[Federal Register Volume 75, Number 59 (Monday, March 29, 2010)]
[Notices]
[Pages 15500-15572]
From the Federal Register Online via the Government Publishing 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
[[Page 15500]]
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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.........................
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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.
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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\
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\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.
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[[Page 15570]]
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USEPA. 2003a. Analytical Feasibility Support Document for the Six-
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(Reassessment of Feasibility for Chemical Contaminants). EPA 815-R-
03-003. March 2003.
USEPA. 2003b. EPA Protocol for Review of Existing National Primary
Drinking Water Regulations. EPA Report 815-R-03-002. Washington, DC:
Office of Ground Water and Drinking Water. June 2003. Available on
the Internet at: http://www.epa.gov/safewater/standard/review/pdfs/support_6yr_protocal_final.pdf.
USEPA. 2003c. Exposure and Human Health Reassessment of 2,3,7,8-
Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds.
Preliminary Review Draft. National Center for Environmental
Assessment, Research and Development.
USEPA. 2003d. IRIS, Xylenes. Available on the Internet at: http://www.epa.gov/ncea/iris/subst/0270.htm.
USEPA. 2003e. National Primary Drinking Water Regulations;
Announcement of Completion of EPA's Review of Existing Drinking
Water Standards; Notice. Federal Register. Vol. 68, No. 138. p.
42908, July 18, 2003.
USEPA. 2004a. IRIS, 1,2-Dibromoethane. Available on the Internet at:
http://www.epa.gov/ncea/iris/subst/0361.htm.
USEPA. 2004b. National Primary Drinking Water Regulations: Minor
Corrections and Clarification to Drinking Water Regulations;
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Federal Register. Volume 69, Number 124. p. 38850, June 29, 2004.
USEPA. 2004c. Reregistration Eligibility Decision (RED)--
Methoxychlor. EPA Report 738-R-04-010. Washington, DC: Office of
Prevention, Pesticides, and Toxic Substances. June 2004. Available
on the Internet at: http://www.epa.gov/oppsrrd1/REDs/methoxychlor_red.htm.
USEPA. 2005a. IRIS, Barium. Available on the Internet at: http://www.epa.gov/ncea/iris/subst/0010.htm.
USEPA. 2005b. IRIS, Toluene. Available on the Internet at: http://www.epa.gov/ncea/iris/subst/0118.htm.
USEPA. 2005c. Reregistration Eligibility Decision (RED)--2,4-D. EPA
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Substances. June 2005. Available on the Internet at: http://www.epa.gov/oppsrrd1/REDs/24d_red.pdf.
USEPA. 2005d. Reregistration Eligibility Decision (RED) for
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http://www.epa.gov/oppsrrd1/reregistration/REDs/
[[Page 15571]]
endothall--red.pdf.
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the Chloroacetanilides. Washington, DC: Office of Pesticide
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USEPA. 2006b. Addendum to the 2002 Lindane Reregistration
Eligibility Decision (RED). EPA Report 738-R-06-028. Washington, DC:
Office of Prevention, Pesticides, and Toxic Substances. July 2006.
Available on the Internet at: http://www.epa.gov/oppsrrd1/REDs/lindane_red_addendum.pdf.
USEPA. 2006c. Finalization of Atrazine IRED, and Completion of
Tolerance Reassessment and Reregistration Eligibility Process.
Washington, DC: Office of Prevention, Pesticides, and Toxic
Substances. April 2006. Available on the Internet at: http://www.epa.gov/oppsrrd1/REDs/atrazine_combined_docs.pdf.
USEPA. 2006d. Interim Reregistration Eligibility Decision (IRED)--
Carbofuran. EPA Report 738-R-06-031. Office of Prevention,
Pesticides, and Toxic Substances. August 2006. Available on the
Internet at: http://www.epa.gov/oppsrrd1/reregistration/REDs/carbofuran_ired.pdf.
USEPA. 2006e. Lindane; Cancellation Order. Federal Register. Vol.
71, No. 239. p. 74905, December 13, 2006.
USEPA. 2006f. National Primary Drinking Water Regulations: Ground
Water Rule; Final Rule. Federal Register. Vol. 71, No. 216. p.
65574, November 8, 2006.
USEPA. 2006g. National Primary Drinking Water Regulations: Long Term
2 Enhanced Surface Water Treatment Rule; Final Rule. Federal
Register. Vol. 71, No. 3. p. 654, January 5, 2006.
USEPA. 2006h. National Primary Drinking Water Regulations: Stage 2
Disinfectants and Disinfection Byproducts Rule; Final Rule. Federal
Register. Vol. 71, No. 2. p. 388, January 4, 2006.
USEPA. 2006i. Reregistration Eligibility Decision (RED)--Simazine.
EPA Report 738-R-06-008. Washington, DC: Office of Prevention,
Pesticides, and Toxic Substances. April 2006. Available on the
Internet at: http://www.epa.gov/oppsrrd1/REDs/simazine_red.pdf.
USEPA. 2007a. Advisory on EPA's Assessments of Carcinogenic Effects
of Organic and Inorganic Arsenic: A Report of the U.S. EPA Science
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Internet at: http://yosemite.epa.gov/sab/sabproduct.nsf/
EADABBF40DED2A0885257308006741EF/$File/sab-07-008.pdf.
USEPA. 2007b. Draft Toxicological Review of Acrylamide: In Support
of Summary Information on the Integrated Risk Information System
(IRIS). Federal Register. Vol. 72, No. 248. p. 73813, December 28,
2007.
USEPA. 2007c. Integrated Risk Information System (IRIS);
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245. p. 72715, December 21, 2007.
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at: http://www.epa.gov/ncea/iris/subst/0197.htm.
USEPA. 2007e. Unregulated Contaminant Monitoring Regulation (UCMR)
for Public Water Systems; Revisions; Final Rule. Federal Register.
Vol. 72, No, 2. p. 367, January 4, 2007.
USEPA. 2007f. National Primary Drinking Water Regulations for Lead
and Copper: Short-Term Regulatory Revisions and Clarifications;
Final Rule. Federal Register. Vol. 72, No. 195. p. 57782, October
10, 2007.
USEPA. 2007g. Safe Drinking Water Information System/Federal version
(SDWIS/FED) FY2006 Inventory Data. Available online at http://www.epa.gov/ogwdw000/databases/pivottables.html.
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USEPA. 2009d. Occurrence Analysis for Potential Source Waters for
the Second Six-Year Review of National Primary Drinking Water
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[[Page 15572]]
Journal of Chinese Preventive Medicine. v. 21, pp. 262-264.
Dated: December 17, 2009.
Lisa P. Jackson,
Administrator.
[FR Doc. 2010-6624 Filed 3-26-10; 8:45 am]
BILLING CODE 6560-50-P