UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

 WASHINGTON D.C. 20460 

 

OFFICE OF THE ADMINISTRATOR 

SCIENCE ADVISORY BOARD 

January 29, 2009 

EPA-SAB-09-011 

The Honorable Lisa P. Jackson 

Administrator 

U.S. Environmental Protection Agency 

1200 Pennsylvania Avenue, N.W. 

Washington, D.C. 20460 

Subject: SAB Advisory on EPA's Draft Third Drinking Water Contaminant Candidate 

List (CCL 3) 

Dear Administrator Jackson, 

 EPA’s Office of Ground Water and Drinking Water requested that the Science Advisory 

Board (SAB) Drinking Water Committee (hereafter, the DWC or Committee) provide advice on 

EPA’s Draft Third Drinking Water Contaminant Candidate List (CCL 3). Contaminants on the 

CCL 3 can be chosen by the Agency to undergo a regulatory determination (which will 

determine whether or not to regulate the contaminant). The CCL 3 also influences the research 

agenda and other rules such as the Unregulated Contaminant Monitoring Rule. 

 The Agency asked whether the Federal Register Notice (FRN) and support documents are 

clear, transparent, and adequate to provide an understanding of the overall processes and 

selection of contaminants for the draft CCL 3. The Committee concludes that the documentation 

of the processes lacks transparency. The CCL 3 uses a more data-driven process than previous 

CCLs, as well as some models and algorithms, to whittle the universe of contaminants 

(Universe) to a Preliminary CCL (PCCL) and the CCL. However, EPA also used experts’ 

professional judgments to revise the process and to modify the contaminants on the list. These 

modifications were not readily apparent in the current documentation. An understanding of the 

decision-making process is an important criterion for transparency, according to the reviews by 

the National Research Council and National Drinking Water Advisory Council. The Committee 

recommends that EPA develop a CCL 3 process flow chart for chemicals and for pathogens that 

includes links to other documents (data and models) used, as well as delineates where expert 

judgment was used. Developing one or more flowcharts will: (1) increase transparency; (2) 

allow a stakeholder to track the progress of a contaminant through the system; (3) highlight 

decisions that might suggest improvements for future CCL processes; and (4) clarify why 

contaminants that were included on previous CCL lists were excluded from the draft CCL 3. 
2

 The Committee was asked whether the draft CCL 3 list includes contaminants that have 

the highest potential to occur in public water systems and cause adverse human health effects. 

This question goes to the heart of prioritization and decision-making in the selection process 

from the Universe to the PCCL to the CCL 3. The Committee’s major conclusions are: 

• For chemicals, the list is too large to achieve the stated objectives of the CCL process or 

to review by the DWC in the time allocated. To fulfill the Agency’s objectives of 

choosing chemicals that have the greatest opportunity for improving the safety of 

drinking water and protecting public health, the Committee recommends additional 

prioritization of the current list. A shorter list will clarify which chemicals have a 

reasonable probability of being selected for regulatory determination. 

• For pathogens, the waterborne disease outbreak data base was used to address both 

occurrence and health effects. This data base does not adequately address whether there 

is a substantial likelihood that the pathogen will occur in public water systems with a 

frequency and at levels of public health concern. The Committee recommends that 

occurrence be based on endemic disease data and published literature on occurrence. 

The Committee was asked to provide any data that suggest: (1) contaminants that are 

currently on the draft CCL 3 list should not be listed; and (2) contaminants that are not currently 

on the draft CCL 3 list should be listed. The Committee concludes that the draft CCL 3 includes 

contaminants that should not be listed and excludes contaminants that should be included. 

Rather than attempting to examine each of the 104 contaminants on the draft CCL 3, the 

Committee offers suggestions that could be used to identify chemicals and pathogens that should 

have a lower priority for regulatory determinations. Similarly, the Committee provides sources 

of additional, publicly available data that are expected to raise the priority of contaminants of 

greater public health concern. 

 Thank you for the opportunity to provide advice on this important process. The SAB 

Drinking Water Committee looks forward to receiving your response regarding this advisory. 

 Sincerely, 

 /Signed/ /Signed/ 

Dr. Deborah L. Swackhamer, Chair Dr. Joan B. Rose, Chair 

Science Advisory Board Drinking Water Committee 

Enclosure
NOTICE 

This report has been written as part of the activities of the EPA Science Advisory Board (SAB), 

a public advisory group providing extramural scientific information and advice to the 

Administrator and other officials of the Environmental Protection Agency. The SAB is 

structured to provide balanced, expert assessment of scientific matters related to problems facing 

the Agency. This report has not been reviewed for approval by the Agency and, hence, the 

contents of this report do not necessarily represent the views and policies of the Environmental 

Protection Agency, nor of other agencies in the Executive Branch of the Federal government, nor 

does mention of trade names of commercial products constitute a recommendation for use. 

Reports of the SAB are posted on the EPA website at http://www.epa.gov/sab. 

i
U.S. Environmental Protection Agency 

Science Advisory Board 

Drinking Water Committee 

CHAIR

Dr. Joan B. Rose, Professor and Homer Nowlin Chair for Water Research, Department of 

Fisheries and Wildlife, Michigan State University, East Lansing, MI 

OTHER MEMBERS

Dr. Mark Borchardt, Director, Public Health Microbiology Laboratory, Marshfield Clinic 

Research Foundation, Marshfield, WI 

Dr. John Colford, Professor, Division of Public Health, Biology & Epidemiology, School of 

Public Health, University of California, Berkeley, CA 

Dr. Penelope Fenner-Crisp, Independent Consultant, North Garden, VA 

Dr. Stanley B. Grant, Professor, Department of Chemical Engineering, School of Engineering, 

University of California, Irvine, Irvine, CA 

Dr. Jeffrey Griffiths, Associate Professor, Public Health and Family Medicine, School of 

Medicine, Tufts University, Boston, MA 

Dr. Gary King, Professor of Microbial Biology, Department of Biological Sciences, Louisiana 

State University, Baton Rouge, LA 

Dr. Joseph R. Landolph, Jr., Associate Professor, Molecular Microbiology and Immunology 

and Pathology, Keck School of Medicine and Associate Professor of Molecular Pharmacology 

and Pharmaceutical Science, School of Pharmacy, University of Southern California, Los 

Angeles, CA 

Dr. Desmond F. Lawler, Bob R. Dorsey Professor of Engineering, Department of Civil, 

Architectural and Environmental Engineering, University of Texas, Austin, TX 

Dr. Christine Owen, Water Quality Assurance Officer, Tampa Bay Water, Clearwater, FL 

Dr. Richard Sakaji, Manager, Planning and Analysis for Water Quality, East Bay Municipal 

Utility District, Oakland, CA 

ii
Dr. Gary Sayler, Beaman Distinguished Professor, Joint Institute for Biological Sciences, Oak 

Ridge National Laboratory, University of Tennessee, Knoxville, TN 

Dr. David Sedlak, Professor, Department of Civil and Environmental Engineering, University 

of California-Berkeley, Berkeley, CA 

Dr. Gina Solomon, Senior Scientist, Health and Environment Program, Natural Resources 

Defense Council, San Francisco, CA 

Dr. Laura Steinberg, Professor, Department of Environmental and Civil Engineering, Southern 

Methodist University, Dallas, TX 

Ms. Susan Teefy, Principal Engineer, Water Quality and Treatment Solutions, Inc., Castro 

Valley, CA 

SCIENCE ADVISORY BOARD STAFF

Dr. Resha M. Putzrath, Designated Federal Officer, 1200 Pennsylvania Avenue, Washington, 

DC, Phone: 202-343-9978, Fax: 202-233-0643, (putzrath.resha@epa.gov) 

iii
U.S. Environmental Protection Agency 

Science Advisory Board 

CHAIR

Dr. Deborah Swackhamer, Professor of Environmental Health Sciences and Co-Director Water 

Resources Center, Water Resources Center, University of Minnesota, St. Paul, MN 

SAB MEMBERS

Dr. David T. Allen, Professor, Department of Chemical Engineering, University of Texas, 

Austin, TX 

Dr. John Balbus, Chief Health Scientist, Environmental Health Program, Environmental 

Defense Fund, Washington, DC 

Dr. Gregory Biddinger, Coordinator, Natural Land Management Programs, Toxicology and 

Environmental Sciences, ExxonMobil Biomedical Sciences, Inc., Houston, TX 

Dr. Timothy Buckley, Associate Professor and Chair, Division of Environmental Health 

Sciences, School of Public Health, The Ohio State University, Columbus, OH 

Dr. Thomas Burke, Professor, Department of Health Policy and Management, Johns Hopkins 

Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD 

Dr. James Bus, Director of External Technology, Toxicology and Environmental Research and 

Consulting, The Dow Chemical Company, Midland, MI 

Dr. Deborah Cory-Slechta, Professor, Department of Environmental Medicine, School of 

Medicine and Dentistry, University of Rochester, Rochester, NY 

Dr. Terry Daniel, Professor of Psychology and Natural Resources, Department of Psychology, 

Environmental Perception Laboratory, University of Arizona, Tucson, AZ 

Dr. Otto C. Doering III, Professor, Department of Agricultural Economics, Purdue University, 

W. Lafayette, IN 

Dr. David A. Dzombak, Walter J. Blenko Sr. Professor of Environmental Engineering, 

Department of Civil and Environmental Engineering, College of Engineering, Carnegie Mellon 

University, Pittsburgh, PA 

Dr. T. Taylor Eighmy, Assistant Vice President for Research and Director of Strategic 

Initiatives, Office of the Vice President for Research, University of New Hampshire, Durham, 

NH 

iv
Dr. Baruch Fischhoff, Howard Heinz University Professor, Department of Social and Decision 

Sciences, Department of Engineering and Public Policy, Carnegie Mellon University, Pittsburgh, 

PA 

Dr. James Galloway, Professor, Department of Environmental Sciences, University of Virginia, 

Charlottesville, VA 

Dr. John P. Giesy, Professor, Department of Zoology, Michigan State University, East Lansing, 

MI 

Dr. James K. Hammitt, Professor, Center for Risk Analysis, Harvard University, Boston, MA 

 

Dr. Rogene Henderson, Senior Scientist Emeritus, Lovelace Respiratory Research Institute, 

Albuquerque, NM 

Dr. James H. Johnson, Professor and Dean, College of Engineering, Architecture & Computer 

Sciences, Howard University, Washington, DC 

Dr. Bernd Kahn, Professor Emeritus and Director, Environmental Radiation Center, Nuclear 

and Radiological Engineering Program, Georgia Institute of Technology, Atlanta, GA 

Dr. Agnes Kane, Professor and Chair, Department of Pathology and Laboratory Medicine, 

Brown University, Providence, RI 

Dr. Meryl Karol, Professor Emerita, Graduate School of Public Health, University of 

Pittsburgh, Pittsburgh, PA 

Dr. Catherine Kling, Professor, Department of Economics, Iowa State University, Ames, IA 

Dr. George Lambert, Associate Professor of Pediatrics, Director, Center for Childhood 

Neurotoxicology, Robert Wood Johnson Medical School-UMDNJ, Belle Mead, NJ 

Dr. Jill Lipoti, Director, Division of Environmental Safety and Health, New Jersey Department 

of Environmental Protection, Trenton, NJ 

Dr. Lee D. McMullen, Water Resources Practice Leader, Snyder & Associates, Inc., Ankeny, 

IA 

Dr. Judith L. Meyer, Distinguished Research Professor Emeritus, Odum School of Ecology, 

University of Georgia, Athens, GA 

Dr. Jana Milford, Professor, Department of Mechanical Engineering, University of Colorado, 

Boulder, CO 

Dr. Christine Moe, Eugene J. Gangarosa Professor, Hubert Department of Global Health, 

v
Rollins School of Public Health, Emory University, Atlanta, GA 

Dr. M. Granger Morgan, Lord Chair Professor in Engineering; Professor and Department 

Head, Department of Engineering and Public Policy, Carnegie Mellon University, Pittsburgh, PA 

Dr. Duncan Patten, Research Professor , Department of Land Resources and Environmental 

Sciences, Montana State University, Bozeman, MT, USA 

Mr. David Rejeski, Director, Foresight and Governance Project , Woodrow Wilson 

International Center for Scholars, Washington, DC 

Dr. Stephen M. Roberts, Professor, Department of Physiological Sciences, Director, Center for 

Environmental and Human Toxicology, University of Florida, Gainesville, FL 

Dr. Joan B. Rose, Professor and Homer Nowlin Chair for Water Research, Department of 

Fisheries and Wildlife, Michigan State University, East Lansing, MI 

Dr. Jonathan M. Samet, Professor and Chair , Department of Epidemiology, Bloomberg School 

of Public Health, Johns Hopkins University, Baltimore, MD 

Dr. James Sanders, Director and Professor, Skidaway Institute of Oceanography, Savannah, 

GA 

Dr. Jerald Schnoor, Allen S. Henry Chair Professor, Department of Civil and Environmental 

Engineering, Co-Director, Center for Global and Regional Environmental Research, University 

of Iowa, Iowa City, IA 

Dr. Kathleen Segerson, Professor, Department of Economics, University of Connecticut, Storrs, 

CT 

Dr. Kristin Shrader-Frechette, O'Neil Professor of Philosophy, Department of Biological 

Sciences and Philosophy Department, University of Notre Dame, Notre Dame, IN 

Dr. V. Kerry Smith, W.P. Carey Professor of Economics , Department of Economics, W.P 

Carey School of Business, Arizona State University, Tempe, AZ 

Dr. Thomas L. Theis, Director, Institute for Environmental Science and Policy, University of 

Illinois at Chicago, Chicago, IL 

Dr. Valerie Thomas, Anderson Interface Associate Professor, School of Industrial and Systems 

Engineering, Georgia Institute of Technology, Atlanta, GA 

Dr. Barton H. (Buzz) Thompson, Jr., Robert E. Paradise Professor of Natural Resources Law 

at the Stanford Law School and Perry L. McCarty Director, Woods Institute for the Environment 

Director, Stanford University, Stanford, CA 

vi
Dr. Robert Twiss, Professor Emeritus, University of California-Berkeley, Ross, CA 

Dr. Thomas S. Wallsten, Professor, Department of Psychology, University of Maryland, 

College Park, MD 

Dr. Lauren Zeise, Chief, Reproductive and Cancer Hazard Assessment Branch, Office of 

Environmental Health Hazard Assessment, California Environmental Protection Agency, 

Oakland, CA 

LIAISONS 

Dr. Steven Heeringa, (FIFRA SAP), Research Scientist and Director, Statistical Design Group, 

Institute for Social Research (ISR), University of Michigan, Ann Arbor, MI 

Dr. Melanie Marty, (CHPAC Chair), Chief, Air Toxicology and Epidemiology Branch, Office of 

Environmental Health Hazard Assessment, California EPA, Oakland, CA 

Dr. Henry Anderson, (CHPAC Alternate), Chief Medical Officer, Division of Public Health, 

Wisconsin Division of Public Health, Madison, WI 

SCIENCE ADVISORY BOARD STAFF 

Mr. Thomas Miller, Designated Federal Officer, 1200 Pennsylvania Avenue, NW 

1400F, Washington, DC, 20460 

vii
Table of Contents 

Executive Summary ......................................................................... ix 

1.0 Background and Introduction ...................................................... 1 

2.0 EPA’s Charge Questions ................................................... 2 

3.0 Response to Charge Questions .................................................... 3 

3.1 Charge Question 1 ......................................................... 3 

3.2 Charge Question 2 ......................................................... 6 

3.2.1 Models and Selection Processes ................................. 7 

3.2.2 Decisions Regarding Data Sets .................................. 8 

3.2.3 Use of the CCL for Regulatory Decisions ................... 11 

3.3 Charge Question 3 ......................................................... 11 

3.4 Charge Question 4.......................................................... 13 

4.0 References ............................................................................ 16 

Enclosure A .................................................................................... 17 

viii
Executive Summary

EPA’s Office of Ground Water and Drinking Water requested that the Science Advisory Board 

(SAB) Drinking Water Committee (hereafter, the Committee or DWC) provide advice on EPA’s 

Draft Third Drinking Water Contaminant Candidate List (CCL 3) and the process used to derive 

it. This list is the source of contaminants that are considered for a regulatory determination. In 

addition, the CCL 3 interfaces with the Agency’s research agenda. The charge questions posed 

to the DWC by EPA were: 

1. Please comment on whether the Federal Register Notice and support documents are clear, 

transparent, and adequate to provide an understanding of the overall processes and 

selection of contaminants for the draft CCL 3. 

2. Please comment on whether the draft CCL 3 list represents those contaminants that have 

the highest potential to occur in public water systems and cause adverse human health 

effects. 

3. Please provide any data that may suggest that contaminants which are currently on the 

draft CCL 3 list should not be listed. 

4. Please provide any data that may suggest that contaminants which are currently not on 

the draft CCL 3 list should be listed. 

