United States
Environmental Protection
\r ^1 # %Agency
Office of Water
EPA 823-D-21-001
October 2021
Technical Support for Adopting and
Implementing EPA's 2016 Selenium Criterion in
Water Quality Standards
Draft

-------
Technical Support for Adopting and Implementing
EPA's 2016 Selenium Criterion in Water Quality
Standards
Draft
While this document cites statutes and regulations that contain requirements applicable to water
quality standards, it does not impose legally binding requirements on EPA, states, authorized
tribes, other regulatory authorities, or the regulated community, and may not apply to a
particular situation based upon the circumstances. EPA, state, tribal and other decision makers
retain the discretion to adopt approaches on a case-by-case basis that differ from those provided
in this technical support document as appropriate and consistent with statutory and regulatory
requirements. EPA may update this document as new information becomes available. In addition
to this document, EPA has related documents that provide considerations and recommendations
on implementing the national CWA section 304(a) recommended selenium criterion for
freshwater, which are available at EPA's selenium website: https://www. epa. sov wqc aquatic-
life-criterion-selenium.
1

-------
Table of Contents
1.0 Introduction	1
1.1	EPA's National CWA section 304(a) Recommended Chronic Aquatic Life Selenium
Criterion in Freshwater	1
1.2	Selenium Technical Support Materials	3
2.0 Adopting EPA's National CWA section 304(a) Recommended Selenium Criterion ... .4
2.1	The Four-Part Criterion	4
2.2	Options for Site-specific Water Column Criterion Elements	9
2.2.1	Adoption of Site-specific Water Column Criterion Elements through a
Performance-Based Approach	10
2.2.2	Adoption of Site-specific Water Column Criterion Elements Individually	12
2.3	Relationship of EPA's National CWA section 304(a) Recommended Selenium
Criterion to the Great Lakes Initiative	13
3.0 Options for Implementing EPA's Selenium Criterion	14
3.1	Site-specific Fish Tissue Criterion Elements	14
3.1.1	Site-specific Fish Tissue Criterion Elements Using the Species Recalculation
Procedure	14
3.1.2	Site-specific Fish Tissue Criterion Elements for Sites with Naturally Elevated
Selenium Levels	17
3.2	Water Quality Standards Variances	18
3.3	Revision to Designated Uses	19
3.4	Compliance Schedules	21
11

-------
List of Acronyms
BAF
Bioaccumulation factor
CFR
Code of Federal Regulations
CWA
Clean Water Act
EPA
Environmental Protection Agency
FR
Federal Register
GLI
Great Lakes Initiative
HAC
Highest attainable condition
NDPES
National Pollutant Discharge Elimination System
SSD
Species sensitivity distribution
TMDL
Total maximum daily load
UAA
Use attainability analysis
WQBELs
Water quality-based effluent limits
WQC
Water quality criteria
WQS
Water quality standards

-------
Definitions1
Water quality criterion element
A magnitude, frequency, and duration for a particular media type. The water quality criterion
elements for selenium are related through a hierarchy, with fish tissue criterion elements having
primacy over water column criterion elements, and the egg-ovary criterion element having
primacy over all other criterion elements.
Steady state
An organism is in steady state when the rates of chemical uptake and depuration are equal and
tissue concentrations remain constant over time.2 For the purposes of the national CWA section
304(a) recommended selenium criterion, steady state refers to conditions where sufficient time
has passed after the introduction of a new or increased discharge of selenium into a water body
so that fish tissue concentrations of selenium are no longer increasing.3
Performance-based approach
A water quality criterion that is a transparent process, such as a criterion derivation methodology,
rather than a specific outcome, such as a concentration of a pollutant. This process or
methodology is sufficiently detailed and has suitable safeguards that ensure predictable,
repeatable outcomes. Approval of this process or methodology would also serve for CWA
purposes as the approval of each outcome generated from following that process or method.4
Bioaccumulation
The uptake and retention of a chemical by an aquatic organism from all surrounding media (e.g.,
water, food, sediment).5
Dissolved total selenium
All species of selenium that are dissolved into the water column and that would be measured in a
water sample after it has been passed through a 0.45 |im membrane filter. 6
1	This glossary is meant to provide plain language definitions for key terms used in this document. Individuals
should consult the regulations to identify whether there are legal definitions of these terms.
2	USEPA. 2003. Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health
(2000) Volume 2: Development of National Bioaccumulation Factors. EPA-882-R-03-030. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
https://nepis.epa. gov/Exe/ZvPDF.cgi/P1005EZQ.PDF?Dockev=P 1005EZQ.PDF
3	USEPA. 2021. 2021 Revision to: Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater 2016.
EPA 822-R-21-006. U.S. Enviromnental Protection Agency, Office of Water, Washington DC.
https://www.epa.gov/sYStem/files/documents/2021-08/selenium-freshwater2016-2021-revision.pdf
4	EPA Review and Approval of State and Tribal Water Quality Standards 65 Fed. Reg. 24641 (Apr. 27, 2000)
5	USEPA. 2003. Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health
(2000) Volume 2: Development of National Bioaccumulation Factors. EPA-882-R-03-030. U.S. Environmental
Protection Agency, Office of Water, Washington, DC.
https://nepis.epa.gov/Exe/ZvPDF.cgi/P1005EZQ.PDF?Dockev=P 1005EZQ.PDF
6	Protho, M.G. USEPA. 1993. Memorandum: Office of Water Policy and Technical Guidance on Interpretation and
Implementation of Aquatic Life Metals Criteria. Office of Water, Washington DC.
https://www.epa.gov/sites/production/files/2019-03/documents/metals-criteria-interpret-aalife-memo.pdf
iv

-------
Site specific criterion/site specific criterion element
Water quality criterion/criterion element that is modified to reflect site-specific conditions. A
criterion/criterion element that is developed to protect aquatic life at a particular site, usually by
taking into account a site's physical, chemical, and/or biological conditions (i.e., water quality
characteristics or species composition).7
Critical species
In the context of the recalculation procedure, a resident species that (a) is commercially or
recreationally important at the site, or (b) is listed as threatened or endangered under section 4 of
the Endangered Species Act, or (c) is a species for which there is firm evidence that its loss
would yield an unacceptable impact on the site's commercially or recreationally important
species, endangered species, abundances of a variety of other species, or structure or function.8
7	USEPA. 2017. Water Quality Standards Handbook. Chapter 3: Water Quality Criteria. EPA-823-B-17-001. U.S.
Environmental Protection Agency, Office of Water, Washington, DC. https://www.epa.gov/sites/default/files/2014-
10/documents/handbook-chapter3 .pdf
8	USEPA. 2013. Revised Deletion Process for the Site-Specific Recalculation Procedure for Aquatic Life Criteria.
EPA 823-R-13-001. U.S. Environmental Protection Agency, Office of Water, Washington, DC,
www.epa.gov/sites/production/files/2015-08/documents/revised deletion process for the site-
specific recalculation procedure for aquatic life criteria.pdf.
v

-------
1.0 Introduction
1.1 EPA's National CWA section 304(a) Recommended Chronic
Aquatic Life Selenium Criterion in Freshwater
In 2016, the United States Environmental Protection Agency (EPA) updated its national Clean
Water Act (CWA) section 304(a) recommended chronic aquatic life criterion for selenium in
freshwater systems to reflect the latest scientific information. This information indicates that
toxicity to aquatic life is driven by dietary exposures and that the reproductive life-stages of egg-
laying vertebrates are the most sensitive to the toxic effects of selenium. The criterion has four
criterion elements: (1) a fish egg-ovary criterion element; (2) a fish whole-body and/or muscle
criterion element; (3) a water column criterion element (one value for lentic and one value for
lotic aquatic systems); and (4) a water column intermittent criterion element (to account for
potential chronic effects from short-term exposures to high concentrations in lentic and lotic
aquatic systems) (see Table 1). Under EPA's 2016 CWA section 304(a) recommended selenium
criterion the fish tissue criterion elements have primacy over water column elements, except
where there are no fish, where fish tissue data do not meet state or tribal quality assurance
procedures, or for water bodies with new discharges where selenium concentrations in fish tissue
might not have stabilized. EPA also recommends that the egg-ovary tissue criterion element has
primacy over whole-body and muscle tissue criterion elements.
Toxicity data indicate that the selenium concentration in fish eggs and ovaries is the most robust
and consistent measurement endpoint directly tied to adverse reproductive effects in aquatic
organisms. Toxicity to developing embryos and larvae is directly linked to egg selenium
concentration.9 EPA derived the whole-body, muscle tissue, and water column elements from the
egg-ovary element so that states and authorized tribes could more readily implement water
quality criteria (WQC) based on EPA's national CWA section 304(a) recommended selenium
criterion. The assessment of the available data on chronic selenium exposure for fish,
invertebrates, and amphibians indicates that a criterion element derived from fish is expected to
be protective of the aquatic community, since other taxa appear to be less sensitive to selenium
than fish. EPA did not develop an acute criterion for selenium when it updated the chronic
criterion because although selenium may cause acute toxicity at high concentrations, the most
deleterious effects on aquatic organisms are due to selenium's bioaccumulative properties. The
chronic effects of bioaccumulated selenium occur at lower concentrations than acute effects.
In the case of bioaccumulative compounds like selenium, acute toxicity studies do not address
risks that result from chronic exposure to chemicals via the diet (through the food web pathway).
Such studies also do not account for the accumulation kinetics of many bioaccumulative
compounds, such as selenium, and may underestimate effects from long-term accumulation in
9 USEPA. 2021. 2021 Revision to: Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater 2016.
EPA 822-R-21-006. U.S. Environmental Protection Agency, Office of Water, Washington DC.
https://www.epa.gov/svstem/files/documents/2021-08/selenium-freshwater2016-2Q21-revision.pdf
1

