United States
Environmental Protection
\*^l m %Agency
Office of Water
EPA 820-F-16-010
September 2016
Technical Support for Adopting and Implementing
EPA's 2016 Selenium Criterion in Water Quality
Standards
Draft

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EPA Draft for Public Comment
Technical Support for Adopting and Implementing
EPA's 2016 Selenium Criterion in Water Quality
Standards
This document provides information on the adoption and implementation of the 2016 selenium
criterion. 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, tribes, other regulatory authorities, or the regulated community and its content might 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
fi'om those provided in this document as appropriate and consistent with statutory and
regulatory requirements. EPA could update this document as new information becomes
available. In addition to this document, EPA has other documents which provide considerations
and recommendations on implementing the selenium criterion and can be found at EPA's
selenium website: https://www.epa.sov/wqc/aquatic-Ufe-criterion-selemxm.
Table of Contents
Background	2
1.0 Adopting EPA's Selenium Criterion Recommendations	2
1.1	The Four-Part Criterion	2
1.2	Options for Site-specific Water Column Elements of the Criterion	6
1.2.1	Adoption of Site-specific Water Column Elements Individually	7
1.2.2	Adoption of Site-specific Water Column Elements through a Performance-Based
Approach	7
1.3	Relationship of EPA's 2016 Selenium Criterion to the Great Lakes Initiative	8
2.0 Options for Implementing EPA '.s Selenium Criterion	9
2.1	Site-specific Fish Tissue Criterion Elements Using the Species Recalculation Procedure	9
2.2	Variances	10
2.3	Revision to Designated Uses	11
2.4	Compliance Schedules	12
Appendix A: Example Criterion Table for States and Authorized Tribes Using the
Performance-based Approach	14
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Background
The U.S. Environmental Protection Agency (EPA) updated its national recommended chronic
aquatic life criterion for selenium in freshwater to reflect the latest scientific information, which
indicates that toxicity to aquatic life is driven by dietary exposures. The criterion has four
elements: (1) a fish egg-ovary element, (2) a fish whole-body and/or muscle element, (3) a water
column element (one value for lentic and one value for lotic aquatic systems), and (4) a water
column intermittent element to account for potential chronic effects from short-term exposures
(one value for lentic and one value for lotic aquatic systems). EPA's Aquatic Life Ambient Water
Quality Criterion for Selenium-Freshwater 2016 contains a recommendation that states and
authorized tribes1 adopt into their water quality standards (WQS) a selenium criterion that
includes all four elements.2
1.0	Adopting EPA's Selenium Criterion Recommendations
1.1	The Four-Part Criterion
As described in EPA's Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater
2016,3 the Agency recommends that states and authorized tribes adopt into WQS one selenium
criterion composed of four elements: two fish tissue elements (i.e., egg-ovary and whole-body
and/or muscle) and two water column elements (i.e., 30-day average and intermittent exposure).
EPA recommends that states and authorized tribes clearly express all four elements as a single
criterion composed of multiple parts and clearly indicate that the whole-body/muscle element
supersedes the two water column elements and that the egg-ovary element supersedes any other
element. The egg-ovary element supersedes all other elements because it was derived from
extensive toxicity data and served as the basis for deriving all the other elements. Including all
four elements of the selenium criterion in state or tribal WQS ensures protection from excessive
selenium when egg-ovary data are unavailable.
States and authorized tribes also can develop, adopt, and submit for EPA approval site-specific
criteria for individual sites (see section 1.2 for more information on options for developing and
adopting site-specific criteria).
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 might continue to pose a risk to fish after short-term
1	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.
2	USEPA (U.S. Enviromnental Protection Agency). 2016. Aquatic Life Ambient Water Quality Criterion for
Selenium-Freshwater 2016. EPA 822-R-16-006. U.S. Enviromnental Protection Agency, Office of Water,
Washington DC. https://www.epa.gov/wqc/aquatic-life-criterion-selenium-documents.
3	Ibid.
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elevated ambient levels return to normal. Therefore, EPA recommends an intermittent element to
provide protection from long-term chronic effects caused by short-term elevation of selenium in
aquatic systems.