In regard to whether the Federal Register Notice (FRN, EPA 2008) and support 

documents are clear, transparent, and adequate to provide an understanding of the overall 

processes and selection of contaminants for the draft CCL 3, the Committee concludes that the 

documentation, i.e., the FRN, is not transparent. Committee members with decades of 

experience reviewing and analyzing EPA regulatory documents could not follow specific 

contaminants through the process as presented in the FRN. The document is not clear. 

Interpretation by several Committee members of the published CCL 3 processes differed 

and were only clarified after discussion with EPA staff. The lack of clarity in the process led 

to frustration, and Committee members who tried to follow the decision-making process for one 

or more contaminants could not do so. The Committee recommends that both the FRN and the 

EPA web sites contain citations for all documents used in the process, and that the web site post 

the documents and/or hyperlinks directly to each document, as well as the location of the 

regulatory docket. 

The Committee recommends that EPA develop CCL 3 process flow charts for chemicals 

and pathogens. These flow charts should include links to other documents (data and models) 

used, as well as delineate where expert judgment was used to go from the universe of 

contaminants (Universe) to the Preliminary CCL (PCCL) to the CCL 3. Developing flowcharts 

that a stakeholder can use to track the progress of a contaminant through the system (with the 

appropriate references and URLs for each step) would not only make the process more 

transparent, but they might also highlight decisions that might suggest improvements for future 

CCL processes. The Committee also recommends that EPA document and justify why certain 

ix
contaminants that were included on previous CCL lists were excluded from the draft CCL 3. 

This will improve readers’ understanding of the evolution of the process as well as its 

transparency. 

In regard to whether the draft CCL 3 list represents those contaminants that have the 

highest potential to occur in public water systems and cause adverse human health effects, the 

CCL 3 does not clearly achieve the stated objectives of the CCL process for prioritization. 

If the goal is to consider at least five contaminants per five-year review cycle for regulatory 

determinations, a process that yields 104 contaminants has not whittled the Universe sufficiently 

to be efficient or effective. Such a large list can not clearly communicate which contaminants 

might – or might not – be considered for regulatory determination. The Committee has several 

specific recommendations. For chemicals, explanations should be attached to each bullet 

(Section III.A.4; page 9644 of the FRN), as it moves from the PCCL to the CCL, so that the 

decision rules are more clearly explicated for the high, medium, and low uncertainty bins. It is 

further recommended by the Committee that EPA should “re-train” the model, this time using 

only chemicals that would fall into the medium certainty bin. Certainty and data should drive the 

prioritization of the contaminants, where there is sufficient information to make a regulatory 

determination. For pathogens, the cutoff for moving from the PCCL to the CCL 3 was arbitrary 

and not determined based on priority. The Committee recommends that occurrence based on 

endemic disease data and published literature on occurrence be used to modify the 

priorities/rankings of the pathogen PCCL. 

With regard to providing any data that may suggest that contaminants which are currently 

on (or not on) the draft CCL 3 list, and should not be listed (or should be listed), the list is too 

large for the committee to complete a full review of these issues in the time allotted. There are

104 contaminants on the draft CCL 3, and members of the Committee could not effectively 

review each contaminant on the draft CCL 3, or the numerous potential contaminants that 

are not on the draft CCL 3. Rather, the Committee chose to present some critical examples of 

contaminants that their expertise and experience suggested should not have a sufficiently high 

priority to be on the draft CCL 3 and suggest reasons why the current process might have 

excluded others. 

 

• For chemical contaminants, the Committee recommends that EPA should evaluate 

whether pesticides that have been or are about to be cancelled completely should be on 

the list for additional SDWA regulation. This determination could be made after some 

assessment of use, occurrence (transport and fate), and particularly persistence, which 

will help to determine if the agent as used previously would have any ongoing 

contamination issues. This will assist in the determination of whether the contaminant 

should be considered for a regulatory determination or not. In some cases, these types of 

pesticides may not require additional regulation and should be excluded from the CCL 

process. The Committee recognizes that at least some evaluation of cancelled pesticides 

would be necessary. 

• The Committee also recommends that N-nitrosodimethylamine (NDMA), methyl tertiary 

butyl ether (MTBE), perchlorate, and perfluorooctanoic acid (PFOA) should be a high 

x
xi

priority for consideration by the Agency, because there is a higher degree of certainty 

about their toxicity, occurrence, and treatability. 

• For pathogenic contaminants, the Committee noted that two globally important 

waterborne pathogens, Adenovirus and Mycobacteria, were excluded from the draft CCL 

3. These pathogens should be on the list. Other pathogens, Vibrio cholera and 

Entamoeba, were included and should be excluded from the list. Rare outbreaks, and the 

outbreak data base in general, were used in determining the ranking and placement on the 

CCL 3. The Committee recommends that endemic disease data sets, numbers of 

outbreaks, geographical distribution of outbreaks and outbreak venues, as well as the 

peer-reviewed literature (which would better inform occurrence in U.S. waters), be used 

for the pathogens. Both the use of more of the publicly available data, as well as more 

comprehensive use of the databases already used to develop the CCL process, would 

improve the ranking. 

• The CCL 3 process also does not evaluate some of the less direct, potential hazards of 

contaminants. For example, exposure to antibiotics may lead to antibiotic resistant 

pathogens. The CCL 3 process does not identify this impact as a threat to human health. 

The CCL is used for several diverse purposes, and the CCL process may need to be 

modified to reflect these uses. At a minimum, a further prioritization of the CCL should be 

undertaken for each of these purposes. For example, the CCL 3 list should be used to distinguish 

between those contaminants with nearly a sufficiency of information for regulatory 

determination and those with greater uncertainty, i.e., with the need for collection of additional 

data before a contaminant would move off the CCL 3 toward a regulatory determination. 

The Committee’s full report follows and begins with background information on the CCL 

3 process with web addresses where additional information can be found. The Agency’s charge 

questions are then presented, first in toto and then separated with the Committee’s response to 

each question. The final section contains references cited by the Committee. 
1.0 Background and Introduction

EPA’s Office of Ground Water and Drinking Water requested that the Science Advisory 

Board (SAB) Drinking Water Committee provide advice on EPA’s Draft Third Drinking Water 

Contaminant Candidate List (CCL 3) and the process used to derive it. The CCL 3 is a list which 

contains potentially harmful drinking water contaminants that may require regulations in the 

future that are currently not regulated. The process for the CCL 3 is outlined in the Federal 

Register Notice (FRN; EPA, 2008 available at: http://www.epa.gov/fedrgstr/EPAWATER/2008/February/Day-21/w3114.pdf). This document states: 

 “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.” 

EPA’s web page titled, “Drinking Water Contaminant Candidate List and Regulatory 

Determinations,” (available at: http://www.epa.gov/safewater/ccl/ccl3.html#overview) states: 

“In developing the draft CCL 3, we implemented a different process from that used for 

CCL 1 and CCL 2. This new process builds on evaluations used for previous CCLs and 

was based on substantial expert input and recommendations from the National Academy 

of Science’s National Research Council (NRC) and the National Drinking Water 

Advisory Council (NDWAC). 

“We used a multi-step CCL process to identify contaminants for inclusion on the draft 

CCL 3. The key steps include: 

• Identifying a broad universe of potential drinking water contaminants (called the 

CCL 3 Universe). We initially considered approximately 7,500 potential chemical 

and microbial contaminants. 

1
• Applying screening criteria to the universe we identified 560 of those 

contaminants that should be further evaluated (the preliminary CCL or PCCL) 

based on a contaminant’s potential to occur in public water systems and the 

potential for public health concern. 

• We then selected 104 contaminants from the PCCL to include on the CCL based 

on more detailed evaluation of occurrence and health effects and expert judgment 

applied in a transparent reproducible manner. 

• We incorporated information from the public, expert input, and expert review in 

the CCL process.” 

Information regarding the CCL processes and lists can be accessed through the CCL web page 

at: http://www.epa.gov/safewater/ccl/index.html. 

The DWC of EPA’s SAB met in a public session on April 23 – 24, 2008 in Washington, 

DC, to review the draft CCL 3. The Committee held a subsequent teleconference call on August 

13, 2008 to discuss its draft advisory report. The Chartered SAB conducted quality reviews of 

this document on October 28, 2008 in Washington, DC and approved the report on December 16, 

2008 by teleconference. 

2.0 EPA’s Charge Questions 

 

 The new process developed in response to the recommendations of the NRC and 

NDWAC, as well as the specific chemicals and microbial pathogens on the draft CCL 3 list, 

were subject to review. The charge questions posed to the DWC by EPA follow; the full memo 

is in Enclosure A. 

