5 percent emissions reduction 
requirement under CAA section 189(d), but is nevertheless now attaining 
the relevant NAAQS, the EPA believes that the Clean Data Policy may 
apply to the obligations of the state to make an attainment plan 
submission to meet the requirements of CAA section 189(d). Once such an 
area is attaining the relevant NAAQS, a clean data determination would 
suspend the CAA section 189(d) submission requirement.
3. Comments and Responses
    Comment: Several commenters supported the EPA's proposal to codify 
the clean data policy in the final rule because they believe the policy 
is lawful and relieves states from unnecessary planning burdens in 
areas where the NAAQS is met. Some commenters stated the policy has 
specifically been upheld by the D.C. Circuit in the context of review 
of nationally applicable implementation rules for the EPA's ozone NAAQS 
[Natural Res. Def. Council v. EPA, 571 F.3d 1245, 1260-61 (D.C. Cir. 
2009)]. Other commenters, however, asserted that they ``reiterate their 
previous comments regarding the illegality of the Clean Data Policy.'' 
To the extent that the Agency planned to continue to follow the policy, 
these commenters agreed with the EPA's interpretation that only those 
requirements tied to an area's demonstration of attainment should be 
suspended. To that end, the commenters requested clarification that 
measures that have been responsible for the area's attainment must be 
submitted and approved into the SIP even following a Clean Data 
Determination. Similarly, other commenters requested clarification as 
to EPA's statement that ``Thus, where an area is already attaining the 
standard, no additional RACM are required, but all measures adopted 
into the SIP prior to attainment would remain.'' The commenter wondered 
if ``all measures adopted into the SIP'' includes measures that were 
included and identified as RACT or RACM in the original SIP, even if 
those measures have not yet been submitted to EPA in regulatory form.
    Finally, some commenters noted that the Act requires that RACM/RACT 
be

[[Page 58129]]

implemented within 4 years of a nonattainment designation and stated 
that, as sources reduce emissions of PM2.5 and regional PM 
precursors due to national rules yet to be fully implemented (e.g., 
Boiler NESHAPS, CSAPR) it is entirely possible that an area may attain 
the standard prior to complete implementation of RACM/RACT. The 
commenters stated that, if an area attains the NAAQS prior to 
implementation of the planning requirements, it is meaningless and 
overly burdensome to require the area to continue implementing RACM/
RACT.
    Response: The EPA disagrees with commenters who allege, without 
explanation, that the Clean Data Policy is ``illegal.'' Rather, as 
noted by supportive commenters, the EPA has long interpreted certain 
CAA requirements that are designed to bring an area into attainment to 
serve no purpose once an area is attaining, and thus has interpreted 
the Act as permitting the Agency to suspend the requirements to submit 
revisions to the SIP addressing those requirements. This position has 
been upheld by multiple Circuit Courts of Appeals.\251\
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    \251\ See, e.g., NRDC v. EPA, 571 F.3d 1245 (D.C. Cir. 2009); 
Sierra Club v. EPA, 99 F.3d 1551 (10th Cir. 1996); Latino Issues 
Forum v. EPA, Nos. 06-75831 and 08-71238 (9th Cir. March 2, 2009) 
(memorandum opinion).
---------------------------------------------------------------------------

    In response to the requests for clarification of which RACM 
requirements are suspended by a CDD, we note that, for over 30 years, 
the EPA has consistently interpreted the RACM requirement in CAA 
section 172(c)(1) to apply only to those measures that, individually or 
collectively, contribute to expeditious attainment of the NAAQS. The 
suspension of the statutory requirement to submit RACM is premised on 
the idea that, ``[t]o the extent an area is already achieving 
attainment as expeditiously as possible, imposition of additional 
control [measures] would not hasten achievement of the NAAQS. In such a 
situation, the EPA may reasonably conclude that no control [measures] 
are reasonably available and the area need not implement further 
[measures] to satisfy the [RACM] requirement.'' See NRDC v. EPA, 571 
F.3d 1245, 1253 (D.C. Cir. 2009). Thus, upon the EPA's finalization of 
a CDD for a particular NAAQS, the EPA formally suspends the obligation 
to submit attainment-related plan elements for that particular NAAQS, 
including RACM. A CDD does not, however, affect the criteria in CAA 
section 107(d)(3)(E) for redesignation to attainment, including the 
requirement for the state to demonstrate to the EPA's satisfaction that 
the improvement in air quality is due to ``permanent and enforceable 
reductions in emissions resulting from implementation of the applicable 
implementation plan'' and other permanent and enforceable reductions. 
Thus, to the extent certain state/local control measures were necessary 
to an area's attainment of the NAAQS, the state may need to submit 
those measures to the EPA for SIP approval in order to meet the 
statutory criteria for redesignation in CAA section 107(d)(3)I, 
notwithstanding the suspension of planning obligations under a CDD.
    In this case, it is not clear to the EPA what the commenter means 
by the phrase ``original SIP,'' since the SIP is only those measures 
that have been submitted and approved by the EPA. To the extent that a 
measure was adopted into the SIP prior to an area's attainment of the 
NAAQS, and therefore contributed to an area's attainment, that measure 
is therefore required to remain as part of the SIP. We infer that the 
comment might be referring to commitments that were approved into a SIP 
to adopt future measures, or that commenters might be asking for 
clarification regarding measures that have been adopted locally or at a 
state level prior to the area's coming into attainment but have not yet 
been submitted to the EPA for approval into the federally-approved SIP. 
As explained above, a CDD has no effect on the state's obligation to 
demonstrate that an area's improvement in air quality is due to 
``permanent and enforceable'' emissions reductions in order to meet the 
statutory requirements for redesignation to attainment in CAA section 
107(d)(3)(E). Additionally, a CDD does not alter the effect of any 
measure (including any state commitment) that has already been approved 
into a SIP, even if that measure is a commitment to adopt or submit a 
future measure. Once approved into a SIP, such a measure becomes an 
enforceable emission standard or limitation subject to EPA or citizen 
enforcement under CAA section 304, which cannot be altered except 
through a SIP revision approved by the EPA. Along those same lines, 
even if an area has adopted into its SIP RACM/RACT but has yet to fully 
implement those measures when the area first starts attaining the 
NAAQS, a CDD does not excuse the area from continuing to implement its 
SIP requirements, i.e., the RACM/RACT measures that have been approved 
into the SIP. The CDD merely suspends the requirement to submit RACM/
RACT, that is, additional measures on top of what brought the area into 
attainment; a state may only stop implementing those measures already 
in its SIP through a SIP revision approved by the EPA.
    Comment: Some commenters supported the EPA's proposal to retain the 
BACM/BACT submission requirement even with a CDD (80 FR 15444). Other 
commenters, however, stated that, once the EPA makes an attainment 
determination, the EPA should suspend the requirements to submit BACM/
BACT and that to do otherwise is illogical.
    Response: The EPA is finalizing the option that requires BACM/BACT 
to be submitted even if the EPA has issued a CDD for an area. As 
discussed in our proposal and earlier in this section, the legal 
underpinning of the Clean Data Policy is that the EPA interprets the 
CAA not to require the submission of requirements that are designed to 
get an area to attainment once that area is already attaining the 
NAAQS. Thus, only those ``attainment planning'' requirements are 
suspended by a CDD. It is therefore illogical for the EPA to extend the 
Clean Data Policy to the submission of the BACM/BACT requirement for 
Serious Areas. Because the EPA interprets BACM/BACT as independent of 
attainment, as discussed above in Section VII.D of the preamble, the 
requirement to submit BACM/BACT continues to apply regardless of 
whether the EPA has determined that the area is attaining.

