[Federal Register Volume 75, Number 59 (Monday, March 29, 2010)]
[Notices]
[Pages 15499-15572]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2010-6624]



[[Page 15499]]

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Part II





Environmental Protection Agency





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National Primary Drinking Water Regulations; Announcement of the 
Results of EPA's Review of Existing Drinking Water Standards and 
Request for Public Comment and/or Information on Related Issues; Notice

Federal Register / Vol. 75, No. 59 / Monday, March 29, 2010 / 
Notices

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ENVIRONMENTAL PROTECTION AGENCY

[EPA-HQ-OW-2008-0747; FRL-9130-3]
RIN 2040-AE90


National Primary Drinking Water Regulations; Announcement of the 
Results of EPA's Review of Existing Drinking Water Standards and 
Request for Public Comment and/or Information on Related Issues

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notice; 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) and 
determine which, if any, need to be revised. The purpose of the review, 
called the Six-Year Review, is to identify those NPDWRs for which 
current health effects 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. EPA 
has completed its detailed review of 71 NPDWRs and at this time 
believes that four NPDWRs are candidates for regulatory revision. These 
four NPDWRs are acrylamide, epichlorohydrin, tetrachloroethylene, and 
trichloroethylene. EPA requests public comment and/or relevant 
information that will assist the Agency as we move forward with 
regulatory action to revise these four NPDWRs. In addition to the 71 
NPDWRs discussed in detail in today's action, this review also includes 
14 other NPDWRs that need no detailed review because of recent or 
ongoing revision actions.

DATES: Comments must be received on or before May 28, 2010, 60 days 
after publication in the Federal Register.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-OW-
2008-0747, by one of the following methods:
     http://www.regulations.gov: Follow the online instructions 
for submitting comments.
     Mail: Water Docket, Environmental Protection Agency, 
Mailcode: 2822T, 1200 Pennsylvania Ave., NW., Washington, DC 20460.
     Hand Delivery: EPA Docket Center Public Reading Room, EPA 
Headquarters West, Room 3334, 1301 Constitution Ave., NW., Washington, 
DC. Such deliveries are only accepted during the Docket's normal hours 
of operation, and special arrangements should be made for deliveries of 
boxed information.
    Instructions: Direct your comments to Docket ID No. EPA-HQ-OW-2008-
0747. EPA's policy is that all comments received will be included in 
the public docket without change and may be made available online at 
http://www.regulations.gov, including any personal information 
provided, unless the comment includes information claimed to be 
Confidential Business Information (CBI) or other information whose 
disclosure is restricted by statute. Do not submit information that you 
consider to be CBI or otherwise protected using http://www.regulations.gov. Please contact EPA prior to submitting CBI.
    The http://www.regulations.gov Web site is an ``anonymous access'' 
system, which means EPA will not know your identity or contact 
information unless you provide it in the body of your comment. If you 
send an e-mail comment directly to EPA without going through http://www.regulations.gov your e-mail address will be automatically captured 
and included as part of the comment that is placed in the public docket 
and made available on the Internet. If you submit an electronic 
comment, EPA recommends that you include your name and other contact 
information in the body of your comment and with any disk or CD-ROM you 
submit. If EPA cannot read your comment due to technical difficulties 
and cannot contact you for clarification, EPA may not be able to 
consider your comment. Electronic files should avoid the use of special 
characters, any form of encryption, and be free of any defects or 
viruses. For additional instructions on submitting comments, go to 
section I.B of this document.
    Docket: All documents in the docket are listed in the http://www.regulations.gov index. Although listed in the index, some 
information is not publicly available, e.g., CBI or other information 
whose disclosure is restricted by statute. Certain other material, such 
as copyrighted material, will be publicly available only in hard copy. 
Publicly available docket materials are available either electronically 
in http://www.regulations.gov or in hard copy at the Water Docket, EPA/
DC, EPA West, Room 3334, 1301 Constitution Ave., NW., Washington, DC. 
The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday 
through Friday, excluding legal holidays. The telephone number for the 
Public Reading Room is (202) 566-1744, and the telephone number for the 
EPA Docket Center is (202) 566-2426.

FOR FURTHER INFORMATION CONTACT: For technical inquiries contact: Rajiv 
Khera, (202) 564-4881, or Karen Wirth, (202) 564-5246, Office of Ground 
Water and Drinking Water, Environmental Protection Agency. 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.

Abbreviations and Acronyms Used in This Action

>--greater than
2,4-D--2,4-dichlorophenoxyacetic acid
[mu]g/L--microgram per liter
AMG--Alternative Monitoring Guidelines
ASDWA--Association of State Drinking Water Administrators
ATSDR--Agency for Toxic Substances and Disease Registry
AWWA--American Water Works Association
BAT--best available technology
CARC--Cancer Assessment Review Committee
CBI--Confidential Business Information
CCL--Contaminant Candidate List
CFR--Code of Federal Regulations
Cr III--trivalent chromium
Cr VI--hexavalent chromium
CWS--community water system
DBPs--disinfection byproducts
DBCP--1,2-dibromo-3-chloropropane
DBPR--Disinfectants and Disinfection Byproducts Rule
DEHA--di(2-ethylhexyl)adipate
DEHP--di(2-ethylhexyl)phthalate
DWEL--drinking water equivalent level
EDB--ethylene dibromide
EPA--U.S. Environmental Protection Agency
EQL--estimated quantitation level
ESA--ethanesulfonic acid
FR--Federal Register
FQPA--Food Quality Protection Act
GAC--granular activated carbon
GWR--Ground Water Rule
HAA5--haloacetic acids
IARC--International Agency for Research on Cancer
ICR--Information Collection Request
IRED--Interim Reregistration Eligibility Decision
IRIS--Integrated Risk Information System
LCR--Lead and Copper Rule
LH--lutenizing hormone
LOAEL--lowest-observed-adverse-effect level
LT2ESWTR--Long-Term 2 Enhanced Surface Water Treatment Rule
MCL--maximum contaminant level
MCLG--maximum contaminant level goal
MDL--method detection limit
mg/kg-day--milligrams per kilogram of body weight per day
mg/L--milligrams per liter
MOA--mode of action
MRL--minimum reporting level
N--nitrogen
NAS--National Academy of Sciences

[[Page 15501]]

NAWQA--National Water Quality Assessment
NCFAP--National Center for Food and Agricultural Policy
NCOD--National Drinking Water Contaminant Occurrence Database
NDWAC--National Drinking Water Advisory Council
NELAC--National Environmental Laboratory Accreditation Conference
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
OPP--Office of Pesticide Programs
ORD--Office of Research and Development
OW--Office of Water
PCBs--polychlorinated biphenyls
PCE--tetrachloroethylene
PE--Performance Evaluation
pCi/L--picoCurie per liter
PN--public notification
ppb--part per billion (e.g., microgram per liter)
ppm--part per million (e.g., milligram per liter)
PQL--practical quantitation limit
PT--Performance Testing
PTA--packed tower aeration
PWS--public water system
R2S2--Regulatory Review Support Spreadsheet
RED--Reregistration Eligibility Decision
RfD--reference dose
RSC--relative source contribution
SAB--Science Advisory Board
SSCT--Small System Compliance Technology
SDWA--Safe Drinking Water Act
SDWIS/FED--Safe Drinking Water Information System/Federal version
SMCL--secondary maximum contaminant level
SOC--synthetic organic chemical
STORET--STOrage and RETrieval data system
SWTR--Surface Water Treatment Rule
T3--triiodothyronine (thyroid hormone)
T4--levothyroxine (thyroid hormone)
TCDD--tetrachlorodibenzo-p-dioxin
TCE--trichloroethylene
TNCWS--transient, non-community water system
TP--trichlorophenoxypropionic acid
TRED--Interim Tolerance Reassessment and Risk Management Decisions
TRI--Toxics Release Inventory
TSC--Technical Support Center
TT--treatment technique
TTHM--total trihalomethanes
USDA--U.S. Department of Agriculture
UCMR 2--second Unregulated Contaminant Monitoring Rule
USGS--U.S. Geological Survey
VOC--volatile organic compound
WS--water supply

Table of Contents

I. General Information
    A. Does This Action Apply to My Public Water System?
    B. How Should I Submit Comments on This Action?
    C. What Should I Consider as I Prepare My Comments for EPA?
II. Statutory Requirements for the Six-Year Review
III. Stakeholder Involvement in the Six-Year Review Process
    A. How Have Stakeholders Been Involved in the Review Process?
    B. How Did EPA Incorporate Feedback from the Science Advisory 
Board's 2002 Comments on the Six-Year Review Protocol?
IV. Regulations Included in the Six-Year Review
V. EPA's Protocol for Reviewing the NPDWRs Included in This Action
    A. What Was EPA's Review Process?
    B. How Did EPA Conduct the Initial Review and Evaluate Key 
Technical Elements of the NPDWRs?
    1. Initial Review
    2. Health Effects
    3. Analytical Feasibility
    4. Occurrence and Exposure Analysis
    5. Treatment Feasibility
    6. Other Regulatory Revisions
    C. How Did EPA Factor Children's Health Concerns Into the 
Review?
VI. Results of EPA's Review of NPDWRs
    A. What Are the Review Result Categories?
    1. No Action at This Time and the NPDWR is Still Appropriate
    2. Candidate for Revision
    B. What Are the Details of EPA's Review of Each NPDWR?
    1. Acrylamide
    2. Alachlor
    3. Alpha Particle Emitters
    4. Antimony
    5. Arsenic
    6. Asbestos
    7. Atrazine
    8. Barium
    9. Benzene
    10. Benzo(a)pyrene
    11. Beryllium
    12. Beta Particle and Photon Emitters
    13. Cadmium
    14. Carbofuran
    15. Carbon Tetrachloride
    16. Chlordane
    17. Chromium
    18. Cyanide
    19. 2,4-D (2,4-Dichlorophenoxyacetic acid)
    20. Dalapon (2,2-Dichloropropionic Acid)
    21. Di(2-ethylhexyl)adipate (DEHA)
    22. Di(2-ethylhexyl)phthalate (DEHP)
    23. 1,2-Dibromo-3-chloropropane (DBCP)
    24. 1,2-Dichlorobenzene (o-Dichlorobenzene)
    25. 1,4-Dichlorobenzene (p-Dichlorobenzene)
    26. 1,2-Dichloroethane (Ethylene Dichloride)
    27. 1,1-Dichloroethylene
    28. cis-1,2-Dichloroethylene
    29. trans-1,2-Dichloroethylene
    30. Dichloromethane (Methylene Chloride)
    31. 1,2-Dichloropropane
    32. Dinoseb
    33. Diquat
    34. Endothall
    35. Endrin
    36. Epichlorohydrin
    37. Ethylbenzene
    38. Ethylene Dibromide (EDB; 1,2-Dibromoethane)
    39. Fluoride
    40. Glyphosate
    41. Heptachlor
    42. Heptachlor Epoxide
    43. Hexachlorobenzene
    44. Hexachlorocyclopentadiene
    45. Lindane (gamma-Hexachlorocyclohexane)
    46. Mercury (Inorganic)
    47. Methoxychlor
    48. Monochlorobenzene (Chlorobenzene)
    49. Nitrate (as N)
    50. Nitrite (as N)
    51. Oxamyl (Vydate)
    52. Pentachlorophenol
    53. Picloram
    54. Polychlorinated Biphenyls (PCBs)
    55. Combined Radiums (226 and 228)
    56. Selenium
    57. Simazine
    58. Styrene
    59. 2,3,7,8-TCDD (Dioxin)
    60. Tetrachloroethylene
    61. Thallium
    62. Toluene
    63. Toxaphene
    64. 2,4,5-TP (Silvex; 2,4,5-Trichlorophenoxypropionic Acid)
    65. 1,2,4-Trichlorobenzene
    66. 1,1,1-Trichloroethane
    67. 1,1,2-Trichloroethane
    68. Trichloroethylene
    69. Uranium
    70. Vinyl chloride
    71. Xylenes (Total)
VII. EPA's Request for Comments
    A. Request for Comment and/or Information on the Candidates for 
Revision
    B. Request for Information/Data on Other Review Topics
    C. Requests for Information on the Impacts of Climate Change on 
Water Quality
VIII. EPA's Next Steps
IX. References

SUPPLEMENTARY INFORMATION:

I. General Information

A. 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 review of existing 
NPDWRs and its conclusions about which of these warrants new regulatory 
action at this time. EPA requests public comment on the four NPDWRs 
identified as candidates for revision, with a specific focus on 
comments and/or relevant information that will inform the regulatory 
revisions.

B. How Should I Submit Comments on This Action?

    Please see Section VII for the issues related to this notice for 
which EPA requests comment and/or information. EPA will accept written 
or electronic comments (please do not send both). Instructions for 
submitting comments are in the preceding section. EPA prefers 
electronic comments. No

[[Page 15502]]

facsimiles (faxes) will be accepted. Commenters who want EPA to 
acknowledge receipt of their comments should also send a self-
addressed, stamped envelope.
    The Agency intends to address the comments received on the four 
NPDWRs identified as candidates for revision in subsequent Federal 
Register notices proposing and finalizing the regulatory revisions, and 
in documents that will be made available in the docket for those 
notices.

C. What Should I Consider as I Prepare My Comments for EPA?

    You may find the following suggestions helpful for preparing your 
comments:
     Explain your views as clearly as possible.
     Describe any assumptions that you used.
     Provide any technical information and/or data you used 
that support your views.
     If you estimate potential burden or costs, explain how you 
arrived at your estimate.
     Provide specific examples to illustrate your concerns.
     Offer alternatives.
     Make sure to submit your comments by the comment period 
deadline.
     To ensure proper receipt by EPA, identify the appropriate 
docket identification number in the subject line on the first page of 
your response. It would also be helpful if you provided the name, date, 
and Federal Register citation related to your comments.

II. 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 1996 SDWA Amendments, EPA completed and published 
the results of its first Six-Year Review (Six-Year Review 1) July 18, 
2003 (68 FR 42908, USEPA, 2003e) after developing a systematic 
approach, or protocol, for the review of NPDWRs. EPA has applied the 
same protocol with minor refinements (revised protocol) to the second 
Six-Year Review of NPDWRs (Six-Year Review 2). Section V of today's 
action describes the protocol and the minor refinements used for the 
Six-Year Review 2 and section VI describes the review findings for each 
of the NPDWRs covered by the current effort (see Table IV-1).

III. Stakeholder Involvement in the Six-Year Review Process

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

    The Agency developed a Six-Year Review protocol during the first 
review cycle with extensive stakeholder inputs, including a stakeholder 
meeting, Agency presentations at a variety of meetings, and 
consultation with the National Drinking Water Advisory Council (NDWAC). 
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 (67 FR 19030, April 
17, 2002, USEPA, 2002c). 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. As discussed in 
more detail in section V of today's action, EPA continues to follow the 
general protocol recommended by the NDWAC.

B. How Did EPA Incorporate Feedback From the Science Advisory Board's 
2002 Comments on the Six-Year Review Protocol?

    In June 2002 and during the Six-Year Review 1, EPA consulted with 
the Science Advisory Board (SAB) Drinking Water Committee and requested 
their review and comment on whether the protocol that EPA developed 
based on the NDWAC's recommendations was consistently applied and 
appropriately documented. The SAB provided verbal feedback regarding 
the transparency and clarity of EPA's criteria for making its Six-Year 
Review 1 decisions. At that time, EPA revised the protocol to better 
explain how the decision criteria were applied. For the Six-Year Review 
2 and to increase transparency and clarity, EPA also developed a more 
detailed decision tree and an automated tool, called the Regulatory 
Review Support Spreadsheet (R2S2). The more detailed decision tree 
incorporates the sequential relationships between the various NPDWR 
review elements and R2S2 tracks each contaminant through the decision 
making process. The Agency has documented the decision tree and the 
automated tool in the document, ``EPA Protocol for the Second Review of 
Existing National Primary Drinking Water Regulations (Updated)'' 
(USEPA, 2009a).

IV. Regulations Included in the Six-Year Review

    Table IV-1 lists all the NPDWRs established to date. The table also 
reports the maximum contaminant level goal (MCLG), which is ``set at 
the level at which no known or anticipated adverse effects on the 
health of persons occur and which allows an adequate margin of safety'' 
(SDWA section 1412(b)(4)), and the maximum contaminant level (MCL), 
which is the maximum permissible level of a contaminant in water 
delivered to any user of a public water system and ``is as close to the 
maximum contaminant level goal as is feasible'' (SDWA section 
1412(b)(4)(B)), except for contaminants that have a treatment technique 
(TT) in lieu of an MCL because it is not ``economically or technically 
feasible'' to set an MCL (SDWA section 1412(b)(7)(A)).\1\ Of these 85 
NPDWRs, EPA has reviewed 14 as part of recent or ongoing regulatory 
actions and, as a result, they are not subject to a detailed review in 
today's notice. The review for the remaining 71 is discussed in detail 
in today's action.
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    \1\ Under limited circumstances, SDWA Section 1412(b)(6)(A) also 
gives the Administrator the discretion to promulgate an MCL that is 
less stringent than the feasible level and that ``maximizes health 
risk reduction benefits at a cost that is justified by the 
benefits.''

[[Page 15503]]



                                           Table IV-1--Contaminants With NPDWRs Included in Six-Year Review 2
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         Contaminants                  MCLG  (mg/L) \1\                 MCL  (mg/L) \1\            Contaminants     MCLG  (mg/L) \1\     MCL (mg/L) \1\
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Acrylamide....................  0.............................  TT............................  Epichlorohydrin..  0.................  TT
Alachlor......................  0.............................  0.002.........................  Ethylbenzene.....  0.7...............  0.7
Alpha particles...............  0 (pCi/L).....................  15 (pCi/L)....................  Ethylene           0.................  0.00005
                                                                                                 dibromide (EDB).
Antimony......................  0.006.........................  0.006.........................  Fluoride.........  4.................  4
Arsenic.......................  0.............................  0.01..........................  Giardia lamblia..  0.................  TT
Asbestos......................  7 (million fibers/L)..........  7 (million fibers/L)..........  Glyphosate.......  0.7...............  0.7
Atrazine......................  0.003.........................  0.003.........................  Haloacetic acids   n/a \2\...........  0.06
                                                                                                 (HAA5).
Barium........................  2.............................  2.............................  Heptachlor.......  0.................  0.0004
Benzene.......................  0.............................  0.005.........................  Heptachlor         0.................  0.0002
                                                                                                 Epoxide.
Benzo(a)pyrene................  0.............................  0.0002........................  Hexachlorobenzene  0.................  0.001
Beryllium.....................  0.004.........................  0.004.........................  Hexachlorocyclope  0.05..............  0.05
                                                                                                 ntadiene.
Beta particles................  0 (millirems/yr)..............  4 (millirems/yr)..............  Lead.............  0.................  TT
Bromate.......................  0.............................  0.01..........................  Legionella.......  0.................  TT
Cadmium.......................  0.005.........................  0.005.........................  Lindane..........  0.0002............  0.0002
Carbofuran....................  0.04..........................  0.04..........................  Mercury            0.002.............  0.002
                                                                                                 (Inorganic).
Carbon tetrachloride..........  0.............................  0.005.........................  Methoxychlor.....  0.04..............  0.04
Chloramines...................  4.............................  4.............................  Monochlorobenzene  0.1...............  0.1
                                                                                                 (Chlorobenzene).
Chlordane.....................  0.............................  0.002.........................  Nitrate (as        10................  10
                                                                                                 nitrogen, N).
Chlorine......................  4.............................  4.............................  Nitrite (as N)...  1.................  1
Chlorine dioxide..............  0.8...........................  0.8...........................  Oxamyl (Vydate)..  0.2...............  0.2
Chlorite......................  0.8...........................  1.............................  Pentachlorophenol  0.................  0.001
Chromium (total)..............  0.1...........................  0.1...........................  Picloram.........  0.5...............  0.5
Coliform......................  0% \3\........................  5% \3\........................  Polychlorinated    0.................  0.0005
                                                                                                 biphenyls (PCBs).
Copper........................  1.3...........................  TT............................  Radium...........  0 (pCi/L).........  5 (pCi/L)
Cryptosporidium...............  0.............................  TT............................  Selenium.........  0.05..............  0.05
Cyanide.......................  0.2...........................  0.2...........................  Simazine.........  0.004.............  0.004
2,4-Dichlorophenoxyacetic acid  0.07..........................  0.07..........................  Styrene..........  0.1...............  0.1
 (2,4-D).
Dalapon.......................  0.2...........................  0.2...........................  2,3,7,8-           0.................  3.00E-08
                                                                                                 Tetrachlorodiben
                                                                                                 zo-p-dioxin
                                                                                                 (2,3,7,8-TCDD or
                                                                                                 dioxin).
Di(2-ethylhexyl)adipate (DEHA)  0.4...........................  0.4...........................  Tetrachloroethyle  0.................  0.005
                                                                                                 ne (PCE).
Di(2-ethylhexyl)phthalate       0.............................  0.006.........................  Thallium.........  0.0005............  0.002
 (DEHP).
1,2-Dibromo-3-chloropropane     0.............................  0.0002........................  Toluene..........  1.................  1
 (DBCP).
1,2-Dichlorobenzene (o-         0.6...........................  0.6...........................  Total              n/a \4\...........  0.08
 Dichlorobenzene).                                                                               trihalomethanes
                                                                                                 (TTHM).
1,4-Dichlorobenzene (p-         0.075.........................  0.075.........................  Toxaphene........  0.................  0.003
 Dichlorobenzene).
1,2-Dichloroethane (Ethylene    0.............................  0.005.........................  2,4,5-             0.05..............  0.05
 dichloride).                                                                                    Trichlorophenoxy
                                                                                                 pro-pionic acid
                                                                                                 (2,4,5-TP or
                                                                                                 Silvex).
1,1-Dichloroethylene..........  0.007.........................  0.007.........................  1,2,4-             0.07..............  0.07
                                                                                                 Trichlorobenzene.
cis-1,2-Dichloroethylene......  0.07..........................  0.07..........................  1,1,1-             0.2...............  0.2
                                                                                                 Trichloroethane.
trans-1,2-Dichloroethylene....  0.1...........................  0.1...........................  1,1,2-             0.003.............  0.005
                                                                                                 Trichloroethane.
Dichloromethane (Methylene      0.............................  0.005.........................  Trichloroethylene  0.................  0.005
 chloride).                                                                                      (TCE).
1,2-Dichloropropane...........  0.............................  0.005.........................  Uranium..........  0 ([mu]g/L).......  30 ([mu]g/L)
Dinoseb.......................  0.007.........................  0.007.........................  Vinyl chloride...  0.................  0.002
Diquat........................  0.02..........................  0.02..........................  Viruses..........  0.................  TT
Endothall.....................  0.1...........................  0.1...........................  Xylenes (total)..  10................  10
Endrin........................  0.002.........................  0.002.........................
--------------------------------------------------------------------------------------------------------------------------------------------------------
1. Units are in milligrams per liter (mg/L) unless otherwise noted, e.g., micrograms per liter ([mu]g/L) and picoCuries per liter (pCi/L). Milligrams
  per liter are equivalent to parts per million (ppm) and micrograms per liter are equivalent to parts per billion (ppb).
2. There is no MCLG for all five haloacetic acids. MCLGs for some of the individual contaminants are: dichloroacetic acid (zero), trichloroacetic acid
  (0.02 mg/L), and monochloroacetic acid (0.07 mg/L). Bromoacetic acid and dibromoacetic acid are regulated with this group but have no MCLGs.
3. No more than 5.0% samples total coliform-positive in a month.
4. There is no MCLG for total trihalomethanes. MCLGs for some of the individual contaminants are: bromodichloromethane (zero), bromoform (zero),
  dibromochloromethane (0.06 mg/L), and chloroform (0.07mg/L).


[[Page 15504]]

V. EPA's Protocol for Reviewing the NPDWRs Included in This Action

A. What Was EPA's Review Process?

    The protocol document, ``EPA Protocol for the Review of Existing 
National Primary Drinking Water Regulations (Updated)'' (USEPA, 2009a), 
contains a detailed description of the process the Agency used to 
review the NPDWRs discussed in today's action. EPA's primary goal was 
to identify and prioritize candidates for regulatory revision 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 for 
systems and their customers while maintaining the level of public 
health protection.\2\ This section provides an overview of the review 
process and section V.B provides a more detailed description of how EPA 
applied the process to the review of the NPDWRs discussed in today's 
action.
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    \2\ Note that the legislative history of the 1996 SDWA 
Amendments indicate that Congress envisioned the possibility that a 
relaxed standard might be appropriate under circumstances that would 
not result in a lessening of the level of public health protection 
(see Senate Report Number 104-169, 104th Congress, 1st Session, 1995 
at 38). In other words, an MCL could be relaxed (i.e., increased) in 
cases where a revised health risk assessment leads to a less 
stringent (higher) MCLG than the existing MCL so that the level of 
health protection is maintained. There have been several instances 
in which revised health assessments have suggested higher MCLGs and 
the Agency could have considered relaxing the MCLs. In these 
instances and because SDWA allows EPA to determine when revisions 
are appropriate, the Agency decided that there would be a negligible 
gain in public health protection and/or cost savings and any 
revision would be a low priority activity because of competing 
workload priorities, the administrative costs associated with 
rulemaking, and the burden on States and the regulated community to 
implement any regulatory changes.
---------------------------------------------------------------------------

    EPA applied the following basic principles to the review process:
     The Agency sought to avoid redundant review efforts. 
Because EPA has reviewed information for 14 contaminants as part of 
recent or ongoing regulatory actions, they are not subject to the 
detailed review in today's notice.
     EPA evaluated the potential for new information to affect 
NPDWRs in a manner consistent with existing policies and procedures for 
developing NPDWRs. For example, in determining whether a possible 
change in analytical feasibility existed, the Agency considered the 
current policy and procedures for calculating the practical 
quantitation level for drinking water contaminants.\3\
---------------------------------------------------------------------------

    \3\ The following Federal Register notices describe the process 
the Agency has used to determine analytical feasibility for drinking 
water contaminants: 50 FR 46880, November 13, 1985 (USEPA, 1985); 52 
FR 25690, July 8, 1987 (USEPA, 1987); 54 FR 22062, May 22, 1989 
(USEPA, 1989b). For this Six Year Review effort and to supplement 
the analytical feasibility evaluation, the Agency also reviewed 
extensive minimum reporting level (MRL) data obtained from States 
and primacy entities as part of the Six-Year Review information 
collection request (ICR) for SDWA compliance monitoring data.
---------------------------------------------------------------------------

     Because any possible change in an MCLG affects other NPDWR 
elements, EPA will not generally consider potential revisions to any 
contaminant with a health effects assessment in process that would not 
be completed during the review period, where either the contaminant's 
MCL is equal to its MCLG or the MCL is based on the 1996 SDWA 
Amendments' cost-benefit provision. The rationale for this outcome is 
that any new information from the health effects assessment could 
affect the MCL or the assessment of the benefits associated with the 
MCL for these contaminants. Therefore, the Agency does not believe it 
is appropriate to consider revisions to these NPDWRs while a health 
effects assessment is ongoing.
     For those contaminants with ongoing health assessments 
that have MCLGs equal to or greater than zero and MCLs limited by 
analytical feasibility or the standard is based on a Treatment 
Technique, EPA conducted a further review of the potential to revise 
the MCL or TT. The rationale for this approach is that the MCL or TT is 
based on technology limitations and therefore, EPA should consider 
whether there have been improvements in technology and whether any 
revision might provide a meaningful opportunity to improve or at least 
maintain public health protection. If EPA found that there were no 
changes in technology (i.e., analytical feasibility or a TT) or if 
changes were possible but there was no meaningful opportunity to 
improve public health protection or reduce costs (while maintaining 
public health protection), these contaminants remained in the ongoing 
health effects assessment category.
     For this review, EPA considered new information from 
health effects assessments that were completed by a March 1, 2009 
cutoff date. If an updated assessment is completed after the March 1, 
2009 information cutoff date, then EPA will review the update and any 
new conclusions or additional information associated with the 
contaminant during the next review cycle or during the revision of an 
NPDWR (e.g., acrylamide, PCE and TCE). If the health effects 
assessments are not completed in time for the regulatory revisions for 
acrylamide, PCE and TCE, EPA does not plan to change the existing MCLG 
of zero. EPA is currently considering how best to evaluate the benefits 
for these regulatory revisions if the EPA health effects assessments 
are not complete. One option would be to use the same health effects 
information that was used for promulgating the original regulation. 
Another option is to consider using other best available, peer-reviewed 
health risk assessments that are complete as the Agency is proceeding 
with the regulatory revisions. EPA requests comment on these options 
and any other options that the public considers appropriate to evaluate 
the benefits.
     The Agency may consider accelerating a review and 
potential revision for a particular NPDWR before the next review cycle 
when justified by new public health risk information.
     During the review, EPA identified areas where information 
is inadequate or unavailable (data gaps) or emerging and is needed to 
determine whether revision to an NPDWR is appropriate. When the Agency 
is able to fill such gaps or fully evaluate the emerging information, 
the Agency will consider it as part of the next review cycle. The 
Agency may consider accelerating a review and potential revision for a 
particular NPDWR if the information becomes available before the next 
review cycle and if review and a potential revision are justified by 
new public health risk information.
     EPA applied the Agency's peer review policy (USEPA, 
2000d), where appropriate, to any new analyses.
    During Six-Year Review 1, the Agency developed a systematic 
approach or protocol (USEPA, 2003b). The Agency based this protocol on 
the recommendations of the NDWAC, through internal Agency 
deliberations, and discussions with the diverse group of stakeholders 
involved in drinking water and its protection. The overview of the 
protocol in Figure V-1 shows the sequence of key decisions that led to 
EPA assigning each NPDWR to one of two major categories of outcomes in 
the Six-Year Review 2. The two major outcomes of the review are either: 
1) The NPDWR is still appropriate and no action is necessary at this 
time, or 2) the NPDWR is a candidate for revision. The reasons for a 
Six-Year Review outcome of no further action at this time include at 
least one or more of the following reasons:
     The NPDWR has been reviewed or is being reviewed in a 
recent or ongoing action;
     The NPDWR has an ongoing health effects assessment (i.e., 
for those

[[Page 15505]]

NPDWRs with an MCL set at the MCLG or the MCL is based on the SDWA cost 
benefit provision);
     EPA is considering whether a new health effects assessment 
is needed;
     EPA did not identify any new, relevant information that 
indicate changes to the NPDWR;
     New information indicate a possible change to the MCLG 
and/or MCL but changes to the NPDWR are a low priority activity due to 
negligible gains in public health protection and/or cost savings; or
     There are data gaps or emerging information that needs to 
be evaluated.
[GRAPHIC] [TIFF OMITTED] TN29MR10.000

    During the current Six-Year Review, the Agency assessed the 
protocol and determined it remained appropriate and suitable for the 
second review. The research requirements and decision-making process of 
the Six-Year Review 2 protocol are essentially the same as those 
implemented during Six-Year Review 1. The Agency made some minor 
refinements to enhance the Agency's effectiveness in applying the 
protocol to the review of NPDWRs. The

[[Page 15506]]

refinements that address SAB's comments about the clarity and the 
transparency of the protocol's decision making process are described in 
the next two paragraphs. Section V.B describes the key technical 
elements and any refinements in the data and/or the analysis methods 
used during Six-Year Review 2.
    The primary refinement to the protocol during Six-Year Review 2 is 
the implementation of a more detailed ``decision tree'' than either the 
one used during Six-Year Review 1 (USEPA, 2003b) or the overview shown 
in Figure V-1. The protocol is broken down into a series of questions 
about whether there is new information for a contaminant that suggests 
potential to revise each of the NPDWR elements. These questions are 
logically ordered into a decision tree that incorporates the sequential 
relationships between the different NPDWR elements. For example, when 
EPA establishes an MCL, it must generally set the MCL as close to the 
MCLG as feasible. Consequently, for a contaminant that has an MCL equal 
to its MCLG, EPA must make decisions about the availability and 
adequacy of new information regarding the possibility to revise the 
MCLG before decisions regarding the possibility to revise the MCL. It 
also means that if there is no possibility to revise a contaminant's 
MCLG and the MCL is already equal to the MCLG, then there is no basis 
for revising the MCL. In this instance, the MCL branch of the decision 
tree is not reached, and it is not necessary to make related decisions 
such as whether the practical quantitation limit (PQL) can be revised. 
This approach results in a more efficient review process. EPA also 
developed an automated tool called the R2S2 that tracks each 
contaminant's movement through the decision tree, including the revise/
take no action outcomes. This tool enhances transparency throughout the 
decision process. The automation also streamlines the decision process 
and facilitates the Agency's reporting of its review results. The 
Agency has documented the decision tree and the automated tool in the 
document entitled, ``EPA Protocol for the Second Review of Existing 
National Primary Drinking Water Regulations (Updated)'' (USEPA, 2009a).

B. How Did EPA Conduct the Initial Review and Evaluate Key Technical 
Elements of the NPDWRs?

    This section describes the specific technical reviews that EPA 
conducted, including the initial review, health effects, analytical 
methods, occurrence and exposure, treatment feasibility, and economic 
analysis.
1. Initial Review
    EPA's initial review of all the contaminants included in the Six-
Year Review 2 involved a simple identification of the NPDWRs that were 
being reviewed under concurrent EPA actions or had been reviewed and 
revised in EPA actions completed since 2002. Table V-1 provides a list 
of the 14 contaminants that met one of these criteria and identifies 
the recent or ongoing action in which the contaminant has been reviewed 
or is undergoing review. While these 14 contaminants are part of the 
Six-Year Review 2, they were not subject to any detailed analysis given 
that new information on these contaminants has been recently reviewed 
under separate actions. However, EPA requests comments on these 
contaminants along with the other contaminants discussed in detail in 
this notice.
    The remaining 71 contaminants pass through this step to the review 
of the technical NPDWR elements, which are described in the following 
sections.

  Table V-1--NPDWRs That Have Been Reviewed or Are Being Reviewed Under
                        Recent or Ongoing Actions
------------------------------------------------------------------------
         Contaminant/indicator               Recent or ongoing action
------------------------------------------------------------------------
                         Disinfection Byproducts
------------------------------------------------------------------------
Bromate................................  Stage 2 DBPR.
Chlorite\1\............................  Stage 2 DBPR.
HAA5: monochloroacetic acid,             Stage 2 DBPR.
 dichloroacetic acid, trichloroacetic
 acid, monobromoacetic acid,
 dibromoacetic acid.
TTHMs: chloroform,                       Stage 2 DBPR.
 bromodichloromethane,.
dibromochloromethane, bromoform........
------------------------------------------------------------------------
                         Disinfectant Residuals
------------------------------------------------------------------------
Chloramines\1\.........................  Stage 2 DBPR.
Chlorine\1\............................  Stage 2 DBPR.
Chlorine dioxide.......................  Stage 2 DBPR.
------------------------------------------------------------------------
                               Inorganics
------------------------------------------------------------------------
Copper.................................  Under consideration for long-
                                          term revisions.
Lead...................................  LCR Short-Term Revisions
                                         Under consideration for long-
                                          term revisions.
------------------------------------------------------------------------
                             Microorganisms
------------------------------------------------------------------------
Coliform...............................  Total Coliform Rule-making
                                          currently underway.
Cryptosporidium........................  LT2ESWTR.
Giardia lamblia........................  LT2ESWTR.
Legionella \2\.........................  LT2ESWTR,
                                         CCL3 \3\.
Viruses \2\............................  LT2ESWTR, GWR, CCL3 \3\.
------------------------------------------------------------------------
DBPR--Disinfectants and Disinfection Byproducts Rule.
LT2ESWTR--Long-Term 2 Enhanced Surface Water Treatment Rule.
LCR--Lead and Copper Rule.
GWR--Ground Water Rule.

[[Page 15507]]

 
Dates of promulgation are as follows:
Stage 2 DBPR: 71 FR 388, January 4, 2006 (USEPA, 2006h).
LT2ESWTR: 71 FR 654, January 5, 2006 (USEPA, 2006g).
LCR Short-Term Regulatory Revisions: 72 FR 57782, October 10, 2007
  (USEPA, 2007f).
GWR: 71 FR 65574, November 8, 2006 (USEPA, 2006f).
\1\ Although the standard for this disinfectant was not revised as part
  of the Stage 2 DBPR, regulatory revisions need to be considered in
  conjunction with other disinfectant residuals and disinfection
  byproducts.
\2\ LT2ESWTR and GWR promulgated treatment techniques that built upon
  and enhanced the existing regulations (Surface Water Treatment Rule,
  Interim Enhanced Surface Water Treatment Rule, and Long-Term 1
  Enhanced Surface Water Treatment Rule) that address broad categories
  of microorganisms in treated water.
\3\ Listed on the third Drinking Water Contaminant Candidate List or
  CCL3 (74 FR 51850, October 8, 2009 (USEPA, 2009l) in order to capture
  health and treatment information that may not be addressed by the
  current regulations.


    2. Health Effects
    The document, ``Six-Year Review 2 --Health Effects Assessment--
Summary Report'' (USEPA, 2009b), describes how EPA reviewed the 
contaminants discussed in today's action and provides the results of 
the health effects technical review. The principal objectives of the 
health effects review are to identify: (1) Contaminants for which a new 
health effects assessment indicates that a change in MCLG might be 
appropriate (e.g., because of a change in cancer classification or a 
reference dose (RfD)), and (2) contaminants for which the Agency 
identifies new health effects information suggesting a need to initiate 
a new health effects assessment.
    To meet the first objective, the Agency reviewed the results of 
health effects assessments completed under the following programs and 
identified, where feasible, possible MCLG values.
     EPA Integrated Risk Information System (IRIS).
     EPA Office of Pesticide Programs (OPP).
     National Academy of Sciences (NAS; when commissioned by 
EPA).
    To meet the second objective, the Agency first conducted an 
extensive literature review to identify peer-reviewed studies. Then the 
Agency reviewed the studies to determine whether there was new health 
effects information such as reproductive and developmental toxicity 
that potentially affects the MCLG of any of the remaining contaminants 
that do not have an ongoing health effects assessment, including those 
with recently completed health effects assessments.
    Table V-2 reflects the outcome of the health effects review for the 
NPDWRs discussed in today's action. EPA placed each contaminant into 
one of the following 13 categories.
     Agency health effects assessment in process and not 
completed as of March 1, 2009. The Agency currently is conducting a 
health effects assessment for the contaminant. That assessment will 
consider all available, relevant studies on the toxicology of the 
contaminant, including developmental and reproductive toxicity. This 
outcome contains three categories of contaminants.
     Category 1 contains 15 contaminants with MCLGs equal to or 
greater than zero and either MCLs that are limited by analytical 
feasibility or TT standards. For this category, EPA conducted further 
review of the potential for revisions to the MCL due to possible 
changes in analytical feasibility. The Agency's review of new 
information that might affect the MCL for one of these contaminants is 
a refinement of the protocol. During Six-Year Review 1, EPA took no 
further action on any contaminants with ongoing health effects 
assessments. EPA generally sets each MCL as close to the MCLG as is 
feasible, and a common limitation is the availability of analytical 
methods to reliably measure the contaminant.
     Category 2 contains two contaminants (arsenic and uranium) 
that have MCLGs equal to zero and MCLs that are based on the costs and 
benefits balancing provision in SDWA 1412(b)(6)(A). Any changes in the 
ongoing health effects assessment could impact the evaluation of 
benefits for these contaminants. Therefore, EPA has decided to take no 
further action to evaluate these two contaminants until completion of 
the health effects assessment.
     Category 3 contains 13 contaminants with non-zero MCLGs 
and MCLs generally equal to their respective MCLGs. Because EPA cannot 
determine whether there is potential to revise either the MCLG or the 
MCL until after the health effects assessment is completed, EPA plans 
to take no further action on these contaminants at this time.
     New health effects assessment completed since Six-Year 
Review 1. An IRIS or OPP assessment has been completed since 2002. EPA 
also conducted a follow-up literature search to confirm that no new 
information became available following the completion of the new health 
effects assessment. Table V-2 shows four categories of contaminants 
with new health effects assessments: four with results indicating 
potential for lower MCLG (Category 4), five with results indicating 
potential for higher MCLG (Category 5), two with results indicating the 
MCLG remains appropriate (Category 6), and three contaminants for which 
emerging information following the completion of a health effects 
assessment or a pending pesticide cancellation decision may affect 
EPA's review (Category 7).
     Literature review only conducted during Six-Year Review 2. 
For the contaminants that did not have an ongoing health effects 
assessment or a new one completed during the current review period, EPA 
conducted a review of the health effects literature to identify whether 
there was new information with potential to revise the MCLG. There are 
six categories of contaminants.
     Three categories pertain to contaminants that had a health 
effects assessment completed during Six-Year Review 1, including two 
with possible lower MCLGs (Category 8), three with possible higher 
MCLGs (Category 9), and three with no potential to revise their MCLGs 
(Category 10). During Six-Year Review 1, the Agency determined that 
possible changes to these contaminants' NPDWRs were a low priority 
activity for the Agency because of: competing workload priorities, the 
administrative costs associated with rulemaking, and the burden on 
States and the regulated community to implement any regulatory changes. 
As part of Six-Year Review 2, EPA is assessing whether there is new 
information that affects this determination.
     Category 11 contains five contaminants for which the 
Agency identified new information, described in section VI, that could 
impact the MCLG and, therefore, these contaminants are considered 
potential nominees for a new health assessment.
     Category 12 contains seven carcinogens for which the 
literature review sought new information on whether there might be a 
nonlinear mode of action or other reproductive and developmental health 
effects.

[[Page 15508]]

     Category 13 contains seven contaminants with non-zero 
MCLGs, for which EPA conducted a full literature search, including 
developmental and reproductive toxicity.

