[Federal Register Volume 89, Number 69 (Tuesday, April 9, 2024)]
[Proposed Rules]
[Pages 24758-24775]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-07450]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 131
[EPA-HQ-OW-2023-0325; FRL 11009-03-OW]
RIN 2040-AG35
Mercury Criterion To Protect Aquatic Life in Idaho
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule; notice of public hearing.
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SUMMARY: The Environmental Protection Agency (EPA) is proposing to
promulgate a Federal Clean Water Act (CWA) chronic aquatic life ambient
water quality criterion for waters under the state of Idaho's
jurisdiction to protect aquatic life from the effects of
[[Page 24759]]
exposure to harmful concentrations or levels of total mercury (i.e.,
including methylmercury and inorganic mercury). In 2008, the EPA
disapproved the state's revision of its mercury aquatic life criteria.
The state has not adopted and submitted revised mercury aquatic life
criteria to the EPA to address the EPA's 2008 disapproval. Therefore,
the EPA is proposing a Federal mercury criterion to protect aquatic
life uses in Idaho.
DATES: Comments must be received on or before June 10, 2024. Public
Hearing: The EPA will hold two public hearings during the public
comment period. Please refer to the SUPPLEMENTARY INFORMATION section
for additional information on the public hearings.
ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-
OW-2023-0325, by any of the following methods:
Federal eRulemaking Portal: https://www.regulations.gov/
(our preferred method). Follow the online instructions for submitting
comments.
Mail: U.S. Environmental Protection Agency, EPA Docket
Center, Office of Water Docket, Mail Code 28221T, 1200 Pennsylvania
Avenue NW, Washington, DC 20460.
Hand Delivery or Courier: EPA Docket Center, WJC West
Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004.
The Docket Center's hours of operations are 8:30 a.m. to 4:30 p.m.,
Monday through Friday (except Federal Holidays).
Instructions: All submissions received must include the Docket ID
No. for this rulemaking. Comments received may be posted without change
to https://www.regulations.gov/, including any personal information
provided. For detailed instructions on sending comments and additional
information on the rulemaking process, see the ``Public Participation''
heading of the SUPPLEMENTARY INFORMATION section of this document. The
EPA is offering two public hearings on this proposed rulemaking. Refer
to the SUPPLEMENTARY INFORMATION section below for additional
information.
FOR FURTHER INFORMATION CONTACT: Kelly Gravuer, Office of Water,
Standards and Health Protection Division (4305T), Environmental
Protection Agency, 1200 Pennsylvania Avenue NW, Washington, DC 20460;
telephone number: (202) 566-2946; email address: [email protected].
SUPPLEMENTARY INFORMATION:
This proposed rulemaking preamble is organized as follows:
I. Public Participation
A. Written Comments
B. Participation in Public Hearings
II. General Information
A. Does this action apply to me?
III. Background
A. Statutory and Regulatory Authority
B. Sources of Mercury and Effects on Aquatic Life
C. History of Mercury Aquatic Life Criteria in Idaho
D. General Recommended Approach for Deriving Aquatic Life
Criteria
IV. Proposed Mercury Aquatic Life Criterion for Idaho
A. Scope of the EPA's Proposed Rule
B. Proposed Mercury Criterion
C. Implementation
V. Endangered Species Act
VI. Applicability of EPA-Promulgated Water Quality Standards When
Final
VII. Implementation and Alternative Regulatory Approaches
A. NPDES Permit Compliance Schedules
B. Site-Specific Criteria
C. WQS Variances
D. Designated Uses
VIII. Economic Analysis
IX. Statutory and Executive Orders Reviews
A. Executive Order 12866 Regulatory Planning and Review and
Executive Order 14094 Modernizing Regulatory Review
B. Paperwork Reduction Act (PRA)
C. Regulatory Flexibility Act (RFA)
D. Unfunded Mandates Reform Act (UMRA)
E. Executive Order 13132 (Federalism)
F. Executive Order 13175 (Consultation and Coordination With
Indian Tribal Governments)
G. Executive Order 13045 (Protection of Children From
Environmental Health and Safety Risks)
H. Executive Order 13211 (Actions That Significantly Affect
Energy Supply, Distribution, or Use)
I. National Technology Transfer and Advancement Act of 1995
J. Executive Order 12898: Federal Actions To Address
Environmental Justice in Minority Populations and Low-Income
Populations and Executive Order 14096: Revitalizing Our Nation's
Commitment to Environmental Justice for All
I. Public Participation
A. Written Comments
Submit your comments, identified by Docket ID No. EPA-HQ-OW-2023-
0325, at https://www.regulations.gov (our preferred method), or the
other methods identified in the ADDRESSES section. Once submitted,
comments cannot be edited or removed from the docket. The EPA may
publish any comment received to its public docket. Do not submit to the
EPA's docket at https://www.regulations.gov any information you
consider to be Confidential Business Information (CBI), Proprietary
Business Information (PBI), or other information whose disclosure is
restricted by statute. Multimedia submissions (audio, video, etc.) must
be accompanied by a written comment. The written comment is considered
the official comment and should include discussion of all points you
wish to make. The EPA will generally not consider comments or comment
contents located outside of the primary submission (i.e., on the web,
cloud, or other file sharing system). Please visit https://www.epa.gov/dockets/commenting-epa-dockets for additional submission methods; the
full EPA public comment policy; information about CBI, PBI, or
multimedia submissions; and general guidance on making effective
comments.
B. Participation in Public Hearings
The EPA is offering two online public hearings so that interested
parties may provide oral comments on this proposed rulemaking. For more
details on the online public hearings and to register to attend the
hearings, please visit https://www.epa.gov/wqs-tech/mercury-criterion-protect-aquatic-life-idaho.
II. General Information
A. Does this action apply to me?
Entities that discharge mercury to waters under Idaho's
jurisdiction \1\ that are subject to relevant aquatic life designated
uses--such as industrial facilities and municipalities that manage
stormwater, separate sanitary, or combined sewer systems--could be
indirectly affected by this rulemaking because Federal water quality
standards (WQS) promulgated by the EPA would be the applicable WQS for
Clean Water Act (CWA) purposes. Specifically, these WQS would be the
applicable standards that must be used in CWA regulatory programs, such
as permitting under the National Pollutant Discharge Elimination System
(NPDES) (CWA section 402) \2\ and identifying impaired waters under CWA
section 303(d). Categories and entities that could be affected include
the following:
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\1\ Throughout this preamble, the phrase ``waters under Idaho's
jurisdiction'' refers to waters of the United States under Idaho's
jurisdiction, since the Clean Water Act applies to waters of the
United States.
\2\ Before any water quality-based effluent limit would be
included in an NPDES permit, the permitting authority (here, the
Idaho Department of Environmental Quality [IDEQ]), must first
determine whether a discharge ``will cause or has the reasonable
potential to cause, or contribute to an excursion above any WQS.''
40 CFR 122.44 (d)(1)(i) and (ii).
[[Page 24760]]
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Examples of potentially affected
Category entities
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Industry.......................... Industrial point sources discharging
mercury to waters under Idaho's
jurisdiction.
Municipalities, including those Publicly owned treatment works or
with stormwater or combined sewer similar facilities responsible for
system outfalls. managing stormwater, separate
sanitary, or combined sewer systems
that discharge mercury to waters
under Idaho's jurisdiction.
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This table is not intended to be exhaustive, but rather provides a
guide for readers regarding entities that could be indirectly affected
by this action. If you have questions regarding the applicability of
this action to a particular entity, consult the person listed in the
FOR FURTHER INFORMATION CONTACT section above.
III. Background
A. Statutory and Regulatory Authority
CWA section 101(a)(2) establishes a national goal of ``water
quality which provides for the protection and propagation of fish,
shellfish, and wildlife, and provides for recreation in and on the
water'' (hereafter, collectively referred to as ``101(a)(2) uses''),
wherever attainable. The EPA's regulation at 40 CFR 131.10(g) and (h)
implements this statutory provision by requiring that WQS protect
101(a)(2) uses unless those uses are shown to be unattainable.
Under the CWA, states have the primary responsibility for
establishing, reviewing, and revising WQS applicable to their waters
(CWA section 303(c)). WQS define the desired condition of a water body,
in part, by designating the use or uses to be made of the water and by
setting the numeric or narrative water quality criteria to protect
those uses (40 CFR 131.2, 131.10, and 131.11). There are two primary
categories of water quality criteria: human health criteria and aquatic
life criteria. Human health criteria protect designated uses such as
public water supply, recreation, and fish and shellfish consumption.
Aquatic life criteria protect designated uses such as survival, growth,
and reproduction of fish, invertebrates, and other aquatic species.
Regardless of their category, water quality criteria ``must be based on
sound scientific rationale and must contain sufficient parameters or
constituents to protect the designated use. For waters with multiple
use designations, the criteria shall support the most sensitive use''
(40 CFR 131.11(a)(1)).
Section 304(a) of the CWA directs the EPA to periodically develop
and publish recommended water quality criteria ``accurately reflecting
the latest scientific knowledge'' on the effects of pollutants on human
health and welfare, including effects on aquatic life, as well as
information on those pollutants, including their concentration and
dispersal and how pollutants affect receiving waters (CWA section
304(a)(1)). Those recommendations are available to states for use in
developing their own water quality criteria (CWA section 304(a)(3)).
When states establish criteria, the EPA's regulation at 40 CFR
131.11(b)(1) specifies that they should establish numeric criteria
based on: (1) the EPA's CWA section 304(a) recommended criteria, (2)
modified 304(a) recommended criteria that reflect site-specific
conditions, or (3) other scientifically defensible methods.
CWA section 303(c)(2)(B), added to the CWA in the 1987 amendments
to the Act,\3\ requires states to adopt numeric criteria, where
available, for all toxic pollutants listed pursuant to CWA section
307(a)(1) (i.e., priority toxic pollutants \4\) for which the EPA has
published CWA section 304(a) recommended criteria, the discharge or
presence of which could reasonably be expected to interfere with the
states' designated uses.
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\3\ Water Quality Act Amendments of 1987, Public Law 100-4, 101
Stat. 7.
\4\ See 40 CFR part 423, Appendix A--126 Priority Pollutants.
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States are required to hold a public hearing to review applicable
WQS at least once every three years and, if appropriate, revise or
adopt new standards (CWA section 303(c)(1); 40 CFR 131.20(a)). Any new
or revised WQS must be submitted to the EPA for review and approval or
disapproval (CWA section 303(c)(2)(A) and (c)(3)). If the EPA
disapproves a new or revised WQS because it is inconsistent with the
requirements of the CWA, the EPA must notify the state within 90 days
and ``specify the changes to meet such requirements'' (CWA section
303(c)(3)). If the state does not adopt changes to comply with the Act
within 90 days of notification, the EPA must promptly propose a new or
revised WQS for the waters involved (CWA section 303(c)(3) and (4)).
B. Sources of Mercury and Effects on Aquatic Life
Mercury is a naturally occurring metal that can be enriched in some
mineral deposits (e.g., cinnabar) and is often present as an impurity
in coal. In Idaho, there are several areas with geologically enriched
mercury deposits.
Human activities can result in the release and transport of mercury
to the aquatic environment primarily through the deposition of mercury
that was released to the atmosphere, discharges to water, and leaching
from mercury-bearing strata exposed due to mining or other activities.
Historically, mercury was both mined directly and used in hardrock and
placer gold mining in Idaho, resulting in a legacy of elevated mercury
levels in several parts of the state. Industrial processes (e.g.,
chemical manufacture and metals processing) are the predominant sources
of current mercury emissions to air in Idaho and nationally. Globally,
natural sources of mercury are less significant than anthropogenic
sources and include the weathering of mercury-containing rocks,
volcanoes, and geothermal activity.\5\ In Idaho, hot springs throughout
the state are a natural mercury source.\6\ Because atmospheric releases
of mercury, whether natural or human-caused, can ultimately be
deposited in waterways far from their point of emission, some of the
mercury in Idaho's environment originated outside the state.
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\5\ UN Environment, 2019. Global Mercury Assessment 2018. UN
Environment Programme, Chemicals and Health Branch. Geneva,
Switzerland. https://www.unep.org/resources/publication/global-mercury-assessment-2018.
\6\ U.S. Geological Survey. 1985. Geochemistry and hydrology of
thermal springs in the Idaho Batholith and adjacent areas, Central
Idaho. Water Resources Investigations Report 85-4172. H.W. Young,
Boise, Idaho.
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In water, mercury can occur in a dissolved form or bound to
particles. The main forms of dissolved mercury in the aquatic
environment are inorganic mercury and methylmercury. Aquatic organisms
can take up both forms of mercury through dietary exposure and through
direct water column exposure. Aquatic organisms tend to take up mercury
more rapidly than they eliminate it, causing mercury (especially
methylmercury) to bioaccumulate. Methylmercury can also biomagnify
(i.e., increase in concentration at successively higher trophic levels)
within aquatic food webs, whereas inorganic mercury does not. Because
of methylmercury's potential for
[[Page 24761]]
biomagnification, dietary exposure is of greater concern than direct
water column exposure for mercury toxicity.
