UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON D.C. 20460
OFFICE OF THE ADMINISTRATOR
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,

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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.1
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
1 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://vosemite.epa.gov/sab/sabproduct.nsf/F6E197AC88A38CCD85257D49004D9EDC/$File/Rodewald Memorandum W
OUS+Rulc 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
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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, Bristol-
Myers Squibb, Princeton, NJ
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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, Tri-
Cities, 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
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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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