Environmental Assessment for Final Supplemental Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating Point Source Category


SERA—

United States
Environmental Protection
Agency

Environmental Assessment for Final
Supplemental Effluent Limitations Guidelines
and Standards for the Steam Electric Power
Generating Point Source Category

April 2024

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U.S. Environmental Protection Agency
Office of Water (4303T)
1200 Pennsylvania Avenue, NW
Washington, DC 20460

EPA-821-R-24-005

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This document was prepared by the Environmental Protection Agency. Neither the United States
Government nor any of its employees, contractors, subcontractors, or their employees make any warrant,
expressed or implied, or assume any legal liability or responsibility for any third party's use of or the
results of such use of any information, apparatus, product, or process discussed in this report, or
represents that its use by such party would not infringe on privately owned rights.

Questions regarding this document should be directed to:

U.S. EPA Engineering and Analysis Division (4303T)

1200 Pennsylvania Avenue NW
Washington, DC 20460
(202) 566-1000

Hi

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Contents

1.	Introduction	1

1.1	Background on Steam Electric Power Plant Wastewater Discharges	1

1.2	Scope of the EA	2

2.	Literature Review of the Environmental and Human Health Concerns Associated with the Evaluated
Wastestreams	5

2.1	Pollutants Discharged in the Evaluated Wastestreams	5

2.1.1	Metals and Toxic Bioaccumulative Pollutants	5

2.1.2	Nutrients	6

2.1.3	TDS and Salinity	6

2.1.4	Bromine/Bromide	7

2.1.5	Iodine/Iodide	8

2.2	Potential Impacts from the Evaluated Wastestreams	9

2.2.1	Ecological Impacts	10

2.2.2	Human Health Effects	12

2.2.3	Groundwater Impacts	13

2.2.4	CCR Surface Impoundments as Attractive Nuisances	14

3.	Environmental Assessment Methodology	16

3.1	Pollutant Loadings for the Evaluated Wastestreams	16

3.2	Pollutant Exposure Pathways	18

3.3	Environmental Impacts Selected for Qualitative and Quantitative Assessments in the EA	20

3.4	Overview of the IRW Model	21

3.4.1	Structure of the IRW Model	21

3.4.2	Pollutants Evaluated by the IRW Model	23

3.5	Proximity Analysis	26

3.6	Downstream Analysis	26

3.7	Scope of the Evaluated Plants and Immediate Receiving Waters	27

4.	Results of the Quantitative Environmental Assessment for the Final Supplemental Rule	31

4.1	Environmental Impacts Identified by the IRW Model	31

4.1.1	Water Quality Impacts	32

4.1.2	Wildlife Impacts	35

4.1.3	Human Health Impacts	37

4.2	Discharges to Sensitive Environments	43

4.2.1	Impaired Waters	44

4.2.2	Fish Consumption Advisories	47

4.2.3	Drinking Water Resources	49

4.3	Impacts in Downstream Surface Waters	49

4.4	Summary of Key Environmental and Human Health Improvements	51

5.	References	52

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Attachments

Attachment A . Additional IRW Model Results

List of Figures

Figure 1. Overview of the IRW Model 23

Figure 2. Locations of Immediate Receiving Waters Evaluated in the Environmental Assessment for

the Final Supplemental Rule 30

Figure 3. Immediate Receiving Waters Impaired by Mercury 45

Figure 4. Immediate Receiving Waters Impaired by Metals Other Than Mercury 46

Figure 5. Immediate Receiving Waters Impaired by Nutrients 46

Figure 6. Immediate Receiving Waters with Fish Consumption Advisories for Mercury 48

List of Tables

Table 1. Wastestreams Evaluated in the EA 2

Table 2. Estimated Annual Baseline Mass Pollutant Loadings and Estimated Reduction in Loadings

Under Regulatory Options for the Evaluated Wastestreams3 17

Table 3. Steam Electric Power Plant Wastewater Environmental Pathways and Routes of Exposure

Evaluated in the Environmental Assessment for the Final Supplemental Rule 19

Table 4. Water Quality Benchmarks: NRWQC and MCLs 24

Table 5. Sediment Biota and Wildlife Benchmarks: TECs and NEHCs 25

Table 6. Human Health Benchmarks: Oral RfDs and CSFs 25

Table 7. Plants, Generating Units, and Immediate Receiving Waters Evaluated in the Environmental

Assessment for the Final Supplemental Rule 28

Table 8. Plants, Generating Units, and Immediate Receiving Waters with Pollutant Loadings Under

Baseline and Regulatory Options for the Final Supplemental Rule 29

Table 9. Modeled IRWs with Exceedances of NRWQC and MCLs Under Baseline and Regulatory

Options 32

Table 10. Modeled IRWs with Exceedances of NRWQC and MCLs, by Pollutant, Under Baseline and

Regulatory Options 34

Table 11. Modeled IRWs with Exceedances of TECs and NEHCs Under Baseline and Regulatory

Options 36

Table 12. Modeled IRWs with Exceedances of Oral RfD (Noncancer Human Health Effects) Under

Baseline and Regulatory Options 38

Table 13. Modeled IRWs with LECR Greater Than One-in-a-Million (Cancer Human Health Effects)

Under Baseline and Regulatory Options 39

Table 14. Modeled IRWs with Exceedances of Oral RfDs by Race/Ethnicity Under Baseline and

Regulatory Options 40

Table 15. Modeled IRWs with LECR Greater Than One-in-a-Million (Cancer Human Health Effects)

Race/Ethnicity Under Baseline and Regulatory Options 41

Table 16. Comparison of Modeled T4 Fish Tissue Concentrations to Fish Advisory Screening Values
Under Baseline and Regulatory Options 42

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Table 17. Modeled IRWs Identified as CWA Section 303(d) Impaired Waters, Fish Consumption

Advisory Waters, or Drinking Water Resources Under Baseline and Regulatory Options	43

Table 18. Modeled IRWs Identified as CWA Section 303(d) Impaired Waters for Pollutants Present in

the Evaluated Wastestreams Under Baseline and Regulatory Options	45

Table 19. Modeled IRWs Identified as Fish Consumption Advisory Waters for Pollutants Present in

the Evaluated Wastestreams Under Baseline and Regulatory Options	48

Table 20. Modeled IRWs Identified as Located Within 5 Miles of a Drinking Water Resource Under
Baseline and Regulatory Options	49

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List of Abbreviations

AETX

aetokthonotoxin

BA

bottom ash

BAT

best available technology economically achievable

BCA

benefit and cost analysis

Br-DBP

brominated disinfection byproduct

CCR

coal combustion residuals

CFR

Code of Federal Regulations

CRL

combustion residual leachate

CSF

cancer slope factor

CWA

Clean Water Act

DBP

disinfection byproduct

DCN

document control number

D-FATE

Downstream Fate and Transport Equations

DNA

deoxyribonucleic acid

DWTP

drinking water treatment plant

EA

environmental assessment

EGU

electric generating unit

EJ

environmental justice

ELGs

effluent limitations guidelines and standards

EPA

U.S. Environmental Protection Agency

FGD

flue gas desulfurization

FR

Federal Register

FW

freshwater

HAAs

haloacetic acids

HANs

haloacetonitriles

HH 0

human health for the consumption of organism only

HH WO

human health for the consumption of water and organism

l-DBP

iodinated disinfection byproduct

IRIS

Integrated Risk Information System

IRW

immediate receiving water

lb/year

pounds per year

LC50

median lethal concentration

LECR

lifetime excess cancer risk

MCL

maximum contaminant level

MRL

minimal risk level

mg/kg

milligrams per kilogram

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mg/kg-day	milligrams per kilogram body weight per day

mg/L	milligrams per liter

|ag/g	micrograms per gram

N	nitrogen

NEHC	no effect hazard concentration

NHDPIus	National Hydrography Dataset Plus

NRWQC	National Recommended Water Quality Criteria

POTW	publicly owned treatment works

ppm	parts per million

PSES	pretreatment standards for existing sources

RfD	reference dose

RIA	regulatory impact analysis

S02	sulfur dioxide

T3	trophic level 3

T4	trophic level 4

TDD	technical development document

TDS	total dissolved solids

TEC	threshold effect concentration

THMs	trihalomethanes

TKN	total Kjeldahl nitrogen

TSS	total suspended solids

UV	ultraviolet

VM	vacuolar myelinopathy

WHO	World Health Organization

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1. Introduction

The U.S. Environmental Protection Agency (EPA) promulgated revised effluent limitations guidelines and
standards (ELGs) for the Steam Electric Power Generating Point Source Category (40 CFR 423) on
November 3, 2015 (80 FR 67838), referred to hereinafter as the "2015 rule." Following promulgation, the
EPA received seven petitions for review of the 2015 rule and the Administrator announced his decision to
reconsider the 2015 rule. The EPA finalized a revision to the regulations for the Steam Electric Power
Generating category (85 FR 64650, October 13, 2020), referred to as the "2020 rule," which established
revised ELGs for flue gas desulfurization (FGD) wastewater and bottom ash (BA) transport water
discharged from steam electric power plants. See the Technical Development Document for Final
Supplemental Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating Point
Source Category, or TDD (EPA-821-R-24-004) for more background and information on the rulemaking
history.

This 2024 supplemental rulemaking is based on a review of the ELGs promulgated in 2020 under
Executive Order 13990. The supplement rule covers best available technology economically achievable
(BAT) and pretreatment standards for existing sources (PSES) requirements for FGD wastewater, BA
transport water, combustion residual leachate (CRL), and legacy wastewater from steam electric power
plants. It also establishes new source performance standards (NSPS) and pretreatment standards for new
sources (PSNS) for CRL.

In support of the development of the 2015 rule and the 2020 rule, the EPA conducted an environmental
assessment (EA) to evaluate the environmental impact of pollutant loadings discharged by steam electric
power plants and assess the potential environmental improvement from pollutant loading changes under
the rules. The EPA documented the EA in the September 2015 report Environmental Assessment for the
Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating Point Source
Category (EPA-821-R-15-006) (U.S. EPA, 2015a), referred to hereinafter as the "2015 EA," and the
Supplemental Environmental Assessment for Revisions to the Effluent Limitations Guidelines and
Standards for the Steam Electric Power Generating Point Source Category (EPA-821-R-20-002) (U.S. EPA,
2020a), referred to hereinafter as the "2020 EA." To support the 2024 final rule, the EPA updated its EA
for the 2015 rule and 2020 rule to include the steam electric power plants discharging one or more of the
four wastestreams. In addition, the EPA evaluated potential cumulative impacts from multiple pollutants
(Joint Toxic Action analysis) in support of the proposed rulemaking.

The Clean Water Act does not require that the EPA assess the water-quality-related environmental
impacts, or the benefits, of its ELGs, and the Agency did not make its decisions in the final rule based on
the expected benefits of the rule. The EPA does, however, inform itself and the public of the benefits of
its proposed and final rules, as required by Executive Order 12866. See the Benefit and Cost Analysis for
Final Supplemental Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating
Point Source Category, or BCA Report (EPA-821-R-24-006). This EA report presents the EPA's evaluation of
the potential environmental impacts due to pollutant loadings under baseline discharge practices [i.e.,
following full implementation of the requirements under the 2015 rule and 2020 rule and any known
retirements, fuel conversions, and treatment technologies in place at in-scope steam electric power
plants) and the improvements to those impacts under the evaluated regulatory options.

1.1 Background on Steam Electric Power Plant Wastewater Discharges

Based on demonstrated impacts documented in literature and modeled receiving water pollutant
concentrations, discharges of steam electric power plant wastewater can affect the water quality in
receiving waters, affect the wildlife in the surrounding environments, and pose a human health risk to
nearby communities. There is substantial evidence that certain pollutants found in these wastewater
discharges, such as mercury and selenium, propagate from the aquatic environment to terrestrial food
webs, indicating a potential for broader impacts on surrounding ecological systems by diminishing

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population diversity and disrupting community dynamics. Ecosystem recovery from exposure to these
pollutants can be extremely slow, and even short periods of exposure (e.g., less than a year) can cause
observable ecological impacts that last for years.

Steam electric power plants often discharge wastewater into waterbodies used for fishing, for recreation,
and/or as sources of drinking water. Many studies have raised concerns about the toxicity of these
wastestreams and their impacts on downstream drinking water treatment systems. For example, these
discharges can elevate halogen levels in surface water, which may contribute to disinfection byproduct
formation at downstream drinking water treatment plants. Leaching of pollutants from surface
impoundments and landfills containing combustion residuals is known to affect off-site groundwater and
drinking water wells at concentrations above maximum contaminant level drinking water standards,
posing a threat to human health.

1.2 Scope of the EA

The Steam Electric Power Generating Point Source Category ELGs apply to establishments whose
generation of electricity is the predominant source of revenue or principal reason for operation, and
whose generation results primarily from a process using fossil-type fuels (coal, oil, or gas), fuel derived
from fossil fuel (e.g., petroleum coke, synthesis gas), or nuclear fuel in conjunction with a thermal cycle
using the steam water system as the thermodynamic medium. The EPA evaluated four wastestreams
from steam electric power plants whose limitations and standards would be revised under the new
rulemaking: FGD wastewater, BA transport water, CRL, and legacy wastewater, as described in Table 1.

Table 1. Wastestreams Evaluated in the EA

Evaluated
Wastestream

Description

FGD

wastewater

Wastewater generated from a wet FGD scrubber system. Wet FGD systems are used to
control sulfur dioxide (SO2) and mercury emissions from the flue gas generated in the
plant's electric generating unit (EGU).

The pollutant concentrations in FGD wastewater vary from plant to plant depending on the
coal type, the burning of refined coal, the sorbents and additives used, the materials used
to construct the FGD system, the FGD system operation, the level of recycle within the
absorber, and the air pollution control systems operated upstream of the FGD system. FGD
wastewater contains total dissolved solids (TDS), total suspended solids (TSS), nutrients,
halogens, metals, and other toxic and bioaccumulative pollutants, such as arsenic and
selenium (see the TDD [U.S. EPA, 2024a] for further details).

BA transport
water

Water used to convey the BA particles collected at the bottom of the EGU.

BA transport waters contain halogens, TDS, TSS, metals, and other toxic and
bioaccumulative pollutants, such as arsenic and selenium (see the TDD [U.S. EPA, 2024a] for
details). The effluent from BA surface impoundments typically contains low concentrations
of TSS; however, arsenic, bromide, selenium, and metals are still present in the wastewater,
predominantly in dissolved form.

CRL

Leachate is composed of liquid, including any suspended or dissolved constituents in the
liquid, that has percolated through waste or other materials emplaced in a landfill, or that
passes through the surface impoundment's containment structure (e.g., bottom, dikes,
berms). CRL includes seepage and/or leakage from a combustion residual landfill or
impoundment unit.

CRL contains pollutants similar to those in FGD wastewater.

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Table 1. Wastestreams Evaluated in the EA

The goal of the EA is to answer the following questions about pollutant loadings from the four evaluated
wastestreams:

•	What are the environmental concerns?

•	What are baseline environmental impacts to water quality and wildlife and impacts to human health?

•	What are the potential improvements to water quality, wildlife, and human health under the
regulatory options?

This EA report presents the EPA's evaluation of environmental concerns and potential exposures
(ecological and human) to pollutants commonly found in wastewater discharges from steam electric
power plants. The EPA carried out both qualitative and quantitative analyses. Qualitative analyses
included reviewing additional literature documenting site impacts and pollutant-specific research.
Quantitative analyses included assessing the pollutant loadings to receiving waters—including those
designated as impaired or with a fish consumption advisory—under baseline and the evaluated regulatory
options and reviewing the effects of pollutant exposure on ecological and human receptors. To quantify
impacts associated with these discharges, the EPA used a computer model to estimate pollutant
concentrations in the immediate receiving waters, pollutant concentrations in fish tissue, and potential
exposure doses to ecological and human receptors from fish consumption. The EPA compared the values
calculated by the model to benchmark values to assess the extent of the environmental impacts
nationwide. The EPA evaluated the impacts of FGD wastewater, BA transport water, CRL,1 and legacy
wastewater discharges.

The EPA evaluated three regulatory options, summarized in Table VI1-1 of the preamble to the final rule.
The EPA evaluated 112 plants that discharge FGD wastewater, BA transport water, CRL, and/or legacy
wastewater directly or indirectly to surface waters under baseline and/or the regulatory options and
performed the quantitative modeling of pollutants in the immediate receiving water on a subset of 100 of
these plants. The analyses presented in this report account for notice of planned participation as
described in Section VI of the preamble to the final rule. See Section 3.7 of this report for additional
details on the scope of this EA.

The assessments described in this EA report focus on environmental impacts caused by exposure to
pollutants in the evaluated wastestreams through the surface water exposure pathway. However, the
final rule may have other environmental impacts unrelated to exposure to pollutants in wastewater
discharges. Examples include changes in groundwater and surface water withdrawals by plants and

1 The EPA is establishing a new subcategory for discharges of unmanaged CRL, which the EPA is defining in this rule
to mean the following: (1) discharges of CRL that the permitting authority determines are the functional equivalent
of a direct discharge to a waters of the United States (WOTUS) through groundwater or (2) discharges of CRL that
has leached from a waste management unit into the subsurface and mixed with groundwater prior to being
captured and pumped to the surface for discharge directly to a WOTUS (see Section VII.C.5 of the preamble to the
final rule). This subcategory of CRL is not evaluated in the EA.

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changes in air emissions due to changes in electricity use, transportation requirements, and the profile of
electricity generation. These impacts are discussed in the EPA's BCA Report (U.S. EPA, 2024b).

This EA report does not discuss impacts caused by pollutants in unmanaged CRL. See Section VII.C.5 of the
preamble to the final rule.

This report presents the methodology and results of the qualitative and quantitative analyses performed
for the EA to support the supplemental rule. In addition to this EA, the final rule is supported by several
reports:

• Technical Development Document for Final Supplemental Effluent Limitations Guidelines and
Standards for the Steam Electric Power Generating Point Source Category (TDD), Document No. EPA-
821-R-24-004 (U.S. EPA, 2024a). This report includes background on the final rule, the industry, and
treatment technologies and pollution prevention techniques; it also documents the EPA's engineering
analyses to support the supplemental rule, including cost estimates, wastewater characterization and
pollutant loadings, and a non-water-quality environmental impact assessment.

• Benefit and Cost Analysis for Final Supplemental Effluent Limitations Guidelines and Standards for the
Steam Electric Power Generating Point Source Category (BCA Report), Document No. EPA-821-R-24-
006 (U.S. EPA, 2024b). This report summarizes the monetary benefits and societal costs of
implementing the regulatory options.

• Regulatory Impact Analysis for Final Supplemental Effluent Limitations Guidelines and Standards for
the Steam Electric Power Generating Point Source Category (RIA), Document No. EPA-821-R-24-007
(U.S. EPA, 2024c). This report presents a profile of the steam electric power generating industry, a
summary of the costs and impacts associated with the regulatory options, and an assessment of the
supplemental rule's impact on employment and small businesses.

• Environmental Justice Analysis for Final Supplemental Effluent Limitations Guidelines and Standards
for the Steam Electric Power Generating Point Source Category (EJ Report). Document No. EPA-821-R-
24-008 (U.S. EPA, 2024d). This report presents the environmental justice (EJ) analysis to support the
supplemental rule, including screening analysis to identify communities with potential EJ concerns,
community outreach, literature review, and risk analysis.

The ELGs for the Steam Electric Power Generating Category are based on data generated or obtained in
accordance with the EPA's Quality System and Information Quality Guidelines. The EPA's quality
assurance and quality control activities for this rulemaking include developing, approving, and
implementing quality assurance project plans for the use of environmental data generated or collected
from sampling and analyses, existing databases, and literature searches, and for developing any models
that used environmental data.

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2. Literature Review of the Environmental and Human Health
Concerns Associated with the Evaluated Wastestreams

Discharges of the evaluated wastestreams from steam electric power plants—flue gas desulfurization
(FGD) wastewater, bottom ash (BA) transport water, combustion residual leachate (CRL), and legacy
wastewater—contain toxic and bioaccumulative pollutants (e.g., selenium, mercury, arsenic, nickel),
halogens (containing bromides, chlorides, or iodides), nutrients, and total dissolved solids (TDS), which
can cause environmental harm through the contamination of surface waters. Certain pollutants in the
discharges pose a danger to ecological communities due to their persistence in the environment and
bioaccumulation in organisms. These factors can slow ecological recovery and can have long-term
impacts on aquatic organisms, wildlife, and human health. Many studies document ecological impacts
such as fish mortality, genotoxicity, and lower fish survival and reproduction rates resulting from
exposure to pollutants in steam electric power plant discharges (Brandt et al., 2017 and 2019; Carlson
and Adriano, 1993; Hopkins et al., 2000; Javed et al., 2016; Lemly, 1997b and 2018; Rowe et al., 1996 and
2002). Halogens associated with steam electric power plant discharges also raise ecological and human
health concerns. Halogens in source water for drinking water treatment plants (DWTPs) can interact with
disinfection processes to form halogenated disinfection byproducts (DBPs), which can pose a risk to
human health (Cantor et al., 2010; Chisholm et al., 2008; Dong et al., 2019; Hanigan et al., 2017; National
Toxicology Program, 2018; Regli et al., 2015; Richardson et al., 2007 and 2008; Richardson and Plewa,
2020; U.S. EPA, 2016a; Villanueva et al., 2004, 2007, and 2015; Wagner and Plewa, 2017; Wei et al., 2013;
Yang et al., 2014).

The EPA documented environmental and human health concerns from steam electric power plant
discharges in the 2015 final environmental assessment, or 2015 EA (U.S. EPA, 2015a) and the 2020 EA
(U.S. EPA, 2020a). For this EA, the EPA conducted a supplemental literature review in 2022 that consisted
of identifying and evaluating peer-reviewed journal articles and other materials published since its last full
literature review (2010) that focus on current environmental, ecological, and human health impacts
resulting from discharges of pollutants in the evaluated wastestreams. The EPA also incorporated
relevant articles submitted with public comments and published since the 2022 review into its analysis for
the final rule. This section summarizes relevant findings from the EPA's literature reviews, including an
overview of the pollutants discharged in the evaluated wastestreams and their associated environmental
concerns. Some of the articles documented impacts of steam electric power plant discharges but did not
provide specific wastestream details. When such details were documented in reviewed articles, the EPA
included details on applicable wastestreams. See the memorandum Literature Review for the 2024 Steam
Electric Supplemental Rule Environmental Assessment (U.S. EPA, 2024e) for details.

2.1 Pollutants Discharged in the Evaluated Wastestreams

Several variables can affect the composition of steam electric power plant wastewater, including fuel
composition (e.g., parent coal composition varies by coal type and geographic region and inclusion of
other fuels in the combustion process), air pollution control technologies (e.g., use of dry versus wet
systems), and management techniques used to dispose of the wastewater (e.g., whether the plant
commingles its wastestreams) (Carlson and Adriano, 1993; Rowe et al., 2002). Commingling steam
electric power plant wastewaters in surface impoundments can result in a complex mixture of pollutants
in the effluent that is released to the environment (Rowe et al., 2002).

2.1.1 Metals and Toxic Bioaccumulative Pollutants

Studies commonly cite metals and toxic bioaccumulative pollutants (e.g., arsenic, mercury, and selenium)
as the primary cause of ecological damage following exposure to steam electric power plant wastewater
(U.S. EPA, 2015a). An important consideration in evaluating these pollutants is their bioavailability,
defined as the ability of a particular contaminant to be assimilated into the tissues of exposed organisms.

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A pollutant's bioavailability is affected by the characteristics of both the pollutant [e.g., speciation,
particle size) and the surrounding environment [e.g., temperature, pH, salinity, oxidation-reduction
potential, total organic content, suspended particulate content, and water velocity). Metals and toxic
bioaccumulative pollutants in steam electric power plant wastewater are present in both soluble [i.e.,
dissolved) and particulate [i.e., suspended) form. For example, the EPA collected sampling data for FGD
wastewater in support of the steam electric effluent limitations guidelines and standards. These data
show that some pollutants, such as arsenic, are present mostly in particulate form while other pollutants,
such as selenium and boron, are present mostly in soluble form (ERG, 2012). Environmental conditions
influence the tendency of a dissolved pollutant to remain in solution or precipitate out of solution, sorb to
either organic or inorganic suspended matter in the water column, or sorb to the mixture of materials
[e.g., clays and humic matter) found in sediments (U.S. EPA, 2007). Pollutants that precipitate out of
solution can become concentrated in the sediments of a waterbody. Organisms will bioaccumulate
pollutants by consuming pollutant-enriched sediments and suspended particles, filtering ambient water
containing dissolved pollutants, or both.

Appendix A of the 2020 EA (U.S. EPA, 2020a) provides examples of potential adverse impacts to humans,
wildlife, and aquatic organisms resulting from exposure to metals and toxic bioaccumulative pollutants in
the evaluated wastestreams and provides the minimal risk level (MRL) for human oral exposure (or similar
benchmark value) for reference. Adverse impacts from steam electric power plant discharges of these
pollutants are discussed further in the 2015 EA (U.S. EPA, 2015a).

2.1.2 Nutrients

Nutrients [e.g., phosphorus and nitrogen) are essential components for plants and animals to grow and
develop; however, increased nutrient concentrations can upset the delicate balance of nutrient supply
and demand required to maintain aquatic life in surface waters. For example, excess nutrients can cause
harmful algal blooms and low oxygen (hypoxia) in surface waters. These are primarily problems for
estuaries, such as the Chesapeake Bay, and coastal waters, such as the Gulf of Mexico. Nutrient loadings
from multiple power plants are especially a concern for waterbodies that are nutrient-impaired or in
watersheds that have nutrient problems downstream. Nutrient concentrations present in steam electric
power plant wastewater are primarily attributed to the fuel composition and air pollution controls in the
combustion process.