D. CAA Section 179B/International Border Areas

1. Specific Requirements
    a. Summary of Proposal. Section 179B of the CAA, titled 
``International Border Areas,'' applies to areas that would attain the 
relevant NAAQS by the statutory attainment date ``but for'' emissions 
emanating from outside the U.S. Under CAA section 179B, if applicable, 
the provision modifies subpart 4 attainment plan obligations applicable 
to areas designated nonattainment for any PM NAAQS. The EPA proposed 
and sought comment on two approaches that would give greater clarity to 
the agency's existing interpretation of the RACM/RACT and additional 
reasonable measure requirements for Moderate area attainment plans to 
be approved under CAA section 179B. The first proposed interpretation 
would have clarified that the control strategy for an area that could 
attain by the Moderate area attainment date, ``but for'' foreign 
emissions of direct PM2.5 or its precursors, must include 
all control measures identified by the state to be

[[Page 58130]]

technologically and economically feasible and implementable on sources 
in the area by the end of the sixth calendar year following designation 
of the area. Under this approach, inclusion of such measures would 
satisfy requirements for RACM and RACT (for measures that can be 
implemented within four years) and additional reasonable measures (for 
measures than can be implemented within six years but not within four). 
The proposal also sought comment on a possible exception for any such 
measures that collectively would not be effective in reducing ambient 
PM2.5 levels in the area. The second proposed approach would 
have required a state to demonstrate that its selected control measures 
for a Moderate nonattainment area would achieve reductions in 
PM2.5 levels that exceeded the applicable NAAQS in 
proportion to their contribution to overall PM2.5 levels. 
Inclusion of these proportional measures would thus satisfy RACM/RACT 
and additional reasonable measures under the second approach. The EPA 
sought comment on these two approaches to clarify what constitutes a 
reasonable control strategy in the context of a SIP submitted pursuant 
to CAA section 179B.
    The EPA also proposed that any Moderate area attainment plan 
submitted under CAA section 179B must include an RFP plan with required 
air quality targets consistent with the RFP Option 2. In addition, the 
EPA proposed requirements for establishing and reporting on 
quantitative milestones for areas with approved ``but for'' 
demonstrations.
b. Final Rule
    Section 179B(a) of the CAA provides that the EPA shall approve an 
attainment plan for a nonattainment area that is an international 
border area if: (i) the attainment plan meets all other applicable 
requirements of the CAA, and (ii) the submitting state can demonstrate 
satisfactorily that ``but for emissions emanating from outside of the 
United States,'' the area would attain and maintain the relevant NAAQS. 
In addition, CAA section 179B(d) provides that if a state demonstrates 
that an area would have attained the NAAQS but for emissions emanating 
from outside the U.S., then the area is not subject to the mandatory 
reclassification element of CAA section 188(b)(2) for Moderate areas 
that fail to attain by the applicable attainment date.
    Under CAA section 179B, areas affected by emissions from outside 
the U.S. continue to have attainment plan obligations. First, even if 
the area is impacted by emissions from outside the U.S., that fact does 
not affect the designation of the area. Such an area that is violating 
the relevant NAAQS will be designated nonattainment even if emissions 
from outside the U.S. contribute to that violation. Second, as a result 
of that designation, the state is required to meet the applicable 
attainment plan requirements for the relevant NAAQS. Section 179B of 
the CAA does not negate the attainment plan requirements. Rather, it 
allows the EPA to approve an attainment plan that demonstrates 
attainment and maintenance of the NAAQS ``but for'' international 
emissions.
    The EPA has determined that under the best reading of CAA section 
179B, states remain obligated to meet the attainment plan requirements 
other than the requirement to demonstrate attainment and maintenance of 
the relevant NAAQS. This determination is based upon the fact that 
179B(a)(1) explicitly states that such an attainment plan must meet all 
the requirements of the CAA with that exception. The applicable 
requirements for an attainment plan for PM2.5 include those 
requirements that apply to a Moderate area attainment plan. Those 
requirements include an emissions inventory, RACM and RACT, additional 
reasonable measures, RFP, quantitative milestones, contingency 
measures, NNSR and motor vehicle emissions budgets for transportation 
conformity purposes. The Addendum includes a discussion of the 
applicable attainment plan requirements in the context of developing a 
SIP subject to CAA section 179B. In it, the EPA clarified that ``RACM/
RACT must be implemented to the extent necessary to demonstrate 
attainment by the applicable attainment date if emissions emanating 
from outside the U.S. were not included in the analysis.'' \252\ The 
EPA further encouraged states ``to reduce emissions beyond the minimum 
necessary to satisfy the `but for' test in order to reduce the PM 
concentrations to which their populations are exposed.'' \253\ However, 
the EPA acknowledged that ``if . . . States . . . were also required, 
because of contributions to PM10 violations caused by 
foreign emissions, to shoulder more of a regulatory and economic burden 
than States not similarly affected. . .such a requirement would 
unfairly penalize States containing international border areas and 
effectively undermine the purpose of CAA section 179B. Indeed, to the 
extent an affected State can satisfactorily demonstrate that 
implementation of such measures clearly would not have advanced the 
attainment date, the EPA could conclude they are unreasonable and hence 
do not constitute RACM.'' \254\
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    \252\ Addendum to the General Preamble, 59 FR 41998 (August 16, 
1994), at page 42001.
    \253\ Ibid.
    \254\ Ibid.
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    In the proposal, the EPA specifically took comment on the most 
appropriate way to address the RACM and RACT requirements. The past 
interpretation of RACM and RACT requirements in the context of CAA 
section 179B was considered when the agency proposed an option to allow 
a state not to adopt such measures if the state could demonstrate that 
collectively the measures will not be effective in reducing 
PM2.5 levels in the area. Some commenters supported this 
exception, stating that it would prevent wasting resources on 
ineffective measures. Some commenters stated that requiring 
implementation of all RACM/RACT and additional reasonable measures 
circumvents Congressional intent and the CAA. Other commenters 
disagreed, stating that these areas should implement all measures due 
to the importance to public health.
    Regarding RACM/RACT and additional reasonable measures, the EPA 
reviewed the comments received and its past interpretation of RACM and 
RACT requirements in the context of CAA section 179B attainment plans 
for PM2.5 NAAQS. The EPA is persuaded that this approach is 
most appropriate and most consistent with the Act and with the control 
requirements for other Moderate areas that demonstrate they cannot 
practicably attain by the Moderate area attainment date. See section 
51.1009(a)(4)(ii). In longstanding guidance the EPA has encouraged 
states ``to reduce emissions beyond the minimum necessary to satisfy 
the `but for' test in order to reduce the PM10 
concentrations to which their populations are exposed.'' \255\ Given 
that the primary purpose of an attainment plan is to ensure expeditious 
attainment of the NAAQS and protection of public health and welfare 
through implementation of control measures that achieve emissions 
reductions, adopting an interpretation that would allow for continued 
emissions of pollutants that the state could reasonably reduce would be 
antithetical to the objectives of the CAA. Just as it is appropriate 
and consistent with the Act to adopt reasonable measures (i.e., RACT/
RACM or additional reasonable measures) in areas that cannot 
practicably attain by the attainment date, as previously discussed, it 
is also appropriate and

[[Page 58131]]

consistent with the Act to adopt reasonable measures in areas that 
cannot attain due to international emissions.
---------------------------------------------------------------------------

