
[Federal Register Volume 82, Number 7 (Wednesday, January 11, 2017)]
[Proposed Rules]
[Pages 3518-3552]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2016-31262]



[[Page 3517]]

Vol. 82

Wednesday,

No. 7

January 11, 2017

Part III





Environmental Protection Agency





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40 CFR Part 141





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

  Federal Register / Vol. 82 , No. 7 / Wednesday, January 11, 2017 / 
Proposed Rules  

[[Page 3518]]


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ENVIRONMENTAL PROTECTION AGENCY

[EPA-HQ-OW-2016-0627; FRL-9957-49-OW]

40 CFR Part 141

RIN 2040-ZA26


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

AGENCY: Environmental Protection Agency (EPA).

ACTION: Request for public comments.

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SUMMARY: The Safe Drinking Water Act (SDWA) requires the U.S. 
Environmental Protection Agency (EPA) to conduct a review every six 
years of existing national primary drinking water regulations (NPDWRs) 
and determine which, if any, need to be revised. The purpose of the 
review, called the Six-Year Review, is to evaluate current information 
for regulated contaminants to determine if there is new information on 
health effects, treatment technologies, analytical methods, occurrence 
and exposure, implementation and/or other factors that provides a 
health or technical basis to support a regulatory revision that will 
improve or strengthen public health protection. EPA has completed a 
detailed review of 76 NPDWRs and at this time has determined that eight 
NPDWRs are candidates for regulatory revision. The eight NPDWRs are 
included in the Stage 1 and the Stage 2 Disinfectants and Disinfection 
Byproducts Rules, the Surface Water Treatment Rule, the Interim 
Enhanced Surface Water Treatment Rule and the Long Term 1 Enhanced 
Surface Water Treatment Rule. EPA requests comments on the eight NPDWRs 
identified as candidates for revision and will consider comments and 
data as it proceeds with determining whether further action is needed. 
In addition, as part of this Six-Year Review, EPA identified 12 other 
NPDWRs that were or continue to be addressed in recently completed, 
ongoing or pending regulatory actions. EPA thus excluded those 12 
NPDWRs from detailed review. This document is not a final regulatory 
decision, but rather the initiation of a process that will involve more 
detailed analyses of factors relevant to deciding whether a rulemaking 
to revise an NPDWR should be initiated.

DATES: Comments must be received on or before March 13, 2017.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-OW-
2016-0627, to the Federal eRulemaking Portal: http://www.regulations.gov. Follow the online instructions for submitting 
comments. Once submitted, comments cannot be edited or withdrawn. EPA 
may publish any comment received to its public docket. Do not submit 
electronically any information you consider to be Confidential Business 
Information (CBI) or other information whose disclosure is restricted 
by statute. Multimedia submissions (audio, video, etc.) must be 
accompanied by a written comment. The written comment is considered the 
official comment and should include discussion of all points you wish 
to make. EPA will generally not consider comments or comment contents 
located outside of the primary submission (i.e. on the web, cloud, or 
other file sharing system). For additional submission methods, the full 
EPA public comment policy, information about CBI or multimedia 
submissions, and general guidance on making effective comments, please 
visit http://www2.epa.gov/dockets/commenting-epa-dockets.
    Mail: Water Docket, Environmental Protection Agency, Mail code: 
2822T, 1200 Pennsylvania Ave. NW., Washington, DC 20460.
    Hand Delivery: EPA Docket Center Public Reading Room, EPA 
Headquarters West, Room 3334, 1301 Constitution Ave. NW., Washington, 
DC. Hand deliveries are only accepted during the Docket's normal hours 
of operation, and special arrangements should be made for deliveries of 
boxed information.

FOR FURTHER INFORMATION CONTACT: For technical inquiries contact: 
Richard Weisman, (202) 564-2822, or Kesha Forrest, (202) 564-3632, 
Office of Ground Water and Drinking Water, Environmental Protection 
Agency. For general 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 10 a.m. 
to 5:30 p.m. Eastern Time.

SUPPLEMENTARY INFORMATION:

Abbreviations and Acronyms Used in This Action

ADWR--Aircraft Drinking Water Rule
AGI--Acute Gastrointestinal Illness
AOC--Assimilable Organic Carbon
ASDWA--Association of State Drinking Water Administrators
ATSDR--Agency for Toxic Substances and Disease Registry
AWWA--American Water Works Association
BAT--Best Available Technology
CBI--Confidential Business Information
CDC--Centers for Disease Control and Prevention
CFR--Code of Federal Regulations
CT--Concentration x Contact Time
cVOCs--Carcinogenic Volatile Organic Compounds
CWS--Community Water System
DBCP--1,2-Dibromo-3-Chloropropane
DBP--Disinfection Byproducts
D/DBP--Disinfectants/Disinfection Byproducts
D/DBPR--Disinfectants/Disinfection Byproducts Rule
DEHA--Di(2-ethylhexyl)adipate
DEHP--Di(2-ethylhexyl)phthalate
DOC--Dissolved Organic Carbon
DPD--N,N-diethyl-p-phenylenediamine
EDB--Ethylene Dibromide
EJ--Environmental Justice
EO--Executive Order
EPA--U.S. Environmental Protection Agency
EQL--Estimated Quantitation Level
FAC--Federal Advisory Committee
FBRR--Filter Backwash Recycling Rule
FDA--U.S. Food and Drug Administration
FRN--Federal Register Notice
GAC--Granulated Activated Carbon
GWR--Ground Water Rule
GWUDI--Ground Water Under the Direct Influence of Surface Water
HAA5--Haloacetic Acids (five) (sum of monochloroacetic acid, 
dichloroacetic acid, trichloroacetic acid, monobromoacetic acid and 
dibromoacetic acid)
HAAs--Haloacetic Acids
HAV--Hepatitis A Virus
HPC--Heterotrophic Plate Count
IARC--International Agency for Research on Cancer
ICR--Information Collection Request
IESWTR--Interim Enhanced Surface Water Treatment Rule
IRIS--Integrated Risk Information System
LT1--Long-Term 1 Enhanced Surface Water Treatment Rule
LT2--Long-Term 2 Enhanced Surface Water Treatment Rule
MCL--Maximum Contaminant Level
MCLG--Maximum Contaminant Level Goal
MDBP--Microbial and Disinfection Byproducts
MDL--Method Detection Limit
MRDL--Maximum Residual Disinfectant Level
MRDLG--Maximum Residual Disinfectant Level Goal
MRL--Minimum Reporting Level
NAS--National Academy of Sciences
NCWS--Non-Community Water System
NDMA--N-Nitrosodimethylamine
NDWAC--National Drinking Water Advisory Council
NIH--National Institutes of Health
NPDWR--National Primary Drinking Water Regulation
NRC--National Research Council
NTNCWS--Non-Transient Non-Community Water System
NTP--National Toxicology Program
PCBs--Polychlorinated Biphenyls
PCE--Tetrachloroethylene
PHS--U.S. Public Health Service

[[Page 3519]]

PT--Proficiency Testing
PQL--Practical Quantitation Limit
PWS--Public Water System
qPCR--Quantitative Polymerase Chain Reaction
RfD--Reference Dose
RICP--Research and Information Collection Partnership
RSC--Relative Source Contribution
RTCR--Revised Total Coliform Rule
SDWA--Safe Drinking Water Act
SMCL--Secondary Maximum Contaminant Level
SOC--Synthetic Organic Chemical
SWTR--Surface Water Treatment Rule
SWTRs--Surface Water Treatment Rules (including SWTR, IESWTR and 
LT1)
SYR--Six-Year Review
TCE--Trichloroethylene
TC/EC--Total Coliforms/E. coli
TCR--Total Coliform Rule
THM--Trihalomethanes
TTHM--Total Trihalomethanes (sum of four THMs: chloroform, 
bromodichloromethane, dibromochloromethane and bromoform)
TNCWS--Transient Non-Community Water System
TOC--Total Organic Carbon
TT--Treatment Technique
UCFWR--Uncovered Finished Water Reservoirs
UCMR--Unregulated Contaminant Monitoring Rule
USGS--U.S. Geological Survey
UV--Ultraviolet
WBDOSS--Waterborne Disease Outbreak Surveillance System
WHO--World Health Organization

Table of Contents

I. General Information
    A. Does this action apply to me?
    B. What should I consider as I prepare my comments for EPA?
II. Statutory Requirements for the Six-Year Review
III. Stakeholder Involvement in the Six-Year Review Process
IV. Regulations Included in the Six-Year Review 3
V. EPA's Protocol for Reviewing the NPDWRs Included in This Action
    A. What was EPA's review process?
    B. How did EPA conduct the review of the NPDWRs?
    1. Initial Review
    2. Health Effects
    3. Analytical Feasibility
    4. Occurrence and Exposure Analysis
    5. Treatment Feasibility
    6. Risk-Balancing
    7. Other Regulatory Revisions
    C. How did EPA factor children's health concerns into the 
review?
    D. How did EPA factor environmental justice concerns into the 
review?
VI. Results of EPA's Review of NPDWRs
    A. What are the review result categories?
    1. The NPDWR is Not Appropriate for Revision at This Time
    2. The NPDWR is a Candidate for Revision
    B. What are the detailed results of EPA's third six-year review 
cycle?
    1. Chemical Phase Rules/Radionuclides Rules
    2. Fluoride
    3. Disinfectants/Disinfection Byproducts Rules (D/DBPRs)
    4. Microbial Contaminants Regulations
VII. EPA's Request for Comments
References

I. General Information

A. Does this action apply to me?

    This action itself does not impose any requirements on individual 
people or entities. Instead, it notifies interested parties of EPA's 
review of existing national primary drinking water regulations (NPDWRs) 
and its conclusions about which of these NPDWRs may warrant new 
regulatory action at this time. EPA requests public comment on the 
eight NPDWRs identified as candidates for revision. EPA will consider 
comments received as the Agency moves forward with determining whether 
regulatory actions are necessary for the eight NPDWRs.

B. What should I consider as I prepare my comments for EPA?

    Please see Section VII for the topic areas related to this document 
for which EPA requests comment and/or information. EPA will accept 
written or electronic comments (please do not send both). Instructions 
for submitting comments can be found in the ADDRESSES section of this 
document. EPA prefers electronic comments. No facsimiles (faxes) will 
be accepted. Commenters who want EPA to acknowledge receipt of their 
written comments should also send a self-addressed, stamped envelope.
    You may find the following suggestions helpful when preparing your 
comments:
     Explain your views as clearly as possible.
     Describe any assumptions that you used.
     Provide any technical information and/or data you used 
that support your views.
     If you estimate potential burden or costs, explain how you 
arrived at your estimate.
     Provide specific examples to illustrate your concerns.
     Offer alternatives.
     Make sure to submit your comments by the comment period 
deadline.
    To ensure proper receipt by EPA, identify the appropriate docket 
identification number in the subject line on the first page of your 
response. It would also be helpful if you provide the name, date, and 
volume/page numbers of the Federal Register document you are commenting 
on.

II. Six-Year Review--Statutory Requirements and Next Steps

    Under the Safe Drinking Water Act (SDWA), as amended in 1996, EPA 
must periodically review existing NPDWRs and, if appropriate, revise 
them. Section 1412(b)(9) of the SDWA states: ``The Administrator shall, 
not less often than every six years, review and revise, as appropriate, 
each national primary drinking water regulation promulgated under this 
title. Any revision of a national primary drinking water regulation 
shall be promulgated in accordance with this section, except that each 
revision shall maintain, or provide for greater, protection of the 
health of persons.''
    Pursuant to the 1996 SDWA Amendments, EPA completed and published 
the results of its first Six-Year Review (Six-Year Review 1) on July 
18, 2003 (68 FR 42908, USEPA, 2003b) and the second Six-Year Review 
(Six-Year Review 2) on March 29, 2010 (75 FR 15500, USEPA, 2010h), 
after developing a systematic approach, or protocol, for the review of 
NPDWRs.
    In this document EPA is announcing the results of the third Six-
Year Review (Six-Year Review 3). Consistent with the process applied in 
the Six-Year Review 2, EPA is requesting comments on this document and 
will consider the public comments and/or any new, relevant data 
submitted for the eight NPDWRs listed as candidates for revision as the 
Agency proceeds with determining whether revisions of these regulations 
are necessary. The announcement whether or not the Agency intends to 
revise an NPDWR (pursuant to SDWA Sec.  1412(b)(9)) is not a regulatory 
decision. Instead, it initiates a process that will involve more 
detailed analyses of health effects, analytical and treatment 
feasibility, occurrence, benefits, costs and other regulatory matters 
relevant to deciding whether a rulemaking to revise an NPDWR should be 
initiated. The Six-Year Review results do not obligate the Agency to 
revise an NPDWR in the event that EPA determines during the regulatory 
process that revisions are no longer appropriate and discontinues 
further efforts to revise the NPDWR. Similarly, the fact that an NPDWR 
has not been selected for revision means only that EPA believes that 
regulatory changes to a particular NPDWR are not appropriate at this 
time for the reasons given in this action; future reviews may identify 
information that leads to an initiation of the revision process.
    The reasons that EPA has identified an NPDWR as a ``candidate for 
revision''

[[Page 3520]]

is that, at a minimum, the revision presents a meaningful opportunity 
to:
     Improve the level of public health protection, and/or
     Achieve cost savings while maintaining or improving the 
level of public health protection.

III. Stakeholder Involvement in the Six-Year Review Process

    The Agency has involved interested stakeholders in the Six-Year 
Review 3 process. Below are examples of such involvement:

     In November 2014, EPA briefed the National Drinking 
Water Advisory Council (NDWAC) on the Six-Year Review protocol and 
the key elements of that protocol as they relate to the microbial 
and disinfection byproducts (MDBP) rules. The briefing included 
information on how EPA is implementing NDWAC's previous 
recommendations (NDWAC, 2000) on the Six-Year Review process in 
review of the MDBP rules;
     In January 2015, states provided input (through the 
Association of State Drinking Water Administrators (ASDWA)) on rule 
implementation issues related to the NPDWRs being reviewed as part 
of the Six-Year Review 3 (ASDWA, 2016);
     EPA initiated a series of public stakeholder meetings 
about the review of the Long Term 2 Enhanced Surface Water Treatment 
Rule (LT2). These meetings were held in accordance with the 
recommendation of the MDBP Federal Advisory Committee (FAC) \1\ to 
have public meetings following the first round of monitoring under 
the LT2, and as a result of the Executive Order (E.O.) 13563 
``Improving Regulation and Regulatory Review.'' \2\ E.O. 13563 
states that regulations shall be based ``on the open exchange of 
information and perspectives among state, local, and tribal 
officials, experts in relevant disciplines, affected stakeholders in 
the private sector, and the public as a whole.'' Some affected 
stakeholders recommended that EPA include the LT2 among the Agency's 
top priorities for review under E.O. 13563. EPA included the LT2 in 
its ``Improving our Regulations: Final Plan for Periodic 
Retrospective Review of Existing Regulations'' (USEPA, 2011). EPA 
agreed to ``assess and analyze new data/information regarding 
occurrence, treatment, analytical methods, health effects, and risk 
from all relevant waterborne pathogens to evaluate whether there are 
new or additional ways to manage risk while assuring equivalent or 
improved protection, including with respect to the covering of 
finished water reservoirs'' (USEPA, 2011). EPA hosted three public 
meetings in Washington, DC, on December 7, 2011, April 24, 2012 and 
November 15, 2012. EPA presented information about: The LT2 
requirements, monitoring data collected under the LT2, analytical 
methods, forecasts about the second round of monitoring and the 
treatment technique requirements. In addition to presentations to 
educate the public, the meetings included public statements, panel 
discussions, question and answer sessions and requests by EPA to 
provide data and information about the implementation of the LT2 to 
inform the regulatory review.
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    \1\ https://www.epa.gov/sites/production/files/2015-11/documents/stage_2_m-dbp_agreement_in_principle.pdf.
    \2\ E.O. 13563 requires federal agencies to ``consider how best 
to promote retrospective analysis of rules that may be outmoded, 
ineffective, insufficient, or excessively burdensome, and to modify, 
streamline, expand, or repeal them in accordance with what has been 
learned.'' The order required each federal agency to develop a plan 
``consistent with law and its resources and regulatory priorities.'' 
https://www.gpo.gov/fdsys/pkg/FR-2011-01-21/pdf/2011-1385.pdf.
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IV. Regulations Included in the Six-Year Review 3

    Table IV-1 lists all 88 NPDWRs established to date. The table also 
reports the maximum contaminant level goal (MCLG) and the maximum 
contaminant level (MCL). The MCLG is ``set at the level at which no 
known or anticipated adverse effects on the health of persons occur and 
which allows an adequate margin of safety'' (SDWA Sec.  1412(b)(4)). 
The MCL is the maximum permissible level of a contaminant in water 
delivered to any user of a public water system (PWS) and generally ``is 
as close to the maximum contaminant level goal as is feasible'' (SDWA 
Sec.  1412(b)(4)(B)).\3\ Where it is not ``economically or technically 
feasible'' to set an MCL, EPA can establish a treatment technique (TT), 
which must prevent adverse health effects ``to the extent feasible'' 
(SDWA Sec.  1412(b)(7)(A)). In the case of disinfectants (e.g., 
chlorine, chloramines and chlorine dioxide), the values reported in the 
table are not MCLGs and MCLs, but maximum residual disinfectant level 
goals (MRDLGs) and maximum residual disinfectant levels (MRDLs).
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    \3\ Under limited circumstances, SDWA Sec.  1412(b)(6)(A) also 
gives the Administrator the discretion to promulgate an MCL that is 
less stringent than the feasible level and that ``maximizes health 
risk reduction benefits at a cost that is justified by the 
benefits.''
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    Table IV-1 also includes NPDWRs that EPA identified as candidates 
for revision in past Six-Year Reviews. During the Six-Year Review 1, 
EPA identified the Total Coliform Rule (TCR) as a candidate for 
revision.\4\ EPA published the Revised Total Coliform Rule (RTCR) in 
2013 (78 FR 10270, USEPA, 2013a). Four additional NPDWRs for 
acrylamide, epichlorohydrin, tetrachloroethylene (PCE) and 
trichloroethylene (TCE) were identified as candidates for revision 
during the Six-Year Review 2. Of the 88 NPDWRs, EPA identified 12 as 
part of recently completed, ongoing or pending regulatory actions; as a 
result, these 12 are not subject to a detailed review for the Six-Year 
Review 3. This action involves the remaining 76 NPDWRs. EPA applied the 
same protocol used for previous Six-Year Reviews, with minor 
clarifications (USEPA, 2016f), to the Six-Year Review 3 process. 
Section V of this action describes the revised protocol used for the 
Six-Year Review 3 and Section VI describes the results of the review of 
the NPDWRs.
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    \4\ The NPDWRs apply to specific contaminants/parameters or 
groups of contaminants. Historically, when issuing new or revised 
standards for these contaminants/parameters, EPA has often grouped 
the standards together in more general regulations, such as the 
Total Coliform Rule, the Surface Water Treatment Rule or the Phase V 
rules. In this action, however, for clarity, EPA discusses the 
drinking water standards as they apply to each specific regulated 
contaminant/parameter (or group of contaminants), not the more 
general regulation in which the contaminant/parameter was regulated.
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    In addition to the regulated chemicals, radiological and 
microbiological contaminants included in the previous reviews, this 
document also includes the review of the MDBP regulations that were 
promulgated under the following actions: The Ground Water Rule (GWR); 
the Surface Water Treatment Rules (SWTRs); the Disinfectants and 
Disinfection Byproducts (D/DBP) Rules; and the Filter Backwash 
Recycling Rule (FBRR). EPA reviewed the LT2 in response to EO 13563 
(USEPA, 2011) and as part of the Six-Year Review 3 process.

                                                    Table IV-1--NPDWRs Included in Six-Year Review 3
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                                                               MCL or TT (mg/L) \1\ \2\     Contaminants/                           MCL or TT (mg/L) \2\
    Contaminants/parameters         MCLG (mg/L) \1\ \3\                  \3\                 parameters      MCLG (mg/L) \1\ \3\            \3\
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Acrylamide....................  0..........................  TT.........................  Ethylbenzene....  0.7..................  0.7
Alachlor......................  0..........................  0.002......................  Ethylene          0....................  0.00005
                                                                                           dibromide (EDB).
Alpha/photon emitters.........  0 (pCi/L)..................  15 (pCi/L).................  Fluoride........  4.0..................  4.0
Antimony......................  0.006......................  0.006......................  Giardia lamblia   0....................  TT
                                                                                           \4\.
Arsenic.......................  0..........................  0.010......................  Glyphosate......  0.7..................  0.7

[[Page 3521]]

