[Federal Register Volume 82, Number 5 (Monday, January 9, 2017)]
[Rules and Regulations]
[Pages 2760-2807]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2016-30640]
[[Page 2759]]
Vol. 82
Monday,
No. 5
January 9, 2017
Part III
Environmental Protection Agency
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40 CFR Part 300
Addition of a Subsurface Intrusion Component to the Hazard Ranking
System; Final Rule
Federal Register / Vol. 82, No. 5 / Monday, January 9, 2017 / Rules
and Regulations
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 300
[EPA-HQ-SFUND-2010-1086; FRL-9956-58-OLEM]
RIN 2050-AG67
Addition of a Subsurface Intrusion Component to the Hazard
Ranking System
AGENCY: Environmental Protection Agency (EPA).
ACTION: Final rule.
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SUMMARY: The U.S. Environmental Protection Agency (EPA) is adding a
subsurface intrusion (SsI) component to the Hazard Ranking System
(HRS), which is the principal mechanism that EPA uses to evaluate sites
for placement on the National Priorities List (NPL). The NPL is a list
of national priorities among the known or threatened releases of
hazardous substances, pollutants or contaminants throughout the United
States. Sites on the NPL are priorities for further investigation to
determine if further response actions are warranted. The subsurface
intrusion component (this addition) expands the number of available
options for EPA and state and tribal organizations performing work on
behalf of EPA to evaluate actual and potential threats to public health
from releases of hazardous substances, pollutants, or contaminants.
This addition enables EPA to directly consider human exposure to
hazardous substances, pollutants, or contaminants that enter regularly
occupied structures through subsurface intrusion in assessing a site's
relative risk, and thus, enable sites with subsurface intrusion
contamination to be evaluated for placement on the NPL.
DATES: This final rule is effective February 8, 2017.
ADDRESSES: The EPA has established a docket for this action under
Docket ID No. EPA-HQ-SFUND-2010-1086. All documents in the docket are
listed on the http://www.regulations.gov Web site. Although listed in
the index, some information is not publicly available, e.g., CBI 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 form.
Publicly available docket materials are available electronically
through http://www.regulations.gov or in hard copy at the EPA Docket
Center Reading Room (see https://www.epa.gov/dockets/epa-docket-center-reading-room for more information).
FOR FURTHER INFORMATION CONTACT: Terry Jeng, phone: (703) 603-8852,
email: [email protected], Site Assessment and Remedy Decisions Branch,
Assessment and Remediation Division, Office of Superfund Remediation
and Technology Innovation (Mail Code 5204P), U.S. Environmental
Protection Agency, 1200 Pennsylvania Avenue NW, Washington, DC 20460;
or the Superfund Hotline, phone (800) 424-9346 or (703) 412-9810 in the
Washington, DC metropolitan area.
SUPPLEMENTARY INFORMATION: The information presented in this preamble
is organized as follows:
I. Statutory Authority for Regulatory Change
II. Background
A. The Hazard Ranking System
B. Site Assessment and the Superfund Remedial Process
C. Impact of the SsI Addition on Current Cleanup Programs,
Resources and Cost
D. Impact of the Subsurface Intrusion Addition on the Hazard
Ranking System
III. Overview of the Final Rule
A. HRS Structure With the Subsurface Intrusion Component
B. SsI Component Addition
1. New Definitions
2. Delineation of Areas of Subsurface Intrusion
a. Area of Observed Exposure (AOE)
b. Area of Subsurface Contamination (ASC)
3. Likelihood of Exposure
a. Observed Exposure
b. Potential for Exposure
c. Calculation of the Likelihood of Exposure Factor Category
Value
4. Waste Characteristics
a. Toxicity/Degradation
b. Hazardous Waste Quantity
c. Calculation of the Waste Characteristics Factor Category
Value
5. Targets
a. Identification of Eligible Targets
b. Exposed Individual and Levels of Exposure
c. Population
d. Resources
e. Calculation of the Targets Factor Category Value
6. Calculation and Incorporation of the SsI Component Score Into
the HRS Site Score
a. Calculation of the SsI Component Score
b. Incorporation of the SsI Component Score Into the Soil
Exposure and Subsurface Intrusion Pathway Score
c. Incorporation of the Soil Exposure and Subsurface Intrusion
Pathway Score Into a Site Score
C. Testing the SsI Component
1. Conceptual Site Model/Sensitivity Analysis
2. Test Site (Tier 1) Summaries
3. Pilot Study
IV. Summary of Changes to the HRS
A. Changes Since Proposal
B. Summary of Updates to the HRS (Sections 2, 5, 6, and 7)
V. Discussion of Major Comments
A. Responses to Comments on EPA Questions Posed in the Proposed
Rule
B. Major Comment Theme Summaries and Responses
VI. 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 Risks 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. Executive Order 12580: Superfund Implementation
L. Congressional Review Act (CRA)
I. Statutory Authority for Regulatory Change
EPA has revised the HRS, the principal mechanism for placing sites
on the NPL, to add a component for evaluating the threat or potential
threat posed by subsurface intrusion to protect human health and the
environment. Without an evaluation of threats posed by subsurface
intrusion contamination, the HRS is not a complete assessment because
it omits a known pathway of human exposure to contamination. The
addition of subsurface intrusion to the HRS is compliant with
Comprehensive Environmental Response, Compensation, and Liability Act
(CERCLA) Section 105(a)(8)(A), which requires EPA to prioritize sites
based on ``the population at risk, the hazard potential of hazardous
substances at such facilities, the potential for contamination of
drinking water supplies, the potential for direct human contact [and]
the potential for destruction of sensitive ecosystems. This addition to
the HRS also improves the agency's ability to identify priority sites
for further investigation and enhances EPA's ability, in dialogue with
other federal agencies and the states and tribes, to determine the most
appropriate state or federal authority to address sites. For
information on alternatives to this rulemaking that were considered for
addressing subsurface intrusion contamination, please see the
[[Page 2761]]
preamble to the proposed HRS SsI Addition [81 FR 10372, February 29,
2016].
Additionally, the Government Accountability Office (GAO) stated in
its May 2010 report \1\:
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\1\ EPA's Estimated Costs to Remediate Existing Sites Exceed
Current Funding Levels, and More Sites are Expected to Be Added to
the National Priorities List, GAO Report to Congressional
Requesters, GAO-10-380, May 2010.
EPA may not be listing some sites that pose health risks that
are serious enough that the sites should be considered for inclusion
on the NPL. While EPA is assessing vapor intrusion contamination at
listed NPL sites, EPA does not assess the relative risks posed by
vapor intrusion when deciding which sites to include on the NPL. By
not including these risks, states may be left to remediate those
sites without federal assistance, and given states' constrained
budgets, some states may not have the ability to clean up these
sites on their own . . . However, if these sites are not assessed
and, if needed, listed on the NPL, some seriously contaminated
hazardous waste sites with unacceptable human exposure may not
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otherwise be cleaned up.
The authority for these technical modifications to the HRS is in
section 105(a)(8)(A) of CERCLA enacted in 1980. Under CERCLA, the
National Oil and Hazardous Substances Pollution Contingency Plan (NCP)
(40 CFR 300) must include criteria for determining priorities among
releases or threatened releases for the purpose of taking remedial or
removal actions. Section 105(a)(8)(A) of CERCLA required EPA to
establish:
[C]riteria for determining priorities among releases or
threatened releases [of hazardous substances] throughout the United
States for the purpose of taking remedial action and, to the extent
practicable, taking into account the potential urgency of such
action, for the purpose of taking removal action. Criteria and
priorities . . . shall be based upon relative risk or danger to
public health or welfare or the environment. . .taking into account
to the extent possible the population at risk, the hazard potential
of hazardous substances at such facilities, the potential for
contamination of drinking water supplies, the potential for direct
human contact [and] the potential for destruction of sensitive
ecosystems. . . .
To meet this requirement and provide criteria to set priorities,
EPA adopted the HRS as Appendix A to the NCP (47 FR 31180, July 16,
1982). The HRS was last revised on December 14, 1990 (55 FR 51532) to
include the evaluation of additional threats to ensure a complete
assessment of the relative risk that a site may pose to the public.
Section 105(a)(8)(B) of CERCLA requires that the statutory criteria
described in section 105(a)(8)(A) be used to prepare a list of national
priorities among the known releases, or threatened releases throughout
the United States. The NPL is Appendix B of the NCP (40 CFR 300,
Appendix B).
In 1986, Congress passed the Superfund Amendments and
Reauthorization Act (SARA) (Pub. L. 99-499), which added section
105(c)(1) to CERCLA, requiring EPA to amend the HRS to assure ``to the
maximum extent feasible, that the hazard ranking system accurately
assesses the relative degree of risk to human health and the
environment posed by sites and facilities subject to review.'' In
addition, CERCLA section 115 authorizes EPA to promulgate any
regulations necessary to carry out the provisions of CERCLA.
Furthermore, the Congressional Conference Report on SARA included
the absolute standard against which HRS revisions could be assessed:
This standard is to be applied within the context of the purpose
for the National Priorities List; i.e., identifying for the States
and the public those facilities and sites which appear to warrant
remedial actions. * * * This standard does not, however, require the
Hazard Ranking System to be equivalent to detailed risk assessments,
quantitative or qualitative, such as might be performed as part of
remedial actions. The standard requires the Hazard Ranking System to
rank sites as accurately as the Agency believes is feasible using
information from preliminary assessments and site inspections * * *
Meeting this standard does not require long-term monitoring or an
accurate determination of the full nature and extent of
contamination at sites or the projected levels of exposure such as
might be done during remedial investigations and feasibility
studies. This provision is intended to ensure that the Hazard
Ranking System performs with a degree of accuracy appropriate to its
role in expeditiously identifying candidates for response actions.
[H.R. Rep. No. 962, 99th Cong., 2nd Sess. at 199-200 [1986]]
When the HRS was last revised in 1990, the technology to detect and
evaluate subsurface intrusion threats was not sufficiently developed.
For example, there were no health-based benchmark concentration values
for residences or standardized technologies for sampling indoor air,
precision of analytical equipment prior to computerization was limited,
and associations between contaminated ground water and soil vapors were
not well understood. However, it is now possible for subsurface
intrusion threats to be evaluated in a more comprehensive manner.
Therefore, it is now appropriate, given the potential that subsurface
intrusion presents for direct human contact, to add to the HRS the
consideration of threats due to subsurface intrusion.
This final rule ensures the HRS does not omit a known pathway of
human exposure to contamination due to subsurface intrusion of released
hazardous substances and provides a mechanism for assessing subsurface
intrusion threats and identifying sites for placement on the NPL.
Furthermore, these sites are now eligible for Superfund-financed
remedial actions.
II. Background
The HRS is a crucial part of the agency's program for determining
which sites are a priority for further remedial investigation and
possible cleanup under CERCLA. To understand the importance of this
rulemaking it is necessary to understand the role of the HRS in
identifying sites for the NPL, the role of the HRS in the overall site
assessment and Superfund remedial process, and this final rule's
impacts on current and future Superfund activities. In addition, it is
also necessary to understand the impact of adding the SsI component to
the HRS.
A. The Hazard Ranking System
The HRS is a scoring system used to assess the relative risk
associated with actual or potential releases of hazardous substances
from a site based on the information that can be collected in a
preliminary assessment (PA) and site inspection (SI). The HRS is not a
tool for conducting a quantitative risk assessment and was designed to
be a measure of relative risk among sites rather than absolute site-
specific risk. As required by CERCLA, EPA has designed the Superfund
program to focus its resources on the priority sites. Consequently, the
initial studies--the PA and SI--which are performed on a large number
of sites, are relatively modest in scope and cost compared to the
remedial investigations and feasibility studies subsequently performed
on NPL sites.
Because of the need to expeditiously perform PAs and SIs, Congress
placed certain constraints on the data requirements for an HRS
evaluation. The required HRS data should be information that, for most
sites, can be collected during a screening level site inspection or
that are already available. Thus, the HRS does not rely on data that
require extensive sampling or repeated sampling over extended periods
of time. However, EPA allows for the expansion of the typical SI to
allow for additional data collection for more complex sites that cannot
be adequately characterized using standard SI methodologies. The HRS
has also been designed so that it can be applied consistently to a wide
variety of sites, enabling sites to be
[[Page 2762]]
ranked relative to each other with respect to actual or potential
hazards.
Based on the state of the science, site specific data may be
collected beyond that which is normally available after a typical site
inspection. In these situations, the HRS in general, and the SsI
component, can incorporate that data into the HRS evaluation. For
example, the SsI component can use site-specific data as follows:
Determination of the Hazardous Waste Quantity Factor
Value--If the mass of all hazardous substances can be adequately
determined (i.e., is known or can be estimated with reasonable
confidence), the HRS requires this estimate (identified as a Tier A
estimate) be used to assign the hazardous waste quantity for all
regularly occupied structures in an area of exposure (AOE) for which
this information is available. See section 2.4.2 and 5.2.1.2.2 of the
HRS.
Determining the extent of an ASC--If sufficient data are
available and state of the science shows there is no unacceptable risk
due to subsurface intrusion into a regularly occupied structure located
within an ASC, that structure or subunit can be excluded from the ASC.
Therefore, such structures would not be included in the evaluation of
the Hazardous Waste Quantity Factor or in the determination of other
factors evaluated based on structures or subunits within an ASC. See
section 5.2.0 of the HRS.
Populations within the ASC--If sufficient structure-
specific concentration data is available and state of the science shows
there is no unacceptable risk of exposure to populations in a regularly
occupied structure in an ASC, those populations are not included in the
evaluation of the Targets Factor Category. See section 5.2.1.3 of the
HRS.
EPA notes that if other site-specific information is available that
clearly demonstrates that the site does not pose an unacceptable risk
to human health via subsurface intrusion, there are points during the
PA or SI process, where further evaluation of the site for the
subsurface intrusion threat by the Superfund program can be terminated.
Please see section B. of this preamble for further information on the
Site Assessment process.
As EPA explained when it originally adopted the HRS, ``the HRS is a
means for applying uniform technical judgment regarding the potential
hazards presented by a facility relative to other facilities. It does
not address the feasibility, desirability, or degree of cleanup
required.'' (47 FR 31220, July 16, 1982).
The HRS uses a structured value analysis approach to scoring sites.
This approach assigns values to factors related to or indicative of
risk. The basic elements of the HRS are factors that are based on
information that can be collected in a limited screening assessment. A
scale of numerical rating values is provided for each factor and a
value is assigned to each factor based on conditions at the site.
Individual values are then weighted. The factors are grouped into three
factor categories--observed release/route characteristics, waste
characteristics, and targets--and are combined to obtain factor
category scores. Each factor category has a maximum value, as does each
of the component factors within the category. The relevant factor
category scores are multiplied together within each pathway and
normalized to obtain a pathway score. The pathway scores are combined
using a root-mean-square approach to calculate the overall site score;
that is, the final HRS score is the square root of the sum of the
squares of the pathway scores divided by the square root of the number
of HRS pathways. If all pathway scores are low, the HRS score will be
low. However, the final score will be relatively high even if only one
pathway score is high. EPA considers this an important requirement for
the HRS scoring because some extremely dangerous sites pose threats
through only one migration mode. For example, at a site, leaking drums
of hazardous substances may be contaminating drinking water wells,
thereby posing a significant threat via the groundwater migration
pathway. But if the drums are buried deeply enough and the hazardous
substances are not very volatile, the drums may not release any
hazardous substances and not pose a threat to the air or to surface
water.
EPA emphasizes that the HRS score is a number between 0 and 100,
which reflects relative risk amongst candidate NPL sites. An HRS site
score is not a measure of actual site-specific risk.
B. Site Assessment and the Superfund Remedial Process
EPA's Superfund remedial site assessment process evaluates sites to
ascertain if further investigation is needed for determining whether an
unacceptable risk is present.
The majority of sites evaluated through the EPA's site assessment
program do not meet the criteria for possible placement on the NPL and
are ``screened out'' of the Superfund Remedial process. (See Figure 1.
Status of EPA's Site Assessments). Since EPA adopted the HRS, 52, 859
sites have been assessed under EPA's Superfund program. Of those sites,
1,782 were placed on the NPL, as of September 2016.
Site Assessment Strategy
The site assessment process is structured as a series of limited
investigations which may include: (1) A Pre-CERCLA screening
assessment; (2) a preliminary assessment; and (3) a site inspection or
expanded site inspection (Figure 2. Site Assessment Process, below,
illustrates this process). If a site progresses through the site
assessment process for further investigation, the requirements for
documenting risk become increasingly rigorous. The following includes a
summary of the major phases of the site assessment process.
A Pre-CERCLA Screening is an initial review of existing
information on a possible Superfund site. If a release of a hazardous
substance has occurred or if the potential of a hazardous substance to
release exists the site may be eligible for further remedial evaluation
under CERCLA authority. If further evaluation is warranted the site
should be entered into the remedial assessment active site inventory
for further assessment.
The PA decision process parallels an HRS analysis, but
makes environmental ``worst-case'' assumptions of possible significant
risk regarding transport of contamination to receptors based on minimal
available information and professional judgment.
The SI collects information to confirm the accuracy of the
PA assumptions. The information should be sufficient to support an HRS
evaluation with minimal further investigation.
If placement on the NPL is pursued, the information
collected during the SI provides the basis for supporting the HRS
scoring scenario.
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The following discussion provides further information on each of
these phases.
Pre-CERCLA Screening Assessment
A Pre-CERCLA Screening is used to establish whether:
A release or potential release of a hazardous substance
has occurred at a site;
The site is eligible for further remedial assessment under
CERCLA authority;
The site needs further attention under Superfund or
another cleanup program; and
The site warrants entry into the federal Superfund
program's active site inventory for further assessment or response.
Determining whether releases of hazardous substances, pollutants,
or contaminants can be addressed by CERCLA requires the application of
site-specific facts to CERCLA statutory requirements and EPA policy.
The initial determination as to whether a site warrants further
investigation is based on three site-specific facts including: (1)
Evidence of an actual release or potential to release; (2) targets
impacted by a release of contamination at the site; and (3)
documentation that a target has been exposed to a hazardous substance
released from the site. Examples of targets include populations,
drinking water wells, drinking water surface intakes, municipal wells,
fisheries and sensitive environments.
Preliminary Assessment
A PA uses readily available data to determine if there is evidence
of a release that poses an unacceptable possible threat as specified in
the NCP (40 CFR 300.420).
The PA is a limited-scope investigation performed by
States and/or EPA on every CERCLA site
The PA may include the collection of readily available
information and an on- or off-site reconnaissance may be conducted
The PA distinguishes, based on already existing
information, between sites that appear to pose little or no threat to
human health and the environment and sites that require further
investigation to determine if the threat to human health and the
environment is unacceptable.
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If based on the results of a PA, EPA determines that a site
warrants further screening under the CERCLA remedial program, the
agency initiates a site inspection
Site Inspection
The purpose of the SI is to collect the data necessary to perform
an HRS evaluation. An SI determines if a release of a hazardous
substance poses an actual or potential threat to human health or the
environment, to determine if there is an immediate threat to people or
the environment in the area, and to collect sufficient data to enable
the site to be scored using the HRS. EPA may expand the site inspection
scope as needed. This expanded site inspection (ESI) collects
additional data beyond what is collected in the standard site
inspection to evaluate sites for HRS scoring. ESIs are reserved for
more complex sites that cannot be adequately characterized using
standard site inspection methods.
SI investigators typically collect waste and environmental
samples to determine the substances present at a site and whether they
are being released to the environment, as well as other information to
perform an HRS evaluation.
EPA distinguishes, based on the information collected
during the SI, between sites that appear to pose little or no threat to
human health and the environment and sites that require further
investigation to determine if the threat to human health and the
environment exists.
If the information indicates a threat, EPA determines the
best approach for addressing the threat, which can be placement on the
NPL or use of an alternative authority.
If at any time in this site assessment process, EPA determines that
sufficient information indicates the site poses no unacceptable risk,
or if it can be addressed under alternative authorities it can be
removed from the process. Also, if an imminent or substantial
endangerment to public health is identified, EPA can initiate CERCLA
removal actions.
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The NPL Rulemaking Process
The NPL is a list of national priorities for further investigation
amongst the known or threatened releases of hazardous substances,
pollutants or contaminants throughout the United States. The list,
which is appendix B of the NCP (40 CFR part 300), is required under
section 105(a)(8)(B) of CERCLA, as amended. Section 105(a)(8)(B)
defines the NPL as a list of ``releases'' and the highest priority
``facilities'' and requires that the NPL be revised at least annually.
The NPL is intended primarily to guide the EPA in determining which
sites warrant further investigation to assess the nature and extent of
public health and environmental risks associated with a release of
hazardous substances, pollutants or contaminants. The NPL is of only
limited significance, however, as it does not assign liability to any
party or to the owner of any specific property. Also, placing a site on
the NPL does not mean that any remedial or removal action necessarily
need be taken.
For purposes of listing, the NPL includes two sections, one of
sites that are generally evaluated and cleaned up by the EPA (the
``General Superfund section'') and one of sites that are owned or
operated by other federal agencies (the ``Federal Facilities
section''). With respect to the Federal Facilities sites, these sites
are generally being addressed by other federal agencies. Under
Executive Order 12580 (52 FR 2923, January 29, 1987) and CERCLA section
120, each federal agency is responsible for carrying out most response
actions at facilities under its own jurisdiction, custody or control,
although the EPA is responsible for preparing a Hazard Ranking System
(``HRS'') score and determining whether the facility is placed on the
NPL and having oversight authority at the sites for further actions.
NPL Site Selection Process
The NPL is required to be revised annually and it is intended
primarily to guide EPA in determining which sites warrant further
investigation to assess the nature and extent of public health and
environmental risks associated with a release of hazardous substances,
pollutants or contaminants. This selection process is illustrated in
figure 3, below. Sites with HRS scores of 28.50 or greater are eligible
for placement on the NPL. Only non-Federal Facility sites on the NPL
are eligible for Superfund-financed remedial actions. Once a site is
determined to be NPL-caliber and a decision has been made that the
federal Superfund program should manage the site cleanup, EPA regions
apply a strong initial presumption in favor of placement on the NPL.
Once the site is proposed for the NPL (i.e., announced in the
Federal Register), a 60-day comment period is initiated to allow the
public to comment on the proposal. EPA responds to all public comments,
and depending on the results of the public comment period, the site
could be removed from consideration for placement of the NPL; re-
proposed in the future due to public comments; or placed on the NPL.
Once the site is placed on the NPL, the rulemaking can be challenged in
court under the Administrative Procedure Act (APA). If no challenge is
made or if the court finds the rulemaking consistent with APA
requirements, it is then eligible for further investigation under the
Superfund remedial program. (Figure 3. Process for Placing a Site on
the NPL).
[GRAPHIC] [TIFF OMITTED] TR09JA17.060
C. Impact of the SsI Addition on Current Cleanup Programs, Resources
and Cost
This SsI addition to the HRS will have the most significant impact
on EPA's Superfund cleanup program. This regulatory change expands
available options for EPA and organizations performing work on behalf
of EPA (state and tribal partners) to evaluate actual and potential
threats to public health and the environment from subsurface intrusion
contamination. This modification to the HRS, by itself, only augments
the criteria for applying the HRS. It has no effect on small
businesses.
This final rule will not affect the status of sites currently on or
proposed to the NPL. Sites that are currently on or proposed to the NPL
have already been evaluated under another pathway (i.e., ground water
migration, air migration, surface water migration, or soil exposure)
and have been shown to or are projected to qualify for placement on the
NPL. The method selected for including the SsI evaluation in the HRS
site score can only result in an increase in a site score, Therefore,
all sites qualifying for the NPL based on its HRS site score prior to
this final rule will continue to do so. It is consistent with section
105(c)(3) of CERCLA, as amended, that these sites will not be re-
evaluated. This final rule will not disrupt EPA's placement of sites on
the NPL.
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The possible impact on federal agencies other than EPA performing
Superfund actions will be less than that on private sites being
addressed by EPA. Federal agencies currently address subsurface
intrusion issues as part of their environmental programs and
authorities. Executive Order 12580 delegates broad CERCLA authority to
federal agencies for responding to actual and potential releases of
hazardous substances where a release is either on, or the sole source
of the release is from, any facility or vessel under the jurisdiction,
custody, or control of the federal agency. Federal agencies are
required to exercise this authority consistent with the requirements of
CERCLA section 120, as amended, and implement regulations under the
NCP, for both NPL and non-NPL sites. Therefore, federal agencies are in
a position to proactively identify and respond to risks posed by
subsurface intrusion of hazardous substances into regularly occupied
structures for all populations who live and work in areas where the
subsurface environment may create exposures. If it is determined that
releases of hazardous substances pose immediate threats to public
health and the environment, EPA fully expects that the appropriate
federal agency will continue to undertake response actions to address
such threats. Many federal agencies, including EPA, have developed or
are developing new or updated agency-specific policy and guidance
documents to address subsurface intrusion threats.
As a result of federal agency existing environmental programs and
authorities, this rulemaking is not anticipated to have a significant
impact to the resources and costs to federal cleanup programs.
Since EPA's overall appropriated Superfund budget as well EPA's
cooperative agreement budget for performing site assessments will
continue to remain relatively steady, EPA anticipates that this final
rule will not result in additional site assessments nor the placement
of more sites on the NPL during any particular interval, but rather a
shift in the make-up of the type of sites included on the NPL. EPA will
continue to review sites as part of Superfund remedial site assessment
to determine whether sites are eligible for further remedial evaluation
under CERCLA authorities and prioritize sites that pose the highest
risk. This is not a change to how EPA currently evaluates and
prioritizes sites for the NPL. Because the level of effort required to
evaluate a site, regardless of pathway, varies on a site-by-site basis,
depending on the size and extent of contamination at the site, it
cannot be predicted with any certainly that there will be an increase
in cost or level of effort for any particular site due to this
rulemaking.
This rulemaking, which could lead to the inclusion of a site on the
NPL that did not qualify for the NPL previously, does not itself impose
any costs on outside parties; it does not establish that EPA will
necessarily undertake response actions, nor does it require any action
by a private party or determine liability for site response costs.
Costs are limited to screening relevant sites for subsurface intrusion
contamination during site inspections and the resulting HRS evaluation
and documentation record preparation. Costs that arise from site
remedial responses are the result of site-specific decisions made post-
listing, not directly from the act of listing itself. These costs are a
result of a release of hazardous substances and would not be incurred
if hazardous substances had not been released.
Later Superfund-related decisions that consider information
collected under the HRS SsI Addition could separately have specific
economic costs and benefits (e.g., remediation costs and reduced risk),
but these impacts are contingent upon a series of separate and
sequential actions after listing a site on the NPL. Therefore, addition
of subsurface intrusion to the HRS is several regulatory steps removed
from imposing costs on private entities.
This rulemaking does not impose any requirements on small entities,
and therefore can be certified as no Significant Economic Impact on a
Substantial Number of Small Entities (SISNOSE). With the exception of
other federal agencies, site assessments are performed by EPA and on
behalf of EPA by states and tribes in cooperative agreement
partnerships with EPA. Under section 601 of the Regulatory Flexibility
Act, federal agencies do not fit under the definition of small
business, small entity, small organization or small governmental
jurisdiction.
D. Impact of the Subsurface Intrusion Addition on the Hazard Ranking
System
This final rule, with the addition of a subsurface intrusion
component, does not change the purpose of the HRS, its fundamental
structure or its application. It does not change the balance between
the pathways or calculation of the overall HRS site score and the same
cutoff score to qualify a site for the NPL is maintained. The current
approach for scoring the ground water, surface water, and air migration
pathways is not being altered by the addition of a subsurface intrusion
component. EPA added the subsurface intrusion threat as a component to
the present soil exposure pathway because its structure already focuses
on populations actually or potentially coming into direct contact with
hazardous substances. The re-structured pathway is called the ``Soil
Exposure and Subsurface Intrusion'' pathway and now allows for the
consideration of the threat posed by subsurface contaminant intrusion.
The Soil Exposure and Subsurface Intrusion pathway retains the existing
two soil exposure threats (resident population and nearby population)
in the pathway as one component, with subsurface intrusion as the
second component.
The narrow technical modifications resulting from this Final Rule
reflect the agency's actions to encompass additional risks posed by
releases of hazardous substances and to address the SARA statutory
requirement that EPA amend the HRS to assure ``to the maximum extent
feasible, that the HRS accurately assesses the relative degree of risk
to human health and the environment posed by sites subject to review.''
Thus, the fundamental purpose and structure of the HRS approach has not
changed with this amendment to the HRS to include the consideration of
subsurface intrusion.
III. Overview of the Final Rule
This final rule revises the 1990 HRS to include a component for
evaluating the threats posed from subsurface intrusion. The following
sections discuss the structure of the HRS, the subsurface intrusion
component within the HRS, the major factors of the subsurface intrusion
addition, and how the evaluation will be performed using a structure
consistent with the other threats, components, and pathways in the HRS,
but taking into account the unique parameters impacting the probability
of exposure to subsurface intrusion. All sites that qualified for the
NPL under the 1990 HRS, would still qualify for the NPL under this
revised HRS. For a more comprehensive description and rationale of
changes, see the February 29, 2016 Proposed Rule [81 FR 10372, February
29, 2016].
A. HRS Structure With the Subsurface Intrusion Component
EPA added the evaluation of the relative risk posed by subsurface
intrusion of hazardous substances into regularly occupied structures by
restructuring the soil exposure pathway from the 1990 HRS to include
subsurface intrusion. The soil exposure pathway has been renamed the
soil exposure and subsurface intrusion pathway to reflect both
components of
[[Page 2767]]
the new pathway. No changes are included in the other three HRS
pathways, with the exception of the use of a reference concentration
instead of a reference dose to determine a hazardous substance's
health-based benchmark in the air migration pathway. See Figure 4 for a
depiction of how the promulgated addition fits into the HRS structure.
[GRAPHIC] [TIFF OMITTED] TR09JA17.061
As explained in the preamble to the proposed HRS SsI addition, the
subsurface intrusion component is added as a new component of the soil
exposure and subsurface intrusion pathway. The soil exposure pathway
included in the 1990 HRS is retained as one component of the Soil
Exposure and Subsurface Intrusion pathway. The scoring of the soil
exposure component remains unaltered, but the score is assigned as the
soil exposure component score, not the pathway score. (See section 5.1
of the HRS). As discussed in greater detail below, the SsI component
has the same basic structure, scoring, and weighting as other parts of
the HRS.
The score for the soil exposure and subsurface intrusion pathway is
based on a combination of the two component scores--soil exposure and
subsurface intrusion but the pathway score is capped at the same value
as other HRS pathways. The soil exposure component score is added to
the subsurface intrusion component score to determine the pathway
score. The two component scores are additive to reflect that
populations may be exposed via both routes: The soil exposure component
reflects exposures to people when outside a structure and focuses on
ingestion, and the subsurface intrusion component reflects exposures
inside a structure and focuses on inhalation. Hence, the addition of
the two component scores reflects the potential cumulative risk of
multiple exposure routes and is not double counting the same relative
risk.
A maximum pathway score is not contingent on scoring both the soil
exposure and subsurface intrusion components. It is possible for a site
to have only one component evaluated and still reach the maximum
pathway score. Because the scoring of the soil exposure component is
not being altered, this component would contribute the same score to
the overall site score absent the addition of subsurface intrusion.
B. SsI Component Addition
The structure of the HRS is fundamentally the same for all
individual pathways, components, and/or threats. The design of the HRS
reflects a conceptual understanding of how hazardous substance releases
from CERCLA sites can result in risks to public health and welfare and
the environment. The risk scenario at these sites is a function of:
The probability of exposure to (or releases to a medium in
a migration pathway of) hazardous substances,
The expected magnitude and duration of the releases or
exposures,
The toxicity or other potential adverse effects to a
receptor associated with a target from the releases,
[[Page 2768]]
For the three migration pathways, the probability that the
release will reach a target and the expected change in the
concentration of hazardous substances during the movement from the
location of the contamination to the targets. For the exposure pathway,
the probability a receptor will be exposed at the target location,
The expected dose to the receptor, and
The expected number and type of the receptors.