For information on how to use the four-part criterion for the purposes of National Pollutant
Discharge Elimination System (NPDES) permitting and waterbody assessment, listing, and total
maximum daily load (TMDL) development, see Frequently Asked Questions (FAQs):
Implementing WOS that Include Elements Similar or Identical to EPA's 2016 Selenium Criterion
in Clean Water Act Section 402 NPDES Programs and 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, respectively.4 5
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-ovary2
Fish Whole-body
or Muscle3
Monthly Average
Exposure
Intermittent Exposure5
Magnitude
15.1 mg/kg dw
8.5 mg/kg dw
whole-body
or
11.3 mg/kg dw
muscle (skinless,
boneless filet)
1.5 (xg/L in lentic
aquatic systems
3.1 (xg/L in lotic
aquatic systems
WQCint =
WQC^q—day Cbkgrnd(\ fint)
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.
3.	Fish whole-body or muscle tissue supersedes water column element when both fish tissue and water concentrations are measured.
4.	Water column values are based on dissolved total selenium in water and are derived from fish tissue values via
bioaccumulation modeling. Water column values are the applicable criterion element in the absence of steady-state condition
fish tissue data.
5.	Where WQC3o-dayis the water column monthly element for either lentic or lotic waters; Cbkgmdis the average background
selenium concentration; and tint is the fraction of any 30-day period during which elevated selenium concentrations occur, with
fint 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.
4	USEPA (U.S. Environmental Protection Agency). 2016. Frequently Asked Questions (FAOs): Implementing WOS
that Include Elements Similar or Identical to EPA's 2016 Selenium Criterion in Clean Water Act Section 402 NPDES
Programs. U.S. Environmental Protection Agency, Office of Water, Washington DC.
5	USEPA (U.S. Enviromnental Protection Agency). 2016. 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. U.S. Enviromnental Protection Agency, Office of Water, Washington DC.
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EPA recommends that states and authorized tribes adopt all four elements of the criterion, as laid
out in Table 1, into their WQS. Footnote 1 indicates that, 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 2016,6 new inputs are defined as new activities resulting in the release of selenium
into a lentic or lotic aquatic system. 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
until the new selenium input achieves a quasi-steady-state balance in the aquatic system. 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., 2-3 years) in lentic systems.
Achievement of steady-state in an aquatic system also depends on the hydrodynamics of the
aquatic system (particularly reservoirs with multiple riverine inputs), 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, 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 and using site-specific
data to gain a better understanding of the selenium bioaccumulation dynamics in a receiving
water and to determine when steady-state conditions have been reached.
Footnotes 2 and 3 describe the structure of the criterion and explain that the criterion explicitly
affirms the primacy of the whole-body and/or muscle element over the water column elements,
and the egg-ovary element over any other element. This means when assessing a waterbody
against EPA's recommended criterion, egg-ovary measurements are the ultimate arbiter followed
by whole-body and/or muscle measurements, and lastly by water column measurements (see
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)1
Footnote 4 indicates that EPA's recommended water column elements were derived from the
egg-ovary element via mechanistic bioaccumulation modeling (Presser and Luoma 2010).8
Footnote 4 also indicates that, absent steady-state fish tissue data, the recommended water
column element should be used to implement the criterion. There are a few situations in which
6	USEPA (U.S. Environmental Protection Agency). 2016. Aquatic Life Ambient Water Quality Criterion for
Selenium-Freshwater 2016. EPA 822-R-16-006. U.S. Environmental Protection Agency, Office of Water,
Washington DC. https://www.epa.gov/wac/aauatic-life-criterion-selenium-documents.
7	USEPA (U.S. Enviromnental Protection Agency). 2016. 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. U.S. Enviromnental Protection Agency, Office of Water, Washington DC.
8	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.
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this might happen: (1) in Ashless waters, 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
20169), (2) in waters with new inputs of selenium where steady-state fish tissue data cannot not
be collected, or (3) when fish tissue data are not available because they were not collected or did
not meet state or tribal quality assurance procedures.