[[Page 15509]]

[GRAPHIC] [TIFF OMITTED] TN29MR10.001

    In addition to identifying for which contaminants there is 
information that potentially affects the MCLG, the health effects 
review indicates which contaminants proceed to other review steps under 
the protocol. Several

[[Page 15510]]

contaminants proceed to the analytical methods review to determine 
whether improvements in analytical methods indicate potential to revise 
the practical quantitation limit (PQL) in the NPDWRs. As Table V-3 
shows, 14 contaminants from Category 1 proceed to the analytical 
methods review--despite an ongoing health effects assessment--because 
their MCLs are limited by their respective PQLs. These 14 include alpha 
particles; benzo(a)pyrene; beta particles; carbon tetrachloride; DEHP; 
1,2-dichloroethane; dichloromethane; pentachlorophenol; PCBs; radium; 
dioxin; tetrachloroethylene; thallium; trichloroethylene. In addition, 
two contaminants in Category 6 (benzene and EDB) and two in Category 10 
(chlordane and vinyl chloride) have MCLs that are limited by PQLs and, 
therefore, these contaminants proceed to the analytical methods review 
even though their health effects assessments indicated no change to 
their respective MCLG values. Similarly, six contaminants in Category 
12 (DBCP; 1,2-dichloropropane; heptachlor; heptachlor epoxide; 
hexachlorobenzene; toxaphene) and one in Category 13 (1,1,2-
trichloroethane) have MCLs that are limited by their respective PQL 
and, therefore, proceed to the analytical methods review despite there 
being no new information on health effects.
    Among the contaminants having new health effects information during 
either Six-Year Review 2 or the previous review that potentially 
affects their respective MCLG values (i.e., potentially lower MCLGs), 
four in Category 4 (2,4-D; endothall; toluene; total xylenes) and two 
in Category 8 (hexachlorocyclopentadiene and oxamyl) proceed to the 
analytical methods review. For each of these contaminants, EPA 
evaluated whether analytical feasibility might become a limiting factor 
if EPA were to consider a lower MCLG and whether new information 
indicates there is a potential to revise the PQL.
    Two contaminants (acrylamide from Category 1 and epichlorohydrin 
from Category 12) bypass the analytical methods review because they 
have TT standards and PQLs are not a limiting factor for the standards. 
Five contaminants from Category 5 (alachlor; barium; diquat; 
glyphosate; 1,1,1-trichloroethane) and three from Category 9 (1,1-
dichloroethylene; lindane; picloram) bypass the analytical methods 
review because the new health effects information identified either 
during Six-Year Review 2 or Six-Year Review 1 indicated possible 
increases in their respective MCLGs. Each of these contaminants has a 
PQL that is lower than its MCLG and, therefore, a review of whether the 
PQL could be lower is inconsequential.

Table V-3--Contaminants Proceeding to Analytical Feasibility Review From
                          Health Effects Review
------------------------------------------------------------------------
                                             Contaminants proceeding to
     Health effects review category\1\         analytical feasibility
                                                       review
------------------------------------------------------------------------
Health Effects Assessment in Process
 During Information Review Period for the
 Notice (and not available by the March 1,
 2009 cutoff date):
    Category 1............................  14 of 15 proceeding because
                                             PQL limits MCL: alpha
                                             particles; benzo(a)pyrene;
                                             beta particles; carbon
                                             tetrachloride; DEHP; 1,2-
                                             dichloroethane;
                                             dichloromethane;
                                             pentachlorophenol; PCBs;
                                             radium; dioxin;
                                             tetrachloroethylene;
                                             thallium;
                                             trichloroethylene.
                                             Acrylamide bypasses the
                                             analytical review because
                                             it does not have a PQL.
    Category 2............................  0 of 2 proceeding because
                                             there is no potential to
                                             revise MCL unless completed
                                             health effects assessment
                                             indicates change to
                                             benefits analysis (arsenic
                                             and uranium).
    Category 3............................  0 of 13 did not proceed
                                             because MCL set at MCLG and
                                             health assessment still in
                                             process.
Health Effects Assessment Completed Since
 Six-Year Review 1:
    Category 4............................  4 of 4 proceeding to
                                             evaluate whether PQL is or
                                             could be below possible
                                             MCLG: 2,4-D; endothall;
                                             toluene; total xylenes.
    Category 5............................  0 of 5 proceeding; all 5
                                             bypass analytical review
                                             because PQL not a factor in
                                             review.
    Category 6............................  2 of 2 proceeding because
                                             PQL limits MCL: benzene and
                                             EDB.
    Category 7............................  0 of 3 proceeding because
                                             there is no potential to
                                             revise an MCL that is based
                                             on the MCLG under review.
Literature Review Only:
    Category 8............................  2 of 2 proceeding to
                                             evaluate whether PQL is or
                                             could be below possible
                                             MCLG:
                                             hexachlorocyclopentadiene;
                                             oxamyl.
    Category 9............................  0 of 3 proceeding; all 3
                                             bypass analytical review
                                             because PQL not a factor in
                                             review.
    Category 10...........................  2 of 3 proceeding because
                                             PQL limits MCL: chlordane
                                             and vinyl chloride.
    Category 11...........................  0 of 3 proceeding because
                                             there is no potential to
                                             revise an MCL that is based
                                             on the MCLG that may be
                                             further reviewed.
    Category 12...........................  6 of 7 proceeding because
                                             PQL limits MCL: DBCP; 1,2-
                                             dichloropropane;
                                             heptachlor; heptachlor
                                             epoxide; hexachlorobenzene;
                                             toxaphene epichlorohydrin
                                             bypasses the analytical
                                             review because it does not
                                             have a PQL.
    Category 13...........................  1 of 7 proceeding because
                                             PQL limits MCL: 1,1,2-
                                             trichloroethane.
------------------------------------------------------------------------
\1\ These categories correspond to the categories in Table V-2.

3. Analytical Feasibility
    EPA has a process in place to approve new analytical methods for 
drinking water contaminants; therefore, the review and approval of 
potential new methods are outside the scope of the Six-Year Review 
protocol. EPA recognizes, however, that the approval and addition of 
new and/or improved analytical methods (since the promulgation of the 
NPDWRs considered under this section of the review) may enhance the 
ability of laboratories to quantify contaminants at lower levels. This 
ability of laboratories to measure a contaminant at lower levels could 
affect its PQL, the value at which an MCL is set when it is limited by 
analytical feasibility. Therefore, the Six-Year Review process includes 
a

[[Page 15511]]

review of whether there have been changes in analytical feasibility for 
the subset of the NPDWRs that reached this stage of the decision tree. 
These include contaminants with or without ongoing health effects 
assessments that have MCLs limited by analytical feasibility and 
contaminants with possible MCLGs that are lower than their current 
PQLs.
    The document, ``Analytical Feasibility Support Document for the 
Second Six-Year Review of Existing National Primary Drinking Water 
Regulations'' (USEPA, 2009c), describes the process EPA used to 
evaluate whether changes in 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) 
Performance Evaluation (PE) data from Water Supply (WS) studies, which 
is the preferred alternative when sufficient 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, 1989b)).
    The review protocol for Six-Year Review 1 utilized data from PE 
studies, which were laboratory accreditation studies conducted under 
EPA oversight until 1999, when the program was privatized. Now, the 
National Environmental Laboratory Accreditation Conference (NELAC) 
conducts the accreditation program via Performance Testing (PT) 
studies. PQL reassessments discussed in this notice are based on the 
Six-Year 1 PE data collected through late 1999 and laboratory passing 
rate PT data collected from late 1999 through 2004. One PT provider 
made pass/fail rates from PT studies available to EPA. This major 
provider accounts for a large portion of the PT results nationwide 
(USEPA, 2009c).
    Using PE or PT 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 range (see 54 FR 22062 at 22100, May 22, 1989 (USEPA, 
1989b)). For Six-Year Review 2, EPA did not have sufficient PT and PE 
data to recalculate any PQL values, in part because the spiked 
concentrations were rarely far enough below current PQLs. Instead, EPA 
used the PT and PE passing rate results (i.e., the percent of 
laboratories passing a performance test for a given study) at and below 
the current PQL to determine whether data may support a lower PQL.
    When PT results were not available below the PQL or when the 
results did not provide conclusive indications regarding a potential to 
revise a PQL, EPA used two alternate approaches to estimate possible 
PQLs: an approach based on the minimum reporting levels (MRLs) obtained 
as part of the Six-Year Review Information Collection Request (ICR) 
(see section V.B.4), and an approach based on method detection limits 
(MDL). While EPA prefers to use laboratory performance data to 
calculate a PQL, the MRL and MDL information can be valuable for this 
review to indicate whether it is possible to quantitate at levels below 
the current PQL.
    A laboratory reports an MRL when it does not detect a particular 
contaminant in a sample of water. The MRL is the lowest concentration 
level of a contaminant that a laboratory can reliably measure or 
quantitate within specified limits of precision and accuracy under 
routine laboratory operating conditions using a given method (USEPA, 
2009c). MRL values were included with the data provided by the States 
in response to the Six-Year Review ICR. EPA evaluated the distribution 
of MRL values for each contaminant to identify the mode or value 
occurring most frequently for that contaminant (i.e., the modal MRL) 
and estimated the percentage of MRL values that are equal to or less 
than the modal MRL. When this percentage was at least 80 percent and 
the modal MRL was below the PQL, EPA chose to use this modal MRL value 
as an estimated quantitation limit (also referred to as an EQL 
throughout this document). The use of modal MRLs is a refinement of the 
protocol, necessitated by limited availability of PT and PE data below 
the current PQL and made possible by the extensive amount of 
information included in the Six-Year Review ICR dataset (see section 
V.B.4).
    When the MRL data did not meet the 80 percent threshold used for 
deriving an EQL via this approach, EPA used an MDL approach to derive 
an EQL. As noted previously, this approach has been used in the past to 
derive PQLs for regulated contaminants. In addition, this same approach 
was used to identify possible analytical feasibility levels for Six-
Year Review 1 (USEPA, 2003a). In deriving these levels, the Agency used 
the MDLs associated with the analytical methods approved by EPA for 
drinking water analysis. EPA obtained MDL values from individual 
analytical methods developed and approved by EPA for use on drinking 
water. EPA applied a multiplier to these MDL values and based the EQL 
on the midpoint of the resulting range (i.e., the mean if there are two 
MDLs or a median if there are more than two MDLs). The multiplier is 10 
for most contaminants except dioxin and EDB, which have PQLs that were 
historically based on an MDL multiplier of 5.\4\ EPA also used the MDL 
multiplier approach to confirm whether EQLs based on MRL data are 
consistent with the range of values based on an MDL multiplier 
approach.
---------------------------------------------------------------------------

    \4\ As noted in Table V-4 and sections VI.38 and VI.59, EPA 
found that there was no potential to lower the PQL for dioxin and 
EDB. Even if EPA had used a 10 x MDL multiplier for these two 
contaminant instead of the 5 x MDL multiplier, this would not have 
changed the outcome of the analytical feasibility assessments.
---------------------------------------------------------------------------

    EPA used the EQL thresholds derived via the modal MRL or MDL-
multiplier approaches for the occurrence analysis (see section V.B.4) 
to help the Agency determine if there may be a meaningful opportunity 
to improve public health protection. It should be noted, however, that 
the EQL does not represent the Agency's intent to promulgate new PQLs 
with this notice. Any revisions to PQLs will be part of future rule 
making efforts.
    EPA performed analytical feasibility analyses for the contaminants 
identified in Table V-3 as proceeding to this portion of the review. 
Table V-4 shows the contaminants gathered into three more general 
categories and the outcomes of the Agency's review.
     A health effects assessment indicates potential for lower 
MCLG. This category includes the six contaminants identified in the 
health effects review as having information indicating the potential 
for a lower MCLG--four with new health effects assessments completed 
during Six-Year Review 2 and two with health effects assessments 
completed during Six-Year Review 1. Although their current MCLs are not 
limited by a PQL, EPA reviewed analytical feasibility to determine if 
analytical feasibility might limit the potential for MCL revisions. For 
two contaminants (endothall and oxamyl), the current PQL is higher than 
the possible MCLG identified in the health effects review. For these 
contaminants, the potential to lower their PQLs based on PE and PT data 
is inconclusive, but MRL and MDL data indicate the potential to revise 
the PQL. EPA thus proceeded to evaluate occurrence data to determine 
whether a lower PQL, and thus the MCL, may provide a meaningful 
opportunity to improve public health protection. The current PQL is not 
a limiting factor for the

[[Page 15512]]

remaining four contaminants identified by the health effects review as 
having possible changes in their MCLG (i.e., 2,4-D, 
hexachlorocyclopentadiene, toluene, and xylenes).
     Contaminants with ongoing health effects assessments and 
existing MCLs are based on analytical feasibility. This category 
includes 14 contaminants with ongoing health assessments with existing 
MCLs that are greater than their MCLGs because they are limited by 
analytical feasibility. One contaminant has a non-zero MCLG (thallium) 
and the remaining 13 contaminants have MCLGs equal to zero. Although a 
risk assessment is in process for these contaminants, because SDWA 
requires the Agency to set the MCL as close to the MCLG as feasible, 
EPA evaluated whether the PQL is likely to be lower for these 
contaminants. For four of these contaminants (carbon tetrachloride, 
1,2-dichloroethane, tetrachloroethylene, and trichloroethylene), EPA 
concluded that new information from PT studies, along with MRL and MDL 
data, indicate the potential to revise the PQL. For one contaminant 
(dichloromethane), data from PT studies are inconclusive, but MRL and 
MDL data indicate the potential to revise the PQL. For these five 
contaminants, EPA proceeded to evaluate occurrence data to determine 
whether lowering the PQL, and thus the MCL, may provide a meaningful 
opportunity to improve public health protection.\5\ For the remaining 
nine contaminants, either EPA did not have sufficient new information 
to evaluate analytical feasibility or EPA concluded that new 
information does not indicate the potential for a PQL revision. 
Consequently, the outcome of the review for these nine contaminants is 
to take no action at this time.
---------------------------------------------------------------------------

    \5\ If EPA found that there was no meaningful opportunity to 
revise the MCL (i.e., carbon tetrachloride, 1,2-dichloroethane and 
dichloromethane), these contaminants remained in the health effects 
assessment in process category.
---------------------------------------------------------------------------

     Contaminants without ongoing health effects assessments or 
for which no new health risk information was identified and for which 
existing MCLs are based on analytical feasibility and greater than 
their MCLGs. For the 11 contaminants in this category, EPA evaluated 
available PT and PE data as well as MRL and MDL data to determine 
whether there is potential to lower the PQL and thereby set the MCL 
closer to the MCLG. For five of these contaminants (benzene chlordane, 
1,2-dichloropropane, hexachlorobenzene, and 1,1,2-trichloroethane) EPA 
concluded that new information from PT studies, along with MRL and MDL 
data, indicates that while it might be possible to set a lower PQL, the 
data are insufficient to support an actual PQL recalculation at this 
time. Consequently, the outcome of the review for these contaminants is 
to take no action at this time. For five additional contaminants (DBCP, 
heptachlor, heptachlor epoxide, toxaphene, and vinyl chloride), the 
data from PT studies are inconclusive, but MRL and/or MDL data indicate 
potential for a lower PQL, as indicated in Table V-4. For these five 
contaminants, EPA proceeded to evaluate occurrence data to determine 
whether lowering the PQL, and thus the MCL, may provide a meaningful 
opportunity to improve public health protection. For the final 
contaminant, ethylene dibromide (EDB), none of the data sources 
indicate potential to revise and the outcome of the review for this 
contaminant is to take no action at this time.
    Table V-4 lists the type of data that indicate potential for a PQL 
reduction. The list includes ``PT'' when the PQL reassessment based on 
PT and PE data (USEPA, 2009c) reports that a reduction is supported. 
The list also includes ``MRL'' and ``MDL'' when either of these 
approaches indicates potential for PQL reduction. A result of ``PQL 
reduction supported'' without a ``PT'' in the list indicate that the 
PQL reassessment outcome is uncertain, but other data (i.e., MRL and/or 
MDL) indicate potential for PQL reduction. When the PQL reassessment 
outcome is that the current PQL remains appropriate, Table V-4 shows 
the result ``Data do not support PQL reduction.'' The contaminant 
specific discussions in section VI of today's action provide the 
results of the analytical feasibility review for all the contaminants 
in Table V-4.

     Table V-4--NPDWRs Included in the Analytical Feasibility Reassessment and the Result of That Assessment
----------------------------------------------------------------------------------------------------------------
           Contaminant                 Current PQL             Analytical feasibility reassessment result
----------------------------------------------------------------------------------------------------------------
          6 Contaminants Identified Under the Health Effects Review as Having Potential for Lower MCLG
----------------------------------------------------------------------------------------------------------------
2,4-D (possible MCLG: 0.04 mg/L).  0.005 mg/L........  PQL not limiting.
Endothall (possible MCLG: 0.05 mg/ 0.09 mg/L.........  PQL reduction supported (MRL, MDL).
 L).
Hexachlorocyclopentadiene          0.001 mg/L........  PQL not limiting.
 (possible MCLG: 0.04 mg/L).
Oxamyl (possible MCLG: 0.002 mg/   0.02 mg/L.........  PQL reduction supported (MRL, MDL).
 L).
Toluene (possible MCLG: 0.6 mg/L)  0.005 mg/L........  PQL not limiting.
Total xylenes (possible MCLG: 1    0.005 mg/L........  PQL not limiting.
 mg/L).
----------------------------------------------------------------------------------------------------------------
 14 Contaminants with Ongoing Health Effects Assessments (as of March 1, 2009) and MCLs Are Based on Analytical
                                        Feasibility and Higher than MCLGs
----------------------------------------------------------------------------------------------------------------
Alpha particles..................                          No PQL and no new information.
Benzo(a)pyrene...................  0.0002 mg/L.......  Data do not support PQL reduction.
                                  ------------------------------------------------------------------------------
Beta particles...................                          No PQL and no new information.
                                  ------------------------------------------------------------------------------
Carbon Tetrachloride.............  0.005 mg/L........  PQL reduction supported (PT, MRL, MDL).
DEHP.............................  0.006 mg/L........  Data do not support PQL reduction.
1,2-dichloroethane...............  0.005 mg/L........  PQL reduction supported (PT, MRL, MDL).
Dichloromethane..................  0.005 mg/L........  PQL reduction supported (MRL, MDL).
Pentachlorophenol................  0.001 mg/L........  Data do not support PQL reduction.
PCBs.............................  0.0005 mg/L.......  Data do not support PQL reduction.
                                  ------------------------------------------------------------------------------
Radium...........................                          No PQL and no new information.
                                  ------------------------------------------------------------------------------

[[Page 15513]]

 
Dioxin...........................  3E-08 mg/L........  Data do not support PQL reduction.
Tetrachloroethylene..............  0.005 mg/L........  PQL reduction supported (PT, MRL, MDL).
Thallium.........................  0.002 mg/L........  Data do not support PQL reduction.
Trichloroethylene................  0.005 mg/L........  PQL reduction supported (PT, MRL, MDL).
----------------------------------------------------------------------------------------------------------------
   11 Contaminants without Ongoing Health Effects Assessments and MCLs Are Based on Analytical Feasibility and
                                                Higher than MCLGs
----------------------------------------------------------------------------------------------------------------
Benzene..........................  0.005 mg/L........  PQL reduction supported (PT, MRL, MDL).
Chlordane........................  0.002 mg/L........  PQL reduction supported (PT, MRL, MDL).
DBCP.............................  0.0002 mg/L.......  PQL reduction supported (MDL).
1,2-dichloropropane..............  0.005 mg/L........  PQL reduction supported (PT, MRL, MDL).
EDB..............................  0.0005 mg/L.......  Data do not support PQL reduction.
Heptachlor.......................  0.0004 mg/L.......  PQL reduction supported (MRL, MDL).
Heptachlor epoxide...............  0.0002 mg/L.......  PQL reduction supported (MRL, MDL).
Hexachlorobenzene................  0.001 mg/L........  PQL reduction supported (PT, MRL, MDL).
Toxaphene........................  0.003 mg/L........  PQL reduction supported (MRL, MDL).
1,1,2-trichloroethane............  0.005 mg/L........  PQL reduction supported (PT, MRL, MDL).
Vinyl chloride...................  0.002 mg/L........  PQL reduction supported (MRL).
----------------------------------------------------------------------------------------------------------------
mg/L--milligrams per liter......................................................................................
----------------------------------------------------------------------------------------------------------------

    EPA conducted occurrence and exposure analyses for the contaminants 
in Table V-4 for which a PQL reduction is supported or the PQL is not 
limiting. This includes the 6 contaminants with new health effects 
assessments that indicate potentially lower MCLGs, 5 of the 14 
contaminants with ongoing health effects assessments and MCLs limited 
by PQLs, and 10 of the 11 contaminants without ongoing health effects 
assessments and MCLs limited by PQLs.
4. Occurrence and Exposure Analysis
    To support the national contaminant occurrence assessments under 
Six-Year Review 2, EPA conducted an Information Collection Request. 
Through this process EPA requested that all States and primacy entities 
voluntarily submit their SDWA compliance monitoring data. This request 
was for the submission of compliance monitoring data collected between 
January 1998 and December 2005 for 79 regulated contaminants. A total 
of 51 States and entities provided compliance monitoring data that 
included all analytical detection and non-detection records. These data 
represent the national occurrence of regulated contaminants in public 
drinking water systems. Through extensive data management efforts, 
quality assurance evaluations, and communications with State data 
management staff, EPA established a high quality dependable contaminant 
occurrence database consisting of data from 45 States and two Indian 
Tribes (see map in Figure V-2). Details of the data management and data 
quality assurance evaluations are available in the support document 
entitled, ``Analysis of Occurrence Data from the Second Six-Year Review 
of Existing National Primary Drinking Water Regulations'' (USEPA, 
2009f).

[[Page 15514]]

[GRAPHIC] [TIFF OMITTED] TN29MR10.002

    The contaminant occurrence data from the 45 States and two Indian 
Tribes comprise more than 15 million analytical records from 
approximately 132,000 public water systems. Approximately 254 million 
people are served by these public water systems nationally. Records 
were submitted for 16 inorganic chemicals, 32 synthetic organic 
chemicals, 21 volatile organic chemicals, 7 radiological contaminants, 
and 3 microbiological \6\ contaminants. The number of States and public 
water systems represented in the dataset varies across contaminants 
because of variability in voluntary State data submissions and 
contaminant monitoring schedules. This is the largest, most 
comprehensive set of drinking water compliance monitoring data ever 
compiled and analyzed by EPA.
---------------------------------------------------------------------------

    \6\ The compliance monitoring data for the microbiological 
contaminants were collected to support ongoing rule development so 
these data have not been analyzed separately in this action.
---------------------------------------------------------------------------

    EPA used a two-stage analytical approach to analyze these data and 
characterize the national occurrence of contaminants.\7\ The first 
stage of analysis provides a straightforward evaluation of contaminant 
occurrence. This stage 1 occurrence analysis is a simple, non-
parametric count of occurrence of regulated contaminants in public 
water systems.\8\ A typical stage 1 occurrence analysis generates a 
count of the number (or percentage) of systems with at least one 
analytical detection having a concentration greater than a 
concentration threshold of interest, i.e., a possible MCLG or EQL. It 
provides a health protective approach that may be more appropriate for 
contaminants that produce health effects after shorter than lifetime 
exposure periods (e.g., several months or less). This approach also 
generates a conservative (i.e., upwardly biased) estimate of the number 
of potential systems having contaminant occurrence at levels of 
interest for contaminants having health risks that are only related to 
chronic or long-term exposure over many years.
---------------------------------------------------------------------------

    \7\ The use of the stage 1 and stage 2 terminology should not be 
confused with the Stage 1 and Stage 2 Disinfectants and Disinfection 
By Products Rulemakings. Instead, this terminology has been used to 
describe the two stages of the occurrence analyses performed for 
Six-Year Review 2, as well as Six-Year Review 1.
    \8\ These analyses are conservative in the sense that they are 
protective of human health (i.e., they are more likely to 
overestimate risks to human health than underestimate them).
---------------------------------------------------------------------------

    The stage 2 occurrence analysis estimates national contaminant 
occurrence by generating estimated long-term mean concentrations of a 
specific contaminant at systems nationally. This provides occurrence 
analyses that are less conservative than the stage 1 occurrence 
analysis (because the stage 2 occurrence analysis is based on estimated 
mean concentrations rather than on single maximum concentrations), and 
also provides occurrence analyses that may be more reflective of 
potential chronic exposure. Generally, the stage 1 occurrence analysis 
reflects a rough approximation of peak occurrence while the stage 2 
occurrence analysis is based on estimated average occurrence. A 
complete description of the two-stage analytical approach and a 
detailed presentation of occurrence estimates are available in the 
support document entitled, ``Analysis of Occurrence Data from the 
Second Six-Year Review of Existing National Primary Drinking Water 
Regulations'' (USEPA, 2009f).
    EPA calculated the system means for the stage 2 occurrence analysis 
using a simple arithmetic average of all detection and non-detection 
data for each public water system. Because the contaminant 
concentrations associated with the non-detection data are unknown, EPA 
assigned three different values to the non-detection results to 
estimate a range of system-level means, which then allowed EPA to 
estimate number and percent of systems with estimated means exceeding 
selected threshold values. Two of the three values are based on the MRL 
values that accompany the non-detection results in the Six-Year Review 
ICR dataset. The MRL is the lowest level that can be reliably achieved 
within specified limits of precision and accuracy under routine 
laboratory operating conditions using a given method. The three values 
that EPA substituted for non-detection results were MRL, \1/2\ MRL, and 
zero.
    The most conservative approach was to assume that all non-detection 
results

[[Page 15515]]

were equal to the MRL. This approach yields an upper-bound estimate of 
each system's level of exposure. EPA also explored the less 
conservative assumption that concentrations of the non-detection 
results were uniformly distributed between the MRL and zero, thereby 
substituting one-half the MRL for all non-detection results. Finally, 
EPA considered the assumption that the actual concentration for each 
non-detection result was typically much smaller than the MRL, 
supporting the use of zero to represent each non-detection. This method 
yielded a lower-bound estimate of the system's mean. This simplified 
approach differs from the stage 2 occurrence analysis approach in the 
Six-Year Review 1, which used more sophisticated modeling methods to 
address the non-detection results. That analysis, however, was based on 
a substantially smaller dataset (i.e., data from 16 States instead of 
45 States). (Note that many States substitute zero for all non-
detections when determining compliance with the NPDWRs.) EPA uses each 
of the assumptions in the stage 2 occurrence analyses in order to 
obtain reasonable bounds on the actual system mean concentrations. Once 
the system means were calculated for each of the three substitution 
methods, the results means were then compared to the various thresholds 
of interest (e.g., the number and percent of systems with a mean 
concentration above a health threshold of concern).
    The two-stage analytical approach was previously developed for Six-
Year Review 1. The data management and general occurrence analytical 
approach were peer-reviewed for use under the Six-Year Review 1.
    EPA conducted the stage 2 occurrence analysis for 5 of the 14 
NPDWRs in Table V-4 with ongoing health effects assessment and MCLs 
that are limited by PQLs for which EPA identified analytical 
feasibility data supporting possible PQL revision: carbon 
tetrachloride; dichloromethane; 1,2-dichloroethane; 
tetrachloroethylene; and trichloroethylene. EPA also conducted the 
stage 2 occurrence analysis for the five contaminants with health 
effects assessment changes that indicate potential to reduce the MCLG 
and the ten contaminants that do not have ongoing health effects 
assessments, but do have MCLs limited by PQLs and new data indicate 
potential to reduce the PQLs (see Table V-4). Note that EPA conducted 
the Stage 1 analysis for one contaminant with health effects assessment 
changes that indicate a potential to reduce the MCLG (i.e., oxamyl) 
because the health endpoint is associated with acute exposure. EPA used 
the results of these analyses to identify which possible NPDWR 
revisions present a meaningful opportunity to improve the level of 
health protection. Section VI contains the occurrence estimates for 
each of the 21 contaminants (shown in Table V-4) having either new 
information suggesting potentially lower MCLGs or MCLs based on PQLs 
that might be lower based on new information.
    Because the Six-Year Review ICR data reflect water quality at entry 
points to the distribution system, the occurrence analysis method 
described above is not adequate to evaluate the cost savings potential 
for the nine contaminants that have health effects assessment changes 
that indicate potential for higher MCLG values (see Table V-2). EPA 
lacks the comprehensive information on source water quality and 
existing treatment needed to determine how many systems would be able 
to alter treatment practices were an MCLG to increase. To review the 
potential for cost savings, EPA conducted a qualitative assessment of 
the potential for treatment cost savings based on three factors: the 
magnitude of the difference between the current MCLG and the possible 
MCLG; available source water occurrence information; and the potential 
for systems having best available technologies (BATs) or small system 
compliance technologies (SSCTs) to realize operational cost savings 
(USEPA, 2009g).
    There is no comprehensive database of water quality in drinking 
water sources. Therefore, EPA used source water quality information 
from two national data sources, the National Water Quality Assessment 
(NAWQA) program conducted by the U.S. Geological Survey (USGS), and 
EPA's STORET (short for STOrage and RETrieval) data system, which are 
part of EPA's Office of Ground Water and Drinking Water's National 
Contaminant Occurrence Database (NCOD). The STORET data come from a 
variety of monitoring programs and the NAWQA data come from watershed 
or ``study units'' that USGS selected to reflect important hydrologic 
and ecological resources; critical sources of contaminants, including 
agricultural, urban, and natural sources; and a high percentage of 
population served by municipal water supply and irrigated agriculture. 
The original 51 study units account for more than 70 percent of total 
water use (excluding thermoelectric and hydropower) and more than 50 
percent of the population's supply of drinking water (Gilliom et al., 
2006). For each dataset, EPA estimated the number and percent of 
monitoring locations with at least one sample result above each 
contaminant's current MCL, and above a possible MCLG based on the new 
information from the contaminant's health effects assessment. Although 
these results do not indicate how many systems may be treating for each 
contaminant, they provide the best available information regarding the 
frequency of contaminant occurrence at levels of interest. Section VI 
reports the results by contaminant.
5. Treatment Feasibility
    An NPDWR either identifies the BATs for meeting an MCL, or 
establishes enforceable treatment technique requirements. For the 
NPDWRs addressed in section VI of today's action, two have TT 
requirements and the rest have an MCL. All of the MCLs are set equal to 
the MCLG or the PQL or by benefit-cost analysis; none are currently 
limited by treatment feasibility. As a refinement for Six-Year Review 
2, EPA considered treatment feasibility after identifying contaminants 
with potential to lower an MCL or change a TT that constituted a 
meaningful opportunity to improve the level of health protection. The 
EPA document, ``Water Treatment Technology Feasibility Support Document 
for Chemical Contaminants for the Second Six-Year Review of National 
Primary Drinking Water Regulations'' (USEPA, 2009g), describes the 
process EPA used to evaluate treatment feasibility, where appropriate, 
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 two 
MCL-type NPDWRs (tetrachloroethylene and trichloroethylene) where EPA 
determined that lowering the PQL and thus the MCL could lead to a 
meaningful opportunity to improve public health protection, to 
determine whether treatment feasibility would be a limiting factor.
    Based on this evaluation, the Agency believes that treatment 
capabilities would be adequate to support a lower MCL value for these 
contaminants for which a lower MCL may be appropriate (USEPA, 2009g). 
EPA's assessment of the treatment technologies for these

[[Page 15516]]

contaminants that are specified as BAT in the current NPDWR and some of 
the small system compliance technologies specified by EPA in 1998 
(USEPA, 1998b), shows that they are effective enough to achieve 
concentrations as low as the EQL. If EPA were to determine that it is 
appropriate to revise these NPDWRs, it would undertake a more thorough 
review of treatment feasibility, including a consideration of costs, to 
determine whether treatment feasibility would be a constraint or not.
b. Treatment Technique-Type Rules
    EPA reviewed two chemical NPDWRs--acrylamide and epichlorohydrin 
(both classified B2 carcinogens)--for which a TT is set in lieu of an 
MCL. The TT requirement limits the allowable acrylamide and 
epichlorohydrin monomer levels in polymeric coagulant aids and their 
dosages for drinking water treatment, storage, and distribution. 
Although a health effects assessment for acrylamide is ongoing, it is a 
carcinogen with an MCLG of zero and the draft health effects assessment 
indicates that the cancer classification remains the same. As a 
refinement in Six-Year Review 2, EPA considered new information to 
determine if the TTs for these contaminants may need to be revised. 
This information indicates that improvements in manufacturing 
capabilities have reduced the residual monomer content in acrylamide 
and epichlorohydrin-based polymeric coagulants aids and these changes 
would support revisions to the TTs for acrylamide and epichlorohydrin. 
Sections VI.B.1 and VI.B.36 of today's action summarize these issues 
for acrylamide and epichlorohydrin, respectively.
6. Other Regulatory Revisions
    In addition to possible revisions to MCLGs, MCLs, and TTs, EPA 
considered whether other regulatory revisions are needed, such as 
monitoring and system reporting requirements, as a part of the Six-Year 
Review 2. EPA utilized the protocol established during the Six-Year 
Review 1 to evaluate which implementation issues to consider (USEPA, 
2003b). EPA's protocol focused on items that were not already being 
addressed, or had not been addressed, through alternative mechanisms 
(e.g., as a part of a recent or ongoing rulemaking). EPA considered 
potential implementation-related revisions in these cases if the 
revisions:
     Represented a change to an NPDWR, as defined under section 
1401 of SDWA; \9\
---------------------------------------------------------------------------

    \9\ The subject of the Six-Year-Review, as specified in section 
1412(b)(9) of the SDWA, is ``each national primary drinking water 
regulation,'' as defined under section 1401 of the SDWA.
---------------------------------------------------------------------------

     Were ``ready'' for rulemaking--that is, the problem to be 
resolved had been clearly defined, and specific options to address the 
problem had been formulated; and
     Would clearly improve the level of public health 
protection and/or provide a meaningful opportunity for cost savings 
(either monetary or burden reduction) while not lessening public health 
protection.
a. Issues Identified by the EPA/State Workgroup
    To gather input regarding implementation-related concerns and help 
the Agency identify the top one or two issues for Six-Year Review 2 
(USEPA, 2009h), EPA requested that the Association of State Drinking 
Water Administrators (ASDWA) form a workgroup of member States and 
primacy agencies. In the fall of 2007, ten member States agreed to 
participate and confer with EPA on a joint EPA/State workgroup. The 
State/EPA workgroup initially identified 22 issues, but narrowed the 
list to 4 items. Of these four items, three appeared to be within the 
scope of this NPDWR review, and EPA agreed that an information or fact 
sheet might be appropriate for the fourth item regarding public 
notification (PN) requirements for fluoride.\10\ The EPA/State 
workgroup agreed that public input via the Federal Register would 
provide additional insight on the national scope of these three issues 
(i.e., Are the issues isolated to a few States or more widespread?), 
the importance of these issues to other States as well as water 
systems, and ideas on potential resolutions. Table V-5 provides a brief 
description of the remaining three issues and some of the potential 
solutions discussed in the workgroup meetings.
---------------------------------------------------------------------------

    \10\ Currently, PWSs that exceed the fluoride MCL of 4.0 mg/L 
are required to notify their customers within 30 days of the 
exceedance. If a PWS exceeds the fluoride SMCL of 2.0 mg/L, they are 
required to notify their customers within 12 months of the 
exceedance. The States voiced concerns about (1) the confusion that 
occurs between the different PN requirements for the MCL and the 
SMCL, and (2) the timeliness of the PN requirement for the SMCL. The 
workgroup indicated that waiting 12 months to notify customers of an 
exceedance of the SMCL does not adequately protect young children 
from dental fluorosis during a critical stage of tooth enamel 
development. The participating States requested that EPA consider 
regulatory revisions to clarify the PN requirements and better 
reflect the health and aesthetic implications of each. EPA noted 
that PN requirements are not within the scope of this NPDWR review. 
However the Agency agreed that a fact or information sheet may be 
useful to clarify any confusion.
---------------------------------------------------------------------------

    EPA is requesting public input and further information on these 
three implementation issues to better inform future State/EPA workgroup 
discussions. More specifically, EPA would like to gauge how many States 
and/or public water utilities may be affected by these issues, and 
which one or two issues are most important to States. EPA also requests 
input and suggestions from commenters regarding any other potential 
solutions to the issues. As part of the public comment process, EPA 
also welcomes any data on the occurrence of nitrates and/or nitrites in 
the distribution system, especially as it may relate to nitrification 
associated with the use of chloramines for disinfection.

Table V-5--Issues Identified by the EPA/State Workgroup That Fall Within
                     the Scope of This NPDWR Review
------------------------------------------------------------------------
                               Examples of potential solutions discussed
     Implementation issue                   by the workgroup
------------------------------------------------------------------------
Change the location of          Location of Monitoring
 nitrate-nitrite monitoring    --Move sampling location from the entry
 to address possible            point to the distribution to within the
 nitrification within the       distribution system.
 distribution system for       --Or, maintain entry point sampling and
 water systems using            also sample in the distribution system.
 chloramines\1\

[[Page 15517]]

 
                                Frequency of Monitoring
                               --Consider sampling in conjunction with
                                DBPs, TCR or some other scheme.
                                EPA notes that 40 Code of
                                Federal Regulations (CFR) 141.23(a)(2)
                                may allow surface water systems
                                discretion to locate the sampling point
                                in the distribution system if that is
                                more representative of the source after
                                treatment.\2\
Reduce the monitoring for       Consider revisions to change the
 ground water systems with      frequency of monitoring, the trigger
 historically low levels of     level and the duration of time for
 nitrate-nitrite.               systems to qualify for reduced
                                monitoring. Examples included:
                               --A monitoring frequency of 3, 6, or 9
                                years (consistent with the existing
                                standardized monitoring framework) or
                                some other frequency.
                               --A new trigger level set at either \1/2\
                                the MCL (or some other fraction), the
                                PQL/MDL (or some other level of
                                detection), or another appropriate
                                level.
                               --As for the duration of how long a
                                system would need to meet the trigger
                                level in order to be allowed to begin
                                reduced monitoring, some options
                                included a 3-, 6-, or 9-year period
                                (consistent with the standardized
                                monitoring framework) or a 5-, 10-, or
                                15-year period.
                                Or consider providing a waiver
                                option to give States discretion to
                                reduce monitoring.
                                Or consider a non-regulatory
                                option such as the Alternative
                                Monitoring Guidelines (which some
                                considered too burdensome).
Revise the monitoring           Revise all contaminant rules to
 requirements for Non           include additional monitoring
 Community Water Systems        requirements for Transient Non Community
 (NCWS) to better target the    Water Systems (TNCWS), as well as
 potential health risks         radionuclide monitoring requirements for
 associated with chronic        Non Transient Non Community Water
 contaminants. In light of      Systems (NTNCWS).
 the probability and            Or review existing regulated
 magnitude of health threats,   contaminants and include TNCWS
 some monitoring requirements   monitoring requirements based on the
 for these systems may be       relative health risk from chronic
 insufficient, and others may   exposure.
 be excessive.                  Or develop general language that
                                would apply to all contaminant rules,
                                giving States the discretion to require
                                additional monitoring for contaminants
                                that pose chronic exposure risks and can
                                have acute health effects at elevated
                                levels potentially found at TNCWSs (the
                                preferred option from States).
                                Note: For some of these options,
                                EPA would need to evaluate whether
                                sufficient occurrence and exposure
                                information is available for TNCWS and
                                NTNCWS to assess the need for revised
                                monitoring strategies.
------------------------------------------------------------------------
\1\ The health effects technical review identified new information on
  developmental effects of nitrate and nitrite, as well as data
  regarding its carcinogenicity, that may indicate the need to update
  the Agency's risk assessment (see section VI.B.49 and VI.B.50 of
  today's action). In light of this information, EPA is considering
  nitrate and nitrite as potential candidates for new health effects
  assessments. If new assessments are initiated and completed, EPA will
  be able to determine the potential impacts on the MCLG, MCL, and/or
  monitoring requirements, and what future actions may or may not be
  appropriate.
\2\ 40 CFR 141.23(a)(2) states: Surface water systems shall take a
  minimum of one sample at every entry point to the distribution system
  after any application of treatment or in the distribution system at a
  point which is representative of each source after treatment
  (hereafter called a sampling point) beginning in the initial
  compliance period. The system shall take each sample at the same
  sampling point unless conditions make another sampling point more
  representative of each source or treatment plant.

b. Other Issues (Synthetic Organic Chemicals Trigger Levels)
    40 CFR 141.24(h)18 of the national primary drinking water 
regulations lists detection limits for the synthetic organic chemicals 
(SOCs), including pesticides. These detection limits serve as triggers 
for determining whether the compliance monitoring frequency for SOCs 
may be reduced; public water systems detecting SOCs at or below trigger 
concentration can qualify for reduced monitoring. Several Regions and 
States have requested guidance and clarification on the use of 
detection limits in monitoring of drinking water samples for SOCs. The 
primary concern is that some laboratories have reported difficulty in 
achieving the detection limits for some SOCs on a regular basis and, in 
those cases, the water systems that they support are not able to 
qualify for reduced monitoring.
    EPA is seeking information about the extent and magnitude of any 
issues related to the ability of laboratories to achieve the SOC 
trigger levels specified in section 141.24(h)(18). EPA wishes to 
determine if this issue is widespread or limited to specific SOCs and/
or specific laboratories. EPA is requesting that stakeholders provide 
information/data to support their concerns related to SOC triggers.

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

    The 1996 amendments to SDWA require special consideration of all 
sensitive populations (e.g., infants, children, pregnant women, 
elderly, and individuals with a history of serious illness) in the 
development of drinking water regulations (section 1412(b)(3)(C)(V) of 
SDWA, as amended in 1996). As a part of the Six-Year Review 2, EPA 
completed a literature search covering developmental and reproductive 
endpoints (e.g., fertility, embryo survival, developmental delays, 
birth defects, and endocrine effects) for regulated chemicals that have 
not been the subject of a health effects assessment during this review 
period (see section V.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 that might 
not be addressed by the current NPDWR: Nitrate, nitrite, and selenium. 
In each case, where the literature search indicated a need to consider 
recent studies of developmental or reproductive toxicity, EPA is 
considering whether to nominate the contaminant for a new health 
effects assessment.

VI. Results of EPA's Review of NPDWRs

    Table VI-1 lists EPA's review results for each of the 71 NPDWRs 
discussed in this section of today's action along with the principal 
rationale for the review outcomes. Table VI-1 also includes a list of 
the 14 NPDWRs that have been or are being reviewed/revised by recent or 
ongoing regulatory actions.