    \255\ Ibid.
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    Therefore, the EPA requires that Moderate area attainment plans 
approved under CAA section 179B must implement all technologically and 
economically feasible measures that can be implemented on sources in 
the area by the end of the sixth calendar year following designation of 
the area (i.e., RACM and RACT and additional reasonable measures). This 
requirement is intended to ensure that the area makes reasonable 
progress toward attaining the standard even if such measures are not 
expected to yield attainment by the statutory Moderate area attainment 
date. This approach parallels the requirements described in Section 
IV.D in this preamble, pursuant to CAA section 189(a)(1), for Moderate 
PM2.5 nonattainment areas that cannot practicably attain the 
NAAQS by the latest statutory attainment date for the area. Requiring 
the implementation of all reasonable measures is even more important in 
the context of a Moderate area for which CAA section 179B applies 
because sources in such areas will not be subject to the more stringent 
BACM/BACT, MSM, or 5 percent requirement because such areas are not 
subject to mandatory reclassification as Serious areas pursuant to CAA 
section 179B(d). Thus, the only level of PM2.5 control 
requirements that will likely ever apply to these sources is the less-
stringent RACM/RACT and additional reasonable measures level of 
control; therefore, all the sources in the area should reduce emissions 
if such reduction is reasonable since the public in those areas will 
continue to be subject to ambient levels of emissions that the agency 
has determined are unsafe notwithstanding implementation of those 
reasonable measures. Additionally, the EPA notes that the process to 
determine RACM already allows states to identify the subset of all 
control measures that are technologically and economically feasible, 
which should be adequate to prevent significant wasting of resources on 
ineffective measures.
    The EPA has determined that it will not finalize the proposed 
option of achieving reductions in PM2.5 levels in proportion 
to the area's contribution to overall PM2.5 levels. The EPA 
received several comments on the proposed option to allow states to 
implement control measures for a Moderate nonattainment area with a 
plan approved under CAA section 179B that would achieve reductions in 
PM2.5 levels in proportion to the area's contribution to 
overall PM2.5 levels. Although some commenters supported the 
possibility of proportionally implementing control measures, other 
commenters raised possible negative consequences of this option. 
Commenters highlighted the difficulty that states would face in 
apportioning responsibility for emissions between foreign and non-
foreign sources, which would be necessary under the proportional 
approach. These commenters also disagreed as to whether the EPA or 
states should be responsible to determine the proportional allocation 
of international emissions. The EPA is also concerned that a 
proportional approach would introduce too much complexity into an 
already complex analytical process. Additionally, the EPA notes that no 
other NAAQS pollutant offers a proportional approach to implementation 
of control measures and is not convinced that there are sufficient 
reasons to finalize this approach for PM2.5 nonattainment 
areas.
    Section 179B(d) of the CAA states that any area for which the state 
establishes to the EPA's satisfaction that the area ``would have 
attained the NAAQS by the applicable attainment date, but for emissions 
emanating from outside the United States, shall not be subject to the 
provisions of section [188(b)(2)].'' CAA section 188(b)(2) requires the 
EPA to determine, within 6 months following the applicable attainment 
date for a Moderate PM2.5 nonattainment area, whether the 
area attained the NAAQS by that date and to reclassify the area as 
Serious if it is not in attainment after the applicable attainment 
date. For any Serious area subject to an EPA determination of failure 
to attain by the Serious area attainment date, CAA section 189(d) 
requires the state to submit plan revisions which provide for 
attainment of the PM2.5 NAAQS and for annual emissions 
reductions of not less than 5 percent until the area attains. These 
planning requirements in section 189(d) apply only upon the EPA's 
determination that a Serious area has failed to attain the applicable 
NAAQS by the Serious area attainment date. Because section 179B(d) 
explicitly provides that any area that satisfies the ``but for'' 
attainment test in CAA section 179B shall not be subject to the 
provisions for reclassification to Serious upon failure to attain in 
CAA section 188(b)(2), the consequences for failure to attain by the 
Serious area attainment date in section 189(d) generally do not apply 
to such areas.
    In the event that the EPA has already reclassified an international 
border area as Serious, when the state submits a ``but for'' 
demonstration under section 179B, all of the Serious area requirements 
that apply to the area (e.g., the requirements to implement BACM/BACT 
and additional feasible measures) would remain in effect. This is 
because at the time the state submits the ``but for'' demonstration, 
these statutory requirements already apply. Upon the EPA's approval of 
a Serious area plan and section 179B demonstration for such an area, 
however, the EPA would no longer be obligated to make a determination 
of failure to attain by the Serious area attainment date triggering the 
additional planning requirements of section 189(d). Consistent with 
Congress's clear intent in section 179B(d) to relieve Moderate 
PM2.5 nonattainment areas that satisfy the ``but for'' 
attainment test of the additional planning obligations that result from 
a mandatory determination of failure to attain by the Moderate area 
attainment date, the EPA interprets section 179B as also relieving 
Serious PM2.5 nonattainment areas of the additional planning 
obligations in section 189(d) that result from a mandatory 
determination of failure to attain by the Serious area attainment date, 
once the EPA approves the state's Serious area plan and section 179B 
demonstration.
    Where a Serious area fails to attain by the Serious area attainment 
date and is therefore subject to the requirements of section 189(d), 
the EPA's approval of a section 189(d) plan and 179B demonstration 
would mean that the EPA is no longer obligated to make further 
determinations of failure to attain or to trigger additional planning 
requirements. The EPA intends to review each SIP submission containing 
a ``but for'' attainment demonstration for an international border area 
for compliance with the requirements of section 179B.
    The EPA notes that, with one exception for contingency measures, 
the final rule provisions governing for the RFP, quantitative 
milestone, and contingency measure requirements for PM2.5 
nonattainment areas are the same for areas seeking plan approval under 
CAA section 179B as they are for any other area. For example, the EPA 
requires that as part of any Moderate area attainment plan submitted 
under CAA section 179B, a state must include an RFP plan developed 
consistent with the process described in Section IV.F of this preamble 
as a Moderate nonattainment area that cannot practicably attain the 
relevant NAAQS by the statutory attainment date. In addition, the EPA 
requires that the state must identify quantitative milestones for the 
area to be achieved 4.5 years and

[[Page 58132]]

7.5 years from the date of designation of the area. The EPA will apply 
the same requirements for establishing and reporting on quantitative 
milestones for Moderate nonattainment areas with an approved ``but 
for'' demonstration under CAA section 179B as for all other Moderate 
nonattainment areas, as described in Section IV.G of this preamble. 
Furthermore, the state must include as part of any attainment plan 
submission made for such an area contingency measures that are ready to 
be implemented quickly and with minimal further action by the state or 
by the EPA in the event the EPA determines that such area failed to 
meet RFP or quantitative milestone requirements. The contingency 
measures should achieve approximately 1 year's worth of emissions 
reductions as calculated by the state for purposes of the RFP analysis. 
The exception to the contingency measure requirement for areas with 
approved CAA section 179B demonstrations is that contingency measures 
for failure to attain are not required in such plans, because under CAA 
section 179B(d) the EPA is not required to make determinations 
concerning attainment for such areas. Further explanation of 
contingency measures can be found in Section IV.H of this preamble.
    Regarding the ``but for'' demonstrations under CAA section 179B, 
the EPA has historically evaluated these demonstrations on a case-by-
case basis, based on the individual circumstances and data provided by 
the submitting state. These demonstrations have included information 
such as ambient air quality monitoring data, modeling scenarios, 
emissions inventory data and meteorological or satellite data.\256\ The 
Moderate area attainment demonstration modeling and other elements of 
the attainment demonstration must show attainment and maintenance of 
the NAAQS but for the emissions from outside of the U.S. However, CAA 
section 179B does not provide authority to exclude monitoring data 
influenced by international transport from regulatory determinations 
related to attainment and nonattainment.
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    \256\ Ibid. The Addendum includes further examples of 
information a state may present for the EPA to consider as part of 
the ``but for'' demonstration, including additional monitors in 
international border areas, more detailed emissions inventories, and 
speciation data that identifies PM2.5 components from 
foreign sources.
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    Where international transport of emissions contributes to an 
exceedance or violation, such data may be excluded from consideration 
only if they were significantly influenced by exceptional events under 
section 319(b) of the CAA. If the data meet the criteria contained in 
the EPA's Exceptional Events Rule, the exceedance can be addressed by 
that rule.\257\ Specifically, if the EPA concurs with a state's request 
to exclude affected data, the event-influenced data are officially 
noted and removed from the data set used to calculate official design 
values, which may be used as part of a regulatory determination.
---------------------------------------------------------------------------

    \257\ See 40 CFR 40 CFR 50.1, 50.14 and 51.930.
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    The EPA expects that the best approach for evaluating the potential 
impacts of international transport on nonattainment is for states to 
work with the EPA on a case-by-case basis to determine the most 
appropriate information and analytical methods for each area's unique 
situation. The EPA will work with states that are developing 
exceptional events demonstrations and attainment plans for which CAA 
section 179B is relevant, and ensure the states have the benefit of the 
EPA's understanding of international transport of PM2.5 and 
PM2.5 precursors.
c. Comments and Responses
    Comment: Commenters stated the EPA should not require the state to 
implement a section 189(d) 5 percent reduction plan, since attaining 
such reductions may well be impossible if there are significant 
international emissions.
    Response: The EPA agrees that as long as the affected nonattainment 
area satisfactorily meets the provisions of CAA section 179B, that area 
should not be subjected to the additional requirements of CAA section 
189(d) even if the area fails to attain.
    Comment: Commenters stated that requiring implementation of all 
RACM and RACT for CAA section l79B nonattainment areas would penalize 
rural communities and would run counter to the intent of CAA section 
179B of providing regulatory relief to areas affected by foreign 
emissions.
    Response: For the reasons stated earlier, the EPA has determined 
that section 179B nonattainment areas should be required to implement 
control measures to the same extent as a Moderate nonattainment area 
that demonstrates it will not be able to attain the PM2.5 
NAAQS by the statutory attainment date.
    Comment: Some commenters stated that the EPA's current 
interpretation of section 179B and the agency's guidance which 
encourages states ``to reduce emissions beyond the minimum necessary to 
satisfy the `but for' test,'' circumvents Congressional intent and the 
CAA and establishes a second ambient air quality threshold not related 
to the NAAQS.
    Response: The EPA disagrees that encouraging states to minimize 
emissions as much as possible to protect public health circumvents 
Congressional intent. The EPA has determined that the reasonable 
control measure requirements outlined in section 51.1009(a)(4)(ii) 
represent the most appropriate interpretation of the CAA in line with 
the overriding Congressional intent to protect and improve air quality 
thereby enabling the associated public health benefit.
    Comment: Some commenters stated that if an area's demonstration is 
approved under CAA section 179B, any contingency measures should only 
be required to obtain emissions reductions in proportion to the 
contribution of emissions excluding the international pollution, or at 
least to the contribution of emissions reductions that the state can 
feasibly attain.
    Response: The EPA agrees that contingency measures relate to the 
domestic portion of emissions affecting the nonattainment area. The 
state will not be required to develop contingency measures to make up 
for those emissions coming from international sources. The EPA 
emphasizes that contingency measures for a section 179B area will be 
for failure to meet RFP requirements, not for failure to attain.
    However, the EPA expects states with a section 179B area to follow 
the guidance and requirements outlined in Section IV.H of this preamble 
to identify contingency measures that can provide emissions reductions 
from sources within the state's jurisdiction. As discussed in Section 
IV.H of the preamble, this should include an explanation of the amount 
of anticipated emissions reductions to be accomplished by the 
contingency measures. If such an area is unable to identify 
approximately 1 year's worth of emissions reductions to constitute 
contingency measures, the explanation should describe the factors 
considered by the state when reaching this conclusion.