The above considerations are addressed in three factor categories:
Likelihood of exposure (or release), waste characteristics, and
targets.
The following subsections describe the structure of the subsurface
intrusion component and how this structure is consistent conceptually
with the existing structure of the other HRS pathways and components:
(1) New definitions, (2) delineation of areas of subsurface intrusion,
(3) likelihood of exposure, (4) waste characteristics, (5) targets, and
(6) calculating and incorporating the subsurface intrusion component
score into the HRS site score.
1. New Definitions--See Section 1.1 of the HRS \2\
---------------------------------------------------------------------------
\2\ For references to a specific section of the HRS addition,
please refer to the regulatory text of the rulemaking.
---------------------------------------------------------------------------
EPA has added 15 new definitions to the HRS, section 1.1, along
with updated nomenclature to existing definitions. EPA received no
comments on the 14 proposed new definitions to the rule; therefore, EPA
is finalizing the new definitions as proposed with the following
change: The term surficial ground water has been changed to shallow
ground water for clarity. In addition, EPA has added the term non-
aqueous phase liquid (NAPL) to the definition section because EPA added
consideration of NAPLs to the assignment of degradation factor values
and the weighting of targets in the area of subsurface contamination
(ASC).
2. Delineation of Areas of Subsurface Intrusion--See Section 5.2.0 of
the HRS
EPA has included in the subsurface intrusion component evaluation
two areas in which exposure due to subsurface intrusion contamination
exists or is likely to exist: (1) Areas of observed exposure--areas in
which contaminant intrusion into regularly occupied structures has been
documented, and (2) areas of subsurface contamination--areas in which
subsurface contamination underlying regularly occupied structures (such
as in shallow ground water or soil vapor) has been documented, but at
which either sampling of indoor air has not documented that subsurface
contamination has entered a regularly occupied structure or no sampling
of indoor air has been undertaken.
a. Area of Observed Exposure (AOE) (See Section 5.2.0 of the HRS)
An area (or areas) of observed exposure at a site is identified
based on the location of regularly occupied structures with a
documented significant increase in hazardous substance concentrations
above background levels resulting at least in part from subsurface
intrusion attributable to the site being evaluated. The area
encompassed by such structures constitutes the area of observed
exposure (AOE). Other regularly occupied structures within this
encompassed area (or areas) are also inferred to be in the AOE unless
available information indicates otherwise.
b. Area of Subsurface Contamination (ASC)--See Section 5.2.0 of the HRS
An area (or areas) of subsurface contamination is identified as an
area outside that of the AOE, at which subsurface contamination has
been documented at levels meeting observed release criteria
(contamination at levels significantly above background and the
significant increase can be attributed at least in part to the site).
The contamination would be present in subslab or semi-enclosed or
enclosed crawl space samples or in a subsurface sample. (See section
2.3 of the HRS for observed exposure criteria.) In addition, EPA is
limiting the delineation of an ASC to be based on the location of
subsurface contamination meeting the criteria for observed exposure or
observed release and has a vapor pressure greater than or equal to one
torr or a Henry's constant greater than or equal to 10-5
atm-m\3\/mol. The populations in an ASC are assigned a weighting value
ranging from 0.1 to 0.9 depending on such factors as the distance of
subsurface contamination to a regularly occupied structure's
foundation, the sample media, and the presence of a non-aqueous phase
liquid (NAPL).
3. Likelihood of Exposure--See Section 5.2.1.1 of the HRS
A key factor considered in the HRS relative risk ranking is whether
any exposure to a hazardous substance via subsurface intrusion has
occurred, or if not, whether there is a probability that exposure could
occur in a regularly occupied structure. This is termed the likelihood
of exposure for the subsurface intrusion component.
a. Observed Exposure--See Section 5.2.1.1.1 of the HRS
For HRS purposes, an observed exposure is established if it can be
documented that a hazardous substance from the site being evaluated has
moved through the subsurface and has entered at least one regularly
occupied structure.
b. Potential for Exposure--See Section 5.2.1.1.2 of the HRS
When an observed exposure has not been established, the potential
for exposure can be determined for any regularly occupied structure
located in an ASC.
The evaluation of the potential for exposure for the subsurface
intrusion component uses the same concept and framework used to
estimate the potential to release in other pathways. This involves
predicting the probability of exposure in an area of subsurface
contamination based on structural containment features of the regularly
occupied structure and a hazardous substance's physical and chemical
properties and the physical subsurface properties that influence the
probability that intrusion is occurring. These factor values include:
Structure Containment
Depth to Contamination
Vertical Migration
Vapor Migration Potential
Consistent with potential to release determinations in the HRS, the
potential for exposure for this component is calculated by summing
depth to contamination, vertical migration and vapor migration
potential factor values and multiplying the sum by the containment
factor value to determine a potential for exposure factor value.
c. Calculation of the Likelihood of Exposure Factor Category Value--See
Section 5.2.1.1.3 of the HRS
As in all HRS pathways and components, the likelihood of exposure
factor category value is assigned based on the higher of the observed
exposure (or release) value or the potential for exposure (or release)
value. The maximum value assigned for the likelihood of exposure factor
category is 550 and is assigned if observed exposure is documented. If
observed exposure is not documented, the value assigned when evaluating
potential for exposure ranges between 0 and 500.
[[Page 2769]]
4. Waste Characteristics--See Section 5.2.1.2 of the HRS
The waste characteristics factor category is based on factors that
are related to the relative risk considerations included in the basic
HRS structure. The factors considered in determining the waste
characteristics factor category value are the toxicity of the hazardous
substances, the ability of the hazardous substance to degrade, and an
estimate of the quantity of the hazardous substances to which occupants
could be exposed.
a. Toxicity/Degradation--See Section 5.2.1.2.1 of the HRS
The combined toxicity/degradation factor includes consideration of
both the toxicity and the possibility for degradation of hazardous
substances being evaluated for HRS purposes. The toxicity factor in the
overall HRS structure reflects the toxicity of a hazardous substance
associated with a source, release or exposure at a site, and is
assigned the same factor value for all the pathways and components in
the HRS. Any hazardous substance identified in an observed exposure
within the AOE or meeting the observed release criteria in either the
AOE or ASC will be assigned a toxicity factor value.
The degradation factor represents the possibility for a substance
to degrade in the subsurface prior to intruding into a regularly
occupied structure. The subsurface intrusion component evaluates
degradation based on the substance being evaluated, the depth to
contamination, and the presence of a NAPL. It also assumes the presence
of biologically active soil unless information indicates otherwise. If
it has been documented that a hazardous substance has been found to
have entered a regularly occupied structure, regardless of the
substance or the site conditions, the degradation value is assigned to
reflect the likelihood that the substance is not significantly
degrading in the subsurface. Additionally, any eligible hazardous
substance present in the subsurface below an AOE or ASC as a NAPL at
depth less than 30 feet is assigned a degradation value to reflect the
likelihood that the substance will not significantly degrade in the
subsurface environment.
The toxicity and degradation factors are multiplied together to
assign a combined factor value. If multiple substances are present, the
highest combined factor value is selected for use in determining the
waste characteristics factor category value, as discussed below.
b. Hazardous Waste Quantity--See Section 5.2.1.2.2 of the HRS
The waste quantity factor value for this component reflects only
the amount of hazardous substances that people are exposed to, that is,
the amount in regularly occupied structures. EPA has retained a four-
tiered hierarchical approach consistent with the HRS as well as minimum
waste quantity factors. The estimation of waste quantity for the
subsurface intrusion component considers the regularly occupied
structures located within the AOE and ASC. For sites at which the
component waste quantity (the sum waste quantities for all regularly
occupied structures in the AOE and ASC) is below 10, a minimum factor
of 10 would apply, the same as in other pathways and components. The
minimum waste quantity factors are included because of insufficient
information at many sites to adequately estimate waste quantity with
confidence.
c. Calculation of the Waste Characteristics Factor Category Value--See
Section 5.2.1.2.3 of the HRS
As in all HRS pathways and components, the waste characteristics
category value is the product of the waste characteristics factor
values (e.g., toxicity/degradation factor value) for the SsI component
and the hazardous waste quantity factor value, all of which are scaled
so as to be weighted consistently in all pathways. Similar to the
likelihood of exposure factor category, the waste characteristics
factor category is subject to a maximum value to maintain the balance
between factor categories. This approach is consistent with the 1990
HRS structure.
5. Targets--See Section 5.2.1.3 of the HRS
The targets factor is based upon estimates of the expected dose to
each receptor associated with a target and the number and type of
receptors present at each target. In assessing human risk, it is
critical to understand the nature and extent of exposure to
individuals, populations, and resources.
a. Identification of Eligible Targets--See Section 5.2.1.3 of the HRS
The soil exposure and subsurface intrusion pathway uses the same
target categories used in the HRS soil exposure pathway, including
exposed individual, resident populations, workers, and resources.
However, unlike the HRS soil exposure pathway, workers are to be
evaluated as exposed individuals and as part of the population within
an area of subsurface contamination instead of being evaluated under a
separate worker factor value.
b. Exposed Individual and Levels of Exposure--See Section 5.2.1.3.1 of
the HRS
i. Identifying Levels of Exposure and Benchmarks for Subsurface
Intrusion
In the SsI component, targets in the AOE are considered actually
contaminated, whereas, those in the ASC are considered potentially
contaminated. The targets in an AOE are further divided into Level I
and II, based on whether the hazardous substance concentrations are at
or above identified health-based benchmarks.
The targets within an ASC are categorized based on the type of
sample (e.g., gas, soil, water), the distance of the sample from the
targets (e.g., the depth of the sample below the structure), and
whether a NAPL is present. Weighting factors ranging from 0.1 to 0.9
are then assigned accordingly.
ii. Exposed Individual--See Section 5.2.1.3.1 of the HRS
The evaluation of exposed individuals in the SsI component includes
individuals living, attending school or day care, or working in a
regularly occupied structure. Individuals in the eligible target
population are expected to be exposed to the highest concentration of
the hazardous substance in question for a significant time.
c. Population--See Section 5.2.1.3.2 of the HRS
The population factor for the SsI component includes all
populations qualifying as exposed individuals, including residents,
students, workers, and those attending day care. Workers are weighted
slightly differently than other exposed individuals to reflect that a
worker's exposure is limited to the time present in a workplace. The
number of workers present in a structure or subunit is adjusted by an
appropriate factor reflecting whether or not they are a full-time or
part-time worker.
i. Weighting of Targets in the Area of Observed Exposure (AOE)--See
Sections 5.2.1.3.2.1 and 5.2.1.3.2.2 of the HRS
Consistent with the weighting of populations throughout the HRS,
the subsurface intrusion component will weight targets in an AOE
subject to Level I contaminant concentrations by a factor of 10 and
weight targets subject to Level II contaminant concentrations by a
factor of 1. Eligible populations include individuals living, working,
and
[[Page 2770]]
attending school or day care in regularly occupied structures.
Within the AOE, those populations in regularly occupied structures
for which observed exposures have not been established but the
structures are surrounded by regularly occupied structures in which
observed exposures have been identified, are also considered as
actually contaminated unless evidence indicates otherwise. Targets
inferred to be exposed to this contamination will be weighted as Level
II as there are no actual sample results to compare against benchmarks.
In the case of multi-story/multi-subunit structures, all regularly
occupied subunits on a level with an observed exposure and all levels
below are considered to be within an AOE, unless available information
indicates otherwise. For multi-story/multi-subunit structures located
within an AOE, but where an observed exposure has not been documented,
only those regularly occupied spaces on the lowest level are considered
to be within an AOE, unless available information indicates otherwise.
ii. Weighting of Targets in the Area of Subsurface Contamination
(ASC)--See Section 5.2.1.3.2.3 of the HRS
Due to the variability in subsurface intrusion rates, the potential
weighting factor values for targets within an ASC range from 0.1 to 0.9
and depend on where the subsurface contamination has been found and
whether a NAPL is present.
Potential targets are weighted to reflect the distance to or the
depth at which contamination is found and whether a NAPL is present.
The weighting factors applied to populations being evaluated based on
the presence of subsurface contamination containing a NAPL reflects
greater subsurface source concentrations and an increased probability
that contaminant intrusion into a regularly occupied structure from the
subsurface will result in a concentration significantly above
background levels for the site. In the case of multi-story/multi-
subunit structures, all regularly occupied subunits on a level above
one where an observed exposure has been documented or inferred, or
where a gaseous indoor air sample meeting observed release criteria is
present, are considered to be located within an ASC, unless available
information indicates otherwise. For multi-story/multi-subunit
structures located only within an ASC, only those regularly occupied
subunits within the lowest level are considered in an HRS evaluation.
Eligible populations in an ASC include individuals living in,
attending school or day care, and working in regularly occupied
structures. However, the number of workers is adjusted to reflect that
their exposure is limited to the time they are in a workplace.
d. Resources--See Section 5.2.1.3.3 of the HRS
Resources for this component include regularly occupied structures
that are located within a defined AOE or ASC and in which populations
may be exposed to contamination due to subsurface intrusion. Libraries,
recreational facilities, and religious or tribal structures used by
individuals may qualify as eligible resources.
e. Calculation of the Targets Factor Category Value--See Section
5.2.1.3.4 of the HRS
The Target Factor Category Value is the sum of all the Target
Factor values.
6. Calculation and Incorporation of the SsI Component Score Into the
HRS Site Score
The following subsections summarize the calculation of the
subsurface intrusion component score, how the component score is used
in the calculation of the soil exposure and subsurface intrusion
pathway score, and how, in turn, the pathway score is subsequently
incorporated into the HRS site score.
a. Calculation of the SsI Component Score--See Section 5.2.2 of the HRS
The SsI Component score is the product of the likelihood of
exposure factor category value, the waste characteristics factor
category value, and the targets factor category value; that value is
divided by a weighting factor so that it has equal magnitude to other
component scores (subject to a maximum value).
b. Incorporation of the SsI Component Score into the Soil Exposure and
Subsurface Intrusion Pathway Score--See Section 5.3 of the HRS
The Soil Exposure and Subsurface Intrusion pathway score is a
combination of the two component scores.
c. Incorporation of the Soil Exposure and Subsurface Intrusion Pathway
Score Into a Site Score--See Section 2.1.1 of the HRS
EPA did not change the methodology used to assign an overall site
score due to the addition of the subsurface intrusion component to the
soil exposure pathway and renaming that pathway the soil exposure and
subsurface intrusion pathway. The overall site score remains a function
of four pathway scores and the same weighting is given to each pathway
score as in the 1990 HRS.
C. Testing the SsI Component
The SsI component was tested extensively throughout the development
of this rule, using multiple methods. The main goals of testing the
component included:
Ensuring the addition of the SsI component to the soil
exposure pathway did not change relative contribution to the site score
as the other HRS pathways and maintained the same relative risk of a
site with a similar threshold for qualifying for the NPL.
Ensuring the number of targets subject to actual
contamination needed to achieve a site score sufficient for NPL
proposal remained consistent across pathways.
Ensuring that applying the SsI component as part of an HRS
evaluation would not result in identification of sites with a low level
of risk or would not identify sites with a high level of risk.
These goals were met by using conceptual simulations to project the
effectiveness and appropriateness for factor values, by developing and
testing numerous example site scenarios to refine the model and by
applying the model to test sites to determine its efficacy. The
following information provides details on the approaches used to test
the SsI component.
1. Conceptual Site Model/Sensitivity Analysis
Sensitivity analyses were performed during development of the rule
to test the SsI component and identify and assign the relative
magnitude of the factors having the greatest impact on the HRS site
score. The analyses illustrated the types of sites that would qualify
for the NPL considering subsurface intrusion contamination, and sites
that would qualify for the NPL considering the contribution of
subsurface intrusion contamination to other pathways. The scenarios
illustrate different site characteristics and different factor value
weightings. An initial conceptual site scenario evaluation was
developed with varying likelihood of intrusion levels, zone of
contamination, waste characteristics and levels of contamination. The
conceptual site scenario evaluation was varied to reflect possible
ranges in the factors considered in the HRS evaluation.
The first phase of testing estimated site scores based on options
considered
[[Page 2771]]
for identifying eligible targets and delineating target areas. The
testing was conducted using factor values, factor category values, and
scoring algorithms consistent with other parts of the HRS. This ensured
relative risk was evaluated and consistently weighted among pathways. A
second phase was conducted for identifying target areas delineated by
AOEs and ASCs of various site scenarios to test the HRS addition and to
illustrate the features of sites that would qualify for the NPL
considering vapor intrusion contamination. To illustrate the subsurface
intrusion component and contribution of weighting of factor values,
three comprehensive site scoring scenarios were evaluated: A site would
not qualify for placement on the NPL (score below 28.50), a site would
marginally qualify for the NPL (score of or about 28.50), and a site
would exceed the scoring criterion for the NPL (site score considerably
above 28.50). Based on this final rule, the results revealed that sites
without areas of observed exposures and a typical waste characteristic
value would require a minimum of 685 receptors living, working or
attending school or daycare above an area of subsurface contamination
to receive a score of 28.50 based on shallow subsurface sampling. Sites
with documented subsurface intrusion into an occupied structure, a
typical waste characteristic value and indoor air samples below health-
based benchmarks would require a minimum of 223 receptors to receive a
score of 28.50. This illustrates that this final rule will not result
in a large number of sites qualifying for the NPL as it is unlikely
this number of receptors in an area of subsurface contamination will
commonly occur. This is the similar number of receptors needed for a
site to qualify for the NPL in other pathways.
2. Test Sites (Tier 1)
To support the final rulemaking, EPA conducted a screening-level
assessment of sites with identified subsurface intrusion threats. As a
first step in collecting the list of sites potentially affected by the
final rule, EPA consulted with site assessment experts that work in
Superfund to identify potential site candidates. EPA also reached out
to state counterparts, in particular to state programs that were known
to have taken a more thorough investigation of the subsurface intrusion
pathway at sites. Through this process, EPA identified approximately
1,073 sites. These sites are not currently on the NPL, and all have a
potential or identified SsI threat. Within the group of sites
potentially affected by the HRS SsI Addition, EPA defined four
categories:
1. Tier 4: Sites identified as having a suspected SsI threat based
on EPA's Superfund database and Agency for Toxic Substances and Disease
Registry keyword searches, as well as EPA or state self-identification,
but for which no sampling data were obtained;
2. Tier 3: Sites identified as having characteristics or evidence
that indicate SsI may have occurred or will occur;
3. Tier 2: Sites identified as having an SsI threat documented by
subslab, crawl space, or indoor air samples, but insufficient HRS-
required evaluation factors to qualify for the NPL; and
4. Tier 1: Sites identified as having an SsI threat with documented
actual exposure of a sufficient number of targets with enough other
HRS-required evaluation factors to suggest the site may qualify for the
NPL.
EPA selected the Tier 1 sites for use in testing the SsI component
evaluation process. The 11 Test Sites had documentation of indoor
contamination due to subsurface intrusion based on actual sampling data
and other typically HRS-required data. Of the 11 sites scored, 9 were
projected to score 28.50 or higher using only the SsI component. 1 site
was projected to score 28.50 or higher only by including both the
scores from the SsI component evaluation and the ground water migration
pathway evaluation in the site score. It was unknown whether these
sites would qualify for the NPL when they were chosen as Test Sites, as
the SsI scoring process had not been developed. The Test Site with a
projected score below 28.50 did not qualify for the NPL even though the
site was located in a mixed-used residential and industrial area,
illustrating that not all sites in an urban area will qualify for the
NPL.
That 10 of the 11 Test Sites have a projected HRS site score of
28.50 or greater using the SsI component is not an indication that the
addition of the SsI component will result in a large number of SsI
sites qualifying for the NPL; this would be a possible projection if
the Test Sites were chosen randomly so as to represent a typical SsI
site. The Test Sites were not randomly chosen, but instead were
specifically chosen because they have a documented subsurface intrusion
threats at the sites and sufficient available data to test all parts of
the SsI component. The Test Sites all had areas of observed exposure;
most had more than 38 structures at the site (some with hundreds of
structures), and all but two Test Sites had at least 50 targets (more
than half had over 100 targets). Each site was also associated with
volatile hazardous substances that are considered hazardous to human
health at low concentrations. Appendix B of the Technical Support
Document (TSD) for this final rulemaking provides a summary of these
scoring evaluations.
3. Pilot Study
The main purpose of the Pilot Study was to identify sites currently
being evaluated for SsI by the EPA regions with a suspected subsurface
intrusion threat and determine whether an SI would provide enough
information to score a site under the new component. Additional goals
of the Pilot Study were to gather data and determine if design of the
SsI model is practical and gives expected results; identify a range for
the cost of a projected SsI site assessment; and assist in developing
future guidelines for SsI assessments. A total of 10 sites were
identified across 5 of the 10 EPA Regions. The pilot studies were not
intended to identify sites for placement on the NPL, and not all sites
considered for the pilot studies achieved an HRS score greater than (or
equal to) 28.50. However, collecting actual data for the purposes of
generating an SsI component score, ensured the HRS was considering
subsurface intrusion threats appropriately. Ultimately, the pilot
studies were used to proof the concept and validate the SsI component
in terms of the application of selected weighting factor values and the
efficacy for accurately identifying sites with significant relative
risk.
IV. Summary of Changes to the HRS
Comments on the Proposed Rule were received from 15 organizations/
individuals. The commenters included state and federal agencies,
industry associations, community groups, consultants, and private
citizens. No major conceptual or structural changes were necessary
based on comments received during the public comment period. While many
of the comments focused on the structure of the SsI component, there
was not sufficient rationale for making major changes to the basic
structure of the SsI component. There were minor revisions made based
on comments, which help refine the mechanics of assigning an HRS site
score. As a result, the SsI component better reflects current science
and better aligns with underlying concepts in the OSWER Technical Guide
for Assessing and Mitigating the Vapor Intrusion Pathway from
Subsurface Sources to Indoor Air (VI Guide). These changes had no
impact on the overall structure of the SsI component and do not impact
the relative weighting among the HRS
[[Page 2772]]
pathways or the level of risk required to qualify for the NPL.
A. Changes Since Proposal
1. Consideration of Contaminated Ground Water Intrusion
Section 5.2 was revised to clarify that areas of subsurface
contamination are only delineated based on the presence of hazardous
substances meeting the criteria for observed exposure or observed
release and have a vapor pressure greater than or equal to one torr or
a Henry's constant greater than or equal to 10-5 atm-m\3\/
mol. However, if samples indicate intrusion of liquids containing
hazardous substances has occurred into regularly occupied structures,
the samples of that liquid are still used in delineating an Area of
Observed Exposure to reflect the threat to targets. These revisions
were made to correct a seeming inconsistency in wording between the
discussion in the preamble to the proposed rule and the proposed
regulatory language.
2. Consideration of Non-Aqueous Phase Liquids (NAPLs) in Weighting of
Targets in an ASC
Table 5-21, Weighting Factor Values for Populations within an Area
of Subsurface Contamination, of the HRS was revised to include
consideration of the presence of NAPLs identified in an area of
subsurface contamination. These additions increase the weighting of the
population in an area of subsurface contamination to the SsI component
score. These revisions were in response to comments that the proposed
addition did not reflect the magnitude of contaminant concentrations in
the evaluation of targets in the area of subsurface contamination.
While EPA considers it unlikely that the actual aerial distribution and
magnitude of contaminant concentrations can be determined in an area of
observed contamination during a site inspection, if NAPLs are
identified as present, EPA agrees that there is a greater risk to
receptors than if no NAPL is present.
3. Modifications to the Determination of Degradation Factor Values
Section 5.2.1.2.1.2 of the HRS was revised to make it easier for
the reader to determine degradation factor values and to add
consideration of the presence of NAPLs. Commenters asserted that the
text was difficult to follow and that the presence of NAPLs was a major
factor in the impact of degradation. A new table, Table 5-18 of the
HRS, simplifying the assignment of degradation factor values based on
the depth to contamination and a substance's half-life was inserted to
replace proposed text. Additionally, if no half-life information is
available for a hazardous substance and the substance is not already
assigned a degradation factor value of 1, a value of 1 will be
assigned. This modification further simplifies the degradation
evaluation and is also protective of human health, for if no half-life
information is available for a hazardous substance, EPA cannot assume
that degradation will occur. In addition, parent-daughter relationships
between substances are no longer considered in the assignment of the
degradation factor value, in part to simplify the assignment and in
part to reflect the variation in rates of degradation due to site-
specific subsurface conditions. Even if degradation occurs, if a
contaminant is at high enough concentration to exist as a NAPL at
depths less than or equal to 30 feet, it is more likely to pose a
threat to populations in overlying structure.
4. Modifications Made to Section 5.2.1.1.2.1, Structure Containment and
Table 5-12
Section 5.2.1.1.2.1 and Table 5-12 of the HRS were revised in
response to comments on the rationale for assigning containment values
to individual structures. The assignment of a structure containment
factor value assigned to structures in Table 5-12 with vapor mitigation
systems or other response actions was revised. These revisions were
made in response to a comment questioning why response actions taken by
federal, state, and tribal authorities are treated differently than
those taken by private entities in determining containment for a
structure. The language regarding treatment of removals by federal,
state, and tribal authorities has been removed from Table 5-12 and the
corresponding containment value was assigned a 1. This change allows a
consideration of public and private removal actions to be evaluated in
a consistent manner.
Section 5.2.1.1.2.1 and Table 5-12 of the HRS was also revised to
remove from the table the direction of the assignment of a structure
containment value for a regularly occupied structure with unknown
containment features. This direction, which assigns a value of
``greater than zero'' to this situation, was moved to the text in
section 5.2.1.1.2.1 of the HRS. This revision was made in response to a
comment questioning the rationale for the various containment values
and was made to improve the continuity of the table, which directs the
assignment of values when containment features of the structure are
known. A structure with a containment factor value of greater than zero
cannot be used in assigning a potential for exposure factor value. EPA
considers it appropriate that the potential for exposure factor value
should be based on actual field observations. However a structure with
a structure containment value of greater than zero allows the structure
to be evaluated for assigning waste characteristics values (e.g., a
hazardous waste quantity factor value) and for assigning target factor
values. EPA considers the inclusion of structures with unknown
containment features in the calculation of waste characteristics and
targets values appropriate as it reflects that very few structures are
built to be sufficiently air tight to prevent subsurface intrusion.
5. Consideration of Hydraulic Conductivity in Vertical Migration
Table 5-14 of the HRS was revised to allow assignment of an
effective porosity/permeability factor value based on site-specific
measurements of hydraulic conductivity, if known. This addition was
made in response to a comment suggesting the rule be modified to allow
use of site-specific information for this purpose when available.
6. Changes to Definitions
The term surficial ground water was re-named shallow ground water
and was changed to be consistent with current EPA usage.
EPA has added the term non-aqueous phase liquid (NAPL) to the
definition section. EPA added consideration of the identification of
concentrations of hazardous substances high enough to indicate the
presence of NAPLs in the subsurface during a site inspection to the
assignment of degradation factor values and the weighting of targets in
the ASC. The presence of NAPLs in the subsurface demonstrates the
hazardous substances will be present at high concentrations for a
significant time period at that location and the high concentration is
not a transient situation.
B. Summary of Updates to the HRS (Sections 2, 5, 6, and 7)
1. Addition of an SsI Component to the HRS (Sections 2, 5, and 7)
a. The addition of a subsurface intrusion component is added to the
1990 Soil Exposure pathway as section 5.2 in Chapter 5 of the 2016
Revised HRS. The new pathway name is the soil exposure and subsurface
intrusion pathway. The existing method for evaluating the soil exposure
threat will remain unchanged.
b. Chapter 2: Evaluations Common to All Pathways is updated to
reflect the
[[Page 2773]]
addition of the subsurface intrusion component to the renamed the soil
exposure and subsurface intrusion pathway. The evaluations for the
migration pathways and the soil exposure component remain unchanged. A
parallel structure was added for the subsurface intrusion component.
c. Chapter 7: Sites Containing Radioactive Substances is updated to
reflect how radioactive substances are evaluated using the added
subsurface intrusion component.
2. Terminology Updates Affecting Specific Sections of the HRS (Sections
2, 5 & 6)
The following terms are updated to reflect current terminology and
procedures used by EPA in performing risk assessments.
a. Ambient Water Quality Criteria: Ambient Water Quality Criteria
(AWQC) are now identified also as National Recommended Water Quality
Criteria (NRWQC). In addition, the acute AWQC are now identified as the
Criterion Maximum Concentration (CMC) and the chronic criteria are
referred to as the Criterion Continuous Concentration (CCC). (See
section 1.1 of the HRS.) These criteria are used to determine the level
of threat to environmental targets.
b. Reference Concentrations: For inhalation exposures, EPA is
adopting the use of Reference Concentrations (RfCs) instead of
Reference Doses (RfDs) when determining non-cancer-related risk levels.
RfCs are used in determining the level of threat to human targets due
to possible inhalation and when determining the toxicity of the
substances.
c. Cancer Unit Risk: For inhalation exposures, EPA is adopting the
use of Inhalation Unit Risk (IUR) instead of cancer slope factors in
determining cancer-related risk levels. IURs are used in determining
the level of threat to human targets due to possible inhalation and
when determining the toxicity of the substances.
d. Weight-of-Evidence Groupings: The 2005 EPA weight-of-evidence
groupings supporting the designation of a substance as a human
carcinogen have been incorporated into the HRS algorithm for assigning
the toxicity factor value. (The former EPA weight-of-evidence
categories included as part of the 1990 HRS have been retained as EPA
has not yet completed assigning all substances to the revised
categories and are doing so at the time the EPA substance literature
reviews are updated.)
V. Discussion of Major Comments
Comments on the Proposed Rule were received from 15 organizations/
individuals. The commenters included state and federal agencies,
industry associations, community groups, consultants, and private
citizens. This section discusses the major issues raised by commenters,
which are summarized, and EPA's summary of responses. In addition, EPA
solicited and received input from commenters on three technical
questions posed in the Preamble to the Proposed Rule.
A support document, Response to Comments on the 2016 Revisions to
the Hazard Ranking System (HRS), that includes all issues raised during
the public comment period, comments received on the questions posed in
the preamble to the proposed rule and EPA's more comprehensive response
to each issue, is available in the docket for this rulemaking.
A. Responses to Comments on EPA Questions Posed in the Proposed Rule
Question 1: Is there a way to determine the presence and extent of
biologically active soil at a site during a limited site investigation?
If so, what soil characteristics should EPA consider to determine
whether biologically active soil is documented to be present?
EPA received multiple comments in response to this question. One
commenter suggested that this activity is beyond the scope of the site
assessment process, while another commenter suggested that EPA consider
measuring specific compounds or other factors reflecting biological
activity when conducting soil vapor analysis. A third commenter
remarked that half-lives faster than 100 days are presumably due to
aerobic biodegradation and that most vadose zone soils that are not
grossly impacted are considered biologically active. A commenter also
suggested using soil characteristics reflected in soil surveys to
reflect the possibility that biologically active soil could be present.
No commenter suggested practical methods to determine site-specific
biological activity throughout a site or over time.
The HRS SsI addition was revised to clarify the assumption of the
presence of biologically soil in evaluating the degradation factor
unless evidence indicates otherwise (see section 5.2.1.2.1.2 of the
HRS).
Question 2: How could EPA further take into account the difference
in dilution and air exchange rates in large industrial buildings as
compared to smaller residential and commercial structures when
calculating the hazardous waste quantity for the HRS SsI Addition?
EPA received multiple comments in response to this question. One
commenter suggested developing intrusion screening values based on
exposure scenarios for ``most sensitive individual'' and ``industrial''
models. One commenter indicated that there is not a dependable way to
account for the differences between large commercial/industrial
structures and smaller residential/commercial structures. Another
commenter noted that there are several parameters (e.g., building
energy efficiency) that would impact the differences in dilution and
air exchange rates and which are generally unavailable during an
initial assessment. A commenter discussed developing a sliding scale
based on the size of the building and the building's general use to
account for the differences in contaminant clearance rates.
