[Federal Register Volume 67, Number 74 (Wednesday, April 17, 2002)]
[Proposed Rules]
[Pages 19029-19090]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 02-9154]



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Part III





Environmental Protection Agency





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40 CFR Part 141



National Primary Drinking Water Regulations; Announcement of the 
Results of EPA's Review of Existing Drinking Water Standards and 
Request for Public Comment; Proposed Rule

Federal Register / Vol. 67, No. 74 / Wednesday, April 17, 2002 / 
Proposed Rules

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 141

[FRL-7167-9]
RIN 2040-AD67


National Primary Drinking Water Regulations; Announcement of the 
Results of EPA's Review of Existing Drinking Water Standards and 
Request for Public Comment

AGENCY: Environmental Protection Agency (EPA).

ACTION: Review of regulations; request for comments.

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SUMMARY: The Safe Drinking Water Act (SDWA) requires the United States 
Environmental Protection Agency (EPA) to conduct a periodic review of 
existing National Primary Drinking Water Regulations (NPDWRs). EPA is 
requesting public comment on the results of its review of 69 NPDWRs 
that were established prior to 1997, including 68 chemical NPDWRs and 
the Total Coliform Rule (TCR). The intended purpose of the review is to 
identify those NPDWRs for which current health risk assessments, 
changes in technology, and/or other factors, provide a health or 
technical basis to support a regulatory revision that will improve or 
strengthen public health protection. Based on its review, and pending 
an evaluation of public comments, the Agency preliminarily believes 
that the 68 chemical NPDWRs remain appropriate at this time, and that 
the TCR should be revised.

DATES: EPA must receive public comments on this action by June 17, 
2002.

ADDRESSES: Please send your comments to the W-01-14 Comments Clerk. 
Submit electronic comments to: [email protected]. Written comments 
should be mailed to: Water Docket (MC-4101), U.S. Environmental 
Protection Agency, 1200 Pennsylvania Avenue, NW., Washington, DC, 
20460. Hand deliveries should be delivered to EPA's Water Docket at 
East Tower Basement (EB Room 57), Waterside Mall, 401 M Street, SW., 
Washington, DC, 20460. You may contact the docket at (202) 260-3027 
between 9 a.m. and 3:30 p.m. Eastern Time, Monday through Friday. 
Comments may be submitted electronically. See SUPPLEMENTARY INFORMATION 
for file formats and other information about electronic filing and 
docket review.

FOR FURTHER INFORMATION CONTACT: For technical inquiries contact: Judy 
Lebowich, (202) 564-4884, e-mail: [email protected], or Wynne 
Miller, (202) 564-4887, e-mail: [email protected]. For general 
information about, and copies of, this document or information about 
the existing NPDWRs discussed in this action, contact the Safe Drinking 
Water Hotline. Callers within the United States may reach the Hotline 
at (800) 426-4791. The Hotline is open Monday through Friday, excluding 
Federal holidays, from 9 a.m. to 5:30 p.m. Eastern Time.

SUPPLEMENTARY INFORMATION:

How Should I Submit Comments on This Action?

    EPA will accept written or electronic comments (please do not send 
both). EPA prefers electronic comments. Commenters should use a 
separate paragraph for each issue discussed. No facsimiles (faxes) will 
be accepted. Commenters who want EPA to acknowledge receipt of their 
comments should also send a self-addressed, stamped envelope. If you 
submit written comments, please submit an original and three copies of 
your comments and enclosures (including references).
    Electronic comments must be submitted in WordPerfect 8 (or an older 
version) or ASCII file format. Compressed or zipped files will not be 
accepted. You may file electronic comments on this action online at 
many Federal Depository Libraries.
    The Agency's response-to-comments document for the final decision 
will address the comments received on this action, and the response-to-
comments document will be made available in the docket.

How Can I Obtain Materials in the Docket?

    The docket is available for inspection from 9:00 a.m. to 4:00 p.m., 
Monday through Friday, excluding legal holidays, at the Water Docket, 
East Tower Basement (EB Room 57), Waterside Mall, USEPA, 401 M Street, 
SW; Washington, DC. For access to docket (Docket Number W-01-14) 
materials, please call (202) 260-3027 between 9:00 a.m. and 3:30 p.m., 
Eastern Time, Monday through Friday, to schedule an appointment.

Does This Action Apply to My Public Water System?

    This action itself does not impose any requirements on anyone. 
Instead, it notifies interested parties of EPA's preliminary revise/not 
revise decisions for 69 NPDWRs.

Abbreviations and Acronyms Used in This Action

>--greater than
2,4-D--2,4-dichlorophenoxyacetic acid
AA--activated alumina
AI--adequate intake
ASDWA--Association of State Drinking Water Administrators
ATSDR--Agency for Toxic Substances and Disease Registry
AWWA--American Water Works Association
BAT--best available technology
BMD--benchmark dose
bw--body weight
CCL--Contaminant Candidate List
CFR--Code of Federal Regulations
CMR--Chemical Monitoring Reform
CWS--community water system
DBCP--1,2-dibromo-3-chloropropane
DBPR--Disinfectants and Disinfection Byproducts Rule
DEHA--di(2-ethylhexyl)adipate
DEHP--di(2-ethylhexyl)phthalate
DRI--dietary reference intake
DWEL--drinking water equivalent level
EDB--ethylene dibromide
EPA--U.S. Environmental Protection Agency
EPTDS--entry points to a distribution system
FR--Federal Register
GAC--granular activated carbon
GC/MS--gas chromatography/mass spectrometry
HHS--Department of Health and Human Services
HPC--heterotrophic plate count
I--daily drinking water intake
IESWTR--Interim Enhanced Surface Water Treatment Rule
IRIS--Integrated Risk Information System
LCR--Lead and Copper Rule
LOAEL--lowest-observed-adverse-effect level
LT1ESWTR--Long-Term 1 Enhanced Surface Water Treatment Rule
LT2ESWTR--Long-Term 2 Enhanced Surface Water Treatment Rule
MCL--maximum contaminant level
MCLG--maximum contaminant level goal
M/DBP--Microbial/Disinfection Byproducts
MDL--method detection limit
MF--modifying factor
MFL--million fibers per liter
mg/kg/day--milligrams per kilogram of body weight per day
mg/L--milligrams per liter
MSRC--Mercury Study Report to Congress
MTD--maximum tolerated dose
N--nitrogen
NAS--National Academy of Sciences
NCOD--National Drinking Water Contaminant Occurrence Database

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NDWAC--National Drinking Water Advisory Council
NIPDWR--National Interim Primary Drinking Water Regulation
NOAEL--no-observed-adverse-effect level
NPDWR--National Primary Drinking Water Regulation
NRC--National Research Council
NTNCWS--non-transient, non-community water system
NTP--National Toxicology Program
NWIS--National Water Information System
OGWDW--Office of Ground Water and Drinking Water
OPP--Office of Pesticide Programs
OW--Office of Water
PAC--powdered activated carbon
PCBs--polychlorinated biphenyls
POU--point-of-use
ppm--part per million
PQL--practical quantitation level
PTA--packed tower aeration
PWS--public water system
RDA--recommended dietary allowance
RfD--reference dose
RO--reverse osmosis
RSC--relative source contribution
SAB--Science Advisory Board
SDWA--Safe Drinking Water Act
SDWIS--Safe Drinking Water Information System
SMCL--secondary maximum contaminant level
SOC--synthetic organic chemical
SWTR--Surface Water Treatment Rule
TCR--Total Coliform Rule
TNCWS--transient, non-community water system
TT--treatment technique
TTHM--total trihalomethanes
UF--uncertainty factor
UL--tolerable upper intake level
URCIS--Unregulated Contaminant Information System
VOC--volatile organic chemical
WS--water supply

Table of Contents

I. Background and Summary of Today's Action
    A. What are the Statutory Requirements for the Six-Year Review?
    B. What is the Schedule for Reviewing Existing NPDWRs?
II. Stakeholder Involvement in the Six-Year Review Process
    A. How Have Stakeholders Been Involved in the Review Process?
    B. How Does EPA Plan to Involve the Science Advisory Board 
(SAB)?
III. Regulations Included in the Six-Year Review
IV. EPA's Protocol for Reviewing the NPDWRs Included in Today's 
Action
    A. What was EPA's Review Process?
    1. Initial Technical Review
    2. In-Depth Technical Review
    B. How Did EPA Review the Chemical NPDWRs?
    1. Health Effects
    2. Analytical Feasibility
    3. Treatment Feasibility
    4. Other Regulatory Revisions
    5. Occurrence and Exposure Analysis
    6. Economic Considerations
    C. How Is EPA Reviewing the Total Coliform Rule?
    D. How Did EPA Factor Children's Health Concerns into the 
Review?
    V. EPA's Preliminary Decisions Based on its Review of NPDWRs 
Included in Today's Action
    A. What Preliminary Decisions Has EPA Made Regarding the 
Chemical NPDWRs?
    1. Acrylamide
    2. Alachlor
    3. Antimony
    4. Asbestos
    5. Atrazine
    6. Barium
    7. Benzene
    8. Benzo[a]pyrene
    9. Beryllium
    10. Cadmium
    11. Carbofuran
    12. Carbon Tetrachloride
    13. Chlordane
    14. Chromium
    15. Copper
    16. Cyanide
    17. 2,4-D (2,4-Dichlorophenoxyacetic Acid)
    18. Dalapon (2,2-Dichloropropionic Acid)
    19. 1,2-Dibromo-3-chloropropane (DBCP)
    20. 1,2-Dichlorobenzene (o-Dichlorobenzene)
    21. 1,4-Dichlorobenzene (p-Dichlorobenzene)
    22. 1,2-Dichloroethane (Ethylene Dichloride)
    23. 1,1-Dichloroethylene
    24. cis-1,2-Dichloroethylene
    25. trans-1,2-Dichloroethylene
    26. Dichloromethane (Methylene Chloride)
    27. 1,2-Dichloropropane
    28. Di(2-ethylhexyl)adipate (DEHA)
    29. Di(2-ethylhexyl)phthalate (DEHP)
    30. Dinoseb
    31. Diquat
    32. Endothall
    33. Endrin
    34. Epichlorohydrin
    35. Ethylbenzene
    36. Ethylene Dibromide (EDB; 1,2-Dibromoethane)
    37. Fluoride
    38. Glyphosate
    39. Heptachlor
    40. Heptachlor Epoxide
    41. Hexachlorobenzene
    42. Hexachlorocyclopentadiene
    43. Lead
    44. Lindane (-Hexachlorocyclohexane)
    45. Mercury (Inorganic)
    46. Methoxychlor
    47. Monochlorobenzene (Chlorobenzene)
    48. Nitrate (as N)
    49. Nitrite (as N)
    50. Oxamyl (Vydate)
    51. Pentachlorophenol
    52. Picloram
    53. Polychlorinated Biphenyls (PCBs)
    54. Selenium
    55. Simazine
    56. Styrene
    57. 2,3,7,8-TCDD (Dioxin)
    58. Tetrachloroethylene
    59. Thallium
    60. Toluene
    61. Toxaphene
    62. 2,4,5-TP (Silvex; 2,4,5-Trichlorophenoxypropionic Acid)
    63. 1,2,4-Trichlorobenzene
    64. 1,1,1-Trichloroethane
    65. 1,1,2-Trichloroethane
    66. Trichloroethylene
    67. Vinyl Chloride
    68. Xylenes (Total)
    B. What Preliminary Decision Has EPA Made Regarding the Total 
Coliform Rule?
    1. Background
    2. Technical Reviews
    3. Preliminary Decision
VI. Request for Comments
    A. On Which Issues is EPA Soliciting Public Comment?
    B. Request for Comments on Use of Plain Language
VII. EPA's Next Steps
VIII. References
Appendix A: Background on the Calculation of MCLG and Cancer 
Classification System

List of Tables

Table III-1: Pre-1997 NPDWRs Included in Today's Action
Table III-2: NPDWRs Not Included in Today's Action
Table IV-1: Summary of the Outcome of the Six-Year Health Effects 
Review
Table IV-2: Chemical NPDWRs Included in the Analytical Feasibility 
Reassessment and the Result of that Assessment
Table IV-3: Chemical NPDWRs Included in the Treatment Feasibility 
Analysis
Table V-1: Preliminary Revise/Not Revise Decisions for the 68 
Chemical NPDWRs and TCR
Table V-2: Benzene Occurrence
Table V-3: Beryllium Occurrence
Table V-4: Chlordane Occurrence
Table V-5: Chromium Occurrence
Table V-6: 1,2-Dibromo-3-chloropropane Occurrence
Table V-7: Dichloromethane Occurrence
Table V-8: 1,2-Dichloropropane Occurrence
Table V-9: Heptachlor Occurrence
Table V-10: Heptachlor Epoxide Occurrence
Table V-11: Hexachlorobenzene Occurrence
Table V-12: Oxamyl Occurrence
Table V-13: Picloram Occurrence
Table V-14: Toxaphene Occurrence
Table V-15: 1,1,2-Trichloroethane Occurrence
Table VI-1: Issues on Which EPA is Requesting Public Comment or Data
Table A-1: Cancer Classification Systems Used by EPA

List of Figures

Figure 1: Overview of the Protocol for the Revise/Not Revise 
Decision
Figure 2: Distribution of State Rankings: Manufacturing 
Establishments per Square Mile vs. Total Farm Agricultural Chemical 
Expenses
Figure 3: Geographic Distribution of the 16-State Cross-Section Used 
for Occurrence Analysis

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I. Background and Summary of Today's Action

A. What Are the Statutory Requirements for the Six-Year Review?

    Under the SDWA, as amended in 1996, EPA must periodically review 
existing national primary drinking water regulations (NPDWRs) and, if 
appropriate, revise them. Section 1412(b)(9) of SDWA states:

    The Administrator shall, not less often than every 6 years, 
review and revise, as appropriate, each national primary drinking 
water regulation promulgated under this title. Any revision of a 
national primary drinking water regulation shall be promulgated in 
accordance with this section, except that each revision shall 
maintain, or provide for greater, protection of the health of 
persons.

Pursuant to the SDWA 1996 Amendments, EPA developed a systematic 
approach, or protocol, for the review of NPDWRs discussed in today's 
action. EPA has applied the protocol discussed in section IV of today's 
action to the Agency's initial Six-Year Review of NPDWRs for total 
coliforms and 68 inorganic and organic chemicals, published prior to 
the SDWA 1996 Amendments (i.e., pre-1997 NPDWRs). Section III of 
today's action identifies these NPDWRs and section V of today's action 
contains a summary of the review findings for each of these 69 NPDWRs 
(see Table III-1).
    While the Agency expects that modifications to the protocol will be 
made in subsequent six-year reviews to address changing circumstances, 
the Agency expects to use the framework developed for the current 
review as the starting point. EPA, therefore, is seeking public comment 
on the protocol that has been applied to the current review.

B. What Is the Schedule for Reviewing Existing NPDWRs?

    EPA plans to publish its final findings with respect to the initial 
review of these 69 NPDWRs in the Federal Register (FR) in the August 
2002 time frame.
    In addition to these 69 NPDWRs, there are additional pre-1997 
NPDWRs, which are being or have been reviewed separately from today's 
action. Section III explains how the Agency plans to satisfy the Six-
Year Review requirement for those regulations. In most cases, EPA has 
performed or is performing the review in conjunction with recent or 
ongoing rulemakings. NPDWRs published after the 1996 SDWA Amendments 
will be reviewed as a part of the 2002-2008 review cycle.

II. Stakeholder Involvement in the Six-Year Review Process

A. How Have Stakeholders Been Involved in the Review Process?

    Stakeholders include:
     The general public;
     Congress;
     Other Federal agencies;
     State, Tribal, and local officials;
     Public health/health care providers;
     Public interest groups;
     Public water suppliers;
     National trade associations;
     Environmental groups;
     Manufacturers; and
     Agricultural producers.
    EPA involved stakeholders by: holding a stakeholder meeting; 
participating in national meetings, workshops, and technical forums; 
meeting informally with associations and technical experts; posting 
information on the Office of Ground Water and Drinking Water's 
(OGWDW's) web page (www.epa.gov/safewater/); and publishing this FR 
notice on the Six-Year Review.
    EPA invited representatives from State and Tribal communities, 
public water systems (PWSs), public health organizations, academia, 
environmental and public interest groups, engineering firms, and other 
stakeholders to a stakeholder meeting in Washington, DC, in November 
1999 (64 FR 55711, October 14, 1999 (USEPA, 1999c)). Approximately 50 
participants attended, including representatives from the invited 
groups. EPA discussed its preliminary strategy for the Six-Year Review 
and invited stakeholder comment. Stakeholders generally agreed that EPA 
had identified the appropriate key elements for the review; however, in 
some cases, stakeholders suggested that EPA needed to be more proactive 
in seeking out new information that might affect the regulatory 
decision (USEPA, 1999e). For more detailed information about this 
stakeholder meeting, the docket for this action (Docket Number W-01-14) 
contains the stakeholder meeting discussion papers, the agenda, the 
participant list, presentation materials, and an executive meeting 
summary which includes the specific comments and questions posed by 
stakeholders. The executive meeting summary is also available on EPA's 
drinking water web page, http://www.epa.gov/safewater/ccl/novmtg.html.
    In the Spring of 2000, the National Drinking Water Advisory Council 
(NDWAC) formed a working group to develop recommendations regarding the 
process the Agency should apply to conduct a periodic and systematic 
review of existing NPDWRs. The Working Group held two meetings and a 
conference call during June through September 2000 (USEPA, 2000b; 
USEPA, 2000c; USEPA, 2000d). The NDWAC approved the Working Group's 
recommendations in November 2000 and formally provided them to EPA in 
December 2000 (NDWAC, 2000). The NDWAC recommended that EPA's review 
include consideration of five key elements, as appropriate: health 
effects, analytical and treatment feasibility, implementation-related 
issues, occurrence and exposure, and economic impacts. The NDWAC 
suggested that the Agency conduct an initial screening review of each 
NPDWR to identify potential candidates for an in-depth analysis. As 
discussed in more detail in section IV of today's action, EPA has 
followed the general protocol recommended by the NDWAC.
    In addition to the November 1999 stakeholder meeting and 
consultation with the NDWAC, EPA representatives have delivered 
presentations at a variety of meetings held by other organizations, 
including: two American Water Works Association (AWWA) Technical 
Advisory Workgroup meetings, one held in February 2001 in Washington, 
DC, and one held in February 2002 in San Diego, CA; a meeting held by 
the Association of State Drinking Water Administrators (ASDWA) in March 
2001 in Alexandria, VA; and the annual AWWA meeting held in Washington, 
DC in June 2001. At each of these meetings, stakeholders were given the 
opportunity to comment on the protocol by which EPA was planning to 
perform the review of existing NPDWRs. EPA received valuable input from 
stakeholders on the planned protocol.

B. How Does EPA Plan To Involve the Science Advisory Board (SAB)?

    EPA plans to consult with the SAB Drinking Water Committee on 
today's action. The Agency will request their review and comment on 
whether the protocol EPA developed based on the NDWAC recommendations 
was consistently applied and appropriately documented.

III. Regulations Included in the Six-Year Review

    Table III-1 lists the pre-1997 NPDWRs covered by today's action and 
the rulemaking by which they were originally promulgated. Table III-2 
lists the NPDWRs not covered by today's action. These include the 
remaining pre-1997 NPDWRs which are being or have already been reviewed 
in separate actions and the NPDWRs promulgated after the 1996 SDWA 
Amendments. The

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NPDWRs listed in Table III-2 will be included in the 2002-2008 review 
round. Section V of today's action summarizes the results of the review 
of 68 pre-1997 chemical NPDWRs and the NPDWR for total coliforms.

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IV. EPA's Protocol for Reviewing the NPDWRs Included in Today's 
Action

A. What Was EPA's Review Process?

    The document, ``EPA Protocol for the Review of Existing National 
Primary Drinking Water Regulations'' (USEPA, 2002f), contains a 
detailed description of the process the Agency used to review the 69 
NPDWRs discussed in today's action. EPA's primary goal was to identify 
and prioritize candidates for regulatory revision in order to target 
those revisions that are most likely to result in an increased level of 
public health protection and/or result in substantial cost savings 
while maintaining the level of public health protection. This section 
provides an overview of the review process. Sections IV.B and IV.C of 
today's action provide a more detailed description of how EPA applied 
the process to the review of 68 chemical NPDWRs and the TCR, 
respectively.
    EPA applied the following basic principles to the review process:
     Health effects, analytical feasibility, treatment data, 
and analyses underlying existing regulations remain adequate and 
relevant, except in those instances where reliable, peer-reviewed, new 
data are available that indicate a need to re-evaluate an NPDWR (e.g., 
where a change in health risk assessment has occurred).
     If new data were available, EPA determined whether changes 
in existing standards were warranted. For example, in determining 
whether there was a change in analytical feasibility, the Agency 
applied the current policy and procedures for calculating the practical 
quantitation level for drinking water contaminants.\1\
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    \1\ See: 50 FR 46880, November 13, 1985 (USEPA, 1985); 52 FR 
25690, July 8, 1987 (USEPA, 1987); 54 FR 22062, May 22, 1989 (USEPA, 
1989a).
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     EPA was unable to complete evaluation of certain new data 
within the time available for the review. For example, if a new health 
risk assessment for a contaminant was not completed during the review 
cycle, EPA generally made a ``not revise'' decision on the rationale 
that it was not appropriate to revise the regulation while the 
assessment was ongoing. When an updated assessment is completed, EPA 
will review the update and any new conclusions or additional 
information associated with the contaminant during the next review 
cycle. The Agency may make a determination to revise a particular NPDWR 
before August 2008 where justified by new public health risk 
information.
     During the review, EPA identified areas where information 
is inadequate or unavailable (data gaps) and is needed before an NPDWR 
may be considered as a candidate for revision. Where the Agency has 
been unable to fill such gaps during the review process, today's action 
provides information about the data gaps so that further research and 
data collection can be considered as part of the second review cycle. 
For example, the review may identify a need to better understand new 
treatment technologies. Such an information gap will need to be 
considered in the context of EPA's overall OGWDW research strategy.
     During the review process, the Agency did not consider 
potential regulatory revisions that were already the subject of other 
rulemaking activities.
     EPA applied the Agency's peer review policy (USEPA, 
2000i), where appropriate, to any new analyses.
    Figure 1 provides an overview of the review process. To most 
efficiently utilize limited resources and assure

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continued public health protection, the Agency conducted the review in 
two phases: (1) an initial technical review of all 69 NPDWRs discussed 
in today's action; and (2) an in-depth technical evaluation of those 
NPDWRs identified during the initial review as potential candidates for 
revision.
1. Initial Technical Review
    The initial review phase included these three screening and general 
evaluation steps:
     Health effects review. Identify NPDWRs for which the 
Agency has revised health risk assessments that indicate possible 
changes to the maximum contaminant level goal (MCLG) and perhaps to the 
maximum contaminant level (MCL);
     Current technology review. Identify NPDWRs where 
improvements in analytical measurement or treatment feasibility might 
allow the MCL to be established closer to the MCLG, or where 
adjustments in treatment technique (TT) requirements might be 
appropriate; and/or
     Other regulatory revisions review. Identify NPDWRs where 
adjustments to system monitoring and reporting requirements might be 
appropriate and where such changes are not already being considered as 
a part of another activity.
    EPA generally determined that an NPDWR was not a candidate for 
revision after the initial review if a health risk assessment was in 
process or was initiated as a result of the review, since the Agency 
does not believe it is appropriate to revise the NPDWR while a health 
risk assessment is underway. The Agency also determined that an NPDWR 
was not a candidate for revision after the initial screening if none of 
the initial screening analyses identified a health or technological 
basis for a regulatory revision.

2. In-Depth Technical Review

    The Agency subjected the remaining NPDWRs to more in-depth 
technical analyses. If the initial review indicated a possible revision 
to the MCLG/MCL, EPA further considered health and technology factors 
that might affect the development of a revised MCLG/MCL or revised 
MCLG/TT requirements. The Agency also estimated potential occurrence 
and exposure at PWSs at concentrations of regulatory interest for the 
chemical NPDWRs and conducted a qualitative evaluation of economic 
impacts. EPA based the qualitative economic evaluation primarily on 
available occurrence and exposure data, to determine whether the 
possible revision was likely to present an opportunity for significant 
gains in public health protection and/or significant cost savings that 
could be realized without lessening the level of public health 
protection.
    In the case of three contaminants, EPA identified data gaps that 
could not be filled during the current review cycle. Figure 1 shows the 
identification of data gaps as the final step in the review; however, 
in some instances, data gaps were identified during earlier steps in 
the process. Where this occurred, EPA did not conduct some or all of 
the remaining analyses. If the Agency identified data gaps, EPA 
determined not to revise the NPDWR.
    After completing these comprehensive analyses, EPA identified those 
NPDWRs that remain appropriate at this time, and those NPDWRs that may 
be appropriate for revision.
    Today's action discusses the Agency's preliminary determinations 
and seeks public comment on them. After considering the public comments 
received and any new peer-reviewed data that may become available to 
the Agency, EPA will publish its final decision in the FR.
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B. How Did EPA Review the Chemical NPDWRs?