Footnote 5 describes the equation and input parameters for the intermittent element. For more
information, see section 3.3 of EPA's Aquatic Life Ambient Water Quality Criterion for
Selenium-Freshwater 2016.10
Footnote 6 explains the duration component of the fish tissue elements. These elements were
developed to protect fish 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. States and authorized tribes have flexibility in how they
interpret a discrete fish sample to represent a population. Generally fish collected to calculate
average tissue concentrations for 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
Fish Tissue Monitoring for Implementation of EPA's 2016 Selenium Criterion contains
additional information on sampling fish populations.11
The frequency component of the fish tissue elements of the selenium criterion differs from the
typical "once-in-three years on average" frequency of water column criteria. Selenium is a
bioaccumulative pollutant; therefore elevated levels in various ecological compartments
(e.g., biota, surficial sediments) require a long period to decrease, and 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 criteria return frequency is not
appropriate for selenium in fish tissue, as this could lead to sustained ecological impacts. 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 2016.12
9	USEPA (U.S. Environmental Protection Agency). 2016. Aquatic Life Ambient Water Quality Criterion for
Selenium-Freshwater 2016. EPA 822-R-16-006. U.S. Environmental Protection Agency, Office of Water,
Washington, DC. https://www.epa.gov/wqc/aquatic-life-criterion-selenium-documents.
10	Ibid.
11	USEPA (U.S. Enviromnental Protection Agency). 2016. Technical Support for Fish Tissue Monitoring for
Implementation of EPA's 2016 Selenium Criterion. U.S. Enviromnental Protection Agency, Office of Water,
Washington, DC.
12	USEPA (U.S. Enviromnental Protection Agency). 2016. Aquatic Life Ambient Water Quality Criterion for
Selenium-Freshwater 2016. EPA 822-R-16-006. U.S. Enviromnental Protection Agency, Office of Water,
Washington, DC. https://www.epa.gov/wac/aauatic-life-criterion-selenium-documents.
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1.2 Options for Site-specific Water Column Elements of the Criterion
As stated above, EPA recommends that when states and authorized tribes adopt this criterion,
they adopt all four elements, including the 30-day average water column element. The
relationship between the concentration of selenium in the tissues of fish and the concentration of
selenium in the water column, however, can vary substantially among aquatic systems. The
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 provided two methodologies for deriving site-specific water column
translations. One is the mechanistic model used by EPA to derive its default water column
criterion elements;13 the other uses an empirical bioaccumulation factor approach. Both are
described in detail in appendix K of Aquatic Life Ambient Water Quality Criterion for Selenium-
Freshwater 2016.14 Both methodologies provide acceptable approaches to translating the
recommended fish tissue criterion elements into site-specific water column criterion elements.
The site-specific selenium criteria developed by EPA for the San Francisco Bay and Delta in
California are a good example of how to properly derive site-specific water column elements for
selenium.15 Note that the criteria for the San Francisco Bay and Delta were derived to protect
aquatic dependent wildlife and aquatic life (i.e., clam eating fish and birds) and were greatly
influenced by the presence of an invasive clam species that efficiently accumulates selenium.16
There are two approaches to adopting and submitting any site-specific selenium criterion
elements to EPA: states and authorized tribes may adopt and submit individual criterion elements
each time they are derived, or they may adopt and submit a performance-based approach to site-
specific criterion element derivation. Both are described more fully below. States and authorized
tribes should carefully consider the relative merits of each approach; some considerations are
discussed further in 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.17
13	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. Ecosvstem-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.
14	Ibid.
15	https://www.epa.gov/was-teclVwater-aualitv-standards-establisliment-revised-numeric-criteria-selenium-san-
francisco-bav (81 FR 46042, July 15, 2016)
16	The site-specific nature of this effort results in components that likely will not be generally applicable. In addition
to the clam (prey) tissue element and particulate water column element, the criterion elements are not hierarchical
and are independently applicable.
17	USEPA (U.S. Enviromnental Protection Agency). 2016. 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. U.S. Enviromnental Protection Agency, Office of Water, Washington DC.
