EPA # 815-Z-02-002
Wednesday,
April 17, 2002
Part m
Environmental
Protection Agency
40 CFR Part 141
National Primary Drinking Water
Regulations; Announcement of the Results
of EPA's Review of Existing Drinking
Water Standards and Request for Public
Comment; Proposed Rule
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Federal Register/Vol. 67, No. 74/Wednesday, April 17, 2002/Proposed Rules
ENVIRONMENTAL PROTECTION
AGENCY
40 CFR Part 141
[FRL-7167-9]
FUN 2040-AD67
National Primary Drinking Water
Regulations; Announcement of the
Results of EPA's Review of Existing
Drinking Water Standards and Request
for Public Comment
AGENCY: Environmental Protection
Agency (EPA).
ACTION: Reviexv of regulations; request
for comments,
SUMMARY: The Safe Drinking Water Act
(SDWA) requires the United States
Environmental Protection Agency (EPA)
to conduct a periodic review of existing
National Primary Drinking Water
Regulations (NPDWRs). EPA is
requesting public comment on the
results of its review of 69 NPDWRs that
were established prior to 1997,
including 68 chemical NPDWRs and the
Total Coliform Rule (TCR). The
intended purpose of the review is to
identify those NPDWRs for which
current health risk assessments, changes
in technology, and/or other factors,
provide a health or technical basis to
support a regulatory revision that will
improve or strengthen public health
protection. Based on its review, and
pending an evaluation of public
comments, the Agency preliminarily
believes that the 68 chemical NPDWRs
remain appropriate at this time, and that
the TCR should be revised.
DATES: EPA must receive public
comments on this action by June 17,
2002.
ADDRESSES: Please send your comments
to the W-01-14 Comments Clerk.
Submit electronic comments to: ow-
docket@epa.gov. Written comments
should be mailed to: Water Docket (MC-
4101), U.S. Environmental Protection
Agency, 1200 Pennsylvania Avenue,
NW., Washington, DC, 20460. Hand
deliveries should be delivered to EPA's
Water Docket at East Tower Basement
(EB Room 57), Waterside Mall, 401M
Street, SW., Washington, DC, 20460.
You may contact the docket at (202)
260-3027 between 9 a.m. and 3:30 p.m.
Eastern Time, Monday through Friday.
Comments may be submitted
electronically. See SUPPLEMENTARY
INFORMATION for file formats and other
information about electronic filing and
docket review.
FOR FURTHER INFORMATION CONTACT: For
technical inquiries contact: Judy
Lebowich, (202) 564-4884, e-mail:
lebowich.judy@epa.gov, or Wynne
Miller, (202) 564-4887, e-mail:
miller.wynne@epa.gov. For general
information about, and copies of, this
document or information about the
existing NPDWRs discussed in this
action, contact the Safe Drinking Water
Hotline. Callers within the United States
may reach the Hotline at (800) 426-
4791. The Hotline is open Monday
through Friday, excluding Federal
holidays, from 9 a.m. to 5:30 p.m.
Eastern Time.
SUPPLEMENTARY INFORMATION:
How Should I Submit Comments on
This Action?
EPA will accept written or electronic
comments (please do not send both).
EPA prefers electronic comments.
Commenters should use a separate
paragraph for each issue discussed. No
facsimiles (faxes) will be accepted.
Commenters who want EPA to
acknowledge receipt of their comments
should also send a self-addressed,
stamped envelope. If you submit written
comments, please submit an original
and three copies of your comments and
enclosures (including references).
Electronic comments must be
submitted in WordPerfect 8 (or an older
version) or ASCII file format.
Compressed or zipped files will not be
accepted. You may file electronic
comments on this action online at many
Federal Depository Libraries.
The Agency's response-to-comments
document for the final decision will
address the comments received on this
action, and the response-to-comments
document will be made available in the
docket.
How Can I Obtain Materials in the
Docket?
The docket is available for inspection
from 9:00 a.m. to 4:00 p.m., Monday
through Friday, excluding legal
holidays, at the Water Docket, East
Tower Basement (EB Room 57),
Waterside Mall, USEPA, 401 M Street,
SW; Washington, DC. For access to
docket (Docket Number W-01-14)
materials, please call (202) 260-3027
between 9:00 a.m. and 3:30 p.m.,
Eastern Time, Monday through Friday,
to schedule an appointment.
Does This Action Apply to My Public
Water System?
This action itself does not impose any
requirements on anyone. Instead, it
notifies interested parties of EPA's
preliminary revise/not revise decisions
for 69 NPDWRs.
Abbreviations and Acronyms Used in
This Action
>—greater than
2,4-D—2,4-dichlorophenoxyacetic acid
AA—activated alumina
AI—adequate intake
ASDWA—Association of State Drinking
Water Administrators
ATSDR—Agency for Toxic Substances
and Disease Registry
AWWA—American Water Works
Association
BAT—best available technology
BMD—benchmark dose
bw—body weight
CCL—Contaminant Candidate List
CFR—Code of Federal Regulations
CMR—Chemical Monitoring Reform
CWS—community water system
DBCP—l,2-dibromo-3-chloropropane
DBPR—Disinfectants and Disinfection
Byproducts Rule
DEHA—di(2-ethylhexyl)adipate
DEHP—di(2-ethylhexyl)phthalate
DRI—dietary reference intake
DWEL—drinking water equivalent level
EDB—ethylene dibromide
EPA—U.S. Environmental Protection
Agency
EPTDS—entry points to a distribution
system
FR—Federal Register
GAG—granular activated carbon
GC/MS—gas chromatography/mass
spectrometry
HHS—Department of Health and
Human Services
HPC—heterotrophic plate count
I—daily drinking water intake
IESWTR—Interim Enhanced Surface
Water Treatment Rule
IRIS—Integrated Risk Information
System
LCR—Lead and Copper Rule
LOAEL—lowest-observed-adverse-effect
level
LT1ESWTR—-Long-Term 1 Enhanced
Surface Water Treatment Rule
LT2ESWTR—Long-Term 2 Enhanced
Surface Water Treatment Rule
MCL—maximum contaminant level
MCLG—maximum contaminant level
goal
M/DBP—Microbial/Disinfection
Byproducts
MDL—method detection limit
MF—modifying factor
MFL—million fibers per liter
mg/kg/day—milligrams per kilogram of
body weight per day
mg/L—milligrams per liter
MSRC—Mercury Study Report to
Congress
MTD—maximum tolerated dose
N—nitrogen
NAS—National Academy of Sciences
NCOD—National Drinking Water
Contaminant Occurrence Database
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Federal Register/ Vol. 67, No. 74/Wednesday, April 17, 2002/Proposed Rules
19031
NDWAC—National Drinking Water
Advisory Council
NIPDWR—National Interim Primary
Drinking Water Regulation
NOAEL—no-observed-adverse-effect
level
NPDWR—National Primary Drinking
Water Regulation
NRG—National Research Council
NTNCWS—non-transient, non-
community water system
NTP—National Toxicology Program
NWIS—National Water Information
System
OGWDW—Office of Ground Water and
Drinking Water
OPP—Office of Pesticide Programs
OW—Office of Water
PAC—powdered activated carbon
PCBs—polychlorinated biphenyls
POU—point-of-use
ppm—part per million
PQL—practical quantitation level
PTA—packed tower aeration
PWS—public water system
RDA—recommended dietary allowance
RfD—reference dose
RO—reverse osmosis
RSC—relative source contribution
SAB—Science Advisory Board
SDWA—Safe Drinking Water Act
SDWIS—Safe Drinking Water
Information System
SMCL—secondary maximum
contaminant level
SOC—synthetic organic chemical
SWTR—Surface Water Treatment Rule
TCR—-Total Coliform Rule
TNCWS—transient, non-community
water system ,
TT—treatment technique
TTHM—total trihalomethanes
UF—uncertainty factor
UL—tolerable upper intake level
URCIS—Unregulated Contaminant
Information System
VOC—volatile organic chemical
WS—water supply
Table of Contents
I. Background and Summary of Today's
Action
A. What are the Statutory Requirements for
the Six-Year Review?
B. What is the Schedule for Reviewing
Existing NPDWRs?
II. Stakeholder Involvement in the Six-Year
Review Process
A. How Have Stakeholders Been Involved
in the Review Process?
B. How Does EPA Plan to Involve the
Science Advisory Board (SAB)?
III. Regulations Included in the Six-Year
Review
IV. EPA's Protocol for Reviewing the
NPDWRs Included in Today's Action
A. What was EPA's Review Process?
1. Initial Technical Review
2. In-Depth Technical Review
B. How Did EPA Review the Chemical
NPDWRs?
1. Health Effects
2. Analytical Feasibility , '^
3. Treatment Feasibility
4. Other Regulatory Revisions
5. Occurrence and Exposure Analysis
6. Economic Considerations
C. How Is EPA Reviewing the Total
Coliform Rule?
D. How Did EPA Factor Children's Health
Concerns into the Review?
V. EPA's Preliminary Decisions Based on
its Review of NPDWRs Included in
Today's Action
A. What Preliminary Decisions Has EPA
Made Regarding the Chemical NPDWRs?
1. Acrylamide
2. Alachlor
3. Antimony
4. Asbestos
5. Atrazine
6. Barium
7. Benzene
8. Benzo[a]pyrene
9. Beryllium
10. Cadmium
11. Carbofuran
12. Carbon Tetrachloride
13. Chlordane
14. Chromium
15. Copper
16. Cyanide
17. 2,4-D (2,4-Dichlorophenoxyacetic Acid)
18. Dalapon (2,2-Dichloropropionic Acid)
19. l,2-Dibromo-3-chloropropane (DBCP)
20.1,2-Dichlorobenzene (o-
Dichlorobenzene)
21.1,4-Dichlorobenzene (p-
Dichlorobenzene)
22. 1,2-Dichloroethane (Ethylene
Bichloride)
23.1,1-Dichloroethylene
24. cis-l,2-Dichloroethylene
25. trans-l,2-Dichloroethylene
26. Dichloromethane (Methylene Chloride)
27. 1,2-Dichloropropane
28. Di(2-ethylhexyl)adipate (DEHA)
29. Di(2-ethylhexyl)phthalate (DEHP)
30. Dinoseb
31. Diquat
32. Endothall
33. Endrin
34. Epichlorohydrin
35. Ethylbenzene
36. Ethylene Dibromide (EDB; 1,2-
Dibromoethane)
37. Fluoride
38. Glyphosate
39. Heptachlor
40. Heptachlor Epoxide
41. Hexachlorobenzene
42. Hexachlorocyclopentadiene
43. Lead
44. Lindane (-Hexachlorocyclohexane)
45. Mercury (Inorganic)
46. Methoxychlor
47. Monochlorobenzene (Chlorobenzene)
48. Nitrate (as N)
49. Nitrite (as N)
50. Oxamyl (Vydate)
51. Pentachlorophenol
52. Picloram
53. Polychlorinated Biphenyls (PCBs)
54. Selenium
55. Simazine
56. Styrene
57. 2,3,7,8-TCDD (Dioxin)
58. Tetrachloroethylene
59. Thallium
60. Toluene
61. Toxaphene
62. 2,4,5-TP (Silvex; 2,4,5-
Trichlorophenoxypropionic Acid)
63.1,2,4-Trichlorobenzene
64.1,1,1-Trichloroethane
65. 1,1,2-Trichloroethane
66. Trichloroethylene
67. Vinyl Chloride
68. Xylenes (Total)
B. What Preliminary Decision Has EPA
Made Regarding the Total Coliform Rule?
1. Background
2. Technical Reviews
3. Preliminary Decision
VI. Request for Comments
A. On Which Issues is EPA Soliciting
Public Comment?
B. Request for Comments on Use of Plain
Language
VII. EPA's Next Steps
VIII. References
Appendix A: Background on the Calculation
of MCLG and Cancer Classification
System
List of Tables
Table IH-1: Pre-1997 NPDWRs Included in
Today's Action
Table III-2: NPDWRs Not Included in
Today's Action
Table IV-1: Summary of the Outcome of the
Six-Year Health Effects Review
Table IV-2: Chemical NPDWRs Included in
the Analytical Feasibility Reassessment
and the Result of that Assessment
Table IV-3: Chemical NPDWRs Included in
the Treatment Feasibility Analysis
Table V-l: Preliminary Revise/Not Revise
Decisions for the 68 Chemical NPDWRs
and TCR
Table V—2: Benzene Occurrence
Table V-3: Beryllium Occurrence
Table V-r4: Chlordane Occurrence
Table V-5: Chromium Occurrence
Table V-6: l,2-Dibromo-3-chloropropane
Occurrence .
Table V-7: Dichloromethane Occurrence
Table V-8:1,2-Dichloropropane Occurrence
Table V-9: Heptachlor Occurrence
Table V-10: Heptachlor Epoxide Occurrence
Table V-ll: Hexachlorobenzene Occurrence
Table V—12: Oxamyl Occurrence
Table V-13: Picloram Occurrence
Table V-14: Toxaphene Occurrence
Table V-15:1,1,2-Trichloroethane
Occurrence
Table VI-1: Issues on Which EPA is
Requesting Public Comment or Data
Table A-l: Cancer Classification Systems
Used by EPA
List of Figures
Figure 1: Overview of the Protocol for the
Revise/Not Revise Decision
Figure 2: Distribution of State Rankings:
Manufacturing Establishments per
Square Mile vs. Total Farm Agricultural
Chemical Expenses
Figure 3: Geographic Distribution of the 16-
State Cross-Section Used for Occurrence
Analysis
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Federal Register/Vol. 67, No. 74/Wednesday, April 17, 2002/Proposed Rules
I. Background and Summary of Today's
Action
A. What Are the Statutory Requirements
for the Six-Year Review?
Under the SDWA, as amended in
1996, EPA must periodically review
existing national primary drinking water
regulations (NPDWRs) and, if
appropriate, revise them. Section
1412(bX9) of SDWA states:
The Administrator shall, not less often
than every 6 years, review and revise, as
appropriate, each national primary drinking
water regulation promulgated under this title.
Any revision of a national primary drinking
water regulation shall be promulgated in
accordance with this section, except that
each revision shall maintain, or provide for
greater, protection of the health of persons.
Pursuant to the SDWA 1996
Amendments, EPA developed a
systematic approach, or protocol, for the
review of NPDWRs discussed in today's
action. EPA has applied the protocol
discussed in section IV of today's action
to the Agency's initial Six-Year Review
of NPDWRs for total coliforms and 68
inorganic and organic chemicals,
published prior to the SDWA 1996
Amendments (i.e., pre-1997 NPDWRs).
Section in of today's action identifies
these NPDWRs and section V of today's
action contains a summary of the review
findings for each of these 69 NPDWRs
(see Table IH-1).
While the Agency expects that
modifications to the protocol will he
made in subsequent six-year reviews to
address changing circumstances, the
Agency expects to use the framework
developed for the current review as the
starting point. EPA, therefore, is seeking
public comment on the protocol that has
been applied to the current review.
B. What Is the Schedule for Reviewing
Existing NPDWRs?
EPA plans to publish its final findings
with respect to the initial review of
these 69 NPDWRs in the Federal
Register (FR) in the August 2002 time
frame.
In addition to these 69 NPDWRs,
there are additional pre-1997 NPDWRs,
which are being or have been reviewed
separately from today's action. Section
III explains how the Agency plans to
satisfy the Six-Year Review requirement
for those regulations. In most cases, EPA
has performed or is performing the
review in conjunction with recent or
ongoing rulemakings. NPDWRs
published after the 1996 SDWA
Amendments will be reviewed as a part
of the 2002-2008 review cycle.
n. Stakeholder Involvement in the Six-
Year Review Process
A. How Have Stakeholders Been
Involved in the Review Process?
Stakeholders include:
• The general public;
• Congress;
• Other Federal agencies;
• State, Tribal, and local officials;
• Public health/health care providers;
• Public interest groups;
• Public water suppliers;
• National trade associations;
• Environmental groups;
• Manufacturers; and
• Agricultural producers.
EPA involved stakeholders by:
holding a stakeholder meeting;
participating in national meetings,
workshops, and technical forums;
meeting informally with associations
and technical experts; posting
information on the Office of Ground
Water and Drinking Water's (OGWDW's)
web page (www.epa.gov/safewater/);
and publishing this FR notice on the
Six-Year JReview.
EPA invited representatives from
State and Tribal communities, public
water systems (PWSs), public health
organizations, academia, environmental
and public interest groups, engineering
firms, and other stakeholders to a
stakeholder meeting in Washington, DC,
in November 1999 (64 FR 55711,
October 14, 1999 (USEPA, 1999c)).
Approximately 50 participants attended,
including representatives from the
invited groups. EPA discussed its
preliminary strategy for the Six-Year
Review and invited stakeholder
comment. Stakeholders generally agreed
that EPA had identified the appropriate
key elements for the review; however, in
some cases, stakeholders suggested that
EPA needed to be more proactive in
seeking out new information that might
affect the regulatory decision (USEPA,
1999e). For more detailed information
about this stakeholder meeting, the
docket for this action (Docket Number
W-01-14) contains the stakeholder
meeting discussion papers, the agenda,
the participant list, presentation
materials, and an executive meeting
summary which includes the specific
comments and questions posed by
stakeholders. The executive meeting
summary is also available on EPA's
drinking water web page, http://
www.epa.gov/safewater/ccl/
novmtg.html.
In the Spring of 2000, the National
Drinking Water Advisory Council
(NDWAC) formed a working group to
develop recommendations regarding the
process the Agency should apply to
conduct a periodic and systematic
review of existing NPDWRs. The
Working Group held two meetings and
a conference call during June, through
September 2000 (USEPA, 2000b;
USEPA, 2000c; USEPA, 2000d). The
NDWAC approved the Working Group's
recommendations in November 2000
and formally provided them to EPA in
December 2000 (NDWAC, 2000). The
NDWAC recommended that EPA's
review include consideration of five key
elements, as appropriate: health effects,
analytical and treatment feasibility,
implementation-related issues,
occurrence and exposure, and economic
impacts. The NDWAC suggested that the
Agency conduct an initial screening
review of each NPDWR to identify
potential candidates for an in-depth
analysis. As discussed in more detail in
section IV of today's action, EPA has
followed the general protocol
recommended by the NDWAC.
In addition to the November 1999
stakeholder meeting and consultation ._
with the NDWAC, EPA representatives
have delivered presentations at a variety
of meetings held by other organizations,
including: two American Water Works
Association (AWWA) Technical
Advisory Workgroup meetings, one held
in February 2001 in Washington, DC,
and one held in February 2002 in San
Diego, CA; a meeting held by the
Association of State Drinking Water
Administrators (ASDWA) in March
2001 in Alexandria, VA; and the annual
AWWA meeting held in Washington,
DC in June 2001. At each of these
meetings, stakeholders were given the
opportunity to comment on lie protocol
by which EPA was planning to perform
the review of existing NPDWRs. EPA
received valuable input from
stakeholders on the planned protocol.
B. How Does EPA Plan To Involve the
Science Advisory Board (SAB)?
EPA plans to consult with the SAB
Drinking Water Committee on today's
action. The Agency will request their
review and comment on whether the
protocol EPA developed based on the
NDWAC recommendations was
consistently applied and appropriately
documented.
HI. Regulations Included in the Six-
Year Review
Table HI-l lists the pre-1997 NPDWRs
covered by today's action and the
rulemaking by which they were
originally promulgated. Table III-2 lists
the NPDWRs not covered by today's
action. These include the remaining pre-
1997 NPDWRs which are being or have
already been reviewed in separate
actions and the NPDWRs promulgated
after the 1996 SDWA Amendments. The
_
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19033
NPDWRs listed in Table HI-2 will be
included in the 2002-2008 review
round. Section V of today's action 68 pre-1997 chemical NPDWRs and the
summarizes the relults of the review of NPDWR for total coliforms.
BILLING CODE 6560-50-P
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Federal Register/Vol. 67, No. 74/Wednesday, April 17, 2002/Proposed Rules
Table HI-1: Pre-1997 NPDWRs Included in Today's Action
Contaminant
Corresponding NPDWR
Chemical Contaminants
Acrylamide
Alachlor
Antimony
Asbestos
Atrazine
Barium
Benzene
3en7.o[a]pyrenc
Beiyllium
Cadmium
Carbofuran
Carbon tetrachloride
Chlordanc
Chromium (total)
Copper
Cyanide
2,4-D
Dalnpon
,2-Dibromo-3-
uhloropropane (DBCP)
,2-Dichlorobenzene (o-
)ichlorobenzene)
,4-Dich!orobenzenc (p-
Dichlorobenzenc)
,2-Dichloroethane
Ethylenc dichloride)
,1-Diehloroethylene
cis-l,2-Dichlorocthylene
trans- 1,2-
3ichloroethylenc
)lchloromethane
vlethylene chloride)
1 ,2-Diehloropcopane
Di(2-cthylhexyl)adipate
(DEHA)
Di(2-ctbylhexyl)
phthalate (DEHP)
)inoscb
3iquat
Indothall
Phase II Rule
Phase II Rule
Phase V Rule
Phase 11 Rule
Phase II Rule
Phase IIB Rule
Phase I Rule
Phase V Rule
Phase V Rule,
Phase II Rule
Phase II Rule
Phase I Rule
Phase II Rule
Phase 11 Rule
Lead and Copper Rule (LCR)
Phase V Rule
Phase JI Rule
Phase V Rule
Phase II Rule
Phase II Rule
Phase I Rule
Phase I Rule
Phase I Rule
Phase II Rule
Phase II Rule
Phase V Rule
Phase 11 Rule
Phase V Rule
Phase V Rule
Phase V Rule
Phase V Rule
Phase V Rule
Contaminant
Corresponding NPDWR
Chemical Contaminants (continued)
Endrin
Bpichlorohydrin
Ethylbenzene
Bthylene dibromide
(EDB)
Fluoride
Glyphosate
.leptachlor
rieptachlor epoxide
iexachlorobenzene
iexachlorocyclopcnta-
diene
..ead
Lindane
Vlercury (Inorganic)
Methoxychlor
Monochlorobenzene
Chlorofaenzene)
titrate (as N)
Nitrite (as N)
Oxamyl (Vydate)
'entachlorophenol
'icloram
Polychlorinated biphenyls
(PCBs)
Selenium
Simazine
Styrene
2,3,7,8-TCDD (Dioxin )
"etrachloroethylene
"hallium
Toluene
'oxaphene
2,4,5-TP (Silvex)
1 ,2,4-Trichlorobenzene
,1,1 -Trichloroethane
Phase V Rule
Phase 11 Rule
Phase II Rule
Phase II Rule
Fluoride Rule; Phase II Rule
revised monitoring requirements
Phase V Rule
Phase II Rule
Phase 11 Rule
Phase V Rule
Phase V Rule
LCR
Phase 11 Rule
Phase II Rule
Phase II Rule
Phase II Rule
Phase II Rule
Phase II Rule
Phase V Rule
Phase IIB Rule
Phase V Rule
Phase II Rule
Phase II Rule
Phase V Rule
Phase II Rule
Phase V Rule
Phase II Rule
Phase V Rule
Phase II Rule
Phase H Rule
Phase II Rule
Phase V Rule
Phase I Rule
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19035
Table ffl-1: Pre-1997 NPDWRs Included in Today's Action
Corresponding NPDWR
Contaminant Corresponding NFDWR
Chemical Contaminants (continued)
Trichloroethylene
Vinyl chloride
Xylenes (total)
,1,2-Trichloroethane
Phase I Rule
Phase I Rule
Phase II Rule
Phase V Rule
Microorganisms
Total coliforms
(including fecal coliform
and E. coif)
Total Coliform Rule (TCR)
Dates of original promulgation are as follows:
- Phase II Rule: 56 FR 3526, January 30,1991 (USEPA, 1991a)
- Phase V Rule: 57 FR 31776, July 17, 1992 (USEPA, 1992)
- Phase IIB Rule: 56 FR 30266, July 1, 1991 (USEPA, 1991c)
Phase [ Rule: 52 FR 25690, July 8, 1987 (USEPA, 1987)
- I.CR: 56 FR 26460, June 7,1991 (USEPA, 1991b)
- Fluoride Rule: 51 FR 113 96, April 2, 1986 (USEPA, 1986a)
- TCR: 54 FR 27544, June 29, 1989 (USEPA, 1989c)
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Federal Register/Vol. 67, No. 74/Wednesday, April 17, 2002/Proposed Rules
Table IH-2: NPDWRs Not Included in Today's Action
Contaminant/Indicator
Corresponding NPDWR1
Reason Not Included
Chemical Contaminants
Arsenic
Pre-1986 National Interim Primary
Drinking Water Regulation (NIPDWR)
Reviewed/revised under January 22,
2001 Arsenic Rule2'3
Radionuclides
Beta particles and photon emitters
Gross alpha particle activity
Radium-226/228 (combined)
Uranium
Pre-1 986 NIPDWR
2000 Radionuclides Rule
Reviewed/revised under December 7,
2000 Radionuclides Rule2
Promulgated after 1996. NPDWR
established in the December 7, 2000
Radionuclides Rule2
Microorganisms
Crvptosporidhim
Giardta lambia
Hcterotrophic plate count (HPC)
Leeionella
Turbidity
Viruses
Interim Enhanced Surface Water
Treatment Rule (IESWTR)
Long-Term 1 Enhanced Surface Water
Treatment Rule (LT1ESWTR)
Surface Water Treatment Rule (SWTR);
IESWTR; LT IESWTR
SWTR
SWTR
SWTR; IESWTR; LTIESWTR
SWTR; IESWTR; LTIESWTR
Subject of ongoing rulemaking activity -
Long-Term 2 ESWTR (LT2ESWTR)
(November 2003)"
Disinfection Byproducts
Bromatc ion
Chlorite ion
Haloacetic acids: Monobromoacetic
acid; Dibromoacetic acid;
Monochloroacetic acid;
Dichloroacctic acid; and
Trichloroacetic acid
Total Trihalomethanes (TTHMs):
Chloroform; Bromodichloro-
mcthanc; Dibromochloromethane;
and Bromoform
Stage 1 Disinfectants and Disinfection
Byproducts Rule Stage I (DBPR)
TTHM Rule; Requirements revised
under Stage 1 DBPR
Revised rule promulgated after 1996 and
additional revisions to be considered
under Stage 2 DBPR (July 2003)"
Revised rule promulgated after 1996 and
additional revisions to be considered
under Stage 2 DBPR (July 2003)4
Disinfectant Residuals
Chlorine
Chloramines
Chlorine dioxide
Stage 1 DBPR
Revised rule promulgated after 1996
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19037
Table III-2: NPDWRs Not Included in Today's Action
ContaminantTEndicator | Corresponding NPDWR1
Reason Not Included
1 Dates of original promulgation are as follows:
- Arsenic Rule: 40 FR 59566, December 24, 1975 (USEPA, 1975)
- Radionuclides Rule: 41 FR 28402, July 9, 1976 (USEPA, 1976)
- IESWTR: 63 FR 69478, December 16,1998 (USEPA, 1998c)
- LT1ESWTR: 67 FR 1811, January 14,2002 (USEPA, 2002b)
- SWTR: 54 FR 27486, June 29, 1989 (USEPA, 1989c)
- Stage 1 DBPR Rule: 63 FR 69389, December 16, 1998 (USEPA, 1998b)
- TTHM Rule: 44 FR 68624, November 29, 1979 (USEPA, 1979)
2 Indicates date of rule revision.
- Arsenic Rule: 66 FR 6976, January 22,2001 (USEPA, 2001a)
- Radionuclides Rule: 65 FR 76707, December 7,2000 (USEPA, 2000g)
3 After promulgation of the revised arsenic NPDWR on January 22,2001, EPA initiated a review of the new maximum contaminant
level (MCL) and postponed the effective date of the rule until February 22,2002. EPA requested independent expert panel reviews
of the science, cost and benefits analyses for the January 2001 rule, and in July 2001, sought additional public comment on a range o:
MCLs Following receipt of the final expert panel reports in the Fall of 2001, EPA requested comment on the reports. EPA will
continue to evaluate the expert panel reports, the voluminous comments received during these comment periods, and other relevant
information and comments as they become available as part of the next six-year review; EPA expects to make a final decision on
whether to revise the January 2001 rule as part of that six-year review, which is due in August 2008. In the meantime, as announced
by the Administrator on October 31,2001, EPA will not further postpone the January 2001 rule, and EPA also does not expect to
take any other additional action relative to the July 2001 proposal in the interim. The revised arsenic MCL became effective on
February 22,2002. The date for compliance with the MCL remains January 23,2006.
4 Indicates anticipated date of promulgation.
BILLING CODE 6560-SO-C
IV. EPA's Protocol for Reviewing the
NPDWRs Included in Today's Action
A. What Was EPA's Review Process?
The document, "EPA Protocol for the
Review of Existing National Primary
Drinking Water Regulations" (USEPA,
2002f), contains a detailed description
of the process the Agency used to
review the 69 NPDWRs discussed in
today's action. EPA's primary goal was
to identify and prioritize candidates for
regulatory revision in order to target
those revisions that are most likely to
result in an increased level of public
health protection and/or result in
substantial cost savings while
maintaining the level of public health
protection. This section provides an
overview of the review process. Sections
IV.B and IV.C of today's action provide
a more detailed description of how EPA
applied the process to the review of 68
chemical NPDWRs and the TCR,
respectively.
EPA applied the following basic
principles to the review process:
• Health effects, analytical feasibility,
treatment data, and analyses underlying
existing regulations remain adequate
and relevant, except in those instances
where reliable, peer-reviewed, new data
are available that indicate a need to re-
evaluate an NPDWR (e.g., where a
change in health risk assessment has
occurred).
• If new data were available, EPA
determined whether changes in existing
standards were warranted. For example,
in determining whether there was a
change in analytical feasibility, the
Agency applied the current policy and
procedures for calculating the practical
quantitation level for drinking water
contaminants.1
• EPA was unable to complete
evaluation of certain new data within
the time available for the review. For
example, if a new health risk assessment
for a contaminant was not completed
during the review cycle, EPA generally
made a "not revise" decision on the
rationale that it was not appropriate to
revise the regulation while the
assessment was ongoing. When an
updated assessment is completed, EPA
will review the update and any new
conclusions or additional information
associated with the contaminant during
the next review cycle. The Agency may
i See: 50 FR 46880, November 13,1985 {USEPA,
1985); 52 FR 25690, July 8, 1987 (USEPA, 1987); 54
FR 22062,-May 22,1989 (USEPA, 1989a).
make a determination to revise a
particular NPDWR before August 2008
where justified by new public health
risk information.
• During the review, EPA identified
areas where information is inadequate
or unavailable (data gaps) and is needed
before an NPDWR may be considered as
a candidate for revision. Where the
Agency has been unable to fill such gaps
during the review process, today's
action provides information about the
data gaps so that further research and
data collection can be considered as part
of the second review cycle. For
example, the review may identify a need
to better understand new treatment
technologies. Such an information gap
will need to be considered in the
context of EPA's overall OGWDW
research strategy.
• During the review process, the
Agency did not consider potential
regulatory revisions that were already
the subject of other rulemaking
activities.
• EPA applied the Agency's peer
review policy {USEPA, 20001), where
appropriate, to any new analyses.
Figure 1 provides an overview of the
review process. To most efficiently
utilize limited resources and assure
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continued public health, protection, the
Agency conducted the review in two
phases: (1) an initial technical review of
all 69 NPDWRs discussed in today's
action; and (2) an in-depth technical
evaluation of those NPDWRs identified
during the initial review as potential
candidates for revision.
1. Initial Technical Review
The initial review phase included
these three screening and general
evaluation steps:
• Health effects review. Identify
NPDWRs for which the Agency has
revised health risk assessments that
indicate possible changes to the
maximum contaminant level goal
(MCLG) and perhaps to the maximum
contaminant level (MCL);
• Current technology review. Identify
NPDWRs where improvements in
analytical measurement or treatment
feasibility might allow the MCL to be
established closer to the MCLG, or
where adjustments in treatment
technique (TT) requirements might be
appropriate; and/or
• Other regulatory revisions review.
Identify NPDWRs where adjustments to
system monitoring and reporting
requirements might be appropriate and
where such changes are not already
being considered as a part of another
activity.
EPA generally determined that an
NPDWR was not a candidate for
revision after the initial review if a
health risk assessment was in process or
was initiated as a result of the review,
since the Agency does not believe it is
appropriate to revise the NPDWR while
a health risk assessment is underway.
The Agency also determined that an
NPDWR was not a candidate for
revision after the initial screening if
none of the initial screening analyses
identified a health or technological basis
for a regulatory revision.
2. In-Depth Technical Review
The Agency subjected the remaining
NPDWRs to more in-depth technical
analyses. If the initial review indicated
a possible revision to the MCLG/MCL,
EPA further considered health and '
technology factors that might affect the
development of a revised MCLG/MCL or
revised MCLG/TT requirements. The
Agency also estimated potential
occurrence and exposure at PWSs at
concentrations of regulatory interest for
the chemical NPDWRs and conducted a
qualitative evaluation of economic
impacts. EPA based the qualitative
economic evaluation primarily on
available occurrence and exposure data,
to determine whether the possible
revision was likely to present an
opportunity for significant gains in
public health protection and/or
significant cost savings that could be
realized without lessening the level of
public health protection.
In the case of three contaminants,
EPA identified data gaps that could not
be filled during the current review
cycle. Figure 1 shows the identification
of data gaps as the final step in the
review; however, in some instances,
data gaps were identified during earlier
steps in the process. Where this
occurred, EPA did not conduct some or
all of the remaining analyses. If the
Agency identified data gaps, EPA
determined not to revise the NPDWR.
After completing these
comprehensive analyses, EPA identified
those NPDWRs that remain appropriate
at this time, and those NPDWRs that
may be appropriate for revision.
Today's action discusses the Agency's
preliminary determinations and seeks
public comment on them. After
considering the public comments
received and any new peer-reviewed
data that may become available to the
Agency, EPA will publish its final
decision in the FR.
BILLING CODE 6560-50-P
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19039
Figure 1: Overview of the Protocol for the Revise/Not Revise Decision
NPDWRs under review
Initial Technical Review
Health effects, analytical methods and
treatment feasibility, and other regulatory
revisions
Is a health risk assessment
in process/planned?
Yes
Pending health
risk assessment
No
Does the review suggest possible changes
in MCLG/MCL/TT and/or other
regulatory revisions?
No
w
NPDWR remains appropriate
after data/information review
Yes
In-depth Technical Analysis
New risk assessment, analytical methods feasibility,
treatment effectiveness, occurrence and exposure
and economic implications.
Is a significant gam in
public health protection or significant
cost savings likely to occur?
Are the data sufficient to support
regulatory revision?
