Document ID: EPA-HQ-OW-2007-1189-0001
Agency: epa
Document Type: Notice
Title: Drinking Water Contaminant Candidate List 3--Draft
Posted Date: 2008-02-21T05:00Z

[Federal Register: February 21, 2008 (Volume 73, Number 35)]
[Notices]               
[Page 9627-9654]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr21fe08-134]                         

[[Page 9627]]

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Part II

Environmental Protection Agency

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Drinking Water Contaminant Candidate List 3--Draft; Notice

[[Page 9628]]

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ENVIRONMENTAL PROTECTION AGENCY

[EPA-HQ-OW-2007-1189 FRL-8529-7]
RIN 2040-AD99

 
Drinking Water Contaminant Candidate List 3--Draft

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notice.

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SUMMARY: EPA is publishing for public review and comment a draft list 
of contaminants that are currently not subject to any proposed or 
promulgated national primary drinking water regulations, that are known 
or anticipated to occur in public water systems, and which may require 
regulations under the Safe Drinking Water Act (SDWA). This is the third 
Contaminant Candidate List (CCL 3) published by the Agency since the 
SDWA amendments of 1996.
    This draft CCL 3 includes 93 chemicals or chemical groups and 11 
microbiological contaminants. The EPA seeks comment on the draft CCL 3, 
the approach used to develop the list, and other specific contaminants.

DATES: Comments must be received on or before May 21, 2008.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-OW-
2007-1189, by one of the following methods:
     http://www.regulations.gov: Follow the on-line 

instructions for submitting comments.
     Mail: Water Docket, Environmental Protection Agency, 
Mailcode: 2822T, 1200 Pennsylvania Ave., NW., Washington, DC 20460.
     Hand Delivery: Water Docket, EPA Docket Center (EPA/DC) 
EPA West, Room 3334, 1301 Constitution Ave., NW., Washington, DC. Such 
deliveries are only accepted during the Docket's normal hours of 
operation, and special arrangements should be made for deliveries of 
boxed information.
    Instructions: Direct your comments to Docket ID No. EPA-HQ-OW-2007-
1189. EPA's policy is that all comments received will be included in 
the public docket without change and may be made available online at 
http://www.regulations.gov, including any personal information 

provided, unless the comment includes information claimed to be 
Confidential Business Information (CBI) or other information whose 
disclosure is restricted by statute. Do not submit information that you 
consider to be CBI or otherwise protected through http://www.regulations.gov or e-mail. The http://www.regulations.gov Web site 

is an ``anonymous access'' system, which means EPA will not know your 
identity or contact information unless you provide it in the body of 
your comment. If you send an e-mail comment directly to EPA without 
going through http://www.regulations.gov your e-mail address will be 

automatically captured and included as part of the comment that is 
placed in the public docket and made available on the Internet. If you 
submit an electronic comment, EPA recommends that you include your name 
and other contact information in the body of your comment and with any 
disk or CD-ROM you submit. If EPA cannot read your comment due to 
technical difficulties and cannot contact you for clarification, EPA 
may not be able to consider your comment. Electronic files should avoid 
the use of special characters, any form of encryption, and be free of 
any defects or viruses. For additional instructions on submitting 
comments, go to Unit I.B of the SUPPLEMENTARY INFORMATION section of 
this document.
    Docket: All documents in the docket are listed in the http://www.regulations.gov
 index. Although listed in the index, some 

information is not publicly available, e.g., CBI or other information 
whose disclosure is restricted by statute. Certain other material, such 
as copyrighted material, will be publicly available only in hard copy. 
Publicly available docket materials are available either electronically 
in http://www.regulations.gov or in hard copy at the Water Docket, EPA/

DC, EPA West, Room 3334, 1301 Constitution Ave., NW., Washington, DC. 
The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday 
through Friday, excluding legal holidays. The telephone number for the 
Public Reading Room is (202) 566-1744, and the telephone number for the 
EPA Docket Center is (202) 566-2426.

FOR FURTHER INFORMATION CONTACT: For information on chemical 
contaminants contact Thomas Carpenter, Office of Ground Water and 
Drinking Water, Standards and Risk Management Division, at (202) 564-
4885 or e-mail carpenter.thomas@epa.gov. For information on microbial 
contaminants contact Tracy Bone, Office of Ground Water and Drinking 
Water, at 202-564-5257 or e-mail bone.tracy@epa.gov. For general 
information contact the EPA Safe Drinking Water Hotline at (800) 426-
4791 or e-mail: hotline-sdwa@epa.gov.

Abbreviations and Acronyms

< --less than
< =--less than or equal to
>--greater than
>=--greater than or equal to
[mu]--microgram, one-millionth of a gram
[mu]g/L--micrograms per liter
ATSDR--Agency for Toxic Substances and Disease Registry
AWWA--American Water Works Association
CASRN--Chemical Abstract Services Registry Number
CDC--Centers for Disease Control and Prevention
CCL--Contaminant Candidate List
CCL 1--EPA's First Contaminant Candidate List
CCL 2--EPA's Second Contaminant Candidate List
CCL 3--EPA's Third Contaminant Candidate List
CFR--Code of Federal Regulations
CUS/IUR--Chemical Update System/Inventory Update Rule
DBP--disinfection byproduct
DWEL--drinking water equivalent level
EPA--United States Environmental Protection Agency
ESA--ethanesulfonic acid
FDA--United States Food and Drug Administration
FR--Federal Register
g--gram
HAAs--haloacetic acids
IOCs--inorganic contaminants
IRIS--Integrated Risk Information System
kg--kilogram
L--liter
LD50--lethal dose 50; an estimate of a single dose that is 
expected to cause the death of 50 percent of the exposed animals; it is 
derived from experimental data.
lbs--pounds
LOAEL--lowest-observed-adverse-effect level
MCL--maximum contaminant level
MCLG--maximum contaminant level goal
MRDD--maximum recommended daily dose
mg/kg--milligrams per kilogram body weight
mg/kg/day--milligrams per kilogram body weight per day
mg/L--milligrams per liter
MMWR--Morbidity and Mortality Weekly Report
NAS--National Academy of Sciences
NCI--National Cancer Institute
NCOD--National Contaminant Occurrence Database
NDWAC--National Drinking Water Advisory Council
NOAEL--no-observed-adverse-effect level

[[Page 9629]]

NRC--National Academy of Sciences' National Research Council
NPDWR--national primary drinking water regulation
NTP--National Toxicology Program
OPP--Office of Pesticide Programs
PFOA--perfluorooctanoic acid
PFOS--perfluorooctane sulfonic acid
PWS--public water system
RfD--reference dose
SAB--Science Advisory Board
SDWA--Safe Drinking Water Act
TCR--Total Coliform Rule
TD50--tumorigenic dose 50; The dose-rate which if 
administered chronically for the standard life-span of the species will 
have a 50% probability of causing tumors at some point during that 
period.
TRI--Toxics Release Inventory
TDS--training data set
UCM--Unregulated Contaminant Monitoring
UCMR 1--First Unregulated Contaminant Monitoring Regulation
UCMR 2--Second Unregulated Contaminant Monitoring Regulation
US--United States of America
USDA--United States Department of Agriculture
USGS--United States Geological Survey
WBDO--waterborne disease outbreak
WHO--World Health Organization
yr--year
SUPPLEMENTARY INFORMATION:
I. General Information
    A. Does this Action Impose Any Requirements on My Public Water 
System?
    B. What Should I Consider as I Prepare My Comments for EPA?
II. Purpose, Background, and Summary of This Action
    A. What is the Purpose of This Action?
    B. Background on the CCL, Regulatory Determinations, and 
Unregulated Contaminant Monitoring
    1. Statutory Requirements for CCL and Regulatory Determinations
    2. The First Contaminant Candidate List
    3. The Regulatory Determinations for CCL 1
    4. The Second Contaminant Candidate List
    5. The Regulatory Determinations for CCL 2
    6. The Unregulated Contaminant Monitoring Rule
    7. The Third Contaminant Candidate List
    C. Summary of the Approach Used to Identify and Evaluate 
Candidates for CCL 3
    D. What is on EPA's Draft CCL 3?
III. What Analyses Did EPA Use To Develop the Draft CCL 3?
    A. Classification Approach for Chemicals
    1. Identifying the Universe
    2. Screening from the Universe to a PCCL
    3. Using Classification Models to Develop the CCL 3
    4. Selection of the Draft CCL 3--Chemicals
    B. Classification Approach for Microbial Contaminants
    1. Developing the Universe
    2. The Universe to PCCL
    3. The PCCL to Draft CCL Process
    4. Selection of the Draft CCL 3 Microbes from the PCCL
    C. Public Input
    1. Nominations & Surveillance
    2. External Expert Review and Input
    3. How are the CCL and UCMR Interrelated for Specific Chemicals 
and Groups?
IV. Request for Comment
    A. Pharmaceuticals
    B. Perfluorooctanoic acid and Perfluorooctane sulfonic acid
    C. Helicobacter pylori
V. EPA's Next Steps
VI. References

I. General Information

A. Does This Action Impose Any Requirements on My Public Water System?

    The draft Contaminant Candidate List 3 (CCL 3) or the final CCL 3, 
when published, will not impose any requirements on anyone. Instead, 
this action notifies interested parties of the availability of EPA's 
draft CCL 3 and seeks comment on the contaminants listed.

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

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

II. Purpose, Background, and Summary of This Action

    This section briefly summarizes the purpose of this action, the 
statutory requirements, previous activities related to the Contaminant 
Candidate List (CCL), and the approach used to develop the CCL 3.

A. What Is the Purpose of This Action?

    The Safe Drinking Water Act (SDWA), as amended in 1996, requires 
EPA to publish a list of currently unregulated contaminants that may 
pose risks for drinking water (referred to as the Contaminant Candidate 
List, or CCL) and to make determinations on whether to regulate at 
least five contaminants from the CCL with a national primary drinking 
water regulation (NPDWR) (section 1412(b)(1)). The 1996 SDWA requires 
the Agency to publish both the CCL and the regulatory determinations 
every five years. The purpose of this action is to present EPA's draft 
list of contaminants on the CCL 3, a description of the selection 
process, and the rationale used to make the list.
    This action also includes a request for comment on the Agency's 
draft CCL 3, the approach used to develop the list, and other specific 
contaminants.

B. Background on the CCL, Regulatory Determinations, and Unregulated 
Contaminant Monitoring

1. Statutory Requirements for CCL and Regulatory Determinations
    Section 1412(b) (1) of SDWA, as amended in 1996, requires EPA to 
publish the Contaminant Candidate List every five years. SDWA specifies 
that the list must include contaminants that are not subject to any 
proposed or promulgated NPDWRs, are known or anticipated to occur in 
public water systems (PWSs), and may require regulation under SDWA.
    The 1996 SDWA Amendments also specify three criteria to determine 
whether a contaminant may require regulation:
     The contaminant may have an adverse effect on the health 
of persons;
     The contaminant is known to occur or there is a 
substantial likelihood that the contaminant will occur in public water 
systems with a frequency and at levels of public health concern; and
     In the sole judgment of the Administrator, regulation of 
such contaminant presents a meaningful opportunity for health risk 
reduction for persons served by public water systems.
    In developing the draft CCL 3, the Agency considered the best 
available data and information for unregulated contaminants. As 
required under the Safe Drinking Water Act, EPA evaluated substances 
identified in section 101(14) of the Comprehensive Environmental 
Response, Compensation, and Liability Act of 1980 and substances 
registered as pesticides under the Federal Insecticide, Fungicide, and 
Rodenticide Act. In addition to these required data sources, the Agency 
also developed the National Contaminant Occurrence Database (NCOD) 
established under section 1445(g) of SDWA. Substances from NCOD were 
included in the initial set

[[Page 9630]]

of contaminants considered for the draft CCL 3.
    SDWA also directs the Agency to consider the health effects and 
occurrence information for unregulated contaminants to identify those 
contaminants that present the greatest public health concern related to 
exposure from drinking water. In selecting contaminants for the draft 
CCL 3, adverse health effects that may pose a greater risk to subgroups 
which represent a meaningful portion of the population were considered. 
Adverse health effects associated with infants, children, pregnant 
women, the elderly, and individuals with a history of serious illness 
were evaluated for both chemicals and microbes. The specific analyses 
and evaluations used by the Agency are discussed and cited in the 
relevant sections of this notice.
2. The First Contaminant Candidate List
    Following the 1996 SDWA Amendments, EPA sought input from the 
National Drinking Water Advisory Council (NDWAC) on the process that 
should be used to identify contaminants for inclusion on the first CCL 
(CCL 1). For chemical contaminants, the Agency developed screening and 
evaluation criteria based on the recommendations provided by NDWAC. For 
microbiological contaminants, NDWAC recommended that the Agency seek 
external expertise to identify and select potential waterborne 
pathogens. As a result, an external group of microbiologists and public 
health experts developed the criteria for screening, conducted an 
evaluation of microbial agents, and selected the initial list of 
microbiological contaminants for the CCL 1.
    The draft CCL 1 was published on October 6, 1997 (62 FR 52193 
(USEPA, 1997)). After consideration of all comments, EPA published the 
final CCL 1, which included 50 chemical and 10 microbiological 
contaminants, on March 2, 1998 (63 FR 10273 (USEPA, 1998 b)). A more 
detailed discussion of how EPA developed CCL 1 can be found in the 1997 
and the 1998 Federal Register notices (62 FR 52193 (USEPA, 1997) and 63 
FR 10273 (USEPA, 1998 b)).
3. The Regulatory Determinations for CCL 1
    EPA published its preliminary regulatory determinations for a 
subset of contaminants listed on CCL 1 on June 3, 2002 (67 FR 38222 
(USEPA, 2002 b)). The Agency published its final regulatory 
determinations on July 18, 2003 (68 FR 42898 (USEPA, 2003 a)). EPA 
identified 9 contaminants from the 60 contaminants listed on CCL 1 that 
had sufficient data and information available to make regulatory 
determinations. The 9 contaminants were Acanthamoeba, aldrin, dieldrin, 
hexachlorobutadiene, manganese, metribuzin, naphthalene, sodium, and 
sulfate. The Agency determined that a national primary drinking water 
regulation was not necessary for any of these 9 contaminants. The 
Agency issued guidance on Acanthamoeba and health advisories for 
magnesium, sodium, and sulfate.
4. The Second Contaminant Candidate List
    The Agency published its draft second CCL (CCL 2) Federal Register 
notice on April 2, 2004 (69 FR 17406 (USEPA, 2004)) and the final CCL 2 
Federal Register notice on February 24, 2005 (70 FR 9071 (USEPA, 2005 
b)). The CCL 2 carried forward the 51 remaining chemical and microbial 
contaminants that were listed on CCL 1.
5. The Regulatory Determinations for CCL 2
    EPA published its preliminary regulatory determinations for a 
subset of contaminants listed on CCL 2 on May 1, 2007 (72 FR 24015 
(USEPA, 2007 d)). EPA identified 11 contaminants from the 51 
contaminants listed on CCL 2 that had sufficient data and information 
available to make preliminary regulatory determinations. The 11 
contaminants are boron, the dacthal mono- and di-acid degradates, 1,1-
dichloro-2,2-bis (p-chlorophenyl) ethylene (DDE), 1,3-dichloropropene, 
2,4-dinitrotoluene, 2,6-dinitrotoluene, s-ethyl propylthiocarbamate 
(EPTC), fonofos, terbacil, and 1,1,2,2-tetrachloroethane. The Agency 
has made a preliminary determination that a national primary drinking 
water regulation is not necessary for any of these 11 contaminants. The 
Agency is scheduled to publish its final regulatory determinations in 
2008. In the May 1, 2007 FR notice, the Agency indicated that 
additional information was needed to make the regulatory determinations 
for perchlorate and methyl tertiary butyl ether (MTBE) and provided a 
summary of the current health effects, occurrence, and exposure 
information.
6. The Unregulated Contaminant Monitoring Rule
    SDWA provides EPA with the authority to require all large and a 
subset of small systems to monitor for unregulated contaminants. EPA 
may require monitoring for up to 30 contaminants under the Unregulated 
Contaminant Monitoring Rule (UCMR). Since the 1996 SDWA amendments, the 
Agency has issued two UCMRs (UCMR 1 and UCMR 2). UCMR 1 was promulgated 
on September 17, 1999 (64 FR 50556 (USEPA, 1999)) and UCMR 2 on January 
4, 2007 (72 FR 367 (USEPA, 2007 a)), followed by two revisions 
published later in January 2007 (72 FR 3916 (USEPA, 2007 b) and 72 FR 
4328 (USEPA, 2007 c)). Monitoring under UCMR 2 will take place during 
the 2008-2010 time period.
    UCMR 2 requires monitoring for several pesticides and pesticide 
degradates, five polybrominated diphenyl ether (PBDE) flame retardants, 
a group of nitrosamines and two munitions (TNT and RDX). All of the 
chemicals on UCMR 2 were included among the contaminants evaluated for 
CCL 3. Data collected under the UCMR are an important source of 
occurrence information for the CCL process.
7. The Third Contaminant Candidate List
    In 1998, the Agency sought advice from the National Academy of 
Sciences' National Research Council (NRC) on how to improve the CCL 
process. The NRC published its recommendations on the CCL process in 
2001 (NRC, 2001). The NRC proposed a broader, more reproducible process 
to identify the CCL than the process used by EPA in the first CCL. The 
NRC recommended that EPA develop and use a multi-step process for 
creating CCL 3 and future CCLs, whereby a broadly defined ``universe'' 
of potential drinking water contaminants is identified, assessed, and 
reduced to a preliminary CCL (PCCL) using simple screening criteria. 
All of the contaminants on the PCCL would then be assessed in more 
detail using a classification tool to evaluate the likelihood that 
specific contaminants could occur in drinking water at levels and at 
frequencies that pose a public health concern.
    In 2002, the Agency sought input from the National Drinking Water 
Advisory Council (NDWAC) on how to implement the NRC's recommendations 
to improve the CCL process. NDWAC agreed that EPA should proceed with 
the NRC's recommendations and provided some additional considerations, 
including the overarching principles the Agency should follow. The 
NDWAC workgroup met 10 times between September 2002 and May 2004. The 
NDWAC issued its recommendations in ``The National Drinking Water 
Advisory Council Report on the CCL Classification Process to the U.S. 
Environmental Protection Agency'' (NDWAC, 2004).