 
Asbestos......................  7 (million fibers/L).......  7 (million fibers/L).......  Haloacetic acids  n/a \5\..............  0.060
                                                                                           (HAA5).
Atrazine......................  0.003......................  0.003......................  Heptachlor......  0....................  0.0004
Barium........................  2..........................  2..........................  Heptachlor        0....................  0.0002
                                                                                           epoxide.
Benzene.......................  0..........................  0.005......................  Heterotrophic     n/a..................  TT
                                                                                           bacteria \6\.
Benzo[a]pyrene................  0..........................  0.0002.....................  Hexachlorobenzen  0....................  0.001
                                                                                           e.
Beryllium.....................  0.004......................  0.004......................  Hexachlorocyclop  0.05.................  0.05
                                                                                           entadiene.
Beta/photon emitters..........  0 (millirems/yr)...........  4 (millirems/yr)...........  Lead............  0....................  TT
Bromate.......................  0..........................  0.010......................  Legionella......  0....................  TT
Cadmium.......................  0.005......................  0.005......................  Lindane.........  0.0002...............  0.0002
Carbofuran....................  0.04.......................  0.04.......................  Mercury           0.002................  0.002
                                                                                           (inorganic).
Carbon tetrachloride..........  0..........................  0.005......................  Methoxychlor....  0.04.................  0.04
Chloramines...................  4..........................  4.0........................  Monochlorobenzen  0.1..................  0.1
                                                                                           e
                                                                                           (Chlorobenzene).
Chlordane.....................  0..........................  0.002......................  Nitrate (as N)..  10...................  10
Chlorine......................  4..........................  4.0........................  Nitrite (as N)..  1....................  1
Chlorine dioxide..............  0.8........................  0.8........................  Oxamyl (Vydate).  0.2..................  0.2
Chlorite......................  0.8........................  1.0........................  Pentachloropheno  0....................  0.001
                                                                                           l.
Chromium (total)..............  0.1........................  0.1........................  Picloram........  0.5..................  0.5
Copper........................  1.3........................  TT.........................  Polychlorinated   0....................  0.0005
                                                                                           biphenyls
                                                                                           (PCBs).
Cryptosporidium...............  0..........................  TT.........................  Radium..........  0 (pCi/L)............  5 (pCi/L)
Cyanide.......................  0.2........................  0.2........................  Selenium........  0.05.................  0.05
2,4-Dichlorophenoxyacetic acid  0.07.......................  0.07.......................  Simazine........  0.004................  0.004
 (2,4-D).
Dalapon.......................  0.2........................  0.2........................  Styrene.........  0.1..................  0.1
Di(2-ethylhexyl)adipate (DEHA)  0.4........................  0.4........................  2,3,7,8-TCDD      0....................  3.00E-08
                                                                                           (Dioxin).
Di(2-ethylhexyl)phthalate       0..........................  0.006......................  Tetrachloroethyl  0....................  0.005
 (DEHP).                                                                                   ene.
1,2-Dibromo-3-chloropropane     0..........................  0.0002.....................  Thallium........  0.0005...............  0.002
 (DBCP).
1,2-Dichlorobenzene (o-         0.6........................  0.6........................  Toluene.........  1....................  1
 Dichlorobenzene).
1,4-Dichlorobenzene (p-         0.075......................  0.075......................  Total coliforms   n/a..................  TT
 Dichlorobenzene).                                                                         (under ADWR \7\
                                                                                           and RTCR \8\).
1,2-Dichloroethane (Ethylene    0..........................  0.005......................  Total             n/a \9\..............  0.080
 dichloride).                                                                              Trihalomethanes
                                                                                           (TTHM).
1,1-Dichloroethylene..........  0.007......................  0.007......................  Toxaphene.......  0....................  0.003
cis-1,2-Dichloroethylene......  0.07.......................  0.07.......................  2,4,5-TP          0.05.................  0.05
                                                                                           (Silvex).
trans-1,2-Dichloroethylene....  0.1........................  0.1........................  1,2,4-            0.07.................  0.07
                                                                                           Trichlorobenzen
                                                                                           e.
Dichloromethane (Methylene      0..........................  0.005......................  1,1,1-            0.20.................  0.2
 chloride).                                                                                Trichloroethane.
1,2-Dichloropropane...........  0..........................  0.005......................  1,1,2-            0.003................  0.005
                                                                                           Trichloroethane.
Dinoseb.......................  0.007......................  0.007......................  Trichloroethylen  0....................  0.005
                                                                                           e.
Diquat........................  0.02.......................  0.02.......................  Turbidity \6\...  n/a..................  TT
E. coli.......................  0..........................  MCL \10\ and TT \8\........  Uranium.........  0....................  0.030
Endothall.....................  0.1........................  0.1........................  Vinyl Chloride..  0....................  0.002
Endrin........................  0.002......................  0.002......................  Viruses.........  0....................  TT
Epichlorohydrin...............  0..........................  TT.........................  Xylenes (total).  10...................  10
--------------------------------------------------------------------------------------------------------------------------------------------------------
1. MCLG: The maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on the health of persons would occur,
  allowing an adequate margin of safety.
2. MCL: The maximum level allowed of a contaminant in water which is delivered to any user of a public water system.
TT: An enforceable procedure or level of technological performance which public water systems must follow to ensure control of a contaminant.
3. Units are in milligrams per liter (mg/L) unless otherwise noted. Milligrams per liter are equivalent to parts per million. For chlorine, chloramines
  and chlorine dioxide, values presented are MRDLG and MRDL.
4. The current preferred taxonomic name is Giardia duodenalis, with Giardia lamblia and Giardia intestinalis as synonymous names. However, Giardia
  lamblia was the name used to establish the MCLG in 1989. Elsewhere in this document, this pathogen will be referred to as Giardia spp. or simply
  Giardia unless discussing information on an individual species.
5. There is no MCLG for all five haloacetic acids. MCLGs for some of the individual contaminants are: Dichloroacetic acid (zero), trichloroacetic acid
  (0.02 mg/L), and monochloroacetic acid (0.07 mg/L). Bromoacetic acid and dibromoacetic acid are regulated with this group, but have no MCLGs.
6. Includes indicators that are used in lieu of direct measurements (e.g., of heterotrophic bacteria, turbidity).
7. The Aircraft Drinking Water Rule (ADWR) 40 CFR part 141 Subpart X, promulgated October 19, 2009, covers total coliforms.
8. Under the RTCR, a PWS is required to conduct an assessment if it exceeded any of the TT triggers identified in 40 CFR 141.859(a). It is also required
  to correct any sanitary defects found through the assessment.
9. There is no MCLG for total trihalomethanes (TTHM). MCLGs for some of the individual contaminants are: Bromodichloromethane (zero), bromoform (zero),
  dibromochloromethane (0.06 mg/L), and chloroform (0.07 mg/L).
10. A PWS is in compliance with the E. coli MCL unless any of the conditions identified under 40 CFR 141.63(c) occur.


[[Page 3522]]

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

A. What was EPA's review process?

Overview
    This section provides an overview of the process the Agency used to 
review the NPDWRs discussed in this action. The protocol document, 
``EPA Protocol for the Third Review of Existing National Primary 
Drinking Water Regulations,'' contains a detailed description of the 
process the Agency used to review the NPDWRs (USEPA, 2016f). The 
foundation of this protocol was developed for the Six-Year Review 1 
based on the recommendations of the NDWAC (2000). The Six-Year Review 3 
process is very similar to the process implemented during the Six-Year 
Review 1 and the Six-Year Review 2, with some clarifications to the 
elements related to the review of NPDWRs included in the MDBP rules. 
Figure V-1 presents an overview of the Six-Year review protocol and 
review outcomes.
    The primary goal of the Six-Year Review process is to identify and 
prioritize NPDWRs for possible regulatory revision. The two major 
outcomes of the detailed review are either:
    1. The NPDWR is not appropriate for revision and no action is 
necessary at this time.
    2. The NPDWR is a candidate for revision.
    The reasons for a Six-Year Review outcome of ``not appropriate for 
revision at this time'' can include:
     Regulatory action--recently completed, ongoing or pending. 
The NPDWR was recently completed, is being reviewed in an ongoing 
action, or is subject to a pending action.
     Ongoing or planned health effects assessment. The NPDWR 
has an ongoing health effects assessment (i.e., especially for those 
NPDWRs with an MCL set at the MCLG or where the MCL is based on the 
SDWA cost benefit provision), or EPA is considering whether a new 
health effects assessment is needed.
     No new information. EPA did not identify any new, relevant 
information that indicates changes to the NPDWR.
     Data gaps/emerging information. There are data gaps or 
emerging information that need to be evaluated.
     Low priority and/or no meaningful opportunity. New 
information indicates a possible change to the MCLG and/or MCL but 
changes to the NPDWR are not warranted due to one or more of the 
following reasons: (1) Possible changes present negligible gains in 
public health protection; (2) possible changes present limited 
opportunity for cost savings while maintaining the same or greater 
level of health protection; and (3) possible changes are a low priority 
because of competing workload priorities, limited return on the 
administrative costs associated with rulemaking and the burden on 
states and the regulated community associated with implementing any 
regulatory change that would result.
    Alternatively, the reasons for a Six-Year Review outcome that an 
NPDWR is a ``candidate for revision'' are that, at a minimum, the 
revision presents a meaningful opportunity to:
     Improve the level of public health protection, and/or
     Achieve cost savings while maintaining or improving the 
level of public health protection.
    Individual regulatory provisions of NPDWRs that are evaluated as 
part of the Six-Year Review are: MCLG, MCL, MRDLG, MRDL, TT, other 
treatment technologies such as best available technology (BAT), and 
regulatory requirements, such as monitoring requirements.
    For example, the microbial regulations include TT requirements 
because there is no reliable method that is economically and 
technically feasible to measure the microbial contaminants covered by 
those regulations. These TT requirements rely on the use of indicators 
that can be measured in drinking water, such as the concentration of a 
disinfectant, to provide public health protection. As part of the Six-
Year Review 3, EPA evaluated new information related to the use of 
those indicators to determine if there is a meaningful opportunity to 
improve the level of public health protection. Results of EPA's review 
of the MDBP regulations are presented in Sections VI.B.3 and VI.B.4.
    For the purpose of this document (except where noted for clarity), 
discussions of the review of MCLGs and MCLs should be assumed to also 
apply to the review of MRDLGs and MRDLs for disinfectants.
Basic Principles
    EPA applied a number of basic principles to the Six-Year Review 
process:
     The Agency sought to avoid redundant review efforts. 
Because EPA has reviewed information for certain NPDWRs as part of 
recently completed, ongoing or pending regulatory actions, these NPDWRs 
are not subject to the detailed review in this document.
     The Agency does not believe it is appropriate to consider 
revisions to NPDWRs for contaminants with an ongoing or planned health 
effect assessment and for which the MCL is set equal to the MCLG or 
based on benefit-cost analysis. This principle stems from the fact that 
any new health effects information could affect the MCL via a change in 
the MCLG or the assessment of the benefits associated with the MCL. 
Therefore, EPA noted that these NPDWRs are not appropriate for revision 
and no action is necessary at this time if the health effects 
assessment would not be completed during the review period for each 
contaminant that has either an MCL that is equal to its MCLG or an MCL 
that is based on the 1996 SDWA Amendments' cost-benefit provision. If 
the health effects assessment is completed before the next Six-Year 
Review, EPA will consider these NPDWRs at that time.
     In evaluating the potential for new information to affect 
NPDWRs, EPA assumed no change to existing policies and procedures for 
developing NPDWRs. For example, in determining whether new information 
affected the feasibility of analytical methods for a contaminant, the 
Agency assumed no change to current policies and procedures for 
calculating practical quantitation levels.
     EPA considered new information from health effects 
assessments that were completed by the information cutoff date. 
Assessments completed after this cutoff date will be reviewed by EPA 
during the next review cycle or (if applicable) during the revision of 
an NPDWR. The information cutoff date for the Six-Year Review 3 was 
December 2015.
     During the review, EPA identified areas where information 
is inadequate or unavailable (data gaps) or emerging and is needed to 
determine whether revision to an NPDWR is appropriate. To the extent 
EPA is able to fill data gaps or fully evaluate the emerging 
information, the Agency will consider the information as part of the 
next review cycle.
     EPA may consider accelerating review and potential 
revision for a particular NPDWR before the next review cycle when 
justified by new public health risk information.
     Finally, EPA assured scientific analyses supporting the 
review were consistent with the Agency's peer review policy (USEPA, 
2015a).

[[Page 3523]]

[GRAPHIC] [TIFF OMITTED] TP11JA17.006

B. How did EPA conduct the review of the NPDWRs?

    The protocol for the Six-Year Review 3 is broken down into a series 
of questions that can inform a decision about the appropriateness of 
revising an NPDWR. These questions are logically ordered into a 
decision tree. This section provides an overview of each of the review 
elements that EPA considered for each NPDWR during the Six-Year Review 
3, including the following: Initial review, health effects, analytical 
feasibility, occurrence and exposure, treatment feasibility, risk 
balancing and other regulatory revisions. The final review combines the 
findings from all of these review elements to recommend whether an 
NPDWR is a candidate for revision. Further information about the review 
elements is described in the protocol document (USEPA, 2016f). Results 
from the review of these elements are presented in Section VI.
1. Initial Review
    EPA's initial review of all the contaminants included in the Six-
Year Review 3 involved a simple identification of the NPDWRs that have 
either been recently completed, or are being reviewed in an ongoing or 
pending action since the last Six-Year Review (cutoff date was August 
2008). In addition, the initial review also identified contaminants 
with ongoing health effects assessments that have an MCL equal to the 
MCLG. Excluding such contaminants from the Six-Year Review 3 prevents 
duplicative agency efforts.
2. Health Effects
    The principal objectives of the health effects review are to 
identify: (1) Contaminants for which a new health effects assessment 
indicates that a change in the MCLG might be appropriate (e.g., because 
of a change in cancer classification or a change in reference dose 
(RfD)), and (2) contaminants for which new health effects information 
indicates a need to initiate a new health effects assessment.
    To meet the first objective, EPA reviewed the results of health 
effects assessments completed before December 2015, the information 
cutoff date for the Six-Year Review 3.
    To meet the second objective, the Agency conducted an extensive 
literature review to identify peer-reviewed studies published before 
December 2015. The Agency reviewed the studies to determine whether 
there was new health effects information, such as reproductive and 
developmental toxicity data, that could potentially affect the MCLG, or 
otherwise change the Agency's understanding of the health effects of 
contaminants under consideration. EPA then evaluated the need to plan 
the initiation of a new health effects assessment.
3. Analytical Feasibility
    When establishing an NPDWR, EPA identifies a practical quantitation 
limit (PQL), which is ``the lowest achievable level of analytical 
quantitation during routine laboratory operating conditions within 
specified limits of precision and accuracy'', as noted in the November 
13, 1985, Federal Register proposed rule (50 FR 46880, USEPA, 1985). 
EPA has a separate process in place to approve new analytical methods 
for drinking water contaminants; therefore, review and approval of 
potential new methods is outside the scope of the Six-Year Review 
protocol. EPA recognizes, however, that the approval and adoption in 
recent years of new and/or improved analytical methods may enable 
laboratories to quantify contaminants at lower levels than was possible 
when NPDWRs were originally promulgated. This ability of laboratories 
to measure a contaminant at lower levels could affect its PQL, the 
value at which an MCL is set when it is limited

[[Page 3524]]

by analytical feasibility. Therefore, the Six-Year Review process 
includes an examination of whether there have been changes in 
analytical feasibility that could possibly change the PQL for the 
subset of the NPDWRs that reached this stage of the review.
    To determine if changes in analytical feasibility could possibly 
support changes to PQLs, EPA relied primarily on two alternate 
approaches to develop an estimated quantitation limit (EQL): an 
approach based on the minimum reporting levels (MRLs) obtained as part 
of the Six-Year Review 3 Information Collection Request (ICR), and an 
approach based on method detection limits (MDLs).
    An MRL is the lowest level or contaminant concentration that a 
laboratory can reliably achieve within specified limits of precision 
and accuracy under routine laboratory operating conditions using a 
given method. The MRL values provide direct evidence from actual 
monitoring results about whether quantitation below the PQL using 
current analytical methods is feasible. An MDL is a measure of 
analytical method sensitivity. MDLs have been used in the past to 
derive PQLs for regulated contaminants.
    EPA used the EQL as a threshold for occurrence analysis to help the 
Agency determine if there may be a meaningful opportunity to improve 
public health protection. It should be noted, however, that the use of 
an EQL does not necessarily indicate the Agency's intention to 
promulgate a new PQL. Any revision to PQLs will be part of future 
rulemaking efforts if EPA has determined that an NPDWR is a candidate 
for revision.
4. Occurrence and Exposure Analysis
    The occurrence and exposure analysis is conducted in conjunction 
with other review elements to determine if there is a meaningful 
opportunity to revise an NPDWR by:
     Estimating the extent of contaminant occurrence, i.e., the 
number of PWSs in which contaminants occur at levels of interest 
(health-effects-based thresholds or analytical method limits), and
     Evaluating the number of people potentially exposed to 
contaminants at these levels.
    To evaluate national contaminant occurrence under the Six-Year 
Review 3, EPA reviewed data from the Six-Year Review 3 ICR database 
(SYR3 ICR database), the UCMR datasets (USEPA, 2016j) and other 
relevant sources.
    For the Six-Year Review 3, EPA collected SDWA compliance monitoring 
data through use of an ICR (75 FR 6023, USEPA, 2010a). EPA requested 
that all states and primacy entities (tribes and territories) 
voluntarily submit their compliance monitoring data for regulated 
contaminants in public drinking water systems. Specifically, EPA 
requested the submission of compliance monitoring data and related 
information collected between January 2006 and December 2011 for 
regulated contaminants and related parameters (e.g., water quality 
indicators). Forty-six states plus eight primacy agencies provided 
data. The assembled data constitute the largest, most comprehensive set 
of drinking water compliance monitoring data ever compiled and analyzed 
by EPA to inform decision making, containing almost 47 million records 
from approximately 167,000 PWSs, serving approximately 290 million 
people nationally. Through extensive data management efforts, quality 
assurance evaluations, and communications with state data management 
staff, EPA established the SYR3 ICR database (USEPA, 2016i). The number 
of states and PWSs represented in the dataset varies across 
contaminants because of variability in state data submissions and 
contaminant monitoring schedules. Except as noted in Section VI, EPA 
believes that these data are of sufficient quality to inform an 
understanding of the national occurrence of regulated contaminants and 
related parameters. Details of the data management and data quality 
assurance evaluations are available in the supporting document (USEPA, 
2016q). The resulting database is available online on the Six-Year 
Review Web site (https://www.epa.gov/dwsixyearreview).
5. Treatment Feasibility
    An NPDWR either identifies the BAT for meeting an MCL, or 
establishes enforceable TT requirements. EPA reviews treatment 
feasibility to ascertain if there are technologies that meet BAT 
criteria for a hypothetical more stringent MCL, or if there is new 
information that demonstrates an opportunity to improve public health 
protection through revision of an NPDWR TT requirement.
    To be a BAT, the treatment technology must meet several criteria 
such as having demonstrated consistent removal of the target 
contaminant under field conditions. Although treatment feasibility and 
analytical feasibility together address the technical feasibility 
requirement for an MCL, historically, treatment feasibility has not 
been a limiting factor for MCLs. The result of this review element is a 
determination of whether treatment feasibility would pose a limitation 
to revising an MCL or provide an opportunity to revise the TT 
requirement.
6. Risk-Balancing
    EPA reviews risk-balancing to examine how the Six-Year Review can 
address tradeoffs in risks among different NPDWRs and take into account 
unregulated contaminants as well. Under this review, EPA considers 
whether a change to an MCL and/or TT will increase the public health 
risk posed by one or more contaminants, and, if so, the Agency 
considers revisions that will balance overall risks. This review 
element is relevant only to the NPDWRs included in the MDBP rules, 
which were promulgated to address risk-balancing between microbial and 
DBP requirements, and among differing types of DBPs. The risk-balancing 
approach was based on the SDWA requirements that EPA ``minimize the 
overall risk of adverse health effects by balancing the risk from the 
contaminant and the risk from other contaminants the concentrations of 
which may be affected by the use of a TT or process that would be 
employed to attain the maximum contaminant level or levels'' (SDWA 
Sec.  1412(b)(5)(B)(i)).
    EPA reviewed risk-balancing between microbial and DBP contaminants. 
For example, EPA considered the potential impact on DBP concentrations 
should there be a consideration to increase the stringency of microbial 
NPDWRs. This approach also was used during the development of more 
recent MDBP rules such as the LT2 rule and the Stage 2 Disinfectants/
Disinfection Byproducts Rule (D/DBPR) rule. In addition, EPA reviewed 
risk-balancing between different types of DBP contaminants. Depending 
on the stringency of potential DBP regulations, compliance strategies 
used by the regulated community might have the effect of increasing the 
concentrations of other types of contaminants, both regulated and 
unregulated. EPA considered these potential compliance strategies when 
conducting its Six-Year Review 3 with a goal to balance the overall 
health risks.
7. Other Regulatory Revisions
    In addition to possible revisions to MCLGs, MCLs and TTs, EPA 
evaluated whether other revisions are needed to regulatory provisions, 
such as monitoring and system reporting requirements. EPA focused this 
review element on issues that were not already being addressed through 
alternative mechanisms, such as a recently completed, ongoing or 
pending regulatory action. EPA also reviewed implementation-related 
NPDWR

[[Page 3525]]

concerns that were ``ready'' for rulemaking--that is, the problem to be 
resolved had been clearly identified, along with specific options to 
address the problem that could be shown to either clearly improve the 
level of public health protection, or represent a meaningful 
opportunity for achieving cost savings while maintaining the same level 
of public health protection. The result of this review element is a 
determination regarding whether EPA should consider revisions to the 
monitoring and/or reporting requirements of an NPDWR.

C. How did EPA factor children's health concerns into the review?

    The 1996 amendments to SDWA require special consideration of 
sensitive life stages and populations (e.g., infants, children, 
pregnant women, elderly and individuals with a history of serious 
illness) in the development of drinking water regulations (SDWA Sec.  
1412(b)(3)(C)(V)). As a part of the Six-Year Review 3, EPA completed a 
literature search covering developmental and reproductive endpoints 
(e.g., fertility, embryo survival, developmental delays, birth defects 
and endocrine effects) for information published as of December 2015 
for regulated chemicals that had not been the subject of a health 
effects assessment during this review period. EPA reviewed the results 
of the literature searches to identify any studies that might suggest a 
need to revise MCLGs. These studies were considered in EPA's review of 
NPDWRs, which is discussed in Section VI.

D. How did EPA factor environmental justice concerns into the review?

    Executive Order (E.O.) 12898, ``Federal Actions to Address 
Environmental Justice in Minority Populations or Low-Income 
Populations,'' establishes a federal policy for incorporating 
environmental justice (EJ) into federal agency missions by directing 
agencies to identify and address disproportionately high and adverse 
human health or environmental effects of its programs, policies and 
activities on minority and low-income populations. EPA evaluates 
potential EJ concerns when developing regulations. This Six-Year Review 
was developed in compliance with E.O. 12898. Should the Six-Year Review 
lead to a decision to revise an NPDWR, any subsequent rulemakings will 
include an EJ component and an opportunity for public comment.

VI. Results of EPA's Review of NPDWRs

    Table VI-1 lists the results of EPA's review for each of the 76 
NPDWRs discussed in this section of this action, along with the 
principal rationale for the review outcomes. Table VI-1 also includes a 
list of the 12 NPDWRs that have been recently completed, or have 
ongoing or pending regulatory actions.

                                Table VI-1--Summary of Six-Year Review 3 Results
----------------------------------------------------------------------------------------------------------------
 
----------------------------------------------------------------------------------------------------------------
Not Appropriate for Revision at     Recently completed,    1,2-Dichloroethane           E. coli.
 this Time.                          ongoing or pending     (Ethylene dichloride).      Lead.
                                     regulatory action.    1,2-Dichloropropane........  Tetrachloroethylene
                                                           Benzene....................   (PCE).
                                                           Carbon Tetrachloride.......  Total coliforms (under
                                                                                         ADWR and RTCR).
                                                           Copper                       Trichloroethylene (TCE)
                                                           Dichloromethane (Methylene   Vinyl chloride.
                                                            chloride).
Not Appropriate for Revision at     Health effects         Alpha/photon emitters......  Mercury \1\
 this Time \2\.                      assessment in         Arsenic....................  Nitrate \1\
                                     process (as of        Atrazine...................  Nitrite \1\
                                     December 2015) or     Benzo(a)pyrene (PAHs)......  o-Dichlorobenzene \1\
                                     contaminant           Beta/photon emitters.......  p-Dichlorobenzene \1\
                                     nominated for health  Cadmium \1\................  Polychlorinated
                                     assessment.           Chromium...................   biphenyls (PCBs).
                                                           Di(2-ethylhexyl) phthalate   Radium.
                                                            (DEHP) \1\.                 Simazine.
                                                           Ethylbenzene...............  Uranium \1\
                                                           Glyphosate.................
                                    No new information,    1,2-Dibromo-3-chloropropane  Dalapon.
                                     NPDWR remains          (DBCP).                     Di(2-ethylhexyl)adipate
                                     appropriate after     2,4,5-TP (Silvex)..........   (DEHA).
                                     review.               Antimony...................  Dinoseb.
                                                           Asbestos...................  Endrin.
                                                           Bromate....................  Ethylene dibromide.
                                                           Chloramines (under D/DBPR).  Pentachlorophenol.
                                                           Chlorine (under D/DBPR)....  Thallium.
                                                           Chlorine dioxide...........  trans-1,2-
                                                           Chlorobenzene                 Dichloroethylene.
                                                            (monochlorobenzene).        Turbidity.
                                    Low priority and/or    1,1,1-Trichloroethane......  Epichlorohydrin.
                                     no meaningful         1,1,2-Trichloroethane......  Fluoride.
                                     opportunity.          1,1-Dichloroethylene.......  Heptachlor.
                                                           1,2,4-Trichlorobenzene.....  Heptachlor epoxide.
                                                           2,3,7,8-TCDD (Dioxin)......  Hexachlorobenzene.
                                                           2,4-D......................  Hexachlorocyclopentadien
                                                           Acrylamide.................   e.
                                                           Alachlor...................  Lindane.
                                                                                        Methoxychlor.
                                                           Barium                       Oxamyl (Vydate).
                                                           Beryllium..................  Picloram.
                                                           Carbofuran.................  Selenium.
                                                           Chlordane..................  Styrene.
                                                           cis-1,2-Dichloroethylene...  Toluene.
                                                           Cyanide....................  Toxaphene.
                                                           Diquat.....................  Xylenes.
                                                           Endothall..................