1. Please comment on whether the Federal Register Notice and support documents are clear, 

transparent, and adequate to provide an understanding of the overall processes and 

selection of contaminants for the draft CCL 3. 

2. Please comment on whether the draft CCL 3 list represents those contaminants that have 

the highest potential to occur in public water systems and cause adverse human health 

effects. 

3. Please provide any data that may suggest that contaminants which are currently on the 

draft CCL 3 list should not be listed. 

4. Please provide any data that may suggest that contaminants which are currently not on 

the draft CCL 3 list should be listed. 

 

2
3.0 Response to Charge Questions 

3.1 Charge Question 1 

Please comment on whether the Federal Register Notice and support documents are 

clear, transparent, and adequate to provide an understanding of the overall processes and 

selection of contaminants for the draft CCL 3. 

Committee Response

The FRN (EPA, 2008) that describes the process is not transparent and is not 

adequate to provide an overall understanding of the selection of contaminants for the draft 

CCL 3. At the April meeting, Committee members, each with decades of experience 

reviewing and analyzing EPA regulatory documents, stated that they could not follow 

specific contaminants through the process as presented in the FRN. 

The Committee affirms that the process used to produce the CCL 3 represents a major 

improvement from the processes used to generate CCL 1 and CCL 2. The processes used to 

generate the first two lists relied heavily upon expert opinion, best professional judgment, and 

stakeholder nominations. Potential health risks contributed to the first part of the assessment, 

followed secondarily by whether the contaminant occurred in drinking water. The CCL 3 

process outlined in the FRN uses a more data-driven, systematic approach, focusing on assessing 

information (including surrogate information) to identify contaminants based on: the potential or 

known occurrence in drinking water; and their potential or known ability to cause adverse effects 

in people. As recommended by the NRC and NDWAC, the CCL 3 process attempted to address 

the Universe and developed a PCCL. Expert panels were used along the way as part of the 

review and to modify the process. During the assessment, 6000 chemical contaminants and 1400 

pathogens were identified. The Committee views the current process as a first iteration of a 

data-derived CCL, and acknowledges that, as recommended by the NDWAC, the process 

should be adaptive to improve and further develop with additional experience and data. The 

Committee’s comments on the limitations of the current process should be viewed in this 

context. 

Numerous challenges must be overcome when whittling the initial Universe down to a 

CCL. EPA has documented its decision-making process, described its attempts to identify biases 

in that process, and obtained expert feedback on the process. In general, the approach is 

scientifically justified and, particularly for the chemical list, is a labor-intensive process that 

includes the development of mathematical models to create the chemical list. The current 

models are useful in sorting through the chemical and pathogen contaminants, but as discussed 

further in this report, are expected to improve during additional iterations of the process. 

The Committee found that use of an only data-supported process, i.e., without 

professional judgment, for the CCL 3 (as described in the FRN) generated a list of contaminants 

that is suboptimal. Based on the changes made by EPA’s panel of internal experts, the 

Committee infers that EPA’s scientists also agreed that expert judgment was necessary at several 

points in the process for developing the CCL 3. Therefore, EPA requested the opinions of 

3
internal experts for professional assessment of chemicals or pathogens to revise the process, and 

thus the contaminants, on the draft CCL 3. The Committee was not concerned that, in 

developing the process, a review was needed and mid-course corrections were undertaken. 

Rather, the Committee found that these modifications (or suggestions) by Agency staff that 

were accepted or rejected were not readily apparent as the Committee reviewed the 

documentation in the FRN. In addition, the justifications for the decisions in which expert 

opinion was accepted or rejected were not articulated. The Committee found that this lack of 

full transparency would impede the ability of other people to repeat the CCL 3 process and 

obtain the same results as EPA – either with the current contaminants or with additional 

contaminants that might be of interest. In particular, the Committee could not discern at 

which steps the data drove the primary outcome and at which steps the experts were used 

to address key decisions in the process. Such reproducibility of process was a stated criterion 

for transparency made by the NRC and NDWAC. Additionally, some of the information about 

individual contaminants and decisions made about them were only available in the regulatory 

docket. Committee members either did not know that the docket might contain such information 

or had difficulty locating the docket and/or the information desired. 

 The Committee recommends that both the FRN and the EPA web sites contain citations 

for all of the documents used in this process, and that the web site post the documents and/or 

hyperlinks directly to each document, as well as the location of the regulatory docket. 

Additionally, use of hypertext in an online matrix of the contaminants might allow interested 

parties to readily access the appropriate section of the documents where the information 

influenced the related decisions in the process. Such a hypertext matrix could also be used to 

provide readers with a summary of indicators or critical criteria, such as potency-toconcentration ratios, occurrence data, mode-of-action decisions, health effects of concern, model 

scores, expert panel conclusions, etc. 

The document is not clear. At the April meeting, Committee members asked for 

clarification of the process for selecting the draft CCL. After additional information was 

presented by representatives of EPA's Office of Water, several Committee members stated 

that they had interpreted the text or tables differently, based on their independent reading 

of the FRN. These statements apply both to the process used to select the chemicals and to 

the process used to select the pathogens. 

The lack of clarity in the process led to frustration, as Committee members attempted to 

determine why specific contaminants on the PCCL were retained or removed from the group of 

contaminants that would become the draft CCL 3. Committee members who tried to follow 

the decision-making process for one or more contaminants could not do so. The process for 

selecting the chemicals was quite clear and logically presented until after the three models were 

run and the resulting lists were created. At that point, the presentation became very murky. 

Committee members expressed the difficulty in determining what supporting data were used for 

each of the chemicals that did get onto the list. For example, it is not shown what level of 

certainty “bin” each came from, what the data were in the exposure and health effects category, 

and what the modeled list-not list determinations were. A table presenting these results is 

recommended. In addition, it would be helpful to show similar results for at least a subset of the 

chemicals that remained on the PCCL, to help inform the reader as to why these were not 

4
selected. The Committee specifically raised numerous questions about the bullet points in 

section 4 on p. 9644 of the FRN. It was not clear from the text that the 36 chemicals in the high 

certainty bin, for example, were included irrespective of the model results, whereas the 24 

pesticides chosen from the medium certainty bin included only those with an “L” or an “L-L?” 

ranking. This information needs to be clarified. In addition, there needs to be a clearly written 

justification for diverging from the results of the model at the end of the process. 

The Committee recommends that explanations be attached to each bullet (Section 

III.A.4., page 9644 of the FRN) for the chemical list as it moves from the PCCL to the CCL so 

that the decision rules are more clearly explicated for the high, medium, and low uncertainty 

bins. Since the “training” of the model used chemicals from all certainty bins, the Committee 

also recommends that EPA “re-train” the model, using only chemicals that would fall into the 

medium certainty bin, i.e., the bin of chemicals for which the model was ultimately used. Clear 

identification of certainty of the data should then drive the prioritization of the contaminants in 

those cases where there is sufficient information to make a regulatory determination. 

The Committee recommends that EPA develop one or more flow charts that a 

stakeholder can use to track the progress of a contaminant through the system, with the 

appropriate references and URLs for each step. Such flow charts would not only make the 

process more transparent, but they might also highlight decisions that suggest improvements for 

future CCL processes. Also, parameters chosen for the models or specification decisions, should 

be provided (in more detail than is provided in Appendix E of the FRN). The CCL 3 process 

flow charts should include links to other documents (data and models) used, as well as delineate 

where expert judgment was used to go from the Universe to the PCCL to the CCL 3. The 

Committee also recommends that EPA document and justify why certain contaminants that were 

included on previous CCL lists were excluded from the draft CCL 3. This will improve readers’ 

understanding of the evolution of the CCL process, as well as its transparency. 

Other recommendations for the chemical selection process include: 

• To further improve the clarity of the process, approaches that were discarded should be 

moved to the end of the document, perhaps in an appendix. 

• The training set used for the initial calibration of the model for chemicals should be 

readily available in the documentation via links to the web site. 

• Additional deficiencies should be corrected in the details of the presentation of the 

process. Details are lacking, for example, as to how fate parameters like the 

octanol/water partition coefficients were used in the evaluation. 

• All parameters should include the appropriate units, e.g., on LD50 and related parameters 

in Exhibit 9. 