Candidate
for Revision
No Revision
at this time
Negligible gain in
public health protection
and/or cost savings
Data gaps - determine
research needs
1. Publish FR notice with preliminary revise/not revise decisions.
2. Review Public Comments and consider revising decisions in
context of new information.
3. Publish FR notice with final list of NPDWRs to be revised.
BILLING CODE 6560-50-C
B. How Did EPA Review the Chemical
NPDWRs?
This section describes the specific
technical reviews that EPA conducted
for the chemical NPDWRs.
1. Health Effects
The document, "Six-Year Review-
Chemical Contaminants—Health Effects
Technical Support Document" (USEPA,
20021), describes how EPA reviewed the
chemical contaminants discussed in
today's action and provides the results
of the health effects technical review.
The principal objective of the health
effects review was to identify each
contaminant for which a new health risk
assessment indicated that a change in
MCLG might be appropriate. For most of
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the chemical NPDWRs discussed in
today's action, the MCLG is derived
from the cancer classification and/or the
reference dose (RfD), as described in
Appendix A. Therefore, the health
effects technical review focused on
whether there has been a change to
these values. The Agency reviewed the
results of health risk assessments
completed under the following
programs to determine if there had been
a change in critical effect or dose-
response pattern that indicates the
possible need for an MCLG revision.
• EPA Integrated Risk Information
System (IRIS);
• EPA Office of Pesticide Programs
(OPP);
• Agency for Toxic Substances and
Disease Registry (ATSDR); and
• National Academy of Sciences
(NAS).
Table IV-1 reflects the outcome of the
health effects review for the 68 chemical
NPDWRs discussed in today's action.
EPA placed each contaminant into one
of the following categories.
• New risk assessment 1997 or later.
An IRIS, OPP, ATSDR, and/or NAS
assessment has been completed in 1997
or later. These assessments have
considered developmental and
reproductive toxicity as a part of the
assessment. The Agency considers these
assessments to be recent enough that it
is not necessary to conduct a literature
search to identify any additional
relevant studies that have become
available on the toxicological effects of
these contaminants. In cases where the
health risk assessment resulted in a
change in the critical effect, or the dose-
response pattern for a regulated
contaminant, and where that change
could result in a change in the MCLG,
EPA subjected the NPDWR to more in-
depth analysis as a part of the review
process. Where recent assessments were
conducted by an agency other than EPA
and new developmental and
reproductive data were identified, EPA
initiated an update of its assessment.
• New risk assessment since
promulgation, but prior to 1997. An
IRIS, OPP, ATSDR, and/or NAS
assessment has been completed since
the NPDWR was promulgated but prior
to 1997. None of these assessments
reflected a change in RfD or cancer
classification. However, since these
assessments may not have specifically
considered developmental and
reproductive health effects, EPA
conducted a full literature search,
including developmental and
reproductive toxicity, for those
NPDWRs with non-zero MCLGs to
identify any relevant studies lhat might
affect the MCLGs of these contaminants.
EPA did not identify any chemicals for
which developmental or reproductive
effects might now be the critical effect.2
• Agency risk assessment in process
and not completed as of February 2002.
• The Agency currently is conducting a
health risk assessment for the
contaminant. That assessment will
consider all relevant studies that have
become available on the toxicology of
the contaminant, including
developmental and reproductive
toxicity. EPA does not believe it is
appropriate to revise the MCLG for these
contaminants at this time.
• Original NPDWR risk assessment.
No health risk assessment has been
2 A zero MCLG is already considered protective
of public health and new information on
developmental and reproductive effects would not
affect the MCLG. However, for those NPDWRs with
a zero MCLG, EPA reviewed available information
to inquire whether data show a nonlinearity of the
dose-response; EPA did not find any data to support
such a mode of action (USEPA, 2002i).
conducted since promulgation of the
NPDWR. The Agency conducted a full
toxicological literature search, including
developmental and reproductive
toxicity, for each of these contaminants
with non-zero MCLGs (see footnote 2) to
identify new toxicological studies that
might have an impact on the MCLGs. In
a few instances, the results of the
literature search indicate that it might
be appropriate to revise the RfD and/or
cancer classification. EPA initiated
updates to the risk assessments for these
chemicals, and established a schedule
for their completion. EPA does not
believe it is appropriate to revise the
MCLG at this time.
Thus, only contaminants in the first
category might be potential candidates
for an MCLG revision at this time.
The initial health effects review
identified beryllium, oxamyl, and
picloram as potential candidates for an
MCLG revision, depending on the
outcome of the more in-depth, health
effects review and on the other technical
analyses (e.g., analytical feasibility,
treatment, occurrence, etc.). The initial
health effects review also identified
changes in the RfD for chromium as
well a$ data gaps with respect to its
potential carcinogenicity via oral
ingestion. EPA also identified health
effects-related data gaps for fluoride.
Contaminants in any of the categories
except the third (risk assessment in
process) may be candidates for a new
assessment if the initial health effects
review identified new studies that may
affect the contaminant's RfD or cancer
classification. EPA has initiated a new
assessment for cyanide, di(2-
ethylhexyl)adipate, and thallium as a
result of the health effects technical
review.
BILLING CODE 6560-50-P
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19041
Table IV- 1: Summary of the Outcome of the Six-Year Health Effects Review for Chemical NPDWRs
Risk Assessment
Timing
New risk
assessment 1997
or later
New risk
assessment
since
promulgation
but prior to
1997
Zero MCLG
Non-zero MCLG
Agency risk
assessment in
process and not
completed as of
February 2002
Original
NPDWRrisk
assessment
Zero MCLG
Non-zero MCLG
Literature Search
Status/Results
Reproductive/
developmental
endpoints only
Already
considered in
the assessment,
so literature
search not
necessary
Literature not
reviewed since
zero MCLG is
protective
New information
does not support
a need to revise
the RfD or
cancer
classification
Literature search
addressed as part
of ongoing
assessment
Literature not
reviewed since
zero MCLG is
protective
New information
New information
does not support
a need to revise
the RfD or
cancer
classification
Other
lexicological
endpoints
Already
considered in
the assessment,
so literature
search not
necessary
Zero MCLG
remains
appropriate
New information
does not support
a need to revise
the RfD or
cancer
classification
Literature search
addressed as part
of ongoing
assessment
Zero MCLG
remains
appropriate
Literature not
reviewed - to be
considered in
new assessment
New information
does not support
a need to revise
the RfD or
cancer
classification
Outcome of
Health Effects
Review
Change in assessment
Change in assessment
but negligible gain in
health protection
No change in
assessment
New assessment
initiated or planned
Zero MCLG retained
No revisions to
MCLG
Not appropriate to
revise MCLG at this
time
Zero MCLG retained
Initiated new
assessment as aresult
of health effects
review
No revisions to
MCLG
Contaminants
4 Total - Beryllium; Chromium; Oxamyl; Picloram
1 Total - Hexachlorocyclopentadiene
8 Total - Barium; Benzene; Chlordane; Dichloromethane;
Lead; Mercury (inorganic); Selenium; Vinyl chloride
2 Total - Cyanide, Fluoride1
S Total - l,2-Dibromo-3-chloropropane; Heptachlor;
Heptachlor epoxide; Hexachlorobenzene; Toxaphene
5 Total - cis-l,2-Dichloroethylene; trans- 1,2-
Dichloroethylene; Endrin; Nitrate; Nitrite
33 Total 2- Aery lamide; Alachlor; Antimony; Asbestos; ,
Atrazine; Benzo[a]pyrene; Cadmium; Carbofuran; Carbon
tetrachloride; Copper; 2,4-D; 1 ,2-DichIorobenzene;
1 ,4-Dichlorobenzene; 1,2-Dichloroethane;
1,1-DichIoroethylene; Di(2-ethylhexyl)phthalate; Diquat,
Endothall; Ethylbenzene; Ethylene dibromide; Glyphosate;
Lindane; Methoxychlor; Pentachlorophenol;
Polychlorinated biphenyls; Simazine; Styrene}
2,3,7,8-TCDD (Dioxin); Tetrachloroethylene; Toluene;
1,1,1-Trichloroethane; Trichloroethylene; Xylenes (total)
2 Total - 1,2-Dichloropropane; Epichlorohydrin
2 Total - Di(2-ethylhexyl)adipate; Thallium
6 Total - Dalapon; Dinoseb; Monochlorobenzene; 2,4,5-
TP (Silvex); 1,2,4-Trichlorobenzene; 1,1,2-
Trichloroethane
' See contaminant specific discussion for fluoride in section V.A.37.
2 These 33 contaminants do not include risk assessments initiated as a result of the Six-Year Review. For copper, NAS recommended
retaining the MCLG. ', :
BILLING CODE 6560-50-C
2. Analytical Feasibility
Since EPA has a process in place to
approve new analytical methods for
drinking water contaminants, the actual
review and approval of potential new
methods are outside the scope of the
Six-Year Review protocol. EPA
recognizes that the approval and
addition of new and/or improved
analytical methods (since the
promulgation of the NPDWRs under this
review) may enhance the ability of
laboratories to quantify contaminants at
lower levels. For this reason, EPA
evaluated whether there have been
changes in analytical feasibility for a
subset of the 68 chemical NPDWRs
discussed in today's action. The
document, "Analytical Feasibility
Support Document for the Six-Year
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Federal Register/ Vol. 67, No. 74/Wednesday, April 17, 2002/Proposed Rules
Review of Existing National Primary
Drinking Water Regulations
(Reassessment of Feasibility for
Chemical Contaminants)" [USEPA,
2002d), describes the process EPA used
to evaluate possible changes in
analytical feasibility and provides the
results of the analytical feasibility
analyses. The purpose of these analyses
is to determine whether changes in the
practical quantitation level (PQL) are
possible in those instances where the
MCL is limited, or might be limited, by
analytical feasibility. EPA uses the PQL
to estimate the level at which
laboratories can routinely measure a
chemical contaminant in drinking
\vater. Historically, EPA has used two
main approaches to determine a PQL for
SDVVA analytes: (1) data from water
supply (WS) Studies, the preferred
alternative when sufficient WS data are
available; or (2) a multiplier method, in
which the PQL is calculated by
multiplying the EPA-derived method
detection limit (MDL) by a factor of 5 or
10 (50 FR 46880, November 13,1985
(USEPA, 1985); 52 FR 25690, July 8,
1987 (USEPA, 1987); 54 FR 22062, May
22,1989 (USEPA, 1989a)).
EPA performed the analytical
feasibility analyses under two
circumstances. First, for those
contaminants where the MCL is
currently limited by analytical
feasibility (i.e., the MCL is set at the
PQL) and the MCLG is still appropriate, •
EPA evaluated the currently approved
methods for those contaminants and
available WS data to determine whether
it might be possible to lower the PQL
and hence set an MCL that is closer to
the MCLG. Section V of today's action
provides the results of the analytical
feasibility review of 11 contaminants
that are not currently undergoing a
health risk assessment and for which
the MCL was limited by analytical
feasibility. These 11 contaminants
include 10 with zero MCLGs3 and 1
with a non-zero MCLG. Of these 11,
EPA identified 10 where the data
indicate it might be possible to set a
lower PQL (see Table IV-2). Although
the data are indicative of a lower PQL
for these 10, they are not definitive and
considered to be insufficient to support
an actual recalculation at this time. To
determine whether it was worthwhile to
gather more definitive data for PQL
recalculation, EPA estimated what the
potentially lower PQL could be for these
10 analytes and used these values in the
occurrence and exposure analyses.4 As
3 Although they have a zero MCLG, EPA excluded
lead and epichlorohydrin from the analytical
feasibility review since they are TT rules and do not
have an MCL.
« Using WS data to derive the PQL for chemical
NPDWRs involves determining the concentration of
an analyte at which 75 percent of EPA Regional and
State laboratories achieve results within a specified
acceptance window (see 54 FR 22062 at 22100, May
22,1989 (USEPA, 1989a)). In re-evaluating more
recent WS data for the Six-Year Review, sufficient
data were not available around the 75 percent
critierion to actually recalculate the PQL. However,
if the passing rates for the EPA Regional and State
laboratories exceeded 80 to 85 percent at spike
concentrations close to the current PQL, this
information was considered to be indicative of a
possible change in the PQL. If data indicated a
possible change in the PQL, EPA then evaluated the
distribution of the analytical methods used to
analyze the spike samples in the WS studies.
Evaluation of the method usage over time allowed
EPA to determine the analytical methods that
appear to be the most widely used for the analysis
discussed for specific contaminants in
section V of today's action, EPA believes
that a negligible gain in public health
exists at the possibly lower PQL for 9 of
these 10 NPDWRs. The results of the
occurrence and exposure analysis for
dichloromethane, using the possibly
lower PQL as a concentration value,
indicate that it may be appropriate to
consider gathering data to recalculate a
more definitive PQL for this analyte.
The second circumstance under
which EPA re-evaluated the PQL was
for three of the four contaminants
identified under the health effects
technical review as potential candidates
for revision (see Table IV—2). These
three contaminants were evaluated to
determine if any potential MCL revision
would be limited by analytical
feasibility. Based on this review, EPA
believes that analytical feasibility may
be a limiting factor for revising the MCL
for oxamyl (see section V.A.50 of
today's action for a more detailed
discussion). The Agency believes that
analytical feasibility would not be a
limiting factor for the remaining two
contaminants identified by the health
effects review as having potential
changes in their MCLG (i.e., beryllium
and chromium).
BILLING CODE 6560-50-P
of a particular contaminants. Knowledge of which
analytical methods are the most widely used, along
with the MDL for these methods, and a 10 times
MDL multiplier allowed EPA to estimate where the
potential lower limit of quantitation may lie today.
This estimated PQL was used as a value in the
occurrence analysis to help the Agency determine
if there may be a significant gain in public health
protection if EPA were to consider gathering the
information needed to recalculate the PQL.
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Table IV-2: Chemical NPDWRs Included in the Analytical Feasibility
Reassessment and the Result of that Assessment
SDWA Chemical Contaminant
Current PQL (mg/L)1
(PQL at the time of the
original promulgation)
Result of the Six-Year Analytical
Feasibility Reassessment
Eleven NPDWRs Limited by Analytical Feasibility2 (MCL, set at the PQL)
1
2
3
4
5
6
7
8
9
10
11
Benzene
Chlordane
1 ,2-Dibromo-3-chloropropane
(DBCP)
Dichloromethane
1 .2-DichIoropropane
lleptachlor
Heptachlor epoxide
Hexachlorobenzene
Toxaphene
1 , 1 ,2-Trichloroethane
(Non-zero MCLG = 0.003 mg/L)
Viny) chloride
0.005
0.002
0.0002
0.005
0.005
0.0004
0.0002
0.001
0.003
0.005
0.002 .
WS data indicate possible change
WS data indicate possible change
WS data indicate possible change
WS data indicate possible change
WS data indicate possible change
WS data indicate possible change
WS data indicate possible change
WS data indicate possible change
WS data indicate possible change
WS data indicate possible change
Current PQL still appropriate
Three of the Four NPDWRs Identified Under the Health Effects Review as Potential Candidates for Revision3
1
2
3
Beryllium
Chromium (total - Cr III and VI)
Oxamyl (Vydate)
0.001
0.01
0.02
Current PQL not a limiting factor
Current PQL not a limiting factor
Current PQL may be a limiting factor
' Milligrams per liter (mg/L).
2 Although 23 NPDWRs have MCLs that were set due to the limits of analytical feasibility, KPA is only discussing the results
of the analytical feasibility analysis for these 1 1, since the remaining 12 are undergoing or scheduled for a health risk
reassessment.
3 Since the health effects review for picloram indicates a potential increase in the MCLG, it is not necessary to evaluate
BILLING CODE 6560-50-C
3. Treatment Feasibility
An NPDWR either identifies the Best
Available Technology (BAT) for meeting
an MCL, or establishes enforceable
treatment technique (TT) requirements.
Currently, for all the chemical NPDWRs
covered in today's action that include
an MCL, the MCL is set equal to either
the MCLG or the PQL. None of these
MCLs are currently limited by treatment
feasibility. Thus, as a part of the Six-
Year Review process, EPA only needed
to review available information on
treatment technologies if either of the
following conditions applied:
• The health effects technical review
identified a potential change to the
MCLG/MCL (applied to 4 NPDWRs}; or
• A health risk assessment is not in
process for the contaminant and one of
the following two conditions apply:
(1) the analytical feasibility review
identified a possible change to the PQL
and thus to the MCL (applied to 10
NPDWRs); or
(2) the NPDWR is a TT-type rule
(applied to 3 NPDWRs).
The draft EPA document, "Water
Treatment Technology Feasibility
Support Document for Chemical
Contaminants; In Support of EPA Six-
Year Review of National Primary
Drinking Water Regulations" (USEPA,
2002k), describes the process EPA used
to evaluate treatment feasibility, where
appropriate, for the chemical NPDWRs
discussed hi today's action and provides
the results of these analyses. As a part
of this review, EPA utilized the same
sources that have been the primary
resources in development of EPA
regulations and guidance, including
published EPA treatment reports, peer-
reviewed journals, and other technology
sources, as well as information received
from. EPA stakeholders.
a.MCL-type Rules. EPA evaluated
existing treatment technology
information for 14 MCL-type NPDWRs
(see Table FV-3) to determine whether
treatment feasibility would be a limiting
factor if EPA were to lower the MCL. In
addition and where appropriate, EPA
evaluated the likelihood that systems
would discontinue existing treatment if
EPA were to raise the MCL.
Based upon this preliminary
evaluation, the Agency believes that
treatment capabilities would be
adequate to support a lower MCL value,
if EPA were to revise the MCL for any
of the contaminants for which a lower
MCL may be appropriate (USEPA,
2002k). Treatment technologies
specified as BAT within the current
NPDWR, and small system compliance
technologies which were specified by
EPA in 1998 (USEPA, 1998a) are
considered to be efficient and practical
for implementation at PWSs. However,
if EPA were to determine that it is
appropriate to revise any of these
NPDWRs, it would undertake a more
thorough review of treatment feasibility,
including a consideration of costs, to
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Federal Register/Vol. 67, No. 74/Wednesday, April 17, 2002/Proposed Rules
determine whether treatment feasibility
would be a constraint or not. In a few
instances, the Agency identified some
potential treatment effectiveness
research needs that will be considered
in the context of the overall drinking
water research strategy.5 The revise/not
revise decisions discussed in section V
of today's action do not depend on EPA
addressing these research needs.
In two instances (beryllium 6 and
picloram), the outcome of the health
effects technical review indicated it
might be appropriate to raise the MCLG/
MCL. For these two. contaminants, BATs
specified in the NPDWR are also BATs
for several other contaminants (USEPA,
2002k). Available data are insufficient
for EPA to determine how many PWSs
are specifically treating for either of
these contaminants using the same
treatment for co-occurring contaminants
and/or for secondary benefits. The
Agency thus cannot determine whether
these water systems would discontinue
existing treatment if the MCL were to be
raised (USEPA, 2002c; USEPA, 2002k).
However, in both cases, relatively few
systems would be affected so there
would be little potential for significant
cost savings at a national level.
BILLING CODE 6560-50-P
Table IV-3: Chemical NPDWRs Included in the Treatment Feasibility Analysis
Ten Contaminants Where Analytical Feasibility Assessments Indicate Potential for an MCL Change
1
2
3
4
5
Benzene
'Chlordane
1 ,2-Dibromo-3-chloropropane (DBCP)
Dichloromethane
1 ,2-Dichloropropane
6
1
8
9
10
Heptachlor
Heptachlor Epoxide
Hexachlorobenzene
Toxaphene
1 , 1 ,2-Trichloroethane
Four Contaminants Where Health Effects Assessments Indicate Potential for an MCLG/MCL Change
1
2
Beryllium
Chromium
3
4
Oxamyl
Picloram
BILLING CODE 6560-50-C
b. Treatment Technique-type Rules.
EPA reviewed three of the four chemical
NPDWRs for which a TT is set in lieu
of an MCL (copper, epichlorohydrin,
and load). A health risk assessment is in
process for the fourth TT-type NPDWR,
acrylamide.
The Agency found no new
information relating to new treatment or
other technology which would support
a revision to the TT for epichlorohydrin
at this time. EPA also reviewed issues
relating to current TT requirements for
copper and lead that were identified by
EPA and/or stakeholders. Sections
V.A.15 and V.A.43 of today's action
summarize these issues for copper and •
lead, respectively. EPA believes these
TT requirements remain appropriate at
this time; however, EPA has identified
a few potential treatment effectiveness
research needs and will consider them
in the context of the overall drinking
water research strategy (USEPA, 2002k).
4. Other Regulatory Revisions
In addition to possible revisions to
MCLGs, MCLs, and TTs, EPA
considered other regulatory revisions,
such as monitoring and system
reporting requirements, as a part of the
Six-Year Review process. EPA focused
this review on issues that are not
already being addressed, or have not
been addressed, through alternative
mechanisms (e.g., as part of a recent or
ongoing rulemaking, hi conjunction
with possible chemical monitoring
reform, etc.). Where appropriate
alternative mechanisms do not exist,
EPA considered these implementation-
related concerns if the potential revision
met the following criteria:
• It indicated a potential change in
the 40 Code of Federal Regulations
(CFR) 141 requirements;
• It was "ready" for rulemaking—that
is, the problem to be resolved has been
clearly identified and specific option(s)
have been formulated to address the
problem; and
• It met at least one of the following
conditions:
—Clearly improved the level of public
health protection; and/or
—Represented a significant cost savings
while maintaining or improving the
public health protection.
The document, "Consideration of
Other Regulatory Revisions for
Chemical Contaminants in Support of
the Six-Year Review of National Primary
Drinking Water Regulations'' (USEPA,
2002e) summarizes the specific issues
identified during the review process.
Some of these issues (e.g., the need to
specifically define new system/new
source monitoring requirements for
chemical contaminants) have already
been addressed in the recently
published arsenic and radionuclides
NPDWRs (66 FR 6975, January 22, 2001
(USEPA, 2001a); 65 FR 76707,
December 7, 2000 (USEPA, 2000g)).
Additional issues are contaminant-
specific, and are discussed in
conjunction with the review of the
NPDWR in section V of today's action.
5. Occurrence and Exposure Analysis
EPA's goal in evaluating contaminant
occurrence was to estimate the number
of PWSs at which contaminants occur at
levels of regulatory interest in drinking
water, and to evaluate the number of
people exposed to these levels. For its
occurrence analysis, EPA used drinking
water compliance monitoring data from
16 States, collected in the 1993 to 1997
time frame, and statistically analyzed
the data to estimate occurrence. The
* Rafor to Iho document, "Water Treatment
Technology Feasibility Support Document for
Chemical Contaminants; In Support of EPA Six-
Year Review of National Primary Drinking Water
Regulations " (USEPA, 2002k) for a description of
these research needs.
0 As discussed in section V.A.9.D of today 's
action, the outcome of the health effects technical
review indicates it might be possible to either lower
or raise the MCLG/MCL.
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19045
support document "Occurrence
Estimation Methodology and
Occurrence Findings Report for the Six-
Year Regulatory Review" describes in
detail the development of the data set
and the statistical methodology for
analysis (USEPA, 2002g). This section
presents a summary of the data and
analysis.
a. Development of the 16-State
Contaminant Occurrence Data Set. For
the current Six-Year Review, EPA used
PWS contaminant monitoring results,
voluntarily provided by 16 States, as the
primary source of information. EPA
selected these States based on their
geographic diversity and on their
agricultural and industriarpollution
potential. EPA also used data from a
number of additional sources for
comparative purposes. These secondary
sources include the Safe Drinking Water
Information System (SDWIS), the U.S.
' Geological Survey's National Water
Information System (NWIS), EPA's
Unregulated Contaminant Information
System (URCIS), and other privately-
and publicly-available data sources
(USEPA, 2002g). In future reviews
rounds, EPA plans to use the National
Drinking Water Contaminant
Occurrence Database (NCOD) as the
primary data source when conducting
the occurrence and exposure analyses as
a part of the Six-Year Review process.
EPA is in the process of populating the
NCOD, however, sufficient data from
the NCOD are not yet available.
EPA developed the 16-State
contaminant occurrence data set in two
stages. In the first stage, EPA developed
an 8-State cross-section to support
occurrence analyses for its Chemical
Monitoring Reform (CMR) evaluation.
The Agency selected the eight States for
use in a national analysis because they
provided the best data quality and
completeness, and formed a balanced
national cross-section of occurrence
data based on the States' geographic
distribution and relative rankings in
pollution potential, as described later in
this section. The methodology for
selecting the State data sets is described
in an EPA report, "A Review of
Contaminant Occurrence in Public
Water Systems" (USEPA, 1999d). EPA
had this-report externally peer reviewed
and also received public comment from
stakeholders. In the second stage, for the
current Six-Year Review, EPA
augmented the data from the CMR 8-
State data set with data from 8
additional States. The resulting data set
includes 13 million analytical results,
from approximately 41,000 PWSs in 16
States. For the 14 contaminants that
EPA identified for detailed occurrence
analysis, i.e., those with either new
health effects information or a potential
change in the PQL (see Table IV-3 of
today's action), the number of analytical
results per contaminant varies from
about 34,000 to greater than 200,000; the
number of PWSs with data varies from
about 8,000 to 23,000; and the number
of States providing relevant data varies
from 13 to 16.
All samples in the 16-State data set
were standard SDWA compliance
samples. Data were limited to those
with confirmed water source and
sampling type information. "Special"
samples, "investigation" samples
(investigating a contaminant problem,
that would likely bias the results), or
samples of unknown type were
excluded from further analysis. EPA
conducted various quality control and
review checks of the results, including
follow-up questions to the States^
providing the data to clarify potential
reporting inconsistencies, records with
invalid codes, or use of analytical units.
The Agency then compiled State data
sets into a single database with a unified
format.
In selecting a cross-section of State
data sets that is generally representative
of the U.S., EPA considered two broad
factors: geographic or spatial diversity,
and pollution potential. Geographic
diversity in the data set helps to ensure
that contaminant occurrence data come
from areas representing the range of
climatic and hydrologic conditions
across the U.S. A range of agricultural
and industrial pollution potential helps
to ensure that the data represent the
range of likely contaminant occurrence
across the United States.
As indicators of States' pollution
potential, EPA used two primary
measures: the number of manufacturing
facilities per square mile (to reflect the
potential for VOC occurrence), and the
• total expenditures on farm agricultural
chemicals (to reflect the potential for
synthetic organic chemical (SOC)
occurrence). In order to construct a
cross-section with a balance of pollution
potential, EPA divided the 50 States
into high and low pollution potential
groups based on their rank orderings
with respect to the two primary
pollution potential indicators. For each
of the two pollution potential
indicators, EPA ranked the 50 States
from \ to 50 (1 being the highest and 50
being the lowest). The States were then
plotted on a two-dimensional scatter
plot (see Figure 2), with the x- and y-
axes representing the manufacturing
and agricultural ranking, respectively, of
each State. The amount spent on
agricultural chemicals per State
increases along the y-axis from bottom
to top. The number of manufacturing
establishments per square mile per State
increases along the x-axis from left to
right. EPA then reviewed the rankings
and selected a subset of 16 States (the
"cross-section States") in order to give
approximate balance across the range of
pollution indicators.
BILLING CODE 6560-50-P
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Federal Register/Vol. 67, No. 74/Wednesday, April 17, 2002/Proposed Rules
Figore 2: Distribution of State Rankings: Manufacturing Establishments
per Square Mile vs. Total Farm Agricultural Chemical Expenses
NE
SD-
KY-
SC-
VT-
CA
JL
Ml
OR
AL
MT
NJ
MM
Ranking of the No. of Manufacturing Establishments/ Sq. Mile
LOW HIGH
1
25
50
T
o
V
o
A
.
o •
0
o
0
o
T°
T
o
o
1*1
o
1
o
o
0
o
T
o
o
0
o
o
o
^ o
%i
m
T
O
O
o
o
O
o
o
o
HIGH
LOW
50
MT MM
25
e
W)
I
J
OR
AL
MI CA BL
SD NE
—i 1 1—r—
TX KY VT SC
—T 1—
IN FL
• Original 8-State Cross-Section
^ Additional 8-State Cross Section
O All Other States
BILLING CODE 65EO-GO-C
the States with the most.manufacturing therefore, have the greatest amount of
The bold cross in the center of Figure establishments per square mile and the pollution potential based on these
2 separates the plot into four quadrants, greatest amount of farm agricultural manufacturing and agricultural
The upper right-hand quadrant contains chemical expenses. These States, indicators. The lower left-hand quadrant
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Federal Register/Vol. 67, No. 74/Wednesday,. April 17, 2002/Proposed Rules 19047
contains the States with the least
amount of manufacturing
establishments per square mile and the
least amount of farm agricultural .
chemical expenses. This quadrant,
therefore, contains the States with the
least amount of pollution potential,
based on these indicators. To identify
the location of each of the 16 States
within the quadrants, find the
intersection of the State name from the
. x- and the y-axes. This intersection
should be represented by either a filled-
in circle (one of the original 8 States),
or a filled-in triangle (one of the
additional 8 States).
The Agency performed analyses to
verify the validity of this approach. The
results of these analyses support the
applicability of these indicators relative
to pollution potential. The mean
concentration values for select
contaminants were estimated for groups
of top quartile and bottom quartile
States. The cross-section development
approach presumes that the top quartile
States have a higher pollution potential
than the bottom quartile States, and,
therefore, the estimated mean
concentrations for the top quartile States
should be greater than those for the
bottom quartile States. The estimated
mean concentration values for the top
quartile States were always higher than
the mean concentration for the bottom
quartile States with the lone exception
of heptachlor (a very low occurrence
SOC).
EPA believes the distribution of the
16 selected States is representative of
the national distribution of States with
respect to these pollution indicators.
Eight of the selected States comprised
EPA's original 8-State cross-section that
was used for the CMR analyses; EPA
solicited occurrence data from the
remaining eight. The geographic
distribution of the resulting 16-State
cross-section is shown in Figure 3.
Other, secondary pollution potential
indicators were also considered in order
to help ensure that the data were
representative of the range of pollution
potential across the U.S.
While this cross-section does not
represent a statistical random sample of
States, and thus, does not capture all
local variations in occurrence, EPA,
nonetheless, believes that the data set
provides a reliable picture of overall
distribution of contaminant occurrence
in the U.S.
BILLING CODE 6560-50-P
Figure 3: Geographic Distribution of the 16-State Cross-Section Used for Occurrence
Analysis
Initial 8-State Cross-Section
Additional 8-State Cross-Section
States not included in Cross-Section
BILLING CODE 6560-50-C
b. Analysis of Contaminant
Occurrence. Statistical analysis of
contaminant occurrence was focused at
the water system level. The goal was to
estimate the fraction of PWSs with
contaminant occurrence above levels of
regulatory interest, and the
corresponding fraction of people
exposed to those levels.
Occurrence analysis proceeded in two
stages. For the initial, or "Stage 1"
analysis, EPA computed simple
occurrence measures which are more
straightforward and conservative than a
full probabilistic analysis. In this stage
of analysis, EPA estimated the percent
of PWSs and total population served by
PWSs with at least one analytical result
exceeding concentrations equal to
specified contaminant levels. EPA
considered three specified contaminant
levels: The lower limit of detection
reported by the States, one-half the
current MCL, and the current MCL. Of
the 68 chemicals discussed in today's
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Federal Register/Vol. 67, No. 74/Wednesday, April 17, 2002/Proposed Rules
action, 60 were analyzed in this way.
The exceptions were:
• The two contaminants for •which
not enough data were available (dioxin
and asbestos);
• The four contaminants for which
the NPDWR specifies a TT-type
requirement instead of an MCL
(acrylamide, copper, epichlorohydrin,
and lead); and
• The two contaminants for which
EPA did not request data, since the
Agency determined there was no health
or technological basis for revising, and
because these data would have required
extra effort for States to transmit (nitrate
and nitrite).
Because of the simple and conservative
nature of Stage 1 estimates, EPA used
thorn only as preliminary indicators of
contaminant occurrence, to guide
further analysis. The occurrence support
document (USEPA, 2002g) includes the
details of the Stage 1 analyses.
Following the initial occurrence
analysis, EPA performed a more
detailed, "Stage 2" statistical analysis of
occurrence for the 14 contaminants '
identified as potential candidates by the
health effects and analytical feasibility
technical reviews. This analysis used a
statistical model, known as a Bayesian
hierarchical model, to estimate the
number of systems (and the
corresponding affected populations)
with mean contaminant concentrations
above the levels of regulatory interest.
Statistical modeling is usually required
in order to estimate mean contaminant
concentrations, because many sample
concentrations are non-detects, meaning
that the true concentration is unknown
and may range anywhere from zero to
the detection limit of the analytical
method. In the hierarchical model,
individual samples are assumed to be
log-normally distributed within entry
points to a distribution system (EPTDS)
(e.g., wells or treatment plants); EPTDS
means are assumed to be log-normally
distributed within each water system;
and system means are assumed to be
log-normally distributed nationwide.
This model can be applied to estimate
the number of systems with mean
concentrations above levels of interest,
and also the amount of variability
between sources within a system.
Population exposure can also be
estimated at the same time, by using
information from EPA's SDWIS database
about the population served by each
system in the database. The hierarchical
model has important advantages:
• It provides a unified model for
estimating occurrence, both between
and within systems;
• It uses information about non-
delected concentrations; and
• It provides uncertainty intervals
around each estimate, taking into
account both sampling variability over
tune and across systems, and
uncertainty due to non-detected
concentrations.
Details of the hierarchical model, and
its application to estimating mean
contaminant concentrations, are
provided in the occurrence support
document (USEPA, 2002g).
The results of the Stage 2 analyses for
each of the 14 contaminants listed in
Table IV—3 are presented in section V.A
of today's action. These results
represent only the systems in EPA's 16-
State database. EPA considered this the
most straightforward and accurate way
to present the data that were available
for the review process. As indicated in
the preceding discussion of the
development of the analysis of
contaminant occurrence, EPA
developed the more refined Stage 2
analysis based on the preliminary
evaluation using the results of the Stage
1 analysis. A detailed explanation of
this process is provided in EPA's
occurrence support document and is
available for review and comment
(USEPA, 2002g).
For those contaminants where
occurrence was evaluated with respect
to the revise/not revise decision, EPA
used the Stage 2 occurrence analysis for
the 16 States to determine the
percentage of PWSs that could be ,
impacted, and the percentage of the
exposed population served by these
systems. Section V contains a
discussion of the incremental
percentage of systems and the
incremental percentage of the
population served by these systems.
That is, EPA considered the difference
between levels of occurrence and
exposure above the current MCL and the
occurrence and exposure at the
potentially revised level(s).