[[Page 3526]]

 
Candidate for Revision............  New information......  Chlorite...................  Heterotrophic Bacteria.
                                                           Cryptosporidium (under       Legionella.
                                                            SWTR, IESWTR, LT1).         TTHM.
                                                           Giardia lamblia............  Viruses (under SWTR).
                                                           Haloacetic Acids (HAA5)....
----------------------------------------------------------------------------------------------------------------
\1\ Contaminants nominated for Integrated Risk Information System (IRIS) assessments per SYR Protocol.
\2\ LT2, FBRR, and GWR also identified as not appropriate for revision at this time. See Section VI.B.4 for
  additional information on the results of EPA's review of these regulations.

A. What are the review result categories?

    For each of the 76 NPDWRs discussed in detail in the following 
sections of this action, the review outcomes fall in one of the 
following categories:
1. The NPDWR is Not Appropriate for Revision at This Time
    The current NPDWR remains appropriate and no action is necessary at 
this time. In this category, NPDWRs are grouped under the following 
subcategories:
     Health effects assessment in process (as of December 2015) 
or contaminant nominated for health assessment,
     No new information and NPDWR remains appropriate after 
review,
     Data gaps/emerging information, and
     No meaningful opportunity.
2. The NPDWR Is a Candidate for Revision
    The NPDWR is a candidate for revision based on the review of new 
information.

B. What are the detailed results of EPA's third six-year review cycle?

1. Chemical Phase Rules/Radionuclides Rules
Background
    The NPDWRs for chemical contaminants, collectively called the Phase 
Rules, were promulgated between 1987 and 1992 (after the 1986 SDWA 
amendments). In December 2000, EPA promulgated final radionuclide 
regulations, which were issued as interim rules in July 1976. 
Information related to the review for fluoride is discussed separately 
in Section VI.B.2.
Summary of Review Results
    EPA has decided that it is not appropriate at this time to revise 
any of the NPDWRs covered under the Phase Rules or Radionuclide Rules. 
These NPDWRs were determined not to be candidates for revision for one 
or more of the following reasons: There was no new information to 
suggest possible changes in MCLG/MCL; new information did not present a 
meaningful opportunity for health risk reduction or cost savings while 
maintaining/improving public health protection; or there was an ongoing 
or pending regulatory action. Details related to the review of all 
Phase Rules and Radionuclide Rules contaminants can be found in the 
``Chemical Contaminant Summaries for the Third Six-Year Review of 
National Primary Drinking Water Regulations'' (USEPA, 2016b).
Initial Review
    The initial review identified 12 chemical contaminants with NPDWRs 
under the Chemical Phase Rules that were being considered as part of 
ongoing or pending regulatory actions, and 61 chemical or radionuclide 
NPDWRs were identified as appropriate for review. The NPDWRs with 
ongoing or pending regulatory actions included eight carcinogenic 
volatile organic compounds (cVOCs), lead, copper, acrylamide and 
epichlorohydrin.
    In 2011, EPA announced its plans to address a group of regulated 
and unregulated cVOCs in a single regulatory effort. The eight 
regulated VOCs being currently evaluated for a potential cVOCs group 
regulation include: Benzene; carbon tetrachloride; 1,2-dichloroethane; 
1,2-dichloropropane; dichloromethane; PCE; TCE; and vinyl chloride. The 
regulatory revisions to TCE and PCE, initiated as an outcome of the 
Six-Year Review 2, are also being considered as part of the group 
regulatory effort. Since a regulatory effort is ongoing for these eight 
contaminants, they were excluded from a detailed review as part of the 
third Six-Year Review.
    The NPDWRs for acrylamide and epichlorohydrin were also previously 
identified as candidates for regulatory revision and were pending 
regulatory action. The polyacrylamides and epichlorohydrin-based 
polymers available today for water treatment have lower residual 
monomer content than when EPA promulgated residual content as a TT 
(USEPA, 2016s). For example, the 90th percentile concentration of 
acrylamide residual monomer levels was approximately one-half the 
residual level listed in the current TT and no residual epichlorohydrin 
was detected. The health benefits associated with the lower impurity 
levels are already being realized by communities throughout the 
country; therefore, a regulatory revision will minimally affect health 
risk. Given resource limitations, competing workload priorities, and 
administrative costs and burden to states to adopt any regulatory 
changes associated with the rulemaking, as well as limited potential 
health benefits, these NPDWRs are considered a low priority and no 
longer candidates for revision at this time.
    EPA is also currently considering Long-Term Revisions to the Lead 
and Copper Rule; and therefore, evaluation of that NPDWR under the Six-
Year Review process would be redundant.
Health Effects
    The principal objectives of the health effects review are to 
identify: (1) Contaminants for which a new health effects assessment 
indicates that a change in MCLG might be appropriate (e.g., because of 
a change in cancer classification or an RfD), and (2) contaminants for 
which the Agency has identified new health effects information 
suggesting a need to initiate a new health effects assessment.
    Before identifying chemical NPDWR contaminants for which an updated 
MCLG may be appropriate, EPA first identified chemicals with ongoing or 
planned EPA health effects assessments. As of December 31, 2015, 19 
chemical/radiological contaminants reviewed had ongoing or planned 
formal EPA health effects assessments. Table VI-2 below lists the 19 
contaminants with ongoing or planned EPA assessments and the status of 
those reviews.

[[Page 3527]]



  Table VI-2--Six-Year Review Chemical/Radiological Contaminants With Ongoing or Planned EPA Health Assessments
----------------------------------------------------------------------------------------------------------------
          Chemical/radionuclide                                            Status
----------------------------------------------------------------------------------------------------------------
Alpha/photon emitters....................  EPA is conducting a review of alpha and beta photo emitters.
Arsenic, inorganic.......................  Inorganic arsenic is being assessed by the EPA IRIS Program. The
                                            assessment status can be found at: (https://cfpub.epa.gov/ncea/iris2/atoz.cfm).
Atrazine.................................  Atrazine and simazine are being assessed under EPA's pesticide
                                            registration review process.
Benzo(a)pyrene...........................  Benzo(a)pyrene is being assessed by the EPA IRIS Program. The
                                            assessment status can be found at: (https://cfpub.epa.gov/ncea/iris2/atoz.cfm).
Beta/photon emitters.....................  EPA is conducting a review of alpha and beta photo emitters.
Cadmium..................................  Cadmium is included in the EPA IRIS Multi-Year Agenda.
Chromium (VI) as part of total Cr).......  Chromium VI is being assessed by the EPA IRIS Program. The assessment
                                            status can be found at: (https://cfpub.epa.gov/ncea/iris2/atoz.cfm).
DEHP.....................................  DEHP is included in the EPA IRIS Multi-Year Agenda.
Ethylbenzene.............................  Ethylbenzene is being assessed by the EPA IRIS Program. The
                                            assessment status can be found at: (https://cfpub.epa.gov/ncea/iris2/atoz.cfm).
Glyphosate...............................  GlyphosateGlyphosate is being assessed under EPA's pesticide
                                            registration review process.
Mercury..................................  Mercury is included in the EPA IRIS Multi-Year Agenda.
Nitrate..................................  Nitrate is included in the EPA IRIS Multi-Year Agenda.
Nitrite..................................  Nitrite is included in the EPA IRIS Multi-Year Agenda.
o-Dichlorobenzene........................  o-Dichlorobenzene is included in the EPA IRIS Multi-Year Agenda.
p-Dichlorobenzene........................  p-Dichlorobenzene is included in the EPA IRIS Multi-Year Agenda.
PCBs.....................................  PCBs are being assessed by the EPA IRIS Program. The assessment
                                            status can be found at: (https://cfpub.epa.gov/ncea/iris2/atoz.cfm).
Radium (226, 228)........................  EPA is conducting a review of radium.
Simazine.................................  Atrazine and simazine are being assessed under EPA's pesticide
                                            registration review process.
Uranium..................................  Uranium is included in the EPA IRIS Multi-Year Agenda.
----------------------------------------------------------------------------------------------------------------

    For chemicals that were not excluded due to an ongoing or planned 
health effects assessment by EPA, or by the National Academy of 
Sciences (NAS), commissioned by EPA, a more detailed review was 
undertaken. Of the chemicals that underwent a more detailed review, EPA 
identified 21 for which there have been official Agency changes in the 
RfD and/or in the cancer risk assessment from oral exposure or new 
relevant non-EPA assessments that might support a change to the MCLG. 
These 21 chemicals were further evaluated as part of the Six-Year 
Review 3 to determine whether they were candidates for regulatory 
revision. Table VI-3 lists the 21 chemicals with available new health 
effects information and the sources of the relevant new information. As 
shown in this table, 11 chemical contaminants have information that 
could support a lower MCLG and 10 contaminants have new information 
that could support a higher MCLG.

  Table VI-3--Chemicals With Available New Health Assessment That Could
                        Support a Change in MCLG
------------------------------------------------------------------------
             Chemical                     Relevant new assessment
------------------------------------------------------------------------
                       Potential Decrease in MCLG
------------------------------------------------------------------------
Carbofuran.......................  USEPA, 2008a (OPP).
Cyanide..........................  USEPA, 2010e (IRIS).
cis-1,2-Dichloroethyelene........  USEPA, 2010d (IRIS).
Endothal.........................  USEPA, 2005f (OPP).
Hexachloropentadiene.............  USEPA, 2001a (IRIS).
Methoxychlor.....................  CalEPA 2010a.
Oxamyl...........................  USEPA, 2010f (OPP).
Selenium.........................  Health Canada 2014.
Styrene..........................  CalEPA 2010b.
Toluene..........................  USEPA, 2005c (IRIS).
Xylenes..........................  USEPA, 2003a (IRIS).
------------------------------------------------------------------------
                       Potential Increase in MCLG
------------------------------------------------------------------------
Alachlor.........................  USEPA, 2006a (OPP).
Barium...........................  USEPA, 2005b (IRIS).
Beryllium........................  USEPA, 1998a (IRIS).
1,1-Dichloroethylene.............  USEPA, 2002b (IRIS).
2,4 Dichlorophenoxy-acetic Acid..  USEPA, 2013b (OPP).
Diquat...........................  USEPA, 2002a (OPP).
Lindane..........................  USEPA, 2002d (OPP).
Picloram.........................  USEPA, 1995 (OPP).
1,1,1-Trichloroethane............  USEPA, 2007a (IRIS).
1,2,4-Trichlorobenzene...........  ATSDR, 2010.
------------------------------------------------------------------------


[[Page 3528]]

    Details of the health effects review of the chemical and 
radiological contaminants are documented in the ``Six-Year Review 3--
Health Effects Assessment for Existing Chemical and Radionuclides 
National Primary Drinking Water Regulations--Summary Report'' (USEPA, 
2016h).
Analytical Feasibility
    EPA performed analytical feasibility analyses for the contaminants 
that reached this portion of the review. These contaminants included 
the 11 chemical contaminants identified under the health effects review 
as having potential for a lower MCLG and an additional 14 contaminants 
with MCLs based on analytical feasibility and MCLs higher than the 
current MCLGs. The document ``Analytical Feasibility Support Document 
for the Third Six-Year Review of National Primary Drinking Water 
Regulations: Chemical Phase Rules and Radionuclides Rules'' (USEPA, 
2016a) describes the first step in the process EPA used to evaluate 
whether changes in PQL are possible in those instances where the MCL is 
limited, or may be limited, by analytical feasibility. The EQL analysis 
is documented in the '' Development of Estimated Quantitation Levels 
for the Third Six-Year Review of National Primary Drinking Water 
Regulations (Chemical Phase Rules)'' (USEPA, 2016d).
    Table VI-4 shows the outcomes of EPA's analytical feasibility 
review for two general categories of drinking water contaminants: 
Contaminants where health effects assessments indicate potential for 
lower MCLGs; and contaminants where existing MCLs are based on 
analytical feasibility.
     A health effects assessment indicates potential for lower 
MCLG. This category includes the 11 contaminants identified in the 
health effects review as having information indicating the potential 
for a lower MCLG. EPA reviewed analytical feasibility to determine if 
analytical feasibility could limit the potential for MCL revisions. For 
six contaminants (carbofuran, cyanide, endothall, methoxychlor, oxamyl 
and styrene), the current PQL is higher than the potential new MCLG 
identified in the health effects review. For these contaminants, the 
PQL assessment did not support reduction of the current PQL, or data 
were inconclusive or insufficient to reach a conclusion. Consequently, 
analytical feasibility could be a limiting factor for setting the MCL 
equal to the potential new MCLG. The current PQL is not a limiting 
factor for the remaining five contaminants identified by the health 
effects review for possible changes in their MCLG (i.e., cis-1,2-
dichloroethylene, hexachlorocyclopentadiene, selenium, toluene and 
xylene).
     Contaminants for which existing MCLs are based on 
analytical feasibility. This category includes 14 contaminants with 
existing MCLs that are greater than their MCLGs because they are 
limited by analytical feasibility. Two of the contaminants (thallium 
and 1,1,2-trichloroethanetrichloroethane) are non-carcinogenic and have 
a non-zero MCLG and the remaining 12 contaminants are carcinogens with 
MCLGs equal to zero. EPA evaluated whether the PQL could be lowered for 
each of these contaminants. For one contaminant, 1,1,2-trichloroethane, 
EPA concluded that new information from Proficiency Testing (PT) 
studies, along with MRL and MDL data, indicate the potential to revise 
the PQL. For two contaminants (dioxin and PCBs), data from PT studies 
were inconclusive, but MRL and MDL data indicated the potential to 
revise the PQL. For five contaminants (chlordane, heptachlor, 
heptachlor epoxide, hexachlorobenzene and toxaphene) data from PT and 
MRL studies were inconclusive, but MDL data indicate the potential to 
revise the PQL. For the remaining five contaminants, either EPA did not 
have sufficient new information to evaluate analytical feasibility or 
EPA concluded that new information does not indicate the potential for 
a PQL revision.
    Where these evaluations indicated the potential for a PQL 
reduction, Table VI-4 lists the type of data that support this 
conclusion. The notation ``PT'' indicates that the PQL reassessment 
based on PT data (USEPA, 2016a) supports the reduction. The notations 
``MRL'' and ``MDL'' indicates that these two approaches support PQL 
reduction. The findings based on PT offer more certainty. When the PQL 
reassessment outcome is that the current PQL remains appropriate, Table 
VI-4 shows the result ``Data do not support PQL reduction.''

 Table VI-4--NPDWRs Included in Analytical Feasibility Reassessment and
                        Result of That Assessment
------------------------------------------------------------------------
                                   Current PQL    Analytical feasibility
          Contaminant               ([mu]g/L)      reassessment result
------------------------------------------------------------------------
  11 Contaminants Identified Under the Health Effects Review as Having
                        Potential for Lower MCLG
------------------------------------------------------------------------
Carbofuran.....................               7  Data do not support PQL
                                                  reduction.
Cyanide........................             100  Data do not support PQL
                                                  reduction.
cis-1,2-Dichloroethylene.......               5  PQL not limiting.
Endothall......................              90  PQL reduction supported
                                                  (MRL, MDL).
Hexachlorocyclopentadiene......               1  PQL not limiting.
Methoxychlor...................              10  PQL reduction supported
                                                  (PT, MRL).
Oxamyl.........................              20  PQL reduction supported
                                                  (MRL, MDL).
Selenium.......................              10  PQL not limiting.
Styrene........................               5  PQL reduction supported
                                                  (PT, MRL, MDL).
Toluene........................               5  PQL not limiting.
Xylene.........................               5  PQL not limiting.
------------------------------------------------------------------------
  14 Contaminants With MCLs Based on Analytical Feasibility and Higher
                               Than MCLGs
------------------------------------------------------------------------
Benzo(a)pyrene.................             0.2  Data do not support PQL
                                                  reduction.
Chlordane......................               2  PQL reduction supported
                                                  (MRL, MDL).
1,2-Dibromo-3-chloropropane                 0.2  Data do not support PQL
 (DBCP).                                          reduction.
Di(2-ethylhexyl)phthalate                     6  Data do not support PQL
 (DEHP).                                          reduction.
Ethylene dibromide (EDB).......            0.05  Data do not support PQL
                                                  reduction.
Heptachlor.....................             0.4  PQL reduction supported
                                                  (MDL).
Heptachlor Epoxide.............             0.2  PQL reduction supported
                                                  (MDL).
Hexachlorobenzene..............               1  PQL reduction supported
                                                  (PT, MDL).
Pentachlorophenol..............               1  Data do not support PQL
                                                  reduction.

[[Page 3529]]

 
PCBs...........................             0.5  Data do not support PQL
                                                  reduction.
Dioxin.........................      3.0 x 10-5  PQL reduction supported
                                                  (MRL, MDL).
Thallium.......................               2  Data do not support PQL
                                                  reduction.
Toxaphene......................               3  PQL reduction supported
                                                  (MDL).
1,1,2-Trichloroethane..........               5  PQL reduction supported
                                                  (PT, MRL, MDL).
------------------------------------------------------------------------

Occurrence and Exposure
    Using the SYR3 ICR database, EPA conducted an assessment to 
evaluate national occurrence of regulated contaminants and estimate the 
potential population exposed to these contaminants. The details of the 
current chemical occurrence analysis are documented in ``The Analysis 
of Regulated Contaminant Occurrence Data from Public Water Systems in 
Support of the Third Six-Year Review of National Primary Drinking Water 
Regulations: Chemical Phase Rules and Radionuclides Rules'' (USEPA, 
2016p). Based on benchmarks identified in the health effects and 
analytical feasibility analyses, EPA conducted the occurrence and 
exposure analysis for 18 contaminants.
    This analysis shows that these 18 contaminants occur at levels 
above the identified benchmark in a very small percentage of systems, 
which serve a very small percentage of the population, indicating that 
revisions to NPDWRs are unlikely to provide a meaningful opportunity to 
improve public health protection across the nation. Therefore, these 
contaminants were not identified as candidates for regulatory revision. 
Table VI-5 lists the benchmarks used to conduct the occurrence 
analysis, the total number of systems with mean concentrations 
exceeding a benchmark and the estimated population served by those 
systems.

                   Table VI-5--Occurrence and Potential Exposure Analysis for Chemical NPDWRs
----------------------------------------------------------------------------------------------------------------
                                                                                           Population served by
                                                                Number (and percentage)    systems with a mean
                                                 Benchmark \1\   of systems with a mean    concentration higher
                  Contaminant                       (ug/L)        concentration higher     than benchmarks (and
                                                                    than benchmarks        percentage of total
                                                                                               population)
----------------------------------------------------------------------------------------------------------------
           Contaminants Identified Under the Health Effects Review as Having Potential for Lower MCLG
----------------------------------------------------------------------------------------------------------------
Carbofuran....................................              >5                1 (0.00%)            993 (0.0004%)
Cyanide.......................................             >50               98 (0.27%)          574,038 (0.27%)
cis-1,2-Dichloroethylene......................             >10                4 (0.01%)            5,569 (0.00%)
Endothall.....................................             >50                1 (0.01%)             993 (0.001%)
Hexachlorocyclopentadiene.....................             >40                0 (0.00%)                0 (0.00%)
Methoxychlor..................................              >1               1 (0.003%)             993 (0.000%)
Oxamyl........................................              >9                2 (0.01%)           9,742 (0.004%)
Selenium......................................             >40               49 (0.10%)          135,685 (0.05%)
Styrene.......................................            >0.5             117 (0.210%)         571,425 (0.217%)
Toluene.......................................            >600                0 (0.00%)                0 (0.00%)
Xylene........................................          >1,000               2 (0.004%)            825 (0.0003%)
----------------------------------------------------------------------------------------------------------------
                  Contaminants With MCLs Based on Analytical Feasibility and Higher Than MCLGs
----------------------------------------------------------------------------------------------------------------
Chlordane.....................................              >1                3 (0.01%)           1,353 (0.001%)
Heptachlor....................................            >0.1                3 (0.01%)            1,643 (0.00%)
Heptachlor Epoxide............................           >0.04               14 (0.04%)          11,659 (0.005%)
Hexachlorobenzene.............................            >0.1               6 (0.016%)           8,703 (0.004%)
2,3,7,8-TCDD (Dioxin).........................       >0.000005                2 (0.06%)           1,450 (0.002%)
Toxaphene.....................................              >1                6 (0.02%)          715,106 (0.32%)
1,1,2-Trichloroethane.........................              >3                0 (0.00%)                0 (0.00%)
----------------------------------------------------------------------------------------------------------------

    In addition, EPA performed a source water occurrence analysis for 
the 10 chemical contaminants in which updated health effects 
assessments indicated the possibility to increase (i.e., render less 
stringent) the MCLG values. EPA conducted this analysis to determine if 
there was a meaningful opportunity to achieve cost savings while 
maintaining or improving the level of public health protection. The 
data available to characterize contaminant occurrence was limited 
because there is no comprehensive dataset that characterizes source 
water quality for drinking water systems. Data from the U.S. Geological 
Survey (USGS) National Water Quality Assessment program and the U.S. 
Department of Agriculture Pesticide Data Program water monitoring 
survey provide useful insights into potential contaminant occurrence in 
source water. The analysis of the available contaminant occurrence data 
for potential drinking water sources indicated relatively low 
contaminant occurrence in the concentration ranges of interest. As a 
consequence, EPA could not conclude that there is a meaningful 
opportunity for system cost savings by increasing the MCLG and/or MCL 
for these 10 contaminants. The results of this

[[Page 3530]]

analysis were documented in ``Occurrence Analysis for Potential Source 
Waters for the Third Six-Year Review of National Primary Drinking Water 
Regulations'' (USEPA, 2016e).
Treatment Feasibility
    Currently, all of the MCLs for chemical and radiological 
contaminants are set equal to the MCLGs or PQLs or are based on 
benefit-cost analysis; none are currently limited by treatment 
feasibility. EPA considers treatment feasibility after identifying 
contaminants with the potential to lower the MCLG/MCL that constitute a 
meaningful opportunity to improve public health. No such contaminants 
were identified in the occurrence and exposure analysis described 
above.
Other Regulatory Revisions
    In addition to possible revisions to MCLGs, MCLs and TTs, EPA 
considered whether other regulatory revisions are needed to address 
implementation issues, such as revisions to monitoring and system 
reporting requirements, as a part of the Six-Year Review 3. EPA used 
the protocol to evaluate which implementation issues to consider 
(USEPA, 2016f). EPA's protocol focused on items that were not already 
being addressed, or had not been addressed, through alternative 
mechanisms (e.g., as a part of a recent or ongoing rulemaking).
Implementation Issues Identified for the Six-Year Review 3
    EPA compiled information on implementation related issues 
associated with the Chemical Phase Rules. EPA also identified 
unresolved implementation issues/concerns from previous Six-Year 
Reviews. EPA shared the list of identified potential implementation 
issues with a group of state representatives convened by ASDWA to 
obtain input from state drinking water agencies concerning the 
significance and relevance of the issues (ASDWA, 2016). The complete 
list of implementation issues related to the Phase Rules and 
Radionuclide Rules is presented in ``Consideration of Other Regulatory 
Revisions in Support of the Third Six-Year Review of the National 
Primary Drinking Water Regulations: Chemical Phase Rules and 
Radionuclide Rules'' (USEPA, 2016c).
    The Agency determined that the following three issues, identified 
by state stakeholders, were within the scope of NPDWR review and were 
the most substantive:
    a. Nitrogen monitoring in consecutive systems and the distribution 
system,
    b. Alternative nitrate-nitrogen MCL of 20 mg/L for non-community 
water systems (NCWSs), and
    c. Synthetic organic chemical (SOC) detection limits.
    Table VI-6 provides a brief description of the three issues and the 
Agency's findings to date.

