United States Office of Water EPA-821-R-15-006 

Environmental Protection Washington, DC 20460 September 2015

Agency 

Environmental Assessment 

for the Effluent Limitations 

Guidelines and Standards 

for the Steam Electric Power 

Generating Point Source 

Category
Environmental Assessment for the Effluent 

Limitations Guidelines and Standards for the 

Steam Electric Power Generating Point 

Source Category 

EPA-821-R-15-006 

September 2015 

U.S. Environmental Protection Agency 

Office of Water (4303T) 

Engineering and Analysis Division 

1200 Pennsylvania Avenue, NW 

Washington, DC 20460 
Acknowledgements and Disclaimer

This report was prepared by the U.S. 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. 
Table of Contents

TABLE OF CONTENTS

Page 

ACRONYMS ................................................................................................................................. VIII

GLOSSARY ..................................................................................................................................... XI

SECTION 1 INTRODUCTION..........................................................................................................1-1

SECTION 2 BACKGROUND AND SCOPE ........................................................................................2-1

SECTION 3 ENVIRONMENTAL AND HUMAN HEALTH CONCERNS..............................................3-1

3.1 Types of Pollutants Discharged in Steam Electric Power Plant Wastewater ...........3-2

3.1.1 Metals and Toxic Bioaccumulative Pollutants .............................................3-2

3.1.2 Nutrients .......................................................................................................3-9

3.1.3 TDS...............................................................................................................3-9

3.2 Loadings Associated with Steam Electric Power Plant Wastewater ......................3-12

3.2.1 Annual Baseline Pollutant Loadings ..........................................................3-13

3.2.2 Comparison of Steam Electric Power Plant Loadings to Other 

Industries ....................................................................................................3-15

3.2.3 Comparison of Steam Electric Power Plant Loadings to Publicly 

Owned Treatment Works ...........................................................................3-16

3.3 Environmental Impacts from Steam Electric Power Plant Wastewater .................3-20

3.3.1 Ecological Impacts .....................................................................................3-20

3.3.2 Human Health Effects ................................................................................3-27

3.3.3 Damage Cases and Other Documented Surface Water Impacts ................3-28

3.3.4 Damage Cases and Other Documented Ground Water Impacts ................3-35

3.3.5 Potential for Impacts to Occur in Other Locations .....................................3-37

3.4 Discharge to Sensitive Environments .....................................................................3-38

3.4.1 Pollutant Loadings to the Great Lakes Watershed .....................................3-38

3.4.2 Pollutant Loadings to the Chesapeake Bay Watershed ..............................3-40

3.4.3 Proximity to Impaired Waters ....................................................................3-42

3.4.4 Proximity to Fish Consumption Advisory Waters .....................................3-44

3.4.5 Proximity to Threatened and Endangered Species Habitats .......................3-45

3.4.6 Proximity to Drinking Water Resources ....................................................3-46

3.5 Long Environmental Recovery Times Associated with Pollutants in Steam 

Electric Power Plant Wastewater............................................................................3-47

SECTION 4 ASSESSMENT OF EXPOSURE PATHWAYS ..................................................................4-1

4.1 Discharge and Leaching to Surface Waters ..............................................................4-2

4.1.1 Factors Controlling Environmental Impacts in Surface Waters ...................4-2

4.1.2 Assessment of the Surface Water Exposure Pathway ..................................4-4

4.2 Leaching to Ground Water .......................................................................................4-7

4.2.1 Factors Controlling Environmental Impacts to Ground Water ....................4-7

4.2.2 Assessment of the Ground Water Exposure Pathway ................................4-12

4.3 Combustion Residual Surface Impoundments as Attractive Nuisance ..................4-12

i 
Table of Contents

TABLE OF CONTENTS (Continued)

Page 

SECTION 5 SURFACE WATER MODELING...................................................................................5-1

5.1 Immediate Receiving Water (IRW) Model ..............................................................5-1

5.1.1 Water Quality Module..................................................................................5-3

5.1.2 Wildlife Module ...........................................................................................5-8

5.1.3 Human Health Module ...............................................................................5-10

5.2 Ecological Risk Modeling ......................................................................................5-12

SECTION 6 CURRENT IMPACTS FROM STEAM ELECTRIC POWER GENERATING

INDUSTRY.........................................................................................................................6-1

6.1 Water Quality Impacts ..............................................................................................6-1

6.2 Wildlife Impacts .......................................................................................................6-3

6.2.1 Impacts to Wildlife Indicator Species ..........................................................6-3

6.2.2 Impacts to Fish and Waterfowl due to Dietary Selenium Exposure ............6-4

6.2.3 Impacts to Benthic Organisms......................................................................6-6

6.3 Human Health Impacts .............................................................................................6-7

6.3.1 National-Scale Cohort Analysis ...................................................................6-8

6.3.2 Environmental Justice Analysis .................................................................6-12

SECTION 7 ENVIRONMENTAL IMPROVEMENTS UNDER THE FINAL RULE................................7-1

7.1 Pollutant Removals Under the Regulatory Options..................................................7-5

7.2 Key Environmental Improvements ...........................................................................7-9

7.2.1 Improvements in Water Quality Under the Final Rule ................................7-9

7.2.2 Reduced Threat to Wildlife Under the Final Rule ......................................7-13

7.2.3 Reduced Human Health Cancer Risk Under the Final Rule ......................7-15

7.2.4 Reduced Threat of Non-Cancer Human Health Effects Under the 

Final Rule ...................................................................................................7-15

7.2.5 Reduced Human Health Risk for Environmental Justice Analysis ............7-15

7.3 Pollutant-Specific Improvements ...........................................................................7-16

7.3.1 Arsenic........................................................................................................7-16

7.3.2 Mercury ......................................................................................................7-19

7.3.3 Selenium .....................................................................................................7-21

7.3.4 Cadmium ....................................................................................................7-25

7.3.5 Thallium .....................................................................................................7-25

7.4 Improvements to Sensitive Environments .............................................................7-28

7.4.1 Impaired Waters .........................................................................................7-28

7.4.2 Threatened and Endangered Species ..........................................................7-31

7.4.3 Fish Advisory Waters .................................................................................7-31

7.5 Improvements to Watersheds.................................................................................7-31

7.6 Environmental and Human Health Improvements in Downstream Surface 

Water.......................................................................................................................7-34

7.7 Attractive Nuisances ...............................................................................................7-37

7.8 Other Secondary Improvements .............................................................................7-37

7.9 Unresolved Drinking Water Impacts Due to Bromide Discharges ........................7-38

SECTION 8 CASE STUDY MODELING...........................................................................................8-1

8.1 Case Study Modeling Methodology .........................................................................8-2

ii
TABLE OF CONTENTS (Continued)

Table of Contents

Page 

8.1.1 Selection of Case Study Locations for Modeling .........................................8-2

8.1.2 Scope and Technical Approach for Case Study Modeling...........................8-7

8.1.3 Development and Execution of WASP Models .........................................8-11

8.1.4 Use of WASP Water Quality Model Outputs .............................................8-13

8.1.5 Limitations of Case Study Modeling ..........................................................8-14

8.2 Quantified Environmental Impacts and Improvements from Case Study 

Modeling.................................................................................................................8-14

8.2.1 Black Creek Case Study .............................................................................8-15

8.2.2 Etowah River Case Study...........................................................................8-24

8.2.3 Lick Creek & White River Case Study ......................................................8-31

8.2.4 Ohio River Case Study ...............................................................................8-41

8.2.5 Mississippi River Case Study.....................................................................8-47

8.2.6 Lake Sinclair Case Study............................................................................8-52

8.3 Comparison of Case Study and IRW Modeling Results ........................................8-58

SECTION 9 CONCLUSIONS ...........................................................................................................9-1

SECTION 10 REFERENCES .........................................................................................................10-1

Appendix A: Literature Review Methodology and Results 

Appendix B: Proximity Analyses Supporting Tables 

Appendix C: Water Quality Module Methodology 

Appendix D: Wildlife Module Methodology 

Appendix E: Human Health Module Methodology 

Appendix F: Overview of Ecological Risk Modeling Setup and Outputs 

Appendix G: Overview of Case Study Modeling Setup and Outputs 

Appendix H: Additional Model Results

Appendix I: Analyses for Alternate Scenario with Clean Power Plan

Appendix J: EA Loadings and TDD Loadings: Sensitivity Analysis 

iii
List of Tables 

LIST OF TABLES

Page 

Table 2-1. Steam Electric Power Plant Wastestreams Evaluated in the EA................................ 2-2