Mercury is a potent neurotoxin that causes neurological damage,
which can result in behavioral changes and ultimately in reduced growth
and reproduction in aquatic organisms. Dietary exposure to
methylmercury has been shown to impair reproduction in fish. Aquatic
invertebrates are typically more tolerant to both inorganic and
methylmercury exposures than vertebrates, with larval stages tending to
be the most sensitive. However, there are exceptions to this general
pattern. For example, the red swamp crayfish \7\ was found to be the
fourth most sensitive (out of 19 mostly vertebrate) species for which
data were available to derive this mercury criterion (see section IV.B.
in this preamble below).
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\7\ Although the red swamp crayfish (Procambarus clarkii) is not
native to Idaho, it serves as a surrogate for similar native
invertebrate species for which toxicity data were not available.
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In general, mercury cycling in the aquatic environment is affected
by pH, temperature, oxidation-reduction (redox) potential, and the
availability of nutrients, humic acids, and complexing agents. The
conversion of inorganic mercury to the more toxic methylmercury occurs
in anoxic environments, such as wetlands. Higher mercury methylation
rates tend to occur in areas with higher anerobic microbial activity
and when inorganic mercury is in a form that is bioavailable to the
microbial community.\8\ Mercury has a high affinity for sorbing to
sediments as well as dissolved and particulate matter suspended in the
water column. This sorption to sediments can allow sediments to serve
as a source of mercury to the water column long after mercury-releasing
activities have ceased.
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\8\ USEPA. 2023. Technical Support Document: Aquatic Life Water
Quality Criterion for Mercury in Idaho. U.S. Environmental
Protection Agency, Office of Water, Washington, DC. https://www.epa.gov/wqs-tech/mercury-criterion-protect-aquatic-life-idaho.
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C. History of Mercury Aquatic Life Criteria in Idaho
On June 25, 1996, the EPA approved Idaho's numeric aquatic life
mercury criteria (0.012 [mu]g/L chronic and 2.1 [mu]g/L acute) under
CWA section 303(c). In 2003, the Idaho Department of Environmental
Quality (``IDEQ'') began a negotiated rulemaking in response to a
petition from the Idaho Mining Association to update Idaho's mercury
criteria. As a result of that negotiated rulemaking, Idaho adopted and,
on August 8, 2005, submitted revised standards to the EPA for review
under CWA section 303(c). IDEQ's revised standards removed the acute
and chronic numeric aquatic life criteria for mercury and added a
footnote ``g'' to the state's toxic criteria table. Footnote ``g''
stated that Idaho's existing narrative criteria for toxics would apply
instead of the numeric criteria and that the existing human health
criterion for methylmercury would be protective of aquatic life in most
situations.
On December 12, 2008, the EPA disapproved Idaho's removal of
numeric acute and chronic aquatic life criteria for mercury and their
replacement with footnote ``g,'' stating that these revisions were
inconsistent with CWA section 303(c) and 40 CFR 131.11.\9\ The EPA
noted that ``the supporting documentation that Idaho had submitted
[did] not provide specific information which would demonstrate that the
designated aquatic life uses in Idaho are assured protection from
discharges of mercury that would adversely affect water quality and/or
the attainment of the aquatic life uses.'' The EPA further stated that
Idaho's Implementation Guidance for the Mercury Water Quality Criteria
\10\ (which primarily pertains to Idaho's human health criteria for
mercury) did not ``contain definitive information on how the State
would translate the fish tissue criterion developed to protect human
health to a value which could be used to protect aquatic life.''
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\9\ Letter from Michael F. Gearheard, Director, EPA Region 10
Office of Water and Watersheds to Barry Burnell, Water Quality
Program Administrator, Idaho Department of Environmental Quality,
Re: EPA's Disapproval of Idaho's Removal of Mercury Acute and
Chronic Freshwater Aquatic Life Criteria, Docket No. 58-0102-0302
(December 12, 2008).
\10\ Idaho Department of Environmental Quality. 2005.
Implementation Guidance for the Idaho Mercury Water Quality
Criteria. Boise, ID. https://www2.deq.idaho.gov/admin/LEIA/api/document/download/4836.
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To remedy this disapproval, the EPA specified ``several options
Idaho could consider in establishing mercury criteria that are based on
scientifically defensible methods and protect Idaho's designated
aquatic life uses.'' These options included (1) evaluating the
protectiveness of the EPA's existing recommended 304(a) numeric acute
aquatic life criterion for mercury (1.4 [micro]g/L); (2) evaluating the
protectiveness of Idaho's previous numeric chronic aquatic life
criterion for mercury (0.012 [micro]g/L); (3) evaluating development of
Idaho-specific numeric acute and chronic aquatic life criteria for
mercury; and (4) evaluating the use of a combination of protective
numeric water column values and numeric wildlife criteria appropriate
for Idaho species. The EPA also pointed out that it was not
recommending Idaho use the EPA's existing 304(a) numeric chronic
aquatic life criterion for mercury (0.77 [micro]g/L) as one of the
options. The EPA explained that information arising after the
derivation of that 304(a) criterion had indicated that it may not
adequately protect certain fish species that are present in Idaho.
The EPA concluded that ``[u]ntil Idaho develops and adopts and EPA
approves revisions to [the] numeric acute and chronic aquatic life
criteria for mercury, the numeric aquatic life mercury criteria
applicable to the designated aquatic life uses in Idaho that are
effective for Clean Water Act [p]urposes are the previously adopted
acute (2.1 [mu]g/L) and chronic (0.012 [mu]g/L) mercury criteria which
EPA approved'' in 1996. No revisions to Idaho's aquatic life mercury
criteria have been made since the EPA's December 2008 disapproval.
Idaho's WQS acknowledge the EPA's 2008 disapproval and state that the
mercury aquatic life criteria that were published in the 2004 Idaho
Administrative Code (prior to adoption of the disapproved standards)
still apply and are effective for CWA purposes.\11\ Those criteria are
currently being implemented for CWA purposes including NPDES permitting
in the state.
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\11\ IDAPA 58--Department of Environmental Quality, Surface and
Wastewater Division, 58.01.02--Water Quality Standards. https://adminrules.idaho.gov/rules/current/58/580102.pdf.
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On June 14, 2013, Northwest Environmental Advocates filed suit in
the Federal district court for the District of Idaho against the
National Marine Fisheries Service and the Fish and Wildlife Service
(the Services).\12\ The complaint alleged that the Services
unreasonably delayed or unlawfully withheld completion of Endangered
Species Act (ESA) consultation with the EPA regarding new and revised
WQS that Idaho submitted in 1996 and/or 1997. On September 24, 2013,
Northwest Environmental Advocates were joined by the Idaho Conservation
League (collectively, the plaintiffs) in filing an amended complaint
adding various CWA and ESA claims against the EPA regarding dozens of
Idaho WQS submissions dating back to 1994.
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\12\ Nw. Env't Advocs. v. United States Env't Prot. Agency, No.
1:13-cv-263 (D. Idaho filed June 14, 2013).
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By 2020, all claims against the EPA except one had either been
dismissed on statute of limitations grounds or included in a stipulated
dismissal agreed upon by the parties. The remaining claim alleged that
the EPA failed to act under section 303(c)(4) of the CWA to promulgate
aquatic life
[[Page 24762]]
mercury criteria for Idaho following the EPA's December 12, 2008
disapproval of the state's revisions to its mercury criteria. On July
19, 2021, the Court issued a decision on that claim in favor of the
plaintiffs, concluding that, as a result of its disapproval, the EPA
was subject to a mandatory duty to promulgate new criteria for the
state.\13\ The Court directed the parties to file briefs regarding an
appropriate remedy. The parties negotiated a settlement and entered
into a Stipulated Order on Remedy on October 4, 2022.\14\ The Order
states that the EPA will sign for publication in the Federal Register
proposed aquatic life mercury criteria for the state of Idaho within 18
months of its entry with the Court (i.e., by April 4, 2024).
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\13\ Nw. Env't Advocs. v. United States Env't Prot. Agency, 549
F. Supp. 3d 1218 (D. Idaho 2021).
\14\ Stipulated Order on Remedy, Nw. Env't Advocs. v. United
States Env't Prot. Agency, No. 1:13-cv-263 (D. Idaho October 4,
2022).
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With regard to the form of the proposed criteria, the Stipulated
Order on Remedy states that ``[i]n recognition of the comparative ease
of translating water column concentrations and values into permit
effluent limitations and wasteload allocations, EPA commits to
developing proposed Mercury Criteria that include water column
concentrations, or default water column values that can be modified on
a case-by-case basis, if EPA determines there are sufficient data
available to support this form of criteria.''
D. General Recommended Approach for Deriving Aquatic Life Criteria
The EPA developed the mercury criterion for Idaho in this proposed
rulemaking consistent with the EPA's Guidelines for Deriving Numerical
National Water Quality Criteria for the Protection of Aquatic Organisms
and Their Uses (referred to as the ``Aquatic Life Guidelines'').\15\
The EPA's Aquatic Life Guidelines describe a method to estimate the
highest concentration (magnitude) of a substance in water--averaged
over a given time period (duration) and that should not be exceeded
more than the allowable number of times during a specified time period
(frequency)--that will not present a significant risk to the aquatic
organisms in the water. The Aquatic Life Guidelines recommend using
toxicity test data from a minimum of eight taxa of aquatic organisms to
derive criteria. These taxa are intended to be representative of a wide
spectrum of aquatic life, and act as surrogates for untested species.
Therefore, the specific test organisms do not need to be present in the
water(s) where the criteria will apply.
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\15\ USEPA. 1985. Guidelines for Deriving Numerical National
Water Quality Criteria for the Protection of Aquatic Organisms and
Their Uses. U.S. Environmental Protection Agency, Office of Research
and Development, Duluth, MN, Narragansett, RI, Corvallis, OR. PB85-
227049. https://www.epa.gov/sites/production/files/2016-02/documents/guidelines-water-quality-criteria.pdf.
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Aquatic life criteria are typically represented as concentrations
of a pollutant in the water column with two magnitudes: one associated
with a shorter-term (acute) duration and another associated with a
longer-term (chronic) duration. However, depending on the mode of
toxicity, for some pollutants, an acute-only or chronic-only water
column criterion is appropriate.\16\ For example, for pollutants where
toxicity to aquatic life is primarily driven by diet (i.e., the
consumption of contaminated prey) rather than by direct exposure to
dissolved contaminants in the water column, longer-term water column
measurements that capture the degree of likely pollutant uptake via
dietary exposure--such as measurements with a 30-day average (chronic)
duration--are often the most appropriate water column-based measure of
their toxicity to aquatic life. Furthermore, for some pollutants,
measurements of pollutant concentrations within the tissues of aquatic
organisms provide a more direct measure of toxicity (to both the
organisms themselves, and to humans consuming those organisms) than
water column measurements. For bioaccumulative pollutants such as
mercury, where exposure is primarily through diet, both of these
rationales apply, with tissue measurements and longer-term water column
measurements providing more appropriate measures of toxicity than the
1-hour and 4-day water column measurements that capture the toxic
effects of many other pollutant types.
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\16\ https://www.epa.gov/wqc/national-recommended-water-quality-criteria-aquatic-life-criteria-table#table.
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Because tissue measurements provide a more direct measure of
toxicity for bioaccumulative pollutants such as mercury, the EPA has
considered it appropriate to establish tissue criteria for these
pollutants. However, criteria expressed as organism tissue
concentrations can prove challenging to implement in CWA programs such
as NPDES permitting and Total Maximum Daily Loads (TMDLs) because these
programs typically demonstrate that water quality standards are met by
using a water column concentration to calculate a load-based effluent
limit or daily load, respectively. In recent years, the EPA has
developed tissue-based national criteria recommendations for certain
bioaccumulative pollutants and then assessed the degree to which
available knowledge and data support translating those tissue criteria
to water column criteria at the site, state, or national level.
For exceedance frequency, most water column aquatic life criteria
developed by the EPA include a recommended exceedance frequency of no
more than once in three years. The EPA based this maximum exceedance
frequency recommendation of once every three years on the time aquatic
ecosystems require to recover from the exceedances. For water column
criteria, an exceedance occurs when the average concentration over the
duration of the averaging period is above the criterion. Because fish
tissue concentrations of bioaccumulative pollutants reflect longer-term
uptake and elimination dynamics and tend to change slowly over time,
their frequency and duration components tend to be different than those
of water column criteria. Specifically, for fish tissue criteria, the
EPA recommends for bioaccumulative pollutants 17 18 that the
criteria be expressed with an ``instantaneous measurement'' duration
and be considered exceeded if a fish tissue sample measurement from a
single sampling event (defined as a composited tissue sample from each
fish species or a central tendency estimate of individual tissue
samples from each fish species, collected from a given site or
waterbody in a discrete sampling period) exceeds the criterion
value.\19\
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\17\ 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.
\18\ USEPA. 2022. Draft Aquatic Life Ambient Water Quality
Criteria for Perfluorooctanoic Acid (PFOA). EPA-842-D-22-001. U.S.