E. Enforcement and Compliance

    a. Summary of Proposal. The agency proposed that in general, in 
order for a SIP regulation to be enforceable, it must clearly spell out 
which sources or source types are subject to its requirements and what 
its requirements (e.g., emission limits or work practices) are. The EPA 
proposed that an enforceable regulation would also specify the 
timeframes within which these requirements must be met, and

[[Page 58133]]

definitively state the recordkeeping and monitoring requirements 
appropriate to the type of sources being regulated. Additionally, the 
EPA proposed that an enforceable regulation would also contain test 
procedures in order to determine whether sources are in compliance.
    b. Final Rule. Section 172(c)(6) in subpart 1 of the CAA requires 
nonattainment SIPs to ``include enforceable emission limitations, and 
such other control measures, means or techniques . . . as well as 
schedules and timetables for compliance, as may be necessary or 
appropriate to provide for attainment.'' In the remanded 2007 
PM2.5 Implementation Rule, the EPA described the general 
elements that characterize an enforceable SIP regulation, recognizing 
that enforceable SIP regulations may address the elements in different 
ways depending on the type of source category being regulated. The 
agency continues to believe and hereby finalizes that in general, in 
order for a SIP regulation to be enforceable, it must clearly spell out 
which sources or source types are subject to its requirements and what 
its requirements (e.g., emission limits or work practices) are. An 
enforceable regulation would also specify the timeframes within which 
these requirements must be met, and definitively state the 
recordkeeping and monitoring requirements appropriate to the type of 
sources being regulated. The recordkeeping and monitoring requirements 
would have to be sufficient to enable the state or the EPA to determine 
whether the source is complying with the emission limit on a continuous 
basis. An enforceable regulation would also contain test procedures in 
order to determine whether sources are in compliance.
    The EPA continues to believe that complete and effective 
regulations that ensure compliance with an applicable emissions limit 
must include requirements for both performance testing of emissions and 
ongoing monitoring of the compliance performance of control measures, 
and the agency requires that SIP regulations that establish emission 
limits include the following for performance testing:
    (1) Indicator(s) of compliance--the pollutant or pollutants of 
interest (e.g., filterable and condensable PM2.5) and the 
applicable units of measurement for expressing compliance (e.g., ng/J 
of heat input, lb/hr);
    (2) Test method--reference to a specific EPA or other published set 
of sample collection and analytical procedures, equipment design and 
performance criteria, and the calculations providing data in units of 
the indicator of compliance (Section IX.K of this preamble presents a 
discussion of specific test methods for condensable PM2.5 
emissions);
    (3) Sample collection characteristics--conditions related to the 
sample collection portion of the performance test. Such conditions 
would include duration of sampling period, either on a time or volume 
collected basis; the number of runs comprising a test (e.g., three runs 
per test); and the averaging period, i.e., the time over which the 
emissions limit is averaged (e.g., 8 hours); and,
    (4) Frequency--the time between emissions or performance tests 
(e.g., within 30 days of facility start-up and once each successive 
quarter, every 6-month period, or yearly).
    In order to be complete with regard to compliance monitoring 
provisions, the EPA requires that regulations adopted into the SIP must 
include the following critical elements:
    (1) Indicator(s) of performance--the parameter or parameters 
measured or observed for demonstrating proper operation of the 
pollution control measure or compliance with the applicable emissions 
limitation or standard. Indicators of performance could include direct 
or predicted emissions measurements, process or control device (and 
capture system) operational parametric values that correspond to 
compliance with efficiency or emissions limits, and recorded findings 
of verification of work practice activities, raw material or fuel 
pollutant content, or design characteristics. Indicators could be 
expressed as a single maximum or minimum value, a function of process 
variables (e.g., within a range of pressure drops), a particular 
operational or work practice status (e.g., a damper position, 
completion of a waste recovery task), raw material or fuel pollutant 
content, or an interdependency between two or more variables;
    (2) Measurement technique--the means used to gather and record 
information of or about the indicators of performance. The components 
of the measurement technique include the detector type or analytical 
method, location and installation specifications, inspection 
procedures, and quality assurance and quality control measures. 
Examples of measurement approaches include continuous emissions 
monitoring systems (CEMS), continuous opacity monitoring systems 
(COMS), continuous parametric monitoring systems (CPMS), performance 
testing, vendor or laboratory analytical data, and manual inspections 
and data collection that include making records of process conditions, 
raw materials or fuel specifications, or work practices. Directly 
enforceable emission measurements, such as PM CEMS, are preferred 
wherever feasible. Where COMS are feasible, it should be clear that 
opacity is a directly enforceable standard, not merely an indicator of 
compliance;
    (3) Averaging time--the period over which to average data to verify 
compliance with the emissions limitation or standard or proper 
operation of the pollution control measure. Examples of averaging time 
include a 3-hour average in units of the emissions limitation, a 30-day 
rolling average emissions value, a daily average of a control device 
operational parametric range, periodic (e.g., monthly, annual) average 
of raw materials or fuel pollutant content, and an instantaneous alarm;
    (4) Monitoring frequency--the number of monitoring data values 
recorded over a specified time interval. Examples of monitoring 
frequencies include at least one data value every 15 minutes for CEMS 
or CPMS, at least every 10 seconds for COMS, upon receipt or 
application of raw materials or fuel to the process, or at least once 
per operating day (or week, month, etc.) for performance testing, work 
practice verification, or equipment design inspections; and,
    (5) Reporting and record retention requirements--criteria for 
retaining monitoring and test data in an electronic form and periodic 
electronic reporting of information as needed to the compliance office. 
Electronic record retention and submission have been widely adopted, 
and the EPA believes that such readily accessible documentation could 
be used by state, federal and other analysts to spot trends and non-
compliance more easily than if these entities conducted reviews of 
paper documents. The EPA also recommends that compliance reports be 
made available online so that the general public can readily access the 
information without the need to submit Freedom of Information Act 
(FOIA) requests to the EPA. The EPA is in the process of revising 
federal rules to make similar requirements apply.
    The EPA acknowledges that one way for regulatory authorities to 
have owners or operators of regulated sources demonstrate compliance 
via ongoing monitoring is to use a Compliance Assurance Monitoring 
(CAM) rule-type approach.\258\ Under such an approach,

[[Page 58134]]

an owner or operator would be able to establish operating ranges of 
continuously monitored parameters determined through concurrent 
performance testing as indicators of performance. A CAM rule-type 
approach would require owners or operators who chose parameter 
monitoring as indicative of compliance to immediately take corrective 
action should a measured parameter value occur outside the demonstrated 
range associated with compliance. Moreover, concurrent performance 
testing and parameter measurement would be necessary on a periodic 
basis, generally annually, and may be necessary on a more frequent 
basis to reverify or reset parameter value range, particularly when the 
operating range is exceeded. Failure of the owner or operator to take 
immediate corrective action would constitute a violation of the 
applicable rule. Moreover, failure of a parameter range to demonstrate 
compliance when reverification or resetting performance testing 
occurred would also constitute a violation of the emission limit. This 
implementation rule does not prohibit states from taking a CAM rule 
type approach and making parameters directly enforceable limits.
---------------------------------------------------------------------------

    \258\ See the CAM rule, available at 40 CFR part 64.
---------------------------------------------------------------------------

    The EPA continues to believe that approval of regulations adopted 
into SIPs should ensure that these critical elements are present and 
clearly defined to be approvable. In particular, the compliance 
obligations, including emissions limits and other applicable 
requirements, should be representative of and accountable to the 
assumptions used in a state's attainment demonstration. This 
accountability should include the ability to transfer the applicable 
regulatory requirements to a title V operating permit subject to the 
EPA and public review.\259\
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    \259\ Under the title V regulations, sources have an obligation 
to include in their title V permit applications, among other 
components, all emissions of pollutants for which the source is 
major, and all emissions of regulated air pollutants. See, e.g., 40 
CFR 70.5(c)(3). The definition of regulated air pollutant in 40 CFR 
70.2 includes any pollutant for which the NAAQS has been 
promulgated, including PM2.5.
---------------------------------------------------------------------------