EPA did not make any changes to the final rule based on the
comments received as the type of information requested in these
responses is generally not available during a typical site inspection.
The HRS has also been designed so that it can be applied consistently
to a wide variety of sites. The HRS is not a tool for conducting
quantitative risk assessment and was designed to be a measure of
relative risk among sites rather than absolute site-specific risk.
Question 3: The HRS SsI addition considers source strength in
delineating ASCs and AOEs, in scoring in likelihood of exposure, in
assigning waste quantity specifically when estimating hazardous
constituent quantity and in weighting targets in an ASC. The HRS
algorithm for all pathways incorporates the consideration of source
strength in determining an HRS site score. Could EPA further take into
account source strength in performing an HRS evaluation?
EPA received multiple comments in response to this question. One
commenter suggested that EPA assign a higher score when the contaminant
concentration is high (e.g., when a non-aqueous phase liquid is
present) to account for source strength. Comments were also received
that reflected the difficulty of accessing large low concentration
sources and how to account for that in considering source strength.
Another commenter remarked that there may be a large ground water plume
without a discrete source that would cause an increased risk of vapor
intrusion; and that a large diffuse source is different from having a
concentrated discrete source. One commenter
[[Page 2774]]
provided a copy of the proposed rule with their suggested edits
reflecting the evaluation of source strength in assigning HRS specific
factors.
The assignment of a degradation factor value (see section
5.2.1.2.1.2 of the HRS) and the weighting factors for targets in an
area of subsurface contamination (see Table 5-21 of the HRS) were
revised to include consideration of source strength; specifically in
the situation where NAPLs are present.
B. Major Comment Theme Summaries and Responses
Statutory Authority and Rationale for the Proposed HRS Addition
Justification for Revising the HRS
EPA received comments suggesting that sufficient justification or
rationale for the need to revise the HRS has not been provided and that
a revision to the HRS is unnecessary because the 1990 HRS adequately
evaluates the relative risk posed by a site and identifies those
priority sites for further investigation.
The rationale for revising the HRS to add a subsurface intrusion
component is EPA's statutory authority. Specifically, CERCLA
105(a)(8)(A), requires EPA to amend the HRS ``to assure to the maximum
extent feasible, that the HRS accurately assess the relative degree of
risk to human health and the environment posed by sites and facilities
subject to review.'' Contamination due to subsurface intrusion is a
known risk to human health and the ability to evaluate those risks is
consistent with the CERCLA 105 mandate. The 1990 HRS did not evaluate
the risk posed by subsurface intrusion when evaluating sites for the
NPL. As part of the development of this rule, EPA identified high
priority sites with significant contamination due to SsI that could not
be evaluated using the 1990 HRS for possible placement on the NPL. With
the addition of the SsI component to the HRS, sites can now be
evaluated more comprehensively to consider the relative risk posed by a
site.
Priority for Drinking Water Sites
EPA received comments suggesting that the proposed HRS SsI addition
conflicts with CERCLA's statutory mandate regarding prioritizing
drinking water sites.
The revision to the HRS to add a subsurface intrusion component is
not in conflict with the CERCLA 105 mandate to prioritize drinking
water sites. The priority given by EPA under CERCLA to sites with a
high risk of populations exposed to hazardous substances in drinking
water has not decreased with the addition of a subsurface intrusion
component to the HRS. In fact, the score for some sites with
contaminated drinking water supplies may increase because sites with
contaminated drinking water may also be associated with subsurface
intrusion contamination and the combination of the ground water
migration pathway score and the SsI component score may increase the
overall site score. Furthermore, EPA notes that drinking water is a
priority identified by CERCLA, but it is not the only priority
identified in CERCLA 105, which also mandates the prioritization of
dangers of direct human contact, for which SsI is one example.
The addition of the SsI component does not change the priority
given to drinking water sites. It does not change the scoring of
contaminated drinking water supplies under the HRS, reduce in anyway
the overall HRS score for any site based on drinking water
contamination (or any other threat due to exposure to released
hazardous substances in the HRS), or change the site score of 28.50
being the HRS score that qualifies sites for placement on the NPL. If a
site qualifies for placement on the NPL based on its HRS score
reflecting drinking water contamination prior to the addition of the
SsI component, it will continue to do so. Adding an evaluation of the
SsI component can only increase an overall site score. The algorithm
used to combine pathways scores to obtain an overall site score results
in an increase in the overall site score with the evaluation of
additional pathways, components and threats scored. In fact, the SsI
addition may raise the overall site score at some sites with ground
water drinking water contamination from below the 28.50 cut-off score
to above it. This may occur because, as stated above, a site's HRS
score can increase with the scoring of additional threats. Sites with
ground water contaminated by volatile substances and used for drinking
water are also sites at which the ground water contamination may
volatilize and intrude into overlying regularly occupied structures.
Thus, a site at which ground water contamination has occurred but does
not have an HRS score above 28.50 based only on the ground water
threat, may have an overall HRS site score above 28.50 based on the
combination of the scores for the contaminated drinking water and SsI
threats.
Furthermore, EPA notes that CERCLA 118 refers to CERCLA sections104
and 108, which address activities that occur pre- or post-NPL-listing,
and not to the section of CERCLA that addresses site ranking using the
HRS, which is addressed in CERCLA section 105. CERCLA Section 105 and
specifically 105(a)(8)(A) requires EPA to prioritize sites based on
``the population at risk, the hazard potential of hazardous substances
at such facilities, the potential for contamination of drinking water
supplies, the potential for direct human contact [and] the potential
for destruction of sensitive ecosystems.'' Since subsurface intrusion
contamination is a direct human contact threat, the addition of a
subsurface intrusion component, which addresses this threat, is
mandated by CERCLA.
Resource Impacts of the Proposed HRS Addition
Increased Cost and Level of Effort
EPA received comments suggesting that contrary to EPA's suggestion
that the HRS SsI addition may not result in more site assessments per
year and only minimal cost increases, commenters claimed that there
will be substantial increases in cost and level of effort for states
and federal agencies, due to the complexity in assessing subsurface
intrusion sites.
EPA acknowledges that in some cases the scope of a typical site
inspection (SI) may need to be expanded to collect the information
necessary to evaluate the SsI threat present at a site. EPA also
acknowledges that sites that did not qualify previously for the NPL,
may now do so. The number of samples and level of effort required to
evaluate a site using the 1990 HRS pathways or components already
varies on a site-by-site basis depending on the size and extent of
contamination at the site. Therefore, it cannot be predicted with
certainty that there will be an overall increase in cost or level of
effort for any particular site due to the HRS SsI addition. However,
the overall budget for performing site assessments per year is not
expected to change significantly. EPA's budget for site assessment is
dependent on Congressional appropriation and EPA does not expect the
rulemaking to impact the appropriation. EPA's budget for site
assessment has remained relatively constant for the last several years.
Hence, EPA expects that the allocation of available resources may be
changed to reflect this rulemaking but will continue to be optimized by
EPA, its state and tribal partners, and with other federal agencies to
evaluate priority sites. However, the number of site assessments or NPL
proposals conducted each year will not significantly increase.
[[Page 2775]]
Potential Limitations With Implementing the HRS SsI Addition
Scope of Site Inspection
EPA received comments stating that the type and amount of
information available for collection during a time-limited site
inspection would be insufficient to properly evaluate a site using the
HRS SsI addition and would be beyond the scope of site evaluations
typically conducted at the preliminary assessment or site inspection
stage.
During development of the HRS SsI addition EPA considered the type
of information that could be collected during a time-limited site
inspection when selecting the factors to include in an evaluation of
the subsurface intrusion component. The purpose of the site inspection
(NCP 300.420(c)) is to determine if a release of a hazardous substance
poses an actual or potential threat to human health or the environment,
to determine if there is an immediate threat to people or the
environment, and to collect sufficient data to enable the site to be
scored using the HRS. EPA also notes that neither the NCP nor the HRS
requires a certain number of samples be collected during an SI, because
the number of samples required to evaluate a site varies on a site-by-
site basis and the possible risk pathways being evaluated. However, to
properly evaluate the subsurface intrusion component, additional
information may be required beyond that collected during a typical
current site inspection may be required; this is consistent with the
need to collect data on the threat posed by a different pathway. In
these instances, as stated in EPA's Guidance for Performing Site
Inspections under CERCLA (September 1992), an expanded site inspection
(ESI) may be required. The objective of the ESI is to collect data that
was not collected during an initial site inspection. Furthermore, EPA
found that information required for an SsI evaluation was available
based on a pilot study which included several candidate NPL sites. The
pilot study was performed in part to demonstrate the availability of
the necessary data from screening level investigations. Therefore, EPA
considers that the information required to properly evaluate the
subsurface intrusion component can be obtained during the site
assessment process.
Need for Guidance
EPA received comments questioning or requesting additional
information or guidance regarding the type and amount of data to
collect, data collection methods, and how to apply the subsurface
intrusion component to a site. Commenters also suggested it was
difficult to properly evaluate and comment on the proposed HRS SsI
addition without a thorough understanding of how the SsI component
would be implemented and that promulgation should be delayed until
guidance is developed.
The HRS does not provide prescriptive methods for performing site
investigations for any HRS pathway evaluation because the methods used
during the collection and analysis of environmental samples depend on
site conditions and could not be written to cover all possible
situations and could also become outdated in the future. Additionally,
it is outside the scope of the HRS to identify and describe methods for
conducting a subsurface intrusion screening for HRS purposes. The
sampling and data collection information in the EPA OSWER VI Guide,
(particularly in section 6 of the guide) are an appropriate resource
for gathering data for HRS purposes. For example, Section 6.4 of the
guide identifies basic principles, methods and procedures for indoor
air sampling. In addition, states, federal agencies, and private
contractors have considerable experience in VI investigations and
collecting VI-related data. Guidance on implementation of the proposed
SsI addition is not necessary for evaluating the SsI component, which
is a scoring mechanism not procedures for data collection. Any guidance
developed will provide details on collecting data to support an HRS SsI
evaluation. EPA also notes that to delay addressing sites that may pose
a significant human health risk until all necessary guidance documents
have been developed would not be consistent with EPA's mandate to
protect human health. Therefore, EPA does not agree that promulgation
of the HRS SsI addition needs to be delayed until guidance documents
related to its implementation have been developed.
Roles of the HRS SsI Addition and the 2015 OSWER VI Guide
EPA received comments suggesting that the HRS SsI addition is not
consistent with the VI Guide, published in June 2015 and will create
confusion when evaluating sites for SsI.
The VI Guide and HRS SsI rule work in concert to establish national
consistency in the evaluation of SsI threats. The HRS SsI addition and
the OSWER VI Guide both address the threat posed by vapor intrusion and
use the same principles, sampling procedures and concepts to
characterize the threat posed by vapor intrusion as the sites. However,
the HRS SsI addition and the OSWER VI Guide serve different purposes
and support different phases of EPA's site remediation process with
different data quality requirements and different enabling
legislations.
The purpose of the OSWER VI Guide is to guide the investigation and
assessment of the threat posed by vapor intrusion into structures from
all sources under all Office of Land and Emergency Management (OLEM,
formerly OSWER) programs, particularly actions taken under CERCLA and
RCRA. This guidance is used to support decisions by EPA on whether
vapor intrusion is posing an unacceptable risk to human health based on
sufficient site specific data. It contains principles for making such a
decision, as well as procedures and guidance for collecting the
information necessary to make these decisions.
The HRS and the SsI addition is part of the NCP, (the regulations
implementing CERCLA) required by CERCLA to identify priority sites for
further investigation based on screening level information (Such sites
are identified for the public by placing the sites on the NPL, a
separate rulemaking process). This prioritization is based on the
possible cumulative relative risk amongst all candidate sites posed by
releases of hazardous substances to human health and the environment by
either migration to receptors or by direct contact with the
contamination, such as by subsurface intrusion. The HRS is only a
method for assigning a relative score to candidate sites. It is not a
method for determining site specific risk. The HRS SsI addition is not
guidance. The HRS SsI addition does not address such subjects as data
collection and sampling procedures: Many of the procedures and many of
the guidelines in the OSWER VI Guide are also applicable for HRS
purposes if they can be implemented as part of a screening level
assessment.
Given that the purposes for the two documents are considerably
different and based on different levels of information, it is not an
issue that decision criteria are different in the two documents. It is
certainly possible that, based on an HRS evaluation, EPA may determine
a site warrants further investigation, and that after further
investigation is performed EPA may decide no remediation is necessary.
However until further information is collected during a remedial
investigation, such an outcome cannot be predicted. Furthermore, such a
situation is not an indication the results of the HRS evaluation was
incorrect.
[[Page 2776]]
Application of HRS SsI Component
Inferring Contamination
EPA received comments suggesting that by inferring contamination
between sampling locations, the extent of the risk is overstated. The
commenters considered identifying targets as actually or potentially
exposed based on inference to inflate the HRS site score. It was also
suggested that this method conflicts with the other HRS pathways.
The HRS is not a quantitative risk assessment. Instead, the HRS SsI
addition score reflects the possible threat posed by subsurface
intrusion at one site relative to other sites. By inferring
contamination in an AOE or an ASC between sampling locations, it is not
assumed that all populations within the two areas are exposed to
contamination from the subsurface. Inferring contamination also allows
sites with large populations within the two areas to be ranked higher
than sites with smaller populations. If the HRS scoring required
sampling every structure a sufficient number of times to assure that
all exposed targets were accounted for, the scope of the sampling
effort would be beyond that of a screening tool and more consistent
with the scope of a remedial investigation.
Inference of contamination between sampling locations is also
assumed in other HRS pathways. The other pathways allow the inference
of contamination based on the location of samples documenting the
presence of contamination attributable to the site being investigated.
For example, in the soil exposure component, inference of contamination
is done by drawing AOC boundaries based on sample locations and
inferring that those targets associated with the properties within the
boundaries are actually exposed.
In the SsI component, unless site-specific information indicates
otherwise, when delineating an AOE or an ASC, populations in occupied
structures within an AOE are inferred to be actually exposed, and,
populations in occupied structures within an ASC are inferred to likely
be exposed to contamination.
Purpose of Hazardous Waste Quantity
Commenters noted that as explained in the TSD for the proposed HRS
SsI Addition, the hazardous waste quantity factor serves as a surrogate
for the contaminant dose that populations may be exposed to. Commenters
asserted that the hazardous waste quantity factor is not adequately
reflective of this dose to be used as a surrogate.
The commenters appear to be confusing consideration of waste
quantity as a surrogate for dose in an HRS evaluation with the
calculation of a site-specific risk level based on the ratio of waste
quantity to receptors. EPA is not projecting a specific risk level
based on the waste quantity alone when it performs an HRS evaluation.
Other HRS factors such as the population associated with the
structures, the probability of a release into the occupied structures,
the possibility of degradation, and the toxicity of the substances are
also considered,
The decision to include waste quantity as a surrogate for dose in
all pathways and components in the HRS algorithm was made when the HRS
was last revised in 1990 (see Section V.3 of the proposed 1988 HRS, 53
FR 51692, December 23, 1988; Section III.C of the 1990 HRS, 55 FR
51542, December 14, 1990). The decision was based on the concept that
determining an accurate dose that receptors would be exposed to was
beyond the scope of information available after a site inspection. It
is not possible to accurately predict the hazardous substance
concentration that receptors would be exposed to over a representative
exposure period based on information collected during a site inspection
due to the variability in exposure levels over time and space. Instead,
hazardous waste quantity is used as a surrogate for dose in the sense
that the quantity of the hazardous substances is at least qualitatively
correlated to the magnitude of the exposure. If there is no waste
quantity, there will be no exposure; as the waste quantity increases,
the greater the possibility of exposure to hazardous substances that a
receptor may come in contact with. EPA agrees this is not a perfect
correlation, and has built into the HRS four order of magnitude ranges
for assigning factor values that reflect the imperfection of this
correlation.
In addition, the inclusion of hazardous waste quantity in the
subsurface intrusion component is consistent with its inclusion in all
the other existing HRS pathway evaluations and is consistent with the
goal that the scoring of the new component not impact the balance built
into overall HRS site scoring algorithm among the HRS pathways.
Furthermore, for determining waste quantity for the SsI component,
EPA made a specific alteration to how waste quantity is calculated as
compared to other HRS pathway. EPA decided to only include the amount
of hazardous substance that actually enters into or that could enter
into occupied structures, not the total amount in the release to the
environment, based on the rationale that at least some of the original
release in the subsurface would vent directly to the atmosphere.
Therefore only the amount of hazardous substances that has entered into
occupied structures or the amount located under structures is reflected
in the estimate. This was achieved by not estimating the waste quantity
based on the area or the volume of the contaminated media in the
subsurface, but instead on the volume of the structures, or the basal
area if the volume cannot be determined.
Finally, no comments were received that provided a viable
alternative to the proposed method of estimating hazardous waste
quantity. Commenters stated the amount of exposure was overestimated
for large buildings because in general larger buildings have lower air
exchange rates and suggested that this consideration be built into the
estimation methods for all structures. However, the commenters did not
present data to document this generality nor suggest how to determine
the air exchange rate for all structures if it is not provided by the
building owner. EPA notes that if air exchange rates are available, the
present estimation method (which has not changed since proposal) allows
for a hazardous waste quantity estimate using that information (see,
HRS section 5.2.1.2.2 Tier B, hazardous wastestream quantity).
While some commenters suggested procedures for determining a more
accurate hazardous waste quantity for specific situations they did not
suggest how the hazardous waste quantity calculated for these
situations could be relatively ranked against sites where equivalent
information was not available. When developing a hazardous waste
quantity factor in 1988, EPA performed studies that showed this level
of information was not available at all sites, and was not likely to be
collectible during a limited screening assessment. Therefore, EPA
considers it inappropriate to incorporate the suggested procedures into
the HRS.
In addition, EPA proposed the present hazardous waste quantity
estimation process as part of the revision of the HRS in 1988. At that
time EPA requested the Science Advisory Board's (SAB's) assistance on
the use of concentration data in determining the hazardous waste
quantity factor as part of the overall SAB peer review of the HRS
changes. The current method for use of concentration data in
determining the hazardous waste quantity factor is based on the SAB's
recommendation.
Establishment of Attribution
Commenters noted that establishing that indoor air contamination is
[[Page 2777]]
attributable to subsurface intrusion will be very complex to
demonstrate given all other possible origins of the indoor
contamination (e.g., outdoor air, consumer products).
The HRS SsI addition, just as in other HRS pathways and components,
does not require absolute proof that the significant increase in indoor
contaminant concentrations is due to subsurface intrusion. It only
requires at least part of the significant increase be attributable to
subsurface intrusion. EPA expects to use multiple lines-of-evidence in
meeting the attribution requirement as discussed in various comments.
The VI Guide outlines use of multiple lines-of-evidence and provides
guidance on how to distinguish subsurface intrusion from other sources
of vapor intrusion. As is done for other HRS pathways and components,
the HRS standard for establishing attribution is to establish a
reasoned explanation that is not shown to be incorrect during public
review of placement of a proposed site on the NPL.
Establishing Observed Exposure
EPA received comments suggesting that the criteria for establishing
background for the SsI component is too complex given the variability
in sampling for SsI and that a significant difference between the
background level and release concentration is not an adequate measure
for establishing an observed exposure in a regularly occupied
structure.
EPA agrees that establishing a background level for indoor air can
be difficult. However, it does not mean that the HRS criteria for
establishing actual exposure should not be used. Methods for
establishing background levels are too site-specific to be discussed in
the HRS regulation, which is a scoring methodology. Instead, as
occurred after the 1990 HRS was promulgated, criteria for establishing
background was refined based on actual experience gained as sites were
being scored. EPA expects the same to occur for the HRS SsI component.
Comparison of background levels and indoor air concentrations are
used only to establish that the contaminant level in a structure is
elevated (i.e., significantly different). This is only the first step
in establishing observed exposure. The second step is to attribute at
least a part of the significant increase to subsurface intrusion.
The argument that vapor intrusion rates are too variable to justify
the use of the same procedure for establishing observed releases or
exposures as in other parts of the HRS is invalid. Hazardous substance
concentrations are unpredictably variable temporally and spatially for
all HRS pathways and SsI variability is no different in that regard.
For example, in the surface water migration pathway overland flow
threat, the hazardous substance may only be entering surface water via
runoff due to rain events. No runoff occurs if it is not raining. The
amount entering surface water in this situation has been shown to vary
with the length of time between rains, which impacts the amount of
material deposited and available for entrainment into the runoff.
Runoff also varies with the portion of each rain cycle whether the
sample is collected at the beginning, middle or end of a rain event. At
the beginning of a rain event all erodible materials are present and
available. During the middle or during a high intensity period of rain,
the force of the rain drops can dislodge and entrain hazardous
substances at greater rates that during low intensity periods. At the
end of a rain event, it may be that much of the hazardous substances
have already been washed away. In continuous air releases, the
contaminant concentration can vary by order of magnitudes with distance
from the source, with wind direction and wind speed all of which can
cause differences in concentrations spatially due to the three
dimensionality of the atmosphere, and cannot be predicted or accounted
for based on a screening assessment. Even in ground water
contamination, the contaminant plume's concentration can vary spatially
depending on the rate of ground water movement from the original spill
concentrations. It is not possible to account for these factors that
can drastically impact the contaminant concentration at a sampling
location, based on screening level information.
For example, variation in the occurrence of releases is no greater
in the SsI component than would be expected in point-source air
releases or spills to surface water.
Degradation
Commenters suggested changes in how the degradation factor value
for the subsurface intrusion component is assigned. Other comments
dealt with conditions associated with assigning different degradation
factor values based on the depth of biologically active soil and the
half-lives of individual hazardous substances. In addition, commenters
suggested moving the consideration of degradation from the waste
characteristics factor category value calculations to the likelihood of
exposure factor category value calculations.
After evaluation of the comments, EPA modified the assignment of
the degradation factor to simplify the evaluation and to consider the
presence of non-aqueous phase liquids (NAPLs); other changes suggested
by commenters were not implemented. Some changes were not made because
a sufficient rationale was not provided to justify a change. Regarding
the placement of the degradation factor in the HRS equation, the
consideration of an individual substance's characteristics in the waste
characteristics factor category is consistent with other HRS pathways
and components. Furthermore, whether the degradation factor is put in
the likelihood of release or waste characteristic factor category, the
impact of the factor on the score would be similar.
Targets
EPA received comments on the weightings assigned to targets in both
the AOE and ASC. Commenters suggested that the weightings reflect the
strength of the attribution argument that the significant increase in
indoor air concentrations is due to subsurface intrusion and also
reflect the concentration of the contaminants in the subsurface.
After consideration of these comments, EPA has changed the
weightings of targets in the ASC to reflect the presence of NAPLs
(i.e., to reflect contaminant concentrations in the subsurface). EPA
did not incorporate any changes into the weightings of targets based on
the strength of attribution or concentration of contaminants in the
subsurface. Regarding the strength of an attribution argument, the HRS
does not recognize gradations of attribution in any other pathway or
component and therefore for consistency, will not in this component.
EPA notes that with the limited sampling that occurs during an SI, it
is not reasonable to project the concentration of contaminants in the
subsurface over time or distance.
VI. Statutory and Executive Order Reviews
Additional information about these statutes and Executive Orders
can be found at https://www.epa.gov/laws-regulations/laws-and-executive-orders.
A. Executive Order 12866: Regulatory Planning and Review and Executive
Order 13563: Improving Regulation and Regulatory Review
This action is a significant regulatory action that was submitted
to the Office of Management and Budget (OMB) for review. This action
may raise novel
[[Page 2778]]
legal or policy issues arising out of legal mandates, the President's
priorities, or the principles set forth in the EO. Any changes made in
response to OMB recommendations have been documented in the docket.
EPA prepared an analysis of the potential costs and benefits
associated with this action. This analysis, Addition of a Subsurface
Intrusion (SsI) Component to the Hazard Ranking System (HRS):
Regulatory Impact Analysis is available in the docket for this action.
B. Paperwork Reduction Act (PRA)
This action does not impose any new information collection burden
under the PRA. OMB has previously approved the information collection
activities contained in the existing regulations and has assigned OMB
control number 2050-0095.
This regulatory change will only affect how EPA and organizations
performing work on behalf of EPA (state or tribal partners) conduct
site assessments and HRS scoring at sites where certain environmental
conditions exist. This regulatory change will result in data collection
at these types of sites to allow evaluation under the HRS. EPA expects
that the total number of site assessments performed and the number of
sites added to the NPL per year will not increase, but rather expects
that there will be a realignment and reprioritization of its internal
resources and state cooperative agreement funding.
C. Regulatory Flexibility Act (RFA)
I certify that this action will not have a significant economic
impact on a substantial number of small entities under the RFA. This
action will not impose any requirements on small entities. This
regulatory change enables the HRS evaluation to directly consider human
exposure to hazardous substances that enter building structures through
subsurface intrusion. This addition to the HRS would not impose direct
impacts on any other entities. For additional discussion on this
subject, see section 4.9 of the Regulatory Impact Analysis (see the
docket for this action).
D. Unfunded Mandates Reform Act (UMRA)
This action does not contain any unfunded mandate as described in
UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect
small governments. The action imposes no enforceable duty on any state,
local, or tribal governments or the private sector.
E. Executive Order 13132: Federalism
This action does not have federalism implications. It will not have
substantial direct effects on the states, on the relationship between
the national government and the states, or on the distribution of power
and responsibilities among the various levels of government.
F. Executive Order 13175: Consultation and Coordination With Indian
Tribal Governments
This action does not have tribal implications, as specified in
Executive Order 13175. EPA's evaluation of a site using the HRS does
not impose any costs on a tribe (except those already in a cooperative
agreement relationship with EPA). Thus, Executive Order 13175 does not
apply to this action.
Although Executive Order 13175 does not apply to this action, EPA
consulted with tribal officials through meetings and correspondence,
including a letter sent to all federally recognized tribes asking for
comment on the ``Notice of Opportunity for Public Input'' that was
published in the Federal Register on January 31, 2011 (76 FR 5370), and
public listening sessions regarding the decision to proceed with the
development of this action. All tribal comments indicated support for
this action.
G. Executive Order 13045: Protection of Children From Environmental
Health Risks and Safety Risks
EPA interprets Executive Order 13045 as applying only to those
regulatory actions that concern environmental health or safety risks
that EPA has reason to believe may disproportionately affect children,
per the definition of ``covered regulatory action'' in section 2-202 of
the Executive Order. This action is not subject to Executive Order
13045 because it does not concern an environmental health risk or
safety risk.
H. Executive Order 13211: Actions Concerning Regulations That
Significantly Affect Energy Supply, Distribution or Use
This action is not a ``significant energy action'' because it is
not likely to have a significant adverse effect on the supply,
distribution, or use of energy. The site assessment activities affected
by this rule are limited in scope and number and rely on existing
energy distribution systems. Further, we have concluded that this rule
would not significantly expand the energy demand for site assessments,
and would not require an entity to conduct any action that would
require significant energy use, that would significantly affect energy
supply, distribution, or usage. Thus, Executive Order 13211 does not
apply to this action.
I. National Technology Transfer and Advancement Act
This rulemaking does not involve technical standards.
J. Executive Order 12898: Federal Actions To Address Environmental
Justice in Minority Populations and Low-Income Populations
The EPA believes the human health or environmental or environmental
risk addressed by this action will not have potential
disproportionately high and adverse human health or environmental
effects on, low-income or indigenous populations. The results of this
evaluation are contained in section 4.3 (and all subsections) of the
Regulatory Impact Analysis for this rulemaking. A copy of the Addition
of a Subsurface Intrusion (SsI) Component to the Hazard Ranking System
(HRS): Regulatory Impact Analysis is available in the docket for this
action.
K. Executive Order 12580--Superfund Implementation
Executive Order 12580, section 1(d), states that revisions to the
NCP shall be made in consultation with members of the National Response
Team (NRT) prior to publication for notice and comment. Revisions shall
also be made in consultation with the Director of the Federal Emergency
Management Agency (FEMA) and the Nuclear Regulatory Commission (NRC) to
avoid inconsistent or duplicative requirements in the emergency
planning responsibilities of those agencies. Executive Order 12580
delegates responsibility for revision of the NCP to EPA.
The agency has complied with Executive Order 12580 to the extent
that it is related to the addition of a new component to the HRS,
through consultation with members of the NRT.
L. Congressional Review Act (CRA)
This action is subject to the CRA, and the EPA will submit a rule
report to each House of the Congress and to the Comptroller General of
the United States. This action is not a ``major rule'' as defined by 5
U.S.C. 804(2).
List of Subjects in 40 CFR Part 300
Environmental protection, Air pollution control, Chemicals,
Hazardous substances, Hazardous waste, Intergovernmental relations,
Natural resources, Oil pollution, Penalties, Reporting and
recordkeeping
[[Page 2779]]
requirements, Superfund, Water pollution control, Water supply.
Dated: December 7, 2016.
Gina McCarthy,
Administrator.
For the reasons set out in the preamble, Title 40, Chapter 1 of the
Code of Federal Regulations is amended as follows:
PART 300--NATIONAL OIL AND HAZARDOUS SUBSTANCES POLLUTION
CONTINGENCY PLAN
0
1. The authority citation for part 300 continues to read as follows:
Authority: 33 U.S.C. 1321(d); 42 U.S.C. 9601-9657; E.O. 13626,
77 FR 56749, 3 CFR, 2013 Comp., p. 306; E.O. 12777, 56 FR 54757, 3
CFR, 1991 Comp., p. 351; E.O. 12580, 52 FR 2923, 3 CFR, 1987 Comp.,
p. 193.
0
2. Amend Appendix A to Part 300:
0
a. In section 1.1 by:
0
i. Removing the definition heading ``Ambient Water Quality Criteria
(AWQC) and adding ``Ambient Water Quality Criteria (AWQC)/National
Recommended Water Quality Criteria'', in its place; and removing the
text ``maximum acute or chronic toxicity'' and adding ``maximum acute
(Criteria Maximum Concentration or CMC) or chronic (Criterion
Continuous Concentration or CCC) toxicity.'' in its place;
0
ii. Adding in alphabetical order the definition ``Channelized flow'';
0
iii. Revising the definition ``Chronic toxicity'';
0
iv. Adding in alphabetical order the definition ``Crawl space'';
0
v. Revising the definitions ``Distance weight'' and ``Half-life'';
0
vi. Amending the definition ``HRS pathway'' by removing the word
``soil,'' and adding ``soil exposure and subsurface intrusion,'' in its
place;
0
vii. Adding in alphabetical order the definitions ``Indoor air'',
``Inhalation Unit Risk (IUR)'', ``Non-Aqueous Phase Liquid (NAPL)'',
``Preferential subsurface intrusion pathways'', and ``Reference
concentration (RfC)'';
0
viii. Revising the definition ``Reference dose (RfD)'';
0
ix. Adding in alphabetical order the definition ``Regularly occupied
structures'';
0
x. Revising the definition ``Screening concentration'';
0
xi. Adding in alphabetical order the definition ``Shallow ground
water'';
0
xii. Revising the definition ``Slope factor (also referred to as cancer
potency factor)'';
0
xiii. Adding in alphabetical order the definitions ``Soil gas'', ``Soil
porosity''; ``Subslab'', ``Subsurface intrusion'', ``Unit risk'', and
``Unsaturated zone''; and
0
xiv. Revising the definition ``Weight-of-evidence''.
0
b. Revising section 2.0;
0
c. Revising section 5.0;
0
d. In section 6.0 by revising Table 6-14; and
0
e. In section 7.0 by:
0
i. Revising Table 7-1;
0
ii. Under Table 7-1, the second undesignated paragraph, revising the
third sentence;
0
iii. Revising sections 7.1, 7.1.1, and 7.1.2; 7.2.1; 7.2.3; 7.2.4;
7.2.5.1, 7.2.5.1.1 through 7.2.5.1.3; 7.2.5.2; 7.2.5.3; 7.3, 7.3.1, and
7.3.2; and
0
iv. Adding section 7.3.3.