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1.2.1	Adoption of Site-specific Water Column Elements Individually
States and authorized tribes can 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 before they are
applicable for Clean Water Act (CWA) purposes, such as NPDES permitting, waterbody
assessment and listing, and TMDL development.
1.2.2	Adoption of Site-specific Water Column 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 facilitate the translation of the fish tissue criterion concentration elements into site-
specific water concentration values. This is considered a performance-based approach to
developing site-specific criteria. Any translation procedure must be sufficiently detailed and
include suitable safeguards to ensure repeatable, predictable outcomes; and result in criterion
element values that protect the applicable designated use. Once the state or authorized tribe
adopts and EPA approves such a set of procedures, however, each resulting site-specific criterion
does not need to be adopted or approved. Importantly, for public transparency, the state or
authorized tribe should maintain a list of the resulting site-specific criteria 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 a site-specific water column element.
If a state or authorized tribe chooses to adopt a performance-based approach, one method for
incorporation into their standards could be to add a footnote to EPA's 2016 selenium criterion
table (Table 1) and then adopt the table into their standards. By doing this, the state or tribe will
have referenced in rule a translation procedure that is scientifically defensible; produces
repeatable, predictable outcomes; and results in criterion element values that protect the
applicable designated use.
As an example, the footnote could say:
Site-specific water column criteria elements will be derived using the mechanistic model
and associated procedures laid out in appendix K of Aquatic Life Ambient Water Quality
Criterion for Selenium-Freshwater 2016.18 To derive scientifically defensible site-
specific water column criteria elements, appropriate input parameters (as described in
Appendix K) will be selected to adequately represent the water body of interest.
See appendix A for an example criterion table that could be used to incorporate a performance-
based approach. A state or authorized tribe might want to include both translation procedures in
their performance-based approach but should specify in what circumstances they would use one
or the other.
18 Ibid.
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States and authorized tribes should consider the tradeoffs associated with these different
approaches to site-specific water column element derivation. The adoption and EPA approval of
individual site-specific water column elements could potentially be easier to apply in assessment,
listing, and TMDL development, as well as NPDES permit development.
On the other hand, the performance-based approach provides states and authorized tribes the
flexibility to adaptively derive site-specific water column targets to account for the most up-to-
date data and information for the site without making it necessary for states and authorized tribes
to adopt and for EPA to approve site-specific criteria elements each time those elements are
derived. Under the performance-based approach, stakeholders would have the opportunity to
provide comments on the derivation process (e.g., translator mechanisms) during the water
quality standards adoption process under section 303(c). However, comments on the site-specific
water column elements derived through the performance-based approach would be received in
response to individual actions through each of the implementing programs. The performance-
based approach likely involves more coordination among the implementation programs to ensure
that they are aiming to achieve the same desired condition in the water body.
EPA discussed the performance-based approach to setting water quality standards at EPA Review
and Approval of State and Tribal Water Quality Standards, 65 Fed. Reg. 24641, at 24648 (Apr.
27, 2000).
1.3 Relationship of EPA's 2016 Selenium Criterion to the Great Lakes Initiative
EPA's recommendations for the freshwater selenium criterion do not supersede the requirements
applicable to the Great Lakes at Title 40 of the Code for Federal Regulations (CFR) Part 132.
Those requirements, known as the Great Lakes Initiative (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 water quality criteria
[WQC]) that are consistent with (asprotective as) regulations EPA promulgated on March 23,
1995 (see 60 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 EPA recommended 304(a) selenium criterion. If a state or
authorized tribe uses a site-specific translation to derive site-specific water column elements for
a particular waterbody, 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 element would take into account a
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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.
2.0	Options for Implementing EPA's Selenium Criterion
There is some flexibility available to states and authorized tribes when they adopt EPA's 2016
selenium criterion. Options include deriving site-specific fish tissue criterion elements, adopting
WQS variances, revising designated uses, providing for dilution allowances, and granting
compliance schedules. This document describes how each option can fit within a state's or
authorized tribe's WQS adoption and implementation processes.