  Table VI-6--Chemical Rule Implementation Issues Identified That Fall
                   Within the Scope of an NPDWR Review
------------------------------------------------------------------------
       Implementation issue               Description and findings
------------------------------------------------------------------------
Nitrogen Monitoring in Consecutive  Current nitrite and nitrate
 Systems and the Distribution        standards are measured at the point
 System.                             of entry to the distribution
                                     system. Under some conditions,
                                     nitrification of ammonia in water
                                     system distribution networks could
                                     potentially result in increased
                                     total nitrite or nitrate
                                     concentrations at the point of use.
                                    To address the concern, certain
                                     water systems could develop and
                                     implement a nitrification
                                     monitoring program, which would
                                     include changing or adding
                                     additional monitoring locations.
                                    Research is needed to further
                                     evaluate the extent of this
                                     potential issue, including
                                     development of criteria to identify
                                     the specific systems where
                                     distribution system monitoring
                                     could be targeted. If the outcome
                                     of the research suggests that the
                                     magnitude of the problem represents
                                     a meaningful opportunity to improve
                                     public health protection, the
                                     regulation could be considered for
                                     revision.
Alternative Nitrate-Nitrogen MCL    EPA evaluated the possibility of
 of 20 mg/L for NCWS.                removing or further restricting the
                                     option for some NCWSs to use an
                                     alternative nitrate-nitrogen MCL of
                                     up to 20 mg/L. The nitrate-nitrogen
                                     MCL in PWSs is 10 mg/L. However,
                                     Sec.   141.11 of the Code of
                                     Federal Regulations (CFR) provides
                                     that states have the discretion to
                                     allow some NCWSs to use an
                                     alternative nitrate-nitrogen MCL of
                                     up to 20 mg/L if certain conditions
                                     are met, including conditions where
                                     water will not be available to
                                     children under six months of age.
                                    Other provisions related to this
                                     issue are included in Sec.   141.23
                                     of the CFR, which pertains to
                                     monitoring. This section states:
                                     ``Transient, non-community water
                                     systems shall conduct monitoring to
                                     determine compliance with the
                                     nitrate and nitrite MCL in Sec.
                                     Sec.   141.11 and 141.62 (as
                                     appropriate) in accordance with
                                     this section.'' The monitoring
                                     section does not address non-
                                     transient non-community water
                                     systems (NTNCWSs) eligibility to
                                     use an alternative nitrate MCL.
                                    Two potential concerns identified
                                     with the current rule provisions
                                     are:
                                       Potential health concerns
                                       other than methemoglobinemia
                                       associated with the ingestion of
                                       nitrate-nitrogen, such as
                                       possible effects on fetal
                                       development.
                                       The fact that the
                                       alternative MCL was initially
                                       intended to be used by entities
                                       such as industrial plants that do
                                       not provide drinking water to
                                       children under six months of age
                                       (44 FR 42254, USEPA, 1979).
                                       Industrial plants are generally
                                       considered to be NTNCWSs.
                                       Therefore, it is possible the
                                       alternative MCL was intended to
                                       apply specifically to NTNCWSs and
                                       not transient non-community water
                                       systems (TNCWSs).
                                    The Agency has nominated nitrate and
                                     nitrite for an IRIS assessment as a
                                     result of the Six-Year Review
                                     process, and both of these
                                     contaminants are listed in the IRIS
                                     multi-year plan. An updated
                                     assessment is needed that evaluates
                                     health effects other than
                                     methemoglobinemia. Specifically, an
                                     assessment is needed that evaluates
                                     potential health effects of nitrate-
                                     nitrogen at levels between 10 and
                                     20 mg/L on adult populations. When
                                     completed, the IRIS assessment may
                                     support initiation of a rule
                                     revision if potential adverse
                                     health effects were identified at
                                     drinking water concentrations below
                                     the alternative nitrate MCL of 20
                                     mg/L for populations other than
                                     infants less than six-months of
                                     age.

[[Page 3531]]

 
Synthetic Organic Chemical (SOC)    According to states, some
 Detection Limits.                   laboratories have reported
                                     difficulty in achieving the
                                     detection limits for some SOCs on a
                                     regular basis. Section 40 CFR
                                     141.24(h)18 provides detection
                                     limits for the SOCs, including some
                                     pesticides. PWSs that do not detect
                                     a SOC contaminant above these
                                     concentrations may qualify for
                                     reduced monitoring frequency for
                                     individual contaminants. It was
                                     reported that some SOCs may have
                                     detection limits that are lower
                                     than levels that can be
                                     economically and efficiently
                                     achieved by laboratories using
                                     approved methods. Thus, some water
                                     systems may not be able to qualify
                                     for reduced monitoring if the
                                     laboratories cannot achieve the
                                     listed detection limits. This issue
                                     was also identified as a concern by
                                     the states during the Six-Year
                                     Review 2.
                                    To address the SOC method detection
                                     limits, the Agency investigated the
                                     MRL values for SOCs from the SYR 3
                                     ICR and found there was an existing
                                     approved analytical method for each
                                     SOC that laboratories can use to
                                     achieve the appropriate detection
                                     limits in order to reduce
                                     monitoring requirements.
                                    Using the MRL values, the Agency
                                     evaluated the percentage of records
                                     in the ICR database at or below the
                                     detection limit. EPA considered
                                     this percentage as an indication of
                                     laboratories' collective ability to
                                     detect contaminant concentrations
                                     at or below these levels. The
                                     Agency found that for most of the
                                     SOCs, nearly half of the records
                                     were at or below the detection
                                     limit listed in the regulation
                                     while other SOCs had a sufficient
                                     number of records below the
                                     detection limit to determine that
                                     there was an approved analytical
                                     method that could be used.
------------------------------------------------------------------------

2. Fluoride

Background

    Fluoride can occur naturally in drinking water as a result of the 
geological composition of soils and bedrock. Some areas of the country 
have high levels of naturally occurring fluoride. EPA established the 
current NPDWR to reduce the public health risk associated with exposure 
to high levels of naturally occurring fluoride in drinking water 
sources.
    Low levels of fluoride are frequently added to drinking water 
systems as a public health protection measure for reducing the 
incidence of cavities. The decision to fluoridate a community water 
supply is made by the state or local municipality, and is not mandated 
by EPA or any other federal entity. The U.S. Public Health Service 
(PHS) recommendation for community water fluoridation is 0.7 mg/L (U.S. 
Department of Health and Human Services, 2015). Fluoride is also added 
to various consumer products (such as toothpaste and mouthwash) because 
of its beneficial effects at low level exposures.
    EPA published the current NPDWR on April 2, 1986 (51 FR 11396, 
USEPA, 1986) to reduce the public health risk associated with exposure 
to high levels of naturally occurring fluoride in drinking water 
sources. The current NPDWR established an MCLG and MCL of 4.0 mg/L to 
protect against the most severe stage of skeletal fluorosis (referred 
to as the ``crippling'' stage) (NRC, 2006a). EPA also established a 
secondary maximum contaminant level (SMCL) for fluoride of 2.0 mg/L to 
protect against moderate and severe dental fluorosis, which was 
considered at the time to be a cosmetic effect. As provided under the 
statute, the SMCL is not enforceable in the same manner as the MCL. 
Public notification is required when PWSs exceed the MCL or SMCL.
    EPA has reviewed the NPDWR for fluoride in previous Six-Year Review 
cycles. As a result of the first Six-Year Review (68 FR 42908, USEPA, 
2003b), EPA requested that the National Research Council (NRC) of the 
National Academies of Sciences (NAS) conduct a review of the health and 
exposure data on orally ingested fluoride. In 2006, the NRC published 
the results of its review and concluded that severe dental fluorosis is 
an adverse health effect when it causes both a thinning and pitting of 
the enamel, a situation that compromises the function of the enamel in 
protecting against decay and infection (NRC, 2006a). The NRC 
recommended that EPA develop a dose-response assessment for severe 
dental fluorosis as the critical effect and update an assessment of 
fluoride exposure from all sources.
    During the Six-Year Review 2, the Agency was in the process of 
developing a dose-response assessment of the non-cancer impacts of 
fluoride on severe dental fluorosis and the skeletal system. In 
addition, EPA was in the process of updating its evaluation of the 
relative source contribution (RSC) of drinking water to total fluoride 
exposure considering the contributions from dental products, foods, 
pesticide residues, and other sources such as ambient air and 
medications. These assessments were not completed at the time of the 
Six-Year Review 2; thus, no action was taken under the Six-Year Review 
2 (75 FR 15500, USEPA, 2010h).
    In 2010, EPA published fluoride health assessments. The ``Dose 
Response Analysis for Non-Cancer Effects'' (USEPA, 2010b) identified an 
oral RfD for fluoride of 0.08 milligrams per kilograms per day (mg/kg/
day) based on studies of severe dental fluorosis among children in the 
six months to 14 year age group (USEPA, 2010b). The ``Exposure and 
Relative Source Contribution Analysis'' (USEPA, 2010c) concluded that 
the RSC values for drinking water range from 40 to 70 percent, with the 
higher values associated with infants fed with powdered formula or 
concentrate reconstituted with residential tap water (70%) and with 
adults (60%). The major contributors to total daily fluoride intakes 
for these age groups are drinking water, commercial beverages, solid 
foods and swallowed fluoride-containing toothpaste (USEPA, 2010c).
Summary of Review Results
    The Agency has determined that a revision to the NPDWR for fluoride 
is not appropriate at this time. EPA acknowledges information regarding 
the exposure and health effects of fluoride (as discussed later in the 
``Health Effects'' and ``Occurrence and Exposure'' sections). However, 
with EPA's identification of several other significant NPDWRs as 
candidates for near-term revision (see Sections VI.B.3 and VI.B.4), 
potential revision of the fluoride NPDWR is a lower priority that would 
divert significant resources from the higher priority candidates for 
revision that the Agency has identified, as well as other high priority 
work within the drinking water office. These other candidates for 
revision include the Stage 1 and Stage 2 Disinfectants and Disinfection 
Byproducts Rules (D/DBPRs) that apply to approximately 42,000 PWSs, and 
for which EPA has identified the potential to further reduce

[[Page 3532]]

bladder cancer risks attributed to exposure to DBPs; the Surface Water 
Treatment Rules, for which the Agency has identified the potential to 
further reduce risks from a myriad of serious waterborne diseases 
(e.g., giardiasis, cryptosporidiosis, legionellosis, hepatitis, 
meningitis and encephalitis) for approximately 12,000 surface water 
systems; and the pending revisions to the lead and copper NPDWR which 
apply to approximately 68,000 PWSs.
    While EPA has evaluated the available health effects and exposure 
information related to fluoride (as discussed later in the ``Health 
Effects'' and ``Occurrence and Exposure'' sections), the Agency also 
recognizes that new studies on fluoride are currently being performed. 
These include new studies that address health endpoints of concern 
other than dental fluorosis. Based on the NRC recommendations, EPA 
evaluated dental fluorosis for the purposes of this action. EPA will 
continue to monitor the evolving science, and, when appropriate, will 
reconsider the fluoride NPDWR's relative priority for revision and take 
any other available and appropriate action to address fluoride risks 
under SDWA.
    Finally, most community water systems (CWSs) that provide 
fluoridation of their drinking water have already lowered their 
fluoridation level to a single level of 0.7 mg/L from a previous range 
of 0.7 to 1.2 mg/L to accommodate the updated PHS recommendation (U.S. 
Department of Health and Human Services, 2015). The U.S. Food and Drug 
Administration (FDA) also issued a letter to bottled water 
manufacturers recommending that they not add fluoride to bottled water 
in excess of the revised PHS recommendations (FDA, 2015). In addition, 
the FDA stated it intends to revise the quality standard regulation for 
fluoride added to bottled water to be consistent with the updated PHS 
recommendation. Therefore, EPA anticipates that a significant portion 
of the population's exposure to fluoride in drinking water, as well as 
some commercial beverages that use fluoridated water from CWSs and 
certain bottled water, has already been or will be reduced. 
Notwithstanding this action's decision, EPA will continue to address 
risk associated with fluoride in drinking water, with a specific focus 
on the small systems with naturally occurring fluoride in their source 
waters.
Initial Review
    EPA did not identify any recent, ongoing or pending action on 
fluoride that would exclude fluoride from the Six-Year Review 3.
Health Effects
    The NRC (2006a) evaluated the impact of fluoride on reproduction 
and development, neurotoxicity and behavior, the endocrine system, 
genotoxicity, cancer and other effects, in addition to the tooth and 
bone effects. At fluoride levels below 4.0 mg/L, the NRC found no 
evidence substantial enough to support adverse effects other than 
severe dental fluorosis and skeletal fractures. The NRC concluded that 
the available data were inadequate to determine if a risk of effects on 
other endpoints exists at an MCLG of 4.0 mg/L and made recommendations 
for additional research.
    EPA assessments (USEPA, 2010b; 2010c) found that the RSC values are 
lower than the RSC of 100 percent used to derive the original MCLG of 
4.0 mg/L, where EPA assumed that drinking water was the sole source of 
exposure to fluoride. EPA has concluded that information on the dose-
response and exposure assessment may support lowering the MCLG to 
reflect levels that would protect against risk of severe dental 
fluorosis and skeletal fractures.
    As part of this Six-Year Review, EPA reviewed health effects data 
on the impact of fluoride on reproduction and development, 
neurotoxicity and behavior, the endocrine system, genotoxicity, cancer 
and other effects that were identified by the NRC as requiring 
additional research (NRC, 2006a). EPA noted limitations in some of 
these studies such as lack of details and confounding factors. Overall, 
the new data were insufficient to alter the NRC conclusion that severe 
dental fluorosis is the critical health effects endpoint for the MCLG.
    Based upon the recommendations of the NRC, EPA has evaluated dental 
fluorosis as a critical endpoint of concern for this Six-Year Review 
(USEPA, 2010b; 2010c). However new studies are underway to examine 
other health endpoints (i.e., developmental neurobehavior effects, 
endocrine disruption and genotoxicity). One example is an ongoing 
National Toxicology Program (NTP) systematic review of animal studies 
that examined the impact of fluoride on learning and memory (NTP, 
2016). For more information about fluoride developmental neurotoxicity 
visit the National Toxicology Program Web site at https://ntp.niehs.nih.gov/pubhealth/hat/noms/fluoride/neuro-index.html. 
Additional information related to the review of the fluoride NPDWR is 
provided in the ``Six-Year Review 3 Health Effects Assessment Summary 
Report'' (USEPA, 2016h).
Analytical Feasibility
    The current PQL for fluoride is 0.5 mg/L (USEPA, 2009a). EPA has 
not identified any changes in analytical feasibility that could limit 
its ability to revise the MCL/MCLG for fluoride.
Occurrence and Exposure
    EPA analyzed fluoride occurrence using the SYR3 ICR database, which 
contains fluoride analytical results from approximately 47,000 PWSs in 
49 states/entities from 2006 to 2011. Sample records for fluoridated 
water (i.e., in which a system adds fluoride to maintain a 
concentration in the 0.7 to 1.2 mg/L range) were omitted from the 
analysis because the fluoridated systems would not be impacted by 
revisions to the fluoride NPDWR. EPA estimated the number and percent 
of systems that have mean fluoride concentrations exceeding various 
benchmarks and the corresponding estimates of population served by 
those systems. The data indicated that about 130 systems (0.3 percent), 
serving approximately 60,000 people (0.03 percent), had an estimated 
system mean concentration exceeding the current MCL of 4.0 mg/L, 
whereas more than 900 systems (2 percent), serving approximately 1.5 
million people (0.8 percent), had an estimated system mean 
concentration greater than the SMCL of 2.0 mg/L. Among these systems, 
many are small systems (serving fewer than 10,000 people) and very 
small systems (serving fewer than 500 people). Evaluations based on 
mean (or average) fluoride concentrations generally reflect an 
approximation of chronic (long-term) exposure. It is important to note 
that these average concentration-based evaluations help to inform Six-
Year Review results, but do not assess compliance with regulatory 
standards nor should be viewed as compliance forecasts for PWSs.
Treatment Feasibility
    A BAT or small system compliance technology for fluoride was not 
established in the Code of Federal Regulations (40 CFR 141.62). 
However, EPA (1998d) identified activated alumina and reverse osmosis 
as BATs for fluoride.
    Activated alumina is the most commonly used treatment technology 
for fluoride removal. It is capable of removing fluoride to 
concentrations well below the MCL of 4.0 mg/L, but with a shortened 
media life at lower target concentrations. Membrane technologies, such 
as reverse osmosis, nanofiltration, and electrodialysis, are

[[Page 3533]]

also capable of removing fluoride to very low levels (<0.3 mg/L). They 
are often used to remove fluoride along with other contaminants such as 
total dissolved solids, arsenic, and uranium. In general, these 
technologies are costly and complex to operate--and thus likewise 
present potential challenges for small water systems (USEPA, 2014a).
3. Disinfectants/Disinfection Byproducts Rules (D/DBPRs)
Background
    The D/DBPRs were promulgated in two stages--Stage 1 in 1998 (63 FR 
69390, USEPA, 1998b) and Stage 2 in 2006 (71 FR 388, USEPA, 2006d). 
Disinfection byproducts (DBPs) are formed when the disinfectants 
commonly used in PWSs to kill microorganisms react with organic and 
inorganic matter in source water. DBPs have been associated with 
potential adverse health effects, including cancer and developmental 
and reproductive effects. Monitoring parameters within the D/DBPRs 
consist of the following: DBPs--TTHM, HAA5, bromate and chlorite; 
disinfectants--chlorine, chloramines and chlorine dioxide; and water 
quality indicators--total organic carbon (TOC) and alkalinity. The 
rules include MCLGs/MRDLGs, as well as MCLs/MRDLs and TT requirements, 
which were developed for individual parameters considering their health 
risks.
    For organic DBPs, the concern is potential increased risk of cancer 
and short-term adverse reproductive and developmental effects. For 
bromate, the concern is potential increased risk of cancer. Chlorite (a 
regulated DBP) and chlorine dioxide (a disinfectant) are associated 
with methemoglobinemia, and for infants, young children and pregnant 
women, effects on the thyroid are also of concern. For chlorine and 
chloramines, health effects include eye/nose irritation and stomach 
discomfort (for chloramines, also anemia).
    The D/DBPRs apply to all sizes of CWSs and non-transient non-
community water systems (NTNCWSs) that chemically disinfect their water 
or receive chemically disinfected water (that is, involving any 
disinfectants other than ultraviolet (UV) light), as well as transient 
non-community water systems (TNCWSs) that add chlorine dioxide. The 
rules require that these systems comply with established MCLs, TTs, 
operational evaluation levels for DBPs and MRDLs for disinfectants.
    A major challenge for water suppliers is balancing the risks from 
microbial pathogens and DBPs. The risk-balancing tradeoff approach was 
intended to lower the overall risks from DBP mixtures while continuing 
to provide public health protection from microbial risks.
Summary of Review Results
    EPA has identified the following NPDWRs within the D/DBPRs as 
candidates for revision under this Six-Year Review cycle because of the 
opportunity to further reduce public health risk from exposure to DBPs: 
Chlorite, HAA5 and TTHM. This result is based on a scientific review of 
publicly available information. EPA's review process follows the 
protocol described in Section V of this document. New information has 
strengthened the weight of evidence supporting an association between 
chlorination DBPs and bladder cancer risk compared to the information 
available during development of the existing D/DBPRs. New information 
also is available related to the reproductive/developmental effects 
discussed in the Stage 2 D/DBPR. In addition, new toxicological data 
are available to support the development of MCLGs for some individual 
DBPs currently lacking MCLGs (for example, dibromoacetic acid).
    This result will also provide for additional opportunity to address 
concerns with unregulated DBPs: For example, nitrosamines and chlorate. 
In the Federal Register document for Preliminary Regulatory 
Determination 3 (79 FR 62715, USEPA, 2014b), the Agency stated that 
``because chlorate and nitrosamines are DBPs that can be introduced or 
formed in PWSs partly because of disinfection practices, the Agency 
believes it is important to evaluate these unregulated DBPs in the 
context of the review of the existing DBP regulations. DBPs need to be 
evaluated collectively, because the potential exists that the strategy 
used to control a specific DBP could increase the concentrations of 
other DBPs. Therefore, the Agency is not making a regulatory 
determination for chlorate and nitrosamines at this time.''
    Chlorate and chlorite are two different oxidation states of 
chlorine and are chemically inter-convertible. They occur, and can co-
occur, when hypochlorite solution and/or chlorine dioxide are applied 
during the drinking water treatment process. Chlorite is a regulated 
DBP. New information has shown that the relative source contribution 
for chlorite could be lower than previously estimated in the existing 
D/DBPRs, which could lead to a lower MCLG, and that there are common 
health endpoints associated with exposure to chlorite and chlorate.
    Compliance monitoring data evaluated for the Six-Year Review 3 show 
widespread occurrence of DBPs and their organic precursors (as measured 
as TOC) in drinking water. Research that has been published since the 
development of the Stage 2 D/DBPR has improved EPA's understanding of 
the effectiveness of and limitations associated with various treatment 
approaches, such as those for removal of precursors, use of 
disinfectants other than chlorine and localized treatment.
    Given that this is the first time EPA is conducting a Six-Year 
Review of the D/DBPRs, extensive information about review findings is 
provided below, with further information provided in EPA's ``Six-Year 
Review 3 Technical Support Document for Disinfectants/Disinfection 
Byproducts Rules'' (USEPA, 2016l). Additional information related to 
the review of D/DBPRs is provided in the ``Six-Year Review 3 Technical 
Support Document for Chlorate'' (USEPA, 2016k) and the ``Six-Year 
Review 3 Technical Support Document for Nitrosamines'' (USEPA, 2016o).
Initial Review
    There are no recently completed, ongoing or pending regulatory 
actions on the D/DBPRs that would exclude them from the Six-Year Review 
3.
Health Effects
    Under the Stage 1 and 2 D/DBPRs, toxicology studies for specific 
DBPs and disinfectant residuals were used to inform MCLGs (and cancer 
potency factors where MCLGs are zero) and MRDLGs. Epidemiology studies 
were used to estimate potential risks from DBP mixtures (due to cancer 
and developmental/reproductive effects) and support the benefits 
analysis. Epidemiology studies supported a potential association 
between exposures to elevated THM4 levels in chlorinated drinking water 
and cancer, but the evidence was insufficient to establish a causal 
relationship. The most consistent evidence was for bladder cancer. For 
the development of the benefits analysis for both the Stage 1 and the 
Stage 2 D/DBPRs, EPA used five bladder cancer case-control epidemiology 
studies that were conducted in the 1980s and 1990s (Cantor et al., 
1985; 1987; McGeehin et al., 1993; King and Marrett, 1996; Freedman et 
al., 1997; Cantor et al., 1998). In addition, EPA used one meta-
analysis (Villanueva et al., 2003) and one pooled analysis (Villanueva 
et al., 2004). The five case-control studies used similar (though not 
identical) exposure metrics based on years of exposure to chlorinated 
drinking water (primarily chlorinated surface water) to