Table 2-2. Number of Plants Evaluated in the EA....................................................................... 2-4

Table 3-1. Key Metals and Toxic Bioaccumulative Pollutants Found In Steam Electric 

Power Plant Wastewater .................................................................................................. 3-3

Table 3-2. Annual Baseline Pollutant Discharges from Steam Electric Power Plants 

(Evaluated Wastestreams).............................................................................................. 3-14

Table 3-3. Pollutant Loadings for the Final 2010 Effluent Guidelines Planning Process: 

Top 10 Point Source Categories .................................................................................... 3-15

Table 3-4. Comparison of Average Pollutant Loadings in the Evaluated Wastestreams to 

an Average POTW......................................................................................................... 3-18

Table 3-5. Estimated Number of POTW Equivalents for Total Pollutant Loadings from

the Evaluated Wastestreams .......................................................................................... 3-19

Table 3-6. Summary of Studies Evaluating Lethal Effects of Pollutants in Steam Electric 

Power Plant Wastewater ................................................................................................ 3-25

Table 3-7. Median Lethal Concentrations (LC50) for Pollutants in Steam Electric Power 

Plant Wastewater ........................................................................................................... 3-26

Table 3-8. Summary of Select Sites with Documented Surface Water Impacts from Steam

Electric Power Plant Wastewater................................................................................... 3-30

Table 3-9. Number and Percentage of Immediate Receiving Waters Identified as 

Sensitive Environments ................................................................................................. 3-38

Table 3-10. Pollutant Loadings to the Great Lakes Watershed from the Evaluated 

Wastestreams ................................................................................................................. 3-40

Table 3-11. Pollutant Loadings to the Chesapeake Bay Watershed from the Evaluated 

Wastestreams ................................................................................................................. 3-41

Table 3-12. Number and Percentage of Immediate Receiving Waters Classified as 

Impaired for a Pollutant Associated with the Evaluated Wastestreams ........................ 3-42

Table 3-13. Comparison of Number and Percentage of Steam Electric Power Plants 

Located within 5 Miles of a Drinking Water Resource ................................................. 3-47

Table 4-1. Steam Electric Power Plant Wastewater Environmental Pathways and Routes 

of Exposure Evaluated in the EA..................................................................................... 4-2

Table 4-2. Receiving Water Types for Steam Electric Power Plants Evaluated in the EA......... 4-3

Table 4-3. Exceedances of MCLs in Leachate Under Acidic, Neutral, and Basic 

Conditions........................................................................................................................ 4-9

Table 4-4. Range of Fly Ash and FGD Gypsum Total Content and Combustion Residual 

Leaching Test Results (Initial Screening Concentrations) for Trace Metals ................. 4-11

Table 5-1. Pollutants Considered for Analysis in the Immediate Receiving Water Model ......... 5-5

iv
List of Tables (Continued) 

List of Tables 

Page 

Table 6-1. Number and Percentage of Immediate Receiving Waters with Estimated 

Water Concentrations that Exceed the Water Quality Criteria at Baseline ..................... 6-2

Table 6-2. Number and Percentage of Immediate Receiving Waters That Exceed Wildlife 

Fish Consumption NEHCs for Minks and Eagles (by Waterbody Type) at 

Baseline............................................................................................................................ 6-4

Table 6-3. Number and Percentage of Immediate Receiving Waters That Exceed Wildlife 

Fish Consumption NEHCs for Minks and Eagles (by Pollutant) at Baseline .................. 6-5

Table 6-4. Number and Percentage of Immediate Receiving Waters with Sediment 

Pollutant Concentrations Exceeding CSCLs for Sediment Biota at Baseline ................. 6-7

Table 6-5. Number and Percentage of Immediate Receiving Waters That Exceed Human 

Health Evaluation Criteria (Lifetime Excess Cancer Risk) for Inorganic Arsenic at 

Baseline............................................................................................................................ 6-9

Table 6-6. Number and Percentage of Immediate Receiving Waters That Exceed NonCancer Oral Reference Dose Values at Baseline ........................................................... 6-10

Table 6-7. Number and Percentage of Immediate Receiving Waters That Exceed NonCancer Oral Reference Dose Values at Baseline by Pollutant ...................................... 6-11

Table 6-8. Comparison of T4 Fish Tissue Concentrations at Baseline to Fish Advisory 

Screening Values ........................................................................................................... 6-12

Table 6-9. Number and Percentage of Immediate Receiving Waters That Exceed Human 

Health Evaluation Criteria (Lifetime Excess Cancer Risk) for Inorganic Arsenic at 

Baseline, by Race or Hispanic Origin............................................................................ 6-13

Table 6-10. Number and Percentage of Immediate Receiving Waters That Exceed NonCancer Oral Reference Dose Values at Baseline, by Race or Hispanic Origin ............. 6-14

Table 7-1. Regulatory Options for the Wastestreams Evaluated in the EA................................. 7-2

Table 7-2. Description of Environmental Improvements Associated with the Final Rule .......... 7-3

Table 7-3. Steam Electric Power Generating Industry Pollutant Removals for Metals, 

Bioaccumulative Pollutants, Nutrients, Chlorides, and TDS Under Regulatory 

Options............................................................................................................................. 7-7

Table 7-4. Steam Electric Power Generating Industry TWPE Removals for Metals, 

Bioaccumulative Pollutants, Nutrients, Chlorides, and TDS Under Regulatory 

Options............................................................................................................................. 7-8

Table 7-5. Key Environmental Improvements Under the Regulatory Options ......................... 7-11

Table 7-6. Number of Immediate Receiving Waters with Sediment Pollutant 

Concentrations Exceeding CSCLs for Sediment Biota Under the Regulatory 

Options........................................................................................................................... 7-14

Table 7-7. Key Environmental Improvements for Arsenic Under the Regulatory Options ...... 7-17

Table 7-8. Key Environmental Improvements for Mercury Under the Regulatory Options ..... 7-20

v 
List of Tables (Continued) 

List of Tables 

Page 

Table 7-9. Key Environmental Improvements for Selenium Under the Regulatory 

Options........................................................................................................................... 7-23

Table 7-10. Key Environmental Improvements for Cadmium Under the Regulatory 

Options........................................................................................................................... 7-26

Table 7-11. Key Environmental Improvements for Thallium Under the Regulatory 

Options........................................................................................................................... 7-27

Table 7-12. Pollutant Removals to Impaired Waters by Impairment Type ............................... 7-29

Table 7-13. Pollutant Removals to the Great Lakes Watershed Under the Regulatory 

Options........................................................................................................................... 7-33

Table 7-14. Key Environmental Improvements for Downstream Waters Under the 

Regulatory Options ........................................................................................................ 7-35

Table 8-1. Locations Selected for Case Study Modeling ............................................................ 8-4

Table 8-2. Summary of Morrow Generating Site Operations .................................................... 8-15

Table 8-3. Summary of Plant Bowen Operations ...................................................................... 8-25

Table 8-4. Summary of Petersburg Generating Station Operations .......................................... 8-32

Table 8-5. Summary of Bruce Mansfield Operations ................................................................ 8-42

Table 8-6. Summary of W.H. Sammis Operations .................................................................... 8-42

Table 8-7. Summary of Rush Island Operations ........................................................................ 8-48

Table 8-8. Summary of Plant Harllee Branch Operations ......................................................... 8-53

vi
List of Figures 

List of Figures

Page 

Figure 2-1. Locations and Counts of Immediate Receiving Waters in EA Scope and 

Modeling Analyses .......................................................................................................... 2-5

Figure 3-1. Location of Plants that Directly Discharge the Evaluated Wastestreams to a 

Surface Water Impaired due to Mercury ....................................................................... 3-43

Figure 3-2. Location of Plants that Directly Discharge the Evaluated Wastestreams to a 

Surface Water Impaired due to Metals, Other than Mercury......................................... 3-43

Figure 3-3. Location of Plants that Directly Discharge the Evaluated Wastestreams to a 