2.1	Site-specific Fish Tissue Criterion Elements Using the Species Recalculation
Procedure
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. The species
recalculation procedure for deriving site-specific criteria is intended to allow site-specific criteria
to 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 aquatic species that occur at the site and those that were used to derive the national criteria
recommendations. The national dataset might contain aquatic species that are sensitive to a
particular pollutant, but those or comparably sensitive species might not occur at the site. On the
other hand, a species that is critical at the site might be sensitive to the pollutant and require site-
specific criteria that are lower than the national recommended criteria. Because the selenium
criterion is derived based on egg-ovary toxicity data that form the basis for all other criterion
elements, a state or authorized tribe developing site-specific fish tissue elements of the criterion
using the recalculation procedure would likely start with deriving the egg-ovary element and
then other fish-tissue or related water column elements. 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 may not be in the database.
Note that a state or authorized tribe that wants to adopt EPA's national recommendations for the
fish tissue elements, but is interested in developing site-specific water column values, can
proceed as described in section 1.2.
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)). In addition, they should consider how
they will demonstrate that the species (or any species for which the sensitive species might be a
surrogate) is not present at the site before selecting that approach. For additional information on
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the procedure, see EPA's Revised Deletion Process for the Site-Specific Recalculation Procedure
for Aquatic Life Criteria.19
For additional information on site-specific WQC, see EPA's Water Quality Standards
Handbook20
2.2 Variances
States or authorized tribes that determine it is not feasible to attain a newly adopted selenium
criterion and associated designated use should consider using a WQS variance before they
consider revising the designated use (described in section 3) for the affected waterbody. 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 during the term of the WQS variance." WQS variances (regulated at 40 CFR
131.14) ensure that progress is made toward improving overall water quality, while ensuring that
the conditions of the WQS variance do not lower already-attained ambient water quality. This is
accomplished by establishing a highest attainable condition, which serves as the applicable WQS
for implementing NPDES permit limits and requirements throughout the term of the WQS
variance. Although less stringent than the newly adopted criterion, the highest attainable
condition provides a mechanism for incremental progress toward improving water quality and
potentially attaining the designated use and associated criterion in the future. It is important to
note that these permit limits and requirements are applicable only to the discharger(s),
pollutant(s)/parameter(s), and waterbody or waterbody segment(s) identified in the WQS
variance. All other applicable standards not specifically addressed by the WQS variance 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 waterbody/waterbody segment. Because EPA's
2016 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 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 provide
guidance for states and authorized tribes that regulate waters in or contributing to waters of the
Great Lakes System. If the two regulations overlap, the more stringent regulation applies.
19 USEPA (U.S. Environmental Protection Agency). 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.
211 USEPA (U.S. Enviromnental Protection Agency). 1994. Water Quality Criteria. Chapter 3 in Water Quality
Standards Handbook. EPA 823-B-94-005a. U.S. Enviromnental Protection Agency, Office of Water, Washington
DC. http://www.epa.gov/washandbook.
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To help states and authorized tribes in the process of adopting WQS variances, EPA has
developed various support documents such as Checklist For Evaluating State Submission Of
Discharger-Specific Water Quality Standards Variances21 and Developing Credible Rationales
for Variances that Apply to Multiple Dischargers—Frequently Asked Questions.22 WQS
variances are considered new or revised WQS and, therefore, must be reviewed and approved or
disapproved by EPA. For this reason, states and authorized tribes are encouraged to coordinate
with EPA throughout the WQS variance adoption process to reinforce their WQS variance
submissions.
2.3 Revision to Designated Uses
The WQS regulation at 40 CFR 131.10(g) provides that:
[sjtates may designate a use, or remove a use that is not an existing use, if the State
conducts a use attainability analysis as specified... that demonstrates attaining the use is
not feasible because of one of the six factors in this paragraph. If a State adopts a new or
revised water quality standard based on a required use attainability analysis, the State
shall also adopt the highest attainable use, as defined in §131.3(m).