-------
some types of aquatic systems. As described in EPA's 2021 Revision to: Aquatic Life Ambient
Water Quality Criterion for Selenium-Freshwater 2016 (hereafter referred to as Aquatic Life
Ambient Water Quality Criterion for Selenium-Freshwater 2016), EPA also included an
intermittent exposure criterion element to provide protection from the most significant effects of
selenium toxicity, reproductive toxicity, by protecting against selenium bioaccumulation in the
aquatic ecosystem resulting from short-term, high concentration exposure events.10 EPA
recommends, as stated in the Aquatic Life Ambient Water Quality Criterion for Selenium-
Freshwater 2016, that states and authorized tribes11 adopt into their water quality standards
(WQS) a selenium criterion that includes all four criterion elements.12 For more information see
EPA's Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater 2016, which can
be found at https://www.epa.gov/svstem/files/documents/2021-08/selenium-freshwater2016-
2021-revision.pdf
Table 1: Summary of the Recommended Freshwater Selenium Ambient Chronic Water
Quality Criterion for Protection of Aquatic Life.
Media Type
Fish Tissue1
Water Column4
Criterion
Element
Egg-ovary 2
Fish Whole-body
or Muscle3
Monthly
Average
Exposure
Intermittent Exposure5
Magnitude
15.1 mg/kg dry
weight
8.5 mg/kg dry
weight whole-
body
or
11.3 mg/kg dry
weight muscle
(skinless, boneless
fillet)
1.5 (ig/L in lentic
aquatic systems
3.1 (ig/L in lotic
aquatic systems
WQCmt =
WQC^o-fiay Cbkgrndi.^- f int.
f int
Duration
Instantaneous
measurement6
Instantaneous
measurement6
30 days
Number of days/month with an
elevated concentration
Frequency
Not to be
exceeded
Not to be exceeded
Not more than
once in three
years on average
Not more than once in three
years on average
1.	Fish tissue elements are expressed as steady-state.
2.	Egg-ovary supersedes any whole-body, muscle, or water column element when fish egg-ovary concentrations are measured,
except as noted in footnote 4 below.
111USEPA. 2021. 2021 Revision to: Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater 2016.
EPA 822-R-21-006. U.S. Environmental Protection Agency, Office of Water, Washington DC.
https://www.epa.gov/svstem/files/documents/2021-08/selenium-freshwater2016-2Q21-revision.pdf
11	Throughout this document and in the CWA. the term "states" means the fifty states, the District of Columbia, the
Commonwealth of Puerto Rico, the United States Virgin Islands, Guam, American Samoa, and the Commonwealth
of the Northern Mariana Islands. The term "authorized tribe" means those federally recognized Indian tribes with
authority to administer a CWA WQS program.
12	USEPA. 2021. 2021 Revision to: Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater 2016.
EPA 822-R-21-006. U.S. Enviromnental Protection Agency, Office of Water, Washington DC.
https://www.epa.gov/svstem/files/documents/2021-08/selenium-freshwater2016-2021-revision.pdf
2

-------
3.	Fish whole-body or muscle tissue supersedes water column element when both fish tissue and water concentrations are
measured, except as noted in footnote 4 below.
4.	Water column values are based on dissolved total selenium in water and are derived from fish tissue values via
bioaccumulation modeling. When selenium inputs are increasing, water column values are the applicable criterion element in
the absence of steady-state condition fish tissue data.
5.	Where WQC3o-day is the water column monthly element for either lentic or lotic waters; Cbkgmd is the average background
selenium concentration; and tint is the fraction of any 30-day period during which elevated selenium concentrations occur,
with fmt assigned a value >0.033 (corresponding to 1 day).
6.	Fish tissue data provide instantaneous point measurements that reflect integrative accumulation of selenium over time and
space in fish population(s) at a given site.
1.2 Selenium Technical Support Materials
EPA has prepared a four-volume set of documents to provide recommendations to states,
authorized tribes, and other agencies for implementing WQC based on the national CWA section
304(a) recommended selenium criterion.13 These four documents constitute the Technical
Support Materials for EPA's Aquatic Life Ambient Water Quality Criterion for Selenium-
Freshwater 2016.14 Each document of the set focuses on a specific aspect of implementation of
the national CWA section 304(a) recommended selenium criterion. Together, these four EPA
documents provide information that will assist states and authorized tribes with adopting WQC
based on EPA's CWA section 304(a) recommended selenium criterion and implementing it in
various CWA programs.
1)	Technical Support for Adopting and Implementing EPA's Selenium 2016 Criterion in
Water Quality Standards, Draft, provides recommendations for the adoption and
implementation of the national CWA section 304(a) recommended selenium criterion,
including the various flexibilities available to states and tribes using WQS tools.
2)	Technical Support for Fish Tissue Monitoring for Implementation of EPA's 2016 Selenium
Criterion, Draft: provides an overview on how to establish or enhance existing fish tissue
monitoring programs to facilitate implementation of the fish tissue-based criterion
elements in the national CWA section 304(a) recommended selenium criterion.
3)	Frequently Asked Questions: Implementing Water Quality Standards Based on EPA's
2016 Recommended Selenium Criterion in Clean Water Act Section 402 NPDES Permits,
Draft: is intended to help National Pollutant Discharge Elimination System (NPDES)
permit writers understand what permitting guidance (i.e., state or tribal implementation
procedures) may be appropriate to implement state and authorized tribal WQS based on
EPA's CWA section 304(a) recommended selenium criterion. This set of FAQs also
provides recommendations on how to establish water quality-based effluent limits
(WQBELs) in NPDES permits.
13	USEPA. 2021. 2021 Revision to: Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater 2016.
EPA 822-R-21-006. U.S. Environmental Protection Agency, Office of Water, Washington DC.
https://www.epa.gov/sYStem/files/documents/2021-08/selenium-freshwater2016-2021-revision.pdf
14	USEPA. 2021. 2021 Revision to: Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater 2016.
EPA 822-R-21-006. U.S. Enviromnental Protection Agency, Office of Water, Washington DC.
https://www.epa.gov/svstem/files/documents/2021-08/selenium-freshwater2016-2Q21-revision.pdf
3