[[Page 15518]]

A. What Are the Review Result Categories?

    For each of the 71 NPDWRs discussed in detail in the following 
sections of today's action, the review results in one of the following 
outcomes:
1. No Action at This Time and the NPDWR Is Still Appropriate
    The NPDWR is appropriate and no action is necessary at this time 
for one of the following reasons:

    a. A health effects assessment is in process or the Agency is 
considering whether to initiate an assessment. The MCL remains 
appropriate because either, (1) it is equal to the MCLG, (2) the MCL 
is based on SDWA's cost-benefit provision, (3) there is no potential 
to change the MCL based on changes in analytical feasibility, or (4) 
there may be a potential change to the MCL based on analytical 
feasibility, but any such change is unlikely to provide a meaningful 
opportunity to improve public health protection. This group includes 
both contaminants where an assessment is in process, and 
contaminants where EPA identified new health information that may 
warrant a new health effects assessment.
    b. NPDWR remains appropriate after data/information review. 
There is no ongoing health assessment and the outcome of the review 
indicates that the current regulatory requirements remain 
appropriate and, therefore, no regulatory revisions are warranted at 
this time. Any new information available to the Agency either 
supports the current regulatory requirements or does not justify a 
revision.
    c. New information is available that indicates potential for a 
regulatory revision, but no revision recommended because:
     Negligible gain in public health protection and/or cost 
savings: Any resulting changes to the NPDWR would not significantly 
improve the level of public health protection or result in a major 
cost savings for public water systems and their customers.
     Information Gaps or Emerging Information: Either new 
information is emerging that could affect EPA's evaluation of the 
NPDWR or the available data are insufficient to support a definitive 
regulatory recommendation at this time.
2. Candidate for Revision
    The NPDWR is a candidate for revision based on the review of new 
information.

[[Page 15519]]

[GRAPHIC] [TIFF OMITTED] TN29MR10.003


[[Page 15520]]



B. What Are the Details of EPA's Review of Each NPDWR?

1. Acrylamide
    a. Background. EPA published the current NPDWR for acrylamide on 
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). 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, and limits the dosage of such products 
to a maximum of 1 mg/L (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 health 
effects assessment is considering relevant studies on the toxicity of 
acrylamide, including its potential developmental and reproductive 
toxicity. The draft assessment was published in the Federal Register on 
December 28, 2007 (72 FR 73813 (USEPA, 2007b)). The Science Advisory 
Board (SAB) conducted a peer review of the document, which also 
included a review of public comments received on the draft assessment. 
The SAB panel concurred with the Agency's rationale and justification 
for acrylamide being a ``likely human carcinogen'' via mutagenic 
mechanism. At the present time, acrylamide is still under evaluation by 
the Agency, and the IRIS Substance Assessment Tracking System Web site 
(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 
information on the status of the health effects assessment.
    Although there is an ongoing health effects assessment, the MCLG is 
zero and the current TT standard allows exposure at levels above the 
MCLG. Therefore, EPA reviewed whether there is potential to revise the 
TT for acrylamide. EPA has identified information that suggests that 
the residual acrylamide content in water treatment polymers has 
decreased significantly, likely due to improvements in manufacturing 
processes and technologies (USEPA, 2009g). NSF International analyses 
conducted between January 2005 and June 2007 found that, in 66 
polyacrylamide products submitted for certification under NSF Standard 
60, the median residual acrylamide content was 0.006 percent, and the 
90th percentile acrylamide content was 0.025 percent, half of the limit 
set in the treatment technique.
    Acrylamide standards in Europe and Australia are also stricter than 
the NPDWR. Based on the maximum allowable dosage and monomer level in 
the NPDWR, finished water could contain up to 0.5 [mu]g/L (ppb) of 
acrylamide. By contrast, the European Union requires that finished 
water contain less than 0.1 [mu]g/L (parts per billion or ppb) 
acrylamide, and Australia requires that the concentration in finished 
water be less than 0.2 [mu]g/L (ppb). The United Kingdom requires that 
polyacrylamides used in drinking water contain less than 0.02 percent 
residual acrylamide, and that the polyacrylamide dose be less than 0.5 
mg/L (parts per million or ppm) at all times, for a maximum finished 
water concentration of 0.1 [mu]g/L (ppb).
    To assess the occurrence of acrylamide in drinking water, EPA 
sought data on current usage practices for polyacrylamide coagulant 
aids. The Agency is not presently aware of any recent, large-scale 
studies of polymer usage in drinking water facilities, and therefore 
cannot fully characterize the occurrence of acrylamide in drinking 
water. However, the 1996 WATER:\STATS database (described in Levine et 
al., 2004), based on an American Water Works Association (AWWA) survey, 
indicates that 13 percent of ground water systems and 66 percent of 
surface water systems surveyed use a polymer for water treatment. Many 
of these are anionic and nonionic polymers, particularly for ground 
water systems; anionic and nonionic polymers used to treat drinking 
water are most likely polyacrylamides.
    Additional information on the extent of use of polyacrylamide in 
drinking water and the impending health effects assessment will further 
assist the Agency in determining the potential public health benefits 
associated with a revision to the treatment technique for acrylamide. 
Because most polyacrylamides available today have a lower residual 
monomer content than that specified in the current treatment technique 
(USEPA, 2009g), EPA believes that the costs of a revision would be 
minimal and recognizes that the benefits may also be small.
    c. Review Result. The Agency believes it is appropriate to revise 
the NPDWR for acrylamide although a health effects assessment is 
currently in progress. The existing MCLG is still zero (based on the 
current B2 cancer classification) and NSF International data indicate 
that polyacrylamides are widely available with lower residual monomer 
levels than required by the existing NPDWR. Hence, revisions to the 
acrylamide NPDWR will provide a meaningful opportunity to maintain the 
health risk reductions achieved by technological advances in 
manufacturing. If the updated health effects assessment is completed in 
time to consider for the regulatory revision of acrylamide, the Agency 
will consider this final assessment in its evaluation of health 
benefits. As discussed in Section VII, the Agency solicits information 
from the public on the extent of use of polyacrylamide in drinking 
water facilities (since this may provide additional information on the 
occurrence of acrylamide in drinking water) to help inform the 
regulatory revision. EPA notes that any changes to the NPDWR for 
acrylamide may also include revisions to the closely related NPDWR for 
epichlorohydrin.
2. Alachlor
    a. Background. EPA published the current NPDWR for alachlor on 
January 30, 1991 (56 FR 3526 (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 0.002 mg/L, based on 
analytical feasibility.
    b. Technical Reviews. In 2006, the Agency updated its health 
effects assessment of alachlor (USEPA, 2006a). The Agency identified a 
change in this assessment that could lead to a change in the MCLG. This 
assessment considered relevant studies on the toxicity of alachlor 
including developmental and reproductive toxicity. For noncancer 
effects, the assessment confirmed the RfD of 0.01 mg/kg-day (milligrams 
per kilogram of body weight per day). The assessment also concluded 
that alachlor is likely to be a human carcinogen at high doses; not 
likely to be a human carcinogen at low doses, and that a linear dose-
response extrapolation is no longer appropriate. It established a 
health reference value of 0.005 mg/kg-day for the nonlinear cancer 
assessment (USEPA, 2006a). Since the health reference value of 0.005 
mg/kg-day is lower than the RfD of 0.01 mg/kg-day, the Agency used this 
value to calculate a possible MCLG. Based on the health reference value 
of 0.005 mg/kg-day, and assuming a 70-kg adult body weight and 2 liters 
water intake per day, the drinking water equivalent level (DWEL) could 
be 0.2 mg/L. A relative source contribution (RSC) of 20 percent results

[[Page 15521]]

in a possible MCLG of 0.04 mg/L (USEPA, 2009b).
    Since the health review for alachlor indicates that the MCLG could 
possibly increase to 0.04 mg/L (from its current MCLG of zero) and 
because the current MCL is based on a PQL of 0.002 mg/L, neither 
analytical nor treatment feasibility would be a limiting factor for a 
possible higher level of 0.04 mg/L.
    EPA evaluated the results of the occurrence and exposure analyses 
for alachlor to determine whether a revised MCLG/MCL would be likely to 
result in a meaningful opportunity for cost savings to PWSs and their 
customers while maintaining or improving the level of public health 
protection (USEPA, 2009f). Review of health information for alachlor 
indicated that the MCLG could be increased to 0.04 mg/L from its 
current MCLG of zero. Consequently, the MCL of alachlor possibly can 
also increase to 0.04 mg/L. Although the Agency obtained and evaluated 
the finished water occurrence data for alachlor, its usefulness is 
limited for determining potential cost savings to PWSs and their 
customers because the Agency does not know which systems are treating 
for this contaminant. As an alternative, the Agency evaluated available 
data on source water quality and conducted a qualitative assessment of 
treatment cost savings.
    Table VI-2 provides summary data for contaminant occurrence based 
on maximum sample values for the locations included in the STORET and 
NAWQA data. Although the degree to which these occurrence rates 
represent national drinking water source occurrence is uncertain, the 
information shows no to low occurrence at threshold levels of interest. 
This information indicates that any resulting NPDWR change would affect 
systems that rely on source water at less than 0.4 percent of the NAWQA 
locations and less than 1.8 percent of the STORET locations.

   Table VI-2--Ambient Water Quality Monitoring Occurrence Summary for
                                Alachlor
------------------------------------------------------------------------
                                   Number of locations (% of locations)
     Maximum concentration      ----------------------------------------
                                    STORET \1\           NAWQA \2\
------------------------------------------------------------------------
Total..........................  2,252 (100.0%)..  9,236 (100.0%)
Nondetect......................  1,669 (74.1%)...  8,571 (92.8%)
Detected.......................  583 (25.9%).....  665 (7.2%)
Exceeds current MCL of 0.002 mg/ 40 (1.8%).......  35 (0.38%)
 L.
Exceeds alternative value of     0 (0.0%)........  1 (0.01%)
 0.04 mg/L.
------------------------------------------------------------------------
\1\ STORET database 2002-2006.
\2\ NAWQA database 1992-2008.
Source: USEPA, 2009d.

    The BATs and small system compliance technologies for alachlor have 
other beneficial effects, e.g., reduction of other co-occurring 
contaminants, precursors for disinfection byproducts (DBPs) or other 
common impurities. Therefore, if EPA were to consider a higher level, 
the Agency does not know how many PWSs that are currently treating to 
comply with the existing MCL of 0.002 mg/L would be likely to 
discontinue treatment that is already in place (USEPA, 2009d). Also, 
the Agency does not know to what extent affected systems might be able 
to reduce costs given that capital costs are not recoverable. However, 
the Agency recognizes that there may be opportunities to achieve 
operational cost savings if these systems are able to re-optimize 
current treatment.
    Given these considerations, the Agency believes that any resulting 
revision is not likely to provide a meaningful opportunity for cost 
savings. In view of this, any revision would be a low priority activity 
and not appropriate at this time.
    The Agency notes that alachlor and two of its unregulated acid 
degradates (alachlor ethanesulfonic acid or ESA and alachlor oxanilic 
acid or OA\11\) are currently listed on the second Unregulated 
Contaminants Monitoring Rule (UCMR 2) (72 FR 367, January 4, 2007 
(USEPA, 2007e)). The Agency also listed alachlor ESA and OA on the CCL3 
(74 FR 51850, October 8, 2009 (USEPA, 2009l)). Once the UCMR 2 
monitoring results are available for alachlor and its degradates, the 
Agency will be able to more fully evaluate alachlor along with its 
degradates in determining how this information might impact the current 
regulation for alachlor and/or the need for any revised or new 
regulation to capture the impact from the ESA and OA degradates.
---------------------------------------------------------------------------

    \11\ Between 2004 and 2006, the United States Department 
Agriculture's Pesticide Data Program (USDA PDP) collected data for 
alachlor and its ESA and OA degradates from finished and untreated 
water samples for a limited number of water systems (USDA, 2004, 
2005, and 2006). While alachlor was rarely detected (i.e., 0 to 0.8 
percent of the samples by year), the alachlor ESA and OA degradates 
were commonly detected (i.e., 19 to 51 percent of the samples by 
year for the ESA degradate and 7 to 40 percent of the samples by 
year for the OA degradate). The detected values for the ESA and OA 
degradates ranged from 0.0028 to 0.357 [mu]g/L and 0.001 to 0.102 
[mu]g/L, respectively. The detected values for alachlor ranged from 
0.0163 to 0.043 [mu]g/L.
---------------------------------------------------------------------------

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. Although there are new data that support 
consideration of whether to revise the MCLG/MCL for alachlor, EPA does 
not believe a revision to the NPDWR for alachlor is appropriate at this 
time. In making this decision, the Agency considered whether any 
possible revision to the NPDWR for alachlor is likely to provide a 
meaningful opportunity for cost savings to public water systems and 
their customers. Taking into consideration the low occurrence of this 
contaminant in source waters, EPA has decided that any revision to the 
NPDWR would be a low priority activity for the Agency, and, thus, is 
not appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
    In addition, the Agency considers it premature to make any decision 
to revise the alachlor NPDWR pending the final UCMR 2 monitoring 
results.
3. Alpha Particle Emitters
    a. Background. EPA published an interim NPDWR and set an MCL of 15 
pCi/L for gross alpha particle activity on July 9, 1976 (41 FR 28402 
(USEPA, 1976)). As noted in the August 14, 1975 proposal (40 FR 34324 
(USEPA, 1975))

[[Page 15522]]

and a subsequent September 30, 1986 FR notice (51 FR 34836 (USEPA, 
1986a), EPA considered the feasibility of treatment techniques, 
analytical methods and monitoring when establishing the MCL of 15 pCi/
L. EPA also considered the risks associated with other alpha particle 
emitters relative to radium-226, which generally fell within the 
Agency's acceptable risk range of 10-4 to 10-6 at 
the MCL of 15 pCi/L. On December 7, 2000 (65 FR 76708 (USEPA, 2000c)), 
EPA established an MCLG of zero based on a cancer classification of A 
(known human carcinogen) and finalized the NPDWR by retaining the MCL 
of 15 pCi/L. EPA noted in the December 7, 2000, FR notice that new risk 
estimates from Federal Guidance Report 13 reaffirmed that the 15 pCi/L 
gross alpha particle MCL (including radium 226 but excluding uranium 
and radon) was appropriate and protective.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to alpha particle emitters. The 
revised health effects assessment will consider relevant studies on the 
toxicity of alpha particle emitters, including its potential 
developmental and reproductive toxicity. The new health effects 
assessment was not completed by March 1, 2009, the review cutoff date 
for this notice (USEPA, 2009b).
    Although there is an ongoing health effects assessment, the MCLG is 
zero and the current MCL is higher than the MCLG. Therefore, EPA 
reviewed whether there is potential to revise the MCL based on new 
information regarding analytical and treatment feasibility for gross 
alpha particles. EPA promulgated a detection limit of 3 pCi/L in 1976 
(41 FR 28402 (USEPA, 1976)) and retained the use of a detection limit 
as the required measure of sensitivity for radiochemical analysis in 
lieu of an MDL or PQL in the final rule (65 FR 76708 (USEPA, 2000c)). 
EPA did not identify new analytical methods during the current review 
that would feasibly lower the detection limit. In addition, since the 
December 7, 2000, regulation, there is no new information regarding 
treatment feasibility. Since there is no new information regarding 
analytical or treatment feasibility that suggests changes to the MCL, 
EPA does not believe it is necessary to conduct an occurrence analysis 
at this time.
    c. Review Result. The Agency does not believe a revision to the 
NPDWR for gross alpha particles is appropriate at this time because a 
reassessment of the health risks resulting from exposure to alpha 
particles is in progress (USEPA, 2009b). Furthermore, there is no new 
information regarding analytical or treatment feasibility that would 
warrant reconsideration of the MCL.
4. 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 a reference dose of 0.0004 
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 health 
effects assessment will consider relevant studies on the toxicity of 
antimony, including its potential developmental and reproductive 
toxicity. The Agency does not expect the new health effects assessment 
to be completed in the time frame of the current Six-Year Review cycle 
(USEPA, 2009b). On December 21, 2007 (72 FR 72715 (USEPA, 2007c)), the 
Agency noted that the health effects assessment for antimony is in 
process.
    c. Review Result. Since the MCL for antimony is set at its MCLG and 
a reassessment of the health risks resulting from exposure to antimony 
is in progress, the Agency does not believe a revision to the NPDWR is 
appropriate at this time.
5. Arsenic
    a. Background. EPA published the current NPDWR for arsenic on 
January 22, 2001 (66 FR 6976 (USEPA, 2001c)). The NPDWR established an 
MCLG of zero based on a cancer classification of A, known human 
carcinogen. The NPDWR also established an MCL of 0.010 mg/L, which is 
higher than the feasible analytical level of 0.003 mg/L. EPA exercised 
its discretionary authority to set an MCL at a level higher than 
feasible (SDWA Section 1412(b)(6)), based on the finding that a final 
MCL of 0.010 mg/L represents the level that best maximizes health risk 
reduction benefits at a cost that is justified by the benefits (66 FR 
6976 at 7020 (USEPA, 2001c)).
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to arsenic. In June 2007, EPA's 
Science Advisory Board (SAB) issued its evaluation of the Agency's 2005 
draft toxicological review for inorganic arsenic (USEPA, 2007a). In its 
2007 report, SAB supports the continued use of a linear cancer risk 
model for inorganic arsenic, noting that the available data do not 
describe the shape of the dose-response curve at low doses. The new 
health effects assessment (both cancer and noncancer) were not 
completed by March 1, 2009, the review cutoff date for this notice. The 
revised health effects assessments will consider relevant studies on 
the toxicity of arsenic, including its potential developmental and 
reproductive toxicity. The IRIS Substance Assessment Tracking System 
Web site (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-
date information on the status of the health effects assessments.
    c. Review Result. The Agency does not believe a revision to the 
NPDWR for arsenic is appropriate at this time because a reassessment of 
the health risks resulting from exposure to arsenic is ongoing (USEPA, 
2009b). As noted previously, the arsenic MCL is based on the SDWA cost 
benefit provision (Section 1412(b)(6)) and the health effects 
assessment is important for reviewing the benefits associated with the 
basis of the MCL.
6. Asbestos
    a. Background. EPA published the current NPDWR for asbestos on 
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an 
MCLG and an MCL of 7 million fibers/L. EPA evaluated asbestos as a 
Category II \12\ contaminant (equivalent to Group C, possible human 
carcinogen) by the oral route of exposure.
---------------------------------------------------------------------------

    \12\ 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 revised health 
effects assessment will consider relevant studies on the toxicity of 
asbestos, including its potential developmental and reproductive 
toxicity. The Agency does not expect the new health effects assessment 
to be completed in the time frame of the current Six-Year Review cycle 
(USEPA, 2009b). The IRIS Substance Assessment Tracking System Web site 
(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 
information on the status of the health effects assessment.
    c. Review Result. Since the MCL for asbestos is set at its MCLG and 
a reassessment of the health risks resulting from exposure to asbestos 
is in

[[Page 15523]]

progress, the Agency does not believe a revision to the NPDWR is 
appropriate at this time.
7. Atrazine
    a. Background. EPA published the current NPDWR for atrazine on 
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an 
MCLG and an MCL of 0.003 mg/L. EPA based the MCLG on a reference dose 
of 0.005 mg/kg-day and a cancer classification of C, possible human 
carcinogen.
    b. Technical Reviews. In 2006, the Agency finalized a health 
effects assessment for the reregistration of atrazine as a pesticide 
(USEPA, 2006c). This assessment examined an extensive toxicology 
database and included investigation of atrazine's neuroendocrine mode 
of action and related reproductive and developmental effects. The 
assessment established a new RfD of 0.018 mg/kg-day, based on 
attenuation of pre-ovulatory luteinizing hormone (LH) surge, a key 
event indicative of hypothalamic function disruption. In accordance 
with the 1999 Interim Guidelines for Carcinogen Risk Assessment, EPA's 
Cancer Assessment Review Committee (CARC) classified atrazine as ``not 
likely to be carcinogenic to humans'' because the tumor response in the 
Sprague-Dawley rats was determined to be a strain specific mechanism 
which is not relevant to humans.
    c. Review Result. The Agency believes it is not appropriate to 
consider revisions to the NPDWR for atrazine at this time and has place 
atrazine in the emerging information/data gap category because of an 
impending re-evaluation of the Agency's risk assessment for atrazine. 
On October 7, 2009,\13\ the Agency announced its intent to launch a 
comprehensive new evaluation of the atrazine to determine its effects 
on humans. At the end of this process, the Agency will decide whether 
to revise its current risk assessment for atrazine and whether new 
restrictions are necessary to better protect public health. EPA will 
evaluate the pesticide's potential cancer and non-cancer effects on 
humans. Included in this new evaluation will be the most recent studies 
on atrazine and its potential association with birth defects, low birth 
weight, and premature births. Our examination of atrazine will be based 
on transparency and sound science, including independent scientific 
peer review and will help determine whether a change in EPA's 
regulatory position on this pesticide is appropriate.
---------------------------------------------------------------------------

    \13\ Additional information is available at http://www.epa.gov/pesticides/reregistration/atrazine/atrazine_update.htm.
---------------------------------------------------------------------------

8. Barium
    a. Background. EPA published the current NPDWR for barium on July 
1, 1991 (56 FR 30266 (USEPA, 1991b)). The NPDWR established an MCLG and 
an MCL of 2 mg/L. EPA based the MCLG on a reference dose of 0.07 mg/kg-
day and a cancer classification of D, not classifiable as to human 
carcinogenicity via the oral route.
    b. Technical Reviews. In 2005, the Agency updated the health 
effects assessment of barium and revised the RfD from 0.07 mg/kg-day to 
0.2 mg/kg-day (USEPA, 2005a). The change in the RfD could lead to a 
change in the MCLG. This assessment considered relevant studies on the 
toxicity of barium including developmental and reproductive toxicity. 
The assessment concluded that barium is not likely to be carcinogenic 
to humans (USEPA, 2005a). Based on the new IRIS assessment and RfD of 
0.2 mg/kg-day, and assuming 70 kg body weight and 2 liters water intake 
per day, the DWEL could be 7.0 mg/L. An RSC of 80 percent \14\ results 
in a possible MCLG of 6.0 mg/L.
---------------------------------------------------------------------------

    \14\ The present MCLG for barium does not include an RSC because 
the dose used in the calculation applied to only the dose from the 
drinking water. If a new MCLG were to be developed from the animal 
data that support the 2005 IRIS RfD, an RSC would be required. 
Regulations or guidelines pertaining to barium from media other than 
water were not identified. Barium metaborate is a registered 
pesticide but it does not have any food uses and does not have a 
human health ambient water quality guideline value. EPA used the 
subtraction calculation method to determine the possible RSC of 80 
percent for drinking water (the ceiling on RSC specified by the 
methodology).
---------------------------------------------------------------------------

    Analytical feasibility does not pose any limitations for the 
current MCL and would not be a limiting factor if EPA were to raise the 
MCLG. EPA evaluated the results of the occurrence and exposure analyses 
for barium to determine whether a revised MCLG/MCL would be likely to 
result in a meaningful opportunity to achieve cost savings for PWSs and 
their customers while maintaining, or improving, the level of public 
health protection (USEPA, 2009f). Although the Agency obtained and 
evaluated the finished water occurrence data for barium, its usefulness 
is limited for determining potential cost savings to PWSs and their 
customers because the Agency does not know which systems are treating 
for this contaminant. As an alternative, the Agency evaluated available 
data on source water quality and conducted a qualitative assessment of 
treatment cost savings.
    Table VI-3 provides summary data for contaminant occurrence based 
on maximum sample values for the locations included in the STORET and 
NAWQA data. Although the degree to which these occurrence rates 
represent national drinking water source occurrence is uncertain, the 
information shows no to low occurrence at threshold levels of interest. 
This information indicates that any resulting NPDWR change would affect 
systems that rely on source water at less than 0.1 percent of the NAWQA 
locations and less than 1.4 percent of the STORET locations.

   Table VI-3--Ambient Water Quality Monitoring Occurrence Summary for
                                 Barium
------------------------------------------------------------------------
                                   Number of locations (% of locations)
     Maximum concentration      ----------------------------------------
                                    STORET \1\           NAWQA \2\
------------------------------------------------------------------------
Total..........................  16,595 (100.0%).  4,864 (100.0%)
Nondetect......................  2,299 (13.9%)...  43 (0.9%)
Detected.......................  14,296 (86.1%)..  4,821 (99.1%)
Exceeds current MCL/MCLG of 2.0  234 (1.4%)......  3 (0.1%)
 mg/L.
Exceeds alternative value of     163 (1.0%)......  0 (0.0%)
 6.0 mg/L.
------------------------------------------------------------------------
\1\ STORET database 2002-2006.
\2\ NAWQA database 1992-2008.
Source: USEPA, 2009d.


[[Page 15524]]

    The BATs and small system compliance technologies for barium have 
other beneficial effects, e.g., reduction of other co-occurring 
contaminants or other common impurities. Therefore, if EPA were to 
consider a higher level, the Agency does not know how many PWSs that 
are currently treating to comply with the existing MCL of 2 mg/L would 
be likely to discontinue treatment that is already in place (USEPA, 
2009d). Also, the Agency does not know to what extent affected systems 
might be able to reduce costs given that capital costs are not 
recoverable. However, the Agency recognizes that there may be 
opportunities to achieve operational cost savings if these systems are 
able to re-optimize current treatment.
    Given these considerations, the Agency believes that any resulting 
revision is not likely to provide a meaningful opportunity for cost 
savings. In view of this, any revision would be a low priority activity 
and not appropriate at this time.
    c. Review Result. Although there are new data that support 
consideration of whether to revise the MCLG/MCL for barium, EPA does 
not believe a revision to the NPDWR for barium is appropriate at this 
time. In making this decision, the Agency considered whether any 
possible revision to the NPDWR for barium is likely to provide a 
meaningful opportunity for cost savings to public water systems and 
their customers. Taking into consideration the low occurrence of this 
contaminant in source waters, EPA has decided that any revision to the 
NPDWR would be a low priority activity for the Agency, and, thus, is 
not appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
9. 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. In 2000 and 2003, the Agency updated the IRIS 
assessment of benzene. The cancer assessment was completed first and 
characterized benzene as a known human carcinogen by all routes of 
exposure; the one-in-a million risk estimates for cancer by the oral 
route of exposure ranged from 1 [mu]g/L to 10 [mu]g/L (USEPA, 2000b). 
This cancer assessment was also noted in the first Six-Year Review (67 
FR 19030, April 17, 2002 (USEPA, 2002c)). As part of the Six-Year 
Review process, the Agency's Office of Water (OW) conducted a 
literature search through June 2007 for relevant data on the 
carcinogenicity of benzene as well as its potential developmental and 
reproductive toxicity (USEPA, 2009b). While the literature search did 
identify several new studies that evaluated the cancer and noncancer 
effects of benzene, none of the new studies would affect the cancer 
classification, which serves as the basis for the MCLG of zero. A 
recent occupational study (Lan et al., 2004) of the noncancer effects 
of benzene identified hematological effects in workers at levels below 
those previously reported. The Agency for Toxic Substances and Disease 
Registry (ATSDR) (2007) chronic minimum risk level based on the Lan et 
al. (2004) data of 0.0005 mg/kg/day is lower than the IRIS RfD of 0.004 
mg/kg/day. If the ATSDR minimum risk level were used as the basis for a 
noncancer health reference level, the value would be 0.004 mg/l, a 
value that is slightly below the current MCL. Because the MCLG remains 
at zero, the Agency believes that a further review of the health 
effects of benzene is not warranted at this time.
    The current MCL for benzene is based on a PQL of 0.005 mg/L. For 
the Six-Year Review, the Agency considered whether changes in the 
analytical feasibility of benzene might lead to a lower MCL. EPA 
reviewed PE data from the first Six-Year Review cycle and then analyzed 
more recent PT data to determine if the PQL can be revised (i.e., 
analytical feasibility). Passing rates for PE data available through 
late 1999 for benzene are above 95 percent around the current PQL of 
0.005 mg/L, including two studies with true values below the current 
PQL. All passing rates in the PE data exceeded 75 percent. More recent 
PT data from late 1999 through 2004, supplied by a PT provider, also 
show greater than 90 percent passing rates for studies around the PQL, 
including eight with true values below the current PQL. Because most of 
the laboratory passing rates from PE and PT studies exceeded the 75 
percent criterion typically used to derive a PQL, a lowering of the PQL 
for benzene might be possible. These results, however, are insufficient 
to recalculate a revised PQL for benzene because not enough data points 
are available below the current PQL to derive a value at the 75 percent 
passing rate (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: Laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of benzene (Methods 502.2 and 524.2). While 
EPA prefers to use laboratory performance data to calculate the PQL, 
the MRL and MDL information can be valuable for this review to indicate 
whether it is possible to quantitate at levels below the current PQL. 
The Six-Year Review ICR dataset contains MRL values for 139,190 
samples. More than 80 percent of these values are less than or equal 
the modal MRL, 120,308 (86 percent) equal the modal MRL of 0.0005 mg/L, 
and an additional 17,964 (13 percent) are lower than 0.0005 mg/L. 
Therefore, EPA selected the modal MRL as the EQL (USEPA, 2009e). The 
MDLs of approved methods range from 0.00001 to 0.0004 mg/L. Applying a 
multiplier of 10 would give a possible PQL range from 0.0001 to 0.004 
mg/L, which contains the EQL (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of 
information, EPA believes that there is potential to lower the PQL for 
benzene. To determine whether any MCL revision is likely to provide a 
meaningful opportunity to improve public health protection, EPA 
evaluated the occurrence of benzene at the EQL of 0.0005 mg/L and 
additional thresholds of 0.001, and 0.0025 mg/L (USEPA, 2009f). Table 
VI-4 shows the results of the occurrence and exposure analysis for the 
current MCL and these thresholds. The Six-Year Review ICR occurrence 
data have a modal MRL of 0.0005 mg/L, which limits reliable contaminant 
detection to 0.0005 mg/L. As indicated, average concentrations exceed 
the current MCL for 10 of 50,435 systems (0.020 percent) serving 14,000 
people (or 0.006 percent of 227 million people). Note that these 
results are based on the subset of monitoring data provided in response 
to the Six-Year Review ICR and do not necessarily reflect MCL 
violations, which are based on annual average concentrations at entry 
points; Safe Drinking Water Information System/Federal version (SDWIS/
FED) indicates 41 MCL violations for benzene between 1998 and 2005, 
with annual violations ranging from 1 to 12 (USEPA, 2007g). The 
occurrence and exposure analysis shows that average concentrations at 
95 to 123 of 50,435 systems (0.188 to 0.244 percent), serving 304,000 
to 485,000 people (or 0.134 to 0.214 percent of 227

[[Page 15525]]

million people), exceed the EQL of 0.0005 mg/L.

       Table VI-4--Number and Percent of Systems With Mean Concentrations Exceeding Benzene Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                       feasibility-based threshold  (Percentages based on 50,435 systems with
 Regulatory or feasibility-based            benzene data in the  Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                    Nondetect values =  MRL    Nondetect values =  \1/    Nondetect values =  0
                                              \1\                    2\ MRL \2\                    \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  10 (0.020%)..............  10 (0.020%).............  10 (0.020%)
\1/2\ MCL (0.0025 mg/L)..........  16 (0.032%)..............  14 (0.028%).............  14 (0.028%)
2xEQL (0.001 mg/L)...............  70 (0.139%)..............  58 (0.115%).............  52 (0.103%)
EQL (0.0005 mg/L)................  not applicable...........  123 (0.244%)............  95 (0.188%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (Percentages based on 226,947,000 people
                                         served by the systems with benzene data in the Six-Year Review ICR
                                                                 occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based       Nondetect values =        Nondetect values =        Nondetect values =
            threshold              MRL \1\..................  \1/2\ MRL \2\...........  0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  14,000 (0.006%)..........  14,000 (0.006%).........  14,000 (0.006%)
\1/2\ MCL (0.0025 mg/L)..........  111,000 (0.049%).........  110,000 (0.048%)........  110,000 (0.048%)
2xEQL (0.001 mg/L)...............  180,000 (0.079%).........  159,000 (0.070%)........  158,000 (0.070%)
EQL (0.0005 mg/L)................  not applicable...........  485,000 (0.214%)........  304,000 (0.134%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
  Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the
  results equal to this value results in an upwardly biased estimate of the number of systems with mean
  concentrations that exceed this value.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. 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 occurrence and exposure analysis based on 
possible changes in analytical feasibility indicates that any revision 
to the MCL is unlikely to provide a meaningful opportunity to improve 
public health protection. Taking into consideration the low occurrence 
of this contaminant, EPA has decided that any revision to the NPDWR 
would be a low priority activity for the Agency, and, thus, is not 
appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
10. 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 feasibility.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to benzo(a)pyrene. The revised 
health effects assessment will consider relevant studies on the 
toxicity of benzo(a)pyrene, including its potential developmental and 
reproductive toxicity. The new health effects assessment was not 
completed by March 1, 2009, the review cutoff date for this notice 
(USEPA, 2009b). The IRIS Substance Assessment Tracking System Web site 
(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 
information on the status of the health effects assessment.
    Although a risk assessment is in process for benzo(a)pyrene, the 
existing MCLG is zero and the current MCL of 0.0002 mg/L is based on 
the PQL. Therefore, EPA reviewed whether there is potential to revise 
the PQL. EPA reviewed PE data from the first Six-Year Review cycle and 
then analyzed more recent PT data to determine if the PQL can be 
revised (i.e., analytical feasibility). Passing rates for PE data 
available through late 1999 for benzo(a)pyrene are all above 75 
percent. However, the true concentrations were all higher than the 
current PQL of 0.0002 mg/L. More recent PT data from late 1999 through 
2004, supplied by a PT provider, show several true concentrations with 
passing rates less than the 75 percent criterion typically used to 
derive a PQL. All of the true concentrations in the PT data were higher 
than the current PQL. Given the variability in passing rates and the 
lack of data points below the current PQL, a lowering of the PQL for 
benzo(a)pyrene is not appropriate at this time (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of benzo(a)pyrene (Methods 550, 550.1, and 
525.2). While EPA prefers to use laboratory performance data to 
calculate the PQL, the MRL and MDL information can be valuable for this 
review to indicate whether it is possible to quantitate at levels below 
the current PQL. The Six-Year Review ICR dataset contains MRL values 
for 55,487 samples. Fewer than 80 percent of these values are less than 
or equal the modal MRL, 29,769 (54 percent) equal the modal MRL of 
0.00002 mg/L and an additional 970 (2 percent) are lower

[[Page 15526]]

than 0.00002 mg/L. Therefore, EPA did not set the EQL equal to the 
modal MRL (USEPA, 2009e). The MDLs of approved methods are 0.000016, 
0.000029, and 0.00023 mg/L. EPA selected the median value, applied a 
multiplier of 10, and rounded up to 0.0003 mg/L. The result is higher 
than the current PQL and, therefore, EPA did not estimate an EQL 
(USEPA, 2009e). Based on these varied and unrelated approaches/sources 
of information, EPA believes that there is no potential to lower the 
PQL for benzo(a)pyrene. Since the MCL is constrained by the PQL, and 
the PQL is unchanged, EPA does not believe it is necessary to conduct 
an occurrence analysis at this time.
    c. Review Result. 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 in progress (USEPA, 2009b). Furthermore, a review of 
analytical feasibility did not identify a potential to revise the MCL, 
which is limited by feasibility.
11. 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 to the RfD of 0.005 mg/kg-day (57 FR 31776 at 
31785, July 17, 1992 (USEPA, 1992)).
    b. Technical Reviews. As noted in Six Year Review 1 (68 FR 42908, 
USEPA, 2003e), EPA updated its assessment of the health risks resulting 
from exposure to beryllium in 1998 (USEPA, 1998c). The 1998 IRIS 
assessment uses the 1986 EPA cancer guidelines (USEPA, 1986b) and 
classifies beryllium as Group B1, probable human carcinogen, via 
inhalation route. However, the 1998 IRIS assessment states that the 
database is inadequate for assessing the carcinogenicity of ingested 
beryllium and concluded that the human carcinogenic potential of 
ingested beryllium cannot be determined. The Agency considered the 1998 
assessessment in Six Year Review 1 and decided that it was not 
appropriate to revise the NPDWR at that time. EPA has initiated a 
reassessment of the health risks resulting from exposure to beryllium. 
The new assessment was not completed by March 1, 2009, the review 
cutoff date for this notice (USEPA, 2009b). The IRIS Substance 
Assessment Tracking System Web site (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information on the status of the 
health effects assessment.
    c. Review Result. Since the MCL for beryllium is set at its MCLG 
and a reassessment of the health risks resulting from exposure to 
beryllium is in progress, the Agency does not believe a revision to the 
NPDWR is appropriate at this time.
12. Beta Particle and Photon Emitters
    a. Background. EPA published an interim NPDWR and set an MCL of 4 
millirems/yr (mrem/yr) for beta particle and photon emitters on July 9, 
1976 (41 FR 28402 (USEPA, 1976)). As noted in the August 14, 1975 
proposal (40 FR 34324 (USEPA, 1975)) and a subsequent September 30, 
1986 FR (51 FR 34836 (USEPA, 1986a) advanced notice of proposed 
rulemaking, EPA considered the feasibility of treatment techniques, 
analytical methods and monitoring when establishing the MCL of 4 mrem/
yr. EPA also considered the risks associated with beta particle and 
photon emitters, which generally fell within the Agency's acceptable 
risk range of 10-4 to 10-6 at the MCL of 4 mrem/
yr. On December 7, 2000 (65 FR 76708 (USEPA, 2000c)), EPA established 
an MCLG of zero based on a cancer classification of A (known human 
carcinogen) and finalized the NPDWR by retaining the MCL of 4 mrem/yr. 
EPA noted in the December 7, 2000, FR notice that new risk estimates 
from Federal Guidance Report 13 reaffirmed that the 4 mrem/yr MCL was 
appropriate and protective\15\.
---------------------------------------------------------------------------

    \15\ After the December 7, 2000, final regulation, two trade 
associations and several municipal water systems challenged EPA's 
standard for the beta photon emitters by claiming that the Agency 
did not use the best available science when finalizing the standard. 
In February of 2003, the District of Columbia (DC) Circuit Court of 
Appeals upheld EPA's regulation for beta and photon emitters (as 
well as radium 226 and 228 and uranium). In July, 2004, the DC 
Circuit Court of Appeals also upheld the policy and scientific basis 
of EPA's application of the beta particle and photon (man-made) 
drinking water standards to the ground water protection standards 
used for Yucca Mountain under 40 CFR part 197 (66 FR 32073, June 13, 
2001 (USEPA, 2001d)).
---------------------------------------------------------------------------

    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to beta particles. The revised 
health effects assessment will consider relevant studies on the 
toxicity of beta particles, including its potential developmental and 
reproductive toxicity. The new health effects assessment was not 
completed by March 1, 2009, the review cutoff date for this notice 
(USEPA, 2009b).
    Although there is an ongoing health effects assessment, the MCLG is 
zero and the current MCL is higher than the MCLG. Therefore, EPA 
reviewed whether there is potential to revise the MCL based on new 
information available regarding the analytical and treatment 
feasibility for beta particle and photon emitters. EPA promulgated the 
MCL of 4 mrem/yr for man-made beta particle and photon emitters 
(present in any combination) in 1976 (41 FR 28402 (USEPA, 1976)) and 
retained the use of the detection limit as the required measure of 
sensitivity in the December 2000 final rule (65 FR 76708 (USEPA, 
2000c)). The original rule estimated a risk ceiling of 
5.6x10-5 for whole body doses. Limits were set in picoCurie 
units for each nuclide equivalent to a 4 mrem dose. The newer dosimetry 
found in Federal Guidance13 and reported in the December 2000 final 
rule reveals more exact risks that are still within the Agency's 
acceptable limits. While individual dose estimates changed over time, 
the overall limit of 4 mrem was retained along with a two-tiered 
screening level to avoid analyzing each possible nuclide below the 
screen, and still be protective. EPA did not identify new analytical 
methods during the current review that would feasibly lower the 
detection limits for beta particle and photon emitters. In addition, 
since the December 7, 2000 regulation, there is no new information 
regarding treatment feasibility. Since there is no new information 
regarding analytical or treatment feasibility that suggests changes to 
the MCL, EPA does not believe it is necessary to conduct an occurrence 
analysis at this time.
    c. Review Result. The Agency does not believe a revision to the 
NPDWR for beta particles is appropriate at this time because a 
reassessment of the health risks resulting from exposure to beta 
particles is in progress (USEPA, 2009b). Furthermore, there is no new 
information regarding analytical or treatment feasibility that would 
warrant reconsideration of the MCL.
13. Cadmium
    a. Background. EPA published the current NPDWR for cadmium on 
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). 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

[[Page 15527]]

exposure, the Agency classified 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 health 
effects assessment will consider relevant studies on the toxicity of 
cadmium, including its potential developmental and reproductive 
toxicity. The new health effects assessment was not completed by March 
1, 2009, the review cutoff date for this notice (USEPA, 2009b). The 
IRIS Substance Assessment Tracking System Web site (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information 
on the status of the health effects assessment.
    c. Review Result. Since the MCL for cadmium is set at its MCLG and 
a reassessment of the health risks resulting from exposure to cadmium 
is in progress, the Agency does not believe a revision to the NPDWR is 
appropriate at this time.
14. Carbofuran
    a. Background. EPA published the current NPDWR for carbofuran on 
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an 
MCLG and an MCL of 0.04 mg/L. EPA based the MCLG on a reference dose of 
0.005 mg/kg-day and a cancer classification of E, evidence of non-
carcinogenicity for humans.
    b. Technical Reviews. In 2006, the Agency updated health effects 
assessment of carbofuran. The Agency identified a change in this 
assessment that could lead to a change in the MCLG (73 FR 44864, July 
31, 2008 (USEPA, 2008a)). This assessment considered relevant studies 
on the toxicity of carbofuran including developmental and reproductive 
toxicity. The assessment revised the RfD from 0.005 mg/kg-day to an 
acute RfD of 0.00006 mg/kg-day and concluded that carbofuran is not 
likely to be carcinogenic to humans (USEPA, 2006d). Based on the 
revised acute RfD of 0.00006 mg/kg-day, and assuming 10 kg body weight 
and 1 liter water intake per day for a child, the resulting DWEL would 
be 0.0006 mg/L. Using an RSC of 20 percent, a possible new MCLG would 
be 0.00012 mg/L. The default RSC value of 20 percent was selected 
because of the significant exposures resulting from actual food dietary 
exposure for children from 1 to 6 years old, which approaches 100 
percent of the updated RfD (USEPA, 2006d).
    Two recent Agency actions may affect carbofuran presence in food 
and water sources. In May 2009, EPA revoked all tolerances (maximum 
residue limits) for carbofuran, which could prohibit all carbofuran 
residues on food, effective December 31, 2009 (74 FR 23046, May 15, 
2009 (USEPA, 2009i)). The registrant and interested parties raised 
objections and requested a hearing on the tolerance revocations. EPA 
has reviewed the submissions and determined that a hearing was not 
warranted. Revoking carbofuran tolerances is part of a broader series 
of Agency actions to cancel all uses of carbofuran in the United States 
due to dietary, occupational, and ecological risks of concern. 
Following resolution of the current ongoing administrative process for 
resolving the safety of the tolerances, EPA will proceed to cancel the 
remaining uses of carbofuran.
    In addition, prior to the tolerance revocation, the registrant, FMC 
Corporation, voluntarily cancelled 22 uses of carbofuran (74 FR 11551, 
March 18, 2009 (USEPA, 2009j)). Existing stocks of carbofuran can be 
applied to food crops until December 31, 2009, and to non-food crops 
according to the label until supplies are depleted. These decisions are 
expected to reduce exposure to carbofuran and its metabolite (3-
hydroxycarbofuran) in food products and in water, which would affect 
the RSC used to derive a possible MCLG. Therefore, EPA believes that it 
should factor in the effect of these actions, once completed, before 
the Agency determines the potential for an NPDWR revision.
    The occurrence of carbofuran in drinking water is an additional 
source of uncertainty in the review process that is compounded by the 
recent voluntary cancellations and tolerance revocations. The Six-Year 
Review ICR occurrence data are based on the Standardized Monitoring 
Framework for synthetic organic compounds, which is designed to 
evaluate long-term exposure to contaminants with chronic exposure 
health endpoints. As a result, short-term seasonal peaks, which 
correspond to carbofuran application as a pesticide, cannot be readily 
detected in this dataset. The cancellation will reduce carbofuran 
application and the potential for seasonal peaks to occur. Reductions 
in overall carbofuran use is expected to reduce the potential 
occurrence of carbofuran in drinking water sources.
    c. Review Result. Although there are new health data that support 
consideration of whether to revise the MCLG/MCL for carbofuran, the 
ongoing regulatory actions could affect the possible MCLG. Therefore, 
EPA is placing carbofuran in the information gap category due to the 
uncertainty of how the cancellation impacts the MCLG. In addition, EPA 
notes that the decision to cancel the reregistration of carbofuran 
would reduce the presence of this compound in the environment and the 
likelihood of exposure to carbofuran in food and drinking water 
sources. Consequently, EPA believes it is not appropriate to consider 
any revisions to the NPDWR for carbofuran at this time.
15. Carbon Tetrachloride
    a. Background. EPA published the current NPDWR 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 health effects assessment will consider relevant studies on the 
toxicity of carbon tetrachloride, including its potential developmental 
and reproductive toxicity. The new health effects assessment was not 
completed by March 1, 2009, the review cutoff date for this notice 
(USEPA, 2009b). The IRIS Substance Assessment Tracking System Web site 
(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 
information on the status of the health effects assessment.
    Although a risk assessment is in process for carbon tetrachloride, 
the existing MCLG is zero and the current MCL of 0.005 mg/L is based on 
the PQL. Therefore, EPA reviewed whether there is potential to revise 
the PQL. EPA reviewed PE data from the first Six-Year Review cycle and 
then analyzed more recent PT data to determine if the PQL can be 
revised (i.e., analytical feasibility). Passing rates for PE data 
available through late 1999 for carbon tetrachloride are at or above 95 
percent around the current PQL of 0.005 mg/L, including one study with 
a true value below the current PQL. More recent PT data from late 1999 
through 2004, supplied by a PT provider, also show greater than 90 
percent passing rates for studies around the PQL, except for one study 
with a passing rate of 85 percent. Nine PT studies had true values 
below the current PQL. Because most of the laboratory passing rates 
from PE and PT studies exceeded the 75 percent criterion typically used 
to derive a PQL, a lowering of the PQL for carbon tetrachloride might 
be possible. These

[[Page 15528]]

results, however, are insufficient to recalculate a revised PQL for 
carbon tetrachloride because not enough data points are available below 
the current PQL to derive a value at the 75 percent passing rate 
(USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of carbon tetrachloride (Methods 502.2, 
524.2, and 551.1). While EPA prefers to use laboratory performance data 
to calculate the PQL, the MRL and MDL information can be valuable for 
this review to indicate whether it is possible to quantitate at levels 
below the current PQL. The Six-Year Review ICR dataset contains MRL 
values for 139,221 samples. More than 80 percent of these values are 
less than or equal the modal MRL: 119,849 (86 percent) equal the modal 
MRL of 0.0005 mg/L and an additional 16,195 (12 percent) are lower than 
0.0005 mg/L. Therefore, EPA selected the modal MRL as the EQL (USEPA, 
2009e). The MDLs of approved methods range from 0.000002 to 0.00021 mg/
L. Applying a multiplier of 10 would give a possible PQL range from 
0.00002 to 0.0021 mg/L, which contains the EQL (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of 
information, EPA believes that there is potential to lower the PQL for 
carbon tetrachloride. To determine whether any MCL revision is likely 
to provide a meaningful opportunity to improve public health 
protection, EPA evaluated the occurrence of carbon tetrachloride at the 
EQL of 0.0005 mg/L and additional thresholds of 0.001 and 0.0025 mg/L 
(USEPA, 2009f). Table VI-5 shows the results of the occurrence and 
exposure analysis for the current MCL and these thresholds. The 
occurrence and exposure analysis shows that average concentrations 
exceed the current MCL for five of 50,446 systems (0.010 percent), 
serving fewer than 2,000 people (or 0.001 percent of 227 million 
people). Note that these results are based on the subset of monitoring 
data provided in response to the Six-Year Review ICR and do not 
necessarily reflect MCL violations, which are based on annual average 
concentrations at entry points; SDWIS/FED indicates 19 MCL violations 
for carbon tetrachloride between 1998 and 2005 with annual violations 
ranging from 1 to 4 (USEPA, 2007g). Average concentrations for 84 to 
118 of 50,446 systems (0.167 to 0.234 percent), serving 368,000 to 
750,000 people (or 0.162 to 0.330 percent of 227 million people), 
exceed the EQL of 0.0005 mg/L.