    This section describes the specific technical reviews that EPA 
conducted for the chemical NPDWRs.
1. Health Effects
    The document, ``Six-Year Review--Chemical Contaminants--Health 
Effects Technical Support Document'' (USEPA, 2002i), describes how EPA 
reviewed the chemical contaminants discussed in today's action and 
provides the results of the health effects technical review. The 
principal objective of the health effects review was to identify each 
contaminant for which a new health risk assessment indicated that a 
change in MCLG might be appropriate. For most of

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the chemical NPDWRs discussed in today's action, the MCLG is derived 
from the cancer classification and/or the reference dose (RfD), as 
described in Appendix A. Therefore, the health effects technical review 
focused on whether there has been a change to these values. The Agency 
reviewed the results of health risk assessments completed under the 
following programs to determine if there had been a change in critical 
effect or dose-response pattern that indicates the possible need for an 
MCLG revision.
     EPA Integrated Risk Information System (IRIS);
     EPA Office of Pesticide Programs (OPP);
     Agency for Toxic Substances and Disease Registry (ATSDR); 
and
     National Academy of Sciences (NAS).
    Table IV-1 reflects the outcome of the health effects review for 
the 68 chemical NPDWRs discussed in today's action. EPA placed each 
contaminant into one of the following categories.
     New risk assessment 1997 or later. An IRIS, OPP, ATSDR, 
and/or NAS assessment has been completed in 1997 or later. These 
assessments have considered developmental and reproductive toxicity as 
a part of the assessment. The Agency considers these assessments to be 
recent enough that it is not necessary to conduct a literature search 
to identify any additional relevant studies that have become available 
on the toxicological effects of these contaminants. In cases where the 
health risk assessment resulted in a change in the critical effect, or 
the dose-response pattern for a regulated contaminant, and where that 
change could result in a change in the MCLG, EPA subjected the NPDWR to 
more in-depth analysis as a part of the review process. Where recent 
assessments were conducted by an agency other than EPA and new 
developmental and reproductive data were identified, EPA initiated an 
update of its assessment.
     New risk assessment since promulgation, but prior to 1997. 
An IRIS, OPP, ATSDR, and/or NAS assessment has been completed since the 
NPDWR was promulgated but prior to 1997. None of these assessments 
reflected a change in RfD or cancer classification. However, since 
these assessments may not have specifically considered developmental 
and reproductive health effects, EPA conducted a full literature 
search, including developmental and reproductive toxicity, for those 
NPDWRs with non-zero MCLGs to identify any relevant studies that might 
affect the MCLGs of these contaminants. EPA did not identify any 
chemicals for which developmental or reproductive effects might now be 
the critical effect.\2\
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    \2\ A zero MCLG is already considered protective of public 
health and new information on developmental and reproductive effects 
would not affect the MCLG. However, for those NPDWRs with a zero 
MCLG, EPA reviewed available information to inquire whether data 
show a nonlinearity of the dose-response; EPA did not find any data 
to support such a mode of action (USEPA, 2002i).
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     Agency risk assessment in process and not completed as of 
February 2002. The Agency currently is conducting a health risk 
assessment for the contaminant. That assessment will consider all 
relevant studies that have become available on the toxicology of the 
contaminant, including developmental and reproductive toxicity. EPA 
does not believe it is appropriate to revise the MCLG for these 
contaminants at this time.
     Original NPDWR risk assessment. No health risk assessment 
has been conducted since promulgation of the NPDWR. The Agency 
conducted a full toxicological literature search, including 
developmental and reproductive toxicity, for each of these contaminants 
with non-zero MCLGs (see footnote 2) to identify new toxicological 
studies that might have an impact on the MCLGs. In a few instances, the 
results of the literature search indicate that it might be appropriate 
to revise the RfD and/or cancer classification. EPA initiated updates 
to the risk assessments for these chemicals, and established a schedule 
for their completion. EPA does not believe it is appropriate to revise 
the MCLG at this time.
    Thus, only contaminants in the first category might be potential 
candidates for an MCLG revision at this time.
    The initial health effects review identified beryllium, oxamyl, and 
picloram as potential candidates for an MCLG revision, depending on the 
outcome of the more in-depth health effects review and on the other 
technical analyses (e.g., analytical feasibility, treatment, 
occurrence, etc.). The initial health effects review also identified 
changes in the RfD for chromium as well as data gaps with respect to 
its potential carcinogenicity via oral ingestion. EPA also identified 
health effects-related data gaps for fluoride. Contaminants in any of 
the categories except the third (risk assessment in process) may be 
candidates for a new assessment if the initial health effects review 
identified new studies that may affect the contaminant's RfD or cancer 
classification. EPA has initiated a new assessment for cyanide, di(2-
ethylhexyl)adipate, and thallium as a result of the health effects 
technical review.
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2. Analytical Feasibility
    Since EPA has a process in place to approve new analytical methods 
for drinking water contaminants, the actual review and approval of 
potential new methods are outside the scope of the Six-Year Review 
protocol. EPA recognizes that the approval and addition of new and/or 
improved analytical methods (since the promulgation of the NPDWRs under 
this review) may enhance the ability of laboratories to quantify 
contaminants at lower levels. For this reason, EPA evaluated whether 
there have been changes in analytical feasibility for a subset of the 
68 chemical NPDWRs discussed in today's action. The document, 
``Analytical Feasibility Support Document for the Six-Year

[[Page 19042]]

Review of Existing National Primary Drinking Water Regulations 
(Reassessment of Feasibility for Chemical Contaminants)'' (USEPA, 
2002d), describes the process EPA used to evaluate possible changes in 
analytical feasibility and provides the results of the analytical 
feasibility analyses. The purpose of these analyses is to determine 
whether changes in the practical quantitation level (PQL) are possible 
in those instances where the MCL is limited, or might be limited, by 
analytical feasibility. EPA uses the PQL to estimate the level at which 
laboratories can routinely measure a chemical contaminant in drinking 
water. Historically, EPA has used two main approaches to determine a 
PQL for SDWA analytes: (1) data from water supply (WS) studies, the 
preferred alternative when sufficient WS data are available; or (2) a 
multiplier method, in which the PQL is calculated by multiplying the 
EPA-derived method detection limit (MDL) by a factor of 5 or 10 (50 FR 
46880, November 13, 1985 (USEPA, 1985); 52 FR 25690, July 8, 1987 
(USEPA, 1987); 54 FR 22062, May 22, 1989 (USEPA, 1989a)).
    EPA performed the analytical feasibility analyses under two 
circumstances. First, for those contaminants where the MCL is currently 
limited by analytical feasibility (i.e., the MCL is set at the PQL) and 
the MCLG is still appropriate, EPA evaluated the currently approved 
methods for those contaminants and available WS data to determine 
whether it might be possible to lower the PQL and hence set an MCL that 
is closer to the MCLG. Section V of today's action provides the results 
of the analytical feasibility review of 11 contaminants that are not 
currently undergoing a health risk assessment and for which the MCL was 
limited by analytical feasibility. These 11 contaminants include 10 
with zero MCLGs \3\ and 1 with a non-zero MCLG. Of these 11, EPA 
identified 10 where the data indicate it might be possible to set a 
lower PQL (see Table IV-2). Although the data are indicative of a lower 
PQL for these 10, they are not definitive and considered to be 
insufficient to support an actual recalculation at this time. To 
determine whether it was worthwhile to gather more definitive data for 
PQL recalculation, EPA estimated what the potentially lower PQL could 
be for these 10 analytes and used these values in the occurrence and 
exposure analyses.\4\ As discussed for specific contaminants in section 
V of today's action, EPA believes that a negligible gain in public 
health exists at the possibly lower PQL for 9 of these 10 NPDWRs. The 
results of the occurrence and exposure analysis for dichloromethane, 
using the possibly lower PQL as a concentration value, indicate that it 
may be appropriate to consider gathering data to recalculate a more 
definitive PQL for this analyte.
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    \3\ Although they have a zero MCLG, EPA excluded lead and 
epichlorohydrin from the analytical feasibility review since they 
are TT rules and do not have an MCL.
    \4\ Using WS data to derive the PQL for chemical NPDWRs involves 
determining the concentration of an analyte at which 75 percent of 
EPA Regional and State laboratories achieve results within a 
specified acceptance window (see 54 FR 22062 at 22100, May 22, 1989 
(USEPA, 1989a)). In re-evaluating more recent WS data for the Six-
Year Review, sufficient data were not available around the 75 
percent critierion to actually recalculate the PQL. However, if the 
passing rates for the EPA Regional and State laboratories exceeded 
80 to 85 percent at spike concentrations close to the current PQL, 
this information was considered to be indicative of a possible 
change in the PQL. If data indicated a possible change in the PQL, 
EPA then evaluated the distribution of the analytical methods used 
to analyze the spike samples in the WS studies. Evaluation of the 
method usage over time allowed EPA to determine the analytical 
methods that appear to be the most widely used for the analysis of a 
particular contaminants. Knowledge of which analytical methods are 
the most widely used, along with the MDL for these methods, and a 10 
times MDL multiplier allowed EPA to estimate where the potential 
lower limit of quantitation may lie today. This estimated PQL was 
used as a value in the occurrence analysis to help the Agency 
determine if there may be a significant gain in public health 
protection if EPA were to consider gathering the information needed 
to recalculate the PQL.
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    The second circumstance under which EPA re-evaluated the PQL was 
for three of the four contaminants identified under the health effects 
technical review as potential candidates for revision (see Table IV-2). 
These three contaminants were evaluated to determine if any potential 
MCL revision would be limited by analytical feasibility. Based on this 
review, EPA believes that analytical feasibility may be a limiting 
factor for revising the MCL for oxamyl (see section V.A.50 of today's 
action for a more detailed discussion). The Agency believes that 
analytical feasibility would not be a limiting factor for the remaining 
two contaminants identified by the health effects review as having 
potential changes in their MCLG (i.e., beryllium and chromium).
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3. Treatment Feasibility
    An NPDWR either identifies the Best Available Technology (BAT) for 
meeting an MCL, or establishes enforceable treatment technique (TT) 
requirements. Currently, for all the chemical NPDWRs covered in today's 
action that include an MCL, the MCL is set equal to either the MCLG or 
the PQL. None of these MCLs are currently limited by treatment 
feasibility. Thus, as a part of the Six-Year Review process, EPA only 
needed to review available information on treatment technologies if 
either of the following conditions applied:
     The health effects technical review identified a potential 
change to the MCLG/MCL (applied to 4 NPDWRs); or
     A health risk assessment is not in process for the 
contaminant and one of the following two conditions apply:
    (1) the analytical feasibility review identified a possible change 
to the PQL and thus to the MCL (applied to 10 NPDWRs); or
    (2) the NPDWR is a TT-type rule (applied to 3 NPDWRs).
    The draft EPA document, ``Water Treatment Technology Feasibility 
Support Document for Chemical Contaminants; In Support of EPA Six-Year 
Review of National Primary Drinking Water Regulations'' (USEPA, 2002k), 
describes the process EPA used to evaluate treatment feasibility, where 
appropriate, for the chemical NPDWRs discussed in today's action and 
provides the results of these analyses. As a part of this review, EPA 
utilized the same sources that have been the primary resources in 
development of EPA regulations and guidance, including published EPA 
treatment reports, peer-reviewed journals, and other technology 
sources, as well as information received from EPA stakeholders.
    a. MCL-type Rules. EPA evaluated existing treatment technology 
information for 14 MCL-type NPDWRs (see Table IV-3) to determine 
whether treatment feasibility would be a limiting factor if EPA were to 
lower the MCL. In addition and where appropriate, EPA evaluated the 
likelihood that systems would discontinue existing treatment if EPA 
were to raise the MCL.
    Based upon this preliminary evaluation, the Agency believes that 
treatment capabilities would be adequate to support a lower MCL value, 
if EPA were to revise the MCL for any of the contaminants for which a 
lower MCL may be appropriate (USEPA, 2002k). Treatment technologies 
specified as BAT within the current NPDWR, and small system compliance 
technologies which were specified by EPA in 1998 (USEPA, 1998a) are 
considered to be efficient and practical for implementation at PWSs. 
However, if EPA were to determine that it is appropriate to revise any 
of these NPDWRs, it would undertake a more thorough review of treatment 
feasibility, including a consideration of costs, to

[[Page 19044]]

determine whether treatment feasibility would be a constraint or not. 
In a few instances, the Agency identified some potential treatment 
effectiveness research needs that will be considered in the context of 
the overall drinking water research strategy.\5\ The revise/not revise 
decisions discussed in section V of today's action do not depend on EPA 
addressing these research needs.
---------------------------------------------------------------------------

    \5\ Refer to the document, ``Water Treatment Technology 
Feasibility Support Document for Chemical Contaminants; In Support 
of EPA Six-Year Review of National Primary Drinking Water 
Regulations'' (USEPA, 2002k) for a description of these research 
needs.
---------------------------------------------------------------------------

    In two instances (beryllium \6\ and picloram), the outcome of the 
health effects technical review indicated it might be appropriate to 
raise the MCLG/MCL. For these two contaminants, BATs specified in the 
NPDWR are also BATs for several other contaminants (USEPA, 2002k). 
Available data are insufficient for EPA to determine how many PWSs are 
specifically treating for either of these contaminants using the same 
treatment for co-occurring contaminants and/or for secondary benefits. 
The Agency thus cannot determine whether these water systems would 
discontinue existing treatment if the MCL were to be raised (USEPA, 
2002c; USEPA, 2002k). However, in both cases, relatively few systems 
would be affected so there would be little potential for significant 
cost savings at a national level.
---------------------------------------------------------------------------

    \6\ As discussed in section V.A.9.b of today's action, the 
outcome of the health effects technical review indicates it might be 
possible to either lower or raise the MCLG/MCL.
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BILLING CODE 6560-50-C
    b. Treatment Technique-type Rules. EPA reviewed three of the four 
chemical NPDWRs for which a TT is set in lieu of an MCL (copper, 
epichlorohydrin, and lead). A health risk assessment is in process for 
the fourth TT-type NPDWR, acrylamide.
    The Agency found no new information relating to new treatment or 
other technology which would support a revision to the TT for 
epichlorohydrin at this time. EPA also reviewed issues relating to 
current TT requirements for copper and lead that were identified by EPA 
and/or stakeholders. Sections V.A.15 and V.A.43 of today's action 
summarize these issues for copper and lead, respectively. EPA believes 
these TT requirements remain appropriate at this time; however, EPA has 
identified a few potential treatment effectiveness research needs and 
will consider them in the context of the overall drinking water 
research strategy (USEPA, 2002k).
4. Other Regulatory Revisions
    In addition to possible revisions to MCLGs, MCLs, and TTs, EPA 
considered other regulatory revisions, such as monitoring and system 
reporting requirements, as a part of the Six-Year Review process. EPA 
focused this review on issues that are not already being addressed, or 
have not been addressed, through alternative mechanisms (e.g., as part 
of a recent or ongoing rulemaking, in conjunction with possible 
chemical monitoring reform, etc.). Where appropriate alternative 
mechanisms do not exist, EPA considered these implementation-related 
concerns if the potential revision met the following criteria:
     It indicated a potential change in the 40 Code of Federal 
Regulations (CFR) 141 requirements;
     It was ``ready'' for rulemaking--that is, the problem to 
be resolved has been clearly identified and specific option(s) have 
been formulated to address the problem; and
     It met at least one of the following conditions:

--Clearly improved the level of public health protection; and/or
--Represented a significant cost savings while maintaining or improving 
the public health protection.

    The document, ``Consideration of Other Regulatory Revisions for 
Chemical Contaminants in Support of the Six-Year Review of National 
Primary Drinking Water Regulations'' (USEPA, 2002e) summarizes the 
specific issues identified during the review process. Some of these 
issues (e.g., the need to specifically define new system/new source 
monitoring requirements for chemical contaminants) have already been 
addressed in the recently published arsenic and radionuclides NPDWRs 
(66 FR 6975, January 22, 2001 (USEPA, 2001a); 65 FR 76707, December 7, 
2000 (USEPA, 2000g)). Additional issues are contaminant-specific, and 
are discussed in conjunction with the review of the NPDWR in section V 
of today's action.
5. Occurrence and Exposure Analysis
    EPA's goal in evaluating contaminant occurrence was to estimate the 
number of PWSs at which contaminants occur at levels of regulatory 
interest in drinking water, and to evaluate the number of people 
exposed to these levels. For its occurrence analysis, EPA used drinking 
water compliance monitoring data from 16 States, collected in the 1993 
to 1997 time frame, and statistically analyzed the data to estimate 
occurrence. The

[[Page 19045]]

support document ``Occurrence Estimation Methodology and Occurrence 
Findings Report for the Six-Year Regulatory Review'' describes in 
detail the development of the data set and the statistical methodology 
for analysis (USEPA, 2002g). This section presents a summary of the 
data and analysis.
    a. Development of the 16-State Contaminant Occurrence Data Set. For 
the current Six-Year Review, EPA used PWS contaminant monitoring 
results, voluntarily provided by 16 States, as the primary source of 
information. EPA selected these States based on their geographic 
diversity and on their agricultural and industrial pollution potential. 
EPA also used data from a number of additional sources for comparative 
purposes. These secondary sources include the Safe Drinking Water 
Information System (SDWIS), the U.S. Geological Survey's National Water 
Information System (NWIS), EPA's Unregulated Contaminant Information 
System (URCIS), and other privately- and publicly-available data 
sources (USEPA, 2002g). In future reviews rounds, EPA plans to use the 
National Drinking Water Contaminant Occurrence Database (NCOD) as the 
primary data source when conducting the occurrence and exposure 
analyses as a part of the Six-Year Review process. EPA is in the 
process of populating the NCOD, however, sufficient data from the NCOD 
are not yet available.
    EPA developed the 16-State contaminant occurrence data set in two 
stages. In the first stage, EPA developed an 8-State cross-section to 
support occurrence analyses for its Chemical Monitoring Reform (CMR) 
evaluation. The Agency selected the eight States for use in a national 
analysis because they provided the best data quality and completeness, 
and formed a balanced national cross-section of occurrence data based 
on the States' geographic distribution and relative rankings in 
pollution potential, as described later in this section. The 
methodology for selecting the State data sets is described in an EPA 
report, ``A Review of Contaminant Occurrence in Public Water Systems'' 
(USEPA, 1999d). EPA had this report externally peer reviewed and also 
received public comment from stakeholders. In the second stage, for the 
current Six-Year Review, EPA augmented the data from the CMR 8-State 
data set with data from 8 additional States. The resulting data set 
includes 13 million analytical results, from approximately 41,000 PWSs 
in 16 States. For the 14 contaminants that EPA identified for detailed 
occurrence analysis, i.e., those with either new health effects 
information or a potential change in the PQL (see Table IV-3 of today's 
action), the number of analytical results per contaminant varies from 
about 34,000 to greater than 200,000; the number of PWSs with data 
varies from about 8,000 to 23,000; and the number of States providing 
relevant data varies from 13 to 16.
    All samples in the 16-State data set were standard SDWA compliance 
samples. Data were limited to those with confirmed water source and 
sampling type information. ``Special'' samples, ``investigation'' 
samples (investigating a contaminant problem, that would likely bias 
the results), or samples of unknown type were excluded from further 
analysis. EPA conducted various quality control and review checks of 
the results, including follow-up questions to the States providing the 
data to clarify potential reporting inconsistencies, records with 
invalid codes, or use of analytical units. The Agency then compiled 
State data sets into a single database with a unified format.
    In selecting a cross-section of State data sets that is generally 
representative of the U.S., EPA considered two broad factors: 
geographic or spatial diversity, and pollution potential. Geographic 
diversity in the data set helps to ensure that contaminant occurrence 
data come from areas representing the range of climatic and hydrologic 
conditions across the U.S. A range of agricultural and industrial 
pollution potential helps to ensure that the data represent the range 
of likely contaminant occurrence across the United States.
    As indicators of States' pollution potential, EPA used two primary 
measures: the number of manufacturing facilities per square mile (to 
reflect the potential for VOC occurrence), and the total expenditures 
on farm agricultural chemicals (to reflect the potential for synthetic 
organic chemical (SOC) occurrence). In order to construct a cross-
section with a balance of pollution potential, EPA divided the 50 
States into high and low pollution potential groups based on their rank 
orderings with respect to the two primary pollution potential 
indicators. For each of the two pollution potential indicators, EPA 
ranked the 50 States from 1 to 50 (1 being the highest and 50 being the 
lowest). The States were then plotted on a two-dimensional scatter plot 
(see Figure 2), with the x- and y-axes representing the manufacturing 
and agricultural ranking, respectively, of each State. The amount spent 
on agricultural chemicals per State increases along the y-axis from 
bottom to top. The number of manufacturing establishments per square 
mile per State increases along the x-axis from left to right. EPA then 
reviewed the rankings and selected a subset of 16 States (the ``cross-
section States'') in order to give approximate balance across the range 
of pollution indicators.
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    The bold cross in the center of Figure 2 separates the plot into 
four quadrants. The upper right-hand quadrant contains the States with 
the most manufacturing establishments per square mile and the greatest 
amount of farm agricultural chemical expenses. These States, therefore, 
have the greatest amount of pollution potential based on these 
manufacturing and agricultural indicators. The lower left-hand quadrant

[[Page 19047]]

contains the States with the least amount of manufacturing 
establishments per square mile and the least amount of farm 
agricultural chemical expenses. This quadrant, therefore, contains the 
States with the least amount of pollution potential, based on these 
indicators. To identify the location of each of the 16 States within 
the quadrants, find the intersection of the State name from the x- and 
the y-axes. This intersection should be represented by either a filled-
in circle (one of the original 8 States), or a filled-in triangle (one 
of the additional 8 States).
    The Agency performed analyses to verify the validity of this 
approach. The results of these analyses support the applicability of 
these indicators relative to pollution potential. The mean 
concentration values for select contaminants were estimated for groups 
of top quartile and bottom quartile States. The cross-section 
development approach presumes that the top quartile States have a 
higher pollution potential than the bottom quartile States, and, 
therefore, the estimated mean concentrations for the top quartile 
States should be greater than those for the bottom quartile States. The 
estimated mean concentration values for the top quartile States were 
always higher than the mean concentration for the bottom quartile 
States with the lone exception of heptachlor (a very low occurrence 
SOC).
    EPA believes the distribution of the 16 selected States is 
representative of the national distribution of States with respect to 
these pollution indicators. Eight of the selected States comprised 
EPA's original 8-State cross-section that was used for the CMR 
analyses; EPA solicited occurrence data from the remaining eight. The 
geographic distribution of the resulting 16-State cross-section is 
shown in Figure 3. Other, secondary pollution potential indicators were 
also considered in order to help ensure that the data were 
representative of the range of pollution potential across the U.S.
    While this cross-section does not represent a statistical random 
sample of States, and thus, does not capture all local variations in 
occurrence, EPA, nonetheless, believes that the data set provides a 
reliable picture of overall distribution of contaminant occurrence in 
the U.S.
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BILLING CODE 6560-50-C
    b. Analysis of Contaminant Occurrence. Statistical analysis of 
contaminant occurrence was focused at the water system level. The goal 
was to estimate the fraction of PWSs with contaminant occurrence above 
levels of regulatory interest, and the corresponding fraction of people 
exposed to those levels.
    Occurrence analysis proceeded in two stages. For the initial, or 
``Stage 1'' analysis, EPA computed simple occurrence measures which are 
more straightforward and conservative than a full probabilistic 
analysis. In this stage of analysis, EPA estimated the percent of PWSs 
and total population served by PWSs with at least one analytical result 
exceeding concentrations equal to specified contaminant levels. EPA 
considered three specified contaminant levels: The lower limit of 
detection reported by the States, one-half the current MCL, and the 
current MCL. Of the 68 chemicals discussed in today's

[[Page 19048]]

action, 60 were analyzed in this way. The exceptions were:
     The two contaminants for which not enough data were 
available (dioxin and asbestos);
     The four contaminants for which the NPDWR specifies a TT-
type requirement instead of an MCL (acrylamide, copper, 
epichlorohydrin, and lead); and
     The two contaminants for which EPA did not request data, 
since the Agency determined there was no health or technological basis 
for revising, and because these data would have required extra effort 
for States to transmit (nitrate and nitrite).

Because of the simple and conservative nature of Stage 1 estimates, EPA 
used them only as preliminary indicators of contaminant occurrence, to 
guide further analysis. The occurrence support document (USEPA, 2002g) 
includes the details of the Stage 1 analyses.
    Following the initial occurrence analysis, EPA performed a more 
detailed, ``Stage 2'' statistical analysis of occurrence for the 14 
contaminants identified as potential candidates by the health effects 
and analytical feasibility technical reviews. This analysis used a 
statistical model, known as a Bayesian hierarchical model, to estimate 
the number of systems (and the corresponding affected populations) with 
mean contaminant concentrations above the levels of regulatory 
interest. Statistical modeling is usually required in order to estimate 
mean contaminant concentrations, because many sample concentrations are 
non-detects, meaning that the true concentration is unknown and may 
range anywhere from zero to the detection limit of the analytical 
method. In the hierarchical model, individual samples are assumed to be 
log-normally distributed within entry points to a distribution system 
(EPTDS) (e.g., wells or treatment plants); EPTDS means are assumed to 
be log-normally distributed within each water system; and system means 
are assumed to be log-normally distributed nationwide. This model can 
be applied to estimate the number of systems with mean concentrations 
above levels of interest, and also the amount of variability between 
sources within a system. Population exposure can also be estimated at 
the same time, by using information from EPA's SDWIS database about the 
population served by each system in the database. The hierarchical 
model has important advantages:
     It provides a unified model for estimating occurrence, 
both between and within systems;
     It uses information about non-detected concentrations; and
     It provides uncertainty intervals around each estimate, 
taking into account both sampling variability over time and across 
systems, and uncertainty due to non-detected concentrations.
    Details of the hierarchical model, and its application to 
estimating mean contaminant concentrations, are provided in the 
occurrence support document (USEPA, 2002g).
    The results of the Stage 2 analyses for each of the 14 contaminants 
listed in Table IV-3 are presented in section V.A of today's action. 
These results represent only the systems in EPA's 16-State database. 
EPA considered this the most straightforward and accurate way to 
present the data that were available for the review process. As 
indicated in the preceding discussion of the development of the 
analysis of contaminant occurrence, EPA developed the more refined 
Stage 2 analysis based on the preliminary evaluation using the results 
of the Stage 1 analysis. A detailed explanation of this process is 
provided in EPA's occurrence support document and is available for 
review and comment (USEPA, 2002g).
    For those contaminants where occurrence was evaluated with respect 
to the revise/not revise decision, EPA used the Stage 2 occurrence 
analysis for the 16 States to determine the percentage of PWSs that 
could be impacted, and the percentage of the exposed population served 
by these systems. Section V contains a discussion of the incremental 
percentage of systems and the incremental percentage of the population 
served by these systems. That is, EPA considered the difference between 
levels of occurrence and exposure above the current MCL and the 
occurrence and exposure at the potentially revised level(s).
6. Economic Considerations
    While SDWA provides the Agency with broad discretion to consider 
economics in the context of the Six-Year Review, the statute precludes 
EPA from using economics as the sole basis for a revision that would 
provide less health protection than the current standard (i.e., anti-
backsliding). However, if new peer-reviewed scientific health effects 
research indicates that an MCLG could be raised while maintaining 
public health protection, then such a change is permitted. For NPDWRs 
published after the 1996 SDWA Amendments, Congress added specific 
requirements for economic and cost-benefit analyses in their 
development. Where EPA decides to revise an NPDWR based on health 
effects or other technical reasons, economic factors, including 
feasibility and an assessment of costs and benefits in accordance with 
Section 1412(b)(6) of the SDWA, must then be taken into consideration. 
EPA considered likely economic impacts, based primarily on available 
occurrence and exposure data, to qualitatively evaluate whether the 
potential revisions identified by the health and technology reviews may 
present a significant opportunity for improved or strengthened public 
health standards and/or a significant cost savings while maintaining 
public health protection (USEPA, 2002c).

C. How Is EPA Reviewing the Total Coliform Rule?

    The memorandum, ``Six-Year Review of the Total Coliform Rule--
Comments Received'' (USEPA, 2002j), describes the process EPA applied 
to the review of the TCR. Where appropriate, EPA applied the same 
approach to reviewing the TCR as it did to the review of the chemical 
NPDWRs discussed in today's action. However, because of the nature of 
the TCR and the pathogens it controls, the Agency focused its review on 
the implementation-related requirements. As discussed in section V.B of 
today's action, these analyses indicate that a rulemaking to initiate 
possible revisions to the TCR is appropriate at this time.

D. How Did EPA Factor Children's Health Concerns Into the Review?

    The 1996 amendments to SDWA require special consideration of all 
sensitive populations (infants, children, pregnant women, elderly, and 
immunocompromised) in the development of drinking water regulations 
(Section 1412(b)(3)(C)(V) of SDWA, as amended in 1996). Over the past 
decade, the amount of available data on the impact of chemical 
contaminants on conception and early developmental life stages has 
increased dramatically. Accordingly, as a part of the Six-Year Review 
process, EPA completed a literature search covering developmental and 
reproductive endpoints (fertility, embryo survival, developmental 
delays, birth defects, endocrine effects, etc.) for regulated chemicals 
that have a non-zero MCLG and have not been the subject of an updated 
1997 or later risk assessment (see section IV.B.1 of today's action). 
EPA reviewed the output from the literature searches to identify any 
studies that might have an influence on the present MCLG. Three 
chemicals were identified with potential developmental/reproductive 
endpoints of concern: cyanide, di(2-ethylhexyl)adipate (DEHA), and

[[Page 19049]]

thallium (see sections V.A.16, V.A.28, and V.A.59 of today's action). 
In each case, where the literature search indicated a need to consider 
recent studies of developmental or reproductive toxicity, EPA has 
initiated the process to update the Agency risk assessment. Assessments 
conducted by EPA, ATSDR, and NAS in 1997 or later thoroughly considered 
the potential for reproductive and developmental toxicity; thus, 
literature searches for chemicals with such recent assessments were not 
necessary.
    Young children, especially infants, are generally at greater health 
risk from infections caused by waterborne pathogens. Any revision to 
the TCR will maintain or improve the control of waterborne pathogens 
and, therefore, the protection afforded to children.

V. EPA's Preliminary Decisions Based on its Review of NPDWRs 
Included in Today's Action

    Table V-1 lists EPA's preliminary revise/not revise decision for 
each of the 69 NPDWRs discussed in today's action along with the 
principal rationale for the decision. If EPA has decided it is not 
appropriate to revise an NPDWR at this time, that decision is based on 
one of the following reasons.
     Health risk assessment is in process: The Agency is 
currently conducting, or has scheduled, a detailed review of current 
health effects information. Because the results of the assessment are 
not yet available, the Agency does not believe it is appropriate to 
make a ``revise decision'' at this time. In these cases, today's action 
does not include a discussion of the review of other key elements 
(e.g., technology, ``other regulatory revisions'', and occurrence/
exposure analyses). EPA will consider the results of the updated health 
risk assessment during the 2002-2008 review cycle. However, if the 
results of the health risk assessment indicate a compelling need to 
reconsider the MCLG, EPA may decide to accelerate the review schedule 
for that contaminant's NPDWR.
     NPDWR remains appropriate after data/information review: 
The outcome of the review indicates that the current regulatory 
requirements remain appropriate and, therefore, no regulatory revisions 
are warranted. Any new information available to the Agency either 
supports the current regulatory requirements or does not justify a 
revision.
     New information, but no revision recommended because:

    --Negligible gain in public health protection: Any resulting 
changes to the NPDWR would not significantly improve the level of 
public health protection or result in a major cost savings.
    --Information Gaps: Although results of the review support 
consideration of a possible revision, the available data are 
insufficient to support a definitive regulatory decision at this time.