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    NDWAC recommended two guiding principles for construction of the 
CCL universe, which are:
     The universe should include those contaminants that have 
demonstrated or have potential occurrence in drinking water, and
     The universe should include those contaminants that have 
demonstrated or have potential adverse health effects.
    These inclusionary principles apply to the selection of 
contaminants for initial CCL consideration.
    The NDWAC also recommended that the universe of contaminants should 
be screened based on widely available data elements that indicate 
important health effects and occurrence information. This screening 
step should be as simple as possible and capable of identifying 
contaminants of the greatest significance for further consideration. 
Consideration of a classification approach was also recommended to 
increase the transparency and reproducibility of the CCL decision 
process. NDWAC recommended that EPA pursue classification models that 
build on the screening criteria to further characterize the adverse 
health effects and occurrence of chemical contaminants. NDWAC noted 
that the classification models are tools to help prioritize 
contaminants for the CCL. The model results, available information used 
by the model, and expert reviews should be used to determine which 
contaminants are listed for the next CCL. The process to develop the 
models should be viewed as iterative, and EPA should involve experts 
and allow opportunities for meaningful public comment on the evaluation 
of contaminants.
    NDWAC recommended several overarching principles that EPA should 
use to develop the CCL. In addition to the need for transparency and 
public participation, these overarching recommendations include:
     Integrate expert judgment throughout the CCL process. 
Expert judgment is inherent throughout the development of the CCL 
process and in implementing that process once it is developed. Critical 
reviews, involving various types of expert consultation and 
collaboration, will be useful at key points in the new, evolving CCL 
process.
     Conduct an active surveillance and nomination/evaluation 
processes to ensure timely identification of information relevant to 
new and emerging agents.
     Apply an adaptive management approach (i.e., an approach 
that can be refined in future iterations as more knowledge is acquired) 
to implement the CCL process. The development of any model should be an 
adaptive process, and should be reviewed by experts with consideration 
given to updating the process with each successive CCL cycle.
    NDWAC also recognized that there were significant differences in 
the methods and information used to characterize chemical and 
microbiological contaminants. Chemical contaminants tend to be 
characterized by toxicological and occurrence data that can be modeled 
or estimated if measurement is not possible. These discrete 
characteristics are often captured in data sources. For microbes, the 
adverse health effects from exposure are characterized by clinical or 
epidemiological data and there are few methods to estimate or model 
their occurrence. Limited sources of tabular data for microbes may 
require evaluation of primary literature, technical reports, 
monographs, and reference books to identify a universe of microbes for 
consideration. NDWAC recommended the Agency use human pathogens as the 
starting point for identifying microorganisms considered for inclusion 
in the CCL and apply a two-step evaluation of those pathogens.

C. Summary of the Approach Used To Identify and Evaluate Candidates for 
CCL 3

    The Agency revised the CCL process used in previous efforts based 
on the knowledge and experience it has gained from evaluating 
unregulated contaminants and the recommendations and advice from NRC 
and NDWAC. Based on these recommendations the Agency developed and 
implemented a classification approach that identifies priority drinking 
water contaminants in a transparent and reproducible manner that is 
amenable to an adaptive management approach.
    The Agency's approach to classifying contaminants is based on 
available data to characterize the occurrence and adverse health risks 
a contaminant may pose to consumers of public water systems. EPA 
developed and implemented the following multi-step CCL process to 
identify contaminants for inclusion on the Draft CCL 3.
     Identify a broad universe of potential drinking water 
contaminants (called the CCL 3 Universe). EPA evaluated 284 data 
sources that may identify potential chemical and microbial contaminants 
and selected a set of approximately 7,500 chemical and microbial 
contaminants from these data sources for initial consideration.
     Apply screening criteria to the CCL 3 Universe to identify 
those contaminants that should be further evaluated. Contaminants not 
passing the screening criteria remained in the universe. The screening 
criteria EPA developed are based on a contaminant's potential to occur 
in public water systems and the potential for public health concern. 
Applying these criteria narrows the universe of contaminants to a 
Preliminary-CCL (or PCCL).
     Identify contaminants from the PCCL to include on the CCL 
based on a more detailed evaluation of occurrence and health effects. 
For chemicals, EPA used structured classification models as tools to 
evaluate and identify drinking water priority contaminants. Decisions 
to include chemicals were made using the model results and the best 
available data to identify contaminants that may occur in PWSs and may 
cause adverse health effects. EPA used a decision tree approach for 
microbial contaminants to identify those contaminants that have the 
potential to occur in PWSs and transmit waterborne disease. These two 
approaches resulted in a draft list of chemicals and microbes for 
inclusion on the Draft CCL 3.
     Incorporate public input and expert review in the CCL 
process. EPA sought public input by asking for nominations of 
contaminants to consider for the CCL (71 FR 60704 (USEPA, 2006 b)) and 
incorporated these nominations in the three key steps already 
discussed. EPA also convened several expert panels for both chemicals 
and microbes to review, and provide input and comment, on the CCL 3 
process and on a review of a preliminary draft CCL 3.
    Exhibit 1 illustrates the CCL multi-step approach that resulted 
from the Agency's efforts, input, and collaboration with NRC and NDWAC. 
This generalized process is applied to both chemical and microbial 
contaminants, though the specific execution of particular steps differs 
in detail.

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[GRAPHIC] [TIFF OMITTED] TN21FE08.000

    EPA provides a more detailed discussion of the analyses and 
decisions it made to develop the Draft CCL 3 in the EPA Water Docket. 
EPA prepared several support documents that are available for review at 
http://www.regulations.gov. These documents include:

     Three comprehensive support documents for the chemicals 
entitled, ``Contaminant Candidate List 3 Chemicals: Identifying the 
Universe'' (USEPA, 2008 a), ``Contaminant Candidate List 3 Chemicals: 
Screening to a PCCL'' (USEPA, 2008 b), and ``Contaminant Candidate List 
3 Chemicals: Classification of the PCCL to the CCL'' (USEPA, 2008 c). 
These documents describe in detail how the classification process was 
developed and used to select the chemicals for the Draft CCL.
     Three comprehensive support documents for the microbes 
entitled, ``Contaminant Candidate List 3 Microbes: Identifying the 
Universe'' (USEPA, 2008 d), ``Contaminant Candidate List 3 Microbes: 
Screening to the PCCL'' (USEPA, 2008 e), and ``Contaminant Candidate 
List 3 Microbes: PCCL to CCL Process'' (USEPA, 2008 f). These documents 
describe the microbial listing process in detail.
     The Agency also prepared summaries of stakeholder 
involvement and reviews conducted on the CCL process and draft list. 
These documents are also available in the EPA Water Docket and at 
http://www.regulations.gov.

     National Drinking Water Advisory Council Report on the CCL 
Classification Process to the U.S. Environmental Protection Agency, May 
19, 2004.
     A nominations and surveillance report, entitled ``Summary 
of the Nominations for the Third Contaminant Candidate List'' (USEPA, 
2008 g), which describes the nominations process and the contaminants 
that were nominated as part of EPA's process.
     Two documents summarizing the expert review of the 
chemical and microbial processes, entitled ``Chemical Expert Input and 
Review for the Third Contaminant Candidate List'' (USEPA, 2008 h) and 
``Microbial Expert Input and Review for the Third Contaminant Candidate 
List'' (USEPA, 2008 i).

D. What Is on EPA's Draft CCL 3?

 Exhibit 2.--Draft Contaminant Candidate List 3: Microbial Contaminants
------------------------------------------------------------------------
                                Pathogens
-------------------------------------------------------------------------
Caliciviruses
Campylobacter jejuni
Entamoeba histolytica
Escherichia coli (0157)
Helicobacter pylori
Hepatitis A virus
Legionella pneumophila
Naegleria fowleri
Salmonella enterica
Shigella sonnei
Vibrio cholerae
------------------------------------------------------------------------

                          Chemical Contaminants
------------------------------------------------------------------------
               Common name--registry name                      CASRN
------------------------------------------------------------------------
alpha-Hexachlorocyclohexane.............................        319-84-6
1,1,1,2-Tetrachloroethane...............................        630-20-6
1,1-Dichloroethane......................................         75-34-3
1,2,3-Trichloropropane..................................         96-18-4
1,3-Butadiene...........................................        106-99-0
1,3-Dinitrobenzene......................................         99-65-0
1,4-Dioxane.............................................        123-91-1
1-Butanol...............................................         71-36-3
2-Methoxyethanol........................................        109-86-4
2-Propen-1-ol...........................................        107-18-6
3-Hydroxycarbofuran.....................................      16655-82-6
4,4'-Methylenedianiline.................................        101-77-9
Acephate................................................      30560-19-1
Acetaldehyde............................................         75-07-0
Acetamide...............................................         60-35-5
Acetochlor..............................................      34256-82-1
Acetochlor ethanesulfonic acid (ESA)....................     187022-11-3
Acetochlor oxanilic acid (OA)...........................     184992-44-4
Acrolein................................................        107-02-8
Alachlor ethanesulfonic acid (ESA)......................     142363-53-9
Alachlor oxanilic acid (OA).............................     171262-17-2
Aniline.................................................         62-53-3
Bensulide...............................................        741-58-2
Benzyl chloride.........................................        100-44-7
Butylated hydroxyanisole................................      25013-16-5
Captan..................................................        133-06-2
Chloromethane (Methyl chloride).........................         74-87-3
Clethodim...............................................     110429-62-4
Cobalt..................................................       7440-48-4
Cumene hydroperoxide....................................         80-15-9
Cyanotoxins (3).........................................
Dicrotophos.............................................        141-66-2
Dimethipin..............................................      55290-64-7
Dimethoate..............................................         60-51-5
Disulfoton..............................................        298-04-4
Diuron..................................................        330-54-1
Ethion..................................................        563-12-2
Ethoprop................................................      13194-48-4
Ethylene glycol.........................................        107-21-1
Ethylene oxide..........................................         75-21-8
Ethylene thiourea.......................................         96-45-7
Fenamiphos..............................................      22224-92-6
Formaldehyde............................................         50-00-0
Germanium...............................................       7440-56-4
HCFC-22.................................................         75-45-6
Hexane..................................................        110-54-3
Hydrazine...............................................        302-01-2
Methamidophos...........................................      10265-92-6
Methanol................................................         67-56-1
Methyl bromide (Bromomethane)...........................         74-83-9
Methyl tert-butyl ether.................................       1634-04-4

[[Page 9633]]

Metolachlor.............................................      51218-45-2
Metolachlor ethanesulfonic acid (ESA)...................     171118-09-5
Metolachlor oxanilic acid (OA)..........................     152019-73-3
Molinate................................................       2212-67-1
Molybdenum..............................................       7439-98-7
Nitrobenzene............................................         98-95-3
Nitrofen................................................       1836-75-5
Nitroglycerin...........................................         55-63-0
N-Methyl-2-pyrrolidone..................................        872-50-4
N-nitrosodiethylamine (NDEA)............................         55-18-5
N-nitrosodimethylamine (NDMA)...........................         62-75-9
N-nitroso-di-n-propylamine (NDPA).......................        621-64-7
N-Nitrosodiphenylamine..................................         86-30-6
N-nitrosopyrrolidine (NPYR).............................        930-55-2
n-Propylbenzene.........................................        103-65-1
o-Toluidine.............................................         95-53-4
Oxirane, methyl-........................................         75-56-9
Oxydemeton-methyl.......................................        301-12-2
Oxyfluorfen.............................................      42874-03-3
Perchlorate.............................................      14797-73-0
Permethrin..............................................      52645-53-1
PFOA (perfluorooctanoic acid)...........................        335-67-1
Profenofos..............................................      41198-08-7
Quinoline...............................................         91-22-5
RDX (Hexahydro-1,3,5-trinitro-1,3,5-triazine)...........        121-82-4
sec-Butylbenzene........................................        135-98-8
Strontium...............................................       7440-24-6
Tebuconazole............................................     107534-96-3
Tebufenozide............................................     112410-23-8
Tellurium...............................................      13494-80-9
Terbufos................................................      13071-79-9
Terbufos sulfone........................................      56070-16-7
Thiodicarb..............................................      59669-26-0
Thiophanate-methyl......................................      23564-05-8
Toluene diisocyanate....................................      26471-62-5
Tribufos................................................         78-48-8
Triethylamine...........................................        121-44-8
Triphenyltin hydroxide (TPTH)...........................         76-87-9
Urethane................................................         51-79-6
Vanadium................................................       7440-62-2
Vinclozolin.............................................      50471-44-8
Ziram...................................................        137-30-4
------------------------------------------------------------------------

III. What Analyses Did EPA Use To Develop the Draft CCL 3?

A. Classification Approach for Chemicals

1. Identifying the Universe
    In the first step in the approach, EPA compiled potential data 
sources, including sources identified at a stakeholder workshop 
sponsored by the American Water Works Association (AWWA), to develop a 
broad universe of potential drinking water contaminants, as shown in 
Exhibit 1. This compilation identified the 284 data sources that were 
assessed for the CCL Universe.
    EPA developed a decision tree for data source selection that was 
based on four assessment factors, which were applied to all of the 
potential data sources:
     Relevance. Ensures that the data source provided 
information on demonstrated or potential health effects, occurrence, or 
potential occurrence using surrogate information (e.g., environmental 
release, environmental fate, and transport properties);
     Completeness. Ensures that the data source had minimum 
record requirements--contact name, description of the data elements, 
and how the data were obtained;
     Redundancy. Ensures that the data source does not contain 
information identical to other more comprehensive data sources; and
     Retrievability. Ensures that the data in the source are 
formatted for automated retrieval. Each source was accessed on-line (or 
as provided by the source) and reviewed.
    Basic information about the source, its purpose, and the data 
elements it contained, was compiled and documented. Every source was 
evaluated using all assessment factors sequentially. Those sources that 
met all four factors became the prime sources that formed the 
``Universe of Data Sources.'' Sources that passed the first three 
factors, but were not retrievable, were designated as supplemental data 
sources, to be consulted as necessary (e.g., to fill in data gaps) in 
the development of the CCL. Some of the sources that were not easily 
retrievable were identified as ``unique'' or ``exceptional'' because of 
the importance of their data (i.e., the Hazardous Substance Database). 
EPA included chemicals from these sources in the Universe.
    After application of the four assessment factors, 39 sources 
(Exhibit 3) met all four factors or were considered as exceptional. 
These sources were the primary sources used to develop the CCL Chemical 
Universe. The details of the how EPA compiled the list of data sources 
is discussed in the document entitled, ``CCL 3 Chemicals: Identifying 
the Universe'' (USEPA, 2008 a).

 Exhibit 3.--Sources That Comprise the Chemical Universe of Data Sources
                           for the CCL Process
------------------------------------------------------------------------
                           Name of data source
-------------------------------------------------------------------------
1. ATSDR CERCLA Priority List.
2. ATSDR Minimal Risk Levels (MRLs).
3. Chemical Toxicity Database--Ministry of Health and Welfare, Japan.
4. Chemical Update System/Inventory Update Rule (CUS/IUR)--EPA.
5. Cumulative Estimated Daily Intake/Acceptable Daily Intake (CEDI/ADI)
 Database--FDA.
6. Database of Sources of Environmental Releases of Dioxin-Like
 Compounds in the United States--EPA.
7. Distributed Structure Searchable Toxicity Public Database Network
 (DSSTox)--EPA.
8. Everything Added to Food in the United States (EAFUS) Database--FDA.
9. Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) List--
 EPA.
10. Generally Regarded As Safe (GRAS) Substance List--FDA.
11. Guidelines for Canadian Drinking Water Quality (CADW): Summary of
 Guidelines--Health Canada.
12. Hazardous Substances Data Bank (HSDB)--NLM.
13. Health Advisories (HA) Summary Tables--EPA.
14. High Production Volume (HPV) Chemical List--EPA.
15. Indirect Additives Database--FDA.
16. Integrated Risk Information System (IRIS)--EPA.
17. International Agency for Research on Cancer (IARC) Monographs.
18. International Toxicity Estimates for Risk (ITER) Database--TERA.
19. Joint Meeting On Pesticide Residues (JMPR)--2001 Inventory of
 Pesticide Evaluations--WHO, FAO.
20. National Drinking Water Contaminant Occurrence Database (NCOD)--
 Round 1&2--EPA.
21. National Drinking Water Contaminant Occurrence Database (NCOD)--
 Unregulated Contaminant Monitoring Rule (UCMR)--EPA.
22. National Inorganics and Radionuclides Survey (NIRS)--EPA.
23. National Pesticide Use Database--NCFAP.

[[Page 9634]]

24. National Reconnaissance of Emerging Contaminants (NREC)--USGS Toxic
 Substances Hydrology Program.
25. National Toxicology Program (NTP) Studies.
26. National Water Quality Assessment (NAWQA)--USGS.
27. OSHA 1988 Permissible Exposure Limits (PELs)--NIOSH.
28. Pesticide Data Program--USDA.
29. Pesticides Pilot Monitoring Program--USGS/EPA.
30. Risk Assessment Information System (RAIS)--Department of Energy--
 Chemical Factors.
31. Risk Assessment Information System (RAIS)--Department of Energy--
 Health Effects Data.
32. State of California Chemicals Known to the State to Cause Cancer or
 Reproductive Toxicity.
33. Substances Registry System (SRS)--EPA.
34. Syracuse Research Corporation (SRC)--BIODEG.
35. The Toxics Release Inventory (TRI)--EPA.
36. Toxic Substances Control Act (TSCA) List--EPA.
37. Toxicity Criteria Database--California Office of Environmental
 Health Hazard Assessment (OEHHA).
38. University of Maryland--Partial List of Acute Toxins/Partial List of
 Teratogens.
39. WHO Guidelines for Drinking Water Quality: Summary Tables.
------------------------------------------------------------------------

    There were approximately 26,000 unique substances identified from 
the 39 data sources. Because of the large number of unique substances 
identified, EPA developed an initial universe selection process. In the 
first phase of the data evaluation process, EPA identified the 
chemicals that were present in both health effects and occurrence data 
sources. The Agency queried the data sources and found that 
approximately 7,300 chemicals, or about one-third of the chemicals, 
were present in both health effects and occurrence data sources. 
Occurrence was defined broadly to include production data and 
environmental occurrence data. EPA placed these chemicals in the 
chemical universe to be further evaluated for screening to the PCCL. 
EPA then examined the rest of the approximately 18,600 chemicals left 
in the initial universe more closely to determine whether they were 
found only in health effects data sources or only in occurrence data 
sources. EPA found that approximately 5,100 chemicals were in health 
effects data sources only. Many of these chemicals were biochemical 
compounds (e.g., amino acids, sugars, steroids); mixtures and natural 
products (e.g., coal tar, petroleum related substances, rocks, stone, 
wool); and other entries that were identified as unique ``substances'' 
in the data sources but were not chemicals (e.g., turbidity, boot and 
shoe manufacture, surgical implants). EPA evaluated these to identify 
which ones are chemicals of greatest toxicological concern. Many of the 
chemicals fell into the category of greatest toxicological concern due 
to their classification as carcinogens. This is described in the report 
entitled, ``CCL 3 Chemicals: Screening to a PCCL'' (USEPA, 2008 b). 
Through this process, a total of 122 chemicals with only toxicity data 
were added to the 7,300 chemicals already in the CCL Chemical Universe.
    The chemicals found only in occurrence sources were also 
categorized. The approximately 13,500 chemicals with only occurrence 
data were a diverse group, comprised of many different types of 
chemicals. Data sources that provide the amount of an individual 
chemical that is manufactured and produced account for 70 percent (or 
9,344) of the total. The remaining 30 percent of chemicals are from 
various other data sources (i.e., finished water, ambient water, 
environmental release, environmental fate and transport properties, and 
food additives). EPA grouped these chemicals by the type of occurrence 
data for further evaluation. These included the following groupings:
     Chemicals with Finished or Ambient Water Data
     Chemicals with Release Data
     Chemicals with High Production Volumes
    EPA added 42 chemicals with finished or ambient water data to the 
Universe despite the lack of health effects information in the data 
sources because of their demonstrated occurrence in ambient or potable 
water. In addition, disinfection byproducts and water treatment 
additives were added to the Chemical Universe. While there may not have 
been measured occurrence data for these chemicals in the universe of 
data sources, they are considered to have ``default'' occurrence data 
because they are formed in, or intentionally added to, drinking water 
supplies.
    EPA also added 36 chemicals with an environmental release data 
source (e.g., those on the Toxics Release Inventory or with pesticide 
application data) to the Chemical Universe even though they lacked 
health effects data.
    The largest group of chemicals found only in occurrence data 
sources had only production information. These contaminants include: 
organometallics, elements, salts of the inorganic elements, salts of 
organic acids, natural product organics (including oils, fatty acids, 
sugars, intermediary metabolites), and mixtures (e.g., petroleum 
related compounds, hydrocarbons, and others). Over half of the 
production chemicals are compounds and/or complexes of elemental 
constituents; for example, there were about 750 sodium or potassium 
salt compounds alone. In these cases, health effects data are not 
available for the exact compound, but are generally available for other 
related compounds or the key ion or elemental constituent (e.g., 
sodium). Nearly all elements found in inorganic or organic salts are 
represented in the Universe by other compounds with both health effects 
and occurrence data. EPA found only 10 elements (excluding carbon, 
hydrogen, and oxygen, and the inert gasses krypton, neon, and xenon) 
that did not otherwise have representative compounds with health 
effects data in the Universe. EPA added these compounds (i.e., 
europium, gadolinium, gold, lanthanum, praseodymium, platinum, 
polonium, samarium, terbium, and yttrium) to the Universe. After 
evaluation of the characteristics of the chemicals with production data 
and the amounts produced on a yearly basis, and because the primary 
constituents (i.e., elements) of the chemicals were already in the 
Chemical Universe, EPA decided to move only those produced at greater 
than 1 billion pounds per year to the CCL Chemical Universe when they 
lacked health effects information.