6. Economic Considerations
While SDWA provides the Agency
with broad discretion to consider
economics in the context of the Six-Year
Review, the statute precludes EPA from
using economics as the sole basis for a
revision that would provide less health
protection than the current standard
(i.e., anti-backsliding). However, if new
peer-reviewed scientific health effects
research indicates that an MCLG could
be raised while maintaining public
health protection, then such a change is
permitted. For NPDWRs published after
the 1996 SDWA Amendments, Congress
added specific requirements for
economic and cost-benefit analyses in
their development. Where EPA decides
to revise an NPDWR based on health
effects or other technical reasons,
economic factors, including feasibility
and an assessment of costs and benefits
in accordance with Section 1412(b)(6) of
the SDWA, must then be taken into
consideration. EPA considered likely
economic impacts, based primarily on
available occurrence and exposure data,
to qualitatively evaluate whether the
potential revisions identified by the
health and technology reviews may
present a significant opportunity for
improved or strengthened public health
standards and/or a significant cost
savings while maintaining public health
protection (USEPA, 2002c).
C. How Is EPA Reviewing the Total
Coliform Rule?
The memorandum, "Six-Year Review
of the Total Coliform Rule—Comments
Received" (USEPA, 2002J), describes the
process EPA applied to the review of the
TCR. Where appropriate, EPA applied
the same approach to reviewing the TCR
as it did to the review of the chemical
NPDWRs discussed in today's action.
However, because of the nature of the
TCR and the pathogens it controls, the
Agency focused its review on the
implementation-related requirements.
As discussed in section V.B of today's
action, these analyses indicate that a
rulemaking to initiate possible revisions
to the TCR is appropriate at this time.
D. How Did EPA Factor Children's
Health Concerns Into the Review?
The 1996 amendments to SDWA
require special consideration of all
sensitive populations (infants, children,
pregnant women, elderly, and
immunocompromised) in the
development of drinking water
regulations (Section 1412(b)(3)(C)(V) of
SDWA, as amended in 1996). Overlie
past decade, the amount of available
data on the impact of chemical
contaminants on conception and early
developmental life stages has increased
dramatically. Accordingly, as a part of
the Six-Year Review process, EPA
completed a literature search covering
developmental and reproductive
endpoints (fertility, embryo survival,
developmental delays, birth defects,
endocrine effects, etc.) for regulated .
chemicals that have a non-zero MCLG
and have not been the subject of an
updated 1997 or later risk assessment
(see section IV.B.l of today's action).
EPA reviewed the output from the
literature searches to identify any
studies that might have an influence on
the present MCLG. Three chemicals
were identified with, potential
developmental/reproductive endpoints
of concern: cyanide, di(2-
ethylhexyl)adipate (DEHA), and
.
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19049
thallium (see sections V.A.16, V.A.28,
and V.A.59 of today's action). In each.
case, where the literature search
indicated a need to consider recent
studies of developmental or
reproductive toxicity, EPA has initiated
the process to update the Agency risk
assessment. Assessments conducted by
EPA, ATSDR, and NAS in 1997 or later
thoroughly considered the potential for
reproductive and developmental
toxicity; thus, literature searches for
chemicals with such recent assessments
were not necessary.
Young children, especially infants,
are generally at greater health risk from
infections caused by waterborne
pathogens. Any revision to the TCR will
maintain or improve the control of
waterborne pathogens and, therefore,
the protection afforded to children.
V. EPA's Preliminary Decisions Based
on its Review of NPDWRs Included in
Today's Action
Table V—1 lists EPA's preliminary
revise/not revise decision for each of the
69 NPDWRs discussed in today's action
along with the principal rationale for
the decision. If EPA has decided it is not
appropriate to revise an NPDWR at this
time, that decision is based on one of
the following reasons.
• Health risk assessment is in
process: The Agency is currently
conducting, or has scheduled, a detailed
review of current health effects
information. Because the results of the
assessment are not yet available, the
Agency does not believe it is
appropriate to make a "revise decision"
at this time. In these cases, today's '
action does not include a discussion of
the review of other key elements (e.g.,
technology, "other regulatory
revisions", and occurrence/exposure
analyses). EPA will consider the results
of the updated health risk assessment
during the 2002-2008 review cycle.
However, if the results of the health risk
assessment indicate a compelling need
to reconsider the MCLG, EPA may
decide to accelerate the review schedule
for that contaminant's NPDWR.
• NPDWR remains appropriate after
data/information review: The outcome
of the review indicates that the current
regulatory requirements remain
appropriate and, therefore, no regulatory
revisions are warranted. Any new
information available to the Agency
either supports the current regulatory
requirements or does not justify a '
revision.
• New information, but no revision
recommended because:
—Negligible gain in public health
protection: Any resulting changes to the
NPDWR would not significantly
improve the level of public health
protection or result in a major cost
savings.
—Information Gaps: Although results
of the review support consideration of a
possible revision, the available data are
insufficient to support a definitive
regulatory decision at this time. ;
BILLING CODE 6S60-50-P
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Federal Register/Vol. 67, No. 74/Wednesday, April 17, 2002/Proposed Rules
Table V-l: Preliminary Revise/Not Revise Decisions for the 68 Chemical NPDWRs and TCR
Not
Appropriate
for Revision
at this Time
Risk assessment in process:
chemical currently
undergoing an EPA health
risk assessment; .
includes the three initiated as
a result of this review'
(36NPDWRs)
Acrylamide (TT)2 (2004 / 2005)
Alachlor (2002 72003)
Antimony (2002/2003)
Asbestos (2004/2005)
Atrazine (2002)
Benzo[a]pyrene (2002 / 2003)
Cadmium (2002/2003)
Carbofuran (2002 / 2003)
Carbon tetrachloride (2002 / 2003)
Copper (TT)2 (2002/2003)
Cyanide (2004 / 2005)1
2,4-D (2003/2004)
1,2-Dichlorobenzene (2002 / 2003)
1,4-Dichlorobenzene (2002 / 2003)
1,2-Dichloroethane (2002 / 2003)
1,1-Dichloroethylene (2002 / 2003)
Di(2-ethylhexyl)adipate (2003 /2004)1
Di(2-ethylhexyl)phthalate (2002 / 2003)
NPDWR remains appropriate
after data/information review
(17 NPDWRs)
New
information,
but no
revision
recommended
because:
Negligible
gain in health
protection
(12 NPDWRs)
Information
gaps
(BNPDWRs)
Diquat (2002)
Endothall (2003 / 2004)
Ethylbenzene (2002 / 2003)
Ethylene dibromide (2002 / 2003)
Glyphosate (2002 / 2003)
Lindane (2003 / 2004)
Methoxychlor (2002 / 2003)
Pentachlorophenol (2002 / 2003)
Polychlorinated biphenyls (2002 / 2003)
Simazine (2003/2004)
Styrene (2002/2003)
2,3,7,8-TCDD (Dioxin) (2002 / 2003)
Tetrachloroethylene (2002 / 2003)
Thallium (2004 / 2005)'
Toluene (2002/2003)
1,1,1-Trichloroethane (2003 / 2004)
Trichloroethylene (2002 / 2003)
Xylenes (2002/2003)
Barium
Dalapon
cis-l,2-Dichloroethylene
trans-l,2-Dichioroethylene
Dinoseb
Endrin
Epichlorohydrin (TT)2
Hexachlorocyclopentadiene
Lead (TT)2
Mercury
Monochlorobenzene
Nitrate
Nitrite
Selenium
2,4,5-TP (Silvex)
1,2,4-TrichIorobenzene
Vinyl chloride
Benzene
Beryllium
Chlordane
i,2-Dibromo-3-chloropropane
1,2-Dichloropropane
Heptachlor
Heptachlor epoxide
Hexachlorobenzene
Oxamyl
Picloram
Toxaphene
1,1,2-Trichloroethane
Chromium
Dichloromethane3
Fluoride4
Candidates
for Revision
Based on other
regulatory revisions
(1 NPDWR)
Total Coliform Rule (TCR)
1 New information was identified for cyanide, di(2-ethylhexyl)adipate, and thallium as a result of the six-year health effects review,
The Agency has initiated new risk assessments for these three contaminants.
1 TT designates treatment-technique rules (i.e., those NPDWRs for which a treatment technique has been set in place of an MCL).
* Preliminary analysis indicates that there may be an opportunity for improvement in public health protection if the PQL/MCL
were lowered. Additional data are needed to support such a change.
* EPA plans to ask NAS to update the risk assessment for fluoride.
BILLING CODE 656» 50--C
A. What Preliminary Decisions Has
EPA Made Regarding the Chemical
NPDWRs?
1. Acrylamide
a. Background. EPA published the
current NPDWR for acrylamide on
January 30,1991 (56 FR 3526 (USEPA,
1991a)). The NPDWR established an
MCLG of zero based on a cancer
classification of B2, probable human
carcinogen. The NPDWR imposes a TT
requirement that limits the allowable
monomer levels in products used during
drinking water treatment, storage, and
distribution to 0.05 percent acrylamide
in polyacrylamide coagulant aids dosed
at 1 part per million (ppm). Each water
system is required to certify, in writing,
to the State (using third-party or
manufacturer's certification) that the
product used meets these residual
monomers and use-level specifications.
b. Technical Reviews. EPA has
initiated a reassessment of the health
risks resulting from exposure to
acrylamide. The revised risk assessment
will consider relevant studies that have
become available on the toxicity of
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19051
acrylamide including its potential
developmental and reproductive
toxicity. The Agency expects the new
risk assessment to be completed in the
2004 or 2005 time frame (USEPA,
20021).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for acrylamide is appropriate at
this time because a reassessment of the
health risks resulting from exposure to
acrylamide is ongoing.
2. Alachlor
a. Background. EPA published the
current NPDWR for alachlor on January
30,1991 (56 FR 3526 (USEPA, 1991a)).
The NPDWR established an MCLG of
zero based on a cancer classification of
B2, probable human carcinogen. The
NPDWR also established an MCL of
0.002 milligrams per liter (mg/L) based
on analytical feasibility.
b. Technical Reviews. The Agency
updated the health risk assessment for
alachlor in 1998 as a part of the
pesticides reregistration process
(USEPA, 2002i). However, the Agency
has initiated another update to the
alachlor health risk assessment. The
revised risk assessment will consider
relevant studies that have become
available on the toxicity of alachlor
including its potential developmental
and reproductive toxicity. The Agency
expects the new risk assessment to be
completed in the 2002 or 2003 time
frame.
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for alachlor is appropriate at
this time because a reassessment of the
health risks resulting from exposure to
alachlor is ongoing.
3. Antimony
a. Background. EPA published the
current NPDWR for antimony on July
17, 1992 (57 FR 31776 (USEPA, 1992)).
The NPDWR established an MCLG and
an MCL of 0.006 mg/L. EPA based the
MCLG on an R£D of 0.0004 milligrams
per kilogram of body weight per day
(mg/kg/day) and a cancer classification
of D, not classifiable as to human
carcinogenicity.
b. Technical Reviews. EPA has
initiated a reassessment of the health
risks resulting from exposure to
antimony. The revised risk assessment
will consider relevant studies that have
become available on the toxicity of
antimony including its potential
developmental and reproductive
toxicity. The Agency expects the new
risk assessment to be completed in the
2002 or 2003 time frame (USEPA,
2002i).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for antimony is appropriate at
this time because a reassessment of the
health risks resulting from exposure to
antimony is ongoing.
4. .Asbestos
a. Background. EPA published the
current NPDWR for asbestos on January
30,1991 (56 FR 3526 (USEPA, 1991a)).
The NPDWR established an MCLG and
an MCL of 7 million fibers per liter
(MFL) for asbestos fibers exceeding 10
micrometers in length. EPA evaluated
asbestos as a Category II7 contaminant
(equivalent to Group C, possible human
carcinogen) by the oral route of
exposure (see Appendix A of today's
action for discussion of cancer
classifications).
b. Technical Reviews. EPA has
.initiated a reassessment of the health
risks resulting from exposure to
asbestos. The new risk assessment will
consider relevant studies that have
become available on the toxicity of
asbestos, including its potential
developmental and reproductive
toxicity. The Agency expects the new
risk assessment to be completed in the
2004 or 2005 time frame (USEPA,
20021).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for asbestos is appropriate at
this time because a reassessment of the
health risks resulting from exposure to
asbestos is ongoing.
5. Atrazine
a. Background. EPA published the
current NPDWR for atrazine on January
30, 1991 (56 FR 3526 (USEPA, 1991a)).
The NPDWR established an MCLG and
an MCL of 0.003 mg/L. EPA based the
MCLG on an RfD of 0.005 mg/kg/day
and a cancer classification of Group C,
possible human carcinogen, based on
limited evidence of carcinogenicity in
animals in the absence of human data.
EPA published an FR notice in February
1999, in which EPA responded to
recommendations by the Children's
Health Advisory Committee, by
committing to re-evaluate the MCL for
atrazine after the Agency has finalized
7 Category II contaminants include those
.contaminants for which EPA has determined there
is limited evidence of carcinogenicity from drinking
water considering weight of evidence,
phannacokinetics, 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.
its risk assessment (64 FR 5277,
February 3,1999 (USEPA, 1999a)).
b. Technical Reviews. EPA has
initiated a reassessment of the health
risks resulting from exposure to
atrazine. The revised risk assessment
will consider relevant studies that have
become available on the toxicity of
atrazine including its potential
developmental and neuroendocrine
effects. The Agency expects the new risk
assessment to be completed in the 2002
time frame. EPA is in the process of
conducting an occurrence and exposure
analysis.
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for atrazine is appropriate at
this time because a reassessment of the
health risks resulting from exposure to
atrazine is ongoing. EPA has committed
to revisiting the NPDWR for atrazine if
a revision is appropriate once the results
of the revised risk assessment become
available. Therefore, EPA will revisit
this "not revise" decision once the new
risk assessment is completed.
6. Barium
a. Background. EPA published the
current NPDWR for barium on July 1,
1991 (56 FR 30266 (USEPA, 1991c)).
The NPDWR established an MCLG and
an MCL of 2 mg/L. EPA based the MCLG
on an RfD of 0.07 mg/kg/day and a
cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency
updated the health risk assessment for
barium in 1998 and retained the RfD
and cancer classification on which the
1991 MCLG is based (USEPA, 1999f). As
a part of the 1998 assessment, EPA
considered all relevant data on the
toxicity of barium including
developmental and reproductive
toxicity.
A review of analytical or treatment
feasibility is not necessary for barium
because changes to the MCLG are not
warranted at this time and the current
MCL is set at the MCLG. In addition, the
results of EPA's review of possible
"other regulatory revisions" did not
identify any barium-specific issues
(USEPA, 2002e). Since EPA did not
identify a health or technology basis for
revising the barium NPDWR, the
Agency did not conduct a detailed
occurrence and exposure analysis.
c. Preliminary Decision. After
reviewing the results of the pertinent
technical analyses, the Agency believes
the NPDWR for barium remains
appropriate and thus, it is not subject to
revision at this time.
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7. Benzene
a. Background. EPA published the
current NPDWR for benzene on July 8,
1987 (52 FR 25690 (USEPA, 1987)). The
NPDWR established an MCLG of zero
based on a cancer classification of A,
known human carcinogen. The NPDWR
also established an MCL of 0.005 mg/L
based on analytical feasibility.
b. Technical Reviews. The Agency
updated the health risk assessment for
benzene in 2000 and retained the cancer
classification on which the 1987 zero
MCLG is based (USEPA, 2000J; USEPA,
20021). The revised risk assessment
considered relevant studies on the
toxicity of benzene including
developmental and reproductive
toxicity.
The current MCL for benzene is based
on a PQL of 0.005 mg/L. As a part of the
Six-Year Review, EPA analyzed more
recent WS data to determine if it might
be possible to recalculate the PQL
(USEPA, 2002d). In addition, the
Agency evaluated whether more
sensitive analytical methods have been
approved and put into use by a wide
number of laboratories. The analysis of
the WS data indicates that an
improvement in analytical feasibility
might exist. Evaluation of the WS data
shows that EPA Regional and State
laboratories exhibit greater than 95
percent laboratory passing rates at
concentrations around the current PQL
of 0.005 mg/L. Because most of the
laboratory passing rates exceeded the 75
percent criterion typically used to
derive a PQL from WS studies, this
information indicates that a lower PQL
corresponding to the 75 percent passing
rate might exist for benzene. While this
information is indicative of a possibly
lower PQL, the WS data are insufficient
at this time to actually recalculate what
the lower PQL for benzene might be.
Using information about the
analytical methods most widely used to
report results in the WS studies, the
MDLs for these methods, and the 10
times MDL multiplier, EPA estimated
what the possibly lower PQL/MCL
might be. For the analysis of benzene in
the more recent WS studies, laboratories
predominantly used EPA Method 524.2
(Gas Chromatography/Mass
Spectrometry or GC/MS), which has an
upper limit MDL of 0.00004 mg/L. A 10
times MDL multiplier predicts that the
PQL could lie around 0.0004 mg/L. The
0.0004 mg/L value is used as a threshold
in the occurrence analysis, which is
discussed in this section.
Since the analytical feasibility
analysis indicates that the PQL for
benzene (and therefore the MCL) could
possibly be lower if EPA had more
definitive data to recalculate the PQL,
EPA considered whether treatment
feasibility is likely to pose any
limitations (USEPA, 2002k). The current
BATs for benzene are packed tower
aeration (PTA) and granular activated
carbon (GAG). Small system compliance
technologies for benzene include GAG
and several aeration technologies. EPA
believes these BATs are still practical
and would not pose any limitations for
benzene at a possibly lower MCL.
The results of EPA's review of
possible "other regulatory revisions"
did not identify any benzene-specific
issues (USEPA, 2002e).
EPA evaluated the results of the
occurrence and exposure analyses for
benzene to determine whether changes
to the MCL might be appropriate and
likely to result in additional public
health protection if the PQL were
recalculated (USEPA, 2002g; USEPA
2002h). Table V-2 shows the results of
the detailed occurrence and exposure
analysis based on the 16-State cross-
section for the current MCL (0.005 mg/
L) and the possible PQL/MCL based on
the analytical feasibility analysis
(0.0004 mg/L).
BILLING CODE 6560-50-P
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19053
Table V-2: Benzene Occurrence1
Systems2
Threshold
(in mg/L)
Current-MCL 0.005
Possible OQ4
PQL/MCL4 °-0004
1 6 Cross-Section
States - Total
Systems with Data
23,266
23,266
Estimated # Systems
> Threshold
(credible intervals)3'5
7 (4-12)
80 (57-106)
Estimated % Systems
> Threshold
(credible intervals)3
0.0313% (0.0172% - 0.0516%)
0.343% (0.245% -.0.456%)
Population Served by Systems2
Threshold
(in mg/L)
Current MCL 0.005
Possible .of)004
• PQL/MCL4 °-°004
16 Cross-Section
States - Total
Population Served
by Systems with
Data
110,866,600
110,866,600
Estimated Population
Served by Systems >
Threshold
(credible intervals)3- s
10,500 (2,100-33,200)
342,500 (234,200 - 570,100)
Estimated % Population
Served by Systems >
Threshold
(credible intervals)3
0.00947% (0.00188% -0.0300%)
0.309% (0.2 1 1 % - 0.5 1 4%)
Notes:
1 Results are based on the number and percent of systems (and the corresponding population served by those systems) with estimated
mean concentrations above the specified threshold.
2 All percentages are shown to three significant figures. All system values are rounded to the nearest whole system. AH population
values are rounded to the nearest hundred.
3 "Credible intervals" are generated to quantify the uncertainty around each estimated probability in the Bayesian analysis of the
occurrence data. For further explanation of credible intervals and the Bayesian analysis, please see "Occurrence Estimation
Methodology and Occurrence Findings Report for the Six-Year Regulatory Review" (USEPA, 2002g).
' The "possible PQL/MCL" is the possibly lower PQL/MCL as estimated by the analytical feasibility analysis.
5 This value does not necessarily reflect the number of systems out of compliance with the current MCL, because these data were
collected over the 1993 to 1997 time period, and because the value represents the estimated mean value over that time period, not the
running quarterly average on which compliance is based.
BILLING CODE 6560-50-C
The results of the detailed occurrence
and exposure analysis indicate that
approximately 0.3 percent of the 23,266
systems sampled in the 16 cross-section
States and approximately 0.3 percent of
the population served by those systems,
might be affected if EPA were to gather
information to recalculate the PQL (to a
lower PQL of around 0.0004 mg/L) and
revise the MCL accordingly.
c. Preliminary Decision. Although
there are new data that support
consideration of a possibly lower PQL .
(and therefore a possibly lower MCL),
EPA does not believe a revision to the
NPDWR for benzene is appropriate at
this time. The Agency does not have
sufficient data at this time on which to
base a PQL recalculation and hence an
MCL revision. In addition, because the
occurrence of benzene appears to be
minimal between the current MCL and
any likely PQL/MCL revision, the
Agency believes that any potential
revisions to the benzene NPDWR are
unlikely to significantly improve the
level of public health protection.
8. Benzo[a]pyrene
a. Background. EPA published the
current NPDWR for benzo[a]pyrene on
July 17, 1992 (57 FR 31776 (USEPA,
1992)). The NPDWR established an
MCLG of zero based on a cancer
classification of B2, probable human
carcinogen. The NPDWR also
established an MCL of 0.0002 mg/L
based on analytical method feasibility.
b. Technical Reviews. EPA has
initiated a reassessment of the health
risks resulting from exposure to
benzo[a]pyrene. The revised risk
assessment will consider relevant
studies that have become available on
the toxicity of benzo[a]pyrene including
its potential developmental and
reproductive toxicity. The Agency
expects the new risk assessment to be
completed in the 2002 or 2003 time
frame (USEPA, 20021).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for benzo[a]pyrene is
appropriate at this time because a
reassessment of the health risks
resulting from exposure to
benzo[a]pyrene is ongoing.
9. Beryllium
a. Background. EPA published the
current NPDWR for beryllium on July ,
17, 1992 (57 FR 31776 (USEPA, 1992)).
The NPDWR established an MCLG and
an MCL of 0.004 mg/L. EPA, classified
beryllium in Group B2, probable human
carcinogen, based on clear evidence of
its carcinogenicity via inhalation or
injection in several animal species.
However, EPA also placed beryllium in
drinking water Category II for
regulation, based on the weight of
evidence for carcinogenicity via
ingestion, and the potency, exposure
and pharmacokiiietics of this chemical.
EPA derived the MCLG by applying an
additional risk management factor of 10
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to the R£D of 0.005 mg/kg/day (57 FR
31776 at 31785, July 17,1992 (USEPA,
1992)).
b. Technical Reviews. The Agency
updated the health risk assessment of
beryllium in 1998. The 1998
reassessment established a new RfD of
0.002 mg/kg/day and also considered
relevant studies on the toxicity of
beryllium including its developmental
and reproductive toxicity. The 1998
assessment classified inhaled beryllium
as a Bl, probable human carcinogen,
using the 1986 cancer guidelines (51 FR
33992, September 24,1986 (USEPA,
1986b)). Using the 1996 Proposed
Guidelines for Carcinogen Risk
Assessment, the 1998 assessment
characterized inhaled beryllium as a
"likely" carcinogen in humans and
concluded that the human carcinogenic
potential of ingested beryllium could
not be determined (61 FR 17960, April
23,1996 (USEPA, 1996; USEPA,
1998d)). On this basis, EPA will re-
examine the application of the
additional risk management factor of 10
to account for potential carcinogenicity
of beryllium via ingestion that was used
when deriving the current MCLG, if the
Agency determines that an MCLG
revision is appropriate.
EPA believes that any likely revision
to the MCLG for beryllium could range
from 0.01 mg/L to 0.001 mg/L, based on
the change in the RfD in the 1998
assessment, the inclusion or non-
inclusion of the risk management factor,
and using a 20 percent relative source
contribution (RSC).8 Whereas the 0.01
mg/L value assumes no adjustment for
potential carcinogenicity via oral
ingestion (i.e., no 10-fold risk
management factor), the 0.001 mg/L
value retains the current risk
management factor of 10.
Because of changes in the health risk
assessment for beryllium, EPA
considered whether analytical
feasibility is likely to be a limitation if
the Agency were to lower the MCLG/
MCL. The results of the analytical
feasibility analyses indicate that the
current PQL of 0.001 mg/L for beryllium
is still appropriate and is unlikely to
change. Therefore, the Agency believes
the PQL is unlikely to be a limiting
factor if EPA decides to lower the
MCLG/MCL (USEPA, 2002d).
EPA also considered whether
treatment feasibility is likely to pose any
limitations if EPA were to lower the
MCLG/MCL. The current BATs for
beryllium include activated alumina
• This is the RSC used for the current MCLG and
also the default value. EPA has no reason to believe
that the RSC for beryllium would change. See
Appendix A for a further discussion of the RSC.
(AA), ion exchange, lime softening,
coagulation/filtration, and reverse
osmosis (RO) with removal efficiencies
ranging from 80 to 99 percent. Small
system compliance technologies also
include point-of-use (POU) RO and POU
ion exchange. The Agency believes
these BATs are still practical and would
not pose any limitations if the Agency
were to lower the MCLG/MCL (USEPA,
2002k).
The results of EPA's review of
possible "other regulatory revisions"
did not identify any issues which are
specific to beryllium (USEPA, 2002e).
EPA evaluated the results of the
occurrence and exposure analyses for
beryllium to determine whether
possible changes to the MCLG/MCL
would be likely to result in additional
public health protection or an
opportunity for significant cost savings
to PWSs and their customers (USEPA,
2002g; USEPA, 2002h). Table V-3
shows the results of the detailed
occurrence and exposure analysis based
on the 16-State cross-section at the
current MCL (0.004 mg/L), the possible .
lower level of any MCLG/MCL value
(0.001 mg/L), and the possible upper
level of any MCLG/MCL value (0.01 mg/
L).
BILLING CODE 6560-50-P
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19055
Table V-3: Beryllium Occurrence1
Systems2
Threshold
(in mg/L)
Possible upper
level of any
MCLG/MCL "'U1
value4
Current MCL 0.004
Possible lower
level of any
MCLG/MCL U'UU1
value4
1 6 Cross-Section
States - Total
Systems with Data
18,933
18,933
18,933
Estimated # Systems
> Threshold
(credible intervals)3'5
2 (0-4)
15 (7-24)
203 (167-237)
Estimated % Systems
> Threshold
(credible intervals)3
0.00809% (0.000% - 0.02 11 %)
0.0781% (0.0370% - 0.127%)
1 .07% (0.882% - 1 .25%)
Population Served by Systems2
Threshold
(in mg/L)
Possible upper
level of any
MCLG/MCL U'U1
value4
Current MCL 0.004
Possible lower
level of any
MCLG/MCL U'UU1
value4
J 6 Cross-Section
States - Total
Population Served
by Systems with
Data
104,573,700
104,573,700
104,573,700
Estimated Population
Served by Systems >
Threshold
(credible intervals)3'5
2,000 (0-13,400)
21,800 (2,900-81,700)
731,300 (372,400-1,237,100)
Estimated % Population
Served by Systems >
Threshold
(credible intervals)3
0.001 90% (0.000% - 0.0.128%)
0.0208% .(0.00278% -0.0781%)
0.699% • (0.356% -1.18%)
1 Results are based on the number and percent of systems (and the corresponding population served by those systems) with estimated
mean concentrations above the specified threshold.
2 All percentages are shown to three significant figures. All system values are rounded to the nearest whole system. All population
values are rounded to the nearest hundred.
3 "Credible intervals" are generated to quantify the uncertainty around each estimated probability in the Bayesian analysis of the
occurrence data. For further explanation of credible intervals and the Bayesian analysis, please see "Occurrence Estimation
Methodology and Occurrence Findings Report for the Six- Year Regulatory Review" (USEPA, 2002g).
4 These are possible upper and lower MCLG/MCL values based on the change in the RfD, using a 20 percent RSC and whether or not
to consider the risk management factor of 10. The upper level MCLG/MCL value was calculated without applying the 10-fold risk
management factor, whereas the lower level was calculated using the 10-fold risk management factor.
5 This value does not necessarily reflect the number of systems out of compliance with the current MCL, because these data were
collected over the 1993 to 1997 time period, and because the value represents the estimated mean value over that time period, not the
running quarterly average on which compliance is based.
BILLING CODE 6560-50-C
The results of the detailed occurrence
and exposure analysis indicate that
approximately 0.07 percent of the
18,933 systems sampled in the 16 cross-
section States, and approximately 0.02
percent of the population served by
those systems, might be affected if EPA
were to raise the MCLG/MCL. The
current BATs and small system
compliance technology for beryllium
also apply to other contaminants. In
addition to the removal of beryllium,
these, treatment technologies have other
beneficial effects (e.g., reduction of
hardness or other common impurities)
(USEPA, 2002k). Therefore, if EPA were
to raise the MCLG/MCL, the Agency
does not know how many of these PWSs
currently treating to comply with the
current MCL of 0.004 mg/L would
discontinue any treatment that is
already in place. If, on the other hand,
EPA were to retain the risk management
factor and lower the MCLG/MCL, less
than 1 percent of the 18,933 systems
sampled in the 16 cross-section States
and less than 0.7 percent of the
population served by those systems
might be affected.
c. Preliminary Decision. Although
there are new data indicating that it
might be possible to revise the MCLG/
MCL for beryllium, EPA does not
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believe a revision to the NPDWR for
beryllium, either higher or lower, is
appropriate at this time. The Agency
believes that any change in the MCLG/
MCL would be unlikely to significantly
improve the level of public health
protection (if EPA were to lower the
MCLG/MCL) or provide an opportunity
for significant cost savings to PWSs (if
EPA were to raise the MCLG/MCL).
10. Cadmium
a. Background. EPA published the
current NPDWR for cadmium on
January 30,1991 (56 FR 3526 (USEPA,
1991a)). The NPDWR established an
MCLG and an MCL of 0.005 mg/L.
Because of inadequate dose-response
data to characterize the presence or lack
of a carcinogenic hazard from oral
exposure, the Agency regulated
cadmium as a Group D carcinogen, not
classifiable as to human carcinogenicity
by the oral route of exposure. Therefore,
EPA developed the MCLG for cadmium
based on the RfD of 0.0005 mg/kg/day.
b. Technical Jtevfews. EPA has
initiated a reassessment of the health
risks resulting from exposure to
cadmium. The revised risk assessment
will consider relevant studies that have
become available on the toxicity of
cadmium including its potential
developmental and reproductive
toxicity. The Agency expects the new
risk assessment to be completed in the
2002 or 2003 time frame (USEPA,
20021).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for cadmium is appropriate at
this time because a reassessment of the
health risks resulting from exposure to
cadmium is ongoing.
11. Carbofuran
a. Background. EPA published the
current NPDWR for carbofuran on
January 30,1991 (56 FR 3526 (USEPA,
1991a)). The NPDWR established an
MCLG and an MCL of 0.04 mg/L. EPA
based the MCLG on an RfD of 0.005 mg/
kg/day and a cancer classification of E,
evidence of non-carcinogenicity for
humans.
b. Technical Reviews. EPA has
initiated a reassessment of the health
risks resulting from exposure to
carbofuran. The revised risk assessment
will consider relevant studies on the
toxicity of carbofuran including recent
data on neurotoxicity and potential
developmental and reproductive
toxicity. The Agency expects the new
risk assessment to be completed in the
2002 or 2003 time frame (USEPA,
2002i).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for carbofuran is appropriate at
this time because a reassessment of the
health risks resulting from exposure to
carbofuran is ongoing.
12. Carbon Tetrachloride
a. Background. EPA published the
current MCLG for carbon tetrachloride
on July 8,1987 (52 FR 25690 (USEPA,
1987)). The NPDWR established an
MCLG of zero based on a cancer
classification of B2, probable human
carcinogen. The NPDWR also
established an MCL of 0.005 mg/L based
on analytical feasibility.
b. Technical Reviews. EPA has
initiated a reassessment of the health
risks resulting from exposure to carbon
tetrachloride. The revised risk
assessment will consider relevant
studies that have become available on
the toxicity of carbon tetrachloride
including its potential developmental
and reproductive toxicity. The Agency
expects the new risk assessment to be
completed in the 2002 or 2003 time
frame (USEPA, 20021).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for carbon tetrachloride is
appropriate at this time because a
reassessment bf the health risks
resulting from exposure to carbon
tetrachloride is ongoing.
13. Chlordane
a. Background. EPA published the
current NPDWR for chlordane on
January 30,1991 (56 FR 3526 (USEPA,
1991a)). The NPDWR established an
MCLG of zero based on a cancer
classification of B2, probable human
carcinogen. The NPDWR also
established an MCL of 0.002 mg/L based
on analytical feasibility.
b. Technical Reviews. EPA updated its
risk assessment for chlordane in 1998
(USEPA, 1998e). That assessment
included an evaluation of
developmental and reproductive
endpoints. The assessment also retained
the B2 cancer classification, concluding
that chlordane is a probable human
carcinogen using the 1986 EPA
Guidelines for Carcinogen Risk
Assessment (51 FR 33992, September
24,1986 (USEPA, 1986b)). Under the
1996 Proposed Guidelines for
Carcinogen Risk Assessment (61 FR
17960, April 23,1996 (USEPA, 1996)),
chlordane is characterized as a likely
carcinogen by all routes of exposure
and, at the present time, would require
quantification using a linear dose
response, thus, the MCLG of zero
remains appropriate.
EPA based the current MCL for
chlordane on a PQL of 0.002 mg/L. As
a part of the Six-Year Review, EPA
analyzed more recent WS data to
determine if it might be possible to
recalculate the PQL (USEPA, 2002d). In
addition, the Agency evaluated whether
more sensitive analytical methods have
been approved and put into use by a
wide number of laboratories. The results
of these analyses indicate that only a
slight improvement in analytical
feasibility might exist. Evaluation of the
WS data shows that EPA Regional and
State laboratories exhibit greater than 85
percent laboratory passing rates at
concentrations around the current PQL
of 0.002 mg/L. Because most of the
laboratory passing rates exceeded the 75
percent criterion typically tised to
derive a PQL from WS studies, this
information indicates that a lower PQL
corresponding to the 75 percent passing
rate might exist for chlordane. While
this information is indicative of a
possibly lower PQL, the WS data are
insufficient at this time to actually
recalculate what the lower PQL for
chlordane might be.
Using information about the
analytical methods most widely used to
report results in the WS studies, the
MDLs for these methods, and the 10
times MDL multiplier, EPA estimated
what the possibly lower PQL/MCL
might be. For the analysis of chlordane
in the more recent WS studies,
laboratories predominantly used EPA
Methods 505 (Gas Chromatography with
microextraction) and 508 (Gas
Chromatography with Electron Capture
Detector), which have MDLs of 0.00014
mg/L and 0.0000041 mg/L, respectively.