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A. What Preliminary Decisions Has EPA Made Regarding the Chemical 
NPDWRs?

1. Acrylamide
    a. Background. EPA published the current NPDWR for acrylamide on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG of zero based on a cancer classification of B2, probable human 
carcinogen. The NPDWR imposes a TT requirement that limits the 
allowable monomer levels in products used during drinking water 
treatment, storage, and distribution to 0.05 percent acrylamide in 
polyacrylamide coagulant aids dosed at 1 part per million (ppm). Each 
water system is required to certify, in writing, to the State (using 
third-party or manufacturer's certification) that the product used 
meets these residual monomers and use-level specifications.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to acrylamide. The revised risk 
assessment will consider relevant studies that have become available on 
the toxicity of

[[Page 19051]]

acrylamide including its potential developmental and reproductive 
toxicity. The Agency expects the new risk assessment to be completed in 
the 2004 or 2005 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for acrylamide is appropriate at this time because a 
reassessment of the health risks resulting from exposure to acrylamide 
is ongoing.

2. Alachlor

    a. Background. EPA published the current NPDWR for alachlor on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG of zero based on a cancer classification of B2, probable human 
carcinogen. The NPDWR also established an MCL of 0.002 milligrams per 
liter (mg/L) based on analytical feasibility.
    b. Technical Reviews. The Agency updated the health risk assessment 
for alachlor in 1998 as a part of the pesticides reregistration process 
(USEPA, 2002i). However, the Agency has initiated another update to the 
alachlor health risk assessment. The revised risk assessment will 
consider relevant studies that have become available on the toxicity of 
alachlor including its potential developmental and reproductive 
toxicity. The Agency expects the new risk assessment to be completed in 
the 2002 or 2003 time frame.
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for alachlor is appropriate at this time because a 
reassessment of the health risks resulting from exposure to alachlor is 
ongoing.
3. Antimony
    a. Background. EPA published the current NPDWR for antimony on July 
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and 
an MCL of 0.006 mg/L. EPA based the MCLG on an RfD of 0.0004 milligrams 
per kilogram of body weight per day (mg/kg/day) and a cancer 
classification of D, not classifiable as to human carcinogenicity.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to antimony. The revised risk 
assessment will consider relevant studies that have become available on 
the toxicity of antimony including its potential developmental and 
reproductive toxicity. The Agency expects the new risk assessment to be 
completed in the 2002 or 2003 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for antimony is appropriate at this time because a 
reassessment of the health risks resulting from exposure to antimony is 
ongoing.
4. Asbestos
    a. Background. EPA published the current NPDWR for asbestos on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG and an MCL of 7 million fibers per liter (MFL) for asbestos fibers 
exceeding 10 micrometers in length. EPA evaluated asbestos as a 
Category II \7\ contaminant (equivalent to Group C, possible human 
carcinogen) by the oral route of exposure (see Appendix A of today's 
action for discussion of cancer classifications).
---------------------------------------------------------------------------

    \7\ Category II contaminants include those contaminants for 
which EPA has determined there is limited evidence of 
carcinogenicity from drinking water considering weight of evidence, 
pharmacokinetics, potency, and exposure. For Category II 
contaminants, EPA has used two approaches to set the MCLG: Either 
(1) setting the MCLG based upon noncarcinogenic endpoints of 
toxicity (the RfD) then applying an additional risk management 
factor of 1 to 10; or (2) setting the MCLG based upon a theoretical 
lifetime excess cancer risk range of 10-\5\ to 
10-\6\ using a conservative mathematical extrapolation 
model.
---------------------------------------------------------------------------

    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to asbestos. The new risk 
assessment will consider relevant studies that have become available on 
the toxicity of asbestos, including its potential developmental and 
reproductive toxicity. The Agency expects the new risk assessment to be 
completed in the 2004 or 2005 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for asbestos is appropriate at this time because a 
reassessment of the health risks resulting from exposure to asbestos is 
ongoing.
5. Atrazine
    a. Background. EPA published the current NPDWR for atrazine on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG and an MCL of 0.003 mg/L. EPA based the MCLG on an RfD of 0.005 
mg/kg/day and a cancer classification of Group C, possible human 
carcinogen, based on limited evidence of carcinogenicity in animals in 
the absence of human data. EPA published an FR notice in February 1999, 
in which EPA responded to recommendations by the Children's Health 
Advisory Committee, by committing to re-evaluate the MCL for atrazine 
after the Agency has finalized its risk assessment (64 FR 5277, 
February 3, 1999 (USEPA, 1999a)).
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to atrazine. The revised risk 
assessment will consider relevant studies that have become available on 
the toxicity of atrazine including its potential developmental and 
neuroendocrine effects. The Agency expects the new risk assessment to 
be completed in the 2002 time frame. EPA is in the process of 
conducting an occurrence and exposure analysis.
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for atrazine is appropriate at this time because a 
reassessment of the health risks resulting from exposure to atrazine is 
ongoing. EPA has committed to revisiting the NPDWR for atrazine if a 
revision is appropriate once the results of the revised risk assessment 
become available. Therefore, EPA will revisit this ``not revise'' 
decision once the new risk assessment is completed.
6. Barium
    a. Background. EPA published the current NPDWR for barium on July 
1, 1991 (56 FR 30266 (USEPA, 1991c)). The NPDWR established an MCLG and 
an MCL of 2 mg/L. EPA based the MCLG on an RfD of 0.07 mg/kg/day and a 
cancer classification of D, not classifiable as to human 
carcinogenicity.
    b. Technical Reviews. The Agency updated the health risk assessment 
for barium in 1998 and retained the RfD and cancer classification on 
which the 1991 MCLG is based (USEPA, 1999f). As a part of the 1998 
assessment, EPA considered all relevant data on the toxicity of barium 
including developmental and reproductive toxicity.
    A review of analytical or treatment feasibility is not necessary 
for barium because changes to the MCLG are not warranted at this time 
and the current MCL is set at the MCLG. In addition, the results of 
EPA's review of possible ``other regulatory revisions'' did not 
identify any barium-specific issues (USEPA, 2002e). Since EPA did not 
identify a health or technology basis for revising the barium NPDWR, 
the Agency did not conduct a detailed occurrence and exposure analysis.
    c. Preliminary Decision. After reviewing the results of the 
pertinent technical analyses, the Agency believes the NPDWR for barium 
remains appropriate and thus, it is not subject to revision at this 
time.

[[Page 19052]]

7. Benzene
    a. Background. EPA published the current NPDWR for benzene on July 
8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR established an MCLG of 
zero based on a cancer classification of A, known human carcinogen. The 
NPDWR also established an MCL of 0.005 mg/L based on analytical 
feasibility.
    b. Technical Reviews. The Agency updated the health risk assessment 
for benzene in 2000 and retained the cancer classification on which the 
1987 zero MCLG is based (USEPA, 2000j; USEPA, 2002i). The revised risk 
assessment considered relevant studies on the toxicity of benzene 
including developmental and reproductive toxicity.
    The current MCL for benzene is based on a PQL of 0.005 mg/L. As a 
part of the Six-Year Review, EPA analyzed more recent WS data to 
determine if it might be possible to recalculate the PQL (USEPA, 
2002d). In addition, the Agency evaluated whether more sensitive 
analytical methods have been approved and put into use by a wide number 
of laboratories. The analysis of the WS data indicates that an 
improvement in analytical feasibility might exist. Evaluation of the WS 
data shows that EPA Regional and State laboratories exhibit greater 
than 95 percent laboratory passing rates at concentrations around the 
current PQL of 0.005 mg/L. Because most of the laboratory passing rates 
exceeded the 75 percent criterion typically used to derive a PQL from 
WS studies, this information indicates that a lower PQL corresponding 
to the 75 percent passing rate might exist for benzene. While this 
information is indicative of a possibly lower PQL, the WS data are 
insufficient at this time to actually recalculate what the lower PQL 
for benzene might be.
    Using information about the analytical methods most widely used to 
report results in the WS studies, the MDLs for these methods, and the 
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL 
might be. For the analysis of benzene in the more recent WS studies, 
laboratories predominantly used EPA Method 524.2 (Gas Chromatography/
Mass Spectrometry or GC/MS), which has an upper limit MDL of 0.00004 
mg/L. A 10 times MDL multiplier predicts that the PQL could lie around 
0.0004 mg/L. The 0.0004 mg/L value is used as a threshold in the 
occurrence analysis, which is discussed in this section.
    Since the analytical feasibility analysis indicates that the PQL 
for benzene (and therefore the MCL) could possibly be lower if EPA had 
more definitive data to recalculate the PQL, EPA considered whether 
treatment feasibility is likely to pose any limitations (USEPA, 2002k). 
The current BATs for benzene are packed tower aeration (PTA) and 
granular activated carbon (GAC). Small system compliance technologies 
for benzene include GAC and several aeration technologies. EPA believes 
these BATs are still practical and would not pose any limitations for 
benzene at a possibly lower MCL.
    The results of EPA's review of possible ``other regulatory 
revisions'' did not identify any benzene-specific issues (USEPA, 
2002e).
    EPA evaluated the results of the occurrence and exposure analyses 
for benzene to determine whether changes to the MCL might be 
appropriate and likely to result in additional public health protection 
if the PQL were recalculated (USEPA, 2002g; USEPA 2002h). Table V-2 
shows the results of the detailed occurrence and exposure analysis 
based on the 16-State cross-section for the current MCL (0.005 mg/L) 
and the possible PQL/MCL based on the analytical feasibility analysis 
(0.0004 mg/L).
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    The results of the detailed occurrence and exposure analysis 
indicate that approximately 0.3 percent of the 23,266 systems sampled 
in the 16 cross-section States and approximately 0.3 percent of the 
population served by those systems, might be affected if EPA were to 
gather information to recalculate the PQL (to a lower PQL of around 
0.0004 mg/L) and revise the MCL accordingly.
    c. Preliminary Decision. Although there are new data that support 
consideration of a possibly lower PQL (and therefore a possibly lower 
MCL), EPA does not believe a revision to the NPDWR for benzene is 
appropriate at this time. The Agency does not have sufficient data at 
this time on which to base a PQL recalculation and hence an MCL 
revision. In addition, because the occurrence of benzene appears to be 
minimal between the current MCL and any likely PQL/MCL revision, the 
Agency believes that any potential revisions to the benzene NPDWR are 
unlikely to significantly improve the level of public health 
protection.
8. Benzo[a]pyrene
    a. Background. EPA published the current NPDWR for benzo[a]pyrene 
on July 17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an 
MCLG of zero based on a cancer classification of B2, probable human 
carcinogen. The NPDWR also established an MCL of 0.0002 mg/L based on 
analytical method feasibility.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to benzo[a]pyrene. The revised 
risk assessment will consider relevant studies that have become 
available on the toxicity of benzo[a]pyrene including its potential 
developmental and reproductive toxicity. The Agency expects the new 
risk assessment to be completed in the 2002 or 2003 time frame (USEPA, 
2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for benzo[a]pyrene is appropriate at this time because a 
reassessment of the health risks resulting from exposure to 
benzo[a]pyrene is ongoing.
9. Beryllium
    a. Background. EPA published the current NPDWR for beryllium on 
July 17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an 
MCLG and an MCL of 0.004 mg/L. EPA classified beryllium in Group B2, 
probable human carcinogen, based on clear evidence of its 
carcinogenicity via inhalation or injection in several animal species. 
However, EPA also placed beryllium in drinking water Category II for 
regulation, based on the weight of evidence for carcinogenicity via 
ingestion, and the potency, exposure and pharmacokinetics of this 
chemical. EPA derived the MCLG by applying an additional risk 
management factor of 10

[[Page 19054]]

to the RfD of 0.005 mg/kg/day (57 FR 31776 at 31785, July 17, 1992 
(USEPA, 1992)).
    b. Technical Reviews. The Agency updated the health risk assessment 
of beryllium in 1998. The 1998 reassessment established a new RfD of 
0.002 mg/kg/day and also considered relevant studies on the toxicity of 
beryllium including its developmental and reproductive toxicity. The 
1998 assessment classified inhaled beryllium as a B1, probable human 
carcinogen, using the 1986 cancer guidelines (51 FR 33992, September 
24, 1986 (USEPA, 1986b)). Using the 1996 Proposed Guidelines for 
Carcinogen Risk Assessment, the 1998 assessment characterized inhaled 
beryllium as a ``likely'' carcinogen in humans and concluded that the 
human carcinogenic potential of ingested beryllium could not be 
determined (61 FR 17960, April 23, 1996 (USEPA, 1996; USEPA, 1998d)). 
On this basis, EPA will re-examine the application of the additional 
risk management factor of 10 to account for potential carcinogenicity 
of beryllium via ingestion that was used when deriving the current 
MCLG, if the Agency determines that an MCLG revision is appropriate.
    EPA believes that any likely revision to the MCLG for beryllium 
could range from 0.01 mg/L to 0.001 mg/L, based on the change in the 
RfD in the 1998 assessment, the inclusion or non-inclusion of the risk 
management factor, and using a 20 percent relative source contribution 
(RSC).\8\ Whereas the 0.01 mg/L value assumes no adjustment for 
potential carcinogenicity via oral ingestion (i.e., no 10-fold risk 
management factor), the 0.001 mg/L value retains the current risk 
management factor of 10.
---------------------------------------------------------------------------

    \8\ This is the RSC used for the current MCLG and also the 
default value. EPA has no reason to believe that the RSC for 
beryllium would change. See Appendix A for a further discussion of 
the RSC.
---------------------------------------------------------------------------

    Because of changes in the health risk assessment for beryllium, EPA 
considered whether analytical feasibility is likely to be a limitation 
if the Agency were to lower the MCLG/MCL. The results of the analytical 
feasibility analyses indicate that the current PQL of 0.001 mg/L for 
beryllium is still appropriate and is unlikely to change. Therefore, 
the Agency believes the PQL is unlikely to be a limiting factor if EPA 
decides to lower the MCLG/MCL (USEPA, 2002d).
    EPA also considered whether treatment feasibility is likely to pose 
any limitations if EPA were to lower the MCLG/MCL. The current BATs for 
beryllium include activated alumina (AA), ion exchange, lime softening, 
coagulation/filtration, and reverse osmosis (RO) with removal 
efficiencies ranging from 80 to 99 percent. Small system compliance 
technologies also include point-of-use (POU) RO and POU ion exchange. 
The Agency believes these BATs are still practical and would not pose 
any limitations if the Agency were to lower the MCLG/MCL (USEPA, 
2002k).
    The results of EPA's review of possible ``other regulatory 
revisions'' did not identify any issues which are specific to beryllium 
(USEPA, 2002e).
    EPA evaluated the results of the occurrence and exposure analyses 
for beryllium to determine whether possible changes to the MCLG/MCL 
would be likely to result in additional public health protection or an 
opportunity for significant cost savings to PWSs and their customers 
(USEPA, 2002g; USEPA, 2002h). Table V-3 shows the results of the 
detailed occurrence and exposure analysis based on the 16-State cross-
section at the current MCL (0.004 mg/L), the possible lower level of 
any MCLG/MCL value (0.001 mg/L), and the possible upper level of any 
MCLG/MCL value (0.01 mg/L).

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[[Page 19055]]

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    The results of the detailed occurrence and exposure analysis 
indicate that approximately 0.07 percent of the 18,933 systems sampled 
in the 16 cross-section States, and approximately 0.02 percent of the 
population served by those systems, might be affected if EPA were to 
raise the MCLG/MCL. The current BATs and small system compliance 
technology for beryllium also apply to other contaminants. In addition 
to the removal of beryllium, these treatment technologies have other 
beneficial effects (e.g., reduction of hardness or other common 
impurities) (USEPA, 2002k). Therefore, if EPA were to raise the MCLG/
MCL, the Agency does not know how many of these PWSs currently treating 
to comply with the current MCL of 0.004 mg/L would discontinue any 
treatment that is already in place. If, on the other hand, EPA were to 
retain the risk management factor and lower the MCLG/MCL, less than 1 
percent of the 18,933 systems sampled in the 16 cross-section States 
and less than 0.7 percent of the population served by those systems 
might be affected.
    c. Preliminary Decision. Although there are new data indicating 
that it might be possible to revise the MCLG/MCL for beryllium, EPA 
does not

[[Page 19056]]

believe a revision to the NPDWR for beryllium, either higher or lower, 
is appropriate at this time. The Agency believes that any change in the 
MCLG/MCL would be unlikely to significantly improve the level of public 
health protection (if EPA were to lower the MCLG/MCL) or provide an 
opportunity for significant cost savings to PWSs (if EPA were to raise 
the MCLG/MCL).
10. Cadmium
    a. Background. EPA published the current NPDWR for cadmium on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG and an MCL of 0.005 mg/L. Because of inadequate dose-response data 
to characterize the presence or lack of a carcinogenic hazard from oral 
exposure, the Agency regulated cadmium as a Group D carcinogen, not 
classifiable as to human carcinogenicity by the oral route of exposure. 
Therefore, EPA developed the MCLG for cadmium based on the RfD of 
0.0005 mg/kg/day.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to cadmium. The revised risk 
assessment will consider relevant studies that have become available on 
the toxicity of cadmium including its potential developmental and 
reproductive toxicity. The Agency expects the new risk assessment to be 
completed in the 2002 or 2003 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for cadmium is appropriate at this time because a 
reassessment of the health risks resulting from exposure to cadmium is 
ongoing.
11. Carbofuran
    a. Background. EPA published the current NPDWR for carbofuran on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG and an MCL of 0.04 mg/L. EPA based the MCLG on an RfD of 0.005 mg/
kg/day and a cancer classification of E, evidence of non-
carcinogenicity for humans.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to carbofuran. The revised risk 
assessment will consider relevant studies on the toxicity of carbofuran 
including recent data on neurotoxicity and potential developmental and 
reproductive toxicity. The Agency expects the new risk assessment to be 
completed in the 2002 or 2003 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for carbofuran is appropriate at this time because a 
reassessment of the health risks resulting from exposure to carbofuran 
is ongoing.
12. Carbon Tetrachloride
    a. Background. EPA published the current MCLG for carbon 
tetrachloride on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR 
established an MCLG of zero based on a cancer classification of B2, 
probable human carcinogen. The NPDWR also established an MCL of 0.005 
mg/L based on analytical feasibility.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to carbon tetrachloride. The 
revised risk assessment will consider relevant studies that have become 
available on the toxicity of carbon tetrachloride including its 
potential developmental and reproductive toxicity. The Agency expects 
the new risk assessment to be completed in the 2002 or 2003 time frame 
(USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for carbon tetrachloride is appropriate at this time because 
a reassessment of the health risks resulting from exposure to carbon 
tetrachloride is ongoing.
13. Chlordane
    a. Background. EPA published the current NPDWR for chlordane on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG of zero based on a cancer classification of B2, probable human 
carcinogen. The NPDWR also established an MCL of 0.002 mg/L based on 
analytical feasibility.
    b. Technical Reviews. EPA updated its risk assessment for chlordane 
in 1998 (USEPA, 1998e). That assessment included an evaluation of 
developmental and reproductive endpoints. The assessment also retained 
the B2 cancer classification, concluding that chlordane is a probable 
human carcinogen using the 1986 EPA Guidelines for Carcinogen Risk 
Assessment (51 FR 33992, September 24, 1986 (USEPA, 1986b)). Under the 
1996 Proposed Guidelines for Carcinogen Risk Assessment (61 FR 17960, 
April 23, 1996 (USEPA, 1996)), chlordane is characterized as a likely 
carcinogen by all routes of exposure and, at the present time, would 
require quantification using a linear dose response, thus, the MCLG of 
zero remains appropriate.
    EPA based the current MCL for chlordane on a PQL of 0.002 mg/L. As 
a part of the Six-Year Review, EPA analyzed more recent WS data to 
determine if it might be possible to recalculate the PQL (USEPA, 
2002d). In addition, the Agency evaluated whether more sensitive 
analytical methods have been approved and put into use by a wide number 
of laboratories. The results of these analyses indicate that only a 
slight improvement in analytical feasibility might exist. Evaluation of 
the WS data shows that EPA Regional and State laboratories exhibit 
greater than 85 percent laboratory passing rates at concentrations 
around the current PQL of 0.002 mg/L. Because most of the laboratory 
passing rates exceeded the 75 percent criterion typically used to 
derive a PQL from WS studies, this information indicates that a lower 
PQL corresponding to the 75 percent passing rate might exist for 
chlordane. While this information is indicative of a possibly lower 
PQL, the WS data are insufficient at this time to actually recalculate 
what the lower PQL for chlordane might be.
    Using information about the analytical methods most widely used to 
report results in the WS studies, the MDLs for these methods, and the 
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL 
might be. For the analysis of chlordane in the more recent WS studies, 
laboratories predominantly used EPA Methods 505 (Gas Chromatography 
with microextraction) and 508 (Gas Chromatography with Electron Capture 
Detector), which have MDLs of 0.00014 mg/L and 0.0000041 mg/L, 
respectively. A 10 times MDL multiplier predicts that the PQL could 
range from 0.0014 mg/L to 0.000041 mg/L. EPA averaged these two values, 
rounded up to 0.001 mg/L, and used this value as a threshold in the 
occurrence analysis discussed in this section.
    Since the analytical feasibility analysis indicates that the PQL 
for chlordane (and therefore the MCL) could possibly be lower if EPA 
had more definitive data to recalculate the PQL, EPA considered whether 
treatment feasibility is likely to pose any limitations (USEPA, 2002k). 
The current BAT for chlordane is GAC. Small system compliance 
technologies for chlordane include GAC, POU GAC, and powdered activated 
carbon (PAC). Because chlordane is a moderately adsorbed pesticide, EPA 
believes that GAC is still a practical treatment and would not pose any 
limitations for chlordane at a possibly lower MCL.
    The results of EPA's review of possible ``other regulatory 
revisions'' did not identify any issues which are specific to chlordane 
(USEPA, 2002e).

[[Page 19057]]

    EPA evaluated the results of the occurrence and exposure analyses 
for chlordane to determine whether changes to the MCL might be 
appropriate and likely to result in additional public health protection 
if the PQL were recalculated (USEPA, 2002g; USEPA, 2002h). Table V-4 
shows the results of the detailed occurrence and exposure analysis 
based on the 16-State cross-section for the current MCL (0.002 mg/L) 
and the possible PQL/MCL based on the analytical feasibility analysis 
(0.001 mg/L).
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BILLING CODE 6560-50-C
    The detailed occurrence and exposure analysis indicates that 
chlordane is unlikely to occur at the current MCL or any potential MCL 
revision for the States used in the cross-section. Since chlordane uses 
were canceled in the United States in 1988 and since it is subject to 
the United Nations Prior Informed Consent procedure (USEPA, 2002g; 
USEPA, 2002h), EPA expects the occurrence of chlordane in PWSs to be 
rare.
    c. Preliminary Decision. Although there are new data that support 
consideration of a slightly lower PQL (and therefore a possibly lower 
MCL), EPA does not believe a revision to the NPDWR for chlordane is 
appropriate at this time. The Agency does not have sufficient data at 
this time on which to base a PQL recalculation and hence an MCL 
revision. Also, the Agency believes that any change in the PQL would be 
minimal and unlikely to significantly improve the level of public 
health protection because chlordane appears to occur infrequently at 
concentrations at or below the current MCL.
14. Chromium
    a. Background. EPA published the current NPDWR for total chromium 
on January 31, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established 
an MCLG and MCL of 0.1 mg/L. Although the NPDWR regulates total 
chromium, the adverse health effects associated with hexavalent 
chromium (chromium VI) are the basis of the current MCLG since that is 
the more toxic species (56 FR 3526, January 31, 1991 (USEPA, 1991a)). 
EPA based the MCLG on an RfD of 0.005 mg/kg/day and an assumed RSC from 
water of 70 percent for total chromium (refer to Appendix A for a 
description of the RSC). EPA regulated chromium as a Group D 
carcinogen, not classifiable as to human carcinogenicity by the oral 
route of exposure.
    b. Technical Reviews. The Agency updated the risk assessment for 
chromium in 1998 (USEPA, 1998f). The revised risk assessment considered 
relevant studies that were available on the toxicity of chromium 
including potential developmental and reproductive toxicity. Based on 
the revised risk assessment, EPA has identified changes in the health 
risk assessment that support consideration of whether it may be 
appropriate to revise the MCLG and MCL (USEPA, 2002i). The 1998 
assessment revised the RfD for hexavalent chromium (chromium VI) from 
0.005 mg/kg/day to

[[Page 19058]]

0.003 mg/kg/day based on a modification to the original uncertainty 
factor and the addition of a modifying factor because of data on the 
potential for gastrointestinal effects in humans as a result of oral 
exposures. The critical study used as the basis for the RfD did not 
change.
    The 1998 assessment of chromium VI made no change to the cancer 
classification of Group D for oral exposures and determined that the 
carcinogenicity of chromium VI cannot be determined because of a lack 
of sufficient epidemiological or toxicological studies under the 1996 
Proposed Guidelines for Carcinogen Risk Assessment. Chromium VI is a 
Group A known human carcinogen by the inhalation route of exposure.
    Public concern over the adverse health effects of chromium VI has 
increased in recent years. One issue is whether chromium VI is a human 
carcinogen through oral ingestion. In 2001, the State of California 
convened a Blue Ribbon Panel to evaluate the available data on this 
issue. The Panel issued its report in August 2001 (Flegal et al., 2001) 
and found no basis in either the epidemiological or animal data 
published in the literature for concluding that orally ingested 
chromium VI is a carcinogen. The National Toxicology Program (NTP) has 
agreed to study the chronic toxicity and carcinogenicity of chromium VI 
after oral exposure. That effort will include shorter-term toxicity 
studies, two-year rodent toxicity and carcinogenicity studies as well 
as bioavailability, distribution, and mechanistic studies. NTP expects 
the results to be available in the next three to five years (NTP, 
2001).
    The availability of new data on the contribution of dietary 
chromium to total chromium exposure supports a re-evaluation of the RSC 
(NAS, 2001). The Agency applied an RSC of 70 percent in determining the 
current MCLG. Using the new Agency RfD of 0.003 mg/kg/day along with 
the application of 20 percent, 50 percent, or 70 percent as RSC values, 
the Agency believes that any likely revisions to the MCLG could range 
from 0.02 mg/L to 0.07 mg/L. A general evaluation of the data indicates 
that a revised RSC would likely fall within the 20 percent to 50 
percent range.
    Because the results of the health effects review support 
consideration of whether it may be appropriate to revise the NPDWR for 
chromium based on changes in the RfD and possible changes in the RSC 
assumptions, EPA considered whether analytical feasibility is likely to 
be a limitation. The results of the analytical feasibility analyses 
indicate that the current PQL of 0.01 mg/L for chromium is still 
appropriate and is unlikely to change. Therefore, the Agency believes 
the PQL is unlikely to be a limiting factor if EPA decides to revise 
the MCLG/MCL (USEPA, 2002d).
    EPA also considered whether treatment feasibility is likely to pose 
any limitations if EPA were to revise the MCLG/MCL. The current BATs 
for chromium include ion exchange, lime softening, coagulation/
filtration, and RO. Small system compliance technologies also include 
POU RO and POU ion exchange. At the present time, EPA believes these 
BATs are still practical and would not pose any limitations if the 
Agency were to revise the MCLG/MCL (USEPA, 2002k).
    The results of EPA's review of possible ``other regulatory 
revisions'' did not identify any issues which are specific to chromium 
(USEPA, 2002e).
    EPA evaluated the results of the occurrence and exposure analyses 
for chromium to determine whether a revised MCLG/MCL would be likely to 
result in additional public health protection (USEPA, 2002g; USEPA, 
2002h). Table V-5 shows the results of the detailed occurrence and 
exposure analysis based on the 16-State cross-section for the current 
MCLG/MCL (0.1 mg/L), the possible MCLG/MCL value retaining the 70 
percent RSC (0.07 mg/L), the possible MCLG/MCL value using a 50 percent 
RSC (0.05 mg/L), and the possible MCLG/MCL value using a 20 percent RSC 
(0.02 mg/L).