-------
4) Frequently Asked Questions (FAOs): Implementing the 2016 Selenium Criterion in Clean
Water Act Sections 303(d) and 305(b) Assessment, Listing, and Total Maximum Daily
Load (TMDL) Programs, Draft, provides information on how to complete assessments,
list impaired waters, and develop TMDLs based on EPA approved WQS that adhere to
EPA's national CWA section 304(a) recommended selenium criterion, including all four
elements.
2.0	Adopting EPA's National CWA section 304(a) Recommended
Selenium Criterion
2.1	The Four-Part Criterion
As described in EPA's Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater
2016 (2021 selenium criterion document),15 EPA recommends that states and authorized tribes
adopt into their WQS one selenium criterion composed of four criterion elements: two fish tissue
criterion elements (i.e., egg-ovary and whole-body and/or muscle tissue) and two water column
criterion elements (i.e., 30-day average and intermittent exposure). EPA recommends that states
and authorized tribes clearly express all four criterion elements as a single criterion composed of
multiple parts. States and authorized tribes should clearly indicate that fish tissue criterion
elements supersede the water column criterion elements, and that the egg-ovary criterion element
supersedes all other criterion elements. Under EPA's recommended selenium criterion, this
hierarchy applies to all CWA implementation activities. The egg-ovary criterion element
supersedes all other criterion elements because it was derived directly from toxicity data and
served as the basis for deriving all the other criterion elements. This hierarchy should be
described in a state's or authorized tribe's WQS, either in footnotes accompanying the criterion
or as a narrative included with the criterion. EPA recommends using the footnotes provided with
the national CWA section 304(a) recommended selenium criterion (Table 1) to describe the
hierarchal structure, but the language may be modified as long as the hierarchy is appropriately
described. Including all four criterion elements of the selenium criterion in state or tribal WQS
ensures protection from excessive selenium when egg-ovary data are unavailable by allowing
application of the criterion using other fish tissue or water column data. Along with the four
criterion magnitude elements, EPA also recommends adopting the corresponding durations and
frequencies for each of the criterion elements.
The assessment of the available data for fish, invertebrates, and amphibians indicates that fish are
the most sensitive taxa to the impacts from selenium. As such, the criterion elements were
derived from fish toxicity values to be protective of the entire aquatic community, not solely fish
species. When all four criterion elements are applied together, they protect aquatic life from the
chronic effects of exposure to selenium in waters both inhabited by fish and not inhabited by fish
(i.e., fishless).
In addition to the four-part criterion, states or authorized tribes may want to adopt a method to
15 Ibid.
4

-------
derive site-specific water column criterion elements, referred to by EPA in 2000 as a
"performance-based approach". EPA first formalized the concept of a performance-based
approach for a WQS in the preamble of the rule EPA Review and Approval of State and Tribal
Water Quality Standards.16 Here EPA describes this approach as a WQS that is a transparent
process rather than a specific outcome. The state or authorized tribe can adopt a process, such as
a criterion derivation methodology, rather than a specific outcome, such as a concentration of a
pollutant. If a state or authorized tribe adopts a process or methodology that is sufficiently
detailed and has suitable safeguards that ensure predictable, repeatable outcomes, EPA can
approve that process as a WQS. This approval would also serve for CWA purposes as the
approval of each outcome generated from following that process or method. More information
about the performance-based approach and what information should be included in the method
can be found in section 2.2.1.
The national CWA section 304(a) recommended selenium criterion is a chronic criterion. EPA
no longer recommends an acute criterion for short-term ambient exposures because aquatic
organisms are exposed to selenium primarily through their diet. Selenium has the potential to
bioaccumulate in aquatic food webs, where it can continue to pose a risk even after short-term
elevations of the selenium concentration in the water column returns to ambient levels.
Therefore, in place of an acute criterion, EPA recommends an intermittent exposure criterion
element to provide protection from long-term chronic effects caused by short-term elevations of
selenium water column concentrations in aquatic systems.
Table 1, reproduced from the 2021 selenium criterion document, provides an example of how the
four-part criterion could be adopted into a state's or authorized tribe's WQS. EPA recommends
adopting this table (including the frequency and duration components) with all accompanying
footnotes.
Footnote 1 in Table 1 indicates that the fish tissue concentrations of the criterion are expressed as
steady-state. An organism is in steady-state when the rates of chemical uptake and depuration are
equal and tissue concentrations remain constant over time.17
Footnotes 2 and 3 in Table 1 describe the structure of the criterion and explain that the criterion
explicitly affirms the primacy of the whole-body and/or muscle tissue criterion element over the
water column criterion elements, and the egg-ovary criterion element over any other criterion
element. This means when assessing a water body in steady-state conditions against the national
CWA section 304(a) recommended selenium criterion, egg-ovary measurements are the ultimate
arbiter followed by whole-body and/or muscle tissue measurements, and lastly by water column
measurements (see Frequently Asked Questions (FAQs): Implementing the 2016 Selenium
16	EPA Review and Approval of State and Tribal Water Quality Standards 65 Fed. Reg. 24641 (Apr. 27, 2000)
17	USEPA. 2003. Methodology for Deriving Ambient Water Quality Criteria for the Protection of Human Health
(2000) Volume 2: Development ofNational Bio accumulation Factors. EPA-882-R-03-030. U.S. Environmental
Protection Agency, Office of Water, Washington, DC. pp. 1-4.
https://nepis.epa.gov/Exe/ZvPDF.cgi/P1005EZO.PDF?Dockev=P1005EZQ.PDF
5

-------
Criterion in Clean Water Act Sections 303(d) and 305(b) Assessment, Listing, and Total
Maximum Daily Load (TMDL) Programs, I)raft) n
Footnote 4 in Table 1 states that the water column criterion elements of the national CWA
section 304(a) recommended selenium criterion were derived from the egg-ovary criterion
element via mechanistic bioaccumulation modeling (Presser and Luoma 2010).19
Footnote 4 also indicates that when selenium inputs are increasing, the water column criterion
element is the applicable criterion element when steady-state fish tissue data is not available. In
this circumstance, fish tissue data do not fully represent potential effects of selenium on the
aquatic ecosystem, making the use of the water column criterion element more appropriate to
protect the entire aquatic ecosystem. For the purposes of the national CWA section 304(a)
recommended selenium criterion, steady-state refers to conditions where sufficient time has
passed after the introduction of a new or increased discharge of selenium into a water body so
that fish tissue concentrations of selenium are no longer increasing.20 For a fish tissue
measurement to be meaningful, the system from which the sample is taken should not be
experiencing recent new inputs of selenium. In EPA's Aquatic Life Ambient Water Quality
Criterion for Selenium-Freshwater 2016,21 "new inputs" are defined as new anthropogenic
activities resulting in the release of additional selenium into a lentic or lotic aquatic system. New
inputs do not refer to seasonal variability of selenium that occurs naturally within a system (e.g.
spring run-off events or precipitation-driven pulses). New inputs will likely result in a greater
concentration of selenium in the food web and a relatively slow increase in the selenium
concentration in fish tissue. Fish tissue data should not be utilized for implementation of the
criterion until after selenium concentrations in the fish have stopped increasing. Alternatively, if
selenium inputs are decreasing in a water body, the hierarchy of the criterion applies, and fish
tissue data should be used for implementation. Just as the concentrations of selenium increase in
fish tissue at a relatively slow pace, they also decrease at a relatively slow pace compared to
selenium concentrations in water. Selenium can be persistent in an ecosystem and it will take
more time for selenium concentrations to reduce in sediment and biota than it will in water.
18	USEPA. 2021. Frequently Asked Questions (FAOs): Implementing the 2016 Selenium Criterion in Clean Water
Act Sections 303(d) and 305(b) Assessment, Listing, and Total Maximum Daily Load (TMDL) Programs. Draft.
EPA 823-D-21-004. U.S. Environmental Protection Agency, Office of Water, Washington DC.
https://www.epa.gov/wac/aauatic-life-criterion-selenium
19	Presser, T.S. and S.N. Luoma. 2010. A methodology for ecosystem-scale modeling of selenium. Integrated
Environmental Assessment and Management. 6: 685-710.
Presser, T.S. and S.N. Luoma. 2010. Ecosystem-Scale Selenium Modeling in Support of Fish and Wildlife Criteria
Development for the San Francisco Bay-Delta Estuary, California. U.S. Geological Survey, Reston, Virginia.
211 This definition of steady-state applies to the national CWA section 304(a) recommended selenium criterion. It
does not apply to the discussion of steady-state modeling or conditions in the "Technical Support Document for
Water Quality-based Toxics Control" (EPA/505/2-90-001, March 1991).
21 USEPA. 2021. 2021 Revision to: Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater 2016.
EPA 822-R-21-006. U.S. Enviromnental Protection Agency, Office of Water, Washington, DC.
https://www.epa.gov/svstem/files/documents/2021-08/selenium-freshwater2016-2021-revision.pdf
6