A 10 times MDL multiplier predicts that
the PQL could range from 0.0014 mg/L
to 0.000041 mg/L. EPA averaged these
two values, rounded up to 0.001 mg/L,
, and used this value as a threshold in the
occurrence analysis discussed in this
section.
Since the analytical feasibility
analysis indicates that the PQL for
chlordane (and therefore the MCL)
could possibly be lower if EPA had
more definitive data to recalculate the
PQL, EPA considered whether treatment
feasibility is likely to pose any
limitations (USEPA, 2002k). The current
BAT for chlordane is GAG. Small
system compliance technologies for
chlordane include GAG, POU GAG, and
powdered activated carbon (PAC).
Because chlordane is a moderately
adsorbed pesticide, EPA believes that
GAG is still a practical treatment and
would not pose any limitations for
chlordane at a possibly lower MCL.
The results of EPA's review of
possible "other regulatory revisions"
did not identify any issues which are
specific to chlordane (USEPA, 2002e).
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19057
EPA evaluated the results of the
occurrence and exposure analyses for
chlordane to determine whether
changes to the MCL might be
appropriate and likely to result in
additional public health protection if
the PQL were recalculated (USEPA,
2002g; USEPA, 2002h). Table V-4
shows the results of the detailed
occurrence and exposure analysis based BILLING CODE eseo-so-p
on the 16-State cross-section for the
current MCL (0.002 mg/L) and the
possible PQL/MCL based on the
analytical feasibility analysis (0.001 mg/
L).
Table V-4: Chlordane Occurrence1
Systems2
Threshold
(in mg/L)
Current MCL 0.002
Possible
PQL/MCL4 °-°01
16 Cross-Section
States - Total
Systems with Data
13,184
13,184
Estimated # Systems
> Threshold
(credible intervals)3
0 (0-0)
0 (0-0)
Estimated % Systems
> Threshold
(credible intervals)3
0.000% (0.000% - 0.000%)
0.0000910% (0.000% -0.000%)
Population Served by Systems2
Threshold
(in mg/L)
Current MCL 0.002
Possible
PQL/MCL4 °-°U1
16 Cross-Section
States - Total
Population Served
by Systems with
Data
97,459,900
97,459,900
Estimated Population
Served by Systems >
Threshold
(credible intervals)3
0 (0-0)
0 (0-0)
Estimated % Population
Served by Systems >
Threshold
(credible intervals)3
0.000% (0.000% -0.000%)
0.00000146% (0.000% - 0.000%)
Notes:
' Results are based on the number and percent of systems (and the corresponding population served by those systems) with estimated
mean concentrations above the specified threshold.
2 All percentages are shown to three significant figures. All system values are rounded to the nearest whole system. All population
values are rounded to the nearest hundred. .
3 "Credible intervals" are generated to quantify the uncertainty around each estimated probability in the Bayesian analysis of the
occurrence data. For further explanation of credible intervals and the Bayesian analysis, please see "Occurrence Estimation
Methodology and Occurrence Findings Report for the Six- Year Regulatory Review" (USEPA, 2002g).
4 The "possible PQL/MCL" is the possibly lower PQL/MCL as estimated by the analytical feasibility analysis.
BILLING CODE 6560-50-C
The detailed occurrence and exposure
analysis indicates that chlordane is
unlikely to occur at the current MCL or
any potential MCL revision for the
States used in the cross-section. Since
chlordane uses were canceled in the
United States in 1988 and since it is
subject to the United Nations Prior
Informed Consent procedure (USEPA,
_2002g; USEPA, 2002h), EPA expects the
occurrence of chlordane in PWSs to be
rare.
c. Preliminary Decision. Although
there are new data that support
consideration of a slightly lower PQL
(and therefore a possibly lower MCL),
EPA does not believe a revision to the
NPDWR for chlordane is appropriate at
this time. The Agency does not have
sufficient data at this time on which to
base a PQL recalculation and hence an
MCL revision. Also, the Agency believes
that any change in the PQL would be
minimal and unlikely to significantly
improve the level of public health
protection because chlordane appears to
occur infrequently at concentrations at
or below the current MCL.
14. Chromium
a. Background. EPA published the
current NPDWR for total chromium on
January 31,1991 (56 FR 3526 (USEPA,
1991a)). The NPDWR established an
MCLG and MCL of 0.1 mg/L. Although
the NPDWR regulates total chromium,
the adverse health effects associated
with hexavalent chromium (chromium
VI) are the basis of the current MCLG
since that is the more toxic species (56
FR 3526, January 31, 1991 (USEPA,
1991a)). EPA based the MCLG on an RfD
of 0.005 mg/kg/day and an assumed
RSC from water of 70 percent for total
chromium (refer to Appendix A for a
description of the RSC). EPA regulated
chromium as a Group D carcinogen, not
classifiable as to human carcinogenicity
by the oral route of exposure.
b. Technical Reviews. The* Agency
updated the risk assessment for
chromium in 1998 (USEPA, 1998f). The
revised risk assessment considered
relevant studies that were available on
the toxicity of chromium including
potential developmental and
reproductive toxicity. Based on the
revised risk assessment, EPA has
identified changes in the health risk
assessment that support consideration
of whether it may be appropriate to
revise the MCLG and MCL (USEPA,
20021). The 1998 assessment revised the
RfD for hexavalent chromium
(chromium VI) from 0.005 mg/kg/day to
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0.003 mg/kg/day based on a
modification to the original uncertainty
factor and the addition of a modifying
factor because of data on the potential
for gastrointestinal effects in humans as
a result of oral exposures. The critical
study used as the basis for the RfD did
not change.
The 1998 assessment of chromium VI
made no change to the cancer
classification of Group D for oral
exposures and determined that the
carcSnogenicity of chromium VI cannot
be determined because of a lack of
sufficient epidemiological or
lexicological studies under the 1996
Proposed Guidelines for Carcinogen
Risk Assessment. Chromium VI is a
Group A known human carcinogen by
the inhalation route of exposure.
Public concern over the adverse
health effects of chromium VI has
increased in recent years. One issue is
whether chromium VI is a human
carcinogen through oral ingestion. In
2001, the State of California convened a
Blue Ribbon Panel to evaluate the
available data on this issue. The Panel
issued its report in August 2001 (Flegal
et a/., 2001) and found no basis in either
the epidemiological or animal data
published hi the literature for
concluding that orally ingested
chromium VI is a carcinogen. The
National Toxicology Program (NTP) has
agreed to study the chronic toxicity and
carcinogenicity of chromium VI after
oral exposure. That effort will include
shorter-term toxicity studies, two-year
rodent toxicity and carcinogenicity
studies as well as bioavailability,
distribution, and mechanistic studies.
NTP expects the results to be available
in the next three to five years (NTP,
2001).
The availability of new data on the
contribution of dietary chromium to
total chromium exposure supports a re- ,
.evaluation of the RSC (NAS, 2001). The
Agency applied an RSC of 70 percent in
determining the current MCLG. Using
the new Agency RfD of 0.003 mg/kg/day
along with the application of 20 percent,
50 percent, or 70 percent as RSC values,
the Agency believes that any likely
revisions to the MCLG could range from
0.02 mg/L to 0.07 mg/L. A general
evaluation of the data indicates that a
revised RSC would likely fall within the
20 percent to 50 percent range.
Because the results of the health
effects review support consideration of
whether it may be appropriate to revise
the NPDWR for chromium based on
changes in the RfD and possible changes
in the RSC assumptions, EPA
considered whether analytical
feasibility is likely to be a limitation.
The results of the analytical feasibility
analyses indicate that the current PQL
of 0.01 mg/L for chromium is still
appropriate and is unlikely to change.
Therefore, the Agency believes the PQL
is unlikely to be a limiting factor if EPA
decides to revise the MCLG/MCL
(USEPA, 2002d).
EPA also considered whether
treatment feasibility is likely to pose any
limitations if EPA were to revise the
MCLG/MCL. The current BATs for
chromium include ion exchange, lime
softening, coagulation/filtration, and
RO. Small system compliance
technologies also include POO RO and
POU ion exchange. At the present time,
EPA believes these BATs are still
practical and would not pose any
limitations if the Agency were to revise
the MCLG/MCL (USEPA, 2002k).
The results of EPA's review of
possible "other regulatory revisions"
did not identify any issues which are
specific to chromium (USEPA, 2002e).
EPA evaluated the results of the
occurrence and exposure analyses for
chromium to determine whether a
revised MCLG/MCL would be likely to
result in additional public health
protection (USEPA, 2002g; USEPA,
2002h). Table V-5 shows the results of
the detailed occurrence and exposure
analysis based on the 16-State cross-
section for the current MCLG/MCL (0.1
mg/L), the possible MCLG/MCL value
retaining the 70 percent RSC (0.07 mg/
L), the possible MCLG/MCL value using
a 50 percent RSC (0.05 mg/L), and the
possible MCLG/MCL value using a 20
percent RSC (0.02 mg/L).
BILLING CODE 65SO-50-P
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19059
Table V-5: Chromium Occurrence1
Systems2
Threshold
(in mg/L)
Current MCL 0.1
Possible
MCLG/MCL 00?
value retaining the
70%RSC4
Possible
MCLG/MCL OQ5
value using a 50%
RSC4
Possible
MCLG/MCL OQ2
value using a 20%
RSC4
16 Cross-Section
States - Total
Systems with Data
19,695
19,695
19,695
19,695
Estimated # Systems
> Threshold
(credible intervals)3' s
1 (0-3)
3 (0-7)
7 (3 - 13)
73 (54-92)
Estimated % Systems
> Threshold
(credible intervals)3
0.00424% (0.000% - 0.0152)
0.01 33% (0.000% - 0.0355%)
0.0366% (0.0152% - 0.0660%)
0.37 1 % (0.274% - 0.467%)
Population Served by Systems2
Threshold
(in mg/L)
Current MCL 0.1
Possible •
MCLG/MCL 00?
value retaining the
70% RSC4
Possible
MCLG/MCL 005
value using a 50%
RSC4
Possible
MCLG/MCL OQ2
value using a 20%
RSC4
16 Cross-Section
States - Total
Population Served
by Systems with
Data
105,380,000
105,380,000
105,380,000
105,380,000
Estimated Population
Served by Systems >
Threshold
(credible intervals)3'5
1,500 (0 - 8,400)
4,500 (0 - 50,600)
11,300 (600-58,900)
106,600 (47,100-167,700)
Estimated % Population
Served by Systems >
Threshold
(credible intervals)3
0.00139% (0.000% - 0.00793%)
0.00427% (0.000% - 0.048 1%)
0.0108% (0.000580% - 0.0559%)
0.101% (0.0447% - 0.159%)
Notes:
1 Results are based on the number and percent of systems (and the corresponding population served by those systems) with estimated
mean concentrations above the specified threshold.
2 All percentages are shown to three significant figures. All system values are rounded to the nearest whole system. All population
values are rounded to the nearest hundred.
3 "Credible intervals" are generated to quantify the uncertainty around each estimated probability in the Bayesian analysis of the
occurrence data. For further explanation of credible intervals and the Bayesian analysis, please see "Occurrence Estimation
Methodology and Occurrence Findings Report for the Six- Year Regulatory Review" (USEPA, 2002g).
4 These are possible MCLG/MCL values based on changes in the RfD and using RSC values of 70, 50, and 20 percent.
5 This value does not necessarily reflect the number of systems out of compliance with the current MCL, because these data were
collected over the 1993 to 1997 time period, and because the value represents the estimated mean value over that time period, not the
running quarterly average on which compliance is based.
BILLING CODE 6560-5O-C
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The results of detailed occurrence and
exposure analysis indicate that less than
0.4 percent of the 19,695 systems
sampled in the 16 cross-section States
and approximately 0.1 percent of the
population served by those systems,
might he affected if EPA were to lower
the MCL to 0.02 mg/L.
c. Preliminary Decision. Although
EPA has identified a change to the RfD
on which the current MCLG for
chromium is based, the Agency believes
that a decision to revise the chromium
NPDWR at this time is premature in
light of the ongoing NTP studies on the
toxicology and carcinogenicity of
hexavalent chromium. The Agency is
aware of considerable public
controversy on the subject of the
appropriate level for chromium in
drinking water and realizes there are
differing views regarding the severity of
the health effects of chromium in water,
the relative importance of drinking
water as a squrce of chromium as
compared with other sources, and the
chemical form that should serve as the
basis for regulating chromium (total
versus hexavalent chromium}. Because
the NTP studies will not be available in
time for the final revise/not revise
decision, EPA is placing chromium in
the "not revise—data gap" category.
When completed, the NTP results will
be considered either in the next review
round or sooner, if the Agency deems it
appropriate."
15. Copper
a. Background. EPA published the
current NPDWR for copper on June 7,
1991 (56 FR 26460 (USEPA, 199lb)).
The NPDWR established an MCLG of
1.3 mg/L, based on a lowest-observed-
adverse-effect level (LOAEL) of 5.3 mg/
day9, and an action level of 1.3 mg/L for
first-draw samples at the 90th percentile
of taps tested. The NPDWR requires
water systems to monitor for copper at
the tap. Water systems must optimize
corrosion control. This requires water
systems serving more than 50,000
persons and those smaller size systems
that exceed the copper action level to
install corrosion control treatment and
to monitor for specified water quality
control parameters. The regulation also
requires any size system that exceeds
the copper action level to monitor for
copper in source water and, if
appropriate, to install source water
treatment. EPA published revisions to
the copper NPDWR on January 12, 2000
(65 FR 1950 (USEPA, 2000a)). These
"In Juno 1934. EPA published a technical
amendment that provided additional information
on tho basis of the copper MCLG (59 FR 33860, June
30,1904 (USEPA, 1994b)).
revisions made changes to monitoring
and reporting requirements but did not
affect the copper MCLG, action level, or
basic TT requirements.
b. Technical Reviews. In 1999, EPA
requested that the National Research
Council (NRG) of the NAS examine the
available nutritional and toxicological
data for copper and provide a
recommendation regarding the levels in
drinking water that are associated with
adverse effects. The NRG concluded that
copper in drinking water could produce
adverse gastrointestinal effects in some .
individuals at concentrations of about 3
mg/L or greater. In addition, the NRG
advised that individuals who carry a
recessive gene for Wilson's disease
could accumulate excess copper in their
livers at these same concentrations.
Accordingly, the NAS recommended
that EPA retain the MCLG of 1.3 mg/L
while additional data are collected on
the risk to the carriers of the Wilson's
Disease gene and other populations that
may accumulate copper in their livers
(NAS, 2000a).
EPA has initiated an assessment of
health risks resulting from exposure to
copper that will include the findings of
NAS as well as more recently published
data (USEPA, 20021). This assessment
will consider relevant studies on the
toxicity of copper including its effects
on genetically and developmentally
sensitive populations. The Agency
expects the new risk assessment to be
completed in the 2002 or 2003 time
frame (USEPA, 20021).
EPA has received comments on the
copper NPDWR suggesting that EPA
discontinue copper as a regulated
contaminant or change it to a secondary
standard (USEPA, 2002e). EPA is not
aware of any new information that
would warrant such a revision.
EPA has identified several potential
research needs which may be
considered in the context of an overall
drinking water research strategy. These
research needs are described in the
"Water Treatment Technology
Feasibility Support Document for
Chemical Contaminants; In Support of
EPA Six-Year Review of National
Primary Drinking Water Regulations"
(USEPA, 2002k).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for copper is appropriate at this
tune because a reassessment of the
health risks resulting from exposure to
copper is ongoing. Several potential
research needs were identified for
copper. The NAS review of copper in
drinking water concluded that there was
a need to conduct research that would
characterize copper-sensitive
populations (both, population size and
the factors leading to sensitivity) and
further define the contribution of copper
from drinking water to total copper
intake (NAS, 2000a). Treatment-related
research needs for copper are described
in the Six-Year Review treatment
feasibility support document (USEPA,
2002k).
16. Cyanide
a. Background. EPA published-the
current NPDWR for cyanide on July 17,
1992 (57 FR 31776 (USEPA, 1992)). The
NPDWR established an MCLG and MCL
of 0.2 mg/L. The MCLG was developed
based on an RfD of 0.02 mg/kg/day and
a cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The results of
the health effects technical review
identified some information on
reproductive effects from the ATSDR
toxicological profile that indicate the
need to update the Agency's risk ]
assessment for cyanide (USEPA, 20021).
In light of this information, EPA has
initiated a reassessment of the health
risks resulting from exposure to cyanide
and has already solicited scientific
information from the public for
consideration (67 FR 1212, January 9,
2002 (USEPA, 2002a)). The new risk
assessment will consider relevant data
on the toxicity of cyanide including its
potential developmental and
reproductive toxicity. Because the new
assessment is not expected to be
completed until the 2004 or 2005 time
frame, EPA does not believe it is
appropriate to revise the MCLG at this
time.
A review of analytical or treatment
feasibility is not necessary for cyanide
because changes to the MCLG are not
warranted at this time and 'the current
MCL is set at the MCLG. EPA's review
of "other regulatory revisions"
identified a potential revision relating to
an error in the BAT specified for
cyanide in the CFR (USEPA, 2002e).
The CFR currently specifies "chlorine"
as a BAT for cyanide for compliance
with the MCL and with variance and
exemption requirements (40 CFR 141.62
and 142.62, respectively); however, the
CFR should specify "alkaline
chlorination", as BAT. EPA plans to
correct this error through a technical
amendment to the cyanide NPDWR in
the near future. In the meantime, water
systems and States should continue to
be guided by the "Public Water System
Warning: Cyanide" (USEPA, 1994a) that
EPA distributed through its regional
offices. The warning includes
information on the use of chlorination
(non-alkaline) and the potential for
formation of harmful cyanogen chloride
due to reaction of chlorine with cyanide
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19061
in water under those conditions. The
PWS Warning explains this process in
detail and outlines treatment practice,
including contact times, required
chlorine concentrations, and
compensation for temperature effects.
The July 25,1990 proposed regulation
for cyanide discusses the effectiveness
of oxidation of cyanide at high pH levels
(55 PR 30370 at 30419 (USEPA, 1990))
and the PWS Warning discusses
mitigation of the formation of cyanogen
chloride. This information is also
summarized in the six-year review
treatment technology support document
(USEPA, 2002k).
Since the potential regulatory revision
identified by these analyses does not
affect the MCLG or the MCL, EPA does
not believe it is necessary to conduct a
detailed occurrence and exposure
analysis for cyanide.
c. Preliminary Decision. Other than
the technical amendment to correct the
BAT, EPA does not believe a revision to
the NPDWR for cyanide is appropriate
at this time. A reassessment of the
health risks has been initiated and the
Agency does not believe it is
appropriate to revise the NPDWR while
that effort is in process.
17. 2,4-D (2,4-Dichlorophenoxyacetic
Acid)
a. Background. EPA published the
NPDWR for 2,4-D on January 30,1991
(56 FR 3526 (USEPA, 1991a)). The
NPDWR established an MCLG and an
MCL of 0.07 mg/L. EPA developed the
MCLG based on a RfD of 0.01 mg/kg/day
and a cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. EPA has
initiated a reassessment of the health
risks resulting from exposure to 2,4-D.
The revised risk assessment will
consider relevant studies that have
become available on the toxicity of 2,4-
D including its potential developmental
and reproductive toxicity. EPA expects
the new risk assessment to be completed
in the 2003 or 2004 time frame (USEPA,
2002i).
c. Preliminary Decision. The Agency
• does not believe a revision to the
NPDWR for 2,4-D is appropriate at this
time because a reassessment of the
health risks resulting from exposure to
2,4-D is ongoing.
18. Dalapon (2,2-Dichloropropionic
Acid)
a. Background. EPA published the
current NPDWR for dal.apon on July 17,
1992 (57 FR 31776 (USEPA, 1992)). The
NPDWR established an MCLG and an
MCL of 0.2 mg/L. EPA developed the
MCLG based on an RfD of 0.03 mg/kg/
day and a cancer .classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency has
not updated .the health risk assessment
for dalapon since the NPDWR was
published. Therefore, as part of the Six-
Year Review process, EPA conducted a
literature search for relevant data on the
toxicology of dalapon, including its
potential developmental and
reproductive toxicity. The literature
search did not identify any studies that
warrant a review of the RfD or the
cancer classification (USEPA, 2002i).
A review of analytical or treatment
feasibility is not necessary for dalapon
because changes to the MCLG are not
warranted at this time and the current
MCL is set at the MCLG. In addition, the
results of EPA's review of possible
"other regulatory revisions" did not
identify any dalapon-specific issues
(USEPA, 2002e). Since EPA did not
identify a health or technology basis for
revising the dalapon NPDWR, the
Agency did not conduct a detailed
occurrence and exposure analysis.
c. Preliminary Decision. After
reviewing the results of the pertinent
technical analyses, the Agency believes
the NPDWR for dalapon remains
appropriate and thus, it is not subject to
revision at this time.
19. l,2-Dibromo-3-chloropropane'
(DBCP)
a. Background. EPA published the
current NPDWR for DBCP on January
30,1991 (56 FR 3526 (USEPA, 1991a)).
The NPDWR established an MCLG of
zero based on a cancer classification of
B2, probable human carcinogen. The
NPDWR also established an MCL of
0.0002 mg/L based on analytical
feasibility.
b. Technical Reviews. The Agency has
not updated the health risk assessment
for DBCP since the NPDWR was
published; however, ATSDR completed
a toxicological profile for DBCP in 1992
(ATSDR, 1992). This assessment and
other recent information do not warrant
a review of the cancer classification
because there are inadequate data to
support a nonlinear dose response
relationship (USEPA, 20021).
Accordingly, the MCLG remains at zero
and the Agency believes that a further
review of the health effects of DBCP is
not warranted at this time.
EPA based the current MCL for DBCP
on a PQL of 0.0002 mg/L. As a part of
the Six-Year Review, EPA analyzed
more recent WS data to determine if it
might be possible to recalculate the PQL
(USEPA, 2002d). In addition, the
Agency evaluated whether more
sensitive analytical methods have been
approved and put into use by a wide
number of laboratories. The results of
these analyses indicate that a slight
improvement in analytical feasibility
might exist. Evaluation of the WS data
shows that EPA Regional and State
laboratories exhibit greater than 85
percent laboratory passing rates at
concentrations around the current PQL
of 0.0002 mg/L. Because most of the
laboratory passing rates exceeded the 75
percent criterion typically used to
derive a PQL from WS studies, this
information indicates that a lower PQL
corresponding to the 75 percent passing
rate might exist for DBCP. While this
information is indicative of a possibly
lower PQL, the WS data are insufficient
at this time to actually recalculate what
the lower PQL for DBCP might be.
Using information about the
analytical methods most widely used to
report results in the WS studies, the
MDLs for these methods, and the 10
times MDL multiplier, EPA estimated
what the possibly lower PQL/MCL
might be. For the analysis of DBCP in
the more recent WS studies, laboratories
predominantly used EPA Method 504.1
(Gas Chromatography with
microextraction), which has an MDL of
0.00001 mg/L. A 10 times MDL
multiplier predicts that the PQL may be
around 0.0001 mg/L (also one-half the
current MCL). The 0.0001 mg/L value is
used as a threshold in the occurrence
analysis, which is discussed in this
section.
Since the analytical feasibility
analysis indicates that the PQL for
DBCP (and therefore the MCL) could
possibly be lower if EPA had more
definitive data to recalculate the PQL,
EPA considered whether treatment
feasibility is likely to pose any
limitations (USEPA, 2002k). The BATs
for DBCP include aeration and GAG.
Small system compliance technologies
for DBCP include GAG, POU GAG, PAC,
and several aeration technologies. Since
the Henry's Law coefficient for DBCP is
relatively low (i.e., DBCP is "less
strippable" than other contaminants),
GAG may in some cases be the preferred
treatment. Considering that only a slight
improvement in analytical feasibility
may exist, EPA believes that these BATs
are still practical and would not pose
any limitations for DBCP at a possibly
lower MCL.
The results of EPA's review of
possible "other regulatory revisions"
did not identify any issues which are
specific to DBCP (USEPA, 2002e).
EPA evaluated the results of the
detailed occurrence and exposure
analyses for DBCP to determine whether
changes to the MCL might be
appropriate and likely to result in
additional public health protection if
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the PQL were recalculated (USEPA, on the 16-State cross-section at the
2002g; USEPA, 2002h). Table V-6 current MGL (0.0002 mg/L) and the
shows the results of the detailed possible PQL/MCL based on the
occurrence and exposure analysis based
analytical feasibility analysis (0.0001
mg/L).
BILLING CODE 6560-50-P
Table V-6: l,2-Dibromo-3-chloropropane Occurrence1
Systems2
Threshold
(in mg/L)
Current MCL 0.0002
Possible - ___,
PQL/MCL' °-0001
16 Cross-Section
States - Total
Systems with Data
14,042
14,042
Estimated # Systems
> Threshold
(credible intervals)3-5
199 (171-231)
273 (238 -310)
Estimated % Systems
> Threshold
(credible intervals)3
1.41% (1.22%- 1.65%)
1.94% (1.70% -2.21%) .
Population Served by Systems2
Threshold
(in mg/L)
Current MCL 0.0002
PoSS? °-0001
16 Cross-Section
States - Total
Population Served
by Systems with
Data
87,727,200
87,727,200
Estimated Population Served
by Systems > Threshold
(credible intervals)3
2,278,300 (1,853,700 - 3,307,300)
2,828,300 (2, 1 82,700 - 4,353,900)
Estimated % Population
Served by Systems >
Threshold
(credible intervals)3
2.60% (2.11% -3.77%)
3.22% (2.49% -4.96%)
Notes:
1 Results are based on the number and percent of systems (and the corresponding population served by those systems) with estimated
mean concentrations above the specified threshold.
1 All percentages are shown to three significant figures. All system values are rounded to the nearest whole system. All population
values are rounded to the nearest hundred.
3 "Credible intervals" are generated to quantity the uncertainty around each estimated probability in the Bayesian analysis of the
occurrence data. For further explanation of credible intervals and the Bayesian analysis, please see "Occurrence Estimation
Methodology and Occurrence Findings Report for the Six- Year Regulatory Review" (USEPA, 2002g).
4 The "possible PQL/MCL" is the possibly lower PQL/MCL as estimated by the analytical feasibility analysis.
1 This value does not necessarily reflect the number of systems out of compliance with the current MCL, because these data were
collected over the 1993 to 1997 time period, and because the value represents the estimated mean value over that time period, not the
running quarterly average on which compliance is based.
BILLING CODE 6SGO-50-C
The results of detailed occurrence and
exposure analysis indicate that
approximately 0.5 percent of the 14,042
systems sampled in the 16 cross-section
States and approximately 0.6 percent of
the population served by those systems,
might be affected if EPA were to gather
the information to recalculate the PQL
(estimated to be around 0.0001 mg/L)
and to revise the MCL accordingly.
c. Preliminary Decision, Although
there are new data that support
consideration of a slightly lower PQL
{and therefore a possibly lower MCL),
EPA does not believe a revision to the
NPDWR for DBCP is appropriate at this
time. The Agency does not have
sufficient data at this time on which to
base a PQL recalculation and hence an
MCL revision. In addition, because the
occurrence of DBCP appears to be
minimal between the current MCL and
any likely PQL/MCL revision, the
Agency believes that any potential
revisions to the DBCP NPDWR are
unlikely to significantly improve the
level of public health protection.
20.1,2-Dichlorobenzene (o-
Dichlorobenzene)
a. Background, EPA published the
current NPDWR for 1,2-dichlorobenzene
on January 30,1991 (56 FR 3526
(USEPA, 1991a)). The NPDWR
established an MCLG and an MCL of 0.6
mg/L. EPA developed the MCLG based
on an RfD of 0.09 mg/kg/day and a
cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. EPA has
initiated a reassessment of the health
risks resulting from exposure to 1,2-
dichlorobenzene. The revised risk
assessment will consider relevant
studies on the toxicity of 1,2-
dichlorobenzene including its potential
developmental and reproductive
toxicity. The Agency expects the new
risk assessment to be completed in the
2002 or 2003 time frame (USEPA,
2002i).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for 1,2-dichlorobenzene is
appropriate at this time because a
reassessment of the health risks
resulting from exposure to 1,2-
dichlorobenzene is ongoing.
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19063
21.1,4-Dichlorobenzene (p-
Dichlorobenzene)
a. Background. EPA published the
current NPDWR for 1,4-dichlorobenzene
on July 8, 1987 (52 FR 25690 (USEPA,
1987)). The NPDWR established an
MCLG and an MCL of 0.075 mg/L. EPA
developed the MCLG based on an RfD
of 0.1 mg/kg/day and a cancer
classification of C, possible human
carcinogen.
b. Technical Reviews. EPA has
initiated a reassessment of the health
risks resulting from exposure to 1,4-
dichlorobenzene. The revised risk
assessment will consider relevant
studies on the toxicity of 1,4-
dichlorobenzene including its potential
developmental and reproductive
toxicity. The Agency expects the new
risk assessment to be completed in the
2002 or 2003 time frame (USEPA,
2002i).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for 1,4-dichlorobenzene is
appropriate at this time because a
reassessment of the health risks
resulting from exposure to 1,4-
dichlorobenzene is ongoing.
22. 1,2-Dichloroethane (Ethylene
Dichloride)
a. Background. EPA published the
current NPDWR for 1,2-dichloroethane
on July 8, 1987 (52 FR 25690 (USEPA,
1987)). The NPDWR established an
MCLG of zero based on a cancer
classification of B2, probable human
carcinogen. The NPDWR also
established an MCL of 0.005 mg/L based
on analytical feasibility.
b. Technical Reviews. EPA has
. initiated a reassessment of the-health
risks resulting from exposure to 1,2-
dichloroethane. The revised risk
assessment will consider relevant
studies that have become available on
the toxicity of 1,2-dichloroethane
including potential developmental and
reproductive toxicity. The Agency
expects the new risk assessment to be
completed in the 2002 or 2003 time
frame (USEPA, 2002i).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for 1,2-dichloroethane is
appropriate at this time because a
reassessment of the health risks
resulting from exposure to 1,2-
dichloroethane is ongoing.
23.1,1-Dichloroethylene
a. Background. EPA published the
current NPDWR for 1,1-
dichloroethylene on July 8, 1987 (52 FR
25690 (USEPA, 1987)). The NPDWR
established an MCLG and an MCL of
0.007 mg/L. The Agency developed the
MCLG based on ah RfD of 0.009 mg/kg/
day and a cancer classification of C,
possible human carcinogen.
b. Technical Reviews. EPA has
initiated a reassessment of the health
risks resulting from exposure to 1,1-
dichloroethylene. The revised risk
assessment will consider relevant
studies on the toxicity of 1,1-
dichloroethylene including its potential
developmental and reproductive
toxicity. The Agency expects the new
risk assessment to be completed in the
2002 or 2003 time frame (USEPA,
20021).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for 1,1-dichloroethylene is
appropriate at this time because a
reassessment of the health risks
resulting from exposure to 1,1-
dichloroethylene is ongoing.
24. cis-l,2-Dichloroethylene
a. Background. EPA published the
current NPDWR for cis-1,2-
dichloroethylene on January 30,1991
(56 FR 3526 (USEPA, 1991a)). The
NPDWR established an MCLG and MCL
of 0.07 mg/L. The Agency developed the
MCLG based on an RfD of 0.01 mg/kg/
day and a cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency has
not updated the health risk assessment
for cis-l,2-dichloroethylene since the
NPDWR was published; however,
ATSDR completed a toxicological
profile for cis-l,2-dichloroethylene in
1996 (ATSDR, 1996a). This review did
not find data that would warrant a
review of the RfD or cancer
classification. As part of the Six-Year
Review process, EPA conducted a
literature search for relevant data on the
toxicology of cis-l,2-dichloroethylene,
including its potential developmental
and reproductive toxicity. The literature
search did not identify any studies that
warrant a review of the RfD or the
cancer classification (USEPA, 20021).
A review of analytical or treatment
feasibility is riot necessary for cis-1,2-
dichloroethylene because changes to the
MCLG are not warranted at this time
and the current MCL is set at the MCLG.
In addition, the results of EPA's review
of possible "other regulatory revisions"
did not identify any issues that were
specific to cis-l,2-dichloroethylene
(USEPA, 2002e). Since EPA did not
identify a health or technology basis for
revising the cis-l,2-dichloroethylene
NPDWR, the Agency did not conduct a
detailed occurrence and exposure
analysis.
c. Preliminary Decision. After
reviewing the results of the pertinent
technical analyses, the Agency believes
the NPDWR for cis-l,2-dichloroethylene
remains appropriate and thus, it is not
subject to revision at this time.
25. trans-l,2-Dichloroethylene
a. Background. EPA published the
current NPDWR for trans-1,2-
dichloroethylene on January 30,1991
(56 FR 3526 (USEPA, 1991a)). The
NPDWR established an MCLG and an
MCL of 0.1 mg/L. The Agency
developed the MCLG based on an RfD
of 0.02 mg/kg/day and a cancer
classification of D, not classifiable as to
human carcinogenicity.
b. Technical Reviews. The Agency has
not updated the health risk assessment
for trans-l,2-dichloroethylene since the
NPDWR was published; however,
ATSDR completed a toxicological
profile fortrans-l,2-dichloroethylene in
1996 (ATSDR, 1996a). This review did
not find data that would warrant a
review of the RfD or cancer
classification. As part of the Six-Year
Review process, EPA conducted a
literature search for relevant data on the
toxicology of trans-l,2-dlchloroethylene,
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, 20021).
A review of analytical or treatment
feasibility is not necessary for trans-1,2-
dichloroethylene because changes to the
MCLG are not warranted at this time
and the current MCL is set at the MCLG.
In addition, the results of EPA's review
of possible "other regulatory revisions"
did not identify any issues that were
specific to trans-l,2-dichloroethylene
(USEPA, 2002e). Since EPA did not
identify a health or technology basis for
revising the trans-l,2-dichloroethylene
NPDWR,, the Agency did not conduct a
detailed occurrence and exposure
analysis.
c. Preliminary Decision. After
reviewing the results of the pertinent
technical analyses, the Agency believes
the NPDWR for trans-1,2-
dichloroethylene remains appropriate
and thus, it is not subject to revision at
this time.
26. Dichloromethane (Methylene
Chloride)
a. Background. EPA published the
NPDWR for dichloromethane on July 17,
1992 (57 FR 31776 (USEPA, 1992)). The
NPDWR established an MCLG of zero
based on a cancer classification of B2,
probable human carcinogen. The
NPDWR also established an MCL of
0.005 mg/L based on analytical
feasibility.