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    The results of detailed occurrence and exposure analysis indicate 
that less than 0.4 percent of the 19,695 systems sampled in the 16 
cross-section States and approximately 0.1 percent of the population 
served by those systems, might be affected if EPA were to lower the MCL 
to 0.02 mg/L.
    c. Preliminary Decision. Although EPA has identified a change to 
the RfD on which the current MCLG for chromium is based, the Agency 
believes that a decision to revise the chromium NPDWR at this time is 
premature in light of the ongoing NTP studies on the toxicology and 
carcinogenicity of hexavalent chromium. The Agency is aware of 
considerable public controversy on the subject of the appropriate level 
for chromium in drinking water and realizes there are differing views 
regarding the severity of the health effects of chromium in water, the 
relative importance of drinking water as a source of chromium as 
compared with other sources, and the chemical form that should serve as 
the basis for regulating chromium (total versus hexavalent chromium). 
Because the NTP studies will not be available in time for the final 
revise/not revise decision, EPA is placing chromium in the ``not 
revise--data gap'' category. When completed, the NTP results will be 
considered either in the next review round or sooner, if the Agency 
deems it appropriate.
15. Copper
    a. Background. EPA published the current NPDWR for copper on June 
7, 1991 (56 FR 26460 (USEPA, 1991b)). The NPDWR established an MCLG of 
1.3 mg/L, based on a lowest-observed-adverse-effect level (LOAEL) of 
5.3 mg/day \9\, and an action level of 1.3 mg/L for first-draw samples 
at the 90th percentile of taps tested. The NPDWR requires water systems 
to monitor for copper at the tap. Water systems must optimize corrosion 
control. This requires water systems serving more than 50,000 persons 
and those smaller size systems that exceed the copper action level to 
install corrosion control treatment and to monitor for specified water 
quality control parameters. The regulation also requires any size 
system that exceeds the copper action level to monitor for copper in 
source water and, if appropriate, to install source water treatment. 
EPA published revisions to the copper NPDWR on January 12, 2000 (65 FR 
1950 (USEPA, 2000a)). These revisions made changes to monitoring and 
reporting requirements but did not affect the copper MCLG, action 
level, or basic TT requirements.
---------------------------------------------------------------------------

    \9\ In June 1994, EPA published a technical amendment that 
provided additional information on the basis of the copper MCLG (59 
FR 33860, June 30, 1994 (USEPA, 1994b)).
---------------------------------------------------------------------------

    b. Technical Reviews. In 1999, EPA requested that the National 
Research Council (NRC) of the NAS examine the available nutritional and 
toxicological data for copper and provide a recommendation regarding 
the levels in drinking water that are associated with adverse effects. 
The NRC concluded that copper in drinking water could produce adverse 
gastrointestinal effects in some individuals at concentrations of about 
3 mg/L or greater. In addition, the NRC advised that individuals who 
carry a recessive gene for Wilson's disease could accumulate excess 
copper in their livers at these same concentrations. Accordingly, the 
NAS recommended that EPA retain the MCLG of 1.3 mg/L while additional 
data are collected on the risk to the carriers of the Wilson's Disease 
gene and other populations that may accumulate copper in their livers 
(NAS, 2000a).
    EPA has initiated an assessment of health risks resulting from 
exposure to copper that will include the findings of NAS as well as 
more recently published data (USEPA, 2002i). This assessment will 
consider relevant studies on the toxicity of copper including its 
effects on genetically and developmentally sensitive populations. The 
Agency expects the new risk assessment to be completed in the 2002 or 
2003 time frame (USEPA, 2002i).
    EPA has received comments on the copper NPDWR suggesting that EPA 
discontinue copper as a regulated contaminant or change it to a 
secondary standard (USEPA, 2002e). EPA is not aware of any new 
information that would warrant such a revision.
    EPA has identified several potential research needs which may be 
considered in the context of an overall drinking water research 
strategy. These research needs are described in the ``Water Treatment 
Technology Feasibility Support Document for Chemical Contaminants; In 
Support of EPA Six-Year Review of National Primary Drinking Water 
Regulations'' (USEPA, 2002k).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for copper is appropriate at this time because a reassessment 
of the health risks resulting from exposure to copper is ongoing. 
Several potential research needs were identified for copper. The NAS 
review of copper in drinking water concluded that there was a need to 
conduct research that would characterize copper-sensitive populations 
(both population size and the factors leading to sensitivity) and 
further define the contribution of copper from drinking water to total 
copper intake (NAS, 2000a). Treatment-related research needs for copper 
are described in the Six-Year Review treatment feasibility support 
document (USEPA, 2002k).
16. Cyanide
    a. Background. EPA published the current NPDWR for cyanide on July 
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and 
MCL of 0.2 mg/L. The MCLG was developed based on an RfD of 0.02 mg/kg/
day and a cancer classification of D, not classifiable as to human 
carcinogenicity.
    b. Technical Reviews. The results of the health effects technical 
review identified some information on reproductive effects from the 
ATSDR toxicological profile that indicate the need to update the 
Agency's risk assessment for cyanide (USEPA, 2002i). In light of this 
information, EPA has initiated a reassessment of the health risks 
resulting from exposure to cyanide and has already solicited scientific 
information from the public for consideration (67 FR 1212, January 9, 
2002 (USEPA, 2002a)). The new risk assessment will consider relevant 
data on the toxicity of cyanide including its potential developmental 
and reproductive toxicity. Because the new assessment is not expected 
to be completed until the 2004 or 2005 time frame, EPA does not believe 
it is appropriate to revise the MCLG at this time.
    A review of analytical or treatment feasibility is not necessary 
for cyanide because changes to the MCLG are not warranted at this time 
and the current MCL is set at the MCLG. EPA's review of ``other 
regulatory revisions'' identified a potential revision relating to an 
error in the BAT specified for cyanide in the CFR (USEPA, 2002e). The 
CFR currently specifies ``chlorine'' as a BAT for cyanide for 
compliance with the MCL and with variance and exemption requirements 
(40 CFR 141.62 and 142.62, respectively); however, the CFR should 
specify ``alkaline chlorination'', as BAT. EPA plans to correct this 
error through a technical amendment to the cyanide NPDWR in the near 
future. In the meantime, water systems and States should continue to be 
guided by the ``Public Water System Warning: Cyanide'' (USEPA, 1994a) 
that EPA distributed through its regional offices. The warning includes 
information on the use of chlorination (non-alkaline) and the potential 
for formation of harmful cyanogen chloride due to reaction of chlorine 
with cyanide

[[Page 19061]]

in water under those conditions. The PWS Warning explains this process 
in detail and outlines treatment practice, including contact times, 
required chlorine concentrations, and compensation for temperature 
effects. The July 25, 1990 proposed regulation for cyanide discusses 
the effectiveness of oxidation of cyanide at high pH levels (55 FR 
30370 at 30419 (USEPA, 1990)) and the PWS Warning discusses mitigation 
of the formation of cyanogen chloride. This information is also 
summarized in the six-year review treatment technology support document 
(USEPA, 2002k).
    Since the potential regulatory revision identified by these 
analyses does not affect the MCLG or the MCL, EPA does not believe it 
is necessary to conduct a detailed occurrence and exposure analysis for 
cyanide.
    c. Preliminary Decision. Other than the technical amendment to 
correct the BAT, EPA does not believe a revision to the NPDWR for 
cyanide is appropriate at this time. A reassessment of the health risks 
has been initiated and the Agency does not believe it is appropriate to 
revise the NPDWR while that effort is in process.
17. 2,4-D (2,4-Dichlorophenoxyacetic Acid)
    a. Background. EPA published the NPDWR for 2,4-D on January 30, 
1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an MCLG and an 
MCL of 0.07 mg/L. EPA developed the MCLG based on a RfD of 0.01 mg/kg/
day and a cancer classification of D, not classifiable as to human 
carcinogenicity.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to 2,4-D. The revised risk 
assessment will consider relevant studies that have become available on 
the toxicity of 2,4-D including its potential developmental and 
reproductive toxicity. EPA expects the new risk assessment to be 
completed in the 2003 or 2004 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for 2,4-D is appropriate at this time because a reassessment 
of the health risks resulting from exposure to 2,4-D is ongoing.
18. Dalapon (2,2-Dichloropropionic Acid)
    a. Background. EPA published the current NPDWR for dalapon on July 
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and 
an MCL of 0.2 mg/L. EPA developed the MCLG based on an RfD of 0.03 mg/
kg/day and a cancer classification of D, not classifiable as to human 
carcinogenicity.
    b. Technical Reviews. The Agency has not updated the health risk 
assessment for dalapon since the NPDWR was published. Therefore, as 
part of the Six-Year Review process, EPA conducted a literature search 
for relevant data on the toxicology of dalapon, including its potential 
developmental and reproductive toxicity. The literature search did not 
identify any studies that warrant a review of the RfD or the cancer 
classification (USEPA, 2002i).
    A review of analytical or treatment feasibility is not necessary 
for dalapon because changes to the MCLG are not warranted at this time 
and the current MCL is set at the MCLG. In addition, the results of 
EPA's review of possible ``other regulatory revisions'' did not 
identify any dalapon-specific issues (USEPA, 2002e). Since EPA did not 
identify a health or technology basis for revising the dalapon NPDWR, 
the Agency did not conduct a detailed occurrence and exposure analysis.
    c. Preliminary Decision. After reviewing the results of the 
pertinent technical analyses, the Agency believes the NPDWR for dalapon 
remains appropriate and thus, it is not subject to revision at this 
time.
19. 1,2-Dibromo-3-chloropropane (DBCP)
    a. Background. EPA published the current NPDWR for DBCP on January 
30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an MCLG of 
zero based on a cancer classification of B2, probable human carcinogen. 
The NPDWR also established an MCL of 0.0002 mg/L based on analytical 
feasibility.
    b. Technical Reviews. The Agency has not updated the health risk 
assessment for DBCP since the NPDWR was published; however, ATSDR 
completed a toxicological profile for DBCP in 1992 (ATSDR, 1992). This 
assessment and other recent information do not warrant a review of the 
cancer classification because there are inadequate data to support a 
nonlinear dose response relationship (USEPA, 2002i). Accordingly, the 
MCLG remains at zero and the Agency believes that a further review of 
the health effects of DBCP is not warranted at this time.
    EPA based the current MCL for DBCP on a PQL of 0.0002 mg/L. As a 
part of the Six-Year Review, EPA analyzed more recent WS data to 
determine if it might be possible to recalculate the PQL (USEPA, 
2002d). In addition, the Agency evaluated whether more sensitive 
analytical methods have been approved and put into use by a wide number 
of laboratories. The results of these analyses indicate that a slight 
improvement in analytical feasibility might exist. Evaluation of the WS 
data shows that EPA Regional and State laboratories exhibit greater 
than 85 percent laboratory passing rates at concentrations around the 
current PQL of 0.0002 mg/L. Because most of the laboratory passing 
rates exceeded the 75 percent criterion typically used to derive a PQL 
from WS studies, this information indicates that a lower PQL 
corresponding to the 75 percent passing rate might exist for DBCP. 
While this information is indicative of a possibly lower PQL, the WS 
data are insufficient at this time to actually recalculate what the 
lower PQL for DBCP might be.
    Using information about the analytical methods most widely used to 
report results in the WS studies, the MDLs for these methods, and the 
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL 
might be. For the analysis of DBCP in the more recent WS studies, 
laboratories predominantly used EPA Method 504.1 (Gas Chromatography 
with microextraction), which has an MDL of 0.00001 mg/L. A 10 times MDL 
multiplier predicts that the PQL may be around 0.0001 mg/L (also one-
half the current MCL). The 0.0001 mg/L value is used as a threshold in 
the occurrence analysis, which is discussed in this section.
    Since the analytical feasibility analysis indicates that the PQL 
for DBCP (and therefore the MCL) could possibly be lower if EPA had 
more definitive data to recalculate the PQL, EPA considered whether 
treatment feasibility is likely to pose any limitations (USEPA, 2002k). 
The BATs for DBCP include aeration and GAC. Small system compliance 
technologies for DBCP include GAC, POU GAC, PAC, and several aeration 
technologies. Since the Henry's Law coefficient for DBCP is relatively 
low (i.e., DBCP is ``less strippable'' than other contaminants), GAC 
may in some cases be the preferred treatment. Considering that only a 
slight improvement in analytical feasibility may exist, EPA believes 
that these BATs are still practical and would not pose any limitations 
for DBCP at a possibly lower MCL.
    The results of EPA's review of possible ``other regulatory 
revisions'' did not identify any issues which are specific to DBCP 
(USEPA, 2002e).
    EPA evaluated the results of the detailed occurrence and exposure 
analyses for DBCP to determine whether changes to the MCL might be 
appropriate and likely to result in additional public health protection 
if

[[Page 19062]]

the PQL were recalculated (USEPA, 2002g; USEPA, 2002h). Table V-6 shows 
the results of the detailed occurrence and exposure analysis based on 
the 16-State cross-section at the current MCL (0.0002 mg/L) and the 
possible PQL/MCL based on the analytical feasibility analysis (0.0001 
mg/L).
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    The results of detailed occurrence and exposure analysis indicate 
that approximately 0.5 percent of the 14,042 systems sampled in the 16 
cross-section States and approximately 0.6 percent of the population 
served by those systems, might be affected if EPA were to gather the 
information to recalculate the PQL (estimated to be around 0.0001 mg/L) 
and to revise the MCL accordingly.
    c. Preliminary Decision. Although there are new data that support 
consideration of a slightly lower PQL (and therefore a possibly lower 
MCL), EPA does not believe a revision to the NPDWR for DBCP is 
appropriate at this time. The Agency does not have sufficient data at 
this time on which to base a PQL recalculation and hence an MCL 
revision. In addition, because the occurrence of DBCP appears to be 
minimal between the current MCL and any likely PQL/MCL revision, the 
Agency believes that any potential revisions to the DBCP NPDWR are 
unlikely to significantly improve the level of public health 
protection.
20. 1,2-Dichlorobenzene (o-Dichlorobenzene)
    a. Background. EPA published the current NPDWR for 1,2-
dichlorobenzene on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The 
NPDWR established an MCLG and an MCL of 0.6 mg/L. EPA developed the 
MCLG based on an RfD of 0.09 mg/kg/day and a cancer classification of 
D, not classifiable as to human carcinogenicity.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to 1,2-dichlorobenzene. The 
revised risk assessment will consider relevant studies on the toxicity 
of 1,2-dichlorobenzene including its potential developmental and 
reproductive toxicity. The Agency expects the new risk assessment to be 
completed in the 2002 or 2003 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for 1,2-dichlorobenzene is appropriate at this time because a 
reassessment of the health risks resulting from exposure to 1,2-
dichlorobenzene is ongoing.

[[Page 19063]]

21. 1,4-Dichlorobenzene (p-Dichlorobenzene)
    a. Background. EPA published the current NPDWR for 1,4-
dichlorobenzene on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR 
established an MCLG and an MCL of 0.075 mg/L. EPA developed the MCLG 
based on an RfD of 0.1 mg/kg/day and a cancer classification of C, 
possible human carcinogen.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to 1,4-dichlorobenzene. The 
revised risk assessment will consider relevant studies on the toxicity 
of 1,4-dichlorobenzene including its potential developmental and 
reproductive toxicity. The Agency expects the new risk assessment to be 
completed in the 2002 or 2003 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for 1,4-dichlorobenzene is appropriate at this time because a 
reassessment of the health risks resulting from exposure to 1,4-
dichlorobenzene is ongoing.
22. 1,2-Dichloroethane (Ethylene Dichloride)
    a. Background. EPA published the current NPDWR for 1,2-
dichloroethane on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR 
established an MCLG of zero based on a cancer classification of B2, 
probable human carcinogen. The NPDWR also established an MCL of 0.005 
mg/L based on analytical feasibility.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to 1,2-dichloroethane. The revised 
risk assessment will consider relevant studies that have become 
available on the toxicity of 1,2-dichloroethane including potential 
developmental and reproductive toxicity. The Agency expects the new 
risk assessment to be completed in the 2002 or 2003 time frame (USEPA, 
2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for 1,2-dichloroethane is appropriate at this time because a 
reassessment of the health risks resulting from exposure to 1,2-
dichloroethane is ongoing.
23. 1,1-Dichloroethylene
    a. Background. EPA published the current NPDWR for 1,1-
dichloroethylene on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR 
established an MCLG and an MCL of 0.007 mg/L. The Agency developed the 
MCLG based on an RfD of 0.009 mg/kg/day and a cancer classification of 
C, possible human carcinogen.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to 1,1-dichloroethylene. The 
revised risk assessment will consider relevant studies on the toxicity 
of 1,1-dichloroethylene including its potential developmental and 
reproductive toxicity. The Agency expects the new risk assessment to be 
completed in the 2002 or 2003 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for 1,1-dichloroethylene is appropriate at this time because 
a reassessment of the health risks resulting from exposure to 1,1-
dichloroethylene is ongoing.
24. cis-1,2-Dichloroethylene
    a. Background. EPA published the current NPDWR for cis-1,2-
dichloroethylene on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The 
NPDWR established an MCLG and MCL of 0.07 mg/L. The Agency developed 
the MCLG based on an RfD of 0.01 mg/kg/day and a cancer classification 
of D, not classifiable as to human carcinogenicity.
    b. Technical Reviews. The Agency has not updated the health risk 
assessment for cis-1,2-dichloroethylene since the NPDWR was published; 
however, ATSDR completed a toxicological profile for cis-1,2-
dichloroethylene in 1996 (ATSDR, 1996a). This review did not find data 
that would warrant a review of the RfD or cancer classification. As 
part of the Six-Year Review process, EPA conducted a literature search 
for relevant data on the toxicology of cis-1,2-dichloroethylene, 
including its potential developmental and reproductive toxicity. The 
literature search did not identify any studies that warrant a review of 
the RfD or the cancer classification (USEPA, 2002i).
    A review of analytical or treatment feasibility is not necessary 
for cis-1,2-dichloroethylene because changes to the MCLG are not 
warranted at this time and the current MCL is set at the MCLG. In 
addition, the results of EPA's review of possible ``other regulatory 
revisions'' did not identify any issues that were specific to cis-1,2-
dichloroethylene (USEPA, 2002e). Since EPA did not identify a health or 
technology basis for revising the cis-1,2-dichloroethylene NPDWR, the 
Agency did not conduct a detailed occurrence and exposure analysis.
    c. Preliminary Decision. After reviewing the results of the 
pertinent technical analyses, the Agency believes the NPDWR for cis-
1,2-dichloroethylene remains appropriate and thus, it is not subject to 
revision at this time.
25. trans-1,2-Dichloroethylene
    a. Background. EPA published the current NPDWR for trans-1,2-
dichloroethylene on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The 
NPDWR established an MCLG and an MCL of 0.1 mg/L. The Agency developed 
the MCLG based on an RfD of 0.02 mg/kg/day and a cancer classification 
of D, not classifiable as to human carcinogenicity.
    b. Technical Reviews. The Agency has not updated the health risk 
assessment for trans-1,2-dichloroethylene since the NPDWR was 
published; however, ATSDR completed a toxicological profile for trans-
1,2-dichloroethylene in 1996 (ATSDR, 1996a). This review did not find 
data that would warrant a review of the RfD or cancer classification. 
As part of the Six-Year Review process, EPA conducted a literature 
search for relevant data on the toxicology of trans-1,2-
dichloroethylene, including its potential developmental and 
reproductive toxicity. The literature search did not identify any 
studies that warrant a review of the RfD or the cancer classification 
(USEPA, 2002i).
    A review of analytical or treatment feasibility is not necessary 
for trans-1,2-dichloroethylene because changes to the MCLG are not 
warranted at this time and the current MCL is set at the MCLG. In 
addition, the results of EPA's review of possible ``other regulatory 
revisions'' did not identify any issues that were specific to trans-
1,2-dichloroethylene (USEPA, 2002e). Since EPA did not identify a 
health or technology basis for revising the trans-1,2-dichloroethylene 
NPDWR, the Agency did not conduct a detailed occurrence and exposure 
analysis.
    c. Preliminary Decision. After reviewing the results of the 
pertinent technical analyses, the Agency believes the NPDWR for trans-
1,2-dichloroethylene remains appropriate and thus, it is not subject to 
revision at this time.
26. Dichloromethane (Methylene Chloride)
    a. Background. EPA published the NPDWR for dichloromethane on July 
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG of 
zero based on a cancer classification of B2, probable human carcinogen. 
The NPDWR also established an MCL of 0.005 mg/L based on analytical 
feasibility.

[[Page 19064]]

    b. Technical Reviews. The Agency has not updated the health risk 
assessment for dichloromethane since the NPDWR was published; however, 
ATSDR completed a toxicological profile for dichloromethane in 2000 
(USEPA, 2002i). This review did not find any data that would warrant a 
change in the cancer classification on which the 1992 zero MCLG is 
based. The ATSDR toxicological profile considered relevant studies on 
the toxicity of dichloromethane including developmental and 
reproductive toxicity.
    The current MCL for dichloromethane is based on a PQL of 0.005 mg/
L. As a part of the Six-Year Review, EPA analyzed more recent WS data 
to determine if it might be possible to recalculate the PQL (USEPA, 
2002d). In addition, the Agency evaluated whether more sensitive 
analytical methods have been approved and put into use by a wide number 
of laboratories. The analysis of the WS data indicates that a slight 
improvement in analytical feasibility might exist. Evaluation of the WS 
data shows that EPA Regional and State laboratories exhibit greater 
than 90 percent laboratory passing rates at concentrations around the 
current PQL of 0.005 mg/L. Because most of the laboratory passing rates 
exceeded the 75 percent criterion typically used to derive a PQL from 
WS studies, this information indicates that a lower PQL corresponding 
to the 75 percent passing rate might exist for dichloromethane. While 
this information is indicative of a possibly lower PQL, the WS data are 
insufficient at this time to actually recalculate what the lower PQL 
for dichloromethane might be.
    Using information about the analytical methods most widely used to 
report results in the WS studies, the MDLs for these methods, and the 
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL 
might be. For the analysis of dichloromethane in the more recent WS 
studies, laboratories predominantly used EPA Methods 524.2 (GC/MS) and 
502.2 (Purge and Trap Gas Chromatography), which have MDLs of 0.00003 
mg/L and 0.00002 mg/L, respectively. A 10 times MDL multiplier predicts 
that the PQL may be around 0.0003 to 0.0002 mg/L. The Agency used the 
average of these two values (0.00025 mg/L) as a threshold (i.e., 
possible PQL) in the occurrence analysis discussed in this section.
    Since the analytical feasibility analysis indicates that the PQL 
for dichloromethane (and therefore the MCL) could possibly be lower if 
EPA had more definitive data to recalculate the PQL, EPA considered 
whether treatment feasibility is likely to pose any limitations (USEPA, 
2002k). The current BAT for dichloromethane is PTA. EPA believes this 
BAT is still practical and would not pose any limitations for 
dichloromethane at a possibly lower MCL.
    The results of EPA's review of possible ``other regulatory 
revisions'' did not identify any dichloromethane-specific issues 
(USEPA, 2002e).
    EPA evaluated the results of the occurrence and exposure analyses 
for dichloromethane to determine whether changes to the MCL might be 
appropriate and likely to result in additional public health protection 
if the PQL were recalculated (USEPA, 2002g; USEPA, 2002h). Table V-7 
shows the results of the detailed occurrence and exposure analysis 
based on the 16-State cross-section for the current MCL (0.005 mg/L) 
and the possible PQL/MCL based on the analytical feasibility analysis 
(0.00025 mg/L).
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[[Page 19065]]

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    The results of the detailed occurrence and exposure analysis 
indicate that less than 5 percent of the 21,530 systems sampled in the 
16 cross-section States and slightly more than 9 percent of the 
population served by those systems, might be affected if EPA were to 
gather information to recalculate the PQL (to a lower PQL of around 
0.00025 mg/L) and revise the MCL accordingly.
    c. Preliminary Decision. EPA does not believe it is appropriate to 
revise the NPDWR for dichloromethane at this time because the data 
indicating the possibility of a PQL/MCL revision are not sufficient to 
support a regulatory revision at this time. However, EPA believes there 
may be an opportunity for improvement in the level of public health 
protection if the Agency had sufficient data to recalculate the PQL. 
The Agency therefore solicits comment on whether to gather better data 
on which to recalculate the PQL. Any such effort is unlikely to be 
completed in time to inform the revise/not revise decision for the 
final notice but may provide new information for consideration during 
the next six-year review cycle.
27. 1,2-Dichloropropane
    a. Background. EPA published the current NPDWR for 1,2-
dichloropropane on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The 
NPDWR established an MCLG of zero based on a cancer classification of 
B2, probable human carcinogen. The NPDWR also established an MCL of 
0.005 mg/L based on analytical feasibility.
    b. Technical Reviews. EPA has not identified any new information 
that indicates that it is appropriate to revise the cancer 
classification for 1,2-dichloropropane at this time (USEPA, 2002i). 
Because the MCLG remains at zero, the Agency believes that a further 
review of the health effects of 1,2-dichloropropane is not warranted at 
this time.
    The current MCL for 1,2-dichloropropane is based on a PQL of 0.005 
mg/L. As a part of the Six-Year Review, EPA analyzed more recent WS 
data to determine if it might be possible to recalculate the PQL 
(USEPA, 2002d). In addition, the Agency evaluated whether more 
sensitive analytical methods have been approved and put into use by a 
wide number of laboratories. The results of these analyses indicate 
that some improvement in analytical feasibility might exist. Evaluation 
of the WS data shows that EPA Regional and State laboratories exhibit 
greater than 95 percent laboratory passing rates at concentrations 
around the current PQL of 0.005 mg/L. Because most of the laboratory 
passing rates exceeded the 75 percent criterion typically used to 
derive a PQL from WS studies, this information indicates that a lower 
PQL corresponding to the 75 percent passing rate might exist for 1,2-
dichloropropane. While this information is indicative of

[[Page 19066]]

a possibly lower PQL, the WS data are insufficient at this time to 
actually recalculate what the lower PQL for 1,2-dichloropropane might 
be.
    Using information about the analytical methods most widely used to 
report results in the WS studies, the MDLs for these methods, and the 
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL 
might be. For the analysis of 1,2-dichloropropane in the more recent WS 
studies, laboratories predominantly used EPA Methods 524.2 (GC/MS) and 
502.2 (Purge and Trap Gas Chromatography), which have MDLs of 0.00004 
mg/L and 0.00003 mg/L, respectively. A 10 times MDL multiplier predicts 
that the PQL may be around 0.0004 to 0.0003 mg/L. EPA used the 0.0004 
mg/L value as a threshold in the occurrence analysis discussed in this 
section.
    Since the analytical feasibility analysis indicates that the PQL 
for 1,2-dichloropropane (and therefore the MCL) could possibly be lower 
if EPA had more definitive data to recalculate the PQL, EPA considered 
whether treatment feasibility is likely to pose any limitations (USEPA, 
2002k). The current BATs for 1,2-dichloropropane are GAC and PTA. Small 
system compliance technologies for 1,2-dichloropropane include GAC, 
PTA, and several other aeration technologies. EPA believes that these 
BATs are still practical and would not pose any limitations for 1,2-
dichloropropane at a possibly lower MCL.
    The results of EPA's review of possible ``other regulatory 
revisions'' did not identify any issues that are specific to 1,2-
dichloropropane (USEPA, 2002e).
    EPA evaluated the results of the occurrence and exposure analyses 
for 1,2-dichloropropane to determine whether changes to the MCL might 
be appropriate and likely to result in additional public health 
protection if the PQL were recalculated (USEPA, 2002g; USEPA, 2002h). 
Table V-8 shows the results of the detailed occurrence and exposure 
analysis based on the 16-State cross-section for the current MCL (0.005 
mg/L) and the possible PQL/MCL based on the analytical feasibility 
analysis (0.0004 mg/L).
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    The results of the detailed occurrence and exposure analysis 
indicate that less than 0.05 percent of the 21,988 systems sampled in 
the 16 cross-section States and approximately 0.1 percent of the 
population served by those systems, might be affected if EPA were to 
gather the information to recalculate the PQL

[[Page 19067]]