Nutrient loadings to surface waters can affect the ecological stability of freshwater and saltwater aquatic
systems. For example, elevated levels of nutrients can stimulate rapid growth of plants, algae, and
cyanobacteria on or near the waterbody surface, which in turn can obstruct sunlight penetration,
increase turbidity, and decrease dissolved oxygen levels (U.S. EPA, 2015b). Adverse impacts from steam
electric power plant discharges of nutrients are discussed further in the 2015 EA (U.S. EPA, 2015a).

2.1.3 TDS and Salinity

TDS represents the concentration of combined dissolved organic and inorganic matter, whereas salinity
represents the total concentration of dissolved inorganic salts. Common inorganic salts found in TDS can
include cations (positively charged ions), such as calcium, magnesium, potassium, and sodium, and anions
(negatively charged ions), such as carbonates, nitrates, bicarbonates, chlorides, and sulfates. TDS
concentrations in steam electric power plants wastestreams include contributions from dissolved metals
and halogens [e.g., chlorides, bromides, and iodides).

Salts can enter water naturally through erosion of soils and geologic formations and introduction of their
dominant ions to local freshwater systems (Hem, 1985; Olson and Hawkins, 2012; Pond, 2004; U.S. EPA,
2011). In addition to steam electric power plants, other sources of TDS are widespread in the
environment, making it more likely that receiving waters for the discharges of the evaluated
wastestreams already carry excessive TDS loadings. These other sources include mining activities, use of
road salt for de-icing, and discharge of sewage and industrial wastewater (Canedo-Arguelles et al., 2013;
Corsi et al., 2010). Once salinity has increased in freshwater systems, the effect can be persistent. In lentic
waters such as lakes and ponds, even small increases in salt levels can result in long-term increases in

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salinity, lasting months or years (Evans and Frick, 2001). Kaushal et al. (2005) reported that, after
application of deicing salts in winter, chloride concentrations in urban streams remain elevated into
spring, summer, and fall and contribute to an accumulation of salts in groundwater and aquifers that may
persist over several decades.

Harb et al. (2021) studied how changes in freshwater salinity can have environmental impacts on (1)
spray aerosol generation from the breaking of waves and (2) diversity of aquatic bacteria. As waves break,
aquatic bacteria can be aerosolized [i.e., transferred from water to air). Changes in the bacteria being
transferred from water to air could affect regional climate by altering aerosolized bacteria that act as
cloud condensation nuclei [i.e., particles in the air onto which water vapor will condense) and ice-
nucleating particles [i.e., particles for formation of cloud ice crystals). In addition, alterations in the
aerosolized bacteria could affect public health by increasing inhalation exposure to airborne pathogens
(Harb et al., 2021). Harb et al. (2021) sought to understand how increased freshwater salinity can impact
the abundance and diversity of aerosolized aquatic bacteria. In freshwater salinity ranges, researchers
found that aerosolization of bacteria increased as salinity increased. The study found that salinity altered
the transfer of some bacterial families to an aerosol, with some families exhibiting enhanced, diminished,
or no change in water to air transfer (Harb et al., 2021).

Exposure to dissolved bioaccumulative pollutants and halogens found in the evaluated wastestreams may
cause human health and ecological effects. Researchers have documented the potential consequences of
elevated salinity on aquatic ecosystems. Increased salinity has been linked to adverse effects including
increases in invasive species, lower rates of organic matter processing, changes in biogeochemical cycles,
decreased riparian vegetation, and altered composition of primary producers [i.e., plants, bacteria, and
algae) (Canedo-Arguelles et al., 2013). Increases in aquatic salinity may cause shifts in biotic communities,
limit biodiversity, exclude less-tolerant species, and result in acute or chronic effects at specific life stages
(Weber-Scannell and Duffy, 2007). Salt additions can lead to loss of exchangeable cations in soil, and the
mobility and toxicity of some pollutants, especially metals, can be enhanced at high salt concentrations
(Stets et al., 2020). Because interactions between ions can affect the bioavailability and toxicity of
individual TDS constituents, the net ecological effect of elevated TDS levels in the aquatic environment
depends on its ionic composition (Moore et al., 2017; Mount et al., 1993 and 1997). The 2020 EA (U.S.
EPA, 2020a) provides further details on adverse impacts from discharges of TDS and increased salinity in
freshwater systems.

2.1.4 Bromine/Bromide

Bromine is naturally present in coal. Some coal-fired steam electric power plants also add bromine, in the
form of bromide compounds, to their combustion processes to enhance mercury emissions control or
burn refined coal amended with bromide compounds (U.S. EPA, 2020b). After combustion, bromine
partitions in part to FGD wastewater and BA transport water in its anion form, known as bromide (EPRI,
2014; Peng et al., 2013). Documented bromide levels in FGD wastewater vary widely and can exceed 175
milligrams per liter (mg/L) (EPRI, 2009; Good, 2018; U.S. EPA, 2015c and 2020b). Average bromide levels
of 5.1 mg/L have been documented in BA transport wastewaters (U.S. EPA, 2020b). These levels are
higher than the average levels of 0.014 mg/L to 0.2 mg/L reported for freshwater surface waters (Flury
and Papritz, 1993; Health Canada, 2015; McGuire et al., 2002). Field-based and modeling studies
document elevated bromide levels in surface waters downstream of steam electric power plants and
identify FGD wastewater discharges as a substantial source of bromide loadings from the plants (Cornwell
et al., 2018; Good and VanBriesen, 2016, 2017, and 2019; Kolb et al., 2020; McTigue et al., 2014; Ruhl et
al., 2012; States et al., 2013; U.S. DOJ, 2015; U.S. EPA, 2015c).

Bromide has a low toxicity in freshwater aquatic environments compared to substances such as copper or
cadmium cations. Flury and Papritz (1993) present the results from two previous studies on the median
lethal toxic concentration (LC5o) of bromide compared to other chemicals.

• For golden orfe [Leuciscus idus melanotus), the LC5o for bromide is greater than 7,765 mg/L,

compared to 0.32 mg/L for copper and 4.5 to 35.4 mg/L for cadmium (Juhnke and Ludemann, 1978).

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• For fathead minnow (Pimephales promelas), the LC5o for bromide is greater than 67 mg/L, compared
to 0.555 to 1.4 mg/L for copper (Ewell et al., 1986).

Reviews of freshwater aquatic organism toxicology studies cite effect concentrations of bromide that
range from 110 to 4,600 mg/L for single-celled organisms, 2.2 to 11,000 mg/L for invertebrates, and 7.8
to 24,000 mg/L for fish (EPRI, 2014; Flury and Papritz, 1993).

The World Health Organization (WHO) estimates that consumption of drinking water supplies with
bromide concentrations below 2.0 mg/L would meet acceptable daily intake levels for both children and
adults (WHO, 2009). Bromide's toxicity associated with its contribution to DBP formation in drinking
water treatment and distribution systems can be of a greater concern (Krasner et al., 2006; Krasner,
2009; Regli et al., 2015; Richardson and Postigo, 2011; U.S. EPA, 2016a; Yang et al., 2014). DBPs are a
broad class of compounds that form as byproducts of drinking water disinfection, and some of them have
toxic properties. Bromide in source water becomes highly reactive in the presence of commonly used
drinking water disinfectants and can form brominated DBPs (Br-DBPs) at low source water concentrations
(Bond et al., 2014; Chang et al., 2001; Heeb et al., 2014; Landis et al., 2016; Parker et al., 2014;

Richardson et al., 2007; U.S. EPA, 2016a; Wang et al., 2017; Westerhoff et al., 2004). Although multiple
factors affect DBP formation, increases and decreases in source water bromide levels are typically
associated with concurrent increases and decreases in both total DBP and bromide speciation levels in
treated water (AWWARF and U.S. EPA, 2007; Bond et al., 2014; Cornwell et al., 2018; Ged and Boyer,
2014; Hua et al., 2006; Huang et al., 2019; Landis et al., 2016; McTigue et al., 2014; Obolensky and Singer,
2008; Pan and Zhang, 2013; Regli et al., 2015; Sawade et al., 2016; States et al., 2013; Yang and Shang,
2004; Zha et al., 2014).

The 2020 EA (U.S. EPA, 2020a) provides further details on bromide in freshwater systems and adverse
impacts in source water for DWTPs.

2.1.5 Iodine/Iodide

Iodine is naturally present in coal.2 Some coal-fired steam electric power plants also add iodine, in the
form of iodide compounds, to their combustion processes to enhance mercury emissions control or burn
refined coal amended with iodide compounds (ADES, 2016; Gadgil, 2016; ICAC, 2019; Sahu, 2017; Senior
et al., 2016; Sjostrom et al., 2016; Sjostrom and Senior, 2019; Tinuum, 2020).3 Iodine volatilizes during
combustion and partitions to FGD wastewaters and, to a lesser extent, to BA transport waters (ADES,
2016; ICAC, 2019; Meij, 1994; Peng et al., 2013; Sjostrom et al., 2016). In FGD wastewaters, iodine occurs
as iodide/triiodide anions and elemental iodine (Sjostrom et al., 2016). Data on typical iodine
concentrations in FGD wastewater and BA transport waters are limited. One study (Sjostrom et al., 2016)
indicated that iodine concentrations in FGD wastewater should be below about 100 mg/L to ensure
normal FGD system operation and to recover iodine for reuse.

Typical iodine levels in freshwater surface waters are less than 0.020 mg/L, though levels ranging from
0.00001 to 0.212 mg/L have been reported.4 In freshwater, elemental iodine dissociates to its anionic
form and/or reacts with organic material to form iodinated organic compounds. Iodide is highly soluble
and exhibits conservative fate and transport in freshwater (Fuge and Johnson, 1986; Moran et al., 2002).

According to available data, iodide has lower ecotoxicity in freshwater aquatic environments than other
substances such as copper or cadmium cations. For golden orfe (Leuciscus idus melanotus), the LC5o for

2	Native iodine levels in coal range from 0.14 to 12.9 parts per million (ppm) (Bettinelli et al., 2002; Gluskoter et al.,
1977; Good, 2018). One source states that many coals used by utility plants have iodine levels greater than 3 ppm
(Sjostrom et al., 2016).

3	Addition rates are reported to range from 1 to 30 ppm and are typically less than 10 ppm (Gadgil, 2016; ICAC,
2019; Sahu, 2017; Sjostrom et al., 2016).

4The highest measured levels reflect influence of irrigation water return flows in arid areas.

8

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iodide is greater than 4,525 mg/L compared to 0.32 mg/L for copper and 4.5 to 35.4 mg/L for cadmium
(Juhnke and Ludemann, 1978). Estimates of LC5o for iodide range from 860 to 8,230 mg/L for freshwater
fish and from 0.17 to 0.83 mg/L for Daphnia magna, an aquatic invertebrate (Flury and Papritz, 1993;
Laverock et al., 1995). Toxicity to single-celled organisms is reported to be similar to that of bromide
(Bringmann and Kuhn, 1980; Flury and Papritz, 1993). In comparison, elemental iodine toxicity is higher
for freshwater fish, with LC5o concentrations from 0.53 mg/L to greater than 10 mg/L, and is similar to
iodide toxicity for D. magna, with LC5o concentrations from 0.16 to 1.75 mg/L (Laverock et al., 1995;
LeValley, 1982).

For humans, iodine is an essential element for thyroid hormone production and metabolic regulation.
Excessive consumption can lead to hypothyroidism (diminished production of thyroid hormones),
hyperthyroidism (excessive production and/or secretion of thyroid hormones), or thyroiditis
(inflammation of the thyroid gland) (ATSDR, 2004). The MRL for acute and chronic oral exposure to iodide
is 0.01 milligrams per kilogram per day based on endocrine effects (ATSDR, 2023).

As with bromide, most toxicity concerns for iodine/iodide are associated with its contribution to DBP
formation in drinking water treatment and distribution systems. Iodine in source water becomes reactive
during chlorine-, chlorine dioxide-, chloramine-, or ultraviolet (UV)-based disinfection, when it can
combine with organic material in source waters to form iodinated DBPs (l-DBPs) (Bichsel and Von Gunten,
2000; Criquet et al., 2012; Dong et al., 2019; Ersan et al., 2019; Hua et al., 2006; Hua and Reckhow, 2007;
Krasner, 2009; Krasner et al., 2006; Postigo and Zonja, 2019; Richardson et al., 2008; Tugulea et al., 2018;
U.S. EPA, 2016a; Weinberg et al., 2002). Both iodide and iodinated organic compounds in source waters
can contribute to l-DBP formation during drinking water disinfection (Ackerson et al., 2018; Dong et al.,
2019; Duirk et al., 2011; MacKeown et al., 2020; Pantelaki and Voutsa, 2018; Tugulea et al., 2018). lodate,
a non-toxic iodine compound that can form in the presence of oxidants (including certain DWTP
disinfectants), can also contribute to l-DBP formation under certain conditions (Dong et al., 2019; Postigo
and Zonja, 2019; Tian et al., 2017; Xia et al., 2017; Yan et al., 2016; Zhang et al., 2016). l-DBP levels are
influenced by multiple factors and have been found to increase with iodide or total iodine levels in source
water (Criquet et al., 2012; Dong et al., 2019; Gruchlik et al., 2015; Postigo and Zonja, 2019; Tugulea et
al., 2018; Ye et al., 2013; Zha et al., 2014).5

The 2020 EA (U.S. EPA, 2020a) provides further details on iodine and adverse impacts in source water for
DWTPs.

2.2 Potential Impacts from the Evaluated Wastestreams

Changes in surface water chemistry due to contamination from steam electric power plant wastewater
can harm all levels of an ecosystem, including organisms at lower trophic levels; this in turn affects the
ecosystem's food web and fish inhabiting the surface water. Pollutants in surface water can
bioaccumulate in aquatic organisms such as fish. When wildlife or humans ingest these aquatic
organisms, they can be exposed to a higher dose of contamination than through direct exposure to the
surface water. Surface water impacts associated with discharges of steam electric power plant
wastewater include damage to fish populations [i.e., physiological and morphological abnormalities and
various behavioral, reproductive, and developmental effects), decreased diversity in insect populations,
and decline of aquatic macroinvertebrate population (see Section 2.2.1). Impacts that affect humans
include exceedances of National Recommended Water Quality Criteria, fish consumption advisories,
designation of surface waters as impaired (limiting recreational activities), and contamination of
downstream drinking water sources (see Section 2.2.2 and Section 4).

5 Other factors influencing l-DBP formation include pH, temperature, disinfection process type and dosage level,
bromide levels, ammonium levels, organic material levels and type, and treatment and distribution system
residence time.

9

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This section provides an overview of the environmental impacts caused by exposure to pollutants in
discharges of the evaluated wastestreams. It also summarizes additional studies identified as part of the
literature review conducted to support this EA and the final supplemental rulemaking. Details of previous
literature reviews are included in the 2015 EA (U.S. EPA, 2015a) and the 2020 EA (U.S. EPA, 2020a).

2.2.1 Ecological Impacts

Many of the pollutants in steam electric power plant wastewater [e.g., arsenic, mercury, selenium) readily
accumulate in exposed biota. This bioaccumulation is of particular concern due to their impact on higher
trophic levels, local terrestrial environments, and transient species, in addition to the aquatic organisms
directly exposed to the wastewater. Aquatic systems with long residence times and potential
contamination with bioaccumulative pollutants often experience persistent environmental effects
following exposure to steam electric power plant wastewater.

Population decline attributed to exposure to steam electric power plant wastewater can alter the
structure of aquatic communities and cause cascading effects within the food web that result in long-
term impacts to ecosystem dynamics (Rowe et al., 2002). Reductions in organism survival rates from
abnormalities caused by exposure to power plant wastewater, and alterations in interspecies
relationships, such as declining abundance or quality of prey, can delay ecosystem recovery until key
organisms within the food web return to levels prior to power plant wastewater exposure. In a 1980
study of a creek in Wisconsin, fungal decomposition of detritus was limited due to the effects of power
plant wastewater. Because of this reduction in available resources, the population of benthic
invertebrates (which graze on detrital material) declined, as did benthic fish that prey upon small
invertebrates (Magnuson et al., 1980).

Ecological impacts associated with exposure to steam electric power plant wastewater include lethal
impacts, such as fish kills, and sublethal impacts, such as teratogenic deformities, oxidative stress,
deoxyribonucleic acid (DNA) damage, reduced growth, and genotoxicity (Brandt et al., 2017 and 2019;
Carlson and Adriano, 1993; Javed et al., 2016; Lemly, 2018; Rowe et al., 2002). Much of the scientific
literature focuses on selenium as a key pollutant of environmental concern in steam electric power plant
wastewater. Selenium can bioaccumulate to toxic levels in organisms inhabiting environments with low
selenium concentrations. As studied by Lemly (1985), the extent of selenium bioaccumulation depends
on the trophic level of the fish present in the water. Lemly observed that selenium accumulation
increased as the trophic level increased, which potentially correlates with the observed elimination of
multiple higher-tropic-level fish species. The study also found that selenium discharges also affect species
diversity in receiving waters (Lemly, 1985). Selenium discharges can lead to long-term issues in
ecosystems due to prolonged retention in the environment and cycling and propagation in the food chain
(Brandt et al., 2019).

The sublethal effects of selenium vary widely and can affect growth, reproduction, and survival of
susceptible organisms. Scientists have demonstrated that various fish and amphibian species are sensitive
to elevated selenium concentrations similar to those found in steam electric power plant wastewater. In
addition to lethal effects, these fish and amphibian species have developed sublethal symptoms such as
accumulation of selenium in tissue (histopathological effects) and in the blood (hematological effects),
resulting in decreased growth, changes in weight, abnormal morphology, and reduced hatching success
(Coughlan and Velte, 1989; Lemly, 1993 and 2018; Sager and Colfield, 1984; Sorensen, 1988; Sorensen
and Bauer, 1984; Sorensen et al., 1982, 1983, 1984). In addition, selenium is highly teratogenic [i.e., able
to disturb the growth and development of an embryo or fetus) and readily transferable from mother to
egg (Chapman et al., 2009; Janz et al., 2010; Lemly, 1997a; Maier and Knight, 1994).

Although effects documented in the literature primarily focus on selenium, several studies discussed the
sublethal effects of other pollutants, such as arsenic, cadmium, chromium, copper, and lead (Rowe et al.,
2002), and decreased diversity in receiving water fish species (Javed et al., 2016). Sublethal effects from
exposure to pollutants other than selenium in power plant wastewater can include changes to
morphology [e.g., fin erosion, oral deformities), behavior [e.g., ability to swim, catch prey, and escape

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from predators), and metabolism that can negatively affect long-term survival (Rowe et al., 2002).
Vengosh et al. (2019) found concentrations of coal combustion residuals (CCR) pollutants in Sutton Lake,
North Carolina, indicating the potential for unmonitored spills of coal ash into nearby receiving waters.
From samples taken in 2015 and 2018, researchers found that the lake sediment contained one to two
orders of magnitude higher levels of antimony, arsenic, copper, molybdenum, selenium, and thallium
compared to a reference lake. Vengosh et al. (2019) noted recent hurricanes across the area may have
led to flooding of ash ponds (surface impoundments) and contamination of surface waters. Researchers
noted that concentrations in the sediments exceeded freshwater ecological screening standards
(Vengosh et al., 2019).

In the literature reviews for this supplemental rule, the EPA identified studies that discussed concerns
with bromide and halogenated DBPs' impact on ecological receptors and potential impacts from
pollutants in CRL. As noted in Section 2.1.4, bromide is one of the pollutants discharged by steam electric
power plants, and the discharge of bromide and iodine can lead to increased DBP formation at
downstream DWTPs (see Section 2.1.5).

Since 1994, scientists noted the spread of vacuolar myelinopathy (VM), a neurological disease, in bald
eagles, other birds of prey, and waterfowl. At DeGray Lake in Arkansas, more than 70 eagle mortalities
were found in two years, and investigators began noticing eagles and other waterbirds with neurological
impairments across the southeastern United States (Breinlinger et al., 2021). VM has also been found in
other wildlife including amphibians, reptiles, and fish. Field and laboratory studies have shown that VM
can be transferred up the food chain from fish to wildlife and birds of prey. Documented cases in avian
species have been found near artificial waterbodies with abundant aquatic vegetation located in the
southeastern United States. Breinlinger et al. (2021) conducted field studies in southeastern U.S. waters
and laboratory studies to identify the causative agent of VM. The scientist showed that a neurotoxin,
which they termed aetokthonotoxin (AETX), was the causative agent of VM. AETX is produced by
Aetokthonos hydrillicola (cyanobacterium) growing on aquatic vegetation (Hydrilla verticillata). The
researchers noted that AETX's structure has characteristics not previously observed in nature and
investigated the biosynthesis of the neurotoxin. Breinlinger et al. (2021) determined that the biosynthesis
of AETX depends on the bioavailability of bromide, along with other factors [e.g., temperature).

Cui et al. (2021) investigated the potential toxicity and ecological risk to freshwater organisms from
exposure to halogenated DBPs. Research was prompted by the increased use of chlorine as a disinfecting
agent due to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak and increased
DBP levels in wastewater treatment effluent. The organisms studied covered three trophic levels:
phytoplankton (Scenedesmus sp.), zooplankton {Daphnia magna), and fish (Danio rerio). Cui et al. (2021)
found that Scenedesmus sp. were most sensitive to haloacetic acids (HAAs) and Daphnia magna were
most sensitive to haloacetonitriles (HANs) and trihalomethanes (THMs). Cui et al. (2021) cited other
research on the toxicity of brominated DBPs to aquatic organisms and findings that DBPs can have
reproductive impacts on Daphnia magna and adversely affect embryonic development of zebrafish.
Observed impacts from the DBP exposure (for most of the DBPs tested) included the following:

• Inhibited growth for phytoplankton (Scenedesmus sp.).

• Decreased swimming ability (immobilization) for zooplankton (Daphnia magna).

• Induced mortality and abnormal development for fish (Danio rerio).

Frankel et al, (2022) conducted a study to determine the potential impact on freshwater snails
[Planorbella duryi) exposed to CRL trace elements (i.e, aluminum, arsenic, calcium, cadmium, chromium,
copper, iron, lead, magnesium, manganese, and selenium). The study found that "exposure to
environmentally relevant concentrations" of coal ash leachate caused delays in embryonic development,
reduced shell width growth in juveniles, and decrease in egg deposition. Bioaccumulation of arsenic,
cadmium, chromium, and lead occurred in the snails studied, with arsenic and cadmium concentrations in
the tissue reaching over 85,000 and 170,000 times higher than measured in the leachate solution,
respectively.

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2.2.2 Human Health Effects

Exposure to pollutants can increase risk for noncancer effects in humans, including damage to the
circulatory, respiratory, or digestive systems and neurological and developmental effects. Steam electric
power plant wastewater contains toxic pollutants and known or suspected carcinogens [e.g., arsenic and
cadmium). Documented exceedances of drinking water maximum contaminant levels (MCLs)
downstream of steam electric power plants, and the issuance offish advisories in receiving waters,
indicate an ongoing human health concern caused by power plant wastewater discharges. The primary
exposure route investigated in this EA is through fish consumption (see Sections 3 and 4). As noted in
Section 2.1, pollutants in steam electric power plant discharges can bioaccumulate in fish that are then
consumed by recreational and subsistence fishers. For example, Lemly (2014) studied selenium
contamination in fish found in Lake Sutton—a popular fishing location that is also used as a cooling
reservoir for discharges from the L.V. Sutton Steam Plant settling pond before the water moves
downstream into the Cape Fear River. Based on data collected between 1987 and 2011, the selenium
concentration in bluegill (Lepomis macrochirus) exceeded the toxic thresholds established by researchers,
and physical examination showed elevated deformities in the fish [e.g., skeletal and craniofacial defects)
compared to a reference lake (29 percent in Lake Sutton to 0.5 percent in the reference lake).

Researchers noted similar results in morphological abnormalities at other lakes that receive power plant
discharges [e.g., Belews Lake and Hyco Reservoir).

In addition, groundwater and drinking water supplies can be degraded by pollutants in steam electric
power plant wastewater (Cross, 1981). Power plants may dispose of or store CCR, or coal ash, in landfills
or surface impoundments. Leachate and legacy wastewater (see Section 1), which contain pollutants
from the CCR, can migrate from the power plant landfills and surface impoundments via the groundwater
at concentrations that could contaminate public or private drinking water wells and surface waters, even
years following disposal of combustion residuals (National Research Council of the National Academies,
2006).

As discussed in Sections 2.1.4 and 2.1.5, the discharge of bromide and iodine into drinking water sources
is a concern due to the formation of DBPs in DWTPs and their distribution systems.

• Toxicology and epidemiology studies have documented evidence of genotoxic (including mutagenic),
cytotoxic, and carcinogenic properties of DBPs, including Br-DBPs (National Toxicology Program,
2018; Richardson et al., 2007; U.S. EPA, 2016a). Studies have documented evidence of a link between
DBP exposure and bladder cancer and, to a lesser degree, colon and rectal cancer, other cancers, and
reproductive and developmental effects (Cantor et al., 2010; Chisholm et al., 2008; Regli et al., 2015;
Richardson et al., 2007; U.S. EPA, 2016a; Villanueva et al., 2004, 2007, and 2015). Br-DBPs typically
have higher toxicity than their chlorinated analogues (Cortes and Marcos, 2018; Plewa et al., 2008;
Richardson et al., 2007; Sawade et al., 2016; U.S. EPA, 2016a; Yang et al., 2014). Due to bromide's
reactivity and DBP toxicity, elevated bromide levels in source waters have been associated with
elevated health risks from disinfected water (Hong et al., 2007; Kolb et al., 2017; Regli et al., 2015;
Sawade et al., 2016; Wang et al., 2017; Yang et al., 2014). In a 2022 study, Weisman et al. (2022)
estimated that approximately 9,000 of the 79,000 annual bladder cancer cases could potentially be
attributed to trihalomethanes in the drinking water, with 84 percent of the approximately 9,000 cases
are from drinking water systems with surface water, as opposed to groundwater, as the system's
intake source.