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Federal Register/Vol. 67, No. 74/Wednesday, April 17, 2002/Proposed Rules
b. Technical Reviews. The Agency has
not updated the health risk assessment
for dichloromethane since the NPDWR
was published; hoivever, ATSDR .
completed a lexicological profile for
dichloromethane in 2000 (USEPA,
2002i). This review did not find any
data that would warrant a change in the
cancer classification on which the 1992
zero MCLG is based. The ATSDR
lexicological profile considered relevant
studies on the toxicity of
dichloromethane including
developmental and reproductive
toxicity.
The current MCL for dichloromethane
is based on a PQL of 0.005 mg/L. As a
part of the Six-Year Review, EPA
analyzed more recent WS data to
determine if it might be possible to
recalculate the PQL (USEPA, 2002d). In
addition, the Agency evaluated whether
more sensitive analytical methods have
been approved and put into use by a
wide number of laboratories. The
analysis of the WS data indicates that a
slight improvement in analytical
feasibility might exist. Evaluation of the
WS data shows that EPA Regional and
State laboratories exhibit greater than 90
percent laboratory passing rates at
concentrations around the current PQL
of 0.005 mg/L. Because most of the
laboratory passing rates exceeded the 75
percent criterion typically used to
derive a PQL from WS studies, this
information indicates that a lower PQL
corresponding to the 75 percent passing
rate might exist for dichloromethane.
While this information is indicative of
a possibly lower PQL, the WS data are
insufficient at this time to actually
recalculate what the lower PQL for
dichloromethane might be.
Using information about the
analytical methods most widely used to
report results in the WS studies, the
MDLs for these methods, and the 10
times MDL multiplier, EPA estimated
what the possibly lower PQL/MCL
might be. For the analysis of
dichloromethane in the more recent WS
studies, laboratories predominantly
used EPA Methods 524.2 (GC/MS) and
502.2 (Purge and Trap Gas
Chromatography), which have MDLs of
0.00003 mg/L and 0.00002 mg/L,
respectively. A 10 times MDL multiplier
predicts that the PQL may be around
0.0003 to 0.0002 mg/L. The Agency
used the average of these two values
(0.00025 mg/L) as a threshold (i.e.,
possible PQL) in the occurrence analysis
discussed in this section.
Since the analytical feasibility
analysis indicates that the PQL for
dichloromethane (and therefore the
MCL) could possibly be lower if EPA
had more definitive data to recalculate
the PQL, EPA considered whether
treatment feasibility is likely to pose any
limitations (USEPA, 2002k). The current
BAT for dichloromethane is PTA. EPA
believes this BAT is still practical and
would not pose any limitations for
dichloromethane at a possibly lower
MCL.
The results of EPA's review of
possible "other regulatory revisions"
did not identify any dichloromethane-
specific issues (USEPA, 2002e).
EPA evaluated the results of the
occurrence and exposure analyses for
dichloromethane to determine whether
changes to the MCL might be
appropriate and likely to result in
"additional public health protection if
the PQL were recalculated (USEPA,
2002g; USEPA, 2002h). Table V-7
shows the results of the detailed
occurrence and exposure analysis based
on the 16-State cross-section for the
current MCL (0.005 mg/L) and the
possible PQL/MCL based on the
analytical feasibility analysis (0.00025
mg/L).
BILLING CODE 6560-50-P
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19065
Table V-7: Dichloromethane Occurrence1
Systems2
Threshold
(in mg/L)
Current MCL 0.005
Possible nnnfne
PQL/MCL4 °-00025
16 Cross-Section
States -Total
Systems with
Data
21,530
21,530
Estimated # Systems
> Threshold
(credible intervals)3' s
3 (1-6)
1,067 (977 - 1,157)
Estimated % Systems
> Threshold
(credible intervals)3
0.013 1 % (0.00465% - 0.0279%)
4.96% (4.54% - 5.37%)
Population Served by Systems2
Threshold
(in mg/L)
Current MCL 0.005
Possible 000025
PQL/MCL4 °-00025
16 Cross-Section
States - Total
Population Served
by Systems with
Data
110,146,100
110,146,100
Estimated Population Served by
Systems > Threshold
(credible intervals)3' 5
131,200 (200-275,300)
10,350,400 (9,383,400 - 1 1,642,400)
Estimated % Population
Served by Systems >
Threshold
(credible intervals)3
0.119% (0.000159% - 0.250%)
9.40% (8.52% -10.6%)
Notes: ...
' Results are based on the number and percent of systems (and the corresponding population served by those systems) with estimated
mean concentrations above the specified threshold.
2 AH percentages are shown to three significant figures. All system values are rounded to the nearest whole system. All population
values are rounded to the nearest hundred.
3 "Credible intervals" are generated to quantify the uncertainty around each estimated probability in the Bayesian analysis of the
occurrence data. For further explanation of credible intervals and the Bayesian analysis, please see "Occurrence Estimation
Methodology and Occurrence Findings Report for the Six- Year Regulatory Review" (USEPA, 2002g).
4 The "possible PQL/MCL" is the possibly lower PQL/MCL as estimated by the analytical feasibility analysis.
3 This value does not necessarily reflect the number of systems out of compliance with the current MCL, because these data were
collected over the 1993 to 1997 time period, and because the value represents the estimated mean value over that time period, not the
running quarterly average on which compliance is based.
BILLING CODE 6560-50-C
The results of the detailed occurrence
and exposure analysis indicate that less
than 5 percent of the 21,530 systems
sampled in the 16 cross-section States
and slightly more than 9 percent of the
population served by those systems,
might be affected if EPA were to gather
information to recalculate the PQL (to a
lower PQL of around 0.00025 mg/L) and
revise the MCL accordingly.
c. Preliminary Decision. EPA does not
believe it is appropriate to revise the
NPDWR for dichloromethane at this
time because the data indicating the
possibility of a PQL/MCL revision are
not sufficient to support a regulatory
revision at this time. However, EPA
believes there may be an opportunity for
improvement in the level of public
health protection if the Agency had
sufficient data to recalculate the PQL.
The Agency therefore solicits comment
on whether to gather better data on
which to recalculate the PQL. Any such
effort is unlikely to be completed in
time to inform the revise/not revise
decision for the final notice but may
provide new information for
consideration during the next six-year
review cycle.
27. 1,2-Dichloropropane
a. Background. EPA published the
current NPDWR for 1,2-dichloropropane
on January 30,1991 (56 FR 3526
(USEPA, 1991a)). The NPDWR
established an MCLG of zero based on
a cancer classification of B2, probable
human carcinogen. The NPDWR also
established an MCL of 0.005 mg/L based
on analytical feasibility.
b. Technical Reviews. EPA has not
identified any new information that
indicates that it is appropriate to revise
the cancer classification for 1,2-
dichloropropane at this time (USEPA,
2002i). Because the MCLG remains at
zero, the Agency believes that a further
review of the health effects of 1,2-
dichloropropane is not warranted at this
time.
The current MCL for 1,2-
dichloropropane is based on a PQL of
0.005 mg/L. As a part of the Six-Year
Review, EPA analyzed more recent WS
data to determine if it might be possible
to recalculate the PQL (USEPA, 2002d).
hi addition, the Agency evaluated
whether more sensitive analytical
methods have been approved and put
into use by a wide number of
laboratories. The results of these
analyses indicate that some
improvement in analytical feasibility
might exist. Evaluation of the WS data
shows that EPA Regional and State
laboratories exhibit greater than 95
percent laboratory passing rates at
concentrations around the current PQL
of 0.005 mg/L. Because most of the
laboratory passing rates exceeded the 75
percent criterion typically used to
derive a PQL from WS studies, this
information indicates that a lower PQL
corresponding to the 75 percent passing
rate might exist for 1,2-dichloropropane.
While this information is indicative of
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a possibly lower PQL, the WS data are
insufficient at this time to actually
recalculate what the lower PQL for 1,2-
dichloropropane might be.
Using information about the
analytical methods most widely used to
report results in the WS studies, the
MDLs for these methods, and the 10
times MDL multiplier, EPA estimated
what the possibly lower PQL/MCL
might be. For the analysis of 1,2-
dichloropropane in the more recent WS
studies, laboratories predominantly
used EPA Methods 524.2 (GC/MS) and
502.2 (Purge and Trap Gas
Chromatography), which have MDLs of
0.00004 mg/L and 0.00003 mg/L,
respectively. A10 times MDL multiplier
predicts that the PQL may be around
0.0004 to 0.0003 mg/L. EPA used the
0.0004 mg/L value as a threshold in the
occurrence analysis discussed in this
section.
Since the analytical feasibility
analysis indicates that the PQL for 1,2-
dichloropropane (and therefore the
MCL) could possibly be lower if EPA
had more definitive data to recalculate
the PQL, EPA considered whether
treatment feasibility is likely to pose any
limitations (USEPA, 2002k). The current
BATs for 1,2-dichloropropane are GAG
and PTA. Small system compliance
technologies for 1,2-dichloropropane
include GAG, PTA, and several other
aeration technologies. EPA believes that
these BATs are still practical and would
not pose any limitations for 1,2-
dichloropropane at a possibly lower
MCL.
The results of EPA's review of
possible "other regulatory revisions"
did not identify any issues that are
specific to 1,2-dichloropropane (USEPA,
2002e).
EPA evaluated the results of the
occurrence and exposure analyses for
1,2-dichloropropane to determine
whether changes to the MCL might be
appropriate and likely to result in
additional public health protection if
the PQL were recalculated (USEPA,
2002g; USEPA, 2002h). Table V-8
shows the results of the detailed
occurrence and exposure analysis based
on the 16-State cross-section for the
current MCL (0.005 mg/L) and the
possible PQL/MCL based on the
analytical feasibility analysis (0.0004
mg/L).
BILLING CODE 6560-50-P
Table V-8: 1,2-Dichloropropane Occurrence1
Systems2
Threshold
(in mg/L)
Current MCL 0.005
PoXSS °-0004
16 Cross-Section
States - Total
Systems with Data
21,988
21,988
Estimated # Systems
> Threshold
(credible intervals)3' s
1 (0-2)
11 (7-16)
Estimated % Systems
> Threshold
(credible intervals)3
0.00358% (0.000% - 0.009 1 0%)
0.0506% (0.03 1 8% - 0.0728%)
Population Served by Systems2
Threshold
(in mg/L)
Current MCL 0.005
Possible _ _-- .
PQL/MCL' °-0004
16 Cross-Section
States - Total
Population Served
by Systems with
Data
110,450,100
110,450,100
Estimated Population
Served by Systems >
Threshold
(credible intervals)3'5
39,500 (0-142,000)
1 65,700 ( 1 45,000 - 1 97,400)
Estimated % Population
Served by Systems >
Threshold
(credible intervals)3
0.0358% (0.000% -0.1 29%)
0. 1 50% (0. 1 3 1 % - 0. 1 79%)
Notes:
1 Results are based on the number and percent of systems (and the corresponding population served by those systems) with estimated
mean concentrations above the specified threshold.
1 All percentages are shown to three significant figures. All system values are rounded to the nearest whole system. All population
values are rounded to the nearest hundred.
3 "Credible intervals" are generated to quantify the uncertainty around each estimated probability in the Bayesian analysis of the
occurrence data. For further explanation of credible intervals and the Bayesian analysis, please see "Occurrence Estimation
Methodology and Occurrence Findings Report for the Six- Year Regulatory Review" (USEPA, 2Q02g).
4 The "possible PQL/MCL" is the possibly lower PQL/MCL as estimated by the analytical feasibility analysis.
5 This value does not necessarily reflect the number of systems out of compliance with the current MCL, because these data were
collected over the 1 993 to 1 997 time period, and because the value represents the estimated mean value over that time period, not the
running quarterly average on which compliance is based.
BILLING CODE 6560-50-c than 0.05 percent of the 21,988 systems population served by those systems,
The results of the detailed occurrence sampled in the 16 cross-section States might be affected if EPA were to gather
and exposure analysis indicate that less and approximately 0.1 percent of the
the information to recalculate the PQL
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19067
(to a lower PQL of around 0.0004 rag/
L) and revise the MCL accordingly.
' c. Preliminary Decision. Although
there are new data that support
consideration of a possibly lower PQL
(and therefore a possibly lower MCL),
EPA does not believe a revision to the
NPDWR for 1,2-dichloropropane is
appropriate at this time. The Agency
does not have sufficient data at this time
on which to base a PQL recalculation
and hence an MCL revision. In addition,
because the occurrence of 1,2-
dichloropropane appears to be minimal
between the current MCL and any likely
PQL/MCL revision, the Agency believes
that any potential revisions to the 1,2-
dichloropropane NPDWR are unlikely to
significantly improve the level of public
health protection.
28. Di(2-ethylhexyl)adipate (DEHA)
a. Background. EPA published the
NPDWR for DEHA on July 17,1992 (57
FR 31776 (USEPA, 1992)). The NPDWR
established an MCLG and an MCL of 0.4
mg/L. The Agency developed the MCLG
based on an RfD of 0.6 mg/kg/day and
a cancer classification of C, possible
human carcinogen.
b. Technical Reviews. The Agency has
identified data that indicate it may be
appropriate to update the risk
assessment for DEHA (USEPA, 20021).
The literature search on reproductive
and developmental toxicity identified
differences in the evaluation of the
critical study on which the MCLG is
based. Therefore, EPA believes it is
appropriate to update the risk
assessment and evaluate relevant new
studies that have become available on
the toxicity of DEHA and its metabolites
including its potential developmental
and reproductive toxicity. In light of
this information, EPA has initiated a
reassessment of the health risks
resulting from exposure to DEHA and
has already solicited scientific
information from the public for
consideration (67 FR 1212, January 9,
2002 (USEPA, 2002a)). Because the new
assessment is not expected to be
completed until the 2003 or 2004 time
frame, EPA does not believe it is
appropriate to revise the MCLG at this
time.
The current MCL is not limited by the
analytical or treatment feasibility.
Review of these capabilities is not
necessary since no changes to the MCL
are warranted at this time. The results
of EPA's review of possible "other
regulatory revisions" did not identify
any issues that are specific to DEHA
(USEPA, 2002e). Because none of these
analyses indicate a change to the DEHA
regulation, it is not necessary to conduct
a detailed occurrence and exposure
analysis.
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for DEHA is appropriate at this
time. A reassessment of the health risks
has been initiated and the Agency does
not believe it is appropriate to revise the
NPDWR while that effort is in process.
29. Di(2-ethylhexyl)phthalate (DEHP)
a. Background. EPA published the
current NPDWR for DEHP on July 17,
1992 (57 FR 31776 (USEPA, 1992)). The
NPDWR established an MCLG of zero
based on a cancer classification of B2,
probable human carcinogen, and an •
MCL of 0.006 based on analytical
feasibility.
b. Technical Reviews. The Agency has
initiated a reassessment of the health
risks resulting from exposure to DEHP.
Many studies on DEHP and its
metabolites have become available over
the past decade and are being evaluated
as part of the Agency's ongoing
assessment. The new assessment will
evaluate cancer and noncancer
endpoints, including potential
developmental and reproductive
endpoints. EPA expects the new risk
assessment to be completed in the 2002
or 2003 time frame (USEPA, 2002i).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for DEHP is appropriate at this
time because a reassessment of the
health risks resulting from exposure to
DEHP is ongoing.
30. Dinoseb
a. Background. EPA published the
current NPDWR for dinoseb on July 17,
1992 (57 FR 31776 (USEPA, 1992)). The
NPDWR established an MCLG and an
MCL of 0.007 mg/L. The Agency
developed the MCLG based on an RfD
of 0.001 mg/kg/day and a cancer
classification of D, not classifiable as to
human carcinogenicity.
b. Technical Reviews. The Agency has
not updated the health risk assessment
for dinoseb since the NPDWR was
published. Therefore, as part of the Six-
Year Review process, EPA conducted a
literature search for relevant data on the
toxicology of dinoseb, including its
potential developmental and
reproductive toxicity. The literature
search did not identify any studies that
warrant a review of the RfD or the
cancer classification (USEPA, 20021).
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. hi addition, the
results of EPA's review of possible
"other regulatory revisions" did not
' identify any dinoseb-specific issues
(USEPA, 2002e). Since EPA did not
identify a health or technology basis for
revising the dinoseb NPDWR, the
Agency did not conduct a detailed
occurrence and exposure analysis.
c. Preliminary Decision. After
reviewing the results of the pertinent
technical analyses, the Agency believes
the NPDWR for dinoseb remains
appropriate and thus, it is not subject to
revision at this time.
31. Diquat
a. Background. EPA published the
current NPDWR for diquat on July 17,
1992 (57 FR 31776 (USEPA, 1992)). The
NPDWR established an MCLG and an
MCL of 0.02 mg/L. The Agency
developed the MCLG based ori an RfD
of 0.002 mg/kg/day and a cancer
classification of D, not classifiable as to
human carcinogenicity.
b. Technical Reviews. The Agency has
initiated a reassessment of the health
risks from exposure to diquat. The
revised risk assessment will consider
relevant studies that have become
available on the toxicity of diquat,
including its potential developmental
and reproductive toxicity. The Agency
expects the new risk assessment to be
completed in the 2002 time frame
(USEPA, 2002i).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for diquat is appropriate at this
• time because a reassessment of the
health risks resulting from exposure to
diquat is ongoing.
32. Endothall
a. Background. EPA published the
current NPDWR for endothall on July
17,1992 (57 FR 31776 (USEPA, 1992)).
The NPDWR established an MCLG and
an MCL of 0.1 mg/L. The Agency
developed the MCLG based on an RfD
of 0.02 mg/kg/day and a cancer
classification of D, not classifiable as to
human carcinogenicity.
b. Technical Reviews. The Agency has
initiated a reassessment of the health
risks resulting from exposure to
endothall. The revised risk assessment
will consider relevant studies on the
toxicity of endothall including its
potential developmental and
reproductive toxicity. The Agency
expects the new risk assessment to be
completed in the 2003 or 2004 time
frame (USEPA, 20021).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for endothall is appropriate at
this time because a reassessment of the
health risks resulting from exposure to
endothall is ongoing.
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33. Endrin
a. Background. EPA published the
current NPDWR for endrin on July 17,
1992 (57 FR 31776 (USEPA, 1992)}. The
NPDWR established an MCLG and an
MCL of 0.002 mg/L. The Agency
developed the MCLG based on an R£D
of 0.0003 mg/kg/day and a cancer
classification of D, not classifiable as to
human carcinogenicity.
b. Technical Reviews. The Agency has
not updated the health risk assessment
for endrin since the NPDWR was
published; however, ATSDR completed
a toxicological profile for endrin in 1996
(ATSDR, 1996b). This review did not
find data that would warrant a review
of the RfD or cancer classification. As
part of the Six-Year Review process,
EPA conducted a literature search for
relevant data on the toxicology of
endrin, including its potential
developmental and reproductive
toxicity. The literature search did not
identify any studies that warrant a
review of the RfD or the cancer
classification (USEPA, 2002i).
A reviexv of analytical or treatment
feasibility is not necessary for endrin
because changes to the MCLG are not
warranted at this time and the current
MCL is set at the MCLG. In addition, the
results of EPA's review of possible
"other regulatory revisions" did not
identify any endrin-specific issues
(USEPA, 2002e). Since EPA did not
identify a health or technology basis for
revising the endrin NPDWR, the Agency
did not conduct a detailed occurrence
and exposure analysis. (Note: Endrin
uses were canceled in 1986 except for
use on bird perches, which was
canceled in 1991 (USDA, 1998)).
c. Preliminary Decision. After
reviewing the results of the pertinent
technical analyses, the Agency believes
the NPDWR for endrin remains
appropriate and thus, it is not subject to
revision at this time.
34. Epichlorohydrin
a. Background. EPA published the
current NPDWR for epichlorohydrin on
January 30,1991 (56 FR 3526 (USEPA,
1991a)). The NPDWR established an
MCLG of zero based on a cancer
classification of B2, probable human
carcinogen. The NPDWR imposes a TT
requirement that limits the allowable
level of epichlorohydrin monomer in
the polymer that is added to drinking
water as a flocculent to remove
particulates. Each water system is
required to certify, in writing, to the
State (using third-party or
manufacturer's certification) that the
combination (or product) of dose and
monomer level does not exceed the
following level: 0.01 percent residual
epichlorohydrin monomer in polymer
products used during water treatment
and dosed at 20 ppm.
b. Technical Reviews. EPA has not
identified any new information that
indicate that it is appropriate to revise
the cancer classification for
epichlorohydrin at this time. Because
the MCLG remains at zero, the Agency
believes that a further review of the
health effects of epichlorohydrin is not
warranted at this time (USEPA, 20021).
There are no standardized methods
available for epichlorohydrin at low
levels in drinking water (56 FR 3526 at
3558, July 1,1991 (USEPA, 1991a)).
Therefore, no analysis of analytical
feasibility is appropriate for this
contaminant. EPA has no new
information that indicates it is
appropriate to revise the TT
requirement for epichlorohydrin at this
time (USEPA, 2002k). The results of
EPA's review of possible "other
regulatory revisions" did not identify
any issues which are specific to
epichlorohydrin (USEPA, 2002e). Since
EPA did not identify a health or
technology basis for revising the
epichlorohydrin NPDWR, the Agency
did not conduct a detailed occurrence
and exposure analysis.
c. Preliminary Decision. After
reviewing the results of the pertinent
technical analyses, the Agency believes
the NPDWR for epichlorohydrin
remains appropriate and thus, it is not
subject to revision at this time.
35. Ethylbenzene
a. Background. EPA published the
current NPDWR for ethylbenzene on
January 30,1991 (56 FR 3526 (USEPA,
1991a)). The NPDWR established an
MCLG and an MCL of 0.7 mg/L. The
Agency developed the MCLG based on
an RfD of 0.1 mg/kg/day and a cancer
classification of D, not classifiable as to
human carcinogenicity.
b. Technical Reviews. The Agency has
initiated a reassessment of the health
risks resulting from exposure to
ethylbenzene. The revised risk
assessment will consider relevant
studies that have become available on
the toxicity of ethylbenzene, including
its potential developmental and
reproductive toxicity. The Agency
expects the new risk assessment to be
completed in the 2002 or 2003 time
frame (USEPA, 20021).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for ethylbenzene is appropriate
at this time because a reassessment of
the health risks resulting from exposure
to ethylbenzene is ongoing.
36. Ethylene Dibromide (EDB; 1,2-
Dibromoethane)
a. Background. EPA published the
current NPDWR for EDB on January 30,
1991 (56 FR 3526 (USEPA, 1991a)). The
NPDWR established an MCLG of zero
based on a cancer classification of B2,
probable human carcinogen. The
NPDWR also established an MCL of
0.00005 mg/L based on analytical
feasibility.
b. Technical Reviews. The Agency has
initiated a reassessment of the health
risks resulting from exposure to EDB.
The revised risk assessment will
consider relevant studies that have
become available on the toxicity of EDB,
including its developmental and
reproductive toxicity. The Agency
expects the new risk assessment to be
completed in the 2002 or 2003 time
frame (USEPA, 20021).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for EDB is appropriate at this
time because a reassessment of the
health risks resulting from exposure to
EDB is ongoing.
37. Fluoride
a. Background. EPA published the
current NPDWR for fluoride on April 2,
1986 (51 FR 11396 (USEPA, 1986a)).
The NPDWR established an MCLG and
an MCL of 4.0 mg/L. The MCLG was
developed from a lowest effect level for
crippling skeletal fluorosis of 20 mg/day
with continuous exposures over a 20-
year or longer period. The LOAEL was
divided by an uncertainty factor of 2.5
and a drinking water intake of 2 liters/
day (L/day) to obtain the MCLG.
Drinking water was considered to be the
only source of exposure for the
calculation. At the same time, EPA
published a secondary maximum
contaminant level (SMCL) for fluoride
of 2.0 mg/L to protect against dental
fluorosis, which is considered to be an
adverse cosmetic effect. PWSs
exceeding the fluoride SMCL must
provide public notification to their
customers.
Fluoride is unique as a drinking water
contaminant because of its beneficial
effects at,low level exposures, and
because it is voluntarily added to some
drinking water systems as a public
health measure for reducing the
incidence of cavities among the treated
population. The amount of fluoride
added to drinking water for fluoridation
ranges from 0.7 to 1.2 mg/L, depending
on ambient air temperatures. The
decision to fluoridate a water supply is
made by the State or local municipality,
and is not mandated by EPA or any
other Federal entity.
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19069
b. Technical Reviews. In 1997, NAS
established Dietary Reference Intakes
(DRI) for fluoride as a nutrient. As a
component of the DRI, NAS established
age and gender specific tolerable upper
intake levels (UL) to reflect the highest
average daily nutrient intake level likely
to pose no risk of adverse effects to
almost all individuals in the general
population. As intake increases above
the UL, the potential risk of adverse
effects increases. The NAS set the UL
for fluoride at 0.10 mg/kg/day for
infants, toddlers, and children through
eight years of age, to protect them from
moderate enamel fluorosis (NAS, 1997).
A UL of 10 mg/day was established for
adults and for children older than eight
years, based on protection against
skeletal fluorosis. The NAS UL
evaluation of fluoride does not have an
effect on the MCLG/MCL because a 2
liter drinking water intake of 4 mg/L
equals 8mg/day for adults, which is less
than 10 mg/day and allows for fluoride
in food and dental products.
In addition, the NAS established age
and gender specific Adequate Intake
(AI) values for fluoride. AI values are set
when the data do not permit
determination of the more precise and
better known Recommended Dietary
Allowance (RDA). The NAS (1997) AI
for infants, 0 through 6 months, is 0.01
mg/day and for infants, 7 through 12
months, is 0.5 mg/day. Values for
children range from 0.7 mg/day to 3 mg/
day increasing with age. For adults, the
NAS (1997) AI is 3 mg/day for females,
and 4 mg/day for males.
There are new studies regarding the
effects of fluoride on bone that have
been published since EPA established
the MCLG/MCL. EPA believes that it is
important to review these new data,
since effects on bone are the basis of the
present MCLG and MCL. The Agency
has conducted a literature search to
identify reports of the clinical and
epidemiological data on fluoride and
the skeletal system. The results of that
search indicate that a review of the new
data is justified as part of the regulatory
review process. EPA plans to request
NAS to conduct a review of these data.
In light of this planned assessment, EPA
does not believe it is appropriate to
revise the MCLG at this time.
As part of the continuing review of
the new toxicological data for fluoride,
EPA also intends to examine the RSC
used in the 1986 regulation. At that
time, a 100 percent RSC was applied in
setting the regulation. The increased use
of fluoride in dental products, the
tendency for children to swallow these
dental products, and the potential for
increased exposure from foods support
a re-evaluation of the RSC as a
component of the fluoride review.
As a part of the review of possible
"other regulatory revisions," EPA
identified one issue pertaining to the
public notification requirement
associated with exceedance of the SMCL
and the timing of the notification.
Currently, PWSs that exceed the SMCL
of 2.0 mg/L are required to notify their
customers within 12 months of the
exceedance. Concern has been
expressed that this requirement is not
sufficiently timely since dental fluorosis
occurs as a result of exposure to high
levels of fluoride while the tooth enamel
is being laid down. Waiting 12 months
to provide public notification may result
in young children being exposed to high
levels of fluoride during the time at
which they are most vulnerable. The
Agency will consider any such
revisions, if they are still appropriate,
once the results of the NAS evaluation
are available.
c. Preliminary Decision. EPA is
continuing its analyses of relevant
studies that have been published since
1986 regarding the adverse effects of
fluoride on the skeletal system to
determine if these data support
consideration of whether to revise the
current MCLG. As a part of this effort,
the Agency plans to request that NAS
update the fluoride health risk
assessment and review the RSC
assumptions. The Agency therefore
believes it is not appropriate to revise
the NPDWR for fluoride at this time.
When the results of the NAS assessment.
are available, and if they support
consideration of whether a revision to
the MCLG and/or MCL may be
appropriate, EPA will revisit this "not
revise" decision.
38. Glyphosate
a. Background. EPA published the
current NPDWR for glyphosate on July
17, 1992 (57 FR 31776 (USEPA, 1992)).
The NPDWR established an MCLG and
an MCL of 0.7 mg/L. The Agency
developed the MCLG based on an RfD
of 0.1 mg/kg/day and a cancer
classification of D, not classifiable as to
human carcinogenicity.
b. Technical Reviews. The Agency has
initiated a reassessment of the health
risks resulting from exposure to
glyphosate. The revised risk assessment
will consider relevant studies that have
.become available on the toxicity of
glyphosate including its potential
developmental and reproductive
toxicity. The Agency expects the new
risk assessment to be completed in the
2002 or 2003 time frame (USEPA,
2002i).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for glyphosate is appropriate at
this time because a reassessment of the
health risks resulting from exposure to
glyphosate is ongoing.
39. Heptachlor
a. Background. EPA published the
current NPDWR for heptachlor on
January 30,1991 (56 FR 3526 (USEPA,
1991a)). The NPDWR established an
MCLG of zero based on a cancer
classification of B2, probable.human
carcinogen. The NPDWR also
established an MCL of 0.0004 mg/L
based on analytical feasibility.
b. Technical Reviews. The Agency has
not updated the health risk assessment
for heptachlor since the NPDWR was
published; however, ATSDR completed
a toxicological profile for heptachlor in
1993 (ATSDR, 1993). This assessment
and other recent information do not
warrant a review of the cancer
classification because there are
inadequate data to support a nonlinear
dose-response relationship (USEPA,
2002i). Accordingly, the MCLG remains
at zero and the Agency believes that a
further review of the health effects of
heptachlor is not warranted at this tune.
The current MCL for heptachlor is
based on a PQL of 0.0004 mg/L. As a
part of the Six-Year Review, EPA
analyzed more recent WS data to
determine if it might be possible to
recalculate the PQL (USEPA, 2002d). In
addition, the Agency evaluated whether
more sensitive analytical methods have
been approved and put into use by a
wide number of laboratories. The results
of these analyses indicate that some
improvement in analytical feasibility
might exist. Evaluation of the WS data
shows that EPA Regional and State
laboratories exhibit greater than 90
percent laboratory passing rates at
concentrations around the current PQL
of 0.0004 mg/L. Because most of the
laboratory passing rates exceeded the 75
percent criterion typically used to
derive a PQL from WS studies, this
information indicates that a lower PQL
corresponding to the 75 percent passing
rate might exist for heptachlor. While
this information is indicative of a
possibly lower PQL, the WS data are
insufficient at this time to actually
recalculate what the lower PQL for
heptachlor might be.
Using information about the
analytical methods most widely used to
report results in the WS studies, the
MDLs for these methods, and the 10
times MDL multiplier, EPA estimated
what the possibly lower PQL/MCL
might be. For the analysis of heptachlor
in the more recent WS studies,
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laboratories predominantly used EPA
Methods 508 (GC/MS), 505 (GC
microextraction), and 525.2 (Purge and
Trap GC), which have MDLs of
0.0000015 rng/L, 0.000003 mg/L, and
0.00015 mg/L, respectively. A10 times
MDL multiplier predicts PQLs of
0.000015 mg/L, 0.00003 mg/L, and
0.0015 mg/L. EPA chose the
intermediate value, rounded up to
0.0001 mg/L, and used this value as a
threshold in the occurrence analysis
discussed in this section.
Since the analytical feasibility
analysis indicates that the PQL for
heptachlor (and therefore the MCL)
could possibly be lower if EPA had
more definitive data to recalculate the
PQL, EPA considered whether treatment
feasibility is likely to pose any
limitations (USEPA, 2002k). The current
BAT for heptachlor is GAG. Compliance
technologies for small systems include
GAG, PAG, and POU GAC. Since
heptachlor is a moderately adsorbed
contaminant, EPA believes that the BAT
and compliance technologies are still
practical anrl would not pose any
limitations for heptachlor at a possibly
lower MCL.
The results of EPA's review of
possible "other regulatory revisions"
did not identify any heptachlor-specific
issues (USEPA, 2002e).
EPA evaluated the results of the
occurrence and exposure analyses for
heptachlor to determine whether
changes to the MCL might be
appropriate and likely to result in
additional public health protection if
the PQL were recalculated (USEPA,
2002g; USEPA, 2002h). Table V-9
shows the results of the detailed
occurrence and exposure analyses based
on the 16-State cross-section for the
current MCL (0.0004 mg/L) and the
possible PQL/MCL based on the
analytical feasibility analysis (0.0001
mg/L).
BILLING CODE 6560-50-P
Table V-9: Heptachlor Occurrence1
Systems2
Threshold
(in mg/L)
Current MCL 0.0004
Possible - .......
PQL/MCL' °-0001
16 Cross-Section
States - Total
Systems with Data
14,245
14,245
Estimated # Systems
> Threshold
(credible intervals)3
0 (0-0)
0 (0-0)
Estimated % Systems
> Threshold
(credible intervals)3
0.000% (0.000% - 0.000%)
0.0000140% (0.000% - 0.000%)
Population Served by Systems2
Threshold
(in mg/L)
Current MCL 0.0004
Possible 0001
PQL/MCL' °-°001
16 Cross-Section
States - Total
Population Served
by Systems with
Data
96,563,400
96,563,400
Estimated Population
Served by Systems >
Threshold
(credible intervals)3
0 (0-0)
0 (0-0)
Estimated % Population Served
by Systems > Threshold
(credible intervals)3
0.000% (0.000% -0.000%)
0.000000242% (0.000% - 0.000%)
Notes:
1 Results are based on the number and percent of systems (and the corresponding population served by those systems) with estimated
mean concentrations above the specified threshold.
1 All percentages are shown to three significant figures. All system values are rounded to the nearest whole system. All population
values are rounded to the nearest hundred.
3 "Credible intervals" are generated to quantity the uncertainty around each estimated probability in the Bayesian analysis of the
occurrence data. For further explanation of credible intervals and the Bayesian analysis, please see "Occurrence Estimation
Methodology and Occurrence Findings Report for the Six-Year Regulatory Review" (USEPA, 2002g).
4 The "possible PQL/MCL" is the possibly lower PQL/MCL as estimated by the analytical feasibility analysis.
BILLING CODE 6560-50-C
Based on the detailed occurrence and
exposure analysis, heptachlor is
unlikely to occur at the current MCL or
any potential MCL revision for the
States used in the cross-section. Since
all heptachlor uses \vere canceled in the
United States in 1988 (except for fire ant
use), and since it is subject to the United
Nations Prior Informed Consent
procedure (USEPA, 2002g; USEPA,
2002h), EPA expects the occurrence of
heptachlor in PWSs to be rare.
c. Preliminary Decision. Although
there are new data that support
consideration of a slightly lower PQL
(and therefore a possibly lower MCL),
EPA does not believe a revision to the
NPDWR for heptachlor is appropriate at
this time. The Agency does not have
sufficient data at this time on which to
base a PQL recalculation and hence an
MCL revision. Also, the Agency believes
that any change in the PQL would be
minimal and unlikely to significantly
improve the level of public health
protection because heptachlor appears
to occur very infrequently at
concentrations at or below the current
MCL.
