UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C. 20460

OFFICE OF THE DMINISTRATOR

SCIENCE ADVISORY BOARD

September 30, 2014

EPA-SAB-14-007

The Honorable Gina McCarthy

Administrator

U.S. Environmental Protection Agency

1200 Pennsylvania Avenue, N.W.

Washington, D.C. 20460

Subject: Science Advisory Board (SAB) Consideration of the Adequacy of the Scientific and 

Technical Basis of the EPA’s Proposed Rule titled “Definition of Waters of the United 

States under the Clean Water Act”

Dear Administrator McCarthy:

As part of its statutory duties, the Science Advisory Board (SAB) may provide advice and comment to 

you on the adequacy of the scientific and technical basis of certain planned EPA actions. The 

Environmental Research, Development, and Demonstration Authorization Act of 1978 (ERDDAA) 

requires the agency to make available to the SAB proposed criteria documents, standards, limitations,

or regulations provided to any other Federal agency for formal review and comment, together with

relevant scientific and technical information on which the proposed action is based. The SAB may then

provide advice and comments on the adequacy of the scientific and technical basis of the proposed

action.

This letter documents the SAB’s activities related to the proposed rule “Definition of ‘Waters of the 

United States’ Under the Clean Water Act” released on March 25, 2014, and provides advice and 

comments related to that proposal. Briefly, the SAB finds that the available science provides an 

adequate scientific basis for the key components of the proposed rule. Although water bodies differ in 

degree of connectivity that affects the extent of influence they exert on downstream waters (i.e., they 

exist on a “connectivity gradient”), the available science supports the conclusion that the types of water 

bodies identified as waters of the United States in the proposed rule exert strong influence on the 

physical, chemical, and biological integrity of downstream waters. Additional comments regarding the 

Board’s major findings and recommendations to strengthen the science supporting the rule are provided 

below.

Background

In SAB deliberations leading to the letter sent to you on July 26, 2013, Science Advisory Board (SAB) 

Discussions about EPA Planned Actions in the Fall 2012 Unified (Regulatory) Agenda and their 

Supporting Science (EPA-SAB-14-003), the chartered SAB discussed the agency’s plan to propose the 

rule. The Board also discussed the EPA’s plan to use the EPA’s September 2013 draft report, 
Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific 

Evidence (connectivity synthesis document) to inform determinations in the rule. In those discussions, 

the chartered SAB highlighted the importance of the rulemaking and the need for SAB advice and 

comment on the adequacy of the science to support the rule.

An ad hoc panel of the SAB has completed a peer review of the EPA’s draft connectivity synthesis 

report. The SAB’s peer review report was approved on September 26, 2014, and is being finalized to 

send to you shortly. For that peer review, the agency did not ask the SAB to consider the adequacy of 

the science to support the proposed rule. Because this question was not considered during the peer 

review, I requested the panel members to comment on the scientific and technical basis of the EPA 

proposed rule. In response to my request, the SAB panel held public teleconferences on August 20 and 

21, 2014, (79 FR 40100-40101) to discuss this topic.

A Work Group of chartered SAB members considered comments provided by panel members, agency 

representatives, and the public on the adequacy of the science informing the proposed rule. This Work 

Group, chaired by Board member Dr. James Mihelcic, then took the lead in SAB deliberations on this 

topic at a public teleconference held on September 29, 2014, where the chartered Board discussed the 

advice and comments in this letter.

SAB Advice and comment on the science informing the proposed rule

The SAB finds that the available science provides an adequate scientific basis for key components of the 

proposed rule. The following comments summarize major points regarding the adequacy of the scientific 

and technical basis of the proposed action. The SAB also provides recommendations for strengthening 

the science informing the rule.

Tributaries

There is strong scientific evidence to support the EPA’s proposal to include all tributaries within the 

jurisdiction of the Clean Water Act. Tributaries, as a group, exert strong influence on the physical, 

chemical, and biological integrity of downstream waters, even though the degree of connectivity is a 

function of variation in the frequency, duration, magnitude, predictability, and consequences of physical, 

chemical and biological processes.

The Board advises the EPA to reconsider the definition of tributaries because not all tributaries have 

ordinary high water marks. An ordinary high water mark may be absent in ephemeral streams within 

arid and semi-arid environments or in low gradient landscapes where the flow of water is unlikely to 

cause an ordinary high water mark. The Board advises the agency to consider changing the wording in 

the definition to “bed, bank, and other evidence of flow.” In addition, tributaries are not typically 

defined to include lentic systems (e.g., lakes, ponds, wetlands). Thus, the EPA may want to consider

whether flow-through lentic systems should be included as adjacent waters and wetlands, rather than as 

tributaries.