-------
EPA estimates that the concentration of selenium in fish tissue will not reach steady-state for
several months in lotic systems and for longer time periods (e.g., two to three years) in lentic
systems. Achievement of steady-state in an aquatic system depends on the hydrodynamics of the
aquatic system (particularly reservoirs with multiple riverine inputs and controlled releases of
water into downstream water bodies), the location of the selenium input, and the particular food
web. EPA expects the time needed to achieve steady-state with new or increased selenium inputs
to be site-specific. Thus, when selenium concentrations are increasing, EPA recommends that
fish tissue criterion elements not take precedence over the water column criterion elements until
the aquatic system achieves steady-state. In the interim, EPA recommends sampling fish tissue
and water to gain a better understanding of the selenium bioaccumulation dynamics in a
receiving water and to determine when steady-state conditions have been reached.
One term in footnote 4, 'dissolved total selenium', may warrant further clarification. In this case,
'total selenium' refers to the combination of all species of selenium that are dissolved into the
water column and does not refer to the total recoverable form of selenium. Dissolved total
selenium is the selenium that would be measured in a water sample after it has been passed
through a 0.45 |im membrane filter.22 In other words, the criterion is for dissolved selenium in
total, not the individual species of selenium (e.g., selenite or selenate, individually).
Footnote 5 of Table 1 describes the equation and input parameters for the intermittent criterion
element. For more information, see section 3.3 of EPA's Aquatic Life Ambient Water Quality
Criterion for Selenium-Freshwater 2016 23
Footnote 6 of Table 1 explains the duration component of the fish tissue criterion elements.
These criterion elements were developed to protect aquatic populations from impacts caused by
selenium. Fish tissue data provide instantaneous point measurements that reflect integrative
accumulation of selenium over time and space in the fish at a given site.24 States and authorized
tribes have flexibility in how they interpret a discrete fish sample to represent a given species'
population at a site. Generally, fish tissue samples collected to calculate average tissue
concentrations for a species at a site are collected in one sampling event, or over a short time
interval due to logistical constraints and costs for obtaining samples. The Technical Support for
— Protho. M.G. U.S. Environmental Protection Agency. 1993. Memorandum: Office of Water Policy and Technical
Guidance on Interpretation and Implementation of Aquatic Life Metals Criteria. Office of Water, Washington DC.
https://www.epa.gov/sites/production/files/2019-03/documents/metals-criteria-interpret-aalife-memo.pdf
23	USEPA. 2021. 2021 Revision to: Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater 2016.
EPA 822-R-21-006. U.S. Environmental Protection Agency, Office of Water, Washington, DC.
https://www.epa.gov/svstem/files/documents/2021-08/selenium-freshwater2016-2021-revision.pdf
24	See the Technical Support for Fish Tissue Monitoring for Implementation of EPA's 2016 Selenium Criterion,
Draft for information on selection of sampling location and target species to assure appropriate representation of the
water body. Mobility and home range of a species should be considered when selecting a target species to assure
fish tissue is representative of selenium exposure at the sampling location.
7

-------
Fish Tissue Monitoring for Implementation of EPA's 2016 Selenium Criterion, Draft contains
additional information on sampling fish populations.25
The frequency component of the fish tissue criterion elements of the national CWA section
304(a) recommended selenium criterion differs from the typical "once-in-three years on average"
frequency of most water column criteria. Selenium is a bioaccumulative pollutant; therefore,
elevated levels of selenium in various ecological compartments (e.g., biota, surficial sediments)
require a long period of time to decrease. Therefore, the associated aquatic community requires a
long time to recover following reduction or removal of an elevated selenium exposure to a given
system. Thus, the typical frequency component is not appropriate for selenium in fish tissue, as
this could lead to sustained ecological impacts. Therefore, the recommended frequency for the
national CWA section 304(a) recommended selenium criterion is "not to be exceeded". For
additional information regarding duration and frequency, see sections 2.7.6 and 2.7.7 of Aquatic
Life Ambient Water Quality Criterion for Selenium-Freshwater 2016 26
If data for a particular criterion element is not available, the national CWA section 304(a)
recommended selenium criterion can be implemented with one of the other criterion elements,
according to the hierarchy of the criterion. For example, if fish tissue data are not available, but
water column data are, the criterion can be implemented using the water column criterion
element. This situation may occur for Ashless waters or when fish tissue data are not available
because they were not collected or did not meet state or tribal quality assurance procedures.
Fishless waters are defined as waters with insufficient instream habitat and/or flow to support a
population of any fish species on a continuing basis, or waters that once supported populations of
one or more fish species but no longer support fish (see the executive summary of EPA's Aquatic
Life Ambient Water Quality Criterion for Selenium-Freshwater 2016).21
States and authorized tribes also can develop, adopt, and submit for EPA approval, site-specific
criteria for individual sites (see sections 2.2 and 3.1 for information on options for developing
and adopting site-specific criteria). In addition, states and authorized tribes can develop a
methodology for deriving site-specific water column criterion elements for individual sites,
which can be adopted in addition to the four-part criterion and submitted to EPA for approval.
Once approved, this process can be followed to develop site-specific water column criterion
elements for state or tribal waters. Section 2.2.1 provides more information on the performance-
based approach. While EPA presents some methods for developing site-specific criteria in this
25	USEPA. 2021. Technical Support for Fish Tissue Monitoring for Implementation of EPA 's 2016 Selenium
Criterion. Draft. EPA-823-D-21-002. U.S. Environmental Protection Agency, Office of Water, Washington, DC.
https://www.epa.gov/wqc/aquatic-life-criterion-selenium
26	USEPA. 2021. 2021 Revision to: Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater 2016.
EPA 822-R-21-006. U.S. Enviromnental Protection Agency, Office of Water, Washington DC.
https://www.epa.gov/sYStem/files/documents/2021-08/selenium-freshwater2016-2021-revision.pdf
27	USEPA. 2021. 2021 Revision to: Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater 2016.
EPA 822-R-21-006. U.S. Enviromnental Protection Agency, Office of Water, Washington DC.
https://www.epa.gov/svstem/files/documents/2021-08/selenium-freshwater2016-2Q21-revision.pdf
8

-------
document and in the national CWA section 304(a) recommended selenium criterion document,
any method that is scientifically defensible may be used to develop site-specific criteria.
2.2 Options for Site-specific Water Column Criterion Elements
As stated above, EPA recommends that when states and authorized tribes adopt this criterion,
they adopt all four criterion elements, including the 30-day average water column criterion
element. The relationship between the concentration of selenium in the tissues of fish and the
concentration of selenium in the water column, however, can differ substantially between
different aquatic systems. The chemical form of selenium, species of fish, the species and
proportion of prey, and a variety of site-specific biogeochemical factors affect selenium
bioaccumulation and thus determine the allowable concentration of selenium in ambient water
that is protective of aquatic life. Because of the site-specific nature of this relationship, EPA
provides two methodologies for deriving site-specific water column criterion elements:
1)	The mechanistic modeling approach
2)	The empirical bioaccumulation factor (BAF) approach.
The mechanistic modeling approach uses scientific knowledge of the physical and chemical
processes underlying bioaccumulation to specifically model bioaccumulation and trophic transfer
through the food web, to establish a relationship between the concentrations of selenium in the
water column and the concentration of selenium in the tissue of aquatic organisms. The
mechanistic modeling approach uses site-specific models of trophic transfer of selenium through
aquatic food webs to translate the egg-ovary criterion element into an equivalent site-specific
water concentration. This approach was used by EPA to derive its default water column criterion
elements.28 Alternatively, the empirical bioaccumulation factor approach establishes a site-
specific relationship between water column selenium concentrations and fish tissue selenium
concentrations by measuring both matrices directly and using the ratio between them to
determine a site-specific water column criterion element. Both approaches are described in detail
in Appendix K of Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater
2016.29 Both methodologies provide acceptable approaches to translating the recommended fish
tissue criterion elements into site-specific water column criterion elements. In addition, a state or
authorized tribe can develop site-specific criteria using other methodologies as long as they are
scientifically defensible and protective of the applicable designated uses, pursuant to 40 Code of
Federal Regulations (CFR)131.11(b)(l)(iii). The proposed site-specific selenium criteria
developed by EPA for the San Francisco Bay and Delta in California are good examples of how
to properly derive site-specific water column criterion elements for selenium using the
28	Presser, T.S. and S.N. Luoma. 2010. A methodology for ecosystem-scale modeling of selenium. Integrated
Environmental Assessment and Management 6:685-710.
Presser, T.S. and S.N. Luoma. 2010. Ecosystem-Scale Selenium Modeling in Support of Fish and Wildlife Criteria
Development for the San Francisco Bav-Delta Estuarv, California. U.S. Geological Survey, Reston, Virginia.
29	Ibid.
9