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19071
40. Heptachlor Epoxide
a. Background. EPA published the
current NPDWR for heptachlor epoxide,
a degradate of heptachlor, on January
30,1991 (56 FR 3526 (USEPA, 1991a)).
The NPDWR established an MCLG of
zero based on a cancer classification of
B2, probable human carcinogen. The
NPDWR also established an MCL of
0.0002 mg/L based on analytical ,
feasibility.
b. Technical Reviews. The Agency has
not updated the health risk assessment
for heptachlor epoxide since the
NPDWR was published; however,
ATSDR completed a toxicological
profile for heptachlor epoxide in 1993
(ATSDR, 1993). This review did not find
data that would warrant a review of the
cancer classification because there are
inadequate data to support a nonlinear
dose response. Accordingly, the MCLG
remains at zero and the Agency believes
that a further review of the health effects
of heptachlor epoxide is not warranted
at this time.
The current MCL for heptachlor
epoxide is based on a PQL of 0.0002 mg/
L. As a part of the Six-Year Review, EPA
analyzed more recent WS data to
determine if it might be possible to
recalculate the PQL (USEPA, 2002d). In
addition, the Agency evaluated whether
more sensitive analytical methods have
been approved and put into use by a
wide number of laboratories. The results
of these analyses indicate that a slight
improvement in analytical feasibility
might exist. Evaluation of the WS data
shows that EPA Regional and State
laboratories exhibit greater than 85
percent laboratory passing rates at
concentrations around the current PQL
of 0.0002 mg/L. Because most of the
laboratory passing rates exceeded the 75
percent criterion typically used to
derive a PQL from WS studies, this
information indicates that a lower PQL
corresponding to the 75 percent passing
rate might exist for heptachlor epoxide.
While this information is indicative of
a possibly lower PQL, the WS data are
insufficient at this time to actually
recalculate what the lower PQL for
heptachlor epoxide might be.
Using information about the
analytical methods most widely used to
report results in the WS studies, the
MDLs for these methods, and the 10
times MDL multiplier, EPA estimated
what the possibly lower PQL/MCL
might be. For the analysis of heptachlor
epoxide in the more recent WS studies,
laboratories predominantly used EPA
Methods 505 (GC microextraction), 508
(GC/MS), and 525.2 (Purge and Trap
GC), which have MDLs of 0.000004 mg/
L, 0.0000059 mg/L, and 0.00013 mg/L,
respectively. A 10 times MDL multiplier
predicts PQLs of 0.00004 mg/L,
0.000059 mg/L, and 0.0013 mg/L. EPA
chose the intermediate value, rounded
up to 0.0001 mg/L, and used this value
as a threshold in the occurrence analysis
discussed in this section.
Since the analytical feasibility
analysis indicates that the PQL for
heptachlor epoxide (and therefore the
MCL) could possibly be lower if EPA
had more definitive data to recalculate
the PQL, EPA considered whether
treatment feasibility is likely to pose any
limitations (USEPA, 2002k). The current
BAT for heptachlor epoxide is GAG.
Compliance technologies for small
systems include GAG, PAC, and POU
GAC. EPA believes that the BAT and
compliance technologies would not
pose any limitations for heptachlor
epoxide at a possibly lower MCL.
The results of EPA's review of
possible "other regulatory revisions"
did not identify any issues that are
specific to heptachlor epoxide (USEPA,
2002e).
EPA evaluated the results of the
occurrence and exposure analyses for
heptachlor epoxide to determine
whether changes to the MCL might be
appropriate and likely to result in
additional public health protection if
the PQL were recalculated (USEPA,
2002g; USEPA, 2002h). Table V-10
shows the results of the detailed
occurrence and exposure analyses based
on the 16-State cross-section for the
current MCL (0.0002 mg/L), and the
possible PQL/MCL based on the
analytical feasibility analysis (0.0001
mg/L).
BILLING CODE 6560-50-P
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Table V-10: Heptachlor Epoxide Occurrence1
Systems2
Threshold
(in mg/L)
Current MCL 0.0002
PcSS? °-°001
16 Cross-Section
States - Total
Systems with Data
14,133
14,133
Estimated # Systems
> Threshold
(credible intervals)3
0 (0-0)
0 (0-0)
Estimated % Systems
> Threshold
(credible intervals)3
0.000% (0.000% - 0.000%)
0.000% (0.000% - 0.000%)
Population Served by Systems1
Threshold
(in mg/L)
Current MCL 0.0002
Possible nnnni
PQL/MCL4 °-0001
16 Cross-Section
States - Total
Population Served
by Systems with
Data
96,222,900
96,222,900
Estimated Population
Served by Systems >
Threshold
(credible intervals)3
0 (0-0)
0 (0-0)
Estimated % Population Served
by Systems > Threshold
(credible intervals)3
0.000% (0.000% - 0.000%)
0.000% (0.000% -0.000%)
Notes:
1 Results are based on the number and percent of systems (and the corresponding population served by those systems) with estimated
mean concentrations above the specified threshold.
1 All percentages are shown to three significant figures. All system values are rounded to the nearest whole system. All population
values are rounded to the nearest hundred.
3 "Credible intervals" are generated to quantify the uncertainty around each estimated probability in the Bayesian analysis of the
occurrence data. For further explanation of credible intervals and the Bayesian analysis, please see "Occurrence Estimation
Methodology and Occurrence Findings Report for the Six-Year Regulatory Review" (USEPA, 2002g).
' The "possible PQL/MCL" is the possibly lower PQL/MCL as estimated by the analytical feasibility analysis.
BILLING CODE 6560-50-C
Based on detailed occurrence and
exposure analysis, it appears that
heptachlor epoxide is unlikely to occur
at the current MCL or any potential
MCL revision for the States used in the
cross-section. Since the parent of
heptachlor epoxide (i.e., heptachlor)
was canceled for use (except for fire ant
use) in the United States and since it is
subject to the United Nations Prior
Informed Consent procedure (USEPA,
2002g; USEPA, 2002h), EPA expects the
occurrence of heptachlor epoxide in
PWSs to be rare.
c, Preliminary Decision. Although
there are new data that support
consideration of a slightly lower PQL
(and therefore a possibly lower MCL),
EPA does not believe a revision to the
NPDWR for heptachlor epoxide is
appropriate at this time. The Agency
does not have sufficient data at this time
on which to base a PQL recalculation
and hence an MCL revision. Also, the
Agency believes that any change in the
PQL would be minimal and unlikely to
significantly improve the level of public
health protection because heptachlor
epoxide appears to occur infrequently at
concentrations at or below the current
MCL.
41. Hexachlorobenzene
a. Background. EPA published the
current NPDWR for hexachlorobenzene
on July 17,1992 (57 FR 31776 (USEPA,
1992)). The NPDWR established an
MCLG of zero based on a cancer
classification of B2, probable human
carcinogen. The NPDWR also
established an MCL of 0.001 mg/L based
on analytical feasibility.
b. Technical Reviews. The Agency has
not updated the health risk assessment
for hexachlorobenzene since the
NPDWR was published; however,
ATSDR completed a toxicological
Erofile for hexachlorobenzene in 1996
YTSDR, 1996c). This assessment and
other recent information do not warrant
a review of the cancer classification
because there are inadequate data to
support a nonlinear dose-response
relationship (USEPA, 20021).
Accordingly, the MCLG remains at zero
and the Agency believes that a further
review of the health effects of
hexachlorobenzene is not warranted at
this time.
The current MCL for
hexachlorobenzene is based on a PQL of
0.001 mg/L. As a part of the Six-Year
Review, EPA analyzed more recent WS
data to determine if it might be possible
to recalculate the PQL (USEPA, 2002d).
In addition, the Agency evaluated
whether more sensitive analytical
methods have been approved and put
into use by a wide number of
laboratories. The results of these
analyses indicate that some '
improvement in analytical feasibility
might exist. Evaluation of the WS data
shows that EPA Regional and State
laboratories exhibit greater than 90
percent laboratory passing rates at
concentrations around the current PQL
of 0.001 mg/L. Because most of the
laboratory passing rates exceeded the 75
percent criterion typically used to
derive a PQL from WS studies, this
information indicates that a lower PQL
corresponding'to the 75 percent passing
rate might exist for hexachlorobenzene.
While this information is indicative of
a possibly lower PQL, the WS data are
insufficient at this time to actually
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Federal Register/Vol. 67, No. 74/Wednesday, April 17, 2002/Proposed Rules 19073
recalculate what the lower PQL for
hexachlorobenzene might be. ,
Using information about the
analytical methods most widely used to
report results in the WS studies, the
MDLs for these methods, and the 10
times MDL multiplier, EPA estimated
what the possibly lower PQL/MCL
might be. For the analysis of
hexachlorobenzene in the more recent
WS studies, laboratories predominantly
used EPA Methods 508 (GC/MS), 505
(GC microextraction), and 525.2 (Purge
and Trap GC), which have MDLs of
0.0000077 mg/L, 0.000002 mg/L and
0.000001 mg/L, respectively. A 10 times
MDL multiplier predicts PQLs of
0.000077 mg/L, 0.00002 mg/L, and
0.00001 mg/L. EPA chose the highest
value, rounded up to 0.0001 mg/L, and
then used this value as a threshold in
the occurrence analysis discussed in
this section.
Since the analytical feasibility
analysis indicates that the PQL for
hexachlorobenzene (and therefore the
MCL) could possibly be lower if EPA
had more definitive data to recalculate
the PQL, EPA considered whether
treatment feasibility is likely to pose any
limitations (USEPA, 2002k). The current
BAT for hexachlorobenzene is GAG.
Compliance technologies for small
systems include GAG, PAC, and POU
GAG. Since hexachlorobenzene is a
moderately adsorbed contaminant, EPA
believes that the BAT and compliance
technologies are still practical and
would not pose any limitations for
hexachlorobenzene at a possibly lower
MCL.
The results of EPA's review of
possible "other regulatory revisions"
did not identify any issues that are
specific to hexachlorobenzene (USEPA,
2002e).
EPA evaluated the results of the
occurrence and exposure analyses for
hexachlorobenzene to determine
whether changes to the MCL might be
appropriate and likely to result in
additional public health protection if
the PQL were recalculated (USEPA,
2002g; USEPA, 2002h). Table V-ll
shows the results of the detailed
occurrence and exposure analyses based
on the 16-State cross-section for the
current MCL (0.001 mg/L) and the
possible PQL/MCL based on the
analytical feasibility analysis (0.0001
mg/L).
BILLING CODE 6560-50-P
Table V-ll: Hexachlorobenzene. Occurrence1
Systems2
Threshold
(in mg/L)
Current MCL 0.001
PoSS? °-0001
16 Cross-Section
States - Total
Systems with
Data
14,011
14,011
Estimated # Systems
> Threshold
(credible intervals)3
0 • (0 - 0)
1 (0-2)
Estimated % Systems
> Threshold
(credible intervals)3
0.000% (0.000% - 0.000%)
0.00287% (0.000% - 0.0143%)
Population Served by Systems2
Threshold
(in mg/L)
Current MCL 0.001
Possible - ---,
PQL/MCL4 °-°001
16 Cross-Section
States - Total
Population Served
by Systems with
Data
94,035,300
94,035,300
Estimated Population Served
by Systems > Threshold
(credible intervals)3
0 (0-0)
16,600 (0-84,300)
Estimated % Population
Served by Systems > Threshold
(credible intervals)3
0.000% (0.000% -0.000%)
0.0176% (0.000% - 0.0896%)
Notes:
1 Results are based on the number and percent of systems (and the corresponding population served by those systems) with estimated
mean concentrations above the specified threshold.
2 All percentages are shown to three significant figures. All system values are rounded to the nearest whole system. All population
values are rounded to the nearest hundred.
3 "Credible intervals" are generated to quantify the uncertainty around each estimated probability in the Bayesian analysis of the
occurrence data. For further explanation of credible intervals and the Bayesian analysis, please see "Occurrence Estimation
Methodology and Occurrence Findings Report for .the Six-Year Regulatory Review" (USEPA, 2002g).
4 The "possible PQL/MCL" is the possibly lower PQL/MCL as estimated by the analytical feasibility analysis.
BILLING CODE 6560-so-c hexachlorobenzene is unlikely to occur MCL revision for the States used in the
The detailed occurrence and exposure at ^ current MCL or any potential cross-section. Since hexachlorobenzene
analysis indicates that
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uses were canceled in the United States
in 1984 and since it is subject to the
United Nations Prior Informed Consent
procedure (USEPA, 2002g; USEPA,
2002h), EPA expects the occurrence of
hexachlorobenzene in PWSs to be rare.
c. Preliminary Decision. Although
there are new data that support
consideration of a possibly lower PQL
(and therefore a possibly lower MCL),
EPA does not believe a revision to the
NPDWR for hexachlorobenzene is
appropriate at this time. The Agency
does not have sufficient data at this time
on which to base a PQL recalculation
and hence an MCL revision. In addition,
because the occurrence of
hexachlorobenzene appears to be
minimal between the current MCL and
any likely PQL/MCL revision, the
Agency believes that any potential
revisions to the hexachlorobenzene
NPDWR are unlikely to significantly
improve the level of public health
protection.
42. Hexachlorocyclopentadiene
a. Background. EPA published the
current NPDWR for
hexachlorocyclopentadiene on July 17,
1992 (57 FR 31776 (USEPA, 1992)). The
NPDWR established an MCLG and an
MCL of 0.05 mg/L. The Agency based
the MCLG on an RfD of 0.007 mg/kg/day
and a cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency
updated the health risk assessment for
hexachlorocyclopentadiene in 2001
(USEPA, 2001c). The revised risk
assessment considered relevant studies
that were available to the Agency on the
toxicity of hexachlorocyclopentadiene
including its potential developmental
and reproductive toxicity. According to
the 1986 EPA Guidelines for Carcinogen
Risk Assessment (51 FR 33992,
September 24,1986 (USEPA, 1986b)),
evaluation of the weight of evidence for
carcinogenicity to humans indicates that
hexachlorocyclopentadiene is most
appropriately categorized as Group E,
evidence of noncarcinogenicity to
humans, via inhalation exposure. In
accordance with EPA's 1996 Proposed
Guidelines for Carcinogen Risk
Assessment (61 FR 17960, April 23,
1996 (USEPA, 1996)),
hexachlorocyclopentadiene is not likely
to be a human carcinogen by the
inhalation route. The potential for
carcinogenicity by the oral route is
unknown. The updated risk assessment
changed the RfD from 0.007 to 0.006
mg/kg/day. The change in RfD was the
result of a change in the procedure used
to model the data but not a change in
the underlying toxicology. The RfD
could result in a slight change to the
MCLG and MCL but that change would
not lead to any significant improvement
in public health protection.
A review of analytical or treatment
feasibility is not necessary for
hexachlorocyclopentadiene because
changes to the MCLG are not warranted
at this time and the current MCL is set
at the MCLG. In addition, the results of
EPA's review of possible "other
regulatory revisions" did not identify
anyhexachlorocyclopentadiene-specific
issues (USEPA, 2002e). Since EPA did
not identify a health or technology basis
for revising the
hexachlorocyclopentadiene NPDWR,
the Agency did not conduct a detailed
occurrence and exposure analysis.
c. Preliminary Decision. After
reviewing the results of the pertinent
technical analyses, the Agency believes
the NPDWR for
hexachlorocyclopentadiene remains
appropriate and thus, it is not subject to
revision at this time.
43. Lead
a. Background. EPA published the
current NPDWR for lead on June 7,1991
(56 FR 26460 (USEPA, 1991b)). The
NPDWR established an MCLG of zero
and a lead action level of 0.015 mg/L at
the 90th percentile of taps tested. The
MCLG for lead is based on three factors:
(1) the occurrence of a variety of low
level health effects for which it is
currently difficult to identify clear
threshold exposure levels below which
there are no risks of adverse health
effects; (2) the Agency's policy goal that
drinking water should contribute
minimal lead to total lead exposures
because a substantial portion of the
sensitive population already exceeds
acceptable blood lead levels; and (3) the
classification of lead as B2, probable
human carcinogen.
The. NPDWR requires water systems
to monitor for lead at the tap. Water
systems must optimize corrosion
control. This requires water systems
serving more than 50,000 persons
(except those with extremely low levels
of lead in their distribution systems)
and those smaller size systems that
exceed the lead action level to install
corrosion control treatment and to
monitor for specified water quality
control parameters. The NPDWR also
includes other TT requirements for
those systems exceeding the lead action
level. These systems must: (1) Monitor
for lead in source water; (2) install
source water treatment, if appropriate;
(3) conduct public education for as long
as they continue to exceed the action
level; and (4) replace the portion of lead
service line in the distribution system
they own, if they continue to exceed the
action level after installing corrosion
control treatment and/or source water
treatment. EPA published revisions to
the lead NPDWR on January 12, 2000
(65 FR 1950 (USEPA, 2000a)). These
revisions made changes to monitoring
and reporting requirements, public
education, and the lead service line
replacement requirements but did not
affect the lead MCLG, action level, or
other TT requirements.
b. Technical Reviews. EPA has not
identified any new assessments that
indicate that it is appropriate to revise
the MCLG for lead at this time (USEPA,
20021). Although ATSDR completed a
toxicological profile for lead in 1999
(ATSDR, 1999), the review did not find
data that would warrant a change in the
MCLG for lead. Because the MCLG
remains at zero, the Agency believes
that a further review of the health effects
of lead is not warranted at this time.
EPA identified several potential
research needs which may be
considered in the context of an overall
drinking water research strategy. These
research needs are described in the
"Water Treatment Technology
Feasibility Support Document of
Chemical Contaminants in Support of
EPA Six-Year Review of National
Primary Drinking Water Regulations"
(USEPA, 2002k).
Some stakeholders have suggested
that EPA allow alternatives to corrosion
control treatment (e.g., monitoring and
flushing at non-transient, non-
community water systems (NTNCWSs))
(USEPA, 2002e). EPA considered these
alternatives as a part of the January 2000
revisions and determined that it was not
appropriate to make such revisions to
the TT requirements for lead and copper
(65 FR 1950, January 12, 2000 (USEPA,
2000a)). If new peer-reviewed scientific
information becomes available, it will
be considered.
EPA also considered several potential
revisions to requirements pertaining to
the monitoring requirements for lead
and copper in drinking water based on
concerns recently expressed by
stakeholders (USEPA, 2002e). As a part
of the Six-Year Review process, EPA
considered issues including: (1) Further
reduction of 'the monitoring
requirements; (2) monitoring for lead
and copper on the same frequency as
other inorganic and organic chemicals;
(3) expanding the monitoring waiver
program to water systems that have not
exceeded one-half the lead and copper
action levels for three monitoring
rounds, regardless of plumbing
materials used; (4) revising the protocol
by which tap water sampling sites are
identified; and (5) allowing fewer than
five tap water samples for NTNCWSs
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19075
that have fewer than five taps. The
Agency addressed all of these issues as
a part of the January 2000 revisions. If
new peer-reviewed scientific
information becomes available, it will
be considered.
The current action level and TT
requirements are not limited by
analytical feasibility, therefore review of
these capabilities is not needed. Since
none of the analyses indicate a change
to the lead regulation at this time, the
Agency did not conduct detailed
occurrence and exposure analyses.
c. Preliminary Decision. EPA does not
believe a revision to the NPDWR for
lead is appropriate because the Agency
is not aware of any new data/
information that provides sufficient
basis for revising the regulatory
requirements at this time. However, the
Agency has identified several
technology-related issues that could
benefit from further research. These
research needs will be considered as a
part of an overall drinking water
.-research strategy. As more research in
jghis area becomes available, the Agency
will consider the results as a part of the
review of the lead NPDWR during future
review cycles.
44. Lindane (y-Hexachlorocyclohexane)
a. Background. EPA published the
current NPDWR for lindane on January
30, 1991 (56 FR 3526 (USEPA, 1991a)).
The NPDWR established" an MCLG and
an MCL of 0.0002 mg/L. The Agency
based the MCLG on an RfD of 0.0003
mg/L and a cancer classification of C,
possible human carcinogen.
b. Technical Reviews. The Agency has
initiated a reassessment of the health
risks resulting from exposure to lindane.
The revised risk assessment will
consider relevant studies that have
become available on the toxicity of
lindane including its potential
developmental and reproductive
toxicity. The Agency expects the new
risk assessment to be completed in the
2003 or 2004 time frame (USEPA,
20021).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for lindane is appropriate at
this time because a reassessment of the
health risks resulting from exposure to
lindane is ongoing.
45. Mercury (Inorganic)
a. Background. EPA published the
current NPDWR for inorganic mercury
on January 30,1991 (56 FR 3526
(USEPA, 1991a)). The NPDWR
established an MCLG and an MCL of
0.002 mg/L. The Agency based the
MCLG on a Drinking Water Equivalent
Level (DWEL) of 0.01 mg/L10 and a
cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. EPA updated
the risk assessment for mercury in 1997
as part of the Mercury Study Report to
Congress (MSRC) (USEPA, 1997b). The
MSRC entailed a review of all available
studies on inorganic mercury including
reproductive and developmental
studies. The MSRC concluded that the
database for inorganic mercury is
suggestive of effects in animals at doses
around 2 mg/kg/day. The data however,
are considered insufficient for risk
assessment based on any single study or •
on the database as a whole. Evaluation
of data for germ cell mutagenicity led to
the conclusion that there is a moderate
weight of evidence for potential to '
produce adverse effects in humans. The
MSRC reviewed and kept the 1987 RfD
of 0.0003 mg/kg/day based on immune-
mediated kidney damage in three
studies conducted in a sensitive strain
of rats.
The MSRC evaluated data for
carcinogenicity of inorganic mercury,
largely from studies of mercuric
chloride. Based on the absence of
human data and limited data in animals,
inorganic mercury was categorized as
Group C, possible human carcinogen;
this determination was posted on IRIS
for mercuric chloride (USEPA, 1995).
The MSRC also applied the proposed
revisions to the Cancer Guidelines (61
FR 17960, April 23,1996 (USEPA,
1996)) to the evaluation of inorganic
mercury. The conclusion was that
inorganic mercury is not likely to be a
human carcinogen under conditions of
exposure generally encountered in the
environment. This was based in part on
the observation that all tumors were
observed at very high doses, in excess
of the maximum tolerated dose (MTD)
and that likely modes of action for these
tumors involved irritation and cytotoxic
effects not expected to occur at
environmental levels.
The revised risk assessments show
that inorganic mercury is not likely to
be a carcinogen at levels found in water
and that there are insufficient data to
categorize inorganic mercury as a
developmental toxicant. The EPA RfD
has not changed, and thus, EPA does
not believe it is appropriate to revise the
MCLG at this time.
A review of analytical or treatment
feasibility is not necessary for mercury
because, in EPA's judgment, changes to
10 The DWEL was recommended by a panel of
experts on mercury, and was derived using the
weight of evidence from the entire inorganic
mercury database. The DWEL was later back-
calculated to an RED of 0.0003 mg/kg/day (USEPA,
1995).
the MCLG are not warranted at this time
and the current MCL is set at the MCLG.
In addition, the results of EPA's review
of possible "other regulatory revisions"
did not identify any mercury-specific
issues (USEPA, 2002e). Since EPA did
not identify a health or technology basis
for revising the mercury NPDWR, the
Agency did not conduct a detailed
occurrence and exposure analysis.
c. Preliminary Decision. After
reviewing the results of the pertinent
technical analyses, the Agency believes
the NPDWR for inorganic mercury
remains appropriate and thus, it is not
subject to revision at this time.
46. Methoxychlor
a. Background. EPA published the
current NPDWR for methoxychlor on
January 30, 1991 (56 FR 3526 (USEPA,
1991a)). The NPDWR established an
MCLG and an MCL of 0.04 mg/L. The
Agency based the MCLG on an RfD of
0.005 mg/kg/day and a cancer
classification of D, not classifiable as to
human carcinogenicity.
b. Technical Reviews. The Agency has
initiated a reassessment of the health
risks resulting from exposure to
methoxychlor. The revised risk
assessment will consider relevant
studies that have become available on
the toxicity of methoxychlor including
its potential developmental and
reproductive toxicity. The Agency
expects the new risk assessment to be
completed in the 2002 or 2003 time
frame (USEPA, 2002i).
c. Preliminary Decision. The Agency •
does not believe a revision to the
NPDWR for methoxychlor is appropriate
at this time because a reassessment of
the health risks resulting from exposure
to methoxychlor is ongoing,
47. Monochlorobenzene
(Chlorobenzene)
a. Background. EPA published the
current NPDWR for monochlorobenzene
on January 30, 1991 (56 FR 3526
(USEPA, 1991a)). The NPDWR
established an MCLG and an MCL of 0.1
mg/L. The Agency based the MCLG on
an RfD of 0.02 mg/kg/day and a cancer
classification of D, not classifiable as to
human carcinogenicity.
b. Technical Reviews. The Agency has
not updated the health risk assessment
for monochlorobenzene since the
NPDWR was published. EPA therefore
conducted a literature search for
relevant studies on the toxicology of
monochlorobenzene including its
potential developmental and
reproductive toxicity as a part of the
Six-Year Review process. The literature
search did not identify any new studies
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that warrant a review of the RfD or the
cancer classification (USEPA, 2002i).
A review of analytical or treatment
feasibility is not necessary for
monochlorobenzene because changes to
the MCLG are not warranted at this time
and the current MCL is set at the MCLG.
In addition, the results of EPA's review
of possible "Other regulatory revisions"
did not identify any
monochlorobenzene-specific issues
(USEPA, 20Q2e). Since EPA did not
identify a health, or technology basis for
revising the monochlorobenzene
NPDVVR, the Agency did not conduct a
detailed occurrence and exposure
analysis.
c. Preliminary Decision. After
reviewing the results of the pertinent
technical analyses, the Agency believes
tho NPDVVR for monochlorobenzene
remains appropriate and thus, it is not
subject to revision at this time.
48. Nitrate (as N)
a. Background. EPA published the
current NPDWR for nitrate on January
30,1991 (56 FR 3526 (USEPA, 1991a)).
The NPDWR established an MCLG and
MCL of 10 mg/L (as nitrogen (N)). The
Agency based the MCLG on an RfD of
1.6 mg/kg/day (as N) and a cancer
classification of D, not classifiable as to
human carcinogenicity.
b. Technical Reviews. The current RfD
and the MCLG were established to
protect infants, the most susceptible
segment of the population. At the
request of EPA ", NAS completed an
assessment of nitrate in 1995 (NAS,
1995) and did not find any new data
that would warrant a review of the RfD
or cancer classification. The literature
search conducted during the'Six-Year
Review also did not identify any new
studies that warrant a review of the RfD
or cancer classification (USEPA, 2002i).
The current MCL is not limited by the
analytical or treatment feasibility.
Review of these capabilities is not
necessary since no changes to the MCL
are warranted at this time.
As a part of the Six-Year Review,
several States have suggested that EPA
revise the current monitoring
requirements for nitrate to allow less
frequent monitoring in systems with
consistently low nitrate/nitrite levels.
Some have suggested that EPA place
nitrate monitoring under.the same
monitoring framework used for most
other inorganic chemicals (USEPA,
2002e). EPA previously considered
these suggestions when the Agency
" This request fulfilled tho commitment EPA
mado to form an intor-agency workgroup to
determine what, if any, oncogonic risks oxist (56 FR
3520 ol 3538, January 30th. 1891 (USEPA, 1991a)).
considered chemical monitoring reform
and decided not to change the frequency
of nitrate monitoring. However, primacy
agencies currently have the flexibility to
reduce nitrate monitoring for ground
water systems from annually to biennial
if the Primacy Agency adopts (and EPA
approves) an alternative monitoring
provision. EPA has established guidance
for such alternative monitoring in the
Alternative Monitoring Guidelines
(USEPA, 1997a). These guidelines were
issued after consultation with
stakeholders and no new information
has been identified that warrants
reconsideration of this issue.
Detailed occurrence and exposure
analysis is not necessary since none of
the analyses indicate a change to the
nitrate regulation at this time.
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for nitrate is appropriate at this
time because: (1) There are no changes
in the health risk assessment for nitrate;
and (2) no other new data were
identified that indicate the need to
revise the NPDWR at this time. (Also see
section V.A.49.C of today's action for a
discussion of the Agency's decision
pertaining to the joint nitrate/nitrite
standard.!
49. Nitrite (as N)
. a. Background. EPA published the
current NPDWR for nitrite on January
30,1991 (56 FR 3526 (USEPA, 1991a)).
The NPDWR established an MCLG and
an MCL of 1.0 mg/L (as N). The Agency
based the MCLG on an RfD of 0.16 mg/
kg/day (as N) and a cancer classification
of D, not classifiable as to human
carcinogenicity. '
b. Technical Reviews. The current RfD
and MCLG were established to protect
infants, the most susceptible segment of
the population. At the request of EPA,
NAS completed an assessment of nitrite
in 1995. (NAS, 1995) and did not find
any new studies that warrant a review
of the RfD or cancer classification. The
literature search conducted" during the
Six-Year Review did not identify any
new studies that warrant a review of the
RfD or the cancer classification (USEPA,
20021).
The current MCL is not limited by the
analytical or treatment feasibility.
Review of these capabilities is not
necessary since no changes to the MCL
are warranted at this time.
As a part of the Six-Year Review of
"other regulatory revisions," EPA
received several suggestions regarding
the current monitoring requirements for
nitrite.12 Stakeholders raised several
potential issues concerning the current
monitoring requirements (USEPA,
2002e). These issues include:
• A need for flexibility for States to
require systems to collect a distribution
system sample for nitrite under certain
circumstances, such as if the entry point
sample is greater than 50 percent of the
MCL, if there is a large amount of
ammonia in the raw water, or if
chloramines are applied;
• A need for flexibility for States to
require systems to monitor for ammonia
in raw water; and
• Flexibility to eliminate nitrite
monitoring when a disinfection residual
is present.
EPA does not believe it has sufficient
data at this time on which to base
possible changes in monitoring
• requirements (USEPA, 2002e).
Detailed occurrence and exposure
analysis is not necessary since none of
the technical analyses indicate a change
to the nitrite regulation at this time.
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for nitrite is appropriate at thij|
time because: (1) There are no changesp
in the health risk assessment for nitrite;
and (2) no other new data were
identified that indicate the need to
revise the NPDWR at this time.
EPA also published an MCLG and an
MCL of 10 mg/L (as N) for the sum of
nitrate and nitrite on January 30,1991
(56 FR 3526 (USEPA, 1991a)). The
Agency established this joint nitrate/
nitrite standard to account for the
possible additive toxicity of these two
chemicals and also to protect against the
deterioration of drinking water quality,
since the presence of nitrite in water is
indicative of water contaminated with
sewage. The Agency has not identified
any new data as a part of the Six-Year
Review process that indicates that this
joint nitrate/nitrite standard needs to be
revised.
50. Oxamyl (Vydate)
a. Background. EPA published the
current NPDWR for oxamyl on July 17,
1992 (57 FR 31776 (USEPA, 1992)). The
NPDWR established an MCLG and an
MCL of 0.2 mg/L. The Agency based the
12 Current monitoring requirements for nitrite: All
community water systems (CWSs), non-transient.
non-community water systems (NTNCWSs), and
transient non-community water systems (TNCWSs)
must monitor for nitrite at each entry point to the
distribution system. If the analytical result is less
than Vz the MCL (0.5 mg/L), then the system must
monitor at a frequency specified by the Primary
Agency. If the sample result is greater than or equal
to Vi the MCL (0.5 mg/L) then the entry point that
exceeded the trigger level must begin quarterly
monitoring. The Primary Agency may reduce the
quarterly monitoring to annual monitoring after the
system has collected four quarters of data. However,
the system must collect subsequent samples during
the quarter that yielded the highest analytical
result.
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19077
MCLG on an RfD of 0.025 mg/kg/day
and a cancer classification of E,
evidence of non-carcinogenicity for
humans.
b. Technical Reviews. The Agency
identified a change in the health
assessment that supports consideration
of whether to revise the MCLG (USEPA,
2002i). EPA updated the risk assessment
in 2000. This new risk assessment
considered relevant studies that had
become available on the toxicity of
oxamyl including its potential
developmental and reproductive
toxicity. The new risk assessment
revised the RfD from 0.025 mg/kg/day to
0.001 mg/kg/day (USEPA, 2000e).
Based on the change in the RfD for
oxamyl and using a 20 percent RSC13,
EPA believes that any revision to the
MCLG is not likely to be lower than
0.007 mg/L.
In setting the MCLG/MCL in 1992, the
Agency determined the PQL for oxamyl
to be 0.02 mg/L and analytical
13 This is the RSC used for the current MCLG and
also the default value. EPA has no reason to believe
that the RSC for oxamyl would change. See
Appendix A for further discussion of the RSC.
feasibility was not considered to be a
limitation. EPA has analyzed more
recent WS data to determine if
analytical feasibility is likely to be a
limiting factor in setting a lower MCL
(USEPA, 2002d). In addition, the
Agency evaluated whether more
sensitive methods have been approved
and are in use by a wide number of
laboratories. The results of these
analyses indicate that analytical
feasibility is likely to be a limiting factor
if EPA were to revise the MCLG and
MCL. Although not definitive, the
available WS data indicate that the PQL
could lie between 0.02 and 0.04 mg/L.
EPA used the 0.02 mg/L and the 0.04
mg/L values as thresholds in the
occurrence analysis discussed in this
section.
Since the health effects technical
review supports consideration of
whether a revision to the MCLG and
MCL may be appropriate, EPA evaluated
whether treatment feasibility is likely to
pose any limitations (USEPA, 2002k).
The current BAT for oxamyl is GAG.
Compliance technologies for small
systems include GAG, PAC, and POU
GAG. EPA believes that the BAT and
compliance technologies are still
practical and would not pose any
limitations for oxamyl at a possibly
lower level (i.e., a possibly lower MCL).
The results of EPA's review of
possible "other regulatory revisions"
did not identify any issues that are
specific to oxamyl (USEPA, 2002e).
EPA evaluated the results of the
occurrence and exposure analyses for
oxamyl to determine whether changes to
the MCL might be appropriate and
likely to result in additional public
health protection if the PQL were
recalculated (USEPA, 2002g; USEPA,
2002h). Table V—12 shows the results of
the detailed occurrence and exposure
analyses based on the 16-State cross-
section for several concentrations: the
current MCL (0.2 mg/L), the possible
upper and lower PQLs based on the
analytical feasibility analysis (0.02 and
0.04 mg/L), and the possible lower limit
of any MCLG value (0.007 mg/L). Based
on the detailed analysis of 16 cross-
section States, it appears that oxamyl is
unlikely to occur at the current MCL or
any potential MCL value.