• In vitro toxicology studies with bacteria and mammalian cells have documented evidence of genotoxic
(including mutagenic), cytotoxic, tumorigenic, and developmental toxicity properties of l-DBPs.
Individual l-DBP species have higher toxicity than their chlorinated and brominated analogues and are
among the most cytotoxic DBPs identified to date (Dong et al., 2019; Hanigan et al., 2017; National
Toxicology Program, 2018; Richardson et al., 2007 and 2008; Richardson and Plewa, 2020; U.S. EPA,
2016a; Wagner and Plewa, 2017; Wei et al., 2013; Yang et al., 2014). While studies have documented
evidence linking disinfected drinking water and DBP exposure to adverse human health effects (see
the 2020 EA: U.S. EPA, 2020a), more research is needed to characterize the contribution of l-DBPs to

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these effects (Cortes and Marcos, 2018; Dong et al., 2019; Postigo and Zonja, 2019; U.S. EPA, 2016a).
In a 2021 study, Long et al. (2021) concluded that iodoacetic acid exposure results in reproductive
and developmental toxicity effects. Because conventional drinking water treatment processes do not
effectively remove iodide from source waters and vary in their reduction of organic material levels
(U.S. EPA, 2016a; Watson et al., 2015), they have the potential to generate l-DBPs when their source
waters contain iodine.

2.2.3 Groundwater Impacts

Pollutants in CCR can leach into groundwater from surface impoundments and landfills. Older surface
impoundments and landfills are of particular concern because they were often built without liners and
leachate collection systems. Liners are typically made of synthetic material, asphalt, clay, or a composite
of materials [e.g., synthetic and clay) and are designed to collect leachate and prevent groundwater
contamination. CCR held in unlined surface impoundments can enter the subsurface and contaminate
groundwater. Pollutants in unlined landfills, used for the dry disposal of CCRs, can also leach as
precipitation flows through the residuals pile and dissolves pollutants; the CRL can eventually migrate into
groundwater. The EPA has promulgated a series of rules to mitigate CCR disposal issues [e.g., seeping of
pollutants into groundwater, airborne pollutants as dust, and surface impoundment failures resulting in
larger coal ash spills), starting with the Disposal of Coal Combustion Residuals from Electric Utilities final
rule (80 FR 21301), which established requirements for the safe disposal of CCR nationwide. Even with
additional requirements in place, pollutants can still enter the groundwater when liners fail or when a
disposal site is situated such that natural groundwater fluctuations come into contact with the disposed
waste.

Before the CCR regulations, the EPA identified more than 30 documented cases where groundwater
contamination from surface impoundments extended beyond the plant boundaries, illustrating the threat
to groundwater and drinking water sources (ERG, 2015a). Based on a review of exceedances of state or
federal groundwater quality standards at surface impoundments, exceedances were most often due to
boron, sulfate, or arsenic (Lewis et al., 2017). In a 2016 study, Harkness et al. (2016) evaluated pollutant
migration from coal ash ponds (surface impoundments) to groundwater and surface waters at sites in the
southeastern United States. The evaluation found pollutants above background concentrations at the
tested sites, including levels above drinking water and ecological impact standards for some surface
waters. The researchers note that the closing of the coal ash surface impoundments did not necessarily
stop the migration of pollutants from the surface impoundments (Harkness et. al., 2016).

Landfills pose their own groundwater contamination risks. If the landfills are not properly lined, the
pollutants in CCR can leach into the soil during precipitation. In areas with acid rain, the precipitation's
low pH can accelerate the leaching of contaminants into groundwater. In addition, heavy precipitation
can not only accelerate leaching, but also carry pollutants in stormwater runoff, potentially contaminating
groundwater or surface water resources (Andersen and Madsen, 1983). Based on a review of CCR landfill
damage cases compiled by the EPA, Lewis et al. (2017) noted that all the landfills were constructed before
1990 (before the Resource Conservation and Recovery Act requirements for liners went into effect), and
only four of the 32 cited landfills were fully lined. As with groundwater exceedances from surface
impoundments, the most common pollutants with exceedances included boron and sulfate. Iron and
manganese had exceedances at more than half of the landfills (Lewis et al., 2017).

Frankel et al. (2023) evaluated potential impacts to Quantico Creek, a tributary to the Chesapeake Bay,
from the leakage of a nearby CRL landfill and coal ash surface impoundments Samples taken from the
creek near the CRL landfill and coal ash surface impoundments were compared to upstream and
downstream locations. Researchers found elevated concentrations of the parameters in the sediment but
not the surface water, with the highest concentrations of pollutants including arsenic, boron, cadmium,
chromium, copper, selenium, and zinc in samples adjacent to the coal ash surface impoundments.
Ecological impacts included reduced species diversity and increased concentrations of aluminum,
cadmium, and zinc in the tissues of banded killfish [Fundulus diaphanous) near the coal ash landfill

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compared to upstream and downstream sites. Frankel et al. (2023) did not find arsenic, chromium, or
selenium in the fish tissue samples.

2.2.4 CCR Surface Impoundments as Attractive Nuisances

An "attractive nuisance" is an area or habitat that attracts wildlife and is contaminated with pollutants at
concentrations high enough to potentially harm exposed organisms. Two methods of handling steam
electric power plant wastewater, surface impoundments and constructed wetlands, are classified as
lentic systems supporting aquatic vegetation and organisms. These methods have been known to attract
wildlife from other terrestrial habitats and therefore can be considered attractive nuisances. For example,
a surface impoundment can affect local wildlife as well as transient species that might rely on them
during critical reproduction periods such as seasonal breeding events (Rowe et al., 2002). Exposure to
steam electric power plant wastewater during sensitive life cycle events is a concern, given that it has
been associated with complete reproductive failure in various vertebrate species (Cumbie and Van Horn,
1978; Gillespie and Baumann, 1986; Lemly, 1997b; Pruitt, 2000).

Several studies have shown that terrestrial fauna nesting near CCR surface impoundments can have
higher levels of arsenic, cadmium, chromium, lead, mercury, selenium, strontium, and vanadium than the
same species at reference sites (Bryan et al., 2003; Burger et al., 2002; Hopkins et al., 1997, 1998, 2000,
2006; Nagle et al., 2001; Rattner et al., 2006). Field studies have also documented adverse effects on
reproduction for turtles and toads living near selenium-laden CCR surface impoundments (Hopkins et al.,
2006; Nagle etal., 2001).

In addition to being attractive nuisances, surface impoundments near surface waters can be a source of
coal ash spills that damage the environment, ecosystems, and downstream waters. Concerns with these
spills include the large economic loss and costs to remediate, along with ecological damage, potential
effects on human health, recreational impacts, and losses of consumptive use and aesthetic value.
Researchers and state agencies have monitored the receiving water ecosystems following coal ash spills,
notably the 2008 coal ash spill that affected the Emory River and Clinch River and the 2014 coal ash spill
to the Dan River.

• Following the 2008 coal ash spill at the Tennessee Valley Authority's Kingston Plant, the Tennessee
Department of Environment and Conservation found exceedances of the more stringent criteria for
chronic exposure offish and aquatic life at least once in January 2009 for several metals [e.g.,
aluminum, cadmium, iron, and lead). Seven months after the spill, all fish collected had
concentrations of selenium above a toxic threshold, and most were still contaminated at that level 14
months after the spill. Twenty-one months after the spill, a high percentage of fish were found with
lesions, deformities, and infections, all symptoms of extreme stress. In addition, studies have shown
elevated levels of arsenic and mercury in sediments near the ash spill, as well as selenium levels
exceeding the MCL in three wells underneath the Kingston Plant's coal ash disposal area, ash
processing area, and gypsum disposal facility (U.S. EPA, 2014). In a study eight years after the coal ash
spill, researchers determined downstream sediment concentrations of arsenic and selenium are likely
from the coal ash; however, other metals in downstream sediment are likely from other
anthropogenic sources (Ramsey et al., 2019).

• In 2011 and 2012, Van Dyke et al. (2017) measured trace contaminant concentrations in freshwater
turtles in the Emory River, Clinch River, and a reference (unaffected) river. Turtles in the Emory River
and Clinch River had higher concentrations of arsenic, copper, iron, mercury, manganese, selenium,
and zinc than turtles in the reference river. However, the concentrations were low relative to values
known to be toxic to other vertebrates. Researchers stated that they found little evidence that the
residual coal ash in the affected rivers had an effect on contaminant bioaccumulation in turtles.

• Ku et al. (2020) evaluated mercury concentration in the Dan River 17 to 29 months following the coal
ash spill, which was much smaller than the spill at the Emory and Clinch rivers. They found that
mercury contamination in the Dan River surface sediments (0-16 centimeters) could be accounted
for by organic matter, rather than the coal ash spill. The study also examined methylmercury

-------
bioaccumulation in invertebrates and fish and did not find evidence of elevated methylmercury
bioaccumulation. The researchers concluded that the mercury contamination from the coal ash spill
was largely absent in the surface sediment and biota three years after the spill. Alternatively, they
suggested that the mercury from the coal ash spill was not typically bioavailable.

• Silva et al. (2023) studied environmental and ecological contamination from ash surface

impoundments at a retired coal-fired power plant and decommissioned nuclear reactor. Researchers
sampled beetles associated with carrion in west central South Carolina and found substantial trace
elements within the beetles' organs and tissues. Compared to the uncontaminated (control) site, the
beetles had higher levels of arsenic, selenium, and thallium. Beetles at the uncontaminated site had
higher levels of chromium, copper, and nickel.

15

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3. Environmental Assessment Methodology

This section presents the EPA's evaluation of environmental concerns and potential exposures to
pollutants commonly found in wastewater discharges from steam electric power plants. It describes the
following:

• Pollutant loadings for the evaluated wastestreams.

• Pollutant exposure pathways.

• Methodologies used to quantify the environmental, ecological, and human health effects of
pollutants discharged to surface waters from the evaluated wastestreams.

• Environmental assessment (EA) scope [i.e., plants and immediate receiving waters).

3.1 Pollutant Loadings for the Evaluated Wastestreams

As discussed in Section 2, the pollutants commonly found in steam electric power plant wastewater—
such as metals, total dissolved solids (TDS), and halogens—can result in impacts to water quality, aquatic
life, wildlife, and human health. The EPA analyzed three regulatory options for the final supplemental
rule, as shown in Table VI1-1 of the rule's preamble. The EPA estimated pollutant loadings for the
evaluated wastestreams considered as part of the supplemental rule as described in Section 6 of the
technical development document (TDD) (U.S. EPA, 2024a). The EPA calculated plant-specific and
receiving-water specific baseline and regulatory option pollutant loadings (in pounds per year) for flue gas
desulfurization (FGD) wastewater, bottom ash (BA) transport water, combustion residual leachate (CRL),
and legacy wastewater being discharged to surface water or through publicly owned treatment works
(POTWs) to surface water.

Most steam electric power plants (over 95 percent) evaluated for the supplemental rule discharge
directly to surface water. Six plants reported transferring BA transport water, FGD wastewater, or CRL to
a POTW rather than discharging directly to surface water.6 For these POTW transfers, the EPA adjusted
the baseline and regulatory option loadings to account for pollutant removals expected during treatment
at the POTW for each analyte. See Section 6 of the TDD for industry-wide annual baseline pollutant
loadings for the evaluated wastestreams, as well as the reductions in pollutant loadings (relative to
baseline) for each of the regulatory options.

The EPA used these pollutant loadings as inputs to support the quantitative evaluation of environmental
impacts via the surface water exposure pathway (see Section 3.2). Table 2 presents baseline pollutant
loadings and the estimated reduction in pollutant loadings under the evaluated regulatory options for
select pollutants. The memorandum Pollutant Loadings Analysis and Supporting Documentation for the
Environmental Assessment of the Final Supplemental Steam Electric Rule (U.S. EPA, 2024h) discusses the
EPA's methodology for estimating pollutant loadings for each immediate receiving water.

6 The EPA excluded CRL discharges at one plant from the EA that indirectly discharges to a POTW that does not
discharge to any receiving waters, and one indirect discharging plant is only included in the proximity analysis (see
U.S. EPA, 2024f).

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Table 2. Estimated Annual Baseline Mass Pollutant Loadings and Estimated Reduction in Loadings
Under Regulatory Options for the Evaluated Wastestreams3

Pollutant

Estimated Baseline
Pollutant Loadings

Estimated Reduction in Pollutant Loadings Relative to
Baseline (lb/year)



(lb/year)

Option A

Option B

Option C

Aluminum

60,400

45,000

58,600

59,300

Arsenic

777

513

700

726

Boron

7,140,000

5,450,000

5,770,000

6,492,000

Bromide (min)b

1,310,000

1,150,000

1,150,000

1,310,000

Bromide (max)b

6,810,000

6,380,000

6,380,000

6,810,000

Cadmium

553

152

512

529

Chlorides

223,000,000

175,000,000

180,000,000

203,000,000

Chromium

21,100

20,800

21,000

21,000

Copper

398

181

348

365

Iodine (min)b

86,100

76,200

76,200

86,100

Iodine (max)b

269,000

250,000

250,000

269,000

Iron

300,000

287,000

299,000

299,000

Lead

230

138

187

200

Magnesium

103,000,000

81,700,000

82,900,000

93,500,000

Manganese

648,000

301,000

565,000

606,000

Mercury

40.0

11.5

38.5

38.8

Molybdenum

22,500

19,700

21,300

31,800

Nickel

3,430

693

3,320

3,350

Nitrogen, totalc

522,000

194,000

194,000

218,000

Phosphorus, total

12,100

8,930

8,930

9,980

Selenium

4,810

205

1,970

2,080

Thallium

781

245

664

695

Total dissolved solids

806,000,000

588,000,000

656,000,000

734,000,000

Vanadium

19,600

19,400

19,500

19,600

Zinc

6,570

2,040

6,310

6,400

Sources: U.S. EPA, 2024a, 2024g, and 2024h.

Abbreviations: lb/year (pounds per year).

Note: Pollutant loadings and removals are rounded to three significant figures.

a—Includes a subset of all steam electric power-generating pollutants of concern. The EPA selected the pollutants listed in this
table based on the following factors: presence of the pollutant in the evaluated wastestreams; documented elevated levels of
the pollutant in surface waters or wildlife from exposure to steam electric power plant wastewater; and magnitude of the
pollutant loadings to receiving waters.

b—The EPA did not identify data indicating the specific halogen additive (i.e., bromine or iodine) used at each plant to reduce
mercury emissions. Therefore, the EPA estimated potential ranges of bromide and iodine loadings.

c—Total nitrogen loadings are the sum of ammonia and nitrate-nitrite (as N) loadings from FGD wastewater, nitrate-nitrite (as
N) and total Kjeldahl nitrogen (TKN) loadings from BA transport water, and nitrate-nitrite (as N) loadings from legacy
wastewater.

17

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The pollutants with the greatest estimated reductions in annual mass loadings under the final rule
(Option B) are TDS (656 million pounds per year, or lb/year, decrease relative to baseline), chlorides
(180 million lb/year decrease), magnesium (83 million lb/year decrease), bromide (between 1.15 and
6.38 million lb/year decrease),7 and boron (5.77 million lb/year decrease).

Implementation timing under the final rule for each plant varies by wastestream, subcategorization, and
the plant's permit renewal schedule. See the preamble for further discussion of the regulatory options
and associated deadlines. Due to the differing timelines for individual wastestreams and plants, the net
reduction in pollutant loadings and corresponding environmental changes will be staggered over time as
the plants implement control technologies. The EA presents the EPA's estimates of environmental
improvements associated with each regulatory option using steady-state annual average pollutant
loadings reflecting full implementation of the effluent limitations guidelines and standards. Therefore, the
results presented in the EA may underestimate short-term environmental impacts for the period before
full implementation of the final rule during which plants transition from current discharges to discharges
associated with full implementation. In addition, the EA did not evaluate the impacts of any discharges
other than the four evaluated wastestreams; therefore, the pollutant loadings and subsequent
quantitative analyses do not represent a complete assessment of environmental impacts from steam
electric power plants.

3.2 Pollutant Exposure Pathways

An exposure pathway is defined as the route a pollutant takes from its source [e.g., combustion residual
surface impoundments) to its endpoint [e.g., a surface water), and how receptors [e.g., fish, wildlife, or
people) can come into contact with it. Exposure pathways are typically described in terms of five
components:

• Source of contamination [e.g., steam electric power plant wastewater).

• Environmental pathway—the environmental medium or transport mechanism that moves the
pollutant away from the source through the environment [e.g., discharges to surface waters).

• Point of exposure—the place [e.g., private drinking water well) where receptors [e.g., people) come
into contact with a pollutant from the source of contamination.

• Route of exposure—the way [e.g., ingestion, skin contact) receptors come into contact with the
pollutant.

• Receptor population—the aquatic life, wildlife, or people exposed to the pollutant.

7 The EPA did not identify data indicating the specific halogen additive (i.e., bromine or iodine) used at each plant to
reduce mercury emissions. Therefore, the EPA estimated potential ranges of bromide and iodine loadings. The EPA
defined the ranges' lower and upper bounds as follows (U.S. EPA, 2024a and 2024g):

- Bromide (min): Bromide loadings in BA transport water and FGD wastewater from native coal content and the
addition of bromide in the flue gas (i.e., as brominated activated carbon). The EPA analyzed additional CRL data
that included bromide concentrations in CRL at five plants; however, more than half of the samples were
nondetect values. Therefore, the EPA did not estimate bromide loadings in CRL. See the memorandum 2024
Final Rule - Combustion Residual Leachate Analytical Data Evaluation (U.S. EPA, 2024m).

- Bromide (max): Same as "Bromide (min)" plus bromide loadings due to the use of refined coal or halogen
addition at the EGU. Assumes all plants burning refined coal or adding halogens at the EGU use bromine
additives.

- Iodine (min): Iodine loadings in FGD wastewater from native coal content only. The EPA had insufficient data to
estimate iodine loadings in other receiving waters.

- Iodine (max): Same as "Iodine (min)" plus iodine loadings due to the use of refined coal or halogen addition at
the EGU. Assumes all plants burning refined coal or adding halogens at the EGU use iodine additives.

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The exposure pathway plays an important role in determining the potential effects of steam electric
power plant wastewater on the environment. For example, the physical and chemical characteristics of
receiving waters can affect the fate and transport of pollutants from combustion residual surface
impoundments to the environment and ultimately impact how the pollutants interact with the biological
community.

The EPA identified four primary exposure pathways of concern for steam electric power plant wastewater
entering the environment. Table 3 presents the environmental pathways, routes of exposure, and
environmental concerns identified from the literature review and the types of analyses conducted to
determine the impacts under baseline and potential environmental improvements under the regulatory
options. In its analyses to determine environmental impacts and improvements, the EPA evaluated each
environmental concern via a given route of exposure and pathway individually [i.e., the combined impact
of multiple routes of exposure were not jointly evaluated).

Table 3. Steam Electric Power Plant Wastewater Environmental Pathways and Routes of Exposure
Evaluated in the Environmental Assessment for the Final Supplemental Rule

Environmental Pathway

Route of Exposure

Environmental Concern

Analysis to Determine
Environmental Impact

Steam electric power plant
wastewater discharges to
surface waters

Direct contact with
surface water

Toxic effects on aquatic
organisms3

Water quality impacts
analysis (quantitative)—
see Sections 4.1.1 and 4.3

Ingestion of surface
water

Degradation of surface
water quality used as intake
to drinking water plants

Direct contact with
sediment

Toxic effects on benthic
organisms3

Wildlife impacts analysis
(quantitative)—see
Sections 4.1.2 and 4.3

Consumption of
aquatic organisms

Bioaccumulation of
contaminants and resulting
toxic effects on wildlife3

Toxic effects on humans
consuming contaminated
fish3

Human health impacts
analysis (quantitative)—
see Sections 4.1.3 and 4.3

Degradation offish
availability for recreational
and subsistence fishers

Human health impacts
analysis (quantitative)—
see Sections 4.1.3 and 4.2

Uncollected CRL
infiltration to nearby
surface waters from
combustion residual
landfill

Direct contact with
surface water or
sediment

Toxic effects on humans
and aquatic wildlife3

Groundwater quality
impacts (qualitative)—see
Section 2.2.3

Uncollected CRL entering
groundwater from
combustion residual
landfill

Ingestion of
groundwater

Changes in groundwater
quality

Contaminated private
drinking water wells

Combustion residual
surface impoundment

Direct contact with
or ingestion of
surface water

Toxic effects on wildlife3

Bioaccumulation of
contaminants in wildlife

Attractive nuisances
(qualitative)—see Section
2.2.4

a—The term "toxic effects" refers to impacts upon exposure, ingestion, inhalation, or assimilation into any organism, either
directly from the environment or indirectly by ingestion through food chains. These effects can include death, disease,
behavioral abnormalities, cancer, genetic mutations, physiological malfunctions (including malfunctions in reproduction), or
physical deformations, in receptors {e.g., aquatic organisms, wildlife, humans) or their offspring.

19

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3.3 Environmental Impacts Selected for Qualitative and Quantitative
Assessments in the EA

The EPA used both qualitative and quantitative assessments to describe the potential environmental
impacts of the evaluated wastestreams [i.e., FGD wastewater, BA transport water, CRL, and legacy
wastewater) from steam electric power plants:

•	Qualitative analysis focused on the impacts of uncollected CRL on groundwater quality and the
potential for combustion residual surface impoundments to serve as attractive nuisances. Section
2.2.3 describes the EPA's findings on the potential for uncollected CRL to cause changes in
groundwater quality and contaminate drinking water sources. Section 2.2.4 presents the EPA's
findings on the potential toxic effects and bioaccumulation of contaminants in wildlife exposed to
combustion residual surface impoundments.

•	Quantitative analyses focused on the surface water exposure pathway. The EPA conducted a
proximity analysis to determine whether evaluated wastestreams discharge into sensitive
environments. See Section 3.5.

The EPA also evaluated the following wildlife and human health impacts caused by discharges of the
evaluated wastestreams to surface waters under baseline as well as the potential reductions in those
impacts under the regulatory options:

•	Wildlife impacts:

o Potential toxic effects to aquatic life based on changes in surface water quality—specifically,
exceedances of the acute and chronic National Recommended Water Quality Criteria (NRWQC)
for freshwater aquatic life,
o Potential toxic effects on sediment biota based on changes in sediment quality within surface

waters—specifically, exceedances of threshold effect concentrations (TECs) for sediment biota,
o Bioaccumulation of contaminants and potential toxic effects on wildlife from consuming

contaminated aquatic organisms—specifically, exceedances of no effect hazard concentrations
(NEHCs), indicating a potential risk of reduced reproduction rates in piscivorous wildlife.

•	Human health impacts:

o Exceedances of the human health NRWQC based on two standards: (1) the standard for the
consumption of water and organisms and (2) the standard for the consumption of organisms
only.

o Exceedances of drinking water maximum contaminant levels (MCLs). Although MCLs apply to
drinking water produced by public water systems and not surface waters themselves, the EPA
identified the extent to which immediate receiving waters exceeded an MCL as an indication of
the degradation of the overall water quality following exposure to the evaluated wastestreams.
o Elevated cancer risk due to consuming fish caught from contaminated receiving waters—

specifically, instances where the calculated lifetime excess cancer risk due to inorganic arsenic is
greater than one excess cancer case risk per one million lifetimes (also expressed as 106).
o Elevated noncancer health risks [e.g., reproductive or neurological impacts) due to consuming
fish caught from contaminated receiving waters—specifically, instances where the calculated
average daily dose of a pollutant exceeds the oral reference dose (RfD) for that pollutant.

The EPA used its Immediate Receiving Water (IRW) Model to perform the quantitative assessment.
Section 3.4 provides an overview of the modeling. Section 3 and Appendices C, D, and E of the 2020 EA
(U.S. EPA, 2020a) provide more details on the IRW Model.

20

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The EPA also evaluated additional wildlife and human health impacts resulting from changes in surface
water quality, including impacts on threatened and endangered species, changes in ecosystem services,
and neurological effects from exposure to lead and mercury. The methodologies and results of these
analyses are presented in the BCA Report (U.S. EPA, 2024b). All analyses compare reductions under the
regulatory options to baseline.

3.4 Overview of the IRW Model

The Immediate Receiving Water (IRW) Model is an integrated series of modules that utilize existing peer-
reviewed methodologies and datasets to estimate environmental and human health risk resulting from
wastewater releases. The EPA used the IRW Model to conduct the quantitative assessment of potential
wildlife and human health impacts described in Section 3.3. This is the same model—including
parameters and benchmark values—described in the 2020 EA (U.S. EPA, 2020a). It is a steady-state
equilibrium-partitioning model that evaluates impacts within the immediate surface water8 where
discharges occur. An equilibrium-partitioning model assumes that dissolved and sorbed pollutants in a
receiving water will quickly attain equilibrium in the immediate vicinity of the discharge point because
they dissolve or sorb in the surface water faster than they can be transported or dispersed outside that
area. The model also assumes that the equilibrium state for each pollutant can be represented by a
partition coefficient that divides the total mass of a pollutant in the waterbody into four compartments:

• Constituents dissolved in the water column.

• Constituents sorbed onto suspended solids in the water column.

• Constituents sorbed onto sediments at the bottom of the waterbody.

• Constituents dissolved in pore water in the sediments at the bottom of the waterbody.

