[Federal Register Volume 88, Number 244 (Thursday, December 21, 2023)]
[Proposed Rules]
[Pages 88315-88336]
[FR Doc No: 2023-27758]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 131

[EPA-HQ-OW-2023-0222; FRL 10760-01-OW]
RIN 2040-AG30

Water Quality Standards To Protect Aquatic Life in the Delaware
River

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: On December 1, 2022, the U.S. Environmental Protection Agency
(EPA) determined that revised water quality standards are necessary to
protect aquatic life in certain water quality management zones of the
Delaware River. Specifically, the EPA issued an Administrator's
Determination, pursuant to the Clean Water Act (CWA), finding that a
revised designated use to protect aquatic life propagation and
corresponding dissolved oxygen criteria to protect that use are
necessary in Zone 3, Zone 4, and the upper portion of Zone 5 (in total,
river miles 108.4 to 70.0) of the Delaware River. The CWA requires the
EPA to publish proposed water quality standards following an
Administrator's Determination. Thus, the EPA is proposing to promulgate
an aquatic life designated use that includes propagation and protective
water quality criteria for dissolved oxygen for Zone 3, Zone 4, and
upper Zone 5 of the Delaware River.

DATES: Comments must be received on or before February 20, 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-2023-0222, 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.-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.

FOR FURTHER INFORMATION CONTACT: Hannah Lesch, Office of Water,
Standards and Health Protection Division (4305T), Environmental
Protection Agency, 1200 Pennsylvania Avenue NW, Washington, DC 20460;
telephone number:<PHONE_NUMBER>; email address: [email protected].

SUPPLEMENTARY INFORMATION: This proposed rule 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. Relevant Ecological History of the Delaware River
    C. Administration of Water Quality Standards in the Delaware
River
    D. Currently Applicable Aquatic Life Designated Uses and
Dissolved Oxygen Criteria
    E. Summary of the EPA's Administrator's Determination
IV. Proposed Water Quality Standards
    A. Scope of EPA's Proposed Rule
    B. Proposed Aquatic Life Designated Use
    C. Dissolved Oxygen Criteria To Protect Aquatic Life Propagation
V. Endangered Species Act Consultation
VI. Applicability
VII. Conditions Where Federal Water Quality Standards Would Not Be
Promulgated or Would Be Withdrawn
    A. Conditions Where Federal Standards Would Not Be Promulgated
    B. Conditions Where Federal Standards Would Be Withdrawn
VIII. Alternative Regulatory Approaches and Implementation
Mechanisms
    A. Water Quality Standards Variances
    B. NPDES Permit Compliance Schedules
    C. Clean Water Act Section 303(d)/305(b) Water Quality
Assessments
IX. Economic Analysis
X. Statutory and Executive Order 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 (NTTAA)
    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-
0222, at https://www.regulations.gov (the EPA's 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 public hearings so that interested parties
may also provide oral comments on this proposed rulemaking. For more
details on the public hearings and to register to attend the hearings,
please visit https://www.epa.gov/wqs-tech/water-quality-standards-delaware-river.

II. General Information

A. Does this action apply to me?

    A range of individuals and entities could be affected by this
rulemaking, if finalized. For example, entities that discharge
pollutants to certain waters under the jurisdiction of the states of
Delaware, New Jersey, and Pennsylvania--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 these waters for CWA purposes (Table 1
of this preamble). 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) under CWA section 402 \1\ and identifying impaired waters under
CWA section 303(d). In addition, individuals and entities who rely on
or benefit from aquatic life in those waters may be indirectly
affected.
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    \1\ Before any water quality-based effluent limit would be
included in an NPDES permit, the permitting authority (here, the
states of Delaware, New Jersey, and Pennsylvania), 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).

      Table 1--Entities Potentially Affected by This Proposed Rule
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                                      Examples of potentially affected
             Category                             entities
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Industry..........................  Industrial point sources discharging
                                     to certain waters in Delaware, New
                                     Jersey, and Pennsylvania.
                                     Commercial fishing operations that
                                     harvest fish.
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 to certain waters in
                                     Delaware, New Jersey, and
                                     Pennsylvania.
Recreation and Tourism............  Anglers and tourists seeking
                                     recreational opportunities related
                                     to aquatic life in certain waters
                                     in Delaware, New Jersey, and
                                     Pennsylvania.
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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'' or
``101(a)(2) goals''), wherever attainable. The EPA's regulation at 40
CFR 131.10(g) 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
reviewing, establishing, 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 protection and
propagation 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)).
    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)). Every
three years, states must also reexamine water body segments that do not
include the 101(a)(2) uses to determine if new information has become
available that indicates the 101(a)(2) uses are attainable, and if so,
revise the WQS accordingly (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)).
    CWA section 303(c)(4)(B) independently authorizes the Administrator
to determine that a new or revised standard is necessary to meet CWA
requirements; this action is frequently referred to as an
``Administrator's Determination.'' Pursuant to CWA section
303(c)(4)(B), after making an Administrator's Determination, the EPA
must propose and promulgate WQS specified in the Administrator's
Determination. If a state adopts and the EPA approves WQS that address
the Administrator's Determination prior to the EPA's promulgation, then
the EPA would no longer be required to promulgate WQS.

B. Relevant Ecological History of the Delaware River

    The Delaware River has historically been home to numerous species
of ecological, recreational, and economic importance; however,
centuries of anthropogenic water quality impacts and habitat
degradation, peaking in the mid-twentieth century, made portions of the
river unsuitable for many aquatic species. In the 1700s and 1800s, many
native fish species in the Delaware River faced declining populations
due to overharvesting and the installation of physical barriers that
prevented fish passage.\2\ Further population declines of native
oxygen-sensitive species--such as the Atlantic Sturgeon (Acipenser
oxyrinchus oxyrinchus), American Shad (Alosa sapidissima), Shortnose
Sturgeon (Acipenser brevirostrum), and Striped Bass (Morone saxatilis),
among others \3\--were linked to accelerating degradation of water
quality through the first half of the 1900s, including seasonal anoxia
(i.e., absence of oxygen) by the mid-twentieth century in Zone 3, Zone
4, and the upper portion of Zone 5 of the Delaware River.\4\
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    \2\ Hardy, C.A. (1999). Fish or Foul: A History of the Delaware
River Basin Through the Perspective of the American Shad, 1682 to
the Present. Pennsylvania History, 66(4), 506-534. https://digitalcommons.wcupa.edu/hist_facpub/13; Secor, D.H. and Waldman, J.
(1999). Historical abundance of Delaware Bay Atlantic sturgeon and
potential rate of recovery. American Fisheries Society Symposium.
23. 203-216. https://www.researchgate.net/publication/291783957_Historical_abundance_of_Delaware_Bay_Atlantic_sturgeon_and_potential_rate_of_recovery; Smith, T.I.J., & Clugston, J.P. (1997)
Status and management of Atlantic sturgeon, Acipenser oxyrinchus, in
North America. Environmental Biology of Fishes 48, 335-346. https://doi.org/10.1023/A:1007307507468; National Marine Fisheries Service.
(1998). Recovery Plan for the Shortnose Sturgeon (Acipenser
brevirostrum). Prepared by the Shortnose Sturgeon Recovery Team for
the National Marine Fisheries Service, Silver Spring, Maryland. 104
pages. https://repository.library.noaa.gov/view/noaa/15971.
    \3\ Stoklosa, A.M., Keller, D.H., Marano, R., and Horwitz, R.J.
(2018). ``A Review of Dissolved Oxygen Requirements for Key
Sensitive Species in the Delaware Estuary.'' Academy of Natural
Sciences of Drexel University. November 2018. https://www.nj.gov/drbc/library/documents/Review_DOreq_KeySensSpecies_DelEstuary_ANStoDRBCnov2018.pdf.
    \4\ See citations in footnote 2 of this preamble; Atlantic
States Marine Fisheries Commission. (1981). Interstate Fisheries
Management Plan for the Striped Bass. http://www.asmfc.org/uploads/file/1981FMP.pdf.
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    Dissolved oxygen is an important water quality parameter that can
significantly influence the distribution and abundance of aquatic
organisms and ecological relationships in aquatic ecosystems. Aquatic
organisms need to obtain adequate levels of dissolved oxygen to
maintain and support normal functioning, including during sensitive
life stages, such as spawning, larval development, and juvenile
growth.\5\ As dissolved oxygen levels decrease in a waterbody, the rate
at which aquatic organisms can obtain oxygen from the water decreases,
resulting in impaired growth and reduced survival. Maintaining a
healthy ecosystem requires dissolved oxygen levels above thresholds
that impair growth and survival of aquatic species.
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    \5\ United States Environmental Protection Agency. (2021).
Factsheet on Water Quality Parameters: Dissolved Oxygen. July 2021.
Document ID: EPA 841F21007B. https://www.epa.gov/system/files/documents/2021-07/parameter-factsheet_do.pdf; United States
Environmental Protection Agency. (2023a). Indicators: Dissolved
Oxygen. June 9, 2023. https://www.epa.gov/national-aquatic-resource-surveys/indicators-dissolved-oxygen.
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1. Causes of Low Dissolved Oxygen in the Specified Zones of the
Delaware River
    Discharges of untreated or poorly treated municipal and industrial
wastewater into the specified zones of the Delaware River have
historically been a major cause of water quality degradation, including
oxygen depletion.\6\ While conditions have significantly improved,
inputs of oxygen-consuming wastes from wastewater dischargers,
especially ammonia (NH3) and ammonium (NH4\+\)
(which in combination are hereafter referred to as ``ammonia
nitrogen''), as well as sediment-water ammonium flux and sediment
oxygen demand continue to be significant sources of oxygen demand in
the specified zones of the Delaware River.\7\
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    \6\ Hardy (1999); Delaware River Basin Commission. (2022a).
Analysis of Attainability: Improving Dissolved Oxygen and Aquatic
Life Uses in the Delaware River Estuary. September 2022 Draft. See
section 3--``Factors that can Improve Dissolved Oxygen in the Fish
Maintenance Area.'' https://www.nj.gov/drbc/library/documents/AnalysisAttainability/AnalysisAttainability_DRAFTsept2022.pdf.
    \7\ Delaware River Basin Commission. (2022b). Modeling
Eutrophication Processes in the Delaware River Estuary--Three-
Dimensional Water Quality Model. https://www.nj.gov/drbc/library/documents/AnalysisAttainability/WQModelCalibrationRpt_DRAFTsept2022.pdf.
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    Along the Delaware River, untreated wastewater discharges typically
occur during and after rainfall due to combined sewer overflows (CSOs),
which are a source of nutrients (i.e., nitrogen and phosphorus),
sediments, and toxic contaminants, and can lead to increased chemical
and biological oxygen demand in the river.\8\ Although the cumulative
impact of historical