Surface Water Impaired due to Nutrients ...................................................................... 3-44

Figure 3-4. Location of Plants that Directly Discharge to a Surface Water with a Fish

Consumption Advisory .................................................................................................. 3-45

Figure 5-1. Overview of IRW Model .......................................................................................... 5-3

Figure 5-2. Water Quality Module: Pollutant Fate in the Waterbody ......................................... 5-7

Figure 5-3. Flowchart of Selenium Ecological Risk Model ...................................................... 5-15

Figure 8-1. Overview of Case Study Modeling Locations .......................................................... 8-3

Figure 8-2. Black Creek WASP Modeling Area ....................................................................... 8-16

Figure 8-3. Etowah River WASP Modeling Area ..................................................................... 8-26

Figure 8-4. Lick Creek and White River WASP Modeling Area .............................................. 8-33

Figure 8-5. Ohio River WASP Modeling Area ......................................................................... 8-43

Figure 8-6. Mississippi River WASP Modeling Area ............................................................... 8-49

Figure 8-7. Lake Sinclair WASP and EDFC Modeling Area.................................................... 8-54

vii 
Acronyms

ACRONYMS 

ASTM American Society for Testing and Materials 

ATSDR Agency for Toxic Substances and Disease Registry

BAF Bioaccumulation factor

BASINS Better Assessment Science Integrating Point and Nonpoint Sources 

BAT Best Available Technology Economically Achievable 

BCF Bioconcentration factor 

BPT Best Practicable Control Technology Currently Available 

CBI Confidential business information 

CCR Coal combustion residuals 

CFR Code of Federal Regulations 

CSCL Chemical stressor concentration limit 

CSF Cancer slope factor 

CWA Clean Water Act 

DBP Disinfection by-products 

DCN Document control number 

DMR Discharge monitoring report 

DOE Department of Energy 

EA Environmental assessment 

EF Enrichment factors

EFDC Environmental Fluid Dynamics Code 

ELGs Effluent Limitations Guidelines and Standards 

EP Extraction procedure 

EPA U.S. Environmental Protection Agency 

ER Exposure-response 

ESA Endangered Species Act 

FGD Flue gas desulfurization 

FGMC Flue gas mercury control 

FR Federal Register 

FWS U.S. Fish and Wildlife Service

IRIS Integrated Risk Information System

IRW Immediate receiving water 

Kdsw Suspended sediment-surface water partition coefficient 

LADD Lifetime average daily dose 

lbs/yr Pounds per year 

LC50 Median lethal concentration

LECR Lifetime excess cancer risk 

viii 
 

 

Acronyms

MCL Maximum contaminant level 

MRL Minimal risk level 

MGD Million gallons per day 

mg/day Milligrams per day 

mg/kg Milligrams per kilogram 

mg/L Milligrams per liter

MW Megawatt 

MWh Megawatt-hour 

NEHC No effect hazard concentration

NHDPlus National Hydrography Dataset Plus 

NOAA National Oceanic and Atmospheric Administration 

NOAEL No-observed-adverse-effect level 

NPDES National Pollutant Discharge Elimination System

NRWQC National Recommended Water Quality Criteria

NSPS New Source Performance Standards 

NWIS National Water Information System 

ORCR Office of Resource Conservation and Recovery 

OSWER Office of Solid Waste and Emergency Response 

PCB Polychlorinated biphenyls 

POC Pollutant of concern 

POTW Publicly owned treatment works

ppm Parts per million

PSES Pretreatment Standards for Existing Sources 

PSNS Pretreatment Standards for New Sources 

RCRA Resource Conservation and Recovery Act 

RfD Reference dose 

RIA Regulatory impact analysis

RSEI Risk-Screening Environmental Indicators 

SDWA Safe Drinking Water Act 

SQuiRT Screening Quick Reference Table 

STORET EPA’s STOrage and RETrieval Data Warehouse 

T3 Trophic level 3 

T4 Trophic level 4 

TC Toxicity characteristic 

TCLP Toxicity characteristic leaching procedure 

TDD Technical Development Document 

TDS Total dissolved solids

TEL Threshold effects level 

ix
Acronyms

TMDL Total maximum daily load 

TOC Total organic carbon 

TRI Toxics Release Inventory 

TSS Total suspended solids

TTF Trophic transfer factor 

TTHM Total trihalomethanes 

TWF Toxic weighting factor 

TWPE Toxic weighted pound equivalent 

μg/g Micrograms per gram

μg/L Micrograms per liter 

USGS United States Geological Survey 

WASP Water Quality Analysis Simulation Program 

WHO World Health Organization 

WMA Wildlife Management Area 

WQI Water quality index 

x 
Glossary

GLOSSARY

Acute – having a sudden onset or lasting a short time. An acute stimulus is severe enough to 

induce a response rapidly. The word acute can be used to define either the exposure or the 

response to an exposure (effect). The duration of an acute aquatic toxicity test is generally 4 days 

or less and mortality is the response usually measured. 

Aquifer – an underground formation or group of formations in rocks and soils containing enough 

ground water to supply wells and springs. 

Benthic – pertaining to the bottom (bed) of a waterbody. 

Bioaccumulation – general term describing a process by which chemicals are taken up by an 

organism either directly from exposure to a contaminated medium or by consumption of food 

containing the chemical, resulting in a net accumulation of the chemical by an organism due to 

uptake from all routes of exposure. 

Bioavailability – the ability of a particular contaminant to be assimilated into the tissues of

exposed organisms. 

Biomagnification – result of the process of bioaccumulation and biotransfer by which tissue 

concentrations of chemicals in organisms at one trophic level exceed tissue concentrations in 

organisms at the next lower trophic level in a food chain. 

Bottom ash – the ash, including boiler slag, which settles in the furnace or is dislodged from 

furnace walls. Economizer ash is included when it is collected with bottom ash. 

Chronic – involving a stimulus that is lingering or continues for a long time; often signifies 

periods from several weeks to years, depending on the reproductive life cycle of the species. This

term can be used to define either the exposure or the response to an exposure (effect). Chronic 

exposures typically induce a biological response of relatively slow progress and long duration. 

Combustion residuals – solid wastes associated with combustion-related power plant processes, 

including fly and bottom ash from coal-, petroleum coke-, or oil-fired units; flue gas 

desulfurization (FGD) solids; flue gas mercury control wastes; and other wastewater treatment 

solids associated with steam electric power plant wastewater. In addition to the residuals that are 

associated with coal combustion, this also includes residuals associated with the combustion of 

other fossil fuels.

Combustion residual leachate – leachate from landfills or surface impoundments containing

combustion residuals. 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). Combustion residual leachate includes seepage and/or leakage from a combustion 

residual landfill or impoundment unit. Combustion residual leachate includes wastewater from 

landfills and surface impoundments located on non-adjoining property when under the 

operational control of the permitted facility.

xi
 

Glossary

Criterion continuous concentration – an estimate of the highest concentration of a material in 

surface water to which an aquatic community can be exposed indefinitely (chronic exposure) 

without resulting in an unacceptable effect.

Criterion maximum concentration – an estimate of the highest concentration of a material in

surface water to which an aquatic community can be exposed briefly (acute exposure) without 

resulting in an unacceptable effect.

Direct discharge – (a) Any addition of any “pollutant” or combination of pollutants to “waters of 

the United States” from any “point source,” or (b) any addition of any pollutant or combination 

of pollutant to waters of the “contiguous zone” or the ocean from any point source other than a 

vessel or other floating craft which is being used as a means of transportation. This definition

includes additions of pollutants into waters of the United States from: surface runoff which is 

collected or channeled by man; discharges though pipes, sewers, or other conveyances owned by 

a State, municipality, or other person which do not lead to a treatment works; and discharges 

through pipes, sewers, or other conveyances, leading into privately owned treatment works. This 

term does not include an addition of pollutants by any “indirect discharger.” 

Edema – swelling caused by fluid in body tissues. 

Effluent limitation – under Clean Water Act (CWA) section 502(11), any restriction, including 

schedules of compliance, established by a state or the Administrator on quantities, rates, and 

concentrations of chemical, physical, biological, and other constituents which are discharged 

from point sources into navigable waters, the waters of the contiguous zone, or the ocean, 

including schedules of compliance. 