Table VI-5--Number and Percent of Systems With Mean Concentrations Exceeding Carbon Tetrachloride Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean Concentrations that are greater than the regulatory or
                                    feasibility-based threshold (Percentages based on 50,446 systems with carbon
 Regulatory or feasibility-based         tetrachloride data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                                              Nondetect values = \1/2\
                                   Nondetect values = MRL\1\           MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  5 (0.010%)...............  5 (0.010%)..............  5 (0.010%)
\1/2\ MCL (0.0025 mg/L)..........  13 (0.026%)..............  12 (0.024%).............  12 (0.024%)
2xEQL (0.001 mg/L)...............  59 (0.117%)..............  50 (0.099%).............  40 (0.079%)
EQL (0.0005 mg/L)................  not applicable...........  118 (0.234%)............  84 (0.167%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (Percentages based on 226,935,000 people
                                     served by the systems with carbon tetrachloride data in the Six-Year Review
                                                               ICR occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based     Nondetect values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
            threshold                          \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  1,800 (0.001%)...........  1,700 (0.001%)..........  1,700 (0.001%)
\1/2\ MCL (0.0025 mg/L)..........  5,800 (0.003%)...........  5,500 (0.002%)..........  5,500 (0.002%)
2xEQL (0.001 mg/L)...............  265,000 (0.117%).........  212,000 (0.093%)........  190,000 (0.084%)
EQL (0.0005 mg/L)................  not applicable...........  750,000 (0.330%)........  368,000(0.162%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
  Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the
  results equal to this value results in an upwardly biased estimate of the number of systems with mean
  concentrations that exceed this value.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. 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 in progress (USEPA, 2009b). Furthermore, the 
occurrence and exposure analysis based on possible changes in 
analytical feasibility indicates that any revision to the MCL is 
unlikely to provide a meaningful opportunity to improve public health 
protection. After consideration of the low occurrence of this 
contaminant, EPA has decided that any revision to the NPDWR would be a 
low priority activity for the Agency, and, thus, is not appropriate to 
revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
16. Chlordane
    a. Background. EPA published the current NPDWR for chlordane on 
January 30, 1991 (56 FR 3526 (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 0.002 mg/L, based on 
analytical feasibility.

[[Page 15529]]

    b. Technical Reviews. As part of the Six-Year Review process, EPA 
conducted a literature search for relevant data on the carcinogenicity 
of chlordane as well as its potential developmental and reproductive 
toxicity. EPA has not identified any new information that indicates 
that it is appropriate to consider revisions to the cancer 
classification for chlordane at this time (USEPA, 2009b). Because the 
MCLG remains at zero, the Agency believes that a further review of the 
health effects of chlordane is not warranted at this time.
    The current MCL for chlordane is based on a PQL of 0.002 mg/L. For 
the Six-Year Review, the Agency considered whether changes in the 
analytical feasibility of chlordane might lead to a lower MCL. EPA 
reviewed PE data from the first Six-Year Review cycle and then analyzed 
more recent PT data to determine if the PQL can be revised (i.e., 
analytical feasibility). Passing rates for PE data available through 
late 1999 for chlordane are above 80 percent around the current PQL of 
0.002 mg/L, including three studies with true values below the current 
PQL. More recent PT data from late 1999 through 2004, supplied by a PT 
provider, also show greater than 80 percent passing rates, except for 
two studies with passing rates equal to or below 75 percent. There are 
no PT studies with true values below the PQL. Because most of the 
laboratory passing rates from PE and PT studies--including three below 
the PQL--exceeded the 75 percent criterion typically used to derive a 
PQL, a lowering of the PQL for chlordane might be possible. These 
results, however, are insufficient to recalculate a revised PQL for 
chlordane because not enough data points are available below the 
current PQL to derive a value at the 75 percent passing rate (USEPA, 
2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of chlordane (Methods 505 and 508). While EPA 
prefers to use laboratory performance data to calculate the PQL, the 
MRL and MDL information can be valuable for this review to indicate 
whether it is possible to quantitate at levels below the current PQL. 
The Six-Year Review ICR dataset contains MRL values for 57,506 samples. 
Fewer than 80 percent of these values are less than or equal the modal 
MRL: 26,893 (47 percent) equal the modal MRL of 0.0002 mg/L and an 
additional 9,764 (17 percent) are lower than 0.0002 mg/L. Therefore, 
EPA did not set the EQL equal to the modal MRL (USEPA, 2009e). The MDLs 
of approved methods are 0.0000041 and 0.00014 mg/L. Applying a 
multiplier of 10 would give possible PQLs of 0.000041 and 0.0014 mg/L. 
EPA took the mean of the two values and, rounded up to 0.001 mg/L for 
the EQL (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of 
information, EPA believes that there is potential to lower the PQL for 
chlordane. To determine whether any MCL revision is likely to provide a 
meaningful opportunity to improve public health protection, EPA 
evaluated the occurrence of chlordane at the EQL of 0.001 mg/L (USEPA, 
2009f). Table VI-6 shows the results of the occurrence and exposure 
analysis for the current MCL and an EQL. The occurrence and exposure 
analysis shows that average concentrations exceed the current MCL for 
one of 31,841 systems (0.003 percent) serving 80 people (or 0.00004 
percent of 182 million people). Note that these results are based on 
the subset of monitoring data provided in response to the Six-Year 
Review ICR do not necessarily reflect MCL violations, which are based 
on annual average concentrations at entry points; SDWIS/FED indicates 
no MCL violations for chlordane between 1998 and 2005 (USEPA, 2007g). 
Average concentrations at one to two of 31,841 systems (0.003 to 0.006 
percent), still serving approximately 80 to 120 people (or 0.00004 to 
0.00007 percent of 182 million people), exceed the EQL of 0.001 mg/L.

      Table VI-6--Number and Percent of Systems With Mean Concentrations Exceeding Chlordane Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                        Systems with mean concentrations that are greater than the regulatory or
                                         feasibility-based threshold (Percentages based on 31,841 systems with
   Regulatory or feasibility-based           chlordane data in the Six-Year Review ICR occurrence dataset)
              threshold               --------------------------------------------------------------------------
                                       Nondetect Values =  MRL  Nondetect Values =  \1/   Nondetect Values =  0
                                                 \1\                   2\ MRL \2\                  \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.002 mg/L).....................  1 (0.003%).............  1 (0.003%).............  1 (0.003%)
EQL (0.001 mg/L).....................  2 (0.006%).............  2 (0.006%).............  1 (0.003%)
----------------------------------------------------------------------------------------------------------------
                                        Corresponding population served (Percentages based on 182,037,000 people
                                          served by the systems with chlordane data in the Six-Year Review ICR
                                                                   occurrence dataset)
                                      --------------------------------------------------------------------------
   Regulatory or feasibility-based        Nondetect Values =       Nondetect Values =       Nondetect Values =
              threshold                MRL \1\................  \1/2\ MRL \2\..........  0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.002 mg/L).....................  80 (0.00004%)..........  80 (0.00004%)..........  80 (0.00004%)
EQL (0.001 mg/L).....................  120 (0.00007%).........  120 (0.00007%).........  80 (0.00004%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
\2\ Results are based on setting all nondetect results equal to 1/2 MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. 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 chlordane is 
appropriate at this time. The occurrence and exposure analysis based on 
possible changes in analytical feasibility indicates that any revision 
to the MCL is unlikely to provide a

[[Page 15530]]

meaningful opportunity to improve public health protection. Taking into 
consideration the low occurrence of this contaminant, EPA has decided 
that any revision to the NPDWR would be a low priority activity for the 
Agency, and, thus, is not appropriate to revise at this time because 
of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
17. Chromium
    a. Background. EPA published the current NPDWR for total chromium 
on January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established 
an MCLG and an MCL of 0.1 mg/L. Although the NPDWR regulates total 
chromium, the adverse health effects associated with hexavalent 
chromium (Cr VI) are the basis of the current MCLG because 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. EPA regulated chromium as a 
Group D carcinogen, not classifiable as to human carcinogenicity by the 
oral route of exposure.
    b. Technical Reviews. The health effects technical review 
identified some information regarding the carcinogenicity of chromium 
that may indicate the need to update the Agency's health effects 
assessment (USEPA, 2009b). In 1998, the Agency (USEPA, 1998d) updated 
the IRIS assessment for Cr VI, which revised the RfD from 0.0048 mg/kg-
day (rounded to 0.005) to 0.003 mg/kg-day. While both RfDs are based on 
the same one-year drinking water rat study (MacKenzie et al., 1958), 
the change in the RfD in 1998 was due to the following factors: (a) A 
slight change in the no-observed-adverse-effect level (NOAEL), (b) a 
modification to the original uncertainty factor, and (c) the addition 
of a modifying factor of three because of data on the potential for 
gastrointestinal effects in humans as a result of oral exposure. There 
is no current RfD for soluble trivalent chromium (soluble Cr III); the 
Cr III RfD of 1.5 mg/kg-day on IRIS (USEPA, 1998e) is for insoluble Cr 
III salts.
    In 2002 and as part of the first Six Year Review (67 FR 19030 
(USEPA, 2002c)), EPA noted that the National Toxicology Program (NTP) 
had agreed to study the chronic toxicity and carcinogenicity of oral 
exposure to Cr VI. The NTP study, conducted with sodium dichromate 
dehydrate (i.e., Cr VI) in rats and mice, is now available (NTP, 2008), 
as is a pre-peer review draft of a similar study with chromium 
picolinate (Cr III) (NTP, 2007). The Cr VI study found clear evidence 
of carcinogenic activity of sodium dichromate dihydrate in male and 
female F344 rats based on increased incidences of squamous cell 
neoplasms of the oral cavity, specifically the squamous epithelium that 
lines the oral mucosa and tongue (NTP, 2008). NTP also concluded that 
there was clear evidence of carcinogenic activity of sodium dichromate 
dihydrate in male and female B6C3F1 mice based on increased incidences 
of neoplasms in the small intestine (adenomas and/or carcinomas of the 
duodenum, jejunum, or ileum). The observed noncancer effects in the Cr 
VI study included histiocytic cellular infiltration in the liver, small 
intestine, and pancreatic and mesenteric lymph nodes of rats and mice, 
and diffuse epithelial hyperplasia in the small intestine of male and 
female mice. A peer-reviewed report for the study of chromium 
picolinate (Cr III) is not yet available. Zhang and Li (1987) evaluated 
the effects of human exposure to Cr VI in drinking water in Chinese 
villages. In a recent analysis of the human data originally reported in 
these Chinese villages, Sedman et al. (2006) further support a 
statistically significant increase in stomach cancer in the population 
exposed to Cr VI in their drinking water, thus suggesting a potential 
for carcinogenicity of Cr VI in drinking water.
    An assessment for chromium VI currently exists on IRIS but does not 
include an evaluation of carcinogenicity via oral ingestion. As a 
result, on December 21, 2007 (72 FR 72715 (USEPA, 2007c)), the Agency 
nominated and included Cr VI on its 2008 IRIS agenda. The Agency is 
currently working with California EPA, New Jersey Department of 
Environmental Protection, and the Centers for Disease Control ATSDR 
(since they have recently developed draft assessments for chromium VI) 
and has posted a schedule for completion and the most up-to-date 
information on the status of the health effects assessment on the IRIS 
Substance Assessment Tracking System Web site (http://cfpub.epa.gov/iristrac/index.cfm).
    A review of analytical or treatment feasibility is not necessary 
for total chromium because changes to the MCLG are not warranted at 
this time and the current MCL is set at the MCLG. Since EPA did not 
identify a health or technology basis for revising the total chromium 
NPDWR, the Agency did not conduct a detailed occurrence and exposure 
analysis.
    c. Review Result. The Agency does not believe a revision to the 
NPDWR for total chromium is appropriate at this time. A reassessment of 
the health risks associated with chromium exposure is being initiated 
and the Agency does not believe it is appropriate to revise the NPDWR 
while that effort is in process.
18. 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 
an MCL of 0.2 mg/L. EPA based the MCLG on a reference dose of 0.02 mg/
kg-day and a cancer classification of D, not classifiable as to human 
carcinogenicity. During the first Six-Year Review cycle, EPA 
recommended a revision to the BATs for cyanide to clarify that 
``chlorine'' should be ``alkaline chlorine'' to avoid potential for the 
formation of harmful cyanogen chloride. EPA promulgated that revision 
in 69 FR 38850, June 29, 2004 (USEPA, 2004b).
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to cyanide. The revised health 
effects assessment will consider relevant studies on the toxicity of 
cyanide, including its potential developmental and reproductive 
toxicity. The new health effects assessment was not completed by March 
1, 2009, the review cutoff date for this notice (USEPA, 2009b). The 
IRIS Substance Assessment Tracking System Web site (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information 
on the status of the health effects assessment.\16\
---------------------------------------------------------------------------

    \16\ Note that cyanide is listed as hydrogen cyanide in the IRIS 
tracking system.
---------------------------------------------------------------------------

    c. Review Result. Since the MCL for cyanide is set at its MCLG and 
a reassessment of the health risks resulting from exposure to cyanide 
is in progress, the Agency does not believe a revision to the NPDWR is 
appropriate at this time.
19. 2,4-D (2,4-Dichlorophenoxyacetic acid)
    a. Background. EPA published the current NPDWR for 2,4-D on January 
30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an MCLG and 
an MCL of 0.07 mg/L. EPA based the MCLG on a reference dose of 0.01 mg/
kg-day and a cancer classification of D, not classifiable as to human 
carcinogenicity.
    b. Technical Reviews. In 2005, the Agency updated its health 
effects assessment of 2,4-D (USEPA, 2005c). The Agency identified a 
change in this

[[Page 15531]]

assessment that could lead to a change in the MCLG. This assessment 
considered relevant studies on the toxicity of 2,4-D including 
developmental and reproductive toxicity. The assessment revised the RfD 
from 0.01 mg/kg-day to 0.005 mg/kg-day and concluded that 2,4-D is not 
classifiable as to its carcinogenicity (USEPA, 2005c). Based on the new 
Office of Pesticide Programs (OPP) assessment and RfD of 0.005 mg/kg-
day, and assuming a 70-kg adult body weight and 2 liters water intake 
per day, the DWEL could be 0.2 mg/L. An RSC of 20 percent results in a 
possible MCLG of 0.04 mg/L (USEPA, 2009b).
    Analytical feasibility does not pose any limitations for the 
current MCL and would not be a limiting factor for the possible MCLG 
decrease under consideration. EPA evaluated the results of the 
occurrence and exposure analyses for 2,4-D to determine whether a 
revised MCLG/MCL would be likely to result in a meaningful opportunity 
to improve the level of public health protection (USEPA, 2009f). Table 
VI-7 shows the results of the occurrence and exposure analysis for the 
current MCL and the possible MCLG set equal to 0.04 mg/L based on the 
new health effects information. The occurrence and exposure analysis 
shows that average concentrations do not exceed the current MCL for any 
system in the analysis. Note that these results are based on the subset 
of monitoring data provided in response to the Six-Year Review ICR and 
do not necessarily reflect MCL violations, which are based on annual 
average concentrations at entry points; SDWIS/FED indicates no MCL 
violations for 2,4-D between 1998 and 2005 (USEPA, 2007g). The 
occurrence and exposure analysis shows that average concentrations do 
not exceed the possible MCLG based on new health effects information 
(0.04 mg/L).

 Table VI-7--Number and Percent of Systems With Mean Concentrations Exceeding 2,4-D Thresholds and Corresponding
                                         Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                    health-based threshold (Percentages based on 33,187 systems with 2,4-D data
    Regulatory or health-based                     in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                    Nondetect values =  MRL    Nondetect values =  \1/    Nondetect values =  0
                                              \1\                    2\ MRL \2\                    \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.07 mg/L)..................  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
Possible MCLG (0.04 mg/L)........  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (Percentages based on 187,451,200 people
                                     served by the systems with 2,4-D data in the Six-Year Review ICR occurrence
                                                                      dataset)
                                  ------------------------------------------------------------------------------
    Regulatory or health-based         Nondetect values =        Nondetect values =        Nondetect values =
            threshold              MRL \1\..................  \1/2\ MRL \2\...........  0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.07 mg/L)..................  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
Possible MCLG (0.04 mg/L)........  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. Although there are new data that support 
consideration of whether to revise the MCLG/MCL for 2,4-D, EPA does not 
believe a revision to the NPDWR for 2,4-D is appropriate at this time. 
In making this decision, the Agency considered whether any possible 
revision to the NPDWR for 2,4-D is likely to provide a meaningful 
opportunity for health risk reductions. Taking into consideration the 
low occurrence of this contaminant, EPA has decided that any revision 
to the NPDWR would be a low priority activity for the Agency, and, 
thus, is not appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
20. 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 based the MCLG on a reference dose of 0.03 mg/
kg-day and a cancer classification of D, not classifiable as to human 
carcinogenicity.
    b. Technical Reviews. 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, 
2009b).
    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. 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. Review Result. EPA's review shows that there are no data 
supporting a change to the dalapon NPDWR. As a result, a revision to 
the NPDWR would not be appropriate at this time.
21. Di(2-ethylhexyl)adipate (DEHA)
    a. Background. EPA published the current 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. EPA based the MCLG on a reference dose of 0.6 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 DEHA. The revised health 
effects assessment will consider relevant studies on the toxicity of 
DEHA, including its potential

[[Page 15532]]

developmental and reproductive toxicity. The new health effects 
assessment was not completed by March 1, 2009, the review cutoff date 
for this notice (USEPA, 2009b). The IRIS Substance Assessment Tracking 
System Web site (http://cfpub.epa.gov/iristrac/index.cfm) has the most 
up-to-date information on the status of the health effects assessment.
    c. Review Result. Since the MCL for DEHA is set at its MCLG and a 
reassessment of the health risks resulting from exposure to DEHA is in 
progress, the Agency does not believe a revision to the NPDWR is 
appropriate at this time.
22. 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. The 
NPDWR also established an MCL of 0.006 mg/L, based on analytical 
feasibility.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to DEHP. The revised health 
effects assessment will consider relevant studies on the toxicity of 
DEHP, including its potential developmental and reproductive toxicity. 
The new health effects assessment was not completed by March 1, 2009, 
the review cutoff date for this notice (USEPA, 2009b). The IRIS 
Substance Assessment Tracking System Web site (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information on the status 
of the health effects assessment.
    Although a risk assessment is in process for DEHP, the existing 
MCLG is zero and the current MCL of 0.006 mg/L is based on the PQL. 
Therefore, EPA reviewed whether there is potential to revise the PQL. 
EPA reviewed PE data from the first Six-Year Review cycle and then 
analyzed more recent PT data to determine if the PQL can be revised 
(i.e., analytical feasibility). Passing rates for PE data available 
through late 1999 for DEHP are below 75 percent for several 
concentrations around the current PQL, including two studies with true 
values below the current PQL. More recent PT data from late 1999 
through 2004, supplied by a PT provider, show passing rates below the 
75 percent criterion for three studies, and all of the true 
concentrations in the PT data were higher than the current PQL. Given 
the passing rates around the current PQL, a lowering of the PQL for 
DEHP is not appropriate at this time (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of DEHP (Methods 525.2 and 506). While EPA 
prefers to use laboratory performance data to calculate the PQL, the 
MRL and MDL information can be valuable for this review to indicate 
whether it is possible to quantitate at levels below the current PQL. 
The Six-Year Review ICR dataset contains MRL values for 50,490 samples. 
Fewer than 80 percent of these values are less than or equal the modal 
MRL: 22,980 (45 percent) equal the modal MRL of 0.001 mg/L and an 
additional 15,842 (31 percent) are lower than 0.001 mg/L. Therefore, 
EPA did not set the EQL equal to the modal MRL (USEPA, 2009e). The MDLs 
of approved methods are 0.0013 and 0.00225 mg/L. Applying a multiplier 
of 10 would give a possible PQL range from 0.013 to 0.0225 mg/L. The 
range is higher than the current PQL and, therefore, EPA did not 
estimate an EQL (USEPA, 2009e). Based on these varied and unrelated 
approaches/sources of information, EPA believes that there is no 
potential to lower the PQL for DEHP. Since the MCL is constrained by 
the PQL, and the PQL is unchanged, EPA does not believe it is necessary 
to conduct an occurrence analysis at this time.
    c. Review Result. 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 in progress (USEPA, 
2009b). Furthermore, a review of analytical feasibility did not 
identify a potential to revise the MCL, which is limited by 
feasibility.
23. 1,2-Dibromo-3-chloropropane (DBCP)
    a. Background. EPA published the current NPDWR for DBCP on January 
30, 1991 (56 FR 3526 (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 0.0002 mg/L, based on analytical 
feasibility.
    b. Technical Reviews. As part of the Six-Year Review process, EPA 
conducted a literature search for relevant data on the carcinogenicity 
of DBCP as well as its potential developmental and reproductive 
toxicity. EPA has not identified any new information that indicates 
that it is appropriate to consider revisions to the cancer 
classification for DBCP at this time (USEPA, 2009b). Because the MCLG 
remains at zero, the Agency believes that a further review of the 
health effects of DBCP is not warranted at this time.
    The current MCL for DBCP is based on a PQL of 0.0002 mg/L. For the 
Six-Year Review, the Agency considered whether changes in the 
analytical feasibility of DBCP might lead to a lower MCL. EPA reviewed 
PE data from the first Six-Year Review cycle and then analyzed more 
recent PT data to determine if the PQL can be revised (i.e., analytical 
feasibility). Passing rates for PE data available through late 1999 for 
DBCP are above 85 percent, including one study with a true value below 
the current PQL. More recent PT data from late 1999 through 2004, 
supplied by a PT provider, also show greater than 75 percent passing 
rates, including three with a true value below the current PQL. Because 
all of the laboratory passing rates from PE and PT studies, including 
four with true values slightly below the PQL, exceeded the 75 percent 
criterion typically used to derive a PQL, a lowering of the PQL for 
DBCP might be possible. These results, however, are insufficient to 
recalculate a revised PQL for DBCP because not enough data points are 
available below the current PQL to derive a value at the 75 percent 
passing rate (USEPA, 2009c).
    EPA examined two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of DBCP (Methods 504.1 and 551.1). While EPA 
prefers to use laboratory performance data to calculate the PQL, the 
MRL and MDL information can be valuable for this review to indicate 
whether it is possible to quantitate at levels below the current PQL. 
However, there are substantial uncertainties in interpreting the MRLs 
(USEPA, 2009e). For example, some States have reported modal MRLs that 
are higher than the MCL. EPA therefore considered only MDL data to 
verify the potential to revise the PQL, and to establish a threshold 
for the occurrence and exposure analysis. The MDLs of approved methods 
are 0.000009 and 0.00001 mg/L. Applying a multiplier of 10 would give a 
possible PQLs of 0.00009 and 0.0001 mg/L. EPA took the mean and rounded 
up to 0.0001 mg/L for the EQL (USEPA, 2009e).
    Based on the PT data and the MDLs for approved methods, EPA 
believes that there may be potential to lower the PQL for DBCP. To 
determine whether any MCL revision is likely to provide a meaningful 
opportunity to improve

[[Page 15533]]

public health protection, EPA evaluated the occurrence of DBCP at the 
EQL of 0.0001 mg/L (USEPA, 2009f). Table VI-8 shows the results of the 
occurrence and exposure analysis for the current MCL and an EQL. The 
occurrence and exposure analysis shows that average concentrations 
exceed the current MCL for 42 of 37,618 systems (0.112 percent) serving 
25,000 people (or 0.013 percent of 194 million people). Note that these 
results are based on the subset of monitoring data provided in response 
to the Six-Year Review ICR and do not necessarily reflect MCL 
violations, which are based on annual average concentrations at entry 
points; SDWIS/FED indicates only nine MCL violations for DBCP between 
1998 and 2005 (USEPA, 2007g). Average concentrations at 92 to 97 of 
37,618 systems (0.245 to 0.258 percent), serving approximately 1.2 to 
1.4 million people (0.610 to 0.713 percent of 194 million people), 
exceed the EQL of 0.0001 mg/L.

 Table VI-8--Number and Percent of Systems With Mean Concentrations Exceeding DBCP Thresholds and Corresponding
                                         Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                     feasibility-based threshold (Percentages based on 37,618 systems with DBCP
 Regulatory or feasibility-based                data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                    Nondetect values =  MRL    Nondetect values =  \1/    Nondetect values =  0
                                              \1\                    2\ MRL \2\                    \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.0002 mg/L)................  42 (0.112%)..............  42 (0.112%).............  42 (0.112%)
EQL (0.0001 mg/L)................  97 (0.258%)..............  93 (0.247%).............  92 (0.245%)
----------------------------------------------------------------------------------------------------------------
                                   Corresponding population served (Percentages based on 193,749,000 people
                                    served by the systems with DBCP data in the Six-Year Review ICR occurrence
                                    dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based       Nondetect values =        Nondetect values =        Nondetect values =
            threshold              MRL \1\..................  \1/2\ MRL \2\...........  0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.0002 mg/L)................  25,000 (0.013%)..........  25,000 (0.013%).........  25,000 (0.013%)
EQL (0.0001 mg/L)................  1,382,000 (0.713%).......  1,371,000 (0.707%)......  1,181,000 (0.610%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
 
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. 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 DBCP is 
appropriate at this time. The occurrence and exposure analysis based on 
possible changes in analytical feasibility indicates that any revision 
to the MCL is unlikely to provide a meaningful opportunity to improve 
public health protection. Taking into consideration the low occurrence 
of this contaminant, EPA has decided that any revision to the NPDWR 
would be a low priority activity for the Agency, and, thus, is not 
appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
24. 1,2-Dichlorobenzene (o-Dichlorobenzene)
    a. Background. EPA published the current NPDWR for 1,2-
dichlorobenzene on January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The 
NPDWR established an MCLG and an MCL of 0.6 mg/L. EPA based the MCLG on 
a reference dose 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 health effects assessment will consider relevant studies on the 
toxicity of 1,2-dichlorobenzene, including its potential developmental 
and reproductive toxicity. The new health effects assessment was not 
completed by March 1, 2009, the review cutoff date for this notice 
(USEPA, 2009b). The IRIS Substance Assessment Tracking System Web site 
(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 
information on the status of the health effects assessment.
    c. Review Result. Since the MCL for 1,2-dichlorobenzene is set at 
its MCLG and a reassessment of the health risks resulting from exposure 
to 1,2-dichlorobenzene is in progress, the Agency does not believe a 
revision to the NPDWR is appropriate at this time.
25. 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 based the MCLG on a 
reference dose 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 health effects assessment will consider relevant studies on the 
toxicity of 1,4-dichlorobenzene, including its potential developmental 
and reproductive toxicity. The new health effects assessment was not 
completed by March 1, 2009, the review cutoff date for this notice 
(USEPA, 2009b). The IRIS Substance Assessment Tracking System Web site 
(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 
information on the status of the health effects assessment.
    c. Review Result. Since the MCL for 1,4-dichlorobenzene is set at 
its MCLG and a reassessment of the health risks resulting from exposure 
to 1,4-

[[Page 15534]]

dichlorobenzene is in progress, the Agency does not believe a revision 
to the NPDWR is appropriate at this time.
26. 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 
health effects assessment will consider relevant studies on the 
toxicity of 1,2-dichloroethane, including its potential developmental 
and reproductive toxicity. The new health effects assessment was not 
completed by March 1, 2009, the review cutoff date for this notice 
(USEPA, 2009b). The IRIS Substance Assessment Tracking System Web site 
(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 
information on the status of the health effects assessment.\17\
---------------------------------------------------------------------------

    \17\ Note that 1,2-dichloroethane is listed as ethylene 
dichloride in the IRIS tracking system.
---------------------------------------------------------------------------

    Although a risk assessment is in process for 1,2-dichloroethane, 
the existing MCLG is zero and the current MCL of 0.005 mg/L is based on 
the PQL. Therefore, EPA reviewed whether there is potential to revise 
the PQL EPA reviewed PE data from the first Six-Year Review cycle and 
then analyzed more recent PT data to determine if the PQL can be 
revised (i.e., analytical feasibility). Passing rates for PE data 
available through late 1999 for 1,2-dichloroethane are above 95 percent 
around the current PQL of 0.005 mg/L, including one study with a true 
value below the current PQL. More recent PT data from late 1999 through 
2004, supplied by a PT provider, also show greater than 90 percent 
passing rates for studies around the current PQL, including seven with 
true values below the current PQL. Because all of the laboratory 
passing rates from PE and PT studies--including several with true 
concentrations below the PQL--exceeded the 75 percent criterion 
typically used to derive a PQL, a lowering of the PQL for 1,2-
dichloroethane might be possible. These results, however, are 
insufficient to recalculate a revised PQL for 1,2-dichloroethane 
because not enough data points are available below the current PQL to 
derive a value at the 75 percent passing rate (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the PQL could be estimated: laboratory MRLs in the 
Six-Year Review ICR dataset, and the MDLs for approved methods for the 
detection of 1,2-dichloroethane (Methods 502.2 and 524.2). While EPA 
prefers to use laboratory performance data to calculate the PQL, the 
MRL and MDL information can be valuable for this review to indicate 
whether it is possible to quantitate at levels below the current PQL. 
The Six-Year Review ICR dataset contains MRL values for 139,085 
samples. More than 80 percent of these values are less than or equal 
the modal MRL: 116,533 (84 percent) equal the modal MRL of 0.0005 mg/L 
and an additional 18,160 (13 percent) are lower than 0.0005 mg/L. 
Therefore, EPA selected the modal MRL as the EQL (USEPA, 2009e). The 
MDLs of approved methods range from 0.00003 to 0.00006 mg/L. Applying a 
multiplier of 10 would give a possible PQL range from 0.0003 to 0.0006 
mg/L, which contains the EQL (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of 
information, EPA believes that there is potential to lower the PQL for 
1,2-dichloroethane. To determine whether any MCL revision is likely to 
provide a meaningful opportunity to improve public health protection, 
EPA evaluated the occurrence of 1,2-dichloroethane at the EQL of 0.0005 
mg/L and additional thresholds of 0.001 and 0.0025 mg/L (USEPA, 2009f). 
Table VI-9 shows the results of the occurrence and exposure analysis 
for the current MCL and these thresholds. The occurrence and exposure 
analysis shows that average concentrations exceed the current MCL for 
three of 50,442 systems (0.006 percent) serving 150 people (or 0.00007 
percent of 227 million people). Note that these results are based on 
the subset of monitoring data provided in response to the Six-Year 
Review ICR and do not necessarily reflect MCL violations, which are 
based on annual average concentrations at entry points; SDWIS/FED 
indicates 27 MCL violations for 1,2-dichloroethane between 1998 and 
2005 (USEPA, 2007g). Average concentrations at 63 to 82 of 50,442 
systems (0.125 to 0.163 percent), serving 210,000 to 277,000 people (or 
0.092 to 0.122 percent of 227 million people), exceed the EQL of 0.0005 
mg/L.

 Table VI-9--Number and Percent of Systems With Mean Concentrations Exceeding 1,2-Dichloroethane Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                     feasibility-based threshold (Percentages based on 50,442 systems with 1,2-
 Regulatory or feasibility-based         dichloroethane data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  3 (0.006%)...............  3 (0.006%)..............  3 (0.006%)
\1/2\ MCL (0.0025 mg/L)..........  9 (0.018%)...............  9 (0.018%)..............  8 (0.016%)
2xEQL (0.001 mg/L)...............  46 (0.091%)..............  37 (0.073%).............  30 (0.059%)
EQL (0.0005 mg/L)................  not applicable...........  82 (0.163%).............  63 (0.125%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (percentages based on 226,934,000 people
                                      served by the systems with 1,2-dichloroethane data in the Six-Year Review
                                                               ICR occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based     Nondetect values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
            threshold                          \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  150 (0.00007%)...........  150 (0.00007%)..........  150 (0.00007%)
\1/2\ MCL (0.0025 mg/L)..........  870 (0.0004%)............  870 (0.0004%)...........  830 (0.0004%)
2xEQL (0.001 mg/L)...............  190,000 (0.084%).........  145,200 (0.064%)........  87,150 (0.038%)

[[Page 15535]]

 
EQL (0.0005 mg/L)................  not applicable...........  277,000 (0.122%)........  210,000 (0.092%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
  Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the
  results equal to this value results in an upwardly biased estimate of the number of systems with mean
  concentrations that exceed this value.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. 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 in progress (USEPA, 2009b). Furthermore, the 
occurrence and exposure analysis based on possible changes in 
analytical feasibility indicates that any revision to the MCL is 
unlikely to provide a meaningful opportunity to improve public health 
protection. After consideration of the low occurrence of this 
contaminant, EPA has decided that any revision to the NPDWR would be a 
low priority activity for the Agency, and, thus, is not appropriate to 
revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
27. 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. EPA based the MCLG on a 
reference dose of 0.01 mg/kg-day and a cancer classification of C, 
possible human carcinogen.
    b. Technical Reviews. In the first Six-Year Review cycle, EPA 
evaluated new information from a health effects assessment completed in 
2002 (USEPA, 2002b). At that time, the Agency could not determine that 
a revision to the NPDWR would provide a meaningful opportunity for cost 
savings to public water systems or their customers, and decided that 
any revision would be a low priority activity for the Agency because of 
competing workload priorities, the administrative costs associated with 
rulemaking, and the burden on States and the regulated community to 
implement any regulatory change (68 FR 42908 (USEPA, 2003e)). The 2002 
assessment considered relevant studies on the toxicity of 1,1-
dichloroethylene including developmental and reproductive toxicity. The 
assessment revised the RfD from 0.01 mg/kg-day to 0.05 mg/kg-day and 
concluded that there is inadequate information to assess carcinogenic 
potential via the oral route (USEPA, 2002b). In the current review 
cycle, EPA conducted a literature search through June 2007 for relevant 
data on the toxicology of 1,1-dichloroethylene, including its potential 
developmental and reproductive toxicity. The literature search did not 
identify any additional new data that would affect the RfD or cancer 
classification (USEPA, 2009b). Based on the 2002 IRIS assessment and 
RfD of 0.05 mg/kg-day, and assuming a 70-kg adult body weight and 2 
liters water intake per day, the DWEL could be 1.75 mg/L. The 2002 
cancer assessment indicates that the risk management factor of 10, 
applied to the current MCLG, may no longer be needed. An RSC of 20 
percent results in a possible MCLG of 0.35 mg/L (USEPA, 2009b).
    Analytical feasibility does not pose any limitations for the 
current MCL and would not be a limiting factor if EPA were to raise the 
MCLG. EPA evaluated the results of the occurrence and exposure analyses 
for 1,1-dichloroethylene to determine whether a revised MCLG/MCL would 
be likely to result in a meaningful opportunity to achieve cost savings 
for PWSs and their customers while maintaining, or improving, the level 
of public health protection (USEPA, 2009f). Although the Agency 
obtained and evaluated the finished water occurrence data for 1,1-
dichloroethylene, its usefulness is limited for potential cost savings 
to PWSs and their customers because the Agency does not know which 
systems are treating for this contaminant. As an alternative, the 
Agency evaluated available data on source water quality and conducted a 
qualitative assessment of treatment cost savings.
    Table VI-10 provides summary data for contaminant occurrence based 
on maximum sample values for the locations included in the STORET and 
NAWQA data. Although the degree to which these occurrence rates 
represent national drinking water source occurrence is uncertain, the 
information shows no to low occurrence at threshold levels of interest. 
This information indicates that any resulting NPDWR change would affect 
systems that rely on source water at less than 0.02 percent of the 
NAWQA locations. The STORET results are driven by the 157 sampling 
locations in Phoenix, Arizona, that have a maximum sample above the MCL 
of 0.007 mg/L. Five of these locations also account for those having a 
maximum sample that exceeds 0.35 mg/L.

[[Page 15536]]



            Table VI-10--Ambient Water Quality Monitoring Occurrence Summary for 1,1-Dichloroethylene
----------------------------------------------------------------------------------------------------------------
                                                            Number of locations (% of locations)
          Maximum concentration           ----------------------------------------------------------------------
                                                       STORET \1\                          NAWQA \2\
----------------------------------------------------------------------------------------------------------------
Total....................................  2,448 (100.0%)....................  5,788 (100.0%)
Nondetect................................  1,498 (61.2%).....................  5,636 (97.37%)
Detected.................................  950 (38.8%).......................  152 (2.63%)
Exceeds current MCLG of 0.007 mg/L.......  165 (6.7%)........................  1 (0.02%)
Exceeds alternative value of 0.35 mg/L...  5 (0.2%)..........................  0 (0.0%)
----------------------------------------------------------------------------------------------------------------
\1\ STORET database 2002-2007.
\2\ NAWQA database 1992-2008.
Source: USEPA, 2009d.