Environmental Protection Agency, Office of Water, Washington, DC.
https://www.epa.gov/system/files/documents/2022-04/pfoa-report-2022.pdf; USEPA. 2022. Draft Aquatic Life Ambient Water Quality
Criteria for Perfluorooctane Sulfonate (PFOS). EPA-842-D-22-002.
U.S. Environmental Protection Agency, Office of Water, Washington,
DC. https://www.epa.gov/system/files/documents/2022-04/pfos-report-2022.pdf.
\19\ As previously stated, since fish tissue concentrations of
bioaccumulative pollutants tend to change slowly over time, any
exceedance indicates that waterbody conditions may not be protective
of aquatic life.
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IV. Proposed Mercury Aquatic Life Criterion for Idaho
A. Scope of the EPA's Proposed Rule
The final criterion resulting from this proposed rulemaking would
establish
[[Page 24763]]
levels of mercury appropriate for the protection and maintenance of a
viable aquatic life community in waters under Idaho's jurisdiction that
are designated for aquatic life uses. The criterion would apply to all
of Idaho's aquatic life use designations and would replace the current
CWA-effective acute and chronic mercury criteria.
B. Proposed Mercury Criterion
Since mercury is significantly more toxic through chronic dietary
exposure than through water-based exposure, the EPA developed a
proposed chronic criterion that is based on dietary exposures. The EPA
did not develop a separate acute or chronic criterion from the results
of toxicity tests with only water-based exposure. Because the most
harmful effects of mercury on aquatic organisms are due to its
bioaccumulative properties and because the resulting chronic effects
are observed at lower mercury concentrations than acute effects, this
chronic criterion based on dietary exposure is expected to additionally
protect aquatic communities from any potential acute effects of
mercury. For reasons described below, the EPA concluded that this
chronic mercury criterion should integrate consideration of both
relative organismal sensitivity (i.e., inherent toxicity) and relative
exposure potential (i.e., bioaccumulation) across the aquatic species
for which data are available. A summary of the EPA's approach is
described below; for more details, please see the Technical Support
Document included in the docket for this rulemaking.\20\
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\20\ USEPA. 2023. Technical Support Document: Aquatic Life Water
Quality Criterion for Mercury in Idaho. U.S. Environmental
Protection Agency, Office of Water, Washington, DC. https://www.epa.gov/wqs-tech/mercury-criterion-protect-aquatic-life-idaho.
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1. Inherent Toxicity Data
To account for inherent toxicity, the EPA evaluated toxicity
studies in which the authors fed food spiked with methylmercury and/or
inorganic mercury to aquatic organisms for an appropriate chronic
duration (based on the taxon and the endpoint of interest, ranging up
to 249 days in this data set \21\). The EPA then assessed each study
that measured the organisms' resulting tissue mercury levels and
associated toxicity effects. The tissue mercury levels in these studies
were measured as methylmercury or total mercury. Although the toxicity
reported in most of these studies was primarily due to methylmercury,
the toxicity observed in at least some aquatic taxa was likely due to
the combined effects of inorganic and methylmercury.
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\21\ The chronic studies used in the derivation of the mercury
criterion followed taxa-specific exposure duration requirements from
various test guidelines (i.e., EPA's 1985 Aquatic Life Criteria
Guidelines: https://www.epa.gov/sites/production/files/2016-02/documents/guidelines-water-quality-criteria.pdf and EPA OCSPP's 2016
Ecological Effects Test Guidelines: https://www.epa.gov/test-guidelines-pesticides-and-toxic-substances/series-850-ecological-effects-test-guidelines) when available. Thus, most studies
consisted of partial life-cycle tests of sufficient length to
ascertain whether dietary exposure to mercury had a deleterious
effect on the endpoint of interest. For studies involving amphibian
taxa, only dietary exposure studies using fully aquatic life stages
(larvae, tadpoles, and metamorphs) of these species were considered.
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Idaho's aquatic life uses call for water quality appropriate for
the protection and maintenance of a viable aquatic life community,
including active self-propagating populations of salmonid fishes where
appropriate habitat is available and the salmonid spawning use is
designated. To protect these aquatic life designated uses, the EPA
seeks to protect aquatic life and health of the aquatic community by
minimizing adverse effects on the assessment endpoints of survival,
growth, and reproduction in the taxa present in the aquatic community.
Measures of effect (such as increased mortality, reduction in organism
weight, or the number of eggs laid per female fish) reported in each
study were used to quantify changes in the assessment endpoints of
survival, growth, and reproduction. As with recent national recommended
bioaccumulative pollutant criteria, the EPA selected the
EC10--the concentration that results in a 10% difference in
a measure of effect (e.g., a 10% decrease in number of eggs laid per
female) in the test population--as the numeric metric for the measures
of effect, wherever possible. The EC10 estimates a low level
of effect that is different from controls but is not expected to cause
severe effects at the population level for a bioaccumulative
contaminant. For studies with experimental designs that did not provide
sufficient test concentrations to calculate an EC10, the EPA
generally used an estimate of the No Observed Effect Concentration
(NOEC) as a surrogate for the EC10.\22\
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\22\ USEPA. 2023. Technical Support Document: Aquatic Life Water
Quality Criterion for Mercury in Idaho. U.S. Environmental
Protection Agency, Office of Water, Washington, DC. https://www.epa.gov/wqs-tech/mercury-criterion-protect-aquatic-life-idaho.
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The EPA collected chronic dietary toxicity test data of sufficient
quality across the eight diverse taxonomic groups (including
vertebrates and invertebrates) recommended in the Aquatic Life
Guidelines. Quantitative data were available for 19 species within 18
genera. For each toxicity study, the EPA recorded the type of tissue in
which the mercury concentration had been measured (muscle or whole-
body) and then used conversion factors derived from the literature to
create two equivalent data sets: one in terms of muscle tissue
concentrations and the other in terms of whole-body tissue
concentrations. This approach allowed the EPA to develop two tissue
criterion elements (one for muscle tissue and one for whole-body
tissue).
2. Bioaccumulation Data
The EPA estimated bioaccumulation using the bioaccumulation factor
(BAF) approach; a BAF is the ratio of the concentration of a chemical
in the tissue of an aquatic organism to the concentration of the
chemical dissolved in ambient water at the site of sampling. Because
mercury bioaccumulation, and thus BAFs, can be affected by multiple
site-specific factors (see section III.B. in this preamble above), it
is desirable to base BAFs on field-collected data from the location(s)
to which the criterion will be applied. Consequently, the EPA assembled
a data set of paired (i.e., collected in the same waterbody within one
year) aquatic organism tissue and water samples from Idaho. The data
set contained data from 30 fish species and one crayfish species.
Although no paired tissue and water data from Idaho were found for
amphibians, the EPA conducted a literature search and identified paired
tissue and water data for the wood frog (resident in Northern Idaho)
that had been collected in Maine and Vermont; these data were added to
the data set to ensure consideration and protection of Idaho
amphibians.
From this data set, the EPA calculated species-level BAFs by first
taking the median for a species at a site in a particular year, then
the median across years within a site, then the median across sites for
a species to get one median BAF per species.
3. Development of Fish Tissue Criterion Elements: Magnitude
Having assembled data on both toxicity and bioaccumulation for a
suite of aquatic species relevant to protection and maintenance of a
viable aquatic life community in Idaho, the EPA proceeded to develop
the muscle and whole-body tissue criterion elements. The EPA noted that
there were large ranges of toxicological sensitivity and
bioaccumulation potential across taxa. Two specific issues were
apparent
[[Page 24764]]
related to differing bioaccumulation rates among species for mercury.
First, the two amphibians in the toxicity data set were the two
most sensitive species based on dietary exposure (inherent toxicity),
but also have by far the lowest mercury bioaccumulation potential.
Fish, on the other hand, are comparatively more tolerant to inherent
(direct) toxicity, but generally more vulnerable to mercury pollution
due to their higher mercury bioaccumulation potential. Therefore,
establishing a criterion based solely on inherent toxicity data, i.e.,
without considering bioaccumulation differences, would be
inappropriate. The EPA also aimed to develop a criterion that was
practical and implementable, recognizing that Idaho typically samples
fish (rather than amphibians) for CWA implementation purposes.
Therefore, in consideration of the bioaccumulation data, the EPA is
proposing a chronic criterion for mercury based on fish and aquatic
invertebrate inherent toxicity data, which also protects amphibians.
Second, mercury bioaccumulation potential among fish species varies
widely (up to 20-fold differences) due primarily to their diets: as
trophic level increases so does mercury bioaccumulation. In order to
protect higher trophic level fish, such as salmonids, which are
commercially, recreationally, and ecologically important in Idaho, the
EPA made adjustments to account for known bioaccumulation differences
among fish species. Doing so ensures that higher trophic level fish
species are protected when evaluating sampling data from lower trophic
level species (e.g., bluegill, suckers, pumpkinseed) for implementation
purposes.
To address these two issues, the EPA used a modified approach based
on the ``good science'' clause in the Aquatic Life Guidelines \23\ to
integrate inherent toxicity and bioaccumulation. Briefly, to address
the first issue (the most sensitive organisms having by far the lowest
bioaccumulation potential), the EPA calculated both tissue criterion
elements using the fish and aquatic invertebrate data (i.e., excluding
amphibians) and then analyzed whether the resulting criterion elements
would be protective of all aquatic species in the data set in light of
their inherent toxicity and bioaccumulation differences (see further
details below).
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\23\ The Aquatic Life Guidelines note that a modified approach
may be needed in some situations, directing users to: ``On the basis
of all available pertinent laboratory and field information,
determine if the criterion is consistent with sound scientific
evidence. If it is not, another criterion, either higher or lower,
should be derived using appropriate modifications of these
Guidelines.'' (pg. 30).
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To address the second issue, the EPA evaluated the differences in
bioaccumulation between fish species in the data set and developed
adjustment factors that can be used when sampling fish for
implementation. If a high trophic level adult fish (e.g., trophic level
4) is sampled and found to have mercury tissue concentrations at (or
below) the criterion level, it would be reasonable to assume that all
aquatic species in that water body are protected (i.e., because lower
trophic level species are expected to have lower levels of mercury
bioaccumulation). However, if a lower trophic level fish is sampled and
found to be below the criterion level, it does not necessarily mean
that higher trophic level fish are protected. To resolve this issue,
the EPA developed a method to estimate the tissue mercury levels of
higher trophic level adult fish resident in that water body to
determine whether all aquatic species in that water body are protected.
To make these estimates, the EPA developed Bioaccumulation Trophic
Adjustment Factors (BTAFs). The BTAF is an adjustment factor applied to
the tissue sample data from a lower trophic level fish and is based on
the relative relationship of bioaccumulation rates of the highest
trophic level fish species as compared to lower trophic level fish
species. The EPA first assigned all the fish in the bioaccumulation
data set to one of three trophic categories: low (trophic level 2 or
TL2), medium (trophic level 3 or TL3), or high (trophic level 4 or
TL4).\24\ The EPA then developed two BTAFs by calculating the ratio
between the trophic level BAFs: one to be used if a TL2 species is
sampled (representative TL4 BAF/representative TL2 BAF) and another to
be used if a TL3 species is sampled (representative TL4 BAF/
representative TL3 BAF). To calculate representative BAFs, the EPA used
the median of BAFs for species at that trophic level from the species-
level BAF data set for TL3 (TL3 BAF = 108,418 L/kg, n = 21) and TL4
(TL4 BAF = 378,150 L/kg, n = 6) fish. For the representative TL2 BAF,
due to the paucity of TL2 fish species in the data set (n = 3), the EPA
used the 20th centile of the full distribution of the species-level
median BAFs (TL2 BAF = 67,203 L/kg, n = 30). The EPA's use of the 20th
centile ensures appropriate protection for aquatic species in Idaho
(i.e., providing water quality appropriate for the protection and
maintenance of a viable aquatic life community as specified by Idaho's
aquatic life uses) and is consistent with previous EPA approaches for
bioaccumulative chemicals.25 26
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\24\ Fish species were binned into three trophic magnitude
categories largely corresponding to trophic levels designated in
Essig 2010 (Arsenic, mercury, and selenium in fish tissue and water
from Idaho's major rivers: A statewide assessment. Idaho Department
of Environmental Quality, Boise, ID. https://www2.deq.idaho.gov/admin/LEIA/api/document/download/3472) based on Zaroban et al. 1999
(Classification of species attributes for Pacific Northwest
freshwater fishes. Northwest Sci. 73(2): 81-93). In some instances,
additional information regarding trophic ecology and other
attributes of Pacific Northwest fish species resident in Idaho were
also incorporated into the trophic level categorization
determination (Brown, C.J.D. 1971. Fishes of Montana. Bozeman, MT:
Big Sky Books/Montana State University. 207 p.; Zaroban et al. 1999.
Classification of species attributes for Pacific Northwest
freshwater fishes. Northwest Sci. 73(2): 81-93; Froese, R. and D.
Pauly. Editors. 2022. FishBase. World Wide Web electronic
publication. www.fishbase.org).
\25\ USEPA. 2022. Draft Aquatic Life Ambient Water Quality
Criteria for Perfluorooctanoic Acid (PFOA). EPA-842-D-22-001. U.S.