CSOs on sediment oxygen demand in the Delaware River has not been
estimated, CSOs can over time increase or maintain sediment oxygen
demand as untreated organic material settles on the riverbed and is
broken down by oxygen consuming bacteria (thus, removing oxygen from
the water column), a process that continues long after the end of an
overflow event.\9\ CSOs have been a persistent source of pollutants in
the specified zones of the Delaware River for over a century. For
example, sewer overflows from Philadelphia in the early 1900s deposited
over 200,000 tons of solids per year, which, in combination with other
solid wastes, created deposits 12 feet deep in the river.\10\ From July
1, 2021, to June 30, 2022, Philadelphia's wastewater system alone
discharged over 1.7 billion cubic feet of CSOs into the Delaware
River.\11\
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    \8\ Miskewitz, R. and Uchrin, C. (2013). In-Stream Dissolved
Oxygen Impacts and Sediment Oxygen Demand Resulting from Combined
Sewer Overflow Discharges. Journal of Environmental Engineering,
139(10). https://doi.org/10.1061/(ASCE)EE.1943-7870.0000739.
    \9\ Miskewitz and Uchrin (2013).
    \10\ Hardy (1999).
    \11\ Philadelphia Water Department. (2022). Combined Sewer
Management Program Annual Report. Stormwater Management Program
Annual Report. See Appendix D--``NPDES Annual CSO Status Report FY
2022,'' Table 2--``Overflow Summary for 7/1/2021-6/30/2022.''
https://water.phila.gov/pool/files/fy22-npdes-annual-report.pdf.
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    Although most point source discharges today are treated, treated
effluent can still contain high levels of ammonia nitrogen, which
depletes oxygen in the water as bacteria oxidize ammonia into nitrite,
nitrate and dinitrogen gas.\12\ During the reporting periods from July
through October 2022, major wastewater treatment facilities along the
Delaware River discharged ammonia nitrogen at monthly average
concentrations ranging from a low of 0.07 milligrams nitrogen per liter
(mg-N/L) at the Florence Township Sewage Treatment Plant in New Jersey
(discharging into Zone 2 of the Delaware River) to a high of 35 mg-N/L
at the Camden County Municipal Utilities Authority in New Jersey
(discharging into Zone 3 of the Delaware River).\13\
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    \12\ United States Environmental Protection Agency. (2023b).
Ammonia. https://www.epa.gov/caddis-vol2/ammonia.
    \13\ Each individual reporting period is one month long. For the
reporting period ending on September 30, 2022, Florence Township
Municipal Building discharged an average of .07 mg/L of ammonia. For
the reporting period ending on July 31, 2022, Camden County
Municipal Utilities Authority discharged an average of 35 mg/L of
ammonia. Source: U.S. Environmental Protection Agency. Integrated
Compliance Information System (ICIS). Database. Retrieved June 29,
2023.
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2. Endangered Species in the Specified Zones of the Delaware River
    The Delaware River is home to two oxygen-sensitive fish species--
Shortnose Sturgeon and Atlantic Sturgeon--that are protected under the
Federal Endangered Species Act (ESA). All populations of Shortnose
Sturgeon were listed as endangered in 1967.\14\ Across the U.S.,
Shortnose Sturgeon face ongoing threats due to water pollution, habitat
degradation, and fisheries bycatch, among other factors.\15\ While the
historic population size of Shortnose Sturgeon in the Delaware River
remains unknown, in 2006 the population was estimated to be
approximately 12,000 adults.\16\ The New York Bight distinct population
segment (DPS) of Atlantic Sturgeon--which includes the population found
in the Delaware River--was listed as endangered under the ESA in
2012.\17\ In 2017, the National Oceanic and Atmospheric Administration
(NOAA Fisheries) designated the Delaware River, among others, as
critical habitat for the New York Bight DPS of Atlantic Sturgeon,\18\
and reaffirmed its endangered listing in 2022 following a five-year
review of its status.\19\ The remnant population of the New York Bight
DPS of Atlantic Sturgeon faces ongoing threats due to water quality in
natal rivers, such as the Delaware River, as well as climate change,
ship strikes, fisheries bycatch, habitat loss, and entanglement in
fishing gear.20 21 Like the Shortnose Sturgeon, the historic
population size of Atlantic Sturgeon is not well documented. However,
in 1890, when the population was already declining, there were
approximately 180,000 female Atlantic Sturgeon in the Delaware
River.\22\ Despite improvements in dissolved oxygen levels since the
1970s, it is estimated that only 125-250 adult Atlantic Sturgeon
currently return to spawn in the Delaware River.\23\
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    \14\ Federal Register, Vol. 32, No. 48 (32 FR 4000). March 11,
1967. https://www.fisheries.noaa.gov/s3//2022-12/4000-4002.pdf.
    \15\ NOAA Fisheries. (2023a). Shortnose Sturgeon--Overview.
https://www.fisheries.noaa.gov/species/shortnose-sturgeon.
    \16\ Id.; NOAA Fisheries. (2023b). Shortnose Sturgeon--
Populations. https://www.fisheries.noaa.gov/species/shortnose-sturgeon#populations.
    \17\ Federal Register, Vol. 77, No. 24. February 6, 2012. 77 FR
5879. https://www.federalregister.gov/documents/2012/02/06/2012-1946/endangered-and-threatened-wildlife-and-plants-threatened-and-endangered-status-for-distinct.
    \18\ Federal Register, Vol. 82, No. 158 (82 FR 39160). August
17, 2017. 50 CFR part 226. https://www.federalregister.gov/documents/2017/08/17/2017-17207/endangered-and-threatened-species-designation-of-critical-habitat-for-the-endangered-new-york-bight.
    \19\ National Marine Fisheries Service. (2022). New York Bight
Distinct Population Segment of Atlantic Sturgeon (Acipenser
oxyrinchus oxyrinchus), 5-Year Review: Summary and Evaluation.
February 17, 2022. https://www.fisheries.noaa.gov/resource/document/new-york-bight-distinct-population-segment-atlantic-sturgeon-5-year-review.
    \20\ Ibid. See Section 2.3.2, ``Five-Factor Analysis (threats,
conservation measures, and regulatory mechanisms)'', A. through E.,
pp. 14-25.
    \21\ Dunton, K.J., Jordaan, A., Conover, D.O., McKown, K.A.,
Bonacci, L.A., and Frisk, M.G. (2015). Marine Distribution and
Habitat Use of Atlantic Sturgeon in New York Lead to Fisheries
Interactions and Bycatch. Marine and Coastal Fisheries 7:18-32.
https://doi.org/10.1080/19425120.2014.986348; Atlantic Sturgeon
Bycatch Working Group. (2022). Action Plan to Reduce Atlantic
Sturgeon Bycatch in Federal Large Mesh Gillnet Fisheries. NOAA
National Marine Fisheries Service. https://media.fisheries.noaa.gov/2022-09/Final-Action-Plan-to-Reduce-Atlantic-Sturgeon-Bycatch.pdf.
    \22\ Secor and Waldman (1999).
    \23\ White, S.L., Sard, N.M., Brundage, H.M., Johnson, R.L.,
Lubinski, B.A., Eackles, M.S., Park, I.A., Fox, D.A., and Kazyak,
D.C. (2022). Evaluating Sources of Bias in Pedigree-Based Estimates
of Breeding Population Size. Ecological Applications 32(5): e2602.
https://doi.org/10.1002/eap.2602.
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    In addition to being listed as endangered under the ESA, available
evidence suggests that Shortnose Sturgeon and Atlantic Sturgeon are the
most oxygen-sensitive species in the specified zones of the Delaware
River. In general, all sturgeon species share common life history
traits,\24\ among which they are recognized to be relatively more
sensitive to low dissolved oxygen levels compared to other co-occurring
fish.25 26 Sturgeons are considered unusually sensitive to
hypoxia given their documented metabolic and behavioral responses and
limited ability to oxyregulate.\27\ Juvenile Atlantic Sturgeon are
particularly sensitive to low dissolved oxygen levels, especially at
high water temperatures,\28\ such as those typically present at the
peak of summer in the Delaware River.\29\ A literature review across
oxygen-

sensitive species in the Delaware River indicates that Atlantic
Sturgeon, particularly the juvenile life stage, have the highest
documented dissolved oxygen requirements for growth and survival when
compared to other oxygen-sensitive species in the specified zones of
the Delaware River.\30\ In its five-year review of the listing of the
New York Bight DPS of Atlantic Sturgeon, NOAA Fisheries observed a
continuation of low dissolved oxygen conditions in the Delaware River
around the expected location of age 0-1 Atlantic Sturgeon.\31\ Low
oxygen levels can lead to habitat displacement effects whereby juvenile
Atlantic Sturgeon seeking relief are constrained to waters that remain
suboptimal for growth due to other limiting factors (e.g., higher
salinity waters).\32\ NOAA Fisheries also noted studies linking age 0-1
Atlantic Sturgeon capture rates in the fall to the preceding summer
dissolved oxygen conditions in the Delaware River, providing further
evidence that low dissolved oxygen levels are a contributor to the
mortality of juvenile Atlantic Sturgeon.\33\
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    \24\ Federal Register, Vol. 82, No. 158 (82 FR 39161). August
17, 2017. 50 CFR part 226. pp. 39161-39163. https://www.federalregister.gov/documents/2017/08/17/2017-17207/endangered-and-threatened-species-designation-of-critical-habitat-for-the-endangered-new-york-bight.
    \25\ Ibid. p. 39162, see Dees (1961), Sulak and Clugston (1999),
Billard and Lecointre (2001), Secor and Niklitschek (2002), and
Pikitch et al. (2005), cited therein.
    \26\ Stoklosa et al. (2018) ; Secor, D.H. and Niklitschek, E.J.
(2001). Hypoxia and Sturgeons: Report to the Chesapeake Bay Program
Dissolved Oxygen Criteria Team. March 29, 2001.Reference Number:
[UMCES] CBL 01-0080. https://www.researchgate.net/publication/277065759_Hypoxia_and_Sturgeons_report_to_the_Chesapeake_Bay_Program_Dissolved_Oxygen_Criteria_Team.
    \27\ Secor and Niklitschek (2001). Oxyregulation refers to an
organism's ability to maintain metabolic rates as the oxygen level
in the water declines.
    \28\ Secor, D., and T. Gunderson. (1998). Effects of hypoxia and
temperature on survival, growth, and respiration of juvenile
Atlantic sturgeon, Acipenser oxyrinchus. Fishery Bulletin 96:603-
613.; Niklitschek, E. (2001). Bioenergetics modeling and assessment
of suitable habitat for juvenile Atlantic and shortnose sturgeons
(Acipenser oxyrinchus and A. brevirostrum) in the Chesapeake Bay.
University of Maryland at College Park.
    \29\ More information is available in the associated document,
Technical Support Document for the Proposed Rule: Water Quality
Standards to Protect Aquatic Life in the Delaware River.
    \30\ Stoklosa et al. (2018).
    \31\ National Marine Fisheries Service (2022). See Section
<IP_ADDRESS>, ``Present or threatened destruction, modification, or
curtailment of its habitat or range.''
    \32\ Ibid. See Allen et al. (2014), cited therein.
    \33\ Ibid. See Moberg and DeLucia (2016), Stetzar et al. (2015),
and Park (2020), cited therein.
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3. Dissolved Oxygen Trends in the Specified Zones of the Delaware River
    Dissolved oxygen levels in Zone 3, Zone 4, and the upper portion of
Zone 5 of the Delaware River mirror trends in historic pollutant
loading and recent pollution control efforts in the river. Average
summer dissolved oxygen levels in the Delaware River near Chester,
Pennsylvania (Zone 4) declined from near saturation in the late 1880s
to near zero (i.e., anoxia) in the 1950s and 1960s.\34\ Starting in
1970, dissolved oxygen levels began to increase steadily in association
with declining ammonia nitrogen concentrations in the river.\35\
Reductions in nutrient concentrations, including ammonia nitrogen, have
been documented across the Delaware River watershed through at least
2018.\36\ However, dissolved oxygen levels in the summer remain low
enough to limit the growth and survival of oxygen-sensitive species and
life stages, such as juvenile Atlantic Sturgeon.\37\ Recent modeling
studies have shown that further reductions in pollutant loading,
including a reduction in the volume and frequency of CSOs as well as
enhanced treatment of ammonia nitrogen discharges, could significantly
improve the dissolved oxygen conditions in the relevant zones of the
Delaware River.\38\
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    \34\ Sharp, J. (2010). Estuarine oxygen dynamics: What can we
learn about hypoxia from long-time records in the Delaware estuary?
Limnology and Oceanography, 55(2), 535-548.
    \35\ Sharp (2010).
    \36\ Shoda, M.E., and Murphy, J.C. (2022). Water-quality trends
in the Delaware River Basin calculated using multisource data and
two methods for trend periods ending in 2018. U.S. Geological Survey
Scientific Investigations Report 2022-5097. https://doi.org/10.3133/sir20225097.
    \37\ More information is available in the associated document,
Technical Support Document for the Proposed Rule: Water Quality
Standards to Protect Aquatic Life in the Delaware River; Delaware
River Basin Commission (2022a); Niklitschek, E., and D. Secor.
(2009a). Dissolved oxygen, temperature and salinity effects on the
ecophysiology and survival of juvenile Atlantic sturgeon in
estuarine waters: I. Laboratory results. Journal of Experimental
Marine Biology and Ecology 381:S150-S160. https://doi.org/10.1016/j.jembe.2009.07.018; Stoklosa et al. (2018).
    \38\ Delaware River Basin Commission (2022a, 2022b).
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C. Administration of Water Quality Standards in the Delaware River

    In 1961, the Delaware River Basin Compact established the Delaware
River Basin Commission (DRBC), comprised of the states of Delaware, New
Jersey, New York,\39\ and Pennsylvania and the Federal Government, to
jointly manage the Delaware River Basin's water resources.\40\ Through
DRBC, each state participates in the shared governance of this regional
resource and maintains sovereign rights over the portion of the river
within its jurisdiction.\41\
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    \39\ Although portions of the Delaware River Estuary are within
New York's jurisdiction, the EPA's proposed rulemaking is not
applicable to waters under New York's jurisdiction (see section
IV.A. of this preamble: Scope of EPA's Proposed Rule). Therefore,
the EPA does not discuss New York's WQS further in this proposed
rulemaking.
    \40\ DRBC was established pursuant to Federal law (75 Stat. 688
(1961)).
    \41\ Delaware River Basin Compact, art. 1, ``Short Title,
Definitions, Purpose and Limitations,'' Sec.  1.3(a), (b), & (c)
``Purpose and Findings,'' pp. 3 & 4, and art. 5, ``Pollution
Control,'' Sec.  5.5(b), ``Further Jurisdiction,'' p. 11, (1961),
available at https://www.nj.gov/drbc/library/documents/compact.pdf.
---------------------------------------------------------------------------

    Pursuant to the Delaware River Basin Compact, DRBC adopts WQS for
interstate waters, including the Delaware River Estuary.\42\ However as
noted above, under the CWA, states have the primary responsibility for
reviewing, establishing, and revising WQS applicable to their waters,
and must submit new or revised WQS to the EPA for review and approval
or disapproval.
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    \42\ Delaware River Basin Compact, art. 5, ``Pollution
Control,'' Sec.  5.2, ``Policy and Standards,'' p. 11 (1961),
available at https://www.nj.gov/drbc/library/documents/compact.pdf
(DRBC ``may adopt and from time to time amend and repeal rules,
regulations and standards to control . . . future pollution and
abate existing pollution''). DRBC, the states, and the EPA refer to
these rules, regulations, and standards as equivalent to WQS under
the CWA. As such, the term WQS is used herein to refer to these
rules, regulations, and standards.
---------------------------------------------------------------------------

    Given the unique interjurisdictional management of the Delaware
River Estuary, WQS are submitted to the EPA for review through a
process coordinated across the state, regional, and Federal levels.
This process begins when DRBC adopts WQS for the Delaware River
Estuary. To comply with CWA section 303(c), the Estuary states of
Delaware, New Jersey, and Pennsylvania have provisions in their state
WQS regulations that explicitly reference or implicitly incorporate
DRBC's WQS as the applicable WQS for the portions of the river under
their jurisdictions. When DRBC adopts new or revised WQS, each relevant
member state submits a certification to the EPA from that state's
attorney general or other appropriate legal authority, in accordance
with 40 CFR 131.6(e). Those certifications provide that DRBC's new or
revised WQS were duly adopted pursuant to state law. The EPA then
reviews whether those WQS are consistent with the CWA and the EPA's
implementing regulation and approves or disapproves them.