The revisions and additions read as follows:
Appendix A to Part 300--Hazard Ranking System
* * * * *
1.1 Definitions
* * * * *
Channelized flow: Natural geological or manmade features such as
karst, fractures, lava tubes, and utility conduits (e.g., sewer
lines), which allow ground water and/or soil gas to move through the
subsurface environment more easily.
Chronic toxicity: Measure of toxicological responses that result
from repeated exposure to a substance over an extended period of
time (typically 3 months or longer). Such responses may persist
beyond the exposure or may not appear until much later in time than
the exposure. HRS measures of chronic toxicity include Reference
Dose (RfD) and Reference Concentration (RfC) values.
* * * * *
Crawl space: The enclosed or semi-enclosed area between a
regularly occupied structure's foundation (e.g., pier and beam
construction) and the ground surface. Crawl space samples are
collected to determine the concentration of hazardous substances in
the air beneath a regularly occupied structure.
* * * * *
Distance weight: Parameter in the HRS air migration pathway,
ground water migration pathway, and the soil exposure component of
the soil exposure and subsurface intrusion pathway that reduces the
point value assigned to targets as their distance increases from the
site. [unitless].
* * * * *
Half-life: Length of time required for an initial concentration
of a substance to be halved as a result of loss through decay. The
HRS considers five decay processes for assigning surface water
persistence: Biodegradation, hydrolysis, photolysis, radioactive
decay, and volatilization. The HRS considers two decay processes for
assigning subsurface intrusion degradation: Biodegradation and
hydrolysis.
* * * * *
Indoor air: The air present within a structure.
Inhalation Unit Risk (IUR): The upper-bound excess lifetime
cancer risk estimated to result from continuous exposure to an agent
(i.e., hazardous substance) at a concentration of 1[mu]g/m\3\ in
air.
* * * * *
Non-Aqueous Phase Liquid (NAPL): Contaminants and substances
that are water-immiscible liquids composed of constituents with
varying degrees of water solubility.
* * * * *
Preferential subsurface intrusion pathways: Subsurface features
such as animal burrows, cracks in walls, spaces around utility
lines, or drains through which a hazardous substance moves more
easily into a regularly occupied structure.
* * * * *
Reference concentration (RfC): An estimate of a continuous
inhalation exposure to the human population that is likely to be
without an appreciable risk of deleterious effects during a
lifetime.
Reference dose (RfD): An estimate of a daily oral exposure to
the human population that is likely to be without an appreciable
risk of deleterious effects during a lifetime.
Regularly occupied structures: Structures with enclosed air
space, where people either reside, attend school or day care, or
work on a regular basis, or that were previously occupied but
vacated due to a site-related hazardous substance(s). This also
includes resource structures (e.g., library, church, tribal
structure).
* * * * *
Screening concentration: Media-specific benchmark concentration
for a hazardous substance that is used in the HRS for comparison
with the concentration of that hazardous substance in a sample from
that media. The screening concentration for a specific hazardous
substance corresponds to its reference concentration for inhalation
exposures or reference dose for oral exposures, as appropriate, and,
if the substance is a human carcinogen with either a weight-of-
evidence classification of A, B, or C, or a weight-of-evidence
classification of carcinogenic to humans, likely to be carcinogenic
to humans or suggestive evidence of carcinogenic potential, to that
concentration that corresponds to its 10-6 individual
lifetime excess cancer risk for inhalation exposures or for oral
exposures, as appropriate.
Shallow ground water: The uppermost saturated zone, typically
unconfined.
* * * * *
Slope factor (also referred to as cancer potency factor):
Estimate of the probability of response (for example, cancer) per
unit intake of a substance over a lifetime. The slope factor is
typically used to estimate upper-bound probability of an individual
developing cancer as a result of exposure to a particular level of a
human carcinogen with either a weight-of-evidence classification of
A, B, or C, or a weight-of-evidence classification of carcinogenic
to humans, likely to be carcinogenic to humans or having suggestive
evidence of carcinogenic potential. [(mg/kg-day)-1 for
non-radioactive substances and (pCi)-1 for radioactive
substances].
[[Page 2780]]
Soil gas: The gaseous elements and compounds in the small spaces
between particles of soil.
Soil porosity: The degree to which the total volume of soil is
permeated with pores or cavities through which fluids (including air
or gas) can move. It is typically calculated as the ratio of the
pore spaces within the soil to the overall volume of the soil.
* * * * *
Subslab: The area immediately beneath a regularly occupied
structure with a basement foundation or a slab-on-grade foundation.
Subslab samples are collected to determine the concentration of
hazardous substances in the soil gas beneath a home or building.
Subsurface intrusion: The migration of hazardous substances from
the unsaturated zone and/or ground water into overlying structures.
* * * * *
Unit risk: The upper-bound excess lifetime cancer risk estimated
to result from continuous exposure to an agent (i.e., hazardous
substance) at a concentration of 1 [mu]g/L in water, or 1 [mu]g/m\3\
in air.
Unsaturated zone: The portion of subsurface between the land
surface and the zone of saturation. It extends from the ground
surface to the top of the shallowest ground water table (excluding
localized or perched water).
* * * * *
Weight-of-evidence: EPA classification system for characterizing
the evidence supporting the designation of a substance as a human
carcinogen. The EPA weight-of-evidence, depending on the date EPA
updated the profile, includes either the groupings:
Group A: Human carcinogen--sufficient evidence of
carcinogenicity in humans.
Group B1: Probable human carcinogen--limited evidence
of carcinogenicity in humans.
Group B2: Probable human carcinogen--sufficient
evidence of carcinogenicity in animals.
Group C: Possible human carcinogen--limited evidence of
carcinogenicity in animals.
Group D: Not classifiable as to human carcinogenicity--
applicable when there is no animal evidence, or when human or animal
evidence is inadequate.
Group E: Evidence of noncarcinogenicity for humans.
Or the descriptors:
Carcinogenic to humans.
Likely to be carcinogenic to humans.
Suggestive evidence of carcinogenic potential.
Inadequate information to assess carcinogenic
potential.
Not likely to be carcinogenic to humans.
2.0 Evaluations Common to Multiple Pathways
2.1 Overview. The HRS site score (S) is the result of an
evaluation of four pathways:
Ground Water Migration (Sgw).
Surface Water Migration (Ssw).
Soil Exposure and Subsurface Intrusion
(Ssessi).
Air Migration (Sa).
The ground water and air migration pathways use single threat
evaluations, while the surface water migration and soil exposure and
subsurface intrusion pathways use multiple threat evaluations. Three
threats are evaluated for the surface water migration pathway:
Drinking water, human food chain, and environmental. These threats
are evaluated for two separate migration components--overland/flood
migration and ground water to surface water migration. Two
components are evaluated for the soil exposure and subsurface
intrusion pathway: Soil exposure and subsurface intrusion. The soil
exposure component evaluates two threats: Resident population and
nearby population, and the subsurface intrusion component is a
single threat evaluation.
The HRS is structured to provide a parallel evaluation for each
of these pathways, components, and threats. This section focuses on
these parallel evaluations, starting with the calculation of the HRS
site score and the individual pathway scores.
2.1.1 Calculation of HRS site score. Scores are first calculated
for the individual pathways as specified in sections 2 through 7 and
then are combined for the site using the following root-mean-square
equation to determine the overall HRS site score, which ranges from
0 to 100:
[GRAPHIC] [TIFF OMITTED] TR09JA17.062
2.1.2 Calculation of pathway score. Table 2-1, which is based on
the air migration pathway, illustrates the basic parameters used to
calculate a pathway score. As Table 2-1 shows, each pathway
(component or threat) score is the product of three ``factor
categories'': Likelihood of release, waste characteristics, and
targets. (The soil exposure and subsurface intrusion pathway uses
likelihood of exposure rather than likelihood of release.) Each of
the three factor categories contains a set of factors that are
assigned numerical values and combined as specified in sections 2
through 7. The factor values are rounded to the nearest integer,
except where otherwise noted.
2.1.3 Common evaluations. Evaluations common to all four HRS
pathways include:
Characterizing sources.
--Identifying sources (and, for the soil exposure and subsurface
intrusion pathway, areas of observed contamination, areas of
observed exposure and/or areas of subsurface contamination [see
sections 5.1.0 and 5.2.0]).
--Identifying hazardous substances associated with each source
(or area of observed contamination, or observed exposure, or
subsurface contamination).
--Identifying hazardous substances available to a pathway.
Table 2-1--Sample Pathway Scoresheet
------------------------------------------------------------------------
Value
Factor category Maximum value assigned
------------------------------------------------------------------------
Likelihood of Release
------------------------------------------------------------------------
1. Observed Release..................... 550 ..............
2. Potential to Release................. 500 ..............
3. Likelihood of Release (higher of 550 ..............
lines 1 and 2).........................
------------------------------------------------------------------------
Waste Characteristics
------------------------------------------------------------------------
4. Toxicity/Mobility.................... (\a\) ..............
5. Hazardous Waste Quantity............. (\a\) ..............
6. Waste Characteristics................ 100 ..............
------------------------------------------------------------------------
Targets
------------------------------------------------------------------------
7. Nearest Individual................... .............. ..............
7a. Level I......................... 50 ..............
7b. Level II........................ 45 ..............
7c. Potential Contamination......... 20 ..............
7d. Nearest Individual (higher of 50 ..............
lines 7a, 7b, or 7c)...............
8. Population........................... (\b\) ..............
8a. Level I......................... (\b\) ..............
8b. Level II........................ (\b\) ..............
[[Page 2781]]
8c. Potential Contamination......... (\b\) ..............
8d. Total Population (lines .............. ..............
8a+8b+8c)..........................
9. Resources............................ 5 ..............
10. Sensitive Environments.............. (\b\) ..............
10a. Actual Contamination........... (\b\) ..............
10b. Potential Environments......... (\b\) ..............
10c. Sensitive Environments (lines (\b\) ..............
10a+10b)...........................
11. Targets (lines 7d+8d+9+10c)......... (\b\) ..............
12. Pathway Score is the product of
Likelihood of Release, Waste
Characteristics, and Targets, divided
by 82,500. Pathway scores are limited
to a maximum of 100 points.............
------------------------------------------------------------------------
\a\ Maximum value applies to waste characteristics category. The product
of lines 4 and 5 is used in Table 2-7 to derive the value for the
waste characteristics factor category.
\b\ There is no limit to the human population or sensitive environments
factor values. However, the pathway score based solely on sensitive
environments is limited to a maximum of 60 points.
Scoring likelihood of release (or likelihood of exposure)
factor category.
--Scoring observed release (or observed exposure or observed
contamination).
--Scoring potential to release when there is no observed
release.
Scoring waste characteristics factor category.
--Evaluating toxicity.
[ssquf] Combining toxicity with mobility, persistence,
degradation and/or bioaccumulation (or ecosystem bioaccumulation)
potential, as appropriate to the pathway (component or threat).
[ssquf] Evaluating hazardous waste quantity.
--Combining hazardous waste quantity with the other waste
characteristics factors.
[ssquf] Determining waste characteristics factor category value.
Scoring targets factor category.
--Determining level of contamination for targets.
These evaluations are essentially identical for the three
migration pathways (ground water, surface water, and air). However,
the evaluations differ in certain respects for the soil exposure and
subsurface intrusion pathway.
Section 7 specifies modifications that apply to each pathway
when evaluating sites containing radioactive substances.
Section 2 focuses on evaluations common at the pathway,
component, and threat levels. Note that for the ground water and
surface water migration pathways, separate scores are calculated for
each aquifer (see section 3.0) and each watershed (see sections
4.1.1.3 and 4.2.1.5) when determining the pathway scores for a site.
Although the evaluations in section 2 do not vary when different
aquifers or watersheds are scored at a site, the specific factor
values (for example, observed release, hazardous waste quantity,
toxicity/mobility) that result from these evaluations can vary by
aquifer and by watershed at the site. This can occur through
differences both in the specific sources and targets eligible to be
evaluated for each aquifer and watershed and in whether observed
releases can be established for each aquifer and watershed. Such
differences in scoring at the aquifer and watershed level are
addressed in sections 3 and 4, not section 2.
2.2 Characterize sources. Source characterization includes
identification of the following:
Sources (and areas of observed contamination, areas of
observed exposure, or areas of subsurface contamination) at the
site.
Hazardous substances associated with these sources (or
areas of observed contamination, areas of observed exposure, or
areas of subsurface contamination).
Pathways potentially threatened by these hazardous
substances.
Table 2-2 presents a sample worksheet for source
characterization.
2.2.1 Identify sources. For the three migration pathways,
identify the sources at the site that contain hazardous substances.
Identify the migration pathway(s) to which each source applies. For
the soil exposure and subsurface intrusion pathway, identify areas
of observed contamination, areas of observed exposure, and/or areas
of subsurface contamination at the site (see sections 5.1.0 and
5.2.0).
Table 2-2--Sample Source Characterization Worksheet
Source: __
A. Source dimensions and hazardous waste quantity.
Hazardous constituent quantity: __
Hazardous wastestream quantity: __
Volume: __
Area: __
Area of observed contamination: __
Area of observed exposure: __
Area of subsurface contamination: __
B. Hazardous substances associated with the source.
--------------------------------------------------------------------------------------------------------------------------------------------------------
Available to pathway
---------------------------------------------------------------------------------------------------------------------------
Air Surface Water (SW) Soil Exposure/Subsurface Intrusion (SESSI)
-------------------------- ------------------------------------------------------------------------------------
Hazardous substance Soil exposure Subsurface Intrusion
Ground ----------------------------------------------------------
Gas Particulate Water (GW) Overland/ GW to SW Area of Area of
flood Resident Nearby observed subsurface
exposure contamination
--------------------------------------------------------------------------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------------------------------------------------------------------------
--------------------------------------------------------------------------------------------------------------------------------------------------------
2.2.2 Identify hazardous substances associated with a source.
For each of the three migration pathways, consider those hazardous
substances documented in a source (for example, by sampling, labels,
manifests, oral or written statements) to be
[[Page 2782]]
associated with that source when evaluating each pathway. In some
instances, a hazardous substance can be documented as being present
at a site (for example, by labels, manifests, oral or written
statements), but the specific source(s) containing that hazardous
substance cannot be documented. For the three migration pathways, in
those instances when the specific source(s) cannot be documented for
a hazardous substance, consider the hazardous substance to be
present in each source at the site, except sources for which
definitive information indicates that the hazardous substance was
not or could not be present.
For an area of observed contamination in the soil exposure
component of the soil exposure and subsurface intrusion pathway,
consider only those hazardous substances that meet the criteria for
observed contamination for that area (see section 5.1.0) to be
associated with that area when evaluating the pathway.
For an area of observed exposure or area of subsurface
contamination (see section 5.2.0) in the subsurface intrusion
component of the soil exposure and subsurface intrusion pathway,
consider only those hazardous substances that:
Meet the criteria for observed exposure, or
Meet the criteria for observed release in an area of
subsurface contamination and have a vapor pressure greater than or
equal to one torr or a Henry's constant greater than or equal to
10-\5\ atm-m\3\/mol, or
Meet the criteria for an observed release in a
structure within, or in a sample from below, an area of observed
exposure and have a vapor pressure greater than or equal to one torr
or a Henry's constant greater than or equal to 10-\5\
atm-m\3\/mol.
2.2.3 Identify hazardous substances available to a pathway. In
evaluating each migration pathway, consider the following hazardous
substances available to migrate from the sources at the site to the
pathway:
Ground water migration.
--Hazardous substances that meet the criteria for an observed
release (see section 2.3) to ground water.
--All hazardous substances associated with a source with a
ground water containment factor value greater than 0 (see section
3.1.2.1).
Surface water migration--overland/flood component.
--Hazardous substances that meet the criteria for an observed
release to surface water in the watershed being evaluated.
--All hazardous substances associated with a source with a
surface water containment factor value greater than 0 for the
watershed (see sections 4.1.2.1.2.1.1 and 4.1.2.1.2.2.1).
Surface water migration--ground water to surface water
component.
--Hazardous substances that meet the criteria for an observed
release to ground water.
--All hazardous substances associated with a source with a
ground water containment factor value greater than 0 (see sections
4.2.2.1.2 and 3.1.2.1).
Air migration.
--Hazardous substances that meet the criteria for an observed
release to the atmosphere.
--All gaseous hazardous substances associated with a source with
a gas containment factor value greater than 0 (see section
6.1.2.1.1).
--All particulate hazardous substances associated with a source
with a particulate containment factor value greater than 0 (see
section 6.1.2.2.1).
For each migration pathway, in those instances when the
specific source(s) containing the hazardous substance cannot be
documented, consider that hazardous substance to be available to
migrate to the pathway when it can be associated (see section 2.2.2)
with at least one source having a containment factor value greater
than 0 for that pathway.
In evaluating the soil exposure and subsurface intrusion
pathway, consider the following hazardous substances available to
the pathway:
Soil exposure component--resident population threat.
--All hazardous substances that meet the criteria for observed
contamination at the site (see section 5.1.0).
Soil exposure component--nearby population threat.
--All hazardous substances that meet the criteria for observed
contamination at areas with an attractiveness/accessibility factor
value greater than 0 (see section 5.1.2.1.1).
Subsurface intrusion component.
--All hazardous substances that meet the criteria for observed
exposure at the site (see section 5.2.0).
--All hazardous substances with a vapor pressure greater than or
equal to one torr or a Henry's constant greater than or equal to
10-\5\ atm-m\3\/mol that meet the criteria for an
observed release in an area of subsurface contamination (see section
5.2.0).
--All hazardous substances that meet the criteria for an
observed release in a structure within, or in a sample from below,
an area of observed exposure (see section 5.2.0).
2.3 Likelihood of release. Likelihood of release is a measure of
the likelihood that a waste has been or will be released to the
environment. The likelihood of release factor category is assigned
the maximum value of 550 for a migration pathway whenever the
criteria for an observed release are met for that pathway. If the
criteria for an observed release are met, do not evaluate potential
to release for that pathway. When the criteria for an observed
release are not met, evaluate potential to release for that pathway,
with a maximum value of 500. The evaluation of potential to release
varies by migration pathway (see sections 3, 4 and 6).
Establish an observed release either by direct observation of
the release of a hazardous substance into the media being evaluated
(for example, surface water) or by chemical analysis of samples
appropriate to the pathway being evaluated (see sections 3, 4 and
6). The minimum standard to establish an observed release by
chemical analysis is analytical evidence of a hazardous substance in
the media significantly above the background level. Further, some
portion of the release must be attributable to the site. Use the
criteria in Table 2-3 as the standard for determining analytical
significance. (The criteria in Table 2-3 are also used in
establishing observed contamination for the soil exposure component
and for establishing areas of observed exposure and areas of
subsurface contamination in the subsurface intrusion component of
the soil exposure and subsurface intrusion pathway, see section
5.1.0 and section 5.2.0). Separate criteria apply to radionuclides
(see section 7.1.1).
Table 2-3--Observed Release Criteria for Chemical Analysis
------------------------------------------------------------------------
-------------------------------------------------------------------------
Sample Measurement < Sample Quantitation Limit.\a\
No observed release is established.
Sample Measurement >= Sample Quantitation Limit.\a\
An observed release is established as follows:
If the background concentration is not detected (or is less
than the detection limit), an observed release is established when
the sample measurement equals or exceeds the sample quantitation
limit.\a\
If the background concentration equals or exceeds the
detection limit, an observed release is established when the sample
measurement is 3 times or more above the background concentration.
------------------------------------------------------------------------
\a\ If the sample quantitation limit (SQL) cannot be established,
determine if there is an observed release as follows:
--If the sample analysis was performed under the EPA Contract Laboratory
Program, use the EPA contract-required quantitation limit (CRQL) in
place of the SQL.
--If the sample analysis is not performed under the EPA Contract
Laboratory Program, use the detection limit (DL) in place of the SQL.
2.4 Waste characteristics. The waste characteristics factor
category includes the following factors: Hazardous waste quantity,
toxicity, and as appropriate to the pathway or threat being
evaluated, mobility, persistence, degradation, and/or
[[Page 2783]]
bioaccumulation (or ecosystem bioaccumulation) potential.
2.4.1 Selection of substance potentially posing greatest hazard.
For all pathways (components and threats), select the hazardous
substance potentially posing the greatest hazard for the pathway
(component or threat) and use that substance in evaluating the waste
characteristics category of the pathway (component or threat). For
the three migration pathways (and threats), base the selection of
this hazardous substance on the toxicity factor value for the
substance, combined with its mobility, persistence, and/or
bioaccumulation (or ecosystem bioaccumulation) potential factor
values, as applicable to the migration pathway (or threat). For the
soil exposure component of the soil exposure and subsurface
intrusion pathway, base the selection on the toxicity factor alone.
For the subsurface intrusion component of the soil exposure and
subsurface intrusion pathway, base the selection on the toxicity
factor value for the substance, combined with its degradation factor
value. Evaluation of the toxicity factor is specified in section
2.4.1.1. Use and evaluation of the mobility, persistence,
degradation, and/or bioaccumulation (or ecosystem bioaccumulation)
potential factors vary by pathway (component or threat) and are
specified under the appropriate pathway (component or threat)
section. Section 2.4.1.2 identifies the specific factors that are
combined with toxicity in evaluating each pathway (component or
threat).
2.4.1.1 Toxicity factor. Evaluate toxicity for those hazardous
substances at the site that are available to the pathway being
scored. For all pathways and threats, except the surface water
environmental threat, evaluate human toxicity as specified below.
For the surface water environmental threat, evaluate ecosystem
toxicity as specified in section 4.1.4.2.1.1.
Establish human toxicity factor values based on quantitative
dose-response parameters for the following three types of toxicity:
Cancer--Use slope factors (also referred to as cancer
potency factors) combined with weight-of-evidence ratings for
carcinogenicity for all exposure routes except inhalation. Use
inhalation unit risk (IUR) for inhalation exposure. If an inhalation
unit risk or a slope factor is not available for a substance, use
its ED10 value to estimate a slope factor as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.063
Noncancer toxicological responses of chronic exposure--
use reference dose (RfD) or reference concentration (RfC) values as
applicable.
Noncancer toxicological responses of acute exposure--
use acute toxicity parameters, such as the LD50.
Assign human toxicity factor values to a hazardous substance
using Table 2-4, as follows:
If RfD/RfC and slope factor/inhalation unit risk values
are available for the hazardous substance, assign the substance a
value from Table 2-4 for each. Select the higher of the two values
assigned and use it as the overall toxicity factor value for the
hazardous substance.
If either an RfD/RfC or slope factor/inhalation unit
risk value is available, but not both, assign the hazardous
substance an overall toxicity factor value from Table 2-4 based
solely on the available value (RfD/RfC or slope factor/inhalation
unit risk).
If neither an RfD/RfC nor slope factor/inhalation unit
risk value is available, assign the hazardous substance an overall
toxicity factor value from Table 2-4 based solely on acute toxicity.
That is, consider acute toxicity in Table 2-4 only when both RfD/RfC
and slope factor/IUR values are not available.
If neither an RfD/RfC, nor slope factor/inhalation unit
risk, nor acute toxicity value is available, assign the hazardous
substance an overall toxicity factor value of 0 and use other
hazardous substances for which information is available in
evaluating the pathway.
Table 2-4--Toxicity Factor Evaluation
------------------------------------------------------------------------
Assigned value
------------------------------------------------------------------------
Chronic Toxicity (Human)
------------------------------------------------------------------------
Reference dose (RfD) (mg/kg-day):
RfD < 0.0005.......................................... 10,000
0.0005 <= RfD < 0.005................................. 1,000
0.005 <= RfD < 0.05................................... 100
0.05 <= RfD < 0.5..................................... 10
0.5 <= RfD............................................ 1
RfD not available..................................... 0
Reference concentration (RfC) (mg/m\3\):
RfC < 0.0001.......................................... 10,000
0.0001 <= RfC < 0.006................................. 1,000
0.006 <= RfC < 0.2.................................... 100
0.2 <= RfC < 2.0...................................... 10
2.0 <= RfC............................................ 1
RfC not available..................................... 0
------------------------------------------------------------------------
----------------------------------------------------------------------------------------------------------------
Carcinogenicity (human)
-----------------------------------------------------------------------------------------------------------------
B or Likely to be C or Suggestive evidence
A or Carcinogenic to humans carcinogenic to humans of carcinogenic potential Assigned value
----------------------------------------------------------------------------------------------------------------
Weight-of-evidencea/Slope factor (mg/kg-day)-1
----------------------------------------------------------------------------------------------------------------
0.5 <= SF \b\........................... 5 <= SF................... 50 <= SF.................. 10,000
0.05 <= SF < 0.5........................ 0.5 <= SF < 5............. 5 <= SF < 50.............. 1,000
SF < 0.05............................... 0.05 <= SF < 0.5.......... 0.5 <= SF < 5............. 100
SF < 0.05................. SF < 0.5.................. 10
Slope factor not available.............. Slope factor not available Slope factor not available 0
----------------------------------------------------------------------------------------------------------------
Weight-of-evidence a/Inhalation unit risk ([mu]g/m3)
----------------------------------------------------------------------------------------------------------------
0.00004 <= IUR \c\...................... 0.0004 <= IUR............. 0.004 <= IUR.............. 10,000
0.00001 <= IUR < 0.00004................ 0.0001 <= IUR < 0.0004.... 0.001 <= IUR < 0.004...... 1,000
IUR < 0.00001........................... 0.00001 <= IUR < 0.0001... 0.0001 <= IUR < 0.001..... 100
< 0.00001................. IUR < 0.0001.............. 10
Inhalation unit risk not available...... Inhalation unit risk not Inhalation unit risk not 0
available. available.
----------------------------------------------------------------------------------------------------------------
\a\ A, B, and C, as well as Carcinogenic to humans, Likely to be carcinogenic to humans, and Suggestive evidence
of carcinogenic potential refer to weight-of-evidence categories. Assign substances with a weight-of-evidence
category of D (inadequate evidence of carcinogenicity) or E (evidence of lack of carcinogenicity), as well as
inadequate information to assess carcinogenic potential and not likely to be carcinogenic to humans a value of
0 for carcinogenicity.
\b\ SF = Slope factor.
\c\ IUR = Inhalation Unit Risk.
----------------------------------------------------------------------------------------------------------------
Acute Toxicity (human)
-----------------------------------------------------------------------------------------------------------------
Dermal LD50 (mg/kg) Dust or mist LC50 Gas or vapor LC50
Oral LD50 (mg/kg) (mg/l) (ppm) Assigned value
----------------------------------------------------------------------------------------------------------------
LD50 < 5......................... LD50 < 2........... LC50 < 0.2......... LC50 < 20.......... 1,000
[[Page 2784]]
5 <= LD50 < 50................... 2 <= LD50 < 20..... 0.2 <= LC50 < 2.... 20 <= LC50 <200.... 100
50 <= LD50 < 500................. 20 <= LD50 < 200... 2 <= LC50 <20...... 200 <= LC50 <2,000. 10
500 <= LD50...................... 200 <= LD50........ 20 <= LC50......... 2,000 <= LC50...... 1
LD50 not available............... LD50 not available. LC50 not available. LC50 not available. 0
----------------------------------------------------------------------------------------------------------------
If a toxicity factor value of 0 is assigned to all hazardous
substances available to a particular pathway (that is, insufficient
toxicity data are available for evaluating all the substances), use
a default value of 100 as the overall human toxicity factor value
for all hazardous substances available to the pathway. For hazardous
substances having usable toxicity data for multiple exposure routes
(for example, inhalation and ingestion), consider all exposure
routes and use the highest assigned value, regardless of exposure
route, as the toxicity factor value. For HRS purposes, assign both
asbestos and lead (and its compounds) a human toxicity factor value
of 10,000.
Separate criteria apply for assigning factor values for human
toxicity and ecosystem toxicity for radionuclides (see sections
7.2.1 and 7.2.2).
2.4.1.2 Hazardous substance selection. For each hazardous
substance evaluated for a migration pathway (or threat), combine the
human toxicity factor value (or ecosystem toxicity factor value) for
the hazardous substance with a mobility, persistence, and/or
bioaccumulation (or ecosystem bioaccumulation) potential factor
value as follows:
Ground water migration.
--Determine a combined human toxicity/mobility factor value for
the hazardous substance (see section 3.2.1).
Surface water migration--overland/flood migration
component.
--Determine a combined human toxicity/persistence factor value
for the hazardous substance for the drinking water threat (see
section 4.1.2.2.1).
--Determine a combined human toxicity/persistence/
bioaccumulation factor value for the hazardous substance for the
human food chain threat (see section 4.1.3.2.1).
--Determine a combined ecosystem toxicity/persistence/
bioaccumulation factor value for the hazardous substance for the
environmental threat (see section 4.1.4.2.1).
Surface water migration--ground water to surface water
migration component.
--Determine a combined human toxicity/mobility/persistence
factor value for the hazardous substance for the drinking water
threat (see section 4.2.2.2.1).
--Determine a combined human toxicity/mobility/persistence/
bioaccumulation factor value for the hazardous substance for the
human food chain threat (see section 4.2.3.2.1).
--Determine a combined ecosystem toxicity/mobility/persistence/
bioaccumulation factor value for the hazardous substance for the
environmental threat (see section 4.2.4.2.1).
Air migration.
--Determine a combined human toxicity/mobility factor value for
the hazardous substance (see section 6.2.1).
Determine each combined factor value for a hazardous substance
by multiplying the individual factor values appropriate to the
pathway (or threat). For each migration pathway (or threat) being
evaluated, select the hazardous substance with the highest combined
factor value and use that substance in evaluating the waste
characteristics factor category of the pathway (or threat).
For the soil exposure and subsurface intrusion pathway,
determine toxicity and toxicity/degradation factor values as
follows:
Soil exposure and subsurface intrusion--soil exposure
component.
--Select the hazardous substance with the highest human toxicity
factor value from among the substances that meet the criteria for
observed contamination for the threat evaluated and use that
substance in evaluating the waste characteristics factor category
(see section 5.1.1.2.1).
Soil exposure and subsurface intrusion--subsurface
intrusion component.
--Determine a combined human toxicity/degradation factor value
for each hazardous substance being evaluated that:
[ssquf] Meets the criteria for observed exposure, or
[ssquf] Meets the criteria for observed release in an area of
subsurface contamination and has a vapor pressure greater than or
equal to one torr or a Henry's constant greater than or equal to
10-5 atm-m\3\/mol, or
[ssquf] Meets the criteria for an observed release in a
structure within, or in a sample from below, an area of observed
exposure and has a vapor pressure greater than or equal to one torr
or a Henry's constant greater than or equal to 10-5 atm-
m\3\/mol.
--Select the hazardous substance with the highest combined
factor value and use that substance in evaluating the waste
characteristics factor category (see sections 5.2.1.2.1 and
5.2.1.2).
2.4.2 Hazardous waste quantity. Evaluate the hazardous waste
quantity factor by first assigning each source (or area of observed
contamination, area of observed exposure, or area of subsurface
contamination) a source hazardous waste quantity value as specified
below. Sum these values to obtain the hazardous waste quantity
factor value for the pathway being evaluated.
In evaluating the hazardous waste quantity factor for the three
migration pathways, allocate hazardous substances and hazardous
wastestreams to specific sources in the manner specified in section
2.2.2, except: Consider hazardous substances and hazardous
wastestreams that cannot be allocated to any specific source to
constitute a separate ``unallocated source'' for purposes of
evaluating only this factor for the three migration pathways. Do
not, however, include a hazardous substance or hazardous wastestream
in the unallocated source for a migration pathway if there is
definitive information indicating that the substance or wastestream
could only have been placed in sources with a containment factor
value of 0 for that migration pathway.