Evaluated wastestreams – subset of steam electric power plant wastewaters evaluated in the 

environmental assessment (EA) and Benefits and Cost Analysis that includes FGD wastewater, 

fly ash transport water, bottom ash transport water, and combustion residual leachate collected

from landfills or surface impoundments. 

Exposure – the contact or co-occurrence of a stressor with a receptor.

Flue gas desulfurization (FGD) wastewater – wastewater generated specifically from the wet

FGD scrubber system that comes into contact with the flue gas or the FGD solids, including but 

not limited to, the blowdown or purge from the FGD scrubber system, overflow or underflow 

from the solids separation process, FGD solids wash water, and the filtrate from the solids 

dewatering process. Wastewater generated from cleaning the FGD scrubber, cleaning FGD 

solids separation equipment, cleaning the FGD solids dewatering equipment, or that is collected

in floor drains in the FGD process area is not considered FGD wastewater.

Flue gas mercury control (FGMC) wastewater – wastewater generated from an air pollution

control system installed or operated for the purpose of removing mercury from flue gas. This 

includes fly ash collection systems when the particulate control system follows sorbent injection

or other controls to remove mercury from flue gas. FGD wastewater generated at plants using 

oxidizing agents to remove mercury in the FGD system and not in a separate FGMC system is 

not included in this definition. 

xii 
Glossary

Fly ash – the ash that is carried out of the furnace by a gas stream and collected by a capture 

device such as a mechanical precipitator, electrostatic precipitator, and/or fabric filter. 

Economizer ash is included in this definition when it is collected with fly ash. Ash is not 

included in this definition when it is collected in wet scrubber air pollution control systems 

whose primary purpose is particulate removal. 

Gasification wastewater – any wastewater generated at an integrated gasification combined cycle 

operation from the gasifier or the syngas cleaning, combustion, and cooling processes. 

Gasification wastewater includes, but is not limited to the following: sour/grey water; CO2/steam 

stripper wastewater; sulfur recovery unit blowdown, and wastewater resulting from slag handling 

or fly ash handling, particulate removal, halogen removal, or trace organic removal. Air

separation unit blowdown, noncontact cooling water, and runoff from fuel and/or byproduct piles 

are not considered gasification wastewater. Wastewater that is collected intermittently in floor

drains in the gasification process areas from leaks, spills and cleaning occurring during normal

operation of the gasification operation is not considered gasification wastewater.

Ground water – water that is found in the saturated part of the ground underneath the land 

surface.

Hematological – pertaining to or emanating from blood cells. 

Histopathological – pertaining to tissue changes. 

Immediate receiving water – the segment of a receiving water where discharges from a point 

source enter the surface water. The segment is defined by the hydrographic dataset supporting 

the analysis (e.g., National Hydrography Dataset Plus, Version 1). 

Impaired waters – a surface water is classified as a 303(d) impaired water when pollutant 

concentrations exceed water quality standards and the surface water can no longer meet its

designated uses (e.g., drinking, recreation, and aquatic habitat). 

Indirect discharge – wastewater discharged or otherwise introduced to a publicly owned 

treatment works (POTW). 

Invertebrates – animals without a backbone or spinal column; macroinvertebrates are 

invertebrates that can be seen without a microscope (macro), such as aquatic insects, worms, 

clams, snails, and crustaceans.

Landfill – a disposal facility or part of a facility where solid waste, sludges, or other process 

residuals are placed in or on any natural or manmade formation in the earth for disposal and

which is not a storage pile, a land treatment facility, a surface impoundment, an underground 

injection well, a salt dome or salt bed formation, an underground mine, a cave, or a corrective

action management unit. 

Leachate – see combustion residual leachate. 

Lentic – pertaining to still or slow-moving water, such as lakes or ponds. 

xiii 
Glossary

Lethal – causing death by direct action. 

Lotic – pertaining to flowing water, such as streams and rivers. 

Median lethal concentration (LC50) – a statistically or graphically estimated concentration that is

expected to be lethal to 50 percent of a group of organisms under specified conditions. 

Mortality – death rate or proportion of deaths in a population. 

Partition coefficient – the ratio of a pollutant concentration in one medium compared to another 

(e.g., dissolved in the water column, sorbed to suspended sediment, and sorbed to benthic 

sediment in a receiving water). 

Piscivorous – habitually feeds on fish. 

Plant-receiving water – the combination of a steam electric power plant and the immediate

receiving water into which evaluated wastestreams are discharged from that plant. 

Point source – any discernable, confined, and discrete conveyance, including but not limited to, 

any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock,

concentrated animal feeding operation, or vessel or other floating craft from which pollutants are

or may be discharged. The term does not include agricultural stormwater discharges or return 

flows from irrigated agriculture. See CWA section 502(14), 33 U.S.C. 1362(14); 40 CFR §122.2. 

Population – an aggregate of individuals of a species within a specified location in space and 

time. 

Publicly owned treatment works (POTW) – any device or system, owned by a state or 

municipality, used in the treatment (including recycling and reclamation) of municipal sewage or 

industrial wastes of a liquid nature that is owned by a state or municipality. This includes sewers, 

pipes, or other conveyances only if they convey wastewater to a POTW providing treatment. See

CWA section 212, 33 U.S.C. 1292; 40 CFR §§122.2, 403.3. 

Receptor – the ecological or human entity exposed to a stressor. 

Receiving water – surface waters into which treated waste or untreated waste are discharged,

including those portions of the surface water downstream from the point source. 

Sediment – particulate material lying below water.

Sensitivity – in relation to toxic substances, organisms that are more sensitive exhibit adverse 

(toxic) effects at lower exposure levels than organisms that are less sensitive. 

Steam electric power plant wastewater – wastewaters associated with or resulting from the 

combustion process, including ash transport water from coal-, petroleum coke-, or oil-fired units; 

air pollution control wastewater (e.g., FGD wastewater, FGMC wastewater, carbon capture 

wastewater); and leachate from landfills or surface impoundments containing combustion

residuals. 

xiv
 

Glossary

Stressor – any physical, chemical, or biological entity that can induce an adverse response. 

Sublethal – below the concentration that directly causes death. Exposure to sublethal 

concentrations of a substance can produce effects on behavior, biochemical, and/or physiological 

functions, and the structure of cells and tissues in organisms. 

Surface water – all waters of the United States, including rivers, streams, lakes, reservoirs, and 

seas.

Teratogenic – able to disturb the growth and development of an embryo or fetus. 

Transport water – any wastewater that is used to convey fly ash, bottom ash, or economizer ash 

from the ash collection or storage equipment, or boiler, and has direct contact with the ash. 

Transport water does not include low volume, short duration discharges of wastewater from

minor leaks (e.g., leaks from valve packing, pipe flanges, or piping) or minor maintenance events 

(e.g., replacement of valves or pipe sections). 

Trophic level – position of an organism in the food chain.

Toxic pollutants – as identified under the CWA, 65 pollutants and classes of pollutants, of which 

126 specific substances have been designated priority toxic pollutants. See Appendix A to 40 

CFR §423. 

xv
 

 

 

 

 

 

Section 1—Introduction

SECTION 1

INTRODUCTION 

The U.S. Environmental Protection Agency (EPA) is promulgating revised effluent 

limitations guidelines and standards (ELGs) for the Steam Electric Power Generating Point 

Source Category (40 CFR 423). In support of the development of the final rule, EPA conducted 

an environmental assessment (EA) to evaluate the environmental impact of pollutant loadings 

released under current (i.e., baseline) discharge practices and assess the potential environmental 

improvement from pollutant loading removals under the final rule.1

Based on evidence in the literature, documented damage cases, and modeled receiving 

water pollutant concentrations, it is clear that current steam electric power plant wastewater

discharge practices impact the water quality in receiving waters, impact the wildlife in the 

surrounding environments, and pose a human health threat to nearby communities. Substantial 

evidence exists that metals (e.g., arsenic, cadmium, mercury, selenium) from steam electric 

power plant wastewater discharges transfer from the aquatic environment to terrestrial food 

webs, indicating a potential for broader impacts to ecological systems by altering population 

diversity and community dynamics in the areas surrounding steam electric power plants. 