[[Page 9635]]

    EPA added a total of 269 chemicals with only occurrence data to the 
CCL 3 Chemical Universe. The rest of the substances included in the 
original data sources were not included in the Universe.
    The initial selection process brought into the CCL Chemical 
Universe all substances from the data sources that met the defined 
selection criteria, described above. Upon further review, EPA found the 
Chemical Universe also contained regulated as well as unregulated 
compounds, mixtures, and some substances that were not really 
chemicals. To further refine the initial list, EPA removed chemicals 
with a national primary drinking water regulation. These contaminants 
are already regulated; thus, their inclusion in the CCL process is 
unnecessary and does not meet the statutory requirement for selection 
of the CCL. EPA removed 1,006 chemicals, which is more than the number 
of primary drinking water standards. This is because regulated 
contaminants can be found in many forms and because many contaminants 
are regulated as part of a class or group(s). For example, EPA removed 
approximately 780 radionuclides from the initial list, because they are 
regulated as alpha and beta emitters. Also removed were various salts 
of regulated elements, and entries for individual trihalomethanes, 
haloacetic acids, polychlorinated biphenyls and polyaromatic 
hydrocarbons that are regulated as a group. The Agency has determined 
that it is inappropriate to include aldicarbs (aldicarb, aldicarb 
sulfoxide, and aldicarb sulfone) and nickel on the CCL. These 
contaminants are subject to regulation under SDWA section 1412(b)(2) 
and thus are not part of the contaminant selection process specified 
under SDWA section 1412(b)(1). In response to an administrative 
petition from the manufacturer Rhone-Poulenc, the Agency issued an 
administrative stay of the effective date of the maximum contaminant 
levels (MCLs) for aldicarbs, and they never became effective. NPDWRs 
for nickel were promulgated on July 17, 1992 (57 FR 31776 (USEPA, 
1992)), but the MCL was later vacated and remanded by the D.C. Court of 
Appeals in response to a joint motion by EPA and industry parties 
challenging the nickel MCL and MCLG. Because these contaminants are 
subject to separate regulatory consideration, EPA has not included them 
in the CCL process.
    EPA also removed substances that are considered a mixture of 
chemicals. EPA defines a mixture in this case as a combination of two 
or more chemicals/items that are not defined as a unique substance. 
Examples of substances in this category include ``chlorinated 
compounds, aliphatic alcohols with more than 14 carbon atoms (c>14), 
coal-tar-containing shampoo, petroleum-related substances, resin acids, 
and rosin acids.'' Undefined mixtures, such as ``diesel engine 
exhaust'' were also included in this group.
    EPA also removed ``non-chemically defined'' entries from further 
consideration for the initial list. Examples include: ``solar 
radiation, wood dust, surgical implants, and welding fumes.'' Some of 
these substances are present in the data sources because they have been 
evaluated for their potential to cause cancer.
    The final step removed biological agents from the initial list. 
Contaminants in this category are biological organisms that are being 
evaluated as part of the CCL 3 Microbiological Universe. Entries for 
biological entities were uploaded from the universe of data sources 
from various health effects data sources and pesticide data sources. 
Many biological entities were also removed as non-chemically defined.
    During this phase of the data evaluation, 1,717 chemicals or 
substances were removed from the initial Chemical Universe, leaving 
approximately 6,000 chemicals that were designated as the CCL 3 
Universe. A list of the CCL Chemical Universe is provided in the 
docket. EPA further evaluated these 6,000 chemicals in the next key 
step of the process.
2. Screening from the Universe to a PCCL
    The next step in the CCL selection approach involved narrowing the 
Universe of chemicals to a PCCL, as shown in Exhibit 1. EPA considered 
and built upon NDWAC recommendations that the screening process be 
based on a contaminant's potential to occur in public water systems and 
the potential for public health concern, to select those contaminants 
that should move to the PCCL for further evaluation. The screening 
approach:
     Identifies chemicals that have relatively high toxicity 
with high potential to occur in PWSs;
     Identifies chemicals that have relatively high toxicity 
with minimal actual or potential occurrence in drinking water;
     Identifies chemicals that have high potential to occur in 
PWSs with relatively moderate toxicity; and
     Considers and uses as many of the available types of 
health effects and occurrence data identified in the data source 
evaluations as practical.
    EPA compared the chemicals' health effects relative to their 
occurrence and developed analyses that specifically incorporate many 
types of available data into the screening criteria. The health effects 
information included quantitative, descriptive, or categorical 
information. Within each of these broad types of health effects 
information, there are multiple types of reported health related values 
from multiple sources. The health effects analyses conducted by EPA 
identified approaches to compare each of these data types and 
identified similarities among chemicals that could be used to define 
toxicity categories. The occurrence information also included many 
types of available data representative of a chemical's potential to 
occur in water. Occurrence data ranged from quantified detection in 
PWSs, to environmental release, to production data.
    The basic framework EPA used in screening is shown in Exhibit 4. 
EPA categorized the CCL Chemical Universe contaminants by their 
toxicity along the vertical axis and by their occurrence on the 
horizontal axis. This allows for separation of chemicals into those 
that move to the PCCL based on their toxicity and occurrence properties 
(e.g., upper right in Exhibit 4) and those that are not further 
evaluated and remain in the CCL Chemical Universe (e.g., lower left in 
Exhibit 4).
    EPA used a set of test chemicals to develop the screening criteria. 
This set of chemicals included regulated and unregulated chemicals that 
provided comprehensive information on health effects and occurrence in 
finished and/or ambient water as well as environmental release and 
production volume. EPA then used these criteria to select chemicals for 
the PCCL for further consideration. The following sections summarize 
how EPA developed the screening criteria by evaluating the available 
data for chemicals in the Universe, using the framework (Exhibit 4) and 
the test chemicals. A more detailed discussion is provided in the 
support document entitled, ``CCL 3 Chemicals: Screening to a PCCL'' 
(USEPA, 2008 b).

[[Page 9636]]

[GRAPHIC] [TIFF OMITTED] TN21FE08.001

a. Health Effects Data Elements
    EPA evaluated the toxicity information and health effects data 
compiled from the data sources in the Universe and these data varied 
greatly. Some of these data are quantitative (e.g., RfD, LOAEL, NOAEL, 
LD50) and some are descriptive (e.g., cancer classifications 
or predictions). EPA designed the screening process to accommodate both 
types of health effects data.
    The quantitative toxicity elements and values available in the 
Universe included the following:
     RfDs and equivalent (RfD-eq): RfDs, Minimum Risk Levels 
(MRLs) from ATSDR, Tolerable Daily Intakes (TDIs) from the World Health 
Organization (WHO), and Public Health Goals (PHGs) from California EPA. 
A reference dose is an estimate (with uncertainty spanning perhaps an 
order of magnitude) of a daily oral exposure to the human population 
(including sensitive subgroups) that is likely to be without an 
appreciable risk of deleterious effects during a lifetime. There are 
slight differences among Agencies in the methodologies used for some of 
the RfD equivalents.
     NOAELs--No Observed Adverse Effect Levels. The NOAEL is 
the highest dose evaluated in a study or group of studies that does not 
have a biologically significant adverse effect on the species evaluated 
as compared to controls.
     LOAELS--Lowest Observed Adverse Effect Levels. The LOAEL 
is the lowest dose evaluated in a study or group of studies that has a 
biologically significant adverse effect on the species evaluated as 
compared to the controls.
     TD50s--Tumorigenic dose 50. The dose-rate which 
if administered chronically for the standard life-span of the species 
will have a 50 percent probability of causing tumors at some point 
during that period.
     MRDD--Maximum Recommended Daily Dose. Recommendations for 
the maximum adult daily therapeutic doses for pharmaceuticals.
     LD50s--Lethal dose 50; an estimate of a single 
dose that is expected to cause the death of 50 percent of the exposed 
animals; it is derived from experimental data.
    EPA used descriptive cancer data to group data elements into 
toxicity categories that provide gradation based upon the strength of 
the data. Sources for the descriptive cancer data included:
     U.S. EPA Cancer Groupings.
     IARC Cancer Groupings.
     NTP weight-of-evidence findings from cancer bioassays.
     National Cancer Institute (NCI) weight-of-evidence 
findings from cancer bioassays.
     EPA Water Disinfection By-Products with Carcinogenicity 
Estimates (DBP-CAN) groupings based on carcinogenic potential derived 
from Quantitative Structure Activity Relationship (QSAR) projections.
    EPA divided the chemicals in the Universe into five toxicity 
categories for screening based upon the distribution of the toxicity 
value for each type of quantitative data element and/or the qualitative 
information on cancer weight-of evidence. The five toxicity categories 
are designated 1 through 5, with Toxicity Category 1 containing 
chemicals in the most toxic grouping and Toxicity Category 5 the least 
toxic grouping.
    Based upon the distribution of the chemicals for each quantitative 
data element, EPA selected ranges of toxicity values for each toxicity 
category that differed based upon the type of data element. For 
example, the range of toxicity values that place a LOAEL in Toxicity 
Category 1 differs from the values used for a LD50. Exhibit 
5 displays the ranges for each data element and their respective 
Toxicity Categories.
    Additional information which describes how EPA performed the 
analyses to select the toxicity categories is described in the document 
entitled, ``CCL 3 Chemicals: Screening to a PCCL'' (USEPA, 2008 b).

              Exhibit 5.--Potency Measures for Universe Data Elements Partitioned Based on Toxicity
                                              [mg/kg/day or mg/kg]
----------------------------------------------------------------------------------------------------------------
                                                  RfD            NOAEL        LOAEL         MRDD         LD50
----------------------------------------------------------------------------------------------------------------
Toxicity Category 1......................            < 0.0001        < 0.01        < 0.01        < 0.01           < 1
Toxicity Category 2......................      0.0001-< 0.001      0.01-< 1      0.01-< 1      0.01-< 1        1-< 50
Toxicity Category 3......................        0.001-< 0.05        1-< 10        1-< 10        1-< 10      50-< 500
Toxicity Category 4......................          0.05-< 0.1     10-< 1000     10-< 1000     10-< 1000     500-5000
Toxicity Category 5......................               >0.1        >1000        >1000        >1000        >5000
----------------------------------------------------------------------------------------------------------------

    EPA partitioned the cancer-related data elements in the Universe 
into the Toxicity Categories as shown in Exhibit 6. The cancer data 
placed chemicals in only the three highest Toxicity Categories. EPA did 
not use quantitative measures of dose-response for carcinogenicity in 
the screening criteria because more chemicals have categorical data and 
can be analyzed using this descriptive data than by cancer slope 
factors. In addition, EPA

[[Page 9637]]

did not use descriptors indicating lack of carcinogenic potential or 
insufficient data to determine carcinogenic potential in categorizing 
chemicals because those descriptors apply only to the cancer endpoint 
and do not consider noncancer effects associated with exposure to the 
chemical.

                             Exhibit 6.--Partitioning of Cancer Data Based on TD50 Values and Weight-of-Evidence Descriptors
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                       TD50              EPA                 IARC/HC                NTP                  NCI                DSS-Tox
--------------------------------------------------------------------------------------------------------------------------------------------------------
 Toxicity Category 1**...........         < 0.1  Group A; Human        Group 1............  CE 2 species/2       P 2 species/2        H.
                                                 Carcinogen.                                sexes; or 2          sexes; or 2
                                                                                            species; or 2        species; or 2
                                                                                            sexes.               sexes.
 Toxicity Category 2.............      0.1-100  Groups B1 and B2;     Group 2A...........  Combinations of CE,  Combinations of P,   HM.
                                                 likely carcinogens.                        SE, EE, and NE.      E and N.
 Toxicity Category 3.............         >100  Group C; Suggestive   Group 2B...........  Combinations of SE,  Combinations of E    M and LM.
                                                 evidence of                                EE, and NE.          and N.
                                                 carcinogenicity.
--------------------------------------------------------------------------------------------------------------------------------------------------------
** Cancer data placed chemicals in only the three highest Toxicity Categories.
CE = clear evidence, SE = some evidence, EE = equivocal evidence, NE = no evidence.
P = positive, N = Negative, E = equivocal.
H = high probability, HM = high to medium probability, M = medium probability, LM = medium to low probability.

     EPA chose a conservative approach in the screening process to 
categorize each chemical's toxicity and evaluated all the available 
health effects dose-response and categorical data elements for a given 
chemical. Chemicals were assigned to the highest toxicity category 
indicated after an evaluation of all the available data. Accordingly, 
if a chemical had just one data element that places it in Toxicity 
Category 1, it was categorized as such even if some of the other data 
elements for that same chemical may place it in a lower toxicity 
category. For example, if a chemical is classified as a 2A carcinogen 
by IARC, it was placed in Toxicity Category 2 using the descriptive 
cancer data even if a quantified LOAEL from a different study places it 
in Toxicity Category 3.
b. Occurrence Data Elements
    EPA evaluated the occurrence data elements for each chemical and 
placed them on the horizontal axis of the screening table. In assessing 
the data, EPA found that the data elements that represent a chemical's 
potential to occur in drinking water vary greatly. EPA's goal was to 
determine which data elements best represented the potential to occur 
in drinking water. EPA considered and evaluated data elements in the 
following categories:
     Finished Water--measures of concentration and frequency of 
detections.
     Ambient Water--measures of concentration and frequency of 
detections.
     Total Releases in the Environment--pounds per year and 
number of States.
     Pesticide Application Rates--pounds per year and number of 
States.
     Production volume--pounds per year.
    In addition to evaluating quantitative data elements listed above, 
EPA also considered chemicals with descriptive data based upon their 
likelihood of occurring in drinking water. Examples of descriptive 
occurrence data elements include characterization as a disinfection 
byproduct or a drinking water treatment chemical.
    EPA used the following hierarchal approach to select the occurrence 
data element used to screen a chemical: Finished Water or Ambient Water 
> Environmental Release Data > Production Data.
    The highest data elements in the hierarchy are the finished and 
ambient water data; the lowest, the production data. Environmental 
release data from the Toxics Release Inventory (TRI) and pesticide 
application amounts occupy the middle position in the hierarchy.
    EPA also decided that when multiple data values exist for the 
chemicals within a given component of the hierarchy, the most 
conservative data value is used. For example, in the case of a chemical 
that has finished water data and ambient water data, EPA selected the 
highest reported concentration as the occurrence value used in 
screening.
    EPA obtained the finished water data elements from the National 
Contaminant Occurrence Database (NCOD), the Unregulated Contaminant 
Monitoring (UCM) Rounds 1 and 2, the National Inorganic Radionuclides 
Survey (NIRS), the Unregulated Contaminant Monitoring Regulation (UCMR) 
monitoring, the Information Collection Rule database for disinfection 
byproducts, the U.S. Department of Agriculture (USDA) Pesticide Data 
Program (PDP), and the U.S. Geological Survey (USGS) Pesticides Pilot 
Monitoring Program (PPMP). These sources included data elements such as 
percent samples with detections, percent drinking water systems with 
detections, mean and/or median detected concentrations, and highest 
observed concentrations.
    EPA obtained ambient water values from the USGS National Water 
Quality Assessment Program (NAWQA), the USGS Toxics Substances 
Hydrology program's National Reconnaissance of Emerging Contaminants 
(NREC) and related studies, and the PPMP. These sources included data 
elements such as percent samples with detections, percent sites with 
detections, mean and/or median detected concentrations, and highest 
observed concentrations.
    The environmental release data are those reported for 2004 from the 
TRI and the National Pesticide Use Database, developed by the National 
Center for Food and Agricultural Policy (NCFAP). The available 
environmental release data elements include: total releases to the 
environment (lbs/yr), number of States with releases, pesticide total 
mass active ingredient applied nationally (lbs/yr), and number of 
States with pesticide application. EPA chose to use the pounds released 
per year into the environment for screening because the mass applied to 
the environment was more directly related to a potential concentration 
in water than the number of States where a chemical is released or 
applied.
    EPA used the Toxic Substances Control Act (TSCA) chemical 
production volume ranges reported under the Chemical Update System/
Inventory Update Rule (CUS/IUR) to assess production volume. EPA 
selected the most recent year of data available for each particular 
chemical. CUS/IUR reports chemical production volume ranges rather than 
as exact values of