In evaluating the hazardous waste quantity factor for the soil
exposure component of the soil exposure and subsurface intrusion
pathway, allocate to each area of observed contamination only those
hazardous substances that meet the criteria for observed
contamination for that area of observed contamination and only those
hazardous wastestreams that contain hazardous substances that meet
the criteria for observed contamination for that area of observed
contamination. Do not consider other hazardous substances or
hazardous wastestreams at the site in evaluating this factor for the
soil exposure component of the soil exposure and subsurface
intrusion pathway.
In evaluating the hazardous waste quantity factor for the
subsurface intrusion component of the soil exposure and subsurface
intrusion pathway, allocate to each area of observed exposure or
area of subsurface contamination only those hazardous substances and
hazardous wastestreams that contain hazardous substances that:
Meet the criteria for observed exposure, or
Meet the criteria for observed release in an area of
subsurface contamination and have a vapor pressure greater than or
equal to one torr or a Henry's constant greater than or equal to
10-5 atm-m\3\/mol, or
Meet the criteria for an observed release in a structure
within, or in a sample from below, an area of observed exposure and
have a vapor pressure greater than or equal to one torr or a Henry's
constant greater than or equal to 10-5 atm-m\3\/mol.
Do not consider other hazardous substances or hazardous
wastestreams at the site in evaluating this factor for the
subsurface intrusion component of the soil exposure and subsurface
intrusion pathway. When determining the hazardous waste quantity for
multi-subunit structures, use the procedures identified in section
5.2.1.2.2.
2.4.2.1 Source hazardous waste quantity. For each of the three
migration pathways, assign a source hazardous waste quantity
[[Page 2785]]
value to each source (including the unallocated source) having a
containment factor value greater than 0 for the pathway being
evaluated. Consider the unallocated source to have a containment
factor value greater than 0 for each migration pathway.
For the soil exposure component of the soil exposure and
subsurface intrusion pathway, assign a source hazardous waste
quantity value to each area of observed contamination, as applicable
to the threat being evaluated.
For the subsurface intrusion component of the soil exposure and
subsurface intrusion pathway, assign a source hazardous waste
quantity value to each regularly occupied structure within an area
of observed exposure or an area of subsurface contamination that has
a structure containment factor value greater than 0. If sufficient
data is available and state of the science shows there is no
unacceptable risk due to subsurface intrusion into a regularly
occupied structure located within an area of subsurface
contamination, that structure can be excluded from the area of
subsurface contamination.
For determining all hazardous waste quantity calculations except
for an unallocated source or an area of subsurface contamination,
evaluate using the following four measures in the following
hierarchy:
Hazardous constituent quantity.
Hazardous wastestream quantity.
Volume.
Area.
For the unallocated source, use only the first two measures. For
an area of subsurface contamination, evaluate non-radioactive
hazardous substances using only the last two measures and evaluate
radioactive hazardous substances using hazardous wastestream
quantity only. See also section 7.0 regarding the evaluation of
radioactive substances.
Separate criteria apply for assigning a source hazardous waste
quantity value for radionuclides (see section 7.2.5).
2.4.2.1.1 Hazardous constituent quantity. Evaluate hazardous
constituent quantity for the source (or area of observed
contamination) based solely on the mass of CERCLA hazardous
substances (as defined in CERCLA section 101(14), as amended)
allocated to the source (or area of observed contamination), except:
For a hazardous waste listed pursuant to section 3001
of the Solid Waste Disposal Act, as amended by the Resource
Conservation and Recovery Act of 1976 (RCRA), 42 U.S.C. 6901 et
seq., determine its mass for the evaluation of this measure as
follows:
--If the hazardous waste is listed solely for Hazard Code T (toxic
waste), include only the mass of constituents in the hazardous waste
that are CERCLA hazardous substances and not the mass of the entire
hazardous waste.
--If the hazardous waste is listed for any other Hazard Code
(including T plus any other Hazard Code), include the mass of the
entire hazardous waste.
For a RCRA hazardous waste that exhibits the
characteristics identified under section 3001 of RCRA, as amended,
determine its mass for the evaluation of this measure as follows:
--If the hazardous waste exhibits only the characteristic of
toxicity (or only the characteristic of EP toxicity), include only
the mass of constituents in the hazardous waste that are CERCLA
hazardous substances and not the mass of the entire hazardous waste.
--If the hazardous waste exhibits any other characteristic
identified under section 3001 (including any other characteristic
plus the characteristic of toxicity [or the characteristic of EP
toxicity]), include the mass of the entire hazardous waste.
Based on this mass, designated as C, assign a value for
hazardous constituent quantity as follows:
For the migration pathways, assign the source a value
for hazardous constituent quantity using the Tier A equation of
Table 2-5.
For the soil exposure and subsurface intrusion
pathway--soil exposure component, assign the area of observed
contamination a value using the Tier A equation of Table 5-2
(section 5.1.1.2.2).
For the soil exposure and subsurface intrusion
pathway--subsurface intrusion component, assign the area of observed
exposure a value using the Tier A equation of Table 5-19 (section
5.2.1.2.2).
If the hazardous constituent quantity for the source (or area of
observed contamination or area of observed exposure) is adequately
determined (that is, the total mass of all CERCLA hazardous
substances in the source and releases from the source [or in the
area of observed contamination or area of observed exposure] is
known or is estimated with reasonable confidence), do not evaluate
the other three measures discussed below. Instead assign these other
three measures a value of 0 for the source (or area of observed
contamination or area of observed exposure) and proceed to section
2.4.2.1.5.
If the hazardous constituent quantity is not adequately
determined, assign the source (or area of observed contamination or
area of observed exposure) a value for hazardous constituent
quantity based on the available data and proceed to section
2.4.2.1.2.
Table 2-5--Hazardous Waste Quantity Evaluation Equations
------------------------------------------------------------------------
Equation for
Tier Measure Units assigning value
\a\
------------------------------------------------------------------------
A.............. Hazardous constituent lb........... C
quantity (C).
B \b\.......... Hazardous wastestream lb........... W/5,000
quantity (W).
C \b\.......... Volume (V)........... .................
Landfill............. yd\3\........ V/2,500
Surface impoundment.. yd\3\........ V/2.5
Surface impoundment yd\3\........ V/2.5
(buried/backfilled).
Drums \c\............ gallon....... V/2.5
Tanks and containers yd\3\........ V/2.5
other than drums.
Contaminated soil.... yd\3\........ V/2,500
Pile................. yd\3\........ V/2.5
Other................ yd\3\........ V/2.5
D \b\.......... Area (A).............
Landfill............. ft\2\........ A/3,400
Surface impoundment.. ft\2\........ A/13
Surface impoundment ft\2\........ A/13
(buried/backfilled).
Land treatment....... ft\2\........ A/270
Pile \d\............. ft\2\........ A/13
Contaminated soil.... ft\2\........ A/34,000
------------------------------------------------------------------------
\a\ Do not round to nearest integer.
\b\ Convert volume to mass when necessary: 1 ton = 2,000 pounds = 1
cubic yard = 4 drums = 200 gallons.
\c\ If actual volume of drums is unavailable, assume 1 drum = 50
gallons.
\d\ Use land surface area under pile, not surface area of pile.
2.4.2.1.2 Hazardous wastestream quantity. Evaluate hazardous
wastestream quantity for the source (or area of observed
contamination or area of observed exposure) based on the mass of
hazardous wastestreams plus the mass of any additional CERCLA
pollutants and contaminants (as defined in CERCLA section 101[33],
as amended) that are allocated to the source (or area of
[[Page 2786]]
observed contamination or area of observed exposure). For a
wastestream that consists solely of a hazardous waste listed
pursuant to section 3001 of RCRA, as amended or that consists solely
of a RCRA hazardous waste that exhibits the characteristics
identified under section 3001 of RCRA, as amended, include the mass
of that entire hazardous waste in the evaluation of this measure.
Based on this mass, designated as W, assign a value for
hazardous wastestream quantity as follows:
For the migration pathways, assign the source a value
for hazardous wastestream quantity using the Tier B equation of
Table 2-5.
For the soil exposure and subsurface intrusion
pathway--soil exposure component, assign the area of observed
contamination a value using the Tier B equation of Table 5-2
(section 5.1.1.2.2).
For the soil exposure and subsurface intrusion
pathway--subsurface intrusion component, assign the area of observed
exposure a value using the Tier B equation of Table 5-19 (section
5.2.1.2.2).
Do not evaluate the volume and area measures described below if
the source is the unallocated source or if the following condition
applies:
The hazardous wastestream quantity for the source (or
area of observed contamination or area of observed exposure) is
adequately determined--that is, total mass of all hazardous
wastestreams and CERCLA pollutants and contaminants for the source
and releases from the source (or for the area of observed
contamination) is known or is estimated with reasonable confidence.
If the source is the unallocated source or if this condition
applies, assign the volume and area measures a value of 0 for the
source (or area of observed contamination) and proceed to section
2.4.2.1.5. Otherwise, assign the source (or area of observed
contamination) a value for hazardous wastestream quantity based on
the available data and proceed to section 2.4.2.1.3.
2.4.2.1.3 Volume. Evaluate the volume measure using the volume
of the source (or the volume of the area of observed contamination,
area of observed exposure, or area of subsurface contamination). For
the soil exposure and subsurface intrusion pathway, restrict the use
of the volume measure to those areas of observed contamination,
areas of observed exposure, or areas of subsurface contamination as
specified in sections 5.1.1.2.2 and 5.2.1.2.2.
Based on the volume, designated as V, assign a value to the
volume measure as follows:
For the migration pathways, assign the source a value
for volume using the appropriate Tier C equation of Table 2-5.
For the soil exposure and subsurface intrusion
pathway--soil exposure component, assign the area of observed
contamination a value for volume using the appropriate Tier C
equation of Table 5-2 (section 5.1.1.2.2).
For the soil exposure and subsurface intrusion
pathway--subsurface intrusion component, assign the value based on
the volume of the regularly occupied structures within the area of
observed exposure or area of subsurface contamination using the Tier
C equation of Table 5-19 (section 5.2.1.2.2).
If the volume of the source (or volume of the area of observed
contamination, area of observed exposure, or area of subsurface
contamination, if applicable) can be determined, do not evaluate the
area measure. Instead, assign the area measure a value of 0 and
proceed to section 2.4.2.1.5. If the volume cannot be determined (or
is not applicable for the soil exposure and subsurface intrusion
pathway), assign the source (or area of observed contamination, area
of observed exposure, or area of subsurface contamination) a value
of 0 for the volume measure and proceed to section 2.4.2.1.4.
2.4.2.1.4 Area. Evaluate the area measure using the area of the
source (or the area of the area of observed contamination, area of
observed exposure, or area of subsurface contamination). Based on
this area, designated as A, assign a value to the area measure as
follows:
For the migration pathways, assign the source a value
for area using the appropriate Tier D equation of Table 2-5.
For the soil exposure and subsurface intrusion
pathway--soil exposure component, assign the area of observed
contamination a value for area using the appropriate Tier D equation
of Table 5-2 (section 5.1.1.2.2).
For the soil exposure and subsurface intrusion
pathway--subsurface intrusion component, assign a value based on the
area of regularly occupied structures within the area of observed
exposure or area of subsurface contamination using the Tier D
equation of Table 5-19 (section 5.2.1.2.2).
2.4.2.1.5 Calculation of source hazardous waste quantity value.
Select the highest of the values assigned to the source (or areas of
observed contamination, areas of observed exposure, or areas of
subsurface contamination) for the hazardous constituent quantity,
hazardous wastestream quantity, volume, and area measures. Assign
this value as the source hazardous waste quantity value. Do not
round to the nearest integer.
2.4.2.2 Calculation of hazardous waste quantity factor value.
Sum the source hazardous waste quantity values assigned to all
sources (including the unallocated source) or areas of observed
contamination, areas of observed exposure, or areas of subsurface
contamination for the pathway being evaluated and round this sum to
the nearest integer, except: If the sum is greater than 0, but less
than 1, round it to 1. Based on this value, select a hazardous waste
quantity factor value for the pathway from Table 2-6.
Table 2-6--Hazardous Waste Quantity Factor Values
------------------------------------------------------------------------
Hazardous waste quantity value Assigned value
------------------------------------------------------------------------
0....................................................... 0
1 \a\ to 100............................................ \b\ 1
Greater than 100 to 10,000.............................. 100
Greater than 10,000 to 1,000,000........................ 10,000
Greater than 1,000,000.................................. 1,000,000
------------------------------------------------------------------------
\a\ If the hazardous waste quantity value is greater than 0, but less
than 1, round it to 1 as specified in text.
\b\ For the pathway, if hazardous constituent quantity is not adequately
determined, assign a value as specified in the text; do not assign the
value of 1.
For a migration pathway, if the hazardous constituent quantity
is adequately determined (see section 2.4.2.1.1) for all sources (or
all portions of sources and releases remaining after a removal
action), assign the value from Table 2-6 as the hazardous waste
quantity factor value for the pathway. If the hazardous constituent
quantity is not adequately determined for one or more sources (or
one or more portions of sources or releases remaining after a
removal action) assign a factor value as follows:
If any target for that migration pathway is subject to
Level I or Level II concentrations (see section 2.5), assign either
the value from Table 2-6 or a value of 100, whichever is greater, as
the hazardous waste quantity factor value for that pathway.
If none of the targets for that pathway is subject to
Level I or Level II concentrations, assign a factor value as
follows:
--If there has been no removal action, assign either the value from
Table 2-6 or a value of 10, whichever is greater, as the hazardous
waste quantity factor value for that pathway.
--If there has been a removal action:
[ssquf] Determine values from Table 2-6 with and without
consideration of the removal action.
[ssquf] If the value that would be assigned from Table 2-6
without consideration of the removal action would be 100 or greater,
assign either the value from Table 2-6 with consideration of the
removal action or a value of 100, whichever is greater, as the
hazardous waste quantity factor value for the pathway.
[ssquf] If the value that would be assigned from Table 2-6
without consideration of the removal action would be less than 100,
assign a value of 10 as the hazardous waste quantity factor value
for the pathway.
For the soil exposure component of the soil exposure and
subsurface intrusion pathway, if the hazardous constituent quantity
is adequately determined for all areas of observed contamination,
assign the value from Table 2-6 as the hazardous waste quantity
factor value. If the hazardous constituent quantity is not
adequately determined for one or more areas of observed
contamination, assign either the value from Table 2-6 or a value of
10, whichever is greater, as the hazardous waste quantity factor
value.
For the subsurface intrusion component of the soil exposure and
subsurface intrusion pathway, if the hazardous constituent
[[Page 2787]]
quantity is adequately determined for all areas of observed
exposure, assign the value from Table 2-6 as the hazardous waste
quantity factor value. If the hazardous constituent quantity is not
adequately determined for one or more areas of observed exposure,
assign either the value from Table 2-6 or assign a factor value as
follows:
If any target for the subsurface intrusion component is
subject to Level I or Level II concentrations (see section 2.5),
assign either the value from Table 2-6 or a value of 100, whichever
is greater, as the hazardous waste quantity factor value for this
component.
If none of the targets for the subsurface intrusion
component is subject to Level I or Level II concentrations and if
there has been a removal or other temporary response action that
does not permanently interrupt target exposure form subsurface
intrusion, assign a factor value as follows:
--Determine the values from Table 2-6 with and without consideration
of the removal or other temporary response action.
--If the value that would be assigned from Table 2-6 without
consideration of the removal or other temporary response action
would be 100 or greater, assign either the value from Table 2-6 with
consideration of the removal action or a value of 100, whichever is
greater, as the hazardous waste quantity factor value for the
component.
--If the value that would be assigned from Table 2-6 without
consideration of the removal or other temporary response action
would be less than 100, assign a value of 10 as the hazardous waste
quantity factor value for the component.
Otherwise, if none of the targets for the subsurface
intrusion component is subject to Level I or Level II concentrations
and there has not been a removal action, assign a value from Table
2-6 or a value of 10, whichever is greater.
2.4.3 Waste characteristics factor category value. Determine the
waste characteristics factor category value as specified in section
2.4.3.1 for all pathways and threats, except the surface water-human
food chain threat and the surface water-environmental threat.
Determine the waste characteristics factor category value for these
latter two threats as specified in section 2.4.3.2.
2.4.3.1 Factor category value. For the pathway (component or
threat) being evaluated, multiply the toxicity or combined factor
value, as appropriate, from section 2.4.1.2 and the hazardous waste
quantity factor value from section 2.4.2.2, subject to a maximum
product of 1x10\8\. Based on this waste characteristics product,
assign a waste characteristics factor category value to the pathway
(component or threat) from Table 2-7.
Table 2-7--Waste Characteristics Factor Category Values
------------------------------------------------------------------------
Waste characteristics product Assigned value
------------------------------------------------------------------------
0....................................................... 0
Greater than 0 to less than 10.......................... 1
10 to less than 1x10\2\................................. 2
1x10\2\ to less than 1x10\3\............................ 3
1x10\3\ to less than 1x10\4\............................ 6
1x10\4\ to less than 1x10\5\............................ 10
1x10\5\ to less than 1x10\6\............................ 18
1x10\6\ to less than 1x10\7\............................ 32
1x10\7\ to less than 1x10\8\............................ 56
1x10\8\ to less than 1x10\9\............................ 100
1x10\9\ to less than 1x10\10\........................... 180
1x10\10\ to less than 1x10\11\.......................... 320
1x10\11\ to less than 1x10\12\.......................... 560
1x10\12\................................................ 1,000
------------------------------------------------------------------------
2.4.3.2 Factor category value, considering bioaccumulation
potential. For the surface water-human food chain threat and the
surface water-environmental threat, multiply the toxicity or
combined factor value, as appropriate, from section 2.4.1.2 and the
hazardous waste quantity factor value from section 2.4.2.2, subject
to:
A maximum product of 1x10\12\, and
A maximum product exclusive of the bioaccumulation (or
ecosystem bioaccumulation) potential factor of 1x10\8\.
Based on the total waste characteristics product, assign a waste
characteristics factor category value to these threats from Table 2-
7.
2.5 Targets. The types of targets evaluated include the
following:
Individual (factor name varies by pathway, component,
and threat).
Human population.
Resources (these vary by pathway, component, and
threat).
Sensitive environments (included for the surface water
migration pathway, air migration pathway, and soil exposure
component of the soil exposure and subsurface intrusion pathway).
The factor values that may be assigned to each type of target
have the same range for each pathway for which that type of target
is evaluated. The factor value for most types of targets depends on
whether the target is subject to actual or potential contamination
for the pathway and whether the actual contamination is Level I or
Level II:
Actual contamination: Target is associated either with
a sampling location that meets the criteria for an observed release
(or observed contamination or observed exposure) for the pathway or
with an observed release based on direct observation for the pathway
(additional criteria apply for establishing actual contamination for
the human food chain threat in the surface water migration pathway,
see sections 4.1.3.3 and 4.2.3.3). Sections 3 through 6 specify how
to determine the targets associated with a sampling location or with
an observed release based on direct observation. Determine whether
the actual contamination is Level I or Level II as follows:
--Level I:
[ssquf] Media-specific concentrations for the target meet the
criteria for an observed release (or observed contamination or
observed exposure) for the pathway and are at or above media-
specific benchmark values. These benchmark values (see section
2.5.2) include both screening concentrations and concentrations
specified in regulatory limits (such as Maximum Contaminant Level
(MCL) values), or
[ssquf] For the human food chain threat in the surface water
migration pathway, concentrations in tissue samples from aquatic
human food chain organisms are at or above benchmark values. Such
tissue samples may be used in addition to media-specific
concentrations only as specified in sections 4.1.3.3 and 4.2.3.3.
--Level II:
[ssquf] Media-specific concentrations for the target meet the
criteria for an observed release (or observed contamination or
observed exposure) for the pathway, but are less than media-specific
benchmarks. If none of the hazardous substances eligible to be
evaluated for the sampling location has an applicable benchmark,
assign Level II to the actual contamination at the sampling
location, or
[ssquf] For observed releases or observed exposures based on
direct observation, assign Level II to targets as specified in
sections 3, 4, 5, and 6, or
[ssquf] For the human food chain threat in the surface water
migration pathway, concentrations in tissue samples from aquatic
human food chain organisms, when applicable, are below benchmark
values.
--If a target is subject to both Level I and Level II concentrations
for a pathway (component or threat), evaluate the target using Level
I concentrations for that pathway (component or threat).
Potential contamination: Target is subject to a
potential release (that is, target is not associated with actual
contamination for that pathway or threat).
Assign a factor value for individual risk as follows (select the
highest value that applies to the pathway, component or threat):
50 points if any individual is exposed to Level I
concentrations.
45 points if any individual is exposed to Level II
concentrations.
Maximum of 20 points if any individual is subject to
potential contamination. The value assigned is 20 unless reduced by
a distance or dilution weight appropriate to the pathway. Assign
factor values for population and sensitive environments as follows:
Sum Level I targets and multiply by 10. (Level I is not
used for sensitive environments in the soil exposure component of
the soil exposure and subsurface intrusion and air migration
pathways.)
Sum Level II targets.
Multiply potential targets in all but the soil exposure
and subsurface intrusion pathway by distance or dilution weights
appropriate to the pathway, sum, and divide by 10. Distance or
dilution weighting accounts for diminishing exposure with increasing
distance or dilution within the different pathways. For targets
within an area
[[Page 2788]]
of subsurface contamination in the subsurface intrusion component of
the soil exposure and subsurface intrusion pathway, multiply by a
weighting factor as directed in section 5.2.1.3.2.3.
Sum the values for the three levels.
In addition, resource value points are assigned within all
pathways for welfare-related impacts (for example, impacts to
agricultural land), but do not depend on whether there is actual or
potential contamination.
2.5.1 Determination of level of actual contamination at a
sampling location. Determine whether Level I concentrations or Level
II concentrations apply at a sampling location (and thus to the
associated targets) as follows:
Select the benchmarks applicable to the pathway
(component or threat) being evaluated.
Compare the concentrations of hazardous substances in
the sample (or comparable samples) to their benchmark concentrations
for the pathway (component or threat), as specified in section
2.5.2.
Determine which level applies based on this comparison.
If none of the hazardous substances eligible to be
evaluated for the sampling location has an applicable benchmark,
assign Level II to the actual contamination at that sampling
location for the pathway (component or threat).
In making the comparison, consider only those samples, and only
those hazardous substances in the sample, that meet the criteria for
an observed release (or observed contamination or observed exposure)
for the pathway, except: Tissue samples from aquatic human food
chain organisms may also be used as specified in sections 4.1.3.3
and 4.2.3.3 of the surface water-human food chain threat. If any
hazardous substance is present in more than one comparable sample
for the sampling location, use the highest concentration of that
hazardous substance from any of the comparable samples in making the
comparisons.
Treat sets of samples that are not comparable separately and
make a separate comparison for each such set.
2.5.2 Comparison to benchmarks. Use the following media-specific
benchmarks for making the comparisons for the indicated pathway (or
threat):
Maximum Contaminant Level Goals (MCLGs)--ground water
migration pathway and drinking water threat in surface water
migration pathway. Use only MCLG values greater than 0.
Maximum Contaminant Levels (MCLs)--ground water
migration pathway and drinking water threat in surface water
migration pathway.
Food and Drug Administration Action Level (FDAAL) for
fish or shellfish--human food chain threat in surface water
migration pathway.
EPA Ambient Water Quality Criteria (AWQC/National
Recommended Water Quality Criteria) for protection of aquatic life--
environmental threat in surface water migration pathway.
EPA Ambient Aquatic Life Advisory Concentrations
(AALAC)--environmental threat in surface water migration pathway.
National Ambient Air Quality Standards (NAAQS)--air
migration pathway.
National Emission Standards for Hazardous Air
Pollutants (NESHAPs)--air migration pathway. Use only those NESHAPs
promulgated in ambient concentration units.
Screening concentration for cancer corresponding to
that concentration that corresponds to the 10-6
individual cancer risk for inhalation exposures (air migration
pathway or subsurface intrusion component of the soil exposure and
subsurface intrusion pathway) or for oral exposures (ground water
migration pathway; drinking water and human food chain threats in
surface water migration pathway; and soil exposure and subsurface
intrusion pathway).
Screening concentration for noncancer toxicological
responses corresponding to the RfC for inhalation exposures (air
migration pathway and subsurface intrusion component of the soil
exposure and subsurface intrusion pathway) or RfD for oral exposures
(ground water migration pathway; drinking water and human food chain
threats in surface water migration pathway; and soil exposure and
subsurface intrusion pathway).
Select the benchmark(s) applicable to the pathway (component or
threat) being evaluated as specified in sections 3 through 6.
Compare the concentration of each hazardous substance from the
sampling location to its benchmark concentration(s) for that pathway
(component or threat). Use only those samples and only those
hazardous substances in the sample that meet the criteria for an
observed release (or observed contamination or observed exposure)
for the pathway, except: Tissue samples from aquatic human food
chain organisms may be used as specified in sections 4.1.3.3 and
4.2.3.3. If the concentration of any applicable hazardous substance
from any sample equals or exceeds its benchmark concentration,
consider the sampling location to be subject to Level I
concentrations for that pathway (or threat). If more than one
benchmark applies to the hazardous substance, assign Level I if the
concentration of the hazardous substance equals or exceeds the
lowest applicable benchmark concentration.
If no hazardous substance individually equals or exceeds its
benchmark concentration, but more than one hazardous substance
either meets the criteria for an observed release (or observed
contamination or observed exposure) for the sample (or comparable
samples) or is eligible to be evaluated for a tissue sample (see
sections 4.1.3.3 and 4.2.3.3), calculate the indices I and J
specified below based on these hazardous substances.
For those hazardous substances that are carcinogens (that is,
those having either a carcinogen weight-of-evidence classification
of A, B, or C or a weight-of-evidence classification of carcinogenic
to humans, likely to be carcinogenic to humans, or suggestive
evidence of carcinogenic potential), calculate an index I for the
sample location as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.064
Where:
Ci = Concentration of hazardous substance i in sample (or
highest concentration of hazardous substance i from among comparable
samples).
SCi = Screening concentration for cancer corresponding to
that concentration that corresponds to its 10-6
individual cancer risk for applicable exposure (inhalation or oral)
for hazardous substance i.
n = Number of applicable hazardous substances in sample (or
comparable samples) that are carcinogens and for which an
SCi is available.
For those hazardous substances for which an RfD or RfC is
available, calculate an index J for the sample location as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.065
Where:
Cj = Concentration of hazardous substance j in sample (or
highest concentration of hazardous substance j from among comparable
samples).
CRj = Screening concentration for noncancer toxicological
responses corresponding to RfD or RfC for applicable exposure
(inhalation or oral) for hazardous substance j.
m = Number of applicable hazardous substances in sample (or
comparable samples) for which a CRj is available.
If either I or J equals or exceeds 1, consider the sampling
location to be subject to Level I concentrations for that pathway
(component or threat). If both I and J are less than 1, consider the
sampling location to be subject to Level II concentrations for that
pathway (component or threat). If, for the sampling location, there
are sets of samples that are not comparable, calculate I and J
separately for each such set, and use the highest calculated values
of I and J to assign Level I and Level II.
See sections 7.3.1 and 7.3.2 for criteria for determining the
level of contamination for radioactive substances.
* * * * *
5.0 Soil Exposure and Subsurface Intrusion Pathway
5.0.1 Exposure components. Evaluate the soil exposure and
subsurface intrusion pathway based on two exposure components:
Soil exposure component (see section 5.1).
Subsurface intrusion component (see section 5.2).
Score one or both components considering their relative
importance. If only one component is scored, assign its score as the
soil exposure and subsurface intrusion pathway score. If both
components are scored, sum the two scores and assign it as the soil
exposure and subsurface intrusion pathway score, subject to a
maximum of 100.
[[Page 2789]]
[GRAPHIC] [TIFF OMITTED] TR09JA17.066
5.1 Soil exposure component. Evaluate the soil exposure
component based on two threats: Resident population threat and
nearby population threat. Evaluate both threats based on three
factor categories: Likelihood of exposure, waste characteristics,
[[Page 2790]]
and targets. Figure 5-1 indicates the factors included within each
factor category for each type of threat.
Determine the soil exposure component score (Sse) in
terms of the factor category values as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.067
Where:
LEi = Likelihood of exposure factor category value for
threat i (that is, resident population threat or nearby population
threat).
WCi = Waste characteristics factor category value for
threat i.
Ti = Targets factor category value for threat i.
SF = Scaling factor.
Table 5-1 outlines the specific calculation procedure.
Table 5-1--Soil Exposure Component Scoresheet
------------------------------------------------------------------------
Factor categories and factors Maximum value Value assigned
------------------------------------------------------------------------
Resident Population Threat
------------------------------------------------------------------------
Likelihood of Exposure:
1. Likelihood of Exposure........... 550
Waste Characteristics:
2. Toxicity......................... (\a\)
3. Hazardous Waste Quantity......... (\a\)
4. Waste Characteristics............ 100
Targets:
5. Resident Individual.............. 50
6. Resident Population:.............
6a. Level I Concentrations...... (\b\)
6b. Level II Concentrations..... (\b\)
6c. Resident Population (lines (\b\)
6a + 6b).......................
7. Workers.......................... 15
8. Resources........................ 5
9. Terrestrial Sensitive (\c\)
Environments.......................
10. Targets (lines 5 + 6c + 7 + 8 + (\b\)
9).................................
Resident Population Threat Score:
11. Resident Population Threat (\b\)
(lines 1 x 4 x 10).................
------------------------------------------------------------------------
Nearby Population Threat
------------------------------------------------------------------------
Likelihood of Exposure:
12. Attractiveness/Accessibility.... 100
13. Area of Contamination........... 100
14. Likelihood of Exposure.......... 500
Waste Characteristics:
15. Toxicity........................ (\a\)
16. Hazardous Waste Quantity........ (\a\)
17. Waste Characteristics........... 100
Targets:
18. Nearby Individual............... 1
19. Population Within 1 Mile........ (\b\)
20. Targets (lines 18 + 19)......... (\b\)
Nearby Population Threat Score:
21. Nearby Population Threat (lines (\b\)
14 x 17 x 20)......................
Soil Exposure Component Score:
22. Soil Exposure Component Score 100
\d\ (Sse), (lines [11 + 21]/82,500,
subject to a maximum of 100).......
------------------------------------------------------------------------
\a\ Maximum value applies to waste characteristics category.
\b\ Maximum value not applicable.
\c\ No specific maximum value applies to factor. However, pathway score
based solely on terrestrial sensitive environments is limited to
maximum of 60.
\d\ Do not round to nearest integer.
5.1.0 General considerations. Evaluate the soil exposure
component based on areas of observed contamination:
Consider observed contamination to be present at
sampling locations where analytic evidence indicates that:
--A hazardous substance attributable to the site is present at a
concentration significantly above background levels for the site
(see Table 2-3 in section 2.3 for the criteria for determining
analytical significance), and
--This hazardous substance, if not present at the surface, is
covered by 2 feet or less of cover material (for example, soil).
Establish areas of observed contamination based on
sampling locations at which there is observed contamination as
follows:
--For all sources except contaminated soil, if observed
contamination from the site is present at any sampling location
within the source, consider that entire source to be an area of
observed contamination.
--For contaminated soil, consider both the sampling location(s) with
observed contamination from the site and the area lying between such
locations to be an area of observed contamination, unless available
information indicates otherwise.
If an area of observed contamination (or portion of
such an area) is covered by a permanent, or otherwise maintained,
essentially impenetrable material (for example, asphalt) that is not
more than 2 feet thick, exclude that area (or portion of the area)
in evaluating the soil exposure component.
For an area of observed contamination, consider only
those hazardous substances that meet the criteria for observed
contamination for that area to be associated with that area in
evaluating the soil exposure component (see section 2.2.2).
[[Page 2791]]
If there is observed contamination, assign scores for the
resident population threat and the nearby population threat, as
specified in sections 5.1.1 and 5.1.2. If there is no observed
contamination, assign the soil exposure component of the soil
exposure and subsurface intrusion pathway a score of 0.