    The BATs and small system compliance technologies for 1,1-
dichloroethylene have other beneficial effects, e.g., reduction of 
other co-occurring contaminants, precursors for DBPs, or other common 
impurities. Therefore, if EPA were to consider a higher level, the 
Agency does not know how many PWSs that are currently treating to 
comply with the existing MCL of 0.007 mg/L would be likely to 
discontinue treatment that is already in place (USEPA, 2009d). Also, 
the Agency does not know to what extent affected systems might be able 
to reduce costs given that capital costs are not recoverable. However, 
the Agency recognizes that there may be opportunities to achieve 
operational cost savings if these systems are able to re-optimize 
current treatment.
    Given these considerations, the Agency believes that any resulting 
revision is not likely to provide a meaningful opportunity for cost 
savings. In view of this, any revision would be a low priority activity 
and not appropriate at this time.
    c. Review Result. Although there are new data that support 
consideration of whether to revise the MCLG/MCL for 1,1-
dichloroethylene, EPA does not believe a revision to the NPDWR for 1,1-
dichloroethylene is appropriate at this time. In making this decision, 
the Agency considered whether any possible revision to the NPDWR for 
1,1-dichloroethylene is likely to provide a meaningful opportunity for 
cost savings to public water systems and their customers. Taking into 
consideration the low occurrence of this contaminant in source waters, 
EPA has decided that any revision to the NPDWR would be a low priority 
activity for the Agency, and, thus, is not appropriate to revise at 
this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
28. cis-1,2-Dichloroethylene
    a. Background. EPA published the current NPDWR for cis-1,2-
dichloroethylene on January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The 
NPDWR established an MCLG and an MCL of 0.07 mg/L. EPA based the MCLG 
on a reference dose 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 cis-1,2-dichloroethylene. The 
revised health effects assessment will consider relevant studies on the 
toxicity of cis-1,2-dichloroethylene, including its potential 
developmental and reproductive toxicity. The new health effects 
assessment was not completed by March 1, 2009, the review cutoff date 
for this notice (USEPA, 2009b). The IRIS Substance Assessment Tracking 
System Web site (http://cfpub.epa.gov/iristrac/index.cfm) has the most 
up-to-date information on the status of the health effects assessment.
    c. Review Result. Since the MCL for cis-1,2-dichloroethylene is set 
at its MCLG and a reassessment of the health risks resulting from 
exposure to cis-1,2-dichloroethylene is in progress, the Agency does 
not believe a revision to the NPDWR is appropriate at this time.
29. trans-1,2-Dichloroethylene
    a. Background. EPA published the current NPDWR for trans-1,2-
dichloroethylene on January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The 
NPDWR established an MCLG and an MCL of 0.1 mg/L. EPA based the MCLG on 
a reference dose of 0.02 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 trans-1,2-dichloroethylene. The 
revised health effects assessment will consider relevant studies on the 
toxicity of trans-1,2-dichloroethylene, including its potential 
developmental and reproductive toxicity. The new health effects 
assessment was not completed by March 1, 2009, the review cutoff date 
for this notice (USEPA, 2009b). The IRIS Substance Assessment Tracking 
System Web site (http://cfpub.epa.gov/iristrac/index.cfm) has the most 
up-to-date information on the status of the health effects assessment.
    c. Review Result. Since the MCL for trans-1,2-dichloroethylene is 
set at its MCLG and a reassessment of the health risks resulting from 
exposure to trans-1,2-dichloroethylene is in progress, the Agency does 
not believe a revision to the NPDWR is appropriate at this time.
30. Dichloromethane (Methylene Chloride)
    a. Background. EPA published the current 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.
    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to dichloromethane. The revised 
health effects assessment will consider relevant studies on the 
toxicity of dichloromethane, including its potential developmental and 
reproductive toxicity. The new health effects assessment was not 
completed by March 1, 2009, the review cutoff date for this notice 
(USEPA, 2009b). The IRIS Substance Assessment Tracking System Web site 
(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 
information on the status of the health effects assessment.\18\
---------------------------------------------------------------------------

    \18\ Note that dichloromethane is listed as methylene chloride 
in the IRIS tracking system.
---------------------------------------------------------------------------

    Although a risk assessment is in process for dichloromethane, the 
existing MCLG is zero and the current MCL of 0.005 mg/L is based on the 
PQL. Therefore, EPA reviewed whether there is potential to revise the 
PQL. EPA reviewed PE data from the first Six-Year

[[Page 15537]]

Review cycle and then analyzed more recent PT data to determine if the 
PQL can be revised (i.e., analytical feasibility). Passing rates for PE 
data available through late 1999 for dichloromethane are all above 90 
percent for studies near the PQL. More recent PT data from late 1999 
through 2004, supplied by a PT provider, also show greater than 85 
percent passing rates for studies around the PQL, except for one study 
with a passing rate of 76 percent. However, all of the true 
concentrations in the PE and PT data were higher than the current PQL 
of 0.005 mg/L. Given the lack of PE and PT study results below the 
current PQL to derive a value at the 75 percent passing rate, PE and PT 
data are insufficient to support a PQL reduction (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: Laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of dichloromethane (Methods 502.2 and 524.2). 
While EPA prefers to use laboratory performance data to calculate the 
PQL, the MRL and MDL information can be valuable for this review to 
indicate whether it is possible to quantitate at levels below the 
current PQL. The Six-Year Review ICR dataset contains MRL values for 
138,445 samples. More than 80 percent of these values are less than or 
equal the modal MRL: 121,532 (88 percent) equal the modal MRL of 0.0005 
mg/L and an additional 11,294 (8 percent) are lower than 0.0005 mg/L. 
Therefore, EPA selected the modal MRL as the EQL (USEPA, 2009e). The 
MDLs of approved methods range from 0.00002 to 0.00009 mg/L. Applying a 
multiplier of 10 would give a possible PQL range from 0.0002 to 0.0009 
mg/L, which includes the EQL (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of 
information, there is evidence of a potential to lower the PQL for 
dichloromethane even though the PE and PT data are insufficient to 
support a PQL reduction. To determine whether any MCL revision is 
likely to provide a meaningful opportunity to improve public health 
protection, EPA evaluated the occurrence of dichloromethane at the EQL 
of 0.0005 mg/L and additional thresholds of 0.001 and 0.0025 mg/L 
(USEPA, 2009f). Table VI-11 shows the results of the occurrence and 
exposure analysis for the current MCL and these thresholds. The 
occurrence and exposure analysis shows that average concentrations 
exceed the current MCL for 13 to 17 of 50,169 systems (0.026 to 0.034 
percent) serving 11,000 to 12,000 people (or 0.005 percent of 227 
million people). Note that these results are based on the subset of 
monitoring data provided in response to the Six-Year Review ICR and do 
not necessarily reflect MCL violations, which are based on annual 
average concentrations at entry points; SDWIS/FED indicates 67 MCL 
violations for dichloromethane between 1998 and 2005 with annual 
violations ranging from 4 to 14 (USEPA, 2007g). Average concentrations 
at 383 to 579 of 50,169 systems (0.763 to 1.154 percent), serving 
approximately 1.8 to 3.5 million people (or 0.813 to 1.542 percent of 
227 million people), exceed the EQL of 0.0005 mg/L.

  Table VI-11--Number and Percent of Systems With Mean Concentrations Exceeding Dichloromethane Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                       feasibility-based threshold (percentages based on 50,169 systems with
 Regulatory or feasibility-based        dichloromethane data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  17 (0.034%)..............  16 (0.032%).............  13 (0.026%)
EQL (0.0025 mg/L)................  53 (0.106%)..............  51 (0.102%).............  46 (0.092%)
EQL (0.001 mg/L).................  276 (0.550%).............  208 (0.415%)............  169 (0.337%)
EQL (0.0005 mg/L)................  not applicable...........  579 (1.154%)............  383 (0.763%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (percentages based on 226,844,000 people
                                     served by the systems with dichloromethane data in the Six-Year Review ICR
                                                                 occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based     Nondetect values = MRL   Nondetect values = \1/2\    Nondetect values = >0
            threshold                          \1\                     MRL \2\                     \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  12,000 (0.005%)..........  12,000 (0.005%).........  11,000 (0.005%)
EQL (0.0025 mg/L)................  44,000 (0.019%)..........  40,000 (0.018%).........  39,000 (0.017%)
EQL (0.001 mg/L).................  1,517,000 (0.669%).......  1,386,000 (0.611%)......  946,000 (0.417%)
EQL (0.0005 mg/L)................  not applicable...........  3,497,000 (1.542%)......  1,844,000 (0.813%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
  Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the
  results equal to this value results in an upwardly biased estimate of the number of systems with mean
  concentrations that exceed this value.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    During Six-Year Review 1, a stakeholder questioned the feasibility 
of lowering the PQL for dichloromethane below 0.001 mg/L because its 
use in EPA analytical methods makes it a common laboratory contaminant 
(68 FR 42908 (USEPA, 2003e)). EPA responded that the high passing rates 
among PE studies at concentrations close to the current PQL of 0.005 
mg/L would not be expected if this were the case and that EPA had no 
data to suggest that the occurrence estimates reflected monitoring 
sample contamination (68 FR 42908 (USEPA, 2003e)). For Six-Year Review 
2, EPA notes that it does not have PE or PT study results at either 
0.001 mg/L or 0.0005 mg/L and, therefore, cannot assess the potential 
for laboratory contamination of dichloromethane to affect passing rates 
at this level. A USGS study of volatile organic compound (VOC) 
occurrence (Moran, 2006) indicates this potential exists at low 
concentrations. The study presented dichloromethane laboratory 
reporting levels for newer low-level

[[Page 15538]]

analytical methods (i.e., defined as the level that limits the 
frequency of false positives and false negatives to 1 percent of test 
results) that ranged from 0.00006 mg/L to 0.00757 mg/L, with a median 
value of 0.00038 mg/L. The report noted that the laboratory reporting 
levels for dichloromethane tend to be higher than levels for other VOCs 
such as PCE (levels ranging from 0.000027 mg/L to 0.0005 mg/L with a 
median of 0.0001 mg/L) and TCE (ranging from 0.000038 mg/L to 0.0005 
mg/L with a median of 0.000038 mg/L) because it was a frequent 
laboratory contaminant.
    A USGS study of ground water, source water, and drinking water 
quality indicated consistently lower dichloromethane (methylene 
chloride) occurrence frequencies compared to either PCE or TCE, which 
are among the most frequently occurring VOCs included in the study 
(Moran, 2006). Table VI-12 provides a summary of the occurrence results 
reported in the USGS study. This study also determined that population 
density was the strongest predictor of dichloromethane occurrence.

       Table VI-12--Summary of USGS VOC Occurrence Study Findings for Dichloromethane (Methylene Chloride)
----------------------------------------------------------------------------------------------------------------
                                         Ground water samples     Source water samples    Drinking water samples
----------------------------------------------------------------------------------------------------------------
Number...............................  5,054..................  577....................  1,680
Type.................................  3,877 NAWQA 1,177 Other  Ground water sources     Ground water community
                                        sources.                 for community water      water systems.
                                                                 systems.
Location.............................  National...............  National...............  New England and Mid-
                                                                                          Atlantic States.
Dichloromethane Results..............   3% exceed        0.2% (1          3% exceed
                                        0.00002 mg/L.            sample) exceed 0.0002    0.0002 mg/L.
                                        <1% exceed       mg/L.                    Ranked 11th of
                                        0.0002 mg/L.             Ranked 8th of    51 VOCs in detection
                                        Ranked 30th of   52 VOCs based on         frequency.
                                        55 VOCs based on         median concentration     Ranked 31st of
                                        median concentration     (0.0017 mg/L--1          55 solvents in median
                                        (0.00005 mg/L).          sample).                 concentration (0.001
                                                                                          mg/L).
PCE..................................   11% exceed       4% exceed        4% exceed
                                        0.00002 mg/L.            0.0002 mg/L.             0.0002 mg/L.
                                        4% exceed        Ranked 16th of   Ranked 7th of
                                        0.0002 mg/L.             52 VOCs based on         51 VOCs in detection
                                        Ranked 12th of   median concentration     frequency.
                                        55 VOCs based on         (0.0009 mg/L).           Ranked 11th of
                                        median concentration                              55 solvents in median
                                        (0.00007 mg/L).                                   concentration (0.0014
                                                                                          mg/L).
TCE..................................   5% exceed        3% exceed        4% exceed
                                        0.00002 mg/L.            0.0002 mg/L.             0.0002 mg/L.
                                        2.5% exceed      Ranked 10th of   Ranked 8th of
                                        0.0002 mg/L.             52 VOCs based on         51 VOCs in detection
                                        Ranked 20th of   median concentration     frequency.
                                        55 VOCs based on         (0.0015 mg/L).           Ranked 8th of
                                        median concentration                              55 solvents in median
                                        (0.00012 mg/L).                                   concentration (0.0015
                                                                                          mg/L).
----------------------------------------------------------------------------------------------------------------
Source: Moran, 2006.

    EPA compared Six-Year Review ICR occurrence patterns for 
dichloromethane with contaminant release information to determine if 
drinking water occurrence corresponds with potential contaminant 
sources reported in the Toxics Release Inventory (TRI) and found that 
the states with the majority of systems with mean concentrations that 
exceed 0.0005 mg/L did not tend to be the States with the highest 
dichloromethane releases (Moran, 2006). Table VI-13 provides summary 
information from that comparison. In particular, the numbers of system 
means exceeding 0.0005 mg/L in Montana and Alaska seem inconsistent 
with TRI release information and the USGS study finding that population 
density is the strongest predictor of dichloromethane occurrence.
    Because of data gaps regarding the feasibility of PQL reduction and 
potential occurrence data accuracy at the lowest EQL, EPA concluded 
that revising the MCL may not constitute a meaningful opportunity to 
improve the level of public health protection.

                                               Table VI-13--Stage 2 Occurrence Summary for Dichloromethane
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                       Systems with mean > 0.0005 mg/   Total reported TRI on-site or off-site    Total reported TRI on-site or off-site
                                           L Nondetect = \1/2\ MRL     disposal or release of dichloromethane--  disposal or release of dichloromethane--
                                      --------------------------------         all industries, 2006 \1\                  all industries, 2004 \1\
 
                State                                                 ----------------------------------------------------------------------------------
                                           Number      Percent of 579                            Percent of 6.8                           Percent of 7.9
                                                        total systems           Pounds            Million Total           Pounds           Million Total
                                                                                                     Pounds                                   Pounds
--------------------------------------------------------------------------------------------------------------------------------------------------------
MT...................................              67              12  22,700..................               0  30,600.................               0
TX...................................              45               8  314,120.................               5  410,103................               5
FL...................................              40               7  31,451..................               0  246,775................               3
AK...................................              37               6  No data.................               0  No data................               0
IN...................................              29               5  509,303.................               7  699,783................               9
WI...................................              28               5  111,403.................               2  98,113.................               1
MO...................................              27               5  51,002..................               1  32,860.................               0
CA...................................              26               4  149,423.................               2  86,554.................               1
OH...................................              24               4  192,237.................               3  203,269................               3
NM...................................              21               4  No data.................               0  No data................               0

[[Page 15539]]

 
IL...................................              19               3  279,024.................               4  285,101................               4
AL...................................              18               3  319,529.................               5  375,650................               5
MN...................................              17               3  39,851..................               1  81,309.................               1
CO...................................              15               3  18,475..................               0  17,003.................               0
MI...................................              13               2  75,141..................               1  129,959................               2
WY...................................              13               2  No data.................               0  No data................               0
IA...................................              12               2  2,348...................               0  1,657..................               0
MD...................................              12               2  36,990..................               1  31,347.................               0
NC...................................              12               2  49,800..................               1  600,032................               8
NY...................................              11               2  322,382.................               5  712,197................               9
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Source: TRI Explorer Chemical Report Summary on-line state summaries for 2006 and 2004.

    c. Review Result. The Agency does not believe a revision to the 
NPDWR for dichloromethane is appropriate at this time because a 
reassessment of the health risks resulting from exposure to 
dichloromethane is in progress (USEPA, 2009b). In view of the fact that 
dichloromethane is a common laboratory contaminant, there is 
uncertainty regarding the extent to which a PQL revision is feasible or 
whether the Six-Year Review ICR data are reliable at concentrations 
well below the current PQL. Furthermore, the occurrence and exposure 
analysis based on possible changes in analytical feasibility indicates 
that any revision to the MCL is unlikely to provide a meaningful 
opportunity to improve public health protection. After consideration of 
these factors, EPA has decided that any revision to the NPDWR would be 
a low priority activity for the Agency, and, thus, is not appropriate 
to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
31. 1,2-Dichloropropane
    a. Background. EPA published the current NPDWR for 1,2-
dichloropropane on January 30, 1991 (56 FR 3526 (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 
0.005 mg/L, based on analytical feasibility.
    b. Technical Reviews. As part of the Six-Year Review process, EPA 
conducted a literature search for relevant data on the carcinogenicity 
of 1,2-dichloropropane as well as its potential developmental and 
reproductive toxicity. EPA has not identified any new information that 
indicates that it is appropriate to consider revisions to the cancer 
classification for 1,2-dichloropropane at this time (USEPA, 2009b). 
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. For the Six-Year Review, the Agency considered whether changes in 
the analytical feasibility of 1,2-dichloropropane might lead to a lower 
MCL. EPA reviewed PE data from the first Six-Year Review cycle and then 
analyzed more recent PT data to determine if the PQL can be revised 
(i.e., analytical feasibility). Passing rates for PE data available 
through late 1999 for 1,2-dichloropropane are above 90 percent near the 
current PQL of 0.005 mg/L, but there were no results for PE studies 
with true values below the current PQL. More recent PT data from late 
1999 through 2004, supplied by a PT provider, also show greater than 90 
percent passing rates around the PQL, including nine studies with true 
values below the current PQL. Because most of the laboratory passing 
rates from PE and PT studies--including several with true 
concentrations below the PQL--exceeded the 75 percent criterion 
typically used to derive a PQL, a lowering of the PQL for 1,2-
dichloropropane might be possible. These results, however, are 
insufficient to recalculate a revised PQL for 1,2-dichloropropane 
because not enough data points are available below the current PQL to 
derive a value at the 75 percent passing rate (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of 1,2-dichloropropane (Methods 502.2 and 
524.2). While EPA prefers to use laboratory performance data to 
calculate the PQL, the MRL and MDL information can be valuable for this 
review to indicate whether it is possible to quantitate at levels below 
the current PQL. The Six-Year Review ICR dataset contains MRL values 
for 139,237 samples. More than 80 percent of these values are less than 
or equal the modal MRL: 119,831 (86 percent) equal the modal MRL of 
0.0005 mg/L and an additional 18,311 (13 percent) are lower than 0.0005 
mg/L. Therefore, EPA selected the modal MRL as the EQL (USEPA, 2009e). 
The MDLs of approved methods range from 0.00003 to 0.00004 mg/L. 
Applying a multiplier of 10 would give a possible PQL range from 0.0003 
to 0.0004 mg/Lwhich supports the EQL (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of 
information, EPA believes that there is potential to lower the PQL for 
1,2-dichloropropane. To determine whether any MCL revision is likely to 
provide a meaningful opportunity to improve public health protection, 
EPA evaluated the occurrence of 1,2-dichloropropane at the EQL of 
0.0005 mg/L and additional thresholds of 0.001 and 0.0025 mg/L (USEPA, 
2009f). Table VI-14 shows the results of the occurrence and exposure 
analysis for the current MCL and these thresholds. The occurrence and 
exposure analysis shows that average concentrations do not exceed the 
current MCL for any system in the analysis. Note that these results are 
based on the subset of monitoring data provided in response to the Six-
Year

[[Page 15540]]

Review ICR and do not necessarily reflect MCL violations, which are 
based on annual average concentrations at entry points; SDWIS/FED 
indicates three MCL violations for 1,2-dichloropropane between 1998 and 
2005 (USEPA, 2007g). Average concentrations at 47 to 61 of 50,437 
systems (0.093 to 0.121 percent), serving 296,000 to 494,000 people 
(0.130 to 0.218 percent of 227 million people), exceed the EQL of 
0.0005 mg/L.

Table VI-14--Number and Percent of Systems With Mean Concentrations Exceeding 1,2-Dichloropropane Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                     feasibility-based threshold (percentages based on 50,437 systems with 1,2-
 Regulatory or feasibility-based        dichloropropane data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
\1/2\ MCL (0.0025 mg/L)..........  2 (0.004%)...............  2 (0.004%)..............  2 (0.004%)
2xEQL (0.001 mg/L)...............  27 (0.054%)..............  24 (0.048%).............  21 (0.042%)
EQL (0.0005 mg/L)................  not applicable...........  61 (0.121%).............  47 (0.093%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding Population Served (percentages based on 226,912,000 people
                                     served by the systems with 1,2-dichloropropane data in the Six-Year Review
                                                               ICR occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based     Nondetect values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
            threshold                          \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
\1/2\ MCL (0.0025 mg/L)..........  120 (0.00005%)...........  120 (0.00005%)..........  120 (0.00005%)
2xEQL (0.001 mg/L)...............  286,000 (0.126%).........  286,000 (0.126%)........  284,000 (0.125%)
EQL (0.0005 mg/L)................  not applicable...........  494,000 (0.218%)........  296,000 (0.130%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
  Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the
  results equal to this value results in an upwardly biased estimate of the number of systems with mean
  concentrations that exceed this value.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. 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 occurrence and 
exposure analysis based on possible changes in analytical feasibility 
indicates that any revision to the MCL is unlikely to provide a 
meaningful opportunity to improve public health protection. Taking into 
consideration the low occurrence of this contaminant, EPA has decided 
that any revision to the NPDWR would be a low priority activity for the 
Agency, and, thus, is not appropriate to revise at this time because 
of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
32. 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. EPA based the MCLG on a reference dose of 0.001 
mg/kg-day and a cancer classification of D, not classifiable as to 
human carcinogenicity.
    b. Technical Reviews. 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, 
2009b).
    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. 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. Review Result. EPA's review shows that there are no data 
supporting a change to the dinoseb NPDWR. As a result, a revision to 
the NPDWR would not be appropriate at this time.
33. 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. EPA based the MCLG on a reference dose of 0.0022 
mg/kg-day and a cancer classification of D, not classifiable as to 
human carcinogenicity.
    b. Technical Reviews. In 2001, the Agency updated its health 
effects assessment of diquat (USEPA, 2001a). A subsequent reassessment 
of tolerances for residues in or on raw agricultural products (USEPA, 
2002d) did not identify any new health effects information and based 
the updated tolerances on health effects information in the 2001 
assessment (USEPA, 2001a). The Agency identified a change in this 
assessment that could lead to a change in the MCLG. This assessment 
considered relevant studies on the toxicity of diquat including 
developmental and reproductive toxicity. The assessment revised the RfD 
from 0.002 mg/kg-day to 0.005 mg/kg-day and developed a cancer 
classification of E, evidence of noncarcinogenicity (USEPA, 2001a). 
Based on the new OPP assessment and RfD of 0.005 mg/kg-day, and 
assuming a 70-kg adult body weight and 2 liters water intake per day, 
the DWEL could

[[Page 15541]]

be 0.175 mg/L. An RSC of 20 percent results in a possible MCLG of 0.035 
mg/L, rounded to 0.04 mg/L.
    Analytical feasibility does not pose any limitations for the 
current MCL and would not be a limiting factor if EPA were to raise the 
MCLG. EPA evaluated the available occurrence and exposure information 
for diquat to determine whether a revised MCLG/MCL would be likely to 
result in a meaningful opportunity to achieve cost savings for PWSs and 
their customers while maintaining, or improving, the level of public 
health protection (USEPA, 2009f). Although the Agency obtained and 
evaluated the finished water occurrence data for diquat, its usefulness 
is limited for determining potential cost savings to PWS and their 
customers because the Agency does not know which systems are treating 
for this contaminant. As an alternative, the Agency evaluated available 
data on source water quality and conducted a qualitative assessment of 
treatment cost savings. Because the primary informations sources used 
to evaluate potential source water occurrence--STORET and NAWQA--do not 
report monitoring results for diquat, the Agency obtained available 
information on diquat use and fate and transport.
    Diquat's primary uses are as an algaecide, defoliant, desiccant, 
and herbicide (USEPA, 1995a). The most recent pesticide application 
estimates in the Pesticide Use Database developed by the National 
Center for Food and Agricultural Policy (NCFAP) indicate overall 
cropland application of almost 270,000 pounds in 1997, primarily on 
potato and alfalfa crops (NCFAP, 2000). The NCFAP based these estimates 
on State-level pesticide usage patterns for the period 1994-1998 and 
State-level crop acreage for 1997. These estimates reflect several 
limitations: they do not include noncropland applications, the data 
sources vary in quality, and State-level pesticide use data gaps are 
filled using data for nearby states. The USGS estimated county-level 
pesticide usage for 2002 based on crop acreage estimates in the 2002 
Census of Agriculture and State-level application rates for the period 
1999-2004 developed by the CropLife Foundation (USGS, no date), which 
implemented the NCFAP method for estimating pesticide usage (Gianessi 
and Regner, 2006) and, therefore, has similar limitations. The USGS 
estimates total diquat application to crops of approximately 200,000 
pounds per year, with potatoes accounting for almost 90 percent of 
these applications (USGS, no date). Diquat use on crops occurred 
primarily in regions of New England, the Great Lakes, North Dakota, the 
Pacific Northwest, California, and Florida. In comparison to other 
commonly used pesticides, diquat has the lowest national estimate for 
use on crops (Gianessi and Regner, 2006).
    The Reregistration Eligibility Decision (RED) for Diquat Dibromide 
(USEPA, 1995a) notes that although diquat is persistent (i.e., it does 
not hydrolyze and is resistant to degradation), it becomes immobile 
when it adsorbs to soil particles and, therefore, is not expected to 
contaminate ground water. Furthermore, diquat dissipates quickly from 
surface water because it adsorbs to soil sediments, vegetation, and 
organic matter; the estimated half-life is 1 to 2 days for diquat in 
surface water based on a study of two ponds in Florida (USEPA, 1995a). 
These factors indicate the possibility of low occurrence in drinking 
water sources.
    The BAT and small system compliance technologies for diquat have 
other beneficial effects, e.g., removing other co-occurring 
contaminants. Therefore, if EPA were to consider a higher level, the 
Agency does not know how many PWSs that are currently treating to 
comply with the existing MCL of 0.02 mg/L would be likely to 
discontinue treatment that is already in place (USEPA, 2009d). Also, 
the Agency does not know to what extent affected systems might be able 
to reduce costs given that capital costs are not recoverable. However, 
the Agency recognizes that there may be opportunities to achieve 
operational cost savings if these systems are able to re-optimize 
current treatment.
    Given these considerations, the Agency believes that any resulting 
revision is not likely to provide a meaningful opportunity for cost 
savings. In view of this, any revision would be a low priority activity 
and not appropriate at this time.
    c. Review Result. Although there are new data that support 
consideration of whether to revise the MCLG/MCL for diquat, EPA does 
not believe a revision to the NPDWR for diquat is appropriate at this 
time. In making this decision, the Agency considered whether any 
possible revision to the NPDWR for diquat is likely to provide a 
meaningful opportunity for cost savings to public water systems and 
their customers. After consideration of this factor, EPA has decided 
that any revision to the NPDWR would be a low priority activity for the 
Agency, and, thus, is not appropriate to revise at this time because 
of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
34. 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. EPA based the MCLG on a reference dose of 
0.02 mg/kg-day and a cancer classification of D, not classifiable as to 
human carcinogenicity.
    b. Technical Reviews. In 2005, the Agency updated its health 
effects assessment of endothall (USEPA, 2005d). The Agency identified a 
change in this assessment that could lead to a change in the MCLG. This 
assessment considered relevant studies on the toxicity of endothall 
including developmental and reproductive toxicity. The assessment 
revised the RfD from 0.02 mg/kg-day to 0.007 mg/kg-day and concluded 
that endothall is unlikely to be carcinogenic to humans (USEPA, 2005d). 
Based on the new OPP assessment and RfD of 0.007 mg/kg-day, and 
assuming a 70-kg adult body weight and 2 liters water intake per day, 
the DWEL could be 0.245 mg/L. An RSC of 20 percent results in a 
possible MCLG of 0.05 mg/L.
    Because of a possible change in the MCLG for endothall, EPA 
considered whether analytical feasibility is likely to be a limitation 
if the Agency were to consider lowering the MCL to 0.05 mg/L (the 
possible MCLG). EPA reviewed PE data from the first Six-Year Review 
cycle and then analyzed more recent PT data to determine if the PQL can 
be revised (i.e., analytical feasibility). Passing rates for PE data 
available through late 1999 for endothall are generally above 80 
percent, but there were no results for PE studies with true values 
below the current PQL of 0.09 mg/L. More recent PT data from late 1999 
through 2004, supplied by a PT provider, show passing rates above 75 
percent for most studies, but there are four studies with passing rates 
equal to or less than the 75 percent criterion, including two close to 
the current PQL. No PT studies had true values below the current PQL. 
Given the variable results from the PT studies and the lack of PE and 
PT study results below the current PQL, PE and PT data are insufficient 
to support a PQL reduction (USEPA, 2009c).
    While the PT data are not sufficient to support a lowering of the 
PQL for endothall at this time, the current PQL of 0.09 mg/L is greater 
than the possible MCLG. It would therefore limit a possible revision to 
the MCL. EPA

[[Page 15542]]

evaluated two alternative sources of information to determine whether 
they indicate any potential to revise the PQL: laboratory minimum 
reporting levels in the Six-Year Review ICR dataset, and the MDLs for 
the approved method for the detection of endothall (Method 548.1). 
While EPA prefers to use laboratory performance data to calculate the 
PQL, the MRL and MDL information can be valuable for this review to 
indicate whether it is possible to quantitate at levels below the 
current PQL. The Six-Year Review ICR dataset contains MRL values for 
21,792 samples. Of these, 21,445 (98 percent) have an MRL value of 0.05 
mg/L or lower. Because more than 80 percent of the MRL values are at or 
below the possible MCLG of 0.05 mg/L, EPA selected that value as the 
minimum threshold for the occurrence and exposure analysis (USEPA, 
2009e). The MDL of the approved method is 0.00179 mg/L. Applying a 
multiplier of 10 would give a possible PQL of 0.0179 mg/L,which is 
below the possible MCLG (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of 
information, there is evidence of a potential to lower the PQL for 
endothall even though the PE and PT data are insufficient to support a 
PQL reduction. To determine whether any MCL revision is likely to 
provide a meaningful opportunity to improve public health protection, 
EPA evaluated the occurrence of endothall at the possible MCLG of 0.05 
mg/L (USEPA, 2009f). Table VI-15 shows the results of the occurrence 
and exposure analysis for the current MCL and the possible MCLG set 
equal to 0.05 mg/L based on the new health effects information and the 
laboratory minimum reporting levels in the Six-Year Review ICR dataset. 
The occurrence and exposure analysis shows that average concentrations 
do not exceed the current MCL for any system in the analysis. Note that 
these results are based on the subset of monitoring data provided in 
response to the Six-Year Review ICR and do not necessarily reflect MCL 
violations, which are based on running annual average concentrations at 
entry points; nevertheless, SDWIS/FED indicates no MCL violations for 
endothall between 1998 and 2005 (USEPA, 2007g). The average 
concentration at one of the 14,156 systems (0.007 percent), serving 
10,000 people (or 0.008 percent of 119 million people), exceeds the 
possible MCLG based on new health effects information (0.05 mg/L).

     Table VI-15--Number and Percent of Systems With Mean Concentrations Exceeding Endothall Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                     health-based threshold (percentages based on 14,156 systems with endothall
    Regulatory or health-based                  data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.1 mg/L)...................  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
Possible MCLG (0.05 mg/L)........  1 (0.007%)...............  1 (0.007%)..............  1 (0.007%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (percentages based on 118,536,800 people
                                        served by the systems with endothall data in the Six-Year Review ICR
                                                                 occurrence dataset)
                                  ------------------------------------------------------------------------------
    Regulatory or health-based     Nondetect values = MRL     Nondetect values = \1/2\  Nondetect values = 0 \3\
            threshold               \1\                        MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (0.1 mg/L)...................  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
Possible MCLG (0.05 mg/L)........  10,000 (0.008%)..........  10,000 (0.008%).........  10,000 (0.008%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. Although there are new data that support 
consideration of whether to revise the MCLG/MCL for endothall, EPA does 
not believe a revision to the NPDWR for endothall is appropriate at 
this time. In making this decision, the Agency considered whether any 
possible revision to the NPDWR for endothall is likely to provide a 
meaningful opportunity for health risk reductions. Taking into 
consideration the low occurrence of this contaminant, EPA has decided 
that any revision to the NPDWR would be a low priority activity for the 
Agency, and, thus, is not appropriate to revise at this time because 
of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
35. 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. EPA based the MCLG on a reference dose of 0.0003 
mg/kg-day and a cancer classification of D, not classifiable as to 
human carcinogenicity.
    b. Technical Reviews. 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, 
2009b).
    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. 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.
    c. Review Result. EPA's review shows that there are no data 
supporting a change to the endrin NPDWR. As a result, a revision to the 
NPDWR would not be appropriate at this time.

[[Page 15543]]

36. Epichlorohydrin
    a. Background. EPA published the current NPDWR for epichlorohydrin 
on January 30, 1991 (56 FR 3526 (USEPA, 1991c)). 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 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 mg/L (ppm).
    b. Technical Reviews. As part of the Six-Year Review process, EPA 
conducted a literature search for relevant data on the carcinogenicity 
of epichlorohydrin as well as its potential developmental and 
reproductive toxicity. EPA has not identified any new information that 
indicates that it is appropriate to consider revisions to the cancer 
classification for epichlorohydrin at this time (USEPA, 2009b). 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.
    EPA has identified information that suggests that the residual 
epichlorohydrin content in water treatment polymers has decreased 
significantly, likely due to improvements in manufacturing processes 
and technologies (USEPA, 2009g). NSF International analyses conducted 
between January 2005 and June 2007 found that, in 84 epichlorohydrin-
based polymers/co-polymers submitted for certification under NSF 
Standard 60, the residual epichlorohydrin content was always below the 
detection limit of 0.002 percent.
    Epichlorohydrin standards in Europe and Australia are also stricter 
than the NPDWR. Based on the concentration of dose and monomer level in 
the NPDWR, finished water could contain up to 2 [mu]g/L (ppb) of 
epichlorohydrin. By contrast, the European Union requires that finished 
water contain less than 0.1 [mu]g/L (ppb) epichlorohydrin, and 
Australia requires that the concentration in finished water be less 
than 0.5 [mu]g/L (ppb). The United Kingdom requires that polymers used 
in drinking water contain less than 0.002 percent residual 
epichlorohydrin, and the dose of these polymers be less than 5 mg/L 
(ppm) at all times, for a maximum finished water concentration of 0.1 
[mu]g/L (ppb).
    To assess the occurrence of epichlorohydrin in drinking water, EPA 
sought data on current usage practices for polymers containing it. The 
Agency is not presently aware of any recent, large-scale studies of 
polymer usage in drinking water facilities, and therefore cannot fully 
characterize the occurrence of epichlorohydrin in drinking water. 
However, cationic polymers used in water treatment often contain 
epichlorohydrin. The 1996 WATER:\STATS database (described in Levine et 
al., 2004), based on an AWWA survey, indicates that 13 percent of 
ground water systems and 66 percent of surface water systems surveyed 
use a polymer for water treatment. Many of these are cationic polymers, 
particularly for surface water systems; cationic polymers used to treat 
drinking water often use epichlorohydrin monomer.
    Additional information on the extent of use of epichlorohydrin 
based polymers/co-polymers in drinking water would further assist the 
Agency in evaluating the potential public health benefits associated 
with a revision to the treatment technique for epichlorohydrin. Because 
most epichlorohydrin-based polymers available today have a 
significantly lower residual monomer content than that specified in the 
treatment technique (2009g), EPA believes that the costs of a revision 
would be minimal and recognizes that benefits may also be small.
    c. Review Result. The Agency believes it is appropriate to revise 
the NPDWR for epichlorohydrin. The existing MCLG is zero (based on the 
current B2 cancer classification) and NSF International data indicate 
that epichlorohydrin based polymers/copolymers are widely available 
with lower monomer levels than required by the existing NPDWR. Hence, 
revisions to the epichlorohydrin NPDWR will provide a meaningful 
opportunity to maintain the health risk reductions achieved by 
technological advances in manufacturing. As discussed in Section VII, 
the Agency solicits public comment on the use of epichlorohydrin-based 
polymers/co-polymers in drinking water facilities (since this may 
provide additional information on the occurrence of epichlorohydrin in 
drinking water) to help inform the regulatory revisions. EPA notes that 
any changes to the NPDWR for epichlorohydin may also include revisions 
to the closely related NPDWR for acrylamide.
37. Ethylbenzene
    a. Background. EPA published the current NPDWR for ethylbenzene on 
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an 
MCLG and an MCL of 0.7 mg/L. EPA based the MCLG on a reference dose of 
0.1 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 ethylbenzene. The revised 
health effects assessment will consider relevant studies on the 
toxicity of ethylbenzene, including its potential developmental and 
reproductive toxicity. The new health effects assessment was not 
completed by March 1, 2009, the review cutoff date for this notice 
(USEPA, 2009b). The IRIS Substance Assessment Tracking System Web site 
(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 
information on the status of the health effects assessment.
    c. Review Result. Since the MCL for ethylbenzene is set at its MCLG 
and a reassessment of the health risks resulting from exposure to 
ethylbenzene is in progress, the Agency does not believe a revision to 
the NPDWR is appropriate at this time.
38. Ethylene Dibromide (EDB; 1,2-Dibromoethane)
    a. Background. EPA published the current NPDWR for EDB on January 
30, 1991 (56 FR 3526 (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 0.00005 mg/L, based on analytical 
feasibility.
    b. Technical Reviews. The Agency updated the health effects 
assessment for EDB in 2004 and retained the cancer classification on 
which the 1991 MCLG is based (USEPA, 2004a). As a part of the 2004 
assessment, EPA considered relevant studies on the toxicity of EDB, 
including its potential developmental and reproductive toxicity.
    The current MCL for EDB is based on a PQL of 0.00005 mg/L. For the 
Six-Year Review, the Agency considered whether changes in the 
analytical feasibility of EDB might lead to a lower MCL. EPA reviewed 
PE data from the first Six-Year Review cycle and then analyzed more 
recent PT data to determine if the PQL can be revised (i.e., analytical 
feasibility). Passing rates for PE data available through late 1999 for 
EDB are all 75 percent or higher. However, the true concentrations were 
all higher than the current PQL of 0.00005 mg/L. More

[[Page 15544]]

recent PT data from late 1999 through 2004, supplied by a PT provider, 
likewise show passing rates of 75 percent or higher, but again, all of 
the true concentrations in the PT data were higher than the current 
PQL. Because of the lack of data below the PQL, a lowering of the PQL 
for EDB is not appropriate at this time (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of EDB (Methods 504.1 and 551.1). While EPA 
prefers to use laboratory performance data to calculate the PQL, the 
MRL and MDL information can be valuable for this review to indicate 
whether it is possible to quantitate at levels below the current PQL. 
The Six-Year Review ICR dataset contains MRL values for 83,063 samples. 
Fewer than 80 percent of these values are less than or equal the modal 
MRL: 26,926 (32 percent) equal the modal MRL of 0.00001 mg/L and an 
additional 454 (0.5 percent) are lower than 0.00001 mg/L. Therefore, 
EPA did not set the EQL equal to the modal MRL (USEPA, 2009e). The MDLs 
of approved methods are 0.00001 and 0.000032 mg/L. Applying a 
multiplier of 5, which was used to establish the PQL, would give a 
possible PQL range from 0.00005 to 0.00016 mg/L. The result is higher 
than or equal to the current PQL and, therefore, EPA did not estimate 
an EQL (USEPA, 2009e). Based on these varied and unrelated approaches/
sources of information, EPA believes that there is no potential to 
lower the PQL. Since the MCL is constrained by the PQL, and the PQL is 
unchanged, EPA does not believe it is necessary to conduct an 
occurrence analysis at this time.
    c. Review Result. EPA did not identify new data that support 
consideration of a possibly lower PQL (and therefore a possibly lower 
MCL). Therefore, EPA does not believe a revision to the NPDWR for EDB 
is appropriate at this time.
39. Fluoride
    a. Background. EPA published the current NPDWR for fluoride on 
April 2, 1986 (51 FR 11396 (USEPA, 1986c)). 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 lowest-
observed-adverse-effect level (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 was considered to be an adverse 
cosmetic effect. PWSs exceeding the fluoride SMCL must provide public 
notification to their customers.
    Fluoride is unique 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.
    b. Technical Reviews. As a result of the first Six-Year Review of 
the fluoride NPDWR (67 FR 19030 (USEPA, 2002c) (preliminary); 68 FR 
42908 (USEPA, 2003e) (final)), EPA requested that the National Research 
Council (NRC) of the National Academies of Science (NAS) conduct a 
review of the recent health and exposure data on orally ingested 
fluoride. In 2006, the NRC published the results of their evaluation in 
a report entitled, Fluoride in Drinking Water: A Scientific Review of 
EPA's Standards. Based on its review, NRC concluded that severe dental 
fluorosis is an adverse health effect when it causes confluent thinning 
and pitting of the enamel, a situation that compromises the function of 
the enamel in protecting the dentin and eventually the pulp from decay 
and infection. There was consensus among the committee that severe 
dental fluorosis is an effect that should be avoided and that 
``exposure at the MCLG clearly puts children at risk of developing 
severe enamel fluorosis.'' In addition, the committee examined the 
scientific data on the impact of fluoride on the strength and structure 
of bone and the majority concluded that the MCLG ``is not likely to be 
protective against bone fractures.'' NRC recommended that EPA use the 
available dose-response data for the effects of fluoride on severe 
dental fluorosis and skeletal fractures in combination with data on the 
relative contribution of drinking water to total fluoride exposure to 
identify an MCLG that would be protective against these effects.
    The NRC also evaluated the impact of fluoride on reproduction and 
development, neurotoxicity and behavior, the endocrine system, 
genotoxicity, cancer and other effects. They concluded that the 
available data were inadequate to determine if a risk for effects on 
these endpoints exists at an MCLG of 4 mg/L and made recommendations 
for additional research. After considering the genotoxicity data, 
cancer studies in humans and animals, and studies of mode of action in 
cell systems, NRC determined that the evidence on the potential of 
fluoride to initiate or promote cancers, particularly of the bone, is 
tentative and mixed. They recommended that EPA await the results and 
publication of an in-process hospital-based, case-control study of 
osteosarcoma and fluoride exposure from the Harvard School of Dental 
Medicine before determining if an Agency update of the cancer risk 
assessment for fluoride is necessary.\19\
---------------------------------------------------------------------------

    \19\ At this time, the results of the osteosarcoma cancer study 
recommended by NAS have not been published.
---------------------------------------------------------------------------

    c. Review Result. The Agency does not believe a revision to the 
NPDWR for fluoride is appropriate at this time because the Agency's 
Office of Water (OW) is in the process of developing its dose-response 
assessment of the noncancer impacts of fluoride on severe dental 
fluorosis and the skeletal system. In addition, the OW is updating its 
evaluation of the relative contribution of drinking water to total 
fluoride exposure considering the contributions from dental products, 
foods, pesticide residues, and other sources such as ambient air and 
medications. Once the Agency completes and publishes peer reviewed 
versions of these in-process assessments, it will be able to determine 
the potential impacts on the MCLG, MCL, and/or the SMCL and whether any 
revisions to these would be appropriate.
40. 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. EPA based the MCLG on a reference dose of 
0.1 mg/kg-day and a cancer classification of D, not classifiable as to 
human carcinogenicity.
    b. Technical Reviews. In 2002, the Agency updated its health 
effects assessment of glyphosate (USEPA, 2002a). The Agency identified 
a change in this assessment that could lead to a change in the MCLG. 
This assessment considered relevant studies on the toxicity of 
glyphosate including developmental and reproductive toxicity. The 
assessment revised the RfD from 0.1 mg/kg-day to 2 mg/kg-day and

[[Page 15545]]

concluded that glyphosate has evidence of non-carcinogenicity in humans 
(USEPA, 2002a). Based on the new OPP assessment and RfD of 2 mg/kg-day, 
and assuming a 70-kg adult body weight and 2 liters water intake per 
day, the DWEL could be 70 mg/L. An RSC of 20 percent results in a 
possible MCLG of 14 mg/L, (USEPA, 2009b).
    Analytical feasibility does not pose any limitations for the 
current MCL and would not be a limiting factor if EPA were to raise the 
MCLG. EPA evaluated the results of the occurrence and exposure analyses 
for glyphosate to determine whether a revised MCLG/MCL would be likely 
to result in a meaningful opportunity to achieve cost savings for PWSs 
and their customers while maintaining, or improving, the level of 
public health protection (USEPA, 2009f). Although the Agency obtained 
and evaluated the finished water occurrence data for glyphosate, its 
usefulness is limited for determining potential cost savings to PWSs 
and their customers because the Agency does not know which systems are 
treating for this contaminant. As an alternative, the Agency evaluated 
available data on source water quality and conducted a qualitative 
assessment of treatment cost savings.
    Table VI-16 provides summary data for contaminant occurrence based 
on maximum sample values for the locations included in the STORET and 
NAWQA data. Although the degree to which these occurrence rates 
represent national drinking water source occurrence is uncertain, the 
information shows no to low occurrence at thresholds levels of 
interest. This information indicates that any resulting NPDWR change 
would not affect systems that rely on source water at any of the NAWQA 
or STORET locations.