As described in Section 5 of the 2015 EA (U.S. EPA, 2015a), the EPA developed the IRW Model to quantify
the environmental impacts to surface waters, wildlife, and human health from the wastestreams
evaluated for the regulatory options. In developing the model, the EPA considered the type of receiving
waters commonly affected by steam electric power plants and the pollutants typically found in the
evaluated wastestreams. The IRW Model quantified the environmental risks within rivers/streams and
lakes/ponds/reservoirs and evaluated impacts from nine toxic, bioaccumulative pollutants: arsenic,
cadmium, copper, lead, mercury, nickel, selenium, thallium, and zinc. Section 4.1 presents the results of
the IRW Model analyses based on baseline and regulatory option pollutant loadings for the evaluated
wastestreams, along with the limitations and uncertainties of the IRW Model.

3.4.1 Structure of the IRW Model

The IRW Model has three interrelated modules: the Water Quality Module, the Wildlife Module, and the
Human Health Module, which are described in further detail in this section. Figure 1 provides an overview
of the model's inputs and the connections among the three modules.

• The Water Quality Module uses plant-specific input data (annual average pollutant loadings and
cooling water flow rates) and receiving-water-specific input data [e.g., annual average flow rate, lake
volume) to calculate annual average total and dissolved pollutant concentrations in the water column

8 The lengths of the immediate receiving waters for the EA, as defined in the National Hydrography Dataset Plus
(NHDPIus) Version 2, range from about 0.20 to 18 miles. The upstream and downstream boundaries are defined in
NHDPIus Version 2, and each plant outfall is located somewhere along the associated immediate receiving water
(i.e., the outfalls are not specifically indexed to the upstream end, midpoint, or downstream end). See the
memorandum Receiving Waters Characteristics Analysis and Supporting Documentation for the Environmental
Assessment of the Final Supplemental Steam Electric Rule (U.S. EPA, 2024f) for details on the immediate discharge
zone and length of stream reach represented at each discharge location.

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and sediment. The module compares these concentrations to selected water quality benchmark
values (NRWQC and MCLs) as an indicator of potential impacts on aquatic life and human health.

• The Wildlife Module uses the annual average water column pollutant concentrations from the Water
Quality Module to calculate the bioaccumulation of pollutants in fish tissue, providing results for both
trophic level 3 (T3) and trophic level 4 (T4) fish.9 The module compares these concentrations, and the
sediment concentrations calculated by the Water Quality Module, to benchmark values that
represent potential impacts on exposed sediment biota (TECs)10 and piscivorous wildlife (NEHCs). The
EPA chose minks and eagles as representative piscivorous wildlife that consume T3 and T4 fish,
respectively.

• The Human Health Module uses the fish tissue concentrations from the Wildlife Module to calculate
noncancer and cancer risks to human populations from consuming fish caught from contaminated
receiving waters. The EPA performed this analysis using two sets offish consumption rates:11

o A "standard cohort" data set with consumption rates for recreational fishers and subsistence
fishers (and their families), with separate age categories for adult and child fishers. Subsistence
fishers are people who rely on self-caught fish for a larger share of their food intake than
recreational fishers.

o A data set with consumption rates for recreational and subsistence fishers in different

race/ethnicity categories (non-Hispanic White; non-Hispanic Black; Mexican-American; other
Hispanic; and other, including multiple races). The EPA used this data set to evaluate whether the
human health impacts under baseline or reductions under the regulatory options (relative to
baseline) will disproportionately affect minority groups.12

Appendices C, D, and E to the 2020 EA (U.S. EPA, 2020a) describe the IRW Model equations, input data,
and environmental parameters in detail. The appendices also describe the limitations and assumptions
for each module. Section 5.1 of the 2015 EA (U.S. EPA, 2015a) provides more information on the IRW
Model, including a detailed discussion of the equilibrium-partition modeling methodology used in the
Water Quality Module.

9 T3 fish {e.g., carp, smelt, perch, catfish, sucker, bullhead, sauger) are those that primarily consume invertebrates
and plankton, while T4 fish {e.g., salmon, trout, walleye, bass) are those that primarily consume other fish.

10 In the case of the TEC for selenium, exceedances of the TEC represent potential impacts on higher trophic levels
due to consumption of sediment biota with elevated levels of selenium.

11 See the memorandum Fish Consumption Rates Used in the EA Human Health Module (ERG, 2015b) for details on
the selection of fish consumption rates for these analyses.

12 The EPA also conducted an environmental justice (EJ) analysis using data from the EPA's EJScreen, the EA, and the
benefits analysis. See Environmental Justice Analysis for Final Supplemental Effluent Limitations Guidelines and
Standards for the Steam Electric Power Generating Point Source Category (U.S. EPA, 2024d) for more details.

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Risk to
Sediment
Biota

Risk to
Aquatic
Life and
Human
Health

Figure 1. Overview of the IRW Model
3.4.2 Pollutants Evaluated by the IRW Model

The IRW Model analyzed nine toxic pollutants, all of which can bioaccumulate in fish and impact wildlife
and human receptors via fish consumption. These pollutants were arsenic, cadmium, copper, lead,
mercury, nickel, selenium, thallium, and zinc. The EPA evaluated the same pollutants in the 2020 EA.
Table 4 through Table 6 include the benchmarks used in the IRW Model. The EPA identified two updates
to benchmarks and incorporated these revised values in the IRW Model:

1.	The EPA vacated the cadmium aquatic life criteria (freshwater, chronic) as documented in U.S.
EPA (2016c). For the final rule EA, the EPA revised the benchmark as documented in U.S EPA
(2001), which is also the value used in the 2015 EA.

2.	The Agency for Toxic Substances and Disease Registry Minimal Risk Levels (MRLs) included an
updated oral reference dose for copper. The EPA revised the benchmark to be 0.02 milligrams
per kilogram body weight per day (mg/kg-day) (ATSDR, 2023).

23

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Table 4. Water Quality Benchmarks: NRWQC and MCLs

Pollutant

FW Acute
NRWQCa'b'c (mg/L)

FW Chronic
NRWQCa'b'c
(mg/L)

HH WO
NRWQCa'b
(mg/L)

HH O
NRWQCa'b
(mg/L)

MCLa'd
(mg/L)

Arsenic

0.34

0.15

0.000018®

0.00014®

0.01

Cadmium

0.0018f'e

0.00025fg

—

—

0.005

Copper

0.014'1

0.009'1

1.3

—

1.3 (action level); 1.0'

Lead

0.065f

0.0025f

—

—

0.015 (action level)

Mercury

0.0014

0.00077

—

—

0.002s

Nickel

0.47f

0.052f

0.61

4.6

—

Selenium

Lentic: 0.045'
Lotic: 0.094

Lentic: 0.0015k
Lotic: 0.0031k

0.17

4.2

0.05

Thallium

—

—

0.00024

0.00047

0.002

Zinc

0.12f

0.12f

7.4

26

5'

Sources: U.S. EPA, 2001, 2009a, 2009b, 2016b, 2016c, and 2020c.

Abbreviations: FW (freshwater); HH 0 (human health organisms only); HH WO (human health water and organisms); MCL
(maximum contaminant level); mg/L (milligrams per liter); NRWQC (National Recommended Water Quality Criteria),
a—"—" designates instances where a benchmark value does not exist for the pollutant.

b—Unless otherwise noted, pollutant concentrations were compared to NRWQC from the EPA's National Recommended Water
Quality Criteria (U.S. EPA, 2009b).

c—Benchmark value is expressed in terms of the dissolved pollutant in the water column. For all pollutants except selenium,
this is calculated using a total-to-dissolved conversion factor (U.S. EPA, 2009b).

d—Unless otherwise noted, pollutant concentrations were compared to the MCL from the EPA's National Primary Drinking

Water Regulations (U.S. EPA, 2009a).

e—Benchmark value is for inorganic form of pollutant.

f—The FW NRWQC for this metal is expressed as a function of hardness (mg/L) in the water column. The values given here
correspond to a hardness of 100 mg/L.

g—The cadmium benchmark values are from the EPA's Aguatic Life Ambient Water Quality Criteria for Cadmium—2016 (U.S.
EPA, 2016c) for FW acute NRWQC and the EPA's Update of Ambient Water Quality Criteria for Cadmium (U.S. EPA, 2001) for
FW chronic NRWQC.

h—For this analysis, the EPA calculated FW NRWQC for copper using the Biotic Ligand Model and input water quality data that
are representative of the ecoregions containing surface waters that receive discharges of the evaluated wastestreams (and
their downstream waters) (U.S. EPA, 2020c).

i—The EPA evaluated both the action level of 1.3 mg/L and the secondary (nonenforceable) drinking water standard of 1.0
mg/L for copper (U.S. EPA, 2020d). The results presented in Section 4 and Attachment A are based on the number of
immediate receiving waters with exceedances of the lower secondary drinking water standard (1.0 mg/L).
j—The selenium benchmark values are based on the NRWQC from the EPA's Aguatic Life Ambient Water Quality Criteria for
Selenium—Freshwater 2016 (U.S. EPA, 2016b). The selenium acute NRWQC, as calculated here, assumes a background
selenium concentration of zero and an intermittent exposure duration of one day, which is the shortest exposure period to be
used when applying the criterion. This serves as an intermittent exposure element of the chronic water quality criterion,
intended to address short-term exposures that contribute to chronic effects through selenium bioaccumulation. "Lentic"
pertains to still or slow-moving water, such as lakes or ponds. "Lotic" pertains to flowing water, such as streams and rivers,
k—The selenium benchmark values are based on the NRWQC from the EPA's Aguatic Life Ambient Water Quality Criteria for
Selenium—Freshwater 2016 (U.S. EPA, 2016b). The selenium chronic water column NRWQC applies only in the absence offish
tissue measurements. Use of this water column benchmark value may therefore over- or underestimate the number of
exceedances.

I—The EPA has not defined an MCL or action level for zinc. This benchmark value represents the secondary (nonenforceable)
drinking water standard for zinc (U.S. EPA, 2020d).

24

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Table 5. Sediment Biota and Wildlife Benchmarks: TECs and NEHCs

Pollutant

TEC (mg/kg)a

NEHC for Minks
(T3 Fish) (ng/g)b

NEHC for Eagle
(T4 Fish) (ng/g)b

Arsenic

9.79

7.65

22.4

Cadmium

0.99

5.66

14.7

Copper

31.6

41.2

40.5

Lead

35.8

34.6

16.3

M e rc u ry/met hy 1 me rc u ry

0.18

0.37c

0.5C

Nickel

22.7

12.5

67.1

Selenium

2

1.13

4

Thallium

	d

	d

	d

Zinc

121

904

145

Abbreviations: mg/kg (milligrams per kilogram); NEHC (no effect hazard concentration); T3 (trophic level 3); T4 (trophic level 4);
TEC (threshold effect concentration); |ig/g (micrograms per gram),
a—Sources: Lemly (2018) for selenium; MacDonald et al. (2000) for all other pollutants,
b—Source: USGS, 2008.

c—No NEHC benchmark for methylmercury. The EPA compared the modeled methylmercury concentrations to the total
mercury NEHC, which may underestimate the impact to wildlife,
d—No benchmark value identified; pollutant excluded from evaluation.

Table 6. Human Health Benchmarks: Oral RfDs and CSFs

Pollutant

Oral RfD
(mg/kg-day)

CSF
(mg/kg-day) 1

Notes

Arsenic, inorganic

3.00 xlO 4

1.50

Oral RfD and CSF for drinking water
ingestion

Cadmium

1.00 x lO 3

	a

Oral RfD for food consumption

Copper

2.00 x lO 2

	a

Used the intermediate oral MRL as the
oral RfD (ATSDR, 2023)

Lead, total

	b

	a



Methylmercury

1.00 X 10-4

	a

Oral RfD for fish consumption only

Nickel

2.00 x lO 2

	a

Oral RfD for soluble salts; used for
food consumption

Selenium

5.00 x lO 3

	a

Oral RfD for food consumption

Thallium

1.00 x 10"5

	a

Used value cited in U.S. EPA (2012),
for soluble thallium as the oral RfD;
used for chronic oral exposure

Zinc

3.00 x 10 1

	a

Oral RfD for food consumption

Sources: ATSDR (2023) for copper, U.S. EPA (2012) for thallium, and U.S. EPA (2019) for all other pollutants.

Abbreviations: CSF (cancer slope factor); mg/kg-day (milligrams per kilogram body weight per day); MRL (minimal risk level);
RfD (reference dose).

a—No benchmark value identified; pollutant excluded from evaluation.

b—As documented in IRIS (https://www.epa.gov/iris), the EPA concluded that it was inappropriate to develop an RfD as some
of the effects from lead exposure, "particularly changes in the levels of certain blood enzymes and in aspects of children's
neurobehavioral development, may occur at blood lead levels so low as to be essentially without a threshold." The CDC
identified 10 micrograms per deciliter (|ig/dl_) as the blood lead level of concern in children; see the BCA Report (U.S. EPA,
2024b) for the EPA's analysis of lead impacts.

25

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Like the 2020 EA, this EA did not use water quality modeling to assess the impacts associated with
discharges of TDS, bromides, chlorides, or nutrients (total nitrogen and total phosphorus). The EPA did
not have partition coefficients needed to model the pollutants in receiving water using the equilibrium-
partition equations presented in Appendix C of the 2020 EA (U.S. EPA, 2020a). The EPA did include some
of these pollutants in the surface water quality modeling of immediate and downstream waters, which
was performed for the economic benefits analysis (see the BCA Report, U.S. EPA, 2024b).

3.5 Proximity Analysis

The pollutant loadings, ecological impacts, and human health concerns discussed in Section 2 and
Section 3.2 are also of concern due to the proximity of many steam electric power plants to sensitive
environments where the characteristics of plant wastewater may contribute to the impairment of water
quality [e.g., 303(d)-listed waters and waters with fish advisories) or pose a threat to threatened and
endangered species (see the BCA Report, U.S. EPA, 2024b). The EPA identified the number of surface
waters that receive discharges of the evaluated wastestreams and are located near the following sensitive
environments:

• Immediate receiving waters that states, territories, and authorized tribes have identified, pursuant to
section 303(d) of the Clean Water Act (CWA), as impaired waterbodies that can no longer meet their
designated uses [e.g., drinking, recreation, aquatic habitat) due to pollutant concentrations above
water quality standards. These are also known as "CWA section 303(d)—Iisted waterbodies."

• Immediate receiving waters for which states, territories, and authorized tribes have issued fish
consumption advisories, which indicates that pollutant concentrations in the tissues offish inhabiting
those waters are considered unsafe for human consumption at any or some consumption levels.

• Immediate receiving waters within five miles of drinking water resources, including intakes and
reservoirs, public wells, and sole-source aquifers.

The EPA also assessed the potential for discharges of the evaluated wastestreams to cause or contribute
to fish advisories, thereby posing a human health risk. The EPA compared the T4 fish tissue
concentrations from the Wildlife Module to fish consumption advisory screening values. Screening values
are concentrations of target analytes in fish or shellfish tissue that are of potential public health concern;
they are used as threshold values to which levels of contamination in similar tissue collected from the
ambient environment can be compared. Exceedance of screening values indicates that more intensive
site-specific monitoring and/or evaluation of human health risks should be conducted (U.S. EPA, 2000,
Table 5-3).13

The EPA's memorandum Proximity Analyses and Supporting Documentation for the Environmental
Assessment of the Final Supplemental Steam Electric Rule (U.S. EPA, 2024j) describes the methodology
used to evaluate the proximity of steam electric power plant discharges to sensitive environments.

Section 4.2 of this report presents the results of the proximity analysis.

The EPA also performed further spatial analyses to identify public drinking water supply intakes
downstream from discharges of the evaluated wastestreams. See the BCA Report (U.S. EPA, 2024b) for
details on the methodology and results of that analysis.

3.6 Downstream Analysis

As part of the economic benefits analysis, the EPA used a separate pollutant fate and transport model
(Downstream Fate and Transport Equations, or D-FATE) to calculate the concentrations of pollutants in
surface waters downstream from the immediate receiving water for each plant that discharges the

13 See the memorandum IRW Model: Water Quality, Wildlife, and Human Health Analyses and Supporting
Documentation for the Environmental Assessment of the Final Supplemental Steam Electric Rule (U.S. EPA, 2024i) for
documentation of the fish advisory screening level analysis.

-------
evaluated wastestreams. See the BCA Report (U.S. EPA, 2024b) for a detailed discussion of the D-FATE
model and the analysis, which uses annual average pollutant loadings and surface water flow rates.

The EPA used these downstream concentrations from D-FATE as inputs for an analysis that identified
which downstream reaches would have at least one exceedance of a water quality, wildlife, or human
health benchmark value under baseline or regulatory option loadings. The EPA used this approach to
estimate the extent (in river miles) of impacts in downstream surface waters under baseline and the
changes in these impacts under the regulatory options evaluated. Results are presented in Section 4.3 of
this report. See the memorandum Downstream Modeling Analysis and Supporting Documentation for the
Environmental Assessment of the Final Supplemental Steam Electric Rule (U.S. EPA, 20241) for details on
the methodology for this analysis.

3.7 Scope of the Evaluated Plants and Immediate Receiving Waters

The EPA estimates that 277 coal-fired electric generating units (EGUs) operated at 148 plants will be
operating after December 31, 2028. Section 3 of the TDD (U.S. EPA, 2024a) describes how the EPA
updated the industry profile to reflect changes since the 2020 rule. Section 5 and Section 6 of the TDD
describe the population of plants and EGUs that the EPA estimated compliance costs and pollutant
loadings under baseline (for 246 coal-fired EGUs operated at 110 plants)14 and the regulatory options.

The scope of the EA includes the 110 plants and their discharges of one or more of the evaluated
wastestreams (FGD wastewater, BA transport water, CRL, or legacy wastewater) directly or indirectly to
surface waters under baseline and/or one or more regulatory options.15 The EPA performed quantitative
assessments to support the EA using its IRW Model, described in Section 3.4. The IRW Model, which
excludes discharges to the Great Lakes and estuaries, encompasses 100 plants that discharge to 114
immediate receiving waters.16 The IRW Model excludes Great Lake and estuarine immediate receiving
waters because the specific hydrodynamics and scale of the analysis required to appropriately model and
quantify pollutant concentrations in these types of waterbodies are more complex than can be
represented in the IRW Model. The excluded waterbodies include Lake Erie, Lake Michigan (three stream
reaches), Lake Superior, Escambia River, Hillsborough Bay, Big Lake, and Sutherland Reservoir. These nine
immediate receiving waters (stream reaches) receive evaluated wastestream discharges from ten plants;
see Receiving Waters Characteristics Analysis and Supporting Documentation for the Environmental
Assessment of the Final Supplemental Steam Electric Rule (U.S. EPA, 2024f) for further details.

Table 7 presents the number of plants, generating units, and immediate receiving waters evaluated in the
EA. Figure 2 shows the locations of the immediate receiving waters evaluated in the EA proximity analysis
and indicates those that are included in the IRW Model. See the memorandum Receiving Waters
Characteristics Analysis and Supporting Documentation for the Environmental Assessment of the Final

14 The EPA made plant adjustments after running the final rule analyses, and two plants (and their respective
receiving waters) were not included in the pollutant loadings presented in this report or in the IRW Model. The EPA
did include the receiving waters in the proximity analysis. Both plants are expected to retire or undergo fuel
conversion by 2034. See Updates to Estimated Compliance Costs and Pollutant Loadings (U.S. EPA, 2024n) and
Pollutant Loadings Analysis and Supporting Documentation for the Environmental Assessment of the Final
Supplemental Steam Electric Rule (U.S. EPA, 2024h).

15 Of the 110 plants in the EA, 106 discharge directly to surface water, three discharge indirectly to POTWs, and one
discharges wastestreams both directly and indirectly. The EPA excluded CRL discharges at one plant from the EA
that indirectly discharges to a POTW that does not discharge to any receiving waters (U.S. EPA, 2024f). Discharges
from two additional plants, not included in the count of 110 plants, were not included in the pollutant loadings
analysis or IRW Model (only the proximity analysis); see U.S. EPA (2024h and 2024n). One plant is a direct
discharging plant and the other is an indirect discharging plant.

16 Ten of the 110 plants included in the EA discharge to more than one immediate receiving water.

-------
Supplemental Steam Electric Rule (U.S. EPA, 2024f) for the list of immediate receiving waters and details
on the EPA's methodology for identifying them.

The number of evaluated plants and generating units, and the number of the associated immediate
receiving waters, vary across baseline and the regulatory options evaluated for the final rule. This is due
to differences in the stringency of controls, applicability of these controls based on subcategorization, and
estimates of the control technologies that plants would implement to meet requirements (see the
preamble for details). Table 8 presents the number of plants, generating units, and immediate receiving
waters with nonzero pollutant loadings for baseline and each regulatory option evaluated.

Table 7. Plants, Generating Units, and Immediate Receiving Waters Evaluated in the Environmental

Assessment for the Final Supplemental Rule

Category

Baseline

Option A

Option B

Option C

Downstream and Proximity Analyses3

Plants

112

Electric generating units'3

249

219

123

Immediate receiving waters

125

105

Subset Also Evaluated in Pollutant Loadings?

Plants

110

Electric generating units'3

246

219

123

Immediate receiving waters

123

105

Subset Also Evaluated in IRW Mode

ja,c

Plants

100

Electric generating units'3

222

198

103

Immediate receiving waters

114

Sources: U.S. EPA, 2024f and 2024h.

Abbreviations: IRW (immediate receiving water).

a—The EPA made plant adjustments after running the final rule analyses, and two plants (and their respective receiving waters)
are not included in the pollutant loadings presented in the report or in the IRW Model. The EPA did include the receiving
waters in the proximity analysis. Both plants are expected to retire or undergo fuel conversion by 2034. See U.S. EPA (2024h
and 2024n).

b—Legacy wastewater discharges at two plants are not associated with an active coal-fired generating unit,
c—The IRW Model excludes discharges to nine immediate receiving waters that are one of the Great Lakes and or an estuary
because the specific hydrodynamics and scale of the analysis required to appropriately model and quantify pollutant
concentrations in these types of waterbodies are more complex than can be represented in the IRW Model.

-------
125 Immediate Receiving Waters in
Pros imity Analyse s

114 Rivers and Lakes Also
Evaluated with the IRW Model

Figure 2. Locations of immediate Receiving Waters Evaluated in the Environmental Assessment for the Final Supplemental Rule

30

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4. Results of the Quantitative Environmental Assessment for
the Final Supplemental Rule

The EPA used the plant-specific and receiving-water-specific pollutant loadings, described in Section 3.1,
to determine the environmental impacts of the evaluated wastestreams—i.e., flue gas desulfurization
(FGD) wastewater, bottom ash (BA) transport water, combustion residual leachate (CRL), and legacy
wastewater—from steam electric power plants. This section presents the results of the quantitative
analyses described in Sections 3.3 through 3.6, which include the following:

• Use of the EPA's Immediate Receiving Water (IRW) Model to:

o Estimate the annual average pollutant concentrations in immediate receiving waters due to
discharges of the evaluated wastestreams under baseline and the regulatory options, estimate
the bioaccumulation of pollutants in fish tissue within those waters, and estimate the daily and
lifetime pollutant exposure doses among humans who consume those fish,
o Compare the estimated concentrations and estimated exposure doses to various benchmark

values as indicators of potential water quality, wildlife, and human health impacts,
o Evaluate the estimated changes in those impacts under the regulatory options, as compared to
baseline.

• A proximity analysis to identify immediate receiving waters that are designated as Clean Water Act
(CWA) section 303(d)—Iisted impaired waterbodies; have been issued fish consumption advisories; or
are within five miles of drinking water resources, including intakes and reservoirs, public wells, and
sole-source aquifers.

• Use of pollutant fate and transport model (D-FATE) outputs to estimate potential water quality,
wildlife, and human health impacts in downstream surface waters under baseline and evaluate the
estimated changes in those impacts under the regulatory options.

The BCA Report (U.S. EPA, 2024b) discusses the EPA's evaluation of other impacts that were not
quantified in the environmental assessment.

4.1 Environmental Impacts Identified by the IRW Model

The IRW Model includes modules assessing potential changes in impacts on water quality, wildlife, and
human health in waters receiving discharges of the evaluated wastestreams from steam electric power
plants.17 See Section 3.4 of this document and Appendices C, D, and E of the 2020 environmental
assessment (EA) (U.S. EPA, 2020a) for details on the IRW Model's structure and methodology, including
equations, input data, and environmental parameters.

The following sections present the environmental impact results estimated from each module for the
nine modeled pollutants: arsenic, cadmium, copper, lead, mercury, nickel, selenium, thallium, and zinc.
The results identify modeled exceedances of water quality, wildlife, and human health benchmark values
under baseline and the reduction in those exceedances under each regulatory option. Appendix A
includes additional IRW Model outputs.

17 The EA encompasses a total of 125 immediate receiving waters and 112 plants (some of which discharge to
multiple receiving waters). The EPA made plant adjustments after running final rule analyses, and two plants and
their respective receiving waters were only included in the proximity analysis. Both plants are expected to retire or
undergo fuel conversion by 2034. See U.S. EPA (2024h and 2024n). The IRW Model, which excludes the Great Lakes
and estuaries, analyzes a total of 114 immediate receiving waters and loadings from 100 plants.

-------
4.1.1 Water Quality Impacts

The IRW Water Quality Module assesses the quality of surface waters that receive discharges of the
evaluated wastestreams by comparing estimated pollutant concentrations in the water column to the
National Recommended Water Quality Criteria (NRWQC) and drinking water maximum contaminant
levels (MCLs)18 under baseline and each regulatory option. The Water Quality Module results described in
this section are based on estimated annual average pollutant loadings and flow rates. The module
considers modeled exceedances of the freshwater acute NRWQC, freshwater chronic NRWQC, human
health water and organism (HH WO) NRWQC, human health organism only (HH 0) NRWQC, and drinking
water MCL.