Environmental Protection Agency, Office of Water, Washington, DC.
https://www.epa.gov/system/files/documents/2022-04/pfoa-report-2022.pdf; USEPA. 2022. Draft Aquatic Life Ambient Water Quality
Criteria for Perfluorooctane Sulfonate (PFOS). EPA-842-D-22-002.
U.S. Environmental Protection Agency, Office of Water, Washington,
DC. https://www.epa.gov/system/files/documents/2022-04/pfos-report-2022.pdf.
\26\ 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.
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Therefore, the EPA is proposing that if a TL2 fish is sampled, its
muscle tissue mercury concentration (converted from whole-body tissue
concentration where appropriate, as discussed below) must be multiplied
by 5.6 (378,150 L kg-1/67,203 L kg-1) to estimate
the muscle tissue mercury concentration of a TL4 fish in the same water
body, and that estimate must be compared to the muscle tissue criterion
element (225 ng total mercury (THg)/g wet weight (ww)) to determine
whether the criterion is met. Similarly, if a TL3 fish is sampled, its
muscle tissue mercury concentration must be multiplied by 3.5 (378,150
L kg-1/108,418 L kg-1) and the resulting value
compared to the muscle tissue criterion element. If an adult TL4 fish
species is sampled, its muscle tissue mercury concentration must be
compared directly to the muscle tissue criterion element. Because the
BAFs in this data set were calculated using muscle tissue
concentrations, it is most appropriate to use the BTAFs to adjust
muscle (rather than whole-body) tissue concentration measurements. If
whole-body tissue samples are taken from TL2 or TL3 fish, the EPA is
proposing that those measurements must be converted
[[Page 24765]]
to a muscle tissue equivalent (by dividing by 0.72, a conversion factor
derived from the literature \27\) before multiplying by the appropriate
BTAF and comparing the result to the muscle tissue criterion element.
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\27\ USEPA. 2023. Technical Support Document: Aquatic Life Water
Quality Criterion for Mercury in Idaho. U.S. Environmental
Protection Agency, Office of Water, Washington, DC. https://www.epa.gov/wqs-tech/mercury-criterion-protect-aquatic-life-idaho.
---------------------------------------------------------------------------
Trophic level assignments for fish species found in Idaho are
included in the Technical Support Document \28\ and should be used
where available. Additional sources for trophic level assignment cited
in the Technical Support Document should be consulted to assign trophic
levels for other species. In some cases, consultation with state
fisheries experts may be necessary. At this time, the EPA has developed
BTAFs for fish based on Idaho species with available BAF data. The EPA
requests comment on whether there is interest in sampling species other
than fish to determine compliance with the criterion, and if so,
whether any data exist to develop appropriate BTAFs for those other
species.
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\28\ Ibid.
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Having confirmed that the most bioaccumulative species (i.e., those
at the highest trophic level) would be protected by the tissue
criterion with BTAF adjustments applied as appropriate, the EPA
analyzed whether a tissue criterion derived based solely on fish and
aquatic invertebrates (excluding the two amphibian species) would be
protective of all aquatic species in the data set. Comparing the
amphibian BAF (8,222 L/kg) to the median TL4 fish BAF (378,150 L/kg),
the EPA found that amphibians would be expected to bioaccumulate
approximately 46 times less mercury than the median TL4 fish when
exposed to the same mercury levels. Therefore, if a TL4 fish is sampled
and found to have a mercury level equivalent to the muscle tissue
criterion value (225 ng THg/g ww), amphibians in that same water body
would be expected to have muscle tissue concentrations of approximately
4.9 ng THg/g ww, well below the EC10 of the most sensitive
amphibian species (33.7 ng THg/g ww). Similar reasoning would apply if
TL2 or TL3 fish species were sampled and adjusted with the BTAFs to an
estimated TL4 muscle tissue concentration at or below 225 ng THg/g ww;
in all cases, estimated amphibian muscle tissue concentrations in that
water body would be below the most sensitive amphibian's
EC10. Therefore, the EPA concluded that the tissue criterion
elements protect the full suite of aquatic species (including
amphibians) without being unnecessarily stringent.
The EPA's proposed tissue criterion elements are expressed as total
mercury (THg) (i.e., including methylmercury and inorganic mercury). As
noted above, both forms of mercury can bioaccumulate and have toxic
effects, although only methylmercury biomagnifies. Furthermore, the
analysis of total mercury incorporates the measurement of
methylmercury, but costs less and uses less complex analytical methods
than the measurement of methylmercury alone. Additionally, measurement
of total mercury in fish tissue has served as the basis for quantifying
mercury concentrations in fish tissue monitoring programs implemented
by the EPA and many states, including Idaho.
4. Development of the Water Column Criterion Element: Magnitude
To develop the water column criterion element, the EPA first needed
to assign a BAF to each species in the toxicity data set to facilitate
the translation from tissue to water, since not all species in the
toxicity data set were also present in the bioaccumulation data set. To
determine appropriate BAFs for the fish species without species-
specific BAFs, the EPA calculated TL-specific BAFs by taking the 80th
centile of the median species-level BAFs for all fish within that TL.
The EPA's use of the 80th centile here is consistent with the process
for deriving water column criteria for other bioaccumulative
pollutants.29 30 The EPA then assigned the most
representative BAF (i.e., species- or genus-level where available,
otherwise trophic-level) to each fish species in the toxicity data
set.\31\ Nearly all BAFs were derived from field-collected Idaho tissue
and water data, representing a diverse range of site-specific
relationships between mercury in tissue and water across the state of
Idaho (see TSD section 3.5 for more details). The EPA then translated
the tissue-based toxicity value for each species in the toxicity data
set to a water column-based toxicity value by dividing the species'
tissue-based toxicity value by its assigned BAF.
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\29\ 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.
\30\ USEPA. 2022. Draft Aquatic Life Ambient Water Quality
Criteria for Perfluorooctanoic Acid (PFOA). EPA-842-D-22-001. U.S.
Environmental Protection Agency, Office of Water, Washington, DC.
https://www.epa.gov/system/files/documents/2022-04/pfoa-report-2022.pdf; USEPA. 2022. Draft Aquatic Life Ambient Water Quality
Criteria for Perfluorooctane Sulfonate (PFOS). EPA-842-D-22-002.
U.S. Environmental Protection Agency, Office of Water, Washington,
DC. https://www.epa.gov/system/files/documents/2022-04/pfos-report-2022.pdf.
\31\ For invertebrates, the EPA assigned the crayfish BAF to the
other invertebrates in the data set (daphnid, mayfly, and clam). For
amphibians, the EPA assigned the wood frog BAF.
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The EPA ranked the translated water column-based toxicity values by
sensitivity and calculated the water column criterion element per the
Aquatic Life Guidelines calculation method to arrive at a final water
column value of 2.1 ng/L (see Table 1 to proposed 40 CFR 131.XX(b)). No
exclusions or adjustments to this criterion element were needed to
account for bioaccumulation differences because in this case both
mercury toxicity and bioaccumulation in aquatic species were directly
incorporated into the water column criterion element derivation. The
EPA is proposing to express the water column criterion element as total
mercury in whole water (not dissolved or filtered)--i.e., including
methylmercury and inorganic mercury measured from an unfiltered water
sample. The EPA chose this unit rather than dissolved mercury for the
following reasons. First, the water column data used to derive the BAFs
were from unfiltered water samples. Second, NPDES regulations (40 CFR
122.45(c)) require that permit effluent limits be expressed as total
recoverable metal (with limited exceptions), so most point source
discharge monitoring data for mercury (in Idaho and elsewhere) is from
unfiltered samples. Third, because the primary route of mercury
toxicity is through dietary exposure, particulate mercury may
contribute to toxicity (in contrast to some other metals for which the
primary route of toxicity is absorption from water, and for which
measurements of the dissolved fraction may therefore be more
appropriate).
For most of the paired aquatic organism tissue and water samples
that were available for the calculation of Idaho BAFs, the unfiltered
water samples were collected during the July to October period. In
Idaho flowing waters, discharge rates and turbidity tend to be highest
in the spring due to snowmelt, whereas they tend to be lower during the
July to October time period (i.e., under baseflow conditions). In an
analysis of time series data from several Idaho rivers, the EPA found
that there are higher total mercury concentrations during high flow
periods (see Technical Support Document
[[Page 24766]]
section 3.1.2 for more details \32\). The EPA calculated BAFs using
unfiltered water samples collected primarily during baseflow
conditions, and then used those BAFs to calculate the water column
criterion element. Therefore, water samples collected during baseflow
conditions would be most representative of the data used to derive this
criterion element.
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\32\ USEPA. 2023. Technical Support Document: Aquatic Life Water
Quality Criterion for Mercury in Idaho. U.S. Environmental
Protection Agency, Office of Water, Washington, DC. https://www.epa.gov/wqs-tech/mercury-criterion-protect-aquatic-life-idaho.
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5. Frequency and Duration of Water Column and Fish Tissue Criterion
Elements
The EPA also determined appropriate frequencies and durations for
the tissue and water column criterion elements. For the tissue
criterion elements, because fish tissue mercury concentrations change
slowly (e.g., changing on the order of 2-3% per year), fish tissue
collected from a site can be assumed to integrate and represent the
mercury bioaccumulation dynamics at that site over several years.
Therefore, the EPA is proposing an ``instantaneous measurement''
duration for the fish tissue criterion elements (Table 1 to proposed 40
CFR 131.XX(b)) because fish tissue measurements already reflect longer-
term bioaccumulation dynamics. For similar reasons and considering that
fish tissue mercury concentrations are relatively slow to respond to a
decrease in mercury inputs, the EPA is proposing a frequency of ``not
to exceed'' for the fish tissue criterion elements (Table 1 to proposed
40 CFR 131.XX(b)).
For the water column criterion element, the EPA considered observed
durations of mercury methylation processes affecting trophic transfer
and of mercury bioaccumulation and elimination processes in aquatic
organisms and, consistent with the duration components of other
bioaccumulative contaminants,33 34 set the duration at 30
days (Table 1 to proposed 40 CFR 131.XX(b)). For the frequency aspect,
the EPA considered the number of times mercury concentrations in water
could exceed the criterion over time without negatively affecting the
aquatic community and determined that a once-in-three years exceedance
frequency is appropriate (Table 1 to proposed 40 CFR 131.XX(b)), based
on the ability of an aquatic ecosystem to recover from stress caused by
a toxic pollutant such as mercury.35 36
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\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.
\34\ USEPA. 2022. Draft Aquatic Life Ambient Water Quality
Criteria for Perfluorooctanoic Acid (PFOA). EPA-842-D-22-001. U.S.
Environmental Protection Agency, Office of Water, Washington, DC.
https://www.epa.gov/system/files/documents/2022-04/pfoa-report-2022.pdf; USEPA. 2022. Draft Aquatic Life Ambient Water Quality
Criteria for Perfluorooctane Sulfonate (PFOS). EPA-842-D-22-002.
U.S. Environmental Protection Agency, Office of Water, Washington,
DC. https://www.epa.gov/system/files/documents/2022-04/pfos-report-2022.pdf.
\35\ USEPA. 1985. Guidelines for Deriving Numerical National
Water Quality Criteria for the Protection of Aquatic Organisms and
Their Uses. U.S. Environmental Protection Agency, Office of Research
and Development, Duluth, MN, Narragansett, RI, Corvallis, OR. PB85-
227049. https://www.epa.gov/sites/production/files/2016-02/documents/guidelines-water-quality-criteria.pdf.
\36\ USEPA. 2023. Proceedings from the EPA Frequency and
Duration Experts Workshop September 11-12, 2019. U.S. Environmental
Protection Agency, Office of Water, Washington, DC. https://www.epa.gov/system/files/documents/2023-02/proceedings-frequency-duration-workshop.pdf.
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6. Structure of Criterion
The EPA requests comment on two alternatives for the relationship
of the fish tissue and water column elements. The first alternative,
preferred by the EPA, is for the fish tissue criterion elements to
supersede the water column criterion element in a hierarchical
structure (Table 1 to proposed 40 CFR 131.XX(b)). Because the tissue
criterion elements were estimated directly from toxicity studies,
whereas the water column criterion element required the use of BAFs to
translate those tissue values, the water column element is a step
removed from the toxicity values. These translations introduced some
uncertainty into the water column values since species-specific BAFs
from Idaho were not available for every species. In other words, the
EPA has greater confidence in the tissue criterion elements, and
therefore greater confidence in implementation decisions made using
these criterion elements. If the EPA were to finalize this hierarchical
structure, a water body would be attaining its aquatic life designated
use if a tissue criterion element was met, even if its water column
criterion element was exceeded.
The second alternative is for the fish tissue and water column
criterion elements to be independently applicable. Because major
sources of mercury to aquatic systems in Idaho are legacy mining
contamination and atmospheric deposition, water column measurements of
mercury from a waterbody are expected to be relatively stable over
time. In contrast, pollutants with new and increasing direct sources
tend to have more variable measurements over time, depending on the
anthropogenic source of the pollutant. This expected relative stability
of water column concentrations over time suggests that, while the EPA
has relatively greater confidence in the fish tissue elements, as noted
above, it would also be reasonable to conclude that a water body that
is not meeting the water column element may be worthy of further
evaluation, even if the fish tissue elements are being met. If the EPA
were to finalize an independently applicable criterion structure, a
water body would not be attaining its aquatic life designated use if
either a tissue criterion element or the water column criterion element
was exceeded. The EPA requests comment on the most appropriate
relationship (hierarchical or independently applicable) of the fish
tissue and water column elements.