D. Currently Applicable Aquatic Life Designated Uses and Dissolved
Oxygen Criteria

    In 1967, DRBC adopted WQS for the zones of the Delaware River
included in this proposed rule.\43\ Based on the conditions of the
Delaware River at the time, DRBC concluded that ``propagation of fish''
was not attainable for Zone 3, Zone 4, and the upper portion of Zone 5
(in total, river miles 108.4 to 70.0) of the Delaware River (hereafter,
referred to as ``specified zones'' or ``relevant zones''),\44\ due to
the presence of industrial and municipal discharges and associated low
dissolved oxygen levels. DRBC, therefore, adopted WQS to include
``maintenance of resident fish and other aquatic life,'' ``passage of
anadromous fish,'' and a dissolved oxygen criterion of 3.5 mg/L, as a
daily average, for these

zones of the Delaware River.45 46 Because these WQS provide
for the ``maintenance'' and ``passage'' of aquatic life (i.e.,
``protection'') but not the ``propagation of fish, shellfish and
wildlife,'' these WQS are not consistent with the goals specified in
CWA section 101(a)(2). However, these WQS adopted in 1967 remain
applicable for Zone 3, Zone 4, and the upper portion of Zone 5 of the
Delaware River as directly referred to or implicitly incorporated in
Delaware's, New Jersey's, and Pennsylvania's WQS.
---------------------------------------------------------------------------

    \43\ Delaware River Basin Commission. (2013). Delaware River
Basin Water Code. https://www.nj.gov/drbc/library/documents/watercode.pdf.
    \44\ A map showing the Delaware River watershed and the
specified zones is available in the docket (Docket ID No. EPA-HQ-OW-
2023-0222) as well as in each of the support documents associated
with this rule: Technical Support Document for the Proposed Rule:
Water Quality Standards to Protect Aquatic Life in the Delaware
River; Economic Analysis for the Proposed Rule: Water Quality
Standards to Protect Aquatic Life in the Delaware River; and
Environmental Justice Analysis for the Proposed Rule: Water Quality
Standards to Protect Aquatic Life in the Delaware River.
    \45\ Delaware River Basin Commission. (2015). ``Existing Use
Evaluation for Zones 3, 4, & 5 of the Delaware Estuary Based on
Spawning and Rearing of Resident and Anadromous Fishes.'' September
30, 2015. https://www.state.nj.us/drbc/library/documents/ExistingUseRpt_zones3-5_sept2015.pdf.
    \46\ Anadromous fish are species that are born and reared as
juveniles in freshwater, migrate to marine waters where they spend
most of their adult lives, and return to their natal, freshwater
rivers to spawn.
---------------------------------------------------------------------------

1. Delaware's, New Jersey's, and Pennsylvania's Current Aquatic Life
Designated Uses
    As described in section III.C. of this preamble, Delaware, New
Jersey, and Pennsylvania each has its own WQS for the specified zones
of the Delaware River under its jurisdiction. Delaware's current
aquatic life designated use for the specified zones of the Delaware
River includes all life stages, thus including the propagation
component of the CWA section 101(a)(2) use. New Jersey's aquatic life
designated use for the specified zones of the Delaware River
incorporate by reference the designated uses in DRBC's Water Quality
Regulations. Pennsylvania's aquatic life designated uses for the
specified zones of the Delaware River align with DRBC's ``maintenance''
and ``passage'' designated use (Table 2 of this preamble). Therefore,
neither New Jersey's nor Pennsylvania's aquatic life designated use for
the specified zones of the Delaware River include the propagation
component of the CWA section 101(a)(2) use.

  Table 2--Current Aquatic Life Designated Uses in Zone 3, Zone 4, and
                   Upper-Zone 5 of the Delaware River
------------------------------------------------------------------------
             Entity                           Designated use
------------------------------------------------------------------------
DRBC \1\........................  Maintenance of resident fish and other
                                   aquatic life, passage of anadromous
                                   fish, wildlife.
Delaware \2\....................  Fish, Aquatic Life & Wildlife.\3\
New Jersey \4\..................  The designated uses for the mainstem
                                   Delaware River and Delaware Bay are
                                   those contained in the DRBC Water
                                   Quality Regulations.
Pennsylvania \5\................  Warm Water Fishes (Maintenance Only);
                                   Migratory fishes (Passage Only).\6\
------------------------------------------------------------------------
\1\ Delaware River Basin Commission. ``Administrative Manual--Part III
  Water Quality Regulations with Amendments Through December 7, 2022.''
  Accessed May 3, 2023. https://www.nj.gov/drbc/library/documents/WQregs.pdf.
\2\ Delaware Administrative Code. ``7401 Surface Water Quality
  Standards.'' Title 7 Natural Resources & Environmental Control.
  Delaware Department of Natural Resource and Environmental Control.
  Accessed May 3, 2023. https://regulations.delaware.gov/AdminCode/title7/7000/7400/7401.pdf.
\3\ Delaware defines Fish, Aquatic Life & Wildlife as, ``all animal and
  plant life found in Delaware, either indigenous or migratory,
  regardless of life stage or economic importance.'' A footnote
  specifies that this use includes shellfish propagation.
\4\ New Jersey Administrative Code. ``N. J. A. C. 7:9B Surface Water
  Quality Standards.'' Accessed May 3, 2023. https://dep.nj.gov/wp-content/uploads/rules/rules/njac7_9b.pdf.
\5\ Pennsylvania Code. ``Chapter 93. Water Quality Standards.''
  Commonwealth of Pennsylvania. Accessed May 3, 2023. https://www.pacodeandbulletin.gov/secure/pacode/data/025/chapter93/025_0093.pdf.
\6\ Pennsylvania defines its ``Warm Water Fishes'' designated use as,
  ``Maintenance and propagation of fish species and additional flora and
  fauna which are indigenous to a warm water habitat'' and defines its
  ``Migratory Fishes'' designated use as, ``Passage, maintenance and
  propagation of anadromous and catadromous fishes and other fishes
  which move to or from flowing waters to complete their life cycle in
  other waters.'' For the specified zones of the Delaware River,
  Pennsylvania excluded propagation from the designated uses by
  specifying ``Maintenance Only'' and ``Passage Only'' in parentheses.

2. Delaware's, New Jersey's, and Pennsylvania's Current Dissolved
Oxygen Criteria
    For dissolved oxygen in the relevant zones, all three states
incorporate DRBC's water quality criteria by reference; therefore,
DRBC's dissolved oxygen criteria are the applicable criteria for the
relevant zones in each state (Table 3 of this preamble). As explained
above with respect to the aquatic life designated use, DRBC's dissolved
oxygen criteria for the specified zones of the Delaware River do not
protect for aquatic life propagation and are therefore not consistent
with CWA section 101(a)(2) goals.

Table 3--Current Dissolved Oxygen Criteria in Zone 3, Zone 4, and Upper-
                      Zone 5 of the Delaware River
------------------------------------------------------------------------
             Entity               Dissolved oxygen aquatic life criteria
------------------------------------------------------------------------
DRBC \1\........................  24-hour average concentration shall
                                   not be less than 3.5 mg/l. During the
                                   periods from April 1 to June 15, and
                                   September 16 to December 31, the
                                   dissolved oxygen shall not have a
                                   seasonal average less than 6.5 mg/l
                                   in the entire zone.
Delaware \2\....................  For waters of the Delaware River and
                                   Delaware Bay, duly adopted Delaware
                                   River Basin Commission (DRBC) Water
                                   Quality Regulations shall be the
                                   applicable criteria.
New Jersey \3\..................  For parameters with criteria in the
                                   DRBC Water Quality Regulations, the
                                   criteria contained therein are the
                                   applicable criteria.
Pennsylvania \4\................  See DRBC Water Quality Regulations.
------------------------------------------------------------------------
\1\ Delaware River Basin Commission. ``Administrative Manual--Part III
  Water Quality Regulations with Amendments Through December 7, 2022.''
  Accessed May 3, 2023. https://www.nj.gov/drbc/library/documents/WQregs.pdf.
\2\ Delaware Administrative Code. ``7401 Surface Water Quality
  Standards.'' Title 7 Natural Resources & Environmental Control.
  Delaware Department of Natural Resource and Environmental Control.
  Accessed May 3, 2023. https://regulations.delaware.gov/AdminCode/title7/7000/7400/7401.pdf.
\3\ New Jersey Administrative Code. ``N. J. A. C. 7:9B Surface Water
  Quality Standards.'' Accessed May 3, 2023. https://dep.nj.gov/wp-content/uploads/rules/rules/njac7_9b.pdf.
\4\ Pennsylvania Code. ``Chapter 93. Water Quality Standards.''
  Commonwealth of Pennsylvania. Accessed May 3, 2023. https://www.pacodeandbulletin.gov/secure/pacode/data/025/chapter93/025_0093.pdf.

3. Intersection of Delaware's, New Jersey's, and Pennsylvania's Current
Aquatic Life Designated Uses and Dissolved Oxygen Criteria With CWA
101(a)(2) Goals
    Table 4 of this preamble provides a summary outlining whether
Delaware's, New Jersey's, and Pennsylvania's current aquatic life
designated uses align with CWA section 101(a)(2) goals and whether each
state's current dissolved oxygen criteria are protective of an aquatic
life designated use that includes propagation. As explained above,
Delaware is the only state that includes aquatic life propagation in
its designated uses for the specified zones of the Delaware River.
However, none of the three states' dissolved oxygen water quality
criteria for the specified zones are protective of fish and shellfish
propagation. Therefore, none of the states, and by extension none of
the specified zones of the Delaware River, currently has a set of WQS
for aquatic life that are fully consistent with the CWA section
101(a)(2) goals (i.e., ``water quality which provides for the
protection and propagation of fish, shellfish, and wildlife [. . .]'').

 Table 4--Intersection of Delaware's, New Jersey's, and Pennsylvania's Current Aquatic Life Designated Uses and
                               Dissolved Oxygen Criteria With CWA 101(a)(2) Goals
----------------------------------------------------------------------------------------------------------------
                                                                                Dissolved oxygen
                                                                Designated use includes   criteria protective of
                State                     Applicable zone(s)     CWA section 101(a)(2)         aquatic life
                                                                 propagation component         propagation
----------------------------------------------------------------------------------------------------------------
Delaware.............................  Upper-5................  Yes....................  No.
New Jersey...........................  3, 4, Upper-5..........  No.....................  No.
Pennsylvania.........................  3, 4...................  No.....................  No.
----------------------------------------------------------------------------------------------------------------

E. Summary of the EPA's Administrator's Determination

    On December 1, 2022, the EPA determined that the CWA section
101(a)(2) use of propagation is now attainable and therefore revised
WQS are necessary to protect aquatic life in certain water quality
management zones of the Delaware River.\47\ Specifically, the EPA
issued an Administrator's Determination, pursuant to CWA section
303(c)(4)(B), finding that a revised designated use to protect aquatic
life propagation and corresponding dissolved oxygen criteria to protect
that use are necessary in Zone 3, Zone 4, and the upper portion of Zone
5 (in total, river miles 108.4 to 70.0) of the Delaware River. The
Administrator's Determination can be accessed at https://www.epa.gov/wqs-tech/federally-promulgated-water-quality-standards-specific-states-territories-and-tribes.
---------------------------------------------------------------------------

    \47\ December 1, 2022. Letter from Radhika Fox, Assistant
Administrator, EPA Office of Water, to Steven J. Tambini, Executive
Director, Delaware River Basin Commission; Shawn M. Garvin,
Secretary, Delaware Department of Natural Resources and
Environmental Control; Shawn M. LaTourette, Commissioner, New Jersey
Department of Environmental Protection; and Ramez Ziadeh, Acting
Secretary, Pennsylvania Department of Environmental Protection.
---------------------------------------------------------------------------

IV. Proposed Water Quality Standards

A. Scope of EPA's Proposed Rule

    In accordance with the Administrator's Determination, the EPA's
proposed rule, if finalized, would apply to Zone 3, Zone 4, and the
upper portion of Zone 5 of the Delaware River (in total, river miles
108.4 to 70.0), for the states of Delaware, New Jersey, and
Pennsylvania (Table 5 of this preamble).

