Thursday, 

February 21, 2008 

Part II 

Environmental 

Protection Agency 

Drinking Water Contaminant Candidate 

List 3—Draft; Notice 


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9628 Federal Register / Vol. 73, No. 35 / Thursday, February 21, 2008 / Notices 

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. 

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: hotlinesdwa@epa.gov. 

Abbreviations and Acronyms 

<—less than 

≤—less than or equal to 

>—greater than 

≥—greater than or equal to 

μ—microgram, one-millionth of a gram 

μg/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 


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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 doserate 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 


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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 diacid degradates, 1,1-dichloro-2,2-bis (pchlorophenyl) 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 multistep 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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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 

alphaHexachlorocyclohexane .... 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 

CHEMICAL CONTAMINANTS—Continued 

Common name—registry 

name CASRN 

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 


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CHEMICAL CONTAMINANTS—Continued 

Common name—registry 

name CASRN 

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 

CHEMICAL CONTAMINANTS—Continued 

Common name—registry 

name CASRN 

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. 


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EXHIBIT 3.—SOURCES THAT COMPRISE THE CHEMICAL UNIVERSE OF DATA SOURCES FOR THE CCL PROCESS—

Continued 

Name of data source 

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. 


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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), coaltar-containing shampoo, petroleumrelated 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 nonchemically 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). 


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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 ByProducts 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 


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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 

Carcinogen.

Group 1 ................. CE 2 species/2 

sexes; or 2 species; or 2 sexes.

P 2 species/2 

sexes; or 2 species; or 2 sexes.

H. 

Toxicity Category 2 0.1–100 Groups B1 and B2; 

likely carcinogens.

Group 2A .............. Combinations of 

CE, SE, EE, and 

NE.

Combinations of P, 

E and N.

HM. 

Toxicity Category 3 >100 Group C; Suggestive evidence of 

carcinogenicity.

Group 2B .............. Combinations of 

SE, EE, and NE.

Combinations of E 

and N.

M and LM. 

** 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 


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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 

Health effects 

Occurrence 

(by data type) 

Finished/ambient 

water concentrations 

Release amount 

(per year) 

Production volume 

(per year) 

Toxicity Category 1 ........................ All Concentrations ........................ All Amounts .................................. All Amounts. 

Toxicity Category 2 ........................ ≥1 μg/l ........................................... ≥10,000 lbs/yr ............................... ≥500,000 lbs/yr. 

Toxicity Category 3 ........................ ≥10 μg/l ......................................... ≥100,000 lbs/yr ............................. ≥10 M lbs/yr. 

Toxicity Category 4 ........................ ≥100 μg/l ....................................... ≥1 M lbs/yr .................................... ≥50 M lbs/yr. 

Toxicity Category 5 ........................ ≥1000 μg/l ..................................... ≥10 M lbs/yr .................................. ≥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. 


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EXHIBIT 8.—SUMMARY OF TOTAL CHEMICALS THAT PASSED SCREENING FOR PCCL BY SCREENING CATEGORIES

Toxicity categories 

Finished or 

ambient 

water concentration 

Pesticide 

app 

Total releases Production 

volume Totals 

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 lognormal. 

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 


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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 noncancer 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; differences in organ weights, body weights 

or changes in biochemical parameters with minimal clinical 

significance.

Transient, adaptive effects. 

4 ................ Cellular/physiological changes that could lead to disorders (risk 

factors or precursor effects).

Considers cellular/physiological changes in the body that are 

used as indicators of disease susceptibility. 

5 ................ Significant functional changes that are reversible or permanent 

changes of minimal toxicological significance.

Considers those disorders in which the removal of chemical exposure will restore health back to prior condition. 

6 ................ Significant, irreversible, non-lethal conditions or disorders .......... Considers those disorders that persist for over a long period of 

time but do not lead to death. 

7 ................ Developmental or reproductive effects ......................................... Considers those chemicals that cause developmental effects or 

that impact the ability of a population to reproduce. 

8 ................ Tumors or disorders likely leading to death ................................. Considers chemical 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. Persistencemobility is determined by chemical 


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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 


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(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: 


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• 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

3-Models decision % of PCCL Total # 

PCCL 

Finished or 

ambient 

water 

Release Production 

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 postmodel 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 


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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 


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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

Pathogen class Total 

Screening Criteria Pathogens 

screened 

out 

On PCCL 

1 2 3 4 5 6 7 8 9 10 11 12 

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 


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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 nonCDC 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 U.S. since CDC surveillance initiated in 1973 ..... 5 

Has caused at least one documented WBDO in the U.S. 

since CDC surveillance initiated in 1973 .......................... 4 

Has caused documented 

WBDOs at any time in the 

U.S. ....................................... 3 

Has caused documented 

WBDOs in countries other 

than the U.S. ......................... 2 

Has never caused WBDOs in 

any country, but has been 

epidemiologically associated 

with water-related disease .... 1 

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 noncultural 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). 


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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

Outcome category Score 

Manifestation in population class 

General 

population 

Children/ 

infants Elderly Pregnant women 

Chronic 

disease 

Does the organism cause significant mortality (> 1/1,000 

cases)?.

7 

Does the organism cause pneumonia, meningitis, hepatitis, 

encephalitis, endocarditis, cancer, or other severe manifestations of illness necessitating long term hospitalization 

(> week)?.

6 

Does the illness result in long term or permanent dysfunction 

or disability (e.g., sequelae)?.

5 

Does the illness require short term hospitalization? (< week)? 4 

Does the illness require physician intervention? ....................... 3 

Is the illness self-limiting within 72 hours (without requiring 

medical intervention)?.

2 

Does the illness result in mild symptoms with minimal or no 

impact on daily activities?.

1 

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 

Pathogen WBDO Occurrence Normalized 

health score Total1 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 


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EXHIBIT 18.—PATHOGENS ON THE PCCL—Continued 

Pathogen WBDO Occurrence Normalized 

health score Total1 score 

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, 


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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 


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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

Nominator 

Number of individual contaminants or 

specific examples from 

nominated 

groups 

Types and groups of contaminants 

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 Disease 1 Acanthamoeba. 

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 Alkylphenolpolyethoxylates (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 


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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 


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9652 Federal Register / Vol. 73, No. 35 / Thursday, February 21, 2008 / Notices 

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. Thirtyfive 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 


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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 WaterborneDisease Outbreaks Associated with 

Drinking Water—United States, 2001–

2002. MMWR Surveillance Summaries, 

53(SS08); 23–45. 

CDC. 2006. Surveillance for WaterborneDisease 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/suppl1/49–68darnerud/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—


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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 


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