[[Page 9638]]

release, and provides production data for all chemicals produced in 
volumes exceeding 10,000 lbs/yr. The production data are reported in 5 
categories that range from less than 10,000 lbs/yr to greater than 1 
billion lbs/yr. Therefore, EPA chose to use those ranges as the 
occurrence subdivisions for the production data.
    The occurrence data were grouped by powers of 10 and arrayed from 
low to high across the horizontal axis of the screening table (Exhibit 
4). The document entitled ``CCL 3 Chemicals: Screening to a PCCL'' 
(USEPA, 2008b) describes the analyses in greater detail.
    In some cases, disinfection byproducts and water treatment 
chemicals lacked quantitative data elements in the Universe. However, 
both groups have a strong potential to be present in drinking water. 
EPA moved chemicals in these two categories forward to the PCCL for 
further evaluation even when limited health effects and/or occurrence 
information were available.
c. Selection of the PCCL
    The last step in the screening process used the intersections 
between health effects and occurrence data elements in the screening 
table (Exhibit 4) to establish the PCCL selection line. As noted above, 
the health data elements were grouped by the 5 toxicity categories with 
the element showing the highest potency determining placement in the 
screening table. EPA selected the highest available data element in the 
occurrence hierarchy to determine placement of a chemical on the 
horizontal axis in the screening table. Because the chemicals were 
evaluated using a hierarchical approach for their occurrence elements, 
EPA developed separate criteria for each of the occurrence elements, 
and used the placement of a group of test chemicals that had all or 
nearly all of the occurrence data elements, to establish the position 
of the PCCL selection line. The test chemicals were selected from 
regulated and past CCL chemicals. Each had data to illustrate whether 
it was or was not of concern as a drinking water contaminant.
    As a secondary analysis, EPA evaluated existing Drinking Water 
Equivalent Levels (DWELs) to confirm whether they would make the PCCL. 
The DWELS were derived from the lower RfD potency for each of the RfD 
Toxicity Categories. The DWEL (mg/L) is calculated from the RfD in mg/
kg/day by multiplying the RfD by an adult body weight of 70 kg and 
dividing by a drinking water intake of 2 L/day (rounded to one 
significant figure).When comparing the position of the set of DWELs to 
the PCCL selection line, all four toxicity categories would be put on 
the PCCL. This analysis supports the position of the PCCL selection 
line for chemicals with finished or ambient water concentration data.
    EPA also used the test chemicals to determine the PCCL selection 
line for the other occurrence data elements--total releases to the 
environment (i.e., TRI, pesticide application data) and production 
data. For example, the test chemicals were placed in Exhibit 4 based on 
their release data to guide the placement of the line that separated 
the ``pass to the PCCL'' chemicals from the ``do not pass to the PCCL'' 
chemicals. In general, the PCCL selection line was positioned so that 
regulated and most prior CCL chemicals would be selected for the PCCL.
    EPA also analyzed the test chemicals with respect to occurrence, 
releases, and production data. The test data fit well for the former 
two categories. For the latter, the fit was not as good so EPA chose to 
set the PCCL selection line at the point where all chemicals produced 
at greater than 100 million pounds per year pass to the PCCL even if 
they fall in the lowest toxicity category.
    The criteria for moving a chemical with finished or ambient water, 
environmental release, and production data to the PCCL are displayed in 
Exhibit 7.

                        Exhibit 7.--Criteria for a Chemical To Pass Screening to the PCCL
----------------------------------------------------------------------------------------------------------------
                                                               Occurrence (by data type)
                                      --------------------------------------------------------------------------
            Health effects              Finished/ambient water    Release amount (per     Production volume (per
                                            concentrations               year)                    year)
----------------------------------------------------------------------------------------------------------------
Toxicity Category 1..................  All Concentrations.....  All Amounts............  All Amounts.
Toxicity Category 2..................  [gteqt]1 [mu]g/l.......  [gteqt]10,000 lbs/yr...  [gteqt]500,000 lbs/yr.
Toxicity Category 3..................  [gteqt]10 [mu]g/l......  [gteqt]100,000 lbs/yr..  [gteqt]10 M lbs/yr.
Toxicity Category 4..................  [gteqt]100 [mu]g/l.....  [gteqt]1 M lbs/yr......  [gteqt]50 M lbs/yr.
Toxicity Category 5..................  [gteqt]1000 [mu]g/l....  [gteqt]10 M lbs/yr.....  [gteqt]100 M lbs/yr.
----------------------------------------------------------------------------------------------------------------

    EPA added DBPs and drinking water additives that lacked 
quantitative occurrence data but fell in the Toxicity Category 1 or 
Toxicity Category 2 groupings to the PCCL because of their high 
probability for being present in disinfected and treated drinking 
water.
    The screening process provides a data-driven, objective, and 
transparent process for selecting the PCCL from the Universe. All 
Toxicity Category 1 chemicals (i.e., most toxic) were captured 
regardless of their occurrence category. The occurrence threshold 
required for the PCCL selection became less inclusive as the 
contaminant toxicity decreased. The screening of the CCL 3 Universe 
resulted in the selection of 532 chemical contaminants for the PCCL 
from the approximately 6,000 chemicals that were screened. The 
categorical summary of chemicals that passed the screening is 
illustrated in Exhibit 8. A complete chemical PCCL list can be found in 
Appendix B of the document entitled, ``CCL 3 Chemicals: Screening to a 
PCCL'' (USEPA, 2008b). The 532 PCCL chemicals were further scrutinized 
as part of the next key step in the process. Some of the contaminants 
on the PCCL had limited data available for the scoring protocols and 
could not be run through the models. The 32 contaminants that had 
limited data identified in the appendixes to the ``Classification of 
the PCCL to the CCL'' support document (EPA 2008c) and will remain on 
the PCCL until new data are identified for further evaluation.

[[Page 9639]]

          Exhibit 8.--Summary of Total Chemicals That Passed Screening for PCCL by Screening Categories
----------------------------------------------------------------------------------------------------------------
                                            Finished or
           Toxicity categories             ambient water    Pesticide       Total      Production      Totals
                                           concentration       app        releases       volume
----------------------------------------------------------------------------------------------------------------
Toxicity Category 1......................            29             4            56            38           127
Toxicity Category 2......................            33            26            32            61           152
Toxicity Category 3......................            36            31            21            66           154
Toxicity Category 4......................             5             4            10            63            82
Toxicity Category 5......................             0             0             0            17            17
----------------------------------------------------------------------------------------------------------------

3. Using Classification Models To Develop the CCL 3
    The 532 PCCL chemicals were further scrutinized as part of this key 
step in the process by using classification models as tools to aid in 
the selection of the draft CCL 3. As experience is gained, the EPA 
expects to modify and improve the development of the classification 
process for future CCLs.
    From the inception of the development of the CCL classification 
process, EPA intended to use classification models as a decision 
support tool. EPA envisioned that, after testing and evaluation, models 
would be used to process complex data in a consistent, objective, and 
reproducible manner and provide a prioritized listing of candidate 
contaminants for the last stage of the CCL process--an expert review 
and evaluation. Model application also would help EPA focus resources 
for the expert review and evaluation of the highest priority potential 
contaminants.
    An overview of the classification model approach used to further 
evaluate chemicals on the PCCL is described in the following sections. 
A detailed discussion of the process is provided in a document 
entitled, ``Contaminant Candidate List 3 Chemicals: Classification of 
the PCCL to the CCL'' (USEPA, 2008c). The development of this 
classification process involves the following steps:
     Development of the Attribute Scoring Protocols.
     Development of the Training Data Set.
     Application of the Classification Models.
     Evaluation of Classification Model Output and Selection of 
the CCL.
    To use models to evaluate and classify the PCCL contaminants for 
listing on the CCL, EPA needed to develop methods to interrelate the 
important measures (i.e., attributes) that represent a contaminant's 
health effects and potential for occurrence in drinking water. Four 
attributes were selected: Potency, severity, prevalence, and magnitude. 
Protocols were developed for scoring each attribute.
    EPA also tested and evaluated the results of several classification 
models to determine which ones might provide the best decision support 
tools. To make this evaluation, EPA developed a chemical data set and 
used the data set to ``train'' the classification models. The selected 
models were utilized to process the data for the PCCL chemicals and 
provide a prioritized listing of candidate contaminants for the expert 
review and evaluation.
a. Development of the Attribute Scoring Protocols
    EPA used attributes to characterize different chemicals on the 
basis of similar qualities or traits. These qualities or traits 
represent the likelihood of occurrence or potential for adverse health 
effects of each contaminant. Throughout the process of evaluating the 
attributes EPA recognized that a wide range of data elements would have 
to be used for each attribute to characterize chemicals on the PCCL. To 
evaluate PCCL chemicals with differing types of occurrence and health 
effects data as potential CCL contaminants, one must be able to 
establish consistent relationships among the different types of data 
that represent measures of the attributes. If the same data were 
available for all contaminants, the comparison and prioritization of 
candidates would be less complex. To consistently apply the best 
available data for PCCL chemicals, EPA normalized the different types 
of data into scales and scoring protocols that accept a variety of 
input data, apply a consistent framework, and compare different types 
of data. The following sections describe how EPA developed the scales 
and scoring protocols for the health effects and occurrence attributes.
i. Health Effects Attributes
    Potency and severity are the attributes used to describe health 
effects. EPA defines potency as the lowest dose of a chemical that 
causes an adverse health effect and severity is based on the adverse 
health effect associated with the dose used to define the measure of 
potency. In other words, potency was scored on the dose that produced 
the adverse effect and severity was scored based on the health-related 
significance of the adverse effect (e.g., from dermatitis to organ 
effects to cancer). These two attributes are interrelated, in that the 
severity is linked to the measure of potency.
    The following toxicological parameters were used to evaluate 
potency:
     Reference Dose (RfD) or equivalent.
     Cancer potency (concentration in water for 10-4 
cancer risk).
     No-Observed-Adverse-Effect Level (NOAEL).
     Lowest-Observed-Adverse-Effect Level (LOAEL).
     Rat oral median Lethal Dose (LD50).
    EPA developed a ``learning set'' of about two hundred chemicals to 
calibrate the potency scoring protocols. Once the data for the learning 
set of chemicals was collected, EPA arrayed and graphically displayed 
the data to analyze their range and distribution. EPA selected a 
distribution based on logarithms (base 10) of the toxicity parameters 
rounded to the nearest integer because it provided a spread of the 
chemical toxicity parameters across the range and the curve was roughly 
log-normal.
    EPA used a log-based distribution to establish a potency scoring 
equation for each toxicity parameter. This was accomplished by 
assigning the most frequent (modal) value in each distribution a score 
of 5 on a 10 point scale. When the toxicity parameter was one log more 
toxic than the modal value, a score of 6 was assigned. Similarly, when 
the parameter was one log less toxic than the modal value a score of 4 
was given, and so on. EPA developed an equation for each toxicity 
parameter that equated the modal value to a score of 5 and calculated 
the potency score. Because the modal rounded log differed for the 
different measures of toxicity, it was necessary to use a different 
equation for each to normalize the mode to a score of 5. The

[[Page 9640]]

resultant equations are summarized in Exhibit 9.

                Exhibit 9.--Scoring Equations for Potency
------------------------------------------------------------------------

-------------------------------------------------------------------------
RfD Score = 10 - (Log10 of RfD + 7).
NOAEL Score = 10 - (Log10 of NOAEL + 4).
LOAEL Score = 10 - (Log10 of LOAEL + 4).
LD50 Score = 10 - (Log10 of LD50 + 2).
10-\4\ cancer risk Score = 10 - (Log10 of the 10-4 cancer risk + 6).
------------------------------------------------------------------------

    For distributions that spanned more than 5 orders of magnitude 
above or below the mode, scores for the tails of the distribution were 
truncated at 1 and 10. Conversely, for distributions that did not span 
5 full orders of magnitude above and below the mode, not all scores 
between 1 and 10 were used. For example, the distribution of the 10-4 
values for cancer risk was skewed, with values up to 5 orders of 
magnitude above the modal value (more potent carcinogens) but only 2 
orders of magnitude below the mode (less potent carcinogens). This 
meant that the lowest potency score for this toxicity parameter was a 
``3.''
    EPA tested the scoring process by using a subset of contaminants 
with values from multiple data elements considered in the process. In 
the testing of the potency scoring process, EPA scored all of the 
chemicals in the learning set for each toxicity parameter to examine 
the consistency across scores for the non-cancer measures of potency. 
EPA evaluated the agreement of non-cancer scores across the RfD, NOAEL, 
LOAEL and LD50 inputs and found the scores for any given compound to be 
generally consistent across parameters. Because of the general 
consistency among scores, EPA determined that a hierarchy of RfD> 
NOAEL> LOAEL> LD50 would be used in the scoring of potency. This 
hierarchy gives preference to the potency value with the richest 
supporting data set (the RfD--or equivalent values) and gives the 
lowest ranking to the LD50 because it is a measure of acute rather than 
chronic toxicity. If data are available for both the cancer and 
noncancer endpoints, the higher of the cancer or noncancer potency is 
selected and the critical effect of the higher measure of potency is 
used to score the severity.
    Severity refers to the relative impact of an adverse health affect. 
Just as toxicity increases with dose, the severity of the observed 
effect also increases. A low dose effect could be a simple increase in 
liver weight while the same chemical at a higher dose could cause 
cirrhosis of the liver. For consistency, the measure of severity that 
was used for scoring the PCCL chemicals was the effect or effects seen 
at the LOAEL. Restricting severity scores to the effects at the LOAEL 
ties them to the data used to derive the potency score.
    The severity measures used to score the PCCL chemicals differ from 
those used for potency, prevalence, and magnitude because they are 
descriptive rather than quantitative. Accordingly, they are less 
amenable to automation and often require more scientific judgment in 
their application. To guide scoring for severity, EPA developed the 
nine-point scale displayed in Exhibit 10, and a compendium of nearly 
250 descriptions of critical effects grouped by their severity scores 
(e.g., ``Chronic irritation without histopathology changes'' equals a 
score of 3).

       Exhibit 10.--Final Nine-Point Scoring Protocol for Severity
------------------------------------------------------------------------
       Score             Critical effect             Interpretation
------------------------------------------------------------------------
1.................  No adverse effect........
2.................  Cosmetic effects.........  Considers those effects
                                                that alter the
                                                appearance of the body
                                                without affecting
                                                structure or functions.
3.................  Reversible effects;        Transient, adaptive
                     differences in organ       effects.
                     weights, body weights or
                     changes in biochemical
                     parameters with minimal
                     clinical significance.
4.................  Cellular/physiological     Considers cellular/
                     changes that could lead    physiological changes in
                     to disorders (risk         the body that are used
                     factors or precursor       as indicators of disease
                     effects).                  susceptibility.
5.................  Significant functional     Considers those disorders
                     changes that are           in which the removal of
                     reversible or permanent    chemical exposure will
                     changes of minimal         restore health back to
                     toxicological              prior condition.
                     significance.
6.................  Significant,               Considers those disorders
                     irreversible, non-lethal   that persist for over a
                     conditions or disorders.   long period of time but
                                                do not lead to death.
7.................  Developmental or           Considers those chemicals
                     reproductive effects.      that cause developmental
                                                effects or that impact
                                                the ability of a
                                                population to reproduce.
8.................  Tumors or disorders        Considers chemical
                     likely leading to death.   exposures that result in
                                                a fatal disorder and all
                                                types of tumors.
9.................  Death....................
------------------------------------------------------------------------

    Severity scores 1 through 6 represent a progression in the severity 
of the observed effect. Severity score 7 is used for all studies where 
the effect observed is a reproductive and/or developmental effect 
allowing the Agency to track the chemicals that pose developmental or 
reproductive concerns consistent with the 1996 SDWA. A severity score 
of 8 was used to track all cases where cancer is the basis for the 
potency score.
ii. Occurrence Attributes
    EPA used prevalence and magnitude to describe the potential to 
occur in drinking water. Prevalence measures how widespread the 
occurrence of the contaminant is in the environment or how widely the 
contaminant may be distributed. The prevalence measure indicates the 
percent of public water systems or monitoring sites across the nation 
with detections, number of States with releases, or the total pounds 
produced nationally. Magnitude relates to the quantity of a contaminant 
that may be found in the environment. The magnitude measures include 
the median concentration of detections in water or the total pounds of 
the chemical released into the environment. In most cases the same data 
element (e.g., detections in drinking water or amount released into the 
environment) could be used to determine the prevalence, based on the 
spatial distribution and magnitude based on the amounts. However, where 
production data were used to determine prevalence, there was no 
corresponding direct measure of magnitude, so persistence and mobility 
data were used as surrogate indicators of potential magnitude.
    Production/persistence and mobility data are assigned the lowest 
level in the hierarchy of data available for prevalence and magnitude. 
Persistence-mobility is determined by chemical

[[Page 9641]]

properties that measure or estimate environmental fate characteristics 
of a contaminant and affect their likelihood to occur and persist in 
the water environment. Data sources that could provide occurrence data 
ranged from direct measure of concentrations in water to annual 
measures of environmental release or production. EPA compiled a second 
subset or learning set of 207 chemicals, with available data for all of 
the occurrence attribute data elements that measured prevalence and 
each of the data elements that measured magnitude, to calibrate 
protocols for prevalence and magnitude.
    The data available for the prevalence attribute consisted of 
measurements of a contaminant's occurrence across the United States. 
The prevalence measures have finite ranges such as zero to 100 percent 
of samples/sites or 1 to 50 States depending on the reporting 
requirements of the available data source. Accordingly, the scaling of 
scores for prevalence focused on establishing appropriate groupings of 
the number of sites or States impacted across the 1 to 10 scoring 
scale.
    The relationship between production or even environmental release 
data and the actual occurrence in drinking water is complex. Where 
actual water measurements are available, they are the preferred data 
element to score prevalence because they are the most direct measures 
of occurrence in drinking water. EPA selected the following hierarchy 
for scoring prevalence:
     Percent of PWSs with detections (national scale data).
     Percent of ambient water sites or samples with detections 
(national scale data).
     Number of States reporting application of the contaminant 
as a pesticide.
     Number of States reporting releases (total) of the 
chemical.
     Production volume in lbs/yr.