Ecosystem recovery from exposure to pollutants in power plant wastewater discharges 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 discharge wastewater, which contains numerous pollutants,2

into waterbodies used for recreation and can present a threat to human health. Due to steam

electric power plant wastewater discharges, fish advisories have been issued to protect the public

from exposure to fish with elevated pollutant concentrations. Leaching of pollutants from surface 

impoundments and landfills containing combustion residuals is known to impact off-site ground 

water and drinking water wells at concentrations above maximum contaminant level (MCL) 

drinking water standards, posing a threat to human health.3

In this report, EPA uses the term “steam electric power plant wastewater” to represent all 

combustion-related wastewaters that contain pollutants covered by the revised steam electric 

ELGs. For the EA, EPA evaluated only a subset of the wastestreams: flue gas desulfurization 

(FGD) wastewater, fly ash transport water, bottom ash transport water, and combustion residual 

1

 The Clean Water Act does not require that EPA assess the water-related environmental impacts, or the benefits, of 

its ELGs, and EPA did not make its decision on the final steam electric ELGs based on the expected benefits of the 

rule. EPA does, however, inform itself of the benefits of its rule, as required by Executive Order 12866. See the

Benefits and Cost Analysis for the Effluent Limitations Guidelines and Standards for the Steam Electric Power 

Generation Point Source Category (EPA-821-R-15-005).

2

 The steam electric ELGs control the discharge of pollutants to surface waters and do not specifically regulate 

“wastewater.” To allow for more concise discussion in this EA report, EPA occasionally refers to “wastewater” 

discharges and impacts without specifically referencing the pollutants in the wastewater discharges. 3

 In this EA, EPA evaluated the threats to human health and the environment associated with pollutants leaching into 

ground water from surface impoundments and landfills containing combustion residuals. If these leached pollutants 

do not constitute the discharge of a pollutant to surface waters, then they are not controlled under the steam electric

ELGs. While the Coal Combustion Residuals (CCR) rulemaking is the major controlling action for these pollutant

releases to ground water, the ELGs could indirectly reduce impacts to ground water. These secondary improvements 

are discussed in Section 7.8.

1-1 
 

 

Section 1—Introduction

leachate collected from landfills or surface impoundments). The goal of the EA was to answer 

the following five questions regarding pollutant loadings from the evaluated wastestreams: 

 What are the environmental concerns under current (i.e., baseline) discharge 

practices? 

 What are the environmental and exposure pathways for steam electric power plant 

wastewater discharges to impact water quality, wildlife, and human health? 

 What are the baseline environmental impacts to water quality and wildlife? 

 What are the impacts to human health from baseline discharges? 

 What are the potential improvements to water quality, wildlife, and human health 

under the final rule? 

The EA evaluated environmental concerns and potential exposures (wildlife and humans) 

to pollutants commonly found in wastewater discharges from steam electric power plants. EPA 

completed both qualitative and quantitative analyses. Qualitative analyses included reviewing 

documented site impacts in literature and damage cases; assessing the pollutant loadings to 

receiving waters and sensitive environments; and reviewing the effects of pollutant exposure on 

ecological and human receptors. To quantify baseline impacts and improvements under the final 

rule, EPA developed computer models to determine pollutant concentrations in the immediate 

and downstream receiving waters, pollutant concentrations in fish tissue, and exposure doses to 

ecological and human receptors from fish consumption. EPA compared the values calculated by

the models to benchmarks to determine the extent of the environmental impacts nationwide. EPA 

also developed a model to determine the risk of reproductive impacts among fish and waterfowl 

that have been exposed, via their diet, to selenium from steam electric power plant wastewater 

discharges. 

This report presents the methodology and results of the qualitative and quantitative

analyses performed to evaluate baseline discharges from steam electric power plants and

improvements under the final rule. The analyses presented in this report incorporate some

adjustments to current conditions in the industry. For example, these analyses account for

publicly announced plans from the steam electric power generating industry to retire or modify 

steam electric generating units at specific power plants. These analyses also account for changes 

to the industry that are expected to occur as a result of the recent CCR rulemaking by EPA’s 

Office of Solid Waste and Emergency Response (OSWER). These analyses, however, do not 

reflect changes in the industry that may occur as a result of the Clean Power Plan [Clean Air Act 

Section 111(d)].4

In addition to the EA, the final steam electric ELGs are supported by a number of reports 

including: 

Regulatory Impact Analysis for Effluent Limitations Guidelines and Standards for the 

Steam Electric Power Generation Point Source Category, Document No. EPA-821-R-15-004. 

This report presents a profile of the steam electric power generating industry, a summary of the 

4

 EPA completed a parallel set of quantitative EA analyses that reflect changes in the industry that may occur as a 

result of the Clean Power Plan. Appendix I provides the results of those analyses. 

1-2 
Section 1—Introduction

costs and impacts associated with the regulatory options, and an assessment of the final rule’s

impact on employment and small businesses. 

Benefits and Cost Analysis for the Effluent Limitations Guidelines and Standards for the 

Steam Electric Power Generation Point Source Category (Benefits and Cost Analysis),

Document No. EPA-821-R-15-005. This report summarizes the monetary benefits and societal 

costs that result from implementation of the final rule.

Technical Development Document for Effluent Limitations Guidelines and Standards for 

the Steam Electric Power Generating Point Source Category (TDD), Document No. EPA-821­

R-15-007. This report includes background on the final rule; applicability and summary of the

final rule; industry description; wastewater characterization and identification of pollutants of 

concern; treatment technologies and pollution prevention techniques; and documentation of 

EPA’s engineering analyses to support the final rule including cost estimates, pollutant loadings, 

and non-water-quality impact assessment. 

These reports are available in the public record for the final rule and on EPA’s website at 

http://water.epa.gov/scitech/wastetech/guide/steam_index.cfm. 

The ELGs for the Steam Electric Power Generating Point Source Category are based on 

data generated or obtained in accordance with EPA’s Quality Policy and Information Quality

Guidelines. EPA’s quality assurance and quality control activities for this rulemaking include the

development, approval, and implementation of Quality Assurance Project Plans for using 

environmental data generated or collected from all sampling and analyses, existing databases, 

and literature searches, and for developing any models that used environmental data. Unless

otherwise stated within this document, EPA evaluated the data used and associated data analyses 

as described in these quality assurance documents to ensure they are of known and documented 

quality, meet EPA's requirements for objectivity, integrity, and utility, and are appropriate for the 

intended use. 

1-3 
 

 

Section 2—Background and Scope

SECTION 2

BACKGROUND AND SCOPE 

Many steam electric power plants use large 

surface impoundments to store and treat

wastewaters. These impoundments are

hydrologically connected to surface and

ground water. 

The final steam electric effluent limitations guidelines and standards (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 utilizing 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 final rule applies to discharges associated with both the 

combustion turbine and steam turbine portions of a combined cycle generating unit (see 40 CFR 

423.10). EPA is revising or establishing best available technology economically achievable 

(BAT) limitations, new source performance standards (NSPS), pretreatment standards for

existing sources (PSES), and pretreatment standards for new sources (PSNS) that apply to certain 

discharges of seven wastestreams: flue gas desulfurization (FGD) wastewater, fly ash transport 

water, bottom ash transport water, combustion residual leachate, flue gas mercury control 

(FGMC) wastewater, gasification wastewater, and nonchemical metal cleaning wastes. See the 

Technical Development Document (TDD)

(EPA-821-R-15-007) for more information on

the rule applicability and definitions, industry 

description, wastestreams and pollutants of 

concern, treatment technologies, baseline and 

regulatory option pollutant loadings, costs of

implementing treatment technologies, and 

revised standards. 

As discussed in Section 1, EPA uses 

the term “steam electric power plant 

wastewater” to represent all combustionrelated wastewaters covered by the revised 

steam electric ELGs. For the environmental 

assessment (EA), EPA evaluated only a subset 

of the wastestreams (see Table 2-1 below).5

“Combustion residuals” are the solid wastes 

associated with combustion-related power

plant processes, including fly and bottom ash;

FGD solids; FGMC wastes; and other wastewater treatment solids associated with steam electric 

power plant wastewater. Steam electric power plants generate solid residuals from fuel 

combustion and from emission control technologies. These solid residuals include fly ash, 

bottom ash, and FGD solids. Plants remove these solid materials through both wet and dry 

handling methods. Dry handling typically involves transferring the solids to a storage silo or 

outdoor storage pile, to be either disposed of in a landfill or, depending on the particular residual, 

5

 EPA evaluated technology options associated with FGMC wastewater, gasification wastewater, and nonchemical 

metal cleaning wastes as part of the regulatory options. However, no plants currently discharge FGMC wastewater, 

all existing gasification plants are operating the technology used as the basis for the regulatory option, and EPA will

continue to reserve BAT/NSPS/PSES/PSNS for nonchemical metal cleaning wastes, as previously established 

regulations do. Therefore, EPA estimated zero compliance costs and zero pollutant reductions associated with these

wastestreams and did not include these three wastestreams in the EA. 