-------
mechanistic modeling approach.30 These systems have food webs that are well understood and
there is a substantial amount of data available to appropriately define the dynamics of selenium
cycling and bioaccumulation in the system. This allowed for the appropriate parameters to be
utilized in the model to derive protective criteria. Note that the proposed criteria for the San
Francisco Bay and Delta were derived to protect aquatic life and aquatic-dependent wildlife (i.e.,
clam eating fish and birds) (as opposed to just aquatic life) and were greatly influenced by the
presence of an invasive clam species that efficiently accumulates selenium.31
There are two approaches to adopting and submitting site-specific selenium water column
criterion elements to EPA for review under section 303(c) of the CWA: states and authorized
tribes may adopt and submit a performance-based approach for deriving site-specific water
column criterion elements or they may adopt and submit individual water column criterion
elements each time they are derived. Both are described in more detail below. States and
authorized tribes should carefully consider the relative merits of each approach; some
considerations are discussed further in Frequently Asked Questions (FAOs): Implementing the
2016 Selenium Criterion in Clean Water Act Sections 303(d) and 305(b) Assessment, Listing,
and Total Maximum Daily Load (TMDL) Programs, Draft32 When developing a performance-
based approach or an individual site-specific criterion element, EPA recommends consulting
with your EPA regional office early and often during the process.
2.2.1 Adoption of Site-specific Water Column Criterion Elements
through a Performance-Based Approach
States and authorized tribes can choose to adopt into their WQS and submit to EPA a set of
procedures to translate the fish tissue criterion elements into site-specific water column criterion
elements. This is considered a performance-based approach to developing site-specific water
column criterion elements. Any translation procedure must be transparent, sufficiently detailed,
and include suitable safeguards to ensure repeatable, predictable outcomes. In addition, the
resulting water column criterion elements must protect the applicable designated use. Once EPA
approves the procedures of the performance-based approach consistent with CWA section
303(c), each resulting site-specific water column criterion element generated consistent with the
CWA effective performance-based approach does not need to be adopted into the states' or
authorized tribes' WQS regulations or individually approved by EPA under CWA section
303(c). By approving the performance-based approach as consistent with CWA section 303(c),
311USEPA. July 15, 2016. Water Quality Standards; Establishment of revised Numeric Criteria for Selenium for the
San Francisco Bay and Delta, State of California. 81 Fed. Reg. 46030, https://www.epa.gov/was-tech/water-qualitv-
standards-establisliment-revised-numeric-criteria-selenium-san-francisco-bav.
31	The site-specific nature of this effort results in components that likely will not be generally applicable. In addition
to the clam (prey) tissue criterion element and particulate water column criterion element, the criteria are not
hierarchical and are independently applicable.
32	USEPA. 2021. Frequently Asked Questions (FAQs): Implementing the 2016 Selenium Criterion in Clean Water
Act Sections 303(d) and 305(b) Assessment, Listing, and Total Maximum Daily Load (TMDL) Programs. Draft.
EPA-823-D-21-004. U.S. Enviromnental Protection Agency, Office of Water, Washington, DC.
https://www.epa.gov/wac/aauatic-life-criterion-selenium
10

-------
EPA is affirming that each resulting site-specific water column criterion element is scientifically
defensible and protective of the applicable designated use.
Importantly, for public transparency, EPA strongly recommends the state or authorized tribe
maintain a list of the resulting site-specific water column criterion elements and underlying data
used for their respective derivations on their publicly accessible website. EPA also encourages
states and authorized tribes to coordinate closely with EPA when developing a performance-
based approach and when conducting the first few studies to develop site-specific water column
criterion elements.
In Aquatic Life Ambient Water Quality Criterion for Selenium - Freshwater 2016, EPA provides
recommendations for site-specific water column translation procedures in Appendix K.33 The
procedures described in this appendix can be used as a starting point for developing a
performance-based approach to derive site-specific water column criterion elements. Appendix
K presents the general methods for conducting a site-specific water column translation by either
the mechanistic model approach or the BAF approach. In addition, it presents a number of
options for determining the values to use as input parameters in both of these methods. States or
authorized tribes should decide which of those options they will use for their performance-based
approach or describe in their WQS regulations under which circumstances each option will be
used. In addition to the general methods included in Appendix K, states and authorized tribes
should consider including additional methods in their performance-based approach that will help
to make the procedure more transparent and repeatable. These could include methods for: 1)
selecting sites and sampling locations within a site, 2) determining what aquatic species are
present at the site, 3) selecting target species, 4) selecting tissue type for sampling, 5) sampling
plans including spatial and temporal considerations at a site, whether individual or composite
samples will be collected, the total number of samples that will be collected per replicate, and the
number of replicates that will be collected, 6) extrapolating trophic transfer factors or conversion
factors from existing data, and 7) specifying how data will be processed and analyzed. States and
authorized tribes should also consider what level of protection will appropriately protect the
designated use of the water body, which will influence what percentile of the resulting data set
should be used for the final criterion value. States' and authorized tribes' methods for their
performance-based approaches should be clear and definitively state which methods will be
followed in particular situations. For example, a state's or authorized tribe's performance-based
approach should specifically address Ashless waters by either including a method specifically
designed to derive a site-specific water column criterion element for a Ashless water or
specifying that the performance-based approach cannot be used to derive a site-specific water
column criterion element for a fishless water. An example of a detailed performance-based
33 USEPA. 2021. 2021 Revision to: Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater 2016.
EPA 822-R-21-006. U.S. Environmental Protection Agency, Office of Water, Washington DC.
https://www.epa.gov/sYStem/files/documents/2021-08/selenium-freshwater2016-2021-revision.pdf
11

-------
approach is the Draft Translation of Selenium Tissue Criterion elements to Site-specific Water
Column Criterion Elements for California Version 1, August 8, 2018.34
If a state or authorized tribe chooses to adopt a performance-based approach, one method for
incorporation into their WQS regulations could be to add a footnote to the national CWA section
304(a) recommended selenium criterion table (Table 1) that references the document that
describes the state or authorized tribe's translation methodology, sampling plans, and data
analysis and then adopt the table with the added footnote into their WQS regulations. By doing
this in rule, the state or authorized tribe will have incorporated by reference their translation
procedure that is scientifically defensible, produces repeatable, predictable outcomes and results
in criterion elements that protect the applicable designated use.
2.2.2 Adoption of Site-specific Water Column Criterion Elements
Individually
States and authorized tribes can choose to adopt and submit to EPA site-specific water column
criterion elements each time they are derived using one of the methodologies described in
Appendix K or another scientifically defensible approach. These site-specific water column
criterion elements must protect the designated use and must be reviewed and approved by EPA
under CWA section 303(c) before they are applicable for CWA purposes, such as NPDES
permitting, waterbody assessment and listing, and TMDL development.
One instance where a state may want to develop a site-specific water column criterion element is
for fishless waters. A site-specific water column criterion element for a fishless water will need
to be protective of the aquatic community present in those waters and assure protection of
downstream designated uses. When deriving a site-specific water column criterion element for
fishless waters, it may be appropriate to use the mechanistic model35 to translate from either a
fish tissue criterion element or an invertebrate toxicity threshold. Fish tissue criterion elements
should be used to protect the whole aquatic community if fish populations were once supported
in that water body or for protection of fish downstream, depending on the type of water body
downstream and the fish present in that downstream water body. Invertebrate toxicity thresholds
may be appropriate if fish currently and historically have not used the water body. If using an
invertebrate toxicity threshold, state and authorized tribes would need to assure that the resulting
water column criterion element is protective of the uses in downstream water bodies. Currently
(October 2021) EPA is not aware of sufficient toxicity data on invertebrates for an invertebrate
toxicity threshold for selenium. However, as new toxicity data become available, this may be an
appropriate taxa to use for deriving site-specific water column criterion elements for fishless
34	USEPA. 2018. Draft Translation of Selenium Tissue Criterion elements to Site-specific Water Column Criterion
Elements for California Version 1, August 8, 2018. U.S. Enviromnental Protection Agency, Office of Water,
Washington, DC, https://www.epa.gov/sites/production/files/2018-12/documents/california selenium 2040-
af79 pba 20181121 508c .pdf
35	See Appendix K of EPA 2021 for a description of the mechanistic model. USEPA. 2021. 2021 Revision to:
Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater 2016. EPA 822-R-21-006. U.S.
Enviromnental Protection Agency, Office of Water, Washington, DC.
https://www.epa.gov/svstem/files/documents/2021-08/selenium-freshwater2016-2021-revision.pdf
12