The production data provide the pounds produced annually of a chemical 
product in the United States. To some extent, this production rate 
represents the commercial importance of the chemical, so EPA 
interpreted the high production tonnage as a likely indication of wide 
use of a commodity chemical and used this information to score 
prevalence. For example, a chemical produced at a billion lbs/yr is 
more likely to be used and released more widely than a compound 
produced at only 10,000 lbs/yr.
    Magnitude represents the quantity of a contaminant that may be in 
the environment. The data sources that provided the first four levels 
of the prevalence hierarchy provided direct measurements of water and 
environmental release that could be used to score magnitude. However, 
the production categories did not supply an appropriate measure for 
magnitude. EPA used the persistence and mobility for chemicals with 
only production data as the basis of the magnitude attribute.
    To keep the process straightforward, EPA used one scale for all 
water concentration data. EPA distributed scores across the range of 
values so that organic contaminants could receive high scores as well 
as the inorganic contaminants (IOCs). Comparisons and adjustments were 
made until there was a reasonable distribution of the scores for 
organic and inorganic contaminants by using a semi-logarithmic scale. 
EPA selected the single scale approach and this is discussed in more 
detail in the report entitled ``CCL 3 Chemicals: Classification of the 
PCCL to the CCL'' (USEPA, 2008 c).
    When developing the calibration scales for the release data, the 
ranges of data were similarly arrayed using a scale based on half-log 
units with a distribution of scores that reflected the distribution of 
the data in the learning set.
    EPA based the persistence and mobility scores on chemical and 
physical properties combined with environmental fate parameters. 
Persistence and mobility act as measures of potential magnitude because 
both fate (i.e., persistence) and transport (i.e., mobility) affect the 
amount of a contaminant to be found in water. The length of time a 
chemical remains in the environment before it is degraded (persistence) 
affects its concentration in water. Similarly, the mobility of a 
chemical, or its ability to be transported to and in water, affects its 
potential to reach and dissolve in the source waters, and thus, the 
ultimate concentration of the chemical in the water.
    EPA considered a number of data elements to measure the mobility of 
a chemical in the environment. The physical/chemical parameters that 
were chosen for the CCL process are:
     Organic Carbon Partition Coefficient (Koc)
     Octanol/Water Partition Coefficient (Kow)
     Soil/Water Distribution Coefficient (Kd)
     Henry's Law Coefficient (KH)
     Solubility

The first 4 measures of mobility represent the equilibrium ratio for 
the partitioning of the contaminant from one medium to another: 
Koc (soil/sediment organic carbon: water), Kow 
(octanol: water), Kd (soil/sediment: water) and Henry's Law 
Coefficient (air: water). Koc, Kow and Kd 
are sometimes expressed as logs of the original measurements. The 
measures of persistence reflect the time the chemical will remain 
unchanged in the environment. Persistence is reflected in the following 
measures of environmental fate:
     Half-Life
     Measured Degradation Rate
     Modeled Degradation Rate

Each of the mobility and persistence data elements listed above are 
presented in hierarchical order, with the most desirable at the top 
(i.e., the first data to be used if available).
    As was the case with prevalence, EPA used a hierarchy in scoring 
magnitude. The hierarchy uses finished water occurrence data if 
available, and if not, the highest available element in the hierarchy 
of finished water data > ambient water data > environmental release 
data > persistence and mobility data. The data elements used in scoring 
magnitude follow:
     Median value of detections from finished water systems 
(PWSs) (national scale data)
     Median value of detections from ambient water sites or 
samples (national scale data)
     Amount of pesticide applied (annual, in pounds)
     Amount of total releases (annual, in pounds)
     Persistence and mobility data
    EPA developed attribute scoring protocols through a step-wise 
process of data selection, data analysis, calibration of scales, and 
evaluation of the functionality of the scores in PCCL to CCL decision-
making. This is discussed in more detail in the report entitled 
``Contaminant Candidate List 3 Chemicals: Classification of the PCCL to 
the CCL'' (USEPA, 2008 c). EPA used the attribute protocols to 
normalize the data for the PCCL chemicals and develop a set of scores 
for the four attributes that are the input into the models. By 
normalizing the data elements, EPA developed a process that can use 
different kinds of data and information (e.g., quantitative and 
descriptive) to develop input to the models and provide a relative 
score for potential contaminants using the attribute scores.
b. Training Data Set for the Classification Models
    The training data set (TDS) for chemicals is the set of data used 
to train

[[Page 9642]]

(or teach) the classification models to mimic EPA expert list-not list 
decisions for PCCL chemicals. EPA compiled this data set in addition to 
the two learning sets to represent the types of chemicals likely to 
move forward to the PCCL. This data set also represents the range of 
possible attribute scores and listing decisions needed to train and 
calibrate the classification models. The TDS used to train the models 
for CCL 3 was comprised of 202 discrete sets of attribute scores for 
chemicals and consensus list-not list decisions made by a team of EPA 
subject matter experts.
    Classification models use statistical approaches for pattern 
recognition and derive mathematical relationships among input variables 
(e.g., measurements or descriptive data) and output from a TDS. EPA 
used classification models to develop a relationship between the 
contaminant attribute scores (input variables) and the classification 
of these contaminants into list-not list categories (output). EPA 
subject matter experts familiar with the technical aspects of the 
attribute data and the selection of drinking water contaminants for 
listing and regulation made the list-not list decisions for the TDS. 
EPA then applied the models to the PCCL to predict likely list-not list 
decisions.
    EPA considered the following key factors in developing the training 
data set:
     Selection of contaminants representing a range of outcomes 
and decisions likely to be encountered in developing a CCL;
     A variety of input data ensuring adequate coverage of 
attribute scores and combinations of scores;
     Chemicals that, when present in drinking water, would 
present a meaningful opportunity for public health improvement if 
regulated; and
     Contaminants that would likely be selected for the PCCL.
    The TDS used for training the classification models consisted of 
202 combinations of attribute scores and the decisions made by EPA 
experts. The TDS included some of the contaminants from the learning 
sets used in developing the scoring protocols for toxicity and 
occurrence. It also included additional contaminants to meet the key 
factor requirements described above. The set of known chemicals chosen 
for the TDS was supplemented with a set of attribute scores and 
decisions that were selected to balance the range of scored attributes 
the classification model would need to evaluate as described further 
below.
    Initially, EPA selected ``data rich'' contaminants from among 
regulated contaminants and previous CCLs because they had a range of 
readily available occurrence and health effects information. EPA 
drinking water subject matter experts and stakeholders reviewed the 
initial list of contaminants and identified additional candidates for 
the TDS. This initial selection process identified 51 chemical 
contaminants. Subsequently, EPA randomly chose 50 contaminants from 
chemicals in the CCL 3 Universe with high health effects potency values 
and accompanying occurrence data because they represented contaminants 
likely to make it to the PCCL. The addition of these 50 contaminants 
resulted in 101 contaminants with data to score attributes.
    The performance of the classification models using the initial TDS 
gave an indication of gaps in the possible attribute space that the set 
of 101 TDS contaminants did not adequately cover. This led EPA to add 
the sets of possible attribute scores to the TDS based on Latin 
hypercube sampling (NIST, 2006; http://www.itl.nist.gov/div898/handbook/glossary.htm#LHC
). Using this approach, EPA added 101 specific 

combinations of attribute scores to fill in gaps in the space defined 
by total possible attribute scores and improve the performance of the 
models. This set of 202 scores and decisions ensured good coverage of 
both ``list'' and ``not list'' outcomes and became the TDS. Models 
trained with the TDS with 202 decisions had greater agreement with EPA 
subject matter experts than those trained with the TDS of 101 
contaminants.
    List-not list decisions were a key component of the TDS. EPA 
subject matter experts made list-not list decisions as individuals and 
as a group, based on attribute scores and based on data that had not 
been converted to attribute scores (actual or raw data). The 
development of the list-not list decisions was an iterative process 
that incorporated revisions to the attribute scoring protocols as 
experience was gained by the EPA experts. EPA resolved differences 
between the decisions based on the scored attributes and the raw data 
by revising the scoring protocols based on the EPA experts' experience 
to improve the correlation of decisions based on scores to those based 
on raw data.
    EPA subject matter experts reviewed and evaluated the health 
effects and occurrence data for each contaminant. Each individual 
reviewer made decisions about how to classify the contaminant and then 
met as a group to discuss their decisions. Early in the process the 
reviewers recognized that clear list or not-list decisions could easily 
be made for some contaminants, but not for other contaminants. For the 
chemicals where the decision whether to list contaminants was not 
clear, two categories were added to the analyses. The categories of 
List? (L?) or Not List? (NL?) allowed the group to identify chemicals 
that were close to the boundary for a List-Not List decision. That is 
L? signifies that the decision is leaning towards listing but with some 
uncertainty, and NL? signifies that the decision is leaning towards not 
listing but with some uncertainty. These additional two categories were 
incorporated into the evaluation and model training process.
    The EPA subject matter experts also reached a consensus decision 
for each contaminant. This consensus decision was used to train the 
models. This is discussed in more detail in the report entitled 
``Contaminant Candidate List 3 Chemicals: Classification of the PCCL to 
the CCL'' (USEPA, 2008c).
c. Evaluation of Classification Models
    EPA identified several different models for possible use in 
selecting contaminants from the PCCL for the CCL: Artificial neural 
networks, classification decision trees, linear models, and 
multivariant adaptive regression splines. EPA evaluated the 
classification models in a two-step process. The first step was the 
evaluation and selection of models from within each of the model 
classes that best predicted the consensus decisions of the subject 
matter experts. The second step was the evaluation of the performance 
of the best models selected from each class (USEPA, 2008c).
    EPA evaluated models based on the 4 attributes that the model was 
able to consider, the types of relationships or mathematical functions 
that the model utilized, and the model's ability to predict 
classifications of the TDS. The iterative training process minimized 
the model's predictive error, thereby reducing incorrect model 
predictions. EPA also evaluated the impact of the attributes used by 
the models and the effects of missing data on the performance of the 
models during the various stages of development.
    EPA evaluated the performance of five models. Three models, 
Artificial Neural Network (ANN), Quick, Unbiased and Efficient 
Statistical Tree (QUEST), and Linear Regression demonstrated consistent 
performance when trained and evaluated with the TDS. The classification 
models were assessed and compared with respect to:

[[Page 9643]]

     The number of correct and incorrect classifications for 
the 202 TDS contaminants.
     The number of ``large'' misclassifications (off by more 
than one category).
     The weighted sum of TDS classification errors.
     Ability to identify intermediate classifications.
     Consistent behavior (e.g., no decreasing classification as 
attribute scores increase).

This is discussed in more detail in the report entitled ``Contaminant 
Candidate List 3 Chemicals: Classification of the PCCL to the CCL'' 
(USEPA, 2008c).
d. Application and Use of Model Results
    From the inception of the development of the CCL classification 
process, EPA intended to use classification models as decision support 
tools. It was envisioned that the models would be used to process 
complex data in a consistent, objective, and reproducible manner and 
provide a prioritized listing of contaminants, allowing EPA to focus 
resources on the expert review and evaluation of the highest priority 
potential contaminants. The ANN, Linear, and QUEST models are three 
different classes of models, with three different mathematical 
approaches, yet they all provided similar results and logical 
determinations. EPA explored simple ways to combine the results of all 
three models, to capture both agreement among models and unique 
results. Both a straightforward, additive approach, and a collective, 
rank-order approach were utilized to provide a prioritized listing of 
contaminants to be considered further and evaluated for possible 
inclusion on the draft CCL 3.
e. Model Outcome and Expert Evaluation
    In the last step of the process, the chemicals on the PCCL were 
scored for their attributes and evaluated by the three models. Some of 
the contaminants on the PCCL had limited data available for the scoring 
protocols and could not be run through the models. The 32 contaminants 
that had limited data are identified in the appendixes to the 
``Classification of the PCCL to the CCL'' support document (EPA 2008c) 
and will remain on the PCCL until new data are identified for further 
evaluation. As part of the evaluation of model output, EPA formulated 
several post-model refinements that were added to the CCL selection 
process. Exhibit 11 illustrates the results of the model output for the 
PCCL contaminants. The PCCL consisted of chemicals with variable health 
effects data, ranging from reference doses (RfD) to Lethal Dose 50s 
(LD50), and occurrence data ranging from measured water 
concentration data from Public Water Systems (PWS) to production volume 
data.

                                Exhibit 11.--Model Results for the PCCL Chemicals
----------------------------------------------------------------------------------------------------------------
                                                                  Total      Finished
                3-Models decision                  % of PCCL       or ambient     Release    Production
                                                                  PCCL        water
----------------------------------------------------------------------------------------------------------------
 L.............................................            9           44            3           24           17
 L-L?..........................................           12           58            9           29           20
 L?............................................           33          163           26           64           73
 NL?-L?........................................            6           30            6           11           13
 NL?...........................................           28          139           29           28           82
 NL?-NL........................................            4           20            7            9            4
 NL............................................            9           46           21            7           18
 N (all).......................................          100          500          101          172          227
----------------------------------------------------------------------------------------------------------------

    Four of the seven decision categories, L, L?, NL?, NL, in the first 
column of Exhibit 11 signify that all of the models were in unanimous 
agreement with the listing decision. The other categories (e.g., NL?-
L?) represent varied agreement where one or two of the models chose one 
category and the other model(s) resulted in a different category. Note 
that none of the models placed a contaminant in a category more than 
one category higher or lower than the other models. That is, no 
contaminants were categorized as ``L'' by one model and as ``NL?'' by 
one of the other models, or visa versa. The models categorized 
approximately one-half of the chemicals on the PCCL as L? or above. 
When analyzed by data type, the majority of chemicals in the List 
category used LD50 data for health effects. This was a 
concern and became an important issue for consideration. The role 
LD50 played in the health effects scoring was discussed 
extensively during the post-model evaluation process.
    As part of the last stage in the CCL classification process, the 
model output was reviewed by a group of internal EPA experts 
representing several offices. This step involved a detailed review of 
the data used for the models and the available supplemental data for 
the chemicals. The EPA experts also deliberated on the method of using 
the model data to produce a draft proposal for CCL 3. The function of 
this review was to critically compare the results from the model to the 
data for the chemicals for a cross section of the modeled contaminants.
    Based upon issues identified by the evaluators, several post model 
refinements were added to the CCL process. Three major issues and 
refinements are described below.
    The relationship between potency and concentration was important 
when deciding whether to list a chemical. However this ratio could only 
be developed when water concentration data were available. Accordingly, 
calculation of the ratio between the health-based value and the 90th 
percentile concentration in finished or ambient water was added as a 
post-model process. The potency/concentration ratio serves as a 
benchmark that suggests a greater concern for a contaminant if the 
ratio is low and a lesser concern when it is high.
    The addition of modeled occurrence data for pesticides and 
estimated concentration in surface and ground water was obtained from 
the EPA Office of Pesticide Programs (OPP). The modeled estimates of 
concentration in water for pesticides are part of the EPA's pesticide 
registration and re-registration evaluations. Once the availability of 
the OPP data for some of the pesticides was confirmed, the data were 
extracted from OPP documents and used to generate a potency/
concentration ratio similar to that used with the water concentration 
data.
    Data certainty was factored into the decision process by 
characterizing health effect and occurrence data

[[Page 9644]]

elements and their relative certainty based upon the type of data that 
was used to score the attribute for the model classification. This 
characterization tagged data elements with high certainty and low 
certainty. The combined certainty measure for a single contaminant 
(i.e., health effects and occurrence tags) was used to place 
contaminants in bins of high, medium and low certainty.
    The high certainty bin consisted of chemicals with direct 
occurrence measured in water and well-studied data for health effects. 
Such contaminants are expected to be good candidates for regulatory 
determination because they provide information that can be considered 
in that process and have minimal research needs. Examples of the data 
used to characterize chemicals in the high certainty bin include 
chemicals with RfDs, LOAELs, and NOAELs, and water concentration data. 
The medium bin consists of chemicals that will need further occurrence 
and/or health effects research. For example, chemicals with well 
studied health effects that only have environmental release data are 
included in the medium bin. Chemicals that are released to the 
environment and need further health effects research are also included 
in the medium bin. The low certainty bin consists of chemicals that 
have limited data, yet these data suggest that further evaluation 
should be pursued. These chemicals may need extensive health effects 
and occurrence research that may require significant resources before 
regulatory determinations can be made. Examples include chemicals with 
only LD50 and/or production volume data. The CCL should 
consist both of chemicals that provide sufficient data to support 
regulatory determinations as well as chemicals that are of concern and 
need to be targeted for additional drinking water research. 
Contaminants from each bin were scrutinized separately in selecting 
which ones should be listed on the CCL 3.
4. Selection of the Draft CCL 3--Chemicals
    The chemicals for the draft CCL 3 were selected from within the 
three certainty bins with the emphasis placed on the source of the 
occurrence data (e.g., measured concentrations, release, and 
production). Four groups of chemicals were placed on the CCL based on 
their modeled scores, the potency-concentration ratios, where 
available, and the estimate of data certainty. They included:
     36 chemicals in the high certainty bin with finished or 
ambient water data and a potency/90th percentile concentration ratio 
< =10.
     24 pesticide chemicals in the medium certainty bin with 
modeled surface and/or ground water data that yielded a potency/
concentration ratio < =10.
     27 chemicals in the medium certainty bin with release data 
that gave modeled L or L-L? rankings.
     8 chemicals in the low certainty bin that were added to 
the CCL as recommended by the public in response to EPA's Federal 
Register notice (71 FR 60704, USEPA, 2006b). The notice requested that 
the public submit chemical and microbial contaminant nominations that 
should be considered for CCL 3. This process is discussed in section 
III.C.1.
    The potency and concentration were compared to develop a ratio that 
was used to select contaminants for the draft CCL 3 from the high 
certainty bin. A ratio between the health-based value and the 90th 
percentile was taken for chemicals with measurements in finished and 
ambient water. Contaminants for this bin were selected for the draft 
CCL 3 when the ratio was < =10, representing occurrence in water at a 
level of concern related to its health effects data.
    The pesticides in the medium bin, where modeled data was obtained 
from OPP, were selected for the draft CCL 3 based on their potency/
concentration ratios. Similar to the chemicals in the high certainty 
bin, pesticides were selected for the draft CCL 3 when the potency/
concentration ratio was < 10, representing potential occurrence in water 
at a level of concern related to its health effects data. The other 
chemicals in the medium bin were selected for the draft CCL 3 based on 
a review of their data and their prioritization from the classification 
models.
    Chemicals in the low certainty bin were selected for the draft CCL 
3 based on a review of their supplemental data and the data submitted 
through the nominations process. Some of the chemicals identified 
through the nominations process were already on the draft CCL 3 based 
on the data EPA collected for the universe. The supplemental data 
provided with the nominations were used to screen the nominated 
chemicals and score the attributes for those that passed the screen. 
The scored attributes were then processed through the models and the 
post-model evaluations. Those that were listed demonstrated adverse 
health effects and a potential to occur in PWSs. Chemicals not selected 
for the draft CCL 3 will remain on the PCCL until additional occurrence 
or health effects data become available to support their reevaluation.