2-1 
 

 

Section 2—Background and Scope

used to create beneficial by-products such as wallboard or cement. However, many plants use 

wet handling systems, which transport the wastes to a surface impoundment (e.g., ash pond) 

using large quantities of water. For example, in wet systems, bottom ash collects at the bottom of 

the boiler in a water bath, and the water containing the bottom ash is then typically transported to

a surface impoundment for storage and/or disposal. Fly ash may be handled similarly after it is 

collected from the particulate collection system. The slurry stream exiting wet FGD systems, 

which contains 10 to 20 percent FGD solids, is typically treated either in a surface impoundment

or in an advanced wastewater treatment system, then discharged to a receiving stream or reused 

in other plant processes. Section 6 of the TDD describes the industry wastestreams in detail. 

Table 2-1 lists the specific wastestreams evaluated in the EA.

Table 2-1. Steam Electric Power Plant Wastestreams Evaluated in the EA 

Evaluated Wastestream Description 

Fly ash transport water Water used to convey the fly ash particles removed from the flue gas via a collection

system. 

Untreated ash transport waters contain significant concentrations of total suspended 

solids (TSS) and metals, including arsenic, calcium, and titanium (see Section 6 of

the TDD for further details). The effluent from surface impoundments generally

contains low concentrations of TSS; however, metals are still present in the 

wastewater, predominantly in dissolved form. 

Bottom ash transport water Water used to convey the bottom ash particles collected at the bottom of the boiler. 

As noted above, untreated ash transport waters contain significant concentrations of 

TSS and metals. 

FGD wastewater Wastewater generated from a wet FGD scrubber system. Wet FGD systems are used

to control sulfur dioxide (SO2) emissions from the flue gas generated in the plant’s 

boiler. 

The pollutant concentrations in FGD wastewater vary from plant to plant depending

on the coal type, the sorbent used, the materials of construction in 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 significant concentrations of chlorides, total dissolved solids (TDS), 

nutrients, and metals, including bioaccumulative pollutants such as arsenic, mercury, 

and selenium (see Section 6 of the TDD for further details).

Combustion residual

leachate 

Collected liquid that has percolated through or drains from a landfill or a surface 

impoundment, where the steam electric power plant disposes of or stores a variety of 

wastes from the combustion process. 

Leachate contains high concentration of metals, such as boron, calcium, chloride, 

and sodium, similar to FGD wastewaters and ash transport water. The metal 

concentrations in the leachate are generally lower than those in FGD wastewater and 

ash transport water (see Section 6 of the TDD for further details). 

2-2 
 

 

Section 2—Background and Scope

Surface impoundments accumulate high 

concentrations of toxic pollutants from fly ash 

transport water, bottom ash transport water, 

and FGD wastewater. 

Surface impoundments act as a physical 

treatment process to remove particulate

material from wastewater through gravitational 

settling. The wastewater in surface 

impoundments can include one specific type of 

wastewater (e.g., fly ash transport water) or a 

combination of wastewaters (e.g., fly ash 

transport water and FGD wastewater).

Additionally, plants may transfer wastewater

streams from other operations into their on-site

impoundments (e.g., cooling tower blowdown 

or metal cleaning wastes). The wastestreams

sent to surface impoundments can also include 

coal pile runoff. Although coal pile runoff is 

not the result of a combustion process, it can 

contain many of the pollutants present in steam 

electric power plant wastewater. Leachate or

seepage may occur from surface impoundments or landfills containing combustion residuals.6

Regardless of whether they use surface impoundments or an advanced treatment system, steam 

electric power plants typically discharge wastewater into the natural environment where 

numerous studies have raised concern regarding the toxicity of these wastestreams [ERG, 2013a;

NRC, 2006; Rowe et al., 2002; U.S. EPA, 2014a through 2014e]. Previous regulations at 40 CFR 

423 control pH and polychlorinated biphenyls (PCBs) discharge from all wastestreams and TSS

and oil and grease from ash transport waters and other “low volume wastes” that include air 

pollution control wastewater (see Section 1 of the TDD). Section 6 of the TDD discusses 

wastewater characterization and selection of pollutants of concern. 

Based on data EPA obtained from the 2010 Questionnaire for the Steam Electric Power

Generating Effluent Guidelines (Steam Electric Survey), EPA estimates that 1,079 steam electric 

power plants are subject to the final rule (see Section 4 of the TDD). EPA limited the scope of 

the EA to those plants that both 1) discharge directly to surface waters and 2) will reduce their 

pollutant loadings as a result of the regulatory options evaluated, based on EPA projections. 

Therefore, the EA scope excludes steam electric power plants that meet any of the following 

criteria: 

 Plants that do not discharge any of the wastestreams that are included in the final rule 

(even if the plant does generate and reuse the wastestream without discharging to 

surface waters).

 Plants that already comply with final rule or have plans to comply with the final rule 

prior to the date when the plants would have to meet the new limitations and 

standards.

6

 In this EA, EPA evaluated the threats to human health and the environment associated with pollutants leaching into 

ground water from surface impoundments and landfills containing combustion residuals. If these leached pollutants 

do not constitute the discharge of a pollutant to surface waters, then they are not controlled under the steam electric

ELGs. While the CCR rulemaking is the major controlling action for these pollutant releases to ground water, the 

ELGs could indirectly reduce impacts to ground water. These secondary improvements are discussed in Section 7.8.

2-3 
 

Section 2—Background and Scope

 Plants that that have announced plans to retire steam generating units (that would 

otherwise be subject to the final rule) prior to the date that the plants would have to 

meet the new limitations and standards.

 Plants that, based on EPA projections, will either convert to dry ash handling or

install tank-based FGD wastewater treatment systems to comply with the CCR 

rulemaking. 

 Plants that discharge only to publicly owned treatment works (POTWs). 

In the EA, EPA evaluated the current impact and potential improvement to the 

environment and human health from 195 plants that discharge directly to surface waters and that 

EPA projects will reduce pollutant loadings as a result of the regulatory options evaluated. Table 

2-2 presents the number of plants by discharge type (direct or indirect) included in the cost and

loadings analysis presented in Sections 9 and 10 of the TDD. 

Table 2-2. Number of Plants Evaluated in the EA

Plant Description 

Number of 

Plants

Number of Plants in Scope of Final Rule

Plants that fall under the applicability of the final rule (40 CFR 423) 1,079 

Cost and Loadings Analysis

Plants for which EPA calculated loadings in the cost and loadings analyses 

(see Sections 9 and 10 of the TDD) 

202 

Plants that discharge only to surface waters (direct discharger) 191 

Plants that discharge only to a POTW (indirect discharger) 7 

Plants that discharge to surface waters and to a POTW (direct and indirect discharger) 4 

Environmental Assessment

Plants evaluated in the EA (includes all direct dischargers)a

 195 

a – For the pollutant loadings and removals presented in this report, EPA included indirect dischargers to protect

confidential business information.

These 195 steam electric power plants discharge to the 222 immediate receiving waters 

illustrated in Figure 2-1 (some plants discharge to multiple receiving waters). The EA includes

qualitative analysis of the pollutant loadings in evaluated wastestreams discharged from these 

plants and the associated potential for environmental and human health impacts. As discussed in

Section 5, EPA developed and executed a national-scale immediate receiving water (IRW)

model to perform further quantitative modeling of the water quality, wildlife, and human health 

impacts associated with discharges from the majority of these plants. The IRW model, which 

excludes discharges to the Great Lakes and estuaries, encompasses 188 steam electric power 

plants that discharge to 209 immediate receiving waters. As discussed in Section 8, EPA also 

performed more detailed case study modeling of discharges from six steam electric power plants. 