5.1.1 Resident population threat. Evaluate the resident
population threat only if there is an area of observed contamination
in one or more of the following locations:
Within the property boundary of a residence, school, or
day care center and within 200 feet of the respective residence,
school, or day care center, or
Within a workplace property boundary and within 200
feet of a workplace area, or
Within the boundaries of a resource specified in
section 5.1.1.3.4, or
Within the boundaries of a terrestrial sensitive
environment specified in section 5.1.1.3.5.
If not, assign the resident population threat a value of 0,
enter this value in Table 5-1, and proceed to the nearby population
threat (section 5.1.2).
5.1.1.1 Likelihood of exposure. Assign a value of 550 to the
likelihood of exposure factor category for the resident population
threat if there is an area of observed contamination in one or more
locations listed in section 5.1.1. Enter this value in Table 5-1.
5.1.1.2 Waste characteristics. Evaluate waste characteristics
based on two factors: toxicity and hazardous waste quantity.
Evaluate only those hazardous substances that meet the criteria for
observed contamination at the site (see section 5.1.0).
5.1.1.2.1 Toxicity. Assign a toxicity factor value to each
hazardous substance as specified in section 2.4.1.1. Use the
hazardous substance with the highest toxicity factor value to assign
the value to the toxicity factor for the resident population threat.
Enter this value in Table 5-1.
5.1.1.2.2 Hazardous waste quantity. Assign a hazardous waste
quantity factor value as specified in section 2.4.2. In estimating
the hazardous waste quantity, use Table 5-2 and:
Consider only the first 2 feet of depth of an area of
observed contamination, except as specified for the volume measure.
Use the volume measure (see section 2.4.2.1.3) only for
those types of areas of observed contamination listed in Tier C of
Table 5-2. In evaluating the volume measure for these listed areas
of observed contamination, use the full volume, not just the volume
within the top 2 feet.
Use the area measure (see section 2.4.2.1.4), not the
volume measure, for all other types of areas of observed
contamination, even if their volume is known.
Enter the value assigned in Table 5-1.
Table 5-2--Hazardous Waste Quantity Evaluation Equations for Soil Exposure Component
----------------------------------------------------------------------------------------------------------------
Equation for assigning
Tier Measure Units value \a\
----------------------------------------------------------------------------------------------------------------
A................................. Hazardous Constituent lb................... C.
Quantity (C).
B\b\............................. Hazardous Wastestream lb................... W/5,000.
Quantity (W).
C \b\............................. Volume (V)................
Surface Impoundment \c\... yd\3\................ V/2.5.
Drums \d\................. gallon............... V/500.
Tanks and Containers Other yd \3\............... V/2.5.
Than Drums.
D \b\............................. Area (A)..................
Landfill.................. ft \2\............... A/34,000.
Surface Impoundment....... ft \2\............... A/13.
Surface Impoundment ft \2\............... A/13.
(Buried/backfilled).
Land treatment............ ft \2\............... A/270.
Pile \e\.................. ft \2\............... A/34.
Contaminated Soil......... ft \2\............... A/34,000.
----------------------------------------------------------------------------------------------------------------
\a\ Do not round nearest integer.
\b\ Convert volume to mass when necessary: 1 ton = 2,000 pounds = 1 cubic yard = 4 drums = 200 gallons.
\c\ Use volume measure only for surface impoundments containing hazardous substances present as liquids. Use
area measures in Tier D for dry surface impoundments and for buried/backfilled surface impoundments.
\d\ If actual volume of drums is unavailable, assume 1 drum = 50 gallons.
\e\ Use land surface area under pile, not surface area of pile.
5.1.1.2.3 Calculation of waste characteristics factor category
value. Multiply the toxicity and hazardous waste quantity factor
values, subject to a maximum product of 1 x 10 \8\. Based on this
product, assign a value from Table 2-7 (section 2.4.3.1) to the
waste characteristics factor category. Enter this value in Table 5-
1.
5.1.1.3 Targets. Evaluate the targets factor category for the
resident population threat based on five factors: Resident
individual, resident population, workers, resources, and terrestrial
sensitive environments.
In evaluating the targets factor category for the resident
population threat, count only the following as targets:
Resident individual--a person living or attending
school or day care on a property with an area of observed
contamination and whose residence, school, or day care center,
respectively, is on or within 200 feet of the area of observed
contamination.
Worker--a person working on a property with an area of
observed contamination and whose workplace area is on or within 200
feet of the area of observed contamination.
Resources located on an area of observed contamination,
as specified in section 5.1.1.
Terrestrial sensitive environments located on an area
of observed contamination, as specified in section 5.1.1.
5.1.1.3.1 Resident individual. Evaluate this factor based on
whether there is a resident individual, as specified in section
5.1.1.3, who is subject to Level I or Level II concentrations.
First, determine those areas of observed contamination subject
to Level I concentrations and those subject to Level II
concentrations as specified in sections 2.5.1 and 2.5.2. Use the
health-based benchmarks from Table 5-3 in determining the level of
contamination. Then assign a value to the resident individual factor
as follows:
Assign a value of 50 if there is at least one resident
individual for one or more areas subject to Level I concentrations.
Assign a value of 45 if there is no such resident
individuals, but there is at least one resident individual for one
or more areas subject to Level II concentrations.
Assign a value of 0 if there is no resident individual.
Enter the value assigned in Table 5-1.
5.1.1.3.2 Resident population. Evaluate resident population
based on two factors: Level I concentrations and Level II
concentrations. Determine which factor applies as specified in
sections 2.5.1 and 2.5.2, using the health-based benchmarks from
Table 5-3. Evaluate populations subject to Level I concentrations as
specified in section 5.1.1.3.2.1 and populations subject to Level II
concentrations as specified in section 5.1.1.3.2.2.
[[Page 2792]]
Table 5-3--Health-Based Benchmarks for Hazardous Substances in Soils
------------------------------------------------------------------------
-------------------------------------------------------------------------
Screening concentration for cancer corresponding to that concentration
that corresponds to the 10 -6 individual cancer risk for oral
exposures.
Screening concentration for noncancer toxicological responses
corresponding to the Reference Dose (RfD) for oral exposures.
------------------------------------------------------------------------
Count only those persons meeting the criteria for resident
individual as specified in section 5.1.1.3. In estimating the number
of people living on property with an area of observed contamination,
when the estimate is based on the number of residences, multiply
each residence by the average number of persons per residence for
the county in which the residence is located.
5.1.1.3.2.1 Level I concentrations. Sum the number of resident
individuals subject to Level I concentrations and multiply this sum
by 10. Assign the resulting product as the value for this factor.
Enter this value in Table 5-1.
5.1.1.3.2.2 Level II concentrations. Sum the number of resident
individuals subject to Level II concentrations. Do not include those
people already counted under the Level I concentrations factor.
Assign this sum as the value for this factor. Enter this value in
Table 5-1.
5.1.1.3.2.3 Calculation of resident population factor value. Sum
the factor values for Level I concentrations and Level II
concentrations. Assign this sum as the resident population factor
value. Enter this value in Table 5-1.
5.1.1.3.3 Workers. Evaluate this factor based on the number of
workers that meet the section 5.1.1.3 criteria. Assign a value for
these workers using Table 5-4. Enter this value in Table 5-1.
Table 5-4--Factor Values for Workers
------------------------------------------------------------------------
Assigned
Number of workers value
------------------------------------------------------------------------
0.......................................................... 0
1 to 100................................................... 5
101 to 1,000............................................... 10
Greater than 1,000......................................... 15
------------------------------------------------------------------------
5.1.1.3.4 Resources. Evaluate the resources factor as follows:
Assign a value of 5 to the resources factor if one or
more of the following is present on an area of observed
contamination at the site:
--Commercial agriculture.
--Commercial silviculture.
--Commercial livestock production or commercial livestock grazing.
Assign a value of 0 if none of the above are present.
Enter the value assigned in Table 5-1.
5.1.1.3.5 Terrestrial sensitive environments. Assign value(s)
from Table 5-5 to each terrestrial sensitive environment that meets
the eligibility criteria of section 5.1.1.3.
Calculate a value (ES) for terrestrial sensitive environments as
follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.068
Where:
Si = Value(s) assigned from Table 5-5 to terrestrial
sensitive environment i.
n = Number of terrestrial sensitive environments meeting section
5.1.1.3 criteria.
Because the pathway score based solely on terrestrial sensitive
environments is limited to a maximum of 60, determine the value for
the terrestrial sensitive environments factor as follows:
Table 5-5--Terrestrial Sensitive Environments Rating Values
------------------------------------------------------------------------
Assigned
Terrestrial sensitive environments value
------------------------------------------------------------------------
Terrestrial critical habitat \a\ for Federal designated 100
endangered or threatened species.......................
National Park
Designated Federal Wilderness Area..................
National Monument...................................
Terrestrial habitat known to be used by Federal 75
designated or proposed threatened or endangered species
National Preserve (terrestrial)
National or State Terrestrial Wildlife Refuge......
Federal land designated for protection of natural
ecosystems.........................................
Administratively proposed Federal Wilderness Area..
Terrestrial areas utilized for breeding by large or
dense aggregations of animals \b\..................
Terrestrial habitat known to be used by State designated 50
endangered or threatened species.......................
Terrestrial habitat known to be used by species
under review as to its Federal designated
endangered or threatened status
State lands designated for wildlife or game management.. 25
State designated Natural Areas
Particular areas, relatively small in size,
important to maintenance of unique biotic
communities........................................
------------------------------------------------------------------------
\a\ Critical habitat as defined in 50 CFR 424.02.
\b\ Limit to vertebrate species.
Multiply the values assigned to the resident population
threat for likelihood of exposure (LE), waste characteristics (WC),
and ES. Divide the product by 82,500.
--If the result is 60 or less, assign the value ES as the
terrestrial sensitive environments factor value.
--If the result exceeds 60, calculate a value EC as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.069
Assign the value EC as the terrestrial sensitive environments
factor value. Do not round this value to the nearest integer.
Enter the value assigned for the terrestrial sensitive
environments factor in Table 5-1.
5.1.1.3.6 Calculation of resident population targets factor
category value. Sum the values for the resident individual, resident
population, workers, resources, and terrestrial sensitive
environments factors. Do not round to the nearest integer. Assign
this sum as the targets factor category value for the resident
population threat. Enter this value in Table 5-1.
5.1.1.4 Calculation of resident population threat score.
Multiply the values for likelihood of exposure, waste
characteristics, and targets for the resident population threat, and
round the product to the nearest integer. Assign this product as the
resident population threat score. Enter this score in Table 5-1.
5.1.2 Nearby population threat. Include in the nearby population
only those individuals who live or attend school within a 1-mile
travel distance of an area of observed contamination at the site and
who do not meet the criteria for resident individual as specified in
section 5.1.1.3.
Do not consider areas of observed contamination that have an
attractiveness/accessibility factor value of 0 (see section
[[Page 2793]]
5.1.2.1.1) in evaluating the nearby population threat.
5.1.2.1 Likelihood of exposure. Evaluate two factors for the
likelihood of exposure factor category for the nearby population
threat: attractiveness/accessibility and area of contamination.
5.1.2.1.1 Attractiveness/accessibility. Assign a value for
attractiveness/accessibility from Table 5-6 to each area of observed
contamination, excluding any land used for residences. Select the
highest value assigned to the areas evaluated and use it as the
value for the attractiveness/accessibility factor. Enter this value
in Table 5-1.
5.1.2.1.2 Area of contamination. Evaluate area of contamination
based on the total area of the areas of observed contamination at
the site. Count only the area(s) that meet the criteria in section
5.1.0 and that receive an attractiveness/accessibility value greater
than 0. Assign a value to this factor from Table 5-7. Enter this
value in Table 5-1.
Table 5-6--Attractiveness/Accessibility Values
------------------------------------------------------------------------
Area of observed contamination Assigned value
------------------------------------------------------------------------
Designated recreational area............................ 100
Regularly used for public recreation (for example, 75
fishing, hiking, softball).............................
Accessible and unique recreational area (for example, 75
vacant lots in urban area).............................
Moderately accessible (may have some access 50
improvements, for example, gravel road), with some
public recreation use..................................
Slightly accessible (for example, extremely rural area 25
with no road improvement), with some public recreation
use....................................................
Accessible, with no public recreation use............... 10
Surrounded by maintained fence or combination of 5
maintained fence and natural barriers..................
Physically inaccessible to public, with no evidence of 0
public recreation use..................................
------------------------------------------------------------------------
Table 5-7--Area of Contamination Factor Values
------------------------------------------------------------------------
Total area of the areas of observed contamination
(square feet) Assigned value
------------------------------------------------------------------------
Less than or equal to 5,000............................. 5
Greater than 5,000 to 125,000........................... 20
Greater than 125,000 to 250,000......................... 40
Greater than 250,000 to 375,000......................... 60
Greater than 375,000 to 500,000......................... 80
Greater than 500,000.................................... 100
------------------------------------------------------------------------
5.1.2.1.3 Likelihood of exposure factor category value. Assign a
value from Table 5-8 to the likelihood of exposure factor category,
based on the values assigned to the attractiveness/accessibility and
area of contamination factors. Enter this value in Table 5-1.
Table 5-8--Nearby Population Likelihood of Exposure Factor Values
--------------------------------------------------------------------------------------------------------------------------------------------------------
Attractiveness/accessibility factor value
Area of contamination factor value ---------------------------------------------------------------------------------------------------------------
100 75 50 25 10 5 0
--------------------------------------------------------------------------------------------------------------------------------------------------------
100..................................... 500 500 375 250 125 50 0
80...................................... 500 375 250 125 50 25 0
60...................................... 375 250 125 50 25 5 0
40...................................... 250 125 50 25 5 5 0
20...................................... 125 50 25 5 5 5 0
5....................................... 50 25 5 5 5 5 0
--------------------------------------------------------------------------------------------------------------------------------------------------------
5.1.2.2 Waste characteristics. Evaluate waste characteristics
based on two factors: toxicity and hazardous waste quantity.
Evaluate only those hazardous substances that meet the criteria for
observed contamination (see section 5.1.0) at areas that can be
assigned an attractiveness/accessibility factor value greater than
0.
5.1.2.2.1 Toxicity. Assign a toxicity factor value as specified
in section 2.4.1.1 to each hazardous substance meeting the criteria
in section 5.1.2.2. Use the hazardous substance with the highest
toxicity factor value to assign the value to the toxicity factor for
the nearby population threat. Enter this value in Table 5-1.
5.1.2.2.2 Hazardous waste quantity. Assign a value to the
hazardous waste quantity factor as specified in section 5.1.1.2.2,
except: consider only those areas of observed contamination that can
be assigned an attractiveness/accessibility factor value greater
than 0. Enter the value assigned in Table 5-1.
5.1.2.2.3 Calculation of waste characteristics factor category
value. Multiply the toxicity and hazardous waste quantity factor
values, subject to a maximum product of 1 x 10\8\. Based on this
product, assign a value from Table 2-7 (section 2.4.3.1) to the
waste characteristics factor category. Enter this value in Table 5-
1.
5.1.2.3 Targets. Evaluate the targets factory category for the
nearby population threat based on two factors: nearby individual and
population within a 1-mile travel distance from the site.
5.1.2.3.1 Nearby individual. If one or more persons meet the
section 5.1.1.3 criteria for a resident individual, assign this
factor a value of 0. Enter this value in Table 5-1.
If no person meets the criteria for a resident individual,
determine the shortest travel distance from the site to any
residence or school. In determining the travel distance, measure the
shortest overland distance an individual would travel from a
residence or school to the nearest area of observed contamination
for the site with an attractiveness/accessibility factor value
greater than 0. If there are no natural barriers to travel, measure
the travel distance as the shortest straight-line distance from the
residence or school to the area of observed contamination. If
natural barriers exist (for example, a river), measure the travel
distance as the shortest straight-line distance from the residence
or school to the nearest crossing point and from there as the
shortest straight-
[[Page 2794]]
line distance to the area of observed contamination. Based on the
shortest travel distance, assign a value from Table 5-9 to the
nearest individual factor. Enter this value in Table 5-1.
Table 5-9--Nearby Individual Factor Values
------------------------------------------------------------------------
Assigned
Travel distance for nearby individual (miles) value
------------------------------------------------------------------------
Greater than 0 to \1/4\...................................... \a\ 1
Greater than \1/4\ to 1...................................... 0
------------------------------------------------------------------------
\a\ Assign a value of 0 if one or more persons meet the section 5.1.1.3
criteria for resident individual.
5.1.2.3.2 Population within 1 mile. Determine the population
within each travel distance category of Table 5-10. Count residents
and students who attend school within this travel distance. Do not
include those people already counted in the resident population
threat. Determine travel distances as specified in section
5.1.2.3.1.
In estimating residential population, when the estimate is based
on the number of residences, multiply each residence by the average
number of persons per residence for the county in which the
residence is located.
Based on the number of people included within a travel distance
category, assign a distance-weighted population value for that
travel distance from Table 5-10.
Calculate the value for the population within 1 mile factor (PN)
as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.070
Where:
Wi=Distance-weighted population value from Table 5-10 for
travel distance category i.
If PN is less than 1, do not round it to the nearest integer; if
PN is 1 or more, round to the nearest integer. Enter this value in
Table 5-1.
5.1.2.3.3 Calculation of nearby population targets factor
category value. Sum the values for the nearby individual factor and
the population within 1 mile factor. Do not round this sum to the
nearest integer. Assign this sum as the targets factor category
value for the nearby population threat. Enter this value in Table 5-
1.
Table 5-10--Distance Weighted Population Values for Nearby Population Threat a
--------------------------------------------------------------------------------------------------------------------------------------------------------
Number of people within the travel distance category
---------------------------------------------------------------------------------------------------------
Travel distance category (miles) 1,001 3,001 10,001 30,001 100,001
0 1 to 11 to 31 to 101 to 301 to to to to to to 300,001 to
10 30 100 300 1,000 3,000 10,000 30,000 100,000 300,000 1,000,000
--------------------------------------------------------------------------------------------------------------------------------------------------------
Greater than 0 to \1/4\....................... 0 0.1 0.4 1.0 4 13 41 130 408 1,303 4,081 13,034
Greater than \1/4\ to \1/2\................... 0 0.05 0.2 0.7 2 7 20 65 204 652 2,041 6,517
Greater than \1/2\ to 1....................... 0 0.02 0.1 0.3 1 3 10 33 102 326 1,020 3,258
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Round the number of people present within a travel distance category to nearest integer. Do not round the assigned distance-weighted population
value to nearest integer.
5.1.2.4 Calculation of nearby population threat score. Multiply
the values for likelihood of exposure, waste characteristics, and
targets for the nearby population threat, and round the product to
the nearest integer. Assign this product as the nearby population
threat score. Enter this score in Table 5-1.
5.1.3 Calculation of soil exposure component score. Sum the
resident population threat score and the nearby population threat
score, and divide the sum by 82,500. Assign the resulting value,
subject to a maximum of 100, as the soil exposure component score
(Sse). Enter this score in Table 5-1.
5.2 Subsurface intrusion component. Evaluate the subsurface
intrusion component based on three factor categories: likelihood of
exposure, waste characteristics, and targets. Figure 5-1 indicates
the factors included within each factor category for the subsurface
intrusion component.
Determine the component score (Sssi) in terms of the
factor category values as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.071
Where:
LE=Likelihood of exposure factor category value.
WC=Waste characteristics factor category value.
T=Targets factor category value.
SF=Scaling factor.
Table 5-11 outlines the specific calculation procedure.
Table 5-11--Subsurface Intrusion Component Scoresheet
------------------------------------------------------------------------
Factor categories and factors Maximum value Value assigned
------------------------------------------------------------------------
Subsurface Intrusion Component:
Likelihood of Exposure:
1. Observed Exposure................ 550
2. Potential for Exposure...........
2a. Structure Containment....... 10
2b. Depth to contamination...... 10
2c. Vertical Migration.......... 15
2d. Vapor Migration Potential... 25
3. Potential for Exposure (lines 2a 500
* (2b + 2c + 2d), subject to a
maximum of 500)....................
4. Likelihood of Exposure (higher of 550
lines 1 or 3)......................
Waste Characteristics:
5. Toxicity/Degradation............. (\a\)
6. Hazardous Waste Quantity......... (\a\)
7. Waste Characteristics (subject to 100
a maximum of 100)..................
Targets:
8. Exposed Individual............... 50
9. Population:......................
9a. Level I Concentrations...... (\b\)
9b. Level II Concentrations..... (\b\)
9c. Population within an Area of (\b\)
Subsurface Contamination.......
9d. Total Population (lines 9a + (\b\)
9b + 9c).......................
[[Page 2795]]
10. Resources....................... 5
11. Targets (lines 8 + 9d + 10)..... (\b\)
Subsurface Intrusion Component Score:
12. Subsurface Intrusion Component 100
(lines 4 x 7 x 11)/82,500 \c\
(subject to a maximum of 100)......
Soil Exposure and Subsurface Intrusion
Pathway Score:
13. Soil Exposure Component + 100
Subsurface Intrusion Component
(subject to a maximum of 100)......
------------------------------------------------------------------------
\a\ Maximum value applies to waste characteristics category.
\b\ Maximum value not applicable.
\c\ Do not round to the nearest integer.
5.2.0 General considerations. The subsurface intrusion component
evaluates the threats from hazardous substances that have or could
intrude into regularly occupied structures from the subsurface.
Evaluate the subsurface intrusion component based on the actual or
potential intrusion of hazardous substances into all regularly
occupied structures that have structure containment values greater
than zero and meet the criteria identified in the section below as
being either in an area of observed exposure or in an area of
subsurface contamination. These structures may or may not have
subunits. Subunits are partitioned areas within a structure with
separate heating, ventilating, and air conditioning (HVAC) systems
or distinctly different air exchange rates. Subunits include
regularly occupied partitioned tenant spaces such as office suites,
apartments, condos, common or shared areas, and portions of
residential, commercial or industrial structures with separate
heating, ventilating, and air conditioning (HVAC) systems.
In evaluating the subsurface intrusion component, consider the
following:
Area(s) of observed exposure: An area of observed
exposure is delineated by regularly occupied structures with
documented contamination meeting observed exposure criteria; an area
of observed exposure includes regularly occupied structures with
samples meeting observed exposure criteria or inferred to be within
an area of observed exposure based on samples meeting observed
exposure criteria (see section 5.2.1.1.1 Observed exposure).
Establish areas of observed exposure as follows:
--For regularly occupied structures that have no subunits, consider
both the regularly occupied structures containing sampling
location(s) meeting observed exposure criteria for the site and the
regularly occupied structure(s) in the area lying between such
locations to be an area of observed exposure (i.e., inferred to be
in an area of observed exposure), unless available information
indicates otherwise.
--In multi-story, multi-subunit, regularly occupied structures,
consider all subunits on a level with sampling locations meeting
observed exposure criteria from the site and all levels below, if
any, to be within an area of observed exposure, unless available
information indicates otherwise.
--In multi-tenant structures, that do not have a documented observed
exposure, but are located in an area lying between locations where
observed exposures have been documented, consider only those
regularly occupied subunits, if any, on the lowest level of the
structure, to be within an area of observed exposure (i.e., inferred
to be in an area of observed exposure, unless available information
indicates otherwise.
Area(s) of subsurface contamination: An area of
subsurface contamination is delineated by sampling locations meeting
observed release criteria for subsurface intrusion, excluding areas
of observed exposure (see Table 2-3 in section 2.3). The area within
an area of subsurface contamination includes potentially exposed
populations. If the significant increase in hazardous substance
levels cannot be attributed at least in part to the site, and cannot
be attributed to other sites, attribution can be established based
on the presence of hazardous substances in the area of subsurface
contamination. Establish areas of subsurface contamination as
follows:
--Exclude those areas that contain structures meeting the criteria
defined as an area of observed exposure.
--Consider both the sampling location(s) with subsurface
contamination meeting observed release criteria from the site and
the area lying between such locations to be an area of subsurface
contamination (i.e., inferred to be in an area of subsurface
contamination). If sufficient data is available and state of the
science shows there is no unacceptable risk due to subsurface
intrusion into a regularly occupied structure located within an area
of subsurface contamination, that structure can be excluded from the
area of subsurface contamination.
Evaluate an area of subsurface contamination based on hazardous
substances that:
[ssquf] Meet the criteria for observed exposure of a chemical
that has a vapor pressure greater than or equal to one torr or a
Henry's constant greater than or equal to 10-\5\ atm-
m\3\/mol, or
[ssquf] Meet the criteria for observed release in an area of
subsurface contamination and have a vapor pressure greater than or
equal to one torr or a Henry's constant greater than or equal to
10-\5\ atm-m\3\/mol, or
[ssquf] Meet the criteria for an observed release in a structure
within, or in a sample from below, an area of observed exposure and
have a vapor pressure greater than or equal to one torr or a Henry's
constant greater than or equal to 10-\5\ atm-m\3\/mol.
--Evaluate all structures with no subunits that have containment
factor values greater than zero, and not documented to meet observed
exposure criteria to be in an area of subsurface contamination if
they are lying between locations of subsurface intrusion samples
meeting observed release criteria.
--Evaluate multi-subunit structures as follows:
[ssquf] If an observed exposure has been documented based on a
gaseous indoor air sample, consider all regularly occupied
subunit(s), if any, on the level immediately above the level where
an observed exposure has been documented (or has been inferred to be
within an area of observed exposure), to be within an area of
subsurface contamination. If sufficient data is available and state
of the science shows there is no unacceptable risk due to subsurface
intrusion on the level immediately above the level where an observed
exposure has been documented (or has been inferred to be within an
area of observed exposure) that level can be excluded from the area
of subsurface contamination.
[ssquf] If observed release criteria have been met based on a
gaseous indoor air sample collected from a level not regularly
occupied, consider all regularly occupied subunit(s), if any, on the
level immediately above the level where the observed release
criteria has been documented, to be within an area of subsurface
contamination. If sufficient data is available and state of the
science shows there is no unacceptable risk due to subsurface
intrusion on the level immediately above the level where the
observed release criteria has been documented that level can be
excluded from the area of subsurface contamination.
[ssquf] If any regularly occupied multi-subunit structure is
inferred to be in an area of subsurface contamination, consider only
those regularly occupied subunit(s), if any, on the lowest level, to
be within an area of subsurface contamination. If sufficient data is
available and state of the science shows there is no unacceptable
risk due to subsurface intrusion on the lowest level, that structure
can be excluded from the area of subsurface contamination.
See Section 7.0 for establishing an area of subsurface
contamination based on the
[[Page 2796]]
presence of radioactive hazardous substances.
If there is no area of observed exposure and no area of
subsurface contamination, assign a score of 0 for the subsurface
intrusion component.
5.2.1 Subsurface intrusion component. Evaluate this component
only if there is an area of observed exposure or area of subsurface
contamination:
Within or underlying a residence, school, day care
center, workplace, or
Within or underlying a resource specified in section
5.2.1.3.3.
5.2.1.1 Likelihood of exposure. Assign a value of 550 to the
likelihood of exposure factor category for the subsurface intrusion
component if there is an area of observed exposure in one or more
locations listed in section 5.2.1. Enter this value in Table 5-11.
5.2.1.1.1 Observed exposure. Establish observed exposure in a
regularly occupied structure by demonstrating that a hazardous
substance has been released into a regularly occupied structure via
the subsurface. Base this demonstration on either of the following
criteria:
Direct observation:
--A solid, liquid, or gaseous material that contains one or more
hazardous substances attributable to the site has been observed
entering a regularly occupied structure through migration via the
subsurface or is known to have entered a regularly occupied
structure via the subsurface, or
--When evidence supports the inference of subsurface intrusion of a
material that contains one or more hazardous substances associated
with the site into a regularly occupied structure, demonstrated
adverse effects associated with that release may be used to
establish observed exposure.
Chemical analysis:
--Analysis of indoor samples indicates that the concentration of
hazardous substance(s) is significantly above the background
concentration for the site for that type of sample (see section
2.3).
--Some portion of the significant increase above background must be
attributable to the site to establish the observed exposure.
Documentation of this attribution should account for possible
concentrations of the hazardous substance(s) in outdoor air or from
materials found in the regularly occupied structure, and should
provide a rationale for the increase being from subsurface
intrusion.
If observed exposure can be established in a regularly occupied
structure, assign an observed exposure factor value of 550, enter
this value in Table 5-11, and proceed to section 5.2.1.1.3. If no
observed exposure can be established, assign an observed exposure
factor value of 0, enter this value in Table 5-11, and proceed to
section 5.2.1.1.2.
5.2.1.1.2 Potential for exposure. Evaluate potential for
exposure only if an observed exposure cannot be established, but an
area of subsurface contamination has been delineated. Evaluate
potential for exposure based only on the presence of hazardous
substances with a vapor pressure greater than or equal to one torr
or a Henry's constant greater than or equal to 10-\5\
atm-m\3\/mol. Evaluate potential for exposure for each area of
subsurface contamination based on four factors: Structure
containment (see section 5.2.1.1.2.1), depth to contamination (see
section 5.2.1.1.2.2), vertical migration (see section 5.2.1.1.2.3)
and vapor migration potential (see section 5.2.1.1.2.4). For each
area of subsurface contamination, assign the highest value for each
factor. If information is insufficient to calculate any single
factor value used to calculate the potential for exposure factor
values at an identified area of subsurface contamination,
information collected for another area of subsurface contamination
at the site may be used when evaluating potential for exposure.
Calculate the potential for exposure value for the site as specified
in section 5.2.1.1.2.5.
5.2.1.1.2.1 Structure containment. Calculate containment for
eligible hazardous substances within this component as directed in
Table 5-12 and enter this value into Table 5-11. Assign each
regularly occupied structure within an area of subsurface
contamination the highest appropriate structure containment value
from Table 5-12 and use the regularly occupied structure at the site
with the highest structure containment value in performing the
potential for exposure calculation. For all regularly occupied
structures with unknown containment features assign a structure
containment value of greater than zero for the purposes of
evaluating targets (see section 5.2.1.3).
Table 5-12--Structure Containment
------------------------------------------------------------------------
Evidence of structure
No. containment Assigned value
------------------------------------------------------------------------
1......................... Regularly occupied structure 10
with evidence of subsurface
intrusion, including
documented observed
exposure or sampling of bio
or inert gases, such as
methane and radon.
2......................... Regularly occupied structure 10
with open preferential
subsurface intrusion
pathways (e.g., sumps,
foundation cracks, unsealed
utility lines).
3......................... Regularly occupied structure 7
with an engineered vapor
migration barrier system
that does not address all
preferential subsurface
intrusion pathways.
4......................... Regularly occupied structure 6
with an engineered passive
vapor mitigation system
without documented
institutional controls
(e.g., deed restrictions)
or evidence of regular
maintenance and inspection.
5......................... Regularly occupied structure 4
with no visible open
preferential subsurface
intrusion pathways from the
subsurface (e.g., sumps,
foundation cracks, unsealed
utility lines).
6......................... Regularly occupied structure 3
with an engineered passive
vapor mitigation system
(e.g., passive venting)
with documented
institutional controls
(e.g., deed restrictions)
or evidence of regular
maintenance and inspection.
7......................... Regularly occupied structure 2
with an engineered, active
vapor mitigation system
(e.g., active venting)
without documented
institutional controls
(e.g., deed restrictions)
and funding in place for on-
going operation, inspection
and maintenance.
8......................... Regularly occupied structure 1
with a permanent
engineered, active vapor
mitigation system (e.g.,
active venting) with
documented institutional
controls (e.g., deed
restrictions) and funding
in place for on-going
operation, inspection and
maintenance.
9......................... Regularly occupied structure 0
with a foundation raised
greater than 6 feet above
ground surface (e.g.,
structure on stilts) or
structure that has been
built, and maintained, in a
manner to prevent
subsurface intrusion.