[[Page 3534]]

estimate odds ratios. All five studies showed an increase in the odds 
ratio for bladder cancer incidence with an increased duration of 
exposure. Using the published odds ratio results from these five 
studies, EPA calculated an estimate for the lifetime cancer risk 
(population attributable risk) that ranged from 2 to 17 percent; 
between 2 and 17 percent of bladder cancers occurring in the U.S. could 
be attributed to long-term exposure to chlorinated drinking water at 
the time of the Stage 1 D/DBPR. Detailed explanations of these 
calculations can be found in the benefits analysis for the Stage 2 D/
DBPR (USEPA, 2005a). The evidence from the studies in 1985 to 1998, the 
meta-analysis in 2003 and the pooled analysis in 2004 was strong enough 
to support the benefit analysis with several thousand potential bladder 
cancer cases per year estimated as being avoided from the combined 
effects of the Stage 1 and Stage 2 D/DBPRs (USEPA, 2005a).
    Studies from the 1970s to 2005 also suggested a possible 
association between adverse developmental/reproductive health effects 
and exposure to chlorinated drinking water. Effects were observed in 
all areas but lacked consistency across studies and did not provide 
enough of a basis to quantify risks or benefits. The adverse 
developmental/reproductive effects consisted of effects on fetal growth 
(small for gestational age, low birth weight and pre-term delivery), 
effects on viability (spontaneous abortion, stillbirth) and 
malformations (neural tube, oral cleft, cardiac or urinary defects).
    Since the development of the Stage 2 D/DBPR, EPA has identified 
additional sources of information related to health effects of DBPs. 
New toxicological information could be used to develop MCLGs for the 
following regulated DBPs (within HAA5): Dibromoacetic acid (NTP, 2007), 
other brominated haloacetic acids not currently regulated, including 
bromochloroacetic acid (NTP, 2009) and bromodichloroacetic acid (NTP, 
2014), plus additional unregulated DBPs such as nitrosamines and 
chlorate (USEPA, 2016k; 2016o).
    EPA has identified new epidemiological, pharmacokinetic and 
pharmacodynamic studies that, considered together with studies 
available during the development of the Stage 2 D/DBPR, add to the 
weight of evidence for bladder cancer being associated with exposure to 
chlorination DBPs (notably those containing bromine) in drinking water.
    Pharmacokinetic and pharmacodynamic studies (Ross and Pegram, 2003; 
2004; Leavens et al., 2007; Stayner et al., 2014; Kenyon et al., 2015), 
in conjunction with epidemiology studies (Villanueva et al., 2007; 
Kogevinas et al., 2010; Cantor et al., 2010), indicate that non-
ingestion routes of exposure (dermal and inhalation) from some 
brominated DBPs may play a significant role in influencing increased 
bladder cancer risk, and that there may be greater concern about sub-
populations with certain genetic characteristics (polymorphisms). EPA's 
``Six-Year Review 3 Technical Support Document for Disinfectants/
Disinfection Byproducts Rules'' (USEPA, 2016l) characterizes the 
research that informs the mode of action by which brominated DBPs may 
be contributing to bladder cancer.
    While uncertainties remain regarding the degree to which specific 
DBPs contributed to the bladder cancer incidence observed in 
epidemiology studies, the collective data suggest a stronger case for 
causality than when the Stage 2 D/DBPR was promulgated (Regli et al., 
2015; USEPA, 2016l). However, the Agency recognizes there are also 
different perspectives on this issue, including suggestions about areas 
for additional research (Hrudey et al., 2015).
    Further, the Agency has identified new information about health 
effects from unregulated DBPs. This includes health effects information 
on chlorate and nitrosamines that, along with occurrence/exposure 
information, was previously noted in the Preliminary Regulatory 
Determination 3 (79 FR 62715, USEPA, 2014b). The Agency is considering 
the health effects of chlorate and nitrosamines within the broader 
context of the health effects of regulated DBPs (USEPA, 2016k; 2016o).
    EPA also identified information about the relative cytotoxicity and 
genotoxicity of many other unregulated DBPs (Richardson et al., 2007; 
Richardson et al., 2008; Plewa and Wagner 2009; Plewa et al., 2010; 
Fern[aacute]ndez et al., 2010; Richardson and Postigo, 2011; Yang et 
al., 2014). Data from in vitro mammalian cell testing, which compared 
the cytotoxicity and genotoxicity of iodinated, brominated, and 
chlorinated DBPs, showed that the iodinated DBPs (those containing 
iodine) were generally more toxic than the brominated DBPs (those 
containing bromine), which were in turn more toxic than the chlorinated 
DBPs (those containing chlorine). Nitrogen-containing DBPs, including 
haloacetonitriles, haloacetamides and halonitromethanes, were more 
cytotoxic and genotoxic than the haloacids and halomethanes that did 
not contain nitrogen.
    Approximately 40 new studies about developmental/reproductive 
effects have become available since the development of the Stage 2 D/
DBPR. These studies address endpoints such as fetal growth (low birth 
weight, small for gestational age and pre-term delivery), congenital 
anomalies and male reproductive outcomes. These studies continue to 
support a potential health concern, though, as discussed above, the 
relationship of DBP exposure to these types of adverse outcomes may not 
be well enough understood to permit quantification of risks or 
benefits. A recent ``four-lab study'' on the effects of DBP mixtures on 
animals, conducted by EPA researchers (Narotsky et al., 2011; 2013; 
2015), suggests diminished concern for many developmental/reproductive 
endpoints.
    EPA also examined data about health effects for inorganic DBPs, 
including information showing that the RSC for chlorite could be lower 
than 80 percent (which could potentially support lowering the MCLG) 
because there is more dietary exposure than previously assumed due to 
the increased use of chlorine dioxide and acidified sodium chlorite as 
disinfectants in the processing of foods (U.S. EPA, 2006e; WHO, 2008). 
In addition, chlorate, chlorite and chlorine dioxide may share common 
health endpoints, namely hematological and thyroid effects (Couri and 
Abdel-Rahman, 1980; Bercz et al., 1982; Moore and Calabrese, 1982; 
Abdel-Rahman et al., 1984; Khan et al., 2005; Orme et al., 1985; NTP, 
2005; USEPA, 2006e; WHO, 2008; Lee et al, 2013; Nguyen et al, 2014).
    The Agency did not identify any relevant data that suggest an 
opportunity to revise the MCLG for bromate, or the MRDLG for chlorine 
or chloramines.
Analytical Feasibility
    The Agency has not identified any improvements to analytical 
feasibility that could lead to improvements to the NPDWRs included in 
the D/DBPRs. Development of these rules was not constrained by the 
availability of analytical methods, and new EPA-approved methods that 
would revise this finding have not been identified. Should new, EPA-
approved methods for one or more D/DBPRs be identified, that 
information might be able to help inform potential future regulatory 
development efforts.
Occurrence and Exposure
    In this Six-Year Review evaluation of D/DBP occurrence and 
exposure, EPA

[[Page 3535]]

evaluated compliance monitoring information collected under the SYR3 
ICR, which was previously discussed in Section V.B.4. EPA also 
evaluated information from the DBP ICR database (USEPA, 2000a) that had 
been used to prepare the original D/DBPRs. Additionally, EPA used data 
from the third monitoring cycle of the Unregulated Contaminant 
Monitoring Rule (UCMR3) to evaluate chlorate occurrence in 2013-2015, 
and data from the UCMR2 to evaluate nitrosamine occurrence in 2008-
2010. This information is briefly described below, with additional 
information in EPA's ``Six-Year Review 3 Technical Support Document for 
Disinfectants/Disinfection Byproducts Rules'' (USEPA, 2016l).
    It is important to note that the information collected through the 
SYR3 ICR spans the years 2006-2011. As such, it primarily reflects 
occurrence following the effective date for the Stage 1 D/DBPR, but 
prior to the effective date for the Stage 2 D/DBPR. These evaluations 
help to inform Six-Year Review results but do not assess compliance 
with regulatory standards.
    New information since the promulgation of the Stage 2 D/DBPR has 
improved our understanding on DBP formation and occurrence. As part of 
this Six-Year Review, EPA has identified literature describing more 
than 600 specific DBPs that have been found in drinking water (e.g., 
Richardson et al., 2007); these include chlorinated, brominated and 
iodinated DBPs, as well as nitrogenous compounds. Additionally, EPA 
identified literature on the sources of precursors (both organic and 
inorganic), as well as the influence that different precursors have on 
DBP formation. For example, some of this literature discusses the 
extent to which brominated or iodinated DBPs might form as a result of 
source water bromide or iodide concentrations (Nguyen et al., 2005; 
Duirk et al, 2011; Lui et al., 2012; Zhang et al., 2012; Callinan et 
al., 2013; Emelko et al., 2013; Mikkelson et al., 2013; Rice et al., 
2013; Samson et al., 2013; Rice and Westerhoff, 2014).
Overview of DBP Occurrence
    EPA collected occurrence information for THMs (includes TTHM along 
with information on four individual species), HAAs (includes HAA5 along 
with information on five individual species), bromate and chlorite as 
part of the SYR3 ICR.
    Data from the SYR3 ICR show that concentrations at or above the 
MCLs for TTHM and HAA5 were found in many surface water systems and, to 
a lesser degree, in ground water systems. Approximately 32 percent of 
surface water systems and five percent of ground water systems reported 
at least one instance of TTHM occurrence at a concentration greater 
than or equal to the MCL of 80 [micro]g/L. For HAA5, approximately 19 
percent of surface water systems and two percent of ground water 
systems reported at least one instance of occurrence at a concentration 
greater than or equal to the MCL of 60 [micro]g/L. EPA anticipates that 
many of these peak concentrations will have been significantly lowered 
based on implementation of the 2006 Stage 2 D/DBPR, which was designed, 
in part, to lower such occurrences.
    Approximately nine percent of systems had one or more samples that 
were greater than or equal to the bromate MCL of 10 [micro]g/L. 
Approximately four percent of systems had one or more samples that were 
greater than or equal to the chlorite MCL of 1,000 [micro]g/L.
    The occurrence of six nitrosamine species was evaluated by EPA 
using data from the UCMR2. These data showed elevated concentrations of 
nitrosamines (relative to their health reference levels) in multiple 
drinking water systems, especially N-nitrosodimethylamine (NDMA) in 
systems that use chloramines (USEPA, 2016o). The Agency is seeking 
public comment regarding potential approaches that provide enhanced 
protection from health risks posed by nitrosamines in drinking water 
systems.
    The occurrence of chlorate was evaluated by EPA using data from the 
UCMR3 (USEPA, 2016j). These data showed that chlorate levels above the 
health reference level of 210 [micro]g/L occurred frequently in systems 
that use hypochlorite, chlorine dioxide or chloramines. In addition, 
EPA evaluated the co-occurrence of chlorite and chlorate and noted that 
these contaminants often co-occur (USEPA, 2016k). The Agency is seeking 
public comment regarding potential approaches that provide enhanced 
protection from health risks posed by chlorite, chlorate and chlorine 
dioxide. See Section VII for more information.
    The American Water Works Association (AWWA), through the Water 
Industry Technical Action Fund #266, conducted its own survey of post-
Stage 2 D/DBPR occurrence for systems that serve more than 100,000 
people. Results from the AWWA survey (Samson, 2015) provide an overview 
of DBP occurrence for 395 systems across 44 states, covering a time 
period from 1980 to 2015.
    In December 2015, EPA issued a proposal for the fourth cycle of the 
UCMR (80 FR 76897, USEPA, 2015b). That proposal includes provisions for 
collection of data about unregulated haloacetic acids and related 
precursors. Such data would help EPA to develop a better understanding 
of patterns of occurrence for those contaminants.
Overview of Water Quality Indicator Occurrence
    The Stage 1 D/DBPR requires that DBP precursors (measured as TOC) 
be monitored in source and treated drinking water. EPA evaluated 
compliance monitoring data from surface water systems for TOC in source 
and treated water, using the SYR3 ICR database. Data from 2011 showed 
that approximately 70 percent of all plants had average TOC 
concentrations greater than 2 mg/L in their source water and that 
approximately 29 percent of plants had average TOC concentrations 
greater than 2 mg/L in their treated water. Under the Stage 1 D/DBPR, a 
system is not required to further remove TOC when its treated water TOC 
level, prior to the point of continuous chlorination, is less than 2 
mg/L. The reader is referred to later portions of this document under 
``DBP Precursor Removal'' for information about EPA's evaluation of TOC 
data relative to the Stage 1 D/DBPR TOC removal requirement.
    As discussed in the background portion of this section, the D/DBPRs 
require systems to maintain disinfectant residual levels (reported as 
free and/or total chlorine) in accordance with the MRDL requirements. 
EPA evaluated free and total chlorine measurements (collected during 
coliform sampling) from the SYR3 ICR database and found that very few 
records exceeded 4.0 mg/L (the MRDL for chlorine and chloramine 
residuals). Additional information is provided in ``Six-Year Review 3 
Technical Support Document for Disinfectants/Disinfection Byproducts 
Rules'' (USEPA, 2016l).
Treatment Feasibility
    During the development of the Stage 1 and Stage 2 D/DBPRs, a 
variety of technologies were evaluated for their effectiveness, 
applicability, unintended consequences and overall feasibility for 
achieving compliance with the TT requirements and MCLs, as well as 
providing a basis for the BATs (63 FR 69390; 71 FR 388; USEPA, 1998b; 
2005a; 2005g; 2006d; 2007b).
    Since the Stage 2 D/DBPR, the Agency has identified information 
that improves our understanding of technologies available for lowering 
occurrence of and exposure to regulated and unregulated DBPs. The 
information addresses the full spectrum of drinking water system

[[Page 3536]]

operations, including removal of organic precursors to DBPs (measured 
as TOC), disinfection practices, source water management and localized 
treatment. The information is briefly discussed below, with additional 
information in EPA's ``Six-Year Review 3 Technical Support Document for 
Disinfectants/Disinfection Byproducts Rules'' (USEPA, 2016l). Overall, 
the information collectively indicates that: (1) Greater removals of 
DBP precursors can and are being achieved compared to the TT 
requirement under the Stage 1 D/DBPR; and (2) occurrence of DBPs can be 
further controlled.
DBP Precursor Removal
    The SYR3 ICR database (USEPA, 2016i) includes paired source and 
treated water TOC data. This information was used to evaluate the 
extent to which TOC was removed from source waters (i.e., percent 
removal) relative to the Stage 1 D/DBPR TOC removal requirement (i.e., 
requirement per the 3x3 matrix, which was established based on three 
different ranges of raw water TOC and alkalinity levels, respectively). 
This TT requirement is applicable to surface water systems that have 
conventional treatment plants, unless such systems meet the alternative 
criteria (63 FR 69390, USEPA, 1998b). The analytical results of TOC 
removal (i.e., comparing TOC levels from source water to treated water) 
can help to characterize national treatment baselines among these 
treatment plants.
    The data show a wide range of percent TOC removal for each 
combination of raw water TOC and alkalinity levels provided in the 
Stage 1 D/DBPR TT requirement. The data also indicate that the mean 
removal for each element of the 3x3 matrix was six to 19 percent 
greater than the requirement. These observations are consistent with 
the notion that ``since the Stage 1 D/DBPR does not require that all 
coagulable dissolved organic matter be removed, there is a potential 
for additional removal of organic matter beyond that required by the 
3x3 matrix'' (McGuire et al., 2014).
    Some of the TOC removal greater than the Stage 1 D/DBPR requirement 
may reflect operational optimization of conventional treatment, 
including use of innovative coagulants/coagulant aids and/or use of 
biofiltration (Yan et al., 2008; Hasan et al., 2010; McKie et al., 
2015; Azzeh et al., 2015; Delatolla et al., 2015; Pharand et al., 
2015). Studies have shown that biological filtration can also reduce 
precursors of the DBPs other than TTHM/HAA5 (Sacher et al., 2008; 
Farr[eacute] et al., 2011; Liao et al., 2014; Krasner et al., 2015). As 
noted by McGuire et al. (2014), if the removal of precursors for DBPs 
other than TTHM/HAA5 becomes part of the treatment goals, then 
performance parameters in addition to TOC may also be needed (e.g., 
parameters indicating both vulnerability and nitrosamine formation 
potential).
    As was known during development of the Stage 1 and the Stage 2 D/
DBPRs, granular activated carbon (GAC) and membranes can be added to 
existing treatment trains to achieve additional reductions of DBP 
formation potential. One longstanding issue has been the extent to 
which organic precursor removal may cause a shift of chlorinated 
species to more brominated species (as described earlier in this 
Section under the ``Health Effects'') when the bromide level is 
relatively high in source water (Summers et al., 1993; Symons et al., 
1993). The ICR Treatment Study database (USEPA, 2000b) provides 
extensive bench- and pilot-scale data by which to evaluate the effects 
of GAC and membrane removal of TOC and resulting shifts in brominated 
THMs. EPA's recent analysis of these data generally shows increased 
percent reduction of brominated THMs as TOC removal by GAC increases 
(e.g., from a target effluent level of two mg/L to one mg/L), 
especially for source waters with high bromide concentrations (USEPA, 
2016l). It also shows that bromoform formation increases as bromide 
concentrations increase and that bromoform becomes the dominating 
species when source water bromide concentrations exceed 200 [micro]g/L.
Disinfection Practices
    Various combinations of disinfectants and precursor removal 
processes have been used to achieve DBP MCLs, while also meeting the 
requirements of the microbial standards. Data from successive national 
drinking water datasets (including the DBP ICR, UCMR2 and UCMR3 
datasets) show that the percentage of systems using disinfectants other 
than chlorine has increased during the past two decades, as had been 
forecasted in the ``Economic Analysis of Stage 2 D/DBPR'' (USEPA, 
2005a). For example, data from the UCMR3 (2013-2015) and the DBP ICR 
(1998) have shown a relative increase in use of chloramines, which is 
associated with the formation of nitrosamines, as a disinfection 
practice.
    EPA reviewed information related to the extent to which different 
types of DBPs may form when disinfectants are applied at different 
points in the treatment train and/or in combination with other 
disinfectants. EPA recognized that the extent to which occurrence and 
associated health effects data may be lacking for one group of DBP 
contaminants versus another, as well as for DBP mixtures, may make 
treatment decisions challenging when trying to evaluate DBP risk 
tradeoffs.
Source Water Management
    New information shows that source waters with relatively elevated 
sewage contributions have been associated with increased nitrosamine 
formation (Westerhoff et al., 2015; Krasner et al., 2013) and that 
source waters with elevated bromide levels from industrial discharges 
have been associated with increased brominated THMs (McTigue et al., 
2014; States et al., 2013). Such factors as these impacts can increase 
the challenge of controlling DBPs during treatment and distribution. 
Weiss et al. (2013) developed a model for making source water selection 
decisions based on real-time DBP precursor concentrations.
    Information shows that bank filtration can reduce dissolved organic 
carbon (DOC) and nitrogenous DBP precursors (Brown et al., 2015; 
Krasner et al., 2015), as well as removing pathogens (USEPA, 2016m).
Localized Treatment
    Localized treatment in distribution systems, such as aeration in 
storage tanks, sometimes with the addition of GAC, has also been shown 
to reduce elevated levels of THMs (Walfoort et al., 2008; Fiske et al., 
2011; Brooke and Collins, 2011; Johnson et al., 2009; Duranceau, 2015). 
Aeration approaches have been most successful in reducing 
concentrations of chloroform and the more volatile brominated species 
but may have little impact on less volatile species (Johnson et al., 
2009; Duranceau, 2015).
Risk-Balancing
    The Agency has considered the risk-balancing aspects of the MDBP 
rules and has determined that potential revisions to the D/DBPRs could 
provide greater protection of public health while still being 
protective of microbial risks. The risk-balancing activities considered 
by the Agency include those between the microbial and disinfection 
byproduct rules, as well as those between different groups of DBPs. 
This includes risk-balancing for the THMs and HAAs included in the D/
DBPRs, additional brominated HAAs, nitrosamines identified in the 
Federal Register document for the Preliminary Regulatory Determination 
3 (79 FR 62715, USEPA, 2014b) and other DBP groups such as iodinated 
DBPs. It also

[[Page 3537]]

includes risk-balancing for inorganic DBPs such as chlorite and 
chlorate (79 FR 62715, USEPA, 2014b).
    Potential revisions could offer enhanced protection from both 
regulated and unregulated DBPs. Potential revisions that consider areas 
such as further constraints on precursors, and/or more targeted 
constraints on precursors (e.g., based on watershed vulnerabilities), 
could minimize the formation of harmful DBPs without compromising 
protection against microbial risks. These potential revisions were 
identified based on a preliminary, qualitative assessment; it is 
important to note that further assessment would be an important 
component of any further rulemaking activities. For example, a 
watershed vulnerability characterization that includes information 
about wastewater (i.e., sewage) contributions, land use (point/non-
point sources of pollution), and streamflow variations over time (for 
example, sewage contributions during low flow conditions), could help 
to inform considerations about DBP formation potentials and possible 
control strategies.
    The Agency is seeking public comment regarding potential revisions 
to D/DBPR. See Section VII for more information. Further discussion 
about potential revisions to existing D/DBPRs will occur as part of a 
separate regulatory development process.
Other Regulatory Revisions
    In addition to evaluating information about health effects, 
analytical feasibility, occurrence and exposure, treatment feasibility 
and risk-balancing related to the NPDWRs included in the D/DBPRs, EPA 
considered whether other regulatory revisions are needed, such as 
revisions to monitoring and system reporting requirements, as a part of 
the Six-Year Review 3. EPA used the protocol to evaluate which of these 
implementation issues to consider (USEPA, 2016f). As with the Chemical 
Phase Rules/Radionuclides Rules, EPA shared the list of identified 
potential implementation issues with the ASDWA to obtain input from 
state drinking water agencies concerning the significance and relevance 
of the issues (ASDWA, 2016). Implementation issues will be considered 
as part of the activities associated with potential future rulemaking 
efforts; some of these might be addressed through regulatory revision 
or clarification, while others might be handled through guidance.
    Examples of implementation-related considerations include the 
following:
Stage 2 D/DBPR Consecutive System Monitoring
    Monitoring in some combined distribution systems may be 
insufficient to adequately characterize DBP exposure. Some large, 
hydraulically complex combined water distribution systems may be 
conducting monitoring that is not adequate to characterize exposure 
throughout the distribution system.
Stage 2 D/DBPR Compliance Monitoring--Chlorine Burn
    Compliance monitoring for DBPs in some systems may not fully 
capture DBP levels to which customers may be exposed during certain 
portions of the year. Systems that use chloramines as a residual 
disinfectant (generally as part of a compliance strategy to meet DBP 
MCLs) often temporarily switch to free chlorine as the residual 
disinfectant for a period (from two to eight weeks) in order to control 
nitrification in the distribution system. This practice is commonly 
called a ``chlorine burn.'' During the chlorine burn, higher levels of 
DBPs are expected to be formed. Systems often conduct their compliance 
monitoring outside of the chlorine burn period; and therefore, 
potentially higher TTHM and HAA5 levels may not be included in 
compliance calculations.
4. Microbial Contaminants Regulations
Background
    Except for the 1989 Total Coliform Rule, which was reviewed under 
the Six-Year Review 1, this is the first time EPA is conducting a Six-
Year Review of the following microbial contaminant regulations:
     Surface Water Treatment Rule (SWTR),
     Interim Enhanced Surface Water Treatment Rule (IESWTR),
     Long Term 1 Enhanced Surface Water Treatment Rule (LT1),
     Long Term 2 Enhanced Surface Water Treatment Rule (LT2),
     Filter Backwash Recycling Rule (FBRR), and
     Ground Water Rule (GWR).
    As discussed in Section V, the Initial Review branch of the 
protocol identifies NPDWRs with recent or ongoing actions and excludes 
them from the review process to prevent duplicative agency efforts. The 
cutoff date for the NPDWRs reviewed under the Six-Year Review 3 was 
August 2008. Based on the Initial Review, EPA excluded the Aircraft 
Drinking Water Rule, which was promulgated in 2009, and the Revised 
Total Coliform Rule (RTCR) (the revision of the 1989 TCR), which was 
promulgated in 2013.
    In this document, the SWTR, the IESWTR and the LT1 are collectively 
referred to as the SWTRs because of the close association among the 
three rules (IESWTR and LT1 were amendments to the SWTR--additional 
information provided in Section VI.B.4.a). The LT2 is discussed 
separately in this document because EPA reviewed the LT2 in accordance 
with the Six-Year Review requirements and the Executive Order 13563 
``Improving Regulation and Regulatory Review'' (also known as 
Retrospective Review). Background information on each of the microbial 
contaminants regulations is presented in the subsequent sections.
    The microbial contaminants regulations establish treatment 
technique (TT) requirements in lieu of MCLs. The review elements of the 
microbial contaminants regulations are: initial review, health effects, 
analytical feasibility, occurrence and exposure, treatment feasibility, 
risk-balancing and other regulatory revisions.
    At this time, the SWTRs are being identified as a candidate for 
regulatory revision, but the LT2, the FBRR and the GWR are not. A 
summary of review findings of each rule is described in the subsequent 
sections. Additional information is provided in the ``Six-Year Review 3 
Technical Support Document for Microbial Contaminant Regulations'' 
(USEPA, 2016n) and the ``Six-Year Review 3 Technical Support Document 
for Long-Term 2 Enhanced Surface Water Treatment Rule'' (USEPA, 2016m).
a. SWTRs
Background
    EPA promulgated the SWTR in June 1989. It requires all water 
systems using surface water sources or ground water under the direct 
influence of surface water (GWUDI) sources (also known as Subpart H 
systems) to remove (via filtration) and/or inactivate (via 
disinfection) microbial contaminants (54 FR 27486, USEPA, 1989). Under 
the SWTR, EPA established NPDWRs for Giardia, viruses, Legionella, 
turbidity and heterotrophic bacteria and set MCLGs of zero for Giardia 
lamblia, viruses and Legionella. Under the IESWTR (63 FR 69477, USEPA, 
1998c) and the LT1 (67 FR 1812, USEPA, 2002c), EPA established an NPDWR 
for Cryptosporidium and set an MCLG of zero.
    The SWTRs established TT requirements in lieu of MCLs in these 
NPDWRs. The 1989 SWTR established TT requirements for systems to 
control G. lamblia by achieving at least 99.9 percent (3-log) removal/
inactivation by