BILLING CODE 6560-50-P
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Table V-12: Oxamyl Occurrence1
Systems2
Threshold
(in mg/L)
Current MCL 0.2
Possible upper PQL< 0.04
Possible lower PQL5 0.02
Possible MCL if
feasible to set at 0.007
MCLG6
16 Cross-Section
States - Total
Systems with Data
13,157
13,157
13,157
13,157
Estimated # Systems
> Threshold
(credible intervals)3
0 (0-0)
0 (0-0)
0 (0-0)
0 (0-0)
Estimated % Systems
> Threshold
(credible intervals)3
0.000% (0.000% - 0.000%)
0.000% (0.000% - 0.000%)
0.000% (0.000% - 0.000%)
0.0000456% (0.000% -0.000%)
Population Served by Systems2
Threshold
(in mg/L)
Current MCL 0.2
Possible upper PQL< 0.04
Possible lower PQL3 0.02
Possible MCL if
feasible to set at 0.007
MCLG0
16 Cross-Section
States - Total
Population Served
by Systems with
Data
92,345,800
92,345,800
92,345,800
92,345,800
Estimated
Population Served
by Systems >
Threshold
(credible intervals)3
0 (0-0)
0 (0-0)
0 (0-0)
0 (0-0)
Estimated % Population Served by
Systems > Threshold
(credible intervals)3
0.000% (0.000% - 0.000%)
0.000% (0.000% - 0.000%)
0.000% (0.000% -0.000%) .
0.0000323% (0.000% - 0.000%)
Notes:
1 Results are based on the number and percent of systems (and the corresponding population served by those systems) with estimated
mean concentrations above the specified threshold.
1 All percentages are shown to three significant figures. All system values are rounded to the nearest whole system. All population
values are rounded to the nearest hundred.
J "Credible intervals" are generated to quantify the uncertainty around each estimated probability in the Bayesian analysis of the
occurrence data. For further explanation of credible intervals and the Bayesian analysis, please see "Occurrence Estimation
Methodology and Occurrence Findings Report for the Six-Year Regulatory Review" (USEPA, 2002g).
* The "possible upper PQL" is the likely upper limit of any potential PQL revision.
5 The "possible lower PQL" is the likely lower limit of any potential PQL revision.
* The "possible MCL if feasible to set at MCLG value" is the lowest level indicated by the new health assessment, assuming there wer<
no limitations due to analytical feasibility.
BILLING CODE 6560-50-C
c. Preliminary Decision. Although
there are new data indicating that it
might ba possible to lower the MCLG
and the MCL, analytical feasibility
limitations would limit the extent to
which the MCL could be revised at the
present time. Because any changes in
the NPDWR based on setting the MCL
at the limitations of analytical feasibility
are unlikely to significantly improve the
level of public health protection, EPA
does not believe a revision to the
NPDWR for oxamyl is appropriate at
this time. In addition, because oxamyl
appears to occur infrequently at ,
concentrations at or below the current
MCL, EPA believes that efforts to
research more sensitive analytical
methods and/or to revise the MCL are
low priority and should not be pursued
at the present time. EPA requests
comment on the extent to which oxamyl
is likely to occur at levels between 0.007
and 0.2 mg/L at PWSs. Commenters
who disagree with the occurrence
evaluation should submit data to
support their rationale and evidence to
show that oxamyl is of national concern
at PWSs at the thresholds evaluated.
EPA does plan to update the Health
Advisory for oxamyl to reflect the new
RfD.
51. Pentachlorophenol
a. Background. EPA published the
current NPDWR for pentachlorophenol
on July 1, 1991 (56 FR 30266 (USEPA,
1991c)). The NPDWR established an
MCLG of zero based on a cancer
classification of B2, probable human
carcinogen. The NPDWR also
established an MCL of 0.001 mg/L,
based on analytical feasibility.
b. Technical Reviews. The Agency has
initiated a reassessment of the health
risks resulting from exposure to
pentachlorophenol. The revised risk
assessment will consider relevant
studies that have become available on
the toxicity of pentachlorophenol
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19079
including its potential developmental
and reproductive toxicity. The Agency
expects the new risk assessment to be
completed in the 2002 or 2003 time
frame (USEPA, 2002i).
c. Preliminary Decision. The Agency
does not helieve a revision to the
NPDWR for pentachlorophenol is
appropriate at this time because a
reassessment of the health risks
resulting from exposure to
pentachlorophenol is. ongoing.
52. Picloram
a. Background. EPA published the
current NPDWR for picloram on July 17,
1992 (57 FR 31776 (USEPA, 1992)). The
NPDWR established an MCLG and an
MCL of 0.5 mg/L. The Agency based the
MCLG on an RfD of 0.07 mg/kg/day and
a cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency
identified a change in the health
assessment that could lead to a change
in the MCLG (USEPA, 2002i). EPA
updated the risk assessment in 1998.
This new risk assessment considered
relevant studies that had become'
available on the toxicity of picloram
including its potential developmental
and reproductive toxicity. The new risk
assessment revised the RfD from 0.07
mg/kg/day to 0.20 mg/kg/day and
classified picloram as Group E, evidence
of noncarcinogenicity for humans,
according to the 1986 Cancer
Guidelines. Picloram has not been
evaluated against the Proposed 1996 .
Cancer Guidelines.
Based on the change in the RfD for
picloram and using a 20 percent RSC,14
EPA believes that any revision to the
MCLG is not likely to be higher than 1
mg/L (an increase in the MCLG).
Analytical or treatment feasibility do
not pose any limitations for the current
MCL and would not be a limiting factor
if EPA were to raise the MCLG. The
Agency's .review of possible "other
regulatory revisions" did not identify
any issues that are specific to picloram
(USEPA, 2002e).
EPA evaluated the results of the
occurrence and exposure analyses for
picloram to determine whether possible
changes to the MCL would be likely to
result in opportunities for significant
cost savings to PWSs and their
customers (USEPA, 2002g; USEPA,
2002h). Table V-13 shows the results of
the detailed occurrence and exposure
analysis based on the 16-State cross-
section for the current MCL (0.5 mg/L),
and the concentration that would be
considered if the EPA revised the MCLG
and MCL (i.e., the possible MCLG/MCL
of 1 mg/L) based on the new RfD and
a 20 percent RSC. Based on the detailed
analysis, it appears that picloram is
unlikely to occur at concentrations
above 0.5 mg/L in the States used for the
cross-section.
BILLING CODE 6560-50-P
Table V-13: Picloram Occurrence1
Systems2
Threshold
(in mg/L)
Possible .
MCLG/MCL4
Current MCL 0.5
16 Cross-Section
States - Total
Systems with Data
12,907
12,907
Estimated # Systems
> Threshold
(credible intervals)3
0 (0-0)
0 (0-0)
Estimated % Systems
> Threshold
(credible intervals)3
0.000% (0.000% - 0.000%)
0.000% (0.000% -0.000%)
Population Served by Systems2
Threshold
(in mg/L)
Possible .
MCLG/MCL4
Current MCL 0.5
.16 Cross-Section
States - Total
Population Served
by Systems with
Data
93,235,500
93,235,500
Estimated Population
Served by Systems >.
Threshold
(credible intervals)3
0 (0-0)
0 (0-0)
Estimated % Population Served
by Systems > Threshold
(credible intervals)3
i
0.000% (0.000% -0.000%)
0.000% (0.000% -0.000%)
Notes: . ' . '
1 Results are based on the number and percent of systems (and the corresponding population served by those systems) with estimated
mean concentrations above the specified threshold.
2 All percentages are shown to three significant figures. All system values are rounded to the nearest whole system. All population
values are rounded to the nearest hundred.
3 "Credible intervals" are generated to quantify the uncertainty around each estimated probability in the Bayesian analysis of the
occurrence data. For further explanation of credible intervals and the Bayesian analysis, please see "Occurrence Estimation
Methodology and Occurrence Findings Report for the Six- Year Regulatory Review" (USEPA, 2002g).
4 The "possible MCLG/MCL revision" is the likely upper limit of any revised MCLG/MCL.
BILLING CODE 6560-50-C
11 This is the RSC used for the current MCLG and
also the default value. EPA has no reason to believe
that the RSC for picloram would change. See
Appendix A for further discussion of the RSC.
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The results of the detailed occurrence
and exposure analysis indicate that few,
if any, of the 12,907 systems sampled in
the 16 cross-section States might be
affected if EPA were to raise the MCLG/
MCL.
c. Preliminary Decision. Although
there are new data that support
consideration of whether to revise the
MCLG/MCL for picloram, EPA does not
believe a revision to the NPDWR for
picloram is appropriate at this time. The
Agency believes that any change in the .
MCLG/MCL would be unlikely to
provide an opportunity for significant
cost savings to PWSs.
53. Polychlorinated Biphenyls (PCBs)
a. Background. EPA published the
current NPDWR for PCBs on January 30,
1991 (56 FR 3526 (USEPA, 1991a)). The
NPDWR established an MCLG of zero
based on a cancer classification of B2,
probable human carcinogen. The
NPDWR also established an MCL of
0.0005 mg/L based on analytical
feasibility.
b. Technical Reviews. The Agency has
initiated a reassessment of the health
risks resulting from exposure to PCBs.
The revised risk assessment will
consider relevant studies that have
become available on the toxicity of PCBs
including their potential developmental
and reproductive toxicity. The Agency
expects the new risk assessment to be
completed in the 2002 or 2003 time
frame (USEPA, 20021).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for PCBs is appropriate at this
time because a reassessment of the
health risks resulting from exposure to
PCBs is ongoing.
54. Selenium
a. Background. EPA published the
current NPDWR for selenium on January
30,1991 (56 FR 3526 (USEPA, 1991a)).
The NPDWR established an MCLG and
an MCL of 0.05 mg/L. The Agency based
the MCLG on an RfD of 0.005 mg/kg/day
and a cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency has
not updated the risk assessment for
selenium since the NPDWR was
published (USEPA, 2002i). However, a
2000 NAS assessment of selenium
supports the current RfD based on •
epidemiological studies of selenosis in
humans (NAS, 2000b). The NAS study
considered relevant studies that were
available on the toxicity of selenium,
including its developmental and
reproductive toxicity, and established a
tolerable upper intake level of 0.4 mg/
day for adolescents and adults, a value
which is equivalent to the RfD.
A review of analytical or treatment
feasibility is not necessary for selenium
because changes to the MCLG are not
warranted at this time, and the current
MCL is set at the MCLG. In addition, the
results of EPA's review of possible
"other regulatory revisions" did not
identify any selenium-specific issues
(USEPA, 2002e). Since EPA did not
identify a health or technology basis for
revising the selenium NPDWR, the
Agency did not conduct a detailed
occurrence and exposure analysis.
c. Preliminary Decision. After
reviewing the results of the pertinent
technical analyses, the Agency believes
the NPDWR for selenium remains
appropriate and thus, it is not subject to
revision at this time. .
55. Simazine
a. Background. EPA published the
current NPDWR for simazine on July 17,
1992 (57 FR 31776 (USEPA, 1992)). The
NPDWR established an MCLG and an
MCL of 0.004 mg/L. The Agency based
the MCLG on an RfD of 0.005 mg/kg/day
and a cancer classification of C, possible
human carcinogen.
'b. Technical Reviews. The Agency has
initiated a reassessment of the health
risks resulting from exposure to
simazine. The revised risk assessment
will consider relevant studies that have
become available on the toxicity of
simazine including its potential
developmental and reproductive
toxicity. The Agency expects the new
risk assessment to be completed in the
2003 or 2004 time frame (USEPA,
20021).
c. Preliminary Decision/The Agency
does not believe a revision to the
NPDWR for simazine is appropriate at
this time because a reassessment of the
health risks resulting from exposure to
simazine is ongoing. The Agency is also
re-examining all the triazines and their
degradation products as part of its CCL
in order to fill any necessary research
gaps to enable the Agency to determine
• whether or not to regulate any or all of
the contaminants in this group of
compounds.
56. Styrene
a. Background. EPA published the
current NPDWR for styrene on January
30,1991 (56 FR 3526 (USEPA, 1991a)).
The NPDWR established an MCLG and
an MCL of 0.1 mg/L. The Agency based
the MCLG on an RfD of 0.2 mg/kg/day
and a cancer classification of C, possible
human carcinogen.
b. Technical Reviews. The Agency has
initiated a reassessment of the health
risks resulting from exposure to styrene.
The revised risk assessment will
consider relevant studies that have
become available on the toxicity of
styrene including its potential
developmental and reproductive
toxicity. The Agency expects the new
risk assessment to be completed in the
2002 or 2003 time frame (USEPA,
20021).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for styrene is appropriate at
this time because a reassessment of the
health risks resulting from exposure to
styrene is ongoing.
57. 2,3,7,8-TCDD (Dioxin)
a. Background. EPA published the
current NPDWR for dioxin on July 17,
1992 (57 FR 31776 (USEPA, 1992)). The
NPDWR established an MCLG of zero
based on a cancer classification of B2,
probable human carcinogen. The
NPDWR also established an MCL of
3xlO~8 mg/L based on analytical -,
feasibility.
b. Technical Reviews. The Agency has
conducted a comprehensive assessment
of the exposure and potential human
health effects of dioxin including its
potential developmental and
reproductive toxicity. The draft
document has been reviewed by the
SAB (USEPA, 2001b). The Agency is
presently in the process of addressing
SAB and public comments, and expects
to complete the risk assessment in the
2002 or 2003 time frame.
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for dioxin is appropriate at this
time because a reassessment of the
health risks resulting from exposure to
dioxin is ongoing.
58. Tetrachloroethylene
a. Background. EPA published the
current NPDWR for tetrachlorpethylene
on January 30, 1991 (56 FR 3526
(USEPA, 1991a)). The NPDWR
established an MCLG of zero based on
a cancer classification of B2, probable
human carcinogen. The NPDWR also
established an MCL of 0.005 mg/L based
on analytical feasibility.
b. Technical Reviews. EPA has
initiated a reassessment of the health
risks resulting from exposure to
tetrachloroethylene. The revised risk
assessment will consider relevant
studies that have become available on
the toxicity of tetrachloroethylene
including its potential developmental
and reproductive toxicity. The Agency
expects the new risk assessment to be
completed in the 2002 or 2003 time
frame (USEPA, 20021).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for tetrachloroethylene is
appropriate at this time because a
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19081
reassessment of the health risks
resulting from exposure to
tetrachloroethylene is ongoing.
59. Thallium
a. Background. EPA published the
current NPDWR for thallium on July 17,
1992 (57 FR 3526 (USEPA, 1991a)). The
NPDWR established an MCLG of 0.0005
mg/L based on an RfD of 0.00007 mg/
kg/day and a cancer classification of ,D,
not classifiable as to human
carcinogenicity. The NPDWR also
established an MCL of 0.002 mg/L based
on analytical feasibility.
b. Technical Reviews. The results of
the health effects technical review
identified some information on
reproductive effects that indicate the
need to update the Agency's risk
assessment for thallium (USEPA, 20021].
In light of this information, EPA has
initiated a reassessment of the health
risks resulting from exposure to
thallium and has already solicited
scientific information from the public
for consideration (67 FR 1212, January
9, 2002 (USEPA, 2002a)). The new risk
assessment will consider relevant data
on the toxicity of thallium including its
potential developmental and
reproductive toxicity. Because the new
assessment is not expected to be
completed until the 2004 or 2005 time
frame, EPA does not believe it is
• appropriate to revise the MCLG at this
time.
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for thallium is appropriate at
this time. A reassessment of the health
risks has been initiated and the Agency
does not believe it is appropriate to
revise the NPDWR while that effort is in
process.
60. Toluene
a. Background. EPA published the
current NPDWR for toluene on January
30, 1991 (56 FR 3526 (USEPA, 1991a)).
' The NPDWR established an MCLG and
an MCL of 1 mg/L. The Agency based
the MCLG on an RfD of 0.2 mg/kg/day
and a cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency has
initiated a reassessment of the health
risks resulting from exposure to toluene.
The revised risk assessment will
consider relevant studies that have
become available on the toxicity of
toluene including its potential
developmental and reproductive
toxicity. The Agency expects the new
risk assessment to be completed in the
2002 or 2003 time frame (USEPA,
20021).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for toluene is appropriate at
this time because a reassessment of the
health risks resulting from exposure to
toluene is ongoing.
61. Toxaphene
a. Background. EPA published the
current NPDWR for toxaphene on
January 30,1991 (56 FR 3526 (USEPA,
1991a)). The NPDWR established an
MCLG of zero based on a cancer
classification of B2, probable human
carcinogen. The NPDWR also
established an MCL of 0.003 mg/L based
on analytical feasibility.
b. Technical Reviews. The Agency has
not updated the health risk assessment
for toxaphene since the NPDWR was
published; however, ATSDR completed
a toxicological profile for toxaphene in
1996 (ATSDR, 1996d). This assessment
and other recent information do not
warrant a review of the cancer
classification because the data indicate
that toxaphene is mutagenic and would
be .evaluated using a linear dose-
response approach (USEPA, 2002i).
Accordingly, the MCLG remains at zero
and the Agency believes that a further
review of the health effects of toxaphene
is not warranted at this time.
The current MCL for toxaphene is
based on a PQL of 0.003 mg/L. As a part
of the Six-Year Review, EPA analyzed
more recent WS data to determine if it
might be possible to recalculate the PQL
(USEPA, 2002d). In addition, the
Agency evaluated whether more
sensitive analytical methods have been
approved and put into use by a wide
number of laboratories. The results of
these analyses indicate that some
improvement in analytical feasibility
might exist. Evaluation of the WS data
shows that EPA Regional and State
laboratories exhibit greater than 90
percent laboratory passing rates at
concentrations around the current PQL
of 0.003 mg/L. Because most of the
laboratory passing rates exceeded the 75
percent criterion typically used to
derive a PQL from WS studies, this
information indicates that a lower PQL
corresponding to the 75 percent passing
rate might exist for toxaphene. While
this information is indicative of a
possibly lower PQL, the WS data are
insufficient at this time to actually
recalculate what the loiter PQL for
toxaphene might be.
Using information about the
analytical methods most widely used to
report results in the WS studies, the
MDLs for these methods, and the 10
times MDL multiplier, EPA estimated
what the possibly lower PQL/MCL
might be. For the analysis of toxaphene
in the more recent WS studies,
laboratories predominantly used EPA
Methods 508 (GC/MS) and 505 (Purge
and Trap GC). No MDL data are
available for EPA Method 508 and the
MDL for 505 is listed as 0.001 mg/L. A
10 times MDL multiplier based on EPA
Method 505 predicts a PQL of 0.01 mg/
L, which is higher than the current PQL.
Therefore, the 10 times multiplier could
not be used to predict a lower PQL and
EPA did not use this higher value as a
threshold in the occurrence analysis f
discussed in this section. Instead, EPA
used concentration thresholds of one-
half the current MCL and the lower
limit of detection reported by the States.
EPA believes if a lower. PQL does exist,
that the magnitude of the change would
be minimal.
Since the analytical feasibility
analysis indicates that the PQL for
• toxaphene (and therefore the MCL)
could possibly be lower if EPA had
more definitive data to recalculate the
PQL, EPA considered whether treatment
feasibility is likely to pose any
limitations (USEPA, 2002k). The current
BAT for toxaphene is GAG. Compliance
technologies for small systems include
GAG, PAC, and POU GAG. EPA believes
that the BAT and compliance
technologies are still practical and
would not pose any limitations for
' toxaphene at a possibly lower MCL.
The results of EPA's review of
possible "other regulatory revisions"
did not identify any issues that are
specific to toxaphene (USEPA, 2002e).
EPA evaluated the results of the
occurrence and exposure analyses for
toxaphene to determine whether
changes to the MCL might be
appropriate and likely to result in
additional public health protection if
EPA had sufficient data to recalculate
the PQL (USEPA, 2002g; USEPA,
2002h). Table V-14 shows the results of
the detailed occurrence and exposure
analyses based on the 16-State cross-
section for the current MCL (0.003 mg/
L), one-half the current MCL (0.0015
• mg/L), and the lower level of detection
reported by the States (0.001 mg/L).
BILLING CODE 6560-50-P
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Table V-14: Toxaphene Occurrence1
Systems2
Threshold
(in mg/L)
Current MCL 0.003
JstheC?!S;t o.oois
MCL
Lower level of
detection Q
reported by
States
16 Cross-Section
States - Total
Systems with
Data
13,805
13,805
13,805
Estimated # Systems
> Threshold
(credible intervals)3
0 (0-0)
0 (0-0)
I4 (0 - 0)
Estimated % Systems
> Threshold
(credible intervals)3
0.000% (0.000% - 0.000%)
0.000% (0.000% - 0.000%)
0.000145% (0.000% -0.000%)
Population Served by Systems2
Threshold
(in mg/L)
Current MCL 0.003
"the Current 0.0015
MCL
Lower level of
dete(-?°n 0.001
reported by
States
16 Cross-Section
States - Total
Population Served
by Systems with
Data
95,108,100
95,108,100
95,108,100
Estimated Population Served
by Systems > Threshold
(credible intervals)3
0 (0-0)
0 (0-0)
800 (0 - 0)
Estimated % Population
Served by Systems > Threshold
(credible intervals)3
0.000% (0.000% - 0.000%)
0.000% (0.000% -0.000%)
0.000833% (0.000% - 0.000%)
Notes:
' Results are based on the number and percent of systems (and the corresponding population served by those systems) with estimated
mean concentrations above the specified threshold.
2 All percentages are shown to three significant figures. AH system values are rounded to the nearest whole system. All population
values are rounded to the nearest hundred.
3 "Credible intervals" are generated to quantify the uncertainty around each estimated probability in the Bayesian analysis of the
occurrence data. For further explanation of credible intervals and the Bayesian analysis, please see "Occurrence Estimation
Methodology and Occurrence Findings Report for the Six- Year Regulatory Review" (USEPA, 2002g).
4 Model output resulted in an estimate of less than half a system; however, the fraction was rounded up to one.
BILLING CODE 65SO-50-C
The detailed occurrence and exposure
analysis indicates that toxaphene is
unlikely to occur at the current MCL or
any potential MCL revision for the
States used! in the cross-section. Since
toxaphene uses were canceled in the
United States in 1990 and since it is
subject to the United Nations Prior
Informed Consent (USEPA, 2002g;
USEPA, 2002h), EPA expects the
occurrence of toxaphene in PWSs to be
rare.
c. Preliminary Decision. Although
there are new data that support
consideration of a possibly lower PQL
(and therefore a possibly lower MCL),
EPA does not believe a revision to the
NPDWR for toxaphene is appropriate at
this time. The Agency does not have
sufficient data at this time on which to
base a PQL recalculation and hence an
MCL revision. Also, the Agency believes
that any change in the PQL would be
minimal and unlikely to significantly
improve the level of public health
protection because toxaphene appears to
occur infrequently at concentrations at
or below the current MCL.
62. 2,4,5-TP (Silvex; 2,4,5-
Trichlorophenoxypropionic Acid)
a. Background. EPA published the
current NPDWR for 2,4,5-TP on January
1 30,1991 (56 FR 3526 (USEPA, 1991a)).
The NPDWR established an MCLG and
an MCL of 0.05 mg/L. The Agency based
the MCLG on an RfD of 0.008 mg/kg/day
and a cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency has
not updated the health risk assessment
for 2,4,5-TP since the NPDWR was
published. Therefore, as part of the Six-
Year Review process, EPA conducted a
literature search for relevant data on the
toxicology of 2,4,5-TP including its
potential developmental and
reproductive toxicity. The literature
search did not identify any new studies
that warrant a review of the RfD or the
cancer classification (USEPA, 20021).
A review of analytical or treatment
feasibility is not necessary for 2,4,5-TP
because changes to the MCLG are not
warranted at this time and the current
MCL is set at the MCLG. In addition, the
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19083
results of EPA's review of possible
"other regulatory revisions" did not
identify any 2,4,5-TP-specific issues
(USEPA, 20026). Since EPA did not
identify a health or technology basis for
revising the 2,4,5-TP NPDWR, the
Agency did not conduct a detailed
occurrence and exposure, analysis.
c. Preliminary Decision. After
reviewing the results of the pertinent
technical analyses, the Agency believes
the NPDWR for 2,4,5-TP remains
appropriate and thus, it is not subject to
revision at this time.
63.1,2,4-Trichlorobenzene
a. Background. EPA published the
current NPDWR for 1,2,4-
trichlorobenzene on July 17,1992 (57
FR 31776 (USEPA, 1992)). The NPDWR
established an MCLG and an MCL of
0.07 mg/L. The Agency based the MCLG
on an RfD of 0.01 mg/kg/day and a
cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency has
not updated the health risk assessment
for 1,2,4-trichlorobenzene since the
NPDWR was published. Therefore, as
part of the Six-Year Review process,
EPA conducted a literature search for
relevant data on the toxicology of 1,2,4-
trichlorobenzene, including its potential
developmental and reproductive
toxicity. The literature search did not
identify any. new studies that warrant a
review of the RfD or the cancer
classification (USEPA, 20021).
A review of analytical or treatment
feasibility is not necessary for 1,2,4-
trichlorobenzene because changes to the
MCLG are not warranted at this time
and the current MCL is set at the MCLG.
In addition, the results of EPA's review .
of possible "other regulatory revisions"
did not identify any 1,2,4-
trichlorobenzene-specific issues
(USEPA, 2002e). Since EPA did not
identify a health or technology basis for
revising the 1,2,4-trichlorobenzene
NPDWR, the Agency did not conduct a
detailed occurrence and exposure
analysis.
c. Preliminary Decision. After
reviewing the results of the pertinent
technical analyses, the Agency believes
the NPDWR for 1,2,4-trichlorobenzene
remains appropriate and thus, it is not
subject to revision at this time.
64.1,1,1-Trichloroethane
a. Background. EPA published the
current NPDWR for 1,1,1-
trichloroethane on July 8, 1987 (52 FR
25690 (USEPA, 1987)). The NPDWR
established an MCLG and an MCL of
0.20 mg/L. The Agency developed the
MCLG based on an RfD of 0.035 mg/kg/
day derived from an inhalation study
and a cancer classification of D, not
classifiable as to human carcinogenicity.
b. Technical Reviews. The Agency has
initiated a reassessment of the health
risks resulting from exposure to 1,1,1-
trichloroethane. The revised risk
assessment will consider relevant
studies that have become available on
the toxicity of toluene including its
'potential developmental and
reproductive toxicity. The Agency
expects the new risk assessment to be
completed in the 2003 or 2004 time
frame (USEPA, 2002i).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for 1,1,1-trichloroethane is
appropriate at this,time because a
reassessment of the health risks
resulting from exposure to 1,1,1-
trichloroethane is ongoing.
65. 1,1,2-Trichloroethane
a. Background. EPA published the
current NPDWR for 1,1,2-
trichloroethane on July 17,1992 (57 FR
31776 (USEPA, 1992)). The NPDWR
established an MCLG of 0.003 mg/L
based on an RfD of 0.004 mg/kg/day and
a cancer classification of C, possible
human carcinogen. The NPDWR also
established an MCL of 0.005 mg/L based
on analytical feasibility.
b. Technical Reviews. The Agency has
not updated the health risk assessment
for 1,1,2-trichloroethane since the
NPDWR was published. Therefore, as
part of the Six-Year Review process,
EPA conducted a literature search for
relevant data on the toxicology of 1,1,2-
trichloroethane including its potential
developmental and reproductive
toxicity. The literature search did not
identify any studies that warrant a
review of the RfD or the cancer
classification (USEPA, 2002i).
The current MCL for 1,1,2-
trichloroethane is based on a PQL of
0.005 mg/L. As a part of the Six-Year
Review, EPA analyzed more recent WS
data to determine if it might be possible
to recalculate the PQL (USEPA, 2002d).
In addition, the Agency evaluated
whether more sensitive analytical
methods have been approved and put
into use by a wide number of
laboratories. The results of these
. analyses indicate that a slight
improvement in analytical feasibility
might exist. Evaluation of the WS data
shows that EPA Regional and State
laboratories exhibit greater than 90
percent laboratory passing rates at
concentrations around the current PQL
of 0.005 mg/L. Because most of the
laboratory passing rates exceeded the 75
percent criterion typically used to
derive a PQL from WS studies, this
information indicates that a lower PQL
corresponding to the 75 percent passing
rate might exist for 1,1,2-
trichloroethane. While this information
is indicative of a possibly lower PQL,
the WS data are insufficient at this time
to actually recalculate what the lower
PQL for 1,1,2-trichloroethane might be.
Using information about the
analytical methods most widely used to •
report results in the WS studies, the
MDLs for these methods, and the 10
times MDL multiplier, EPA estimated
what the possibly lower PQL/MCL
might be. For the analysis of 1,1,2-
trichloroethane in the more recent WS
studies, laboratories predominantly
used EPA Methods 524.2 (GC/MS) and
502.2 (Purge and Trap GC), which both
have upper limit MDLs of 0.00003 mg/
L. A 10 times MDL multiplier predicts
a PQL of 0.0003 mg/L. Since this value
is below the current MCLG, this
supports consideration of whether the
MCL might be set at the MCLG if
sufficient data were available to
recalculate the PQL. EPA did not use
the possibly lower PQL as a threshold
in the occurrence analysis but instead
used 0.003 mg/L (the current MCLG)
since this is the lowest level to which
the MCL would possibly be revised.
Since the analytical feasibility
analysis indicates that the PQL for 1,1,2-
trichloroethane (and therefore the MCL)
could possibly be lower if EPA had
more definitive data to recalculate the
PQL, EPA considered whether treatment
feasibility is likely to pose any
limitations (USEPA, 2002k). The current
BATs for 1,1,2-trichloroethane include
both PTA and GAG. Small system
compliance technologies for 1,1,2-
trichloroethane include GAG and
several aeration technologies. EPA
believes that these BATs and
compliance technologies are still
practical and would not pose any
limitations for 1,1,2-trichloroethane at a
possibly lower level.
The results of EPA's review of
possible "other regulatory revisions"
did not identify any issues that are
specific to 1,1,2-trichloroethane
(USEPA, 2002e).
EPA evaluated the results of the
occurrence and exposure analyses for
1,1,2-trichloroethane to determine
whether changes to the MCL might be
appropriate and likely to result in
additional public health protection if
sufficient data were available to
recalculate the PQL and subsequently
set the MCL at the MCLG (USEPA,
2002g; USEPA, 2002h). Table V-15
shows the results of the detailed
occurrence and exposure analyses based
on the 16-State cross-section for the
current MCL (0.005 mg/L) and the
potentially revised MCL (0.003 mg/L)
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Federal Register/Vol. 67, No. 74/Wednesday, April 17, 2002/Proposed Rules
based on setting the MCL at the MCLG. ' unlikely to occur at the current MCL or any potential MCL revisions in the
Based on the detailed analysis, it States used for the cross-section.
appears that 1,1,2-trichloroethane is BILLING CODE eseo-so-p
Table V-15: l^-Trichloroethane Occurrence1
Systems2
Threshold
(in mg/L)
Current MCL 0.005
Potentially 000-
revisedMCL" °-°°3
16 Cross-Section
States - Total
Systems with Data
22,284
22,284
Estimated # Systems
> Threshold
(credible intervals)3
0 (0-0)
0 (0-0)
Estimated % Systems
> Threshold
(credible intervals)3
0.000% (0.000% - 0.000%)
0.000% (0.000% -0.000%)
Population Served by Systems2
Threshold
(in mg/L)
Current MCL 0.005
P-0teA% 0.003
revised MCL
16 Cross-Section
States - Total
Population Served by
Systems with Data
110,366,500
110,366,500
Estimated Population
Served by Systems >
Threshold
(credible intervals)3
0 (0-0)
0 . (0-0)
Estimated % Population
Served by Systems >
Threshold
(credible intervals)3
0.000% (0.000% - 0.000%)
0.000% (0.000% -0.000%)
Notes:
1 Results are based on the number and percent of systems (and the corresponding population served by those systems) with estimated
mean concentrations above the specified threshold.
1 All percentages are shown to three significant figures. All system values are rounded to the nearest whole system. All population
values are rounded to the nearest hundred.
3 "Credible intervals" are generated to quantify the uncertainty around each estimated probability in the Bayesian analysis of the
occurrence data. For further explanation of credible intervals and the Bayesian analysis, please see "Occurrence Estimation
Methodology and Occurrence Findings Report for the Six-Year Regulatory .Review" (USEPA, 2002g).
* The "potentially revised MCL" is the based on setting the MCL at the MCLG, if EPA had sufficient data to recalculate the PQL and
if it were found that the analytical feasibility was not a limiting factor.
BILLING CODE 6560-50-0
c. Preliminary Decision. Although
there are new data that support
consideration of whether a lower PQL is
possible (and therefore a possibly set the
MCL at the MCLG), EPA does not
believe a revision to the NPDWR for
1,1,2-trichloroethane is appropriate at
this time. The Agency believes that any
potential revision to the MCL is unlikely
to significantly improve the level of
public health protection because 1,1,2-
trichloroethane appears to occur
infrequently at concentrations at or
below the current MCL.
66. Trichloroethylene
a. Background. EPA published the
current NPDWR for trichloroethylene on
July 8,1987 (52 FR 25690 (USEPA,
1987)). The NPDWR established an
MCLG of zero based on a cancer
classification of B2, probable human
carcinogen. The NPDWR also
established an MCL of 0.005 mg/L based
on analytical feasibility.
b. Technical Reviews. EPA has
initiated a reassessment of the health
risks resulting from exposure to
trichloroethylene. The revised risk
assessment will consider relevant
studies that have become available on
the toxicity of trichloroethylene
including its potential developmental
and reproductive toxicity. The Agency
expects the new risk assessment to be
completed in the 2002 or 2003 time
frame (USEPA, 2002i).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for trichloroethylene is
appropriate at this time because a
reassessment of the health risks
resulting from exposure to
trichloroethylene is ongoing.
67. Vinyl Chloride
a. Background. EPA published the
current NPDWR for vinyl chloride on
July 8, 1987 (52 FR 25690 (USEPA,
1987)). The NPDWR established an
MCLG of zero based on a cancer
classification of A, known human
carcinogen. The NPDWR also
established an MCL of 0.002 mg/L based
on analytical feasibility.
b. Technical Reviews. The Agency
updated the health risk assessment of
vinyl chloride in 2000 (USEPA, 2000k).