B. Classification Approach for Microbial Contaminants

    As discussed in CCL 2 (USEPA, 2005b), the Agency evaluated the 
NDWAC, NRC and other recommendations, and used the information to 
develop a pragmatic approach for classifying the microorganisms on the 
draft CCL 3. The CCL 3 approach for microbes, like the approach used 
for chemicals, uses the attributes of occurrence and health effects to 
select the microbial contaminants. EPA's objective is to target 
microorganisms with the highest potential for human exposure and the 
most serious adverse health effects. Parallel to the chemical selection 
process, the Agency considers a broad universe of microbial 
contaminants and systematically narrows that universe down to develop 
the draft CCL 3 in a transparent and scientifically sound CCL process. 
The first step of the CCL 3 approach for microbes identifies a universe 
of potential drinking water contaminants. The second step screens that 
universe of microbiological contaminants to a Preliminary Contaminant 
Candidate List (PCCL). Lastly, EPA selects the draft CCL 3 microbial 
list by ranking the PCCL contaminants based on occurrence in drinking 
water (including waterborne disease outbreaks) and human health 
effects.
1. Developing the Universe
    EPA defined the microbial Universe for the draft CCL 3 as all known 
human pathogens. The Universe process began with the list of 1,415 
recognized human pathogens compiled by Taylor et al. (2001). The Agency 
added organisms to the Universe and updated nomenclature in Taylor et 
al. (2001) to account for emerging pathogens and new taxonomy research.
    As EPA reviewed Taylor et al. (2001), additional pathogens were 
also identified. EPA surveyed fungi in drinking water and identified 
six fungi reported to occur in drinking water distribution systems that 
did not appear on the Taylor list. The added fungi are shown in Exhibit 
12. EPA also added reovirus to the Universe based on additional health 
effects information (Tyler, et al., 2004).
    In October 2006, EPA published a notice (71 FR 60704 (USEPA, 
2006b)) requesting chemical and microbial contaminant nominations as 
part of the process to identify emerging contaminants that should be 
considered for the CCL. As a result of the

[[Page 9645]]

nominations process, 24 microbial contaminants were nominated by the 
public. Twenty-two of the microbes were previously identified by Taylor 
et al. (2001) and are already in the Universe. The two additional 
pathogens nominated were Methylobacterium (with two species) and 
Mimivirus. These two bacterial species, two viral groups and six fungal 
species were added to the Microbial Universe which brings the Microbial 
Universe list to 1,425 pathogens. The full Universe list is available 
in the document, ``Contaminant Candidate List 3 Microbes: Identifying 
the Universe'' (USEPA, 2008d).

           Exhibit 12.--Fungi Added to the Microbial Universe
------------------------------------------------------------------------
                                Pathogen
-------------------------------------------------------------------------
Arthrographis kelrae
Chryosporium zontatum
Geotrichum candidum
Sporotrichum pruinosum
Stachybotrys chartarum
Stemphylium macrosporoideum
------------------------------------------------------------------------

2. The Universe to PCCL
    EPA developed screening criteria to reduce the Universe of all 
human pathogens to just those pathogens that could be transmitted 
through drinking water. For example, pathogens transmitted solely by 
animals, such as the virus that causes rabies, were screened out of the 
Universe and are not included on the PCCL. Screening is based on a 
pathogen's epidemiology, geographical distribution, and biological 
properties in their host and in the environment. EPA moved pathogens 
forward to the PCCL if there was any evidence linking a pathogen to a 
drinking water-related disease. The screening criteria restrict the 
microbial PCCL to human pathogens that may cause drinking water-related 
diseases resulting from ingestion of, inhalation of, or dermal contact 
with drinking water. EPA used 12 screening criteria (Exhibit 13) to 
reduce the pathogens in the microbial CCL universe to the PCCL.

            Exhibit 13.--CCL Screening Criteria for Pathogens
------------------------------------------------------------------------

-------------------------------------------------------------------------
1. All anaerobes.
2. Obligate intracellular fastidious pathogens.
3. Transmitted by contact with blood or body fluids.
4. Transmitted by vectors.
5. Indigenous to the gastrointestinal tract, skin and mucous membranes.
6. Transmitted solely by respiratory secretions.
7. Life cycle incompatible with drinking water transmission.
8. Drinking water-related transmission is not implicated.
9. Natural habitat is in the environment without epidemiological
 evidence of drinking water-related disease.
10. Not endemic to North America.
11. Represented by a pathogen for the entire genus or species (that are
 closely related).
12. Current taxonomy changed from taxonomy used in Universe.
------------------------------------------------------------------------

    Pathogens meeting any single criterion of the 12 criteria were 
removed from further consideration and not moved forward to the PCCL. 
Based upon this screening exercise, 1,396 of the 1,425 pathogens were 
excluded and 29 pathogens moved on to the PCCL. The results of the 
screening process are summarized in Exhibit 14. The screening criteria 
and results of the screening process are discussed in greater detail in 
the supporting document titled ``Contaminant Candidate List 3 Microbes: 
Screening to the PCCL'' (USEPA, 2008 e).

                                                Exhibit 14.--Application of Twelve Screening Criteria to Pathogens in the Microbial CCL Universe
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                Screening Criteria                                         Pathogens
                       Pathogen class                            Total   ------------------------------------------------------------------------------------------------  screened     On PCCL
                                                                             1       2       3       4       5       6       7       8       9      10      11      12        out
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Bacteria....................................................         540     125      14      10      37     117       7       0      29     154       2      28       5         528          12
Viruses.....................................................         219       0       0      26     104       0      19       1      18       0      36       8       0         212           7
Protozoa....................................................          66       0       0       1      29       3       0       4       7       7       0       6       0          57          7*
Helminths...................................................         287       0       0       0      25       0       0     106       0       0     156       0       0         287           0
Fungi.......................................................         313       0       0       0       0      12       1       0       0     297       0       0       0         310           3
    Total...................................................       1,425     125      14      37     195     132      27     111      54     458     194      42       5       1,394         29*
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
* Two additional protozoa,Cryptosporidium and Giardia were not considered for CCL 3 and they are discussed in more detail later.

3. The PCCL to Draft CCL Process
    Pathogens on the PCCL were scored for placement on the draft CCL. 
EPA devised a scoring system to assign a numerical value to each 
pathogen on the PCCL.
    Each of the pathogens on the PCCL was scored using three scoring 
protocols, one protocol each for waterborne disease outbreaks (WBDO), 
occurrence in drinking water, and health effects. The higher of the 
WBDO score or the occurrence score is added to the normalized health 
effects score to produce a composite pathogen score. Pathogens 
receiving high scores were considered for placement on the CCL.
    EPA normalized the health effects score so that occurrence and 
health effects have equal value in determining the ranking of the CCL. 
The equal weighting of occurrence and health effects information 
closely mirrors the risk estimate methods used by EPA during drinking 
water regulation development. This scoring system prioritizes and 
restricts the number of pathogens on the CCL to only those that have 
been strongly associated with drinking water-related disease. Pathogens 
that scored low will remain on the PCCL until additional occurrence 
data, epidemiological surveillance data, or health effects data become 
available to support their reevaluation. It is important to note that 
pathogens for which there are no data documenting a waterborne disease 
outbreak in drinking water earn a low score under the protocols. EPA 
believes that pathogens that have caused a WBDO and have health effects 
data should rank higher than pathogens that have only data on health 
effects but no evidence of a WBDO. The following sections describe

[[Page 9646]]

the three protocols used to score the pathogens on the PCCL and the 
process by which the scores are combined.
a. Waterborne Disease Outbreak Protocol
    The Centers for Disease Control and Prevention (CDC), EPA and the 
Council of State and Territorial Epidemiologists (CSTE) have maintained 
a collaborative surveillance system for collecting and periodically 
reporting data related to occurrences and causes of WBDOs since 1971. 
EPA used the CDC surveillance system as the primary source of data for 
the waterborne disease outbreaks protocol. Reports from the CDC system 
are published periodically in Morbidity and Mortality Weekly Report 
(MMWR).
    For this protocol (Exhibit 15), a pathogen is scored as having a 
WBDO(s) in the U.S. if that pathogen is listed in a CDC waterborne 
disease drinking water surveillance summary (i.e., in the MMWR). A 
pathogen with multiple WBDOs listed by CDC is given the highest score 
under this protocol. EPA also scored non-CDC reported WBDOs and WBDOs 
outside the U.S. as well; however these were given lower scores. WBDOs 
outside the U.S. were scored when information was available from World 
Health Organization publications or other peer-reviewed publications.
    In addition, CDC and EPA acknowledge that the WBDOs reported in the 
surveillance system represent only a portion of the burden of illness 
associated with drinking water exposure (CDC, 2004). The surveillance 
information does not include endemic waterborne disease risks, nor are 
reliable estimates available of the number of unrecognized WBDOs and 
associated cases of illness. Therefore, EPA also considered data as 
indicating a WBDO (even though CDC does not list a WBDO in their MMWR) 
if the non-CDC data showed a link between human illness defined by a 
common water source, a common time period of exposure and/or similar 
symptoms. EPA also considered the use of molecular typing methods to 
link patients and environmental isolates.
    Only two pathogens were given a WBDO score on this basis, 
Mycobacterium avium and Arcobacter butzlerei. They are discussed in 
greater detail in the ``Contaminant Candidate List 3 Microbes: PCCL to 
CCL Process'' (USEPA, 2008 f).

        Exhibit 15.--Waterborne Disease Outbreak Scoring Protocol
------------------------------------------------------------------------
                          Category                              Score
------------------------------------------------------------------------
Has caused multiple (2 or more) documented WBDOs in the                5
 U.S. since CDC surveillance initiated in 1973.............
Has caused at least one documented WBDO in the U.S. since              4
 CDC surveillance initiated in 1973........................
Has caused documented WBDOs at any time in the U.S.........            3
Has caused documented WBDOs in countries other than the                2
 U.S.......................................................
Has never caused WBDOs in any country, but has been                    1
 epidemiologically associated with water-related disease...
------------------------------------------------------------------------

b. Occurrence Protocol
    The second attribute of the scoring process evaluates the 
occurrence of a pathogen in drinking water. Because water-related 
illness may also occur in the absence of recognized outbreaks, EPA 
scored the occurrence (direct detection) of microbes using cultural, 
immunochemical, or molecular detection of pathogens in drinking water 
under the Occurrence Protocol (Exhibit 16). Occurrence characterizes 
pathogen introduction, survival, and distribution in the environment. 
Occurrence implies that pathogens are present in water and that they 
may be capable of surviving and moving through water to produce illness 
in persons exposed to drinking water by ingestion, inhalation, or 
dermal contact.
    Pathogen occurrence is considered broadly to include treated 
drinking water, and all waters using a drinking water source for 
recreational purposes. This attribute does not characterize the extent 
to which a pathogen's occurrence poses a public health threat from 
drinking water exposure. Because viability and infectivity cannot be 
determined by non-cultural methods, the public health significance of 
non-cultural detections is unknown.

          Exhibit 16.--Occurrence Scoring Protocol for Pathogens
------------------------------------------------------------------------
                          Category                              Score
------------------------------------------------------------------------
Detected in drinking water in the U.S......................            3
Detected in source water in the U.S........................            2
Not detected in the U.S....................................            1
------------------------------------------------------------------------

c. Health Effects Protocol
    EPA's health effects protocol evaluates the extent or severity of 
human illness produced by a pathogen across a range of potential 
endpoints. The seven-level hierarchy developed for this protocol 
(Exhibit 17) begins with mild, self-limiting illness and progresses to 
death.
    The final outcome of a host-pathogen relationship resulting from 
drinking water exposure is a function of viability, infectivity, and 
pathogenicity of the microbe to which the host is exposed and the 
host's susceptibility and immune response. SDWA directs EPA to consider 
subgroups of the population at greater risk of adverse health effects 
(i.e., sensitive populations) in the selection of unregulated 
contaminants for the CCL. Sensitive populations may have increased 
susceptibility and may experience increased severity of symptoms, 
compared to the general population. SDWA refers to several categories 
of sensitive populations including the following: children and infants, 
elderly, pregnant women, and persons with a history of serious illness.
    Health effects for individuals with marked immunosuppression (e.g., 
primary or acquired severe immunodeficiency, transplant recipients, 
individuals undergoing potent cytoreductive treatments) are not 
included in this health effects scoring. While such populations are 
considered sensitive subpopulations, immunosuppressed individuals often 
have a higher standard of ongoing health care and protection required 
than the other sensitive populations under medical care. More 
importantly, nearly all pathogens have very high health effect scores 
for the markedly immunosuppressed individuals; therefore there is 
little differentiation between pathogens based on health effects for 
the immunosuppressed subpopulation.
    This protocol scores the representative or common clinical 
presentation for the specific pathogen for the population category 
under consideration. EPA used recently published clinical microbiology 
manuals as the primary data source for the common clinical 
presentation. These manuals take a broad epidemiological view of health 
effects rather than focusing on narrow research investigations. The one 
exception to this approach was EPA's scoring of health effects for 
Helicobacter pylori. H. pylori is discussed in greater detail in 
section IV.C as well as in the support document, ``CCL 3 Microbes: PCCL 
to CCL Process'' (USEPA, 2008 f).

[[Page 9647]]

    To obtain a representative characterization of health effects in 
all populations, EPA evaluated separately the general population and 
these four sensitive populations as to the common clinical presentation 
of illness for that population. EPA added the general population score 
to the highest score among the four sensitive subpopulations for an 
overall health effects score. The resulting score acknowledges that 
sensitive populations have increased risk for waterborne diseases.

                                               Exhibit 17.--Health Effects Scoring Protocol for Pathogens
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                    Manifestation in population class
         Outcome category              Score    --------------------------------------------------------------------------------------------------------
                                                  General population    Children/infants         Elderly           Pregnant women      Chronic disease
--------------------------------------------------------------------------------------------------------------------------------------------------------
Does the organism cause                       7
 significant mortality (> 1/1,000
 cases)?.
Does the organism cause pneumonia,            6
 meningitis, hepatitis,
 encephalitis, endocarditis,
 cancer, or other severe
 manifestations of illness
 necessitating long term
 hospitalization (> week)?.
Does the illness result in long               5
 term or permanent dysfunction or
 disability (e.g., sequelae)?.
Does the illness require short                4
 term hospitalization? (<  week)?.
Does the illness require physician            3
 intervention?.
Is the illness self-limiting                  2
 within 72 hours (without
 requiring medical intervention)?.
Does the illness result in mild               1
 symptoms with minimal or no
 impact on daily activities?.
--------------------------------------------------------------------------------------------------------------------------------------------------------

d. Combining Protocol Scores to Rank Pathogens
    EPA scored and ranked the PCCL using the three attribute scoring 
protocols, occurrence, waterborne disease outbreaks, and health 
effects. These protocols are designed in a hierarchical manner so that 
each pathogen is evaluated using the same criteria and the criteria 
range for each protocol varies from high significance to low 
significance. The three attribute scores are then combined into a total 
score.
    EPA scored pathogens first using the WBDO and occurrence protocols, 
and then selected the highest score. Selection of the higher score from 
the WBDO or occurrence protocol elevates pathogens that have been 
detected in drinking water or source water in the U.S. (occurrence 
score of 2 or 3) above pathogens that have caused WBDOs in other 
countries but not in the U.S. (WBDO score of 2).
    The CCL selection process considered pathogens causing recent 
waterborne outbreaks more important than pathogens detected in drinking 
water without documented disease from that exposure. Direct detection 
of pathogens indicates the potential for waterborne transmission of 
disease. Documented waterborne disease outbreaks provide an additional 
weight of evidence that illness was transmitted and that there was a 
waterborne route of exposure. EPA developed protocols to define a 
hierarchy of the relevance that each of these types of data provide in 
evaluating microbes for the CCL. Combining these two sources of 
occurrence information enabled EPA to consider both emerging pathogens, 
which are detected in water and should be considered, yet are not 
tracked by public health surveillance programs, and those pathogens 
with WBDO data. This hierarchy also acknowledges that organisms 
identified as agents in WBDO are a higher priority for the CCL.
    Next, pathogens were scored using the Health Effects Protocol. All 
five population categories were scored for each pathogen using the most 
common clinical presentation for the specific pathogen for the 
population category under consideration. Because it is recognized that 
pathogens may produce a range of illness from asymptomatic infection to 
fulminate illness progressing rapidly to death, scoring decisions are 
based upon the more common clinical presentation and clinical course 
for the population under consideration, rather than the extremes. The 
pathogen's score for the general population is added to the highest 
score among the four sensitive populations to produce a sum score 
between 2 and 14.
    Finally, EPA normalizes the Health Effects and WBDO/Occurrence 
score because the Agency believes they are of equal importance. The 
highest possible score for WBDO/Occurrence is 5 and the highest 
possible Health Effect score is 14. To equalize this imbalance, the 
Agency multiplies the health effects score by \5/14\. Combining health 
effects data with the WBDO/occurrence data by adding the scores from 
these protocols provides a system that evaluates both the severity of 
potential disease and the potential magnitude of exposure through 
drinking water.
    Exhibit 18 presents the scores for all the PCCL pathogens with the 
exception of Giardia and Cryptosporidium. These two protozoan pathogens 
made it through the screening protocol, however, EPA chose not to score 
or include them on the PCCL because EPA has recently published a 
national primary drinking water regulation that specifically addresses 
these pathogens (January 4, 2006, 71 FR 388 (USEPA, 2006 a) and is 
discussed in more detail later.