The EPA compared the modeled receiving water concentrations to the water quality benchmarks
presented in Table 4. Table 9 summarizes the number of immediate receiving waters exceeding the water
quality benchmarks. Table 10 presents the number of immediate receiving waters with exceedances of
any NRWQC or MCL by pollutant. The EPA identified water quality benchmark exceedances for all nine
pollutants evaluated for one or more immediate receiving waters. Pollutants with exceedances in
multiple receiving waters included arsenic, cadmium, copper, lead, selenium, and thallium. Under
baseline, the EPA estimated that 38 of the 114 immediate receiving waters (33 percent) exceeded one or
more water quality benchmark. Under the final rule (Option B), the number of immediate receiving
waters exceeding a benchmark will decrease by 24 immediate receiving waters.

Table 9. Modeled IRWs with Exceedances of NRWQC and MCLs
Under Baseline and Regulatory Options

Water Quality
Evaluation Benchmark

Pollutant

Number of Modeled IRWs Exceeding Benchmark Value
(Difference Relative to Baseline)3



Baseline

Option A

Option B

Option C

Freshwater acute
NRWQC

Any pollutant

3

2 (-1)

2 (-1)

2 (-1)

Cadmium

3

2 (-1)

l(-2)

l(-2)

Copper

1

1(0)

o (-1)

o (-1)

Nickel

1

1(0)

o (-1)

o (-1)

Selenium

1

1(0)

1(0)

1(0)

Zinc

1

1(0)

o (-1)

o (-1)

Freshwater chronic
NRWQC

Any pollutant

12

11 (-1)

5 (-7)

5 (-7)

Cadmium

8

5 (-3)

2 (-6)

2 (-6)

Copper

2

2(0)

0 (-2)

0 (-2)

Lead

1

1(0)

0 (-1)

0 (-1)

Mercury

1

1(0)

0 (-1)

0 (-1)

Nickel

1

1(0)

0 (-1)

0 (-1)

Selenium

12

11 (-1)

5 (-7)

5 (-7)

Zinc

1

1(0)

0 (-1)

0 (-1)

HH WO NRWQC

Any pollutant

38

28 (-10)

14 (-24)

7 (-31)

Arsenic

38

28 (-10)

14 (-24)

7 (-31)

Nickel

1

1(0)

0 (-1)

0 (-1)

Selenium

1

1(0)

1(0)

1(0)

Thallium

8

7 (-1)

4 (-4)

3 (-5)

18 Table 4 in Section 3 presents the benchmarks values for the pollutants evaluated.

32

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Table 9. Modeled IRWs with Exceedances of NRWQC and MCLs
Under Baseline and Regulatory Options

Water Quality
Evaluation Benchmark

Pollutant

Number of Modeled IRWs Exceeding Benchmark Value
(Difference Relative to Baseline)3



Baseline

Option A

Option B

Option C



Any pollutant

21

14 (-7)

4 (-17)

3 (-18)

HH 0 NRWQC

Arsenic

21

14 (-7)

4 (-17)

3 (-18)

Selenium

1

1(0)

1(0)

1(0)



Thallium

7

5 (-2)

3 (-4)

3 (-4)



Any pollutant

5

4 (-1)

3 (-2)

3 (-2)



Arsenic

4

2 (-2)

2 (-2)

2 (-2)



Cadmium

3

2 (-1)

l(-2)

l(-2)

Drinking water MCL

Lead

2

2(0)

1 (-1)

1 (-1)

Mercury

1

1(0)

0 (-1)

0 (-1)



Selenium

3

3(0)

2 (-1)

2 (-1)



Thallium

2

2(0)

2(0)

2(0)



Zinc

1

1(0)

0 (-1)

0 (-1)

Total Number of Unique Immediate
Receiving Waters'3

38

28 (-10)

14 (-24)

7 (-31)

Source: U.S. EPA, 2024i.

Abbreviations: HH 0 (human health organism only); HH WO (human health water and organism); IRW (immediate receiving
water); MCL (maximum contaminant level); NRWQC (National Recommended Water Quality Criteria).

a—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114
receive discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do
under Option C.

b—Total may not equal the sum of the individual values because some immediate receiving waters have multiple types of
exceedances.

33

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Table 10. Modeled IRWs with Exceedances of NRWQC and MCLs, by Pollutant,
Under Baseline and Regulatory Options

Pollutant

Number of Modeled IRWs Exceeding Benchmark Value
(Difference Relative to Baseline)3



Baseline

Option A

Option B

Option C

Arsenic

38

28 (-10)

14 (-24)

7 (-31)

Cadmium

8

5 (-3)

2 (-6)

2 (-6)

Copper

2

2(0)

0 (-2)

0 (-2)

Lead

2

2(0)

1 (-1)

1 (-1)

Mercury

1

1(0)

0 (-1)

0 (-1)

Nickel

1

1(0)

o (-1)

0 (-1)

Selenium

12

11 (-1)

5 (-7)

5 (-7)

Thallium

8

7(1)

4 (-4)

3 (-5)

Zinc

1

1(0)

0 (-1)

0 (-1)

Any Pollutantb

38

28 (-10)

14 (-24)

7 (-31)

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); MCL (maximum contaminant level); NRWQC (National Recommended Water
Quality Criteria).

a—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114
receive discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do
under Option C.

b—Total may not equal the sum of the individual values because some immediate receiving waters have multiple types of
exceedances.

In the 2020 EA, the EPA conducted a water quality analysis using estimated monthly pollutant loadings
and flow rates to assess the significance of monthly variability in the modeled water quality impacts. The
results were similar to those using the annual average analysis, and the EPA determined the following key
takeaways:

•	Most worst-case months occur during the summer, whereas most best-case months occur during the
winter and early spring.

•	There is potential for impacts on aquatic life during certain periods characterized by low flows, high
loadings, or a combination of the two.

•	Certain geographic areas could experience adverse seasonal cumulative effects due to concurrent, or
nearly concurrent, discharges of evaluated wastestreams from multiple plants.

These results suggest that seasonal water quality impacts from discharges of the evaluated wastestreams
may be more prevalent than indicated by the annual average analysis. Seasonal cumulative effects in
affected watersheds could be particularly pronounced during summer and early autumn. The EPA expects
that swimming, fishing, and boating in local waterways are more common during these seasons,
potentially increasing opportunities for exposure to degraded water quality conditions in the immediate
receiving waters. In addition, fish species that spawn in the affected waterways during these periods
(including federally threatened or endangered species) could have an increased potential for adverse
impacts from pollutant exposure, since the timing of their sensitive life stages would align with worst-case
water quality conditions. See the 2020 EA (U.S. EPA, 2020a) for more details.

34

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Appendix C of the 2020 EA (U.S. EPA, 2020a) provides details on the following limitations and
uncertainties of the IRW Water Quality Module:

• Estimated pollutant loadings are based on data from a subset of steam electric power plants.

• It uses annual-average pollutant loadings and flow rates.

• It does not consider temporal variability and pollutant speciation.

• It does not account for ambient background pollutant concentrations or contributions from other
point and nonpoint sources.

• It assumes that equilibrium is quickly attained within the waterbody following discharge and is
consistently maintained between the water column and surficial bottom sediments.

• It assumes that pollutants dissolved or sorbed within the water column and bottom sediments can be
described by a partition coefficient and other calculation assumptions.

• It assumes that pollutants sorbed to bottom sediments are considered a net loss from the water
column and assumes a pollutant burial rate of zero within the bottom sediment.

4.1.2 Wildlife Impacts

As described in Section 3.4, the IRW Wildlife Module assesses impacts to sediment biota, minks, and
eagles. This analysis expands on the evaluation of potential wildlife impacts based on the Freshwater
Chronic and Acute NRWQC in the Water Quality Module. Table 11 presents the number of immediate
receiving waters with modeled exceedances of the threshold effect concentrations (TECs) and no effect
hazard concentrations (NEHCs)19 under baseline and reduction in those exceedances under the
regulatory options. Results are presented for all pollutants in aggregate and individually for pollutants
with exceedances. The EPA did not have benchmark data to compare thallium concentrations in the
immediate receiving water; therefore, that pollutant is excluded from the wildlife impacts analysis.

Under baseline, the EPA estimated that all eight evaluated pollutants had one or more immediate
receiving water that exceeded sediment TECs. Pollutants with exceedances in multiple receiving waters
included arsenic, cadmium, copper, mercury, nickel, selenium, and zinc. Lead had an exceedance under
baseline and all the regulatory options for one receiving water. Under the final rule (Option B), the
number of immediate receiving waters with exceedances of TECs decreases by at least 70 percent for five
of the eight pollutants (arsenic, cadmium, mercury, nickel, and zinc). Copper and selenium had smaller
improvements under the final rule, with respective reductions of 50 and 54 percent of immediate
receiving waters exceeding the TEC.

Four pollutants (cadmium, mercury, selenium, and zinc) exceeded the NEHCs for minks and eagles under
baseline and the regulatory options. Under the final rule (Option B), the EPA calculated that the number
of immediate receiving waters exceeding the NEHC for minks decreased by 14 immediate receiving
waters for mercury and nine immediate receiving waters for selenium. The number of immediate
receiving waters exceeding the NEHC for eagle decreased by 19 immediate receiving waters for mercury
and nine immediate receiving waters for selenium under the final rule. Under baseline, cadmium and zinc
exceeded NEHC for minks and eagles at one receiving water; the final rule will eliminate these
exceedances.

19 Table 5 in Section 3 presents the benchmarks values for the pollutants evaluated.

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Table 11. Modeled IRWs with Exceedances of TECs and NEHCs
Under Baseline and Regulatory Options

Wildlife Evaluation
Benchmark

Pollutant3

Number of Modeled IRWs Exceeding Benchmark Value
(Difference Relative to Baseline)b



Baseline

Option A

Option B

Option C



Any pollutant

24

24(0)

11 (-13)

7 (-17)



Arsenic

3

2 (-1)

0 (-3)

0 (-3)



Cadmium

8

5 (-3)

2 (-6)

2 (-6)



Copper

2

2(0)

1 (-1)

1 (-1)

Sediment TEC

Lead

1

1(0)

1(0)

1(0)



Mercury

19

9 (-10)

2 (-17)

2 (-17)



Nickel

14

6 (-8)

2 (-12)

2 (-12)



Selenium

24

24(0)

11 (-13)

7 (-17)



Zinc

7

4 (-3)

2 (-5)

2 (-5)



Any pollutant

16

16(0)

6 (-10)

5 (-11)

Fish ingestion
NEHC for minks

Cadmium

1

1(0)

0 (-1)

0 (-1)

Mercury

16

7 (-9)

2 (-14)

2 (-14)

Selenium

15

15 (0)

6 (-9)

5 (-10)



Zinc

1

1(0)

0 (-1)

0 (-1)



Any pollutant

22

17 (-5)

6 (-16)

5 (-17)

Fish ingestion
NEHC for eagles

Cadmium

1

1(0)

0 (-1)

0 (-1)

Mercury

22

15 (-7)

3 (-19)

2 (-20)

Selenium

15

15 (0)

6 (-9)

5 (-10)



Zinc

1

1(0)

0 (-1)

0 (-1)

Any Wildlife Pollutant Benchmark for
Any Pollutant0

24

24(0)

11 (-13)

7 (-17)

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); TEC (threshold effect concentration); NEHC (no effect hazard concentration),
a—Thallium excluded from the analysis (no benchmarks for comparison). No immediate receiving waters exceeded the TEC for
copper and lead. No immediate receiving waters exceeded NEHC benchmarks for arsenic, cadmium, copper, lead, nickel, or
zinc.

b—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114
receive discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do
under Option C.

c—Total may not equal the sum of the individual values because some immediate receiving waters have multiple types of
exceedances.

Appendix D of the 2020 EA (U.S. EPA, 2020a) provides details on the following limitations and
uncertainties of the IRW Wildlife Module:

•	Impact estimates are based on an individual exposure pathway and individual pollutant exposure
rather than cumulative risks across exposure pathways and the interaction of multiple pollutants.

•	Bioaccumulation factors are not available for all pollutants (use of bioconcentration factors does not
account for the accumulation of pollutants via the food web).

•	It does not consider indirect ecological effects such as depletion of food sources.

36

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• It assumes the selected receptor species and receiving water occur together [i.e., all immediate
receiving waters are habitats for the receptor species).

• It assumes the diet of the receptor species consists offish inhabiting the immediate receiving water.

• It assumes all forms of a pollutant are equally bioavailable to ecological receptors.

• Modeling assumes that the receiving water is fully mixed; however, water in lakes might stratify and
affect chemical speciation by stratum.

4.1.3 Human Health Impacts

The IRW Human Health Module evaluates noncancer and cancer human health impacts among various
human cohorts (recreational and subsistence fishers; children and adults; and different race/ethnicity
categories) from consuming fish caught from immediate receiving waters that are contaminated by
discharges of the evaluated wastestreams. The module uses oral reference doses (RfDs) to evaluate
changes in noncancer health risks and a lifetime excess cancer risk (LECR) benchmark value of one-in-a-
million, or 1CT6, to evaluate changes in cancer risk. This analysis expands on the evaluation of potential
human health impacts based on the NRWQC and MCLs in the Water Quality Module.

Under baseline, the EPA estimated the average daily dose of one or more individual pollutant from fish
consumption among subsistence fishers exceed the oral RfDs (noncancer) in 31 to 39 (27 to 34 percent)
of immediate receiving waters, depending on the age group evaluated. Average daily doses among
recreational fishers exceeded oral RfDs in 26 to 28 (23 to 25 percent) of immediate receiving waters. The
lower prevalence of exceedances among recreational fishers is primarily due to their lower average fish
tissue consumption rates. These results suggest that fish in immediate receiving waters can have health
effects on surrounding fisher populations.

As shown in Table 12, the exceedances are primarily driven by mercury (as methylmercury), selenium,
and thallium. The EPA calculated no exceedances for arsenic (inorganic) or nickel (total) under baseline
and the regulatory options. The EPA estimated that the number of immediate receiving waters
contributing to oral RfD (noncancer) exceedances decreased for all standard cohorts [i.e., cohorts that are
not split into different race/ethnicity categories) under all regulatory options. Under the final rule (Option
B), the EPA estimated the following decreases in number of immediate receiving waters with fish that, if
consumed, would exceed oral RfDs:

• Methylmercury—decrease by at least 20 immediate receiving waters for all standard cohorts.

• Selenium—decrease by at least seven immediate receiving waters for all standard cohorts.

• Thallium—decrease by at least eight immediate receiving waters for all standard cohorts.

Although the EPA did not directly assess the potential health effects posed by lead in this EA, the final rule
decreases the annual loadings of lead to the environment by 187 pounds per year compared to
baseline.20 The monetized human health effects associated with changes in lead discharges are discussed
in the BCA Report (U.S. EPA, 2024b).

As part of this rulemaking, the EPA evaluated the joint toxic action of multiple pollutants discharged into
the evaluated wastestreams from steam electric power plants to determine potential cumulative human
health impacts at the immediate receiving waters. See the memorandum Assessment of Human Health
Impacts from Multiple Pollutants in Steam Electric Power Plant Discharges (U.S. EPA, 2024k) for a
summary of the results.

20 For comparison, the 2015 rule reduced lead discharges by 19,200 pounds per year (U.S. EPA, 2015a).

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Table 12. Modeled IRWs with Exceedances of Oral RfD (Noncancer Human Health Effects) Under

Baseline and Regulatory Options

Age and Fishing
Mode Cohort

Pollutant

Number of Modeled IRWs Exceeding Oral RfD
(Difference Relative to Baseline)3



Baseline

Option A

Option B

Option C

Child-

Any pollutant

28

22 (-6)

9 (-19)

6 (-22)

recreational

Cadmium

3

2 (-1)

l(-2)

l(-2)



Methylmercury

28

22 (-6)

8 (-20)

5 (-23)



Selenium

15

15 (0)

6 (-9)

5 (-10)



Thallium

16

15 (-1)

6 (-10)

5 (-11)



Zinc

1

1(0)

0 (-1)

0 (-1)



Any pollutant

39

28 (-11)

15 (-24)

8 (-31)



Cadmium

4

4(0)

2 (-2)

2 (-2)

Child-

Copper

1

1(0)

0 (-1)

0 (-1)

subsistence

Methylmercury

38

28 (-10)

15 (-23)

8 (-30)



Selenium

22

22 (0)

8 (-14)

5 (-17)



Thallium

24

19 (-5)

10 (-14)

7 (-17)



Zinc

1

1(0)

0 (-1)

0 (-1)



Any pollutant

26

18 (-8)

6 (-20)

5 (-21)

Adult—
recreational

Cadmium

1

1(0)

1(0)

1(0)

Methylmercury

25

17 (-8)

5 (-20)

4 (-21)

Selenium

12

12 (0)

5 (-7)

4 (-8)



Thallium

13

9 (-4)

5 (-8)

4 (-9)



Zinc

1

1(0)

0 (-1)

0 (-1)



Any pollutant

31

23 (-8)

9 (-22)

6 (-25)



Cadmium

4

3 (-1)

2 (-2)

2 (-2)

Adult—

Methylmercury

31

23 (-8)

9 (-22)

6 (-25)

subsistence

Selenium

15

15 (0)

6 (-9)

5 (-10)



Thallium

16

15 (-1)

6 (-10)

5 (-11)



Zinc

1

1(0)

0 (-1)

0 (-1)

Any Pollutant and Age/Fishing Mode
Cohortb

39

28 (-11)

15 (-24)

8 (-31)

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); RfD (reference dose).

a—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114
receive discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do
under Option C.

b—Total may not equal the sum of the individual values because some immediate receiving waters have multiple types of
exceedances.

Under baseline, the EPA estimated that nine immediate receiving waters (eight percent) could contain
fish contaminated with inorganic arsenic that present cancer risks greater than the LECR benchmark value
of one-in-a-million for the most sensitive, standard cohort (adult subsistence fishers). Under the final rule
(Option B), the number of immediate receiving waters whose fish exceed this cancer risk threshold will

38

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decrease by seven (78 percent) for this cohort. Table 13 presents the number of immediate receiving
waters where the LECR for inorganic arsenic exceeds one-in-a-million.

Table 13. Modeled IRWs with LECR Greater Than One-in-a-Million (Cancer Human Health Effects)

Under Baseline and Regulatory Options

Number of Modeled IRWs with LECR Greater than One-in-a-Million

Age and Fishing Mode Cohort

(Difference Relative to Baseline)3

Baseline

Option A

Option B

Option C

Child —recreational

0(0)

Child—subsistence

2 (-1)

l(-2)

Adult—recreational

2 (-2)

Adult—subsistence

3 (-6)

2 (-7)

Total Number of Immediate
Receiving Watersb

3 (-6)

2 (-7)

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); LECR (lifetime excess cancer risk).

a—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114
receive discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do
under Option C.

b—Total may not equal the sum of the individual values because some immediate receiving waters have multiple types of
exceedances.

The EPA also performed an analysis using fish consumption rates for recreational and subsistence fishers
in different race/ethnicity categories to assess whether the steam electric power plant wastewater
discharges disproportionately affect minority groups. Table 14 presents the number of immediate
receiving waters in which the modeled average daily dose of any pollutant exceeds the oral RfD. Table 15
presents the number of immediate receiving waters that could contain fish contaminated with inorganic
arsenic that present cancer risks greater than the LECR benchmark value of one-in-a-million. Results in
the tables are presented by cohort (recreational and subsistence fisher) and race/ethnicity category.

As shown in Table 14, the number of immediate receiving waters where the average daily dose of at least
one individual pollutant from fish consumption exceeds the oral RfDs is highest among subsistence fishers
(child or adults) that fall in the "Other, Including Multiple Races" category. The increased prevalence of
exceedances is primarily due to higher average fish tissue consumption rates for this category and fishing
mode. Under the final rule, the EPA estimated reductions in the number of immediate receiving waters
with exceedances of human health risk under the final rule to be between 19 and 23 immediate receiving
waters, depending on the fisher type and cohort.

Inorganic arsenic concentrations in fish resulted in an estimated cancer risk greater than one-in-a-million
to adult subsistence, minority fishers (i.e., excluding the non-Hispanic white cohort) in nine to 11
immediate receiving waters under baseline. Four immediate receiving waters had inorganic arsenic
concentrations in fish above the LECR threshold of one-in-a-million for adult recreational, minority fishers
under baseline. Cancer risks for the child cohorts are lower. The estimated cancer risk among adult
minority fishers is higher than the risk among adult nonminority fishers. The EPA estimated reductions in
the number of immediate receiving waters with exceedances of cancer risk under the final rule to be up
to eight immediate receiving waters, depending on the fisher type and cohort.

Appendix A presents the IRW Human Health Module results by pollutant for each age group and mode of
fishing for both standard and race/ethnicity cohorts.

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Table 14. Modeled IRWs with Exceedances of Oral RfDs by Race/Ethnicity
Under Baseline and Regulatory Options

Age and
Fishing Mode
Cohort

Race/Ethnicity Category

Number of Modeled IRWs Exceeding Oral RfD (Difference
Relative to Baseline)3

Baseline

Option A

Option B

Option C



Non-Hispanic White

26

18 (-8)

6 (-20)

5 (-21)



Non-Hispanic Black

26

19 (-7)

7 (-19)

5 (-21)

Child-

Mexican-American

28

20 (-8)

8 (-20)

5 (-23)

recreational

Other Hispanic

26

19 (-7)

7 (-19)

5 (-21)



Other, Including multiple

races

28

20 (-8)

8 (-20)

5 (-23)



Non-Hispanic White

29

23 (-6)

9 (-20)

6 (-23)



Non-Hispanic Black

31

23 (-8)

9 (-22)

6 (-25)

Child-

Mexican-American

32

25 (-7)

12 (-20)

7 (-25)

subsistence

Other Hispanic

32

23 (-9)

9 (-23)

6 (-26)



Other, including multiple
races

34

26 (-8)

14 (-20)

8 (-26)



Non-Hispanic White

26

18 (-8)

6 (-20)

5 (-21)



Non-Hispanic Black

26

19 (-7)

7 (-19)

5 (-21)

Adult—

Mexican-American

28

20 (-8)

8 (-20)

5 (-23)

recreational

Other Hispanic

26

19 (-7)

7 (-19)

5 (-21)



Other, including multiple
races

28

20 (-8)

8 (-20)

5 (-23)



Non-Hispanic White

29

23 (-6)

9 (-20)

6 (-23)



Non-Hispanic Black

31

23 (-8)

9 (-22)

6 (-25)

Adult—

Mexican-American

32

25 (-7)

12 (-20)

7 (-25)

subsistence

Other Hispanic

32

23 (-9)

9 (-23)

6 (-26)



Other, including multiple
races

34

26 (-8)

14 (-20)

8 (-26)

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); RfD (reference dose).

a—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114
receive discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do
under Option C.

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Table 15. Modeled IRWs with LECR Greater Than One-in-a-Million (Cancer Human Health Effects)
Race/Ethnicity Under Baseline and Regulatory Options

Age and



Number of Modeled IRWs with LECR Above One-in-a-

Fishing Mode

Race/Ethnicity Category

Million (Difference Relative to Baseline)3

Cohort



Baseline

Option A

Option B

Option C



Non-Hispanic White

0

0(0)

0(0)

0(0)



Non-Hispanic Black

0

0(0)

0(0)

0(0)

Child-

Mexican-American

0

0(0)

0(0)

0(0)

recreational

Other Hispanic

0

0(0)

0(0)

0(0)



Other, including multiple
races

0

0(0)

0(0)

0(0)



Non-Hispanic White

2

2(0)

1 (-1)

o (-2)



Non-Hispanic Black

3

2 (-1)

l(-2)

l(-2)

Child-

Mexican-American

3

2 (-1)

l(-2)

l(-2)

subsistence

Other Hispanic

3

2 (-1)

l(-2)

l(-2)



Other, including multiple
races

3

2 (-1)

l(-2)

l(-2)



Non-Hispanic White

4

2 (-2)

2 (-2)

2 (-2)



Non-Hispanic Black

4

2 (-2)

2 (-2)

2 (-2)

Adult—

Mexican-American

4

2 (-2)

2 (-2)

2 (-2)

recreational

Other Hispanic

4

2 (-2)

2 (-2)

2 (-2)



Other, including multiple
races

4

2 (-2)

2 (-2)

2 (-2)



Non-Hispanic White

9

3 (-6)

2 (-7)

2 (-7)



Non-Hispanic Black

9

3 (-6)

2 (-7)

2 (-7)

Adult—

Mexican-American

10

3 (-7)

2 (-8)

2 (-8)

subsistence

Other Hispanic

10

3 (-7)

2 (-8)

2 (-8)



Other, including multiple
races

11

4 (-7)

3 (-8)

2 (-9)

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); LECR (lifetime excess cancer risk).

a—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114
receive discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do
under Option C.

The EPA also compared trophic level 4 (T4) fish tissue pollutant concentrations to fish consumption
advisory screening values to assess the potential for discharges of the evaluated wastestreams to cause
or contribute to fish advisories and pose a human health risk.21 Based on the modeling results, up to 32
immediate receiving waters (28 percent) may contain fish with contamination levels that could trigger
advisories for recreational and/or subsistence fishers under baseline; this decreases to 10 immediate
receiving waters (9 percent) under the final rule (Option B). Mercury and selenium are the pollutants

21 For this analysis, the EPA used the fish consumption advisory screening values from the EPA's Guidance for
Assessing Chemical Contaminant Data for Uses in Fish Advisories, Volume 1 (U.S. EPA, 2000).