(to a lower PQL of around 0.0004 mg/L) and revise the MCL accordingly.
    c. Preliminary Decision. Although there are new data that support 
consideration of a possibly lower PQL (and therefore a possibly lower 
MCL), EPA does not believe a revision to the NPDWR for 1,2-
dichloropropane is appropriate at this time. The Agency does not have 
sufficient data at this time on which to base a PQL recalculation and 
hence an MCL revision. In addition, because the occurrence of 1,2-
dichloropropane appears to be minimal between the current MCL and any 
likely PQL/MCL revision, the Agency believes that any potential 
revisions to the 1,2-dichloropropane NPDWR are unlikely to 
significantly improve the level of public health protection.
28. Di(2-ethylhexyl)adipate (DEHA)
    a. Background. EPA published the NPDWR for DEHA on July 17, 1992 
(57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and an MCL 
of 0.4 mg/L. The Agency developed the MCLG based on an RfD of 0.6 mg/
kg/day and a cancer classification of C, possible human carcinogen.
    b. Technical Reviews. The Agency has identified data that indicate 
it may be appropriate to update the risk assessment for DEHA (USEPA, 
2002i). The literature search on reproductive and developmental 
toxicity identified differences in the evaluation of the critical study 
on which the MCLG is based. Therefore, EPA believes it is appropriate 
to update the risk assessment and evaluate relevant new studies that 
have become available on the toxicity of DEHA and its metabolites 
including its potential developmental and reproductive toxicity. In 
light of this information, EPA has initiated a reassessment of the 
health risks resulting from exposure to DEHA and has already solicited 
scientific information from the public for consideration (67 FR 1212, 
January 9, 2002 (USEPA, 2002a)). Because the new assessment is not 
expected to be completed until the 2003 or 2004 time frame, EPA does 
not believe it is appropriate to revise the MCLG at this time.
    The current MCL is not limited by the analytical or treatment 
feasibility. Review of these capabilities is not necessary since no 
changes to the MCL are warranted at this time. The results of EPA's 
review of possible ``other regulatory revisions'' did not identify any 
issues that are specific to DEHA (USEPA, 2002e). Because none of these 
analyses indicate a change to the DEHA regulation, it is not necessary 
to conduct a detailed occurrence and exposure analysis.
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for DEHA is appropriate at this time. A reassessment of the 
health risks has been initiated and the Agency does not believe it is 
appropriate to revise the NPDWR while that effort is in process.
29. Di(2-ethylhexyl)phthalate (DEHP)
    a. Background. EPA published the current NPDWR for DEHP on July 17, 
1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG of zero 
based on a cancer classification of B2, probable human carcinogen, and 
an MCL of 0.006 based on analytical feasibility.
    b. Technical Reviews. The Agency has initiated a reassessment of 
the health risks resulting from exposure to DEHP. Many studies on DEHP 
and its metabolites have become available over the past decade and are 
being evaluated as part of the Agency's ongoing assessment. The new 
assessment will evaluate cancer and noncancer endpoints, including 
potential developmental and reproductive endpoints. EPA expects the new 
risk assessment to be completed in the 2002 or 2003 time frame (USEPA, 
2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for DEHP is appropriate at this time because a reassessment 
of the health risks resulting from exposure to DEHP is ongoing.
30. Dinoseb
    a. Background. EPA published the current NPDWR for dinoseb on July 
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and 
an MCL of 0.007 mg/L. The Agency developed the MCLG based on an RfD of 
0.001 mg/kg/day and a cancer classification of D, not classifiable as 
to human carcinogenicity.
    b. Technical Reviews. The Agency has not updated the health risk 
assessment for dinoseb since the NPDWR was published. Therefore, as 
part of the Six-Year Review process, EPA conducted a literature search 
for relevant data on the toxicology of dinoseb, including its potential 
developmental and reproductive toxicity. The literature search did not 
identify any studies that warrant a review of the RfD or the cancer 
classification (USEPA, 2002i).
    A review of analytical or treatment feasibility is not necessary 
for dinoseb because changes to the MCLG are not warranted at this time, 
and the current MCL is set at the MCLG. In addition, the results of 
EPA's review of possible ``other regulatory revisions'' did not 
identify any dinoseb-specific issues (USEPA, 2002e). Since EPA did not 
identify a health or technology basis for revising the dinoseb NPDWR, 
the Agency did not conduct a detailed occurrence and exposure analysis.
    c. Preliminary Decision. After reviewing the results of the 
pertinent technical analyses, the Agency believes the NPDWR for dinoseb 
remains appropriate and thus, it is not subject to revision at this 
time.
31. Diquat
    a. Background. EPA published the current NPDWR for diquat on July 
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and 
an MCL of 0.02 mg/L. The Agency developed the MCLG based on an RfD of 
0.002 mg/kg/day and a cancer classification of D, not classifiable as 
to human carcinogenicity.
    b. Technical Reviews. The Agency has initiated a reassessment of 
the health risks from exposure to diquat. The revised risk assessment 
will consider relevant studies that have become available on the 
toxicity of diquat, including its potential developmental and 
reproductive toxicity. The Agency expects the new risk assessment to be 
completed in the 2002 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for diquat is appropriate at this time because a reassessment 
of the health risks resulting from exposure to diquat is ongoing.
32. Endothall
    a. Background. EPA published the current NPDWR for endothall on 
July 17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an 
MCLG and an MCL of 0.1 mg/L. The Agency developed the MCLG based on an 
RfD of 0.02 mg/kg/day and a cancer classification of D, not 
classifiable as to human carcinogenicity.
    b. Technical Reviews. The Agency has initiated a reassessment of 
the health risks resulting from exposure to endothall. The revised risk 
assessment will consider relevant studies on the toxicity of endothall 
including its potential developmental and reproductive toxicity. The 
Agency expects the new risk assessment to be completed in the 2003 or 
2004 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for endothall is appropriate at this time because a 
reassessment of the health risks resulting from exposure to endothall 
is ongoing.

[[Page 19068]]

33. Endrin
    a. Background. EPA published the current NPDWR for endrin on July 
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and 
an MCL of 0.002 mg/L. The Agency developed the MCLG based on an RfD of 
0.0003 mg/kg/day and a cancer classification of D, not classifiable as 
to human carcinogenicity.
    b. Technical Reviews. The Agency has not updated the health risk 
assessment for endrin since the NPDWR was published; however, ATSDR 
completed a toxicological profile for endrin in 1996 (ATSDR, 1996b). 
This review did not find data that would warrant a review of the RfD or 
cancer classification. As part of the Six-Year Review process, EPA 
conducted a literature search for relevant data on the toxicology of 
endrin, including its potential developmental and reproductive 
toxicity. The literature search did not identify any studies that 
warrant a review of the RfD or the cancer classification (USEPA, 
2002i).
    A review of analytical or treatment feasibility is not necessary 
for endrin because changes to the MCLG are not warranted at this time 
and the current MCL is set at the MCLG. In addition, the results of 
EPA's review of possible ``other regulatory revisions'' did not 
identify any endrin-specific issues (USEPA, 2002e). Since EPA did not 
identify a health or technology basis for revising the endrin NPDWR, 
the Agency did not conduct a detailed occurrence and exposure analysis. 
(Note: Endrin uses were canceled in 1986 except for use on bird 
perches, which was canceled in 1991 (USDA, 1998)).
    c. Preliminary Decision. After reviewing the results of the 
pertinent technical analyses, the Agency believes the NPDWR for endrin 
remains appropriate and thus, it is not subject to revision at this 
time.
34. Epichlorohydrin
    a. Background. EPA published the current NPDWR for epichlorohydrin 
on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established 
an MCLG of zero based on a cancer classification of B2, probable human 
carcinogen. The NPDWR imposes a TT requirement that limits the 
allowable level of epichlorohydrin monomer in the polymer that is added 
to drinking water as a flocculent to remove particulates. Each water 
system is required to certify, in writing, to the State (using third-
party or manufacturer's certification) that the combination (or 
product) of dose and monomer level does not exceed the following level: 
0.01 percent residual epichlorohydrin monomer in polymer products used 
during water treatment and dosed at 20 ppm.
    b. Technical Reviews. EPA has not identified any new information 
that indicate that it is appropriate to revise the cancer 
classification for epichlorohydrin at this time. Because the MCLG 
remains at zero, the Agency believes that a further review of the 
health effects of epichlorohydrin is not warranted at this time (USEPA, 
2002i).
    There are no standardized methods available for epichlorohydrin at 
low levels in drinking water (56 FR 3526 at 3558, July 1, 1991 (USEPA, 
1991a)). Therefore, no analysis of analytical feasibility is 
appropriate for this contaminant. EPA has no new information that 
indicates it is appropriate to revise the TT requirement for 
epichlorohydrin at this time (USEPA, 2002k). The results of EPA's 
review of possible ``other regulatory revisions'' did not identify any 
issues which are specific to epichlorohydrin (USEPA, 2002e). Since EPA 
did not identify a health or technology basis for revising the 
epichlorohydrin NPDWR, the Agency did not conduct a detailed occurrence 
and exposure analysis.
    c. Preliminary Decision. After reviewing the results of the 
pertinent technical analyses, the Agency believes the NPDWR for 
epichlorohydrin remains appropriate and thus, it is not subject to 
revision at this time.
35. Ethylbenzene
    a. Background. EPA published the current NPDWR for ethylbenzene on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG and an MCL of 0.7 mg/L. The Agency developed the MCLG based on an 
RfD of 0.1 mg/kg/day and a cancer classification of D, not classifiable 
as to human carcinogenicity.
    b. Technical Reviews. The Agency has initiated a reassessment of 
the health risks resulting from exposure to ethylbenzene. The revised 
risk assessment will consider relevant studies that have become 
available on the toxicity of ethylbenzene, including its potential 
developmental and reproductive toxicity. The Agency expects the new 
risk assessment to be completed in the 2002 or 2003 time frame (USEPA, 
2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for ethylbenzene is appropriate at this time because a 
reassessment of the health risks resulting from exposure to 
ethylbenzene is ongoing.
36. Ethylene Dibromide (EDB; 1,2-Dibromoethane)
    a. Background. EPA published the current NPDWR for EDB on January 
30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an MCLG of 
zero based on a cancer classification of B2, probable human carcinogen. 
The NPDWR also established an MCL of 0.00005 mg/L based on analytical 
feasibility.
    b. Technical Reviews. The Agency has initiated a reassessment of 
the health risks resulting from exposure to EDB. The revised risk 
assessment will consider relevant studies that have become available on 
the toxicity of EDB, including its developmental and reproductive 
toxicity. The Agency expects the new risk assessment to be completed in 
the 2002 or 2003 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for EDB is appropriate at this time because a reassessment of 
the health risks resulting from exposure to EDB is ongoing.
37. Fluoride
    a. Background. EPA published the current NPDWR for fluoride on 
April 2, 1986 (51 FR 11396 (USEPA, 1986a)). The NPDWR established an 
MCLG and an MCL of 4.0 mg/L. The MCLG was developed from a lowest 
effect level for crippling skeletal fluorosis of 20 mg/day with 
continuous exposures over a 20-year or longer period. The LOAEL was 
divided by an uncertainty factor of 2.5 and a drinking water intake of 
2 liters/day (L/day) to obtain the MCLG. Drinking water was considered 
to be the only source of exposure for the calculation. At the same 
time, EPA published a secondary maximum contaminant level (SMCL) for 
fluoride of 2.0 mg/L to protect against dental fluorosis, which is 
considered to be an adverse cosmetic effect. PWSs exceeding the 
fluoride SMCL must provide public notification to their customers.
    Fluoride is unique as a drinking water contaminant because of its 
beneficial effects at low level exposures, and because it is 
voluntarily added to some drinking water systems as a public health 
measure for reducing the incidence of cavities among the treated 
population. The amount of fluoride added to drinking water for 
fluoridation ranges from 0.7 to 1.2 mg/L, depending on ambient air 
temperatures. The decision to fluoridate a water supply is made by the 
State or local municipality, and is not mandated by EPA or any other 
Federal entity.

[[Page 19069]]

    b. Technical Reviews. In 1997, NAS established Dietary Reference 
Intakes (DRI) for fluoride as a nutrient. As a component of the DRI, 
NAS established age and gender specific tolerable upper intake levels 
(UL) to reflect the highest average daily nutrient intake level likely 
to pose no risk of adverse effects to almost all individuals in the 
general population. As intake increases above the UL, the potential 
risk of adverse effects increases. The NAS set the UL for fluoride at 
0.10 mg/kg/day for infants, toddlers, and children through eight years 
of age, to protect them from moderate enamel fluorosis (NAS, 1997). A 
UL of 10 mg/day was established for adults and for children older than 
eight years, based on protection against skeletal fluorosis. The NAS UL 
evaluation of fluoride does not have an effect on the MCLG/MCL because 
a 2 liter drinking water intake of 4 mg/L equals 8mg/day for adults, 
which is less than 10 mg/day and allows for fluoride in food and dental 
products.
    In addition, the NAS established age and gender specific Adequate 
Intake (AI) values for fluoride. AI values are set when the data do not 
permit determination of the more precise and better known Recommended 
Dietary Allowance (RDA). The NAS (1997) AI for infants, 0 through 6 
months, is 0.01 mg/day and for infants, 7 through 12 months, is 0.5 mg/
day. Values for children range from 0.7 mg/day to 3 mg/day increasing 
with age. For adults, the NAS (1997) AI is 3 mg/day for females, and 4 
mg/day for males.
    There are new studies regarding the effects of fluoride on bone 
that have been published since EPA established the MCLG/MCL. EPA 
believes that it is important to review these new data, since effects 
on bone are the basis of the present MCLG and MCL. The Agency has 
conducted a literature search to identify reports of the clinical and 
epidemiological data on fluoride and the skeletal system. The results 
of that search indicate that a review of the new data is justified as 
part of the regulatory review process. EPA plans to request NAS to 
conduct a review of these data. In light of this planned assessment, 
EPA does not believe it is appropriate to revise the MCLG at this time.
    As part of the continuing review of the new toxicological data for 
fluoride, EPA also intends to examine the RSC used in the 1986 
regulation. At that time, a 100 percent RSC was applied in setting the 
regulation. The increased use of fluoride in dental products, the 
tendency for children to swallow these dental products, and the 
potential for increased exposure from foods support a re-evaluation of 
the RSC as a component of the fluoride review.
    As a part of the review of possible ``other regulatory revisions,'' 
EPA identified one issue pertaining to the public notification 
requirement associated with exceedance of the SMCL and the timing of 
the notification. Currently, PWSs that exceed the SMCL of 2.0 mg/L are 
required to notify their customers within 12 months of the exceedance. 
Concern has been expressed that this requirement is not sufficiently 
timely since dental fluorosis occurs as a result of exposure to high 
levels of fluoride while the tooth enamel is being laid down. Waiting 
12 months to provide public notification may result in young children 
being exposed to high levels of fluoride during the time at which they 
are most vulnerable. The Agency will consider any such revisions, if 
they are still appropriate, once the results of the NAS evaluation are 
available.
    c. Preliminary Decision. EPA is continuing its analyses of relevant 
studies that have been published since 1986 regarding the adverse 
effects of fluoride on the skeletal system to determine if these data 
support consideration of whether to revise the current MCLG. As a part 
of this effort, the Agency plans to request that NAS update the 
fluoride health risk assessment and review the RSC assumptions. The 
Agency therefore believes it is not appropriate to revise the NPDWR for 
fluoride at this time. When the results of the NAS assessment are 
available, and if they support consideration of whether a revision to 
the MCLG and/or MCL may be appropriate, EPA will revisit this ``not 
revise'' decision.
38. Glyphosate
    a. Background. EPA published the current NPDWR for glyphosate on 
July 17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an 
MCLG and an MCL of 0.7 mg/L. The Agency developed the MCLG based on an 
RfD of 0.1 mg/kg/day and a cancer classification of D, not classifiable 
as to human carcinogenicity.
    b. Technical Reviews. The Agency has initiated a reassessment of 
the health risks resulting from exposure to glyphosate. The revised 
risk assessment will consider relevant studies that have become 
available on the toxicity of glyphosate including its potential 
developmental and reproductive toxicity. The Agency expects the new 
risk assessment to be completed in the 2002 or 2003 time frame (USEPA, 
2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for glyphosate is appropriate at this time because a 
reassessment of the health risks resulting from exposure to glyphosate 
is ongoing.
39. Heptachlor
    a. Background. EPA published the current NPDWR for heptachlor on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG of zero based on a cancer classification of B2, probable human 
carcinogen. The NPDWR also established an MCL of 0.0004 mg/L based on 
analytical feasibility.
    b. Technical Reviews. The Agency has not updated the health risk 
assessment for heptachlor since the NPDWR was published; however, ATSDR 
completed a toxicological profile for heptachlor in 1993 (ATSDR, 1993). 
This assessment and other recent information do not warrant a review of 
the cancer classification because there are inadequate data to support 
a nonlinear dose-response relationship (USEPA, 2002i). Accordingly, the 
MCLG remains at zero and the Agency believes that a further review of 
the health effects of heptachlor is not warranted at this time.
    The current MCL for heptachlor is based on a PQL of 0.0004 mg/L. As 
a part of the Six-Year Review, EPA analyzed more recent WS data to 
determine if it might be possible to recalculate the PQL (USEPA, 
2002d). In addition, the Agency evaluated whether more sensitive 
analytical methods have been approved and put into use by a wide number 
of laboratories. The results of these analyses indicate that some 
improvement in analytical feasibility might exist. Evaluation of the WS 
data shows that EPA Regional and State laboratories exhibit greater 
than 90 percent laboratory passing rates at concentrations around the 
current PQL of 0.0004 mg/L. Because most of the laboratory passing 
rates exceeded the 75 percent criterion typically used to derive a PQL 
from WS studies, this information indicates that a lower PQL 
corresponding to the 75 percent passing rate might exist for 
heptachlor. While this information is indicative of a possibly lower 
PQL, the WS data are insufficient at this time to actually recalculate 
what the lower PQL for heptachlor might be.
    Using information about the analytical methods most widely used to 
report results in the WS studies, the MDLs for these methods, and the 
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL 
might be. For the analysis of heptachlor in the more recent WS studies,

[[Page 19070]]

laboratories predominantly used EPA Methods 508 (GC/MS), 505 (GC 
microextraction), and 525.2 (Purge and Trap GC), which have MDLs of 
0.0000015 mg/L, 0.000003 mg/L, and 0.00015 mg/L, respectively. A 10 
times MDL multiplier predicts PQLs of 0.000015 mg/L, 0.00003 mg/L, and 
0.0015 mg/L. EPA chose the intermediate value, rounded up to 0.0001 mg/
L, and used this value as a threshold in the occurrence analysis 
discussed in this section.
    Since the analytical feasibility analysis indicates that the PQL 
for heptachlor (and therefore the MCL) could possibly be lower if EPA 
had more definitive data to recalculate the PQL, EPA considered whether 
treatment feasibility is likely to pose any limitations (USEPA, 2002k). 
The current BAT for heptachlor is GAC. Compliance technologies for 
small systems include GAC, PAC, and POU GAC. Since heptachlor is a 
moderately adsorbed contaminant, EPA believes that the BAT and 
compliance technologies are still practical and would not pose any 
limitations for heptachlor at a possibly lower MCL.
    The results of EPA's review of possible ``other regulatory 
revisions'' did not identify any heptachlor-specific issues (USEPA, 
2002e).
    EPA evaluated the results of the occurrence and exposure analyses 
for heptachlor to determine whether changes to the MCL might be 
appropriate and likely to result in additional public health protection 
if the PQL were recalculated (USEPA, 2002g; USEPA, 2002h). Table V-9 
shows the results of the detailed occurrence and exposure analyses 
based on the 16-State cross-section for the current MCL (0.0004 mg/L) 
and the possible PQL/MCL based on the analytical feasibility analysis 
(0.0001 mg/L).
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    Based on the detailed occurrence and exposure analysis, heptachlor 
is unlikely to occur at the current MCL or any potential MCL revision 
for the States used in the cross-section. Since all heptachlor uses 
were canceled in the United States in 1988 (except for fire ant use), 
and since it is subject to the United Nations Prior Informed Consent 
procedure (USEPA, 2002g; USEPA, 2002h), EPA expects the occurrence of 
heptachlor in PWSs to be rare.
    c. Preliminary Decision. Although there are new data that support 
consideration of a slightly lower PQL (and therefore a possibly lower 
MCL), EPA does not believe a revision to the NPDWR for heptachlor is 
appropriate at this time. The Agency does not have sufficient data at 
this time on which to base a PQL recalculation and hence an MCL 
revision. Also, the Agency believes that any change in the PQL would be 
minimal and unlikely to significantly improve the level of public 
health protection because heptachlor appears to occur very infrequently 
at concentrations at or below the current MCL.

[[Page 19071]]

40. Heptachlor Epoxide
    a. Background. EPA published the current NPDWR for heptachlor 
epoxide, a degradate of heptachlor, on January 30, 1991 (56 FR 3526 
(USEPA, 1991a)). The NPDWR established an MCLG of zero based on a 
cancer classification of B2, probable human carcinogen. The NPDWR also 
established an MCL of 0.0002 mg/L based on analytical feasibility.
    b. Technical Reviews. The Agency has not updated the health risk 
assessment for heptachlor epoxide since the NPDWR was published; 
however, ATSDR completed a toxicological profile for heptachlor epoxide 
in 1993 (ATSDR, 1993). This review did not find data that would warrant 
a review of the cancer classification because there are inadequate data 
to support a nonlinear dose response. Accordingly, the MCLG remains at 
zero and the Agency believes that a further review of the health 
effects of heptachlor epoxide is not warranted at this time.
    The current MCL for heptachlor epoxide is based on a PQL of 0.0002 
mg/L. As a part of the Six-Year Review, EPA analyzed more recent WS 
data to determine if it might be possible to recalculate the PQL 
(USEPA, 2002d). In addition, the Agency evaluated whether more 
sensitive analytical methods have been approved and put into use by a 
wide number of laboratories. The results of these analyses indicate 
that a slight improvement in analytical feasibility might exist. 
Evaluation of the WS data shows that EPA Regional and State 
laboratories exhibit greater than 85 percent laboratory passing rates 
at concentrations around the current PQL of 0.0002 mg/L. Because most 
of the laboratory passing rates exceeded the 75 percent criterion 
typically used to derive a PQL from WS studies, this information 
indicates that a lower PQL corresponding to the 75 percent passing rate 
might exist for heptachlor epoxide. While this information is 
indicative of a possibly lower PQL, the WS data are insufficient at 
this time to actually recalculate what the lower PQL for heptachlor 
epoxide might be.
    Using information about the analytical methods most widely used to 
report results in the WS studies, the MDLs for these methods, and the 
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL 
might be. For the analysis of heptachlor epoxide in the more recent WS 
studies, laboratories predominantly used EPA Methods 505 (GC 
microextraction), 508 (GC/MS), and 525.2 (Purge and Trap GC), which 
have MDLs of 0.000004 mg/L, 0.0000059 mg/L, and 0.00013 mg/L, 
respectively. A 10 times MDL multiplier predicts PQLs of 0.00004 mg/L, 
0.000059 mg/L, and 0.0013 mg/L. EPA chose the intermediate value, 
rounded up to 0.0001 mg/L, and used this value as a threshold in the 
occurrence analysis discussed in this section.
    Since the analytical feasibility analysis indicates that the PQL 
for heptachlor epoxide (and therefore the MCL) could possibly be lower 
if EPA had more definitive data to recalculate the PQL, EPA considered 
whether treatment feasibility is likely to pose any limitations (USEPA, 
2002k). The current BAT for heptachlor epoxide is GAC. Compliance 
technologies for small systems include GAC, PAC, and POU GAC. EPA 
believes that the BAT and compliance technologies would not pose any 
limitations for heptachlor epoxide at a possibly lower MCL.
    The results of EPA's review of possible ``other regulatory 
revisions'' did not identify any issues that are specific to heptachlor 
epoxide (USEPA, 2002e).
    EPA evaluated the results of the occurrence and exposure analyses 
for heptachlor epoxide to determine whether changes to the MCL might be 
appropriate and likely to result in additional public health protection 
if the PQL were recalculated (USEPA, 2002g; USEPA, 2002h). Table V-10 
shows the results of the detailed occurrence and exposure analyses 
based on the 16-State cross-section for the current MCL (0.0002 mg/L), 
and the possible PQL/MCL based on the analytical feasibility analysis 
(0.0001 mg/L).
BILLING CODE 6560-50-P

[[Page 19072]]

[GRAPHIC] [TIFF OMITTED] TP17AP02.019

BILLING CODE 6560-50-C
    Based on detailed occurrence and exposure analysis, it appears that 
heptachlor epoxide is unlikely to occur at the current MCL or any 
potential MCL revision for the States used in the cross-section. Since 
the parent of heptachlor epoxide (i.e., heptachlor) was canceled for 
use (except for fire ant use) in the United States and since it is 
subject to the United Nations Prior Informed Consent procedure (USEPA, 
2002g; USEPA, 2002h), EPA expects the occurrence of heptachlor epoxide 
in PWSs to be rare.
    c. Preliminary Decision. Although there are new data that support 
consideration of a slightly lower PQL (and therefore a possibly lower 
MCL), EPA does not believe a revision to the NPDWR for heptachlor 
epoxide is appropriate at this time. The Agency does not have 
sufficient data at this time on which to base a PQL recalculation and 
hence an MCL revision. Also, the Agency believes that any change in the 
PQL would be minimal and unlikely to significantly improve the level of 
public health protection because heptachlor epoxide appears to occur 
infrequently at concentrations at or below the current MCL.
41. Hexachlorobenzene
    a. Background. EPA published the current NPDWR for 
hexachlorobenzene on July 17, 1992 (57 FR 31776 (USEPA, 1992)). The 
NPDWR established an MCLG of zero based on a cancer classification of 
B2, probable human carcinogen. The NPDWR also established an MCL of 
0.001 mg/L based on analytical feasibility.
    b. Technical Reviews. The Agency has not updated the health risk 
assessment for hexachlorobenzene since the NPDWR was published; 
however, ATSDR completed a toxicological profile for hexachlorobenzene 
in 1996 (ATSDR, 1996c). This assessment and other recent information do 
not warrant a review of the cancer classification because there are 
inadequate data to support a nonlinear dose-response relationship 
(USEPA, 2002i). Accordingly, the MCLG remains at zero and the Agency 
believes that a further review of the health effects of 
hexachlorobenzene is not warranted at this time.
    The current MCL for hexachlorobenzene is based on a PQL of 0.001 
mg/L. As a part of the Six-Year Review, EPA analyzed more recent WS 
data to determine if it might be possible to recalculate the PQL 
(USEPA, 2002d). In addition, the Agency evaluated whether more 
sensitive analytical methods have been approved and put into use by a 
wide number of laboratories. The results of these analyses indicate 
that some improvement in analytical feasibility might exist. Evaluation 
of the WS data shows that EPA Regional and State laboratories exhibit 
greater than 90 percent laboratory passing rates at concentrations 
around the current PQL of 0.001 mg/L. Because most of the laboratory 
passing rates exceeded the 75 percent criterion typically used to 
derive a PQL from WS studies, this information indicates that a lower 
PQL corresponding to the 75 percent passing rate might exist for 
hexachlorobenzene. While this information is indicative of a possibly 
lower PQL, the WS data are insufficient at this time to actually

[[Page 19073]]

recalculate what the lower PQL for hexachlorobenzene might be.
    Using information about the analytical methods most widely used to 
report results in the WS studies, the MDLs for these methods, and the 
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL 
might be. For the analysis of hexachlorobenzene in the more recent WS 
studies, laboratories predominantly used EPA Methods 508 (GC/MS), 505 
(GC microextraction), and 525.2 (Purge and Trap GC), which have MDLs of 
0.0000077 mg/L, 0.000002 mg/L and 0.000001 mg/L, respectively. A 10 
times MDL multiplier predicts PQLs of 0.000077 mg/L, 0.00002 mg/L, and 
0.00001 mg/L. EPA chose the highest value, rounded up to 0.0001 mg/L, 
and then used this value as a threshold in the occurrence analysis 
discussed in this section.
    Since the analytical feasibility analysis indicates that the PQL 
for hexachlorobenzene (and therefore the MCL) could possibly be lower 
if EPA had more definitive data to recalculate the PQL, EPA considered 
whether treatment feasibility is likely to pose any limitations (USEPA, 
2002k). The current BAT for hexachlorobenzene is GAC. Compliance 
technologies for small systems include GAC, PAC, and POU GAC. Since 
hexachlorobenzene is a moderately adsorbed contaminant, EPA believes 
that the BAT and compliance technologies are still practical and would 
not pose any limitations for hexachlorobenzene at a possibly lower MCL.
    The results of EPA's review of possible ``other regulatory 
revisions'' did not identify any issues that are specific to 
hexachlorobenzene (USEPA, 2002e).
    EPA evaluated the results of the occurrence and exposure analyses 
for hexachlorobenzene to determine whether changes to the MCL might be 
appropriate and likely to result in additional public health protection 
if the PQL were recalculated (USEPA, 2002g; USEPA, 2002h). Table V-11 
shows the results of the detailed occurrence and exposure analyses 
based on the 16-State cross-section for the current MCL (0.001 mg/L) 
and the possible PQL/MCL based on the analytical feasibility analysis 
(0.0001 mg/L).
BILLING CODE 6560-50-P
[GRAPHIC] [TIFF OMITTED] TP17AP02.020