 Table 5--Zones of the Delaware River Covered by the EPA's Proposed Rule
------------------------------------------------------------------------
  Segment of the Delaware River       River miles       States affected
------------------------------------------------------------------------
Zone 3..........................  108.4 to 95.0.....  New Jersey,
                                                       Pennsylvania.
Zone 4..........................  95.0 to 78.8......  New Jersey,
                                                       Pennsylvania.
Zone 5--Upper Portion...........  78.8 to 70.0......  Delaware, New
                                                       Jersey.
------------------------------------------------------------------------

B. Proposed Aquatic Life Designated Use

    The EPA is proposing to promulgate a revised aquatic life
designated use for the specified zones of the Delaware River to meet
the CWA section 101(a)(2) goals (i.e., ``water quality which provides
for the protection and propagation of fish, shellfish, and wildlife''),
as specified in the EPA's Administrator's Determination.\48\ Although
the relevant zones of the Delaware River are each under the
jurisdiction of two or more states (Table 5 of this preamble), CWA
section 303(c) assigns the individual states the role of adopting WQS.
Therefore, the EPA is evaluating the aquatic life uses on a state-by-
state basis.
---------------------------------------------------------------------------

    \48\ The EPA's Administrator's Determination stated, ``EPA is
determining [. . . that] revised aquatic life designated uses that
provide for propagation of fish, consistent with CWA section
101(a)(2) and 40 CFR 131.20(a) [. . .] are necessary for zone 3,
zone 4, and the upper portion of zone 5 (in total, river miles 108.4
to 70.0) of the Delaware River Estuary, to meet the requirements of
the CWA.''
---------------------------------------------------------------------------

    As explained in section III.D. of this preamble, Delaware's ``Fish,
Aquatic Life & Wildlife'' designated use includes all life stages of
indigenous and migratory organisms; therefore, Delaware's aquatic life
designated use in the specified zones under its jurisdiction is already
consistent with the CWA section 101(a)(2) goals and no revisions to
Delaware's aquatic life designated use are necessary to meet CWA
requirements. In contrast, New Jersey's and Pennsylvania's aquatic life
designated uses for the relevant zones of the Delaware River under
their jurisdiction do not include ``propagation'' and are therefore not
consistent with CWA section 101(a)(2) goals. As explained in section
III.E. of this preamble, the EPA determined that propagation is now an
attainable use in the specified zones of the Delaware River.\49\
Therefore, for the portions of the specified zones under New Jersey's
and Pennsylvania's jurisdiction, a

revised aquatic life designated use that includes propagation is
necessary to meet CWA requirements and ensure that the specified zones
of the Delaware River are consistent with CWA section 101(a)(2) goals.
---------------------------------------------------------------------------

    \49\ December 1, 2022. Letter from Radhika Fox, Assistant
Administrator, EPA Office of Water, to Steven J. Tambini, Executive
Director, Delaware River Basin Commission; Shawn M. Garvin,
Secretary, Delaware Department of Natural Resources and
Environmental Control; Shawn M. LaTourette, Commissioner, New Jersey
Department of Environmental Protection; and Ramez Ziadeh, Acting
Secretary, Pennsylvania Department of Environmental Protection.
---------------------------------------------------------------------------

    Thus, the EPA is proposing to promulgate an aquatic life designated
use for Zone 3, Zone 4, and the upper portion of Zone 5 of the Delaware
River (in total, river miles 108.4 to 70.0) for the states of New
Jersey and Pennsylvania, as follows: Protection and propagation of
resident and migratory aquatic life.

C. Dissolved Oxygen Criteria To Protect Aquatic Life Propagation

    The EPA is proposing to establish dissolved oxygen criteria--
derived from the latest sound scientific information--for Delaware, New
Jersey, and Pennsylvania, for the specified zones of the Delaware
River. The proposed dissolved oxygen criteria would protect the EPA's
proposed designated use for New Jersey and Pennsylvania, as well as
Delaware's current aquatic life designated use for the specified zones.
1. Derivation of Dissolved Oxygen Criteria
    To derive protective dissolved oxygen criteria for the specified
zones of the Delaware River, the EPA used methods adapted from peer-
reviewed literature and data from laboratory studies relevant to
oxygen-sensitive sturgeon species in the Delaware River. Although the
methods and data are from peer-reviewed scientific literature, the EPA
is nonetheless in the process of completing an external peer review on
the application of these methods and data in this context where the EPA
is proposing criteria to protect proposed and applicable aquatic life
designated uses that include propagation. This section presents a
summary of the data and methods that the EPA used to derive protective
dissolved oxygen criteria for this proposed rulemaking. First, the EPA
describes the Agency's existing dissolved oxygen national
recommendations and guidance documents. Then, the EPA explains how the
Agency selected three seasons to derive criteria protective of oxygen-
sensitive species in the relevant zones of the Delaware River. Next,
the EPA details an Atlantic Sturgeon cohort model used to derive
criteria protective of juvenile Atlantic Sturgeon during the season
associated with their growth and development. After that, the EPA
explains how criteria were developed to protect oxygen-sensitive
species during the other two seasons. Lastly, the EPA concludes with an
explanation for proposing criteria expressed as percent oxygen
saturation, rather than as concentration. This section is intended to
be a high-level summary of the EPA's criteria derivation methods and
results for this proposed rulemaking. More details and information are
available in the associated technical support document, Technical
Support Document for the Proposed Rule: Water Quality Standards to
Protect Aquatic Life in the Delaware River. The EPA will consider
information received during the public comment period (detailed above),
in addition to the external peer review of the technical support
document, and accordingly may make changes to the proposed criteria for
a final rule.
Existing the EPA Methodology and Guidance Documents
    Under CWA section 304(a), the EPA publishes, from time to time,
national recommended aquatic life criteria for a variety of pollutants
and parameters. The EPA's national recommended criteria for dissolved
oxygen in freshwater and saltwater environments are from the 1986
Quality Criteria for Water (``Gold Book'') \50\ and the 2000 Ambient
Aquatic Life Water Quality Criteria for Dissolved Oxygen (Saltwater):
Cape Cod to Cape Hatteras (``Virginian Province Document''),\51\
respectively. The EPA's recommendations in the Virginian Province
Document state that, ``in cases where a threatened or endangered
species occurs at a site, and sufficient data exist to suggest that it
is more sensitive at concentrations above the criteria, it is
appropriate to consider development of site-specific criteria based on
this species.'' \52\ As explained previously in section III.B. of this
preamble, Atlantic Sturgeon and Shortnose Sturgeon are federally listed
as endangered under the ESA and are uniquely sensitive to hypoxia.
Given the availability of laboratory data specific to the oxygen
requirements of Atlantic Sturgeon and Shortnose Sturgeon, the EPA chose
to derive site-specific criteria to protect the oxygen-sensitive
endangered species in the specified zones of the Delaware River and not
rely on the national recommendations in the Gold Book or Virginian
Province Document in this instance.
---------------------------------------------------------------------------

    \50\ United States Environmental Protection Agency. (1986).
Quality Criteria for Water 1986. Document ID: EPA 440/5-86-001. May
1, 1986. https://www.epa.gov/sites/default/files/2018-10/documents/quality-criteria-water-1986.pdf.
    \51\ United States Environmental Protection Agency. (2000).
Ambient Aquatic Life Water Quality Criteria for Dissolved Oxygen
(Saltwater): Cape Cod to Cape Hatteras. Document ID: EPA-822-R-00-
012. November 2000. https://www.epa.gov/sites/default/files/2018-10/documents/ambient-al-wqc-dissolved-oxygen-cape-code.pdf.
    \52\ Id. Page 41.
---------------------------------------------------------------------------

Delineating Seasons for Criteria Derivation
    In consideration of available information, including information
developed by DRBC, the EPA is proposing to delineate three distinct
seasons for dissolved oxygen criteria development that are intended to
protect Atlantic Sturgeon early life stages, while also protecting a
range of other aquatic species' sensitive life stages in the specified
zones. The EPA is proposing to define the Spawning and Larval
Development season as occurring from March 1 to June 30, which
generally covers spawning and egg and larval development periods for
many oxygen-sensitive species, including Atlantic Sturgeon, Shortnose
Sturgeon, American Shad, Atlantic Rock Crab, Channel Catfish, Striped
Bass, Largemouth Bass, White Perch, and Yellow Perch.\53\ The EPA is
proposing to define the Juvenile Development season as occurring from
July 1 to October 31 and the Overwintering season as occurring from
November 1 to February 28/29, based on young-of-the-year juvenile
Atlantic Sturgeon growth rates.\54\ By November, growth rates are
reduced by low water temperatures despite relatively high levels of
dissolved oxygen.\55\ While the EPA is proposing to define seasons
largely based on the early life stages of Atlantic Sturgeon, the
proposed seasons also generally correspond with early life stages of
other oxygen-sensitive species in the specified zones of the Delaware
River. By developing criteria that are protective of Atlantic Sturgeon,
which, as described in section III.B. of this preamble, is the most
oxygen-sensitive species in the relevant zones of the Delaware River,
the EPA concluded that the criteria would also be protective of other
less oxygen-sensitive resident and

migratory aquatic species in the specified zones of the Delaware River.
---------------------------------------------------------------------------

    \53\ Stoklosa et al. (2018); Delaware River Basin Commission
(2015); Moberg, T. and M. DeLucia. (2016). Potential Impacts of
Dissolved Oxygen, Salinity and Flow on the Successful Recruitment of
Atlantic Sturgeon in the Delaware River. The Nature Conservancy.
Harrisburg, PA. https://www.conservationgateway.org/ConservationPractices/Freshwater/HabitatProtectionandRestoration/Documents/DelawareAtlanticSturgeonReport_TNC5172016.pdf.
    \54\ Moberg and DeLucia. (2016).
    \55\ This conclusion was based on results of the growth model,
described in sections 3.3.3 and 4.1.2 of the associated document,
Technical Support Document for the Proposed Rule: Water Quality
Standards to Protect Aquatic Life in the Delaware River.
---------------------------------------------------------------------------

Ecological Modeling To Derive Criteria for the Juvenile Development
Season
    The EPA obtained recent and high-quality data from a variety of
sources, described below and detailed in the associated technical
support document, to evaluate oxygen requirements of Atlantic Sturgeon
in each season. The EPA quantified water quality conditions in the
specified zones of the Delaware River using recent and high-quality
monitoring data from two locations in the Delaware River. Since the
Atlantic Sturgeon was listed as an endangered species in 2012, there
have been few recent studies documenting their oxygen requirements.
However, available data on sturgeon growth and mortality from Campbell
and Goodman (2004), Niklitschek and Secor (2009a), and EPA (2003),
along with methods from Niklitschek and Secor (2005) and Niklitschek
and Secor (2009b), water quality monitoring data, and juvenile Atlantic
Sturgeon abundance data from the Delaware Department of Natural
Resources and Environmental Control (DNREC) provided the EPA with
sufficient data to establish quantitative relationships between age-0
juvenile sturgeon growth, mortality, and habitat suitability.\56\
---------------------------------------------------------------------------