-------
waters. Whichever approach is used, states and authorized tribes may also want to consider if the
site-specific water column criterion element is protective of aquatic-dependent oviparous
wildlife, particularly birds, that use the Ashless water as feeding grounds.
Another instance where EPA recommends developing a site-specific water column element is
when the ambient water column concentrations in a water body/waterbody segment are meeting
the national recommended water column criterion elements, but the fish tissue concentrations are
greater than the national recommended fish tissue criterion elements. In this situation the
elevated fish tissue concentrations indicate an impact on the aquatic system and indicate that a
water column criterion element lower than the national recommended water column criterion
element is needed to be protective of aquatic life.
States and authorized tribes should consider the tradeoffs associated with adopting individual
site-specific criterion elements versus adopting a performance-based approach to derive site-
specific water column criterion elements. The adoption and EPA approval of individual site-
specific water column criterion elements could potentially be simpler to apply in assessment,
CWA section 303(d) listing, and TMDL development, as well as in NPDES permit development
as the implementation can immediately proceed with the established criterion element value
rather than having the additional step of calculating the criterion element value using the
criterion derivation methodology. On the other hand, the performance-based approach provides
states and authorized tribes the flexibility to adaptively derive site-specific water column
criterion elements to account for the most up-to-date data and information for the site without
making it necessary for them to submit the site-specific water column criterion element to EPA
for review each time those criterion elements are derived. Under the performance-based
approach, stakeholders would have the opportunity to provide comments on the derivation
process (e.g., translator mechanisms and associated sampling plans, input parameters, and data
analysis methods) during the water quality standards adoption process under CWA section
303(c). However, comments on the resulting site-specific water column criterion elements
derived through the performance-based approach would be received in response to individual
actions through each of the implementing programs, such as during a public notice for an
NPDES permit. The performance-based approach would likely involve more coordination
among the implementation programs to ensure that they are aiming to achieve the same desired
condition in the water body.
2.3 Relationship of EPA's National CWA section 304(a) Recommended
Selenium Criterion to the Great Lakes Initiative
EPA's 304(a) recommendation for the freshwater selenium criterion does not supersede the
requirements applicable to the Great Lakes at Title 40 of the CFR Part 132. Those requirements,
known as the Great Lakes Water Quality Guidance (also known as the Great Lakes Initiative or
GLI), apply to all streams, rivers, lakes, and other bodies of water within the U.S. portion of the
Great Lakes drainage basin. For those waters, a state or authorized tribe must adopt requirements
(including WQC) that are consistent with (asprotective as) regulations EPA promulgated on
13

-------
March 23, 1995 (see 60 Federal Register (FR) 15366, March 23, 1995, and 40 CFR 132.1(b) and
132.4).
Under the Great Lakes system-specific regulations, if a state or authorized tribe adopts a revised
criterion for selenium, EPA in its review must determine if the new criterion is as protective as
the selenium chronic criterion (5 (J,g/L) promulgated in 40 CFR 132.6, Table 2, and whether all
binding implementation procedures are as protective as the GLI procedures (see 40 CFR
132.5(g)). EPA makes its approval/disapproval decisions on a case-by-case basis depending
upon the supporting information. However, EPA expects that GLI states and authorized tribes
would likely be able to demonstrate that the revised selenium criterion is as protective as the GLI
chronic criterion if they adopt the national CWA section 304(a) recommended selenium
criterion. If a state or authorized tribe uses a site-specific translation to derive site-specific water
column criterion elements for a particular water body, translated water concentrations could, in
some cases, be higher than the 5 [j,g/L promulgated in 40 CFR 132.6 and could, in other cases, be
lower, depending on local conditions. EPA expects that they generally would be considered as
protective as the GLI selenium criterion. Additionally, a site-specific water column criterion
element would take into account a broad range of factors, including local conditions, and would
include additional data and a more refined understanding of the mechanisms through which
selenium accumulates and causes toxicity at that site.
3.0	Options for Implementing EPA's Selenium Criterion
There is some flexibility available to states and authorized tribes when they adopt the national
CWA section 304(a) recommended selenium criterion. Options include deriving site-specific fish
tissue criterion elements, adopting WQS variances, revising designated uses, and granting
compliance schedules. This section describes how each option can fit within a state's or
authorized tribe's WQS adoption and implementation processes.
3.1	Site-specific Fish Tissue Criterion Elements
3.1.1 Site-specific Fish Tissue Criterion Elements Using the Species
Recalculation Procedure36
The WQS regulation at 40 CFR 131.1 l(b)(l)(ii) provides states and authorized tribes with the
opportunity to adopt WQC that are ".. .modified to reflect site-specific conditions." As with any
criterion, a site-specific criterion must protect the designated use, must be based on a sound
scientific rationale, and is subject to EPA review and approval or disapproval. One process that
can be used to modify a criterion to site-specific conditions is the recalculation procedure. The
36 USEPA. 2013. Revised Deletion Process for the Site-Specific Recalculation Procedure for Aquatic Life Criteria.
EPA 823-R-13-001. U.S. Environmental Protection Agency, Office of Water, Washington, DC,
www.epa.gov/sites/production/files/2015-08/documents/revised deletion process for the site-
specific recalculation procedure for aquatic life criteria.pdf.
14

-------
recalculation procedure is a process used to modify the taxonomic composition of the toxicity
dataset used for the species sensitivity distribution (SSD) upon which a site-specific criterion is
based, to better match the species assemblage that is expected to occur at the site. The
recalculation procedure creates a site-specific toxicity dataset (and corresponding SSD) that is
appropriate for deriving a site-specific aquatic life criterion by correcting, adding, and/or deleting
test results from the national toxicity dataset for the pollutant of concern based on the resident
species of the site. This procedure is intended to provide flexibility to states and authorized tribes
to derive site-specific criteria that best reflect the expected resident species at a site. The species
recalculation procedure may result in site-specific criteria that differ from national criteria
recommendations (i.e., concentrations that are higher or lower than national recommendations)
when there are demonstrated differences in sensitivity between the expected resident aquatic
species and those that were used to derive the national criteria recommendations.
Critical species also need to be taken into consideration when using the recalculation procedure.
A critical species is a resident species that (a) is commercially or recreationally important at the
site, or (b) is listed as threatened or endangered under section 4 of the Endangered Species Act
(states and authorized tribes may also want to consider species that are candidates for protection
under the Endangered Species Act as critical species), or (c) is a species for which there is firm
evidence that its loss would yield an unacceptable impact on the site's commercially or
recreationally important species, endangered species, abundances of a variety of other species, or
structure or function. The deletion process of the recalculation procedure should not be
undertaken unless toxicity data are available for at least one species in each class of aquatic
plants or animals that contains a critical species. For example, if the site has a salmonid that fits
the designation of a critical species, the Deletion Process should not be undertaken unless
toxicity data for a species in class teleostei are available (possibly via new testing). It is
important to note that species not present at the site but included in the national criterion
database may be surrogates for other species that are present the site but not included in the
national criterion database.
The 304(a) selenium criterion recommendation was developed by first deriving an egg-ovary
criterion element from egg-ovary toxicity data, and then deriving all other criterion elements
from that egg-ovary criterion element. A state or authorized tribe developing site-specific fish
tissue criterion elements using the recalculation procedure would likely start with deriving the
egg-ovary criterion element and then other fish-tissue criterion elements. States and authorized
tribes should also consider corresponding changes to the applicable water column criterion
elements. See section 2.2 for more information.
Note that a state or authorized tribe that wants to adopt EPA's national recommendations for the
fish tissue criterion elements, but is interested in developing site-specific water column values,
can proceed as described in section 2.2.
As with any criteria, states and authorized tribes using the recalculation procedure should ensure
that their site-specific criteria ".. .provide for the attainment and maintenance of the water quality
standards of downstream waters" (40 CFR 131.10(b)). This requirement can be met in a number
15