The process for selection of pathogen contaminants, as outlined in the FRN, was overall 

judged a relatively transparent one. However, derivation of the relative numerical rankings was 

not clear. An analytical protocol was employed; however, it did not discretely quantify potency, 

5
for example, in terms of dose-response relationship as it had for the chemicals proposed for CCL 

3 inclusion. The sources of information and data that were used in candidate selection are clear, 

and the effort to be inclusive in receiving information from non-government organizations 

(NGOs), the public, professional organizations, and municipalities is apparent. The development 

of the Universe and the PCCL were data driven. 

As with the process used to select chemicals, FRN lacked transparency with regard to the 

selection of pathogens. Details about how information was used to assign a numerical rating to 

the pathogens, for example, were not clear. Although outbreak data were critical to the selection 

process, the role of these data, used to rank both the exposure and the health risks, was not 

readily apparent. The cut-off for the PCCL to the CCL 3 for pathogens was arbitrary and not 

determined based on a specific understanding of the data or uncertainty of the data. Thus, 

support for this cut-off was not adequate. The Committee recommends that occurrence based 

on endemic disease data, and published literature on occurrence be used to modify the 

priorities and rankings of the pathogens on the PCCL as they move to the CCL.

3.2 Charge Question 2

Please comment on whether the draft CCL 3 list represents those contaminants that 

have the highest potential to occur in public water systems and cause adverse human 

health effects. 

Committee Response

The CCL 3 does not clearly achieve the stated objectives of the CCL process. If the 

goal is to consider at least five contaminants per five-year review cycle for regulatory 

determinations, a process that yields 104 contaminants has not whittled the Universe 

sufficiently to be efficient or effective. Such a large list can not clearly communicate to the 

DWC, other specific interested parties, and/or the general public which contaminants 

might – or might not – be considered for a meaningful regulatory determination. 

Obtaining the list of contaminants for the draft CCL 3 involved development of a new 

contaminant-selection process. The process of selecting the CCL 3 involved three major steps: 

(1) identifying the Universe of contaminants that might be of concern; (2) using data on 

occurrence and potential to cause adverse effects to obtain a PCCL; and (3) using data, 

processes, and opinions from EPA’s internal experts to refine the selection into a draft CCL. 

This goes to the heart of the question on prioritization and decision making in the selection 

process from the Universe to the PCCL to the CCL. The uncertainty analysis for health effects – 

and particularly for occurrence – should be articulated to address this issue. Selection of the 

databases with specific attributes can determine whether parameters are estimated directly or 

when surrogates must be used. Lack of readily available data can constrain the decision options 

within the process. In particular, data selection should include identifying and obtaining data 

that are necessary for the optimal operation of the CCL process. This applies both to data that 

are appropriate for understanding the occurrence of contaminants and to data on the potential 

health effects of those contaminants. Key areas to improve the process that should be explored 

6
and addressed in the future include: sensitivity analysis of models and data; data uncertainty; 

and data quality. 

The Committee recommends consideration of emerging issues and on-going research 

when selecting chemicals. There are also some clear categories of contaminants that need 

special attention in selecting the CCL including pharmaceuticals, personal care products, 

endocrine disruptors, antibiotics, and algal toxins. Such contaminants may warrant changes in 

the CCL selection processes. General exposure to even low levels of antibiotics in drinking 

water, for example, may lead to antibiotic-resistant pathogens either in a person drinking the 

water or the general environment. The current CCL process for chemicals would not identify 

this as an adverse effect. In addition, opportunistic pathogens (e.g., Serratia and Pseudomonas) 

should be addressed, as waterborne disease from these pathogens in hospital settings has been 

documented. The Committee recommends that EPA explore approaches that would bring in 

these atypical health-related data and occurrence data into the CCL process. 

3.2.1 Models and Selection Processes

Chemical Contaminants

 The discussion in the FRN regarding the methodology for moving chemicals from the 

PCCL to the CCL is organized in a chronological manner. This presentation imparts 

significance to a complex and somewhat cumbersome initial methodology that was ultimately 

subsumed within a new methodological framework proposed by EPA’s internal expert panels. 

This complex, initial approach was not used to determine which chemicals moved from the 

PCCL to the CCL. The actual approach began by dividing the chemical PCCL into three groups 

(high, medium, and low uncertainty) depending on the type of data available to characterize the 

contaminant. For each of these groups, a new decision rule was developed to determine whether 

or not the contaminant should move forward to the CCL. While these decision rules are 

indicated in the bullets in Section III.A.4. (page 9644 of the FRN), the explanations attached to 

each bullet need to be expanded so that the decision rules are more clearly explicated. The initial 

classification model was “trained” using chemicals of all types. Since this model was only used 

for chemicals in the “medium certainty” bin, EPA should “re-train” the model, using only 

chemicals that would fall into this bin. 

 

The Committee noted that the draft CCL 3 gives equal weight to all chemicals, although 

some chemicals are likely to be ready for regulatory determination, while others will require a 

significant amount of additional research before a regulatory determination can be made. Thus, 

the Committee recommends further prioritization within the CCL 3. Additional data and 

processes should be used to priority rank the CCL 3 chemicals, by a method that will 

differentiate between chemicals that have sufficient, existing information for a data-based 

regulatory decision and those that do not. Priority-ranking chemicals may also require 

reformulating or retraining the algorithms, since the dependent variable of the algorithm must 

now indicate whether a contaminant should be studied for regulatory determination, and with 

what urgency the contaminant should be studied. 

7
Pathogen Contaminants

 

The process for moving pathogens from the PCCL to CCL does not sufficiently address 

priority of occurrence or of health impacts. In particular, it is somewhat ambiguous as to how 

the ultimate pathogen scores for this process were developed. For pathogens, it appears that the 

internal EPA experts adjusted the scoring system. This adjustment by expert judgment 

should be presented more prominently, and the decision rules explained in more detail. 

The Committee concludes decisions regarding the selection of data sets, and the level of 

resolution of the information within those data sets, was partially responsible for the suboptimal 

results. The relative weighting of Center for Disease Control and Prevention (CDC) Waterborne 

Disease Outbreaks (WBDO) “Occurrence” and “Health Effect Scoring”, as well as data 

normalization, is described, but not necessarily adequate, for addressing the most important 

pathogens. The Committee recommends that the limitations of WBDO data sets be articulated 

clearly. Such limitations, for example, include underestimation of waterborne disease via a 

passive surveillance and the percentages of outbreaks where no etiological agent is identified. 

Exhibit 15 of the FRN shows evidence of WBDO using the CDC surveillance database. Over 

the more than three-decade period in question, the scoring system does not differentiate between 

pathogens that have caused many outbreaks and those that caused only two outbreaks. 

Furthermore, scoring of the WBDO data does not appear to take into account the geographic 

dispersion of the outbreaks. Also lacking are data on specific, identified pathogens for the 

majority of studied outbreaks. Furthermore, a rudimentary sensitivity analysis of the pathogenweighting criteria would have demonstrated that the results are not robust to small changes in the 

scoring. For example, a change of only "1" unit in WBDO score would move some organisms 

on or off the list. Also, the use of “Occurrence” data does not appear to be a quantitatively 

robust term, i.e., the 1-to-3 ranking scale may have less utility than initially expected. An 

occurrence term of 3 appears only to mean that it has been found in U.S. drinking water, but not 

that it is found with any type of frequency or geographic distribution in U.S. drinking waters. In 

fact, a score of 3 may mean that it was only found once in drinking water. Outbreak data were 

not independent of occurrence, as an outbreak would by itself imply that the organism had been 

found in drinking water and influence that score. This interrelationship gave the WBDO a 

greater weight in the ranking. If the pathogen were only detected once, the exposure potential, 

and therefore the risk, may be quite low. 

3.2.2 Decisions Regarding Data Sets

In several places EPA appears to use data that may not be optimal for its stated intent of 

offering equal protection to water consumers. For example, on page 9640 of the FRN, 

prevalence is defined as “...the percent of public water systems or monitoring sites across the 

nation with detections, number of states with releases...” Neither of these measures takes into 

account the number of people who are potentially exposed to contaminants through these 

drinking water systems. A contaminant that is found in two or three small states could receive 

greater weighting than one found in a large, populous state. Similarly, geographic distribution 

(not necessarily within state boundaries but perhaps watersheds) might be an additional 

consideration for exposure. The reasons for and implications of such decisions should be 

discussed. 

8
The Committee recommends the use of more of the publicly available data and the more 

comprehensive use of the databases already used to develop the CCL 3. In particular, 

information in the peer-reviewed, published literature could be effectively used at certain 

junctures of the process, especially when the list of chemicals or pathogens considered for a 

particular decision is sufficiently small to reduce the burden of a literature search and analysis. 