Within the fish tissue elements, the EPA is proposing that sample
data from TL4 fish supersede sample data from TL3 or TL2 fish. Where
possible, TL4 fish should be sampled to determine whether a fish tissue
criterion element is met, because these data provide a direct
assessment of whether highly bioaccumulative species in the water body
are experiencing tissue mercury levels associated with adverse effects.
This direct assessment is more certain than an assessment based on an
estimated TL4 fish tissue concentration generated by applying the
appropriate BTAF to TL3 or TL2 fish tissue sample data, so if tissue
sample data from fish at multiple trophic levels are available, the TL4
fish sample data would supersede.
The EPA requests comment on two alternatives for the relationship
between TL3 fish sample data and TL2 fish sample data. The first
alternative, preferred by the EPA, is for sample data from TL3 fish to
supersede sample data from TL2 fish (with both still being superseded
by sample data from TL4 fish), for two reasons. First, the trophic
ecology of TL4 fish is closer to that of TL3 fish than TL2 fish.
Second, more data were available to establish the relationship between
TL3 and TL4 fish than between TL2 and TL4 fish.\37\ The second
alternative is for sample data from TL3 fish and sample data from TL2
fish to be independently applicable (with both still being superseded
by sample data from TL4 fish). A rationale
[[Page 24767]]
for this structure would be that TL3 and TL2 sample data are equally
uncertain, relative to TL4 sample data, because BTAFs must be applied
to both. The EPA requests comment on the most appropriate relationship
(hierarchical or independently applicable) of the TL3 fish sample data
and TL2 fish sample data.
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\37\ USEPA. 2023. Technical Support Document: Aquatic Life Water
Quality Criterion for Mercury in Idaho. U.S. Environmental
Protection Agency, Office of Water, Washington, DC. https://www.epa.gov/wqs-tech/mercury-criterion-protect-aquatic-life-idaho.
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In addition to the criterion structure alternatives described
above, the EPA invites public comment on all aspects of the process
used to derive the proposed mercury criterion, including but not
limited to the compilation of toxicity and bioaccumulation data, the
derivation of the proposed tissue criterion element magnitudes and the
water column criterion element magnitude from these data, the
derivation and proposed application of the BTAFs, and the proposed
frequency and duration of the criterion elements.
C. Implementation
The EPA understands that states have certain flexibility with how
they implement WQS. The EPA is recommending possible approaches below
to facilitate consistent implementation of the mercury aquatic life
criterion resulting from this proposed rulemaking for the state's
consideration and for public comment. The EPA recommends that Idaho
develop implementation guidance, potentially building on its existing
implementation guidance for the methylmercury fish tissue human health
criterion,\38\ adding information to clarify how implementation should
proceed given the presence of a water column element and fish tissue
elements as presented in this proposed mercury aquatic life criterion.
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\38\ Idaho Department of Environmental Quality. 2005.
Implementation Guidance for the Idaho Mercury Water Quality
Criteria. Boise, ID. https://www2.deq.idaho.gov/admin/LEIA/api/document/download/4836.
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1. Identification of Impaired Waters and TMDL Development
Section 303(d) of the CWA and the EPA's supporting regulations in
40 CFR 130.7 require states to develop biennial lists of waters
impaired (i.e., not meeting one or more applicable water quality
standards) or threatened by a pollutant and needing a TMDL (i.e., the
Section 303(d) list). States are required to establish a prioritized
schedule for waters on the lists and develop TMDLs for the identified
waters based on the severity of the pollution and the sensitivity of
their uses, among other factors (40 CFR 130.7(b)(4)). A TMDL is a
calculation of the maximum amount of a pollutant that a waterbody can
receive and still safely meet water quality standards, and an
allocation of that load among the various point and/or nonpoint sources
of the pollutant.
The state is required to assemble and evaluate all existing and
readily available water-quality related data and information when
determining which waterbodies belong on the CWA section 303(d) list (40
CFR 130.7(b)(5)). If multiple types of data and information are
collected at a site, they must be assembled and evaluated consistent
with the final structure of the mercury criterion. If the final
criterion has a hierarchical structure as proposed, the fish tissue
criterion elements would supersede the water column criterion element.
If only water column data are available, assessment decisions can be
made by comparing those data to the water column criterion element. If
the final criterion does not have a hierarchical structure, each
element would be its own criterion, and the waterbody would be listed
if any criterion is exceeded. The water column criterion element
proposed here would apply unless site-specific water column criterion
elements were adopted by Idaho and approved by the EPA pursuant to CWA
section 303(c) and the EPA's implementing regulation. Regardless of the
structure of the fish tissue vs. water column elements (hierarchical or
independent criteria), the trophic level hierarchy applies within the
fish tissue criterion element. As noted above (section IV.B.6. in this
preamble), the EPA is proposing that data from TL4 fish would supersede
data from TL3 or TL2 fish, and data from TL3 fish would supersede data
from TL2 fish.
Idaho has flexibility to determine how to evaluate individual and
composite samples for fish tissue. Tissue data provide instantaneous
point measurements that reflect integrative accumulation of mercury
over time and space in fish at a given site. The proposed mercury
criterion provides Idaho with flexibility in how the state can
interpret a discrete fish tissue sample to represent a given species'
population at a site. Generally, fish tissue samples collected to
calculate average tissue concentrations (often in composites) for a
species at a site are collected during one sampling event, or over a
short interval due to logistical constraints and the cost for obtaining
samples. Consistent with the EPA's \39\ and Idaho's \40\ current
recommendations for implementation of selenium fish tissue criterion
elements, a central tendency of fish tissue data may be calculated, or
a composite of fish tissue samples may be analyzed, within a fish
species but should not be calculated or analyzed across species to
determine whether a fish tissue element of this proposed mercury
criterion is met. The EPA recommends that the state clearly describe
its decision-making process in its assessment methodology.
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\39\ USEPA. 2021. Frequently Asked Questions: Implementing EPA's
2016 Selenium Criterion in Clean Water Act Sections 303(d) and
305(b) Assessment, Listing, and Total Maximum Daily Load Programs:
Draft. U.S. Environmental Protection Agency, Office of Water,
Washington, DC. https://www.epa.gov/system/files/documents/2021-10/selenium-faq-cwa305-draft-2021.pdf.
\40\ Idaho Department of Environmental Quality. 2022.
Implementation Guidance for the Idaho Selenium Criteria for Aquatic
Life. Boise, ID. https://www2.deq.idaho.gov/admin/LEIA/api/document/download/16846.
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Although the frequency component is expressed as ``The average
tissue concentration must not be exceeded,'' not meeting a fish tissue
criterion element does not mean that fish populations cannot recover.
As such, if Idaho determines that a fish tissue criterion element is
not met and identifies the water as impaired on their CWA section
303(d) list, Idaho may determine in the future that the criterion is
met based on readily available data and information and remove the
waterbody-pollutant combination from the list. The EPA recommends that
Idaho include in their assessment methodology a discussion of how the
fish tissue criterion elements will be implemented, including
information on how the criterion will be determined to be met after an
exceedance of the fish tissue criterion elements.
2. NPDES Permitting
Under the CWA, WQS are used to derive Water Quality-Based Effluent
Limits (WQBELs) in NPDES permits for point source discharges, thereby
limiting the concentrations or levels of pollutants that may be
discharged into a waterbody to attain and maintain its designated uses.
The EPA is proposing a water column criterion element, which can be
used for NPDES permitting as well as other aspects of implementation.
To account for the 30-day duration of the proposed water column
criterion element, adjustments can be made to WQBEL calculation methods
that assume a 4-day averaging period \41\ as the EPA described in its
Notice of Availability for the 1999 ambient water quality criteria for
[[Page 24768]]
ammonia,\42\ which also included a 30-day duration. However, this water
column criterion element would not prevent Idaho from using the fish
tissue criterion elements for monitoring and regulating pollutant
discharges at the state's discretion.
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\41\ USEPA. 1991. Technical Support Document For Water Quality-
based Toxics Control. EPA/505/2-90-001. U.S. Environmental
Protection Agency, Office of Water, Washington, DC. https://www3.epa.gov/npdes/pubs/owm0264.pdf.
\42\ USEPA. 1999. Water Quality Criteria; Notice of
Availability; 1999 Update of Ambient Water Quality Criteria for
Ammonia. 64 FR 71974-71980 (December 22, 1999). U.S. Environmental
Protection Agency, Office of Water, Washington, DC. https://www.govinfo.gov/content/pkg/FR-1999-12-22/pdf/99-33152.pdf.
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Determination of critical low flows and mixing zones for any
criterion that results from this proposed rulemaking should proceed in
the same manner as for other aquatic life criteria for toxic pollutants
in Idaho, with appropriate adjustments to account for the 30-day
duration of the water column element.
V. Endangered Species Act
On May 7, 2014, the National Marine Fisheries Service (NMFS)
finalized a Biological Opinion \43\ which evaluated whether the EPA's
1996 approval of Idaho's mercury aquatic life criteria--along with EPA
actions in Idaho related to several other pollutants--would jeopardize
the continued existence of threatened and endangered species in Idaho
for which NMFS is responsible. NMFS concluded that the EPA's approval
of the chronic mercury criterion (0.012 [mu]g/L) would jeopardize Snake
River spring/summer Chinook salmon, Snake River fall Chinook salmon,
Snake River sockeye salmon and Snake River Basin steelhead--as well as
adversely modify designated critical habitat for rearing Snake River
salmon and steelhead--due to potential bioaccumulation occurring from
exposure to mercury in the diet. In contrast, NMFS concluded that
exposure of listed salmon and steelhead to mercury at the acute
criterion (2.1 [mu]g/L) was unlikely to result in death or sub-lethal
effects that would result in injury or reduced survival.
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\43\ National Marine Fisheries Service (NMFS). 2014. Endangered
Species Act Section 7(a)(2) Biological Opinion and Magnuson-Stevens
Fishery Conservation and Management Act Essential Fish Habitat (EFH)
Consultation: Idaho Water Quality Standards for Toxic Substances.
Biological Opinion. NMFS Consultation Number: 2000-1484.
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The NMFS biological opinion contained Reasonable and Prudent
Alternatives (RPAs) for the chronic criterion that would avoid the
likelihood of jeopardy to the species. The RPAs directed the EPA to
promulgate a new chronic mercury criterion that would be protective of
aquatic life in Idaho, unless the EPA was able to approve such a
criterion promulgated by the state. NMFS also specified an RPA for
interim protection until this criterion was effective, stating that
``until a new chronic criterion is adopted EPA will use the 2001 EPA/
2005 Idaho human health fish tissue criterion of 0.3 mg/kg wet weight
for WQBELs and reasonable potential to exceed criterion calculations
using the current methodology for developing WQBELs to protect human
health.'' The biological opinion also stated that ``implementation of
the Idaho methylmercury criterion shall be guided by EPA's
methylmercury water quality criteria implementation guidance \44\ or
IDEQ's methylmercury water quality criteria implementation
guidance,\45\ '' and that ``for water bodies for which appropriate fish
tissue data are not available, if the geometric mean of measured
concentrations of total mercury in water is less than 2 ng/L, then the
water body will be presumed to meet the fish tissue criterion of 0.3
mg/kg wet weight. If the water column concentration is greater than 2
ng/L, fish tissue data shall be collected.'' In the biological opinion,
NMFS also opined that one significant digit was the appropriate level
of precision for the total mercury water column value included in their
RPA in light of the limitations of the data set from which it had been
derived. The U.S. Fish and Wildlife Service reached the same conclusion
for bull trout and Kootenai River white sturgeon and their associated
critical habitats in its 2015 Biological Opinion evaluating the EPA's
1996 approval of Idaho's mercury aquatic life criteria and included the
same RPAs for mercury.
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\44\ USEPA. 2010. Guidance for Implementing the January 2001
Methylmercury Water Quality Criterion. EPA 823-R-10-001. U.S.
Environmental Protection Agency, Office of Water, Washington, DC.
https://www.epa.gov/sites/default/files/2019-02/documents/guidance-implement-methylmercury-2001.pdf.
\45\ Idaho Department of Environmental Quality. 2005.
Implementation Guidance for the Idaho Mercury Water Quality
Criteria. Boise, ID. https://www2.deq.idaho.gov/admin/LEIA/api/document/download/4836.
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The EPA's proposed chronic mercury criterion is consistent with the
Services' RPAs, with the proposed muscle tissue criterion element being
more stringent than the human health criterion (0.225 vs. 0.3 mg/kg
\46\ wet weight) and the proposed water column element being comparable
to the RPA water column value (both 2 ng/L using one significant
digit). The EPA will continue to work closely with the Services to
ensure that the mercury criterion that the EPA ultimately finalizes is
protective of federally listed species in Idaho.