  Table VI-16--Ambient Water Quality Monitoring Occurrence Summary for
                               Glyphosate
------------------------------------------------------------------------
                                   Number of locations (% of locations)
      Maximum Concentration      ---------------------------------------
                                      STORET \1\           NAWQA \2\
------------------------------------------------------------------------
Total...........................  241 (100.0%)......  41 (100.0%)
Nondetect.......................  180 (74.7%).......  37 (90.2%)
Detected........................  61 (25.3%)........  4 (9.8%)
Exceeds current MCLG of 0.7 mg/L  0 (0.0%)..........  0 (0.0%)
Exceeds alternative value of      0 (0.0%)..........  0 (0.0%)
 14.0 mg/L.
------------------------------------------------------------------------
\1\ STORET database 2002-2007.
\2\ NAWQA database 1992-2005.
Source: USEPA, 2009d.

    The BAT and small system compliance technologies for glyphosate 
have other beneficial effects, e.g., pretreatment for other co-
occurring contaminants or disinfection. Therefore, if EPA were to 
consider a higher level, the Agency does not know how many PWSs that 
are currently treating to comply with the existing MCL of 0.7 mg/L 
would be likely to discontinue treatment that is already in place 
(USEPA, 2009d). Also, the Agency does not know to what extent affected 
systems might be able to reduce costs given that capital costs are not 
recoverable. However, the Agency recognizes that there may be 
opportunities to achieve operational cost savings if these systems are 
able to re-optimize current treatment.
    Given these considerations, the Agency believes that any resulting 
revision is not likely to provide a meaningful opportunity for cost 
savings. In view of this, any revision would be a low priority activity 
and not appropriate at this time.
    c. Review Result. Although there are new data that support 
consideration of whether to revise the MCLG/MCL for glyphosate, EPA 
does not believe a revision to the NPDWR for glyphosate is appropriate 
at this time. In making this decision, the Agency considered whether 
any possible revision to the NPDWR for glyphosate is likely to provide 
a meaningful opportunity for cost savings to public water systems and 
their customers. Taking into consideration the low occurrence of this 
contaminant in source waters, EPA has decided that any revision to the 
NPDWR would be a low priority activity for the Agency, and, thus, is 
not appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
41. Heptachlor
    a. Background. EPA published the current NPDWR for heptachlor on 
January 30, 1991 (56 FR 3526 (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 0.0004 mg/L, based on 
analytical feasibility.
    b. Technical Reviews. As part of the Six-Year Review process, EPA 
conducted a literature search for relevant data on the carcinogenicity 
of heptachlor as well as its potential developmental and reproductive 
toxicity. EPA has not identified any new information that indicates 
that it is appropriate to consider revisions to the cancer 
classification for heptachlor at this time (USEPA, 2009b). Because the 
MCLG remains at zero, 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. 
For the Six-Year Review, the Agency considered whether changes in the 
analytical feasibility of heptachlor might lead to a lower MCL. EPA 
reviewed PE data from the first Six-Year Review cycle and then analyzed 
more recent PT data to determine if the PQL can be revised (i.e., 
analytical feasibility). Passing rates for PE data available through 
late 1999 for heptachlor are above 90 percent around the current PQL of 
0.0004 mg/L, including three studies with true values below the current 
PQL. All passing rates in the PE data exceeded 80 percent. More recent 
PT data from late 1999 through 2004, supplied by a PT provider, show 
greater than 75 percent passing rates for a majority of studies, but 
there are no studies with true values below the current PQL. There are 
three PT studies with passing rates below 75 percent. Despite this 
variability, most of the laboratory passing rates from PE and PT 
studies, including three with true values below the PQL, exceeded the 
75 percent criterion typically used to derive a PQL. Therefore, a 
lowering of the PQL for heptachlor might be possible. These results, 
however, are insufficient to recalculate a revised PQL for heptachlor 
because not enough data points are available below the current

[[Page 15546]]

PQL to derive a value at the 75 percent passing rate (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of heptachlor (Methods 505, 508, 508.1, 
525.2, and 551.1). While EPA prefers to use laboratory performance data 
to calculate the PQL, the MRL and MDL information can be valuable for 
this review to indicate whether it is possible to quantitate at levels 
below the current PQL. The Six-Year Review ICR dataset contains MRL 
values for 58,758 samples. Fewer than 80 percent of these values are 
less than or equal the modal MRL: 24,918 (42 percent) equal the modal 
MRL of 0.00004 mg/L and an additional 7,966 (14 percent) are lower than 
0.00004 mg/L. Therefore, EPA did not set the EQL equal to the modal MRL 
(USEPA, 2009e). The MDLs of approved methods are 0.000003, 0.0000015, 
0.000005, 0.00015, and 0.000081 mg/L. Applying a multiplier of 10 would 
give a possible PQL range from 0.000015 to 0.0015 mg/L. EPA used the 
median 10xMDL value of 0.00005 mg/L and rounded up to 0.0001 mg/L for 
the EQL (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of 
information, EPA believes that there may be potential to lower the PQL 
for heptachlor. To determine whether any MCL revision is likely to 
provide a meaningful opportunity to improve public health protection, 
EPA evaluated the occurrence of heptachlor at the EQL of 0.0001 mg/L 
and additional threshold of 0.0002 mg/L (USEPA, 2009f). Table VI-17 
shows the results of the occurrence and exposure analysis for the 
current MCL and these thresholds. The occurrence and exposure analysis 
shows that average concentrations exceed the current MCL for one of 
33,020 systems (0.003 percent) serving 325 people (or 0.0002 percent of 
184 million people). Note that these results are based on the subset of 
monitoring data provided in response to the Six-Year Review ICR and do 
not necessarily reflect MCL violations, which are based on annual 
average concentrations at entry points; SDWIS/FED indicates no MCL 
violations for heptachlor between 1998 and 2005 (USEPA, 2007g). Average 
concentrations at 42 of 33,020 systems (0.127 percent), serving 31,500 
people (or 0.017 percent of 184 million people), exceed the EQL of 
0.0001 mg/L.

     Table VI-17--Number and Percent of Systems With Mean Concentrations Exceeding Heptachlor Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                       feasibility-based threshold (percentages based on 33,020 systems with
 Regulatory or feasibility-based           heptachlor data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.0004 mg/L)................  1 (0.003%)...............  1 (0.003%)..............  1 (0.003%)
\1/2\ MCL (0.0002 mg/L)..........  1 (0.003%)...............  1 (0.003%)..............  1 (0.003%)
EQL (0.0001 mg/L)................  42 (0.127%)..............  42 (0.127%).............  42 (0.127%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (percentages based on 184,444,000 people
                                        served by the systems with heptachlor data in the Six-Year Review ICR
                                                                 occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based     Nondetect values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
            threshold                          \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (0.0004 mg/L)................  325 (0.0002%)............  325 (0.0002%)...........  325 (0.0002%)
\1/2\ MCL (0.0002 mg/L)..........  325 (0.0002%)............  325 (0.0002%)...........  325 (0.0002%)
EQL (0.0001 mg/L)................  31,500 (0.017%)..........  31,500 (0.017%).........  31,500 (0.019%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. 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 heptachlor is 
appropriate at this time. The occurrence and exposure analysis based on 
possible changes in analytical feasibility indicates that any revision 
to the MCL is unlikely to provide a meaningful opportunity to improve 
public health protection. Taking into consideration the low occurrence 
of this contaminant, EPA has decided that any revision to the NPDWR 
would be a low priority activity for the Agency, and, thus, is not 
appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
42. Heptachlor Epoxide
    a. Background. EPA published the current NPDWR for heptachlor 
epoxide on January 30, 1991 (56 FR 3526 (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 0.0002 
mg/L, based on analytical feasibility.
    b. Technical Reviews. As part of the Six-Year Review process, EPA 
conducted a literature search for relevant data on the carcinogenicity 
of heptachlor epoxide as well as its potential developmental and 
reproductive toxicity. EPA has not identified any new information that 
indicates that it is appropriate to consider revisions to the cancer 
classification for heptachlor epoxide at this time (USEPA, 2009b). 
Because the MCLG remains at zero, 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. For the Six-Year Review, the Agency

[[Page 15547]]

considered whether changes in the analytical feasibility of heptachlor 
epoxide might lead to a lower MCL. EPA reviewed PE data from the first 
Six-Year Review cycle and then analyzed more recent PT data to 
determine if the PQL can be revised (i.e., analytical feasibility). 
Passing rates for PE data available through late 1999 for heptachlor 
epoxide are above 85 percent around the current PQL of 0.0002 mg/L, 
including two studies with true values below the current PQL. All 
passing rates in the PE data exceeded 80 percent. More recent PT data 
from late 1999 through 2004, supplied by a PT provider, show greater 
than 75 percent passing rates for a majority of studies, but there are 
no studies with true values below the PQL. There are two PT studies 
with passing rates below 75 percent. Despite this variability, most of 
the laboratory passing rates from PE and PT studies exceeded the 75 
percent criterion typically used to derive a PQL. Therefore, a lowering 
of the PQL for heptachlor epoxide might be possible. These results, 
however, are insufficient to recalculate a revised PQL for heptachlor 
epoxide because not enough data points are available below the current 
PQL to derive a value at the 75 percent passing rate (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: Laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of heptachlor epoxide (Methods 505, 508, 
508.1, 525.2, and 551.1). While EPA prefers to use laboratory 
performance data to calculate the PQL, the MRL and MDL information can 
be valuable for this review to indicate whether it is possible to 
quantitate at levels below the current PQL. The Six-Year Review ICR 
dataset contains MRL values for 58,731 samples. Fewer than 80 percent 
of these values are less than or equal the modal MRL: 26,424 (45 
percent) equal the modal MRL of 0.00002 mg/L and an additional 5,969 
(10 percent) are lower than 0.00002 mg/L. Therefore, EPA did not set 
the EQL equal to the modal MRL (USEPA, 2009e). The MDLs of approved 
methods are 0.000004, 0.0000059, 0.000001, 0.00013, and 0.000202 mg/L. 
Applying a multiplier of 10 would give a possible PQL range from 
0.00001 to 0.00202 mg/L. EPA used the median 10 x MDL value of 0.000059 
mg/L and rounded up to 0.0001 mg/L for the EQL (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of 
information, EPA believes that there may be potential to lower the PQL 
for heptachlor epoxide. To determine whether any MCL revision is likely 
to provide a meaningful opportunity to improve public health 
protection, EPA evaluated the occurrence of heptachlor epoxide at an 
EQL of 0.0001 mg/L (USEPA, 2009f). Table VI-18 shows the results of the 
occurrence and exposure analysis for the current MCL and an EQL. The 
occurrence and exposure analysis shows that average concentrations 
exceed the current MCL for one of 33,015 systems (0.003 percent) 
serving 325 people (or 0.0002 percent of 184 million people). Note that 
these results are based on the subset of monitoring data provided in 
response to the Six-Year Review ICR and do not necessarily reflect MCL 
violations, which are based on annual average concentrations at entry 
points; SDWIS/FED indicates two MCL violations for heptachlor epoxide 
between 1998 and 2005 (USEPA, 2007g). Average concentrations at three 
of 33,015 systems (0.009 percent), serving 14,400 people (or 0.008 
percent of 184 million people), exceed the EQL of 0.0001 mg/L.

 Table VI-18--Number and Percent of Systems With Mean Concentrations Exceeding Heptachlor Epoxide Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                       feasibility-based threshold (percentages based on 33,015 systems with
 Regulatory or feasibility-based       heptachlor epoxide data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.0002 mg/L)................  1 (0.003%)...............  1 (0.003%)..............  1 (0.003%)
EQL (0.0001 mg/L)................  3 (0.009%)...............  3 (0.009%)..............  3 (0.009%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (percentages based on 184,478,000 people
                                      served by the systems with heptachlor epoxide data in the Six-Year Review
                                                               ICR occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based     Nondetect values = MRL   Nondetect Values = \1/2\  Nondetect Values = 0 \3\
            threshold                          \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (0.0002 mg/L)................  325 (0.0002%)............  325 (0.0002%)...........  325 (0.002%)
EQL (0.0001 mg/L)................  14,400 (0.008%)..........  14,400 (0.008%).........  14,400 (0.008%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. 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 heptachlor 
epoxide is appropriate at this time. The occurrence and exposure 
analysis based on possible changes in analytical feasibility indicates 
that any revision to the MCL is unlikely to provide a meaningful 
opportunity to improve public health protection. Taking into 
consideration the low occurrence of this contaminant, EPA has decided 
that any revision to the NPDWR would be a low priority activity for the 
Agency, and, thus, is not appropriate to revise at this time because 
of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.

[[Page 15548]]

43. 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. As part of the Six-Year Review process, EPA 
conducted a literature search for relevant data on the carcinogenicity 
of hexachlorobenzene as well as its potential developmental and 
reproductive toxicity. EPA has not identified any new information that 
indicates that it is appropriate to consider revisions to the cancer 
classification for hexachlorobenzene at this time (USEPA, 2009b). 
Because the MCLG remains at zero, 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. For the Six-Year Review, the Agency considered whether changes in 
the analytical feasibility of hexachlorobenzene might lead to a lower 
MCL. EPA reviewed PE data from the first Six-Year Review cycle and then 
analyzed more recent PT data to determine if the PQL can be revised 
(i.e., analytical feasibility). Passing rates for PE data available 
through late 1999 for hexachlorobenzene are above 80 percent around the 
current PQL of 0.001 mg/L, including eight studies with true values 
below the current PQL. More recent PT data from late 1999 through 2004, 
supplied by a PT provider, also show greater than 75 percent passing 
rates for a majority of studies, including eight out of nine studies 
with true values below the current PQL. There are two PT studies with 
passing rates equal to or less than 75 percent, including one with a 
true value below the PQL. Despite this variability, most of the 
laboratory passing rates from PE and PT studies--including several with 
true concentrations below the PQL--exceeded the 75 percent criterion 
typically used to derive a PQL. Therefore, a lowering of the PQL for 
hexachlorobenzene might be possible. These results, however, are 
insufficient to recalculate a revised PQL for hexachlorobenzene because 
not enough data points are available below the current PQL to derive a 
value at the 75 percent passing rate (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: Laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of hexachlorobenzene (Methods 505, 508, 
508.1, 525.2, and 551.1). While EPA prefers to use laboratory 
performance data to calculate the PQL, the MRL and MDL information can 
be valuable for this review to indicate whether it is possible to 
quantitate at levels below the current PQL. The Six-Year Review ICR 
dataset contains MRL values for 58,713 samples. More than 80 percent of 
these values are less than or equal the modal MRL: 40,791 (69 percent) 
equal the modal MRL of 0.0001 mg/L and an additional 7,380 (13 percent) 
are lower than 0.0001 mg/L. Therefore, EPA selected the modal MRL as 
the EQL (USEPA, 2009e). The MDLs of approved methods are 0.000002, 
0.0000077, 0.000001, 0.00013, and 0.000003 mg/L. Applying a multiplier 
of 10 would give a possible PQL range from 0.00001 to 0.0013 mg/L, 
which contains the EQL (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of 
information, EPA believes that there is potential to lower the PQL for 
hexachlorobenzene. To determine whether any MCL revision is likely to 
provide a meaningful opportunity to improve public health protection, 
EPA evaluated the occurrence of hexachlorobenzene at the EQL of 0.0001 
mg/L and an additional threshold of 0.0005 mg/L (USEPA, 2009f). Table 
VI-19 shows the results of the occurrence and exposure analysis for the 
current MCL and these thresholds. The occurrence and exposure analysis 
shows that average concentrations exceed the current MCL for three of 
32,826 systems (0.009 percent) serving 2,000 people (or 0.001 percent 
of 184 million people). Note that these results are based on the subset 
of monitoring data provided in response to the Six-Year Review ICR and 
do not necessarily reflect MCL violations, which are based on annual 
average concentrations at entry points; SDWIS/FED indicates two MCL 
violations for hexachlorobenzene between 1998 and 2005 (USEPA, 2007g). 
Average concentrations at 9 to 16 of 32,826 systems (0.027 to 0.049 
percent), serving approximately 9,000 to 94,000 people (or 0.005 to 
0.051 percent of 184 million people), exceed the EQL of 0.0001 mg/L.

 Table VI-19--Number and Percent of Systems With Mean Concentrations Exceeding Hexachlorobenzene Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                       feasibility-based threshold (percentages based on 32,826 systems with
 Regulatory or feasibility-based       hexachlorobenzene data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.001 mg/L).................  3 (0.009%)...............  3 (0.009%)..............  3 (0.009%)
\1/2\ MCL (0.0005 mg/L)..........  4 (0.012%)...............  4 (0.012%)..............  4 (0.012%)
EQL (0.0001 mg/L)................  not applicable...........  16 (0.049%).............  9 (0.027%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (percentages based on 184,124,800 people
                                    served by the systems with hexachlorobenzene data in the Six-Year Review ICR
                                                                 occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based     Nondetect values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
            threshold                          \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (0.001 mg/L).................  2,000 (0.001%)...........  2,000 (0.001%)..........  2,000 (0.001%)
\1/2\ MCL (0.0005 mg/L)..........  5,000 (0.003%)...........  5,000 (0.003%)..........  5,000 (0.003%)
EQL (0.0001 mg/L)................  not applicable...........  94,000 (0.051%).........  9,000 (0.005%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
  Results are not reported at the EQL of 0.001 mg/L because this is the modal MRL and setting a majority of the
  results equal to this value results in an upwardly biased estimate of the number of systems with mean
  concentrations that exceed this value.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.

[[Page 15549]]

 
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. 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 occurrence and 
exposure analysis based on possible changes in analytical feasibility 
indicates that any revision to the MCL is unlikely to provide a 
meaningful opportunity to improve public health protection. Taking into 
consideration the low occurrence of this contaminant, EPA has decided 
that any revision to the NPDWR would be a low priority activity for the 
Agency, and, thus, is not appropriate to revise at this time because 
of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
44. 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. EPA based the 
MCLG on a reference dose of 0.007 mg/kg-day and a cancer classification 
of D, not classifiable as to human carcinogenicity.
    b. Technical Reviews. In the first Six-Year Review cycle, EPA 
evaluated new information from a health effects assessment completed in 
2001 (USEPA, 2001b). At that time, the Agency could not determine that 
a revision to the NPDWR would provide a meaningful opportunity for 
public health protection (67 FR 19030 (USEPA, 2002c)). The 2001 
assessment considered relevant studies on the toxicity of 
hexachlorocyclopentadiene including developmental and reproductive 
toxicity. The assessment revised the RfD from 0.007 mg/kg-day to 0.006 
mg/kg-day (USEPA, 2001b). In the current review cycle, EPA conducted a 
literature search through June 2007 for relevant data on the toxicology 
of hexachlorocyclopentadiene, including its potential developmental and 
reproductive toxicity. The literature search did not identify any new 
data that would affect the RfD or cancer classification (USEPA, 2009b). 
Based on the 2001 IRIS assessment and RfD of 0.006 mg/kg-day, and 
assuming a 70-kg adult body weight and 2 liters water intake per day, 
the DWEL could be 0.21 mg/L. An RSC of 20 percent results in a possible 
MCLG of 0.04 mg/L (USEPA, 2009b).
    Analytical feasibility does not pose any limitations for the 
current MCL and would not be a limiting factor for the possible MCLG 
decrease under consideration.
    EPA evaluated the results of the occurrence and exposure analyses 
for hexachlorocyclopentadiene to determine whether a revised MCLG/MCL 
would be likely to result in a meaningful opportunity to improve the 
level of public health protection (USEPA, 2009f). Table VI-20 shows the 
results of the occurrence and exposure analysis for the current MCL and 
the possible MCLG. The occurrence and exposure analysis shows that 
average concentrations do not exceed the current MCL for any systems in 
the analysis. Note that these results are based on the subset of 
monitoring data provided in response to the Six-Year Review ICR and do 
not necessarily reflect MCL violations, which are based on running 
annual average concentrations at entry points; SDWIS/FED indicates no 
MCL violations for hexachlorocyclopentadiene between 1998 and 2005 
(USEPA, 2007g). The occurrence and exposure analysis shows that average 
concentration do not exceed the possible MCLG based on health effects 
information (0.04 mg/L).

     Table VI-20--Number and Percent of Systems With Mean Concentrations Exceeding Hexachlorocyclopentadiene
                           Thresholds and Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                          health-based threshold (percentages based on 32,801 systems with
    Regulatory or health-based     hexachlorocyclopentadiene data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.05 mg/L)..................  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
Possible MCLG (0.04 mg/L)........  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (percentages based on 184,738,000 people
                                      served by the systems with hexachlorocyclopentadiene data in the Six-Year
                                                           Review ICR occurrence dataset)
                                  ------------------------------------------------------------------------------
    Regulatory or health-based       Nondetect values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
            threshold                          \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (0.05 mg/L)..................  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
Possible MCLG (0.04 mg/L)........  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. Although there are new data that support 
consideration of whether to revise the MCLG/MCL for 
hexachlorocyclopentadiene, EPA does not believe a revision to the NPDWR 
for hexachlorocyclopentadiene is appropriate at this time. In making 
this

[[Page 15550]]

decision, the Agency considered whether any possible revision to the 
NPDWR for hexachlorocyclopentadiene is likely to provide a meaningful 
opportunity for health risk reductions. Taking into consideration the 
low occurrence of this contaminant, EPA has decided that any revision 
to the NPDWR would be a low priority activity for the Agency, and, 
thus, is not appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
45. Lindane (gamma-Hexachlorocyclohexane)
    a. Background. EPA published the current NPDWR for lindane on 
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an 
MCLG and an MCL of 0.0002 mg/L. EPA based the MCLG on a reference dose 
of 0.0003 mg/kg-day and a cancer classification of C, possible human 
carcinogen.
    b. Technical Reviews. In the first Six-Year Review cycle, EPA 
evaluated new information from a health effects assessment completed in 
2002 (USEPA, 2006b). At that time, the Agency could not determine that 
a revision to the NPDWR would provide a meaningful opportunity for cost 
savings to public water systems or their customers, and decided that 
any revision would be a low priority activity for the Agency because of 
competing workload priorities, the administrative costs associated with 
rulemaking, and the burden on States and the regulated community to 
implement any regulatory change (68 FR 42908, July 18, 2003 (USEPA, 
2003e)). The 2002 assessment considered relevant studies on the 
toxicity of lindane including developmental and reproductive toxicity. 
The assessment revised the RfD from 0.0003 mg/kg-day to 0.0047 mg/kg-
day and classified it as ``Suggestive evidence of carcinogenicity, but 
not sufficient to assess human carcinogenic potential'' (USEPA, 2006b). 
During the current review cycle, all uses of lindane were cancelled 
voluntarily (71 FR 74905, December 13, 2006 (USEPA, 2006e)), effective 
July 1, 2007. However, lindane is a persistent and bioaccumulative 
pesticide. Accordingly, EPA conducted a literature search for relevant 
data on the toxicology of lindane, including its potential 
developmental and reproductive toxicity. The literature search did not 
identify any additional new data that would affect the RfD or cancer 
classification (USEPA, 2009b).The possible revised MCLG is based on the 
2002 OPP assessment and RfD of 0.0047 mg/kg-day, a body weight of 70 
kg, water intake of 2 L/day, and an RSC of 20 percent. Uncertainty 
factors related to reproductive and developmental effects, and/or a 
possible risk management factor based on the suggested evidence of 
carcinogenicity, could be used in developing a possible revised MCLG. 
Depending on the choice of uncertainty factors, the MCLG could range 
between 0.001 mg/L and 0.03 mg/L.
    Analytical feasibility does not pose any limitations for the 
current MCL and would not be a limiting factor if EPA were to raise the 
MCLG. EPA evaluated the results of the occurrence and exposure analyses 
for lindane to determine whether a revised MCLG/MCL would be likely to 
result in a meaningful opportunity to achieve cost savings for PWSs and 
their customers while maintaining, or improving, the level of public 
health protection (USEPA, 2009f). Although the Agency obtained and 
evaluated the finished water occurrence data for lindane, its 
usefulness is limited for determining potential cost savings to PWSs 
and their customers because the Agency does not know which systems are 
treating for this contaminant. As an alternative, the Agency evaluated 
available data on source water quality and conducted a qualitative 
assessment of treatment cost savings.
    Table VI-21 provides summary data for contaminant occurrence based 
on maximum sample values for the locations included in the STORET and 
NAWQA. Although the degree to which these occurrence rates represent 
national drinking water source occurrence is uncertain, the information 
shows no to low occurrence at threshold levels of interest. In the 
upper bound analysis, an NPDWR change would affect systems that rely on 
source water at less than 0.01 percent of the NAWQA locations and less 
than 0.3 percent of the STORET locations. Any MCLG/MCL revision to a 
potentially higher level of 0.001 mg/L (the lower bound) or 0.03 mg/L 
(the upper bound) would likely affect fewer systems.

  Table VI-21--Ambient Water Quality Monitoring Occurrence Summary for
                                 Lindane
------------------------------------------------------------------------
                                 Number of locations  (% of locations)
    Maximum concentration    -------------------------------------------
                                   STORET \1\             NAWQA \2\
------------------------------------------------------------------------
Total.......................  2,691 (100.0%)......  8,195 (100.0%)
Nondetect...................  2,017 (75%).........  8,058 (98.3%)
Detected....................  674 (25%)...........  137 (1.7%)
Exceeds current MCLG of       7 (0.26%)...........  1 (0.01%)
 0.0002 mg/L.
Exceeds upper bound           1 (0.04%)...........  0 (0.0%)
 alternative value of 0.03
 mg/L.
------------------------------------------------------------------------
1 STORET database 2002-2007.
2 NAWQA database 1992-2005.
Source: USEPA, 2009d.

    The BATs and small system compliance technologies for lindane have 
other beneficial effects, e.g., reduction of other co-occurring 
contaminants, precursors for DBPs, or other common impurities. 
Therefore, if EPA were to consider a higher level, the Agency does not 
know how many PWSs that are currently treating to comply with the 
existing MCL of 0.0002 mg/L would be likely to discontinue treatment 
that is already in place (USEPA, 2009d). Also, the Agency does not know 
to what extent affected systems might be able to reduce costs given 
that capital costs are not recoverable. However, the Agency recognizes 
that there may be opportunities to achieve operational cost savings if 
these systems are able to re-optimize current treatment.
    Given these considerations, the Agency believes that any resulting 
revision is not likely to provide a meaningful opportunity for cost 
savings. In view of this, any revision would be

[[Page 15551]]

a low priority activity and not appropriate at this time.
    c. Review Result. Although there are new data that support 
consideration of whether to revise the MCLG/MCL for lindane, EPA does 
not believe a revision to the NPDWR for lindane is appropriate at this 
time. In making this decision, the Agency considered whether any 
possible revision to the NPDWR for lindane is likely to provide a 
meaningful opportunity for cost savings to public water systems and 
their customers. Taking into consideration the low occurrence of this 
contaminant in source waters, EPA has decided that any revision to the 
NPDWR would be a low priority activity for the Agency, and, thus, is 
not appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
46. Mercury (Inorganic)
    a. Background. EPA published the current NPDWR for inorganic 
mercury on January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR 
established an MCLG and an MCL of 0.002 mg/L. The Agency based the MCLG 
on a DWEL of 0.01 mg/L \20\ and a cancer classification of D, not 
classifiable as to human carcinogenicity.
---------------------------------------------------------------------------

    \20\ 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. As part of the Six-Year Review process, EPA 
conducted a literature search for relevant data on the toxicology of 
inorganic mercury, 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, 2009b).
    A review of analytical or treatment feasibility is not necessary 
for inorganic mercury because changes to the MCLG are not warranted at 
this time and the current MCL is set at the MCLG. Since EPA did not 
identify a health or technology basis for revising the inorganic 
mercury NPDWR, the Agency did not conduct a detailed occurrence and 
exposure analysis.
    c. Review Result. EPA's review shows that there are no data 
supporting a change to the inorganic mercury NPDWR. As a result, a 
revision to the NPDWR would not be appropriate at this time.
47. Methoxychlor
    a. Background. EPA published the current NPDWR for methoxychlor on 
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an 
MCLG and an MCL of 0.04 mg/L. EPA based the MCLG on a reference dose of 
0.005 mg/kg-day and a cancer classification of D, not classifiable as 
to human carcinogenicity.
    b. Technical Reviews. As part of the Six-Year Review process, EPA 
conducted a literature search for relevant data on the toxicology of 
methoxychlor, 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, 
2009b). The Six-Year Review 1 stated that the Agency had initiated a 
reassessment of the health risks posed by exposure to methoxychlor (67 
FR 19030 (USEPA, 2002c)). Since 2002, the Agency has cancelled all 
product uses and concluded that the database to complete the health 
effects assessment for methoxychlor was inadequate (USEPA, 2004c). In 
its Reregistration Eligibility Decision, OPP noted substantive data 
gaps for methoxychlor, including lack of Guideline studies for chronic 
systemic toxicity as well as reproductive and developmental toxicity 
(USEPA, 2004c).
    A review of analytical or treatment feasibility is not necessary 
for methoxychlor because changes to the MCLG are not warranted at this 
time and the current MCL is set at the MCLG. Since EPA did not identify 
a health or technology basis for revising the methoxychlor NPDWR, the 
Agency did not conduct a detailed occurrence and exposure analysis.
    c. Review Result. EPA's review shows that there are no data 
supporting a change to the methoxychlor NPDWR. As a result, a revision 
to the NPDWR would not be appropriate at this time.
48. Monochlorobenzene (Chlorobenzene)
    a. Background. EPA published the current NPDWR for 
monochlorobenzene on January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The 
NPDWR established an MCLG and an MCL of 0.1 mg/L. EPA based the MCLG on 
a reference dose of 0.02 mg/kg-day and a cancer classification of D, 
not classifiable as to human carcinogenicity.
    b. Technical Reviews. As part of the Six-Year Review process, EPA 
conducted a literature search for relevant data on the toxicology of 
monochlorobenzene, 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, 2009b).
    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. 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. Review Result. EPA's review shows that there are no data 
supporting a change to the monochlorobenzene NPDWR. As a result, a 
revision to the NPDWR would not be appropriate at this time.
49. Nitrate (as N)
    a. Background. EPA published the current NPDWR for nitrate on 
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an 
MCLG and an MCL of 10 mg/L (as N). EPA based the MCLG on a survey of 
epidemiologic studies of infant methemoglobinemia in populations 
exposed to nitrate contaminated water. No cancer classification is 
currently available for nitrate (USEPA, 2009b).
    b. Technical Reviews. The health effects technical review 
identified new information on developmental effects of nitrate, as well 
as data regarding its carcinogenicity, that may indicate the need to 
update the Agency's health effects assessment (USEPA, 2009b). Several 
studies suggest that nitrate in drinking water can have adverse effects 
on the thyroid (Mukhopadhyay et al., 2005; Tajtakova et al., 2006; Zaki 
et al., 2004). Nitrate has long been known as a competitive inhibitor 
of iodide uptake in the thyroid (Wolff and Maury, 1963). Inhibition of 
iodide uptake can lead to alteration in thyroid hormone levels 
including decreases in levothyroxine (T4) levels. NAS (1995) stated 
that it is likely that the motor changes reported by Markel et al. 
(1989) when the animals were young were not a direct effect of nitrate, 
but were secondary to effects on learning behavior. Based on these 
considerations, a new assessment of the noncancer effects of nitrate 
may be warranted, including consideration of whether methemoglobinemia 
in infants, which is an acute effect, is still the most appropriate 
basis for the chronic exposure limit for nitrate. In addition, recent 
information may suggest the consideration of separate acute and chronic 
values for nitrate.
    The health effects review identified a number of relevant new 
studies that may warrant a review of the cancer

[[Page 15552]]

classification for nitrate. These studies include a number of new 
epidemiology studies (Cocco et al., 2003; Coss et al., 2004; de Roos et 
al., 2003; Mueller et al., 2004; Volkmer et al., 2005; Ward et al., 
2003; Ward et al., 2005a; Ward et al., 2005b; Ward et al., 2006; Yang 
et al., 2007; Zeegers et al., 2006), as well as a recent report from an 
International Agency for Research on Cancer (IARC) Working group 
(Grosse et al., 2006). This latter report concluded that, under 
conditions that result in endogenous nitrosation, ingested nitrate or 
nitrite is probably carcinogenic to humans.
    In light of this information, EPA considers nitrate as a potential 
candidate for a new health effects assessment. The Agency solicits 
feedback on its plans to reassess health risks resulting from exposure 
to nitrate. The Agency also welcomes any scientific information related 
to nitrate health risks from the public. Because EPA considers nitrate 
as a candidate for a new assessment, EPA does not believe it is 
appropriate to consider any possible revisions to the MCLG (as well as 
the MCL) at this time.
    A review of analytical or treatment feasibility is not necessary 
for nitrate because changes to the MCLG are not warranted at this time 
and the current MCL is set at the MCLG. Since EPA did not identify a 
health or technology basis for revising the nitrate NPDWR, the Agency 
did not conduct a detailed occurrence and exposure analysis.
    c. Review Result. The Agency is considering whether to initiate a 
new health assessment for nitrate and therefore does not believe a 
revision to the NPDWR is appropriate at this time.
    As discussed in Section VII, the Agency is asking for input and 
information about several implementation issues related to nitrate (see 
section V.B.6).
50. Nitrite (as N)
    a. Background. EPA published the current NPDWR for nitrite on 
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an 
MCLG and an MCL of 1 mg/L (as N). EPA based the MCLG on extrapolation 
from nitrate, assuming the conversion of 10 percent of nitrate-nitrogen 
to nitrite-nitrogen. No cancer classification is currently available 
for nitrite (USEPA, 2009b).
    b. Technical Reviews. The health effects technical review 
identified new information on developmental effects of nitrite, as well 
as data regarding its carcinogenicity, that may indicate the need to 
update the Agency's health effects assessment (USEPA, 2009b). Several 
studies suggest that nitrate in drinking water can have adverse effects 
on the thyroid (Mukhopadhyay et al., 2005; Tajtakova et al., 2006; Zaki 
et al., 2004). Since nitrite is formed from nitrate, and the current 
nitrite RfD is based on nitrate data, the impact of these new data on a 
nitrite noncancer assessment should be evaluated. Nitrite has long been 
known as a competitive inhibitor of iodide uptake in the thyroid; 
although it is a weaker inhibitor than nitrate (Wolff and Maury, 1963). 
Inhibition of iodide uptake can lead to alteration in thyroid hormone 
levels including decreases in T4. A developmental toxicity study in 
rats (Vorhees et al., 1984) observed statistically significant delays 
in swimming development in addition to pup mortality and body weight 
changes. Based on these considerations, a new assessment of the 
noncancer effects of nitrite may be warranted, including consideration 
of whether methemoglobinemia in infants, which is an acute effect, is 
still the most appropriate basis for the chronic exposure limit for 
nitrite. In addition, recent information may suggest the consideration 
of separate acute and chronic values for nitrite.
    The health effects review identified a number of relevant new 
studies that may warrant a review of the cancer classification for 
nitrate. These studies include a number of new epidemiology studies 
(Cocco et al., 2003; Coss et al., 2004; de Roos et al., 2003; Mueller 
et al., 2004; Volkmer et al., 2005; Ward et al., 2003; Ward et al., 
2005a; Ward et al., 2005b; Ward et al., 2006; Yang et al., 2007; 
Zeegers et al., 2006). In addition, a recent report from an 
International Agency for Research on Cancer (IARC) Working group 
(Grosse et al., 2006) concluded that, under conditions that result in 
endogenous nitrosation, ingested nitrate or nitrite is probably 
carcinogenic to humans.
    In light of this information, EPA considers nitrite as a potential 
candidate for a new health effects assessment. The Agency solicits 
feedback on its plans to reassess health risks resulting from exposure 
to nitrite. The Agency also welcomes any scientific information related 
to nitrite health risks from the public. Because EPA considers nitrite 
as a candidate for a new assessment, EPA does not believe it is 
appropriate to consider any possible revisions to the MCLG (as well as 
the MCL) at this time.
    A review of analytical or treatment feasibility is not necessary 
for nitrite because changes to the MCLG are not warranted at this time 
and the current MCL is set at the MCLG. Since EPA did not identify a 
health or technology basis for revising the nitrite NPDWR, the Agency 
did not conduct a detailed occurrence and exposure analysis.
    c. Review Result. The Agency is considering whether to initiate a 
new health assessment for nitrite and therefore does not believe a 
revision to the NPDWR is appropriate at this time.
    As discussed in Section VII, the Agency is requesting input and 
information about several implementation issues related to nitrite (see 
section V.B.6).
51. 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. EPA based the MCLG on a reference dose of 0.025 mg/
kg-day and a cancer classification of E, evidence of non-
carcinogenicity for humans.
    b. Technical Reviews. In 2000, the Agency updated its health 
effects assessment of oxamyl (USEPA, 2000a). The Agency identified a 
change in this assessment that could lead to a change in the MCLG. This 
assessment considered relevant studies on the toxicity of oxamyl 
including developmental and reproductive toxicity. The assessment 
revised the RfD from 0.025 mg/kg-day to 0.001 mg/kg-day and concluded 
that there is evidence that oxamyl is noncarcinogenic to humans (USEPA, 
2000a). Based on the new OPP assessment and RfD of 0.001 mg/kg-day, and 
assuming a 10-kg child body weight and 1 liter water intake per day, 
the DWEL could be 0.01 mg/L.\21\ An RSC of 20 percent was selected 
based on the actual food dietary exposure (81 percent) for children who 
are 1 to 6 years old (USEPA, 2000a); this RSC results in a possible 
MCLG of 0.002 mg/L (USEPA, 2009b).
---------------------------------------------------------------------------

    \21\ A child's body weight and drinking water intake were used 
to calculate the DWEL because children are the population with the 
highest risk from dietary exposure.
---------------------------------------------------------------------------

    Because of a possible change in the MCLG for oxamyl, EPA considered 
whether analytical feasibility is likely to be a limitation if the 
Agency were to consider lowering the MCL to 0.002 mg/L (the possible 
MCLG). EPA reviewed PE data from the first Six-Year Review cycle and 
then analyzed more recent PT data to determine if it might be possible 
to recalculate the PQL, which is 0.02 mg/L and might be a limit to a 
possible MCLG of 0.002 mg/L (i.e., analytical feasibility). Passing 
rates for PE data available through late 1999 for oxamyl are below 75 
percent for most studies with true concentrations below the

[[Page 15553]]

current PQL of 0.02 mg/L. More recent PT data from late 1999 through 
2004, supplied by a PT provider, show no results below the current PQL 
but had most passing rates above 75 percent with true values at or 
above the current PQL. Given the variable results from the PE and PT 
studies, and the lack of PT data below the current PQL, PE and PT data 
are insufficient to support a PQL reduction (USEPA, 2009c).
    While the PT data are not sufficient to support a lowering of the 
PQL for oxamyl at this time, the present PQL of 0.02 mg/L is greater 
than the possible MCLG. It would therefore limit a possible revision to 
the MCL. EPA evaluated two alternative sources of information to 
determine whether they indicate any potential to quantitate at levels 
as low as the possible MCLG: laboratory minimum reporting levels in the 
Six-Year Review ICR dataset, and the MDLs for approved methods for the 
detection of oxamyl (Methods 531.1 and 531.2). While EPA prefers to use 
laboratory performance data to calculate the PQL, the MRL and MDL 
information can be valuable for this review to indicate whether it is 
possible to quantitate at levels below the current PQL. The Six-Year 
Review ICR dataset contains MRL values for 52,201 samples. Of these, 
45,290 (87 percent) have an MRL value of 0.002 mg/L or lower. Because 
more than 80 percent of the MRL values are at or below the possible 
MCLG of 0.002 mg/L, EPA selected that value as the minimum threshold 
for the occurrence and exposure analysis (USEPA, 2009e). Method 531.1 
has an MDL of 0.00086 mg/L, and Method 532.2 has a detection limit (DL) 
of 0.000065 mg/L. Applying a multiplier of 10 would give a possible PQL 
range from 0.00065 to 0.0086 mg/L, which contains the possible MCLG 
(USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of 
information, there is evidence of a potential to lower the PQL for 
oxamyl even though the PE and PT data are insufficient to support a PQL 
reduction. To determine whether any MCL revision is likely to provide a 
meaningful opportunity to improve public health protection, EPA 
evaluated the occurrence of oxamyl at the possible MCLG of 0.002 mg/L 
(USEPA, 2009f). Table VI-22 shows the results of the occurrence and 
exposure analysis for the current MCL and the possible MCLG. The 
analysis uses single sample or peak results instead of system average 
results because the health endpoint is associated with acute 
exposure.\22\ The occurrence and exposure analysis shows that 
individual sample concentrations exceed the current MCL of 0.2 mg/L for 
one of 30,876 systems (0.003 percent) serving 200 people (or 0.000 
percent of 167 million people). Note that these results are based on 
the subset of monitoring data provided in response to the Six-Year 
Review ICR and do not necessarily reflect MCL violations, which are 
based on running annual average concentrations at entry points; SDWIS/
FED indicates no MCL violations for oxamyl between 1998 and 2005 
(USEPA, 2007g). Individual sample concentrations at 18 of 30,876 
systems (0.058 percent), serving fewer than 0.3 million people (0.177 
percent), exceeded the possible MCLG of 0.002 mg/L at least one time 
between 1998 and 2005.
---------------------------------------------------------------------------

    \22\ The Six-Year Review ICR occurrence data are based on the 
Standardized Monitoring Framework for synthetic organic compounds, 
which is designed to evaluate long-term exposure to contaminants 
with chronic exposure health endpoints. As a result, EPA recognizes 
that short-term seasonal peaks, which correspond to oxamyl 
application as a pesticide, cannot be readily detected in this 
dataset. Nonetheless and as noted, EPA used the peak concentrations 
to evaluate occurrence for oxamyl because the health endpoint is 
associated with acute exposure.