[[Page 3538]]

filtration and/or disinfection, and to control viruses by achieving at 
least 99.99 percent (4-log) removal/inactivation (54 FR 27486, USEPA, 
1989). For a few systems able to meet source water criteria and site-
specific conditions (e.g., protective watershed control program and 
other conditions), they were permitted to achieve the TT requirements 
by using disinfection only.
    The SWTR also established TT requirements for disinfectant 
residuals (54 FR 27486, USEPA, 1989). The residual disinfectant 
concentration at the entry point to the distribution system may not be 
less than 0.2 mg/L for more than four hours. The residual disinfectant 
concentration in the distribution system ``cannot be undetectable in 
more than 5 percent of the samples each month, for any two consecutive 
months that the system serves water to the public.'' (40 CFR 141.72). A 
detectable residual may be established by: (1) an analytical 
measurement or (2) having a heterotrophic bacteria concentration less 
than or equal to 500 per mL measured as heterotrophic plate count 
(HPC). The purpose of these disinfectant residual requirements was to:
     Ensure that the distribution system is properly maintained 
and identify and limit contamination from outside the distribution 
system when it might occur,
     Limit growth of heterotrophic bacteria and Legionella 
within the distribution system, and
     Provide a quantitative limit, which if exceeded would 
trigger remedial action.
    The SWTR also established sanitary survey requirements. The purpose 
of the sanitary survey requirements, which include consideration of 
distribution system vulnerabilities, is to identify water system 
deficiencies that could pose a threat to public health and to permit 
correction of such deficiencies.
    As part of the development of the SWTR, EPA needed to clarify which 
systems would be regulated under Subpart H. In particular, EPA needed 
to clarify when systems that could be considered as ground water 
systems were more appropriate to regulate as surface water systems (for 
example, systems where the drinking water intake was in a riverbed, not 
in the river). Thus, to identify a system as either ground or surface 
water, the SWTR defined ``ground water under the direct influence of 
surface water (GWUDI).'' GWUDI is any water beneath the surface of the 
ground with: (1) significant occurrence of insects or other 
macroorganisms, algae or large-diameter pathogens such as Giardia 
lamblia, or (2) significant and relatively rapid shifts in water 
characteristics such as turbidity, temperature, conductivity or pH that 
closely correlate to climatological or surface water conditions. The 
final SWTR defined GWUDI as being regulated as surface waters because 
Giardia contamination of infiltration galleries, springs and wells have 
been found (Hoffbuhr et al., 1986; Hibler et al., 1987). Some 
contamination of springs and wells have resulted in giardiasis 
outbreaks (Craun and Jakubowski, 1986). Direct influence was to be 
determined for individual sources in accordance with criteria 
established by the state (54 FR 27486, USEPA, 1989). The GWUDI 
designation identifies PWSs using ground water that must be regulated 
as if they are surface water systems. All other PWSs using ground water 
are regulated by the GWR.
    Surface water and GWUDI systems use concentration x time (CT) 
tables published by EPA to determine log-inactivation credits for the 
use of a disinfectant to meet the disinfection TT requirements. The 
``SWTR Guidance Manual'' provides CT tables for Giardia and virus 
inactivation by free chlorine, chloramines, ozone and chlorine dioxide 
(USEPA, 1991). EPA obtained these CT values from bench-scale 
experiments with hepatitis A virus (HAV).
    The IESWTR applies to all PWSs using surface water, or GWUDI, which 
serve 10,000 or more people. The IESWTR established TT requirements for 
Cryptosporidium by requiring filtered systems to achieve at least a 99 
percent (two-log) removal, revising the definition of GWUDI and 
watershed control program under the SWTR to include Cryptosporidium, 
requiring sanitary surveys for all surface water and GWUDI systems, and 
setting disinfection profiling and benchmarking requirements to prevent 
increases in microbial risk while systems complied with the Stage 1 D/
DBPR. The LT1 (67 FR 1812, USEPA, 2002c) extended the requirements from 
the IESWTR to systems serving fewer than 10,000 people.
Summary of Review Results
    EPA identified the following NPDWRs under the SWTR as candidates 
for revision under the Six-Year Review 3 because of the opportunity to 
further reduce residual risk from pathogens (including opportunistic 
pathogens such as Legionella) beyond the risk addressed by the current 
SWTR:
     Giardia lamblia,
     heterotrophic bacteria,
     Legionella,
     viruses, and
     Cryptosporidium (also under IESWTR and LT1).
    This result is based on a scientific review of available 
information, following the protocol described in Section V. Based on 
the availability of new information, the review focused on the 
following major provisions of the SWTRs:
     Requirements to maintain a minimum disinfectant residual 
in the distribution system,
     GWUDI classification, and
     CT criteria for virus disinfection.
    Collectively, the new information suggests an opportunity to revise 
the TT provisions of the SWTRs to provide greater protection of public 
health. More detailed information about the review results related to 
the major provisions of the SWTRs is provided in the following 
subsections.
Requirements To Maintain a Minimum Disinfectant Residual in the 
Distribution System
    EPA evaluated information related to the maintenance of a minimum 
disinfectant level in the distribution system and determined that there 
is an opportunity to reduce residual risk from pathogens (includes 
opportunistic pathogens such as Legionella) beyond the risk addressed 
by the SWTRs. The detectable concentration of disinfectant residual in 
the distribution system may not be adequately protective of microbial 
pathogens because of concerns about analytical methods and the 
potential for false positives (Wahman and Pressman, 2015; Westerhoff et 
al., 2010). Maintaining a disinfectant residual above a set numerical 
value in the distribution system may improve public health protection 
from a variety of pathogens. Such a change could have benefits for 
controlling occurrence of all types of pathogens in distribution 
systems, except for those most resistant to disinfection, such as 
Cryptosporidium.
    Given our understanding of the distribution system vulnerabilities 
(e.g., NRC, 2006b), there may be opportunities to enhance the criteria 
for indicating distribution system integrity, as well as the potential 
health risk that may be associated with pathogens potentially growing 
and released from biofilms. These opportunities include revisiting the 
distribution system disinfectant residual criteria and revisiting the 
existing alternative HPC criteria. The NRC report (2006b) describes 
that water quality integrity is an important factor that water 
professionals must take into account for the protection of public 
health, and that the sudden loss of disinfectant residuals

[[Page 3539]]

can indicate a change in water quality or system characteristics. 
However, the report was inconclusive on the level of disinfectant 
residual that should be provided in distribution systems.
GWUDI Classification
    EPA reviewed information on disease outbreaks, a randomized 
controlled intervention study, pathogenic protozoan occurrence data and 
studies evaluating parasitic protozoan removal surrogates and 
hydrogeologic studies, all of which were completed since the SWTR was 
published. The information suggests that there is an opportunity to 
provide greater public health protection by improved identification of 
unrecognized GWUDI PWSs. The data suggest that the SWTR regulation and 
guidance has performed well in identifying GWUDI for the PWS systems 
most at risk from Giardia and Cryptosporidium presence in ground water. 
However, the information (e.g., Colford et al., 2009) suggests that a 
subset of GWUDI systems are also at risk but are potentially 
misclassified as ground water systems, and therefore, not subject to 
requirements that provide protection against parasitic protozoans. 
Improved public health protection may result if there is improved 
recognition of GWUDI systems, including those that may disinfect but do 
not provide engineered filtration or have not conducted a demonstration 
of performance to document the necessary Cryptosporidium alternative 
treatment and removal required under the LT2. The potential public 
health improvement is most relevant to those systems that have a large 
surface water component and poor subsurface removal capabilities but 
are not yet recognized as GWUDI and warrants further examination in any 
rulemaking activities.
    EPA suggests that the number of potentially misclassified GWUDI 
PWSs may be estimated by: (1) waterborne disease outbreak compilations, 
(2) the UCMR3 occurrence data (aerobic spore detections and 
concentrations), and (3) the SYR2 ICR and the SYR3 ICR (total coliform 
detections). EPA's preliminary characterization of the number of the 
potentially misclassified GWUDI PWSs is described in the ``Six-Year 
Review 3 Technical Support Document for Microbial Contaminant 
Regulations'' (USEPA, 2016n).
CT Criteria for Virus Disinfection
    EPA evaluated whether the current CT criteria based on hepatitis A 
virus (HAV) are sufficiently protective against other types of viruses. 
EPA reviewed disinfection studies relevant to the CT tables published 
in the ``1991 SWTR Guidance Manual'' (USEPA, 1991). Over the years, 
many studies have indicated that HAV is less chlorine-resistant than 
some enteroviruses, such as Coxsackie virus B5 (Black et al., 2009; 
Cromeans et al., 2010; Keegan et al., 2012), and also less chloramine-
resistant than adenovirus (Sirikanchana et al., 2008; Hill and 
Cromeans, 2010). Based on this review, EPA identified a potential need 
to update CT values for virus inactivation by free chlorine or 
chloramines, particularly for water with a relatively high pH. This 
assessment is also relevant to the LT2 and the GWR, which refer to the 
same CT tables in the original ``1991 SWTR Guidance Manual.''
Health Effects
    This section summarizes EPA's review of the information related to 
human health risks from exposure to microbial contaminants in drinking 
water. EPA evaluated whether any new toxicological data, or waterborne 
endemic infection or infectious disease information, would justify 
modifying the MCLGs. EPA reviewed information that included data from 
the Waterborne Disease and Outbreak Surveillance System (WBDOSS) 
collected by the Centers for Disease Control and Prevention (CDC) 
(http://www.cdc.gov/healthywater/surveillance/drinking-surveillance-reports.html) and other available data that documents drinking water-
associated outbreaks.
MCLGs
    The SWTRs set MCLGs of zero for Giardia lamblia, viruses, 
Cryptosporidium, and Legionella since any exposure to these microbial 
pathogens presents a potential health risk. In the Six Year Review 3, 
EPA did not identify new information related to potentially revising 
these MCLGs. New dose-response data from some waterborne pathogens are 
available from both human and animal exposure studies (Teunis et al., 
2002a; 2002b; Armstrong and Haas, 2007; 2008; Buse et al., 2012). 
Concurrently, new models seek to use the new data to provide improved 
infectivity, morbidity and mortality predictions (Messner et al., 2014; 
USEPA, 2016m). The newer models are specifically designed to address 
low dose exposure typical of drinking water rather than high dose 
exposure typical of food ingestion or vaccine studies.
Waterborne Disease Outbreaks Associated With Drinking Water
    EPA reviewed information from the Waterborne Disease and Outbreaks 
Surveillance System about the occurrences and causes of drinking water-
associated outbreaks. This surveillance system is the primary source of 
data concerning such outbreaks in the U.S. (Beer et al., 2015). The 
drinking water-associated outbreak data from 1971-2012 illustrate that 
there is an observable reduction of reported outbreaks over that time 
frame, which may be, at least in part, due to the implementation of the 
TCR and the SWTR beginning in 1991.
    Although the historic number of drinking water-associated outbreaks 
is declining, CDC notes that the level of surveillance and reporting 
activity, as well as reporting requirements, varies across states and 
localities. For these reasons, outbreak surveillance data likely 
underestimate actual values, and should not be used to estimate the 
total number of outbreaks or cases of waterborne disease (Beer et al., 
2015).
    Deficiencies at private wells and premise plumbing systems are 
increasingly responsible for disease outbreaks associated with drinking 
water (Beer et al., 2015). Premise plumbing is the portion of the 
distribution system from the water meter to the consumer tap in homes, 
schools, and other buildings (NRC, 2006b). In 2011-2012, the two most 
frequent deficiencies related to drinking-water-associated outbreaks 
were Legionella in premise plumbing systems (66 percent) and untreated 
ground water (13 percent) (Beer et al., 2015).
    In addition to epidemic illness, sporadic illness (i.e., isolated 
cases not associated with an outbreak) accounts for an unknown but 
probably significant portion of waterborne disease and is more 
difficult to recognize (71 FR 65573, USEPA, 2006b).
    Collectively, the data indicate that outbreaks associated with 
drinking water may have been reduced as a result of drinking water 
regulations. However, opportunities remain to address disease outbreaks 
associated with distribution systems and untreated ground water and, at 
the same time, to potentially address some of the waterborne disease 
outbreaks associated with little to no disinfectant residual in the 
distribution system (Geldreich et al., 1992; Bartrand et al., 2014).
    The precise burden of disease is not well quantified. Five 
primarily waterborne diseases (giardiasis, cryptosporidiosis, 
Legionnaires' disease, otitis externa, and non-tuberculous 
mycobacterial infection) were responsible for over 40,000 
hospitalizations per year at a cost of nearly $1 billion per year 
(Collier et al.,

[[Page 3540]]

2012). Given this information, there are opportunities for substantial 
cost savings if such incidence can be reduced through better risk 
management. Most of these costs are attributed to Legionella and non-
tuberculous mycobacteria. These bacteria can proliferate under 
favorable conditions at locations in the premise plumbing and in some 
parts of the distribution system that are further from the central 
parts of the system, where water has aged the longest and where there 
may be very little to no disinfectant residual. Further, the quality of 
the water delivered to building systems and households can affect these 
pathogens' ability for growth and disease transmission. There are 
opportunities to enhance the current disinfectant residual requirements 
to more effectively kill pathogens or contain their growth, and to 
better indicate, through a stronger signal of the absence of a 
residual, when targeted improvements to treatment practices or 
distribution conditions may provide greater public health protection.
GWUDI-Related Disease Outbreaks
    Wallender et al. (2014) summarized CDC outbreak data for the years 
1971-2008 and determined that GWUDI was a ``contributing factor'' in 11 
percent (six percent with Giardia etiology) of all outbreaks using 
untreated ground water. The total number of untreated ground water 
outbreaks during this time period was 248. Three quarters of the 
outbreaks involved PWSs. These findings indicate that some of the 
ground water systems examined by CDC that are not currently required to 
disinfect are contaminated with pathogens. Reclassifying these 
potentially ``unrecognized'' GWUDI PWSs may provide greater public 
health protection against microbial contamination because these PWSs 
would be subject to stricter requirements. As an example, a 2007 
outbreak of giardiasis occurred in a New Hampshire community (205 
homes) using untreated ground water (Daly et al., 2010). This GWUDI 
misclassification-related outbreak was the largest giardiasis drinking 
water-associated outbreak in the preceding 10 years.
Randomized Controlled Intervention Study
    A randomized, controlled, triple-blinded drinking water 
intervention study was conducted in Sonoma County, California (Colford 
et al., 2009). The purpose of the study was to determine the proportion 
of acute gastrointestinal illnesses (AGI) attributable to drinking 
water. Sonoma County obtained water from five horizontal collector 
wells along the Russian River, four regulated as ground water and one 
regulated as GWUDI (part of the year). Colford et al. (2009) found that 
highly credible AGI in the population aged 55 and over was attributable 
to drinking water exposure. Illness occurred even though the water 
utility met all federal, state and local drinking water regulations.
Pathogenic Protozoa Occurrence in Ground Water
    In a karst aquifer in France, 18 ground water samples were taken 
from the Norville (Haute-Normandie) public water supply well (5,000 
customers, chlorine treatment) and tested for Cryptosporidium oocysts. 
Thirteen of the 18 samples were found to be Cryptosporidium positive by 
solid-phase cytometry; the maximum concentration was four oocyst per 
100 L (Khaldi et al., 2011). These data show that Cryptosporidium in 
karst ground water includes, for some highly vulnerable systems, 
Cryptosporidium occurrence resulting from poor Cryptosporidium removal 
during infiltration from the surface rather than poor removal during 
induced infiltration from nearby surface water. Because the SWTR 
definition assumes that all Cryptosporidium in PWS wells is transported 
from adjacent surface water, it is silent on the issue of 
Cryptosporidium transport directly from the surface, as apparently was 
the case in Norville, France. Karst aquifers are a vital ground water 
resource in the U.S. According to the USGS, about 40 percent of the 
ground water used for drinking water comes from karst aquifers (USGS, 
2004).
Analytical Feasibility
Analytical Methods for Chlorine Residuals
    Because of concerns about analytical methods and the potential for 
false positives, the detectable concentration of disinfectant residuals 
in the distribution system may not be adequately protective of 
microbial pathogens. To further inform these concerns, EPA reviewed 
analytical methods that have been approved for free chlorine, total 
chlorine and chlorine dioxide under the SWTR and the D/DBPRs. Nearly 
all utilities use either the DPD (N,N-diethyl-p-phenylenediamine) or 
amperometric titration methods to measure distribution system 
disinfectant residual, and these measurements are generally performed 
in the field (Wahman and Pressman, 2015). A number of constituents can 
interfere with measurements of disinfectant residuals. In general, most 
strong oxidants will interfere with measurement of chlorine. In 
addition, color, turbidity and particles will also interfere with 
colorimetric techniques such as DPD.
    For some systems using chloramines (a mixture of biocidal inorganic 
chloramines, of which monochloramine is the most effective), the 
presence of organic chloramines can be problematic since these related 
compounds have minimal biocidal properties, they can interfere with 
residual monitoring, and they can give the false impression that the 
finished water contains more active disinfectant than is actually 
present (Wahman and Pressman, 2015; Westerhoff et al., 2010). Organic 
chloramines will continue to form in the distribution system while 
inorganic chloramines decay, and thus areas of the distribution system 
with relatively high water ages may have residuals containing a 
significant amount of organic chloramines (Wahman and Pressman, 2015).
    In addition, EPA reviewed research published regarding potential 
improvements to methods or technologies used in the determination of 
free or total chlorine (Dong et al., 2012; Tang et al., 2014; Saad et 
al., 2005). Analytical methods that can measure inorganic chloramines 
without the organic chloramine interferences are available, but not 
approved for determining compliance with NPDWRs. Field test kits based 
on the indophenol method are available that can specifically measure 
monochloramine without inclusion of mass from dichloramine or organic 
chloramines (Lee et al., 2007).
Use of Aerobic Spores as Pathogenic Protozoa Surrogates
    EPA's existing microbial contaminants regulations require 
monitoring of pathogenic protozoa in source water (e.g., 
Cryptosporidium) and microorganisms that indicate a possible pathway 
for contamination (e.g., total coliform, E. coli). In this Six-Year 
Review, EPA evaluated additional microorganisms that could be used to 
identify PWSs most at risk from Cryptosporidium in ground water. New 
data suggest that aerobic spores are useful surrogates for 
Cryptosporidium occurrence and removal. Aerobic spores originate in 
shallow soil. The spore presence in a sample from a PWS well indicates 
that there is a pathway for water infiltration into the well, either 
vertically from the surface or horizontally from nearby surface water.

[[Page 3541]]

    EPA previously used aerobic spores as surrogate measures of 
Cryptosporidium removal by alternative treatment in a demonstration of 
field performance (USEPA, 2010f). Field demonstrations showed that the 
spores performed well in demonstrating two-log removal of 
Cryptosporidium at Casper, Wyoming, and Kennewick, Washington (USEPA, 
2010f). Spores also performed well in demonstrating that a Nebraska PWS 
was unable to achieve better than two-log removal of Cryptosporidium, 
and that UV or other engineered treatment would be required (State of 
Nebraska, 2013). Headd and Bradford (2015) summarized the relevant 
scientific literature, conducted spore and Cryptosporidium laboratory 
experiments, and performed porous media transport modeling. They found 
that spores are suitable Cryptosporidium surrogates in ground water. 
These new data suggest that aerobic spores are useful as surrogates for 
Cryptosporidium removal estimates via subsurface passage (USEPA, 2010f) 
and may be useful as supplemental surrogates to improve recognition of 
GWUDI systems.
    Locas et al. (2008) found that aerobic spores were present in six 
of nine wells sampled in Quebec, Canada, and in 45 of 109 samples 
taken. The authors conclude that aerobic spore presence is an indicator 
of a change in water quality and warrants further investigation to 
determine the source of potential contamination.
    In EPA's investigation of virus occurrence in untreated PWS wells 
under the UCMR3, 252 of 793 wells (317 of 1,047 samples) were positive 
for aerobic spores (USEPA, 2016j). Measured concentrations spanned 
three orders of magnitude, with about three percent having over 100 
spore-forming units per 100 ml). Because aerobic spores originating in 
soil are found in GWUDI and ground water PWS wells, the UCMR3 data 
suggest that aerobic spores could be used as an indicator of the 
susceptibility of PWS wells to surface water infiltration. Together 
with other indicators and/or parasitic protozoa data from PWS wells, 
newer methods including spores (occurrence, concentration, and/or 
removal estimates) might be useful in identifying unrecognized GWUDI 
PWS wells. The LT2 Toolbox Guidance Manual identified aerobic spores as 
the indicator to determine Cryptosporidium removal for systems using 
bank filtration for LT2 additional treatment requirements (USEPA, 
2010f).
Occurrence and Exposure
    Coliform and/or E. coli occurrence can be an indication of 
conditions supporting bacterial growth or an intrusion event into the 
distribution system. On the other hand, the absence of coliforms and/or 
E. coli does not necessarily mean the absence of pathogens that are 
more resistant to the disinfectant residual. Detection of coliform 
bacteria is commonly associated with low distribution system 
disinfectant residuals. According to LeChevallier et al. (1996), 
disinfectant residuals of 0.2 mg/L or more of free chlorine, or 0.5 mg/
L or more of total chlorine, are associated with reduced levels of 
coliform bacteria.
    To assess the relationship between disinfectant residual and 
occurrence of indicators for pathogens in distribution systems, EPA 
evaluated information about chlorine residuals and total coliforms and 
E. coli (TC/EC) using compliance monitoring data from the SYR3 ICR 
database. EPA paired TC/EC results with field chlorine residual data 
collected at the same time and location. It is important to note that 
these evaluations help to inform the SYR3 results, but do not assess 
compliance with regulatory standards.
    EPA found that there was a lower rate of occurrence of both TC and 
EC as the free or total chlorine residual increased to higher levels 
(note: total chlorine is often used as a measure for systems that use 
chloramines). For example, the TC positive rate was less than one 
percent when chlorine residuals were equal to or greater than 0.2 mg/L 
of free chlorine or 0.5 mg/L of total chlorine. This relationship 
between chlorine residuals and occurrence of TC and EC was similar to 
that reported by the Colorado Department of Public Health and 
Environment (Ingels, 2015).
    A disinfectant residual also serves as an indicator of the 
effectiveness of distribution system best management practices. Best 
management practices include flushing, storage tank maintenance, cross-
connection control, leak detection and effective pipe replacement and 
repair practices. The effective implementation of best management 
practices helps water suppliers to lower chlorine demand and maintain 
an adequate disinfectant residual throughout the distribution system. 
These same practices can also help control DBP formation.
Treatment Feasibility
    EPA reviewed new information related to the TT requirements in the 
SWTR and identified the following treatment-related topics that support 
potential revisions to the SWTRs to improve public health protection:
     Detectable residual for systems using chloramine 
disinfection,
     State implementation of disinfection residual 
requirements,
     Disinfectant residuals for control of Legionella in 
premise plumbing systems,
     HPC alternative to detectable residual measurement, and
     CT criteria for viruses.
    In addition, EPA reviewed key findings by the Research and 
Information Collection Partnership (RICP) on drinking water 
distribution system issues and research and information needs. The RICP 
is a working group formed on the recommendation of the Total Coliform 
Rule Distribution System Advisory Committee to identify specific high-
priority research and information collection activities and to 
stimulate water distribution system research and information collection 
(USEPA, 2008b; USEPA and Water Research Foundation, 2016).
Detectable Residual for Systems Using Chloramine Disinfection
    As discussed in the background portion of this section, for surface 
water systems or GWUDI systems, the SWTR requires that a disinfectant 
residual cannot be undetectable in more than five percent of samples 
each month for any two consecutive months.
    EPA identified two issues that have implications for the 
protectiveness of allowing a detectable residual as a surrogate for 
bacteriological quality: Organic chloramines and nitrification. Organic 
chloramines affect the effectiveness of disinfectant residuals because 
they: (1) Form during the use of free chlorine or chloramines, (2) 
interfere with commonly used analytical methods for free and total 
chlorine measurements, and (3) are poor disinfectants compared to free 
chlorine and monochloramine (Wahman and Pressman, 2015).
    Because chloramination involves introduction of ammonia into 
drinking water, and decomposition of chloramines can further release 
ammonia in the distribution system, chloramine use comes with the risk 
of distribution system nitrification (i.e., the biological oxidation of 
ammonia to nitrite and eventually nitrate). Drinking water distribution 
system nitrification is undesirable and can result in water quality 
degradation. Information shows that maintaining a high enough level of 
total chlorine or monochloramine residuals in the distribution system 
can help prevent both nitrification and residual depletion (Stanford et 
al, 2014).