Similarly, the increasing use of wastewater affected sources of drinking water suggests that 

databases containing information on contaminants in wastewater effluents would inform the 

CCL process. 

Chemical Contaminants

EPA used a hierarchical approach for data sources to indicate health effects. For full 

transparency, the order in this hierarchy of references should be clearly presented. Furthermore, 

for food-use pesticides, it would seem more appropriate to use the population-adjusted dose 

(PAD), i.e., the dose that incorporates the additional uncertainty factor for children under the 

Food Quality Protection Act (FQPA), rather than the reference dose (RfD) in the calculation of a 

health reference level (HRL). Therefore, the Committee recommends that the Agency 

recalculate the health-concentration ratios for those pesticides on the PCCL that have PADs 

smaller than their respective RfDs. It is possible that additional substances may qualify for 

inclusion on the draft CCL 3 because their revised ratio could now be 10 or less. 

Pathogen Contaminants 

The data used (or more specifically, the data not used) and the resulting pathogens 

selected, were not necessarily the optimal set to consider for a regulatory determination. For 

example, a choice was made by EPA to rely primarily on national data sources and use only data 

sources with entries (in this case, for recorded outbreaks) for all of the organisms. This led to 

heavy reliance on CDC databases and lack of use of the peer-reviewed, published scientific 

literature. This process does not necessarily represent the "best available science." While there 

was general agreement that a pathogen’s presence in the WBDO should bring special attention to 

that microbial pathogen, the WBDO grading system does not appear to provide sufficient 

resolution regarding details to be useful as a scoring algorithm without modifiers. Thus, the full 

breadth or ranges of available data were not used. 

The WBDO has several limitations that are not addressed in the FRN. This data base 

does not distinguish between an organism that has caused outbreaks in the Marshall Islands 

(Cholera) and an organism that has caused several outbreaks in the continental U.S. (norovirus 

and Campylobacter). The potential problems caused by highly endemic diseases that are never 

detected as outbreaks (and therefore not in the WBDO) are not fully explained by the Agency in 

the FRN. A supplementary table containing the published, waterborne-attributed, case reports 

for each of the organisms would be useful. There is also a lack of data and discussion about the 

prevalence of organisms in sewage and wastewater. As a result, organisms such as Naegleria or 

Vibrio may receive a pathogen PCCL score higher than expected because of this weighting for 

“Occurrence,” which is tied to whether there has been an outbreak. An environmental 

frequency or distribution score for pathogens, rather than or in addition to its “Occurrence” 

9
score, is needed. The ranking and the cut-off level that separated the PCCL from the CCL 

seemed arbitrary and should be better described (Exhibit 18). 

The potential effect of the information that was not used is less clear. As EPA is aware, 

the CDC is the premier organization in reporting disease statistics and occurrence for organisms 

typically associated with waterborne disease. EPA has partnered well with CDC, including 

evaluating the likelihood of disease outbreaks, as the consequences of global environmental 

change become manifest. CDC also partners with many other organizations and associations in 

disease surveillance. Perhaps most notable are state public health offices, responsible for first 

response in reporting disease associated with water and food-borne exposure. EPA should 

explore methods for accessing such data. CDC accesses a broader base of data, which may or 

may not be immediately available to the EPA, as data indicators for PCCL consideration. Some 

of these sources include United States Geological Service (USGS) well-monitoring programs, 

and the National Environmental Health Association (NEHA). NEHA also has many partner 

organizations such as the Council for State and Territorial Epidemiologists (CSTE). Other 

organizations such as the Bureau of Environmental Epidemiology (Florida) or the New York 

City Department of Environmental Protection, Waterborne Disease Risk Assessment Program, 

may prove useful, as other data or sentinel sources of information on outbreaks. 

 At the international level the United Nations Food and Agricultural Organization (UNFAO) and World Health Organization (WHO) monitor and report relevant outbreak and disease 

incidence. Significantly, the European counterpart to the CDC, the European Center for Disease 

Prevention and Control (ECDC), continues to develop its waterborne disease and monitoring 

program and makes data relatively available through its Enter-net databases for waterborne 

disease organisms. It is likely the EPA is aware of all these sources, but it may wish to 

investigate whether these and other information channels could facilitate more robust and 

quantitative tools in assessment of PCCL consideration and CCL listing. 

 Peer-reviewed research articles in journals and periodicals received less attention as data 

sources than disease monitoring or surveillance data from other agencies, state, or municipal 

sources. Given the relatively limited number of microbial pathogens proposed for inclusion on 

the CCL, reviews of the scientific literature are desirable in addition to the sources that were 

used to develop this draft CCL 3. Exceptions to the process whereby journal articles were used 

for bacteria included publications on Arcobacter and Mycobacterium avium complex (MAC). It 

is likely that other organisms would change position with regard to CCL listing, if outside data 

and professional judgment were used. The literature may also be more current with respect to 

sensitivity, selectivity, and specificity than the information derived from some more standard 

methods. 

 There was discussion in the FRN about not using susceptibility to water treatment to 

guide the selection list. This may be appropriate for the PCCL as well as the CCL. However, as 

with the chemicals, further prioritization is recommended for the CCL 3 with regard to 

sufficiency of the data for regulatory determination as compared with investment in generating 

more data (on methods, occurrence, and health effects). For example, if the Agency 

demonstrates that the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) or 

the Ground Water Rule (GWR) already address risk management for specific pathogens, this fact 

10
could be articulated and influence selection for the CCL. Neither public health nor water 

science benefits from having a number of pathogens on a CCL that can readily be removed once 

they are formally articulated as “controlled”, when is no need to formally establish an MCL or 

treatment technique due to current drinking water treatment which reduces the risk already. The 

large numbers of Legionella cases, and the fact that no current regulatory approach can be 

documented to reduce this risk, for example, suggest that this type of pathogen be given a higher 

priority on the CCL. 

3.2.3 Use of the CCL for Regulatory Decisions

The CCL 3, as currently defined, serves two distinct purposes. The first is to identify 

unregulated contaminants that might have sufficiently high occurrence and produce adverse 

effects of concern, so that resources might be directed to obtaining more information. Toward 

this end, either data on occurrence or data on adverse effects could lead to development of 

sufficiency to move to a regulatory determination. In contrast, the second goal is to select those 

contaminants that should be considered for imminent regulatory determination. In general, such 

action would require the existence of, rather than the generation of, information on both 

occurrence and health effects. Priority setting within the draft CCL 3 should use such criteria. 

Absent this prioritization, the CCL 3 will not achieve its stated goal. 

The number of contaminants on each CCL keeps increasing. However, regulatory 

determinations are only made for 5 to 10 contaminants every five years. The continued increase 

in contaminants on the list may give the public a sense that water quality is declining with time. 

EPA should consider how to address this issue of risk perception in its documents on the CCL 

process. 

3.3 Charge Question 3

Please provide any data that may suggest that contaminants which are currently on 

the draft CCL 3 list should not be listed. 

Committee Response

With 104 contaminants on the draft CCL 3, members of the DWC could not 

effectively review each contaminant. For example, one member provided short summaries 

of a subset of the chemical contaminants (appended to the minutes of the meeting), and the 

list was 15 pages long (available on web site). Instead, the DWC chose to present some 

critical examples of contaminants that their expertise and experience suggested should not 

have a sufficiently high priority to be on the draft CCL 3, and suggest reasons why the 

current process excluded them. 

The DWC concluded that the list of chemicals on the CCL 3 is too large and that it may 

be appropriate for some to remain on the PCCL. Additional priority ranking based on, for 

example, availability of data necessary for a regulatory determination, should be undertaken. 

The CCL serves both to guide the future safety of drinking water via regulatory determinations, 

to focus research (into methods for detection, methods of water treatment, and assessing health 

11
effects), and to interface with other rules such as the Unregulated Contaminant Monitoring Rule 

(UCMR). It is one of the most critical and important activities within the EPA and thus certainly 

deserves the efforts that the Agency has devoted to it. The final list must be viewed within that 

context. 

The DWC acknowledges that any list of contaminants would have some contaminants 

that each expert would prefer to add or to remove. Nonetheless, there was general agreement 

that the current process could be improved to generate a list that would contain fewer surprises. 

For example, members conclude that even a cursory sensitivity analysis could be used to 

improve the scoring systems and justify the cut-off points that were used to retain contaminants. 