Figure 2-1 indicates the immediate receiving waters included in the IRW modeling and case 

study modeling scopes. 

2-4 
Figure 2-1. Locations and Counts of Immediate Receiving Waters in EA Scope and Modeling Ana

Section 

2-5 
Section 2—Background and Scope

EPA used the results from quantitative and qualitative assessments combined with the 

literature review to evaluate and describe the environmental impacts caused by the discharge of

the evaluated wastestreams. EPA organized the remainder of this report into the following

sections: 

 Section 3 describes the environmental concerns associated with the evaluated 

wastestreams, including a discussion of the pollutants of concern and a review of 

damage cases and other documented site impacts showing negative impacts to surface 

water and ground water. 

 Section 4 outlines how ecological and human receptors may be exposed to pollutants 

(i.e., environmental pathways), describes the factors that control environmental 

impacts for each pathway, and gives an overview of the methodology used to 

quantitatively evaluate the environmental and human health impacts. 

 Section 5 presents the modeling performed to support the EA including an overview 

of the national-scale IRW model and the ecological risk model.

 Section 6 presents the environmental and human health impacts based on qualitative 

review and quantitative assessments (modeling of plant-specific discharges) of 

current (baseline) discharges.

 Section 7 presents the improvements to the environment and human health estimated 

from the implementation of the regulatory options. 

 Section 8 describes EPA’s case study modeling of discharges from six steam electric 

power plants, presents the environmental and human health impacts under baseline 

conditions, and discusses the modeled improvements under the final rule. 

 Section 9 presents EPA’s conclusions on the environmental and human health 

improvements estimated under the final rule. 

2-6 
 

 

 

Section 3—Environmental And Human Health Concerns

SECTION 3

ENVIRONMENTAL AND HUMAN HEALTH CONCERNS 

Current scientific literature indicates that steam electric power plant wastewater is not a 

benign waste [NRC, 2006; Rowe et al., 2002]. Many of the common pollutants (e.g., selenium, 

mercury, and arsenic) found in the evaluated wastestreams (i.e., fly ash and bottom ash transport 

water, flue gas desulfurization (FGD) wastewater, and combustion residual leachate) present an 

increased ecological threat due to their tendency to persist in the environment and bioaccumulate 

in organisms. This often results in slow ecological recovery times following exposure. The toxic

impacts of steam electric power plant wastewater discharges on surface waters have been well 

documented in studies of over 30 aquatic ecosystems receiving discharges from steam electric 

power plants.7

Documented exceedances of drinking water maximum contaminant levels (MCLs) 

downstream of steam electric power plants and the issuance of fish advisories in receiving waters

indicate an ongoing human health concern caused by steam electric power plant wastewater 

discharges. EPA identified more than 30 documented cases where ground water contamination 

from surface impoundments extended beyond the plant boundaries, illustrating the threat to 

ground water drinking water sources [ERG, 2015m].8

 In other damage cases, EPA documented 

locations where selenium in power plant wastewater discharges resulted in fish consumption 

advisories being issued for surface waters.

The pollutants commonly discharged in the evaluated wastestreams cause environmental 

harm by contaminating surface water and ground water (e.g., selenium concentrations from 

steam electric power plants have resulted in fish kills). After being released into the environment, 

pollutants can reside for a long time in the receiving waters, bioaccumulating and binding with 

the sediment. There is documented evidence of slow ecological recovery as a result of these 

pollutant discharges. Steam electric power plants also discharge to sensitive environments (e.g., 

impaired waters, waters under a fish consumption advisory, Great Lakes, valuable estuaries, and 

drinking water sources). Some impacts might not be realized for years due to the persistent and

bioaccumulative nature of the pollutants released. Based on EPA’s calculated baseline pollutant

loadings, the total amount of toxic pollutants currently being released in wastewater discharges 

from steam electric power plants is significant and raises concerns regarding the long-term

impacts to aquatic organisms, wildlife, and humans that are exposed to these pollutants. For 

details on the pollutant loadings analysis, see Section 10 of the Technical Development 

Document (TDD) (EPA-821-R-15-007). 

This section details environmental concerns associated with wastewater discharges from

steam electric power plants including changes in surface water quality and sediment 

contamination levels; changes in ground water quality and potential contamination of private 

7

 Sources include ATSDR, 1998a, 1998b and 1998c; Charlotte Observer, 2010; DOE, 1992; EIP, 2010a and 2010b;

Roe et al., 2005; Sorensen et al., 1983; Sorensen, 1988; Specht et al., 1984; and Vengosh et al., 2009. 

8

 In this EA, EPA evaluated the threats to human health and the environment associated with pollutants leaching into 

ground water from surface impoundments and landfills containing combustion residuals. If these leached pollutants 

do not constitute the discharge of a pollutant to surface waters, then they are not controlled under the steam electric

ELGs. While the Coal Combustion Residuals (CCR) rulemaking is the major controlling action for these pollutant

releases to ground water, the ELGs could indirectly reduce impacts to ground water. These secondary improvements 

are discussed in Section 7.8.

3-1
Section 3—Environmental And Human Health Concerns

drinking water wells; bioaccumulation of contaminants in fish and aquatic life, fish eaten by 

piscivorous wildlife (i.e., fish-eating wildlife), and fish eaten by humans; and toxic effects on 

fish and aquatic life. The section is organized into the following subsections: 

 Section 3.1: Types of pollutants discharged in steam electric power plant wastewater.

 Section 3.2: Pollutant loadings associated with steam electric power plant wastewater.

 Section 3.3: Environmental impacts from steam electric power plant wastewater, 

including ecological impacts, human health effects, damage cases and other 

documented site impacts, and potential for impacts to occur in other locations. 

 Section 3.4: Sensitive environments, including pollutant loadings to the Great Lakes 

and Chesapeake Bay watersheds, impaired waters, waters issued fish advisories, 

threatened and endangered species habitats, and drinking water resources. 

 Section 3.5: Long recovery times. 

3.1 TYPES OF POLLUTANTS DISCHARGED IN STEAM ELECTRIC POWER PLANT

WASTEWATER 

This section provides an overview of the pollutants in steam electric power plant 

wastewater discharges that are frequently cited as affecting local wildlife or pose a threat to

human health. A number of variables can affect the composition of steam electric power plant 

wastewater, including fuel composition, type of combustion process, air pollution control 

technologies implemented, and management techniques used to dispose of the wastewater 

[Carlson and Adriano, 1993]. In addition, commingling steam electric power plant wastewater 

with other wastestreams from the plant in surface impoundments can result in a chemically 

complex effluent that is released to the environment [Rowe et al., 2002]. To identify pollutants 

of concern for the final rule, EPA used the following sources of wastewater characterization

data: EPA’s field sampling program; data supplied by industry or members of the public (e.g., in

questionnaire responses and public comments on the proposed rule); and various literature 

sources (see Section 6 of the TDD and the preamble to the final rule for further details on 

pollutants of concern). Pollutants such as metals, nutrients, and total dissolved solids (TDS), 

including chloride and bromides, are the common pollutants found in steam electric power plant 

wastewater that have been associated with documented environmental impacts or could have the

potential to cause environmental impacts based on the loadings and concentrations present in the

evaluated wastestreams. 

3.1.1 Metals and Toxic Bioaccumulative Pollutants

Studies commonly cite metals and toxic bioaccumulative pollutants (e.g., mercury and 

selenium) as the primary cause of ecological damage following exposure to steam electric power 

plant wastewater [Rowe et al., 1996; Lemly, 1997a; Hopkins et al., 2000; Rowe et al., 2002] (see 

Section 3.3.1). An important consideration in evaluating these pollutants is their bioavailability– 

the ability of a particular contaminant to be assimilated into the tissues of exposed organisms. A 

pollutant’s bioavailability is affected by the characteristics of both the pollutant and surrounding 

environment (e.g., temperature, pH, salinity, oxidation-reduction (redox) potential, total organic

content, suspended particulate content, and water velocity). 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 

3-2
 

 

 

 

 

 

 

Section 3—Environmental And Human Health Concerns

materials (e.g., clays and humic matter) found in sediments [U.S. EPA, 2007a]. Pollutants that 

precipitate out of solution can become concentrated in the sediments of a waterbody. Regardless, 

organisms will bioaccumulate pollutants either by consuming pollutant-enriched sediments and 

suspended particles, and/or by filtering ambient water containing dissolved pollutants. 