(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 waterbody to its original condition or to
operate such modification in a way that would result in the attainment of the use; or
21	USEPA (U.S. Environmental Protection Agency). 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.
22	USEPA (U.S. Enviromnental Protection Agency). 2016. Discharger-specific Variances on a Broader Scale:
De\>eloping Credible Rationales for Variances that Apply to Multiple Dischargers—Frequently Asked Questions.
EPA-820-F-13-012. U.S. Enviromnental Protection Agency, Office of Water, Washington DC.
https://nepis.epa. gov/Exe/ZvPDF.cgi/P100IRYU.PDF?Dockev=P 100IRYU.PDF.
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(5)	Physical conditions related to the natural features of the waterbody, 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 waterbody, 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)).
While the WQS regulation allows states and authorized tribes to remove uses that are not
feasible to attain, it does not allow states or authorized tribes to remove uses that are feasible to
attain. Therefore, states and authorized tribes must retain/adopt such feasible uses (i.e., the
highest attainable use) in their state WQS (40 CFR 131.10(g) and (h)).
For additional information on use changes and UAAs, see EPA's Water Quality Standards
Handbook,23 Additional information also is available at
http://water.epa. gov/ scitech/ swguidance/ standards/uses/uaa/.
2.4 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 WQBELs for selenium. The
NPDES permit regulations allow this if (1) the discharger requires time to install treatment
technology or implement other controls necessary to meet the new WQBELs and (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 that the discharger can
ultimately meet its new selenium WQBELs by an as-soon-as-possible date certain in the future.
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.
23 USEPA (U.S. Environmental Protection Agency). 1994. Designation of Uses. Chapter 2 in Water Quality
Standards Handbook. EPA 823-B-94-005a. U.S. Environmental Protection Agency, Office of Water, Washington
DC. http://www.epa.gov/wqshandbook.
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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.24 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 all of 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' Manual25 (September
2010, EPA-833-K-10-001, http://www.epa.gov/npdes/pwmanual) and the memorandum from
EPA's Office of Wastewater Management on compliance schedules for water quality-based
effluent limitations in NPDES permits dated May 10, 2007.
24	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."
25	USEPA (U.S. Enviromnental Protection Agency). 2010. NPDES Permit Writers' Manual. EPA 833-K-10-001.
U.S. Enviromnental Protection Agency, Office of Water, Washington DC.
https://www.epa.gov/npdes/npdes-pennit-writers-manual.
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Appendix A: Example Criterion Table for States and Authorized Tribes
Using the Performance-based Approach
Media Type
Fish Tissue1
Water Column4'7
Criterion
Element
Egg-ovary 2
Fish Whole-body
or Muscle3
Monthly Average
Exposure
Intermittent Exposure5
Magnitude
15.1 mg/kg dw
8.5 mg/kg dw
whole-body
or
11.3 mg/kg dw
muscle (skinless,
boneless filet)
1.5 (xg/L in lentic
aquatic systems
3.1 (xg/L in lotic
aquatic systems
WQCint =
WQC^q—fay ^bkgrnd(^~ fint)
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.
3.	Fish whole-body or muscle tissue supersedes water column element when both fish tissue and water concentrations are measured.
4.	Water column values are based on dissolved total selenium in water and are derived from fish tissue values via
bioaccumulation modeling. Water column values are the applicable criterion element in the absence of steady-state condition
fish tissue data.
5.	Where WQC3o-dayis the water column monthly element, for either a 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
fint 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.
7.	Site-specific water column criteria elements will be derived using the mechanistic model and associated procedures laid out in
appendix K of Aquatic Life Ambient Water Quality Criterion for Selenium-Freshwater 2016.20 To derive scientifically
defensible site-specific water column criteria elements, appropriate input parameters (as described in Appendix K) will be
selected to adequately represent the water body of interest.
26 USEPA (U.S. Environmental Protection Agency). 2016. Aquatic Life Ambient Water Quality Criterion for
Selenium-Freshwater 2016. EPA 822-R-16-006. U.S. Environmental Protection Agency, Office of Water,
Washington, DC. https://www.epa.gov/wqc/aquatic-life-criterion-selenium-documents.
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