[[Page 3542]]

State Implementation of Disinfectant Residual Requirements
    States may adopt federal drinking water regulations or promulgate 
more stringent drinking water requirements, including those for 
disinfectant residuals. Preliminary information shows that 26 states 
require a detectable disinfectant residual in the distribution system. 
Twenty of these 26 states require a minimum free chlorine residual of 
0.2 mg/L or more (Ingels, 2015; Wahman and Pressman, 2015). Five of the 
20 states set standards even more stringent than 0.2 mg/L: Louisiana 
requires at least 0.5 mg/L free chlorine in its emergency rule, while 
Florida, Illinois, Iowa, and Delaware require 0.3 mg/L. For minimum 
total chlorine residual, state requirements vary from 0.05 mg/L (New 
Jersey) to 1.00 mg/L or higher (Kansas, Oklahoma, Iowa, Ohio, and North 
Carolina). North Carolina has a numeric requirement for total chlorine 
residual but not for free chlorine residual.
    Colorado has amended its minimum disinfectant residual requirements 
in the distribution system to be greater than or equal to 0.2 mg/L, 
effective April 1, 2016 (Ingels, 2015). Pennsylvania recently proposed 
to strengthen its disinfectant residual requirements by increasing the 
minimum disinfectant residual in the distribution system to 0.2 mg/L 
free or total chlorine (Pennsylvania Bulletin, 2016). Louisiana's 
Emergency Distribution Disinfectant Residual Rule was established in 
2013 to control Naegleria fowleri, an amoeba found in several PWSs. 
That rule requires a minimum free or total chlorine disinfectant level 
of 0.5 mg/L to be maintained at all times in finished water storage 
tanks and the entire distribution system (Louisiana Department of 
Health and Hospitals, 2013). The state agency intends to continue to 
renew the Emergency Rule until a final rule can be promulgated 
(Louisiana Department of Health and Hospitals, 2014).
Disinfectant Residuals for Control of Legionella in Premise Plumbing 
Systems
    Since the reporting of disease outbreaks due to Legionella began in 
2001, Legionella has been shown to cause more drinking-water-related 
outbreaks than any other microorganism. Addressing premise plumbing 
issues is particularly challenging. Premise plumbing may be largely 
outside of water utilities' operations and management control. Also, 
the characteristic features of premise plumbing (e.g., low 
disinfectants residuals, stagnation, and warm temperature) tend to 
support growth and persistence of opportunistic pathogens.
    Studies indicate that distribution systems can play a role in 
influencing the transmission and contamination of Legionella in premise 
plumbing systems (Lin et al., 1998; States et al., 2013). Hospitals 
served by PWSs using chloramines reported fewer outbreaks of 
legionellosis than those using free chlorine (Kool et al., 1999; 
Heffelginger et al., 2003). Some building systems supplied by PWSs 
which have switched to chloramines have seen marked reduction in the 
colonization of Legionella (Flannery et al., 2006; Moore et al., 2006). 
One implication of these studies is the importance of being able to 
reliably measure and sustain chloramine residuals to increase the 
likelihood of its effectiveness at controlling Legionella in premise 
plumbing systems. On the other hand, some studies have indicated that 
the occurrence of another pathogen, non-tubercular Mycobacterium, may 
increase under chloramination conditions (Pryor et al., 2004; Moore et 
al., 2006; Duda et al., 2014).
    Legionella species can multiply in warm, stagnant water 
environments, such as in community water storage tanks with low 
disinfectant residuals during warm months. Cohn et al. (2014) observed 
increased incidence of legionellosis among institutions and private 
homes near a community water storage tank when the disinfectant 
residual in the storage tank dropped (from greater than 0.2 mg/L to 
less than 0.2 mg/L) during hot summer months. Based on these findings, 
the authors recommended that, regardless of total coliform occurrence, 
remedial actions be taken (e.g., flushing of mains, checking for closed 
valves that can result in hydraulic dead-ends, and possibly installing 
re-chlorination stations) when low chlorine residuals are observed 
during hot summer months. They also noted that this storage tank had 
been cleaned subsequent to the outbreak (Cohn et al., 2014; Ashbolt, 
2015).
    To help address concerns about Legionella, EPA developed a document 
entitled ``Technology for Legionella Control in Premise Plumbing 
Systems: Scientific Literature Review'' (USEPA, 2016r). The document 
summarizes information about the effectiveness of different approaches 
to control Legionella in a building's premise plumbing system. EPA 
expects that use of this document will further improve public health by 
helping primacy agencies, facility maintenance operators, and facility 
owners make science-based risk management decisions regarding treatment 
and control of Legionella in buildings.
    EPA also reviewed the scientific literature on the effectiveness of 
disinfectant residuals at controlling biofilm growth. Many factors 
influence the concentration of the disinfectant residual in the 
distribution system; and therefore, the ability of the residual to 
control microbial growth and biofilm formation. These factors include 
the level of assimilable organic carbon (AOC), the type and 
concentration of disinfectant, water temperature, pipe materials, and 
system hydraulics.
    Problems associated with biofilms in distribution systems include 
enhanced corrosion of pipes and deterioration of water quality. 
Biofilms can provide ecological niches that are suited to the potential 
survival of pathogens (Walker and Morales, 1997; Baribeau et al., 2005; 
Behnke et al., 2011; Wang et al., 2012; Biyela et al., 2012; Revetta et 
al., 2013; Ashbolt, 2015). The biofilm can protect microorganisms from 
disinfectants and can enhance nutrient accumulation and transport 
(Baribeau et al., 2005).
HPC Alternative to Detectable Residual Measurement
    Under the SWTR, a system may demonstrate that its HPC levels are 
less than 500 per mL, at any sampling locations, in lieu of 
demonstrating the presence of a detectable disinfectant residual at 
that location, per primacy agency approval. EPA reviewed new 
information that suggests development of criteria which may be more 
protective than the HPC criterion. For example, criteria used in the 
Netherlands for systems operating without a distribution system 
disinfectant residual provides an example of an alternative criteria 
than the HPC criterion. In the Netherlands, chlorine is not used 
routinely for primary or secondary disinfection. Dutch water systems 
use the following general approach to control microbial activity in the 
distribution system without a disinfectant residual (Smeets et al., 
2009): Produce a biologically stable drinking water; use distribution 
system materials that are non-reactive and biologically stable; and 
optimize distribution system operations and maintenance practices to 
prevent stagnation and sediment accumulation. For the determination of 
a biologically stable water they use AOC as an indicator.
CT Criteria for Virus Disinfection
    EPA reviewed new disinfection studies published since the release 
of the original CT tables. Collectively, the data in the recent 
literature indicate that

[[Page 3543]]

EPA CT values for free chlorine disinfection are sufficient to 
inactivate most enteric viruses in drinking water, except for Coxsackie 
virus B5 at a pH higher than 7.5 (Black et al., 2009; Cromeans et al., 
2010; Keegan et al., 2012).
    EPA's CT values for chlorine incorporate a safety factor of three 
to account for differences between dispersed and aggregated hepatitis A 
virus and between buffered, demand-free water and environmental water. 
In light of new information about the hepatitis A virus and the effects 
of source water quality on chlorine disinfection, EPA concludes that 
the safety factor of three should be re-evaluated to ensure its 
adequacy. A larger safety factor (thus higher EPA CT values) is 
expected to enhance waterborne pathogen control but could lead to 
higher DBP formation and warrants further examination in any rulemaking 
activity.
    Adenovirus is the virus that is most resistant to chloramines, 
through it is very susceptible to free chlorine disinfection. Several 
studies revealed that monochloramine disinfection might not provide 
adequate control of adenovirus in drinking water, particularly in 
waters with relatively high pH and at low temperature (Sirikanchana et 
al., 2008; Hill and Cromeans, 2010).
Research and Information Collection Partnership Findings
    The RICP partners are EPA and Water Research Foundation. EPA 
examined information from the 10 high priority RICP areas in the 
context of the Six-Year Review, particularly information related to the 
effectiveness of sanitary survey and corrective action requirements 
under the IESWTR. However, EPA found limited information that would 
shed light on the frequency and magnitude of distribution system 
vulnerability events (e.g., backflow events, storage tank breeches), 
associated risk implication, and costs for preventing such events from 
occurring. The RICP report identifies potential follow-up research 
areas that could help to address these gaps (USEPA and Water Research 
Foundation, 2016).
Risk-Balancing
    The Agency has considered the risk-balancing aspects of the MDBP 
rules and has determined that potential revisions to the SWTRs could 
provide improved health protection. The risk-balancing activities 
considered by the Agency include those between the microbial and 
disinfection by-product rules, as well as those between different 
groups of DBPs. This includes balancing the reduction in risks from 
microbial pathogens should there be additional requirements to maintain 
a disinfectant residual with the increased risk from D/DBPs resulting 
from such requirements. EPA also considered the potential impact of 
further constraints on DBP precursors on the reduction of demand for 
disinfectant residual. The risk-balancing review was based on a 
preliminary, qualitative assessment of unintended consequences; it is 
important to note that further assessment of such consequences would be 
an important component of any further rulemaking activities.
b. LT2
Background
    EPA promulgated the LT2 on January 5, 2006 (71 FR 654, USEPA, 
2006c). The LT2 applies to all PWSs that use surface water or ground 
water under the direct influence of surface water as drinking water. 
The LT2 builds upon the IESWTR and the LT1 by improving control of 
microbial pathogens, specifically the contaminant Cryptosporidium. The 
purpose of the LT2 is to reduce illness linked with the contaminant 
Cryptosporidium and other disease-causing microorganisms in drinking 
water. The LT2 supplements the IESWTR and the LT1 regulations by 
establishing additional Cryptosporidium treatment requirements for 
higher-risk systems. The LT2 requires source water occurrence 
monitoring which is used to determine additional treatment 
requirements. The LT2 rule provides for additional CT credits for 
Cryptosporidium inactivation by ozone and chlorine dioxide. The LT2 
also provides UV treatment credits for Cryptosporidium, Giardia and 
virus inactivation. EPA recognized that research in the field of 
Cryptosporidium inactivation is ongoing and included a provision in the 
rule that allows unfiltered systems using a disinfectant other than 
chlorine to demonstrate the log inactivation that can be achieved.
    The LT2 also contains provisions to reduce risks from uncovered 
finished water reservoirs (UCFWRs).\5\ The rule ensures that systems 
maintain microbial protection when they take steps to decrease the 
formation of disinfection byproducts in systems that add a chemical 
disinfectant (i.e., other than UV light) or receive a chemically 
disinfected water. Storage of treated drinking water in open reservoirs 
can lead to significant water quality degradation and health risks to 
consumers (USEPA, 1999). Examples of such water quality degradation 
include increases in algal cells, coliform bacteria, heterotrophic 
bacteria, particulates, disinfection byproducts, metals, taste and 
odor, insect larvae, Giardia, Cryptosporidium and nitrate (USEPA, 
1999). Contamination of reservoirs occurs through surface water runoff, 
bird and animal wastes, human activity, algal growth, airborne 
deposition and insects and fish.
---------------------------------------------------------------------------

    \5\ LT2 uses the term `facilities'' instead of `reservoirs'. The 
term reservoirs is used in this document.
---------------------------------------------------------------------------

    The LT2 requires PWSs using uncovered finished water storage 
facilities to either cover the storage facility or treat the storage 
facility discharge (i.e., prior to entering the distribution system) to 
achieve inactivation and/or removal of 4-log virus, 3-log G. lamblia, 
and 2-log Cryptosporidium spp. on a state-approved schedule.
    Under the LT2, PWSs were required to notify their state/primacy 
agency by April 1, 2008, if they used UCFWRs. Additionally, the LT2 
required all PWSs to either meet the requirement to cover the UCFWR, or 
treat the UCFWR discharge to the distribution system or be in 
compliance with a state-approved schedule for meeting these 
requirements no later than April 1, 2009. Under this review, EPA 
evaluated published information to assess whether allowing a state-
approved risk management plan would justify revisions to the LT2.
Summary of Review Results
    Information available since promulgation of the LT2 either supports 
the current regulatory requirements or does not justify a revision. EPA 
determined that no regulatory revisions to the UCFWR requirements of 
the LT2 are warranted at this time based on the review of available 
information.
Health Effects
    EPA reassessed the health risks resulting from exposure to 
Cryptosporidium spp., Giardia lamblia and viruses, as well as other 
potential microbiological risks to human health. The Agency also 
reviewed new information on other pathogens of potential concern to 
determine whether additional measures are warranted to provide greater 
public health protection from these pathogens, particularly in the 
context of the UCFWR provisions of the LT2.
    The principal objectives of this health effects review were to: (1) 
Evaluate whether there are new or additional ways to estimate risks 
from Cryptosporidium and other pathogenic microorganisms in drinking 
water and

[[Page 3544]]

(2) evaluate surveillance and outbreak data on Cryptosporidium and 
other contaminants of potential concern. Based on the review, the new 
information does not justify a revision to the health basis for the LT2 
at this time. For more information regarding EPA's review of health 
effects, see the ``Six-Year Review 3 Technical Support Document for 
Long-Term 2 Enhanced Surface Water Treatment Rule'' (USEPA, 2016m).
Analytical Feasibility
    The LT2 specifies approved analytical methods to determine the 
levels of Cryptosporidium in source waters for the identification of 
additional treatment needs. The LT2 requires systems and/or 
laboratories to use either ``Method 1622: Cryptosporidium in Water by 
Filtration/IMS/FA'' (EPA 815-R-05-001, USEPA, 2005d) or ``Method 1623: 
Cryptosporidium and Giardia in Water by Filtration/IMS/FA'' (EPA 815-R-
05-002, USEPA, 2005e). EPA Methods 1622 or 1623 is used in monitoring 
programs to characterize Cryptosporidium levels in the source water of 
PWSs for the purposes of risk-targeted treatment requirements under the 
LT2. Method recoveries of more than 3,000 matrix spiked samples from 
the first round of monitoring for the LT2 indicated an average recovery 
of oocysts with Methods 1622 and 1623 to be 40 percent. In addition to 
evaluating the results from the first round of monitoring, EPA gathered 
new information on Cryptosporidium analytical methods by investigating 
improvements to Methods 1622 and 1623. EPA evaluated whether the 
required use of a revised method (Method 1623.1) would be justified for 
Round 2 monitoring under the LT2. Though new information is available 
that indicates the potential for a regulatory revision, the Agency does 
not believe it is appropriate to revise the rule to require the use of 
Method 1623.1, since the Agency believes such a change would not 
provide substantially greater protection of public health at the 
national level. The use of Method 1623.1 during the LT2 Round 2 
monitoring is optional, and not required. Since EPA is not planning 
changes to the methods required under the LT2, the schedule for the LT2 
Round 2 monitoring remains the same as described in the final LT2, 
which is scheduled to be completed no later than 2021 for all PWSs.
Occurrence and Exposure
    The LT2 requires PWSs using surface water or ground water under the 
direct influence of surface water to monitor their source waters for 
Cryptosporidium spp. (and/or E. coli) to identify additional treatment 
requirements. PWSs must monitor their source water (i.e., the influent 
water entering the treatment plant) over two different timeframes 
(Round 1 and Round 2) to determine the Cryptosporidium level. 
Monitoring results determine the extent of Cryptosporidium treatment 
requirements under the LT2.
    Under the LT2, the date for PWSs to begin monitoring is staggered 
by PWS size, with smaller PWSs starting at a later time than larger 
systems. According to the LT2 rule requirements, all PWSs were expected 
to complete Round 1 in 2012.
    To reduce monitoring costs, small filtered PWSs (serving fewer than 
10,000 people) initially monitor for E. coli for one year as a 
screening analysis and are required to monitor for Cryptosporidium only 
if their E. coli levels exceed specified trigger values. Small filtered 
PWSs that exceed the E. coli trigger, as well as small unfiltered PWSs, 
must monitor for Cryptosporidium for one or two years, depending on the 
sampling frequency.
    Based on the source water monitoring results, filtered systems were 
classified in one of four risk categories to determine additional 
treatment needed (Bins 1-4). Systems in Bin 1 are required to provide 
no additional Cryptosporidium treatment. Filtered systems in Bins 2-4 
must achieve 1.0-2.5 log of treatment (i.e., 90 to 99.7 percent 
reduction) for Cryptosporidium over and above that provided by 
conventional treatment, depending on the Cryptosporidium 
concentrations. Filtered PWSs must meet the additional Cryptosporidium 
treatment requirements in Bins 2, 3, or 4 by selecting one or more 
technologies from the microbial toolbox of options for ensuring source 
water protection and management, and/or Cryptosporidium removal or 
inactivation. All unfiltered water systems must provide at least 99 or 
99.9 percent (2 or 3-log) inactivation of Cryptosporidium, depending on 
the results of their monitoring. Additionally, all filtered systems 
that provide, or will provide, 5.5 log treatment for Cryptosporidium 
are exempt from monitoring and subsequent bin classification. Systems 
providing 5.5 log Cryptosporidium treatment must notify the state no 
later than the date by which the system must submit a sampling plan.
    Six years after the initial bin classification, filtered systems 
must conduct a second round of monitoring. Round 2 monitoring is in 
place to understand year-to-year occurrence variability. The difference 
observed between occurrence at the time of the ICR Supplemental Surveys 
(USEPA, 2000c) and the LT2 Round 1 monitoring indicates year-to-year 
variability. Round 2 monitoring began in 2015. Under this review, EPA 
considered whether a third round of monitoring would be justified at 
this time, in particular, requiring the use of Method 1623.1. EPA also 
considered whether a modification to the action bin boundaries should 
be made based on requiring Method 1623.1.
    Because of the relatively modest gains in public health protection 
predicted by the Round 2 monitoring EPA does not believe a third round 
of monitoring is justified at this time, even if the Agency were to 
require the use of Method 1623.1 for this monitoring. Round 1 
Cryptosporidium occurrence was lower than expected (3.3-5.3 percent of 
Bin 1 systems from Round 1 would be moved to a higher bin). As 
mentioned earlier, EPA will not require the use of Method 1623.1 for 
Cryptosporidium monitoring. Therefore, EPA will not make changes to the 
action bin boundaries at this time.
Treatment Feasibility
    LT2 includes a variety of treatment and control options, 
collectively termed the ``microbial toolbox,'' that PWSs can implement 
to comply with the LT2's additional Cryptosporidium treatment 
requirements. Most options in the microbial toolbox carry prescribed 
credits toward Cryptosporidium treatment and control requirements. The 
LT2 Toolbox Guidance Manual (USEPA, 2010f) provides guidance on how to 
apply the toolbox options.
    The LT2 also requires all unfiltered PWSs to provide at least 2 to 
3-log (i.e., 99 to 99.9 percent) inactivation of Cryptosporidium. 
Further, under the LT2, unfiltered PWSs must achieve their overall 
inactivation requirements (including Giardia and virus inactivation as 
established by earlier regulations) using a minimum of two 
disinfectants.
    EPA reviewed information available since the promulgation of the 
LT2 on the use of the microbial toolbox to determine if the information 
would support a potential change to the prescribed credits or the 
associated design and operational criteria. In addition, EPA searched 
for information on new and emerging tools that would support their 
potential addition to the toolbox. The Agency also received input on 
the use and effectiveness of the microbial toolbox tools through public 
meetings, research of publicly available information and by actively 
communicating with some systems. EPA

[[Page 3545]]

also considered benefits and/or difficulties observed by the PWSs when 
using the available tools.
    EPA also examined information from some PWSs with UCFWRs to 
evaluate the potential effectiveness of risk management measures taken 
by those PWSs for protecting the finished water in the UCFWRs from 
contamination. The New York City Department of Environmental Protection 
(NYC DEP) has undertaken more activities than any other PWS to protect 
their Hillview Reservoir from contamination. These activities include 
wildlife management (e.g., bird harassment and deterrents, mammal 
relocation), security measures, runoff control, public health 
surveillance, microbial monitoring (e.g., Cryptosporidium, E. coli) and 
a Cryptosporidium and Giardia action plan.\6\ EPA reviewed information 
pertaining to these activities and concluded that the information is 
inadequate to support regulatory changes at the national level. The 
data is also insufficient to demonstrate that risk management 
activities provide equivalent public health protection compared to 
covering the reservoir or treating the outflow from the reservoir.
---------------------------------------------------------------------------

    \6\ http://www.nyc.gov/html/dep/pdf/reports/fad_4.1_waterfowl_managementprogram_annual_report.07-12.pdf.
---------------------------------------------------------------------------