c. Comments and Responses
    Comment: Commenters suggested that the proposal's use of the term 
``indicators of compliance'' is confusing and suggested the EPA should 
simply express that emission limitations must identify the pollutant of 
interest and the units of measurement. The commenters suggested the EPA 
use the term ``measurement method'' and the EPA acknowledge that 
sources may use procedures that are not published by the EPA, 
especially for pollutants for which there is no federally promulgated 
test method, performance specification, or voluntary consensus 
standard. The commenters disagreed that ``averaging time'' is always 
the appropriate term, since it has no applicability for standards that 
use test methods that specify minimum run times or sample volumes, and 
numbers of runs, and suggested the EPA use the term ``sample time or 
volume'' and make clear that it can be a minimum or an absolute value.
    Response: The EPA does not agree with the commenters' suggestion. 
The proposal identified four components associated with demonstrating 
compliance via performance testing--the indicator of compliance (for 
which the commenters expressed concern), the test method, the averaging 
time associated with the test method, and the frequency of conducting 
the test--as well as five components associated with demonstrating 
compliance via ongoing monitoring. However, the commenters appear to 
suggest to expand compliance demonstration techniques beyond testing 
and monitoring. To the extent that SIP regulations are developed that 
do not rely on performance testing or ongoing monitoring as means for 
demonstrating compliance, the EPA agrees that other components, 
including emission limitations that identify the pollutant of interest 
and units of measurement, as suggested by the commenter, would be 
appropriate.
    The EPA believes neither a change in term from ``test method'' to 
``measurement method'' nor an additional acknowledgement regarding its 
current wording ``specific EPA or other published set of [criteria]'' 
is needed. The component to which the commenter refers is based on 
performance testing; ongoing measurement components are covered as 
`measurement technique' in one of the five critical elements for 
ongoing measurement.
    The EPA agrees with the commenters that in some circumstances, test 
methods rely on sample volumes as opposed to specific durations. The 
`averaging time' component of performance tests will be changed to 
`sample collection characteristics', where such characteristics will 
include averaging time, duration, or sample volume and number of runs, 
as applicable. While the EPA does not believe it to be necessary to 
identify that the sample collection characteristics could be minima, 
maxima, or ranges, the preamble discussion associated with this change 
indicates that specific test methods, or regulatory agencies, may 
impose restrictions or specific conditions on sample collection 
characteristics.
    Comment: Some commenters stated the EPA should make clear that 
states can rely on CAM-type parameters as indicators of compliance. The 
commenters stated the EPA should make clear that states that follow the 
CAM rule model are not required to establish those ``indicators'' as 
directly enforceable limitations, as long as the SIP imposes directly 
enforceable review and corrective action requirements that will ensure 
that the source takes corrective action prior to the point when the 
indicator would predict noncompliance with an emission limitation.
    Response: The EPA agrees with the commenters that one way 
regulatory authorities have owners or operators of regulated sources 
demonstrate compliance via ongoing monitoring is to use a CAM rule-type 
approach. Under such an approach, an owner or operator would be able to 
establish operating ranges of continuously monitored parameters 
determined through concurrent performance testing as indicators of 
performance (indicators of compliance are components of performance 
testing). Nothing in the CAM rule precludes an owner or operator from 
establishing parameters as directly enforceable limitations, and 
neither does this rule. The CAM rule-type approach would require owners 
or operators who chose parameter monitoring as indicative of compliance 
to immediately take corrective action should a measured parameter value 
occur outside the demonstrated range associated with compliance. 
Moreover, concurrent performance testing and parameter measurement 
would be necessary on a periodic basis and may be necessary on a more 
frequent basis to reverify or reset a parameter value range. Failure to 
take immediate corrective action would constitute a violation. 
Moreover, failure of a parameter range to demonstrate compliance when 
reverification or resetting performance testing occurred would also 
constitute a violation.
    Comment: Commenters agreed that a compliance monitoring provision 
must specify a ``measurement technique'' and stated the EPA should 
defer to states regarding the most appropriate measurement techniques. 
The commenter disagreed that use of CEMS for ``directly enforceable 
measurements'' is always preferable.
    Response: The EPA appreciates the commenters' support and notes 
that the measurement technique component used in this rule corresponds 
to a similarly-named component contained

[[Page 58135]]

in the definition of monitoring in the general provisions of 40 CFR 
part 63. To the extent that regulatory authorities choose appropriate 
measurement techniques, the EPA agrees with the commenter. The EPA 
believes the commenters take the language regarding use of directly 
enforceable emissions measurements out of context; the EPA said it is 
preferred wherever feasible, not that it is always required.
    Comment: Commenters stated the EPA should make clear that 
``averaging time'' is only required for measurement techniques that 
collect continuous data that will be averaged over some period in order 
to assess source operations; i.e., the element is only essential to 
certain types of compliance monitoring requirements. The commenters 
suggested the EPA should not attempt to impose or require minimum 
frequencies in terms of calendar days, months, or year and urged the 
EPA to allow states flexibility to determine how best to address 
operational variability.
    Response: The EPA disagrees with the commenters, noting that 
averaging time remains an important aspect of demonstrating compliance 
via ongoing monitoring for all types of monitoring. It remains 
important to know how the period over which collected data are used to 
determine compliance, whether that period is daily, hourly, or 
annually. The EPA has not assigned minimum averaging times that 
regulatory authorities must use; however, the EPA expects those 
regulatory authorities to select averaging times appropriate to 
demonstrate compliance for specific types of sources.
    Comment: Commenters supported the EPA's recommendation that 
information demonstrating compliance be made available online for 
general public access (80 FR 15448) so that the public can provide the 
oversight that the Act contemplates (42 U.S.C. 7604). Other commenters 
opposed an absolute requirement that all monitoring, testing, and 
reporting be done electronically since many permits are for small 
businesses who may not have the capital and technical expertise for 
electronic recordkeeping and reporting; commenters recommended that the 
EPA change this criterion into a recommendation that electronic means 
be used where feasible.
    Response: The EPA agrees that electronic reporting and public 
access to information is important. The EPA notes that it is and has 
been moving towards electronic emissions reporting from all regulated 
sources for some time now. New NSPS and NESHAP require electronic 
emissions reporting, and efforts are underway to require existing NSPS 
and NESHAP to use electronic emissions reporting.\260\ Consistent with 
this approach, and with the approach taken by the next generation of 
compliance program,\261\ this rule will assist the shift toward 
electronic reporting to make environmental reporting more accurate, 
complete, and efficient. Moreover, electronic reporting of emissions 
will help us and regulatory authorities better manage information, 
improve effectiveness, and improve transparency.
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    \260\ See 80 FR 15099, March 20, 2015.
    \261\ See http://www2.epa.gov/sites/production/files/2014-09/documents/next-gen-compliance-strategic-plan-2014-2017.pdf.
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F. Multi-Pollutant Considerations

1. Summary of Proposal
    The EPA described many benefits of coordinating air quality 
planning efforts across a range of air quality programs addressing the 
NAAQS, air toxics, and climate change and encouraged states to pursue 
multipollutant planning approaches where possible.
2. Final Rule
    The final rule reiterates many of the points made in support of 
multipollutant planning efforts in the proposal. Efforts to reduce fine 
particle concentrations fit well as part of multi pollutant planning 
efforts because of the involvement of PM2.5 precursor gases 
(i.e., NOX, SO2, VOC, and ammonia) and direct 
PM2.5 emissions in a number of other air quality and climate 
issues. NOX and VOC play important roles in atmospheric 
chemistry and in the formation of ground-level ozone. Certain VOCs and 
constituents of direct PM2.5 are also hazardous air 
pollutants. SO2 and NOX emissions, and their 
reactions with ammonia to form ammonium sulfate and ammonium nitrate, 
have played important roles in acidic deposition, haze in national 
parks, and in fine particle formation. Black carbon from direct 
PM2.5 emissions is an important short-lived climate 
pollutant. Increasing average temperatures due to climate change are 
expected to lead to higher ozone concentrations. Many efforts to 
address traditional air pollutants have important co-benefits in terms 
of reducing emissions of CO2 and other GHGs, and vice versa. 
For these reasons, efforts to reduce air pollution to address multiple 
objectives can provide important benefits to states, the regulated 
community, and the general public.
    Multipollutant planning issues have been an area of strong interest 
by scientists and policymakers for many years. In 1995-1997, the EPA 
sought recommendations from a federal advisory committee with broad 
stakeholder representation on ways to coordinate and make more 
efficient the implementation programs for upcoming ozone and 
PM2.5 standards and the regional haze program. The National 
Academy of Sciences issued ``Air Quality Management in the United 
States,'' a report on multipollutant planning issues and 
recommendations, in 2004. In June 2007, the EPA's CAA Advisory 
Committee (CAAAC) recommended that the agency allow states to integrate 
SIP requirements and other air quality goals into a comprehensive 
plan.\262\ The recommended plan would demonstrate attainment/
maintenance of multiple NAAQS, accomplish sector-based reductions, 
realize risk reductions of HAPs and make improvements in visibility. It 
could also be structured to integrate programs addressing land use, 
transportation, energy and climate.
---------------------------------------------------------------------------

    \262\ Recommendations to the Clean Air Act Advisory Committee: 
Phase II, June 2007, http://www2.epa.gov/caaac/caaac-reports.
---------------------------------------------------------------------------