The updated risk assessment included
relevant studies that were available on
the toxicity of vinyl chloride including
its potential developmental and
reproductive toxicity. According to the
1986 EPA Guidelines for Carcinogen
Risk Assessment, vinyl chloride is
categorized as Group A, known human
carcinogen. Under the Proposed
Guidelines for Carcinogen Risk
Assessment (61 FR 17960, April 23,
1996 (USEPA, 1996)), EPA concluded
that vinyl chloride is a known human
carcinogen by the inhalation route of
exposure, based on human
epidemiological data and, by analogy,
by the oral and dermal routes.
The current MCL for vinyl chloride is
based on a PQL of 0.002 mg/L. As a part
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19085
of the Six-Year Review, EPA analyzed
WS data to determine if it might be
possible to recalculate the PQL. In
addition, the Agency evaluated whether
more sensitive analytical methods have
been approved and put into use by a
wide number of laboratories. Based on
these analyses, the Agency believes the
current PQL, and therefore the MCL, is
still appropriate (USEPA, 2002d).
A review of treatment feasibility is not
necessary for vinyl chloride because no
changes to the MCLG or the MCL are
warranted at this time. In addition, the
. results of EPA's review of possible
"other regulatory revisions" did not
identify any vinyl chloride-specific
issues (USEPA, 2002e). Since EPA did
not identify a health or technology basis
for revising the vinyl chloride NPDWR,
the Agency did not conduct a detailed
occurrence and exposure analysis.
c. Preliminary Decision. After
reviewing the results of the pertinent
technical analyses, the Agency believes
the NPDWR for vinyl chloride remains
appropriate and thus, it is not subject to
revision at this time.
68. Xylenes [Total)
a. Background. EPA published the
current NPDWR for total xylenes on
January 30,1991 (56 FR 3526 (USEPA,
1991a)). The NPDWR established an
MCLG and an MCL of 10 mg/L. The
Agency based the MCLG on an RfD of
2 mg/kg/day and a cancer classification
of D, not classifiable as to human
carcinogenicity.
b. Technical Reviews. The Agency has
initiated a reassessment of the health
1 risks resulting from exposure to xylenes.
The revised risk assessment will
consider relevant studies that have
become available on the toxicity of
xylenes including its potential
developmental and reproductive
toxicity. The Agency expects the new
risk assessment to be completed in the
2002 or 2003 time frame (USEPA,
2002i).
c. Preliminary Decision. The Agency
does not believe a revision to the
NPDWR for xylenes is appropriate at
this time because a reassessment of the
health risks resulting from exposure to
xylenes is ongoing.
B. What Preliminary Decision Has EPA
Made Regarding the Total Coliform
Rule?
1. Background
EPA published the TCR on June 29,
1989 (54 FR 27544 (USEPA, 1989b))..
The TCR is one of several EPA
regulations that protect the public from
pathogens in drinking water. The TCR
requires all PWSs to monitor for the
presence of total coliforms in the
distribution system. Total coliforms are
a group of closely related bacteria that
are (with few exceptions) not harmful to
humans. They are natural and common
inhabitants of the soil and ambient
waters (e.g., lakes, rivers and estuaries),
as well as in the gastrointestinal tract of
animals. A few of these coliforms (fecal
coliforms, including Escherichia coli or
E. coli15) only grow within the
intestinal tract of humans and other
warm-blooded animals. Total coliforms
may be injured by environmental
stresses (e.g., lack of nutrients) and
water treatment (e.g., chlorine
disinfection) in a manner similar to
most bacterial pathogens and many
virus pathogens. Therefore, EPA
considers them a useful indicator of
bacterial and many viral waterborne
enteric pathogens. More specifically, for
drinking water, total coliforms .are used
to determine the adequacy of water
treatment and the integrity of the
distribution system. The absence of total
coliforms in the distribution system
minimizes the likelihood that fecal
pathogens are present. Thus, total
coliforms are used to determine the
vulnerability of a system to fecal
contamination.
The 1989 TCR set an MCLG of zero for
total coliforms because EPA was not
aware of any data in the scientific
literature supporting a particular value
for the concentration of coliforms below
which no known or anticipated adverse
health effects occur, with an adequate
margin of safety. The TCR requires
systems to monitor for total coliforms at
a frequency proportional to the number
of people served. If any sample is total
coliform-positive, the system must:
• Test the positive culture for the
presence of either fecal coliforms or E.
coli;
• Take one set of 3-4 repeat samples
at sites located within five or fewer
sampling sites adjacent to the location
of the routine positive sample within 24
hours; and
• Take at least 5 routine samples the
next month of operation.
2. Technical Reviews
Since the TCR was promulgated in
1989, few technical papers on the
15 EPA is aware that Escherichia coli O157 may
be found in fecally contaminated drinking water. To
date, however, none of the EPA-approved methods
for E. coli and fecal coliforms in drinking water
detect E. coli O157. Nevertheless, E. coli O157, as
is true with nonpathogenic E. coli strains, is always
associated with fecal waste (outside the laboratory)
and should be as susceptible to disinfection as the
nonpathogenic strains. Therefore, the presence of E.
coli O157 should always be accompanied by other
E. coli strains that are detectable by the EPA-
approved methods.
occurrence of coliforms in treated water
have been published. Much of the
recent technical data on coliforms are
associated with biofilm studies,
specifically the factors that facilitate the
growth of coliforms and other microbes
within the distribution system (e.g.,
LeChevallier et al, 1991,1996;
LeChevallier, 1999). In addition, several
studies have been published describing
the performance of new coliform
methods (e.g., Brenner et al., 1993;
Grant, 1997).
One recent study examined the
relationship between total coliforms and
waterborne disease outbreaks (Craun et
dl, 1997). According to the study
results, coliforms were found in 84
percent of the 187 systems during an
outbreak investigation, but in the
months before any outbreak, they were
only detected by 26 percent of these
systems. For outbreaks caused by
Cryptosporidium or Giardia, coliforms
were only found during 38 percent of
the outbreaks. The study, as well as data
from the 1993 outbreak of waterborne
cryptosporidiosis in Milwaukee
(MacKenzie, et al., 1994), continues to
support the premise that coliforms are
an inadequate indicator for
Cryptosporidium oocysts and Giardia
cysts in treated waters, presumably
because these protozoa are appreciably
more resistant to disinfection than the
coliform indicators.
Since promulgation of the TCR, EPA
has received comments from a number
of stakeholders. Stakeholders have
suggested modifications to reduce the
burden of implementing the TCR. EPA
has determined that an opportunity for
implementation burden reduction exists
and will analyze the effect that such
changes would have on public health
protection as part of the Agency's
regulatory development/revision
process. Only those measures which
reduce the TCR implementation burden
while still assuring public health
protection will be considered by EPA.
3. Preliminary Decision
EPA intends to undertake a
rulemaking process to initiate possible
revisions to the TCR. As part of this
process, EPA believes it may be
appropriate to include this rulemaking
in a wider effort to review and address
~ broader issues associated with drinking
• water distribution systems. This would
be one way of addressing some of the
recommendations of the Microbial/
Disinfection Byproducts (M/DBP)
Federal Advisory Committee in the
Stage 2 M/DBP Agreement in Principle
(65 FR 83015, December 29, 2000
(USEPA, 2000h)). As part of the TCR
rulemaking, EPA plans to assess the
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Federal Register./Vol. 67, No. 74/Wednesday, April 17, 2002/Proposed Rules
effectiveness of the current TCR in
reducing public health risk, and what
technically supportable alternative/
additional monitoring strategies ace
available that would decrease economic
burden while maintaining or improving
public health protection.
VI. Request for Comments
A. On Which Issues Is EPA Soliciting
Public Comment?
Today's action solicits public
comment on the following broad issues.
(1) Is EPA's protocol for the review of
the 69 NPDWRs discussed in today's
action reasonable and appropriate?
(2) Based on the review, are EPA's
revise/not revise conclusions
appropriate for each of the 69 NPDWRs?
EPA also invites commenters to
submit any new, relevant peer-reviewed
data pertaining to the NPDWRs
discussed in today's action. Peer-
reviewed data are studies/analyses that
have been reviewed by qualified
individuals (or organizations) who are
independent of those who performed
the work, but who are collectively
equivalent in technical expertise (i.e.,
peers) to those who performed the
original work. A peer review is an in-
depth assessment of the assumptions,
calculations, extrapolations, alternate
interpretations, methodology,
acceptance criteria, and conclusions
pertaining to the specific major
scientific and/or technical work
products and of the documentation that
supports them (USEPA, 2000i). Relevant
data include studies/analyses pertaining
to health effects, analytical feasibility,
treatment feasibility, and occurrence/
exposure related to the contaminants
discussed in today's action.
Table VI—1 summarizes the specific
comments requested in today's action
and provides a cross reference to the
section of today's action where the issue
is discussed.
BILLING CODE 6560-50-P
Table VI-1: Issues on Which EPA is Requesting Public Comment or Data
Description of the Public Input Requested
(1)
(2)
(3)
(4)
(5)
Reasonableness and appropriateness of EPA's protocol
Validity of EPA's methodology and assumptions for estimating
occurrence and suitability of using a national extrapolation
Appropriateness of EPA's revise/not revise decisions
Merit of gathering better data on which to recalculate the PQL for
dichloromethane.
Occurrence data for oxamyl at levels between 0.007 and 0.2 mg/L
Corresponding section in
Notice pertaining to request
Section IV
Section IV.B.5
Section V
Section V.A.26
Section V.A.50
BILLING CODE 6560-50-C
EPA also invites commenters to .
submit any new, relevant peer-reviewed
data pertaining to the NPDWRs
discussed in today's action.
B. Request for Comments on Use of
Plain Language
Executive Order 12866 and the
President's memorandum of June 1,
1998, require each agency to write all
rules in plain language. We invite your
comments on how to make this action
easier to understand. For example:
• Have we organized the material to
suit your needs?
• Are the decisions in the notice and
our rationale for those decisions clearly
stated?
• Does the notice contain technical
language or jargon that isn't clear?
• Would a different format (grouping
and order of sections, use of headings,
paragraphing) make the notice easier to
understand?
• Would more (but shorter) sections
be batter?
• Could we improve clarity by adding
tables, lists, or diagrams?
• What else could we do to make the
notice easier to understand?
VH. EPA's Next Steps
EPA plans a 60-day comment period
following this action. For each NPDWR
for which the Agency has published its
preliminary revise/not revise decision
in today's action, EPA will consider the
public comments received and review
any new peer-reviewed data submitted
in support of those public comments to
determine whether a different revise/not
revise decision is appropriate in light of
the submitted data. The Agency plans to '
publish its final revise/not revise
decisions for these NPDWRs in the
August 2002 time frame.
The publication of a decision to revise
pursuant to SDWA Section 1412(b)(9) is
not the end of the regulatory process,
but is the beginning of one. A decision
to revise starts a regulatory process for
a contaminant that involves more
detailed analyses concerning health
effects, costs, benefits, occurrence, and
other matters relevant to deciding
whether and how an NPDWR should be
revised. At any point in this process,
EPA may find that regulatory revisions
are no longer appropriate and may
discontinue regulatory revision efforts at
that time. Review of that contaminant
would continue in future six-year
reviews.
Similarly, a decision not to revise at
this time means only that EPA does not
believe that regulatory changes to a
particular NPDWR are appropriate now,
based on lack of new data, ongoing
scientific reviews, low priority, or other
reasons discussed in this action. Review
of these contaminants continues and
future six-year reviews may lead to a
decision that regulatory changes are
appropriate.
VHI. References
ATSDR. 1992. Toxicological Profile for 1,2-
Dibromo-3-chloropropane. U.S.
Department of Health and Human
Services, Public Health Service. 164 pp.
Available on the Internet at: http://
www.atsdr.cdc.gov/toxprofiles/
tp36.html.
ATSDR. 1993. Toxicological Profile for
Heptachlor and Heptachlor Epoxide.
U.S. Department of Health and Human
Services, Public Health Service. 162 pp.
Available on the Internet at: http://
www.atsdr.cdc.gov/toxprofiles/
tp!2.html.
ATSDR. 1996a. Toxicological Profile for 1,2-
Dichloroethene. U.S. Department of
Health and Human Services, Public
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19087
Health Service. 196 pp. Available on the
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toxp'rofiles/tp87.html.
ATSDR. 1996b. Toxicological Profile for
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Human Services, Public Health Service.
228 pp. Available on the Internet at:
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tp89.pdf.
ATSDR. 1996C. Toxicological Profile for
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Health and Human Services, Public
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ATSDR. 1996d. Toxicological Profile for
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ATSDR. 1999. Toxicological Profile for Lead.
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Department of Health and Human Services
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MacKenzie W.R., N.J. Hoxie, M.E. Proctor,
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NAS. 1995. Nitrate and nitrite in drinking
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NAS. 1997. Dietary reference intakes for
calcium, phosphorus, magnesium,
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NAS. 2000a. Copper in drinking water.
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NAS. 2000b. Dietary reference intakes for
vitamin C, vitamin E, selenium, and
carotenoids. National Academy Press,
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0309069351/html.
NAS. 2001. Dietary reference intakes for
vitamin A, vitamin K, arsenic, boron,
chromium, copper, iodine, iron,
manganese, molybdenum, nickel,
silicon, vanadium, and zinc. National
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2000. Available on the Internet at:
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NTP. 2001. NTP Study of the Hexavalent
Chromium Compound Sodium
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United States Department of Agriculture
(USDA). 1998. National Agricultural
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USEPA. 1975. Water Programs: National
Interim Primary Drinking Water
Regulations. Federal Register. Vol. 40,
No. 248, p. 59566. December 24,1975.
USEPA. 1976. Interim Primary Drinking
Water Regulations; Promulgation of
Regulations on Radionuclides. Federal
Register. Vol. 41, No. 133. p. 28401, July
.9,1976.
USEPA. 1979. National Interim Primary
Drinking Water Regulations; Control of
Trihalomethanes in Drinking Water.
Federal Register. Vol. 44, No. 231. p.
68624, November 29,1979.
USEPA. 1985. National Primary Drinking
Water Regulations; Volatile Synthetic
Organic Chemicals; Final Rule and
Proposed Rule. Federal Register. Vol. 50,
No. 219. p. 46880, November 13,1985.
USEPA. 1986a. National Primary and
Secondary Drinking Water Regulations;
Fluoride; Final Rule. Federal Register.
Vol. 51, No. 63. p. 11396, April 2,1986.
USEPA. 1986b. EPA Guidelines for
Carcinogen Risk Assessment. Federal
Register. Vol. 51, No. 185. p. 33992,
September 24,1986.
USEPA. 1987. National Primary Drinking
Water Regulations—Synthetic Organic
Chemicals; Monitoring for Unregulated
Contaminants; Final Rule. Federal
Register. Vol. 52, No. 130. p. 25690, July
8,1987.
USEPA. 1989a. National Primary and
Secondary Drinking Water Regulations;
Proposed Rule. Federal Register. Vol. 54,
No. 97. p. 22062, May 22,1989.
USEPA. 1989b. Drinking Water; National
Primary Drinking Water Regulations;
Total Coliforms (Including Fecal
Coliforms and E. coli}; Final Rule.
Federal Register. Vol. 54, No. 124. p.
27544, June 29,1989.
USEPA. 1989c. National Primary Drinking
Water Regulations; Filtration,
Disinfection; Turbidity, Giardia Lamblia,
Viruses, Legionella, and Heterotrophic
Bacteria; Final Rule. Part 2. Federal
Register. Vol. 54, No. 124. p. 27486, June
29,1989.
USEPA. 1990. National Primary and
Secondary Drinking Water Regulations—
Synthetic Organic Chemicals and
Inorganic Chemicals; Proposed Ride.
Federal Register. Vol. 55, No. 143. p.
30370, July 25, 1990.
USEPA. 1991a. National Primary Drinking
Water Regulations—Synthetic Organic
Chemicals and Inorganic Chemicals;
Monitoring for Unregulated
Contaminants; National Primary
Drinking Water Regulations
Implementation; National Secondary
Drinking Water Regulations; Final Rule.
Federal Register. Vol. 56, No. 30. p.
3526, January 30,1991.
USEPA. 1991b. Drinking Water Regulations— •
Maximum Contaminant Level Goals and
National Primary Drinking Water
Regulations for Lead and Copper; Final
Rule. Federal Register. Vol. 56, No. 110.
p. 26460, June 7,1991.
USEPA. 1991c. Drinking Water; National
Primary Drinking Water Regulations;
Monitoring for Volatile Organic
Chemicals; MCLGs and MCLs for
Aldicarb, Aldicarb Sulfoxide, Aldicarb
Sulfone, Pentachlorophenol, and
Barium; Final Rule. Federal Register.
Vol. 56, No. 126. p. 30266, July 1,1991.
USEPA. 1992. Drinking Water; National
Primary Drinking Water Regulations—
Synthetic Organic Chemicals and
Inorganic Chemicals; National Primary
Drinking Water Regulations
Implementation; Final Rule. Federal
Register. Vol. 57, No. 138. p. 31776, July
17,1992.
USEPA. 1994a. Public Water System
Warning: Cyanide. Memo from William
R. Diamond, Acting Director of Drinking
Water Standards Division, Office, of
Ground Water and Drinking Water.
March 7,1994.
USEPA. 1994b. Drinking Water; Maximum
Contaminant Level Goals and National
Primary Drinking Water Regulations for
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19088
Federal Register/Vol. 67, No. 74/Wednesday, April 17, 2002/Proposed Rules
Load and Copper: Final Rule; Technical
Corrections. Federal Register. Vol. 59,
No. 125. p. 33860, June 30,1994.
USEPA. 1995. Integrated Risk Information
System (IRIS}, Mercuric Chloride.
Available on the Internet at: http://
www.epa.gov/iris/subst/0692.htm.
USEPA. 1998. Proposed guidelines for
carcinogen risk assessment Federal
Register. Vol. 61, No. 79. p. 17960, April
23,1996.
USEPA. 1997a. Alternative Monitoring
Guidelines, EPA Report 816-R-97-011.
August 1997. Available on the Internet
at: http://www.epa.gov/safewater/regs/
pmrfin.html.
USEPA. 1997b. Mercury Study Report to
Congress; Volume V: Health Effects of
Mercury and Mercury Compounds. EPA
Report 452-R-97-009. Office of Air
Quality Planning and Standards', Office
of Research and Development. December
1997. Available on the Internet at:
http://www.epa.gov/ttn/oarpg/t3/
reports/volumes.pdf.
USEPA. 19988. Small System Compliance
Technology List for Non-Microbial
Contaminants Regulated Before 1996.
EPA Report 815-R-98-002. September
1998.
USEPA. 1998b. National Primary Drinking
Water Regulations: Disinfectants and
Disinfection Byproducts; Final Rule.
Federal Register. Vol. 63, No. 241. p.
69389, December 16,1998.
USEPA. 1998C. National Primary Drinking
Water Regulations: Interim Enhanced
Surface Water Treatment; Final Rule.
Federal Register. Vol. 63, No. 241. p.
69478, December 16,1998.
USEPA. 1998d, IRIS, Beryllium and
Compounds. Available on the Internet at:
http://www.epa.gov/iris/subst/0012.htm.
USEPA. 1998e. IRIS, Chlordane (Technical).
Available on the Internet at: http://
wwvv.epa.gov/iris/subst/0142.htm.
USEPA. 1998f. IRIS, Chromium (VI).
Available on the Internet at: http://
www.epa.gov/iris/subst/0144.htm.
USEPA. 1999a. Response to
Recommendations from the Children's
Health Protection Advisory Committee
Regarding Evaluation of Existing
Environmental Standards; Notice.
Federal Register. Vol. 64, No. 22. p.
5277, February 3,1999.
USEPA. 1999b. Guidelines for Carcinogen
Risk Assessment. NCEA-F-0644 Review
Draft. U.S. Environmental Protection
Agency Risk Assessment Forum.
Washington, D.C. July 1999.
USEPA. 1999C. Announcement of
Stakeholders Meeting on the Drinking
Water Contaminant Identification and
Selection Process, and the 6-Year Review
of All Existing National Primary
Drinking Water Regulations, as Required
by the Safa Drinking Water Act, as
Amended in 1996; Notice of
Stakeholders Meeting. Federal Register.
Vol. 64, No. 198. p. 55711, October 14,
1999.
USEPA. 1999d, A Review of Contaminant
Occurrence in Public Water Systems.
EPA Report 816-R-99-006. November
1999. Available on the Internet at: http:/
/www.epa.gov/safewater/occur/
nov99_lo.pdf.
USEPA. 1999e. Stakeholder Meeting on the
Contaminant Candidate List and the 6-
Year Review of Existing National
Primary Drinking Water Regulations.
November 1999. Available on the
Internet at: http://www.epa.gov/
safewater/ccl/novmtg.html.
USEPA. 1999f. IRIS, Barium and
Compounds. Available on the Internet at:
http://www.epa.gov/iris/subst/0010.htm.
USEPA. 2000a. National Primary Drinking
Water Regulations for Lead and Copper;
Final Rule. Federal Register. Vol. 65, No.
8. p. 1950, January 12, 2000.
USEPA. 2000b. Working Group Meeting on
Contaminant Candidate List Regulatory
Determinations and the 6-Year Review of
Existing Regulations. Office of Water.
June 2000. Available on the Internet at:
http://www.epa.gov/safewater/ccl/
junemtg.html.
USEPA. 2000c. Working Group Meeting on
Contaminant Candidate List Regulatory
Determinations and the 6-Year Review of
Existing Regulations. Office of Water.
July 2000. Available on the Internet at:
http://www.epa.gov/safewater/ccl/
julymtg.html.
USEPA. 2000d. NDWAC'Working Group
Meeting on Contaminant Candidate List
Regulatory Determinations and the 6-
Year Renew of Existing Regulations.
Office of Water. September 2000.
Available on the Internet at: http://
www.epa.gov/safewater/ccl/
25septmtg.html.
USEPA. 2000e. Interim Reregistration
Eligibility Decision (IRED)—Oxamyl.
EPA Report 738-R-00-015. Office of
Prevention, Pesticides, and Toxic
Substances. October 2000. Available on
the Internet at: http://www.epa.gov/
oppsrrdl/REDs/0253ired.pdf.
USEPA. 2000f. Methodology for Deriving
Ambient Water Quality Criteria for the
Protection of Human Health. EPA Report
882-B-00-004. Office of Water. October
2000.
USEPA. 2000g. National Primary Drinking
Water Regulations; Radionuclides; Final
Rule. Federal Register. Vol. 65, No. 236.
p. 76707, December 7, 2000.
USEPA. 2000h. Stage 2 Microbial and
Disinfection Byproducts Federal
Advisory Committee Agreement in
Principle; Notice. Federal Register. Vol.
65, No. 251. p. 83015, December 29,
2000.
USEPA. 20001. Science Policy Council
Handbook: Peer Review, 2nd Edition.
EPA Report 100-B-OO-OOl. Office of
Science Policy, Office of Research and
Development. December 2000.
USEPA. 2000J. IRIS, Benzene. Available on
the Internet at: http://www.epa.gov/iris/
subst/0276.htm.
USEPA. 2000k. IRIS, Vinyl Chloride.
Available on the Internet at: http://
www.epa.gov/iris/subst/1001.htm.
USEPA. 20001. EPA Summary Report.
Characterization of data variability and
uncertainty: Health effects assessments
in the Integrated Risk Information
System (IRIS). In response to Congress,
HR106-379. EPA Report 635-R-OO-
005F. National Center for Environmental •-
Assessment, Office of Research and
Development.
USEPA. 2001a. National Primary Drinking
Water Regulation; Arsenic and
Clarifications to Compliance and New
Source Contaminants Monitoring; Final
Rule. Federal Register. Vol. 66, No. 14.
p. 6975, January 22, 2001.
USEPA. 2001b. Dioxin Reassessment—An
SAB Review of the Office of Research
and Development's Reassessment of
Dioxin. EPA Report SAB-EC-01-006.
May 2001. Available on the Internet at:
http://www.epa.gov/sab/ec01006.pdf.
USEPA. 2001C. IRIS,
Hexachlorocyclopentadiene. Available
on the Internet at: http://www.epa.gov/
iris/subst/0059.htm.
USEPA. 2002a. Integrated Risk Information
System (IRIS); Announcement of 2002
Program; Request for Information;
Notice. Federal Register. Vol. 67, No. 6.
p. 1212, January 9, 2002.
USEPA. 2002b. National Primary Drinking
Water Regulations: Long-Term 1
Enhanced Surface Water Treatment Rule;
Final Rule. Federal Register. Vol. 67, No.
9. p. 1811, January 14, 2002.
USEPA. 2002c. An Evaluation of Available
Economic Information in Support of the
Six-Year Review of Existing National
Primary Drinking Water Regulations.
Memo from Marc Parrotta, Targeting and
Analysis Branch, Office of Ground Water
and Drinking Water. March 2002.
USEPA. 2002d. Analytical Feasibility
Support Document for the Six-Year
Review of Existing National Primary
Drinking Water Regulations
(Reassessment of Feasibility for
Chemical Contaminants). EPA Report
815-D-02-002. Draft. March 2002.
USEPA. 2002e. Consideration of Other
Regulatory Revisions for Chemical
Contaminants in Support of the Six-Year
Review of National Primary Drinking
Water Regulations. EPA Report 815-D-
02-003. Draft. March 2002.
USEPA. 20021 EPA Protocol for Review of
Existing National Primary Drinking
Water Regulations. EPA Report 815-D-
02-004. Draft. March 2002.
USEPA. 2002g. Occurrence Estimation
Methodology and Occurrence Findings
Report for the Six-Year Regulatory
Review. EPA Report 815-D-02-005.
Draft. March 2002.
USEPA. 2002h. Occurrence Summary and
Use Support Document for the Six-Year
Regulatory Review. EPA Report 815-D-
02-006. Draft. March 2002.
USEPA. 2002i. Six-Year Review—Chemical
Contaminants—Health Effects Technical
Support Document. EPA Report 822-^R-
02-001. Draft. February 2002.
USEPA. 2002J. Six-Year Review of the Total
Coliform Rule—Comments Received.
Memo from Kenneth H. Rotert,
Standards and Risk Reduction Branch,
Office of Ground Water and Drinking
Water. March 2002. •
USEPA. 2002k. Water Treatment Technology
Feasibility Support Document for
Chemical Contaminants; In Support of
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19089
EPA Six-Year Review of National
Primary Drinking Water Regulations.
EPA Report EPA 815-D-02-001. Draft.
February 2002.
Dated: March 28, 2002.
Christine Todd Whitman,
Administrator.
Appendix A: Background on the
Calculation of MCLG and Cancer
Classification System
Since the identification of contaminants for
potential revision may be dependent on
whether or not the maximum contaminant
level goal (MCLG) could change, a brief
explanation of the derivation of the MCLG is
warranted. The MCLG is the maximum level
of a contaminant in drinking water at which
no known or anticipated adverse health
effects occur, allowing for an adequate
margin of safety. MCLGs are non-enforceable
health goals. EPA establishes the maximum
contaminant level (MCL) based on the MCLG.
The MCL is the maximum permissible level
of a contaminant in water .which is delivered
to any user of a public water system. It is
derived based.on the MCLG. Prior to the 1996
Amendments to the Safe Drinking Water Act
(SDWA), the MCL was set as close to the
MCLG as is feasible, taking costs into
consideration. The 1996 Amendments to the
SDWA permit consideration of costs relative
to benefits in establishing a MCL. MCLs are
enforceable standards.
For chemicals exhibiting a threshold for
toxic effects, EPA establishes the MCLG on
the basis of an oral reference dose (RfD). A
change in the RfD could lead to a change in
the MCLG and thus in the MCL. The RfD is
an estimate (with uncertainty spanning
perhaps an order of magnitude) of a daily
oral exposure to the human population
(including sensitive subgroups) that is likely
to be without an appreciable risk of
deleterious noncancer effects during a
lifetime. The RfD is derived as follows:
MCLG =
RfD X bw X RSC
I
RfD =
NOAEL or LOAEL or BMP
UF x MF
Where:
NOAEL = no-observed-adverse-effect level
LOAEL = lowest-observed-adverse-effect
level
BMD = benchmark dose
UF = uncertainty factor
MF = modifying factor
The benchmark dose (BMD) is the statistical
lower confidence limit on the dose estimated
to produce a predetermined level of change
(i.e., 10 percent) in the critical response
relative to the control. The uncertainty factor
(UF) is used to account for extrapolation
uncertainties (e.g., inter-individual variation,
interspecies differences, duration of
exposure, and use of a LOAEL instead of a
NOAEL) and database adequacy. The
modifying factor (MF) is used as a judgment
factor to account for tie confidence in the
critical study (or studies) used in the
derivation of the RfD (USEPA, 20001).
The MCLG is then derived from the RfD as
follows:
Where: :
bw = body weight (70 kg for adult1B)
RSC = relative source contribution, the
fraction of the RfD allocated to drinking
water
I = daily drinking water intake (2 liters for
adults16)
The relative source contribution (RSC) is
one factor which will determine how much
a change in the RfD will lead to a change in
the MCLG. RSC refers to the method of
accounting for human exposure from
multiple sources when setting health-based
'criteria. The purpose of the RSC is to ensure
that the level of a chemical allowed by a
criterion or multiple criteria, when combined
with other identified sources of exposure
common to the population of concern, will
not result in exposures that exceed the RfD.
The policy of considering multiple sources of
exposure when deriving health-based criteria
has become common in EPA's risk
characterizations, as well as criteria and
standard-setting actions. The drinking water
program has applied a ceiling level of 80
percent of the RfD and a floor level of 20
percent of the RfD. That is, the MCLG cannot
account for more than 80 percent of the RfD,
nor less than 20 percent of the RfD. EPA
applies an RSC factor of 20 percent to the RfD
when adequate exposure data do not exist.
EPA has now revised its RSC method
to improve consistency when
considering non-water sources of
exposure (both ingestion exposures (e.g.,
food) and exposures other than the oral
route (e.g., inhalation). The approach is
called the Exposure Decision Tree. RSC
estimates will be made by EPA using
this approach, which allows for use of
either subtraction or percentage
methods, depending on chemical-
specific circumstances, within the 20 to
80 percent range described in the
previous paragraph. For a detailed
discussion on the revised approach,
refer to the "Methodology for Deriving
Ambient Water Quality Criteria for the
Protection of Human Health" (USEPA,
2000f),
It has also been the Agency policy to
apply an additional safety factor to the
RfD for chemicals with equivocal
evidence of carcinogenicity. This
practice is another factor that must be
evaluated to determine the impact of a
change in RfD on the MCLG.
For drinking water contaminants
regulated prior to the 1996 SDWA,
EPA's Office of Water (OW) followed a
three-category regulatory cancer
classification system (Categories I, n, or
in). These categories specify decisions
16 The MCLG for nitrite was based on a 4 kg body
weight and a 0.64 liter drinking water intake for
infants because they are the group most sensitive
to the critical effect.
as to degree of concern for an agent's
carcinogenic potential as a contaminant
of drinking water, and define to some
extent the approach to risk management
which is taken for establishing MCLGs.
Categories I, II, and HI are designations
not defined in guidelines but which
reflect OW policy.
EPA used the six alphanumeric
categories (A, Bl, B2, C, D, E) of the
1986 cancer guidelines (51 FR 33992,
September 24,1986 (USEPA, 1986b)) in
establishing the MCLG. The six-group
classification system is often equated to
the three-category system in the
National Primary Drinking Water
Regulation (NPDWR) Federal Register
announcements. Table A-l describes
the three categories and, with few
exceptions (e.g., beryllium), their usual
equivalent alphanumeric classification.
If a chemical is a known or probable
human carcinogen (Category I, generally
Group A or B), the MCLG is generally
set at zero because it is assumed, in the
absence of other data, that there is no
known threshold for carcinogenicity. If
a chemical falls in Group C, an RfD
approach along with an additional
safety (risk management) factor is used
in deriving the MCLG. The methodology
used for establishing MCLGs for
chemicals with varying degrees of
evidence of carcinogenicity is also
briefly described in Table A-l.
Recent Agency assessments also use
the 1996 Proposed Guidelines for
Carcinogen Risk Assessment (61 FR
17960, April 23, 1996 (USEPA.1996)) or
the draft revised Guidelines for
Carcinogen Risk Assessment (USEPA,
1999b). The proposed guidelines use
standard descriptors as part of the
hazard narrative to express the weight-
of-evidence for carcinogenic hazard
potential. The 1996 descriptors are in
three categories: "Known/likely,"
"cannot be determined," and "not
likely." Subdescriptors are provided
under these categories to further
differentiate an agent's carcinogenic
potential. The new descriptors permit
consideration of exposure route and
mode of action when making an
assessment of carcinogenicity. The
hazard descriptors of the 1996 proposed
Guidelines are given in the text to this
action whenever appropriate. None of
the chemicals discussed in this action
have been evaluated under the 1999
draft revised Guidelines for Carcinogen
Risk Assessment.
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Table A-l: Cancer Classification Systems Used by EPA
Three-category regulatory approach for
establishing M CLGs
, 1 ' i";i£S5St!C SKfeS
Category I
Known or probable human carcinogens:
Strong evidence of carcinogenicity
Sufficient human or animal evidence of
carcinogenicity.
Corresponding five-group classification system of
1986 Cancer Guidelines
£^&4***m J I-/' •?'*"';:'"'' -
Generally Group A or Group B
A: Human carcinogen
Sufficient evidence from epidemiological studies to
support a causal association.
B: Probable human carcinogen
'Bl: Limited evidence of carcinogenicity from
epidemiological studies.
B2: Inadequate evidence or no data from
epidemiological studies; sufficient evidence from
animal studies.
MCLG based 6tt the siO ^Itjvaa addiliitJiialJsafety-factor of up/io 10 to aeii&uftf for possible
-"'cai^nogj|hiciT^oV-if ba^ ^n^^^^^c^r--r^^^^ ^f\^s)a'^'6 ^' ''-"'-' ^
Category H
Limited evidence of carcinogenicity
Some limited but insufficient evidence of
carcinogenicity from animal data.
Generally Group C
Possible human carcinogen
Limited evidence of carcinogenicity in animals in the
absence of human data.
"— ^^^y^m^^^&^^^^^m^ ' "'•,'""'"< ' "'„
Category HI
Inadequate or no evidence of
carcinogenicity in animals
Group D or Group E
D: Not classifiable as to human carcinogenicity
Inadequate human and animal evidence of
carcinogenicity, or no data available.
E: Evidence of non-carcinogenicity for humans
No evidence of carcinogenicity in two different
animal species, or in both epidemiological and animal
studies.
Sources: 51 FR 33992, September 24, 1986 (USEPA, 1986b); and 57 FR 31776, July 17, 1992 (USEPA.1992).
IFRDoc. 02-9154 Filed 4-16-02; 8:45 am]
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