PHA United States	fnTnn*
Environmental Protection
Agency	December 2016
Fact Sheet: Draft Field-Based Methods for Developing
Aquatic Life Criteria for Specific Conductivity
Summary
EPA is soliciting public comments for 60 days on its
draft document, Field-Based Methods for Developing
Aquatic Life Criteria for Specific Conductivity (SC).
Elevated water salinity, or ionic concentration as
measured by SC has been shown to negatively
impact aquatic life in freshwaters. Once this
document is final, states and authorized tribes
located in any region of the country may use the
methods to develop field-based SC criteria for
adoption into water quality standards. The draft
methods are not a regulation and do not impose
legally binding requirements. The methods would
provide assistance to states in developing science-
based SC criteria that reflect ecoregional- or state-
specific factors such as background SCand ionic
composition. The draft methods underwent two
external peer reviews.
What is specific conductivity?
SC is a measure of a mixture of dissolved ions (salts)
in water. As ionic concentration increases, SC
increases. "Specific" conductivity indicates that a
measurement has been standardized to 25°C, a
reference temperature. Measuring SC in the field is
fast and inexpensive. Many state and federal water
resource programs routinely monitor SC in
freshwater systems.
How does elevated conductivity impact
freshwater organisms?
Increased levels of salts (as measured by SC) disrupt
the life cycle of freshwater organisms. Some
freshwater organisms can adjust to saltier waters,
but many are unable to cope with extreme ranges of
salinity. Water with high salt concentrations is toxic
to some stream organisms, changing the
composition and concentrations of salts in the body
that are necessary for tissues and organs to support
biological functions.
What causes elevated conductivity in
freshwater systems?
The sources of ions in streams and lakes may be
natural, reflecting soils and geology, or as the result
of human activities. Mixtures of ions that increase SC
are associated with multiple sources, including
discharge from wastewater treatment facilities,
surface mining, oil and gas exploration, runoff from
urban areas, and discharge of agricultural irrigation
return waters, among others. The two most common
ionic mixtures in streams are those dominated by
either chloride anions (CI") or those dominated by
bicarbonate (HCO3") plus sulfate (SO42") anions.
What is the basis for the draft field-based
methods?
EPA's draft methods are based on effects observed
in streams with different levels of SC and take into
account natural variation in background SC and the
aquatic species adapted to it. The draft document
describes how to derive protective field-based
aquatic life criteria for SC, including how to estimate
a criterion continuous concentration for chronic
exposures, how to estimate a maximum exposure
concentration protective of acute toxicity, and how
to assess geographic applicability and potential
confounding factors. The draft document also
includes information on SC criterion duration and
frequency and case studies that illustrate key
aspects of the methods.

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EPA's draft methods provide flexible approaches
that allow for consideration of natural variation in
ionic composition and concentration. Case studies
demonstrate key aspects of the methods and show
that protective criteria differ across the United
States and depend on background conductivity.
Among the documents EPA relied upon to develop
the draft methods are EPA's Guidelines for Deriving
Numerical National Water Quality Criteria for the
Protection of Aquatic Organisms and Their Uses (U.S.
EPA 1985) and the EPA document, A Field-Based
Aquatic Life Benchmark for Conductivity in Central
Appalachian Streams (U.S. EPA 2011a). The 2011
document, which was reviewed by EPA's Science
Advisory Board (U.S. EPA 2011b), used an extensive
field data set to estimate a numeric SC benchmark.
New analyses and approaches described in the
current draft methods document underwent
independent external peer review in 2014 and 2015.
How can I view the draft document and
supporting information?
EPA has established an official public docket for this
action under Docket ID No. EPA-HQ-OW-2016-0353,
accessed at www.regulations.gov. You may also
download the document and supporting information
from EPA's aquatic life criteria website at:
www.epa.gov/wqc/aquatic-life-ambient-water-
quality-criteria.
Where can I find more information?
Please email Colleen Flaherty at
flaherty.colleen@epa.gov.
References
U.S. EPA (Environmental Protection Agency) (1985)
Guidelines for deriving numeric National Water
Quality Criteria for the protection of aquatic
organisms and their uses. Washington, DC: Office of
Research and Development, Environmental Research
Laboratories. PB85-227049. Available online at:
http://www.epa.gov/sites/production/files/2016-
02/documents/guidel ines-water-quality-criteria.pdf.
U.S. EPA (Environmental Protection Agency). (2011a)
A field-based aquatic life benchmark for conductivity
in Central Appalachian streams. EPA/600/R-10/023F.
Washington, DC: Office of Research and
Development, National Center for Environmental
Assessment. Available online at:
https://cfpub.epa.gov/ncea/cfm/recordisplay.cfm7d
eid=233809
U.S. EPA (Environmental Protection Agency). (2011b)
Review of field-based aquatic life benchmark for
conductivity in Central Appalachian streams.
Washington, DC: Science Advisory Board, Office of
the Administrator. Available online at:
https://yosemite.epa.gOv/sab/sabproduct.nsf/0/EED
F20B88AD4C6388525785E007331F3/$File/EPA-SAB-
ll-006-unsigned.pdf.

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