                                       Exhibit 18.--Pathogens on the PCCL
----------------------------------------------------------------------------------------------------------------
                                                                                       Normalized     Total\1\
                        Pathogen                              WBDO       Occurrence   health score      score
----------------------------------------------------------------------------------------------------------------
Naegleria fowleri.......................................            4             3           5.0           9.0
Legionella pneumophila..................................            5             3           3.6           8.6
Escherichia coli (0157).................................            5             3           3.2           8.2

[[Page 9648]]

Hepatitis A virus.......................................            5             2           3.2           8.2
Shigella sonnei.........................................            5             3           3.2           8.2
Helicobacter pylori.....................................            1             3           5.0           8.0
Campylobacter jejuni....................................            5             3           2.5           7.5
Salmonella enterica.....................................            5             3           2.5           7.5
Caliciviruses...........................................            5             3           2.1           7.1
Entamoeba histolytica...................................            5             3           2.1           7.1
Vibrio cholerae.........................................            5             3           2.1           7.1
Adenovirus..............................................            2             3           3.6           6.6
Enterovirus.............................................            2             3           3.6           6.6
Cyclospora cayetanensis.................................            4             1           2.5           6.5
Mycobacterium avium.....................................            4             3           2.5           6.5
Rotavirus...............................................            4             2           2.5           6.5
Yersinia enterocolitica.................................            5             3           1.4           6.4
Arcobacter butzleri.....................................            4             3           2.1           6.1
Fusarium solani.........................................            1             3           2.9           5.9
Plesiomonas shigelloides................................            4             3           1.8           5.8
Hepatitis E virus.......................................            2             1           3.6           5.6
Toxoplasma gondii.......................................            2             1           3.2           5.2
Aspergillus fumigatus group.............................            1             3           2.1           5.1
Exophiala jeanselmei....................................            1             3           2.1           5.1
Aeromonas hydrophila....................................            1             3           1.8           4.8
Astrovirus..............................................            2             2           1.4           3.4
Microsporidia...........................................            1             2           1.4           3.4
Isospora belli..........................................            2             0           1.1           3.1
Blastocystis hominis....................................            1             0           0.7          1.7
----------------------------------------------------------------------------------------------------------------
1. Total Score = Normalized Health Score + the higher of WBDO or Occurrence scores.

e. Other Criteria Considered for Listing and Scoring Microbes on the 
Draft CCL 3
i. Organisms Covered by Existing Regulations
    EPA considered an additional screening criterion based upon 
contaminants that might be controlled through drinking water monitoring 
requirements under the Total Coliform Rule (TCR) (54 FR 27544, June 29, 
1989 (USEPA, 1989b)). Many of the bacteria in the CCL Universe, 
including the Enterobacteriaceae and members of the genera 
Campylobacter and Vibrio, are associated with fecal contamination and 
as such their presence could be signaled by the total coliform 
monitoring requirements under current drinking water regulations. In 
the TCR, EPA chose to require monitoring for Escherichia coli or fecal 
coliform (and total coliforms) in finished drinking water because it 
provides a broad indication of the potential presence of fecal 
pathogens in drinking water, though more so for bacteria than for 
viruses and protozoa.
    EPA chose not to exclude common enteric bacterial pathogens from 
the PCCL even though they may be indicated by the TCR. Numerous 
waterborne disease outbreaks have occurred in systems that were in 
compliance with drinking water monitoring requirements under the TCR. 
EPA recognizes the frequency of total coliform monitoring under the TCR 
may be limited, especially for smaller systems, thus transitory fecal 
contamination could go undetected. The recognition of these bacterial 
pathogens on the CCL list will provide additional understanding of the 
risks posed by distribution systems.
    The Agency is currently revising the TCR and considering 
distribution water quality issues (because of the pathways of potential 
fecal contamination). Including these pathogens on the CCL emphasizes 
their importance in protecting public health. EPA believes that enteric 
pathogens should be included for further specific regulatory 
consideration in the CCL.
ii. Organisms Covered by Treatment Technique Regulations
    According to SDWA (section 1412(b)(1), as amended in 1996), EPA 
must select CCL contaminants that ``at the time of publication, are not 
subject to any proposed or promulgated national primary drinking water 
regulation * * *.'' In promulgating regulations for contaminants in 
drinking water, EPA can set either a legal limit (MCL) and require 
monitoring for the contaminant in drinking water or, for those 
contaminants that are difficult to measure, EPA can establish a 
treatment technique requirement. The Surface Water Treatment Rule 
(SWTR) (54 FR 27486, June 29, 1989 (USEPA, 1989a)) included MCLGs for 
Legionella, Giardia, and viruses at zero because any amount of exposure 
to these contaminants represents some public health risk. Since 
measuring disease-causing microbes in drinking water is not considered 
to be feasible, EPA established treatment technique requirements for 
these contaminants. The purpose of subsequent treatment technique 
requirements (Interim Enhanced Surface Water Treatment Rule (63 FR 
69478; USEPA 1998a), Long Term Surface Water Treatment Rule 1 (67 FR 
1813; USEPA, 2002a) and the Long Term Surface Water Treatment Rule 2 
(71 FR 654; USEPA, 2006a)) which included an MCLG of zero for 
Cryptosporidium, is to reduce disease incidence associated with 
Cryptosporidium and other pathogenic microorganisms in drinking water. 
These rules apply to all public water systems that use surface water or 
ground water under the direct influence of surface water.
    The Ground Water Rule (71 FR 65573, (USEPA, 2006c)) set treatment 
technique requirements to control for viruses (and pathogenic bacteria) 
because it was not feasible to monitor for viruses (or pathogenic 
bacteria) in drinking water. Under the GWR, if systems detect total 
coliforms in the distribution system, they are required to monitor for 
a fecal indicator (E. coli,

[[Page 9649]]

coliphage, or enterococci) in the source water. If fecal contamination 
is found in the source water, the system must take remedial action to 
address contamination.
    While Cryptosporidium and Giardia have been implicated in WBDOs, 
there is a substantial amount of research regarding health effects and 
sensitivity to various treatment control measures. More importantly, as 
noted above, EPA has recently published a National Primary Drinking 
Water Regulation, The Long Term 2 Surface Water Treatment Rule that 
specifically addresses these pathogens (71 FR 654 (USEPA, 2006a)). 
Therefore, they are excluded from the CCL.
    EPA did not exclude specific viruses and Legionella from 
consideration for the CCL even though they have broad category MCLGs 
and treatment technique requirements. Viruses include a wide range of 
taxa. The treatment and health effects information for different viral 
taxa was very limited when setting the treatment technique requirements 
for surface water and ground water systems. Also, different viral taxa 
have been implicated in various waterborne disease outbreaks for which 
EPA did not have dose response or treatment data when promulgating its 
treatment technique requirements. Legionella has recently been 
identified in numerous WBDOs (e.g., CDC MMWR reports, 2006). 
Additionally EPA received additional information on the occurrence of 
Legionella in distribution systems as part of the nominations process 
(USEPA 2008g). Therefore EPA included viruses and Legionella on the 
draft CCL 3.
iii. Applying Genomic and Proteomic Data to Microbes
    The Agency and NDWAC workgroup evaluated the possibility of using 
genomics and proteomics as data to identify emerging waterborne 
pathogens, opportunistic microorganisms, and other newly identified 
microorganisms. While the application of these data in identifying 
genetic properties that may be pathogenic is a powerful tool for the 
elucidation of pathogenic mechanisms, the technology is yet largely 
unproven and the Agency has decided at this time not to use these 
techniques for CCL application. However, the Agency is monitoring the 
progress of these technologies and as the data improve and genomics 
progresses the Agency may consider them for future CCL development.
4. Selection of the Draft CCL 3 Microbes From the PCCL
    The 29 PCCL pathogens in Exhibit 18 are ranked according to an 
equal weighting of their summed scores for normalized health effects 
and the higher of the individual scores for WBDO and occurrence in 
drinking water. EPA believes this ranking indicates the most important 
pathogens to consider for the draft CCL 3. To determine which of the 29 
PCCL pathogens should be the highest priority for EPA's drinking water 
program and included on the draft CCL 3, the Agency considered both 
scientific and policy factors. The factors included the PCCL scores for 
WBDO, occurrence, and health effects; comments and recommendations from 
the various expert panels; the specific intent of SDWA; and the need to 
focus Agency resources on pathogens to provide the most effective 
opportunities to advance public health protection. After consideration 
of these factors, EPA has determined that the draft CCL 3 will include 
the 11 highest ranked pathogens shown in Exhibit 18.
    Additionally, the Agency notes that, and as can be observed in 
Exhibit 18, there are a few ``natural'' break points in the ranked 
scores for the 29 pathogens, with the top 11 forming the highest ranked 
group of pathogens. EPA does believe that the overall rankings strongly 
reflect the best available scientific data and high quality expert 
input employed in the CCL selection process, and therefore should be 
important factors in helping to identify the top priority pathogens for 
the draft CCL 3.

C. Public Input

1. Nominations and Surveillance
    On October 16, 2006, EPA published a Federal Register notice (71 FR 
60704 (USEPA, 2006 b)) requesting the public to submit chemical and 
microbial contaminant nominations that should be considered for CCL 3. 
EPA evaluated nominated contaminants to identify the data supporting 
their nomination. This section describes EPA's request for contaminants 
and summarizes the nominations received by EPA. A more detailed 
discussion of the contaminants, including a list of the specific 
contaminants nominated, can be found in the CCL 3 Nominations Summary 
in EPA's Water Docket (USEPA, 2008 g).
    The Agency sought CCL nominations for contaminants by framing the 
SDWA requirements in a series of questions to document the anticipated 
or known occurrence in PWS(s) and adverse health effects of potential 
contaminants. The Agency requested that the public respond to these 
questions and provide the documentation and rationale for including a 
contaminant for consideration in the CCL process. The questions posed 
to the public were:
    --What are the contaminant's name, CAS number, and/or common 
synonym (if applicable)?
    --What factors make this contaminant a priority for the CCL 3 
process (e.g., widespread occurrence; anticipated toxicity to humans; 
potentially harmful effects to susceptible populations (e.g., children, 
elderly and immunocompromised); potentially contaminated source water 
(surface or ground water), and/or finished water; releases to air, 
land, and/or water; contaminants manufactured in large quantities with 
a potential to occur in source waters)?
    --What are the significant health effects and occurrence data 
available, which you believe supports the CCL requirement(s) that a 
contaminant may have an adverse effect on the health of persons and is 
known or anticipated to occur in public water systems?
    The Agency compiled the information from the nominations process to 
identify the contaminants nominated and the rationale for the 
nomination and to compare the supporting data to information already 
gathered by EPA.
    The nominations process identified 150 chemical and 24 microbial 
contaminants from 11 organizations and individuals. The organizations 
that nominated contaminants are:
    --American Society of Microbiology (ASM),
    --American Water Works Association (AWWA),
    --Association of Metropolitan Water Agencies (AMWA),
    --Association of State Drinking Water Administrators (ASDWA),
    --Mothers Against Acanthamoeba Disease,
    --Natural Resources Defense Council, (NRDC),
    --Riverkeepers,
    --State of New Jersey Department of Environmental Protection,
    --State of New York Department of Health, and
    --State of Texas Commission on Environmental Quality.
    Exhibit 19 summarizes the types of nominated contaminants and who 
nominated them. The complete list of chemical and microbial 
contaminants nominated can be found in EPA's Water Docket. Some of the 
nominations identified categories of contaminants that the Agency 
should consider for the CCL. There were 23 chemical groups identified 
from the 150 chemical contaminants that were nominated. For

[[Page 9650]]

example, several organizations identified pesticides that are not 
currently regulated under the SDWA as candidates for consideration. 
Other groups identified by the public are listed in Exhibit 19.

                Exhibit 19.--Summary of CCL 3 Nominations
------------------------------------------------------------------------
                                    Number of
                                   individual
                                  contaminants
           Nominator               or specific     Types and groups of
                                  examples from        contaminants
                                    nominated
                                     groups
------------------------------------------------------------------------
ASM............................               2  Mimivirus, Naegleria
                                                  fowleri.
AMWA...........................               3  Nitrosoamines and other
                                                  DBPs.
ASDWA..........................              14  Disinfection byproducts
                                                  (DBPs), unregulated
                                                  pesticides, solvents,
                                                  total petroleum
                                                  hydrocarbons,
                                                  cyanotoxins, 3
                                                  perfluorinated
                                                  contaminants (PFCs),
                                                  viruses, phthalates,
                                                  nitrite, nitrate;
                                                  endocrine disruptors.
AWWA...........................              38  DBPs, pesticides, 16
                                                  specific microbes,
                                                  cyanotoxins, radium,
                                                  1,4-dioxane.
Mothers Against Acanthamoeba                  1  Acanthamoeba.
 Disease.
New Jersey DEP.................               4  PFOS, PFOA,
                                                  trichloropropane,
                                                  tertiary butyl
                                                  alcohol.
New York DOH...................              24  Pharmaceuticals,
                                                  personal care
                                                  products, DBPs, fuel
                                                  oxygenates, 1,4-
                                                  dioxane, herbicides,
                                                  bio-monitoring data.
NRDC...........................              26  Alkylphenolpolyethoxyla
                                                  tes (APEs that may be
                                                  endocrine disrupter
                                                  compounds (EDC)), all
                                                  unregulated
                                                  pesticides,
                                                  perchlorate,
                                                  Mycobacterium avium
                                                  complex (MAC),
                                                  phthalates,
                                                  managanese, bisphenol
                                                  A.
Riverkeeper....................              52  Pharmaceuticals,
                                                  sodium, chloride.
Texas DEQ......................               3  Viruses, nitrite,
                                                  nitrate.
------------------------------------------------------------------------

    The Agency evaluated the nominations to identify contaminants not 
previously considered for the CCL and new pertinent information 
provided by the public. Nominated contaminants were evaluated to 
identify and compare supporting information provided to that used in 
the CCL process. Of the 174 chemical and microbial contaminants 
nominated, 152 contaminants were already being considered by the 
Agency. Seven of the nominated contaminants are currently regulated in 
PWSs and will not be included in the CCL 3 process. Most of the data 
sources cited in the nominations process were already identified for 
the CCL 3 process. The nominations process did identify recently 
published specialized studies from scientific literature that were 
subsequently incorporated in the CCL 3 evaluation process.
    Where new supplemental data was provided for contaminants that had 
not been identified for the draft CCL 3, EPA used the supplemental data 
to screen the nominated chemicals and score the attributes for those 
that passed the screen. EPA then processed the nominated contaminants 
through the models and the post-model evaluations. Twenty of the 
contaminants identified in the nominations process are on the draft CCL 
3.
2. External Expert Review and Input
    EPA actively sought external advice and expert input for the draft 
CCL 3. In addition to their own recommendations, the NRC and NDWAC 
recommended that the Agency seek opportunities to incorporate 
additional expert input in the development of the draft CCL 3. EPA 
convened several external expert panels at integral stages during the 
development of the draft CCL 3. EPA incorporated expert judgment and 
input from the scientific community into the CCL process for both 
chemicals and microbes. The Agency has requested a consultation with 
the Science Advisory Board that will take place in 2008.
    For each expert panel, EPA sought panel members that provided a 
variety of disciplines and expertise. Panel members were encouraged to 
provide comments as individuals based upon their expertise and 
background, not as representatives of their respective organizational 
affiliations. Expert panel members were also encouraged to present 
individual comments if consensus comments were not developed. Separate 
panels were convened to review the draft chemical and microbial CCL 3 
lists and the processes used to develop them. A more detailed 
discussion of the chemical and microbial expert review and input is 
provided in the support documents in the EPA Water Docket. A brief 
overview of the chemical and microbial expert review and stakeholder 
involvement follows.
a. Chemical Expert Input Panels
    In September of 2006, EPA formed two external expert panels to 
provide specific input into the chemical CCL 3 process. In the first 
panel, experts reviewed the data sources and the process used to 
identify the chemical universe. EPA convened the second panel for a 3-
day workshop to review the data and information used to develop 
screening criteria, the data and methodology for the classification 
approach, and to provide overall input into the CCL process. In 
summary, the panels recommended that EPA consider additional data 
sources in the process. They also commented on ways to improve and 
clarify the presentation of EPA efforts, thereby ensuring that the CCL 
3 process for chemicals is more transparent. The expert panel reviewing 
the classification approach identified additional analyses and 
approaches to train and validate the models. The panel specifically 
commented on the varied nature of data elements and sources considered 
in the classification process. The panel recommended that to account 
for these varied data sources, contaminants be flagged based upon data 
certainty, and that uncertainty be considered in making a listing 
decision. The Agency applied their recommendations in the development 
of the draft CCL 3. In addition, the expert panels acknowledged the 
Agency's efforts to transparently present a complex process and noted 
that many of the questions posed by the panels were previously 
considered by EPA. They recommended that additional discussion and 
information in the support documents would add to the clarity of the 
process.
    In March 2007, EPA convened a panel to review the preliminary draft 
CCL 3 list for the chemical contaminants in a two-day workshop. 
Panelists provided

[[Page 9651]]

comments on a preliminary draft list of contaminants after receiving 
supporting materials and presentations from EPA staff. The panel's 
review focused mainly on the chemicals on the draft CCL 3. They 
provided comments on contaminants considered for the draft CCL 3 and 
commented on the supporting data and methods EPA used to identify the 
contaminants selected. They also provided general comments on the 
classification model output and the processes used to select chemical 
contaminants for CCL 3. In addition, they recommended EPA consider a 
strong outreach process to highlight the significant modeling and 
decision making processes used in its development.
    The panel recognized the level of effort and detail that went into 
the development of the modeling process used to create the draft list 
and complimented EPA on these efforts. Comments from all the panels 
were considered by EPA and appropriate changes were incorporated into 
the process/protocols to formulate the draft CCL 3. (Specific 
recommendations and comments are further described in USEPA, 2008h.)
b. Microbial Expert Input Panels
    EPA convened three workshops to review, discuss, and comment on the 
microbes considered and selected for the draft CCL 3. In December 2005, 
a group of expert microbiologists reviewed and commented on the 
universe of human pathogens and the screening criteria used to develop 
the PCCL. This panel agreed that focusing on human pathogens is a 
reasonable and pragmatic way to identify potential drinking water 
contaminants. While the panel suggested that animal pathogens may 
develop the ability to infect humans, they noted that these emerging 
contaminants should not be listed on the CCL based on the theoretical 
potential to become zoonotic pathogens. They also identified additional 
criteria and methods to apply those criteria to the Microbial Universe, 
which EPA incorporated into the CCL process.
    In June 2006, a panel of experts met for three days to review EPA's 
implementation of recommendations by NRC and NDWAC to select microbes 
for the CCL. EPA implemented the NDWAC recommendation to develop a 
process that paralleled the chemical process yet still accounted for 
the different types of data and information that are uniquely available 
for microbial contaminants. Panel members agreed that health effects 
and occurrence of microbes should be evaluated to identify pathogens of 
the greatest health importance. The panel recommended that EPA use a 
decision tree approach for microbes rather than the classification 
approach suggested by NRC and NDWAC.
    The panel further recommended that the Agency consider a different 
selection process than the one used for chemical contaminants, related 
to the different information available for microbes. Based on this 
recommendation, the Agency evaluated options to consolidate the potency 
and severity attributes for microbes into a single health effect 
attribute, developed a waterborne disease outbreak protocol, and 
considered occurrence as a single attribute. The Agency considered 
these and other recommendations as it developed the current three 
attribute selection process discussed in Section III.B. The panel also 
recommended that the Agency consider drinking water treatment and 
removing microbes from further consideration if conventional drinking 
water treatment protects public health. The Agency's considerations of 
these and other recommendations are discussed in the Microbial Expert 
Review support document (USEPA, 2008i).
    In March 2007, EPA convened a third workshop to review the 
preliminary draft CCL 3 list of microbial contaminants. EPA provided 
the panel with background materials and staff presentations. The 
panel's review focused mainly on the draft CCL 3 for microbes. The 
panel also provided comments on the processes used to select the 
microbial contaminants. Panel members commented on specific microbes 
considered for the draft CCL 3 and commented on the data and processes 
EPA used to identify the contaminants selected. The panel noted that 
the Agency considered a comprehensive list of microbes and thought the 
draft CCL 3 was reasonable. The panel also recommended that the Agency 
consider adding a frequency of disease parameter to the health effects 
scoring protocol for future CCLs. For example, while the panel agreed 
with EPA that the health effects for Naegleria fowleri are severe, the 
health effects scoring protocol should consider the limited occurrence 
of disease. The panel also noted that this would help balance the 
consideration of less severe adverse health effects such as 
gastrointestinal illness that are more prevalent with consideration of 
more severe responses that are less prevalent, such as N. fowleri. The 
panel recommended that EPA provide further discussion of the rationale 
to evaluate waterborne disease and health effects equally in the 
protocol. The discussion of the Agency's rationale is included in 
Section III.B and addresses the importance of documented waterborne 
disease outbreaks to identify potential microbial contaminants for the 
CCL. (A more detailed summary of the expert comments is provided in 
USEPA, 2008 i.)
3. How are the CCL and UCMR Interrelated for Specific Chemicals and 
Groups?
    EPA promulgated UCMR 2 on January 4, 2007 (72 FR 367 (USEPA, 2007 
a; see also USEPA, 2007 b and c)). The UCMR program was developed in 
coordination with the CCL. Both programs consider the adverse health 
effects a contaminant may pose through drinking water exposures. 
Sixteen contaminants on the UCMR 2 monitoring list are also on the 
draft CCL 3. The draft CCL 3 includes acetochlor and its degradates, 
alachlor degradates, dimethoate, 1,3-dinitrobenzene, metolachlor and 
its degradates, RDX, terbufos sulfone, and four of the nitrosamines. In 
addition to the health effects data and potential occurrence, the UCMR 
2 also considers analytical methods, availability of analytical 
standards, and laboratory capacity to conduct a nationwide monitoring 
program in selecting contaminants. The UCMR 2 includes nine 
contaminants that are not on draft CCL 3. The five polybrominated flame 
retardants can be measured by the same analytical method used for 
terbufos sulfone. The polybrominated flame retardants lacked sufficient 
occurrence information to be listed on draft CCL 3 (USEPA 2008 b). The 
polybrominated flame retardants are listed on UCMR2 because of recent 
concern that these have become more widespread environmental 
contaminants (e.g., Darnerud et al., 2001) and this monitoring data 
will provide information for future CCLs. Similarly, 2,4,6-
trinitrotoluene (TNT) and two of the nitrosamines also use an 
analytical method in the UCMR 2. The Agency will also use the results 
from UCMR 2 as a source of occurrence information during the selection 
of CCL 4, as well as for CCL 3 regulatory determinations. Alachor was 
listed on UCMR 2, but was removed from consideration for CCL 3 because 
there is an existing MCL.