41

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most likely to exceed screening values. Table 16 presents the number of immediate receiving waters
where the modeled T4 fish tissue concentrations exceed screening values used for fish advisories.22

Table 16. Comparison of Modeled T4 Fish Tissue Concentrations to Fish Advisory
Screening Values Under Baseline and Regulatory Options

Number of IRWs with Modeled T4 Fish Tissue

Pollutant

Screening

Concentrations Exceeding Screening Value (Difference

Value (ppm)

Relative to Baseline)3

Baseline

Option A

Option B

Option C

Recreational Fishers

Arsenic (as inorganic arsenic)13

0.026

Cadmium

Mercury (as methylmercury)

0.4

Selenium

Total for Any Pollutant in
Evaluated Wastestreams0

—

Subsistence Fishers

Arsenic (as inorganic arsenic)13

0.00327

Cadmium

0.491

Mercury (as methylmercury)

0.049

Selenium

2.457

Total for Any Pollutant in
Evaluated Wastestreams0

—

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); ppm (parts per million); T4 (trophic level 4).

b—Screening value presented is for carcinogenic effects (lower value than noncarcinogenic effects).

c—Total may not equal the sum of the individual values because some immediate receiving waters are impaired for multiple
pollutants.

Appendix E of the 2020 EA (U.S. EPA, 2020a) details the following limitations and uncertainties of the IRW
Human Health Module:

• Impact estimates are based on individual exposure pathway and individual pollutant exposure rather
than cumulative risks across exposure pathways and the interaction of multiple pollutants.

• Exposure factors will vary by individual physical characteristics.

• The uncertainties associated with human health benchmark values are present, as described in the
EPA's Guidelines for Carcinogen Risk Assessment (U .S. EPA, 2005) and Integrated Risk Information
System (IRIS) (U.S. EPA, 2019).

22 As described in Section 4.2.2, none of the immediate receiving waters are under fish consumption advisories for
cadmium or selenium; each advisory screening value exceedance shown in Table 16 for these pollutants therefore
indicates a "new" receiving water of concern that may warrant additional monitoring and/or evaluation of human
health risk.

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•	The module assumes that the diet of the human health cohorts consists offish inhabiting the
immediate receiving water.

•	It assumes all forms of a pollutant are equally bioavailable to human health cohorts.

4.2 Discharges to Sensitive Environments

As discussed in Section 3.5, the EPA evaluated pollutant discharges to sensitive environments [i.e.,
impaired waters, fish consumption advisory waters, and drinking water resources). Discharges of the
evaluated wastestreams to CWA section 303(d) impaired waters and fish consumption advisory waters23
may contribute to water quality impairments, increased health risk associated with consuming fish, and a
reduction in the extent of viable downstream fisheries. Discharges of pollutants in the evaluated
wastestreams to drinking water resources would likely be reduced to safe levels as part of intake water
treatment; however, these pollutants could affect the effectiveness of the treatment processes, which
could increase public drinking water treatment costs.24 Table 17 summarizes the number of immediate
receiving waters that are classified as either CWA section 303(d) impaired waters, fish consumption
advisory waters, or drinking water resources under baseline and each regulatory option. The EPA
evaluated 125 immediate receiving waters that receive discharges of the evaluated wastestreams, either
directly or indirectly via POTWs. Of these 125 immediate receiving waters, all 125 receive discharges of
the evaluated wastestreams under baseline, 105 do under Option A, 57 do under Option B, and 18 do
under Option C. Sections 4.2.1 through 4.2.3 present the results of the EPA's assessment of immediate
receiving waters that are sensitive environments.25

Table 17. Modeled IRWs Identified as CWA Section 303(d) Impaired Waters, Fish Consumption
Advisory Waters, or Drinking Water Resources Under Baseline and Regulatory Options

Sensitive Environment Category

Number of Modeled IRWs Receiving Discharges of the Evaluated
Wastestreams (Difference Relative to Baseline)3



Baseline

Option A

Option B

Option C

IRWs receiving discharges of the
evaluated wastestreams

125

105

57

18

Impaired water

64

55 (-9)

24 (-40)

8 (-56)

Subset impaired for one or more
pollutants associated with the evaluated
wastestreams13

43

37 (-6)

17 (-26)

6 (-37)

Fish consumption advisory water

72

60 (-12)

33 (-39)

12 (-60)

Subset with a fish consumption advisory
for one or more pollutants associated
with the evaluated wastestreams0

50

42 (-8)

23 (-27)

10 (-40)

23	Fish consumption advisory waters are waterbodies for which states, territories, and authorized tribes have issued
fish consumption advisories, indicating that pollutant concentrations in the tissues of fish inhabiting those waters
are considered unsafe to consume.

24	For more information on drinking water treatment processes used to reduce or eliminate metals commonly
detected in the evaluated wastestreams from steam electric power plants, see the memorandum Drinking Water
Treatment Technologies That Can Reduce Metal and Selenium Concentrations Associated with Discharges from
Steam Electric Power Plants (ERG, 2013).

25	See the memorandum Proximity Analyses and Supporting Documentation for the Environmental Assessment of the
Final Supplemental Steam Electric Rule (U.S. EPA, 2024j) for a description of the methodology used to evaluate the
proximity of plants to CWA section 303(d) impaired waters, fish consumption advisory waters, and drinking water
resources.

43

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Table 17. Modeled IRWs Identified as CWA Section 303(d) Impaired Waters, Fish Consumption
Advisory Waters, or Drinking Water Resources Under Baseline and Regulatory Options

Sensitive Environment Category

Number of Modeled IRWs Receiving Discharges of the Evaluated
Wastestreams (Difference Relative to Baseline)3

Baseline

Option A

Option B

Option C

Drinking water resource within five
milesd

116

97 (-19)

54 (-62)

16 (-100)

Source: U.S. EPA, 2024j.

Abbreviations: IRW (immediate receiving water).

a—For this proximity analysis, the EPA evaluated 125 immediate receiving waters that receive discharges of the evaluated
wastestreams, either directly or indirectly via a publicly owned treatment works. Of these 125 immediate receiving waters, all
125 receive discharges of the evaluated wastestreams under baseline, 105 do under Option A, 57 do under Option B, and 18 do
under Option C.

b—The subset of immediate receiving waters that were impaired due to one or more of the following pollutants: arsenic,
boron, cadmium, chlorides, chromium, copper, lead, manganese, mercury, metals (other than mercury), nitrogen (reported as
ammonia, nitrate, or nitrite), nutrients, phosphorus, selenium, total dissolved solids, and zinc.

c—The subset of immediate receiving waters with a fish consumption advisory for one or more of the following pollutants:
cadmium, lead, mercury, and selenium.

d—Drinking water resources include intakes and reservoirs, public wells, and sole-source aquifers.

4.2.1 Impaired Waters

The EPA estimated that more than half (64 of 125) of the immediate receiving waters analyzed in this EA
are CWA Section 303(d) impaired waters.26 As shown in Table 18, 18 of the immediate receiving waters
under baseline are impaired for mercury, 16 are impaired for metals (other than mercury),27 and eight
are impaired for nutrients. Figure 3 through Figure 5 present the locations of immediate receiving waters
that are classified as impaired by high concentrations of these three impairment categories. A total of 43
immediate receiving waters under baseline (34 percent) are impaired for a pollutant associated with the
evaluated wastestreams.

Under the final rule (Option B), 40 immediate receiving waters listed as impaired (62.5 percent) will no
longer receive discharges of the evaluated wastestreams.

26 See the memorandum Proximity Analyses and Supporting Documentation for the Environmental Assessment of the
Final Supplemental Steam Electric Rule (U.S. EPA, 2024j) for a complete list of the impairment categories identified

in the EPA's CWA section 303(d) waters proximity analysis.

27 The "metals (other than mercury)" impairment category in the EPA's national CWA section 303(d) impaired
waters data set includes impairments caused by metalloids and nonmetals such as arsenic, boron, and selenium.

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Table IS. Modeled IRWs Identified as CWA Section 303(d) Impaired Waters for Pollutants
Present in the Evaluated Wastestreams Under Baseline and Regulatory Options

Pollutant Causing Impairment

Number of Modeled IRWs Receiving Discharges of the Evaluated
Wastestreams (Difference Relative to Baseline}3



Baseline

Option A

Option B

Option C

Mercury

18

18 (0)

11 (-7)

3 (-15)

Metals, other than mercury13

16

12 (-4)

2 (-14)

2 (-14)

Nutrients

8

8(0)

5 (-3)

l(-7)

TDS

1

0( 1)

0 (-1)

0 (-1)

Total for Pollutants Associated with
the Evaluated Wastestreams0

43

37 (-6)

17 (-26)

6 (-37)

Total for Any Impairment Category

64

55 (-9)

24 (-40)

8 (-56)

Source: U.S. EPA, 2024j.

Abbreviations: CWA (Clean Water Act); IRW (immediate receiving water); TDS (total dissolved solids),
a—For this proximity analysis, the EPA evaluated 125 immediate receiving waters that receive discharges of the evaluated
wastestreams, either directly or indirectly via a publicly owned treatment works. Of these 125 immediate receiving waters, all
125 receive discharges of the evaluated wastestreams under baseline, 105 do under Option A, 57 do under Option B, and 18 do
under Option C.

b—Of the 16 immediate receiving waters classified as impaired for "metals, other than mercury" under baseline, five are
specifically listed as impaired for one or more of the following individual pollutants evaluated in this environmental
assessment: cadmium (1), copper (1), lead (2), manganese (2), selenium (1), and zinc (1). One additional immediate receiving
water is impaired for boron (but not included in the "metals, other than mercury" impairment category),
c—Total may not equal the sum of the individual values because some immediate receiving waters are impaired for multiple
pollutants.

Figure 3. Immediate Receiving Waters Impaired by Mercury

45

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1mm ediate Receiving Waters Impaired by
Metals Other Than Mercury

X Baseline Discharges of Evaluated Wastestreams

- Baseline and Final Rule (Option B) Discharges
of Evaluated Wastestreams

Figure 4. Immediate Receiving Waters Impaired by Metals Other Than Mercury

Imm ediate Receiving Waters Impaired by
Nutrients

Baseline Discharges of Evaluated Wastestreams

q Baseline and Final Rule (Option B) Discharges
of Evaluated Wastestreams

Figure 5. Immediate Receiving Waters Impaired by Nutrients

46

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As shown in Table 2 of this report, the final rule (Option B) results in a decrease in pollutant loadings to
the immediate receiving waters, including sensitive environments. The reduction in loadings will help
impaired waters to recover; decrease the bioaccumulation of toxic pollutants in fish, thereby reducing the
number offish advisories; and reduce stress on threatened and endangered species and sensitive
watersheds such as drinking water resources. The final rule has a net decrease on the loadings of
pollutants to waters that are already impaired for those pollutants. The EPA estimated the following net
changes relative to baseline in pollutant loadings to impaired waters once requirements under the final
rule have been met by the steam electric power plants discharging the evaluated wastestreams to the
impaired waterbodies:

•	Decrease in nitrogen and phosphorus loadings of 4,910 pounds per year (lb/year) and 220 lb/year,
respectively, to nutrient-impaired waters.

•	Decrease in phosphorus loadings of 23.0 lb/year to phosphorus-impaired waters.

•	Decrease in mercury loadings of 5.90 lb/year to mercury-impaired waters.

•	Decrease in loadings to receiving waters impaired for a metal (except mercury), including:

o	Aluminum decrease of 7,190 lb/year,

o	Arsenic decrease of 88.3 lb/year,

o	Boron decrease of 892,000 lb/year,

o	Cadmium decrease of 69.9 lb/year,

o	Chromium decrease of 2,660 lb/year,

o	Copper decrease of 42.8 lb/year,

o	Iron decrease of 37,400 lb/year,

o	Lead decrease of 25.6 lb/year,

o	Magnesium decrease of 12,700,000 lb/year,

o	Manganese decrease of 80,700 lb/year,

o	Nickel decrease of 419 lb/year,

o	Selenium decrease of 267 lb/year,

o	Thallium decrease of 43.2 lb/year,

o	Vanadium decrease of 2,490 lb/year,

o	Zinc decrease of 809 lb/year.

•	Decrease in TDS loadings of 135,000 lb/year to one TDS-impaired waterbody.

4.2.2 Fish Consumption Advisories

The EPA estimated that 58 percent (72 of 125) of the immediate receiving waters analyzed in this EA are
under a fish consumption advisory.28 As shown in Table 19, 50 of the immediate receiving waters under
baseline (40 percent) are under an advisory for a pollutant associated with the evaluated wastestreams.
All of these immediate receiving waters are under a fish consumption advisory for mercury, and one is
under a fish advisory for lead. Figure 6 presents the locations of immediate receiving waters with fish
consumption advisories for mercury.

Under the final rule (Option B), 39 immediate receiving waters with a fish consumption advisory (54
percent reduction) will no longer receive discharges of the evaluated wastestreams. Under the final rule,

28 See the memorandum Proximity Analyses and Supporting Documentation for the Environmental Assessment of the
Final Supplemental Steam Electric Rule (U.S. EPA, 2024j) for a complete list of the types of advisories identified in the
EPA's fish consumption advisories proximity analysis, including advisories due to pollutants that are not associated
with the evaluated wastestreams.

47

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the EPA estimated a decrease in the annual mercury loadings of 22.8 lb/year to immediate receiving
waters with a fish consumption advisory for mercury.

Table 19. Modeled IRWs Identified as Fish Consumption Advisory Waters for Pollutants
Present in the Evaluated Wastestreams Under Baseline and Regulatory Options

Pollutant Causing Fish Consumption
Advisory

Number of Modeled IRWs Receiving Discharges of the Evaluated
Wastestreams (Difference Relative to Baseline)3

Baseline

Option A

Option B

Option C

Lead

1

1(0)

1(0)

0 (-1)

Mercury

50

42 (-8)

23 (-27)

10 (-40)

Total for Pollutants Associated with the
Evaluated Wastestreamsb

50

42 (-8)

23 (-27)

10 (-40)

Total for Any Fish Advisory

72

60 (-12)

33 (-39)

12 (-60)

Source: U.S. EPA, 2024j,

Abbreviations: IRW (immediate receiving water).

a—For this proximity analysis, the EPA evaluated 125 immediate receiving waters that receive discharges of the evaluated
wastestreams, either directly or indirectly via a publicly owned treatment works. Of these 125 immediate receiving waters, all
125 receive discharges of the evaluated wastestreams under baseline, 105 do under Option A, 57 do under Option B, and 18 do
under Option C.

b—Total may not equal the sum of the individual values because some immediate receiving waters are under a fish advisory for
multiple pollutants.

Figure 6. Immediate Receiving Waters with Fish Consumption Advisories for Mercury

48

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4.2.3 Drinking Water Resources

The EPA estimated that 93 percent (116 of 125) of the immediate receiving waters analyzed in this EA are
located within 5 miles of a drinking water resource. Under baseline, 103 of the immediate receiving
waters (82 percent) are located near public wells, 38 immediate receiving waters (30 percent) are located
near drinking water intakes/reservoirs, and two immediate receiving waters (less than 2 percent) are
located near sole-source aquifers. Table 20 presents the number of immediate receiving waters evaluated
under baseline and the regulatory options and the number of those immediate receiving waters located
within 5 miles of a drinking water resource.

Under the final rule (Option B), 62 immediate receiving waters located within 5 miles of a drinking water
resource (53 percent reduction) will no longer receive discharges of the evaluated wastestreams.

As discussed in Section 2.2, drinking water supplies can be degraded by pollutants in steam electric power
plant wastewater (Cross, 1981), and bromide and iodine discharges are of particular concern due to the
formation of disinfection byproducts at drinking water treatment plants and their distribution systems.
Under the final rule, the EPA estimated a decrease in bromide loadings of 945,000 to 6.17 million lb/year
and a decrease in iodine loadings of 66,900 to 241,000 lb/year to immediate receiving waters located
within five miles of drinking water resources.

Table 20. Modeled IRWs Identified as Located Within 5 Miles of a Drinking Water
Resource Under Baseline and Regulatory Options

Type of Drinking Water Resource

Number of Modeled IRWs Receiving Discharges of the Evaluated
Wastestreams (Difference Relative to Baseline)3
Baseline Option A Option B Option C

Intakes and reservoirs

33 (-5)

24 (-14)

5 (-33)

Public wells

104

87 (-16)

49 (-54)

15 (-88)

Sole-source aquifers

2(0)

1 (-1)

0 (-2)

Total for Any Immediate Receiving
Waterb

116

97 (-19)

54 (-62)

16 (-100)

Source: U.S. EPA, 2024j.

Abbreviations: IRW (immediate receiving water).

b—Total may not equal the sum of the individual values because some immediate receiving waters are within five miles of
multiple drinking water resource types.

4.3 Impacts in Downstream Surface Waters

The EPA performed an analysis of surface waters downstream from the immediate receiving water for
each plant that discharges the evaluated wastestreams. The downstream analysis uses the outputs from a
separate pollutant fate and transport model (see the BCA Report, U.S. EPA, 2024b, for a description) to
assess potential water quality, wildlife, and human health impacts in approximately 17,000 river miles of
downstream surface waters. The methodology, which uses estimated annual average pollutant loadings
and surface water flow rates, is summarized in Section 3.6 of this report and presented in further detail in
the memorandum Downstream Modeling Analysis and Supporting Documentation for the Environmental
Assessment of the Final Supplemental Steam Electric Rule (U.S. EPA, 20241).

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Table 21 presents the results of this downstream analysis. This table lists each of the water quality,
wildlife, and human health benchmark values used in the IRW Model29 and indicates the total length of
downstream surface waters for which the EPA calculated an exceedance of a benchmark value for at least
one of the modeled pollutants. Based on the results of the downstream modeling, 777 downstream river
miles are affected by steam electric power plant discharges under baseline. Under the final rule (Option
B), pollutant concentrations exceeding water quality, wildlife, and/or human health benchmarks will
decrease to 411 river miles (47 percent reduction).

Table 21. Modeled Downstream River Miles with Exceedances of Any Pollutant
Evaluation Benchmark Value Under Baseline and Regulatory Options

Evaluation Benchmark

Modeled Downstream River Miles Exceeding Benchmark Value
(Difference Relative to Baseline)3



Baseline

Option A

Option B

Option C

Wa ter Quality Results

Freshwater acute NRWQC

0

0(0)

0(0)

0(0)

Freshwater chronic NRWQC

16.7

16.1 (-0.607)

2.51 (-14.2)

0 (-16.7)

Fluman health water and organism
NRWQC

363

213 (-149)

104 (-258)

78.0 (-285)

Fluman health organism only
NRWQC

121

29.5 (-91.7)

6.38 (-115)

0 (-121)

Drinking water MCL

1.23

1.23 (0)

0 (-1.23)

0 (-1.23)

Wildlife Results

Fish ingestion NEFIC for minks

40.4

27.5 (-12.9)

4.37 (-36.0)

0 (-40.4)

Fish ingestion NEFIC for eagles

121

27.5 (-93.7)

4.37 (-117)

0 (-121)

Human Health Results—Noncancer

Oral RfD for child (recreational)

289

186 (-103)

86.0 (-203)

65.1 (-224)

Oral RfD for adult (recreational)

203

94.8 (-108)

54.0 (-149)

41.5 (-162)

Oral RfD for child (subsistence)

688

469 (-219)

333 (-355)

301 (-387)

Oral RfD for adult (subsistence)

420

294 (-126)

193 (-226)

167 (-253)

Human Health Results—Cancer

LECR for child (recreational)

0

0(0)

0(0)

0(0)

LECR for adult (recreational)

1.23

0 (-1.23)

0 (-1.23)

0 (-1.23))

LECR for child (subsistence)

1.23

0 (-1.23)

0 (-1.23)

0 (-1.23)

LECR for adult (subsistence)

13.0

1.23 (-11.8)

0 (-13.0)

0 (-13.0)

Total for Any Benchmarkb

111

547 (-230)

411 (-366)

379 (-398)

Source: U.S. EPA, 20241.

Abbreviations: LECR (lifetime excess cancer risk); MCL (maximum contaminant level); NEHC (no effect hazard concentration);
NRWQC (National Recommended Water Quality Criteria); RfD (reference dose).

a—River miles are rounded to three significant figures. As part of this analysis, the EPA evaluated approximately 17,000 river
miles of surface waters downstream of immediate receiving waters. For this analysis, the EPA estimated pollutant
concentrations in the immediate receiving water and the downstream receiving waters using the D-FATE model,
b—Total may not equal the sum of the individual values because some river miles exceed multiple benchmarks.

29 The water quality outputs used in the downstream analysis were derived from a pollutant fate and transport
model that does not simulate pollutant partitioning to the benthic layer; therefore, this analysis does not include
comparisons to the sediment TEC.

50

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4.4 Summary of Key Environmental and Human Health Improvements

The EPA estimated that the reduced discharges of pollutants to the immediate receiving waters expected
from the final rule will translate into improvements in water quality and reduction in pollutant exposures
for wildlife and human health in the immediate receiving waters and further downstream from steam
electric power plant discharges. The final supplemental rule will result in the following environmental
improvements as estimated by the EA:

• 63 percent reduction in the number of immediate receiving waters exceeding an NRWQC for the
protection of human health.

• Over 85 percent reduction in the number of immediate receiving waters that support fish whose
tissue pollutant concentrations exceed mercury benchmarks for the protection of piscivorous wildlife
(represented by minks and eagles).

• 69 percent reduction in the number of immediate receiving waters that support fish whose tissue
pollutant concentrations exceed fish consumption advisories.

• 62 percent reduction in the number of immediate receiving waters that support fish whose tissue
pollutant concentrations pose a risk of noncancer health effects in exposed populations.

• 78 percent reduction in the number of immediate receiving waters that support fish whose arsenic
tissue concentrations pose a cancer risk to exposed populations.

As shown in the downstream modeling analysis, discharges of the evaluated wastestreams affect surface
waters beyond the immediate receiving waters. Pollutant removals associated with the final rule will
improve environmental and human health for communities beyond the area immediately surrounding
steam electric power plants.

The environmental improvements quantified in the EA do not encompass the full range of improvements
that will result from the final supplemental rule. For example, the following improvements are not
quantified (or have only limited analysis) in this EA:

• Reducing the loadings of bioaccumulative pollutants to the broader ecosystem, resulting in decrease
in long-term exposures and sublethal ecological effects.

• Reducing sublethal chronic effects of toxic pollutants on aquatic life not captured by the NRWQC.

• Mitigating impacts to the population diversity and community structures of aquatic and aquatic-
dependent wildlife.

• Reducing loadings of pollutants for which the EPA did not perform water quality modeling in support
of the EA [e.g., aluminum, boron, iron, manganese, nutrients, TDS, and vanadium).

o Reducing loadings of bromide and iodine to drinking water resources.

The EPA expects secondary improvements, associated directly or indirectly, as a result of the final
supplemental rule. Pollutant removals not only improve water quality in surface waters but also enhance
their aesthetics [e.g., by improving clarity and decreasing odor and discoloration). Improvements in
surface water quality may improve the quality of source water for downstream drinking water treatment
plants and wells that are influenced by surface water. Such improvements may also improve the quality
of water used for irrigation or for industrial uses (lower contaminant levels). Recreational benefits from
water quality improvements include more enjoyment from swimming, fishing, and boating and
potentially increased revenue from more people partaking of recreational activities. The final rule may
also reduce economic impacts such as cleanup and treatment costs for contamination, reduce water
usage, reduce potential for algal blooms, and decrease air emissions. The BCA Report (U.S. EPA, 2024b)
provides further details on these secondary improvements and other benefits.

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Electric Power Generating Point Source Category. EPA-821-R-20-002. (August). EPA-HQ-OW-
2009-0819-9012.

157. U.S. EPA. 2020b. U.S. Environmental Protection Agency. Supplemental Technical Development
Document for Revisions to the Effluent Limitations Guidelines and Standards for the Steam
Electric Power Generating Point Source Category. EPA-821-R-20-001. (August). EPA-HQ-OW-
2009-0819-8935.

158. U.S. EPA. 2020c. U.S. Environmental Protection Agency. Estimation of Acute and Chronic
Aquatic Life Ambient Freshwater Water Quality Criteria for Copper (for Use in Analyses
Supporting the Revised Steam ELG). (August). EPA-HQ-OW-2009-0819-8995.

159. U.S. EPA. 2020d. U.S. Environmental Protection Agency. Secondary drinking water standards:
Guidance for nuisance chemicals (website). EPA-HQ-OW-2009-0819-8755.

160. U.S. EPA. 2024a. U.S. Environmental Protection Agency. Technical Development Document for
the Final Supplemental Effluent Limitations Guidelines and Standards for the Steam Electric
Power Generating Point Source Category. EPA-821-R-24-004.

161. U.S. EPA. 2024b. U.S. Environmental Protection Agency. Benefit and Cost Analysis for the Final
Supplemental Effluent Limitations Guidelines and Standards for the Steam Electric Power
Generating Point Source Category. EPA-821-R-24-006.

162. U.S. EPA. 2024c. U.S. Environmental Protection Agency. Regulatory Impact Analysis for the Final
Supplemental Effluent Limitations Guidelines and Standards for the Steam Electric Power
Generating Point Source Category. EPA-821-R-24-007.

163. U.S. EPA. 2024d. U.S. Environmental Protection Agency. Environmental Justice Analysis for the
Final Supplemental Effluent Limitations Guidelines and Standards for the Steam Electric Power
Generating Point Source Category. EPA-821-R-24-008.

164. U.S. EPA. 2024e. U.S. Environmental Protection Agency. Literature Review for the 2024 Steam
Electric Supplemental Rule Environmental Assessment. (April). DCN SE11698.