Adjacent Waters and Wetlands

The available science supports the EPA’s proposal to include adjacent waters and wetlands as waters of 

the United States. This is because adjacent waters and wetlands have a strong influence on the physical, 

chemical, and biological integrity of navigable waters. Importantly, the available science supports 

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defining adjacency or determination of adjacency on the basis of functional relationships, not on how 

close an adjacent water is to a navigable water. The Board also notes that local shallow subsurface water 

sources and regional groundwater sources can strongly affect connectivity. Thus, the Board advises the 

EPA that adjacent waters and wetlands should not be defined solely on the basis of geographical 

proximity or distance to jurisdictional waters. The science also supports consideration of the temporal 

dimension of connectivity to define adjacent waters and wetlands. This is particularly important in arid 

systems with intermittent and ephemeral waters.

Other Waters

The scientific literature has established that “other waters” can influence downstream waters, 

particularly when considered in aggregate. Thus, it is appropriate to define “other waters” as waters of 

the United States on a case-by-case basis, either alone or in combination with similarly situated waters 

in the same region. As mentioned previously for adjacent waters, distance should not be the sole 

indicator used to evaluate the connection of “other waters” to jurisdictional waters.

There is also adequate scientific evidence to support a determination that certain subcategories and types 

of “other waters” in particular regions of the United States (e.g., Carolina and Delmarva Bays, Texas 

coastal prairie wetlands, prairie potholes, pocosins, western vernal pools) are similarly situated (i.e., they 

have a similar influence on the physical, chemical and biological integrity of downstream waters and are 

similarly situated on the landscape) and thus could be considered waters of the United States.

Furthermore, as the science continues to develop, other sets of wetlands may be identified as “similarly 

situated.” The Board notes, however, that the existing science does not support excluding groups of 

“other waters” or subcategories thereof.

Exclusions

The Clean Water Act exclusions of groundwater and certain other exclusions listed in the proposed rule

and the current regulation do not have scientific justification. For example, the Clean Water Act

excludes groundwater, including groundwater drained through subsurface drainage systems. The 

available science, however, shows that groundwater connections, particularly via shallow flow paths in 

unconfined aquifers, can be critical in supporting the hydrology and biogeochemical functions of 

wetlands and other waters. Groundwater also can connect waters and wetlands that have no visible 

surface connections.

The proposed rule identifies other exclusions not justified by science. There is, for example, a lack of 

scientific knowledge to determine whether ditches should be categorically excluded. Many ditches in the 

Midwest would be excluded under the proposed rule because they were excavated wholly in uplands,

drain only uplands, and have less than perennial flow. However, these ditches may drain areas that 

would be identified as wetlands under the Cowardin classification system and may provide certain 

ecosystem services. Although gullies, rills, and non-wetland swales are excluded by the rule, the 

proposed rule’s preamble notes that these features can be important conduits for moving water between 

jurisdictional waters, making them important with respect to hydrological and other forms of 

connectivity. Also, although excluded from jurisdiction under the proposed rule, artificial lakes or 

ponds, or reflection pools, created by excavation, diking, or construction can be directly connected to 

jurisdictional waters by groundwater, which may be shallow as well as deep groundwater in unconfined 

aquifers. It is also not clear in the proposed rule how engineered structures would be treated, especially 

given changes in technology, urbanization, or economic sectors. Some examples of such changes in 

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engineered structures include: (1) design of stormwater management systems that more closely mimic 

natural systems (i.e., low impact development technology); (2) demand for lower quality water sources 

that results in construction of desalination brine storage basins; (3) the impact of urbanization that has 

led to construction of artificial lakes and ponds that may have connections to downstream waters; (4) 

agricultural sectors that utilize aquaculture and rice paddies; and (5) expanding domestic energy 

production that results in construction of structures such as oil and gas tank basins and in-stream 

sediment ponds used to collect waste from surface coal mining.

Finally, the SAB has a specific recommendation for strengthening the presentation of the science 

informing this regulatory action. The SAB recommends that the EPA clarify in its general 

communications and in the preamble to the final rule that “significant nexus” is a legal term, not a 

scientific term.