------------------------------------------------------------------------
5.2.1.1.2.2 Depth to contamination. Assign each area of
subsurface contamination a depth to contamination based on the least
depth to either contaminated crawl space or subsurface media
underlying a regularly occupied structure. Measure this depth to
contamination based on the distance between the lowest point of a
regularly occupied structure to the highest known point of hazardous
substances eligible to be evaluated. Use any regularly occupied
structure within an area of subsurface contamination with a
structure containment factor value greater than zero. Subtract from
the depth to contamination the thickness of any subsurface layer
composed of features that would allow channelized flow (e.g., karst,
lava tubes, open fractures, as well as manmade preferential pathways
such as utility conduits or drainage systems).
Based on this calculated depth, assign a factor value from Table
5-13. If the necessary information is available at multiple
locations, calculate the depth to contamination at each location.
Use the location having the least depth to contamination to assign
the factor value. Enter this value in Table 5-11.\\
[[Page 2797]]
Table 5-13--Depth to Contamination
------------------------------------------------------------------------
Depth to
Depth range 1 2 contamination
assigned value
------------------------------------------------------------------------
0 to <10 ft (Including subslab and semi-enclosed or 10
enclosed crawl space contamination)....................
>10 to 20 ft............................................ 8
>20 to 50 ft............................................ 6
>50 to 100 ft........................................... 4
>100 to 150 ft.......................................... 2
>150 ft................................................. 0
------------------------------------------------------------------------
\1\ If any part of the subsurface profile has channelized flow features,
assign that portion of the subsurface profile a depth of 0.
\2\ Measure elevation below any regularly occupied structure within an
area of subsurface contamination at a site. Select the regularly
occupied structure with the least depth to contamination below a
structure.
5.2.1.1.2.3 Vertical migration. Evaluate the vertical migration
factor for each area of subsurface contamination based on the
geologic materials in the interval between the lowest point of a
regularly occupied structure and the highest known point of
hazardous substances in the subsurface. Use any regularly occupied
structure either within an area of subsurface contamination or
overlying subsurface soil gas or ground water contamination. Assign
a value to the vertical migration factor as follows:
If the depth to contamination (see section 5.2.1.1.2.2)
is 10 feet or less, assign a value of 15.
If the depth to contamination is greater than 10 feet,
do not consider layers or portions of layers within the first 10
feet of the depth to contamination (as assigned in section
5.2.1.1.2.2).
If, for the interval between the lowest point of a
regularly occupied structure and the highest point of hazardous
substances in the subsurface, all layers that underlie a portion of
a regularly occupied structure at the site are karst or otherwise
allow channelized flow, assign a value of 15.
Otherwise:
--Select the lowest effective porosity/permeability layer(s) from
within the interval identified above. Consider only layers at least
1 foot thick.--Assign a value for individual layers from Table 5-14
using the hydraulic conductivity of the layer, if available. If the
hydraulic conductivity is not available, assign a value based on the
type of material in the selected layer.
--If more than one layer has the same assigned porosity/permeability
value, include all such layers and sum their thicknesses. Assign a
thickness of 0 feet to a layer with channelized flow features found
within any area of subsurface contamination at the site.
--Assign a value from Table 5-15 to the vertical migration factor,
based on the thickness and assigned porosity/permeability value of
the lowest effective porosity/permeability layer(s).
Determine vertical migration only at locations within an area of
subsurface contamination at the site. If the necessary subsurface
geologic information is available at multiple locations, evaluate
the vertical migration factor at each location. Use the location
having the highest vertical migration factor value to assign the
factor value. Enter this value in Table 5-11.
Table 5-14--Effective Porosity/Permeability of Geologic Materials
------------------------------------------------------------------------
Assigned
Hydraulic porosity/
Type of material conductivity (cm/ permeability
sec) value
------------------------------------------------------------------------
Gravel; clean sand; highly Greater than or 1
permeable fractured igneous and equal to 1 x 10-\3\.
metamorphic rocks; permeable
basalt; karst limestones and
dolomites.
Sand; sandy clays; sandy loams; Less than 1 x 10-\3\ 2
loamy sands; sandy silts;
sediments that are predominantly
sand; highly permeable till
(coarse-grained, unconsolidated
or compact and highly fractured);
peat; moderately permeable
limestones and dolomites (no
karst); moderately permeable
sandstone; moderately permeable
fractured igneous and metamorphic
rocks.
Silt; loams; silty loams; loesses; Less than 1 x 10-\5\ 3
silty clays; sediments that are
predominantly silts; moderately
permeable till (fine-grained,
unconsolidated till, or compact
till with some fractures); low
permeability limestones and
dolomites (no karst); low
permeability sandstone; low
permeability fractured igneous
and metamorphic rocks.
Clay; low permeability till Less than 1 x 10-\7\ 4
(compact unfractured till);
shale; unfractured metamorphic
and igneous rocks.
------------------------------------------------------------------------
Table 5-15--Vertical Migration Factor Values a
--------------------------------------------------------------------------------------------------------------------------------------------------------
Thickness of lowest porosity layer(s) \b\ (feet)
-----------------------------------------------------------------------------------------------
Assigned porosity/permeability value Greater than 5 Greater than Greater than Greater than Greater than
0 to 5 to 10 10 to 20 20 to 50 50 to 100 100 to 150
--------------------------------------------------------------------------------------------------------------------------------------------------------
1....................................................... 15 15 14 11 8 6
2....................................................... 15 14 12 9 6 4
3....................................................... 15 13 10 7 5 2
4....................................................... 15 12 9 6 3 1
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ If depth to contamination is 10 feet or less or if, for the interval being evaluated, all layers that underlie a portion of the structure at the
site are karst or have other channelized flow features, assign a value of 15.
\b\ Consider only layers at least 1 foot thick.
5.2.1.1.2.4 Vapor migration potential. Evaluate this factor for
each area of subsurface contamination as follows:
If the depth to contamination (see section 5.2.1.1.2.2)
is 10 feet or less, assign a value of 25.
Assign a value for vapor migration potential to each of
the gaseous hazardous substances associated with the area of
subsurface contamination (see section 2.2.2) as follows:
--Assign values from Table 5-16 for both vapor pressure and Henry's
constant to each hazardous substance. If Henry's constant cannot be
determined for a hazardous substance, assign that hazardous
substance a value of 2 for the Henry's constant component.
--Sum the two values assigned to each hazardous substance.
--Based on this sum, assign each hazardous substance a value from
Table 5-17 for vapor migration potential.
Assign a value for vapor migration potential to each
area of subsurface contamination as follows:
--Select the hazardous substance associated with the area of
subsurface contamination
[[Page 2798]]
with the highest vapor migration potential value and assign this
value as the vapor migration potential factor value for the area of
subsurface contamination.
Enter this value in Table 5-11.
Table 5-16--Values for Vapor Pressure and Henry's Constant
------------------------------------------------------------------------
Vapor pressure (torr) Assigned value
------------------------------------------------------------------------
Greater than 10......................................... 3
1 to 10................................................. 2
Less than 1............................................. 0
------------------------------------------------------------------------
Henry's constant Assigned
(atm-m\3\/mol) value
------------------------------------------------------------------------
Greater than 10-\3\..................................... 3
Greater than 10\4\ to 10-\3\............................ 2
10-\5\ to 10-\4\........................................ 1
Less than 10-\5\........................................ 0
------------------------------------------------------------------------
Table 5-17--Vapor Migration Potential Factor Values for a Hazardous
Substance
------------------------------------------------------------------------
Sum of values for vapor pressure and Henry's constant Assigned value
------------------------------------------------------------------------
0....................................................... 0
1 or 2.................................................. 5
3 or 4.................................................. 15
5 or 6.................................................. 25
------------------------------------------------------------------------
5.2.1.1.2.5 Calculation of potential for exposure factor value.
For each identified area of subsurface contamination, sum the factor
values for depth to contamination, vertical migration, and vapor
migration potential, and multiply this sum by the factor value for
structure containment. Select the highest product for any area of
subsurface contamination and assign this value as the potential for
exposure factor value for the component. Enter this value in Table
5-11.
5.2.1.1.3 Calculation of likelihood of exposure factor category
value. If observed exposure is established for the site, assign the
observed exposure factor value of 550 as the likelihood of exposure
factor category value for the site. Otherwise, assign the potential
for exposure factor value for the component as the likelihood of
exposure value. Enter the value assigned in Table 5-11.
5.2.1.2 Waste characteristics. Evaluate waste characteristics
based on two factors: toxicity/degradation and hazardous waste
quantity.
5.2.1.2.1 Toxicity/degradation. For each hazardous substance,
assign a toxicity factor value, a degradation factor value and a
combined toxicity/degradation factor value as specified in sections
2.2.3, 2.4.1.2 and 5.2.1.2.1.1 through 5.2.1.2.1.3.
5.2.1.2.1.1 Toxicity. Assign a toxicity factor value to each
hazardous substance as specified in sections 2.2.2 and 2.4.1.1.
5.2.1.2.1.2 Degradation. Assign a degradation factor value to
each hazardous substance as follows:
For any hazardous substance that meets the criteria for
an observed exposure, or if a NAPL is present in the subsurface
below an area of observed exposure or area of subsurface
contamination at a depth less than or equal to 30 feet, assign that
substance a degradation factor value of 1.
For all other situations, assign a degradation factor
value using Table 5-18. Assign the depth to contamination as
directed in section 5.2.1.1.2.2, except if evidence indicates that
biologically active soil is not present throughout the depth beneath
any regularly occupied structure. In this situation, subtract any
thickness of non-biologically active soil from the estimated depth
to contamination.
Table 5-18--Degradation Factor Value Table
----------------------------------------------------------------------------------------------------------------
Half-life
--------------------------------------------------------
Depth to contamination (feet) \a\ >30 days and
>100 Days <=100 days <=30 days
----------------------------------------------------------------------------------------------------------------
<10.................................................... 1 1 1
10 to <=30............................................. 1 1 0.1
>30.................................................... 1 0.5 0.1
----------------------------------------------------------------------------------------------------------------
\a\ When determining the depth to contamination do not include layers of non-biologically-active soil, nor
subsurface intervals with channelized flow (e.g., karst, lava tubes, open fractures, and manmade preferential
pathways as directed in section 5.2.1.1.2.2).
Calculate the half-life for each hazardous substance that meets
subsurface intrusion observed release criteria as follows:
The half-life of a substance in the subsurface is defined for
HRS purposes as the time required to reduce the initial
concentration of the substance in the subsurface by one-half as a
result of the combined decay processes of two components:
Biodegradation and hydrolysis.
Estimate the half-life (t1/2) of a hazardous
substance as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.072
Where:
h=Hydrolysis half-life.
b=Biodegradation half-life.
If either of these component half-lives cannot be estimated for
the hazardous substance from available data, delete that component
half-life from the above equation.
If no half-life information is available for a hazardous
substance and the substance is not already assigned a value of 1,
unless information indicates otherwise, assign a value of 1.
5.2.1.2.1.3 Calculation of toxicity/degradation factor value.
Assign each substance a toxicity/degradation value by multiplying
the toxicity factor value by the degradation factor value. Use the
hazardous substance with the highest combined toxicity/degradation
value to assign the factor value to the toxicity/degradation factor
for the subsurface intrusion threat. Enter this value in Table 5-11.
5.2.1.2.2 Hazardous waste quantity. Assign a hazardous waste
quantity factor value as specified in section 2.4.2. Consider only
those regularly occupied structures or subunits with a non-zero
structure containment value. Also include all regularly occupied
structures or subunits that have had mitigation systems installed as
part of a removal or other temporary response action. If sufficient
structure-specific concentration data is available and state of the
science shows there is no unacceptable risk of exposure to
populations in a regularly occupied structure or subunit in an area
of subsurface contamination, that structure or subunit is not
included in the hazardous waste quantity evaluation. In estimating
the hazardous waste quantity, use Tables 2-5 and 5-19 and:
For Tier A, hazardous constituent quantity, use the
mass of constituents found in the regularly occupied structure(s)
where the observed exposure has been identified.
--For multi-subunit structures, when calculating Tier A, use the
mass of constituents found in the regularly occupied subunit
space(s) where the observed exposure has been identified.
For Tier B, hazardous wastestream quantity, use the
flow-through volume of the regularly occupied structures where the
observed exposure has been identified.
--For multi-subunit structures, when calculating Tier B, use the
flow-through volume of the regularly occupied subunit spaces where
the observed exposure has been identified.
For Tier C, volume, use the volume divisor listed in
Tier C of Table 5-19. Volume is calculated for those regularly
occupied structures located within areas of observed exposure with
observed or inferred
[[Page 2799]]
intrusion and within areas of subsurface contamination.
--In evaluating the volume measure for these listed areas of
observed exposure and areas of subsurface contamination based on a
gaseous/vapor intrusion or the potential for gaseous/vapor
intrusion, consider the following:
[ssquf] Calculate the volume of each regularly occupied
structure based on actual data. If unknown, use a ceiling height of
8 feet.
[ssquf] For multi-subunit structures, when calculating Tier C,
calculate volume for those subunit spaces with observed or inferred
exposure and all other regularly occupied subunit spaces on that
level, unless available information indicates otherwise. If the
structure has multiple stories, also include the volume of all
regularly occupied subunit spaces below the floor with an observed
exposure and one story above, unless evidence indicates otherwise.
[ssquf] For multi-subunit structures within an area of
subsurface contamination and no observed or inferred exposure,
consider only the volume of the regularly occupied subunit spaces on
the lowest story, unless available information indicates otherwise.
For Tier D, area, if volume is unknown, use the area
divisor listed in Tier D of Table 5-19 for those regularly occupied
structures within areas of observed exposure with observed or
inferred intrusion and within areas of subsurface contamination.
--In evaluating the area measure for these listed areas of observed
exposure and areas of subsurface contamination, calculate the area
of each regularly occupied structure (including multi-subunit
structures) or subunit based on actual footprint area data.
[ssquf] If the actual footprint area of the structure(s) is
unknown, use an area of 1,740 square feet for each structure (or
subunit space).
[ssquf] For multi-subunit structures, when calculating Tier D,
calculate area for those subunit spaces with observed or inferred
exposure and all other regularly occupied subunit spaces on that
level, unless available information indicates otherwise. If the
structure has multiple stories, also include the area of all
regularly occupied subunit spaces below the floor with an observed
exposure and one story above, unless evidence indicates otherwise.
[ssquf] For multi-subunit structures within an area of
subsurface contamination and no observed or inferred exposure,
consider only the area of the regularly occupied subunit spaces on
the lowest story, unless available information indicates otherwise.
Table 5-19--Hazardous Waste Quantity Evaluation Equations for Subsurface Intrusion Component
----------------------------------------------------------------------------------------------------------------
Equation for assigning
Tier Measure Units value \a\
----------------------------------------------------------------------------------------------------------------
A......................... Hazardous Constituent Lb........................ C
Quantity (C).
B\b\...................... Hazardous Wastestream Lb........................ W/5,000
Quantity (W).
C\b,c\.................... Volume (V)..................
Regularly occupied yd\3\..................... V/2.5
structure(s) in areas of
observed exposure or
subsurface contamination.
D\b,d\.................... Area (A)....................
Regularly occupied ft\2\..................... A/13
structure(s) in areas of
observed exposure or
subsurface contamination.
----------------------------------------------------------------------------------------------------------------
\a\ Do not round to the nearest integer.
\b\ Convert volume to mass when necessary: 1 ton=2,000 pounds=1 cubic yard=4 drums=200 gallons.
\c\ Calculate volume of each regularly occupied structure or subunit space in areas of observed exposure and
areas of subsurface contamination--Assume 8-foot ceiling height unless actual value is known.
\d\ Calculate area of the footprint of each regularly occupied structure in areas of observed exposure and areas
of subsurface contamination. If the footprint area of a regularly occupied structure is unknown, use 1,740
square feet as the footprint area of the structure or subunit space.
For the subsurface intrusion component, if the hazardous
constituent quantity is adequately determined for all areas of
observed exposure, assign the value from Table 2-6 as the hazardous
waste quantity factor value. If the hazardous constituent quantity
is not adequately determined for one or more areas of observed
exposure or if one or more areas of subsurface contamination are
present, assign either the value from Table 2-6 or assign a factor
value as follows:
If any target for the subsurface intrusion component is
subject to Level I or Level II concentrations (see section 2.5),
assign either the value from Table 2-6 or a value of 100, whichever
is greater, as the hazardous waste quantity factor value for this
component.
If none of the targets for the subsurface intrusion
component is subject to Level I or Level II concentrations and if
there has been a removal action that does not permanently interrupt
target exposure from subsurface intrusion, and if an area of
subsurface contamination exists, assign a factor value as follows:
--Determine the values from Table 2-6 with and without consideration
of the removal action.
--If the value that would be assigned from Table 2-6 without
consideration of the removal action would be 100 or greater, assign
either the value from Table 2-6 with consideration of the removal
action or a value of 100, whichever is greater, as the hazardous
waste quantity factor value for the component.
--If the value that would be assigned from Table 2-6 without
consideration of the removal action would be less than 100, assign a
value of 10 as the hazardous waste quantity factor value for the
component.
Otherwise, if none of the targets for the subsurface
intrusion component is subject to Level I or Level II concentrations
and there has not been a removal action, assign a value from Table
2-6 or a value of 10, whichever is greater.
Enter the value assigned in Table 5-11.
5.2.1.2.3 Calculation of waste characteristics factor category
value. Multiply the toxicity/degradation and hazardous waste
quantity factor values, subject to a maximum product of 1 x 10\8\.
Based on this product, assign a value from Table 2-7 (section
2.4.3.1) to the waste characteristics factor category. Enter this
value in Table 5-11.
5.2.1.3 Targets. Evaluate the targets factor category for the
subsurface intrusion threat based on three factors: Exposed
individual, population, and resources in regularly occupied
structures with structure containment factors greater than 0.
Evaluate only those targets within areas of observed exposure and
areas of subsurface contamination (see section 5.2.0).
In evaluating the targets factor category for the subsurface
intrusion threat, count only the following as targets:
Exposed individual--a person living, attending school
or day care, or working in a regularly occupied structure with
observed exposure or in a structure within an area of observed
exposure or within an area of subsurface contamination.
Population--exposed individuals in a regularly occupied
structure within an area of observed exposure or within an area of
subsurface contamination.
Resources--located within an area of observed exposure
or within an area of subsurface contamination as specified in
section 5.2.1.3.3.
If a formerly occupied structure has been vacated due to
subsurface intrusion attributable to the site, count the initial
targets as if they were still residing in the structure. In
addition, if a removal or temporary response action has occurred
that has not completely mitigated the release, count the initial
targets as if the removal or temporary response action has not
permanently interrupted target exposure from subsurface intrusion.
Evaluate those targets based on conditions at the time of removal of
temporary response action.
[[Page 2800]]
For populations residing in or working in a multi-subunit
structure with multiple stories in an area of observed exposure or
area of subsurface contamination, count these targets as follows:
If there is no observed exposure within the structure,
include in the evaluation only those targets, if any, in the lowest
occupied level. If sufficient structure-specific concentration data
is available and state of the science shows there is no unacceptable
risk of exposure to targets in the lowest level, those targets are
not included in the evaluation.
If there is an observed exposure in any level, include
in the evaluation those targets in that level, the level above and
all levels below. (The weighting of these targets is specified in
Section 5.2.1.3.2.) If sufficient structure-specific concentration
data is available and state of the science shows there is no
unacceptable risk of exposure to targets in the level above where
the observed exposure has been documented, those targets are not
included in the evaluation.
5.2.1.3.1 Exposed individual. Evaluate this factor based on
whether there is an exposed individual, as specified in sections
2.5.1, 2.5.2 and 5.2.1.3, who is subject to Level I or Level II
concentrations.
First, determine those regularly occupied structures or
partitioned subunit(s) within structures in an area of observed
exposure subject to Level I concentrations and those subject to
Level II concentrations as specified as follows (see section 5.2.0):
Level I Concentrations: For contamination resulting
from subsurface intrusion, compare the hazardous substance
concentrations in any sample meeting the observed exposure by
chemical analysis criteria to the appropriate benchmark. Use the
health-based benchmarks from Table 5-20 to determine the level of
contamination.
--If the sample is from a structure with no subunits and the
concentration equals or exceeds the appropriate benchmark, assign
Level I concentrations to the entire structure.
--If the sample is from a subunit within a structure and the
concentration from that subunit equals or exceeds the appropriate
benchmark, assign Level I concentrations to that subunit.
Level II Concentrations: Structures, or subunits within
structures, with one or more samples that meet observed exposure by
chemical analysis criteria but do not equal or exceed the
appropriate benchmark; structures, or subunits, that have an
observed exposure by direct observation; and structures inferred to
be in an area of observed exposure based on samples meeting observed
exposure, are assigned Level II concentrations.
--For all regularly occupied structures, or subunits in such
structures, in an area of observed exposure that are not assigned
Level I concentrations, assign Level II concentrations.
Then assign a value to the exposed individual factor as follows:
Assign a value of 50 if there is at least one exposed
individual in one or more regularly occupied structures subject to
Level I concentrations.
Assign a value of 45 if there are no Level I exposed
individuals, but there is at least one exposed individual in one or
more regularly occupied structures subject to Level II
concentrations.
Assign a value of 20 if there is no Level I or Level II
exposed individual but there is at least one individual in a
regularly occupied structure within an area of subsurface
contamination. Enter the value assigned in Table 5-11.
5.2.1.3.2 Population. Evaluate population based on three
factors: Level I concentrations, Level II concentrations, and
population within an area of subsurface contamination. Determine
which factors apply as specified in section 5.2.1.3.1, using the
health-based benchmarks from Table 5-20. Evaluate populations
subject to Level I and Level II concentrations as specified in
section 2.5.
Table 5-20--Health-Based Benchmarks for Hazardous Substances in the
Subsurface Intrusion Component
------------------------------------------------------------------------
-------------------------------------------------------------------------
Screening concentration for cancer corresponding to that concentration
that corresponds to the 10-6 individual cancer risk using the
inhalation unit risk. For oral exposures use the oral cancer slope
factor.
Screening concentration for noncancer toxicological responses
corresponding to the reference dose (RfD) for oral exposure and the
reference concentration (RfC) for inhalation exposures.
------------------------------------------------------------------------
Count only those persons meeting the criteria for population as
specified in section 5.2.1.3. In estimating the number of
individuals in structures in an area of observed exposure or area of
subsurface contamination if the actual number of residents is not
known, multiply each residence by the average number of persons per
residence for the county in which the residence is located.
5.2.1.3.2.1 Level I concentrations. Assign the population
subject to Level I concentrations as follows:
1. Identify all exposed individuals regularly present in an
eligible structure with a structure containment value greater than
zero, or if the structure has subunits, identify those regularly
present in each subunit, located in an area of observed exposure
subject to Level I concentrations as described in sections 5.2.0 and
5.2.1.3.1. Identify only once per structure those exposed
individuals that are using more than one eligible subunit of the
same structure (e.g., using a common or shared area and other parts
of the same structure).
2. For each structure or subunit count the number of individuals
residing in or attending school or day care in the structure or
subunit.
3. Count the number of full-time and part-time workers in the
structure or subunit(s) subject to Level I concentrations. If
information is unavailable to classify a worker as full- or part-
time, evaluate that worker as being full-time. Divide the number of
full-time workers by 3 and the number of part-time workers by 6, and
then sum these products with the number of other individuals for
each structure or subunit.
4. Sum this combined value for all structures, or subunits,
within areas of observed exposure and multiply this sum by 10.
Assign the resulting product as the combined population factor
value subject to Level I concentrations for the site. Enter this
value in line 9a of Table 5-11.
5.2.1.3.2.2 Level II concentrations. Assign the population
subject to Level II concentrations as follows:
1. Identify all exposed individuals regularly present in an
eligible structure with a structure containment value greater than
zero, or if the structure has subunits, identify those regularly
present in each subunit, located in an area of observed exposure
subject to Level II concentrations as described in sections 5.2.0
and 5.2.1.3.1. Identify only once per structure those exposed
individuals that are using more than one eligible subunit of the
same structure (e.g., using a common or shared area and other parts
of the same structure).
2. Do not include exposed individuals already counted under the
Level I concentrations factor.
3. For each structure or subunit(s), count the number of
individuals residing in or attending school or day care in the
structure, or subunit, subject to Level II concentrations.
4. Count the number of full-time and part-time workers in the
structure or subunit(s) subject to Level II concentrations. If
information is unavailable to classify a worker as full- or part-
time, evaluate that worker as being full-time. Divide the number of
full-time workers by 3 and the number of part-time workers by 6, and
then sum these products with the number of other individuals for
each structure or subunit.
5. Sum the combined population value for all structures within
the areas of observed exposure for the site.
Assign this sum as the combined population factor value subject
to Level II concentrations for this site. Enter this value in line
9b of Table 5-11.
5.2.1.3.2.3 Population within area(s) of subsurface
contamination. Assign the population in area(s) of subsurface
contamination factor value as follows. If sufficient structure-
specific concentration data is available and state of the science
shows there is no unacceptable risk of exposure to populations in a
regularly occupied structure in an area of subsurface contamination,
those populations are not included in the evaluation. (see sections
5.2.0 and 5.2.1.3.1):
1. Identify the regularly occupied structures with a structure
containment value greater than zero and the eligible population
associated with the structures or portions of structures in each
area of subsurface contamination:
For each regularly occupied structure or portion of a
structure in an area of subsurface contamination, sum the number of
all individuals residing in or attending school or day care, in the
structure or portion of the structure in the area of subsurface
contamination.
Count the number of full-time and part-time workers
regularly present in each
[[Page 2801]]
structure or portion of a structure in an area of subsurface
contamination. If information is unavailable to classify a worker as
full- or part-time, evaluate that worker as being full-time. Divide
the number of full-time workers by 3 and the number of part-time
workers by 6. Sum these products with the number of individuals
residing in or attending school or day care in the structure.
Use this sum as the population for the structure.
2. Estimate the depth or distance to contamination at each
regularly occupied structure within an area of subsurface
contamination based on available sampling data, and categorize each
eligible structure based on the depth or distance to contamination
and sample media as presented in Table 5-21. Weight the population
in each structure using the appropriate weighting factors in Table
5-21. If samples from multiple media are available, use the sample
that results in the highest weighting factor.
3. Sum the weighted population in all structures within the
area(s) of subsurface contamination and assign this sum as the
population within an area of subsurface contamination factor value.
Enter this value in line 9c of Table 5-11.
Table 5-21--Weighting Factor Values for Populations Within an Area of
Subsurface Contamination
------------------------------------------------------------------------
Population
Eligible populations \a\ in structures \b\ within an weighting
area of subsurface contamination factor
------------------------------------------------------------------------
Samples From Within Structures or in Crawl Spaces
------------------------------------------------------------------------
1. Population in a structure with levels of 0.9
contamination in a semi-enclosed or enclosed crawl
space sample meeting observed release criteria or
Population in a subunit of a multi-story structure
within an area of subsurface contamination located
directly above a level in an area of observed exposure
or a gaseous indoor air sample meeting observed release
criteria or
Population within a structure where a mitigation system
has been installed as part of a removal or other
temporary response action.
2. Population in a structure where levels of 0.8
contaminants meeting observed release criteria are
inferred based on semi-enclosed or enclosed crawl space
samples in surrounding structures, and a NAPL is
present in those samples...............................
3. Population in a structure where levels of 0.4
contaminants meeting observed release criteria are
inferred based on semi-enclosed or enclosed crawl space
samples in surrounding structures, but no NAPL is
present................................................
------------------------------------------------------------------------
Subsurface Samples From Less Than or Equal to 5 Feet From a Foundation
------------------------------------------------------------------------
4. Population in a structure where levels of 0.8
contaminants meeting observed release criteria are
found or inferred based on any sampling media at or
within five feet horizontally or vertically of the
structure foundation, and a NAPL is present within that
depth..................................................
5. Population in a structure where levels of 0.4
contaminants meeting observed release criteria are
found or inferred based on any sampling media at or
within five feet horizontally or vertically of the
structure foundation, but no NAPL is present within
that depth.............................................
------------------------------------------------------------------------
Subsurface Samples From Greater Than 5 Feet But Less Than or Equal to 30
Feet Depth
------------------------------------------------------------------------
6. Population in a structure where levels of 0.4
contaminants meeting observed release criteria are
found or inferred based on any underlying non-ground
water subsurface sample at a depth greater than 5 feet
but less than or equal to 30 feet from a structure
foundation and a NAPL is present within that depth.....
7. Population in a structure where levels of 0.2
contaminants meeting observed release criteria are
found or inferred based on any underlying non-ground
water subsurface sample at a depth greater than 5 feet
but less than or equal to 30 feet, but no NAPL is
present within that depth..............................
8. Population in a structure where levels of 0.2
contaminants meeting observed release criteria are
found or inferred based on underlying ground water
samples greater than 5 feet from the structure
foundation but less than or equal to 30 feet, and a
NAPL is present in those samples.......................
9. Population in a structure where levels of 0.1
contaminants meeting observed release criteria are
found or inferred based on underlying ground water
samples greater than 5 feet from the structure
foundation but less than or equal to 30 feet, but no
NAPL is present in those samples.......................
------------------------------------------------------------------------
Subsurface Samples From Greater Than 30 Feet Depth
------------------------------------------------------------------------
10. Population in a structure where levels of 0.1
contaminants meeting observed release criteria are
found or inferred based on any underlying sample at
depths greater than 30 feet............................
------------------------------------------------------------------------
\a\ Eligible populations include residents (including individuals living
in, or attending school or day care in the structure), and workers in
regularly occupied structures (see HRS Section 5.2.1.3).
\b\ Eligible structures may include single- or multi-tenant structures
where eligible populations reside, attend school or day care, or work.
These structures may also be mixed use structures.
5.2.1.3.2.4 Calculation of population factor value. Sum the
factor values for Level I concentrations, Level II concentrations,
and population within the area(s) of subsurface contamination.
Assign this sum as the population factor value. Enter this value in
line 9d of Table 5-11.
5.2.1.3.3 Resources. Evaluate the resources factor as follows:
Assign a value of 5 if a resource structure (e.g.,
library, church, tribal facility) is present and regularly occupied
within either an area of observed exposure or area of subsurface
contamination.
Assign a value of 0 if there is no resource structure
within an area of observed exposure or area of subsurface
contamination.
Enter the value assigned in Table 5-11.
5.2.1.3.4 Calculation of targets factor category value. Sum the
values for the exposed individual, population, and resources
factors. Do not round to the nearest integer. Assign this sum as the
targets factor category value for the subsurface intrusion
component. Enter this value in Table 5-11.
5.2.2 Calculation of subsurface intrusion component score.
Multiply the factor category values for likelihood of exposure,
waste characteristics, and targets and round the product to the
nearest integer. Divide the product by 82,500. Assign the resulting
value, subject to a maximum of 100, as the
[[Page 2802]]
subsurface intrusion component score and enter this score in Table
5-11.
5.3 Calculation of the soil exposure and subsurface intrusion
pathway score. Sum the soil exposure component score and subsurface
intrusion component score. Assign the resulting value, subject to a
maximum of 100, as the soil exposure and subsurface intrusion
pathway score (Ssessi). Enter this score in Table 5-11.
6.0 Air Migration Pathway
* * * * *
Table 6-14--Health-based Benchmarks for Hazardous Substances in Air
------------------------------------------------------------------------
-------------------------------------------------------------------------
Concentration corresponding to National Ambient Air Quality
Standard (NAAQS).
Concentration corresponding to National Emission Standards for
Hazardous Air Pollutants (NESHAPs).
Screening concentration for cancer corresponding to that
concentration that corresponds to the 10-\6\ individual cancer risk for
inhalation exposures.
Screening concentration for noncancer toxicological responses
corresponding to the Reference Concentration (RfC) for inhalation
exposures.
------------------------------------------------------------------------
* * * * *
7.0 Sites Containing Radioactive Substances
* * * * *
Table 7-1--HRS Factors Evaluated Differently for Radionuclides
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Subsurface
Surface water Soil exposure intrusion
Ground water pathway Status \a\ pathway Status \a\ component of Status \a\ component of Status \a\ Air pathway Status \a\
SESSI pathway SESSI pathway
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Likelihood of Release......... Likelihood of Likelihood of Likelihood of Likelihood of
Release. Exposure. Exposure. Release.