IV. Request for Comment

    The purpose of this notice is to present the draft CCL 3 and seek 
comment on various aspects of its development. The Agency requests 
comment on the approach used to develop the draft CCL 3 and also 
requests comments on the contaminants selected, including any 
supporting data

[[Page 9652]]

that can be utilized in developing the final CCL 3. A number of 
contaminants considered for the draft CCL 3 may be of particular 
current interest. The following sections provide information for a few 
of the contaminants that are of most interest. Data obtained and 
evaluated for developing the draft CCL 3 and referred to in the 
following sections may be found in the docket for this notice. 
Specifically, the Agency is also asking for public comments on 
pharmaceuticals and perfluorinated compounds to identify any additional 
data and information on their concentrations in finished or ambient 
water and requests comment on how they have been considered in the CCL 
3 process. The Agency is also seeking additional data and information 
on the occurrence and health effects of H. pylori and how this pathogen 
was considered in the CCL 3 process. Information and comments submitted 
will be considered in determining the final CCL 3, as well as in the 
development of future CCLs and in the Agency's efforts to set drinking 
water priorities in the future.

A. Pharmaceuticals

    The Agency evaluated data sources to identify pharmaceuticals and 
personal care products that have the potential to occur in PWSs. The 
primary source of health effects information on pharmaceuticals in the 
universe was the Food and Drug Administration Database on Maximum 
Recommended Daily Doses (MRDD). This database includes the recommended 
adult doses for over 1,200 pharmaceutical agents. Occurrence 
information from USGS Toxics Substances Hydrology program's National 
Reconnaissance of Emerging Contaminants, and related efforts, provided 
ambient water concentration data for 123 contaminants, which include 
pharmaceuticals. Other data sources included TRI and high production 
volume chemical data. From this analysis, EPA included 287 
pharmaceuticals in the Chemical Universe. These pharmaceuticals had 
maximum recommended daily dose information that EPA used to evaluate 
adverse health effects. EPA considered those pharmaceuticals for which 
MRDD values and occurrence information were available and 
pharmaceuticals that were in Toxicity Category 1, using the same 
criteria discussed in Section III.A.2.a. EPA found that less than two 
percent of the pharmaceuticals included in the MRDD database fell into 
this category.
    EPA applied the LOAEL screening protocols to contaminants with MRDD 
values. The LOAEL protocol was used because pharmaceutical agents, 
although used for their beneficial effects, have associated side-
effects that may be adverse. Chemicals evaluated with these data had 
similar modal values and distributions to the toxicity values from 
IRIS. The range of toxicity values in this database covered 9 orders of 
magnitude when evaluated based on their rounded logs. They had the same 
modal value as the LOAELs from IRIS and a very similar distribution. 
Thirty-five percent of the IRIS LOAELS and 38 percent of the MRDDs had 
the modal rounded log. Thirty-three percent of the LOAELs and 19 
percent MRDDs had rounded logs that were lower than the mode, while 31 
percent of the LOAELs and 44% of the MRDDs had rounded logs that were 
above the modal log value.
    The screening process moved approximately 10 percent of the 
pharmaceuticals in the Universe to the PCCL. All toxicity data on those 
chemicals were included in the screening with the most serious 
qualitative or quantitative measure of toxicity determining placement 
in a toxicity category. Only one of the PCCL chemicals (diazinon, a 
veterinary product as well as a pesticide) had water concentration 
data. Two other pharmaceuticals: phenytoin (an anticonvulsant) and 
nitroglycerin (treatment of angina), had release data. The remainder 
were scored for occurrence based on production information, which meant 
that they fell into the low certainty bin for their occurrence 
parameters. Nitroglycerin is the only pharmaceutical that is included 
on the draft CCL 3. EPA is aware of concerns regarding the potential 
presence of pharmaceuticals in water supplies. The Agency is seeking 
additional data and information on the concentrations of 
pharmaceuticals in finished or ambient water and requests comment on 
how pharmaceuticals have been considered in the CCL 3 process.

B. Perfluorooctanoic Acid and Perfluorooctane Sulfonic Acid

    EPA evaluated perfluorinated compounds in the CCL 3 process and 
requests comment on its decisions to include perfluorooctanoic acid 
(PFOA) and not to include perfluorooctane sulfonic acid (PFOS) on the 
draft CCL 3. EPA identified potential health effects and occurrence 
information for these compounds from the data sources discussed in 
Section III. The data used for these compounds are discussed in the 
support documents in more detail. Available analytic methods for these 
chemicals limited the occurrence data for these compounds. The Agency 
identified data on the annual production from CUS/IUR indicating 
limited production and possible release to the environment. Several 
organizations nominated PFOS and PFOA for consideration in the CCL 
process. The nominations noted that these chemicals are persistent in 
the environment and have been detected at varying levels in drinking 
water and ambient water in smaller specialized studies. EPA collected 
the information cited in the nominations and evaluated each of these 
chemicals. The Agency included PFOA on the draft CCL 3 because it met 
the criteria for inclusion on draft CCL 3 based on drinking water 
occurrence studies in Ohio and West Virginia (Emmett, et al., 2006) and 
on health effects data indicated through animal studies (USEPA, 2005 
a).
    The Agency did not include PFOS on the draft CCL 3. Occurrence data 
for PFOS characterized detections in several States (Boulanger, et al., 
2004, Hansen, et al., 2002, Goeden and Kelly, 2006). These data showed 
that levels of detection for PFOS in ambient water ranged from 20 to 
approximately 100 parts per trillion. Data identified in the 
nominations process detected PFOS at higher concentrations in areas 
surrounding landfills known to be contaminated with industrial waste 
containing PFOS. The CCL process did not consider occurrence data from 
targeted studies of contaminated waste sites, however. Such studies are 
usually developed to identify and characterize hazardous waste cleanup 
efforts and may not be representative of occurrence in drinking water 
not in close proximity to the study site. PFOS was phased out of 
production in the U.S. between 2000 and 2002, and regulation limits its 
importation to a very small number of controlled, very low release 
uses, (67 FR 72854; December 9, 2002 (USEPA, 2002 c)). Based on the 
general absence of occurrence data, combined with the phase out, 
effectively eliminating most future releases, PFOS did not meet the 
criteria for CCL 3.
    The Agency is evaluating data related to PFOA in a formal risk 
assessment process under the Toxic Substance Control Act. EPA's Science 
Advisory Board (SAB) completed a review of a draft risk assessment in 
2006 and SAB made recommendations for the further development of the 
risk assessment. A final risk assessment may not be completed for 
several years, as a number of important studies are underway. The 
Agency is also participating in additional research regarding the 
toxicity and persistence of related perfluorochemicals, as well as 
research to help identify where these chemicals

[[Page 9653]]

are coming from and how people may be exposed to them.

C. Helicobacter pylori

    Helicobacter pylori is a pathogen that causes gastric cancer in 
addition to acute gastric ulcers. EPA placed this pathogen on the draft 
CCL. However, the analysis for H. pylori differs from the other 
pathogens due to the long term and/or chronic nature of its health 
effects rather than the more common acute effects of most waterborne 
pathogens. This organism is an emerging pathogen whose impact has only 
recently begun to be understood. Given the slow development of adverse 
health effects due to infection by H. pylori, it is more difficult to 
link contamination of drinking water and show a waterborne disease 
outbreak. Therefore, given the long timeframe of cancer and ulcer 
development (as opposed to the commonly acute gastrointestinal illness 
of nearly all the other pathogens on the PCCL) as well as the ongoing 
nature of the research, EPA used peer-reviewed scientific papers to 
score the health effects of Helicobacter pylori. EPA request comment on 
the process of selection of microbial contaminants that cause chronic 
rather than acute health effects.

V. EPA's Next Steps

    Between now and the publication of the final CCL, the Agency will 
evaluate comments received during the comment period for this notice, 
consult with the SAB, and re-evaluate the criteria used to develop the 
draft CCL and revise the CCL, as appropriate.

VI. References

Boulanger, B., J. Vargo, J.L. Schnoor and K.C. Hornbuckle. 2004. 
Detection of Perfluorooctane Surfactants in Great Lakes Water. 
Environmental Science and Technology, Vol. 38, No. 15. pp 4064-4070.
CDC. 2004. Surveillance for Waterborne-Disease Outbreaks Associated 
with Drinking Water--United States, 2001-2002. MMWR Surveillance 
Summaries, 53(SS08); 23-45.
CDC. 2006. Surveillance for Waterborne-Disease Outbreaks Associated 
with Drinking Water--United States, 2003-2004. MMWR Surveillance 
Summaries, 55(SS12); 31-58.
Darnerud, P.O., G.S. Erickson, T. Johannesson, P.B. Larson, and M. 
Viluksela. 2001. Polybrominated Diphenyl Ethers: Occurrence, Dietary 
Exposure, and Toxicology. Environmental Health Perspectives 
Supplements. Vol. 109, No. S1. Available on the Internet at: http://ehp.niehs.nih.gov/members/2001/suppl-1/49-68darnerud/darnerud-full.html
.

Emmett, E.A., F.S. Shofer, H. Zhang, D. Freeman, C. Desai, L.M. 
Shaw. 2006. Community Exposure to Perfluorooctanoate: Relationships 
Between Serum Concentrations and Exposure Sources, Journal of 
Occupational and Environmental Medicine, Vol. 48, No. 8, pp. 759-
770.
Goeden, H. and J. Kelly. 2006. Perfluorochemicals in Minnesota, 
Minnesota Department of Health, Senate Environment and Natural 
Resources Committee, February 27. Available on the Internet at: 
http://www.health.state.mn.us/divs/eh/hazardous/sites/washington/pfcsmn.pdf
.

Hansen, K.J., H.O. Johnson, J.S. Eldridge, J.L. Blutenhoff and L.A. 
Dick. 2002. Quantitative Characterization of Trace Levels of PFOS 
and PFOA in the Tennessee River. Environmental Science and 
Technology, Vol. 36, No. 8, pp. 1681-1685.
National Drinking Water Advisory Council (NDWAC). 2004. National 
Drinking Water Advisory Council Report on the CCL Classification 
Process to the U.S. Environmental Protection Agency, May 19, 2004.
National Research Council (NRC). 2001. Classifying Drinking Water 
Contaminants for Regulatory Consideration. National Academy Press, 
Washington, DC.
NIST. 2006. NIST/SEMATECH e-Handbook of Statistical Methods. 
Available on the internet at: http://www.itl.nist.gov/div898/handbook/
, (used on May 3, 2007).

Taylor, L.H., S.M. Latham, and M.E. Woolhouse. 2001. Risk factors 
for human disease emergence (Appendix A). Phil. Trans. R. Soc. Lond. 
B. Vol. 256, pp. 983-989.
Tyler, K.T., E.S. Barton, M.L. Ibach, C. Robinson, J.A. Campbell, 
S.M. O'Donnell, T. Valyi-Nagy, P. Clarke, J.D. Wetzel, T.S. Dermody. 
2004. Isolation and Molecular Characterization of a Novel Type 3 
Reovirus from a Child with Meningitis. Jour. Infect. Dis. Vol. 189, 
No. 9, pp. 1664-75.
USEPA. 1989a. National Primary Drinking Water Regulations; 
Filtration, Disinfection; Turbidity, Giardia Lamblia, Viruses, 
Legionella, and Heterotrophic Bacteria; Final Rule. Part 2. Federal 
Register. Vol. 54, No. 124, p. 27486, June 29, 1989.
USEPA. 1989b. Drinking Water; National Primary Drinking Water 
Regulations; Total Coliforms (Including Fecal Coliforms and E. 
Coli). Federal Register. Vol. 54, No. 124, p. 27544, June 29, 1989.
USEPA. 1992. Drinking Water; National Primary Drinking Water 
Regulations--)-Synthetic Organic Chemicals and Inorganic Chemicals; 
National Primary Drinking Water Regulations Implementation; Final 
Rule. Federal Register. Vol. 57, No. 138, p. 31776, July 17, 1992.
USEPA. 1997. Announcement of the Draft Drinking Water Contaminant 
Candidate List; Notice. Federal Register. Vol. 62, No. 193, p. 
52193, October 6, 1997.
USEPA. 1998a. Interim Enhanced Surface Water Treatment; Final Rule. 
Federal Register. Vol. 63, No 241, p. 69478, December 16, 1998.
USEPA. 1998b. Announcement of the Draft Drinking Water Contaminant 
Candidate List; Notice. Federal Register. Vol. 63, No. 40, p. 10273, 
March 2, 1998.
USEPA. 1999. Revisions to the Unregulated Contaminant Monitoring 
Regulation for Public Water Systems. Federal Register. Vol. 64, No. 
180, p. 50556, September 17, 1999.
USEPA. 2002a. Long Term 1 Enhanced Surface Water Treatment Rule; 
Final Rule. Federal Register. Vol. 67, No. 9, p. 1813. January 14, 
2002.
USEPA. 2002b. Announcement of Preliminary Regulatory Determinations 
for Priority Contaminants on the Drinking Water Contaminant 
Candidate List. Federal Register. Vol. 67, No. 106, p. 38222, June 
3, 2002.
USEPA. 2002c. Perfluoroalkyl Sulfonates; Significant New Use Rule. 
Federal Register. Vol 67, No. 236, p. 72854, December 9, 2002.
USEPA. 2003a. Announcement of Regulatory Determinations for Priority 
Contaminants on the Drinking Water Contaminant Candidate List. 
Federal Register. Vol. 68, No. 138, p. 42898, July 18, 2003.
USEPA. 2004. Drinking Water Contaminant Candidate List 2; Notice. 
Federal Register. Vol. 69, No. 64, p. 17406, April 2, 2004.
USEPA. 2005a. Draft Risk Assessment of the Potential Human Health 
Effects Associated with Exposure to Perfluorooctanoic Acid and its 
Salts. OPPTS, SAB Draft. January 4, 2005.
USEPA. 2005b. Notice--Drinking Water Contaminant Candidate List 2; 
Final Notice. Federal Register. Vol. 70, No. 36, p. 9071, February 
24, 2005.
USEPA. 2006a. Long Term 2 Enhanced Surface Water Treatment Rule; 
Final Rule. Federal Register. Vol. 71, No. 3, p. 654, January 5, 
2006.
USEPA. 2006b. Request for Nominations of Drinking Water Contaminants 
for the Contaminant Candidate List; Notice. Federal Register. Vol. 
71, No. 199, p. 60704, October 16, 2006.
USEPA. 2006c. National Primary Drinking Water Regulations: Ground 
Water Rule; Final Rule. Federal Register. Vol. 71, No. 216, p. 
65573, November 8, 2006.
USEPA. 2007 a. Unregulated Contaminant Monitoring Regulation (UCMR) 
for Public Water Systems Revisions; Final Rule. Federal Register. 
Vol. 72, No. 2, p. 367, January 4, 2007.
USEPA. 2007 b. Unregulated Contaminant Monitoring Regulation (UCMR) 
for Public Water Systems Revisions; Correction. Federal Register. 
Vol. 72, No. 17, p. 3916, January 26, 2007.
USEPA. 2007 c. Unregulated Contaminant Monitoring Regulation (UCMR) 
for Public Water Systems Revisions; Correction. Federal Register. 
Vol. 72, No. 19, p. 4328, January 30, 2007.
USEPA. 2007 d. Drinking Water: Regulatory Determinations Regarding 
Contaminants on the Second Drinking Water Contaminant Candidate 
List--

[[Page 9654]]

Preliminary Determinations; Proposed Rule. Federal Register. Vol. 
72, No. 83, p. 24016, May 1, 2007.
USEPA. 2008 a. Contaminant Candidate List 3 Chemicals: Identifying 
the Universe. EPA 815-R-08-002. Draft. February, 2008.
USEPA. 2008 b. Contaminant Candidate List 3 Chemicals: Screening to 
a PCCL. EPA 815-R-08-003. Draft. February, 2008.
USEPA. 2008 c. Contaminant Candidate List 3 Chemicals: 
Classification of the PCCL to the CCL, EPA 815-R-08-004. Draft. 
February, 2008.
USEPA. 2008 d. Contaminant Candidate List 3 Microbes: Identifying 
the Universe, EPA 815-R-08-005. Draft. February, 2008.
USEPA. 2008 e. Contaminant Candidate List 3 Microbes: Screening to 
the PCCL, EPA 815-R-08-006. Draft. February, 2008.
USEPA. 2008 f. Contaminant Candidate List 3 Microbes: PCCL to CCL 
Process, EPA 815-R-08-007. Draft. February, 2008.
USEPA. 2008 g. Summary of Nominations for the Third Contaminants 
Candidate List. EPA 815-R-08-008. Draft. February, 2008.
USEPA. 2008 h. Chemical Expert Input and Review for the Third 
Contaminant Candidate List, EPA 815-R-08-009. Draft. February, 2008.
USEPA. 2008 i. Microbial Expert Input and Review, EPA 815-R-08-010. 
Draft. February, 2008.

    Dated: February 6, 2008.
Benjamin H. Grumbles,
Assistant Administrator, Office of Water.
 [FR Doc. E8-3114 Filed 2-20-08; 8:45 am]

BILLING CODE 6560-50-P