    The LT2 includes disinfection profile and benchmark requirements to 
ensure that any significant change in disinfection, whether for 
disinfection byproducts control under the Stage 2 D/DBPR, improved 
Cryptosporidium control under the LT2, or both, does not significantly 
compromise existing Giardia and virus protection. The profiling and 
benchmarking requirements under the LT2 are similar to those 
promulgated under the IESWTR and the LT1 (USEPA, 2002c) and are 
applicable to systems that make a significant change to their 
disinfection practices.
    EPA did not identify information that would support a potential 
change to the methodology and calculations for developing the 
disinfection profile and benchmark under the LT2. However, EPA 
identified information that would support a potential change to the CT 
values required for virus disinfection (as discussed in the Section 
VI.B.4.a. ``SWTRs''). EPA is considering this information in the review 
of the overall filtration and disinfection requirements in the SWTR.
    Based on the outcome of this review, EPA determined that no 
regulatory revisions to the microbial toolbox options are warranted at 
this time. Any new information available to the Agency either supports 
the current regulatory requirements or does not justify a revision. For 
more information regarding EPA's review of treatment feasibility see 
the ``Six-Year Review 3 Technical Support Document for Long-Term 2 
Enhanced Surface Water Treatment Rule'' (USEPA, 2016m).
c. FBRR
Background
    EPA promulgated the FBRR in 2001 (66 FR 31086, USEPA, 2001b). It 
requires PWSs to review their backwash water recycling practices to 
ensure microbial control is not compromised, and it requires PWSs to 
recycle filter backwash water.
Summary of Review Results
    EPA reviewed this rule as part of the Six-Year Review 3, and the 
result is to take no action on the basis that EPA did not identify any 
relevant information that indicate changes to the NPDWR.
d. GWR
Background
    EPA promulgated the GWR in 2006 (71 FR 65573, USEPA, 2006b) to 
provide protection against microbial pathogens in PWSs using ground 
water sources. The rule establishes a risk-based approach to target 
undisinfected ground water systems that are vulnerable to fecal 
contamination. If a system has an initial total coliform positive in 
the distribution system (based on routine coliform monitoring under the 
RTCR), followed by a fecal indicator positive (E. coli, enterococci or 
coliphage) in a follow-up source water sample, it is considered to be 
at risk of fecal contamination. Systems at risk of fecal contamination 
must take corrective action to reduce potential illness from exposure 
to microbial pathogens. Disinfecting systems that can demonstrate 4-log 
virus inactivation are not subject to the monitoring requirements.
    In addition to the protection provided by the Revised Total 
Coliform Rule (RTCR) and GWR monitoring requirements, systems that do 
not disinfect are also protected by the sanitary survey provisions of 
the GWR and the Level 1 assessment provisions of the RTCR.
Summary of Review Results
    EPA has not identified the GWR as a candidate for revision under 
the Six-Year Review 3 because EPA needs to evaluate emerging 
information from full implementation of the GWR (71 FR 65573, USEPA, 
2006b) and the RTCR (78 FR 10270, USEPA, 2013a) before determining if 
there is an opportunity to improve public health protection. 
Implementation of the GWR was not yet completed for the period of time 
covered by the SYR3 ICR. The RTCR was promulgated in 2013 and became 
effective on April 1, 2016. EPA expects that implementation on the RTCR 
may impact the percent of ground water systems that will be triggered 
into source water monitoring and taking any corrective actions under 
the GWR. Therefore, the effects of the GWR and the RTCR implementation 
in addressing vulnerable ground water systems are not yet known. EPA 
notes that the GWR was also recently reviewed under Section 610 of the 
Regulatory Flexibility Act, which required federal agencies to review 
regulations that have significant economic impact on a substantial 
number of small entities within 10 years after their adoption as final 
rules. The 610 Review of the GWR was recently completed; three comments 
were received. A report is available discussing the 610 Review, 
comments received, and EPA's response to major comments (USEPA, 2016g).
Health Effects
    Borchardt et al. (2012) studied the health effects associated with 
enteric virus occurrence in undisinfected PWS wells in 14 communities 
in Wisconsin. Drinking water samples were assayed for a suite of viral 
pathogens using quantitative polymerase chain reaction (qPCR). 
Community members kept daily diaries to self-report AGI. The study 
found a statistically significant association between enteric virus 
occurrence in the drinking water and AGI incidences in the communities.
    Using the 2005 data, EPA estimated a national average TC detection 
rate of 2.4 percent for routine samples from undisinfected CWSs with 
populations less than 4,100 people (USEPA, 2012). The 14 communities 
(with undisinfected PWS wells) studied by Borchardt et al. (2012) had 
TC detections of 2.3 percent. These data suggest that the 14 
communities studied by Borchardt et al. (2012) had TC detection rates 
no different from an average undisinfected community PWS in the U.S.
Analytical Methods
    Since the promulgation of the GWR in 2006, EPA has approved several 
new methods for the analysis of TC samples used as a trigger for GWR 
source water monitoring, or for source water fecal indicators used 
under the GWR. These methods can be found on the EPA Web site (https://
www.epa.gov/dwanalyticalmethods/approved-

[[Page 3546]]

drinking-water-analytical-methods). However, PWSs are not required to 
use these new methods. Additionally, EPA did eliminate the use of fecal 
coliforms from the RTCR as an indicator of fecal contamination.
Occurrence and Exposure
    New information suggests that total coliform occurrence varies 
among small undisinfected ground water systems, depending upon whether 
the system is a community, non-transient non-community or transient 
non-community PWS (USEPA, 2016n). Statistical modeling of 2011 data 
(about 60,000 systems based on occurrence data collected from 
undisinfected ground water systems) shows that undisinfected transient 
non-community ground water systems have the highest occurrence, at 
approximately four percent median routine TC positive occurrence as 
compared with three percent for undisinfected non-transient non-
community ground water systems and two percent for undisinfected 
community ground water systems (USEPA, 2016n). These occurrence levels 
are similar to those estimated during the development of the RTCR using 
2005 data (USEPA, 2012). Additionally, according to the 2005 and 2011 
datasets, the smaller systems had higher median TC occurrence than the 
larger systems. All positive total coliform samples were assayed for E. 
coli; about one in 20 were E. coli positive.
    A small percentage of undisinfected ground water systems have 
higher TC detection rates. For example, of the 52,000 undisinfected 
transient, non-community ground water systems serving populations less 
than 101 people (the total count is from USEPA, 2006b), EPA (2012) 
estimated that about 2,600 (five percent) of those systems (4.6 percent 
for the 2005 data set) had TC detection rates of 20 percent or more.
    Under the third monitoring cycle of the Unregulated Contaminant 
Monitoring Rule (UCMR3), EPA sampled about 800 randomly selected 
undisinfected ground water systems serving fewer than 100 people for 
virus and virus indicators. These data show that only a small number of 
samples were virus positive by qPCR (16 out of 1,044 or two percent) 
(USEPA, 2016j). This result contrasts significantly with the virus 
positive sample rate from Borchardt et al. (2012) (287 out of 1,204 or 
24 percent). One difference is that Borchardt et al. (2012) sampled 
prior to any treatment in the undisinfected wells (e.g., softening, 
iron/manganese removal). In contrast, many wells in the UCMR3 virus 
study were sampled after softening or other treatment. The UCMR3 
monitoring results are available online at: https://www.epa.gov/dwucmr/data-summary-third-unregulated-contaminant-monitoring-rule.

VII. EPA's Request for Comments and Next Steps

    EPA invites commenters to submit any relevant data or information 
pertaining to the NPDWRs identified in this action as candidates for 
revision, as well as other relevant comments. EPA will consider the 
public comments and/or any new, relevant data submitted for the eight 
NPDWRs listed as candidates for revision as the Agency moves forward in 
determining whether regulatory revisions for these NPDWRs are 
necessary. The announcement whether or not the Agency intends to revise 
an NPDWR (pursuant to SDWA Sec.  1412(b)(9)) is not a regulatory 
decision.
    Relevant data include studies/analyses pertaining to health 
effects, analytical feasibility, treatment feasibility and occurrence/
exposure. This information will inform EPA's evaluation as the Agency 
moves forward determining whether regulatory revisions for these NPDWRs 
are necessary. The data and information requested by EPA include peer-
reviewed science and supporting studies conducted in accordance with 
sound and objective scientific practices, and data collected by 
accepted methods or best available methods (if the reliability of the 
method and the nature of the review justifies use of the data).
    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 the documentation that 
supports them (USEPA, 2015a).
    Specifically, EPA is requesting comment and/or information related 
to the following aspects of potential revisions to the MDBP NPDWRs:
     Potential approaches that could enhance protection from 
DBPs, including both those that are regulated and those currently 
unregulated (e.g., nitrosamines). Specifically, commenters are 
requested to provide information about requiring greater removal of 
precursors (e.g., TOC), and/or more targeted constraints on precursors 
(e.g., based on watershed vulnerabilities) that could provide for an 
improvement in health protection from mixtures of DBPs while 
considering risk-balancing. For example, commenters are requested to 
provide information about an approach that provides for an option to 
either control source water vulnerabilities (e.g., de facto reuse) or 
to further constrain precursors associated with unregulated DBPs. In 
addition, commenters are requested to provide information that 
considers a comprehensive analysis of source waters for the formation 
of a wide variety of byproducts (e.g., TTHM, HAA5, and unregulated DBPs 
such as nitrosamines, brominated and iodinated compounds).
     Potential approaches that could enhance protection from 
chlorite, chlorate, and chlorine dioxide. Specifically, commenters are 
requested to provide information about approaches that could involve, 
for example: Setting standards for systems using hypochlorite that 
address combined exposure to chlorite and chlorate; and setting 
standards for systems using chlorine dioxide (alone or in combination 
with other disinfectants) that address combined exposure from chlorite, 
chlorate, and chlorine dioxide.
     Potential approaches that could provide increased 
protection from microbial pathogens and that take into consideration 
the issues noted about disinfection residual requirements, while 
considering the risk-balancing aspects of the MDBP rules. In addition, 
commenters are requested to provide information about approaches that 
could offer enhanced protection without the use of a chlorine-based 
disinfectant residual in the distribution system, including technology 
and management systems associated with those approaches.
     Information about how frequently PWS monitor for DBPs 
during chlorine burn periods, including revised monitoring schedules 
for DBPs, taking into account occurrence and exposure to DBPs during 
chlorine burn periods, and related short-term health effects on 
sensitive populations.

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Drinking Water Regulations; Amendments. 44 FR 42254. July 19, 1979.
USEPA. 1985. National Primary Drinking Water Regulations; Volatile 
Synthetic Organic Chemicals; Final Rule and Proposed Rule. 50 FR 
46880. November 13, 1985.
USEPA. 1989. National Primary Drinking Water Regulations; 
Filtration, Disinfection; Turbidity, Giardia lamblia, Viruses, 
Legionella, and Heterotrophic Bacteria; Final Rule. Part III. 54 FR 
27486. June 29, 1989.
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Disinfection Requirements for Public Water Systems Using Surface 
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USEPA. 1995. Reregistration Eligibility Decision (RED) for Picloram. 
Office of Prevention, Pesticides and Toxic Substances: Washington, 
DC. EPA738-R95-019. http://archive.epa.gov/pesticides/reregistration/web/pdf/0096.pdf
USEPA. 1998a. Toxicological Review of Beryllium and Compounds (CAS 
No. 7440-41-7): in Support of Summary Information on the Integrated 
Risk Information System (IRIS). National Center for Environmental 
Assessment, Office of Research and Development, Washington, DC. EPA 
635-R-98-008. http://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/0012tr.pdf
USEPA. 1998b. National Primary Drinking Water Regulations; 
Disinfectants and Disinfection Byproducts; Final Rule. 63 FR 69390. 
December 16, 1998.
USEPA. 1998c. National Primary Drinking Water Regulations. Interim 
Enhanced Surface Water Treatment Rule. Final Rule. 63 FR 69477. 
December 16, 1998.
USEPA. 1998d. Small System Compliance Technology: List for the Non-
Microbial Contaminants Regulated Before 1996. EPA 815-R-98-002. 
September 1998.
USEPA. 1999. Uncovered Finished Water Reservoirs Guidance Manual. 
EPA 815-R-99-011. April 1999. Available online at: https://webcache.googleusercontent.com/search?q=cache:SLzRMA1eR7oJ:https://www.epa.gov/dwreginfo/interim-enhanced-surface-water-treatment-rule-documents+&cd=1&hl=en&ct=clnk≷=us.
USEPA. 2000a. ICR Auxiliary 1 Database. EPA 815-C-00-002.
USEPA. 2000b. ICR Treatment Study Database. EPA 815-C-00-003.
USEPA. 2000c. ICR Supplemental Survey Database. Prepared by DynCorp, 
Inc.
USEPA. 2001a. Toxicological Review of Hexachlorocyclopentadiene 
(CASRN 77-47-4): In Support of Summary Information on the Integrated 
Risk Information System (IRIS). National Center for Environmental 
Assessment, Office of Research and Development, Washington, DC. EPA 
600-R-01-013. http://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/0039tr.pdf
USEPA. 2001b. National Primary Drinking Water Regulations: Filter 
Backwash Recycling Rule. 66 FR 31086. June 8, 2001.
USEPA. 2002a. Diquat Dibromide HED Risk Assessment for Tolerance 
Reassessment Eligibility Document (TRED). PC Code No: 032201; DP 
Barcode: D281890; Submission Barcode: S611057. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2009-0920-0007
USEPA. 2002b. Toxicological Review of 1,1-Dichloroethylene (CAS No. 
75-35-4): In Support of Summary Information on the Integrated Risk 
Information System (IRIS). National Center for Environmental 
Assessment, Office of Research and Development: Washington, DC. EPA 
635-R-02-002. http://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/0039tr.pdf
USEPA. 2002c. National Primary Drinking Water Regulations: Long Term 
1 Enhanced Surface Water Treatment Rule. Final Rule. 67 FR 1812. 
January 14, 2002.
USEPA. 2002d. Reregistration Eligibility Decision (RED) for Lindane. 
Office of Prevention, Pesticides and Toxic Substances: Washington, 
DC. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2002-
0202-0027
USEPA. 2003a. Toxicological Review of Xylenes (CAS No.1330-20-7): In 
Support of Summary Information on the Integrated Risk Information 
System (IRIS). National Center for Environmental Assessment, Office 
of Research and Development: Washington, DC. EPA 635-R-03-001. 
http://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/0270tr.pdf
USEPA. 2003b. National Primary Drinking Water Regulations; 
Announcement of Completion of EPA's Review of Existing Drinking 
Water Standards. Notice. 68 FR 42908. July 18, 2003.
USEPA. 2005a. Economic Analysis for the Final Stage 2 Disinfectants 
and Disinfection Byproducts Rule. EPA 815-R-05-010. December 2005.
USEPA. 2005b. Toxicological Review of Barium and Compounds (CAS 
No.7440-39-3): In Support of Summary Information

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on the Integrated Risk Information System (IRIS). National Center 
for Environmental Assessment, Office of Research and Development: 
Washington, DC. EPA 635-R-05-001. http://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/0010tr.pdf
USEPA. 2005c. Toxicological Review of Toluene (CAS No. 108-88-3): In 
Support of Summary Information on the Integrated Risk Information 
System (IRIS). National Center for Environmental Assessment, Office 
of Research and Development: Washington, DC. EPA 635-R-05-004. 
http://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/0118tr.pdf
USEPA. 2005d. Method 1622: Cryptosporidium in Water by Filtration/
IMS/FA. EPA 815-R-05-001.
USEPA. 2005e. Method 1623: Cryptosporidium and Giardia in Water by 
Filtration/IMS/FA. EPA 815-R-05-002.
USEPA. 2005f. Reregistration Eligibility Decision for Endothall 
(Case Number 2245). EPA 738-R-05-008, Office of Prevention, 
Pesticides, and Toxic Substances: Washington, DC. http://archive.epa.gov/pesticides/reregistration/web/pdf/endothall_red.pdf
USEPA. 2005g. Technologies and Costs for the Final Long Term 2 
Enhanced Surface Water Treatment Rule and Final Stage 2 
Disinfectants and Disinfection Byproducts Rule. EPA 815-R-05-012. 
December 2005.
USEPA. 2006a. Acetochlor/Alachlor: Cumulative Risk Assessment for 
the Chloroacetanilides. Office of Prevention, Pesticides and Toxic 
Substances: Washington, DC.
USEPA. 2006b. National Primary Drinking Water Regulations: Ground 
Water Rule; Final Rule. 71 FR 65573. November 8, 2006.
USEPA. 2006c. National Primary Drinking Water Regulations: Long Term 
2 Enhanced Surface Water Treatment Rule; Final Rule. 71 FR 654. 
January 5, 2006.
USEPA. 2006d. National Primary Drinking Water Regulations: Stage 2 
Disinfectants and Disinfection Byproducts Rule; Final Rule. 71 FR 
388. January 4, 2006.
USEPA. 2006e. Reregistration Eligibility Decision (RED) for Chlorine 
Dioxide and Sodium Chlorite (Case 4023). EPA 738-R-06-007. August 
2006.
USEPA. 2007a. Toxicological Review of 1,1,1-Trichloroethane (CAS No. 
71-55-6): In Support of Summary Information on the Integrated Risk 
Information System (IRIS). National Center for Environmental 
Assessment, Office of Research and Development: Washington, DC. EPA-
635-R-03-013. http://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/0197tr.pdf
USEPA. 2007b. Simultaneous Compliance Guidance Manual for the Long-
Term 2 and Stage 2 DBP Rules. EPA 815-R-07-017. March 2007.
USEPA. 2008a. Carbofuran. HED Revised Risk Assessment for the Notice 
of Intent to Cancel (NOIC). PC 090601. DP# 347038. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2007-1088-0034
USEPA. 2008b. Total Coliform Rule/Distribution System (TCRDS) 
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USEPA. 2009a. Analytical Feasibility Support Document for the Second 
Six-Year Review of Existing National Primary Drinking Water 
Regulations. EPA 815-B-09-003. October 2009.
USEPA. 2010a. Agency Information Collection Activities; Submission 
to OMB for Review and Approval; Comment Request; Contaminant 
Occurrence Data in Support of EPA's Third Six-Year Review of 
National Primary Drinking Water Regulations (Renewal); EPA ICR No. 
2231.02, OMB Control No. 2040-0275. 75 FR 6023. February 5, 2010.
USEPA. 2010b. Fluoride: Dose Response Analysis for Non-Cancer 
Effects. EPA 820-R-10-019. December 2010.
USEPA. 2010c. Fluoride: Exposure and Relative Source Contribution 
Analysis. EPA 820-R-10-015. December 2010.
USEPA. 2010d. Integrated Risk Information System (IRIS): 
Toxicological Review of cis-1,2-Dichloroethylene and trans-1,2-
Dichloroethylene in Support of Summary Information. National Center 
for Environmental Assessment, Office of Research and Development: 
Washington, DC. http://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/0418tr.pdf
USEPA. 2010e. Integrated Risk Information System (IRIS): 
Toxicological Review of Hydrogen Cyanide and Cyanide Salts in 
Support of Summary Information. National Center for Environmental 
Assessment, Office of Research and Development: Washington, DC. 
http://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/0060tr.pdf
USEPA. 2010f. Long Term 2 Enhanced Surface Water Treatment Rule 
Toolbox Guidance Manual. EPA 815-R-09-016. April 2010.
USEPA. 2010g. Memorandum: Updated toxicity endpoints for oxamyl. 
Office of Chemical Safety and Pollution Prevention, Washington, DC. 
http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2010-0028-
0011
USEPA. 2010h. National Primary Drinking Water Regulations; 
Announcement of the Results of EPA's Review of Existing Drinking 
Water Standards and Request for Public Comment and/or Information on 
Related Issues. 75 FR 15500. March 29, 2010.
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USEPA. 2012. Economic Analysis for the Final Revised Total Coliform 
Rule. EPA 815-R-12-004. September 2012.
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Water Regulations; Revisions to the Total Coliform Rule; Final Rule. 
78 FR 10270. February 13, 2013.
USEPA. 2013b. Human Health Risk Assessment for a Proposed Use of 
2,4-D Choline on Herbicide-Tolerant Corn and Soybean. Office of 
Chemical Safety and Pollution Prevention. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2014-0195-0007
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Supplies by Activated Alumina. EPA/600/R-14/236. March 2014.
USEPA. 2014b. Announcement of Preliminary Regulatory Determinations 
for Contaminants on the Third Drinking Water Contaminate Candidate 
List; Proposed Rule. 79 FR 62715. October 20, 2014.
USEPA. 2015a. Peer Review Handbook 4th Edition. October 2015. 
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Rule (UCMR4) for Public Water Systems and Announcement of a Public 
Meeting. 70 FR 76897. December 11, 2015. Available online at: 
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USEPA. 2016a. Analytical Feasibility Support Document for the Third 
Six-Year Review of National Primary Drinking Water Regulations: 
Chemical Phase Rules and Radionuclides Rules. EPA-810-R-16-005.
USEPA. 2016b. Chemical Contaminant Summaries for the Third Six-Year 
Review of Existing National Primary Drinking Water Regulations. EPA-
810-R-16-004.
USEPA. 2016c. Consideration of Other Regulatory Revisions in Support 
of the Third Six-Year Review of the National Primary Drinking Water 
Regulations: Chemical Phase Rules and Radionuclides Rules. EPA-810-
R-16-003.
USEPA. 2016d. Development of Estimated Quantitation Levels for the 
Third Six-Year Review of National Primary Drinking Water Regulations 
(Chemical Phase Rules). EPA-810-R-16-002.
USEPA. 2016e. Occurrence Analysis for Potential Source Waters for 
the Third Six-Year Review of National Primary Drinking Water 
Regulations. EPA-810-R-16-008.
USEPA. 2016f. EPA Protocol for the Third Review of Existing National 
Primary Drinking Water Regulations. EPA-810-R-16-007.
USEPA. 2016g. Spring 2016 Regulatory Agenda, Semiannual regulatory 
flexibility agenda and semiannual regulatory agenda. 81 FR 37374. 
June 9, 2016.
USEPA. 2016h. Six-Year Review 3--Health Effects Assessment for 
Existing Chemical and Radionuclides National Primary Drinking Water 
Regulations--Summary Report. EPA-822-R-16-008.
USEPA. 2016i. Six-Year Review 3 ICR Database.
USEPA, 2016j. Occurrence Data for the Unregulated Contaminant 
Monitoring Rule. July 2016.

[[Page 3552]]

USEPA. 2016k. Six-Year Review 3 Technical Support Document for 
Chlorate. EPA-810-R-16-013.
USEPA. 2016l. Six-Year Review 3 Technical Support Document for 
Disinfectants/Disinfection Byproducts Rules. EPA-810-R-16-012.
USEPA. 2016m. Six-Year Review 3 Technical Support Document for Long-
Term 2 Enhanced Surface Water Treatment Rule. EPA-810-R-16-011.
USEPA. 2016n. Six-Year Review 3 Technical Support Document for 
Microbial Contaminant Regulations. EPA-810-R-16-010.
USEPA. 2016o. Six-Year Review 3 Technical Support Document for 
Nitrosamines. EPA-810-R-16-009.
USEPA. 2016p. The Analysis of Regulated Contaminant Occurrence Data 
from Public Water Systems in Support of the Third Six-Year Review of 
National Primary Drinking Water Regulations: Chemical Phase Rules 
and Radionuclides Rules. EPA-810-R-16-014.
USEPA. 2016q. The Data Management and Quality Assurance/Quality 
Control (QA/QC) Process for the Third Six-Year Review Information 
Collection Rule Dataset. EPA-810-R-16-015.
USEPA. 2016r. Technologies for Legionella Control in Premise 
Plumbing Systems: Scientific Literature Review. EPA-810-R-16-001. 
September 2016.
USEPA. 2016s. Support Document for Third Six Year Review of Drinking 
Water Regulations for Acrylamide and Epichlorohydrin. EPA 810-R-16-
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92: 93-99.

    Dated: December 20, 2016.
Gina McCarthy,
Administrator.
[FR Doc. 2016-31262 Filed 1-10-17; 8:45 am]
 BILLING CODE 6560-50-P