Observed Release.............. Yes............. Observed Release Yes............. Observed Yes............. Observed Yes............. Observed Release Yes.
Contamination. Exposure.
Potential to Release.......... No.............. Potential to No.............. Attractiveness/ No.............. Potential for Yes............. Gas Potential to No.
Release. Accessibility Exposure. Release.
to Nearby
Residents.
Containment................... No.............. Overland Flow No.............. Area of No.............. Structure No.............. Gas Containment. No.
Containment. Contamination. Containment.
Net Precipitation............. No.............. Runoff.......... No.............. Area of Observed No.............. Depth to Yes............. Gas Source Type. No.
Exposure. Contamination.
Depth to Aquifer.............. No.............. Distance to No.............. Area of No.............. Vertical No.............. Gas Migration No.
Surface water. Subsurface migration. Potential.
Contamination.
Travel Time................... No.............. Flood Frequency. No.............. Vapor Migration No.............. Particulate No.
Potential. Potential to
Release.
Flood No.............. Particulate No.
Containment. Containment.
Particulate No.
Source Type.
Particulate No.
Migration
Potential.
Waste Characteristics......... Waste Waste Waste Waste
Characteristics. Characteristics. Characteristics. Characteristics.
Toxicity...................... Yes............. Toxicity/ Yes/Yes......... Toxicity........ Yes............. Toxicity/ Yes/Yes......... Toxicity........ Yes.
Ecotoxicity. Degradation.
Mobility...................... No.............. Persistence/.... Yes/No.......... Hazardous Waste Yes............. Hazardous Waste Yes............. Mobility........ No.
Mobility........ Quantity. Quantity.
Hazardous Waste Quantity...... Yes............. Bioaccumu-lation No.............. Hazardous Waste Yes.
Potential. Quantity.
Hazardous Waste Yes.............
Quantity.
Targets....................... Targets......... Targets......... Targets......... Targets.........
Nearest Well.................. Yes.\b\......... Nearest Intake.. Yes.\b\......... Resident Yes.\b\......... Exposed......... Yes.\b\......... Nearest Yes.\b\
Individual. Individual...... Individual.
[[Page 2803]]
Population.................... Yes.\b\......... Drinking Water Yes.\b\......... Resident Yes.\b\......... Population...... Yes.\b\......... Population...... Yes.\b\
Population. Population.
Resources..................... No.............. Resources....... No.............. Workers......... No.............. Resources....... No.............. Resources....... No
Wellhead Protection Area...... No.............. Sensitive Yes.\b\......... Resources....... No.............. Sensitive No
Environments. Environments.
Human Food Chain Yes.\b\......... Terrestrial No..............
Individual. Sensitive
Environments.
Human Food Chain Yes.\b\......... Nearby No..............
Population. Individual.
Population No..............
Within 1 Mile.
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Factors evaluated differently are denoted by ``yes''; factors not evaluated differently are denoted by ``no''.
\b\ Difference is in the determination of Level I and Level II concentrations.
* * * * *
* * * These differences apply largely to the soil exposure and
subsurface intrusion pathway and to sites containing mixed
radioactive and other hazardous substances. * * *
7.1 Likelihood of release/likelihood of exposure. Evaluate
likelihood of release for the three migration pathways and
likelihood of exposure for the soil exposure and subsurface
intrusion pathway as specified in sections 2 through 6, except:
establish an observed release, observed contamination, and/or
observed exposure as specified in section 7.1.1. When an observed
release or exposure cannot be established for a migration pathway or
the subsurface intrusion component of the soil exposure and
subsurface intrusion pathway, evaluate potential to release as
specified in section 7.1.2. When observed contamination cannot be
established, do not evaluate the soil exposure component of the soil
exposure and subsurface intrusion pathway.
7.1.1 Observed release/observed contamination/observed exposure.
For radioactive substances, establish an observed release for each
migration pathway by demonstrating that the site has released a
radioactive substance to the pathway (or watershed or aquifer, as
appropriate); establish observed contamination or observed exposure
for the soil exposure and subsurface intrusion pathway as indicated
below. Base these demonstrations on one or more of the following, as
appropriate to the pathway being evaluated:
Direct observation:
--For each migration pathway, a material that contains one or more
radionuclides has been seen entering the atmosphere, surface water,
or ground water, as appropriate, or is known to have entered ground
water or surface water through direct deposition, or
--For the surface water migration pathway, a source area containing
radioactive substances has been flooded at a time that radioactive
substances were present and one or more radioactive substances were
in contact with the flood waters.
--For the subsurface intrusion component of the soil exposure and
subsurface intrusion pathway, a material that contains one or more
radionuclides has been observed entering a regularly occupied
structure via the subsurface or is known to have entered a regularly
occupied structure via the subsurface. Also, when evidence supports
the inference of subsurface intrusion of a material that contains
one or more radionuclides by the site into a regularly occupied
structure, demonstrated adverse effects associated with that release
may also be used to establish observed exposure by direct
observation.
Analysis of radionuclide concentrations in samples
appropriate to the pathway (that is, ground water, soil, air, indoor
air, soil gas, surface water, benthic, or sediment samples):
--For radionuclides that occur naturally and for radionuclides that
are ubiquitous in the environment:
[ssquf] Measured concentration (in units of activity, for
example, pCi per kilogram [pCi/kg], pCi per liter [pCi/L], pCi per
cubic meter [pCi/m3]) of a given radionuclide in the sample are at a
level that:
[cir] Equals or exceeds a value 2 standard deviations above the
mean site-specific background concentration for that radionuclide in
that type of sample, or
[cir] Exceeds the upper-limit value of the range of regional
background concentration values for that specific radionuclide in
that type of sample.
[ssquf] Some portion of the increase must be attributable to the
site to establish the observed release (or observed contamination or
observed exposure), and
[ssquf] For the soil exposure component of the soil exposure and
subsurface intrusion pathway only, the radionuclide must also be
present at the surface or covered by 2 feet or less of cover
material (for example, soil) to establish observed contamination.
--For man-made radionuclides without ubiquitous background
concentrations in the environment:
[ssquf] Measured concentration (in units of activity) of a given
radionuclide in a sample equals or exceeds the sample quantitation
limit for that specific radionuclide in that type of media and is
attributable to the site.
[ssquf] However, if the radionuclide concentration equals or
exceeds its sample quantitation limit, but its release can also be
attributed to one or more neighboring sites, then the measured
concentration of that radionuclide must also equal or exceed a value
either 2 standard deviations above the mean concentration of that
radionuclide contributed by those neighboring sites or 3 times its
background concentration, whichever is lower.
[ssquf] If the sample quantitation limit cannot be established:
[cir] If the sample analysis was performed under the EPA
Contract Laboratory Program, use the EPA contract-required
quantitation limit (CRQL) in place of the sample quantitation limit
in establishing an observed release (or observed contamination or
observed exposure).
[cir] If the sample analysis is not performed under the EPA
Contract Laboratory Program, use the detection limit in place of the
sample quantitation limit.
[ssquf] For the soil exposure component of the soil exposure and
subsurface intrusion pathway only, the radionuclide must also be
present at the surface or covered by 2 feet or less of cover
material (for example, soil) to establish observed contamination.
Gamma radiation measurements (applies only to observed
contamination or observed exposure in the soil exposure and
subsurface intrusion pathway):
[[Page 2804]]
--The gamma radiation exposure rate, as measured in microroentgens
per hour ([mu]R/hr) using a survey instrument held 1 meter above the
ground surface or floor or walls of a structure (or 1 meter away
from an aboveground source for the soil exposure component), equals
or exceeds 2 times the site-specific background gamma radiation
exposure rate.
--Some portion of the increase must be attributable to the site to
establish observed contamination or observed exposure. The gamma-
emitting radionuclides do not have to be within 2 feet of the
surface of the source.
For the three migration pathways and for the subsurface
intrusion component of the soil exposure and subsurface intrusion
pathway, if an observed release or observed exposure can be
established for the pathway (or component, threat, aquifer, or
watershed, as appropriate), assign the pathway (or component,
threat, aquifer, or watershed) an observed release or observed
exposure factor value of 550 and proceed to section 7.2. If an
observed release or observed exposure cannot be established, assign
an observed release or observed exposure factor value of 0 and
proceed to section 7.1.2.
For the soil exposure component of the soil exposure and
subsurface intrusion pathway, if observed contamination can be
established, assign the likelihood of exposure factor for resident
population a value of 550 if there is an area of observed
contamination in one or more locations listed in section 5.1.1;
evaluate the likelihood of exposure factor for nearby population as
specified in section 5.1.2.1; and proceed to section 7.2. If
observed contamination cannot be established, do not evaluate the
soil exposure component of the soil exposure and subsurface
intrusion pathway.
At sites containing mixed radioactive and other hazardous
substances, evaluate observed release (or component, observed
contamination or observed exposure) separately for radionuclides as
described in this section and for other hazardous substances as
described in sections 2 through 6.
For the three migration pathways and the subsurface intrusion
component of the soil exposure and subsurface intrusion pathway, if
an observed release or observed exposure can be established based on
either radionuclides or other hazardous substances, or both, assign
the pathway (or threat, aquifer, or watershed) an observed release
or observed exposure factor value of 550 and proceed to section 7.2.
If an observed release or observed exposure cannot be established
based on either radionuclides or other hazardous substances, assign
an observed release or observed exposure factor value of 0 and
proceed to section 7.1.2.
For the soil exposure component of the soil exposure and
subsurface intrusion pathway, if observed contamination can be
established based on either radionuclides or other hazardous
substances, or both, assign the likelihood of exposure factor for
resident population a value of 550 if there is an area of observed
contamination in one or more locations listed in section 5.1.1;
evaluate the likelihood of exposure factor for nearby population as
specified in section 5.1.2.1; and proceed to section 7.2. If
observed contamination cannot be established based on either
radionuclides or other hazardous substances, do not evaluate the
soil exposure component of the soil exposure and subsurface
intrusion pathway.
7.1.2 Potential to release/potential for exposure. For the three
migration pathways and the subsurface intrusion component of the
soil exposure and subsurface intrusion pathway, evaluate potential
to release or potential for exposure for sites containing
radionuclides in the same manner as specified for sites containing
other hazardous substances. Base the evaluation on the physical and
chemical properties of the radionuclides, not on their level of
radioactivity. For the subsurface intrusion component of the soil
exposure and subsurface intrusion pathway, if the potential for
exposure is based on the presence of gamma emitting radioactive
substances, assign a potential for exposure factor value of 500 only
if the contamination is found within 2 feet beneath a regularly
occupied structure, otherwise assign a potential for exposure factor
value of 0.
For sites containing mixed radioactive and other hazardous
substances, evaluate potential to release or potential for exposure
considering radionuclides and other hazardous substances together.
Evaluate potential to release for each migration pathway and the
potential for exposure for the subsurface intrusion component of the
soil exposure and subsurface intrusion pathway as specified in
sections 3 through 6, as appropriate.
* * * * *
7.2.1 Human Toxicity. For radioactive substances, evaluate the
human toxicity factor as specified below, not as specified in
section 2.4.1.1.
Assign human toxicity factor values to those radionuclides
available to the pathway based on quantitative dose-response
parameters for cancer risks as follows:
Evaluate radionuclides only on the basis of
carcinogenicity and assign all radionuclides to weight-of-evidence
category A, or weight-of-evidence category ``Carcinogenic to
Humans''.
Assign a human toxicity factor value from Table 7-2 to
each radionuclide based on its slope factor (also referred to as a
cancer potency factor).
--For each radionuclide, use the higher of the slope factors for
inhalation and ingestion to assign the factor value.
--If only one slope factor is available for the radionuclide use it
to assign the toxicity factor value.
--If no slope factor is available for the radionuclide, assign that
radionuclide a toxicity factor value of 0 and use other
radionuclides for which a slope factor is available to evaluate the
pathway.
If all radionuclides available to a particular pathway
are assigned a human toxicity factor value of 0 (that is, no slope
factor is available for all the radionuclides), use a default human
toxicity factor value of 1,000 as the human toxicity factor value
for all radionuclides available to the pathway.
At sites containing mixed radioactive and other hazardous
substances, evaluate the toxicity factor separately for the
radioactive and other hazardous substances and assign each a
separate toxicity factor value. This applies regardless of whether
the radioactive and other hazardous substances are physically
separated, combined chemically, or simply mixed together. Assign
toxicity factor values to the radionuclides as specified above and
to the other hazardous substances as specified in section 2.4.1.1.
At sites containing mixed radioactive and other hazardous
substances, if all radionuclides available to a particular pathway
are assigned a human toxicity factor value of 0, use a default human
toxicity factor value of 1,000 for all those radionuclides even if
nonradioactive hazardous substances available to the pathway are
assigned human toxicity factor values greater than 0. Similarly, if
all nonradioactive hazardous substances available to the pathway are
assigned a human toxicity factor value of 0, use a default human
toxicity factor value of 100 for all these nonradioactive hazardous
substances even if radionuclides available to the pathway are
assigned human toxicity factor values greater than 0.
* * * * *
7.2.3 Persistence/Degradation. In determining the surface water
persistence factor for radionuclides, evaluate this factor based
solely on half-life; do not include sorption to sediments in the
evaluation as is done for nonradioactive hazardous substances.
Assign a persistence factor value from Table 4-10 (section
4.1.2.2.1.2) to each radionuclide based on half-life (t
1/2) calculated as follows:
[GRAPHIC] [TIFF OMITTED] TR09JA17.073
Where:
r = Radioactive half-life.
V = Volatilization half-life.
If the volatilization half-life cannot be estimated for a
radionuclide from available data, delete it from the equation.
Select the portion of Table 4-10 to use in assigning the persistence
factor value as specified in section 4.1.2.2.1.2.
At sites containing mixed radioactive and other hazardous
substances, evaluate the persistence factor separately for each
radionuclide and for each nonradioactive hazardous substance, even
if the available data indicate that they are combined chemically.
Assign a persistence factor value to each radionuclide as specified
in this section and to each nonradioactive hazardous substance as
specified in section 4.1.2.2.1.2. When combined chemically, assign a
single persistence factor value based on the higher of the two
values assigned (individually) to the radioactive and nonradioactive
components.
In determining the subsurface intrusion degradation factor for
radionuclides, when evaluating this factor based solely on half-
life, assign a degradation factor value from section 5.2.1.2.1.2 to
each radionuclide based on half-life (t1/2) calculated as
follows:
[[Page 2805]]
[GRAPHIC] [TIFF OMITTED] TR09JA17.074
Where:
r=Radioactive half-life.
If no radioactive half-life information is available for a
radionuclide and the substance is not already assigned a value of 1,
unless information indicates otherwise, assign a value of 1.
At sites containing mixed radioactive and other hazardous
substances, evaluate the degradation factor separately for each
radionuclide and for each nonradioactive hazardous substance, even
if the available data indicate that they are combined chemically.
Assign a degradation factor value to each radionuclide as specified
in this section and to each nonradioactive hazardous substance as
specified in section 5.2.1.2.1.2. If no radioactive half-life
information is available for a radionuclide and the substance is not
already assigned a value of 1, unless information indicates
otherwise, assign a value of 1. Similarly, if no half-life
information is available for a nonradioactive substance, and the
substance is not already assigned a value of 1, unless information
indicates otherwise, assign a value of 1. When combined chemically,
assign a single persistence or degradation factor value based on the
higher of the two values assigned (individually) to the radioactive
and nonradioactive components.
7.2.4 Selection of substance potentially posing greatest
hazard. For the subsurface intrusion component of the soil exposure
and subsurface intrusion pathway and each migration pathway (or
threat, aquifer, or watershed, as appropriate), select the
radioactive substance or nonradioactive hazardous substance that
potentially poses the greatest hazard based on its toxicity factor
value, combined with the applicable mobility, persistence,
degradation and/or bioaccumulation (or ecosystem bioaccumulation)
potential factor values. Combine these factor values as specified in
sections 2 through 6. For the soil exposure component of the soil
exposure and subsurface intrusion pathway, base the selection on the
toxicity factor alone (see sections 2 and 5).
* * * * *
7.2.5.1 Source hazardous waste quantity for radionuclides. For
each migration pathway, assign a source hazardous waste quantity
value to each source having a containment factor value greater than
0 for the pathway being evaluated. For the soil exposure component
of the soil exposure and subsurface intrusion pathway, assign a
source hazardous waste quantity value to each area of observed
contamination, as applicable to the threat being evaluated. For the
subsurface intrusion component, assign a source hazardous waste
quantity value to each regularly occupied structure located within
areas of observed exposure or areas of subsurface contamination.
Allocate hazardous substances and hazardous wastestreams to specific
sources (or areas of observed contamination, areas of observed
exposure or areas of subsurface contamination) as specified in
sections 2.4.2 and 5.2.0.
7.2.5.1.1 Radionuclide constituent quantity (Tier A). Evaluate
radionuclide constituent quantity for each source (or area of
observed contamination or area of observed exposure) based on the
activity content of the radionuclides allocated to the source (or
area of observed contamination or area of observed exposure) as
follows:
Estimate the net activity content (in curies) for the
source (or area of observed contamination or area of observed
exposure) based on:
--Manifests, or
--Either of the following equations, as applicable:
[GRAPHIC] [TIFF OMITTED] TR09JA17.075
Where:
N=Estimated net activity content (in curies) for the source (or
area of observed contamination or area of observed exposure).
V=Total volume of material (in cubic yards) in a source (or area
of observed contamination or area of observed exposure) containing
radionuclides.
ACi=Activity concentration above the respective
background concentration (in pCi/g) for each radionuclide i
allocated to the source (or area of observed contamination or area
of observed exposure).
n=Number of radionuclides allocated to the source (or area of
observed contamination or area of observed exposure) above the
respective background concentrations.
or,
[GRAPHIC] [TIFF OMITTED] TR09JA17.076
Where:
N=Estimated net activity content (in curies) for the source (or area
of observed contamination or area of observed exposure).
V=Total volume of material (in gallons) in a source (or area of
observed contamination or area of observed exposure) containing
radionuclides.
ACi=Activity concentration above the respective
background concentration (in pCi/1) for each radionuclide i
allocated to the source (or area of observed contamination or area
of observed exposure).
n=Number of radionuclides allocated to the source (or area of
observed contamination or area of observed exposure) above the
respective background concentrations.
--Estimate volume for the source (or volume for the area of observed
contamination or area of observed exposure) based on records or
measurements.
--For the soil exposure component of the soil exposure and
subsurface intrusion pathway, in estimating the volume for areas of
observed contamination, do not include more than the first 2 feet of
depth, except: for those types of areas of observed contamination
listed in Tier C of Table 5-2 (section 5.1.1.2.2), include the
entire depth, not just that within 2 feet of the surface.
--For the subsurface intrusion component of the soil exposure and
subsurface intrusion pathway, in estimating the volume for areas of
observed exposure, only use the volume of air in the regularly
occupied structures where observed exposure has been documented.
Convert from curies of radionuclides to equivalent
pounds of nonradioactive hazardous substances by multiplying the
activity estimate for the source (or area of observed contamination
or area of observed exposure) by 1,000.
Assign this resulting product as the radionuclide
constituent quantity value for the source (or area of observed
contamination or area of observed exposure).
If the radionuclide constituent quantity for the source (or area
of observed contamination or area of observed exposure) is
adequately determined (that is, the total activity of all
radionuclides in the source and releases from the source [or in the
area of observed contamination or area of observed exposure] is
known or is estimated with reasonable confidence), do not evaluate
the radionuclide wastestream quantity measure in section 7.2.5.1.2.
Instead, assign radionuclide wastestream quantity a value of 0 and
proceed to section 7.2.5.1.3. If the radionuclide constituent
quantity is not adequately determined, assign the source (or area of
observed contamination or area of observed exposure) a value for
radionuclide constituent quantity based on the available data and
proceed to section 7.2.5.1.2.
7.2.5.1.2 Radionuclide wastestream quantity (Tier B). Evaluate
radionuclide wastestream quantity for the source (or area of
observed contamination, area of observed exposure, or area of
subsurface contamination) based on the activity content of
radionuclide wastestreams allocated to the source (or area of
observed contamination, area of observed exposure, or area of
subsurface contamination) as follows:
Estimate the total volume (in cubic yards or in
gallons) of wastestreams containing radionuclides allocated to the
source (or area of observed contamination, area of observed
exposure, or area of subsurface contamination).
Divide the volume in cubic yards by 0.55 (or the volume
in gallons by 110) to convert to the activity content expressed in
terms of equivalent pounds of nonradioactive hazardous substances.
Assign the resulting value as the radionuclide
wastestream quantity value for the source (or area of observed
contamination, area of observed exposure, or area of subsurface
contamination).
For the subsurface intrusion component of the soil
exposure and subsurface intrusion pathway, estimate the total
wastestream volume for all regularly occupied structures that have a
containment value >0 and that are located within areas of observed
exposure with observed or inferred intrusion, and
[[Page 2806]]
within areas of subsurface contamination. Calculate the volume of
each regularly occupied structure based on actual data. If unknown,
use a ceiling height of 8 feet.
7.2.5.1.3 Calculation of source hazardous waste quantity value
for radionuclides. Select the higher of the values assigned to the
source (or area of observed contamination, area of observed
exposure, and/or area of subsurface contamination) for radionuclide
constituent quantity and radionuclide wastestream quantity. Assign
this value as the source hazardous waste quantity value for the
source (or area of observed contamination, area of observed
exposure, or area of subsurface contamination). Do not round to the
nearest integer.
7.2.5.2 Calculation of hazardous waste quantity factor value for
radionuclides. Sum the source hazardous waste quantity values
assigned to all sources (or areas of observed contamination, areas
of observed exposure, or areas of subsurface contamination) for the
pathway being evaluated and round this sum to the nearest integer,
except: if the sum is greater than 0, but less than 1, round it to
1. Based on this value, select a hazardous waste quantity factor
value for this pathway from Table 2-6 (section 2.4.2.2).
For a migration pathway, if the radionuclide constituent
quantity is adequately determined (see section 7.2.5.1.1) for all
sources (or all portions of sources and releases remaining after a
removal action), assign the value from Table 2-6 as the hazardous
waste quantity factor value for the pathway. If the radionuclide
constituent quantity is not adequately determined for one or more
sources (or one or more portions of sources or releases remaining
after a removal action), assign a factor value as follows:
If any target for that migration pathway is subject to
Level I or Level II concentrations (see section 7.3), assign either
the value from Table 2-6 or a value of 100, whichever is greater, as
the hazardous waste quantity factor value for that pathway.
If none of the targets for that pathway is subject to
Level I or Level II concentrations, assign a factor value as
follows:
--If there has been no removal action, assign either the value from
Table 2-6 or a value of 10, whichever is greater, as the hazardous
waste quantity factor value for that pathway.
--If there has been a removal action:
[ssquf] Determine values from Table 2-6 with and without
consideration of the removal action.
[ssquf] If the value that would be assigned from Table 2-6
without consideration of the removal action would be 100 or greater,
assign either the value from Table 2-6 with consideration of the
removal action or a value of 100, whichever is greater, as the
hazardous waste quantity factor value for the pathway.
[ssquf] If the value that would be assigned from Table 2-6
without consideration of the removal action would be less than 100,
assign a value of 10 as the hazardous waste quantity factor value
for the pathway.
For the soil exposure component of the soil exposure and
subsurface intrusion pathway, if the radionuclide constituent
quantity is adequately determined for all areas of observed
contamination, assign the value from Table 2-6 as the hazardous
waste quantity factor value. If the radionuclide constituent
quantity is not adequately determined for one or more areas of
observed contamination, assign either the value from Table 2-6 or a
value of 10, whichever is greater, as the hazardous waste quantity
factor value.
For the subsurface intrusion component of the soil exposure and
subsurface intrusion pathway, if the radionuclide constituent
quantity is adequately determined for all areas of observed
exposure, assign the value from Table 2-6 as the hazardous waste
quantity factor value. If the radionuclide constituent quantity is
not adequately determined for one or more areas of observed
exposure, assign either the value from Table 2-6 or a value of 10,
whichever is greater, as the hazardous waste quantity factor value.
7.2.5.3 Calculation of hazardous waste quantity factor value for
sites containing mixed radioactive and other hazardous substances.
For each source (or area of observed contamination, area of observed
exposure, or area of subsurface contamination) containing mixed
radioactive and other hazardous substances, calculate two source
hazardous waste quantity values--one based on radionuclides as
specified in sections 7.2.5.1 through 7.2.5.1.3 and the other based
on the nonradioactive hazardous substances as specified in sections
2.4.2.1 through 2.4.2.1.5, and sections 5.1.1.2.2, 5.1.2.2.2 and
5.2.1.2.2 (that is, determine each value as if the other type of
substance was not present). Sum the two values to determine a
combined source hazardous waste quantity value for the source (or
area of observed contamination, area of observed exposure, or area
of subsurface contamination). Do not round this value to the nearest
integer.
Use this combined source hazardous waste quantity value to
calculate the hazardous waste quantity factor value for the pathway
as specified in section 2.4.2.2, except: if either the hazardous
constituent quantity or the radionuclide constituent quantity, or
both, are not adequately determined for one or more sources (or one
or more portions of sources or releases remaining after a removal
action) or for one or more areas of observed contamination or areas
of observed exposure, as applicable, assign the value from Table 2-6
or the default value applicable for the pathway, whichever is
greater, as the hazardous waste quantity factor value for the
pathway.
7.3 Targets. For radioactive substances, evaluate the targets
factor category as specified in section 2.5 and sections 3 through
6, except: Establish Level I and Level II concentrations at sampling
locations as specified in sections 7.3.1 and 7.3.2 and establish
weighting factors for populations associated with an area of
subsurface contamination in the subsurface intrusion component of
the soil exposure and subsurface intrusion pathway as specified in
section 7.3.3.
For all pathways (components and threats), use the same target
distance limits for sites containing radioactive substances as is
specified in sections 3 through 6 for sites containing
nonradioactive hazardous substances. At sites containing mixed
radioactive and other hazardous substances, include all sources (or
areas of observed contamination, areas of observed exposure, or
areas of subsurface contamination) at the site in identifying the
applicable targets for the pathway.
7.3.1 Level of contamination at a sampling location. Determine
whether Level I or Level II concentrations apply at a sampling
location (and thus to the associated targets) as follows:
Select the benchmarks from section 7.3.2 applicable to
the pathway (or component or threat) being evaluated.
Compare the concentrations of radionuclides in the
sample (or comparable samples) to their benchmark concentrations for
the pathway (or component or threat) as specified in section 7.3.2.
Treat comparable samples as specified in section 2.5.1.
Determine which level applies based on this comparison.
If none of the radionuclides eligible to be evaluated
for the sampling location have an applicable benchmark, assign Level
II to the actual contamination at that sampling location for the
pathway (or component or threat).
In making the comparison, consider only those samples,
and only those radionuclides in the sample, that meet the criteria
for an observed release (or observed contamination or observed
exposure) for the pathway, except: Tissue samples from aquatic human
food chain organisms may also be used for the human food chain
threat of the surface water pathway as specified in sections 4.1.3.3
and 4.2.3.3.
7.3.2 Comparison to benchmarks. Use the following media
specific benchmarks (expressed in activity units, for example, pCi/l
for water, pCi/kg for soil and for aquatic human food chain
organisms, and pCi/m3 for air) for making the comparisons for the
indicated pathway (or threat):
Maximum Contaminant Levels (MCLs)--ground water
migration pathway and drinking water threat in surface water
migration pathway.
Uranium Mill Tailings Radiation Control Act (UMTRCA)
standards--soil exposure component of the soil exposure and
subsurface intrusion pathway only.
Screening concentration for cancer corresponding to
that concentration that corresponds to the 10-6
individual cancer risk for inhalation exposures (air migration
pathway and subsurface intrusion component of the soil exposure and
subsurface intrusion pathway) or for oral exposures (ground water
migration pathway; drinking water or human food chain threats in
surface water migration pathway; and soil exposure and subsurface
intrusion pathway).
--For the soil exposure component of the soil exposure and
subsurface intrusion pathway, include two screening concentrations
for cancer--one for ingestion of surface materials and one for
external radiation exposures from gamma-emitting radionuclides in
surface materials.
Select the benchmark(s) applicable to the pathway (component or
threat) being
[[Page 2807]]
evaluated. Compare the concentration of each radionuclide from the
sampling location to its benchmark concentration(s) for that pathway
(component or threat). Use only those samples and only those
radionuclides in the sample that meet the criteria for an observed
release (or observed contamination or observed exposure) for the
pathway, except: Tissue samples from aquatic human food chain
organisms may be used as specified in sections 4.1.3.3 and 4.2.3.3.
If the concentration of any applicable radionuclide from any sample
equals or exceeds its benchmark concentration, consider the sampling
location to be subject to Level I concentrations for that pathway
(component or threat). If more than one benchmark applies to the
radionuclide, assign Level I if the radionuclide concentration
equals or exceeds the lowest applicable benchmark concentration. In
addition, for the soil exposure and subsurface intrusion pathway,
assign Level I concentrations at the sampling location if measured
gamma radiation exposure rates equal or exceed 2 times the
background level (see section 7.1.1).
If no radionuclide individually equals or exceeds its benchmark
concentration, but more than one radionuclide either meets the
criteria for an observed release (or observed contamination or
observed exposure) for the sample or is eligible to be evaluated for
a tissue sample (see sections 4.1.3.3 and 4.2.3.3), calculate a
value for index I for these radionuclides as specified in section
2.5.2. If I equals or exceeds 1, assign Level I to the sampling
location. If I is less than 1, assign Level II.
At sites containing mixed radioactive and other hazardous
substances, establish the level of contamination for each sampling
location considering radioactive substances and nonradioactive
hazardous substances separately. Compare the concentration of each
radionuclide and each nonradioactive hazardous substance from the
sampling location to its respective benchmark concentration(s). Use
only those samples and only those substances in the sample that meet
the criteria for an observed release (or observed contamination or
observed exposure) for the pathway except: Tissue samples from
aquatic human food chain organisms may be used as specified in
sections 4.1.3.3 and 4.2.3.3. If the concentration of one or more
applicable radionuclides or other hazardous substances from any
sample equals or exceeds its benchmark concentration, consider the
sampling location to be subject to Level I concentrations. If more
than one benchmark applies to a radionuclide or other hazardous
substance, assign Level I if the concentration of the radionuclide
or other hazardous substance equals or exceeds its lowest applicable
benchmark concentration.
If no radionuclide or other hazardous substance individually
exceed a benchmark concentration, but more than one radionuclide or
other hazardous substance either meets the criteria for an observed
release (or observed contamination or observed exposure) for the
sample or is eligible to be evaluated for a tissue sample, calculate
an index I for both types of substances as specified in section
2.5.2. Sum the index I values for the two types of substances. If
the value, individually or combined, equals or exceeds 1, assign
Level I to the sample location. If it is less than 1, calculate an
index J for the nonradioactive hazardous substances as specified in
section 2.5.2. If J equals or exceeds 1, assign Level I to the
sampling location. If J is less than 1, assign Level II.
7.3.3 Weighting of targets within an area of subsurface
contamination. For the subsurface intrusion component of the soil
exposure and subsurface intrusion pathway, assign a weighting factor
as specified in section 5.2.1.3.2.3 except when a structure in an
area of subsurface contamination is delineated or inferred to be
delineated by gamma radiation exposure rates meeting observed
release criteria with a depth to contamination of 2 feet or less.
For those populations residing, working, or attending school or day
care in a structure delineated or inferred to be delineated by gamma
radiation exposure rates meeting observed release criteria with a
depth to contamination of 2 feet or less, assign a weighting factor
of 0.9.
[FR Doc. 2016-30640 Filed 1-6-17; 8:45 am]
BILLING CODE 6560-50-P