BILLING CODE 6560-50-C
    The detailed occurrence and exposure analysis indicates that 
hexachlorobenzene is unlikely to occur at the current MCL or any 
potential MCL revision for the States used in the cross-section. Since 
hexachlorobenzene

[[Page 19074]]

uses were canceled in the United States in 1984 and since it is subject 
to the United Nations Prior Informed Consent procedure (USEPA, 2002g; 
USEPA, 2002h), EPA expects the occurrence of hexachlorobenzene in PWSs 
to be rare.
    c. Preliminary Decision. Although there are new data that support 
consideration of a possibly lower PQL (and therefore a possibly lower 
MCL), EPA does not believe a revision to the NPDWR for 
hexachlorobenzene is appropriate at this time. The Agency does not have 
sufficient data at this time on which to base a PQL recalculation and 
hence an MCL revision. In addition, because the occurrence of 
hexachlorobenzene appears to be minimal between the current MCL and any 
likely PQL/MCL revision, the Agency believes that any potential 
revisions to the hexachlorobenzene NPDWR are unlikely to significantly 
improve the level of public health protection.
42. Hexachlorocyclopentadiene
    a. Background. EPA published the current NPDWR for 
hexachlorocyclopentadiene on July 17, 1992 (57 FR 31776 (USEPA, 1992)). 
The NPDWR established an MCLG and an MCL of 0.05 mg/L. The Agency based 
the MCLG on an RfD of 0.007 mg/kg/day and a cancer classification of D, 
not classifiable as to human carcinogenicity.
    b. Technical Reviews. The Agency updated the health risk assessment 
for hexachlorocyclopentadiene in 2001 (USEPA, 2001c). The revised risk 
assessment considered relevant studies that were available to the 
Agency on the toxicity of hexachlorocyclopentadiene including its 
potential developmental and reproductive toxicity. According to the 
1986 EPA Guidelines for Carcinogen Risk Assessment (51 FR 33992, 
September 24, 1986 (USEPA, 1986b)), evaluation of the weight of 
evidence for carcinogenicity to humans indicates that 
hexachlorocyclopentadiene is most appropriately categorized as Group E, 
evidence of noncarcinogenicity to humans, via inhalation exposure. In 
accordance with EPA's 1996 Proposed Guidelines for Carcinogen Risk 
Assessment (61 FR 17960, April 23, 1996 (USEPA, 1996)), 
hexachlorocyclopentadiene is not likely to be a human carcinogen by the 
inhalation route. The potential for carcinogenicity by the oral route 
is unknown. The updated risk assessment changed the RfD from 0.007 to 
0.006 mg/kg/day. The change in RfD was the result of a change in the 
procedure used to model the data but not a change in the underlying 
toxicology. The RfD could result in a slight change to the MCLG and MCL 
but that change would not lead to any significant improvement in public 
health protection.
    A review of analytical or treatment feasibility is not necessary 
for hexachlorocyclopentadiene because changes to the MCLG are not 
warranted at this time and the current MCL is set at the MCLG. In 
addition, the results of EPA's review of possible ``other regulatory 
revisions'' did not identify any hexachlorocyclopentadiene-specific 
issues (USEPA, 2002e). Since EPA did not identify a health or 
technology basis for revising the hexachlorocyclopentadiene NPDWR, the 
Agency did not conduct a detailed occurrence and exposure analysis.
    c. Preliminary Decision. After reviewing the results of the 
pertinent technical analyses, the Agency believes the NPDWR for 
hexachlorocyclopentadiene remains appropriate and thus, it is not 
subject to revision at this time.
43. Lead
    a. Background. EPA published the current NPDWR for lead on June 7, 
1991 (56 FR 26460 (USEPA, 1991b)). The NPDWR established an MCLG of 
zero and a lead action level of 0.015 mg/L at the 90th percentile of 
taps tested. The MCLG for lead is based on three factors: (1) the 
occurrence of a variety of low level health effects for which it is 
currently difficult to identify clear threshold exposure levels below 
which there are no risks of adverse health effects; (2) the Agency's 
policy goal that drinking water should contribute minimal lead to total 
lead exposures because a substantial portion of the sensitive 
population already exceeds acceptable blood lead levels; and (3) the 
classification of lead as B2, probable human carcinogen.
    The NPDWR requires water systems to monitor for lead at the tap. 
Water systems must optimize corrosion control. This requires water 
systems serving more than 50,000 persons (except those with extremely 
low levels of lead in their distribution systems) and those smaller 
size systems that exceed the lead action level to install corrosion 
control treatment and to monitor for specified water quality control 
parameters. The NPDWR also includes other TT requirements for those 
systems exceeding the lead action level. These systems must: (1) 
Monitor for lead in source water; (2) install source water treatment, 
if appropriate; (3) conduct public education for as long as they 
continue to exceed the action level; and (4) replace the portion of 
lead service line in the distribution system they own, if they continue 
to exceed the action level after installing corrosion control treatment 
and/or source water treatment. EPA published revisions to the lead 
NPDWR on January 12, 2000 (65 FR 1950 (USEPA, 2000a)). These revisions 
made changes to monitoring and reporting requirements, public 
education, and the lead service line replacement requirements but did 
not affect the lead MCLG, action level, or other TT requirements.
    b. Technical Reviews. EPA has not identified any new assessments 
that indicate that it is appropriate to revise the MCLG for lead at 
this time (USEPA, 2002i). Although ATSDR completed a toxicological 
profile for lead in 1999 (ATSDR, 1999), the review did not find data 
that would warrant a change in the MCLG for lead. Because the MCLG 
remains at zero, the Agency believes that a further review of the 
health effects of lead is not warranted at this time.
    EPA identified several potential research needs which may be 
considered in the context of an overall drinking water research 
strategy. These research needs are described in the ``Water Treatment 
Technology Feasibility Support Document of Chemical Contaminants in 
Support of EPA Six-Year Review of National Primary Drinking Water 
Regulations'' (USEPA, 2002k).
    Some stakeholders have suggested that EPA allow alternatives to 
corrosion control treatment (e.g., monitoring and flushing at non-
transient, non-community water systems (NTNCWSs)) (USEPA, 2002e). EPA 
considered these alternatives as a part of the January 2000 revisions 
and determined that it was not appropriate to make such revisions to 
the TT requirements for lead and copper (65 FR 1950, January 12, 2000 
(USEPA, 2000a)). If new peer-reviewed scientific information becomes 
available, it will be considered.
    EPA also considered several potential revisions to requirements 
pertaining to the monitoring requirements for lead and copper in 
drinking water based on concerns recently expressed by stakeholders 
(USEPA, 2002e). As a part of the Six-Year Review process, EPA 
considered issues including: (1) Further reduction of the monitoring 
requirements; (2) monitoring for lead and copper on the same frequency 
as other inorganic and organic chemicals; (3) expanding the monitoring 
waiver program to water systems that have not exceeded one-half the 
lead and copper action levels for three monitoring rounds, regardless 
of plumbing materials used; (4) revising the protocol by which tap 
water sampling sites are identified; and (5) allowing fewer than five 
tap water samples for NTNCWSs

[[Page 19075]]

that have fewer than five taps. The Agency addressed all of these 
issues as a part of the January 2000 revisions. If new peer-reviewed 
scientific information becomes available, it will be considered.
    The current action level and TT requirements are not limited by 
analytical feasibility, therefore review of these capabilities is not 
needed. Since none of the analyses indicate a change to the lead 
regulation at this time, the Agency did not conduct detailed occurrence 
and exposure analyses.
    c. Preliminary Decision. EPA does not believe a revision to the 
NPDWR for lead is appropriate because the Agency is not aware of any 
new data/information that provides sufficient basis for revising the 
regulatory requirements at this time. However, the Agency has 
identified several technology-related issues that could benefit from 
further research. These research needs will be considered as a part of 
an overall drinking water research strategy. As more research in this 
area becomes available, the Agency will consider the results as a part 
of the review of the lead NPDWR during future review cycles.
44. Lindane (-Hexachlorocyclohexane)
    a. Background. EPA published the current NPDWR for lindane on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG and an MCL of 0.0002 mg/L. The Agency based the MCLG on an RfD of 
0.0003 mg/L and a cancer classification of C, possible human 
carcinogen.
    b. Technical Reviews. The Agency has initiated a reassessment of 
the health risks resulting from exposure to lindane. The revised risk 
assessment will consider relevant studies that have become available on 
the toxicity of lindane including its potential developmental and 
reproductive toxicity. The Agency expects the new risk assessment to be 
completed in the 2003 or 2004 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for lindane is appropriate at this time because a 
reassessment of the health risks resulting from exposure to lindane is 
ongoing.
45. Mercury (Inorganic)
    a. Background. EPA published the current NPDWR for inorganic 
mercury on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR 
established an MCLG and an MCL of 0.002 mg/L. The Agency based the MCLG 
on a Drinking Water Equivalent Level (DWEL) of 0.01 mg/L \10\ and a 
cancer classification of D, not classifiable as to human 
carcinogenicity.
---------------------------------------------------------------------------

    \10\ The DWEL was recommended by a panel of experts on mercury, 
and was derived using the weight of evidence from the entire 
inorganic mercury database. The DWEL was later back-calculated to an 
RFD of 0.0003 mg/kg/day (USEPA, 1995).
---------------------------------------------------------------------------

    b. Technical Reviews. EPA updated the risk assessment for mercury 
in 1997 as part of the Mercury Study Report to Congress (MSRC) (USEPA, 
1997b). The MSRC entailed a review of all available studies on 
inorganic mercury including reproductive and developmental studies. The 
MSRC concluded that the database for inorganic mercury is suggestive of 
effects in animals at doses around 2 mg/kg/day. The data however, are 
considered insufficient for risk assessment based on any single study 
or on the database as a whole. Evaluation of data for germ cell 
mutagenicity led to the conclusion that there is a moderate weight of 
evidence for potential to produce adverse effects in humans. The MSRC 
reviewed and kept the 1987 RfD of 0.0003 mg/kg/day based on immune-
mediated kidney damage in three studies conducted in a sensitive strain 
of rats.
    The MSRC evaluated data for carcinogenicity of inorganic mercury, 
largely from studies of mercuric chloride. Based on the absence of 
human data and limited data in animals, inorganic mercury was 
categorized as Group C, possible human carcinogen; this determination 
was posted on IRIS for mercuric chloride (USEPA, 1995). The MSRC also 
applied the proposed revisions to the Cancer Guidelines (61 FR 17960, 
April 23, 1996 (USEPA, 1996)) to the evaluation of inorganic mercury. 
The conclusion was that inorganic mercury is not likely to be a human 
carcinogen under conditions of exposure generally encountered in the 
environment. This was based in part on the observation that all tumors 
were observed at very high doses, in excess of the maximum tolerated 
dose (MTD) and that likely modes of action for these tumors involved 
irritation and cytotoxic effects not expected to occur at environmental 
levels.
    The revised risk assessments show that inorganic mercury is not 
likely to be a carcinogen at levels found in water and that there are 
insufficient data to categorize inorganic mercury as a developmental 
toxicant. The EPA RfD has not changed, and thus, EPA does not believe 
it is appropriate to revise the MCLG at this time.
    A review of analytical or treatment feasibility is not necessary 
for mercury because, in EPA's judgment, changes to the MCLG are not 
warranted at this time and the current MCL is set at the MCLG. In 
addition, the results of EPA's review of possible ``other regulatory 
revisions'' did not identify any mercury-specific issues (USEPA, 
2002e). Since EPA did not identify a health or technology basis for 
revising the mercury NPDWR, the Agency did not conduct a detailed 
occurrence and exposure analysis.
    c. Preliminary Decision. After reviewing the results of the 
pertinent technical analyses, the Agency believes the NPDWR for 
inorganic mercury remains appropriate and thus, it is not subject to 
revision at this time.
46. Methoxychlor
    a. Background. EPA published the current NPDWR for methoxychlor on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG and an MCL of 0.04 mg/L. The Agency based the MCLG on an RfD of 
0.005 mg/kg/day and a cancer classification of D, not classifiable as 
to human carcinogenicity.
    b. Technical Reviews. The Agency has initiated a reassessment of 
the health risks resulting from exposure to methoxychlor. The revised 
risk assessment will consider relevant studies that have become 
available on the toxicity of methoxychlor including its potential 
developmental and reproductive toxicity. The Agency expects the new 
risk assessment to be completed in the 2002 or 2003 time frame (USEPA, 
2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for methoxychlor is appropriate at this time because a 
reassessment of the health risks resulting from exposure to 
methoxychlor is ongoing.
47. Monochlorobenzene (Chlorobenzene)
    a. Background. EPA published the current NPDWR for 
monochlorobenzene on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The 
NPDWR established an MCLG and an MCL of 0.1 mg/L. The Agency based the 
MCLG on an RfD of 0.02 mg/kg/day and a cancer classification of D, not 
classifiable as to human carcinogenicity.
    b. Technical Reviews. The Agency has not updated the health risk 
assessment for monochlorobenzene since the NPDWR was published. EPA 
therefore conducted a literature search for relevant studies on the 
toxicology of monochlorobenzene including its potential developmental 
and reproductive toxicity as a part of the Six-Year Review process. The 
literature search did not identify any new studies

[[Page 19076]]

that warrant a review of the RfD or the cancer classification (USEPA, 
2002i).
    A review of analytical or treatment feasibility is not necessary 
for monochlorobenzene because changes to the MCLG are not warranted at 
this time and the current MCL is set at the MCLG. In addition, the 
results of EPA's review of possible ``other regulatory revisions'' did 
not identify any monochlorobenzene-specific issues (USEPA, 2002e). 
Since EPA did not identify a health or technology basis for revising 
the monochlorobenzene NPDWR, the Agency did not conduct a detailed 
occurrence and exposure analysis.
    c. Preliminary Decision. After reviewing the results of the 
pertinent technical analyses, the Agency believes the NPDWR for 
monochlorobenzene remains appropriate and thus, it is not subject to 
revision at this time.
48. Nitrate (as N)
    a. Background. EPA published the current NPDWR for nitrate on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG and MCL of 10 mg/L (as nitrogen (N)). The Agency based the MCLG on 
an RfD of 1.6 mg/kg/day (as N) and a cancer classification of D, not 
classifiable as to human carcinogenicity.
    b. Technical Reviews. The current RfD and the MCLG were established 
to protect infants, the most susceptible segment of the population. At 
the request of EPA \11\, NAS completed an assessment of nitrate in 1995 
(NAS, 1995) and did not find any new data that would warrant a review 
of the RfD or cancer classification. The literature search conducted 
during the Six-Year Review also did not identify any new studies that 
warrant a review of the RfD or cancer classification (USEPA, 2002i).
---------------------------------------------------------------------------

    \11\ This request fulfilled the commitment EPA made to form an 
inter-agency workgroup to determine what, if any, oncogenic risks 
exist (56 FR 3526 at 3538, January 30th, 1991 (USEPA, 1991a)).
---------------------------------------------------------------------------

    The current MCL is not limited by the analytical or treatment 
feasibility. Review of these capabilities is not necessary since no 
changes to the MCL are warranted at this time.
    As a part of the Six-Year Review, several States have suggested 
that EPA revise the current monitoring requirements for nitrate to 
allow less frequent monitoring in systems with consistently low 
nitrate/nitrite levels. Some have suggested that EPA place nitrate 
monitoring under the same monitoring framework used for most other 
inorganic chemicals (USEPA, 2002e). EPA previously considered these 
suggestions when the Agency considered chemical monitoring reform and 
decided not to change the frequency of nitrate monitoring. However, 
primacy agencies currently have the flexibility to reduce nitrate 
monitoring for ground water systems from annually to biennial if the 
Primacy Agency adopts (and EPA approves) an alternative monitoring 
provision. EPA has established guidance for such alternative monitoring 
in the Alternative Monitoring Guidelines (USEPA, 1997a). These 
guidelines were issued after consultation with stakeholders and no new 
information has been identified that warrants reconsideration of this 
issue.
    Detailed occurrence and exposure analysis is not necessary since 
none of the analyses indicate a change to the nitrate regulation at 
this time.
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for nitrate is appropriate at this time because: (1) There 
are no changes in the health risk assessment for nitrate; and (2) no 
other new data were identified that indicate the need to revise the 
NPDWR at this time. (Also see section V.A.49.c of today's action for a 
discussion of the Agency's decision pertaining to the joint nitrate/
nitrite standard.)
49. Nitrite (as N)
    a. Background. EPA published the current NPDWR for nitrite on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG and an MCL of 1.0 mg/L (as N). The Agency based the MCLG on an RfD 
of 0.16 mg/kg/day (as N) and a cancer classification of D, not 
classifiable as to human carcinogenicity.
    b. Technical Reviews. The current RfD and MCLG were established to 
protect infants, the most susceptible segment of the population. At the 
request of EPA, NAS completed an assessment of nitrite in 1995 (NAS, 
1995) and did not find any new studies that warrant a review of the RfD 
or cancer classification. The literature search conducted during the 
Six-Year Review did not identify any new studies that warrant a review 
of the RfD or the cancer classification (USEPA, 2002i).
    The current MCL is not limited by the analytical or treatment 
feasibility. Review of these capabilities is not necessary since no 
changes to the MCL are warranted at this time.
    As a part of the Six-Year Review of ``other regulatory revisions,'' 
EPA received several suggestions regarding the current monitoring 
requirements for nitrite.\12\ Stakeholders raised several potential 
issues concerning the current monitoring requirements (USEPA, 2002e). 
These issues include:
---------------------------------------------------------------------------

    \12\ Current monitoring requirements for nitrite: All community 
water systems (CWSs), non-transient, non-community water systems 
(NTNCWSs), and transient non-community water systems (TNCWSs) must 
monitor for nitrite at each entry point to the distribution system. 
If the analytical result is less than \1/2\ the MCL (0.5 mg/L), then 
the system must monitor at a frequency specified by the Primary 
Agency. If the sample result is greater than or equal to \1/2\ the 
MCL (0.5 mg/L) then the entry point that exceeded the trigger level 
must begin quarterly monitoring. The Primary Agency may reduce the 
quarterly monitoring to annual monitoring after the system has 
collected four quarters of data. However, the system must collect 
subsequent samples during the quarter that yielded the highest 
analytical result.
---------------------------------------------------------------------------

     A need for flexibility for States to require systems to 
collect a distribution system sample for nitrite under certain 
circumstances, such as if the entry point sample is greater than 50 
percent of the MCL, if there is a large amount of ammonia in the raw 
water, or if chloramines are applied;
     A need for flexibility for States to require systems to 
monitor for ammonia in raw water; and
     Flexibility to eliminate nitrite monitoring when a 
disinfection residual is present.
    EPA does not believe it has sufficient data at this time on which 
to base possible changes in monitoring requirements (USEPA, 2002e).
    Detailed occurrence and exposure analysis is not necessary since 
none of the technical analyses indicate a change to the nitrite 
regulation at this time.
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for nitrite is appropriate at this time because: (1) There 
are no changes in the health risk assessment for nitrite; and (2) no 
other new data were identified that indicate the need to revise the 
NPDWR at this time.
    EPA also published an MCLG and an MCL of 10 mg/L (as N) for the sum 
of nitrate and nitrite on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). 
The Agency established this joint nitrate/nitrite standard to account 
for the possible additive toxicity of these two chemicals and also to 
protect against the deterioration of drinking water quality, since the 
presence of nitrite in water is indicative of water contaminated with 
sewage. The Agency has not identified any new data as a part of the 
Six-Year Review process that indicates that this joint nitrate/nitrite 
standard needs to be revised.
50. Oxamyl (Vydate)
    a. Background. EPA published the current NPDWR for oxamyl on July 
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and 
an MCL of 0.2 mg/L. The Agency based the

[[Page 19077]]

MCLG on an RfD of 0.025 mg/kg/day and a cancer classification of E, 
evidence of non-carcinogenicity for humans.
    b. Technical Reviews. The Agency identified a change in the health 
assessment that supports consideration of whether to revise the MCLG 
(USEPA, 2002i). EPA updated the risk assessment in 2000. This new risk 
assessment considered relevant studies that had become available on the 
toxicity of oxamyl including its potential developmental and 
reproductive toxicity. The new risk assessment revised the RfD from 
0.025 mg/kg/day to 0.001 mg/kg/day (USEPA, 2000e).
    Based on the change in the RfD for oxamyl and using a 20 percent 
RSC \13\, EPA believes that any revision to the MCLG is not likely to 
be lower than 0.007 mg/L.
---------------------------------------------------------------------------

    \13\ This is the RSC used for the current MCLG and also the 
default value. EPA has no reason to believe that the RSC for oxamyl 
would change. See Appendix A for further discussion of the RSC.
---------------------------------------------------------------------------

    In setting the MCLG/MCL in 1992, the Agency determined the PQL for 
oxamyl to be 0.02 mg/L and analytical feasibility was not considered to 
be a limitation. EPA has analyzed more recent WS data to determine if 
analytical feasibility is likely to be a limiting factor in setting a 
lower MCL (USEPA, 2002d). In addition, the Agency evaluated whether 
more sensitive methods have been approved and are in use by a wide 
number of laboratories. The results of these analyses indicate that 
analytical feasibility is likely to be a limiting factor if EPA were to 
revise the MCLG and MCL. Although not definitive, the available WS data 
indicate that the PQL could lie between 0.02 and 0.04 mg/L. EPA used 
the 0.02 mg/L and the 0.04 mg/L values as thresholds in the occurrence 
analysis discussed in this section.
    Since the health effects technical review supports consideration of 
whether a revision to the MCLG and MCL may be appropriate, EPA 
evaluated whether treatment feasibility is likely to pose any 
limitations (USEPA, 2002k). The current BAT for oxamyl is GAC. 
Compliance technologies for small systems include GAC, PAC, and POU 
GAC. EPA believes that the BAT and compliance technologies are still 
practical and would not pose any limitations for oxamyl at a possibly 
lower level (i.e., a possibly lower MCL).
    The results of EPA's review of possible ``other regulatory 
revisions'' did not identify any issues that are specific to oxamyl 
(USEPA, 2002e).
    EPA evaluated the results of the occurrence and exposure analyses 
for oxamyl to determine whether changes to the MCL might be appropriate 
and likely to result in additional public health protection if the PQL 
were recalculated (USEPA, 2002g; USEPA, 2002h). Table V-12 shows the 
results of the detailed occurrence and exposure analyses based on the 
16-State cross-section for several concentrations: the current MCL (0.2 
mg/L), the possible upper and lower PQLs based on the analytical 
feasibility analysis (0.02 and 0.04 mg/L), and the possible lower limit 
of any MCLG value (0.007 mg/L). Based on the detailed analysis of 16 
cross-section States, it appears that oxamyl is unlikely to occur at 
the current MCL or any potential MCL value.
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    c. Preliminary Decision. Although there are new data indicating 
that it might be possible to lower the MCLG and the MCL, analytical 
feasibility limitations would limit the extent to which the MCL could 
be revised at the present time. Because any changes in the NPDWR based 
on setting the MCL at the limitations of analytical feasibility are 
unlikely to significantly improve the level of public health 
protection, EPA does not believe a revision to the NPDWR for oxamyl is 
appropriate at this time. In addition, because oxamyl appears to occur 
infrequently at concentrations at or below the current MCL, EPA 
believes that efforts to research more sensitive analytical methods 
and/or to revise the MCL are low priority and should not be pursued at 
the present time. EPA requests comment on the extent to which oxamyl is 
likely to occur at levels between 0.007 and 0.2 mg/L at PWSs. 
Commenters who disagree with the occurrence evaluation should submit 
data to support their rationale and evidence to show that oxamyl is of 
national concern at PWSs at the thresholds evaluated. EPA does plan to 
update the Health Advisory for oxamyl to reflect the new RfD.
51. Pentachlorophenol
    a. Background. EPA published the current NPDWR for 
pentachlorophenol on July 1, 1991 (56 FR 30266 (USEPA, 1991c)). The 
NPDWR established an MCLG of zero based on a cancer classification of 
B2, probable human carcinogen. The NPDWR also established an MCL of 
0.001 mg/L, based on analytical feasibility.
    b. Technical Reviews. The Agency has initiated a reassessment of 
the health risks resulting from exposure to pentachlorophenol. The 
revised risk assessment will consider relevant studies that have become 
available on the toxicity of pentachlorophenol

[[Page 19079]]

including its potential developmental and reproductive toxicity. The 
Agency expects the new risk assessment to be completed in the 2002 or 
2003 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for pentachlorophenol is appropriate at this time because a 
reassessment of the health risks resulting from exposure to 
pentachlorophenol is ongoing.
52. Picloram
    a. Background. EPA published the current NPDWR for picloram on July 
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and 
an MCL of 0.5 mg/L. The Agency based the MCLG on an RfD of 0.07 mg/kg/
day and a cancer classification of D, not classifiable as to human 
carcinogenicity.
    b. Technical Reviews. The Agency identified a change in the health 
assessment that could lead to a change in the MCLG (USEPA, 2002i). EPA 
updated the risk assessment in 1998. This new risk assessment 
considered relevant studies that had become available on the toxicity 
of picloram including its potential developmental and reproductive 
toxicity. The new risk assessment revised the RfD from 0.07 mg/kg/day 
to 0.20 mg/kg/day and classified picloram as Group E, evidence of 
noncarcinogenicity for humans, according to the 1986 Cancer Guidelines. 
Picloram has not been evaluated against the Proposed 1996 Cancer 
Guidelines.
    Based on the change in the RfD for picloram and using a 20 percent 
RSC,\14\ EPA believes that any revision to the MCLG is not likely to be 
higher than 1 mg/L (an increase in the MCLG).
---------------------------------------------------------------------------

    \14\ This is the RSC used for the current MCLG and also the 
default value. EPA has no reason to believe that the RSC for 
picloram would change. See Appendix A for further discussion of the 
RSC.
---------------------------------------------------------------------------

    Analytical or treatment feasibility do not pose any limitations for 
the current MCL and would not be a limiting factor if EPA were to raise 
the MCLG. The Agency's review of possible ``other regulatory 
revisions'' did not identify any issues that are specific to picloram 
(USEPA, 2002e).
    EPA evaluated the results of the occurrence and exposure analyses 
for picloram to determine whether possible changes to the MCL would be 
likely to result in opportunities for significant cost savings to PWSs 
and their customers (USEPA, 2002g; USEPA, 2002h). Table V-13 shows the 
results of the detailed occurrence and exposure analysis based on the 
16-State cross-section for the current MCL (0.5 mg/L), and the 
concentration that would be considered if the EPA revised the MCLG and 
MCL (i.e., the possible MCLG/MCL of 1 mg/L) based on the new RfD and a 
20 percent RSC. Based on the detailed analysis, it appears that 
picloram is unlikely to occur at concentrations above 0.5 mg/L in the 
States used for the cross-section.
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[[Page 19080]]