    \56\ Campbell, J., and L. Goodman. (2004). Acute sensitivity of
juvenile shortnose sturgeon to low dissolved oxygen concentrations.
Transactions of the American Fisheries Society 133:722-776;
Niklitschek, E., and D. Secor. (2009a). Dissolved oxygen,
temperature and salinity effects on the ecophysiology and survival
of juvenile Atlantic sturgeon in estuarine waters: I. Laboratory
results. Journal of Experimental Marine Biology and Ecology
381:S150-S160. https://doi.org/10.1016/j.jembe.2009.07.018; United
States Environmental Protection Agency. (2003). Ambient Water
Quality Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll
a for the Chesapeake Bay and its Tidal Tributaries. Document ID: EPA
903-R-03-002. April 2003. https://nepis.epa.gov/Exe/ZyPDF.cgi/P100YKPQ.PDF?Dockey=P100YKPQ.PDF; Niklitschek, E.J., and D.H. Secor.
(2005). Modeling spatial and temporal variation of suitable nursery
habitats for Atlantic sturgeon in the Chesapeake Bay. Estuarine,
Coastal and Shelf Science 64:135-148. https://doi.org/10.1016/j.ecss.2005.02.012; Niklitschek, E.J., and D.H. Secor. (2009b).
Dissolved oxygen, temperature and salinity effects on the
ecophysiology and survival of juvenile Atlantic sturgeon in
estuarine waters: II. Model development and testing. Journal of
Experimental Marine Biology and Ecology 381:S161-S172. https://doi.org/10.1016/j.jembe.2009.07.019; USGS 01467200 Delaware River at
Penn's Landing, Philadelphia, PA. Retrieved March 9, 2023. https://waterdata.usgs.gov/nwis/inventory/?site_no=01467200&agency_cd=USGS;
USGS 01477050 Delaware River at Chester PA. Retrieved January 31,
2023. https://waterdata.usgs.gov/nwis/inventory?agency_code=USGS&site_no=01477050; Park, I. (2023). State
of Delaware Annual Compliance Report for Atlantic Sturgeon. Delaware
Division of Fish and Wildlife, Department of Natural Resources and
Environmental Control. September 2023.
---------------------------------------------------------------------------

    The EPA followed the peer-reviewed cohort modeling approach of
Niklitschek and Secor (2005) to evaluate the effects of temperature,
salinity, and dissolved oxygen on the potential growth and mortality of
a hypothetical cohort or group of juvenile Atlantic Sturgeon spawned
during a single year.\57\ The cohort model uses growth and mortality
rates to calculate the instantaneous daily production potential, or the
instantaneous amount of biomass produced per unit of cohort biomass per
day. The EPA used the cohort model to estimate the fraction of the
cohort that survives from July 1 through October 31 (i.e., the Juvenile
Development season) and the relative change in biomass for the same
period.
---------------------------------------------------------------------------

    \57\ Water temperature and salinity can affect the oxygen
requirements of aquatic species and are needed to compute percent
oxygen saturation, a measure of dissolved oxygen availability to
aquatic organisms, from dissolved oxygen concentrations.
---------------------------------------------------------------------------

    As part of the cohort model, the EPA developed a new mortality
model and implemented a peer-reviewed bioenergetics-based growth model
described by Niklitschek and Secor (2009b) to predict the daily
instantaneous mortality rate and growth rate, respectively, for members
of the cohort. To develop a mortality model, the EPA fit a regression
to experimental data to predict mortality resulting from low dissolved
oxygen at any given temperature and percent oxygen saturation.\58\
Mortality rates of juvenile sturgeons increased with declining
dissolved oxygen levels and increased at higher rates with both
declining dissolved oxygen and increasing water temperature. The EPA
validated the results of the mortality model by using observed water
quality data to predict relative abundance of the Atlantic Sturgeon
young-of-year cohort on October 31 and comparing those results to catch
data from DNREC's juvenile abundance surveys.\59\ The growth model
takes a bioenergetic approach that accounts for temperature-controlled
maximum metabolic rates that may be further limited by oxygen levels.
Low oxygen levels limit overall metabolic rates and cause a shift in
the allocation of available energy away from growth. Predicted growth
rates reflect the balance between energy inputs and losses and are
therefore reduced by low oxygen. Water quality monitoring data in the
relevant zones of the Delaware River show that the lowest oxygen levels
coincided with the highest water temperatures, resulting in lower
growth rates than either condition would cause alone.
---------------------------------------------------------------------------

    \58\ Experimental data are from Campbell and Goodman 2004,
Niklitschek and Secor 2009a.
    \59\ USGS 01467200 Delaware River at Penn's Landing,
Philadelphia, PA. Retrieved March 9, 2023. https://waterdata.usgs.gov/nwis/inventory/?site_no=01467200&agency_cd=USGS;
USGS 01477050 Delaware River at Chester, PA. Retrieved January 31,
2023. https://waterdata.usgs.gov/nwis/inventory?agency_code=USGS&site_no=01477050; Park (2023).
---------------------------------------------------------------------------

    Habitat Suitability Indices have been used in the context of fish-
habitat relationships, conservation management, and habitat evaluation
to quantify the capacity of a given habitat to support essential life
functions (e.g., growth, survival, reproduction) of a selected
species.\60\ For this proposed rulemaking, the EPA defined a Habitat
Suitability Index (HSI) for Atlantic Sturgeon as the instantaneous
daily production potential, which was calculated using the cohort
model. HSI evaluates the combined effect of percent oxygen saturation,
water temperature, and salinity on the potential growth and survival of
juvenile Atlantic Sturgeon during the Juvenile Development season. The
EPA used quantile generalized additive models (QGAMs) to quantify
relationships between computed values of HSI in each year and
corresponding seasonal percentiles of daily dissolved oxygen for that
year.\61\ QGAMs can model the non-linear relationship between dissolved
oxygen and HSI as well as predict the expected median HSI, rather than
the expected mean.
---------------------------------------------------------------------------

    \60\ E.g., Woodland, R.J., Secor, D.H., and Niklitschek, E.J.
(2009). Past and Future Habitat Suitability for the Hudson River
Population of Shortnose Sturgeon: A Bioenergetic Approach to
Modeling Habitat Suitability for an Endangered Species. American
Fisheries Society Symposium 69: 589-604; Collier, J.J., Chiotti,
J.A., Boase, J., Mayer, C.M., Vandergoot, C.S., and Bossenbroek,
J.M. (2022). Assessing habitat for lake sturgeon (Acipenser
fulvescens) reintroduction to the Maumee River, Ohio using habitat
suitability index models. Journal of Great Lakes Research. 48(1):
219-228. https://doi.org/10.1016/j.jglr.2021.11.006; Brown, S.K.,
Buja, K.R., Jury, S.H., Monaco, M.E., and Banner, A. (2000). Habitat
Suitability Index Models for Eight Fish and Invertebrate Species in
Casco and Sheepscot Bays, Maine. North American Journal of Fisheries
Management, 20(2): 408-435, https://doi.org/10.1577/1548-8675(2000)020%3C0408:HSIMFE%3E2.3.CO;2.
    \61\ A percentile (e.g., 10th percentile) is the dissolved
oxygen level below which the corresponding fraction (e.g., 10%) of
the daily dissolved oxygen values during the season falls below. In
this case, the season is the Juvenile Development season (July 1-
October 31).
---------------------------------------------------------------------------

    The EPA followed the approach of Niklitschek and Secor (2005) to
define suitable habitat for juvenile Atlantic Sturgeon growth and
survival as habitats with water quality resulting in HSI greater than
zero. When HSI is less than or equal to zero, seasonal average
mortality rates are greater than or equal to seasonal average growth
rates and the overall biomass of the cohort is likely to decrease.
Conversely, a cohort of

juveniles utilizing habitat with HSI greater than zero has the
potential to increase its biomass during the Juvenile Development
season, thus contributing to successful propagation. Therefore, to
derive protective dissolved oxygen criteria, the EPA evaluated seasonal
percentiles of percent oxygen saturation to find the lowest value at
which the QGAMs predict expected median HSI>0 as the minimum thresholds
for percent oxygen saturation that, if attained, would provide suitable
habitat during that seasonal period. The EPA requests comment on the
conclusion that HSI greater than zero defines suitable habitat for
juvenile Atlantic Sturgeon growth and survival, or alternatively, if
evidence could support that a value of HSI less than zero could also be
protective or if a higher HSI threshold may be needed to protect
propagation in the specified zones. Similarly, the EPA requests comment
on its use of QGAM to relate percentiles of dissolved oxygen levels to
the conditional median HSI. These models can be understood to find the
minimum dissolved oxygen level that if achieved would result in an
expectation that HSI would be equal to or greater than zero as often or
more often than if it is less than zero. As an alternative, the QGAM
could predict a lower conditional percentile, providing a high degree
of certainty that HSI would be greater than zero if the dissolved
oxygen level was attained. For example, at the dissolved oxygen level
where the expected 25th percentile HSI=0, HSI would be expected to
equal or exceed zero 75% of the time.
    The predicted HSI value relies on an expected distribution of
percent oxygen saturation values during the season; therefore, the EPA
selected two percent oxygen saturation percentiles as thresholds at or
above which median HSI is expected to be greater than zero to maintain
the expected distribution of percent oxygen saturation values. These
two percentiles--the 10th percentile and the 50th percentile--describe
the protective seasonal distribution of dissolved oxygen values. When
both the 10th percentile and 50th percentile are attained, they
function together to ensure that a detrimental shift in the oxygen
distribution (i.e., a shift causing more low oxygen levels) at either
the low end (10th percentile) or the center (50th percentile) of the
dissolved oxygen distribution has not occurred. Median HSI is expected
to be zero or higher, allowing the annual cohort of juvenile Atlantic
Sturgeon to maintain or increase its biomass, when the 10th percentile
of oxygen saturation is at least 66% and the 50th percentile, or
median, of oxygen saturation is at least 74%. Therefore, the EPA
expects oxygen levels will not impair juvenile Atlantic Sturgeon during
the Juvenile Development season if the 10th percentile of oxygen
saturation is at least 66% and the 50th percentile of oxygen saturation
is at least 74%.
Criteria Development for Spawning and Larval Development and
Overwintering Seasons
    The Atlantic Sturgeon cohort model described above relies on
experimental studies that were conducted using juvenile Atlantic
Sturgeon and therefore provide information that is most relevant to
juvenile growth and survival.\62\ Additionally, the underlying studies
allocated most experimental treatments to water temperatures between 12
[deg]C and 28 [deg]C, with only a single experimental treatment at 6
[deg]C and none at lower water temperatures.\63\ The EPA's cohort
modeling approach therefore does not apply to spawning and larval
development lifestages and has minimal relevance to the overwintering
period. Accordingly, the EPA did not use the cohort model to derive
criteria for the Spawning and Larval Development or the Overwintering
seasons.
---------------------------------------------------------------------------

    \62\ Experimental data are from Campbell and Goodman 2004 and
Niklitschek and Secor 2009a.
    \63\ Niklitschek and Secor 2009a.
---------------------------------------------------------------------------

    Instead, the EPA concluded that Atlantic Sturgeon larvae were
likely to be as sensitive to low dissolved oxygen as juvenile Atlantic
Sturgeon \64\ and that overwintering juveniles have temperature-limited
metabolism and therefore have similar or slightly lower oxygen
requirements than juveniles in warmer waters (e.g., summer water
temperatures).\65\ Thus, the EPA determined that the percent oxygen
saturation threshold that would be protective of juveniles experiencing
stressful (high) water temperatures during the Juvenile Development
season would also be protective of larvae and overwintering juveniles
not experiencing high water temperatures. Therefore, the EPA expects
oxygen levels will not impair Atlantic Sturgeon when the 10th
percentile of oxygen saturation is at least 66% during the Spawning and
Larval Development and Overwintering seasons. The EPA notes that from
2002-2022, the median oxygen level during the Spawning and Larval
Development and Overwintering seasons was well above levels expected to
negatively impact either Atlantic Sturgeon or other oxygen-sensitive
species. Therefore, the EPA concluded that a second criterion for a
50th percentile was not needed during these seasons.
---------------------------------------------------------------------------

    \64\ Stoklosa et al. (2018); United States Environmental
Protection Agency. (2000). Ambient Aquatic Life Water Quality
Criteria for Dissolved Oxygen (Saltwater): Cape Cod to Cape
Hatteras. Document ID: EPA-822-R-00-012. November 2000. https://www.epa.gov/sites/default/files/2018-10/documents/ambient-al-wqc-dissolved-oxygen-cape-code.pdf.
    \65\ Niklitschek and Secor (2009a, 2009b).
---------------------------------------------------------------------------

Criteria Expressed as Percent Oxygen Saturation
    Finally, the EPA derived the proposed criteria in terms of percent
oxygen saturation, rather than in units of concentration (such as
milligrams per liter or mg/L) for two main reasons.\66\ First,
physiological effects of oxygen on aquatic organisms are directly
related to percent oxygen saturation and indirectly related to
dissolved oxygen concentration. As noted by Niklitschek and Secor
(2009a), percent oxygen saturation or partial pressure are the most
biologically relevant measures of oxygen because they determine the
maximum rate at which aquatic organisms may obtain oxygen from the
water. Second, percent oxygen saturation varies with water temperature
less than dissolved oxygen concentration. Because oxygen solubility is
higher in cold water than warm water, dissolved oxygen concentrations
are often much higher in cold water. The strong negative relationship
between dissolved oxygen concentration and temperature can complicate
the interpretation of seasonal dissolved oxygen patterns. For example,
in the Delaware River, dissolved oxygen concentrations increase quickly
during fall as temperatures decrease, even though percent saturation
increases more slowly. In this example, the increasing oxygen
concentration gives the appearance that oxygen availability to aquatic
organisms is increasing more rapidly than it is actually increasing.
For Atlantic Sturgeon, this means that low levels of percent oxygen
saturation may continue to impact growth and survival even though
dissolved oxygen concentrations increase. Given this relationship
between temperature and dissolved oxygen concentration, criteria
expressed as concentration will be above or below the protective
threshold at various times of the year as

temperature changes, whereas criteria expressed as percent oxygen
saturation can be protective throughout the year.
---------------------------------------------------------------------------