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\46\ Idaho's framework for implementing their mercury human
health criterion in their TMDL and NPDES programs uses a mercury
tissue concentration of 0.24 mg/kg, which represents a 20 percent
margin of safety below the 0.3 mg/kg; Idaho Department of
Environmental Quality. 2005. Implementation Guidance for the Idaho
Mercury Water Quality Criteria. Boise, ID. https://www2.deq.idaho.gov/admin/LEIA/api/document/download/4836.
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VI. Applicability of EPA-Promulgated Water Quality Standards When Final
Under the CWA, Congress gave states primary responsibility for
developing and adopting WQS for their waters (CWA section 303(a)
through (c)). Although the EPA is proposing a mercury criterion for the
protection of aquatic life in Idaho, Idaho continues to have the option
to adopt and submit to the EPA mercury criteria for the state's waters
consistent with CWA section 303(c) and the EPA's implementing
regulation at 40 CFR part 131. The EPA encourages Idaho to consider
adoption of mercury criteria protective of aquatic life uses.
Consistent with CWA section 303(c)(4) and the Stipulated Order on
Remedy, if Idaho adopts and submits mercury criteria for the protection
of aquatic life, and the EPA approves such criteria before finalizing
this proposed rulemaking, the EPA will not proceed with the
promulgation for those waters for which the EPA approves Idaho's
criteria. Under those circumstances, Federal promulgation would no
longer be necessary to meet the requirements of the Act.
If the EPA finalizes this proposed rulemaking and Idaho
subsequently adopts and submits mercury criteria for the protection of
aquatic life in Idaho, the EPA would review Idaho's criteria to
determine whether the criteria meet the requirements of section 303(c)
of the CWA and the EPA's implementing regulation at 40 CFR part 131 and
if so, the EPA would approve such criteria. If the EPA's federally
promulgated criterion is more stringent than the EPA-approved state's
criteria, the EPA's federally promulgated criterion would remain the
applicable WQS for purposes of the CWA until the Agency withdraws that
federally promulgated standard. The EPA would expeditiously undertake
such a rulemaking to withdraw the Federal criterion if and when Idaho
adopts and the EPA approves corresponding criteria. After the EPA's
withdrawal of the federally promulgated criterion, the state's EPA-
approved criteria would become the applicable criteria for CWA
purposes. If the EPA-approved state's criteria are as stringent or more
stringent than the federally promulgated criterion, then the state's
criteria would become the CWA applicable WQS upon the EPA's approval of
such criteria (40 CFR 131.21(c)).
[[Page 24769]]
VII. Implementation and Alternative Regulatory Approaches
The Federal WQS regulation at 40 CFR part 131 provides several
approaches that Idaho may utilize, at its discretion, when implementing
or deciding how to implement the final aquatic life criterion resulting
from this proposed rulemaking. Among other things, the EPA's WQS
regulation: (1) allows states and authorized Tribes to authorize the
use of compliance schedules in NPDES permits to meet water quality-
based effluent limits (WQBELs) derived from the applicable WQS (40 CFR
131.15); (2) specifies the requirements for adopting criteria to
protect designated uses, including criteria modified to reflect site-
specific conditions (40 CFR 131.11); (3) authorizes and provides a
regulatory framework for states and authorized Tribes to adopt WQS
variances where it is not feasible to attain the applicable designated
use and criterion for a period of time (40 CFR 131.14); and (4)
specifies how states and authorized Tribes adopt, revise, or remove
designated uses (40 CFR 131.10). Each of these approaches is discussed
in more detail in the next sections.
A. NPDES Permit Compliance Schedules
The EPA's NPDES regulations at 40 CFR 122.47 address how a
permitting authority can use compliance schedules in a permit if a
discharger needs additional time to undertake actions like facility
upgrades or operation changes that will lead to compliance with a WQBEL
based on an applicable WQS that was issued or revised after July 1,
1977. See In The Matter of Star-Kist Caribe, 3 E.A.D. 172, 175, 177
(1990). 40 CFR 122.47 allows a permitting authority to include a
compliance schedule in an NPDES permit, when appropriate, and the
schedule must require compliance with the final WQBEL as soon as
possible. Schedules longer than 1 year must include interim
requirements and dates for their achievement. The EPA's Office of
Wastewater Management 2007 Memorandum, Compliance Schedules for Water
Quality-Based Effluent Limitations in NPDES Permits,\47\ provides
additional information about implementing 40 CFR 122.47 compliance
schedule requirements. The EPA's WQS program regulation at 40 CFR
131.15 requires that a state that intends to allow the use of NPDES
permit compliance schedules adopt specific provisions authorizing their
use and obtain EPA approval under CWA section 303(c) to ensure that a
decision to allow permit compliance schedules is transparent and allows
for public input.\48\ Consistent with 40 CFR 131.15, Idaho has an EPA-
approved WQS for compliance schedules. This WQS allows IDEQ to include
compliance schedules in NPDES permits to meet WQBELs that are
established to ensure that the discharge does not cause or contribute
to an exceedance of the final Federal mercury criterion. In Idaho,
compliance schedules can only be included in permits for new WQBELs
that are more stringent than the WQBEL in a facility's previous NPDES
permit.
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\47\ USEPA. 2007. Compliance Schedules for Water Quality-Based
Effluent Limitations in NPDES Permits. Memo from James A. Hanlon,
Director, Office of Wastewater Management to Alexis Strauss,
Director, Water Division, EPA Region 9. 10 May 2007. https://www3.epa.gov/npdes/pubs/memo_complianceschedules_may07.pdf.
\48\ 80 FR 51022, August 21, 2015.
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B. Site-Specific Criteria
The regulation at 40 CFR 131.11 specifies requirements for
modifying water quality criteria to reflect site-specific conditions.
In the context of this rulemaking, a site-specific criterion (SSC) is
an alternative value to the Federal mercury criterion that would be
applied on an area-wide or water body-specific basis that meets the
regulatory standard of protecting the designated uses, being based on
sound science, and ensuring the protection and maintenance of
downstream WQS. A SSC may be more or less stringent than the otherwise
applicable Federal criterion. A SSC may be called for when further
scientific data and analyses indicate that a different mercury
concentration (e.g., a different fish tissue element) may be needed to
protect the aquatic life designated uses in a particular water body or
portion of a water body. A SSC may also be called for when the
relationship between fish tissue and water column mercury
concentrations at a site differs significantly from the relationship
between fish tissue and water column mercury concentrations in the
Idaho-specific dataset that the EPA used to derive the statewide water
column criterion element.
C. WQS Variances
Idaho could adopt and submit WQS variances for the EPA's approval,
consistent with 40 CFR 131.14, to aid in implementation of this
federally promulgated criterion. The Federal regulation at 40 CFR
131.3(o) defines a WQS variance as a time-limited designated use and
criterion, for a specific pollutant or water quality parameter, that
reflects the highest attainable condition (HAC) during the term of the
WQS variance. A WQS variance may be appropriate if attaining the use
and criterion would not be feasible during a given time period because
of one of the seven factors specified in 40 CFR 131.14(b)(2)(i)(A) but
may be attainable in the future. These factors include where complying
with NPDES permit limits more stringent than technology-based effluent
limits would result in substantial and widespread economic and social
impact. When adopting a WQS variance, states and authorized Tribes
specify the interim requirements by identifying a quantifiable
expression that reflects the HAC during the term of the WQS variance,
establishing the term of the WQS variance, and justifying the term by
describing the pollutant control activities expected to occur over the
specified term of the WQS variance. WQS variances provide a legal
avenue by which NPDES permit limits can be written to comply with the
WQS variance rather than the underlying WQS for the term of the WQS
variance. WQS variances adopted in accordance with 40 CFR 131.14
(including a public hearing consistent with 40 CFR 25.5) provide a
flexible but defined pathway for states and authorized Tribes to issue
NPDES permits with limits that are based on the HAC during the term of
the WQS variance, thus allowing dischargers to make incremental water
quality improvements. If dischargers are still unable to meet the
WQBELs derived from the applicable designated use and criterion once a
WQS variance term ends, the regulation allows the state to adopt a
subsequent WQS variance if it is adopted consistent with 40 CFR 131.14.
D. Designated Uses
The EPA's proposed mercury criterion, once finalized, would apply
to Idaho waters where the protection of aquatic life is a designated
use. The Federal regulation at 40 CFR 131.10 provides requirements for
adopting, revising, and removing designated uses related to aquatic
life and recreation when attaining the use is not feasible based on one
of the six factors specified in the regulation. If Idaho removes the
aquatic life designated use from any of the waters to which the EPA is
proposing to apply this mercury criterion (i.e., from any water
designated for an aquatic life use at the time this criterion is
finalized), the state must adopt the highest attainable aquatic life
[[Page 24770]]
use \49\ and criteria, including a mercury criterion, to protect the
newly designated highest attainable use consistent with 40 CFR 131.11
for those waters. It is possible that criteria other than the federally
promulgated criteria would protect the highest attainable use. If the
EPA were to find Idaho's designated use revision to be consistent with
CWA section 303(c) and the implementing regulation at 40 CFR part 131,
the Agency would approve the revised WQS. The mercury criterion
proposed here, once finalized, would not apply to those waters to which
the aquatic life use no longer applies upon the EPA's approval.
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\49\ If a state or authorized Tribe adopts a new or revised WQS
based on a required use attainability analysis, then it must also
adopt the highest attainable use (40 CFR 131.10(g)). Highest
attainable use is 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 40 CFR 131.10(g) that preclude(s) attainment of the use and any
other information or analyses that were used to evaluate
attainability. There is no required highest attainable use where the
state demonstrates the relevant use specified in section 101(a)(2)
of the Act and sub-categories of such a use are not attainable (see
40 CFR 131.3(m)).
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VIII. Economic Analysis
The complete economic analysis for this proposed rulemaking is
documented in ``Economic Analysis for Proposed Mercury Criterion to
Protect Aquatic Life in Idaho,'' which can be found in the docket for
this rulemaking. For the economic analysis, the EPA assumed the
baseline to be full implementation of Idaho's existing water quality
criteria (i.e., ``baseline criteria''), and then estimated the
incremental impacts for compliance with the mercury criterion in this
proposed rulemaking. Specifically, the EPA assumed full implementation
of Idaho's existing 2.1 [micro]g/L acute (1-hour) and 0.012 [micro]g/L
chronic (4-day) aquatic life water column total mercury criteria and
Idaho's existing 0.3 mg/kg human health fish tissue methylmercury
criterion. To estimate the incremental impacts of compliance, the EPA
focused its economic analysis on two types of costs. First, the EPA
estimated the potential cost impacts to current holders of NPDES
permits. Second, the EPA estimated costs the state of Idaho may bear to
develop Total Maximum Daily Loads (TMDLs) for waters newly identified
as impaired under CWA section 303(d) using the proposed criterion.
Costs might also arise to sectors with operations that include
nonpoint sources of mercury through implementation of TMDLs or through
other voluntary, incentivized, or state-imposed controls. However,
these costs were not included in this economic analysis for several
reasons. First, the CWA, and therefore this proposed rulemaking, does
not regulate nonpoint sources. The EPA recognizes that controls for
nonpoint sources may be part of implementing future TMDLs, but those
decisions would be at the state's discretion. Furthermore, to
reasonably estimate those decisions, the EPA would need to have today
the detailed water quality data that Idaho would have in hand in the
future when they reach those decision points. Second, nonpoint sources
are intermittent, variable, and occur under hydrologic or climatic
conditions associated with precipitation events. As such, any estimate
of these costs would be associated with significant uncertainty.
The EPA seeks public comment on all aspects of the economic
analysis including, but not limited to, its assumptions relating to the
baseline, affected entities, implementation, and compliance costs.
A. Identifying Affected Entities
The proposed criterion would serve as a basis for development of
new or revised NPDES permit conditions for point source dischargers.
The EPA cannot be certain of whether a particular discharger would
change their operations if this proposed criterion were finalized and
the discharger were found to have reasonable potential to cause or
contribute to an exceedance of the criterion. Moreover, the EPA cannot
anticipate how Idaho would implement the criterion. Idaho is authorized
to administer the NPDES program and retains discretion in implementing
WQS. Despite this discretion, if Idaho determines that a permit is
necessary, such permit would need to comply with the EPA's regulations
at 40 CFR 122.44(d)(1)(i). Still, to best inform the public of the
potential impacts of this proposed rulemaking, the EPA made some
assumptions to evaluate the potential costs associated with state
implementation of the EPA's proposed criterion.
Any NPDES permitted facility discharging mercury could potentially
incur incremental compliance costs. The EPA identified 146 facilities
in Idaho with effective or administratively continued individual
permits (for any discharge, not just permits with mercury limits). The
types of affected facilities include sewage treatment facilities and
industrial facilities discharging wastewater to surface waters. In its
analysis of point sources, the EPA did not include facilities on Tribal
lands with permits issued by the EPA because the proposed rulemaking
would not cover Tribal lands.
Of the 146 facilities with individual permits, 17 are stormwater
discharges. The EPA excluded facilities with individual permits for
stormwater discharges (e.g., large or medium municipal separate storm
sewer systems) and facilities covered under general permits for
stormwater discharges because of limited data for such facilities and
permit requirements that typically focus on best management practices
(BMPs). This left 129 point source facilities with individual permits.