165. U.S. EPA. 2024f. U.S. Environmental Protection Agency. Receiving Waters Characteristics
Analysis and Supporting Documentation for the Environmental Assessment of the Final
Supplemental Steam Electric Rule. (April). DCN SE11624.

166. U.S. EPA. 2024g. U.S. Environmental Protection Agency. FGD Halogen Loadings from Steam
Electric Power Plants—2024 Final Rule. (April). DCN SE11703.

167. U.S. EPA. 2024h. U.S. Environmental Protection Agency. Pollutant Loadings Analysis and
Supporting Documentation for the Environmental Assessment of the Final Supplemental Steam
Electric Rule. (April). DCN SE11701.

168. U.S. EPA. 2024i. U.S. Environmental Protection Agency. IRWModel: Water Quality, Wildlife, and
Human Health Analyses and Supporting Documentation for the Environmental Assessment of
the Final Supplemental Steam Electric Rule. (April). DCN SE11700.

-------
169.	U.S. EPA. 2024j. U.S. Environmental Protection Agency. Proximity Analyses and Supporting
Documentation for the Environmental Assessment of the Final Supplemental Steam Electric
Rule. (April). DCN SE11699.

170.	U.S. EPA. 2024k. U.S. Environmental Protection Agency. Assessment of Human Health Impacts
from Multiple Pollutants in Steam Electric Power Plant Discharges. (April). DCN SE11767.

171.	U.S. EPA. 20241. U.S. Environmental Protection Agency. Downstream Modeling Analysis and
Supporting Documentation for the Environmental Assessment of the Final Supplemental Steam
Electric Rule. (April). DCN SE11702.

172.	U.S. EPA. 2024m. U.S. Environmental Protection Agency. 2024 Final Rule - Combustion Residual
Leachate Analytical Data Evaluation. (April). DCN SE11715.

173.	U.S. EPA. 2024n. U.S. Environmental Protection Agency. Updates to Estimated Compliance
Costs and Pollutant Loadings. (April). DCN SE11780.

174.	USGS. 2008. U.S. Geological Survey. Environmental contaminants in freshwater fish and their
risk to piscivorous wildlife based on a national monitoring program. Environmental Monitoring
and Assessment 152:469-494. EPA-HQ-OW-2009-0819-0128.

175.	Van Dyke, J.U., C.M. Bodinof Jachowski, D.A. Steen, B.P. Jackson, and W.A. Hopkins. 2017.
Spatial differences in trace element bioaccumulation in turtles exposed to a partially
remediated coal fly ash spill. Environmental Toxicology and Chemistry 36:201-211. DCN
SE10273.

176.	Vengosh, A., E.A. Cowan, R.M. Coyte, A.J. Kondash, Z. Wang, J.E. Brandt, and G.S. Dwyer. 2019.
Evidence for unmonitored coal ash spills in Sutton Lake, North Carolina: Implications for
contamination of lake ecosystems. Science of the Total Environment 686:1090-1103.
https://doi.Org/10.1016/i.scitotenv.2019.05.188. DCN SE11745.

177.	Villanueva, C.M., K.P. Cantor, S. Cordier, J.J.K. Jaakkola, W.D. King, C.F. Lynch, S. Porru, and M.
Kogevinas. 2004. Disinfection byproducts and bladder cancer: A pooled analysis. Epidemiology
15(3):357-367. EPA-HQ-OW-2009-0819-0933.

178.	Villanueva, C.M., K.P. Cantor, J.O. Grimalt, N. Malats, D. Silverman, A. Tardon, R. Garcia-Closas,
C. Serra, A. Carrato, G. Castano-Vinyals, R. Marcos, N. Rothman, F.X. Real, M. Dosemeci, and M.
Kogevinas. 2007. Bladder cancer and exposure to water disinfection by-products through
ingestion, bathing, showering, and swimming in pools. American Journal of Epidemiology
165(2):148-156. EPA-HQ-OW-2009-0819-7921.

179.	Villanueva, C.M., S. Cordier, L. Font-Ribera, L.A. Salas, and P. Levallois. 2015. Overview of
disinfection by-products and associated health effects. Current Environmental Health Reports
2(1):107-115. EPA-HQ-OW-2009-0819-7852.

180.	Wagner, E.D., and M.J. Plewa. 2017. CHO cell cytotoxicity and genotoxicity analyses of
disinfection by-products: An updated review. Journal of Environmental Sciences 58:64-76. EPA-
HQ-OW-2009-0819-7922.

181.	Wang, Y., M.J. Small, and J.M. VanBriesen. 2017. Assessing the risk associated with increasing
bromide in drinking water sources in the Monongahela River, Pennsylvania. Journal of
Environmental Engineering 143(3):1-10. EPA-HQ-OW-2009-0819-7853.

182.	Watson, K., M.M.J. Farre, and N. Knight. 2015. Enhanced coagulation with powdered activated
carbon or MIEX® secondary treatment: A comparison of disinfection by-product formation and
precursor removal. Water Research 68:454-466. EPA-HQ-OW-2009-0819-7929.

183.	Weber-Scannell, P., and L. Duffy. 2007. Effects of total dissolved solids on aquatic organisms: A
review of literature and recommendations for salmonid species. American Journal of
Environmental Sciences 3:1-6. EPA-HQ-OW-2009-0819-7982.

63

-------
184.	Wei, X., S. Wang, W. Zheng, X. Wang, X. Liu, S. Jiang, J. Pi, Y. Zheng, G. He, and W. Qu. 2013.
Drinking water disinfection byproduct iodoacetic acid induces tumorigenic transformation of
NIH3T3 cells. Environmental Science & Technology 47:5913-5920. EPA-HQ-OW-2009-0819-
7930.

185.	Weinberg, H.S., S.W. Krasner, S.D. Richardson, and A.D. Thruston, Jr. 2002. The Occurrence of
Disinfection By-products (DBPs) of Health Concern in Drinking Water: Results of a Nationwide
DBP Occurrence Study. U.S. Environmental Protection Agency, Office of Research and
Development, National Exposure Research Laboratory. EPA 600-R-02-068. Athens, GA.
(September). EPA-HQ-OW-2009-0819-7855.

186.	Weisman, R., A. Heinrich, F. Letkiewicz, M. Messner, K. Studer, L. Wang, and S. Regli. 2022.
Estimating national exposures and potential bladder cancer cases associated with chlorination
DBPs in U.S. drinking water. Environmental Health Perspectives 130(8). EPA-HQ-OW-2009-
0819-9608.

187.	Westerhoff, P., P. Chao, and H. Mash. 2004. Reactivity of natural organic matter with aqueous
chlorine and bromine. Water Research 38(6): 1502—1513. EPA-HQ-OW-2009-0819-7931.

188.	WHO. 2009. World Health Organization. Bromide in Drinking-Water: Background document for
development of WHO Guidelines for Drinking-Water Quality. WHO/HSE/WSH/09.01/6. Geneva,
Switzerland. EPA-HQ-OW-2009-0819-0155.

189.	Xia, Y., Y.-L. Lin, B. Xu, C.-Y. Hu, Z.-C. Gao, W.-H. Chu, and N.-Y. Gao. 2017. lodinated
trihalomethane formation during chloramination of iodate containing waters in the presence of
zero valent iron. Water Research 124:219-226. EPA-HQ-OW-2009-0819-8075.

190.	Yan, M., M. Li, and X. Han. 2016. Behaviour of l/Br/CI-THMs and their projected toxicities under
simulated cooking conditions: Effects of heating, table salt and residual chlorine. Journal of
Hazardous Materials 314:105-112. EPA-HQ-OW-2009-0819-8076.

191.	Yang, X., and C. Shang. 2004. Chlorination byproduct formation in the presence of humic acid,
model nitrogenous organic compounds, ammonia, and bromide. Environmental Science &
Technology 38(19):4995-5001. EPA-HQ-OW-2009-0819-8077.

192.	Yang, Y., Y. Komaki, S.Y. Kimura, H.-Y. Hu, E.D. Wagner, B.J.B. Marinas, and M.J. Plewa. 2014.
Toxic impact of bromide and iodide on drinking water disinfected with chlorine or chloramines.
Environmental Science & Technology 48:12362-12369. EPA-HQ-OW-2009-0819-7858.

193.	Ye, T., B. Xu, Y.-L. Lin, C.-Y. Hu, L. Lin, T.-Y. Zhang, and N.-Y. Gao. 2013. Formation of iodinated
disinfection by-products during oxidation of iodide-containing waters with chlorine dioxide.
Water Research 47(9):3006-3014. EPA-HQ-OW-2009-0819-8078.

194.	Zha, X.-S., Y. Liu, X. Liu, Q. Zhang, R.-H. Dai, L.-W. Ying, J. Wu, J.-T. Wang, and L. Ma. 2014.

Effects of bromide and iodide ions on the formation of disinfection by-products during
ozonation and subsequent chlorination of water containing biological source matters.
Environmental Science Pollution Research 21(4):2714-2723. EPA-HQ-OW-2009-0819-8079.

195.	Zhang, T.-Y., Y.-L. Lin, A.-Q. Wang, F.-X. Tian, B. Xu, S.-J. Xia, and N.-Y. Gao. 2016. Formation of
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Research 98:199-205. EPA-HQ-OW-2009-0819-8080.

64

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Attachment A. Additional IRW Model Results

This appendix presents pollutant loadings and additional model outputs for all pollutants included in the

Immediate Receiving Water (IRW) Model (arsenic, cadmium, copper, lead, mercury, nickel, selenium,

thallium, and zinc) beyond those discussed in Section 4 of this environmental assessment. It includes the

following tables:

• Table A-l. Modeled IRWs with Exceedances of Benchmark Values for One or More Pollutants Under
Baseline and Regulatory Options

• Table A-2. Modeled IRWs with Exceedances of Arsenic Benchmark Values Under Baseline and
Regulatory Options

• Table A-3. Modeled IRWs with Exceedances of Cadmium Benchmark Values Under Baseline and
Regulatory Options

• Table A-4. Modeled IRWs with Exceedances of Copper Benchmark Values Under Baseline and
Regulatory Options

• Table A-5. Modeled IRWs with Exceedances of Lead Benchmark Values Under Baseline and
Regulatory Options

• Table A-6. Modeled IRWs with Exceedances of Mercury Benchmark Values Under Baseline and
Regulatory Options

• Table A-7. Modeled IRWs with Exceedances of Nickel Benchmark Values Under Baseline and
Regulatory Options

• Table A-8. . Modeled IRWs with Exceedances of Selenium Benchmark Values Under Baseline and
Regulatory Options

• Table A-9. Modeled IRWs with Exceedances of Thallium Benchmark Values Under Baseline and
Regulatory Options

• Table A-10. Modeled IRWs with Exceedances of Zinc Benchmark Values Under Baseline and
Regulatory Options

• Table A-ll. Modeled IRWs with Exceedances of Arsenic Oral Reference Dose Values by Race/Ethnicity
Category Under Baseline and Regulatory Options

• Table A-12. Modeled IRWs with Exceedances of Cadmium Oral Reference Dose Values by
Race/Ethnicity Category Under Baseline and Regulatory Options

• Table A-13. Modeled IRWs with Exceedances of Copper Oral Reference Dose Values by Race/Ethnicity
Category Under Baseline and Regulatory Options

• Table A-14. Modeled IRWs with Exceedances of Mercury (as Methylmercury) Oral Reference Dose
Values by Race/Ethnicity Category Under Baseline and Regulatory Options

• Table A-15. Modeled IRWs with Exceedances of Nickel Oral Reference Dose Values by Race/Ethnicity
Category Under Baseline and Regulatory Options

• Table A-16. Modeled IRWs with Exceedances of Selenium Oral Reference Dose Values by
Race/Ethnicity Category Under Baseline and Regulatory Options

• Table A-17. Modeled IRWs with Exceedances of Thallium Oral Reference Dose Values by
Race/Ethnicity Category Under Baseline and Regulatory Options

• Table A-18. Modeled IRWs with Exceedances of Zinc Oral Reference Dose Values by Race/Ethnicity
Category Under Baseline and Regulatory Options

• Table A-19. Modeled IRWs with Lifetime Excess Cancer Risk for Inorganic Arsenic Exceeding One-in-a-
Million by Race/Ethnicity Category Under Baseline and Regulatory Options

A-l

-------
Table A-l. Modeled IRWs with Exceedances of Benchmark Values for
One or More Pollutants Under Baseline and Regulatory Options

Pollutant Loadings Basis

Industry Pollutant Loadings (lb/year)a

Baseline

Option A

Option B

Option C

Mass loadings for the nine modeled pollutants from 110
steam electric power plants in pollutant loadings analysis'3

17,600

13,400

3,550

3,200



Number of Modeled IRWs Exceeding

Evaluation Benchmark



Benchmark Value0





Baseline

Option A

Option B

Option C

Wa ter Quality Results

Freshwater acute NRWQC

3

2

2

2

Freshwater chronic NRWQC

12

11

5

5

HH WO NRWQC

38

28

14

7

HH O NRWQC

21

14

4

3

Drinking water MCL

5

4

3

3

Wildlife Results

Sediment TEC

24

24

11

7

Fish ingestion NEHC for minks

16

16

6

5

Fish ingestion NEHC for eagles

22

17

6

5

Human Health Results—Fish Consumption Advisories

T4 fish tissue concentration screening value (recreational)

22

16

4

3

T4 fish tissue concentration screening value (subsistence)

32

24

10

6

Human Health Results—Noncancer

Oral RfD for child (recreational)

28

22

9

6

Oral RfD for child (subsistence)

39

28

15

8

Oral RfD for adult (recreational)

26

18

6

5

Oral RfD for adult (subsistence)

31

23

9

6

Human Health Results—Cancer

LECR for child (recreational)

0

0

0

0

LECR for child (subsistence)

3

2

1

1

LECR for adult (recreational)

4

2

2

2

LECR for adult (subsistence)

9

3

2

2

Sources: U.S. EPA, 2024h and 2024i.

Abbreviations: HH 0 (human health organism only); HH WO (human health water and organism); IRW (immediate
receiving water); lb/year (pounds per year); LECR (lifetime excess cancer risk); MCL (maximum contaminant level); NEHC
(no effect hazard concentration); NRWQC (National Recommended Water Quality Criteria); RfD (reference dose); TEC
(threshold effect concentration); T4 (trophic level 4).

a—Values represent the industry loadings and the IRW Model outputs for the following nine evaluated pollutants: arsenic,
cadmium, copper, lead, mercury, nickel, selenium, thallium, and zinc. Pollutant loadings are rounded to three significant
figures.

b—The pollutant loadings analysis includes discharges from 110 plants to 123 immediate receiving waters (some plants
discharge to multiple receiving waters). Of these 123 immediate receiving waters, all 123 receive discharges of the
evaluated wastestreams under baseline, 105 do under Option A, 57 do under Option B, and 18 do under Option C.
c—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and
loadings from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving
waters, all 114 receive discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under
Option B, and 17 do under Option C.

A-2

-------
Table A-2. Modeled IRWs with Exceedances of Arsenic Benchmark Values
Under Baseline and Regulatory Options

Pollutant Loadings Basis

Industry Arsenic Loadings (lb/year)a

Baseline

Option A

Option B

Option C

Mass loadings from 110 steam electric power plants in
pollutant loadings analysis'3

777

264

77.1

50.8



Number of Modeled IRWs Exceeding

Evaluation Benchmark0



Benchmark Valued





Baseline

Option A

Option B

Option C

Water Quality Results

Freshwater acute NRWQC®

0

0

0

0

Freshwater chronic NRWQC®

0

0

0

0

HH WO NRWQCf

38

28

14

7

HH O NRWQCf

21

14

4

3

Drinking water MCL

4

2

2

2

Wildlife Results

Sediment TEC

3

2

0

0

Fish ingestion NEHC for minks

0

0

0

0

Fish ingestion NEHC for eagles

0

0

0

0

Human Health Results—Fish Consumption Advisories

T4 fish tissue concentration screening value (recreational)'6

0

0

0

0

T4 fish tissue concentration screening value (subsistence)'6

0

0

0

0

Human Health Results—Noncancer

Oral RfD for child (recreational)'

0

0

0

0

Oral RfD for child (subsistence)'

0

0

0

0

Oral RfD for adult (recreational)'

0

0

0

0

Oral RfD for adult (subsistence)'

0

0

0

0

Human Health Results—Cancer

LECR for child (recreational)'

0

0

0

0

LECR for child (subsistence)'

3

2

1

1

LECR for adult (recreational)'

4

2

2

2

LECR for adult (subsistence)'

9

3

2

2

Sources: U.S. EPA, 2024h and 2024i.

Abbreviations: HH 0 (human health organism only); HH WO (human health water and organism); IRW (immediate receiving
water); lb/year (pounds per year); LECR (lifetime excess cancer risk); MCL (maximum contaminant level); NEHC (no effect
hazard concentration); NRWQC (National Recommended Water Quality Criteria); RfD (reference dose); TEC (threshold effect
concentration); T4 (trophic level 4).

a—Pollutant loadings are rounded to three significant figures.

b— The pollutant loadings analysis includes discharges from 110 plants to 123 immediate receiving waters (some plants
discharge to multiple receiving waters). Of these 123 immediate receiving waters, all 123 receive discharges of the evaluated
wastestreams under baseline, 105 do under Option A, 57 do under Option B, and 18 do under Option C.
c—All benchmark values are based on total arsenic concentration, unless otherwise stated.

d—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114
receive discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do
under Option C.

e—Benchmark value is based on dissolved arsenic,
f—Benchmark value is based on inorganic arsenic.

g—Values represent number of immediate receiving waters exceeding either the noncarcinogenic or carcinogenic screening
values.

A-3

-------
Table A-3. Modeled IRWs with Exceedances of Cadmium Benchmark Values
Under Baseline and Regulatory Options



Industry Cadmium Loadings (lb/year)a

Pollutant Loadings Basis

Baseline

Option A

Option B

Option C

Mass loadings from 110 steam electric power plants in
pollutant loadings analysis'3

553

401

41.1

23.8

Evaluation Benchmark0

Number of Modeled IRWs Exceeding
Benchmark Valued



Baseline

Option A

Option B

Option C

Wa ter Quality Results

Freshwater acute NRWQC®

3

2

1

1

Freshwater chronic NRWQC®

8

5

2

2

HH WO NRWQC

f

f

f

f

HH O NRWQC

f

f

f

f

Drinking water MCL

3

2

1

1

Wildlife Results

Sediment TEC

8

5

2

2

Fish ingestion NEHC for minks

1

1

0

0

Fish ingestion NEHC for eagles

1

1

0

0

Human Health Results—Fish Consumption Advisories

T4 fish tissue concentration screening value (recreational)

1

1

0

0

T4 fish tissue concentration screening value (subsistence)

4

3

2

2

Human Health Results—Noncancer

Oral RfD for child (recreational)

3

2

1

1

Oral RfD for child (subsistence)

4

4

2

2

Oral RfD for adult (recreational)

1

1

1

1

Oral RfD for adult (subsistence)

4

3

2

2

Human Health Results—Cancer

LECR for child (recreational)

f

f

f

f

LECR for child (subsistence)

f

f

f

f

LECR for adult (recreational)

f

f

f

f

LECR for adult (subsistence)

f

f

f

f

Sources: U.S. EPA, 2024h and 2024i.

Abbreviations: HH 0 (human health organism only); HH WO (human health water and organism); IRW (immediate receiving
water); lb/year (pounds per year); LECR (lifetime excess cancer risk); MCL (maximum contaminant level); NEHC(no effect
hazard concentration); NRWQC (National Recommended Water Quality Criteria); RfD (reference dose); TEC (threshold
effect concentration); T4 (trophic level 4).
a—Pollutant loadings are rounded to three significant figures.

b— The pollutant loadings analysis includes discharges from 110 plants to 123 immediate receiving waters (some plants
discharge to multiple receiving waters). Of these 123 immediate receiving waters, all 123 receive discharges of the
evaluated wastestreams under baseline, 105 do under Option A, 57 do under Option B, and 18 do under Option C.
c—All benchmark values are based on total cadmium concentration, unless otherwise stated.

d—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and
loadings from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters,
all 114 receive discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and
17 do under Option C.

e—Benchmark value is based on dissolved cadmium.

f—A benchmark value is not yet established for this pollutant or was not included in the EPA's analyses.

A-4

-------
Table A-4. Modeled IRWs with Exceedances of Copper Benchmark Values
Under Baseline and Regulatory Options



Industry Copper Loadings (lb/year)a

Pollutant Loadings Basis

Baseline

Option A

Option B

Option C

Mass loadings from 110 steam electric power plants in
pollutant loadings analysis'3

398

217

49.4

32.9

Evaluation Benchmark0

Number of Modeled IRWs Exceeding
Benchmark Valued



Baseline

Option A

Option B

Option C

Water Quality Results

Freshwater acute NRWQC®

1

1

0

0

Freshwater chronic NRWQC®

2

2

0

0

HH WO NRWQC

0

0

0

0

HH O NRWQC

f

f

f

f

Drinking water MCL

0

0

0

0

Wildlife Results

Sediment TEC

2

2

1

1

Fish ingestion NEHC for minks

0

0

0

0

Fish ingestion NEHC for eagles

0

0

0

0

Human Health Results—Fish Consumption Advisories

T4 fish tissue concentration screening value (recreational)

f

f

f

f

T4 fish tissue concentration screening value (subsistence)

f

f

f

f

Human Health Results—Noncancer

Oral RfD for child (recreational)

0

0

0

0

Oral RfD for child (subsistence)

1

1

0

0

Oral RfD for adult (recreational)

0

0

0

0

Oral RfD for adult (subsistence)

0

0

0

0

Human Health Results—Cancer

LECR for child (recreational)

f

f

f

f

LECR for child (subsistence)

f

f

f

f

LECR for adult (recreational)

f

f

f

f

LECR for adult (subsistence)

f

f

f

f

Sources: U.S. EPA, 2024h and 2024i.

Abbreviations: HH 0 (human health organism only); HH WO (human health water and organism); IRW (immediate receiving
water); lb/year (pounds per year); LECR (lifetime excess cancer risk); MCL (maximum contaminant level); NEHC (no effect hazard
concentration); NRWQC (National Recommended Water Quality Criteria); RfD (reference dose); TEC (threshold effect
concentration); T4 (trophic level 4).

a—Pollutant loadings are rounded to three significant figures.

b— The pollutant loadings analysis includes discharges from 110 plants to 123 immediate receiving waters (some plants
discharge to multiple receiving waters). Of these 123 immediate receiving waters, all 123 receive discharges of the evaluated
wastestreams under baseline, 105 do under Option A, 57 do under Option B, and 18 do under Option C.
c—All benchmark values are based on total copper concentration, unless otherwise stated.

d—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114 receive
discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do under
Option C.

e—Benchmark value is based on dissolved copper.

f—A benchmark value is not yet established for this pollutant or was not included in the EPA's analyses.

A-5

-------
Table A-5. Modeled IRWs with Exceedances of Lead Benchmark Values
Under Baseline and Regulatory Options



Industry Lead Loadings (lb/year)a

Pollutant Loadings Basis

Baseline

Option A

Option B

Option C

Mass loadings from 110 steam electric power plants in
pollutant loadings analysis'3

230

91.6

42.9

29.5

Evaluation Benchmark0

Number of Modeled IRWs Exceeding
Benchmark Valued



Baseline

Option A

Option B

Option C

Water Quality Results

Freshwater acute NRWQC®

0

0

0

0

Freshwater chronic NRWQC®

1

1

0

0

HH WO NRWQC

f

f

f

f

HH O NRWQC

f

f

f

f

Drinking water MCL

2

2

1

1

Wildlife Results

Sediment TEC

1

1

1

1

Fish ingestion NEHC for minks

0

0

0

0

Fish ingestion NEHC for eagles

0

0

0

0

Human Health Results—Fish Consumption Advisories

T4 fish tissue concentration screening value (recreational)

f

f

f

f

T4 fish tissue concentration screening value (subsistence)

f

f

f

f

Human Health Results—Noncancer

Oral RfD for child (recreational)

f

f

f

f

Oral RfD for child (subsistence)

f

f

f

f

Oral RfD for adult (recreational)

f

f

f

f

Oral RfD for adult (subsistence)

f

f

f

f

Human Health Results—Cancer

LECR for child (recreational)

f

f

f

f

LECR for child (subsistence)

f

f

f

f

LECR for adult (recreational)

f

f

f

f

LECR for adult (subsistence)

f

f

f

f

Sources: U.S. EPA, 2024h and 2024i.

Abbreviations: HH 0 (human health organism only); HH WO (human health water and organism); IRW (immediate receiving
water); lb/year (pounds per year); LECR (lifetime excess cancer risk); MCL (maximum contaminant level); NEHC (no effect
hazard concentration); NRWQC (National Recommended Water Quality Criteria); RfD (reference dose); TEC (threshold effect
concentration); T4 (trophic level 4).

a—Pollutant loadings are rounded to three significant figures.

b— The pollutant loadings analysis includes discharges from 110 plants to 123 immediate receiving waters (some plants
discharge to multiple receiving waters). Of these 123 immediate receiving waters, all 123 receive discharges of the evaluated
wastestreams under baseline, 105 do under Option A, 57 do under Option B, and 18 do under Option C.
c—All benchmark values are based on total lead concentration, unless otherwise stated.

d—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114
receive discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do
under Option C.

e—Benchmark value is based on dissolved lead.

f—A benchmark value is not yet established for this pollutant or was not included in the EPA's analyses.