    \66\ Percent oxygen saturation and dissolved oxygen
concentration are two different ways to measure oxygen levels in
water. Dissolved oxygen concentration is the amount of oxygen
dissolved in the water, typically represented as milligrams of
oxygen per liter of water. Percent oxygen saturation is the ratio,
expressed as a percentage, of the dissolved oxygen concentration in
the water to the dissolved oxygen concentration when at equilibrium
with the atmosphere.
---------------------------------------------------------------------------

2. Proposed Dissolved Oxygen Criteria
    The EPA's proposed dissolved oxygen criteria cover three distinct
seasons based largely on Atlantic Sturgeon early life stages and are
intended to protect all oxygen-sensitive species in the Delaware River,
as explained above. The Spawning and Larval Development season occurs
between March 1st and June 30th and captures a comprehensive range of
resident aquatic species' spawning periods.\67\ The Juvenile
Development season occurs between July 1st and October 31st and
captures critical early life stage growth and development for young-of-
the-year Atlantic Sturgeon. The Overwintering season occurs between
November 1st and February 28th (or 29th, in a leap year), when juvenile
Atlantic Sturgeon growth is limited by low water temperatures.
---------------------------------------------------------------------------

    \67\ Stoklosa et al. (2018); Delaware River Basin Commission
(2015).
---------------------------------------------------------------------------

    Each season has water quality criteria that each consist of three
components: magnitude, duration, and exceedance frequency. The
magnitude component indicates the required level of dissolved oxygen in
the water, which in this proposal is presented in units of percent
oxygen saturation. The duration component specifies the time period
over which water quality is averaged before comparison with the
criteria magnitude; in this proposal, the duration is a daily
average.\68\ The exceedance frequency component specifies how often
(e.g., percentage of the time) each criterion can be exceeded in each
season while still ensuring that the use is protected. For this
proposed rulemaking, the exceedance frequency is determined based on
the dissolved oxygen percentile from which the magnitude is derived
(i.e., the 10th percentile can be exceeded 10% of the time, which for a
season consisting of 123 days is 12 cumulative days of exceedance). For
dissolved oxygen, an exceedance occurs when the oxygen level in the
water is below the criterion value.
---------------------------------------------------------------------------

    \68\ The EPA selected a daily average duration because it is a
readily measurable indicator of the oxygen levels at a daily
timescale. The daily average is protective because variability of
dissolved oxygen levels on a single day is small in the Delaware
River.
---------------------------------------------------------------------------

    In this proposed rulemaking, the Spawning and Larval Development
and Overwintering seasons each have a single, identical dissolved
oxygen criterion with a magnitude of 66% oxygen saturation, a daily
average duration, and a 10% exceedance frequency (which allows for up
to 12 days of cumulative exceedance during each of these two seasons)
(Table 6 of this preamble). The Juvenile Development season has two
individually applicable dissolved oxygen criteria that together define
a protective seasonal distribution of percent oxygen saturation. The
criteria differ in both magnitude and exceedance frequency and both
levels must be attained. The first Juvenile Development criterion
defines the lower end of the distribution of oxygen levels and consists
of a magnitude of 66% oxygen saturation, a daily average duration, and
a 10% exceedance frequency (which allows for up to 12 days cumulative
exceedance during the season). The second Juvenile Development
criterion defines the center of the distribution and consists of a
magnitude of 74% oxygen saturation, a daily average duration, and a 50%
exceedance frequency (which allows for up to 61 days cumulative
exceedance during the season) (Table 6 of this preamble).

                              Table 6--The EPA's Proposed Dissolved Oxygen Criteria
----------------------------------------------------------------------------------------------------------------
                                             Magnitude
                                             (percent
                 Season                       oxygen               Duration              Exceedance frequency
                                            saturation)
----------------------------------------------------------------------------------------------------------------
Spawning and Larval Development (March 1-             66  Daily verage..............  10% (12 Days Cumulative).
 June 30).
Juvenile Development (July 1-October 31)              66  Daily Average.............  10% (12 Days Cumulative).
                                                      74  Daily Average.............  50% (61 Days Cumulative).
Overwintering (November 1-February 28/                66  Daily Average.............  10% (12 Days Cumulative).
 29).
----------------------------------------------------------------------------------------------------------------

3. Alternative Options Considered
    During the criteria derivation process, the EPA made several
decisions based on the best available sound scientific information to
ensure the dissolved oxygen criteria would be protective of the
applicable and proposed aquatic life designated uses. In this section,
the EPA presents three alternative options the Agency considered. For
each alternative, the EPA examined information currently available at
the time of this proposal. The EPA has concerns about whether each
alternative would be protective of the aquatic life designated uses
that include propagation; therefore, the EPA did not include any of
these alternatives as part of its lead proposed criteria. However, the
EPA requests comment and additional information on whether and how one
or more of these alternatives could protect the applicable and proposed
aquatic life designated uses in the specified zones of the Delaware
River and if so, what anticipated benefits would be associated with the
alternative compared to the EPA's proposed criteria.\69\
---------------------------------------------------------------------------

    \69\ More information is available in the associated document,
Technical Support Document for the Proposed Rule: Water Quality
Standards to Protect Aquatic Life in the Delaware River.
---------------------------------------------------------------------------

    Alternative 1: Dissolved Oxygen Criteria Expressed as Concentration
(mg/L).
    The EPA's proposed dissolved oxygen criteria are expressed as
percent oxygen saturation, as described in section IV.C.1 of this
preamble. However, the EPA recognizes that some stakeholders might be
more familiar with dissolved oxygen criteria expressed as concentration
or might have other reasons for preferring criteria expressed as
concentration. The EPA is seeking comment on whether dissolved oxygen
criteria expressed as concentration (mg/L) would be protective of
oxygen-sensitive species during each season.
    To calculate Juvenile Development season criteria expressed as
concentration (mg/L), the EPA followed an analogous approach to the
method used for determining criteria as percent oxygen saturation, as
explained in section IV.C.1 of this preamble. The EPA used quantile
generalized additive models relating seasonal percentiles of dissolved
oxygen concentration to the expected median habitat suitability index
(HSI). The EPA selected as the alternative criteria values the
dissolved

oxygen concentration for which the expected median HSI is zero (Table 7
of this preamble).
    To calculate dissolved oxygen criteria expressed as concentration
for the Spawning and Larval Development and Overwintering seasons, the
EPA started with the criteria computed as percent oxygen saturation
(Table 6 of this preamble) and converted each of these to a
concentration using each of the following two approaches, which
differed based on water temperature assumptions.\70\ The EPA's first
approach uses the 90th percentile of water temperatures in each season,
whereas the second approach uses the average water temperature in each
season.\71\ The 90th percentile approximates the highest water
temperature in each season, which corresponds to when dissolved oxygen
levels are generally at their lowest and therefore impacts to aquatic
life are most likely to occur. In the Delaware River, the highest
temperatures in the Spawning and Larval Development season occur in
late June and the highest temperatures in the Overwintering season
occur in early November. On the other hand, the EPA's second approach
using an average water temperature results in the concentration that
minimizes the magnitude of deviations in either direction from the
protective level across the season. Because the average water
temperature is lower than the 90th percentile water temperature, the
EPA's second approach resulted in higher dissolved oxygen
concentrations than the first approach (Table 7 of this preamble).
---------------------------------------------------------------------------

    \70\ The EPA assumed salinity = 0 for each conversion from
percent oxygen saturation to concentration in the Spawning and
Larval Development and Overwintering seasons.
    \71\ Seasonal 90th percentile and mean water temperature were
calculated using the daily climatology computed for Chester for
March 1, 2012-June 30th, 2022, for the Spawning and Larval
Development season and November 1, 2011-February 28, 2022, for the
Overwintering season.
---------------------------------------------------------------------------

    In table 7 below, the EPA leads with alternative criteria based on
the 90th percentile water temperatures because existing dissolved
oxygen criteria guidance and criteria derivation efforts in other
states have commonly focused on the warmest conditions that occur,
which are the most critical for mitigating impacts to aquatic life due
to low oxygen.\72\ For consideration, the EPA presents alternative
criteria based on average water temperatures in parentheses.
---------------------------------------------------------------------------

    \72\ United States Environmental Protection Agency. (2000).
Ambient Aquatic Life Water Quality Criteria for Dissolved Oxygen
(Saltwater): Cape Cod to Cape Hatteras. Document ID: EPA-822-R-00-
012. November 2000. https://www.epa.gov/sites/default/files/2018-10/documents/ambient-al-wqc-dissolved-oxygen-cape-code.pdf; Batiuk,
R.A., Breitburg, D.L., Diaz, R.J., Cronin, T.M., Secor, D.H., and
Thursby, G. (2009). Derivation of habitat-specific dissolved oxygen
criteria for Chesapeake Bay and its tidal tributaries. Journal of
Experimental Marine Biology and Ecology 381: S204-S215. https://doi.org/10.1016/j.jembe.2009.07.023.

                  Table 7--Alternative 1: Dissolved Oxygen Criteria Expressed as Concentration
                                                     [mg/L]
----------------------------------------------------------------------------------------------------------------
                                         Water
              Season                  temperature   Magnitude  (mg/        Duration         Exceedance frequency
                                       ([deg]C)           L)
----------------------------------------------------------------------------------------------------------------
Spawning and Larval Development      * 23.3 (14.7)     * 5.6 (6.7)  Daily Average........  10% (12 Days
 (March 1-June 30).                                                                         Cumulative).
Juvenile Development (July 1-              \+\ N/A             5.4  Daily Average........  10% (12 Days
 October 31).                                                                               Cumulative).
N/A \+\...........................             6.1   Daily Average  50% (61 Days
                                                                     Cumulative).
Overwintering (November 1-February    * 12.4 (5.6)     * 7.0 (8.3)  Daily Average........  10% (12 Days
 28/29).                                                                                Cumulative).
----------------------------------------------------------------------------------------------------------------
* The 90th percentile of seasonal water temperature and corresponding criterion is used for the main estimate,
  while the average water temperature and corresponding criterion is shown in parentheses.
\+\ Water temperature is not applicable during the Juvenile Development season because the criteria magnitudes
  are derived from the EPA's Atlantic Sturgeon cohort model, described in section IV.C.1 of this preamble.

    Concentration-based criteria derived using the EPA's first approach
(based on the 90th percentile water temperatures) would be equivalent
to the EPA's proposed 66% oxygen saturation when water temperature is
near the 90th percentile temperature and oxygen is near the lowest
point in each season. However, during periods in each season when water
temperature is lower than the 90th percentile temperature, the
concentration-based criteria would be below the level that is
equivalent to the EPA's proposed 66% oxygen saturation level. For
example, when water temperature is 2 [deg]C in mid-winter, oxygen
saturation is 66% when the dissolved oxygen concentration is 9.1 mg/L.
The EPA therefore has concerns about whether dissolved oxygen criteria
expressed as concentration for this alternative would be protective for
the Spawning and Larval Development and Overwintering seasons. Similar
to the first approach, the concentration derived using the EPA's second
approach (average water temperature) is also below the level that is
equivalent to 66% oxygen saturation when water temperature is below the
seasonal average. During periods in each season when the water
temperature is warmer than the average, concentrations calculated using
the EPA's second approach would result in an oxygen saturation higher
than 66%.\73\
---------------------------------------------------------------------------

    \73\ More information on dissolved oxygen trends in the
specified zones of the Delaware River is available in the associated
rule documents, Technical Support Document for the Proposed Rule:
Water Quality Standards to Protect Aquatic Life in the Delaware
River and Economic Analysis for the Proposed Rule: Water Quality
Standards to Protect Aquatic Life in the Delaware River.
---------------------------------------------------------------------------

    The EPA provided the concentrations in table 7 of this preamble
that result from the methods described above to help facilitate public
comment. The EPA also requests public input and supporting information
about other ways the Agency could develop dissolved oxygen criteria
expressed as concentration--particularly for the Spawning and Larval
Development and Overwintering seasons--to protect the relevant aquatic
life uses in accordance with the CWA.
    Alternative 2: Single Dissolved Oxygen Criterion During the
Juvenile Development Season with a 10% Exceedance Frequency.
    The EPA's proposed dissolved oxygen criteria for the critical
Juvenile Development season consist of two values--one that may be
exceeded 10% of the time and one that may be exceeded 50% of the time--
that must both be met during the season, as explained in section IV.C.1
of this preamble. However, the EPA recognizes that some stakeholders
might prefer the simpler criteria framework a single criterion would
afford or may have other reasons for preferring a single value.