-------
of ways, including using a combination of water quality standards, such as criteria (numeric
criteria and/or narrative criteria) and general policies. Additional information about this
requirement can be found in Protection of Downstream Waters in Water Quality Standards:
Frequently Asked Questions 31 In addition, states and authorized tribes should consider how they
will demonstrate that a species that is being removed from the national dataset (or any species for
which that species might be a taxonomic surrogate) is not present at the site before selecting that
approach. For additional information on the procedure, see EPA's Revised Deletion Process for
the Site-Specific Recalculation Procedure for Aquatic Life Criteria,38 States and authorized
tribes that wish to develop site-specific fish tissue criterion elements based on the revised
deletion process should engage their EPA Regional office early in the process to ensure the
development of sound scientific analyses. The deletion process for site-specific criterion
development is not appropriate for a performance-based approach because different survey
techniques will be needed at different sites to determine which species are currently present.
When developing site-specific criterion elements, consideration should be given to what area is
defined as the site. In the general context of site-specific criteria, a "site" may be a state, region,
watershed, water body, or segment of a water body. The site-specific criterion must provide
adequate protection for the entire site, however the site is defined. For the recalculation
procedure, all species that occur at the site need to be considered when deciding what species, if
any, are to be deleted (or added) from (to) the dataset. Unique populations or less sensitive uses
within sites may justify a designation as a distinct site. If the site contains critical habitat for
endangered or threatened species, EPA will engage in interagency consultation (under the
Endangered Species Act Section 7(a)(2)) with either or both the United States Fish and Wildlife
Service and National Marine Fisheries Service during the review of the proposed site-specific
criterion to determine whether the approval of the site-specific criterion would be likely or not
likely to adversely affect the species and any designated critical habitat. EPA would consider the
potential effect of the action on the species as well as on the physical and biological features of
the critical habitat as well as how EPA's action on the site-specific criterion may affect water
quality required for the species within the critical habitat.
For additional information on site-specific WQC, see chapter 3 of EPA's Water Quality Standards
Handbook39
37	USEPA. 2014. Protection of Downstream Waters in Water Quality Standards: Frequently Asked Questions. EPA
820-F-14-001. U.S. Environmental Protection Agency, Office of Water, Washington, DC,
www.epa.gov/sites/production/files/2018-10/documents/protection-downstream-was-faas.pdf.
38	USEPA. 2013. Revised Deletion Process for the Site-Specific Recalculation Procedure for Aquatic Life Criteria.
EPA 823-R-13-001. U.S. Environmental Protection Agency, Office of Water, Washington, DC,
www.epa.gov/sites/production/files/2015-08/documents/revised deletion process for the site-
specific recalculation procedure for aquatic life criteria.pdf.
39	USEPA. 2017. Chapter 3: Water Quality Criteria in Water Quality Standards Handbook. EPA 823-B-17-001. U.S.
Enviromnental Protection Agency, Office of Water, Washington, DC,
https://www.epa.gov/sites/production/files/2014-10/documents/handbook-chapter3.pdf.
16

-------
3.1.2 Site-specific Fish Tissue Criterion Elements for Sites with
Naturally Elevated Selenium Levels
Natural conditions are generally associated with the condition of ecological integrity, defined as
the structure, composition, function or diversity of a habitat in the absence of human disturbance
or alteration.40 For some areas in the United States, selenium may be elevated in soils and water
bodies under natural conditions. States and authorized tribes have two options when addressing
areas that have naturally elevated selenium concentrations: (1) they may develop site-specific
criteria for water bodies in these locations (e.g., where the current aquatic life designated use is
appropriate) or (2) they may refine or subcategorize the aquatic life use for water bodies in these
areas and set new criteria to be protective of the modified use (See section 3.3 for more
information on the revision of designated uses). These are two separate pathways for
accomplishing the goal of setting appropriate criteria for these water bodies.
To set a site-specific criterion using a natural conditions justification, the state or authorized tribe
would need to demonstrate that the elevated levels of selenium are due to natural conditions and
that no anthropogenic activities (e.g., agriculture, mining, irrigation, coal or oil combustion) are
responsible for elevating selenium concentrations in the water body. In many areas where soils
are elevated in selenium, anthropogenic activities either release selenium or expose soils or rock
to weathering, which results in the release of additional selenium into the water column. When
an anthropogenic activity leads to greater release of selenium than natural weathering, a site-
specific criterion cannot be developed using the natural conditions justification.
When developing a site-specific criterion, the state or authorized tribe must identify the site
boundaries and temporal dynamics to which a natural background criterion applies (i.e., it is
important that such criteria are developed to maintain and protect the spatial and temporal
variation in selenium concentrations under natural conditions). If concentrations vary seasonally,
adoption of seasonal criteria may be appropriate. Where concentrations vary spatially, additional
water body segmentation may be appropriate. In cases where selenium is elevated due to both
natural conditions and anthropogenic activities, methods such as modeling (e.g., historical or
hydrologic modeling) or an examination of past paleolimnological studies may be considered as
an option for defining natural conditions.41 EPA's current national policy regarding the
40	Landres, P.B., P. Morgan, and F.J. Swanson. 1999. Overview of the use of natural variability concepts in
managing ecological systems. Ecological Applications 9(4): pp. 1179-1188.
Davies, S.P. and S.K. Jackson. 2006. The biological condition gradient: A descriptive model for interpreting change
in aquatic ecosystems. Ecological Applications 16(4): pp. 1251-1266.
41	Swetnam, T.W., C.D. Allen and J.L. Betancourt. 1999. Applied historical ecology: Using the past to manage for
the future. Ecological Applications 9(4): pp. 1189-1206.
Hughes, R.M., S.G. Paulsen, and J.L. Stoddard. 2000. EMAP-Surface waters: A multiassemblage, probability
survey of ecological integrity in the U.S.A. Hvdrobiologia 422/423: pp. 429-443.
Kilgour, B.W., and L.W. Stanfield. 2006. Hindcasting reference conditions in streams. American Fisheries Society
Symposium 48: pp. 623-639.
Herlihy, A.T., S.G. Paulsen, J. Van Sickle, J.L. Stoddard, C.P. Hawkins, andL.L. Yuan. 2008. Striving for
consistency in a national assessment: The challenges of applying a reference-condition approach at a continental
scale. Journal of the North American Benthological Society 27(4): pp. 860-877.
17

-------
establishment of site-specific criteria that reflect natural background recommends that interested
states and authorized tribes establish site-specific numeric aquatic life criteria by setting the
criteria values equal to natural background, where natural background is defined as due only to
non-anthropogenic sources (i.e., non-human-induced sources). As articulated in the 1997
memorandum: Establishing Site-Specific Aquatic Life Criteria Equal to Natural Background,42
EPA does not consider it appropriate to adjust criteria to authorize degradation that is a result of
anthropogenic disturbance.
When deriving site-specific fish tissue criterion elements, states and authorized tribes should
consider corresponding changes to the applicable water column criterion elements. See section
2.2 for more information.
3.2 Water Quality Standards Variances
A state or authorized tribe could consider a WQS variance if it determines that it is not feasible
to attain a newly adopted selenium criterion and associated designated use now, but it may be
attainable in the future. A WQS variance may also be considered if there is uncertainty about the
feasibility of meeting the designated use and criterion, but progress can be made by
implementing known controls and tracking environmental improvements. The WQS regulations
at 40 CFR 131.3(o) define a WOS variance as "a time-limited designated use and criterion for a
specific pollutant(s) or water quality parameter(s) that reflect the highest attainable condition
(HAC) during the term of the WQS variance." The WQS variance regulation at 40 CFR 131.14
ensures that incremental progress is made toward improving overall water quality, while not
allowing any lowering of the currently attained ambient water quality. This is accomplished by
establishing a HAC, which serves as the basis for deriving less-stringent NPDES permit limits
and requirements throughout the term of the WQS variance.43 Although less stringent than the
adopted criterion, the HAC still provides a target for incrementally improving water quality until
the applicable designated use and associated selenium criterion become attainable. It is important
to note that these permit limits and requirements are applicable only to the discharger(s),
pollutant(s)/parameter(s), and water body or waterbody segment(s) identified in the WQS
variance. All other applicable standards not specifically addressed by the EPA-approved WQS
variance would continue to apply.
A state or authorized tribe can choose to adopt a WQS variance that is applicable to a single
discharger, multiple dischargers, or an entire water body/waterbody segment. Because the
national CWA section 304(a) recommended selenium criterion is intended to protect aquatic life
(CWA section 101(a)(2)), the state or authorized tribe must provide supporting documentation
demonstrating that attaining the designated use and criterion is not feasible throughout the term
of the WQS variance because of one of the factors listed at 40 CFR 131.14(b)(2)(i)(A). Such a
42	Davies, T. U.S. Environmental Protection Agency. 1997. Memorandum: Establishing Site Specific Aquatic Life
Criteria Equal to Natural Background. Office of Water, Washington DC,
https://www.epa.gov/sites/production/files/2014-08/documents/naturalbackground-memo.pdf
43	WQS variances with a term greater than 5 years must be reevaluated at least every 5 years to determine whether
the HAC is more stringent than originally adopted. See 40 CFR 131.14 (b)(l)(v).
18