A-6

-------
Table A-6. Modeled IRWs with Exceedances of Mercury Benchmark Values
Under Baseline and Regulatory Options

Pollutant Loadings Basis

Industry Mercury Loadings (lb/year)a

Baseline

Option A

Option B

Option C

Mass loadings from 110 steam electric power plants in
pollutant loadings analysis'3

40.0

28.5

1.53

1.21

Evaluation Benchmark0

Number of Modeled IRWs Exceeding
Benchmark Valued



Baseline

Option A

Option B

Option C

Water Quality Results

Freshwater acute NRWQC®

0

0

0

0

Freshwater chronic NRWQC®

1

1

0

0

HH WO NRWQC

f

f

f

f

HH O NRWQC

f

f

f

f

Drinking water MCLe

1

1

0

0

Wildlife Results

Sediment TEC

19

9

2

2

Fish ingestion NEHC for minks'1

16

7

2

2

Fish ingestion NEHC for eagles'1

22

15

3

2

Human Health Results—Fish Consumption Advisories

T4 fish tissue concentration screening value (recreational)'1

22

16

4

3

T4 fish tissue concentration screening value (subsistence)'1

32

24

10

6

Human Health Results—Noncancer

Oral RfD for child (recreational)'1

28

22

8

5

Oral RfD for child (subsistence)'1

38

28

15

8

Oral RfD for adult (recreational)'1

25

17

5

4

Oral RfD for adult (subsistence)'1

31

23

9

6

Human Health Results—Cancer

LECR for child (recreational)

f

f

f

f

LECR for child (subsistence)

f

f

f

f

LECR for adult (recreational)

f

f

f

f

LECR for adult (subsistence)

f

f

f

f

Sources: U.S. EPA, 2024h and 2024i.

Abbreviations: HH 0 (human health organism only); HH WO (human health water and organism); IRW (immediate receiving
water); lb/year (pounds per year); LECR (lifetime excess cancer risk); MCL (maximum contaminant level); NEHC (no effect hazard
concentration); NRWQC (National Recommended Water Quality Criteria); RfD (reference dose); TEC (threshold effect
concentration); T4 (trophic level 4).

a—Pollutant loadings are rounded to three significant figures.

b—The pollutant loadings analysis includes discharges from 110 plants to 123 immediate receiving waters (some plants discharge
to multiple receiving waters). Of these 123 immediate receiving waters, all 123 receive discharges of the evaluated wastestreams
under baseline, 105 do under Option A, 57 do under Option B, and 18 do under Option C.
c—All benchmark values are based on total mercury concentration, unless otherwise stated.

d—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114 receive
discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do under
Option C.

e—Benchmark value is based on dissolved mercury.

f—A benchmark value is not yet established for this pollutant or was not included in the EPA's analyses,
g—Benchmark value is based on inorganic mercury,
h—Benchmark value is based on methylmercury.

A-7

-------
Table A-7. Modeled IRWs with Exceedances of Nickel Benchmark Values
Under Baseline and Regulatory Options



Industry Nickel Loadings (lb/year)a

Pollutant Loadings Basis

Baseline

Option A

Option B

Option C

Mass loadings from 110 steam electric power plants in
pollutant loadings analysis'3

3,430

2,740

113

79.4

Evaluation Benchmark0

Number of Modeled IRWs Exceeding
Benchmark Valued



Baseline

Option A

Option B

Option C

Water Quality Results

Freshwater acute NRWQC®

1

1

0

0

Freshwater chronic NRWQC®

1

1

0

0

HH WO NRWQC

1

1

0

0

HH O NRWQC

0

0

0

0

Drinking water MCL

f

f

f

f

Wildlife Results

Sediment TEC

14

6

2

2

Fish ingestion NEHC for minks

0

0

0

0

Fish ingestion NEHC for eagles

0

0

0

0

Human Health Results—Fish Consumption Advisories

T4 fish tissue concentration screening value (recreational)

f

f

f

f

T4 fish tissue concentration screening value (subsistence)

f

f

f

f

Human Health Results—Noncancer

Oral RfD for child (recreational)

0

0

0

0

Oral RfD for child (subsistence)

0

0

0

0

Oral RfD for adult (recreational)

0

0

0

0

Oral RfD for adult (subsistence)

0

0

0

0

Human Health Results—Cancer

LECR for child (recreational)

f

f

f

f

LECR for child (subsistence)

f

f

f

f

LECR for adult (recreational)

f

f

f

f

LECR for adult (subsistence)

f

f

f

f

Sources: U.S. EPA, 2024h and 2024i.

Abbreviations: HH 0 (human health organism only); HH WO (human health water and organism); IRW (immediate receiving
water); lb/year (pounds per year); LECR (lifetime excess cancer risk); MCL (maximum contaminant level); NEHC (no effect hazard
concentration); NRWQC (National Recommended Water Quality Criteria); RfD (reference dose); TEC (threshold effect
concentration); T4 (trophic level 4).

a—Pollutant loadings are rounded to three significant figures.

b— The pollutant loadings analysis includes discharges from 110 plants to 123 immediate receiving waters (some plants
discharge to multiple receiving waters). Of these 123 immediate receiving waters, all 123 receive discharges of the evaluated
wastestreams under baseline, 105 do under Option A, 57 do under Option B, and 18 do under Option C.
c—All benchmark values are based on total nickel concentration, unless otherwise stated.

d—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114 receive
discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do under
Option C.

e—Benchmark value is based on dissolved nickel.

f—A benchmark value is not yet established for this pollutant or was not included in the EPA's analyses.

A-8

-------
Table A-8. Modeled IRWswith Exceedances of Selenium Benchmark Values
Under Baseline and Regulatory Options



Industry Selenium Loadings (lb/year)a

Pollutant Loadings Basis

Baseline

Option A

Option B

Option C

Mass loadings from 110 steam electric power plants in
pollutant loadings analysis'3

4,810

4,600

2,840

2,730

Evaluation Benchmark0

Number of Modeled IRWs Exceeding
Benchmark Valued



Baseline

Option A

Option B

Option C

Water Quality Results

Freshwater acute NRWQC®

1

1

1

1

Freshwater chronic NRWQC®

12

11

5

5

HH WO NRWQC

1

1

1

1

HH O NRWQC

1

1

1

1

Drinking water MCL

3

3

2

2

Wildlife Results

Sediment TEC

24

24

11

7

Fish ingestion NEHC for minks

15

15

6

5

Fish ingestion NEHC for eagles

15

15

6

5

Human Health Results—Fish Consumption Advisories

T4 fish tissue concentration screening value (recreational)

8

7

3

3

T4 fish tissue concentration screening value (subsistence)

18

18

8

5

Human Health Results—Noncancer

Oral RfD for child (recreational)

15

15

6

5

Oral RfD for child (subsistence)

22

22

8

5

Oral RfD for adult (recreational)

12

12

5

4

Oral RfD for adult (subsistence)

15

15

6

5

Human Health Results—Cancer

LECR for child (recreational)

f

f

f

f

LECR for child (subsistence)

f

f

f

f

LECR for adult (recreational)

f

f

f

f

LECR for adult (subsistence)

f

f

f

f

Sources: U.S. EPA, 2024h and 2024i.

Abbreviations: HH 0 (human health organism only); HH WO (human health water and organism); IRW (immediate receiving
water); lb/year (pounds per year); LECR (lifetime excess cancer risk); MCL (maximum contaminant level); NEHC (no effect hazard
concentration); NRWQC (National Recommended Water Quality Criteria); RfD (reference dose); TEC (threshold effect
concentration); T4 (trophic level 4).

a—Pollutant loadings are rounded to three significant figures.

b— The pollutant loadings analysis includes discharges from 110 plants to 123 immediate receiving waters (some plants
discharge to multiple receiving waters). Of these 123 immediate receiving waters, all 123 receive discharges of the evaluated
wastestreams under baseline, 105 do under Option A, 57 do under Option B, and 18 do under Option C.
c—All benchmark values are based on total selenium concentration, unless otherwise stated.

d—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114 receive
discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do under
Option C.

e—Benchmark value is based on dissolved selenium.

f—A benchmark value is not yet established for this pollutant or was not included in the EPA's analyses.

A-9

-------
Table A-9. Modeled IRWs with Exceedances of Thallium Benchmark Values
Under Baseline and Regulatory Options



Industry Thallium Loadings (lb/year)a

Pollutant Loadings Basis

Baseline

Option A

Option B

Option C

Mass loadings from 110 steam electric power plants in
pollutant loadings analysis'3

781

536

117

85.5

Evaluation Benchmark0

Number of Modeled IRWs Exceeding
Benchmark Valued



Baseline

Option A

Option B

Option C

Water Quality Results

Freshwater acute NRWQC

e

G

G

G

Freshwater chronic NRWQC

e

G

G

G

HH WO NRWQC

8

7

4

3

HH O NRWQC

7

5

3

3

Drinking water MCL

2

2

2

2

Wildlife Results

Sediment TEC

e

G

G

G

Fish ingestion NEHC for minks

e

G

G

G

Fish ingestion NEHC for eagles

e

G

G

G

Human Health Results—Fish Consumption Advisories

T4 fish tissue concentration screening value (recreational)

e

G

G

G

T4 fish tissue concentration screening value (subsistence)

e

G

G

G

Human Health Results—Noncancer

Oral RfD for child (recreational)

16

15

6

5

Oral RfD for child (subsistence)

24

19

10

7

Oral RfD for adult (recreational)

13

9

5

4

Oral RfD for adult (subsistence)

16

15

6

5

Human Health Results—Cancer

LECR for child (recreational)

G

G

G

G

LECR for child (subsistence)

G

G

G

G

LECR for adult (recreational)

G

G

G

G

LECR for adult (subsistence)

G

G

G

G

Sources: U.S. EPA, 2024h and 2024i.

Abbreviations: HH 0 (human health organism only); HH WO (human health water and organism); IRW (immediate receiving
water); lb/year (pounds per year); LECR (lifetime excess cancer risk); MCL (maximum contaminant level); NEHC (no effect hazard
concentration); NRWQC (National Recommended Water Quality Criteria); RfD (reference dose); TEC (threshold effect
concentration); T4 (trophic level 4).

a—Pollutant loadings are rounded to three significant figures.

b— The pollutant loadings analysis includes discharges from 110 plants to 123 immediate receiving waters (some plants
discharge to multiple receiving waters). Of these 123 immediate receiving waters, all 123 receive discharges of the evaluated
wastestreams under baseline, 105 do under Option A, 57 do under Option B, and 18 do under Option C.
c—All benchmark values are based on total thallium concentration, unless otherwise stated.

d—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114 receive
discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do under
Option C.

e—A benchmark value is not yet established for this pollutant or was not included in the EPA's analyses.

A-10

-------
Table A-10. Modeled IRWs with Exceedances of Zinc Benchmark Values
Under Baseline and Regulatory Options



Industry Zinc Loadings (lb/year)a

Pollutant Loadings Basis

Baseline

Option A

Option B

Option C

Mass loadings from 110 steam electric power plants in
pollutant loadings analysis'3

6,570

4,530

265

174

Evaluation Benchmark0

Number of Modeled IRWs Exceeding
Benchmark Valued



Baseline

Option A

Option B

Option C

Water Quality Results

Freshwater acute NRWQC®

1

1

0

0

Freshwater chronic NRWQC®

1

1

0

0

HH WO NRWQC

0

0

0

0

HH O NRWQC

0

0

0

0

Drinking water MCL

1

1

0

0

Wildlife Results

Sediment TEC

7

4

2

2

Fish ingestion NEHC for minks

1

1

0

0

Fish ingestion NEHC for eagles

1

1

0

0

Human Health Results—Fish Consumption Advisories

T4 fish tissue concentration screening value (recreational)

f

f

f

f

T4 fish tissue concentration screening value (subsistence)

f

f

f

f

Human Health Results—Noncancer

Oral RfD for child (recreational)

1

1

0

0

Oral RfD for child (subsistence)

1

1

0

0

Oral RfD for adult (recreational)

1

1

0

0

Oral RfD for adult (subsistence)

1

1

0

0

Human Health Results—Cancer

LECR for child (recreational)

f

f

f

f

LECR for child (subsistence)

f

f

f

f

LECR for adult (recreational)

f

f

f

f

LECR for adult (subsistence)

f

f

f

f

Sources: U.S. EPA, 2024h and 2024i.

Abbreviations: HH 0 (human health organism only); HH WO (human health water and organism); IRW (immediate receiving
water); lb/year (pounds per year); LECR (lifetime excess cancer risk); MCL (maximum contaminant level); NEHC (no effect hazard
concentration); NRWQC (National Recommended Water Quality Criteria); RfD (reference dose); TEC (threshold effect
concentration); T4 (trophic level 4).

a—Pollutant loadings are rounded to three significant figures.

b—The pollutant loadings analysis includes discharges from 110 plants to 123 immediate receiving waters (some plants discharge
to multiple receiving waters). Of these 123 immediate receiving waters, all 123 receive discharges of the evaluated wastestreams
under baseline, 105 do under Option A, 57 do under Option B, and 18 do under Option C.
c—All benchmark values are based on total zinc concentration, unless otherwise stated.

d—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114 receive
discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do under
Option C.

e—Benchmark value is based on dissolved zinc.

f—A benchmark value is not yet established for this pollutant or was not included in the EPA's analyses.

A-ll

-------
Table A-ll. Modeled IRWs with Exceedances of Arsenic Oral Reference Dose Values
by Race/Ethnicity Category Under Baseline and Regulatory Options

Age and Fishing

Race/Ethnicity Category

Number of Modeled IRWs Exceeding Oral RfDa'b

Mode Cohort

Baseline

Option A

Option B

Option C



Non-Hispanic White

0

0

0

0

Child-
recreational

Non-Hispanic Black

0

0

0

0

Mexican-American

0

0

0

0

Other Hispanic

0

0

0

0



Other, including multiple races

0

0

0

0



Non-Hispanic White

0

0

0

0

Child-
subsistence

Non-Hispanic Black

0

0

0

0

Mexican-American

0

0

0

0

Other Hispanic

0

0

0

0



Other, including multiple races

0

0

0

0



Non-Hispanic White

0

0

0

0

Adult—
recreational

Non-Hispanic Black

0

0

0

0

Mexican-American

0

0

0

0

Other Hispanic

0

0

0

0



Other, including multiple races

0

0

0

0



Non-Hispanic White

0

0

0

0

Adult—
subsistence

Non-Hispanic Black

0

0

0

0

Mexican-American

0

0

0

0

Other Hispanic

0

0

0

0



Other, including multiple races

0

0

0

0

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); RfD (reference dose).

a—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114 receive
discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do under
Option C.

b—Benchmark value is based on inorganic arsenic.

A-12

-------
Table A-12. Modeled IRWs with Exceedances of Cadmium Oral Reference Dose Values
by Race/Ethnicity Category Under Baseline and Regulatory Options

Age and Fishing

Race/Ethnicity Category

Number of Modeled IRWs Exceeding Oral RfDa'b

Mode Cohort

Baseline

Option A

Option B

Option C



Non-Hispanic White

1

1

1

1

Child-
recreational

Non-Hispanic Black

1

1

1

1

Mexican-American

2

2

1

1

Other Hispanic

1

1

1

1



Other, including multiple races

2

2

1

1



Non-Hispanic White

3

2

1

1

Child-
subsistence

Non-Hispanic Black

4

3

2

2

Mexican-American

4

4

2

2

Other Hispanic

4

4

2

2



Other, including multiple races

4

4

2

2



Non-Hispanic White

1

1

1

1

Adult—
recreational

Non-Hispanic Black

1

1

1

1

Mexican-American

2

2

1

1

Other Hispanic

1

1

1

1



Other, including multiple races

2

2

1

1



Non-Hispanic White

3

2

1

1

Adult—
subsistence

Non-Hispanic Black

4

3

2

2

Mexican-American

4

4

2

2

Other Hispanic

4

4

2

2



Other, including multiple races

4

4

2

2

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); RfD (reference dose).

a—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114 receive
discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do under
Option C.

b—Benchmark value is based on dissolved cadmium.

A-13

-------
Table A-13. Modeled IRWs with Exceedances of Copper Oral Reference Dose Values
by Race/Ethnicity Category Under Baseline and Regulatory Options

Age and Fishing

Race/Ethnicity Category

Number of Modeled IRWs Exceeding Oral RfDa'b

Mode Cohort

Baseline

Option A

Option B

Option C



Non-Hispanic White

0

0

0

0

Child-
recreational

Non-Hispanic Black

0

0

0

0

Mexican-American

0

0

0

0

Other Hispanic

0

0

0

0



Other, including multiple races

0

0

0

0



Non-Hispanic White

0

0

0

0

Child-
subsistence

Non-Hispanic Black

0

0

0

0

Mexican-American

0

0

0

0

Other Hispanic

0

0

0

0



Other, including multiple races

0

0

0

0



Non-Hispanic White

0

0

0

0

Adult—
recreational

Non-Hispanic Black

0

0

0

0

Mexican-American

0

0

0

0

Other Hispanic

0

0

0

0



Other, including multiple races

0

0

0

0



Non-Hispanic White

0

0

0

0

Adult—
subsistence

Non-Hispanic Black

0

0

0

0

Mexican-American

0

0

0

0

Other Hispanic

0

0

0

0



Other, including multiple races

0

0

0

0

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); RfD (reference dose).

a—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114 receive
discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do under
Option C.

b—Benchmark value is based on total copper.

A-14

-------
Table A-14. Modeled IRWs with Exceedances of Mercury (as Methylmercury) Oral Reference
Dose Values by Race/Ethnicity Category Under Baseline and Regulatory Options

Age and Fishing

Race/Ethnicity Category

Number of Modeled IRWs Exceeding Oral RfDa

Mode Cohort

Baseline

Option A

Option B

Option C



Non-Hispanic White

25

17

5

4

Child-
recreational

Non-Hispanic Black

26

19

6

4

Mexican-American

27

20

8

5

Other Hispanic

26

19

7

5



Other, including multiple races

27

20

8

5



Non-Hispanic White

29

23

9

5

Child-
subsistence

Non-Hispanic Black

31

23

9

6

Mexican-American

32

24

10

6

Other Hispanic

32

23

9

6



Other, including multiple races

33

26

14

8



Non-Hispanic White

25

17

5

4

Adult—
recreational

Non-Hispanic Black

26

19

6

4

Mexican-American

27

20

8

5

Other Hispanic

26

19

7

5



Other, including multiple races

27

20

8

5



Non-Hispanic White

29

23

9

5

Adult—
subsistence

Non-Hispanic Black

31

23

9

6

Mexican-American

32

24

10

6

Other Hispanic

32

23

9

6



Other, including multiple races

33

26

14

8

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); RfD (reference dose).

a—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114 receive
discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do under
Option C.

A-15

-------
Table A-15. Modeled IRWs with Exceedances of Nickel Oral Reference Dose Values
by Race/Ethnicity Category Under Baseline and Regulatory Options

Age and Fishing

Race/Ethnicity Category

Number of Modeled IRWs Exceeding Oral RfDa'b

Mode Cohort

Baseline

Option A

Option B

Option C



Non-Hispanic White

0

0

0

0



Non-Hispanic Black

0

0

0

0

Child-

Mexican-American

0

0

0

0

recreational

Other Hispanic

0

0

0

0



Other, including multiple

0

0

0

0



races



Non-Hispanic White

0

0

0

0



Non-Hispanic Black

0

0

0

0

Child-

Mexican-American

0

0

0

0

subsistence

Other Hispanic

0

0

0

0



Other, including multiple

0

0

0

0



races



Non-Hispanic White

0

0

0

0



Non-Hispanic Black

0

0

0

0

Adult—

Mexican-American

0

0

0

0

recreational

Other Hispanic

0

0

0

0



Other, including multiple

0

0

0

0



races



Non-Hispanic White

0

0

0

0



Non-Hispanic Black

0

0

0

0

Adult—

Mexican-American

0

0

0

0

subsistence

Other Hispanic

0

0

0

0



Other, including multiple

0

0

0

0



races

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); RfD (reference dose).

a—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114 receive
discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do under
Option C.

b—Benchmark value is based on total nickel.

A-16

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Table A-16. Modeled IRWs with Exceedances of Selenium Oral Reference Dose Values
by Race/Ethnicity Category Under Baseline and Regulatory Options

Age and Fishing

Race/Ethnicity Category

Number of Modeled IRWs Exceeding Oral RfDa'b

Mode Cohort

Baseline

Option A

Option B

Option C



Non-Hispanic White

12

12

5

4

Child-
recreational

Non-Hispanic Black

12

12

5

4

Mexican-American

13

13

5

4

Other Hispanic

13

13

5

4



Other, including multiple races

13

13

5

4



Non-Hispanic White

15

15

6

5

Child-
subsistence

Non-Hispanic Black

15

15

6

5

Mexican-American

19

19

8

5

Other Hispanic

17

17

7

5



Other, including multiple races

19

19

8

5



Non-Hispanic White

12

12

5

4

Adult—
recreational

Non-Hispanic Black

12

12

5

4

Mexican-American

13

13

5

4

Other Hispanic

13

13

5

4



Other, including multiple races

13

13

5

4



Non-Hispanic White

15

15

6

5

Adult—
subsistence

Non-Hispanic Black

15

15

6

5

Mexican-American

19

19

8

5

Other Hispanic

17

17

7

5



Other, including multiple races

19

19

8

5

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); RfD (reference dose).

a—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114 receive
discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do under
Option C.

b—Benchmark value is based on total selenium.

A-17

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Table A-17. Modeled IRWs with Exceedances of Thallium Oral Reference Dose Values
by Race/Ethnicity Category Under Baseline and Regulatory Options

Age and Fishing

Race/Ethnicity Category

Number of Modeled IRWs Exceeding Oral RfDa'b

Mode Cohort

Baseline

Option A

Option B

Option C



Non-Hispanic White

13

9

5

4

Child-
recreational

Non-Hispanic Black

13

12

5

4

Mexican-American

15

12

5

4

Other Hispanic

13

12

5

4



Other, including multiple races

15

12

5

4



Non-Hispanic White

16

15

6

5

Child-
subsistence

Non-Hispanic Black

16

15

6

5

Mexican-American

20

18

8

6

Other Hispanic

20

17

6

5



Other, including multiple races

21

19

10

7



Non-Hispanic White

13

9

5

4

Adult—
recreational

Non-Hispanic Black

13

12

5

4

Mexican-American

15

12

5

4

Other Hispanic

13

12

5

4



Other, including multiple races

15

12

5

4



Non-Hispanic White

16

15

6

5

Adult—
subsistence

Non-Hispanic Black

16

15

6

5

Mexican-American

20

18

8

6

Other Hispanic

20

17

6

5



Other, including multiple races

21

19

10

7

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); RfD (reference dose).

a—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114 receive
discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do under
Option C.

b—Benchmark value is based on total thallium.

A-18

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Table A-18. Modeled IRWs with Exceedances of Zinc Oral Reference Dose Values
by Race/Ethnicity Category Under Baseline and Regulatory Options

Age and Fishing

Race/Ethnicity Category

Number of Modeled IRWs Exceeding Oral RfDa'b

Mode Cohort

Baseline

Option A

Option B

Option C



Non-Hispanic White

1

1

0

0

Child-
recreational

Non-Hispanic Black

1

1

0

0

Mexican-American

1

1

0

0

Other Hispanic

1

1

0

0



Other, including multiple races

1

1

0

0



Non-Hispanic White

1

1

0

0

Child-
subsistence

Non-Hispanic Black

1

1

0

0

Mexican-American

1

1

0

0

Other Hispanic

1

1

0

0



Other, including multiple races

1

1

0

0



Non-Hispanic White

1

1

0

0

Adult—
recreational

Non-Hispanic Black

1

1

0

0

Mexican-American

1

1

0

0

Other Hispanic

1

1

0

0



Other, including multiple races

1

1

0

0



Non-Hispanic White

1

1

0

0

Adult—
subsistence

Non-Hispanic Black

1

1

0

0

Mexican-American

1

1

0

0

Other Hispanic

1

1

0

0



Other, including multiple races

1

1

0

0

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); RfD (reference dose).

a—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114 receive
discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do under
Option C.

b—Benchmark value is based on total zinc.

A-19

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Table A-19. Modeled IRWs with Lifetime Excess Cancer Risk for Inorganic Arsenic Exceeding
One-in-a-Million by Race/Ethnicity Category Under Baseline and Regulatory Options

Age and Fishing

Race/Ethnicity Category

Number of Modeled IRWs Exceeding LECRa

Mode Cohort

Baseline

Option A

Option B

Option C



Non-Hispanic White

0

0

0

0

Child-
recreational

Non-Hispanic Black

0

0

0

0

Mexican-American

0

0

0

0

Other Hispanic

0

0

0

0



Other, including multiple races

0

0

0

0



Non-Hispanic White

2

2

1

0

Child-
subsistence

Non-Hispanic Black

3

2

1

1

Mexican-American

3

2

1

1

Other Hispanic

3

2

1

1



Other, including multiple races

3

2

1

1



Non-Hispanic White

4

2

2

2

Adult—
recreational

Non-Hispanic Black

4

2

2

2

Mexican-American

4

2

2

2

Other Hispanic

4

2

2

2



Other, including multiple races

4

2

2

2



Non-Hispanic White

9

3

2

2

Adult—
subsistence

Non-Hispanic Black

9

3

2

2

Mexican-American

10

3

2

2

Other Hispanic

10

3

2

2



Other, including multiple races

11

4

3

2

Source: U.S. EPA, 2024i.

Abbreviations: IRW (immediate receiving water); LECR (lifetime excess cancer risk).

a—The IRW Model, which excludes the Great Lakes and estuaries, analyzes 114 total immediate receiving waters and loadings
from 100 plants (some of which discharge to multiple receiving waters). Of these 114 immediate receiving waters, all 114 receive
discharges of the evaluated wastestreams under baseline, 97 do under Option A, 50 do under Option B, and 17 do under
Option C.

A-20

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