   Table VI-22--Number and Percent of Systems With Peak Concentrations
  Exceeding Oxamyl Thresholds and Corresponding Estimates of Population
                                 Served
------------------------------------------------------------------------
                                         Systems with any sample that is
                                          greater than the regulatory or
                                              health-based threshold
  Regulatory or health-based threshold     (Percentages based on 30,876
                                         systems with oxamyl data in the
                                          six-year review ICR occurrence
                                                     dataset)
------------------------------------------------------------------------
MCL (0.2 mg/L).........................  1 (0.003%)
Possible MCLG (0.002 mg/L).............  18 (0.058%)
------------------------------------------------------------------------
                                         Corresponding population served
                                         (Percentages based on
                                          167,378,400 people served by
                                          the systems
 Regulatory or health-based threshold    with oxamyl data in the Six-
                                          Year Review ICR occurrence
                                          dataset)
------------------------------------------------------------------------
MCL (0.2 mg/L).........................  200 (0.0001%)
Possible MCLG (0.002 mg/L).............  297,000 (0.177%)
------------------------------------------------------------------------
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. Although there are new data that support 
consideration of whether to revise the MCLG/MCL for oxamyl, EPA does 
not believe a revision to the NPDWR for oxamyl is appropriate at this 
time. In making this decision, the Agency considered whether any 
possible revision to the NPDWR for oxamyl is likely to provide a 
meaningful opportunity for health risk reductions. Taking into 
consideration the low occurrence of this contaminant, EPA has decided 
that any revision to the NPDWR would be a low priority activity for the 
Agency, and, thus, is not appropriate to revise at this time because 
of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
52. Pentachlorophenol
    a. Background. EPA published the current NPDWR for 
pentachlorophenol on July 1, 1991 (56 FR 30266 (USEPA, 1991b)). 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. EPA has initiated a reassessment of the 
health risks resulting from exposure to pentachlorophenol. The revised 
health effects assessment will consider relevant

[[Page 15554]]

studies on the toxicity of pentachlorophenol, including its potential 
developmental and reproductive toxicity. The new health effects 
assessment was not completed by March 1, 2009, the review cutoff date 
for this notice (USEPA, 2009b). The IRIS Substance Assessment Tracking 
System Web site (http://cfpub.epa.gov/iristrac/index.cfm) has the most 
up-to-date information on the status of the health effects assessment.
    Although a risk assessment is in process for pentachlorophenol, the 
existing MCLG is zero and the current MCL of 0.001 mg/L is based on the 
PQL. Therefore, EPA reviewed whether there is potential to revise the 
PQL. EPA reviewed PE data from the first Six-Year Review cycle and then 
analyzed more recent PT data to determine if the PQL can be revised 
(i.e., analytical feasibility). Several passing rates in the PE data 
for pentachlorophenol available through late 1999 are below 75 percent, 
and none of the true concentrations were below the current PQL. There 
are six PE studies with passing rates equal to or less than the 75 
percent criterion, and only one of 16 true values in the PE data is 
below the current PQL. More recent PT data from late 1999 through 2004, 
supplied by a PT provider, show passing rates below the 75 percent 
criterion for eight studies, and all of the true concentrations in the 
PT data were higher than the current PQL. Because of the variability in 
passing rates and the lack of data points below the current PQL, a 
lowering of the PQL for pentachlorophenol is not appropriate at this 
time (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: Laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of pentachlorophenol (Methods 515.1, 515.2, 
and 525.2). While EPA prefers to use laboratory performance data to 
calculate the PQL, the MRL and MDL information can be valuable for this 
review to indicate whether it is possible to quantitate at levels below 
the current PQL. The Six-Year Review ICR dataset contains MRL values 
for 59,594 samples. Fewer than 80 percent of these values are less than 
or equal to the modal MRL: 26,666 (45 percent) equal the modal MRL of 
0.00004 mg/L and an additional 2,399 (4 percent) are lower than 0.00004 
mg/L. Therefore, EPA did not set the EQL equal to the modal MRL (USEPA, 
2009e). The MDLs of approved methods are 0.000032, 0.00016, and 0.001 
mg/L. EPA selected the median value, applied a multiplier of 10, and 
rounded up to 0.002 mg/L. The result is higher than the current PQL 
and, therefore, EPA did not estimate an EQL (USEPA, 2009e). Based on 
these varied and unrelated approaches/sources of information, EPA 
believes that there is no potential to lower the PQL for 
pentachlorophenol. Since the MCL is constrained by the PQL, and the PQL 
is unchanged, EPA does not believe it is necessary to conduct an 
occurrence analysis at this time.
    c. Review Result. 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 in progress (USEPA, 2009b). Furthermore, a review 
of analytical feasibility did not identify a potential to revise the 
MCL, which is limited by feasibility.
53. 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. EPA based the MCLG on a reference dose of 0.07 mg/
kg-day and a cancer classification of D, not classifiable as to human 
carcinogenicity.
    b. Technical Reviews. In the first Six-Year Review cycle, EPA 
evaluated new information from a health effects assessment completed in 
1995 (USEPA, 1995b). At that time, the Agency could not determine that 
a revision to the NPDWR would provide a meaningful opportunity for cost 
savings to public water systems or their customers, and decided that 
any revision would be a low priority activity for the Agency because of 
competing workload priorities, the administrative costs associated with 
rulemaking, and the burden on States and the regulated community to 
implement any regulatory change (67 FR 19030 (USEPA, 2002c); 68 FR 
42908 (USEPA, 2003e)). The 1995 assessment considered relevant studies 
on the toxicity of picloram including developmental and reproductive 
toxicity. The assessment revised the RfD from 0.07 mg/kg-day to 0.2 mg/
kg-day and classified picloram as Group E, evidence of 
noncarcinogenicity (USEPA, 1995b). In the current review cycle, EPA 
conducted a literature search through June 2007 for relevant data on 
the toxicology of picloram, including its potential developmental and 
reproductive toxicity. The literature search did not identify any new 
data that would affect the RfD or cancer classification (USEPA, 2009b). 
Based on the 1995 OPP assessment and RfD of 0.2 mg/kg-day, and assuming 
a 70-kg adult body weight and 2 liters water intake per day, the DWEL 
could be 7 mg/L. An RSC of 20 percent results in a possible MCLG of 1 
mg/L (USEPA, 2009b).
    Analytical feasibility does not pose any limitations for the 
current MCL and would not be a limiting factor if EPA were to raise the 
MCLG. EPA evaluated the results of the occurrence and exposure analyses 
for picloram to determine whether a revised MCLG/MCL would be likely to 
result in a meaningful opportunity to achieve cost savings for PWSs and 
their customers while maintaining, or improving, the level of public 
health protection (USEPA, 2009f). Although the Agency obtained and 
evaluated the finished water occurrence data for picloram, its 
usefulness is limited for determining potential cost savings to PWSs 
and their customers because the Agency does not know which systems are 
treating for this contaminant. As an alternative, the Agency evaluated 
available data on source water quality and conducted a qualitative 
assessment of treatment cost savings.
    Table VI-23 provides summary data for contaminant occurrence based 
on maximum sample values for the locations included in the STORET and 
NAWQA data. Although the degree to which these occurrence rates 
represent national drinking water source occurrence is uncertain, the 
information shows no to low occurrence at threshold levels of interest. 
This information indicates that any resulting NPDWR change would not 
affect systems that rely on source water at any of the NAWQA or STORET 
locations.

  Table VI-23--Ambient Water Quality Monitoring Occurrence Summary for
                                Picloram
------------------------------------------------------------------------
                                   Number of locations (% of locations)
      Maximum concentration      ---------------------------------------
                                      STORET \1\           NAWQA \2\
------------------------------------------------------------------------
Total...........................  870 (100%)........  5,772 (100.0%)
Nondetect.......................  745 (85.6%).......  5,733 (99.3%)
Detected........................  125 (14.4%).......  39 (0.7%)

[[Page 15555]]

 
Exceeds current MCLG of 0.5 mg/L  0 (0%)............  0 (0.0%)
Exceeds alternative value of 1.0  0 (0%)............  0 (0.0%)
 mg/L.
------------------------------------------------------------------------
\1\ STORET database 2002-2007.
\2\ NAWQA database 1992-2005.
Source: USEPA, 2009d.

    The BATs and small system compliance technologies for picloram have 
other beneficial effects, e.g., reduction of other co-occurring 
contaminants, precursors for DBPs, or other common impurities. 
Therefore, if EPA were to consider a higher level, the Agency does not 
know how many PWSs that are currently treating to comply with the 
existing MCL of 0.5 mg/L would be likely to discontinue treatment that 
is already in place (USEPA, 2009d). Also, the Agency does not know to 
what extent affected systems might be able to reduce costs given that 
capital costs are not recoverable. However, the Agency recognizes that 
there may be opportunities to achieve operational cost savings if these 
systems are able to re-optimize current treatment.
    Given these considerations, the Agency believes that any resulting 
revision is not likely to provide a meaningful opportunity for cost 
savings. In view of this, any revision would be a low priority activity 
and not appropriate at this time.
    c. Review Result. 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. In making this decision, the Agency considered whether any 
possible revision to the NPDWR for picloram is likely to provide a 
meaningful opportunity for cost savings to public water systems and 
their customers. Taking into consideration the low occurrence of this 
contaminant in source waters, EPA has decided that any revision to the 
NPDWR would be a low priority activity for the Agency, and, thus, is 
not appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
54. Polychlorinated Biphenyls (PCBs)
    a. Background. EPA published the current NPDWR for PCBs on January 
30, 1991 (56 FR 3526 (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 0.0005 mg/L, based on analytical 
feasibility.
    b. Technical Reviews. EPA has initiated a reassessment of the 
cancer health risks resulting from exposure to PCBs. The revised health 
effects assessment will consider relevant studies on the toxicity of 
PCBs, including its potential developmental and reproductive toxicity. 
The new health effects assessment was not completed by March 1, 2009, 
the review cutoff date for this notice (USEPA, 2009b). On December 21, 
2007 (72 FR 72715 (USEPA, 2007c)), the Agency noted that the health 
effects assessment for PCBs is in process.
    Although a risk assessment is in process for PCBs, the existing 
MCLG is zero and the current MCL of 0.0005 mg/L is based on the PQL. 
Therefore, EPA reviewed whether there is potential to revise the PQL. 
EPA reviewed PE data from the first Six-Year Review cycle and then 
analyzed more recent PT data to determine if the PQL can be revised 
(i.e., analytical feasibility). The PE data for PCBs available through 
late 1999 includes only one true concentration below the current PQL, 
and the passing rate for that concentration is below 75 percent. The 
passing rates for studies above the PQL are above 75 percent. More 
recent PT data from late 1999 through 2004, supplied by a PT provider, 
show passing rates above 75 percent for all studies, but includes no 
studies below the current PQL. Because of the lack of data points below 
the current PQL, a lowering of the PQL for PCBs is not appropriate at 
this time (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDL for the approved 
method for the detection of PCBs (Method 508A). While EPA prefers to 
use laboratory performance data to calculate the PQL, the MRL and MDL 
information can be valuable for this review to indicate whether it is 
possible to quantitate at levels below the current PQL. The Six-Year 
Review ICR dataset contains MRL values for 35,178 samples. Fewer than 
80 percent of these values are less than or equal the modal MRL: 23,785 
(68 percent) equal the modal MRL of 0.0001 mg/L and an additional 2,355 
(7 percent) are lower than 0.0001 mg/L. Therefore, EPA did not set the 
EQL equal to the modal MRL (USEPA, 2009e). The MDL of approved method 
is 0.00008 mg/L. Applying a multiplier of 10 would give a possible PQL 
of 0.0008 mg/L. The result is higher than the current PQL, and 
therefore, EPA did not estimate an EQL (USEPA, 2009e). Based on these 
varied and unrelated approaches/sources of information, EPA believes 
that there is no potential to lower the PQL for PCBs. Since the MCL is 
constrained by the PQL, and the PQL is unchanged, EPA does not believe 
it is necessary to conduct an occurrence analysis at this time.
    c. Review Result. 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 in progress (USEPA, 
2009b). Furthermore, a review of analytical feasibility did not 
identify a potential to revise the MCL, which is limited by 
feasibility.
55. Combined Radiums (226 and 228)
    a. Background. EPA published an interim NPDWR and set an MCL of 5 
pCi/L for combined radium 226 and 228 on July 9, 1976 (41 FR 28402 
(USEPA, 1976)). As noted in the August 14, 1975 proposal (40 FR 34324 
(USEPA, 1975)) and a subsequent September 30, 1986 FR notice, EPA 
considered the feasibility of treatment techniques, analytical methods 
and monitoring when establishing the MCL of 5 pCi/L. EPA also 
considered the risks associated with exposure to radium 226 and 228, 
which generally fell within the Agency's acceptable risk range of 
10-4 to 10-6 at the MCL of 5 pCi/L. On December 
7, 2000 (65 FR 76708 (USEPA, 2000c)), EPA established an MCLG of zero 
based on a cancer classification of A (known

[[Page 15556]]

human carcinogen) and finalized the NPDWR by retaining the MCL of 5 
pCi/L. EPA noted in the December 7, 2000 FR notice that new risk 
estimates from Federal Guidance Report 13 reaffirmed that the 5 pCi/L 
MCL was appropriate and protective.\23\ EPA also tightened the 
monitoring requirements for combined radiums by requiring that systems 
monitor for radium 226 and 228 separately.
---------------------------------------------------------------------------

    \23\ After the December 7, 2000 final regulation, two trade 
associations and several municipal water systems challenged EPA's 
standard for combined radiums by claiming that the Agency did not 
use the best available science when finalizing the standard. In 
February of 2003, the DC Circuit Court of Appeals upheld EPA's 
regulation for combined radiums (as well as beta and photon emitters 
and uranium).
---------------------------------------------------------------------------

    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to radiums. The revised health 
effects assessment will consider relevant studies on the toxicity of 
radiums, including its potential developmental and reproductive 
toxicity. The new health effects assessment was not completed by March 
1, 2009, the review cutoff date for this notice (USEPA, 2009b).
    Although there is an ongoing health effects assessment, the MCLG is 
zero and the current MCL is higher than the MCLG. Therefore, EPA 
reviewed whether there is potential to revise the MCL based on new 
information regarding analytical and treatment feasibility for radiums. 
EPA promulgated detection limits of 1 pCi/L for both radium 226 and 
radium 228 in 1976 (41 FR 28402 (USEPA, 1976)) and retained the use of 
a detection limit as the required measure of sensitivity for 
radiochemical analysis in lieu of an MDL or PQL in the final rule (65 
FR 76708, December 7, 2000 (USEPA, 2000c)). EPA did not identify new 
analytical methods during the current review that would feasibly lower 
the detection limits. In addition, since the December 7, 2000, 
regulation, there is no new information regarding treatment 
feasibility. Since there is no new information regarding analytical or 
treatment feasibility that suggests changes to the MCL, EPA does not 
believe it is necessary to conduct an occurrence analysis at this time.
    c. Review Result. The Agency does not believe a revision to the 
NPDWR for combined radiums is appropriate at this time because a 
reassessment of the health risks resulting from exposure to radium is 
in progress (USEPA, 2009b). Furthermore, there is no new information 
regarding analytical or treatment feasibility that would warrant 
reconsideration of the MCL.
56. Selenium
    a. Background. EPA published the current NPDWR for selenium on 
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an 
MCLG and an MCL of 0.05 mg/L. EPA based the MCLG on a maximum safe 
intake\24\ of 0.4 mg/person/day and a cancer classification of D, not 
classifiable as to human carcinogenicity.
---------------------------------------------------------------------------

    \24\ The 0.4 mg/day safe level was based on data (Yang et al., 
1989a, 1989b) that extrapolated from blood selenium levels to 
estimated dietary intake in the studied population. As described in 
the January 30, 1991 FR (56 FR 3526 (USEPA, 1991c)), the Agency 
partially considered selenium's status as a nutrient and did not use 
the typical procedure for deriving the MCLG. Hence, there is no 
specific reference to an RfD for selenium in the 1991 FR notice. 
After the publication of the regulation, IRIS (USEPA, 1991a) posted 
an RfD of 0.005 mg/kg-day for selenium using the same data that are 
the basis of the regulation.
---------------------------------------------------------------------------

    b. Technical Reviews. The health effects technical review 
identified new data that relate to the biological properties of 
selenium in mammalian species, as well as data regarding its cancer and 
anticancer properties, that may indicate the need to update the 
Agency's health effects assessment (USEPA, 2009b). Hawkes and Keim 
(2003) reported thyroid hormone and related metabolism changes in 
subjects treated with deficient, sufficient, and excess dietary 
selenium. The excess selenium dose was associated with a slight 
decrease in triiodothyronine (T3) levels, a thyrotropin increase, and 
an increase in body weight compared to the selenium-sufficient 
subjects. The opposite responses occurred in the selenium-deficient 
subjects. Several studies identified changes in sperm parameters and 
fertility in mice fed either selenium-deficient or excess-selenium 
diets compared to diets with adequate selenium. In addition, new 
information about the metabolism of selenium since the IRIS review 
(USEPA, 1991a, 1993a) suggests that it may be appropriate to 
differentiate between inorganic selenium and organic selenium in the 
form of selenoproteins and selenoaminoacids for an assessment that 
applies to drinking water. Although selenium is not a candidate for an 
MCLG of zero because of its status as a micronutrient, new data 
relevant to the cancer assessment are now available (e.g., Duffield-
Lillico et al., 2003; Su et al., 2005) and may need further evaluation.
    In light of this information, EPA considers selenium as a potential 
candidate for a new health effects assessment. The Agency solicits 
general feedback on its plans to reassess health risks resulting from 
exposure to selenium. The Agency also welcomes any scientific 
information related to selenium health risks from the public. Because 
EPA considers selenium as a candidate for a new assessment, EPA does 
not believe it is appropriate to consider any revisions to the MCLG (as 
well as the MCL) at this time.
    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. 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. Review Result. The Agency is considering whether to initiate a 
new health assessment for selenium and therefore does not believe a 
revision to the NPDWR is appropriate at this time.
57. 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. EPA based the MCLG on a reference dose of 0.005 
mg/kg-day and a cancer classification of C, possible human carcinogen.
    b. Technical Reviews. In 2006, the Agency finalized a health 
effects assessment for the reregistration of simazine as a pesticide 
(USEPA, 2006i). Because the database for simazine's potential 
neuroendocrine effects is less robust than the atrazine database, and 
because simazine and atrazine share a common neuroendocrine mechanism 
of toxicity, the atrazine data were used as bridging data for simazine. 
Thus, the 2006 assessment established a new RfD of 0.018 mg/kg-day for 
simazine, based on the attenuation of pre-ovulatory LH surge from 
atrazine exposure. Similarly, simazine was reclassified in 2006 as 
``not likely to be carcinogenic to humans'' based on weight-of-evidence 
that it is not genotoxic and because the tumor response in the Sprague-
Dawley rats was determined to be a strain specific mechanism which is 
not relevant to humans.
    c. Review Result. The Agency believes it is not appropriate to 
consider revisions to the NPDWR for simazine at this time and has 
placed simazine in the emerging information/data gap category because 
of an impending re-evaluation of the Agency's risk assessment for 
atrazine and the assessment for simazine is based on atrazine data. See 
section VI.7 (atrazine) for additional information.

[[Page 15557]]

58. Styrene
    a. Background. EPA published the current NPDWR for styrene on 
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an 
MCLG and an MCL of 0.1 mg/L. EPA based the MCLG on a reference dose of 
0.2 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 styrene. The revised health 
effects assessment will consider relevant studies on the toxicity of 
styrene, including its potential developmental and reproductive 
toxicity. The new health effects assessment was not completed by March 
1, 2009, the review cutoff date for this notice (USEPA, 2009b). The 
IRIS Substance Assessment Tracking System Web site (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information 
on the status of the health effects assessment.
    c. Review Result. Since the MCL for styrene is set at its MCLG and 
a reassessment of the health risks resulting from exposure to styrene 
is in progress, the Agency does not believe a revision to the NPDWR is 
appropriate at this time.
59. 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 3x10-8 mg/L, based on 
analytical feasibility.
    b. Technical Reviews. In 2003, the Agency prepared a draft human 
health reassessment for dioxin and its related compounds (USEPA, 2003c) 
that underwent external review by the National Academy of Science. In 
their peer review report (NAS, 2006), NAS recommended that EPA 
reevaluate its conclusions regarding the carcinogenicity of dioxin 
based on the criteria set out in the 2005 cancer guidelines; that EPA 
should consider developing more information on the noncancer effects of 
dioxin; and that EPA evaluate new dose-response data released by the 
NTP. The Agency is currently considering the NAS recommendations. The 
Agency does not expect any new health effects assessment to be 
completed in the time frame of the current Six-Year Review cycle 
(USEPA, 2009b). The IRIS Substance Assessment Tracking System Web site 
(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 
information on the status of the health effects assessment.
    Although a health effects assessment is in process for dioxin, the 
existing MCLG is still zero and the current MCL is based on a PQL of 
3x10-8 mg/L. Therefore, EPA reviewed whether there is 
potential to revise the PQL. The PT data currently available for dioxin 
are not sufficient to evaluate the potential for PQL revision (USEPA, 
2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: Laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDL for the approved 
method for the detection of dioxin (Method 1613). While EPA prefers to 
use laboratory performance data to calculate the PQL, the MRL and MDL 
information can be valuable for this review to indicate whether it is 
possible to quantitate at levels below the current PQL. The Six-Year 
Review ICR dataset contains dioxin data for fewer than 2,500 systems, 
which is an insufficient sample size to derive an EQL based on MRL 
data. The MDL of the approved method is 1x10-8 mg/L. 
Applying a multiplier of 5 would yield an EQL of 5x10-8 mg/
L. The result is slightly higher than the current PQL and, therefore, 
EPA did not estimate an EQL. Based on these varied and unrelated 
approaches/sources of information, EPA believes that a PQL reduction 
for dioxin is not appropriate at present. Since the MCL is constrained 
by the PQL, and the PQL is unchanged, EPA does not believe it is 
necessary to conduct an occurrence analysis at this time.
    c. Review Result. 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 in progress 
(USEPA, 2009b). Furthermore, a review of analytical feasibility did not 
identify a potential to revise the MCL, which is limited by 
feasibility.
60. Tetrachloroethylene
    a. Background. EPA published the current NPDWR for 
tetrachloroethylene on January 30, 1991 (56 FR 3526 (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 
0.005 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 health effects assessment will consider relevant studies on the 
toxicity of tetrachloroethylene, including its potential developmental 
and reproductive toxicity. The new health effects assessment was not 
completed by March 1, 2009, the review cutoff date for this notice 
(USEPA, 2009b). The IRIS Substance Assessment Tracking System Web site 
(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 
information on the status of the health effects assessment and 
indicates that tetrachloroethylene is currently undergoing review by 
NAS.
    Although a risk assessment is in process for tetrachloroethylene, 
the existing MCLG is zero and the current MCL of 0.005 mg/L is based on 
the PQL. Therefore, EPA reviewed whether there is potential to revise 
the PQL. EPA reviewed PE data from the first Six-Year Review cycle and 
then analyzed more recent PT data to determine if the PQL could be 
revised (i.e., analytical feasibility). Passing rates for PE data 
available through late 1999 for tetrachloroethylene are above 95 
percent at the lowest concentrations. However, the true concentrations 
were all higher than the current PQL of 0.005 mg/L. More recent PT data 
from late 1999 through 2004, supplied by a PT provider, also show 
greater than 90 percent passing rates for studies around the current 
PQL, including 13 with true values below the PQL. Because most of the 
laboratory passing rates from PE and PT studies exceeded the 75 percent 
criterion typically used to derive a PQL, including several with true 
values below the PQL, a lowering of the PQL for tetrachloroethylene 
might be possible. These results, however, are insufficient to 
recalculate a revised PQL for tetrachloroethylene because not enough 
data points are available below the current PQL to derive a value at 
the 75 percent passing rate (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: Laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of tetrachloroethylene (Methods 502.2, 524.2, 
and 551.1). While EPA prefers to use laboratory performance data to 
calculate the PQL, the MRL and MDL information can be valuable for this 
review to indicate whether it is possible to quantitate at levels below 
the current PQL. EPA also noted that the State of New Jersey uses a PQL 
of 0.001 mg/L, based on a 1987 study of laboratory performance at low 
concentrations that used criteria similar to those in the PT data 
(NJDWQI, 1987). The Six-Year Review ICR dataset contains MRL values for 
138,348 samples. More than 80 percent of these values are less than

[[Page 15558]]

or equal the modal MRL: 117,033 (85 percent) equal the modal MRL of 
0.0005 mg/L and an additional 15,848 (11 percent) are lower than 0.0005 
mg/L. Therefore, EPA selected the modal MRL as the EQL (USEPA, 2009e). 
The MDLs of approved method are 0.00005, 0.00014, and 0.000008 mg/L. 
Applying a multiplier of 10 would give a possible PQL range from 
0.00008 to 0.0014 mg/L, which contains the EQL (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of 
information, EPA believes that there is potential to lower the PQL for 
tetrachloroethylene. To determine whether any MCL revision is likely to 
provide a meaningful opportunity to improve public health protection, 
EPA evaluated the occurrence of tetrachloroethylene at the EQL of 
0.0005 mg/L and additional thresholds of 0.001 and 0.0025 mg/L. Table 
VI-24 shows the results of the occurrence and exposure analysis for the 
current MCL and these thresholds. The occurrence and exposure analysis 
shows that average concentrations exceed the current MCL for 23 to 25 
out of 50,436 systems (0.046 to 0.050 percent) serving approximately 
630, 000 to 1.1 million people (or 0.277 to 0.473 percent of 227 
million people). Note that these results are based on the subset of 
monitoring data provided in response to the Six-Year Review ICR and do 
not necessarily reflect MCL violations, which are based on annual 
average concentrations at entry points; SDWIS/FED indicates 174 MCL 
violations for tetrachloroethylene between 1998 and 2005, with annual 
violations ranging from 10 to 33 (USEPA, 2007g). Average concentrations 
at 412 to 519 of 50,436 systems (0.817 to 1.029 percent), serving 12.4 
to 14.6 million people (or 5.466 to 6.419 percent of 227 million 
people), exceed the lowest EQL of 0.0005 mg/L. While these systems are 
widely distributed and located in most of the States providing data, a 
few large systems (serving 500,000 or more people) account for almost 
half of the exposed population.

Table VI-24--Number and Percent of Systems With Mean Concentrations Exceeding Tetrachloroethylene Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                       feasibility-based threshold (Percentages based on 50,436 systems with
 Regulatory or feasibility-based      tetrachloroethylene data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                                              Nondetect values = \1/2\
                                   Nondetect values = MRL\1\           MRL\2\            Nondetect values = 0\3\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  25 (0.050%)..............  23 (0.046%).............  23 (0.046%)
1/2 MCL (0.0025 mg/L)............  75 (0.149%)..............  71 (0.141%).............  68 (0.135%)
2xEQL (0.001 mg/L)...............  286 (0.568%).............  251 (0.498%)............  220 (0.437%)
EQL (0.0005 mg/L)................  not applicable...........  519 (1.030%)............  412 (0.818%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (Percentages based on 227,009,000 people
                                     served by the systems with tetrachloroethylene data in the Six-Year Review
                                                               ICR occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based   Nondetect values = MRL\1\  Nondetect values = \1/2\   Nondetect values = 0\3\
            threshold                                                   MRL\2\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  1,074,000 (0.473%).......  628,000 (0.277%)........  628,000 (0.277%)
\1/2\ MCL (0.0025 mg/L)..........  1,706,000 (0.752%).......  1,692,000 (0.745%)......  1,647,000 (0.726%)
2xEQL (0.001 mg/L)...............  10,706,000 (4.716%)......  10,177,000 (4.483%).....  9,625,000 (4.240%)
EQL (0.0005 mg/L)................  not applicable...........  14,572,000 (6.419%).....  12,408,000 (5.466%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
  Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the
  results equal to this value results in an upwardly biased estimate of the number of systems with mean
  concentrations that exceed this value.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that a revision to the MCL 
may provide a meaningful opportunity to improve the level of public 
health protection, EPA considered whether treatment feasibility is 
likely to pose any limitations if the MCL were lowered (USEPA, 2009g). 
The current BATs for tetrachloroethylene are packed tower aeration 
(PTA) and granular activated carbon (GAC). Small system compliance 
technologies (SSCTs) for tetrachloroethylene include GAC and several 
aeration technologies. EPA's assessment shows that PTA and GAC are 
effective enough to achieve concentrations as low as the EQL.
    EPA is not currently able to assess the potential health benefits 
from a revised MCL for tetrachloroethylene, because the revised health 
effects assessment is not yet available. However, based on its B2 
cancer classification (MCLG of zero) and the occurrence and exposure 
analysis at possible MCL values, the Agency believes that a revision to 
the MCL may provide a meaningful opportunity to reduce public health 
risks.
    c. Review Result. The Agency believes it is appropriate to revise 
the NPDWR for tetrachloroethylene although a health effects assessment 
is currently in progress. The existing MCLG is zero (based on the 
current B2 cancer classification) and the current MCL is based on a PQL 
(i.e., analytical feasibility) of 0.005 mg/L. The Agency's review 
indicates that analytical feasibility could be as much as 10 times 
lower (~ 0.0005 mg/L) and occurrence at this level appears to be 
relatively widespread. Hence, revisions to the tetrachloroethylene 
NPDWR may provide a meaningful opportunity for health risk reduction. 
If the updated health effects assessment is completed in time to 
consider for the regulatory revision of tetrachloroethylene, the Agency 
will consider this assessment in its evaluation of public health 
benefits associated with any revision. As discussed in Section VII, the 
Agency solicits public comment and/or relevant information that may 
inform the regulatory revision for tetrachloroethylene. EPA is also 
requesting that stakeholders provide information/data about the lowest 
level of quantitation (including the analytical method used) that 
laboratories can reliably and consistently achieve.

[[Page 15559]]

61. Thallium
    a. Background. EPA published the current NPDWR for thallium on July 
17, 1992 (57 FR 31776 (USEPA, 1992)). The NPDWR established an MCLG of 
0.0005 mg/L. EPA based the MCLG on a reference dose 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. EPA completed the risk reassessment for 
thallium in September of 2009 (USEPA, 2009k). Because the new health 
effects assessment was not completed by March 1, 2009, the review 
cutoff date for this notice (USEPA, 2009b), the outcome of this 
assessment has not been included in the current review effort. EPA will 
consider the updated assessment in the next review cycle.
    The current MCL is based on a PQL of 0.002 mg/L. Therefore, EPA 
reviewed whether there is potential to revise the PQL. EPA reviewed PE 
data from the first Six-Year Review cycle and then analyzed more recent 
PT data to determine if the PQL can be revised (i.e., analytical 
feasibility). Passing rates for PE data available through late 1999 for 
thallium are above 80 percent around the current PQL of 0.002 mg/L, 
including one study with a true concentration less than the current 
PQL. More recent PT data from late 1999 through 2004, supplied by a PT 
provider, show passing rates at or above 75 percent, but tending to 
fall below 80 percent as the true concentration approaches the current 
PQL. No studies had true concentrations below the current PQL. Given 
the lack of data points below the current PQL and the low PT passing 
rates close to the PQL, a lowering of the PQL for thallium is not 
appropriate at this time (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of thallium (Methods 200.8 and 200.9). While 
EPA prefers to use laboratory performance data to calculate the PQL, 
the MRL and MDL information can be valuable for this review to indicate 
whether it is possible to quantitate at levels below the current PQL. 
The Six-Year Review ICR dataset contains MRL values for 73,409 samples. 
Fewer than 80 percent of these values are less than or equal the modal 
MRL: 46,273 (63 percent) equal the modal MRL of 0.001 mg/L and an 
additional 11,032 (15 percent) are lower than 0.001 mg/L. Therefore, 
EPA did not set the EQL equal to the modal MRL (USEPA, 2009e). The MDLs 
of approved methods range from 0.0003 to 0.0007 mg/L. Applying a 
multiplier of 10 would give a possible PQL range from 0.003 to 0.007 
mg/L. The result is higher than the current PQL and, therefore, EPA did 
not estimate an EQL (USEPA, 2009e). Based on these varied and unrelated 
approaches/sources of information, EPA believes that there is no 
potential to lower the PQL for thallium. Since the MCL is constrained 
by the PQL, and the PQL is unchanged, EPA does not believe it is 
necessary to conduct an occurrence analysis at this time.
    c. Review Result. The Agency does not believe a revision to the 
NPDWR for thallium is appropriate at this time because a reassessment 
of the health risks resulting from exposure to thallium was in progress 
(USEPA, 2009k) and did not meet the March 1, 2009 cutoff date for this 
review. Furthermore, a review of analytical feasibility did not 
identify a potential to revise the MCL, which is limited by 
feasibility.
62. Toluene
    a. Background. EPA published the current NPDWR for toluene on 
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an 
MCLG and an MCL of 1 mg/L. EPA based the MCLG on a reference dose of 
0.2 mg/kg-day and a cancer classification of D, not classifiable as to 
human carcinogenicity.
    b. Technical Reviews. In 2005, the Agency updated its health 
effects assessment of toluene (USEPA, 2005b). The change in this 
assessment could lead to a change in the MCLG. This assessment 
considered relevant studies on the toxicity of toluene including 
developmental and reproductive toxicity. The assessment revised the RfD 
from 0.2 mg/kg-day to 0.08 mg/kg-day and concluded that there is 
inadequate information to assess the carcinogenic potential of toluene 
(USEPA, 2005b). Although there were no changes in the critical study or 
effect, there were changes in the toxicity database that increase 
concern for immunotoxicity and neurotoxicity via the oral exposure 
route and justified the higher uncertainty factor for the revised RfD 
(USEPA, 2005b). Based on the new IRIS assessment and RfD of 0.08 mg/kg-
day, and assuming a 70-kg adult body weight and 2 liters water intake 
per day, the DWEL could be 2.8 mg/L. An RSC of 20 percent results in a 
possible MCLG of 0.6 mg/L.
    Analytical feasibility does not pose any limitations for the 
current MCL and would not be a limiting factor for the possible MCLG 
decrease under consideration. EPA evaluated the results of the 
occurrence and exposure analyses for toluene to determine whether a 
revised MCLG/MCL would be likely to result in a meaningful opportunity 
to improve the level of public health protection (USEPA, 2009f). Table 
VI-25 shows the results of the occurrence and exposure analysis for the 
current MCL and the possible MCLG set equal to 0.6 mg/L based on the 
new health effects information. The occurrence and exposure analysis 
shows that average concentrations exceed the current MCL for one system 
out of 50,451 (0.002 percent) serving approximately 500 people (0.0002 
percent of 227 million people). Note that these results are based on 
the subset of monitoring data provided in response to the Six-Year 
Review ICR and do not necessarily reflect MCL violations, which are 
based on annual average concentrations at entry points; SDWIS/FED 
indicates MCL violations for toluene at only one system in one year 
between 1998 and 2005 (USEPA, 2007g). Average concentrations at two of 
50,451 systems (0.004 percent), serving 800 people (or 0.0004 percent 
of 227 million people), exceed the possible MCLG based on new health 
effects information (0.06 mg/L).

[[Page 15560]]



      Table VI-25--Number and Percent of Systems With Mean Concentrations Exceeding Toluene Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                   health-based threshold (percentages based on 50,451 systems with toluene data
    Regulatory or health-based                     in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (1 mg/L).....................  1 (0.002%)...............  1 (0.002%)..............  1 (0.002%)
Possible MCLG (0.6 mg/L).........  2 (0.004%)...............  2 (0.004%)..............  2 (0.004%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (percentages based on 226,955,000 people
                                         served by the systems with toluene data in the Six-Year Review ICR
                                                                 occurrence dataset)
                                  ------------------------------------------------------------------------------
    Regulatory or health-based       Nondetect values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
            threshold                          \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (1 mg/L).....................  500 (0.0002%)............  500 (0.0002%)...........  500 (0.0002%)
Possible MCLG (0.6 mg/L).........  800 (0.0004%)............  800 (0.0004%)...........  800 (0.0004%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. Although there are new data that support 
consideration of whether to revise the MCLG/MCL for toluene, EPA does 
not believe a revision to the NPDWR for toluene is appropriate at this 
time. In making this decision, the Agency considered whether any 
possible revision to the NPDWR for toluene is likely to provide a 
meaningful opportunity for health risk reductions. Taking into 
consideration the low occurrence of this contaminant, EPA has decided 
that any revision to the NPDWR would be a low priority activity for the 
Agency, and, thus, is not appropriate to revise at this time because 
of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
63. Toxaphene
    a. Background. EPA published the current NPDWR for toxaphene on 
January 30, 1991 (56 FR 3526 (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 0.003 mg/L, based on 
analytical feasibility.
    b. Technical Reviews. As part of the Six-Year Review process, EPA 
conducted a literature search for relevant data on the carcinogenicity 
of toxaphene as well as its potential developmental and reproductive 
toxicity. EPA has not identified any new information that indicates 
that it is appropriate to consider revisions to the cancer 
classification for toxaphene at this time (USEPA, 2009b). Because the 
MCLG remains at zero, 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. For 
the Six-Year Review, the Agency considered whether changes in the 
analytical feasibility of toxaphene might lead to a lower MCL. EPA 
reviewed PE data from the first Six-Year Review cycle and then analyzed 
more recent PT data to determine if the PQL can be revised (i.e., 
analytical feasibility). Passing rates for PE data available through 
late 1999 for toxaphene are generally above 90 percent around the 
current PQL of 0.003 mg/L, including three studies with true values 
below the current PQL. All passing rates in the PE data exceeded 80 
percent. More recent PT data from late 1999 through 2004, supplied by a 
PT provider, show greater than 80 percent passing rates for a majority 
of studies, but there are no studies with true values below the current 
PQL. There are two PT studies with passing rates equal to or below 75 
percent, at true values well above the current PQL. Despite this 
variability, most of the laboratory passing rates from PE and PT 
studies exceeded the 75 percent criterion typically used to derive a 
PQL, including three with true values below the PQL. Therefore, a 
lowering of the PQL for toxaphene might be possible. These results, 
however, are insufficient to recalculate a revised PQL for toxaphene 
because not enough data points are available below the current PQL to 
derive a value at the 75 percent passing rate (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of toxaphene (Methods 505, 508.1, and 525.2). 
While EPA prefers to use laboratory performance data to calculate the 
PQL, the MRL and MDL information can be valuable for this review to 
indicate whether it is possible to quantitate at levels below the 
current PQL. The Six-Year Review ICR dataset contains MRL values for 
54,529 samples. More than 80 percent of these values are less than or 
equal the modal MRL: 36,763 (67 percent) equal the modal MRL of 0.001 
mg/L and an additional 8,525 (16 percent) are lower than 0.001 mg/L. 
Therefore, EPA selected the modal MRL as the EQL (USEPA, 2009e). The 
MDLs of approved methods are 0.0017, 0.001, and 0.00013 mg/L. Applying 
a multiplier of 10 would give a possible PQL range from 0.0013 to 0.017 
mg/L, which is above the EQL, but includes values below the PQL (USEPA, 
2009e).
    Based on these varied and unrelated approaches/sources of 
information, EPA believes that there may be potential to lower the PQL 
for toxaphene. To determine whether any MCL revision is likely to 
provide a meaningful opportunity to improve public health protection, 
EPA evaluated the occurrence of toxaphene at the EQL of 0.001 mg/L and 
an additional threshold of 0.0015 mg/L (USEPA, 2009f). Table VI-26 
shows the results of the occurrence and exposure analysis for the 
current MCL and these thresholds. The occurrence and exposure analysis

[[Page 15561]]

shows that average concentrations exceed the current MCL for three to 
four of 30,387 systems (0.010 to 0.013 percent) serving 23,000 people 
(or 0.014 percent of 160 million people). Note that these results are 
based on the subset of monitoring data provided in response to the Six-
Year Review ICR and do not necessarily reflect MCL violations, which 
are based on annual average concentrations at entry points; SDWIS/FED 
indicates three MCL violations for toxaphene between 1998 and 2005 
(USEPA, 2007g). Average concentrations at five of 30,387 systems (0.016 
percent), serving 23,000 people (or 0.015 percent of 160 million 
people), exceed the EQL of 0.001 mg/L.