Knowledge about a pesticide’s regulatory status under the Federal Insecticide, Fungicide 

and Rodenticide Act (FIFRA) and FQPA, might obviate retention in a process designed to 

determine whether a regulatory determination is necessary under SDWA. Cancelled pesticides, 

or those for which cancellation is underway, should be considered differently than those 

expected to be used for a longer time. For example, all uses of nitrofen (which is on the draft 

CCL 3) were cancelled in 1983, and existing stocks were depleted within a few years. It appears 

that nitrofen is on the draft CCL 3 because it was listed as a Toxics Release Inventory (TRI) 

release from just one site in just one year. The Committee does not agree that such limited data 

constitutes an appropriate surrogate for exposure for decisions regarding decision on the 

development of a national drinking water standard. Similarly, the Committee questions the value 

of considering, for additional SDWA regulation, those pesticides for which cancellation of all or 

many uses is in progress (e.g., molinate and some organophosphates). The Committee 

recognizes that at least some evaluation of cancelled pesticides would be necessary, so as not to 

be shortsighted on the Agency’s part. The Committee recommends that pesticides no longer in 

use should be removed from the CCL unless an assessment determines that they present ongoing 

contamination issues such as: (1) the potential longevity of pesticides in ecosystems; or (2) fate 

and transport data. In addition, proposed CCL chemicals such as germanium, hexane, and 

quinoline appear to be on the list mainly because they scored highly in one category (e.g., 

production volume for hexane and toxicity for germanium). The Committee recommends that 

such chemicals not be considered for regulatory determinations at this time. 

For the chemical contaminants, the Committee recommends that the models take into 

consideration the level of certainty, and also some measure of the ratio between the 

concentration of concern and the potential drinking water concentration. Thus, some chemicals 

on the draft CCL 3 might remain on the PCCL, as the current data suggest their occurrence in 

public water systems is not at a frequency and concentration that would be of public health 

concern. Furthermore, the databases used by the EPA in the CCL 3 analyses do not include 

much of the journal literature that could be a rich source of information. While these sources 

might be difficult to search for the Universe, these data could more easily be included in the 

PCCL to CCL process, especially for the limited number of pathogens. The use of advanced 

text-processing software should be investigated for this application. E-government initiatives 

throughout the Federal government, as well as a lively and innovative academic community, are 

potential sources of help for EPA in pursuing this approach. Similarly, use of available 

computational toxicology data might improve the selection of chemical contaminants. 

12
The Committee experts in pathogens had not expected to see Entamoeba histolytica and 

Vibrio cholerae on the draft CCL. Other countries’ environmental agencies look to the EPA’s 

CCL. Thus, when the system that is used reveals pathogens that are no longer considered 

waterborne disease risks in the U.S., the reasons for this should be addressed, and the data-based 

numerical approach should be investigated and corrected. The Committee recommends that 

EPA examine data on endemic disease, numbers of outbreaks (dates), and geographic locations 

(Marshall Islands), and venues (the Entamoeba outbreak was listed with other pathogens in a 

prison where sexual transmission is known to occur), as well as provide a better assessment on 

the frequency of occurrence in drinking water supplies in the U.S. These microbial contaminants 

are not likely to occur in public water systems with a frequency and at a concentration of public 

health concern. Clearly, these are globally important, waterborne pathogens; however, for U.S. 

waters their inclusion on the CCL 3 is not warranted. 

3.4 Charge Question 4

Please provide any data that may suggest that contaminants which are currently not 

on the draft CCL 3 list should be listed. 

Committee Response

Given, as stated in the response to the previous question, the draft CCL 3 was too 

long to review the contaminants efficiently, it was not feasible for the DWC to consider all 

possible additional contaminants that might warrant a higher priority for consideration for 

regulatory determination through the CCL process. Moreover, as the FRN was neither 

transparent nor clear, it would not have been possible for the Committee members to have 

provided appropriate data to justify their selection of additional contaminants prior to 

discussion with EPA at the primary review of the document in April. Thus, the DWC 

chose to provide critical examples of contaminants that, given their experience and 

expertise, they expected to be on the draft CCL 3 and suggest – to the best of their current 

understanding of the process – why they might not have made it through the current 

process. 

The Committee recommends that an explanation be included for those contaminants that 

are on the CCL 1 or CCL 2, but were not included in the new list via the new process, with the 

appropriate justification. As already stated, this will improve transparency and understanding of 

the evolution of the process. 

EPA should consider addressing the cumulative effects of chemicals with similar sources 

and mechanisms (or modes) of action, and microbial pathogens with similar potency and disease 

endpoints (for example, diarrhea, pneumonia, or meningitis). The draft CCL 3 was constructed 

with consideration only about individual chemicals and pathogens. Grouping has been used for 

other drinking water contaminants (e.g., trihalomethanes and haloacetic acids) because 

occurrence, health effects, and/or treatment options are related. In the draft CCL 3, (1) 

perflourochemicals and (2) acetochlor, metolachlor, and their degradates are examples where it 

may be helpful to list the compounds as a group. Not all of the compounds in the group may be 

released from the same source, nor would they likely always occur together. A group could 

13
consist of “exposure groups” similar in sources, transport, or solubility. Similarly, “health 

groups” would be composed of contaminants with similar toxicity or adverse health effects. 

Thus, some agents not on the CCL 3 would join their appropriate groups. Additionally, the 

Committee recommends that EPA consider groups of chemicals where only some have been 

considered for regulation because others are not yet in common use. The Committee is 

concerned that, if the group is not considered as a whole, users could substitute a non-regulated 

chemical for a regulated one and, thus, escape regulatory concern. Some groups of chemicals 

may need to be considered in different ways depending on the goal of the analysis. For example, 

many nitrosamines have similar toxicities and carcinogenicities. Therefore, they should be 

considered together when they co-occur in the same drinking water samples when evaluating 

risk. If they do not occur together, if they can not be used as substitutes, or if they require 

different treatment methods for removal, grouping for these purposes is not recommended. 

The Committee concludes that it will be important to consider information regarding 

wastewater concentrations when evaluating potential exposure in the CCL process. In some 

areas of the country, wastewater discharges are increasingly a greater percentage of water 

supplies, and they are being processed into potable water. Wastewater contains a wide variety of 

contaminants including pharmaceuticals, personal care products, enteric pathogens, and other 

emerging contaminants. In the case of pharmaceuticals, perflourinated surfactants, and other 

contaminants that are prevalent in wastewater effluent, EPA may want to consider using data 

obtained in specialized wastewater effluent monitoring programs for the CCL screening process. 

Large water systems may be subjected to significant discharges of wastewater effluent, and 

concentrations of contaminants measured in wastewater effluent could be used as a surrogate for 

concentrations in raw water. An approach for predicting the role of unplanned wastewater reuse 

that may be appropriate for predicting concentrations in raw water sources is presented in 

Anderson et al. (2004). 

The Committee recommends that EPA include the DWC earlier in the process. 

Requesting advice from the DWC at critical junctures throughout the process (e.g., when 

decisions are being made to modify the initially established process), and not just at the end, 

would allow EPA to take better advantage of the expertise of the DWC. 

Chemical Contaminants

The Committee experts in health effects of chemicals conclude that the isomers of 

hexachlorocyclohexane that were on or off the list did not appear appropriate. Pesticides that did 

not appear on the CCL 3 that were mentioned as potentially worthy of listing included some for 

which information was provided to EPA by public commenters, e.g., degradation products of 

dacthal and DDT; Fonofos; Terbacil; s-ethyl dipropylthiocarbamate (EPTC); and 1,3-

dichloropropene (Telone). The absence of data on the occurrence of pharmaceuticals in surface 

waters was also noted. The Committee recommends use of the data from the USGS, or any of 

the numerous studies in the peer-reviewed literature, to include these chemicals. Also, the 

Committee recommends that N-nitrosodimethylamine (NDMA), methyl tertiary butyl ether 

(MTBE), perchlorate, and perfluorooctanoic acid (PFOA) should be a high priority for 

consideration by the Agency, because there is a higher degree of certainty about their toxicity, 

occurrence, and treatability. 

14
The listing criteria for chemicals should consider including a parameter that evaluates 

analytical methods used to quantify the chemical concentrations in occurrence data. Without a 

“standard” method including an established limit of detection, the quality of the occurrence data 

will reflect the capabilities of the analytical laboratories. The potentially significant differences 

in the analytical capabilities should be a component of evaluating the occurrence data. As a 

result, the Committee cautions against using the 90th percentile of the measured water 

concentrations as the denominator in a potency-to-concentration ratio where the cut-off value for 

listing is less than or equal to 10. It is clear that, for the very skewed distributions of 

contaminant concentrations in water, some water utilities could be in a zone of concern, and the 

chemical would still be screened off the list, using the existing, above-stated algorithm and 

criterion for listing. 