    The EPA believes that in many cases it can be more efficient for 
states to develop integrated control strategies that address multiple 
pollutants rather than separate strategies for individual air quality 
programs. An integrated air quality control strategy that reduces 
multiple pollutants can help ensure that reductions are efficiently 
achieved and produce the greatest overall air quality benefits. The EPA 
has encouraged states to take a multi-pollutant approach to managing 
air quality to the extent possible.
    While the agency encourages states to develop multi-pollutant 
plans, it recognizes that certain factors can make such efforts 
challenging. For example, the NAAQS are to be reviewed every 5 years, 
and any revisions to the standards will lead to a series of 
implementation steps required by specific statutory schedules. In some 
cases program requirements and deliverables may not be coordinated 
easily, but in other situations there are good opportunities for 
conducting technical analyses and developing policy approaches that can 
have important health and environmental benefits while addressing 
multiple key air pollution issues at the same time.
    One such opportunity is the increased use of multi-pollutant 
assessments. A multi-pollutant assessment, or one-atmosphere modeling, 
is conducted with a single air quality model (such as CMAQ or CAMx) 
that is capable of simulating transport and formation of

[[Page 58136]]

multiple pollutants simultaneously.\263\ For example, this type of 
model can simulate formation and deposition involving pollutants 
associated with PM2.5, ozone and regional haze, and it can 
include algorithms simulating gas phase chemistry, aqueous phase 
chemistry, aerosol formation and acid deposition. This type of model 
could also include the formation and deposition of key air toxics and 
the chemical interactions that occur with these individual toxic 
species to produce PM2.5 and ozone. It can also account for 
estimated changes in traditional air pollutant emissions resulting from 
programs (such as energy efficiency and renewable energy programs) to 
reduce emissions of CO2 and other greenhouse gases.
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    \263\ Depending on the context, ``multi-pollutant'' can be 
defined in different ways. In this context the agency is defining 
multi-pollutant modeling as simultaneous modeling of 
PM2.5, ozone, key air toxics, and regional haze. Future 
multi-pollutant models may include the ability to model a broader 
array of air toxics as well as greenhouse gases.
---------------------------------------------------------------------------

    Models and data analysis intended to address PM2.5 could 
be beneficial for use in addressing ozone, visibility impairment, and 
climate change. States that undertake multi-pollutant assessments as 
part of their attainment demonstration have the opportunity to assess 
the impact of their PM2.5 strategies on ozone, visibility, 
and climate programs to ensure that optimal emission reduction 
strategies are developed to the extent possible. This could facilitate 
addressing all of these pollutants in a more cost effective manner.
    States may also find it desirable to assess the impact of 
PM2.5, ozone, and/or regional haze control strategies on 
toxic air pollutants regulated under the CAA or under state air toxic 
initiatives. Given the relationships that exist between air toxics and 
the formation of PM2.5 and ozone, states may find that 
controls can be selected to meet goals for PM2.5 and/or 
ozone attainment as well as those of specific air toxic programs.
3. Comments and Response
    Comments: Some commenters urged the EPA to provide assistance to 
those states that might be precluded from developing Multi-Pollutant 
SIPs due to lack of resources. Other commenters stated the EPA should 
support the states' use of various approaches and tools suggested the 
EPA make the Control Strategy (CoST) tool fully available, as well as 
provide any necessary training to facilitate states' ability to 
effectively use the tool. The commenter also suggested that the EPA 
entertain the possibility for states to demonstrate that the controls 
put in place to comply with multi-pollutant CAIR and CSAPR are valid 
and should be accepted as part of attainment demonstrations; allowing 
states to credit emissions reductions that have occurred.
    Response: The Control Strategy Tool (CoST) is a component of the 
EPA's Emissions Modeling Framework that is a client-server system 
developed to support emissions modeling. CoST was developed by the EPA 
to model the emissions reductions and engineering costs associated with 
control strategies applied to point, area, and mobile sources of air 
pollutant emissions to support the analyses of the EPA air pollution 
policies and regulations. Links to the software and documentation are 
available at the EPA's CoST Web site at http://www3.epa.gov/ttnecas1/cost.htm. Note that because of resource limitations, the EPA is not 
able to provide any support for the installation or operation of CoST 
outside of the agency.

G. Measures to Ensure Appropriate Protections for Overburdened 
Populations

1. Summary of Proposal
    The EPA requested comments on ways that states can provide public 
health protection specifically for overburdened populations when 
preparing attainment plans for the PM2.5 NAAQS.
2. Final Rule
    Environmentally overburdened, underserved, and economically 
distressed communities may be subject to a higher risk of pollutant-
related health effects than the general population because they may be 
exposed to higher pollutant concentrations than the general population; 
they may experience a larger health impact at a given pollutant 
concentration; or they may be adversely affected by lower pollutant 
concentrations than the general population.\264\ Thus, the NAAQS review 
process inherently takes into consideration appropriate environmental 
justice factors as part of the standard-setting process for each 
pollutant.
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    \264\ See EPA 2011. Policy Assessment for the Review of the 
Particulate Matter National Ambient Air Quality Standards, Office of 
Air Quality Planning and Standards, Research Triangle Park, NC, EPA 
452/R-11-003, April 2011.
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    Section 109(d) of the CAA requires the EPA to periodically review 
(every 5 years) the science upon which the standards are based and the 
standards themselves. The policy assessment for the 2012 PM NAAQS 
review (U.S. EPA, 2011a, p. 2-60) observed that the highest 
concentrations of PM2.5 in an area tend to be measured at 
monitors located in areas where the surrounding populations are more 
likely to live below the poverty line and to have higher percentages of 
minorities. In its 2012 review of the PM NAAQS, the EPA revised the 
primary annual PM2.5 standard by lowering the level to 12.0 
micrograms per cubic meter ([micro]g/m\3\) to provide increased 
protection against health effects associated with long- and short-term 
PM2.5 exposures.\265\ The agency also (1) revised the form 
of the primary annual PM2.5 standard to eliminate the 
spatial averaging provisions to avoid potential disproportionate 
impacts on at-risk populations; and (2) directed states to relocate a 
limited number of existing monitors to near-roadway sites in large 
urban areas. Both of these actions were informed by scientific evidence 
that underscored the potentially disproportionate exposure to high 
PM2.5 concentrations and therefore disproportionate risk to 
low-income and minority populations.
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    \265\ 78 FR 3086 (January 15, 2013).
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    In conjunction with these revisions, the EPA retained the primary 
24-hour PM2.5 standard, as revised in 2006 (71 FR 61144, 
October 17, 2006), to provide supplemental protection against health 
effects associated with short-term PM2.5 exposures, 
especially in areas with high peak PM2.5 concentrations. 
This suite of primary annual PM2.5 standards provides 
increased public health protection, including the health of at-risk 
populations which include children, older adults, persons with pre-
existing health and lung disease, and persons of lower socioeconomic 
status, against a broad range of PM2.5-related effects that 
include premature mortality, increased hospital admissions and 
emergency department visits, and development of chronic respiratory 
disease.\266\
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    \266\ In the final 2012 PM NAAQS rule, based on information 
presented in the Integrated Science Assessment for Particulate 
Matter (U.S. EPA, 2009, sections 2.2.1 and 8.1.7), the EPA made a 
finding that persons with lower socioeconomic status are at 
increased risk for experiencing adverse health effects related to PM 
exposures (78 FR 3085, January 15, 2013, at page 3104). Persons with 
lower socioeconomic status (SES) have been generally found to have a 
higher prevalence of pre-existing diseases, limited access to 
medical treatment, and increased nutritional deficiencies, which can 
increase this population's risk to PM-related effects (77 FR 38911, 
June 29, 2012).
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    Relationship between direct PM2.5 emissions and PM2.5 precursor