     Table VI-26--Number and Percent of Systems with Mean Concentrations Exceeding Toxaphene Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                       feasibility-based threshold (percentages based on 30,387 systems with
 Regulatory or feasibility-based           toxaphene data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.003 mg/L).................  4 (0.013%)...............  3 (0.010%)..............  3 (0.010%)
\1/2\ MCL (0.0015 mg/L)..........  5 (0.016%)...............  5 (0.016%)..............  5 (0.016%)
EQL (0.001 mg/L).................  not applicable...........  5 (0.016%)..............  5 (0.016%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (percentages based on 160,012,000 people
                                        served by the systems with toxaphene data in the Six-Year Review ICR
                                                                 occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based     Nondetect values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
            threshold                          \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (0.003 mg/L).................  23,000 (0.014%)..........  23,000 (0.014%).........  23,000 (0.014%)
\1/2\ MCL (0.0015 mg/L)..........  23,000 (0.014%)..........  23,000 (0.014%).........  23,000 (0.014%)
EQL (0.001 mg/L).................  not applicable...........  23,000 (0.014%).........  23,000 (0.014%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
  Results are not reported at the EQL of 0.001 mg/L because this is the modal MRL and setting a majority of the
  results equal to this value results in an upwardly biased estimate of the number of systems with mean
  concentrations that exceed this value.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. 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 occurrence and exposure analysis based on 
possible changes in analytical feasibility indicates that any revision 
to the MCL is unlikely to provide a meaningful opportunity to improve 
public health protection. Taking into consideration the low occurrence 
of this contaminant, EPA has decided that any revision to the NPDWR 
would be a low priority activity for the Agency, and, thus, is not 
appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
64. 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, 1991c)). The NPDWR established an 
MCLG and an MCL of 0.05 mg/L. EPA based the MCLG on a reference dose of 
0.008 mg/kg-day and a cancer classification of D, not classifiable as 
to human carcinogenicity.
    b. Technical Reviews. 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 studies that 
warrant a review of the RfD or the cancer classification (USEPA, 
2009b).
    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. 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. Review Result. EPA's review shows that there are no data 
supporting a change to the 2,4,5-TP NPDWR. As a result, a revision to 
the NPDWR would not be appropriate at this time.
65. 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. EPA based the MCLG 
on a reference dose of 0.01 mg/kg-day and a cancer classification of D, 
not classifiable as to human carcinogenicity.
    b. Technical Reviews. The health effects technical review 
identified information regarding the carcinogenicity of 1,2,4-
trichlorobenzene, as well as its noncancer effects, that may indicate 
the need to update the Agency's health effects assessment (USEPA, 
2009b). Two chronic carcinogenicity studies of 1,2,4-trichlorobenzene, 
one in mice (Moore, 1994a) and one in rats (Moore, 1994b), reported 
liver effects in both mice and rats, as well as kidney effects in rats. 
Mice appeared more sensitive than rats for noncancer effects, and mice 
also demonstrated a significant treatment-related increase in the 
incidence of hepatocellular carcinomas. No increased incidence of any 
tumor type was observed in rats. These health effect data could have 
implications for the 1,2,4-trichlorobenzene MCLG because they identify 
effect levels for noncancer effects in the liver and kidney, as well as 
evidence of carcinogenicity in mice.

[[Page 15562]]

    In light of this information, EPA considers 1,2,4-trichlorobenzene 
as a potential candidate for a new health effects assessment. The 
Agency solicits general feedback on its plans to reassess health risks 
resulting from exposure to 1,2,4-trichlorobenzene. The Agency also 
welcomes any scientific information related to 1,2,4-trichlorobenzene 
health risks from the public. Because EPA considers 1,2,4-
trichlorobenzene as a candidate for a new assessment, EPA does not 
believe it is appropriate to consider revisions to the MCLG (as well as 
the MCL) at this time.
    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. 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. Review Result. The Agency is considering whether to initiate a 
new health assessment for 1,2,4-trichlorobenzene and therefore does not 
believe a revision to the NPDWR is appropriate at this time.
66. 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. EPA based the MCLG on a 
reference dose of 0.035 mg/kg-day and a cancer classification of D, not 
classifiable as to human carcinogenicity.
    b. Technical Reviews. In 2007, the Agency updated its health 
effects assessment of 1,1,1-trichloroethane (USEPA, 2007d). The Agency 
identified a change in this assessment that could lead to a change in 
the MCLG. This assessment considered relevant studies on the toxicity 
of 1,1,1-trichloroethane including developmental and reproductive 
toxicity. The assessment revised the RfD from 0.035 mg/kg-day to 2 mg/
kg-day and concluded that there is inadequate information to assess the 
carcinogenic potential of 1,1,1-trichloroethane (USEPA, 2007d). Based 
on the new IRIS assessment and RfD of 2 mg/kg-day, and assuming a 70-kg 
adult body weight and 2 liters water intake per day, the DWEL could be 
70 mg/L. An RSC of 20 percent results in a possible MCLG of 14 mg/L 
(USEPA, 2009b).
    Analytical feasibility does not pose any limitations for the 
current MCL and would not be a limiting factor if EPA were to raise the 
MCLG. EPA evaluated the results of the occurrence and exposure analyses 
for 1,1,1-trichloroethane to determine whether a revised MCLG/MCL would 
be likely to result in a meaningful opportunity to achieve cost savings 
for PWSs and their customers while maintaining, or improving, the level 
of public health protection (USEPA, 2009f). Although the Agency 
obtained and evaluated the finished water occurrence data for 1,1,1-
trichloroethane, its usefulness is limited for determining potential 
cost savings to PWSs and their customers because the Agency does not 
know which systems are treating for this contaminant. As an 
alternative, the Agency evaluated available data on source water 
quality and conducted a qualitative assessment of treatment cost 
savings.
    Table VI-27 provides summary data for contaminant occurrence based 
on maximum sample values for the locations included in the STORET and 
NAWQA data. Although the degree to which these occurrence rates 
represent national drinking water source occurrence is uncertain, the 
information shows no to low occurrence at threshold levels of interest. 
This information indicates that any resulting NPDWR change would affect 
systems that rely on source water at none of the NAWQA locations and at 
less than 0.1 percent of the STORET locations.

  Table VI-27--Ambient Water Quality Monitoring Occurrence Summary for
                          1,1,1-Trichloroethane
------------------------------------------------------------------------
                                 Number of locations  (% of locations)
    Maximum concentration    -------------------------------------------
                                   STORET \1\             NAWQA \2\
------------------------------------------------------------------------
Total.......................  3,429 (100.0%)......  5,788 (100.0%)
Nondetect...................  2,304 (67.2%).......  5,290 (91.4%)
Detected....................  1,125 (32.8%).......  498 (8.6%)
Exceeds current MCLG of 0.2   5 (0.1%)............  0 (0.0%)
 mg/L.
Exceeds alternative value of  0 (0.0%)............  0 (0.0%)
 14 mg/L.
------------------------------------------------------------------------
\1\ STORET database 2002-2008.
\2\ NAWQA database 1992-2008.
Source: USEPA, 2009d.

    The BATs and small system compliance technologies for 1,1,1-
trichloroethane have other beneficial effects, e.g., reduction of other 
co-occurring contaminants, precursors for DBPs, or other common 
impurities. Therefore, if EPA were to consider a higher level, the 
Agency does not know how many PWSs that are currently treating to 
comply with the existing MCL of 0.2 mg/L would be likely to discontinue 
treatment that is already in place (USEPA, 2009d). Also, the Agency 
does not know to what extent affected systems might be able to reduce 
costs given that capital costs are not recoverable. However, the Agency 
recognizes that there may be opportunities to achieve operational cost 
savings if these systems are able to re-optimize current treatment.
    Given these considerations, the Agency believes that any resulting 
revision is not likely to provide a meaningful opportunity for cost 
savings. In view of this, any revision would be a low priority activity 
and not appropriate at this time.
    c. Review Result. Although there are new data that support 
consideration of whether to revise the MCLG/MCL for 1,1,1-
trichloroethane, EPA does not believe a revision to the NPDWR for 
1,1,1-trichloroethane is appropriate at this time. In making this 
decision, the Agency considered whether any possible revision to the 
NPDWR for 1,1,1-trichloroethane is likely to provide a meaningful 
opportunity for cost savings to public water systems and their 
customers. Taking into consideration the low occurrence of this 
contaminant in source waters, EPA has decided that any revision to the 
NPDWR would be a low priority activity for the Agency, and, thus, is 
not appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and

[[Page 15563]]

     The burden on States and the regulated community to 
implement any regulatory change that resulted.
67. 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. EPA based the MCLG on a reference 
dose 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. 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, 2009b).
    The current MCL for 1,1,2-trichloroethane is based on a PQL of 
0.005 mg/L. For the Six-Year Review, the Agency considered whether 
changes in the analytical feasibility of 1,1,2-trichloroethane might 
lead to a lower MCL. EPA reviewed PE data from the first Six-Year 
Review cycle and then analyzed more recent PT data to determine if the 
PQL can be revised (i.e., analytical feasibility). Passing rates for PE 
data available through late 1999 for 1,1,2-trichloroethane are above 95 
percent near the current PQL of 0.005 mg/L, but there were no PE 
studies with true values below the current PQL. More recent PT data 
from late 1999 through 2004, supplied by a PT provider, show greater 
than 90 percent passing rates around the current PQL, including twelve 
studies with true values below the PQL. Because most of the laboratory 
passing rates from PT studies--including several with true 
concentrations below the PQL--exceeded the 75 percent criterion 
typically used to derive a PQL, a lowering of the PQL for 1,1,2-
trichloroethane might be possible. These results, however, are 
insufficient to recalculate a revised PQL for 1,1,2-trichloroethane 
because not enough data points are available below the current PQL to 
derive a value at the 75 percent passing rate (USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether they indicate any potential to quantitate at levels as low as 
the current MCLG: laboratory MRLs in the Six-Year Review ICR dataset, 
and the MDLs for approved methods for the detection of 1,1,2-
trichloroethane (Methods 502.2 and 524.2). While EPA prefers to use 
laboratory performance data to calculate the PQL, the MRL and MDL 
information can be valuable for this review to indicate whether it is 
possible to quantitate at levels below the current PQL. The Six-Year 
Review ICR dataset contains MRL values for 139,672 samples. Of these, 
117,788 (84 percent) equal the modal MRL of 0.0005 mg/L. An additional 
17,142 (12 percent) are lower than 0.0005 mg/L. Because more than 80 
percent of the of MRLs are equal to or less than the current MCLG of 
0.003 mg/L, EPA selected that value as the minimum threshold for the 
occurrence and exposure analysis (USEPA, 2009e). The MDLs of approved 
methods range from 0.00004 to 0.0001 mg/L. Applying a multiplier of 10 
would give a possible PQL range from 0.0004 to 0.001 mg/L, which is 
below the current MCLG (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of 
information, EPA believes that there is potential to lower the PQL for 
1,1,2-trichloroethane. To determine whether any MCL revision is likely 
to provide a meaningful opportunity to improve public health 
protection, EPA evaluated the occurrence of 1,1,2-trichloroethane at 
the current MCLG of 0.003 mg/L (USEPA, 2009f). Table VI-28 shows the 
results of the occurrence and exposure analysis for the current MCL and 
the current MCLG of 0.003 mg/L. The occurrence and exposure analysis 
shows that average concentrations do not exceed the current MCL for any 
system in the analysis. Note that these results are based on the subset 
of monitoring data provided in response to the Six-Year Review ICR and 
do not necessarily reflect MCL violations, which are based on annual 
average concentrations at entry points; SDWIS/FED indicates six MCL 
violations for 1,1,2-trichloroethane between 1998 and 2005 (USEPA, 
2007g). The average concentration at one out of 50,195 systems (0.002 
percent), serving approximately 700 people (or 0.0003 percent of 227 
million people), exceeds the current MCLG of 0.003 mg/L.

 Table VI-28--Number and Percent of Systems With Mean Concentrations Exceeding 1,1,2-Trichloroethane Thresholds
                                and Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                        Systems with mean concentrations that are greater than the regulatory or
                                        health-based threshold (percentages based on 50,195 systems with 1,1,2-
                                          trichloroethane data in the Six-Year Review ICR occurrence dataset)
 Regulatory or health-based threshold --------------------------------------------------------------------------
                                                                                                      Nondetect
                                         Nondetect values = MRL \1\    Nondetect values = \1/2\ MRL   values = 0
                                                                                   \2\                   \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).....................  0 (0.000%)...................  0 (0.000%)...................   0 (0.000%)
Current MCLG (0.003 mg/L)............  1 (0.002%)...................  1 (0.002%)...................   1 (0.002%)
----------------------------------------------------------------------------------------------------------------
                                        Corresponding population served (Percentages based on 226,852,000 people
                                          served by the systems with 1,1,2-trichloroethane data in the Six-Year
                                                             Review ICR occurrence dataset)
                                      --------------------------------------------------------------------------
 Regulatory or health-based threshold    Nondetect values = MRL \1\    Nondetect values = \1/2\ MRL   Nondetect
                                                                                    \2\               values = 0
                                                                                                         \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).....................  0 (0.000%)...................  0 (0.000%)...................   0 (0.000%)
Current MCLG (0.003 mg/L)............  700 (0.0003%)................  700 (0.0003%)................          700
                                                                                                       (0.0003%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.


[[Page 15564]]

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. 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 1,1,2-
trichloroethane is appropriate at this time. The occurrence and 
exposure analysis based on possible changes in analytical feasibility 
indicates that any revision to the MCL is unlikely to provide a 
meaningful opportunity to improve public health protection. Taking into 
consideration the low occurrence of this contaminant, EPA has decided 
that any revision to the NPDWR would be a low priority activity for the 
Agency, and, thus, is not appropriate to revise at this time because 
of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
68. 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 
health effects assessment will consider relevant studies on the 
toxicity of trichloroethylene, including its potential developmental 
and reproductive toxicity. The new health effects assessment was not 
completed by March 1, 2009, the review cutoff date for this notice 
(USEPA, 2009b). The IRIS Substance Assessment Tracking System Web site 
(http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date 
information on the status of the health effects assessment.
    Although a risk assessment is in process for trichloroethylene, the 
existing MCLG is zero and the current MCL of 0.005 mg/L is based on the 
PQL. Therefore, EPA reviewed whether there is potential to revise the 
PQL. EPA reviewed PE data from the first Six-Year Review cycle and then 
analyzed more recent PT data to determine if the PQL can be revised 
(i.e., analytical feasibility). Passing rates for PE data available 
through late 1999 for trichloroethylene are above 95 percent at the 
lowest concentrations. However, the true concentrations were all higher 
than the current PQL of 0.005 mg/L. More recent PT data from 1999 to 
2004, supplied by a PT provider, also show greater than 95 percent 
passing rates for studies around the current PQL, including 6 with true 
values below the PQL. Because most of the laboratory passing rates from 
PE and PT studies exceeded the 75 percent criterion typically used to 
derive a PQL, including several with true values below the PQL, a 
lowering of the PQL for trichloroethylene might be possible. These 
results, however, are insufficient to recalculate a revised PQL for 
trichloroethylene because not enough data points are available below 
the current PQL to derive a value at the 75 percent passing rate 
(USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of trichloroethylene (Methods 502.2, 524.2, 
and 551.1). While EPA prefers to use laboratory performance data to 
calculate the PQL, the MRL and MDL information can be valuable for this 
review to indicate whether it is possible to quantitate at levels below 
the current PQL. EPA also noted that the State of New Jersey uses a PQL 
of 0.001 mg/L, based on a 1987 study of laboratory performance at low 
concentrations that used criteria similar to those in the PT data 
(NJDWQI, 1987). The Six-Year Review ICR dataset contains MRLs for 
138,439 samples. More than 80 percent of these values are less than or 
equal the modal MRL: 118,193 (85 percent) equal the modal MRL of 0.0005 
mg/L and an additional 17,057 (12 percent) are lower than 0.0005 mg/L. 
Therefore, EPA selected the modal MRL as the EQL (USEPA, 2009e). The 
MDLs of approved methods range are 0.00006, 0.00019, and 0.000042 mg/L. 
Applying a multiplier of 10 would give a possible PQL range from 
0.00042 to 0.0019 mg/L, which contains the EQL (USEPA, 2009e).
    Based on these varied and unrelated approaches/sources of 
information, EPA believes that there is potential to lower the PQL for 
trichloroethylene. To determine whether any MCL revision is likely to 
provide a meaningful opportunity to improve public health protection, 
EPA evaluated the occurrence of trichloroethylene at the EQL of 0.0005 
mg/L and additional thresholds of 0.0010 and 0.0025 mg/L (USEPA, 
2009f). Table VI-29 shows the results of the occurrence and exposure 
analysis for the current MCL and these thresholds. The occurrence and 
exposure analysis shows that average concentrations exceed the current 
MCL for 25 out of 50,432 systems (0.050 percent) serving approximately 
410,000 people (or 0.181 percent of 227 million people). Note that 
these results are based on the subset of monitoring data provided in 
response to the Six-Year Review ICR and do not necessarily reflect MCL 
violations, which are based on annual average concentrations at entry 
points; SDWIS/FED indicates 191 MCL violations for trichloroethylene 
between 1998 and 2005 (USEPA, 2007g), with annual violations ranging 
from 12 to 31. Average concentrations at 310 to 388 of 50,432 systems 
(0.615 to 0.769 percent), serving approximately 12.0 to 13.0 million 
people (or 5.237 to 5.670 percent of 227 million people), exceed the 
EQL of 0.0005 mg/L. While these systems are widely distributed and 
located in most of the States providing data, a few large systems 
(serving 500,000 or more people) account for almost half of the exposed 
population.

[[Page 15565]]



 Table VI-29--Number and Percent of Systems With Mean Concentrations Exceeding Trichloroethylene Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                       feasibility-based threshold (percentages based on 50,432 systems with
 Regulatory or feasibility-based       trichloroethylene data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  25 (0.050%)..............  25 (0.050%).............  25 (0.050%)
\1/2\ MCL (0.0025 mg/L)..........  70 (0.139%)..............  68 (0.135%).............  64 (0.127%)
2xEQL (0.001 mg/L)...............  239 (0.474%).............  208 (0.412%)............  182 (0.361%)
EQL (0.0005 mg/L)................  not applicable...........  388 (0.769%)............  310 (0.615%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population served (percentages based on 226,908,000 people
                                    served by the systems with trichloroethylene data in the Six-Year Review ICR
                                                                 occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based     Nondetect Values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
            threshold                          \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (0.005 mg/L).................  410,000 (0.181%).........  410,000 (0.181%)........  410,000 (0.181%)
\1/2\ MCL (0.0025 mg/L)..........  4,765,000 (2.100%).......  4,691,000 (2.067%)......  4,598,000 (2.026%)
2xEQL (0.001 mg/L)...............  10,367,000 (4.569%)......  8,282,000 (3.650%)......  7,399,000 (3.261%)
EQL (0.0005 mg/L)................  not applicable...........  12,866,000 (5.670%).....  11,884,000 (5.237%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
  Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the
  results equal to this value results in an upwardly biased estimate of the number of systems with mean
  concentrations that exceed this value.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that a revision to the MCL 
may provide a meaningful opportunity to improve the level of public 
health protection, EPA considered whether treatment feasibility is 
likely to pose any limitations if the MCL were lowered (USEPA, 2009g). 
The current BATs for trichloroethylene are packed tower aeration (PTA) 
and granular activated carbon (GAC). Small system compliance 
technologies for trichloroethylene include GAC and several aeration 
technologies. EPA's assessment shows that PTA and GAC are effective 
enough to achieve concentrations as low as the EQL.
    EPA is not currently able to assess the potential health benefits 
from a revised MCL for trichloroethylene, because the revised health 
effects assessment is not yet available. However, based on its B2 
cancer classification (MCLG of zero) and the occurrence and exposure 
analysis at possible MCL values, the Agency believes that a revision to 
the MCL may provide a meaningful opportunity to reduce public health 
risks.
    c. Review Result. The Agency believes it is appropriate to revise 
the NPDWR for trichloroethylene although a health effects assessment is 
currently in progress. The existing MCLG is zero (based on the current 
B2 cancer classification) and the current MCL is based on a PQL (i.e., 
analytical feasibility) of 0.005 mg/L. The Agency's review indicates 
that analytical feasibility could be as much as 10 times lower (~ 
0.0005 mg/L) and occurrence at this level appears to be relatively 
widespread. Hence, revisions to the trichloroethylene NPDWR may provide 
a meaningful opportunity for health risk reduction. If the updated 
health effects assessment is completed in time to consider for the 
regulatory revision of trichloroethylene, the Agency will consider this 
assessment in its evaluation of public health benefits associated with 
any revision. As discussed in Section VII, the Agency solicits public 
comment and/or relevant information that may inform the regulatory 
revision for trichloroethylene. EPA is also requesting that 
stakeholders provide information/data about the lowest level of 
quantitation (including the analytical method used) that laboratories 
can reliably and consistently achieve.
69. Uranium
    a. Background. EPA published the current NPDWR for uranium on 
December 7, 2000 (65 FR 76708 (USEPA, 2000c)). The NPDWR established an 
MCLG of zero based on a cancer classification of A, known human 
carcinogen. As noted in the December 2000 FR, uranium has also been 
identified as a nephrotoxic metal (kidney toxicant) and EPA derived a 
drinking water equivalent level of 20 [mu]g/L as a noncancer health 
endpoint for kidney toxicity. The NPDWR also established an MCL of 30 
[mu]g/L, which is higher than the feasible level of 20 [mu]g/L and the 
level associated with kidney toxicity. In December 2000, EPA exercised 
its discretionary authority to set an MCL at a level higher than 
feasible (SDWA Section 1412(b)(6)), based on the finding that 
``benefits do not justify the costs at the feasible level (20 [mu]g/L) 
and that the net benefits are maximized at a level (30 [mu]g/L) that is 
still protective of health with an adequate margin of safety'' (65 FR 
76708 (USEPA, 2000c)) \25\.
---------------------------------------------------------------------------

    \25\ After the December 7, 2000 final regulation, two trade 
associations and several municipal water systems challenged EPA's 
standard for uranium by claiming that the Agency did not use the 
best available science when finalizing the standard. In February of 
2003, the DC Circuit Court of Appeals upheld EPA's regulation for 
uranium (as well as combined radiums, and beta particle and photon 
emitters).
---------------------------------------------------------------------------

    b. Technical Reviews. EPA has initiated a reassessment of the 
health risks resulting from exposure to uranium. The revised health 
effects assessment will consider relevant studies on the toxicity of 
uranium, including its potential developmental and reproductive 
toxicity. The new health effects assessment was not completed by March 
1, 2009, the review cutoff date for this notice (USEPA, 2009b). The 
IRIS Substance Assessment Tracking System Web site (http://cfpub.epa.gov/iristrac/index.cfm) has the most up-to-date information 
on the status of the health effects assessment.
    c. Review Result. The Agency does not believe a revision to the 
NPDWR for uranium is appropriate at this time because a reassessment of 
the health risks resulting from exposure to

[[Page 15566]]

uranium is ongoing (USEPA, 2009b). As noted previously, the uranium MCL 
is based on the SDWA cost benefit provision (Section 1412(b)(6)) and 
the health effects assessment is important for reviewing the benefits 
associated with the basis of the MCL.
70. 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. As part of the Six-Year Review process, EPA 
conducted a literature search for relevant data on the carcinogenicity 
of vinyl chloride as well as its potential developmental and 
reproductive toxicity. EPA has not identified any new information that 
indicates that it is appropriate to consider revisions to the cancer 
classification for vinyl chloride at this time (USEPA, 2009b). Because 
the MCLG remains at zero, the Agency believes that a further review of 
the health effects of vinyl chloride is not warranted at this time.
    The current MCL for vinyl chloride is based on a PQL of 0.002 mg/L. 
For the Six-Year Review, the Agency considered whether changes in the 
analytical feasibility of vinyl chloride might lead to a lower MCL. EPA 
reviewed PE data from the first Six-Year Review cycle and then analyzed 
more recent PT data to determine if the PQL can be revised (i.e., 
analytical feasibility). Passing rates for PE data available through 
late 1999 for vinyl chloride are generally in the 75 to 80 percent 
range near the current PQL of 0.002 mg/L, but there were no results for 
PE studies with true values below the current PQL. More recent PT data 
from late 1999 through 2004, supplied by a PT provider, also show 
greater than 80 percent passing rates for studies around the current 
PQL, including two studies with true values below the PQL. Despite the 
limited data below the PQL, most of the laboratory passing rates from 
PE and PT studies--including two with true concentrations below the 
PQL--exceeded the 75 percent criterion usually used to derive a PQL. 
Therefore, a lowering of the PQL for vinyl chloride might be possible 
(USEPA, 2009c).
    EPA evaluated two alternative sources of information to determine 
whether an EQL below the current PQL could be estimated: laboratory 
MRLs in the Six-Year Review ICR dataset, and the MDLs for approved 
methods for the detection of vinyl chloride (Methods 502.2 and 524.2). 
While EPA prefers to use laboratory performance data to calculate the 
PQL, the MRL and MDL information can be valuable for this review to 
indicate whether it is possible to quantitate at levels below the 
current PQL. The Six-Year Review ICR dataset contains MRL values for 
139,494 samples. More than 80 percent of these values are less than or 
equal the modal MRL: 105,410 (76 percent) equal the modal MRL of 0.0005 
mg/L and an additional 25,723 (18 percent) are lower than 0.0005 mg/L. 
Therefore, EPA selected the modal MRL as the EQL (USEPA, 2009e). The 
MDLs of approved methods range from 0.00017 to 0.00018 mg/L. Applying a 
multiplier of 10 would give a possible PQL range from 0.0017 to 0.0018 
mg/L, which is higher than the EQL, but below the current PQL (USEPA, 
2009e).
    Based on these varied and unrelated approaches/sources of 
information, EPA believes that there may be potential to lower the PQL 
for vinyl chloride. To determine whether any MCL revision is likely to 
provide a meaningful opportunity to improve public health protection, 
EPA evaluated the occurrence of vinyl chloride at the EQL of 0.0005 mg/
L and an additional threshold of 0.001 mg/L (USEPA, 2009f). Table VI-30 
shows the results of the occurrence and exposure analysis for the 
current MCL and these thresholds. The occurrence and exposure analysis 
shows that average concentrations exceed the current MCL for 8 to 11 of 
50,411 systems (0.016 to 0.022 percent) serving fewer than 14,000 
people (or 0.003 to 0.006 percent of 226 million people). Note that 
these results are based on the subset of monitoring data provided in 
response to the Six-Year Review ICR and do not necessarily reflect MCL 
violations, which are based on annual average concentrations at entry 
points; SDWIS/FED indicates 25 MCL violations for vinyl chloride 
between 1998 and 2005 (USEPA, 2007g). Average concentrations at 32 to 
49 of 50,411 systems (0.063 to 0.097 percent), serving 483,000 to 
766,000 people (or 0.213 to 0.338 percent of 226 million people), 
exceed the EQL of 0.0005 mg/L.

   Table VI-30--Number and Percent of Systems With Mean Concentrations Exceeding Vinyl Chloride Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                    feasibility-based threshold (percentages based on 50,411 systems with vinyl
 Regulatory or feasibility-based            chloride data in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (0.002 mg/L).................  11 (0.022%)..............  10 (0.020%).............  8 (0.016%)
\1/2\ MCL (0.001 mg/L)...........  21 (0.042%)..............  18 (0.037%).............  15 (0.030%)
EQL (0.0005 mg/L)................  not applicable...........  49 (0.097%).............  32 (0.063%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding Population Served (Percentages based on 226,464,000 people
                                      served by the systems with vinyl chloride data in the Six-Year Review ICR
                                                                 occurrence dataset)
                                  ------------------------------------------------------------------------------
 Regulatory or feasibility-based     Nondetect values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
            threshold                          \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (0.002 mg/L).................  14,000 (0.006%)..........  12,000 (0.005%).........  6,000 (0.003%)
\1/2\ MCL (0.001 mg/L)...........  56,000 (0.025%)..........  23,000 (0.010%).........  18,000 (0.008%)
EQL (0.0005 mg/L)................  not applicable...........  766,000 (0.338%)........  483,000 (0.213%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset.
  Results are not reported at the EQL of 0.0005 mg/L because this is the modal MRL and setting a majority of the
  results equal to this value results in an upwardly biased estimate of the number of systems with mean
  concentrations that exceed this value.
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.


[[Page 15567]]

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. 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 vinyl chloride 
is appropriate at this time. The occurrence and exposure analysis based 
on possible changes in analytical feasibility indicates that any 
revision to the MCL is unlikely to provide a meaningful opportunity to 
improve public health protection. Taking into consideration the low 
occurrence of this contaminant, EPA has decided that any revision to 
the NPDWR would be a low priority activity for the Agency, and, thus, 
is not appropriate to revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.
71. Xylenes (Total)
    a. Background. EPA published the current NPDWR for total xylenes on 
January 30, 1991 (56 FR 3526 (USEPA, 1991c)). The NPDWR established an 
MCLG and an MCL of 10 mg/L. EPA based the MCLG on a reference dose of 2 
mg/kg-day and a cancer classification of D, not classifiable as to 
human carcinogenicity.
    b. Technical Reviews. In 2003, the Agency updated its health 
effects assessment of xylenes (USEPA, 2003d). The change in this 
assessment could lead to a change in the MCLG. This assessment 
considered relevant studies on the toxicity of xylenes including 
developmental and reproductive toxicity. The assessment revised the RfD 
from 2 mg/kg-day to 0.2 mg/kg-day and concluded that there is 
inadequate information to assess the carcinogenic potential of xylenes 
(USEPA, 2003d). Based on the new IRIS assessment and RfD of 0.2 mg/kg-
day, and assuming a 70-kg adult body weight and 2 liters water intake 
per day, the DWEL could be 7 mg/L. An RSC of 20 percent results in a 
possible MCLG of 1 mg/L.
    Analytical feasibility does not pose any limitations for the 
current MCL and would not be a limiting factor for the possible MCLG 
decrease under consideration. EPA evaluated the results of the 
occurrence and exposure analyses for total xylenes to determine whether 
a revised MCLG/MCL would be likely to result in a meaningful 
opportunity to improve the level of public health protection (USEPA, 
2009f). Table VI-31 shows the results of the occurrence and exposure 
analysis for the current MCL and the possible MCLG set equal to 1 mg/L 
based on the new health effects information. The occurrence and 
exposure analysis shows that average concentrations do not exceed the 
current MCL for any system in the analysis. Note that these results are 
based on the subset of monitoring data provided in response to the Six-
Year Review ICR and do not necessarily reflect MCL violations, which 
are based on annual average concentrations at entry points; SDWIS/FED 
indicates two MCL violations for xylene between 1998 and 2005 (USEPA, 
2007g). The occurrence and exposure analysis shows that average 
concentrations do not exceed the possible MCLG based on new health 
effects information (1 mg/L).

       Table VI-31--Number and Percent of Systems With Mean Concentrations Exceeding Xylene Thresholds and
                                  Corresponding Estimates of Population Served
----------------------------------------------------------------------------------------------------------------
                                      Systems with mean concentrations that are greater than the regulatory or
                                    health-based threshold (percentages based on 47,698 systems with xylene data
    Regulatory or health-based                     in the Six-Year Review ICR occurrence dataset)
            threshold             ------------------------------------------------------------------------------
                                     Nondetect values = MRL   Nondetect values = \1/2\
                                              \1\                      MRL \2\          Nondetect values = 0 \3\
----------------------------------------------------------------------------------------------------------------
MCL (10 mg/L)....................  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
Possible MCLG (1 mg/L)...........  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
----------------------------------------------------------------------------------------------------------------
                                      Corresponding population Served (percentages based on 218,072,000 people
                                    served by the systems with xylene data in the Six-Year Review ICR occurrence
                                                                      dataset)
                                  ------------------------------------------------------------------------------
Regulatory or health-based           Nondetect values = MRL   Nondetect values = \1/2\  Nondetect values = 0 \3\
 threshold.......................              \1\                     MRL \2\
----------------------------------------------------------------------------------------------------------------
MCL (10 mg/L)....................  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
Possible MCLG (1 mg/L)...........  0 (0.000%)...............  0 (0.000%)..............  0 (0.000%)
----------------------------------------------------------------------------------------------------------------
\1\ Results are based on setting all nondetect results equal to MRL values in the Six-Year Review ICR dataset
\2\ Results are based on setting all nondetect results equal to \1/2\ MRL values in the Six-Year Review ICR
  dataset.
\3\ Results are based on setting all nondetect results equal to zero.
Source: USEPA, 2009f.

    Since the occurrence analysis indicates that any revision to the 
MCL is unlikely to provide a meaningful opportunity to improve the 
level of public health protection, it was not necessary to perform any 
additional reviews on treatment feasibility or economic considerations.
    c. Review Result. Although there are new data that support 
consideration of whether to revise the MCLG/MCL for total xylenes, EPA 
does not believe a revision to the NPDWR for total xylenes is 
appropriate at this time. In making this decision, the Agency 
considered whether any possible revision to the NPDWR for total xylenes 
is likely to provide a meaningful opportunity for health risk 
reductions. Taking into consideration the low occurrence of this 
contaminant, EPA has decided that any revision to the NPDWR would be a 
low priority activity for the Agency, and, thus, is not appropriate to 
revise at this time because of:
     Competing workload priorities;
     The administrative costs associated with rulemaking; and
     The burden on States and the regulated community to 
implement any regulatory change that resulted.

VII. EPA's Request for Comments

A. Request for Comment and/or Information on the Candidates for 
Revision

    EPA invites commenters to submit any new, relevant peer-reviewed 
data or information pertaining to the four

[[Page 15568]]

NPDWRs identified in today's action as candidates for revision (i.e., 
acrylamide, epichlorohydrin, tetrechloroethylene and 
trichloroethylene). This information will inform EPA's evaluation as 
the Agency moves forward with the regulatory revisions for these four 
NPDWRs. 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, 2000d). Relevant data include studies/analyses 
pertaining to analytical feasibility, treatment feasibility, and 
occurrence/exposure related to the four NPDWRs candidates for revision 
listed in today's action.\26\ Table VII-1 provides a list of the 
specific items for which EPA is requesting comment and/or information 
for the four candidates for revision. It also provides a cross-
reference to the section addressing the issue.

      Table VII-1--Items for Which EPA Is Requesting Comment and/or
            Information for the Four Candidates for Revision
------------------------------------------------------------------------
                 Issue                           Notice section
------------------------------------------------------------------------
Any new, relevant peer-reviewed data    Section VI.B.1.
 or information that would inform the
 revision of the NPDWR for acrylamide,
 including information pertaining to
 extent of use of polyacrylamide in
 drinking water facilities.
Any new, relevant peer-reviewed data    Section VI.B.36.
 or information that would inform the
 revision of the NPDWR for
 epichlorohydrin, including
 information pertaining to extent of
 use of epichlorohydrin-based polymers/
 co-polymers in drinking water
 facilities.
Any new, relevant peer-reviewed data    Section VI.B.60.
 or information that would inform the
 revision of the NPDWR for
 tetrachloroethylene, including
 information/data about the lowest
 level of quantitation (and analytical
 method used) that laboratories can
 reliably and consistently achieve.
Any new, relevant peer-reviewed data    Sections VI.B.65.
 or information that would inform the
 revision of the NPDWR for
 trichloroethylene, including
 information/data about the lowest
 level of quantitation (and the
 analytical method used) that
 laboratories can reliably and
 consistently achieve.
------------------------------------------------------------------------

B. Request for Information/Data on Other Review Topics

    EPA also invites commenters to submit new, relevant information on 
several other review topics referenced in this notice and listed in 
Table VII-2.

   Table VII-2--Issues for Which EPA Is Requesting Public Input and/or
                               Information
------------------------------------------------------------------------
              Issue                           Notice section
------------------------------------------------------------------------
Location for nitrate and nitrite  Section V.B.6.
 monitoring.
Monitoring frequency for ground   Section V.B.6.
 water systems with low nitrate
 and nitrite concentrations.
Monitoring requirements for non-  Section V.B.6.
 community water systems.
Detection limits that serve as    Section V.B.6.
 triggers to determine
 compliance monitoring frequency
 for SOCs.
New, relevant health effects      Section VI.B.17.
 information that will help the
 Agency decide whether to
 initiate a new health effects
 assessment for chromium.
New, relevant health effects      Sections VI.B.49 and VI.B.50.
 information that will help the
 Agency decide whether to
 initiate or nominate nitrate
 and nitrite for a new health
 effects assessment.
New, relevant health effects      Sections VI.B.56.
 information that will help the
 Agency decide whether to
 initiate or nominate selenium
 for a new health effects
 assessment.
New, relevant health effects      Sections VI.B.65.
 information that will help the
 Agency decide whether to
 initiate or nominate 1,2,4-
 trichlorobenzene for a new
 health effects assessment.
------------------------------------------------------------------------

C. Requests for Information on the Impacts of Climate Change on Water 
Quality

    The Agency recognizes that changes in global climate can impact 
temperature, rainfall patterns, and snow and ice cover. Changes in 
these climate indicators can impact water quantity and water quality. 
In an effort to assess the impacts of climate change on water quality, 
EPA is asking if public water systems and/or States have any 
information or data that illustrates the impact of climate change 
(e.g., changes in rainfall, drought, temperature, and snow/ice cover) 
on the occurrence of contaminants in drinking water, both in source 
water and in finished water. EPA also requests data on changes in the 
variability of occurrence and impacts on drinking water treatment to 
address occurrence or variability changes.
---------------------------------------------------------------------------

    \26\ Note that new health effects studies/information for 
acrylamide, PCE and TCE are being considered as part of the IRIS 
update to these health assessments.
---------------------------------------------------------------------------

VIII. EPA's Next Steps

    EPA will consider the public comments and/or any new, relevant, 
peer-reviewed data submitted for the four NPDWRs listed as candidates 
for revision as the Agency proceeds with the regulatory revisions for 
these regulations. The announcement that the Agency intends to revise 
an NPDWR (pursuant to SDWA section 1412(b)(9)) is not a regulatory 
decision. Instead, it initiates a regulatory process that will involve 
more detailed analyses of health effects, analytical and treatment 
feasibility, occurrence, benefits, costs, and other regulatory matters 
relevant to deciding whether an NPDWR should be revised. The Six-Year 
Review results do not obligate the Agency to revise an NPDWR in the 
event that EPA determines during the regulatory process that revisions 
are no longer

[[Page 15569]]

appropriate and discontinues further efforts to revise an NPDWR. 
Similarly, the fact that an NPDWR has not been selected for revision 
means only that EPA believes that regulatory changes to a particular 
NPDWR are not appropriate at this time for the reasons given in today's 
action; future reviews may identify information that leads to an 
initiation of the revision process.

IX. References

ATSDR (Agency for Toxic Substances and Disease Registry). 2007. 
Toxicological profile for benzene. Atlanta, GA: Agency for Toxic 
Substances and Disease Registry, Public Health Service, U.S. 
Department of Health and Human Services. Available on the Internet 
at: http://www.atsdr.cdc.gov/toxprofiles/tp3.html.
Cocco, P, G. Broccia, et al. 2003. Nitrate in community water 
supplies and incidence of non-Hodgkin's lymphoma in Sardinia, Italy. 
Journal of Epidemiology and Community Health. v. 57, pp. 510-511.
Coss, A., K.P. Cantor, et al. 2004. Pancreatic cancer and drinking 
water and dietary sources of nitrate and nitrite. American Journal 
of Epidemiology. v. 159, pp. 693-701.
de Roos, A.J., M.H. Ward, et al. 2003. Nitrate in public water 
supplies and the risk of colon and rectum cancers. Epidemiology. v. 
14, pp. 640-649.
Duffield-Lillico, A.J., E.H. Slate, et al. 2003. Selenium 
supplementation and secondary prevention of nonmelanoma skin cancer 
in a randomized trial. Journal of the National Cancer Institute. v. 
95, pp. 1477-1481.
Gianessi, L. and N. Reigner. 2006. Pesticide Use in U.S. Crop 
Production: 2002 With Comparison to 1992 and 1997--Fungicides & 
Herbicides. Washington, DC: CropLife Foundation.
Gilliom, R.J., J.E. Barbash, C.G. Crawford, P.A. Hamilton, J.D. 
Martin, N. Nakagaki, L.H. Nowell, J.C. Scott, P.E. Stackelberg, G.P. 
Thelin, and David M. Wolock. 2006. The Quality of Our Nation's 
Waters: Pesticides in the Nation's Streams and Ground Water, 1992-
2001. U.S. Geological Survey Circular 1291.
Grosse, Y., R. Baan, et al. 2006. Carcinogenicity of nitrate, 
nitrite, and cyanobacterial peptide toxins. The Lancet Oncology. v. 
7, pp. 628-629.
Hawkes, W.C., and N.L. Keim. 2003. Dietary selenium intake modulates 
thyroid hormone and energy metabolism in men. Journal of Nutrition. 
v. 133, pp. 3443-3448.
Lan, Q., L. Zhang, et al. 2004. Hematotoxicity in workers exposed to 
low levels of benzene. Science. v. 306, pp. 1774-1776.
Levine, Audrey D., Brian A. Bolto, and David R. Dixon. 2004. 
Reactions of Polyelectrolytes With Other Water Treatment Chemicals. 
AwwaRF Report 2509.
MacKenzie, R.D., R.U. Byerrum, C.F. Decker, et al. 1958. Chronic 
toxicity studies. II. Hexavalent and trivalent chromium administered 
in drinking water to rats. American Medical Association Archives of 
Industrial Health. v. 18, pp. 232-234.
Markel, E, C. Nyakas, and S. Ormai. 1989. Nitrate induced changes in 
sensorimotor development and learning behavior in rats. Acta 
Physiologica Hungarica. v. 74, pp. 69-75.
Moore, M. 1994a. 104-week dietary carcinogenicity study with 1,2,4-
trichlorobenzene in mice. Hazleton Washington, Inc. Rockville, 
Maryland. HWA 2603-102. EPA/OTS Doc 88-930000429.
Moore, M. 1994b. Final report--104-week dietary carcinogenicity 
study with 1,2,4-trichlorobenzene in rats. Hazleton Washington, Inc. 
Rockville, Maryland. HWA 2603-103. OTS0558832. OPPTS-44612.
Moran, M.J. 2006. Occurrence And Implications Of Selected 
Chlorinated Solvents In Ground Water And Source Water In The United 
States And In Drinking Water In 12 Northeast And Mid-Atlantic 
States, 1993-2002. U.S. Geological Survey Scientific Investigations 
Report 2005-5268. Reston, VA: U.S. Geological Survey.
Mueller, B.A., S.S. Nielsen, et al. 2004. Household water source and 
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    Dated: December 17, 2009.
Lisa P. Jackson,
Administrator.
[FR Doc. 2010-6624 Filed 3-26-10; 8:45 am]
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