Pathogen Contaminants

Significant limitations in understanding which microbial pathogens were considered for 

the CCL 3 list include: the lack of occurrence data; very limited surveillance for most of the 

microbial pathogens; and the broad range of potential health effects. The CDC WBDO database, 

for example, is widely acknowledged to be an incomplete reflection of the true number of 

outbreaks. The WBDO does not capture the burden of disease relating to endemic pathogens 

with lower level transmissions. Thus, the Committee recommends the acquisition of better data 

on occurrence and surveillance regarding human disease. In general, given the small numbers of 

pathogens, greater details from the data sets could be used, as well as endemic disease rates. 

Data on occurrence is particularly poor, and thus the literature on surveys will require more 

scrutiny. The Committee recommends that the same exceptions made for Arcobacter and MAC 

in how a WBSO is defined should be applied to the other pathogens for which there is are highquality, peer-reviewed reports. 

Adenovirus and Mycobacteria should be considered for inclusion in the CCL 3. As 

discussed earlier, the weighting of documented outbreaks on health effects, and the approach 

used regarding occurrence ranking, moved Entamoeba and Vibrio higher on the list. The 

Committee recommends that information on endemic disease and occurrence in water, based on 

the literature, be examined for Adenovirus and Mycobacteria. Health effect scoring should also 

distinguish acute from chronic effects. The potential for pathogen occurrence in ambient waters 

could be considered based on contaminants occurrence in wastewater (as described in the 

previous sections). Thus, the Committee concludes that the data sets selected, the scoring 

process used, and the poor occurrence information may have significantly influenced these 

results. It is clear that the process can be improved. 

15
4.0 References 

Anderson, P. D.; D'Aco, V. J.; Shanahan, P.; Chapra, S. C.; Buzby, M. E.; Cunningham, V. L.; 

Duplessie, B. M.; Hayes, E. P.; Mastrocco, F. J.; Parke, N. J.; Rader, J. C.; Samuelian, J. H.; 

Schwab, B. W. 2004. Screening analysis of human pharmaceutical compounds in US surface 

waters. Environmental Science & Technology 38: 838-849. 

Environmental Protection Agency (EPA). 2008. Drinking Water Contaminant Candidate List 3. 

Draft. Federal Register 73:9628-9654. 

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Enclosure A 

Drinking Water Contaminant Candidate List 3 - Draft 

Charge to the EPA Science Advisory Board

March 10, 2008

Overview 

On February 21, 2008, EPA announced its third drinking water Contaminant Candidate List 

(CCL 3). The purpose of this action was to: 

• present EPA’s draft list of contaminants listed on the third CCL (CCL 3); 

• describe the process and basis for selecting the contaminants for the CCL 3; and 

• request public comments on the draft CCL 3. 

EPA’s Office of Water seeks advice from the Science Advisory Board Drinking Water 

Committee (DWC) regarding the draft CCL 3. Specific charge questions are presented below in 

addition to background information regarding the development of the CCL3. 

Background 

The 1996 SDWA Amendments require EPA to publish a list of currently unregulated 

contaminants which are known or anticipated to occur in public water systems and may require 

regulation in drinking water. This list is known as the Contaminant Candidate List (or CCL) and 

SDWA requires EPA to publish the list every five years. Two such lists have already been 

developed and were published in 1998 and 2005. The Act also requires “consultation with the 

scientific community, including the Science Advisory Board,” prior to publishing the CCL. 

SDWA also requires that EPA make determinations on whether to regulate at least five 

contaminants from the list with a national primary drinking water regulation (also on a five year 

cycle). 

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. 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 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 is comprised of members from the general public, State and local agencies, and private 

groups concerned with safe drinking water. It advises the Administrator on key aspects of the 

Agency’s drinking water program. NDWAC agreed that EPA should proceed with the NRC’s 

recommendations and provided some additional considerations, including the overarching 

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principles the Agency should follow. 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.” 

In October of 2006 EPA requested the public to nominate chemical and microbial 

contaminants that should be considered for CCL 3 in the Federal Register. The Agency 

compiled the information from the nominations process to identify the contaminants 

nominated, 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. Only 29 of the 174 

nominated contaminants were not already identified in the CCL process. Each of the 174 

nominated contaminants was then evaluated in the CCL process. 

Chemicals

EPA implemented a multi-step process (as shown in Exhibit 1) to develop the draft third CCL 

(CCL 3). The multi-step process includes the following primary phases: 

 Exhibit 1. Schematic of the CCL Approach 

Evaluation 

Expert Review 

Universe 

PCCL 

Proposed CCL 

Surveillance 

And 

 Nomination 

STEP 1 

Identifying the 

Universe

STEP 2 

Screening 

to a PCCL

STEP 3 

Selecting the 

CCL 

Step 1: Identifying the Universe. Building a broad CCL Universe of potential drinking water 

contaminants for consideration EPA identified and evaluated 39 data sources with information 

on contaminant health effects and occurrence. The resulting “CCL Universe of Chemicals” 

consisted of approximately 6,000 chemicals from these data sources. 

Step 2: Screening the Universe of Chemicals to a PCCL. EPA developed conservative criteria to 

screen chemicals with health effects and occurrence data elements at levels of concern in order to 

narrow the Chemical Universe to a Preliminary CCL (PCCL) of 532 chemicals. EPA used 

conservative criteria to narrow the universe and identify contaminants with greater potential to 

occur in drinking water and greater potential for public health concern for further evaluation. 

EPA selected form several data elements to represent a chemical’s potential to occur in drinking 

water and its potential to cause health effects on humans. 

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Step 3: Classifying the PCCL to Develop a Proposed. CCL. EPA further analyzed and prepared 

the PCCL chemicals for the classification approach and the development of the proposed CCL. 

EPA developed an approach for classifying potential drinking water contaminants that uses 

decision support tools to aid in the development of the CCL. EPA chose four attributes; Potency, 

Severity, Prevalence, and Magnitude, as its key factors in evaluating chemicals. EPA developed 

attribute scoring protocols to normalize the available data for the various types of available data. 

This relative assessment of contaminants used different data measures and defined scoring 

mechanisms for potential drinking water contaminants. The scores were then used as input for 

classification models calibrated using regulated contaminants. This approach ensured that 

attributes were used and applied consistently among potential contaminants. Using the structured 

classification approach (e.g., a classification model) as a tool, along with expert judgment, EPA 

evaluated the results from the classification models to select contaminants for the draft CCL. 

Microbial Pathogens

EPA’s approach in establishing the draft CCL3 builds on the NRC and NDWAC 

recommendation to generate, assess, and reduce a universe of microbial pathogens to formulate a 

subset of microorganisms that would constitute the CCL. The universe for CCL3 includes a 

survey of human pathogens published by Taylor et al. and pathogens nominated to EPA from the 

public Nominations process. Screening criteria are used to indicate the potential for waterborne 

transmission and identify microorganisms to move to the PCCL. A classification approach and 

tools along with expert judgment were used to evaluate the likelihood that specific microbial 

pathogens could occur in drinking water at levels and at frequencies that pose a public health 

risk. For example, all of the contaminants on the PCCL are assessed using attributes (e.g., 

waterborne disease outbreaks, occurrence, health effects) to characterize the potential for the 

microbial pathogen to occur in PWS, cause waterborne disease outbreaks and adverse health 

effects. The outcome of the detailed approach resulted in the microorganisms on the draft CCL 3. 

Past Reviews 

EPA convened several external expert panels at integral stages during the development of the 

Draft CCL 3. Five separate panels reviewed the draft chemical CCL 3 list, the microbial CCL 3 

list, and the processes used to develop them. EPA sought to convene panels that included 

members that had a variety of disciplines and expertise. Panel members were encouraged to 

provide comments based upon their expertise and background and provide comments as 

individuals, not as representatives of their respective organizational affiliations. The results from 

these panels are discussed in the Federal Register Notice and documented in the EPA Water 

Docket. 

Charge to Reviewers 

Review Draft CCL 3 and the specific chemicals and microbial pathogens on the list with a focus 

on the following questions: 

5. Please comment on whether the Federal Register Notice and support documents are clear, 

transparent, and adequate to provide an understanding of the overall processes and 

selection of contaminants for the draft CCL 3? 

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6. Please comment on whether the draft CCL 3 list represents those contaminants that have 

the highest potential to occur in public water systems and cause adverse human health 

effects? 

7. Please provide any data that may suggest that contaminants which are currently on the 

draft CCL3 list should not be listed? 

8. Please provide any data that may suggest that contaminants which are currently not on 

the draft CCL3 list should be listed?