[[Page 58137]]

emissions reductions and at-risk populations. Sources of direct PM 
emissions have their greatest impact on PM2.5 concentrations 
and public health in the general vicinity of the source (e.g., within 
10 miles), while sources of precursor emissions can contribute to 
PM2.5 concentrations more than 100 miles away and are 
considered to have a more regional impact. To date, state 
PM2.5 attainment plans have generally relied to a greater 
extent on reductions of precursor pollutants rather than on reductions 
of direct PM2.5 emissions. Studies show, however, that on a 
per ton basis, the reduction of a ton of direct PM2.5 
emissions leads to greater health benefits than the reduction of a ton 
of SO2 or NOX.\267\
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    \267\ See Fann, N., Fulcher, C., and B. Hubbell, 2009. The 
Influence of location, source, and emission type in estimates of the 
human health benefits of reducing a ton of air pollution. Air 
Quality, Atmosphere & Health. Volume 2, Number 3, 169-176, June 
2009. See also Fann et al., 2011. Maximizing health benefits and 
minimizing inequality: incorporating local-scale data in the design 
and evaluation of air quality policies. Society for Risk Analysis, 
vol. 31, no. 6, p. 908-922, June 2011.
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    The process for developing attainment plans for the current and 
future PM2.5 NAAQS presents a potential opportunity to 
target the health protections afforded by the NAAQS, as the EPA expects 
that attainment for the 2012 PM2.5 NAAQS and future 
PM2.5 NAAQS in nonattainment areas with the most severe 
pollution problems may need to give greater emphasis to reducing direct 
PM2.5 emissions in combination with efforts already underway 
to further reduce precursor emissions. Placing greater emphasis on 
reducing emissions from sources of direct PM2.5 (e.g., 
certain industrial facilities located in more densely populated areas; 
areas with high motor vehicle and other diesel engine emissions, such 
as rail yards and near major roadways; and, areas with high wood smoke 
emissions) could provide the added benefit of reducing exposure to 
PM2.5 in low-income and minority communities.
    Options for states to consider to ensure appropriate protections 
from PM2.5 exposure for overburdened populations. The EPA believes that 
states have sufficient flexibility and discretion under the CAA in 
implementing their attainment strategies to focus resources on 
controlling those sources of emissions that directly and adversely 
affect low-income and other at risk populations. By reducing impacts on 
at-risk populations, states can maximize health benefits, thereby 
creating greater net benefits for the state in a cost-effective 
manner.\268\ In addition, reducing adverse impacts to low-income and 
minority populations advances the environmental justice goal of fair 
treatment for these populations.
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    \268\ Wesson, K., Fann, N., Morris, M, Fox, T., Hubbell, T., 
2010. A multipollutant, risk-based approach to air quality 
management. Case study for Detroit. Atmospheric Pollution Research, 
1, 296-304. The study compared air quality control strategies and 
concluded that the multi-pollutant, risk-based approach was able to 
produce approximately two times greater monetized benefits through 
avoided health impacts and was more cost effective than a pollutant-
by-pollutant approach.
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    There are a number of actions that states could take to focus 
resources in this way. Some of these actions can help identify areas 
where additional ambient monitoring may be needed in low income and 
overburdened communities. Such information can be used to support 
updates to the state's annual monitoring plan.
    Screening is a useful first step in understanding or highlighting 
locations that may be candidates for further review. The EPA has 
developed EJSCREEN, a public screening tool that allows users to access 
high-resolution environmental and demographic information for locations 
in the United States, and compare their selected locations to the rest 
of the state, the EPA region, or the nation. The tool may help users 
identify areas with minority and/or low-income populations, potential 
environmental quality issues, a combination of environmental and 
demographic indicators that is greater than usual, and other factors 
that may be of interest. Other examples of actions to support updates 
to the annual monitoring plan include:

     Develop databases and online mapping tools that enable 
users (including state staff, public, and the regulated community) 
to understand where sources of direct PM2.5 emissions are 
located and where new or modified sources of emissions could have 
potential impacts on low income and other overburdened communities;
     Incorporate existing mapping tools that identify target 
areas in the attainment plan development process and related 
actions; and,
     Analyze emissions data, ambient data, and available 
modeling to identify potential unmonitored PM2.5 hotspots 
in areas with a high percentage of low income, minority or 
indigenous persons (see Section III.E of this preamble for further 
discussion of this option).

    Once target areas for addressing these sensitive population needs 
within a nonattainment area have been identified, the state could 
consider taking any of the following actions, which help target 
emissions reductions that may be needed to attain the PM2.5 
NAAQS:

     Prioritize the selection of control measures that 
target reductions of direct PM2.5, particularly from 
sources located in ``at-risk'' areas as part of the state's RACM and 
RACT analysis (for Moderate nonattainment areas) or BACM and BACT 
analysis (for Serious nonattainment areas), as well as other 
measures needed to demonstrate attainment (see Sections III.D and 
V.D of this preamble, respectively, of this preamble for further 
discussion of this option);
     Improve the understanding of the potential impact of 
minor sources by improving or generating an emissions inventory for 
such minor sources, including sources that are not currently 
required to report emissions, to generate options on how emissions 
can be reduced in the target area;
     Design voluntary programs to reduce VMT and mobile 
source-related PM2.5 emissions (e.g., diesel retrofits);
     Incorporate environmental justice criteria into the 
alternatives analysis to ensure appropriate siting and require 
cumulative impact studies for proposed projects;
     Eliminate exemptions from and/or lower thresholds for 
minor source permitting;
     Prioritize targeted enforcement strategies; and
     Develop a list of potential supplemental environmental 
projects (SEPs) \269\ that could be applied in the target area.
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    \269\ For more information on SEPs, go to https://www.epa.gov/enforcement/supplemental-environmental-projects-seps.

    In addition to the previous steps, states could increase 
opportunities for meaningful involvement of community groups in 
attainment plan development, annual monitoring network plan reviews, 
and permitting processes \270\ for at-risk and minority populations by 
taking the following steps:
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    \270\ See 78 FR 27220 (May 9, 2013) notice of availability, 
``EPA Activities To Promote Environmental Justice in the Permit 
Application Process.''

     Develop advisory boards and/or develop enhanced notice-
and-comment requirements for low income and minority communities to 
assure meaningful involvement relative to projects that impact their 
communities;
     Provide special notice of important actions affecting 
target areas in appropriate languages and with attention to cultural 
barriers;
     Provide advance notification for low income and 
minority communities of upcoming opportunities for public comment on 
SIPs, ambient air monitoring plans, and other relevant actions such 
as permit actions;
     Maintain multi-lingual Web sites and offer translators 
for public meetings and hearings; and,
     Coordinate with the state's EJ coordinator, if 
applicable, to assist with outreach efforts.
3. Comment and Response
    Comment: Some commenters supported the EPA's recommendations for 
measures to ensure protections for

[[Page 58138]]

overburdened communities, but stated that the EPA's proposal to allow 
areas to ignore near-roadway monitors is inconsistent with these 
objectives. The commenter stated that communities near heavily 
trafficked areas tend to be disproportionately low-income minority 
communities that suffer from disproportionately higher PM2.5 
exposure risks; and that the EPA and states should address the 
information gaps that disempower these communities in their ability to 
protect themselves from pollution sources. The commenter also stated 
that making sources disclose and report compliance information and 
providing that information in easy to access formats would go a long 
way to improve the ability of these communities to be informed of their 
risks and to assure compliance in their communities.
    Response: The EPA agrees that near-road monitoring data should not 
be ignored in future attainment planning. However, the EPA wishes to 
clarify that the statements in the proposal referenced the fact that 
the near-road monitors were not required to be in place before January 
1, 2015. Compliance with the PM2.5 standards is based on 3 
years of complete, quality-assured data at a monitor. Thus, the 
earliest that these monitors would have valid design values would be in 
early 2018 (based on data from 2015-2017). This timing makes it 
unlikely that sufficient data from these monitors will be available to 
be considered in attainment demonstrations that are due in 2016. In 
addition, the base modeling year of the attainment demonstration may 
pre-date the startup date of the near-road monitor(s). In this case, it 
may be possible to consider the near-road data in the attainment 
demonstration, but the recommended default projection methodology may 
not be applicable (since the time period of the near-road data may not 
correspond to the 5 year time period centered about the base modeling 
year, as recommended in the modeling guidance). Additionally, near-road 
PM2.5 monitors are only required in the 27 largest 
metropolitan areas of the country, and some PM2.5 
nonattainment areas may not have any near-road monitoring sites. Thus, 
when complete data from near-road PM2.5 ambient monitors 
become available, the data should be used by states and the EPA for all 
aspects of the NAAQS implementation process, from attainment planning 
to the determination of attainment, in a manner similar to any other 
quality-assured PM2.5 monitoring data. States should consult 
with the appropriate the EPA regional office to determine how and when 
near-road data should be used in the PM2.5 NAAQS 
implementation process for specific nonattainment areas.
    With regard to the comment about having easy access to facility 
compliance information, the EPA directs the commenter to the 
Enforcement and Compliance History Online Web site to search for 
facilities to assess compliance with environmental regulations. The 
site provides the ability to investigate pollution sources, examine and 
create enforcement-related maps, or explore an individual state's 
performance. As noted earlier in this section, the EJSCREEN tool can 
also provide important information about estimated pollution impacts in 
specific communities.