    The EPA is seeking comment and supporting information on applying a
single dissolved oxygen criterion with a 10% exceedance frequency
during the Juvenile Development season, including whether criteria
expressed with a single criterion would protect the applicable and
proposed aquatic life designated uses. This could mean applying a
single criterion of 66% oxygen saturation (or 5.4 mg/L, if expressed as
concentration) with a 10% exceedance frequency for the Juvenile
Development season. The Overwintering and Spawning and Larval
Development seasons are unaffected by this alternative.
    The EPA also requests public input and supporting information about
other potential options the Agency could consider for dissolved oxygen
criteria in the form of a single criterion to protect the aquatic life
uses in accordance with the CWA.
    Alternative 3: Inclusion of a 1-in-3-Year Interannual Exceedance
Frequency.
    The EPA's proposed criteria do not include an interannual
exceedance frequency and therefore would need to be met every year.
However, the EPA recognizes that some stakeholders might prefer
criteria with an interannual exceedance frequency to help accommodate
the impact of environmental variability on dissolved oxygen conditions
in the specified zones of the Delaware River. The EPA is seeking
comment and supporting information on the addition of a 1-in-3-year
interannual exceedance frequency as part of the dissolved oxygen
criteria. The EPA is particularly interested in how and why this
approach would protect the applicable and current aquatic life uses.
    If a 1-in-3-year interannual exceedance frequency were included as
part of the dissolved oxygen criteria, it would mean that in any three-
year period, all criteria would need to be attained in at least two
years. An exceedance would occur in any year where one or more of the
criteria were not attained. The following two examples describe how a
1-in-3-year interannual exceedance frequency could function.
    Example 1: If, in a given year, the dissolved oxygen during the
Juvenile Development season fell below 66% saturation more than 10% of
the time, then that year would not meet the Juvenile Development 10th
percentile criterion. Therefore, that year would count as one year of
exceedance towards the 1-in-3-year interannual exceedance frequency. If
another criterion, for example the Spawning and Larval Development
criterion, was not met in that same year, then it would still only
count as one year of exceedance despite the fact that two criteria were
not met that year (Table 8 of this preamble).

     Table 8--Example 1 Scenario Where Dissolved Oxygen Criteria With the 1-in-3-Year Interannual Exceedance
                                                Frequency Are Met
----------------------------------------------------------------------------------------------------------------
                                                            Was the seasonal criterion met?
                Season                --------------------------------------------------------------------------
                                                Year 1                   Year 2                   Year 3
----------------------------------------------------------------------------------------------------------------
Spawning and Larval Development......  No.....................  Yes....................  Yes.
Juvenile Development--10th Percentile  No.....................  Yes....................  Yes.
Juvenile Development--50th Percentile  Yes....................  Yes....................  Yes.
Overwintering........................  Yes....................  Yes....................  Yes.
Does the Full Year Meet Criteria?....  No.....................  Yes....................  Yes.
----------------------------------------------------------------------------------------------------------------

    Example 2: If, in a given year, the dissolved oxygen during the
Juvenile Development season fell below 66% saturation more than 10% of
the time, then that year would not meet the Juvenile Development 10th
percentile criterion. If the following year, the Juvenile Development
season fell below 74% saturation more than 50% of the time, then that
year would not meet the Juvenile Development 50th percentile criterion
(Table 9 of this preamble). In this scenario, the first and second year
in the three-year period both did not meet the criteria; therefore, the
interannual exceedance frequency was not met.

     Table 9--Example 2 Scenario Where Dissolved Oxygen Criteria With the 1-in-3-Year Interannual Exceedance
                                              Frequency Are Not Met
----------------------------------------------------------------------------------------------------------------
                                                            Was the seasonal criterion met?
                Season                --------------------------------------------------------------------------
                                                Year 1                   Year 2                   Year 3
----------------------------------------------------------------------------------------------------------------
Spawning and Larval Development......  Yes....................  Yes....................  Yes.
Juvenile Development--10th Percentile  No.....................  Yes....................  Yes.
Juvenile Development--50th Percentile  Yes....................  No.....................  Yes.
Overwintering........................  Yes....................  Yes....................  Yes.
Does the Full Year Meet Criteria?....  No.....................  No.....................  Yes.
----------------------------------------------------------------------------------------------------------------

    The EPA has historically considered it appropriate to apply a 1-in-
3-year exceedance frequency in the context of aquatic life criteria for
toxic pollutants, based on the ability of aquatic ecosystems to recover
from criteria exceedances and natural variations in flow and the
concentrations of the pollutant in a waterbody.\74\ However, the EPA
does not typically apply this construct to criteria for conventional
water quality parameters like dissolved

oxygen due to inherent differences between these parameters and toxic
pollutants. For example, dissolved oxygen is typically not directly
regulated in the same manner as toxic pollutants because low dissolved
oxygen conditions (such as hypoxia) are a symptom of a related issue,
such as nutrient or ammonia pollution.\75\ The EPA also requests public
input and supporting information regarding any scientific approaches
that can be used to predict the impact of periodic low oxygen levels on
populations of aquatic organisms.
---------------------------------------------------------------------------

    \74\ Stephen, C.E., Mount, D.I., Hansen, D.J., Gentile, J.R.,
Chapman, G.A., and Brungs, W.A. (1985). Guidelines for Deriving
Numerical National Water Quality Criteria for the Protection of
Aquatic Organisms and Their Uses. United States Environmental
Protection Agency. Document ID: PB85-227049. https://www.epa.gov/sites/default/files/2016-02/documents/guidelines-water-quality-criteria.pdf; United States Environmental Protection Agency. (2023).
Proceedings from the EPA Frequency and Duration Experts Workshop:
September 11-12, 2019. Document ID: EPA-820-R-23-002. February 2023.
https://www.epa.gov/system/files/documents/2023-02/proceedings-frequency-duration-workshop.pdf.
    \75\ United States Environmental Protection Agency. (2000).
Ambient Aquatic Life Water Quality Criteria for Dissolved Oxygen
(Saltwater): Cape Cod to Cape Hatteras. Document ID: EPA-822-R-00-
012. November 2000. https://www.epa.gov/sites/default/files/2018-10/documents/ambient-al-wqc-dissolved-oxygen-cape-code.pdf.
---------------------------------------------------------------------------

V. Endangered Species Act Consultation

    Section 7(a)(2) of the Endangered Species Act (ESA) requires that
each Federal Agency ensure that any action authorized, funded, or
carried out by such Agency is not likely to jeopardize the continued
existence of any endangered or threatened species or result in the
destruction or adverse modification of critical habitat. Pursuant to
section 7(a)(2) of the ESA, the EPA will consult with NOAA Fisheries
concerning this rulemaking action proposing a designated aquatic life
use including propagation and associated dissolved oxygen criteria in
the specified zones of the Delaware River. The EPA will work closely
with NOAA Fisheries to ensure that any WQS the Agency finalizes are not
likely to jeopardize the continued existence of any endangered or
threatened species or result in the destruction or adverse modification
of designated critical habitat in the specified zones of the Delaware
River. As a result of this consultation, the EPA may modify some
provisions of this proposed rule.

VI. Applicability

    The EPA is proposing a Federal designated use that would apply in
New Jersey and Pennsylvania, in addition to those states' designated
uses that are already applicable. This means that for the specified
zones of the Delaware River, the EPA is proposing to supplement, rather
than replace, New Jersey's and Pennsylvania's currently applicable
aquatic life designated uses. Therefore, New Jersey's and
Pennsylvania's currently applicable aquatic life designated uses would
remain applicable for CWA purposes. Those states' current water quality
criteria associated with those uses would also remain applicable for
CWA purposes, with the exception of any aquatic life criteria for
dissolved oxygen, which would be replaced by the criteria that the EPA
promulgates through this rulemaking, if finalized.\76\ The EPA
concluded that this approach was the best way to make clear which of
the states' WQS would and would not be revised by this rulemaking, if
finalized. The EPA requests comment on this approach.
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    \76\ In the December 1, 2022, Administrator's Determination, the
EPA determined that revised dissolved oxygen criteria are necessary
to protect a propagation designated use. This proposed rulemaking
includes dissolved oxygen criteria that are protective of all life
stages of resident and migratory aquatic life species in the
Delaware River (section IV.C. of this preamble).
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    In addition, the EPA is proposing dissolved oxygen criteria that
would replace Delaware's, New Jersey's, and Pennsylvania's existing
dissolved oxygen criteria for the specified zones of the Delaware
River. The EPA notes that there are aquatic life criteria for
pollutants and parameters other than dissolved oxygen that are in
effect for CWA purposes--not only in the zones covered by this proposed
rulemaking, but also for other zones of the Delaware River that already
include aquatic life propagation as a designated use; those criteria
are not impacted by this rulemaking.
    Since the EPA is only proposing to promulgate revised dissolved
oxygen criteria for the specified zones of the Delaware River,
Delaware, New Jersey, and Pennsylvania should evaluate whether other
aquatic life criteria should similarly be added or revised for the
specified zones or other zones of the Delaware River. One way these
states can review their WQS is through the triennial review process. As
explained in section III of this preamble, states must review their WQS
at least once every three years and, if appropriate, revise standards
or adopt new standards (40 CFR 131.20(a)). The EPA recommends that
Delaware, New Jersey, and Pennsylvania review their existing aquatic
life criteria during their next triennial review to determine if new or
revised aquatic life criteria would be appropriate to protect all
applicable aquatic life designated uses, including any Federal
designated use that the EPA may promulgate as part of a final rule.

VII. Conditions Where Federal Water Quality Standards Would Not Be
Promulgated or Would Be Withdrawn

    As noted, under the CWA, states and authorized tribes have the
primary responsibility for developing and adopting WQS for their
navigable waters (CWA section 303(a) through (c)). Although the EPA is
proposing a revised aquatic life designated use and protective
dissolved oxygen criteria for the specified zones of the Delaware
River, each state retains the option to adopt and submit to the EPA for
review its own revised designated use and dissolved oxygen criteria
that are consistent with CWA section 303(c) and the EPA's implementing
regulation to address the EPA's Administrator's Determination.

A. Conditions Where Federal Standards Would Not Be Promulgated

    If Delaware, New Jersey, and Pennsylvania adopt and submit revised
WQS that addresses the EPA's December 1, 2022, Administrator's
Determination, and the EPA approves those WQS before finalizing this
proposed rulemaking, then a Federal promulgation would no longer be
required under the CWA. Similarly, if one state adopts and submits WQS
consistent with this proposed rulemaking, and the EPA approves those
WQS before finalizing this proposed rulemaking, then a Federal
promulgation would no longer be required under the CWA for that state.

B. Conditions Where Federal Standards Would Be Withdrawn

    If the EPA finalizes this proposed rulemaking and Delaware, New
Jersey, and Pennsylvania subsequently adopt and submit revised WQS to
the EPA, and the EPA approves those WQS, then the EPA would undertake a
rulemaking to withdraw the federally promulgated use and/or dissolved
oxygen criteria (40 CFR 131.21(c)). Similarly, if one state adopts and
submits revised WQS to the EPA, and the EPA approves those WQS, then
the EPA would undertake a rulemaking to withdraw the federally
promulgated WQS for that state.
    If Delaware's, New Jersey's, and/or Pennsylvania's adopted
dissolved oxygen criteria are as stringent or more stringent than the
federally promulgated criteria, then that state's criteria would
immediately become the CWA-applicable criteria upon the EPA's approval.
If Delaware's, New Jersey's, and/or Pennsylvania's adopted dissolved
oxygen criteria are less stringent than the federally promulgated
criteria, and the EPA approves those less stringent criteria, then
those EPA-approved criteria would become the applicable criteria for
CWA purposes only after the EPA withdraws its federally promulgated
criteria for the relevant state(s).

VIII. Alternative Regulatory Approaches and Implementation Mechanisms

    The Federal WQS regulations at 40 CFR part 131 provide several
approaches that Delaware, New Jersey, and Pennsylvania could use at
each state's discretion when implementing or deciding how to implement
the federally promulgated dissolved oxygen criteria, if finalized. The
EPA has identified two approaches--WQS Variances and NPDES Permit
Compliance Schedules--that might be of particular interest for the
states covered by this proposed rulemaking. Additionally, the EPA
included a discussion about CWA section 303(d)/305(b) water quality
assessments to clarify potential options that may be available to
states in the specific circumstances relevant to this rulemaking.

A. Water Quality Standards Variances

    A WQS variance is 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
(40 CFR 131.3(o)). WQS variances can be used to incrementally improve
water quality where the designated use and criterion are unattainable
for a period of time. The state would need to demonstrate that
attaining the applicable designated use and dissolved oxygen criterion
would not be feasible for a period of time (i.e., during the term of
the WQS variance) because of one of the factors specified in 40 CFR
131.14(b)(2)(i)(A) and specify the actions that will be taken to make
incremental water quality improvements during the term of the WQS
variance.
    If Delaware, New Jersey, and/or Pennsylvania choose/s to adopt a
WQS variance, the state/s must specify in the WQS variance the term and
the interim requirements of the WQS variance. The term must be
justified by describing the pollutant control activities expected to
occur over that term to achieve the HAC. The interim requirements must
be a quantitative expression that reflects the HAC using one of the
options provided at 40 CFR 131.14(b)(1)(ii).
    WQS variances adopted in accordance with 40 CFR 131.14 and approved
by the EPA for CWA purposes provide a legal avenue for states to write
NPDES permit limits that are based on the HAC during the term of the
WQS variance, while simultaneously implementing controls to make
incremental water quality improvements toward ultimately attaining the
applicable designated use and dissolved oxygen criterion.