In addition, the EPA identified one facility covered under an NPDES
general permit that could be affected by the proposed rulemaking based
on the general permit requirements and available effluent data,
bringing the total number of potentially affected facilities to 130. Of
these, 38 are major dischargers and 92 are minor dischargers.
The EPA reviewed Discharge Monitoring Report (DMR) data for the 130
facilities to identify facilities with effluent limitations and/or
monitoring requirements for mercury in their NPDES permits. The EPA's
review of DMR data indicates that 31 facilities with individual permits
(24 majors, 7 minors) have effluent limitations and/or monitoring
requirements for mercury. Of these, 20 (18 majors, 2 minors) are
publicly owned treatment works (POTWs) categorized under North American
Industry Classification System (NAICS) Industry 221320 (Sewage
Treatment Facilities) and 11 (6 majors, 5 minors) are facilities
categorized under other NAICS Industries. The one facility covered
under a non-stormwater general permit with mercury data reported on
DMRs operates under an EPA-issued general permit for Groundwater
Remediation Discharge Facilities in Idaho, which includes mercury
limits applicable to the facility. Table 1 in this preamble summarizes
the potentially affected facilities by type (major or minor) and
category (NAICS Industry 221320 or other NAICS Industries). Table 1 in
this preamble also shows the number of facilities for which DMRs
indicate there are effluent limits and/or monitoring requirements for
mercury, including the facility covered by a general permit for
groundwater remediation discharges.
[[Page 24771]]
Table 1--Potentially Affected Facilities, With Facilities Having Mercury
Effluent Limitations and/or Monitoring Requirements for Mercury Shown in
Parentheses
------------------------------------------------------------------------
Major Minor
Category facilities facilities
------------------------------------------------------------------------
Sewage Treatment Facilities (NAICS 30 (18) 74 (2)
Industry 221320).......................
Industrial (Other NAICS Industries)..... 8 (6) 18 (6)
-------------------------------
Total............................... 38 (24) 92 (8)
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B. Method for Estimating Costs
The EPA grouped facilities with individual permits by major or
minor status and further grouped major facilities in NAICS Industry
221320 by design flow range. The EPA identified the facilities in each
grouping with effluent concentration data for mercury. The EPA reviewed
data for these facilities reported on DMRs accessed through the EPA's
Enforcement and Compliance History Online (ECHO) site and the
facilities' NPDES permits and fact sheets. The EPA used this
information to characterize baseline conditions; determine whether a
discharge would cause, have the reasonable potential to cause, or
contribute to an exceedance of baseline or proposed mercury criteria;
and assess whether the discharge is likely to exceed water quality-
based effluent limitations (WQBELs) derived from baseline and proposed
mercury criteria. Based on this analysis, the EPA identified facilities
that may need to implement additional actions to achieve compliance
with the proposed mercury criterion.
The EPA assumed that dischargers would pursue the least cost means
of compliance with WQBELs derived from the proposed mercury criterion.
Only the costs of compliance actions above the level of controls needed
to comply with baseline criteria are attributable to the proposed
rulemaking. To determine these incremental compliance costs, the EPA
considered potential one-time costs (e.g., costs for developing or
revising a pollutant minimization program (PMP), or applying for a WQS
variance) and annual costs (e.g., costs for implementing a new PMP or
for additional treatment).
For purposes of the analysis, the EPA assumed that major facilities
in NAICS Industry 221320 with no mercury data reported in DMRs for the
past five years would still likely discharge quantifiable
concentrations of mercury, though not at high enough concentrations for
mercury to be a pollutant of concern under the baseline Idaho mercury
criteria (i.e., the facilities currently have no mercury effluent
limits or monitoring requirements). The EPA also assumed that mercury
may become a pollutant of concern at these facilities under the
proposed mercury criterion. Based on these assumptions, the EPA
extrapolated estimated one-time and annual incremental compliance costs
for major facilities in NAICS Industry 221320 for which effluent data
for mercury are available to major facilities in NAICS Industry 221320
with no available effluent data for mercury. Specifically, the EPA
extrapolated cost within each facility flow rate range grouping
proportionally by number of facilities for one-time costs and annual
costs that are not flow-dependent (e.g., if 25% of the facilities with
mercury data would incur one-time costs that do not depend on effluent
flow rate, then the EPA assumed that 25% of facilities not reporting
mercury data would also incur such costs). For flow-dependent annual
costs, the EPA extrapolated based on design flow rate.
The EPA did not extrapolate costs for minor facilities in NAICS
Industry 221320 or for facilities categorized in other NAICS Industries
(major and minor industrial facilities). The EPA assumed that minor
POTWs (NAICS Industry 221320) are less likely than major POTWs to
receive influent from industrial and commercial sources of mercury,
which reduces the likelihood of mercury being a pollutant of concern
for those facilities where it has not already been identified as such.
The EPA also assumed that facilities in other NAICS Industries
(industrial discharges) for which mercury is a potential pollutant of
concern based on the proposed criterion typically would already have
effluent limits or monitoring requirements based on Idaho's baseline
mercury criteria.
The EPA also evaluated potential administrative costs to the state
for developing additional TMDLs under CWA section 303(d) for waters
that may be newly identified as impaired as a result of the proposed
mercury criterion, as well as potential costs for revising existing
TMDLs. Idaho assesses water bodies by assessment units (AUs). AUs are
subdivisions of water body units (WBIDs) which are subdivisions of 8-
digit hydrologic unit codes (HUCs). Using available fish tissue and
ambient water column monitoring data, the EPA compared mercury
concentrations to baseline Idaho mercury criteria and the proposed
mercury criterion, and identified AUs that may be incrementally
impaired (i.e., impaired under the proposed criterion but not under the
baseline criteria). For waters impaired under the baseline criteria,
the EPA assumes that the state will develop TMDLs and implementation
plans to bring all these waters into compliance with baseline criteria.
Therefore, only incremental costs identified to comply with the
proposed criterion above and beyond the baseline are attributable to
this proposed rulemaking.
C. Results
Based on the results for the 32 major and minor facilities (31 with
individual permits and 1 covered under a general permit) with available
effluent monitoring data for mercury, and extrapolation within each
design flow rate range to the 12 additional major NAICS Industry 221320
facilities without mercury data, the EPA estimated a range of total
one-time and total annual costs as shown in Table 2 in this preamble.
[[Page 24772]]
Table 2--Estimated One-Time and Annual Costs to Point Sources
[2022 Dollars]
--------------------------------------------------------------------------------------------------------------------------------------------------------
Total estimated one-time cost Total estimated annual cost (capital costs annualized over
------------------------------------------------------------------------------------------- 20 years at 2%)
-------------------------------------------------------------
Low High Low High
--------------------------------------------------------------------------------------------------------------------------------------------------------
$253,000................................................... $1,220,000 $120,000 $16,800,000
--------------------------------------------------------------------------------------------------------------------------------------------------------
The low end of the one-time cost range reflects an assumption that
most facilities potentially impacted would be able to comply with
revised effluent limitations or would revise an existing PMP to achieve
compliance. The high end of the one-time cost range assumes that
facilities would revise or develop a new PMP and, in some cases,
conduct the studies needed to apply for a WQS variance.
The low end of the annual cost range reflects an assumption that,
for most facilities, one-time actions, if needed, would result in
compliance with revised effluent limitations. The low end annual cost
estimate includes the costs for a limited number of facilities to
implement a new PMP and assumes that facilities implementing a revised
PMP plan do not incur incremental annual costs. The high end of the
annual cost range assumes that some facilities would incur the cost of
implementing a new PMP plan and some facilities would incur capital and
operation and maintenance costs associated with installing and
operating new or additional treatment, in this case non-membrane
filtration for mercury removal.
Based on available fish tissue data, the EPA identified four
instances of lake or reservoir AUs and two instances of river or stream
AUs that may be considered incrementally impaired under the proposed
criterion. In addition, based on ambient water quality data for
mercury, the EPA identified an additional 7 AUs that may be considered
incrementally impaired under the proposed criterion. The EPA estimated
a range for the total cost to develop TMDLs for the 13 AUs potentially
placed on Idaho's CWA section 303(d) list for mercury as a result of
the proposed criterion. These costs were based on single-cause single-
waterbody TMDL development costs. Actual costs may be lower if the
state develops multi-cause or multi-waterbody TMDLs. In addition, Idaho
currently has one approved TMDL for mercury for ID17040213SK007L_0L:
Salmon Falls Creek Reservoir. This TMDL may need to be revised based on
the proposed criterion and any new information that has become
available since the TMDL was approved. Based on administrative costs
associated with TMDL development for the 13 AUs identified as
incrementally impaired and for potential revision of 1 TMDL, the EPA
estimated total costs associated with incremental impairments to be
$586,000 to $629,000.
IX. Statutory and Executive Orders Reviews
A. Executive Order 12866: Regulatory Planning and Review and Executive
Order 14094: Modernizing Regulatory Review
This action is not a significant regulatory action as defined in
Executive Order 12866, as amended by Executive Order 14094, and was
therefore not subject to a requirement for Executive Order 12866
review.
B. Paperwork Reduction Act (PRA)
This action does not impose any new information collection burden
under the PRA. OMB has previously approved the information collection
requirements activities contained in the existing regulation and has
assigned OMB control number 2040-0049. This action does not directly
contain any information collection, reporting, or record-keeping
requirements.
C. Regulatory Flexibility Act (RFA)
I certify that this action will not have a significant economic
impact on a substantial number of small entities under the RFA. This
action will not impose any requirements on small entities.
EPA-promulgated WQS are implemented through various water quality
control programs, including the NPDES program, which limits discharges
to navigable waters except in compliance with a NPDES permit. CWA
section 301(b)(1)(C) \50\ and the EPA's implementing regulation at 40
CFR 122.44(d)(1) provide that all NPDES permits shall include any
limits on discharges that are necessary to meet applicable WQS. Thus,
under the CWA, the EPA's promulgation of WQS establishes standards that
the state implements through the NPDES permit process.
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\50\ 301(b) Timetable for achievement of objectives. In order to
carry out the objective of this chapter there shall be achieved--
(1)(C): not later than July 1, 1977, any more stringent limitation,
including those necessary to meet water quality standards, treatment
standards, or schedules of compliance, established pursuant to any
State law or regulations (under authority preserved by section 1370
of this title) or any other Federal law or regulation, or required
to implement any applicable water quality standard established
pursuant to this chapter.
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After the EPA promulgates a final mercury criterion, the state of
Idaho must ensure that NPDES permits it issues include any limitations
on discharges necessary to comply with the WQS established in the final
rule. While Idaho's implementation of the rule may ultimately result in
new or revised permit conditions for some dischargers, including small
entities, the EPA's action, by itself, does not impose any of these
requirements on small entities; that is, these requirements are not
self-implementing.
D. Unfunded Mandates Reform Act (UMRA)
This action does not contain any unfunded mandates as described in
UMRA, 2 U.S.C. 1531-1538, and does not significantly or uniquely affect
small governments. The action imposes no enforceable duty on any state,
local or Tribal governments or the private sector.
E. Executive Order 13132 (Federalism)
This action does not have federalism implications. The EPA
believes, however, that this action may be of significant interest to
state governments. Consistent with the EPA's policy to promote
communications between the EPA and state and local governments, the EPA
consulted with Idaho officials early in the process of developing this
rulemaking to permit them to have meaningful and timely input into its
development.
On several occasions starting on July 12, 2023, the EPA discussed
the development of this rulemaking with the Idaho Department of
Environmental Quality. Early in this process, the EPA clarified that if
and when the state decides to revise its own mercury aquatic life
criteria, the EPA would assist the state in its process. During these
discussions, the EPA also explained: the scientific basis for the
[[Page 24773]]
fish tissue and water column elements of the mercury criterion; the
external peer review process and the comments the EPA received on the
derivation of the criterion; the EPA's consideration of those comments
and responses; the assumptions and data being used in the economic
analysis associated with the rulemaking; and the overall timing of the
Federal rulemaking effort. The EPA took these discussions with the
state into account during the drafting of this proposed rulemaking.
F. Executive Order 13175 (Consultation and Coordination With Indian
Tribal Governments)
This action does not have Tribal implications as specified in
Executive Order 13175. This rule does not impose substantial direct
compliance costs on federally recognized Tribal governments, nor does
it substantially affect the relationship between the Federal government
and Tribes, or the distribution of power and responsibilities between
the Federal government and Tribes. Thus, Executive Order 13175 does not
apply to this action.
Consistent with the EPA Policy on Consultation and Coordination
with Indian Tribes, the EPA consulted with Tribal officials during the
development of this action. A Summary of Consultation, Coordination and
Outreach with Federally Recognized Tribes on the EPA's Proposed Federal
Promulgation of a Mercury Criterion to Protect Aquatic Life in Idaho is
available in the docket.