H. Tribal Issues

    The 1998 Tribal Authority Rule (TAR) (40 CFR part 49), which 
implements section 301(d) of the CAA, gives tribes the option of 
developing Tribal Implementation Plans (TIPs). Specifically, the TAR 
provides for the tribes to be treated in the same manner as a state in 
implementing certain sections of the CAA. However, tribes are not 
required to develop implementation plans. The EPA determined in the TAR 
that it was inappropriate to treat tribes in a manner similar to a 
state with regard to specific plan submission and implementation 
deadlines for the NAAQS-related requirements, including, but not 
limited to, such deadlines in CAA sections 110(a)(1), 172(a)(2), 182 
187, and 191. See 40 CFR 49.4(a). In addition, the EPA determined it 
was not appropriate to treat tribes similarly to states with respect to 
provisions of the CAA requiring as a condition of program approval the 
demonstration of criminal enforcement authority or providing for the 
delegation of such criminal enforcement authority. See 40 CFR 49.4(g). 
To the extent a tribe is precluded from asserting criminal enforcement 
authority, the federal government will exercise primary criminal 
enforcement responsibility. See 40 CFR 49.8. In such circumstances, 
tribes seeking approval for CAA programs provide potential 
investigative leads to an appropriate federal enforcement agency.
    If a tribe elects to do a TIP, the agency will work with the tribe 
to develop an appropriate schedule that meets the needs of the tribe 
and does not interfere with the attainment of the NAAQS in other 
jurisdictions. The tribe developing a TIP can work with the EPA 
Regional Office on the appropriateness of addressing RFP and other 
substantive SIP requirements that may or may not be appropriate for the 
tribe's situation.
    The CAA and the TAR provide tribes opportunity and flexibility, but 
not the obligation to develop a TIP to address the NAAQS. If a tribe 
elects to develop a TIP, the TAR offers flexibility for the tribe to 
identify and implement on a case-by-case basis only those CAA programs 
or reasonably severable program elements needed to address their 
specific air quality problems. In the TAR, the EPA described this 
flexible implementation approach as a modular approach. Each tribe may 
evaluate the particular activities, including potential sources of air 
pollution within the exterior boundaries of its reservation (or within 
non-reservation areas for which it has demonstrated jurisdiction), that 
cause or contribute to its air pollution problem. A tribe may adopt 
measures for controlling those sources of PM2.5-related 
emissions, as long as these elements of the TIP are reasonably 
severable from other CAA requirements. A TIP must include regulations 
designed to solve specific air quality problems for which the tribe is 
seeking the EPA's approval, as well as a demonstration that the tribal 
air agency has the authority from the tribal government to develop and 
run their program, the capability to enforce their rules, and the 
resources to implement the program they adopt. In addition, the tribe 
must receive an eligibility determination from the EPA to be treated in 
the same manner as a state for the particular matter at issue and to 
receive authorization from the EPA to run a CAA program.
    The EPA would review and approve, where appropriate, these TIPs as 
one step of an overall air quality plan to attain the NAAQS. A tribe 
may step in later to add other elements to the plan, or the EPA may 
step in to fill gaps in the air quality plan as necessary or 
appropriate. In approving a TIP, the agency would evaluate whether the 
plan appropriately coordinates with the overall air quality plan for an 
area when tribal lands are part of a multi-jurisdictional area.
    Because many PM2.5 nonattainment areas will include 
multiple jurisdictions, and in some cases both Indian country and state 
lands, it is particularly important for the tribes and the states to 
work together to coordinate their planning efforts. States need to 
incorporate Indian country emissions in their base emissions 
inventories if Indian country is part of an attainment or nonattainment 
area.\271\ Tribes and

[[Page 58139]]

states should coordinate their planning activities as appropriate to 
ensure that neither is adversely affecting attainment of the NAAQS in 
the area as a whole. Coordinated planning in these areas will help 
ensure that the planning decisions made by the states and tribes 
complement each other and that the nonattainment area makes reasonable 
progress toward attainment and ultimately attains the applicable 
PM2.5 NAAQS. In reviewing and approving individual TIPs and 
SIPs, the EPA will determine if together they are consistent with the 
overall air quality needs of an area.
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    \271\ On January 17, 2014, the United States Court of Appeals 
for the District of Columbia Circuit issued a decision vacating the 
EPA's 2011 rule titled ``Review of New Sources and Modifications in 
Indian Country'' (76 FR 38748, July 1, 2011) with respect to non-
reservation areas of Indian country (See Oklahoma Department of 
Environmental Quality v. EPA, 740 F.3d 185 (D.C. Cir. 2014)). Under 
the court's reasoning, with respect to CAA state implementation 
plans, a state has primary regulatory jurisdiction in non-
reservation areas of Indian country (i.e., Indian allotments located 
outside of reservations and dependent Indian communities) within its 
geographic boundaries unless the EPA or a tribe has demonstrated 
that a tribe has jurisdiction over a particular area of non-
reservation Indian country within the state.
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    To date, very few tribes have submitted for the EPA's approval TIPs 
covering areas over which they have jurisdiction. In the absence of a 
TIP, the EPA is authorized under the TAR to implement CAA programs in 
such areas as necessary or appropriate. For example, an unhealthy air 
quality situation on an Indian reservation may require the EPA to 
develop a FIP to reduce emissions from sources on the reservation. 
Likewise, if the agency determines that sources in an area under tribal 
jurisdiction could interfere with a larger nonattainment area meeting 
the NAAQS by its attainment date, it would develop a FIP for those 
sources in consultation with the tribe as necessary or appropriate.
    States have an obligation to notify other states in advance of any 
public hearing(s) on their state plans if such plans will significantly 
impact such other states. 40 CFR 51.102(d)(5). Under section 301(d) of 
the CAA and the TAR, tribes may become eligible to be treated in a 
manner similar to states (TAS) for this purpose. Affected tribes with 
this status must also be informed of the contents of such state plans 
and given access to the documentation supporting these plans. In 
addition to this mandated process, the EPA encourages states to extend 
the same notice to all affected tribes, regardless of their TAS status.
    Executive Orders and the EPA's Indian policies generally call for 
the EPA to coordinate and consult with tribes on matters that affect 
tribes. Executive Order 13175, titled, ``Consultation and Coordination 
with Indian Tribal Governments'' requires the EPA to develop a process 
to ensure ``meaningful and timely input by tribal officials in the 
development of regulatory policies that have Tribal implications.'' In 
addition, the EPA's policies include the agency's 1984 Indian Policy 
relating to Indian tribes and implementation of federal environmental 
programs, the 2014 Office of Air and Radiation's ``Handbook for 
Interacting with Tribal Governments,'' and the ``EPA Policy on 
Consultation and Coordination with Indian Tribes.'' Consistent with 
these policies, the EPA intends to meet with tribes on activities 
potentially affecting the attainment and maintenance of the current and 
future PM2.5 NAAQS in Indian country, including agency 
actions on SIPs. As such, it would be helpful for states to work with 
tribes with land that is part of the same air quality area during the 
SIP development process and to coordinate with tribes as they develop 
their SIPs.

I. Voluntary Programs for Reducing Ambient PM2.5

1. PM Advance Program
    The EPA believes there are significant advantages for states, 
tribes and local agencies to take steps to reduce direct 
PM2.5 emissions and emissions of PM2.5 precursors 
as early as possible. First and foremost, early reductions help to 
achieve cleaner air sooner, and help to ensure continued health 
protection. Second, early steps could help an area avoid a 
nonattainment designation in the first place, or for an area eventually 
designated as nonattainment, early reductions could help bring the area 
back into attainment sooner, which may lead to qualifying for a CDD and 
subsequent suspension of attainment planning requirements as described 
in Section IX.C of this preamble. In addition, early action to improve 
air quality can help an eventual nonattainment area, particularly an 
area that has never been designated nonattainment before, to establish 
working relationships between key stakeholders. The EPA's expectation 
is that early actions to reduce emissions in such areas would be less 
resource-intensive than actions taken once a nonattainment designation 
has been made, since at that point the implementation of controls would 
need to occur in conjunction with actions to comply with other 
requirements such as nonattainment NSR and transportation conformity.
    In January 2013, the EPA began a new early emissions reduction 
program for attainment areas called ``PM Advance,'' which is much like 
the related ``Ozone Advance'' program that began in April 2012. For 
additional information and a list of areas that are currently 
participating in the program, see https://www.epa.gov/advance.
2. Residential Wood Smoke Programs
    The EPA recognizes that residential wood smoke is a concern for 
many nonattainment areas. The EPA estimates that wood stoves, indoor 
wood furnaces, hydronic heaters and fireplaces emit more than 382,000 
tons of PM2.5 into the air throughout the country each 
year--mostly during the winter months. Residential wood smoke can 
increase fine particle pollution to levels that cause significant 
health concerns (e.g., asthma attacks, heart attacks, premature death). 
Wood smoke causes many counties throughout the U.S. to either exceed 
the national health-based standards for fine particles, or places them 
on the cusp of exceeding the standards. Because wood stoves, hydronic 
heaters and other similar appliances can be used around the clock in 
residential areas, they can cause significant and varying health and 
quality of life issues.
    To reduce fine particle pollution, many PM2.5 
nonattainment areas will need to address residential wood smoke. The 
EPA has developed the ``Strategies for Reducing Residential Wood 
Smoke'' document that provides education and outreach tools, 
information on regulatory approaches to reduce wood smoke, as well as 
information about voluntary programs that communities around the 
country have used.\272\ In addition, it includes methods for 
calculating emissions reductions, funding ideas and the basic 
components of a wood smoke redu