    The results of the detailed occurrence and exposure analysis 
indicate that few, if any, of the 12,907 systems sampled in the 16 
cross-section States might be affected if EPA were to raise the MCLG/
MCL.
    c. Preliminary Decision. Although there are new data that support 
consideration of whether to revise the MCLG/MCL for picloram, EPA does 
not believe a revision to the NPDWR for picloram is appropriate at this 
time. The Agency believes that any change in the MCLG/MCL would be 
unlikely to provide an opportunity for significant cost savings to 
PWSs.
53. Polychlorinated Biphenyls (PCBs)
    a. Background. EPA published the current NPDWR for PCBs on January 
30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an MCLG of 
zero based on a cancer classification of B2, probable human carcinogen. 
The NPDWR also established an MCL of 0.0005 mg/L based on analytical 
feasibility.
    b. Technical Reviews. The Agency has initiated a reassessment of 
the health risks resulting from exposure to PCBs. The revised risk 
assessment will consider relevant studies that have become available on 
the toxicity of PCBs including their potential developmental and 
reproductive toxicity. The Agency expects the new risk assessment to be 
completed in the 2002 or 2003 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for PCBs is appropriate at this time because a reassessment 
of the health risks resulting from exposure to PCBs is ongoing.
54. Selenium
    a. Background. EPA published the current NPDWR for selenium on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG and an MCL of 0.05 mg/L. The Agency based the MCLG on an RfD of 
0.005 mg/kg/day and a cancer classification of D, not classifiable as 
to human carcinogenicity.
    b. Technical Reviews. The Agency has not updated the risk 
assessment for selenium since the NPDWR was published (USEPA, 2002i). 
However, a 2000 NAS assessment of selenium supports the current RfD 
based on epidemiological studies of selenosis in humans (NAS, 2000b). 
The NAS study considered relevant studies that were available on the 
toxicity of selenium, including its developmental and reproductive 
toxicity, and established a tolerable upper intake level of 0.4 mg/day 
for adolescents and adults, a value which is equivalent to the RfD.
    A review of analytical or treatment feasibility is not necessary 
for selenium because changes to the MCLG are not warranted at this 
time, and the current MCL is set at the MCLG. In addition, the results 
of EPA's review of possible ``other regulatory revisions'' did not 
identify any selenium-specific issues (USEPA, 2002e). Since EPA did not 
identify a health or technology basis for revising the selenium NPDWR, 
the Agency did not conduct a detailed occurrence and exposure analysis.
    c. Preliminary Decision. After reviewing the results of the 
pertinent technical analyses, the Agency believes the NPDWR for 
selenium remains appropriate and thus, it is not subject to revision at 
this time.
55. Simazine
    a. Background. EPA published the current NPDWR for simazine on July 
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG and 
an MCL of 0.004 mg/L. The Agency based the MCLG on an RfD of 0.005 mg/
kg/day and a cancer classification of C, possible human carcinogen.
    b. Technical Reviews. The Agency has initiated a reassessment of 
the health risks resulting from exposure to simazine. The revised risk 
assessment will consider relevant studies that have become available on 
the toxicity of simazine including its potential developmental and 
reproductive toxicity. The Agency expects the new risk assessment to be 
completed in the 2003 or 2004 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for simazine is appropriate at this time because a 
reassessment of the health risks resulting from exposure to simazine is 
ongoing. The Agency is also re-examining all the triazines and their 
degradation products as part of its CCL in order to fill any necessary 
research gaps to enable the Agency to determine whether or not to 
regulate any or all of the contaminants in this group of compounds.
56. Styrene
    a. Background. EPA published the current NPDWR for styrene on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG and an MCL of 0.1 mg/L. The Agency based the MCLG on an RfD of 0.2 
mg/kg/day and a cancer classification of C, possible human carcinogen.
    b. Technical Reviews. The Agency has initiated a reassessment of 
the health risks resulting from exposure to styrene. The revised risk 
assessment will consider relevant studies that have become available on 
the toxicity of styrene including its potential developmental and 
reproductive toxicity. The Agency expects the new risk assessment to be 
completed in the 2002 or 2003 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for styrene is appropriate at this time because a 
reassessment of the health risks resulting from exposure to styrene is 
ongoing.
57. 2,3,7,8-TCDD (Dioxin)
    a. Background. EPA published the current NPDWR for dioxin on July 
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG of 
zero based on a cancer classification of B2, probable human carcinogen. 
The NPDWR also established an MCL of 3 x 10-8 mg/L based on 
analytical feasibility.
    b. Technical Reviews. The Agency has conducted a comprehensive 
assessment of the exposure and potential human health effects of dioxin 
including its potential developmental and reproductive toxicity. The 
draft document has been reviewed by the SAB (USEPA, 2001b). The Agency 
is presently in the process of addressing SAB and public comments, and 
expects to complete the risk assessment in the 2002 or 2003 time frame.
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for dioxin is appropriate at this time because a reassessment 
of the health risks resulting from exposure to dioxin is ongoing.
58. Tetrachloroethylene
    a. Background. EPA published the current NPDWR for 
tetrachloroethylene on January 30, 1991 (56 FR 3526 (USEPA, 1991a)). 
The NPDWR established an MCLG of zero based on a cancer classification 
of B2, probable human carcinogen. The NPDWR also established an MCL of 
0.005 mg/L based on analytical feasibility.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to tetrachloroethylene. The 
revised risk assessment will consider relevant studies that have become 
available on the toxicity of tetrachloroethylene including its 
potential developmental and reproductive toxicity. The Agency expects 
the new risk assessment to be completed in the 2002 or 2003 time frame 
(USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for tetrachloroethylene is appropriate at this time because a

[[Page 19081]]

reassessment of the health risks resulting from exposure to 
tetrachloroethylene is ongoing.
59. Thallium
    a. Background. EPA published the current NPDWR for thallium on July 
17, 1992 (57 FR 3526 (USEPA, 1991a)). The NPDWR established an MCLG of 
0.0005 mg/L based on an RfD of 0.00007 mg/kg/day and a cancer 
classification of D, not classifiable as to human carcinogenicity. The 
NPDWR also established an MCL of 0.002 mg/L based on analytical 
feasibility.
    b. Technical Reviews. The results of the health effects technical 
review identified some information on reproductive effects that 
indicate the need to update the Agency's risk assessment for thallium 
(USEPA, 2002i). In light of this information, EPA has initiated a 
reassessment of the health risks resulting from exposure to thallium 
and has already solicited scientific information from the public for 
consideration (67 FR 1212, January 9, 2002 (USEPA, 2002a)). The new 
risk assessment will consider relevant data on the toxicity of thallium 
including its potential developmental and reproductive toxicity. 
Because the new assessment is not expected to be completed until the 
2004 or 2005 time frame, EPA does not believe it is appropriate to 
revise the MCLG at this time.
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for thallium is appropriate at this time. A reassessment of 
the health risks has been initiated and the Agency does not believe it 
is appropriate to revise the NPDWR while that effort is in process.
60. Toluene
    a. Background. EPA published the current NPDWR for toluene on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG and an MCL of 1 mg/L. The Agency based the MCLG on an RfD of 0.2 
mg/kg/day and a cancer classification of D, not classifiable as to 
human carcinogenicity.
    b. Technical Reviews. The Agency has initiated a reassessment of 
the health risks resulting from exposure to toluene. The revised risk 
assessment will consider relevant studies that have become available on 
the toxicity of toluene including its potential developmental and 
reproductive toxicity. The Agency expects the new risk assessment to be 
completed in the 2002 or 2003 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for toluene is appropriate at this time because a 
reassessment of the health risks resulting from exposure to toluene is 
ongoing.
61. Toxaphene
    a. Background. EPA published the current NPDWR for toxaphene on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG of zero based on a cancer classification of B2, probable human 
carcinogen. The NPDWR also established an MCL of 0.003 mg/L based on 
analytical feasibility.
    b. Technical Reviews. The Agency has not updated the health risk 
assessment for toxaphene since the NPDWR was published; however, ATSDR 
completed a toxicological profile for toxaphene in 1996 (ATSDR, 1996d). 
This assessment and other recent information do not warrant a review of 
the cancer classification because the data indicate that toxaphene is 
mutagenic and would be evaluated using a linear dose-response approach 
(USEPA, 2002i). Accordingly, the MCLG remains at zero and the Agency 
believes that a further review of the health effects of toxaphene is 
not warranted at this time.
    The current MCL for toxaphene is based on a PQL of 0.003 mg/L. As a 
part of the Six-Year Review, EPA analyzed more recent WS data to 
determine if it might be possible to recalculate the PQL (USEPA, 
2002d). In addition, the Agency evaluated whether more sensitive 
analytical methods have been approved and put into use by a wide number 
of laboratories. The results of these analyses indicate that some 
improvement in analytical feasibility might exist. Evaluation of the WS 
data shows that EPA Regional and State laboratories exhibit greater 
than 90 percent laboratory passing rates at concentrations around the 
current PQL of 0.003 mg/L. Because most of the laboratory passing rates 
exceeded the 75 percent criterion typically used to derive a PQL from 
WS studies, this information indicates that a lower PQL corresponding 
to the 75 percent passing rate might exist for toxaphene. While this 
information is indicative of a possibly lower PQL, the WS data are 
insufficient at this time to actually recalculate what the lower PQL 
for toxaphene might be.
    Using information about the analytical methods most widely used to 
report results in the WS studies, the MDLs for these methods, and the 
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL 
might be. For the analysis of toxaphene in the more recent WS studies, 
laboratories predominantly used EPA Methods 508 (GC/MS) and 505 (Purge 
and Trap GC). No MDL data are available for EPA Method 508 and the MDL 
for 505 is listed as 0.001 mg/L. A 10 times MDL multiplier based on EPA 
Method 505 predicts a PQL of 0.01 mg/L, which is higher than the 
current PQL. Therefore, the 10 times multiplier could not be used to 
predict a lower PQL and EPA did not use this higher value as a 
threshold in the occurrence analysis discussed in this section. 
Instead, EPA used concentration thresholds of one-half the current MCL 
and the lower limit of detection reported by the States. EPA believes 
if a lower PQL does exist, that the magnitude of the change would be 
minimal.
    Since the analytical feasibility analysis indicates that the PQL 
for toxaphene (and therefore the MCL) could possibly be lower if EPA 
had more definitive data to recalculate the PQL, EPA considered whether 
treatment feasibility is likely to pose any limitations (USEPA, 2002k). 
The current BAT for toxaphene is GAC. Compliance technologies for small 
systems include GAC, PAC, and POU GAC. EPA believes that the BAT and 
compliance technologies are still practical and would not pose any 
limitations for toxaphene at a possibly lower MCL.
    The results of EPA's review of possible ``other regulatory 
revisions'' did not identify any issues that are specific to toxaphene 
(USEPA, 2002e).
    EPA evaluated the results of the occurrence and exposure analyses 
for toxaphene to determine whether changes to the MCL might be 
appropriate and likely to result in additional public health protection 
if EPA had sufficient data to recalculate the PQL (USEPA, 2002g; USEPA, 
2002h). Table V-14 shows the results of the detailed occurrence and 
exposure analyses based on the 16-State cross-section for the current 
MCL (0.003 mg/L), one-half the current MCL (0.0015 mg/L), and the lower 
level of detection reported by the States (0.001 mg/L).
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    The detailed occurrence and exposure analysis indicates that 
toxaphene is unlikely to occur at the current MCL or any potential MCL 
revision for the States used in the cross-section. Since toxaphene uses 
were canceled in the United States in 1990 and since it is subject to 
the United Nations Prior Informed Consent (USEPA, 2002g; USEPA, 2002h), 
EPA expects the occurrence of toxaphene in PWSs to be rare.
    c. Preliminary Decision. Although there are new data that support 
consideration of a possibly lower PQL (and therefore a possibly lower 
MCL), EPA does not believe a revision to the NPDWR for toxaphene is 
appropriate at this time. The Agency does not have sufficient data at 
this time on which to base a PQL recalculation and hence an MCL 
revision. Also, the Agency believes that any change in the PQL would be 
minimal and unlikely to significantly improve the level of public 
health protection because toxaphene appears to occur infrequently at 
concentrations at or below the current MCL.
62. 2,4,5-TP (Silvex; 2,4,5-Trichlorophenoxypropionic Acid)
    a. Background. EPA published the current NPDWR for 2,4,5-TP on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG and an MCL of 0.05 mg/L. The Agency based the MCLG on an RfD of 
0.008 mg/kg/day and a cancer classification of D, not classifiable as 
to human carcinogenicity.
    b. Technical Reviews. The Agency has not updated the health risk 
assessment for 2,4,5-TP since the NPDWR was published. Therefore, as 
part of the Six-Year Review process, EPA conducted a literature search 
for relevant data on the toxicology of 2,4,5-TP including its potential 
developmental and reproductive toxicity. The literature search did not 
identify any new studies that warrant a review of the RfD or the cancer 
classification (USEPA, 2002i).
    A review of analytical or treatment feasibility is not necessary 
for 2,4,5-TP because changes to the MCLG are not warranted at this time 
and the current MCL is set at the MCLG. In addition, the

[[Page 19083]]

results of EPA's review of possible ``other regulatory revisions'' did 
not identify any 2,4,5-TP-specific issues (USEPA, 2002e). Since EPA did 
not identify a health or technology basis for revising the 2,4,5-TP 
NPDWR, the Agency did not conduct a detailed occurrence and exposure 
analysis.
    c. Preliminary Decision. After reviewing the results of the 
pertinent technical analyses, the Agency believes the NPDWR for 2,4,5-
TP remains appropriate and thus, it is not subject to revision at this 
time.
63. 1,2,4-Trichlorobenzene
    a. Background. EPA published the current NPDWR for 1,2,4-
trichlorobenzene on July 17, 1992 (57 FR 31776 (USEPA, 1992)). The 
NPDWR established an MCLG and an MCL of 0.07 mg/L. The Agency based the 
MCLG on an RfD of 0.01 mg/kg/day and a cancer classification of D, not 
classifiable as to human carcinogenicity.
    b. Technical Reviews. The Agency has not updated the health risk 
assessment for 1,2,4-trichlorobenzene since the NPDWR was published. 
Therefore, as part of the Six-Year Review process, EPA conducted a 
literature search for relevant data on the toxicology of 1,2,4-
trichlorobenzene, including its potential developmental and 
reproductive toxicity. The literature search did not identify any new 
studies that warrant a review of the RfD or the cancer classification 
(USEPA, 2002i).
    A review of analytical or treatment feasibility is not necessary 
for 1,2,4-trichlorobenzene because changes to the MCLG are not 
warranted at this time and the current MCL is set at the MCLG. In 
addition, the results of EPA's review of possible ``other regulatory 
revisions'' did not identify any 1,2,4-trichlorobenzene-specific issues 
(USEPA, 2002e). Since EPA did not identify a health or technology basis 
for revising the 1,2,4-trichlorobenzene NPDWR, the Agency did not 
conduct a detailed occurrence and exposure analysis.
    c. Preliminary Decision. After reviewing the results of the 
pertinent technical analyses, the Agency believes the NPDWR for 1,2,4-
trichlorobenzene remains appropriate and thus, it is not subject to 
revision at this time.
64. 1,1,1-Trichloroethane
    a. Background. EPA published the current NPDWR for 1,1,1-
trichloroethane on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR 
established an MCLG and an MCL of 0.20 mg/L. The Agency developed the 
MCLG based on an RfD of 0.035 mg/kg/day derived from an inhalation 
study and a cancer classification of D, not classifiable as to human 
carcinogenicity.
    b. Technical Reviews. The Agency has initiated a reassessment of 
the health risks resulting from exposure to 1,1,1-trichloroethane. The 
revised risk assessment will consider relevant studies that have become 
available on the toxicity of toluene including its potential 
developmental and reproductive toxicity. The Agency expects the new 
risk assessment to be completed in the 2003 or 2004 time frame (USEPA, 
2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for 1,1,1-trichloroethane is appropriate at this time because 
a reassessment of the health risks resulting from exposure to 1,1,1-
trichloroethane is ongoing.
65. 1,1,2-Trichloroethane
    a. Background. EPA published the current NPDWR for 1,1,2-
trichloroethane on July 17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR 
established an MCLG of 0.003 mg/L based on an RfD of 0.004 mg/kg/day 
and a cancer classification of C, possible human carcinogen. The NPDWR 
also established an MCL of 0.005 mg/L based on analytical feasibility.
    b. Technical Reviews. The Agency has not updated the health risk 
assessment for 1,1,2-trichloroethane since the NPDWR was published. 
Therefore, as part of the Six-Year Review process, EPA conducted a 
literature search for relevant data on the toxicology of 1,1,2-
trichloroethane including its potential developmental and reproductive 
toxicity. The literature search did not identify any studies that 
warrant a review of the RfD or the cancer classification (USEPA, 
2002i).
    The current MCL for 1,1,2-trichloroethane is based on a PQL of 
0.005 mg/L. As a part of the Six-Year Review, EPA analyzed more recent 
WS data to determine if it might be possible to recalculate the PQL 
(USEPA, 2002d). In addition, the Agency evaluated whether more 
sensitive analytical methods have been approved and put into use by a 
wide number of laboratories. The results of these analyses indicate 
that a slight improvement in analytical feasibility might exist. 
Evaluation of the WS data shows that EPA Regional and State 
laboratories exhibit greater than 90 percent laboratory passing rates 
at concentrations around the current PQL of 0.005 mg/L. Because most of 
the laboratory passing rates exceeded the 75 percent criterion 
typically used to derive a PQL from WS studies, this information 
indicates that a lower PQL corresponding to the 75 percent passing rate 
might exist for 1,1,2-trichloroethane. While this information is 
indicative of a possibly lower PQL, the WS data are insufficient at 
this time to actually recalculate what the lower PQL for 1,1,2-
trichloroethane might be.
    Using information about the analytical methods most widely used to 
report results in the WS studies, the MDLs for these methods, and the 
10 times MDL multiplier, EPA estimated what the possibly lower PQL/MCL 
might be. For the analysis of 1,1,2-trichloroethane in the more recent 
WS studies, laboratories predominantly used EPA Methods 524.2 (GC/MS) 
and 502.2 (Purge and Trap GC), which both have upper limit MDLs of 
0.00003 mg/L. A 10 times MDL multiplier predicts a PQL of 0.0003 mg/L. 
Since this value is below the current MCLG, this supports consideration 
of whether the MCL might be set at the MCLG if sufficient data were 
available to recalculate the PQL. EPA did not use the possibly lower 
PQL as a threshold in the occurrence analysis but instead used 0.003 
mg/L (the current MCLG) since this is the lowest level to which the MCL 
would possibly be revised.
    Since the analytical feasibility analysis indicates that the PQL 
for 1,1,2-trichloroethane (and therefore the MCL) could possibly be 
lower if EPA had more definitive data to recalculate the PQL, EPA 
considered whether treatment feasibility is likely to pose any 
limitations (USEPA, 2002k). The current BATs for 1,1,2-trichloroethane 
include both PTA and GAC. Small system compliance technologies for 
1,1,2-trichloroethane include GAC and several aeration technologies. 
EPA believes that these BATs and compliance technologies are still 
practical and would not pose any limitations for 1,1,2-trichloroethane 
at a possibly lower level.
    The results of EPA's review of possible ``other regulatory 
revisions'' did not identify any issues that are specific to 1,1,2-
trichloroethane (USEPA, 2002e).
    EPA evaluated the results of the occurrence and exposure analyses 
for 1,1,2-trichloroethane to determine whether changes to the MCL might 
be appropriate and likely to result in additional public health 
protection if sufficient data were available to recalculate the PQL and 
subsequently set the MCL at the MCLG (USEPA, 2002g; USEPA, 2002h). 
Table V-15 shows the results of the detailed occurrence and exposure 
analyses based on the 16-State cross-section for the current MCL (0.005 
mg/L) and the potentially revised MCL (0.003 mg/L)

[[Page 19084]]

based on setting the MCL at the MCLG. Based on the detailed analysis, 
it appears that 1,1,2-trichloroethane is unlikely to occur at the 
current MCL or any potential MCL revisions in the States used for the 
cross-section.
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    c. Preliminary Decision. Although there are new data that support 
consideration of whether a lower PQL is possible (and therefore a 
possibly set the MCL at the MCLG), EPA does not believe a revision to 
the NPDWR for 1,1,2-trichloroethane is appropriate at this time. The 
Agency believes that any potential revision to the MCL is unlikely to 
significantly improve the level of public health protection because 
1,1,2-trichloroethane appears to occur infrequently at concentrations 
at or below the current MCL.
66. Trichloroethylene
    a. Background. EPA published the current NPDWR for 
trichloroethylene on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The 
NPDWR established an MCLG of zero based on a cancer classification of 
B2, probable human carcinogen. The NPDWR also established an MCL of 
0.005 mg/L based on analytical feasibility.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to trichloroethylene. The revised 
risk assessment will consider relevant studies that have become 
available on the toxicity of trichloroethylene including its potential 
developmental and reproductive toxicity. The Agency expects the new 
risk assessment to be completed in the 2002 or 2003 time frame (USEPA, 
2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for trichloroethylene is appropriate at this time because a 
reassessment of the health risks resulting from exposure to 
trichloroethylene is ongoing.
67. Vinyl Chloride
    a. Background. EPA published the current NPDWR for vinyl chloride 
on July 8, 1987 (52 FR 25690 (USEPA, 1987)). The NPDWR established an 
MCLG of zero based on a cancer classification of A, known human 
carcinogen. The NPDWR also established an MCL of 0.002 mg/L based on 
analytical feasibility.
    b. Technical Reviews. The Agency updated the health risk assessment 
of vinyl chloride in 2000 (USEPA, 2000k). The updated risk assessment 
included relevant studies that were available on the toxicity of vinyl 
chloride including its potential developmental and reproductive 
toxicity. According to the 1986 EPA Guidelines for Carcinogen Risk 
Assessment, vinyl chloride is categorized as Group A, known human 
carcinogen. Under the Proposed Guidelines for Carcinogen Risk 
Assessment (61 FR 17960, April 23, 1996 (USEPA, 1996)), EPA concluded 
that vinyl chloride is a known human carcinogen by the inhalation route 
of exposure, based on human epidemiological data and, by analogy, by 
the oral and dermal routes.
    The current MCL for vinyl chloride is based on a PQL of 0.002 mg/L. 
As a part

[[Page 19085]]

of the Six-Year Review, EPA analyzed WS data to determine if it might 
be possible to recalculate the PQL. In addition, the Agency evaluated 
whether more sensitive analytical methods have been approved and put 
into use by a wide number of laboratories. Based on these analyses, the 
Agency believes the current PQL, and therefore the MCL, is still 
appropriate (USEPA, 2002d).
    A review of treatment feasibility is not necessary for vinyl 
chloride because no changes to the MCLG or the MCL are warranted at 
this time. In addition, the results of EPA's review of possible ``other 
regulatory revisions'' did not identify any vinyl chloride-specific 
issues (USEPA, 2002e). Since EPA did not identify a health or 
technology basis for revising the vinyl chloride NPDWR, the Agency did 
not conduct a detailed occurrence and exposure analysis.
    c. Preliminary Decision. After reviewing the results of the 
pertinent technical analyses, the Agency believes the NPDWR for vinyl 
chloride remains appropriate and thus, it is not subject to revision at 
this time.
68. Xylenes (Total)
    a. Background. EPA published the current NPDWR for total xylenes on 
January 30, 1991 (56 FR 3526 (USEPA, 1991a)). The NPDWR established an 
MCLG and an MCL of 10 mg/L. The Agency based the MCLG on an RfD of 2 
mg/kg/day and a cancer classification of D, not classifiable as to 
human carcinogenicity.
    b. Technical Reviews. The Agency has initiated a reassessment of 
the health risks resulting from exposure to xylenes. The revised risk 
assessment will consider relevant studies that have become available on 
the toxicity of xylenes including its potential developmental and 
reproductive toxicity. The Agency expects the new risk assessment to be 
completed in the 2002 or 2003 time frame (USEPA, 2002i).
    c. Preliminary Decision. The Agency does not believe a revision to 
the NPDWR for xylenes is appropriate at this time because a 
reassessment of the health risks resulting from exposure to xylenes is 
ongoing.

B. What Preliminary Decision Has EPA Made Regarding the Total Coliform 
Rule?

1. Background
    EPA published the TCR on June 29, 1989 (54 FR 27544 (USEPA, 
1989b)). The TCR is one of several EPA regulations that protect the 
public from pathogens in drinking water. The TCR requires all PWSs to 
monitor for the presence of total coliforms in the distribution system. 
Total coliforms are a group of closely related bacteria that are (with 
few exceptions) not harmful to humans. They are natural and common 
inhabitants of the soil and ambient waters (e.g., lakes, rivers and 
estuaries), as well as in the gastrointestinal tract of animals. A few 
of these coliforms (fecal coliforms, including Escherichia coli or E. 
coli \15\) only grow within the intestinal tract of humans and other 
warm-blooded animals. Total coliforms may be injured by environmental 
stresses (e.g., lack of nutrients) and water treatment (e.g., chlorine 
disinfection) in a manner similar to most bacterial pathogens and many 
virus pathogens. Therefore, EPA considers them a useful indicator of 
bacterial and many viral waterborne enteric pathogens. More 
specifically, for drinking water, total coliforms are used to determine 
the adequacy of water treatment and the integrity of the distribution 
system. The absence of total coliforms in the distribution system 
minimizes the likelihood that fecal pathogens are present. Thus, total 
coliforms are used to determine the vulnerability of a system to fecal 
contamination.
---------------------------------------------------------------------------

    \15\ EPA is aware that Escherichia coli O157 may be found in 
fecally contaminated drinking water. To date, however, none of the 
EPA-approved methods for E. coli and fecal coliforms in drinking 
water detect E. coli O157. Nevertheless, E. coli O157, as is true 
with nonpathogenic E. coli strains, is always associated with fecal 
waste (outside the laboratory) and should be as susceptible to 
disinfection as the nonpathogenic strains. Therefore, the presence 
of E. coli O157 should always be accompanied by other E. coli 
strains that are detectable by the EPA-approved methods.
---------------------------------------------------------------------------

    The 1989 TCR set an MCLG of zero for total coliforms because EPA 
was not aware of any data in the scientific literature supporting a 
particular value for the concentration of coliforms below which no 
known or anticipated adverse health effects occur, with an adequate 
margin of safety. The TCR requires systems to monitor for total 
coliforms at a frequency proportional to the number of people served. 
If any sample is total coliform-positive, the system must:
     Test the positive culture for the presence of either fecal 
coliforms or E. coli;
     Take one set of 3-4 repeat samples at sites located within 
five or fewer sampling sites adjacent to the location of the routine 
positive sample within 24 hours; and
     Take at least 5 routine samples the next month of 
operation.
2. Technical Reviews
    Since the TCR was promulgated in 1989, few technical papers on the 
occurrence of coliforms in treated water have been published. Much of 
the recent technical data on coliforms are associated with biofilm 
studies, specifically the factors that facilitate the growth of 
coliforms and other microbes within the distribution system (e.g., 
LeChevallier et al., 1991, 1996; LeChevallier, 1999). In addition, 
several studies have been published describing the performance of new 
coliform methods (e.g., Brenner et al., 1993; Grant, 1997).
    One recent study examined the relationship between total coliforms 
and waterborne disease outbreaks (Craun et al., 1997). According to the 
study results, coliforms were found in 84 percent of the 187 systems 
during an outbreak investigation, but in the months before any 
outbreak, they were only detected by 26 percent of these systems. For 
outbreaks caused by Cryptosporidium or Giardia, coliforms were only 
found during 38 percent of the outbreaks. The study, as well as data 
from the 1993 outbreak of waterborne cryptosporidiosis in Milwaukee 
(MacKenzie, et al., 1994), continues to support the premise that 
coliforms are an inadequate indicator for Cryptosporidium oocysts and 
Giardia cysts in treated waters, presumably because these protozoa are 
appreciably more resistant to disinfection than the coliform 
indicators.
    Since promulgation of the TCR, EPA has received comments from a 
number of stakeholders. Stakeholders have suggested modifications to 
reduce the burden of implementing the TCR. EPA has determined that an 
opportunity for implementation burden reduction exists and will analyze 
the effect that such changes would have on public health protection as 
part of the Agency's regulatory development/revision process. Only 
those measures which reduce the TCR implementation burden while still 
assuring public health protection will be considered by EPA.
3. Preliminary Decision
    EPA intends to undertake a rulemaking process to initiate possible 
revisions to the TCR. As part of this process, EPA believes it may be 
appropriate to include this rulemaking in a wider effort to review and 
address broader issues associated with drinking water distribution 
systems. This would be one way of addressing some of the 
recommendations of the Microbial/ Disinfection Byproducts (M/DBP) 
Federal Advisory Committee in the Stage 2 M/DBP Agreement in Principle 
(65 FR 83015, December 29, 2000 (USEPA, 2000h)). As part of the TCR 
rulemaking, EPA plans to assess the

[[Page 19086]]

effectiveness of the current TCR in reducing public health risk, and 
what technically supportable alternative/additional monitoring 
strategies are available that would decrease economic burden while 
maintaining or improving public health protection.