Recommendations for next steps

In conclusion the SAB has determined that the available science, as summarized in the preamble to the 

proposed rule and the EPA technical document peer reviewed by the SAB, provides an adequate 

scientific and technical basis for the proposed rule. The Board has made several recommendations to 

strengthen definitions and reconsider exclusions in the proposal. For a more detailed summary of many 

of the points in this letter, please see the memorandum provided by the Chair of the SAB Panel for the 

Review of the EPA Water Body Connectivity Report.

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The SAB does not expect to provide further advice and comment on the scientific and technical basis for 

the proposed action at this time. We look forward to your response to our comments on the science 

supporting this important rulemaking.

On behalf of the SAB, I thank you for the opportunity to support the EPA through consideration of the 

science supporting this proposed action.

Sincerely,

/Signed/

Dr. David T. Allen, Chair

Science Advisory Board

Enclosure

1) Roster, EPA Science Advisory Board

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September 2, 2014, Memorandum from the Dr. Amanda Rodewald to Dr. David Allen, Comments to the chartered SAB on 

the Adequacy of the Scientific and Technical Basis of the Proposed Rule Titled “Definition of ‘Waters of the United States’ 

Under the Clean Water Act.” Available at 

http://yosemite.epa.gov/sab/sabproduct.nsf/F6E197AC88A38CCD85257D49004D9EDC/$File/Rodewald_Memorandum_W

OUS+Rule_9_2_14.pdf (last accessed 09/29/14).1

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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 

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.

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U.S. Environmental Protection Agency

Science Advisory Board

CHAIR

Dr. David T. Allen, Gertz Regents Professor of Chemical Engineering and the Director of the Center 

for Energy and Environmental Resources, The University of Texas, Austin, TX

MEMBERS

Dr. George Alexeeff, Director, Office of Environmental Health Hazard Assessment, California 

Environmental Protection Agency, Oakland, CA

Dr. Pedro Alvarez, Department Chair and George R. Brown Professor of Engineering, Department 

of Civil & Environmental Engineering, Rice University, Houston, TX

Dr. Joseph Arvai, Svare Chair in Applied Decision Research, Department of Geography, University 

of Calgary, Calgary, Alberta, Canada

Dr. Thomas Burbacher, Professor, Department of Environmental and Occupational Health 

Sciences, School of Public Health, University of Washington, Seattle, WA

Dr. Ingrid Burke, Director and Wyoming Excellence Chair, Haub School and Ruckelshaus Institute 

of Environment and Natural Resources, University of Wyoming, Laramie, WY

Dr. Edward T. Carney, Departmental Senior Science Leader and Director of Predictive Toxicology 

Center, Toxicology & Environmental Research and Consulting, The Dow Chemical Company, 

Midland, MI

Dr. Peter Chapman, Principal and Senior Environmental Scientist, Golder Associates Ltd, 

Vancouver, BC, Canada

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

Psychology, School of Natural Resources, University of Arizona, Tucson, AZ

Dr. George Daston, Victor Mills Society Research Fellow, Global Product Stewardship, The Procter 

& Gamble Company, Mason, OH

Dr. Costel Denson, Managing Member, Costech Technologies, LLC, Newark, DE

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

Lafayette, IN

Dr. Michael Dourson, President, Toxicology Excellence for Risk Assessment, Cincinnati, OH

ii
Dr. Joel Ducoste, Professor, Department of Civil, Construction, and Environmental Engineering, 

College of Engineering, North Carolina State University, Raleigh, NC

Dr. David A. Dzombak, Walter J. Blenko, Sr. University Professor and Head of Civil and 

Environmental Engineering , College of Engineering, Carnegie Mellon University, Pittsburgh, PA

Dr. T. Taylor Eighmy, Vice Chancellor for Research and Engagement, Office of Research, 

University of Tennessee, Knoxville, TN

Dr. Elaine M. Faustman, Professor and Director, Environmental and Occupational Health Sciences, 

University of Washington, Seattle, WA

Dr. R. William Field, Professor, Department of Occupational and Environmental Health, and 

Department of Epidemiology, College of Public Health, University of Iowa, Iowa City, IA

Dr. H. Christopher Frey, Distinguished University Professor, Department of Civil, Construction 

and Environmental Engineering, College of Engineering, North Carolina State University, Raleigh, 

NC

Dr. John P. Giesy, Professor and Canada Research Chair, Veterinary Biomedical Sciences and 

Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada

Dr. Steven Hamburg, Chief Scientist, Environmental Defense Fund, Boston, MA

Dr. Cynthia M. Harris, Director and Professor, Institute of Public Health, Florida A&M University, 

Tallahassee, FL

Dr. Robert J. Johnston, Director of the George Perkins Marsh Institute and Professor, Economics, 