G. Executive Order 13045 (Protection of Children From Environmental
Health and Safety Risks)
The EPA interprets Executive Order 13045 as applying only to those
regulatory actions that concern environmental health or safety risks
that the EPA has reason to believe may disproportionately affect
children, per the definition of ``covered regulatory action'' in
section 2-202 of the Executive Order. Therefore, this action is not
subject to Executive Order 13045 because it does not concern an
environmental health risk or safety risk. Since this action does not
concern human health, the EPA's Policy on Children's Health also does
not apply.
H. Executive Order 13211 (Actions That Significantly Affect Energy
Supply, Distribution, or Use)
This action is not a ``significant energy action'' because it is
not likely to have a significant adverse effect on the supply,
distribution, or use of energy.
I. National Technology Transfer and Advancement Act of 1995
This rulemaking does not involve technical standards.
J. Executive Order 12898: Federal Actions To Address Environmental
Justice in Minority Populations and Low-Income Populations and
Executive Order 14096: Revitalizing Our Nation's Commitment to
Environmental Justice for All
The EPA believes that the human health and environmental conditions
that exist prior to this action do not result in disproportionate and
adverse effects on communities with environmental justice (EJ)
concerns. In the EPA's Economic Analysis for Proposed Mercury Criterion
to Protect Aquatic Life in Idaho (economic analysis), which can be
found in the docket for this rulemaking, Exhibit 5-3 illustrates the
geographic distribution of waters where available data indicate levels
of mercury that exceed Idaho's existing mercury criteria. These waters
are located throughout the state, and waters with the highest levels of
exceedance are similarly found in multiple parts of the state. Given
the widespread nature of these impaired waters across the entire state,
it is unlikely that impaired waters are disproportionately located in
proximity to communities with potential EJ concerns.
The EPA believes that this action is not likely to result in new
disproportionate and adverse effects on communities with EJ concerns.
The EPA's proposed criterion for mercury in Idaho applies to aquatic
life uses and does not directly address human health impacts. However,
this rulemaking, if finalized and implemented, would support the health
and abundance of aquatic life in Idaho and would, therefore, not only
benefit those aquatic species but also benefit human communities that
rely on or use these ecosystems. Compared to higher-income populations,
low-income populations tend to rely more on fishing as a food
source,\51\ and therefore, this rulemaking may especially benefit low-
income communities.
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\51\ Von Stackelberg, K., et al. (2017). Results of a national
survey of high-frequency fish consumers in the United States.
Environmental Research 158, 126-136. https://bgc.seas.harvard.edu/assets/vonstackelberg2017.pdf.
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To achieve the benefits associated with a final rule, the EPA
recognizes that some facilities may need to add pollution control
measures and incur additional compliance costs over time to meet any
new permit conditions or limits resulting from the mercury criterion,
once finalized. The EPA's economic analysis identified three wastewater
treatment plants and one mine that may need to install additional
treatment technologies (e.g., non-membrane filtration) if the criterion
is finalized as proposed. For the wastewater treatment plants, the EPA
analyzed the compliance costs that might be passed on to residential
households alongside the socioeconomic characteristics of those
households.
For the West Boise Water Renewal Facility, the high end of the
estimated annual cost range from the economic analysis is $6.7M. For
the Nampa Wastewater Treatment Facility, the high end of the estimated
annual cost range is $5.1M. For the City of Caldwell Wastewater
Treatment Plant, the high end of the estimated annual cost range is
$2.4M. Based on the estimated number of households served by each
facility \52\ and conservatively assuming that 100% of the additional
treatment costs are borne by residential ratepayers, these costs would
translate to monthly household sewer bill increases of approximately
$7.93, $11.78, and $10.16 for households served by the West Boise,
Nampa, and Caldwell facilities, respectively. These amounts would
represent approximately a 20-30% increase relative to current sewer
bills in these areas.\53\ After this increase, household sewer bills
would represent approximately 0.85%, 1.17%, and 1.05% of the median
household income \54\ in Boise, Nampa, and Caldwell, respectively.
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\52\ The EPA estimated the number of households served by the
West Boise Water Renewal Facility from the 2022 IPDES Permit Fact
Sheet. The EPA estimated the number of households served by the
Nampa Wastewater Treatment Facility and the City of Caldwell
Wastewater Treatment Plant from 2018-2022 American Community Survey
5-year data, since the most recent Permit Fact Sheets for these
facilities were from 2015 and their service areas could be
approximated by U.S. Census Places (Nampa City and Caldwell City).
\53\ https://www.idahopress.com/news/local/boise-voters-overwhelmingly-pass-sewer-bond/article_a72230a4-6875-5708-a41b-c7a9fbce8e6e.html; https://www.cityofnampa.us/1397/2021-Rate-
Increase#:~:text=Sewer%20Rate%20Increase%20Approved%20as%20Part%20of%
20Bond%20Repayment%20Plan&text=Beginning%20October%201%2C%20the%20ave
rage,per%20month%20for%20residential%20customers.
\54\ 2018-2022 American Community Survey 5-year data. https://www.census.gov/data/developers/data-sets/acs-5year.html.
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Using EJScreen, the EPA performed a screening-level analysis of the
socioeconomic characteristics of these communities, focusing on
EJScreen's
[[Page 24774]]
individual socioeconomic indicators.\55\ To interpret EJScreen results,
the EPA used an 80th percentile filter for each indicator,\56\ using
percentiles reflecting comparison to the Idaho population and to the
entire U.S. population. The percentile indicates what percent of the
comparison population (here, Idaho or entire U.S.) has an equal or more
favorable value.
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\55\ People of color, low income, unemployment rate, limited
English speaking households, less than high school education, under
age 5, over age 64, and low life expectancy. See EJScreen Technical
Documentation for Version 2.2 for indicator definitions (https://www.epa.gov/system/files/documents/2023-06/ejscreen-tech-doc-version-2-2.pdf).
\56\ https://www.epa.gov/ejscreen/how-interpret-ejscreen-data.
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When comparing each of the three communities to the entire U.S.
population, the EPA found limited indication of potential EJ concern
that would warrant further analysis; only one indicator in one
community just reached the 80th percentile threshold (the percentage of
people under age 5 in Caldwell, ID was at the 80th percentile). At the
same time, comparing each of the communities to the Idaho population
highlighted some differences in their socioeconomic situations. While
Boise did not exceed the 80th percentile (relative to the Idaho
population) for any of the eight socioeconomic indicators, Nampa
exceeded for two indicators (people of color and limited English
speaking households) and Caldwell exceeded for three indicators (people
of color, limited English speaking households, and less than high
school education) and had another two indicators (under age 5 and
unemployment rate) at the 77th percentile. Therefore, due to the
potentially greater socioeconomic vulnerability as indicated by this
screening-level analysis, these potential (albeit relatively modest)
sewer rate increases may have disproportionate economic impacts in
Caldwell relative to Boise, Nampa, and other Idaho communities.
However, actual impacts would depend on a number of factors,
including how the state implements the criterion, how costs are
financed, and how costs are distributed among ratepayers. States have
wide latitude in how they implement criteria, including the authority
to adopt variances for those facilities for which meeting WQS would
cause substantial and widespread economic and social impact.
Communities can apply for various grants to finance wastewater
treatment upgrades or the state may share part of the cost burden. In
addition, the Bipartisan Infrastructure Law included $50 billion in
funding for infrastructure improvements to the Nation's wastewater and
drinking water systems. Moreover, municipalities may implement customer
assistance or progressive rate structures that reduce the cost burden
on low income households.\57\ Finally, the costs of wastewater
treatment upgrades must be balanced against the potential benefits of
having access to cleaner water. The EPA seeks comment on all potential
EJ impacts of the rulemaking.
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\57\ USEPA. 2023. Clean Water Act Financial Capability
Assessment Guidance. 800b21001. U.S. Environmental Protection
Agency, Office of Water, Washington, DC. https://www.epa.gov/system/files/documents/2023-01/cwa-financial-capability-assessment-guidance.pdf.
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In addition to Executive Order 12898, and in accordance with Title
VI of the Civil Rights Act of 1964, each Federal agency shall ensure
that all programs or activities receiving Federal financial assistance
that affect human health or the environment do not directly, or through
contractual or other arrangements, use criteria, methods, or practices
that discriminate on the basis of race, color, or national origin. With
that directive in mind, in August 2011 the Environmental Justice
Interagency Working Group established a Title VI Committee to address
the intersection of agencies' EJ efforts with their Title VI
enforcement and compliance responsibilities. While the EPA only has an
oversight role for CWA implementation, if Idaho receives Federal funds
for CWA implementation, the state is legally prohibited from
discriminating on the basis of race, color, or national origin under
Title VI when engaging in CWA implementation activities. Additionally,
and in compliance with Executive Order 12898, the EPA expects that
Idaho will consider disproportionately high adverse human health and
environmental effects on communities with EJ concerns when implementing
this rulemaking under the CWA.
The information supporting this Executive Order review is contained
in the EPA's Economic Analysis for Proposed Mercury Criterion to
Protect Aquatic Life in Idaho.
List of Subjects in 40 CFR Part 131
Environmental protection, Indians--lands, Intergovernmental
relations, Reporting and recordkeeping requirements, Water pollution
control.
Michael S. Regan,
Administrator.
For the reasons set forth in the preamble, the EPA proposes to
amend 40 CFR part 131 as follows:
PART 131--WATER QUALITY STANDARDS
0
1. The authority citation for part 131 continues to read as follows:
Authority: 33 U.S.C. 1251 et seq.
Subpart D--Federally Promulgated Water Quality Standards
0
2. Add Sec. 131.XX to read as follows:
Sec. 131.XX Mercury criterion to protect aquatic life in Idaho.
(a) Scope. This section promulgates an aquatic life criterion for
mercury in Idaho.
(b) Criterion for mercury in Idaho. The applicable aquatic life
criterion for mercury is shown in Table 1 to Paragraph (b).
Table 1 to Paragraph (b)--Proposed Chronic Mercury Ambient Water Quality Criterion for the Protection of Aquatic
Life in Idaho
----------------------------------------------------------------------------------------------------------------
Fish muscle tissue 1 2 Fish whole body tissue Water column 1 4 total
Media type 3 total mercury (ng THg/ 1 2 total mercury (ng mercury (ng/L) in whole
g wet weight) THg/g wet weight) water
----------------------------------------------------------------------------------------------------------------
Magnitude............................ 225.................... 162.................... 2.1.
--------------------------------------------------
Duration............................. Instantaneous measurement \5\. 30 day average.
Frequency............................ The average tissue concentration must not be Not more than once in
exceeded. three years on
average.
----------------------------------------------------------------------------------------------------------------
\1\ The proposed criterion elements are hierarchical, with both tissue elements superseding the water column
element. The fish muscle tissue and fish whole body tissue criterion elements are independently applicable.
[[Page 24775]]
\2\ Tissue sample measurements must be based on measurement(s) of the total mercury concentration (in a
composited tissue sample from each fish species or a central tendency estimate of individual tissue samples
from each fish species) collected from a given site or waterbody in a discrete sampling period. These
criterion elements support Idaho's aquatic life uses. Only samples of adult life stage trophic level (TL) 4
fish can be directly compared to the muscle or whole-body criterion elements.
\3\ If adult life stage TL2 or TL3 fish are sampled, a Bioaccumulation Trophic Adjustment Factor (BTAF) must be
applied to the muscle concentrations of those fish. If whole-body tissue from TL2 or TL3 fish is sampled, the
fish whole body--muscle conversion factor of 0.72 must be applied to generate a translated muscle value before
a BTAF is applied to the sample concentration. A TL2 sampled fish concentration must be multiplied by the TL2
BTAF of 5.6 and the resultant value compared to the muscle tissue criterion element. A TL3 sampled fish
concentration must be multiplied by the TL3 BTAF of 3.5 and the resultant value compared to the muscle tissue
criterion element. If multiple adults of different TLs are sampled, the TL4 fish result would supersede TL3
BTAF-applied or TL2 BTAF-applied value outcomes. If TL3 and TL2 fish are sampled, the TL3 BTAF-applied values
supersede the TL2 BTAF-applied values.
\4\ Water column values are based on total mercury in unfiltered or ``whole water'' samples. Total mercury
includes all inorganic and organic species of mercury in the water column. Water samples collected during
baseflow conditions would be most representative of the data used to derive this criterion element. This
criterion element supports Idaho's aquatic life uses.
\5\ Fish tissue data provide integrative measurements that reflect accumulation of mercury over time and space
in aquatic organisms from a given site or waterbody in a discrete sampling period.
(c) Applicability. (1) The criterion in paragraph (b) of this
section applies to all of Idaho's aquatic life use designations and
applies concurrently with other applicable water quality criteria.
(2) The criterion established in this section is subject to Idaho's
general rules of applicability in the same way and to the same extent
as are other federally promulgated and state-adopted numeric criteria
when applied to waters in Idaho designated to protect aquatic life
uses.
(3) For all waters with mixing zone regulations or implementation
procedures, the criterion applies at the appropriate locations within
or at the boundary of the mixing zones and outside of the mixing zones;
otherwise the criterion applies throughout the water body including at
the end of any discharge pipe, conveyance or other discharge point
within the water body.
[FR Doc. 2024-07450 Filed 4-8-24; 8:45 am]
BILLING CODE 6560-50-P