VI. Request for Comments

A. On Which Issues Is EPA Soliciting Public Comment?

    Today's action solicits public comment on the following broad 
issues.
    (1) Is EPA's protocol for the review of the 69 NPDWRs discussed in 
today's action reasonable and appropriate?
    (2) Based on the review, are EPA's revise/not revise conclusions 
appropriate for each of the 69 NPDWRs?
    EPA also invites commenters to submit any new, relevant peer-
reviewed data pertaining to the NPDWRs discussed in today's action. 
Peer-reviewed data are studies/analyses that have been reviewed by 
qualified individuals (or organizations) who are independent of those 
who performed the work, but who are collectively equivalent in 
technical expertise (i.e., peers) to those who performed the original 
work. A peer review is an in-depth assessment of the assumptions, 
calculations, extrapolations, alternate interpretations, methodology, 
acceptance criteria, and conclusions pertaining to the specific major 
scientific and/or technical work products and of the documentation that 
supports them (USEPA, 2000i). Relevant data include studies/analyses 
pertaining to health effects, analytical feasibility, treatment 
feasibility, and occurrence/exposure related to the contaminants 
discussed in today's action.
    Table VI-1 summarizes the specific comments requested in today's 
action and provides a cross reference to the section of today's action 
where the issue is discussed.
BILLING CODE 6560-50-P
[GRAPHIC] [TIFF OMITTED] TP17AP02.025

BILLING CODE 6560-50-C
    EPA also invites commenters to submit any new, relevant peer-
reviewed data pertaining to the NPDWRs discussed in today's action.

B. Request for Comments on Use of Plain Language

    Executive Order 12866 and the President's memorandum of June 1, 
1998, require each agency to write all rules in plain language. We 
invite your comments on how to make this action easier to understand. 
For example:
     Have we organized the material to suit your needs?
     Are the decisions in the notice and our rationale for 
those decisions clearly stated?
     Does the notice contain technical language or jargon that 
isn't clear?
     Would a different format (grouping and order of sections, 
use of headings, paragraphing) make the notice easier to understand?
     Would more (but shorter) sections be better?
     Could we improve clarity by adding tables, lists, or 
diagrams?
     What else could we do to make the notice easier to 
understand?

VII. EPA's Next Steps

    EPA plans a 60-day comment period following this action. For each 
NPDWR for which the Agency has published its preliminary revise/not 
revise decision in today's action, EPA will consider the public 
comments received and review any new peer-reviewed data submitted in 
support of those public comments to determine whether a different 
revise/not revise decision is appropriate in light of the submitted 
data. The Agency plans to publish its final revise/not revise decisions 
for these NPDWRs in the August 2002 time frame.
    The publication of a decision to revise pursuant to SDWA Section 
1412(b)(9) is not the end of the regulatory process, but is the 
beginning of one. A decision to revise starts a regulatory process for 
a contaminant that involves more detailed analyses concerning health 
effects, costs, benefits, occurrence, and other matters relevant to 
deciding whether and how an NPDWR should be revised. At any point in 
this process, EPA may find that regulatory revisions are no longer 
appropriate and may discontinue regulatory revision efforts at that 
time. Review of that contaminant would continue in future six-year 
reviews.
    Similarly, a decision not to revise at this time means only that 
EPA does not believe that regulatory changes to a particular NPDWR are 
appropriate now, based on lack of new data, ongoing scientific reviews, 
low priority, or other reasons discussed in this action. Review of 
these contaminants continues and future six-year reviews may lead to a 
decision that regulatory changes are appropriate.

VIII. References

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U.S. Department of Health and Human Services, Public Health Service. 
164 pp. Available on the Internet at: http://www.atsdr.cdc.gov/toxprofiles/tp36.html.
ATSDR. 1993. Toxicological Profile for Heptachlor and Heptachlor 
Epoxide. U.S. Department of Health and Human Services, Public Health 
Service. 162 pp. Available on the Internet at: http://www.atsdr.cdc.gov/toxprofiles/tp12.html.
ATSDR. 1996a. Toxicological Profile for 1,2-Dichloroethene. U.S. 
Department of Health and Human Services, Public

[[Page 19087]]

Health Service. 196 pp. Available on the Internet at: http://www.atsdr.cdc.gov/toxprofiles/tp87.html.
ATSDR. 1996b. Toxicological Profile for Endrin. U.S. Department of 
Health and Human Services, Public Health Service. 228 pp. Available 
on the Internet at: http://www.atsdr.cdc.gov/toxprofiles/tp89.pdf.
ATSDR. 1996c. Toxicological Profile for Hexachlorobenzene. U.S. 
Department of Health and Human Services, Public Health Service. 352 
pp.
ATSDR. 1996d. Toxicological Profile for Toxaphene. U.S. Department 
of Health and Human Services, Public Health Service. 248 pp. 
Available on the Internet at: http://www.atsdr.cdc.gov/toxprofiles/tp94.pdf.
ATSDR. 1999. Toxicological Profile for Lead. U.S. Department of 
Health and Human Services, Public Health Service. 640 pp. Available 
on the Internet at: http://www.atsdr.cdc.gov/toxprofiles/tp13.pdf.
Brenner, K.P., C.C. Rankin, Y.R. Roybal, G.N. Stelma, P.V. Scarpino, 
and A.P. Dufour. 1993. New medium for the simultaneous detection of 
total coliforms and Escherichia coli in water. Applied and 
Environmental Microbiology. v. 59, pp. 3534-3544.
Craun, G.F., P.S. Berger, and R. Calderon. 1997. Coliform bacteria 
and waterborne disease outbreaks. Journal of the American Water 
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Department of Health and Human Services (HHS). 2001. Memorandum from 
Dr. Scott Masten, Office of Chemical Nomination and Selection, 
Environmental Toxicology Program to NTP Interagency Committee for 
Chemical Evaluation and Coordination. Subject: Hexavalent chromium 
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Flegal, R. et al. 2001. Scientific Review of Toxicological Human 
Health Issues Related to Development of a Public Health Goal for 
Chromium (VI): Report Prepared by the Chromate Toxicity Review 
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Grant, M.A. 1997. A New Membrane Filtration Medium for Simultaneous 
Detection and Enumeration of Escherichia coli and Total Coliforms. 
Applied and Environmental Microbiology. v. 63, pp. 3526-3530.
LeChevallier, M.W. 1999. The case for maintaining a disinfectant 
residual. Journal of the American Water Works Association. v. 91, 
No. 1, pp. 86-94.
LeChevallier, M.W., W. Schulz, and R.G. Lee. 1991. Bacterial 
nutrients in drinking water. Applied and Environmental Microbiology. 
v. 57, pp. 857-862.
LeChevallier, M.W., N.J. Welch, and D.B. Smith. 1996. Full-scale 
studies of factors related to coliform regrowth in drinking water. 
Applied and Environmental Microbiology. v. 62, pp. 2201-2211.
MacKenzie W.R., N.J. Hoxie, M.E. Proctor, M.S. Gradus, K.A. Blair, 
D.E. Peterson, J.J. Kazmierczak, D.A. Addiss, K.R. Fox, J.B. Rose, 
and J.P. Davis. 1994. A massive outbreak in Milwaukee of 
Cryptosporidium infection transmitted through the public water 
supply. New England Journal of Medicine. v. 331, no. 3, pp. 161-167.
NAS. 1995. Nitrate and nitrite in drinking water. National Academy 
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NAS. 1997. Dietary reference intakes for calcium, phosphorus, 
magnesium, vitamin D, and fluoride. National Academy Press, 
Washington, D.C. Available on the Internet at: http://books.nap.edu/books/0309063507/html/index.html.
NAS. 2000a. Copper in drinking water. National Academy Press, 
Washington, D.C. Available on the Internet at: 
http://www.nap.edu/books/0309069394/html.
NAS. 2000b. Dietary reference intakes for vitamin C, vitamin E, 
selenium, and carotenoids. National Academy Press, Washington, D.C. 
Available on the Internet at: http://www.nap.edu/books/0309069351/html.
NAS. 2001. Dietary reference intakes for vitamin A, vitamin K, 
arsenic, boron, chromium, copper, iodine, iron, manganese, 
molybdenum, nickel, silicon, vanadium, and zinc. National Academy 
Press, Washington, D.C. Available on the Internet at: http://www.nap.edu/catalog/10026.html.
NDWAC. 2000. Recommended Guidance for Review of Existing National 
Primary Drinking Water Regulations. November 2000. Available on the 
Internet at: 
http://www.epa.gov/safewater/ndwac/guidfnl.pdf.
NTP. 2001. NTP Study of the Hexavalent Chromium Compound Sodium 
Dichromate Dihydrate. Available on the Internet at: http://ntp-server.niehs.nih.gov/htdocs/Studies/HexChromium/hexchromiumpg.html.
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Agricultural Impact Program--Reregistration Notification Network. 
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USEPA. 1975. Water Programs: National Interim Primary Drinking Water 
Regulations. Federal Register. Vol. 40, No. 248, p. 59566. December 
24, 1975.
USEPA. 1976. Interim Primary Drinking Water Regulations; 
Promulgation of Regulations on Radionuclides. Federal Register. Vol. 
41, No. 133. p. 28401, July 9, 1976.
USEPA. 1979. National Interim Primary Drinking Water Regulations; 
Control of Trihalomethanes in Drinking Water. Federal Register. Vol. 
44, No. 231. p. 68624, November 29, 1979.
USEPA. 1985. National Primary Drinking Water Regulations; Volatile 
Synthetic Organic Chemicals; Final Rule and Proposed Rule. Federal 
Register. Vol. 50, No. 219. p. 46880, November 13, 1985.
USEPA. 1986a. National Primary and Secondary Drinking Water 
Regulations; Fluoride; Final Rule. Federal Register. Vol. 51, No. 
63. p. 11396, April 2, 1986.
USEPA. 1986b. EPA Guidelines for Carcinogen Risk Assessment. Federal 
Register. Vol. 51, No. 185. p. 33992, September 24, 1986.
USEPA. 1987. National Primary Drinking Water Regulations--Synthetic 
Organic Chemicals; Monitoring for Unregulated Contaminants; Final 
Rule. Federal Register. Vol. 52, No. 130. p. 25690, July 8, 1987.
USEPA. 1989a. National Primary and Secondary Drinking Water 
Regulations; Proposed Rule. Federal Register. Vol. 54, No. 97. p. 
22062, May 22, 1989.
USEPA. 1989b. Drinking Water; National Primary Drinking Water 
Regulations; Total Coliforms (Including Fecal Coliforms and E. 
coli); Final Rule. Federal Register. Vol. 54, No. 124. p. 27544, 
June 29, 1989.
USEPA. 1989c. National Primary Drinking Water Regulations; 
Filtration, Disinfection; Turbidity, Giardia Lamblia, Viruses, 
Legionella, and Heterotrophic Bacteria; Final Rule. Part 2. Federal 
Register. Vol. 54, No. 124. p. 27486, June 29, 1989.
USEPA. 1990. National Primary and Secondary Drinking Water 
Regulations--Synthetic Organic Chemicals and Inorganic Chemicals; 
Proposed Rule. Federal Register. Vol. 55, No. 143. p. 30370, July 
25, 1990.
USEPA. 1991a. National Primary Drinking Water Regulations--Synthetic 
Organic Chemicals and Inorganic Chemicals; Monitoring for 
Unregulated Contaminants; National Primary Drinking Water 
Regulations Implementation; National Secondary Drinking Water 
Regulations; Final Rule. Federal Register. Vol. 56, No. 30. p. 3526, 
January 30, 1991.
USEPA. 1991b. Drinking Water Regulations--Maximum Contaminant Level 
Goals and National Primary Drinking Water Regulations for Lead and 
Copper; Final Rule. Federal Register. Vol. 56, No. 110. p. 26460, 
June 7, 1991.
USEPA. 1991c. Drinking Water; National Primary Drinking Water 
Regulations; Monitoring for Volatile Organic Chemicals; MCLGs and 
MCLs for Aldicarb, Aldicarb Sulfoxide, Aldicarb Sulfone, 
Pentachlorophenol, and Barium; Final Rule. Federal Register. Vol. 
56, No. 126. p. 30266, July 1, 1991.
USEPA. 1992. Drinking Water; National Primary Drinking Water 
Regulations--Synthetic Organic Chemicals and Inorganic Chemicals; 
National Primary Drinking Water Regulations Implementation; Final 
Rule. Federal Register. Vol. 57, No. 138. p. 31776, July 17, 1992.
USEPA. 1994a. Public Water System Warning: Cyanide. Memo from 
William R. Diamond, Acting Director of Drinking Water Standards 
Division, Office of Ground Water and Drinking Water. March 7, 1994.
USEPA. 1994b. Drinking Water; Maximum Contaminant Level Goals and 
National Primary Drinking Water Regulations for

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Lead and Copper; Final Rule; Technical Corrections. Federal 
Register. Vol. 59, No. 125. p. 33860, June 30, 1994.
USEPA. 1995. Integrated Risk Information System (IRIS), Mercuric 
Chloride. Available on the Internet at: http://www.epa.gov/iris/subst/0692.htm.
USEPA. 1996. Proposed guidelines for carcinogen risk assessment. 
Federal Register. Vol. 61, No. 79. p. 17960, April 23, 1996.
USEPA. 1997a. Alternative Monitoring Guidelines. EPA Report 816-R-
97-011. August 1997. Available on the Internet at: http://www.epa.gov/safewater/regs/pmrfin.html.
USEPA. 1997b. Mercury Study Report to Congress; Volume V: Health 
Effects of Mercury and Mercury Compounds. EPA Report 452-R-97-009. 
Office of Air Quality Planning and Standards, Office of Research and 
Development. December 1997. Available on the Internet at: 
http://www.epa.gov/ttn/oarpg/t3/reports/volume5.pdf.
USEPA. 1998a. Small System Compliance Technology List for Non-
Microbial Contaminants Regulated Before 1996. EPA Report 815-R-98-
002. September 1998.
USEPA. 1998b. National Primary Drinking Water Regulations: 
Disinfectants and Disinfection Byproducts; Final Rule. Federal 
Register. Vol. 63, No. 241. p. 69389, December 16, 1998.
USEPA. 1998c. National Primary Drinking Water Regulations: Interim 
Enhanced Surface Water Treatment; Final Rule. Federal Register. Vol. 
63, No. 241. p. 69478, December 16, 1998.
USEPA. 1998d. IRIS, Beryllium and Compounds. Available on the 
Internet at: http://www.epa.gov/iris/subst/0012.htm.
USEPA. 1998e. IRIS, Chlordane (Technical). Available on the Internet 
at: http://www.epa.gov/iris/subst/0142.htm.
USEPA. 1998f. IRIS, Chromium (VI). Available on the Internet at: 
http://www.epa.gov/iris/subst/0144.htm.
USEPA. 1999a. Response to Recommendations from the Children's Health 
Protection Advisory Committee Regarding Evaluation of Existing 
Environmental Standards; Notice. Federal Register. Vol. 64, No. 22. 
p. 5277, February 3, 1999.
USEPA. 1999b. Guidelines for Carcinogen Risk Assessment. NCEA-F-0644 
Review Draft. U.S. Environmental Protection Agency Risk Assessment 
Forum. Washington, D.C. July 1999.
USEPA. 1999c. Announcement of Stakeholders Meeting on the Drinking 
Water Contaminant Identification and Selection Process, and the 6-
Year Review of All Existing National Primary Drinking Water 
Regulations, as Required by the Safe Drinking Water Act, as Amended 
in 1996; Notice of Stakeholders Meeting. Federal Register. Vol. 64, 
No. 198. p. 55711, October 14, 1999.
USEPA. 1999d. A Review of Contaminant Occurrence in Public Water 
Systems. EPA Report 816-R-99-006. November 1999. Available on the 
Internet at: http://www.epa.gov/safewater/occur/nov99_lo.pdf.
USEPA. 1999e. Stakeholder Meeting on the Contaminant Candidate List 
and the 6-Year Review of Existing National Primary Drinking Water 
Regulations. November 1999. Available on the Internet at: http://www.epa.gov/safewater/ccl/novmtg.html.
USEPA. 1999f. IRIS, Barium and Compounds. Available on the Internet 
at: http://www.epa.gov/iris/subst/0010.htm.
USEPA. 2000a. National Primary Drinking Water Regulations for Lead 
and Copper; Final Rule. Federal Register. Vol. 65, No. 8. p. 1950, 
January 12, 2000.
USEPA. 2000b. Working Group Meeting on Contaminant Candidate List 
Regulatory Determinations and the 6-Year Review of Existing 
Regulations. Office of Water. June 2000. Available on the Internet 
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USEPA. 2000c. Working Group Meeting on Contaminant Candidate List 
Regulatory Determinations and the 6-Year Review of Existing 
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at: http://www.epa.gov/safewater/ccl/julymtg.html.
USEPA. 2000d. NDWAC Working Group Meeting on Contaminant Candidate 
List Regulatory Determinations and the 6-Year Review of Existing 
Regulations. Office of Water. September 2000. Available on the 
Internet at: http://www.epa.gov/safewater/ccl/25septmtg.html.
USEPA. 2000e. Interim Reregistration Eligibility Decision (IRED)--
Oxamyl. EPA Report 738-R-00-015. Office of Prevention, Pesticides, 
and Toxic Substances. October 2000. Available on the Internet at: 
http://www.epa.gov/oppsrrd1/REDs/0253ired.pdf.
USEPA. 2000f. Methodology for Deriving Ambient Water Quality 
Criteria for the Protection of Human Health. EPA Report 882-B-00-
004. Office of Water. October 2000.
USEPA. 2000g. National Primary Drinking Water Regulations; 
Radionuclides; Final Rule. Federal Register. Vol. 65, No. 236. p. 
76707, December 7, 2000.
USEPA. 2000h. Stage 2 Microbial and Disinfection Byproducts Federal 
Advisory Committee Agreement in Principle; Notice. Federal Register. 
Vol. 65, No. 251. p. 83015, December 29, 2000.
USEPA. 2000i. Science Policy Council Handbook: Peer Review, 2nd 
Edition. EPA Report 100-B-00-001. Office of Science Policy, Office 
of Research and Development. December 2000.
USEPA. 2000j. IRIS, Benzene. Available on the Internet at: http://www.epa.gov/iris/subst/0276.htm.
USEPA. 2000k. IRIS, Vinyl Chloride. Available on the Internet at: 
http://www.epa.gov/iris/subst/1001.htm.
USEPA. 2000l. EPA Summary Report. Characterization of data 
variability and uncertainty: Health effects assessments in the 
Integrated Risk Information System (IRIS). In response to Congress, 
HR 106-379. EPA Report 635-R-00-005F. National Center for 
Environmental Assessment, Office of Research and Development.
USEPA. 2001a. National Primary Drinking Water Regulation; Arsenic 
and Clarifications to Compliance and New Source Contaminants 
Monitoring; Final Rule. Federal Register. Vol. 66, No. 14. p. 6975, 
January 22, 2001.
USEPA. 2001b. Dioxin Reassessment--An SAB Review of the Office of 
Research and Development's Reassessment of Dioxin. EPA Report SAB-
EC-01-006. May 2001. Available on the Internet at: http://www.epa.gov/sab/ec01006.pdf.
USEPA. 2001c. IRIS, Hexachlorocyclopentadiene. Available on the 
Internet at: http://www.epa.gov/iris/subst/0059.htm.
USEPA. 2002a. Integrated Risk Information System (IRIS); 
Announcement of 2002 Program; Request for Information; Notice. 
Federal Register. Vol. 67, No. 6. p. 1212, January 9, 2002.
USEPA. 2002b. National Primary Drinking Water Regulations: Long-Term 
1 Enhanced Surface Water Treatment Rule; Final Rule. Federal 
Register. Vol. 67, No. 9. p. 1811, January 14, 2002.
USEPA. 2002c. An Evaluation of Available Economic Information in 
Support of the Six-Year Review of Existing National Primary Drinking 
Water Regulations. Memo from Marc Parrotta, Targeting and Analysis 
Branch, Office of Ground Water and Drinking Water. March 2002.
USEPA. 2002d. Analytical Feasibility Support Document for the Six-
Year Review of Existing National Primary Drinking Water Regulations 
(Reassessment of Feasibility for Chemical Contaminants). EPA Report 
815-D-02-002. Draft. March 2002.
USEPA. 2002e. Consideration of Other Regulatory Revisions for 
Chemical Contaminants in Support of the Six-Year Review of National 
Primary Drinking Water Regulations. EPA Report 815-D-02-003. Draft. 
March 2002.
USEPA. 2002f. EPA Protocol for Review of Existing National Primary 
Drinking Water Regulations. EPA Report 815-D-02-004. Draft. March 
2002.
USEPA. 2002g. Occurrence Estimation Methodology and Occurrence 
Findings Report for the Six-Year Regulatory Review. EPA Report 815-
D-02-005. Draft. March 2002.
USEPA. 2002h. Occurrence Summary and Use Support Document for the 
Six-Year Regulatory Review. EPA Report 815-D-02-006. Draft. March 
2002.
USEPA. 2002i. Six-Year Review--Chemical Contaminants--Health Effects 
Technical Support Document. EPA Report 822-R-02-001. Draft. February 
2002.
USEPA. 2002j. Six-Year Review of the Total Coliform Rule--Comments 
Received. Memo from Kenneth H. Rotert, Standards and Risk Reduction 
Branch, Office of Ground Water and Drinking Water. March 2002.
USEPA. 2002k. Water Treatment Technology Feasibility Support 
Document for Chemical Contaminants; In Support of

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EPA Six-Year Review of National Primary Drinking Water Regulations. 
EPA Report EPA 815-D-02-001. Draft. February 2002.

    Dated: March 28, 2002.
Christine Todd Whitman,
Administrator.

Appendix A: Background on the Calculation of MCLG and Cancer 
Classification System

    Since the identification of contaminants for potential revision 
may be dependent on whether or not the maximum contaminant level 
goal (MCLG) could change, a brief explanation of the derivation of 
the MCLG is warranted. The MCLG is the maximum level of a 
contaminant in drinking water at which no known or anticipated 
adverse health effects occur, allowing for an adequate margin of 
safety. MCLGs are non-enforceable health goals. EPA establishes the 
maximum contaminant level (MCL) based on the MCLG. The MCL is the 
maximum permissible level of a contaminant in water which is 
delivered to any user of a public water system. It is derived based 
on the MCLG. Prior to the 1996 Amendments to the Safe Drinking Water 
Act (SDWA), the MCL was set as close to the MCLG as is feasible, 
taking costs into consideration. The 1996 Amendments to the SDWA 
permit consideration of costs relative to benefits in establishing a 
MCL. MCLs are enforceable standards.
    For chemicals exhibiting a threshold for toxic effects, EPA 
establishes the MCLG on the basis of an oral reference dose (RfD). A 
change in the RfD could lead to a change in the MCLG and thus in the 
MCL. The RfD is an estimate (with uncertainty spanning perhaps an 
order of magnitude) of a daily oral exposure to the human population 
(including sensitive subgroups) that is likely to be without an 
appreciable risk of deleterious noncancer effects during a lifetime. 
The RfD is derived as follows:
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Where:

NOAEL = no-observed-adverse-effect level
LOAEL = lowest-observed-adverse-effect level
BMD = benchmark dose
UF = uncertainty factor
MF = modifying factor

The benchmark dose (BMD) is the statistical lower confidence limit 
on the dose estimated to produce a predetermined level of change 
(i.e., 10 percent) in the critical response relative to the control. 
The uncertainty factor (UF) is used to account for extrapolation 
uncertainties (e.g., inter-individual variation, interspecies 
differences, duration of exposure, and use of a LOAEL instead of a 
NOAEL) and database adequacy. The modifying factor (MF) is used as a 
judgment factor to account for the confidence in the critical study 
(or studies) used in the derivation of the RfD (USEPA, 20001).
    The MCLG is then derived from the RfD as follows:

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Where:

bw = body weight (70 kg for adult \16\)
RSC = relative source contribution, the fraction of the RfD 
allocated to drinking water
I = daily drinking water intake (2 liters for adults \16\)
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    \16\ The MCLG for nitrite was based on a 4 kg body weight and a 
0.64 liter drinking water intake for infants because they are the 
group most sensitive to the critical effect.
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    The relative source contribution (RSC) is one factor which will 
determine how much a change in the RfD will lead to a change in the 
MCLG. RSC refers to the method of accounting for human exposure from 
multiple sources when setting health-based criteria. The purpose of 
the RSC is to ensure that the level of a chemical allowed by a 
criterion or multiple criteria, when combined with other identified 
sources of exposure common to the population of concern, will not 
result in exposures that exceed the RfD. The policy of considering 
multiple sources of exposure when deriving health-based criteria has 
become common in EPA's risk characterizations, as well as criteria 
and standard-setting actions. The drinking water program has applied 
a ceiling level of 80 percent of the RfD and a floor level of 20 
percent of the RfD. That is, the MCLG cannot account for more than 
80 percent of the RfD, nor less than 20 percent of the RfD. EPA 
applies an RSC factor of 20 percent to the RfD when adequate 
exposure data do not exist.

    EPA has now revised its RSC method to improve consistency when 
considering non-water sources of exposure (both ingestion exposures 
(e.g., food) and exposures other than the oral route (e.g., 
inhalation). The approach is called the Exposure Decision Tree. RSC 
estimates will be made by EPA using this approach, which allows for use 
of either subtraction or percentage methods, depending on chemical-
specific circumstances, within the 20 to 80 percent range described in 
the previous paragraph. For a detailed discussion on the revised 
approach, refer to the ``Methodology for Deriving Ambient Water Quality 
Criteria for the Protection of Human Health'' (USEPA, 2000f).
    It has also been the Agency policy to apply an additional safety 
factor to the RfD for chemicals with equivocal evidence of 
carcinogenicity. This practice is another factor that must be evaluated 
to determine the impact of a change in RfD on the MCLG.
    For drinking water contaminants regulated prior to the 1996 SDWA, 
EPA's Office of Water (OW) followed a three-category regulatory cancer 
classification system (Categories I, II, or III). These categories 
specify decisions as to degree of concern for an agent's carcinogenic 
potential as a contaminant of drinking water, and define to some extent 
the approach to risk management which is taken for establishing MCLGs. 
Categories I, II, and III are designations not defined in guidelines 
but which reflect OW policy.
    EPA used the six alphanumeric categories (A, B1, B2, C, D, E) of 
the 1986 cancer guidelines (51 FR 33992, September 24, 1986 (USEPA, 
1986b)) in establishing the MCLG. The six-group classification system 
is often equated to the three-category system in the National Primary 
Drinking Water Regulation (NPDWR) Federal Register announcements. Table 
A-1 describes the three categories and, with few exceptions (e.g., 
beryllium), their usual equivalent alphanumeric classification. If a 
chemical is a known or probable human carcinogen (Category I, generally 
Group A or B), the MCLG is generally set at zero because it is assumed, 
in the absence of other data, that there is no known threshold for 
carcinogenicity. If a chemical falls in Group C, an RfD approach along 
with an additional safety (risk management) factor is used in deriving 
the MCLG. The methodology used for establishing MCLGs for chemicals 
with varying degrees of evidence of carcinogenicity is also briefly 
described in Table A-1.
    Recent Agency assessments also use the 1996 Proposed Guidelines for 
Carcinogen Risk Assessment (61 FR 17960, April 23, 1996 (USEPA,1996)) 
or the draft revised Guidelines for Carcinogen Risk Assessment (USEPA, 
1999b). The proposed guidelines use standard descriptors as part of the 
hazard narrative to express the weight-of-evidence for carcinogenic 
hazard potential. The 1996 descriptors are in three categories: 
``Known/likely,'' ``cannot be determined,'' and ``not likely.'' 
Subdescriptors are provided under these categories to further 
differentiate an agent's carcinogenic potential. The new descriptors 
permit consideration of exposure route and mode of action when making 
an assessment of carcinogenicity. The hazard descriptors of the 1996 
proposed Guidelines are given in the text to this action whenever 
appropriate. None of the chemicals discussed in this action have been 
evaluated under the 1999 draft revised Guidelines for Carcinogen Risk 
Assessment.
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[FR Doc. 02-9154 Filed 4-16-02; 8:45 am]
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