B. NPDES Permit Compliance Schedules

    The EPA's regulations at 40 CFR 122.47 and 131.15 address how
permitting authorities can use schedules for compliance with a water-
quality-based effluent limitation (WQBEL) in an NPDES permit, if the
discharger needs time to undertake an enforceable sequence of actions--
such as facility upgrades or operation changes--leading to compliance
with the WQBEL. The EPA's regulation at 40 CFR 122.47 allows states
authorized to administer the NPDES program to include compliance
schedules in NPDES permits, when appropriate and where authorized by
the state's WQS, provided the compliance schedule authorizing provision
was approved by the EPA. Such compliance schedules may be used to
implement any CWA-effective WQS, including any WQS that the EPA
promulgates as part of a final rule.

C. Clean Water Act Section 303(d)/305(b) Water Quality Assessments

    If the EPA promulgates revised aquatic life WQS for the specified
zones of the Delaware River and they become effective for CWA purposes,
Delaware, New Jersey, and Pennsylvania will have an obligation under
CWA sections 303(d) and 305(b) to assess whether the WQS are being
attained. The EPA anticipates there may be a period of time immediately
after promulgation of the revised WQS when the WQS will not be attained
because the actions and procedures required to achieve compliance will
take time to implement. In this scenario, any of the relevant zones not
attaining the WQS should be classified as impaired on the relevant
303(d)/305(b) Integrated Report(s) (IR) that is submitted to the EPA
for review.
    Per the CWA and the EPA's implementing regulations, waters that are
assessed as impaired by a pollutant typically require the development
of a Total Maximum Daily Load (TMDL), which is a regulatory planning
tool designed to restore water quality via allocations of pollutant
reductions to relevant point and non-point sources. The EPA regulations
also recognize that other pollution control requirements may obviate
the need for a TMDL. Specifically, impaired waters do not require a
TMDL if: (1) technology-based effluent limitations required by the CWA;
(2) more stringent effluent limitations required by a state, local, or
Federal authority; or (3) other pollution control requirements (e.g.,
best management practices) required by a state, local, or Federal
authority are stringent enough to implement applicable WQS (40 CFR
130.7(b)(1)). Impaired waters that do not require a TMDL because they
satisfy one of these alternatives are commonly referred to as Category
4b waters, as described in the EPA's Integrated Reporting Guidance for
CWA sections 303(d), 305(b), and 314.\77\
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    \77\ The EPA's Integrated Reporting Guidance is available at:
https://www.epa.gov/tmdl/integrated-reporting-guidance-under-cwa-sections-303d-305b-and-314.
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    DRBC developed a model to evaluate sources of pollution that affect
dissolved oxygen levels in the specified zones of the Delaware River
and concluded that point sources are the primary contributor to oxygen
depletion within those zones.\78\ DRBC therefore concluded that further
controls on point sources are needed to achieve dissolved oxygen water
quality conditions that support aquatic life designated uses that
include propagation in the specified zones. The EPA's economic analysis
evaluates point source controls that are expected to result in
dissolved oxygen levels that meet EPA's proposed criteria.\79\ If,
after finalization of this rulemaking, DRBC, Delaware, New Jersey, or
Pennsylvania require effluent limitations and/or other pollution
control requirements that the EPA agrees are stringent enough to
implement the final dissolved oxygen criteria, the specified zones may
be a candidate for Category 4b in future IRs. The EPA will work with
Delaware, New Jersey, and Pennsylvania, in consultation with DRBC, on
future IRs to determine the appropriate assessment status for the
waters that are subject to this rulemaking.
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    \78\ Delaware River Basin Commission (2022a, 2022b).
    \79\ More details are available in the document, Economic
Analysis for the Proposed Rule: Water Quality Standards to Protect
Aquatic Life in the Delaware River.
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IX. Economic Analysis

    The EPA conducted an economic analysis to evaluate the potential
costs and benefits associated with this proposed rulemaking. In the
high-level summary of the EPA's economic analysis below, the EPA first
describes a baseline scenario that is intended to characterize the
world in the absence of the EPA's proposed rule. Next, the EPA
describes development of a policy scenario based on potential pollution
control actions that, if implemented, can be expected to meet the EPA's
proposed dissolved oxygen criteria. Finally, the EPA evaluates the
anticipated costs and benefits associated with the policy scenario and
the EPA's proposed criteria. More details and information

are available in the associated document, Economic Analysis for the
Proposed Rule: Water Quality Standards to Protect Aquatic Life in the
Delaware River.

A. Baseline for the Analysis

    The baseline is intended to characterize the world in the absence
of the EPA's proposed rule. The EPA typically assumes full compliance
with existing regulations and requirements--including CSO long-term
control plans (LTCPs)--even if they are not yet fully implemented, as a
basis for estimating the cost and benefits of proposed regulations.
This baseline approach ensures that the cost and benefits of the
existing regulations and requirements are not double counted.
    In this economic analysis, the EPA assumes that without the
proposed rule, the less stringent WQS (that do not support aquatic life
propagation) currently in effect for CWA purposes would remain in
effect (section III.D. of this preamble). Accordingly, the EPA assumes
that water quality conditions in the specified zones of the Delaware
River, particularly during the Juvenile Development season (July 1-
October 31), would continue to experience low oxygen levels that do not
support aquatic life propagation, even with implementation of existing
and planned CSO LTCPs.\80\ Along the specified zones of the Delaware
River, there are three combined sewer systems with CSO LTCPs that are
relevant for consideration by the EPA as part of the baseline. The
Philadelphia Water Department, Camden County Municipal Utilities
Authority, and Delaware County Regional Water Quality Control Authority
all have LTCPs that are either approved or in progress.\81\ The EPA
expects implementation of these LTCPs, when finalized, to occur
regardless of the EPA's proposed rule. Therefore, the EPA included
estimated CSO volume reductions for these three dischargers as part of
the baseline for this economic analysis.
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    \80\ While the EPA normally assumes full compliance with
existing LTCPs, for this proposed rulemaking, the EPA is also
assuming full compliance with planned LTCPs. Because planned LTCPs
are not final and therefore are subject to change, this adds
uncertainty to the baseline conditions.
    \81\ Delaware River Basin Commission (2022a); DELCORA. (2023).
Combined Sewer System: DELCORA CSO LTCP. https://www.delcora.org/combined-sewer-systems/delcora-cso-ltcp/; Philadelphia Water
Department. (2023). CSO Long Term Control Plan. https://water.phila.gov/reporting/ltcp/; State of New Jersey Division of
Water Quality. (2023). Long Term Control Plan Submittals. https://www.nj.gov/dep/dwq/cso-ltcpsubmittals.htm.
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    DRBC modeled the effect of pollution reduction on dissolved oxygen
levels in the Delaware River and provided the EPA with water quality
simulation results under both baseline and ``restored'' conditions for
the years 2012, 2018, and 2019.\82\ Baseline simulations predict water
quality conditions associated with the discharge of actual wastewater
treatment plant (WWTP) flows at existing levels of treatment and after
full implementation of LTCPs. The restored simulations predict water
quality conditions associated with the discharge of actual WWTP flows
at treatment levels that include additional effluent treatment and
after full implementation of LTCPs.
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    \82\ The EPA determined that the model runs from DRBC were
sufficient for use in this economic analysis.
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    Of the three available years (2012, 2018, and 2019), the EPA
selected the 2019 year as representative of the most typical conditions
in the relevant zones of the Delaware River. In comparison, 2012 had
atypically poor conditions (low percent oxygen saturation, high water
temperature), while 2018 had atypically good conditions (high percent
oxygen saturation, low water temperature). Therefore, model runs used
in this economic analysis are based on 2019 conditions.

B. Development of the Policy Scenario

    There is a wide range of potential paths that Delaware, New Jersey,
and Pennsylvania may choose to take when implementing the EPA's
proposed WQS. For this economic analysis, the EPA relied on available
data to develop a policy scenario based on modeled pollution controls
developed by DRBC that the EPA expects would meet the Agency's proposed
dissolved oxygen criteria. Actual benefits, costs, and impacts will
depend on the choices that states would make in implementing the
proposed WQS, which may differ from the policy scenario in this
economic analysis.
    The EPA's proposed dissolved oxygen criteria apply to three seasons
(section IV.C. of this preamble). Therefore, when developing a policy
scenario for this proposed rulemaking, the EPA evaluated potential
pollution control actions that would be expected to meet the EPA's
criteria in each of the three seasons. The EPA began by evaluating
water quality monitoring data for the past decade from two continuous
monitoring stations in the relevant zones of the Delaware River--Penn's
Landing in Zone 3 and Chester in Zone 4. Based on the monitoring data,
the EPA expects that the Agency's proposed dissolved oxygen criteria
for the Spawning and Larval Development and Overwintering seasons will
likely be met without the need for additional WWTP upgrades or other
controls beyond the baseline conditions (i.e., the LTCPs). Monitoring
data for the Juvenile Development season indicated that additional
pollution control actions are likely necessary to meet the EPA's
proposed criteria in that season. To develop a policy scenario for the
Juvenile Development season, the EPA relied on modeled data from DRBC
predicting oxygen levels in 2019 in the specified zones of the Delaware
River following a set of WWTP pollution control actions for certain
dischargers. Modeled data for restored conditions are described in the
baseline section above, while WWTP controls are described in the cost
section below. The EPA expects that this policy scenario (hereafter,
the ``2019 restored scenario'') will meet the proposed criteria during
the Juvenile Development season.

C. Potential Costs

    The EPA estimated compliance costs for the proposed WQS based on
estimates for WWTPs to reduce effluent ammonia nitrogen concentrations
and raise effluent dissolved oxygen concentrations. Although there are
several causes that contribute to low dissolved oxygen conditions in
the specified zones of the Delaware River, DRBC identified ammonia
nitrogen loadings from WWTPs as the leading cause of oxygen-depletion
in the river.\83\ As a result, for the purpose of this economic
analysis, the EPA assumed that additional pollution control
technologies implemented at WWTPs is the most likely way that Delaware,
New Jersey, and Pennsylvania will implement the proposed WQS.
Therefore, the EPA evaluated WWTP controls rather than other non-point
source controls for this cost analysis.
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    \83\ Delaware River Basin Commission (2022a).
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    The EPA relied on cost information from several DRBC studies to
estimate the costs of achieving the proposed WQS.\84\ DRBC's 2022
Analysis of Attainability report categorized WWTPs as either class A',
A, or B facilities. DRBC determined that discharges from Class A', A,
and B facilities have a major

impact, a marginal impact, or no measurable impact on oxygen levels in
the specified zones, respectively. The EPA's 2019 restored scenario
follows DRBC's approach by including the seven Class A' and two Class A
facilities and excluded the three Class B facilities.\85\
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    \84\ Id.; Kleinfelder Inc. (2021). Nitrogen Reduction Cost
Estimation Study Final Summary Report. https://www.nj.gov/drbc/library/documents/NitrogenReductionCostEstimates_KleinfelderJan2021.pdf; Kleinfelder
Inc. (2023). Delaware River Basin Commission Nitrogen Reduction Cost
Estimation Study--Supplemental Cost Addendum 2 Technical
Memorandum--Final. https://www.nj.gov/drbc/library/documents/NitrogenReductionCostEstimates_Kleinfelder_aug2023addendum.pdf.
    \85\ Delaware River Basin Commission (2022a).
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    The EPA used WWTP-specific (capital, operations and maintenance
(O&M)) compliance costs from Kleinfelder Inc. (2021, 2023) to estimate
compliance costs, based on the discharger classification. Total
compliance costs include the costs associated with both of the
following:
    1. Class A' Facilities: Costs associated with reductions in
effluent ammonia nitrogen concentrations to 1.5 mg/L from May 1 through
October 31 and increases in effluent oxygen concentrations to a monthly
average of 6 mg/L year-round for the seven WWTPs categorized as Class
A' facilities.
    2. Class A Facilities: Costs associated with reductions in effluent
ammonia nitrogen concentrations to 5 mg/L from May 1 through October 31
for the two WWTPs categorized as Class A facilities.
    To estimate annualized compliance costs, the EPA assumed capital
costs occur upfront in 2024 followed by a 5-year construction period.
Consistent with Kleinfelder Inc. (2021, 2023), the EPA assumed O&M
costs occur over a 25-year period from 2029 through 2053. The EPA thus
annualized costs over a 30-year analysis period between 2024 and 2053