-------
demonstration, when combined with the other regulatory requirements of 40 CFR 131.14,
provide the framework for WQS variances as a water quality improvement tool. The regulations
at 40 CFR Part 132 apply to states and authorized tribes that regulate waters in or contributing to
waters of the Great Lakes System. If 40 CFR 131.14 and 40 CFR Part 132 overlap, the more
stringent regulation applies. WQS variances are considered new or revised WQS and, therefore,
must be reviewed and approved or disapproved by EPA to be in effect for CWA purposes.
To help states and authorized tribes in the process of adopting WQS variances, EPA has
developed various resources including a WQS variances website44, the WQS Variance Building
Tool,45 Checklist for Evaluating State Submission of Discharger-Specific Water Quality
Standards Variances,46 and several other resources available on the "Resources" tab of the WQS
Variance Building Tool. States and authorized tribes are encouraged to coordinate with EPA
throughout the WQS variance adoption process to strengthen their WQS variance submissions.
3.3 Revision to Designated Uses
The WQS regulation at 40 CFR 131.10(g) provides that states or authorized tribes may remove a
CWA section 101(a)(2) designated use which is not an existing use, as defined in 40 CFR
131.3(e), or establish subcategories of such use that requires less stringent criteria if the state or
authorized tribe can demonstrate that attaining the designated use is not feasible because of one
or more of the six factors listed in 40 CFR 131.10(g). Those factors are:
(1)	Naturally occurring pollutant concentrations prevent the attainment of the use; or
(2)	Natural, ephemeral, intermittent or low flow conditions or water levels prevent the
attainment of the use, unless these conditions may be compensated for by the
discharge of sufficient volume of effluent discharges without violating state water
conservation requirements to enable uses to be met; or
(3)	Human caused conditions or sources of pollution prevent the attainment of the use
and cannot be remedied or would cause more environmental damage to correct than
to leave in place; or
(4)	Dams, diversions or other types of hydrologic modifications preclude the attainment
of the use, and it is not feasible to restore the water body to its original condition or to
operate such modification in a way that would result in the attainment of the use; or
44	USEPA, Water Quality Standards Variance website, https://www.epa.gov/was-tech/water-qualitv-standards-
variances.
45	USEPA, Water Quality Standards Variance Building Tool, https://www.epa.gov/was-tech/water-qualitv-
standards-variance-building-tool
46	USEPA. 2016. Checklist for Evaluating State Submission of Discharger-Specific Water Quality Standards
Variances. U.S. Environmental Protection Agency, Office of Water. Washington, DC,
https://www.epa.gov/sites/production/files/2016-03/documents/checklist-evaluating-discharger-specific.pdf.
19

-------
(5)	Physical conditions related to the natural features of the water body, such as the lack
of a proper substrate, cover, flow, depth, pools, riffles, and the like, unrelated to water
quality, preclude attainment of aquatic life protection uses; or
(6)	Controls more stringent than those required by sections 301(b) and 306 of the Act
would result in substantial and widespread economic and social impact.
The state or authorized tribe would make such a demonstration through a use attainability
analysis (UAA), which is defined under 40 CFR 131.3(g) as "... a structured scientific
assessment of the factors affecting the attainment of the use which may include physical,
chemical, biological, and economic factors as described in 40 CFR 131.10(g)." A state must
conduct a UAA whenever (1) the state designates for the first time, or has previously designated
for a water body, uses that do not include the uses specified in section 101(a)(2) of the Act; or
(2) the state wishes to remove a designated use that is specified in section 101(a)(2) of the Act, to
remove a subcategory of such a use, or to designate a subcategory of such a use that requires a
criterion less stringent than previously applicable (40 CFR 131.10(j)). If a state or authorized
tribe adopts a new or revised WQS based on a required use attainability analysis, the state or
authorized tribe shall also adopt the highest attainable use, as defined in 40 CFR 131.3(m).47 The
WQS regulations also do not allow states and authorized tribes to remove any uses that are
existing uses. In addition, uses cannot be removed if they can be attained by implementing
effluent limits required under sections 301(b) and 306 of the Act and by implementing cost-
effective and reasonable best management practices for nonpoint source control.
For selenium, there are two particular circumstances where a use change may be appropriate for
a water body. The first is fishless waters. States or authorized tribes may want to recognize the
difference in aquatic communities in these waters by creating a subcategory of the aquatic life
designated use. When doing so, the state or authorized tribe should be sure that protections for
other forms of aquatic life, such as macroinvertebrates, are protected by the revised designated
use and associated criterion. If aquatic-dependent wildlife uses the water body, then the state or
authorized tribe may also want to set a selenium criterion for the protection of these species as
well. The second is water bodies located in areas where the selenium is naturally elevated in the
underlying geology and are thus particularly vulnerable to elevated selenium concentrations in
the water. Ambient selenium concentrations in these water bodies can be exacerbated by
anthropogenic activities. If the conditions in this circumstance are precluding attainment of the
designated use, a limited or modified aquatic life use may be more appropriate for these water
bodies. EPA's regulations at 40 CFR 131.10(g) provide factors related to natural and
anthropogenic conditions for states and authorized tribes to employ in a UAA to justify revising
the aquatic life use (see 40 CFR 131.10(j) for when a UAA is required). If the state or authorized
tribe can justify the aquatic life use change using at least one of the factors at 40 CFR 131.10(g),
47 40 CFR 131.3 (m) defines "highest attainable use" as the "... modified aquatic life, wildlife, or recreation use that
is both closest to the uses specified in section 101(a)(2) of the Act and attainable, based on the evaluation of the
factor(s) in §131.10(g) that preclude(s) attainment of the use and any other information or analyses that were used to
evaluate attainability."
20

-------
then the designated use the state or authorized tribe must adopt in place of the full aquatic life
use must be the highest attainable use for the water body, as required by 40 CFR 131.10(g).
For additional information on use changes and UAAs, see EPA's Water Quality Standards
Handbook,48 Additional information also is available at
http ://water. epa. gov/ scitech/ swguidance/ standards/uses/uaa/.
3.4 Compliance Schedules
If a state or authorized tribe's WQS include a provision authorizing the use of permit compliance
schedules, a compliance schedule can be included in a permit with water quality-based effluent
limits (WQBELs) for selenium. The NPDES permit regulations allow this if (1) the discharger
cannot immediately meet the new WQBEL, and requires time to install treatment technology or
implement other controls necessary to meet the new WQBEL, (2) the permitting authority (the
state in most cases, and EPA in some limited cases) determines that a compliance schedule is
appropriate in light of all the circumstances and, (3) the discharger is required to meet its final
selenium WQBEL as -soon-as-possible. See section 502(17) of the CWA for a definition of
schedules of compliance and 40 CFR 122.47 for more information about the schedules.
Compliance schedules in NPDES permits can be used to meet WQBELs based on WQS adopted
after July 1, 1977, if the state or authorized tribe has indicated clearly in its WQS or
implementing regulations that it intends to allow the use of permit compliance schedules.49 To
ensure that the compliance schedule is enforceable by the permitting authority, the schedule must
consist of a sequence of interim requirements, actions, or operations leading to compliance with
the CWA and its implementing regulations (40 CFR 122.2). If the schedule is longer than 1 year,
it must include annual interim requirements and dates for their achievement (40 CFR
122.47(a)(3)). Additionally, the permit must include a final WQBEL and a date for its
achievement. The decision to include a compliance schedule as well as the dates and interim
requirements must be supported by the administrative record. The permit fact sheet should
include justification for the compliance schedule being determined to be appropriate and why
the chosen time frame was deemed to be as soon as possible. For additional information on
compliance schedules, see section 9.1.3 of EPA's NPDES Permit Writers' Manual50 (September
2010, EPA-833-K-10-001, https://www.epa.gov/sites/production/files/2015-
09/documents/pwm 2010.pdf) and the memorandum from EPA's Office of Wastewater
48	USEPA. 2012. Chapter 2: Designation of Uses in Water Quality Standards Handbook. EPA 823-B-12-002. U.S.
Environmental Protection Agency, Office of Water, Washington, DC,
https://www.epa.gov/sites/production/files/2014-10/documents/handbook-chapter2.pdf.
49	40 CFR 131.15 states that: "If a State intends to authorize the use of schedules of compliance for water quality-
based effluent limits in NPDES permits, the State must adopt a permit compliance schedule authorizing provision.
Such authorizing provision is a water quality standard subject to EPA review and approval under section 303 of the
Act and must be consistent with sections 502(17) and 301(b)(1)(C) of the Act."
511 USEPA. 2010. NPDES Permit Writers' Manual. EPA 833-K-10-001. U.S. Enviromnental Protection Agency,
Office of Water, Washington, DC.
https://www.epa.gov/sites/production/files/2015-09/documents/pwm 2010.pdf.
21

-------
Management on compliance schedules for water quality-based effluent limitations in NPDES
permits dated May 10, 2007.51
51 Hanlon, J.A. U.S. Environmental Protection Agency. 2007. Memorandum: Compliance Schedules for Water
Quality-Based Effluent Limitations in NPDES Permits. Office of Water, Washington DC.
https://www3 .epa.gov/npdes/pubs/memo complianceschedules mav07.pdf
22

-------