Clark University, Worcester, MA

Dr. Kimberly L. Jones, Professor and Chair, Department of Civil Engineering, Howard University, 

Washington, DC

Dr. Catherine Karr, Associate Professor - Pediatrics and Environmental and Occupational Health 

Sciences and Director - NW Pediatric Environmental Health Specialty Unit, University of 

Washington, Seattle, WA

Dr. Madhu Khanna, Professor, Department of Agricultural and Consumer Economics, University of 

Illinois at Urbana-Champaign, Urbana, IL

Dr. Nancy K. Kim, Independent Consultant, Independent Consultant, Albany, NY

Dr. Francine Laden, Mark and Catherine Winkler Associate Professor of Environmental 

Epidemiology, Harvard School of Public Health, and Channing Division of Network Medicine, 

Brigham and Women's Hospital and Harvard Medical School, Boston, MA

Dr. Lois Lehman-McKeeman, Distinguished Research Fellow, Discovery Toxicology, BristolMyers Squibb, Princeton, NJ

iii
Dr. Cecil Lue-Hing, President, Cecil Lue-Hing & Assoc. Inc., Burr Ridge, IL

Dr. Elizabeth Matsui, Associate Professor, Pediatrics, School of Medicine, Johns Hopkins 

University, Baltimore, MD

Dr. Kristina D. Mena, Associate Professor, Epidemiology, Human Genetics, and Environmental 

Sciences, School of Public Health, University of Texas Health Science Center at Houston, El Paso, 

TX

Dr. Surabi Menon, Director of Research, ClimateWorks Foundation, San Francisco, CA

Dr. James R. Mihelcic, Professor, Civil and Environmental Engineering, University of South

Florida, Tampa, FL

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

School of Public Health, Emory University, Atlanta, GA

Dr. H. Keith Moo-Young, Chancellor, Office of Chancellor, Washington State University, TriCities, Richland, WA

Dr. Eileen Murphy, Director of Research Development, Office of Research and Economic 

Development, Rutgers University, Piscataway, NJ

Dr. James Opaluch, Professor and Chair, Department of Environmental and Natural Resource 

Economics, College of the Environment and Life Sciences, University of Rhode Island, Kingston, RI

Dr. Duncan Patten, Emeritus Professor, School of Life Sciences Arizona State University, Tempe, 

AZ

Dr. Martin Philbert, Dean and Professor, Environmental Health Sciences, School of Public Health, 

University of Michigan, Ann Arbor, MI

Mr. Richard L. Poirot, Air Quality Planning Chief, Air Quality and Climate Division, Vermont 

Department of Environmental Conservation, Montpelier, VT

Dr. Stephen Polasky, Fesler-Lampert Professor of Ecological/Environmental Economics, 

Department of Applied Economics, University of Minnesota, St. Paul, MN

Dr. Amanda Rodewald, Director of Conservation Science, Cornell Lab of Ornithology and 

Associate Professor, Department of Natural Resources, Department of Natural Resources, Cornell 

University, Ithaca, NY

Dr. James Sanders, Executive Director, Skidaway Institute of Oceanography, University of Georgia, 

Savannah, GA

Dr. William Schlesinger, President, Emeritus, Cary Institute of Ecosystem Studies, Millbrook, NY

iv
Dr. Gina Solomon, Deputy Secretary for Science and Health, Office of the Secretary, California 

Environmental Protection Agency, Sacramento, CA

Dr. Daniel O. Stram, Professor, Department of Preventive Medicine, Division of Biostatistics, 

University of Southern California, Los Angeles, CA

Dr. Peter S. Thorne, Professor and Head, Department of Occupational & Environmental Health 

Director, Environmental Health Sciences Research Center, University of Iowa, Iowa City, IA

Dr. Paige Tolbert, Professor and Chair, Department of Environmental Health, Rollins School of 

Public Health, Emory University, Atlanta, GA

Dr. Jeanne VanBriesen, Professor, Department of Civil and Environmental Engineering, Carnegie 

Mellon University, Pittsburgh, PA

Dr. John Vena, Professor and Founding Chair, Department of Public Health Sciences, Medical 

University of South Carolina, Charleston, SC

Dr. Peter J. Wilcoxen, Associate Professor, Economics and Public Administration, The Maxwell 

School, Syracuse University, Syracuse, NY

SCIENCE ADVISORY BOARD STAFF

Dr. Angela Nugent, Designated Federal Officer, U.S. Environmental Protection Agency, Science 

Advisory Board, Washington, DC

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