Table 3-1 lists some of the common metals and toxic bioaccumulative pollutants found in 

steam electric power plant wastewater that have been associated with documented health and 

environmental impacts or could potentially cause health and environmental impacts based on the 

loadings and concentrations present in the wastewater. Table 3-1 is intended to highlight the 

pollutants of concern in steam electric power plant wastewater that are associated with health and

environmental impacts; it does not include all pollutants that may cause adverse impacts. 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, EPA sampling data 

collected for FGD wastewater in support of the steam electric ELGs shows 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. The remainder of the section provides additional 

details on several key metals included in the environmental assessment (EA). 

Table 3-1. Key Metals and Toxic Bioaccumulative Pollutants Found In Steam Electric 

Power Plant Wastewater 

Pollutant Examples of Potential Health and Environmental Concerns

Aluminum Aluminum contamination can lead to the inability of fish to maintain the balance of their fluids and

is associated with damage to amphibian eggs and larvae, mostly in areas under acid stress. Human 

exposure to high concentrations has been linked to Alzheimer’s disease.

Arsenic a Arsenic contamination causes liver poisoning, developmental abnormalities, behavioral

impairments, metabolic failure, reduced growth, and appetite loss in fish and is associated with an

increased risk of the liver and bladder cancer in humans. Arsenic is also a potent endocrine 

disruptor at low, environmentally relevant levels. Non-cancer impacts to humans can include 

dermal, cardiovascular, and respiratory effects. Negative impacts can occur both after high-dose

exposure and repeated lower-dose exposures. Chronic exposure via drinking water has been 

associated with excess incidence of miscarriages, stillbirths, preterm births, and low-birth weights. 

Boron Boron can be toxic to vegetation and to wildlife at certain water concentrations and dietary levels. 

Human exposure to high concentrations can cause nausea, vomiting, and diarrhea.

Cadmium Cadmium contamination can lead to developmental impairments in wildlife and skeletal 

malformations in fish. Human exposure to high concentrations in drinking water and food can 

irritate the stomach, leading to vomiting and diarrhea, and sometimes death. Chronic oral exposure 

via diet or drinking water to lower concentrations can lead to kidney damage and weakened bones.

Chromium b Chromium is not known to bioaccumulate in fish; however, high concentrations of chromium can 

damage gills, reduce growth, and alter metabolism in fish. Human exposure to high concentrations

can cause gastrointestinal bleeding and lung problems.

Copper Copper contamination can lead to reproductive failure, gill damage, and reduced sense of smell in

fish. Human exposure to high concentrations can cause nausea, vomiting, diarrhea, and liver and

kidney damage. 

Iron Iron contamination can reduce growth, increase susceptibility to injury and disease, and decrease 

egg hatchability in fish. Human exposure to high concentrations can cause metabolic changes and 

damage to the pancreas, liver, spleen, and heart.

Lead Lead contamination can delay embryonic development, suppress reproduction, and inhibit growth

in fish. Human exposure to high concentrations in drinking water can cause serious damage to the 

brain, kidneys, nervous system, and red blood cells.

3-3
 

 

 

Section 3—Environmental And Human Health Concerns

Table 3-1. Key Metals and Toxic Bioaccumulative Pollutants Found In Steam Electric 

Power Plant Wastewater 

Pollutant Examples of Potential Health and Environmental Concerns

Manganese Manganese primarily accumulates in organisms lower in the food chain such as phytoplankton, 

algae, mollusks, and some fish. Although high levels can be toxic to humans, manganese is not

generally considered toxic when ingested. The most common impacts due to human exposure to

high concentrations involve the nervous system. 

Mercury c Once in the environment, mercury can convert into methylmercury, increasing the potential for

bioaccumulation. Methylmercury contamination can reduce growth and reproductive success in fish

and invertebrates. Human exposure at levels above the MCL for relatively short periods can result 

in kidney and brain damage. Fetuses, infants, and children are particularly susceptible to impaired 

neurological development from methylmercury exposure. 

Nickel At low concentrations, nickel can inhibit the growth of microorganisms and algae. Nickel toxicity

in fish and aquatic invertebrates varies among species and can damage the lungs, immune system, 

liver, and kidneys. Human exposure to high concentrations can cause gastrointestinal and kidney

damage. 

Selenium d Selenium readily bioaccumulates. Elevated concentrations have caused fish kills and numerous 

sublethal effects (e.g., organ damage, decreased growth rates, reproductive failure) to aquatic and 

terrestrial organisms. In humans, short-term exposure at levels above the MCL can cause hair and 

fingernail changes, damage to the peripheral nervous system, and fatigue and irritability. Long-term

exposure can damage the kidney, liver, and nervous and circulatory systems. 

Thallium In humans, short-term exposure to thallium can lead to neurological symptoms, alopecia, 

gastrointestinal effects, and reproductive and developmental damage. Long-term exposures at levels

above the MCL change blood chemistry and damage liver, kidney, intestinal and testicular tissues 

and cause hair loss. 

Vanadium Vanadium contamination can increase blood pressure and cause neurological effects in animals. 

There are very few reported cases of oral exposure to vanadium in humans; however, a few 

reported incidences documented diarrhea and stomach cramps. It also has been linked to the

development of some neurological disorders and cardiovascular diseases.

Zinc Zinc contamination changes behavior, reduces oxygen supply, and impairs reproduction in fish. In

humans, short-term exposure can cause nausea, vomiting, and stomach cramps. Long-term

exposure can cause anemia. 

a – Arsenic exists in two primary forms: arsenic III (arsenite) and arsenic V (arsenate). 

b – Chromium exists in two primary forms: chromium III oxide and chromium VI (hexavalent chromium). 

c – The EA evaluated two forms of mercury: total mercury and methylmercury.

d – Selenium exists in two primary forms: selenium IV (selenite) and selenium VI (selenate).

Selenium

Selenium is the most frequently cited pollutant associated with documented 

environmental impacts to ecological receptors following exposure to steam electric power plant 

wastewater [NRC, 2006]. The toxic potential of selenium is related to its chemical form and 

solubility. The predominant chemical forms of selenium in aquatic systems that receive steam

electric power plant wastewater discharges are selenite and selenate [Besser et al., 1996]. The

uptake of selenium by aquatic organisms is controlled by dissolved oxygen levels, hardness, pH, 

salinity, temperature, and the other chemical constituents present [NPS, 1997]. In alkaline

conditions, selenite [Se(IV)] will oxidize in the presence of oxygen to become selenate [Se(VI)]; 

selenate is both stable and soluble and is the commonly found form of the chemical in alkaline 

soils and waters. In acidic conditions, selenite is insoluble due to its tendency to bind to iron and 

aluminum oxides [WHO, 1987]. Organic forms of selenium are more bioavailable for uptake 

than selenate and selenite and may play an important role determining selenium toxicity in

exposed aquatic organisms [Besser et al., 1993; Rosetta and Knight, 1995]. 

3-4
Toxic Pollutant Impacts to Ecological 

Receptors

 Selenium discharges have caused 

numerous cases of fish kills and 

population decline due to reproductive 

impacts. Bioaccumulation can cause 

selenium-related environmental impacts 

to linger for years even after exposure to 

steam electric power plant wastewater

has ceased.

 Fish and invertebrates exposed to steam 

electric power plant wastewater have 

exhibited elevated mercury levels in 

their tissues and developed sublethal 

effects such as reduced growth and 

reproductive success.

 Elevated arsenic tissue concentrations 

are associated with several biological 

impacts such as liver tissue death, 

developmental abnormalities, and 

reduced growth.

 

 

Section 3—Environmental And Human Health Concerns

The extent to which selenium is found in ecological receptors is affected by 

bioaccumulation, biomagnification, and maternal transfer. Bioaccumulation occurs when an 

organism absorbs a toxic substance through food and exposure to the environment at a faster rate 

than the body can remove the substance. The bioaccumulation of selenium is of particular 

concern due to its potential to impact higher trophic levels through biomagnification [Coughlan 

and Velte, 1989] and offspring through maternal transfer [Hopkins et al., 2006; Nagle et al.,

2001]. A laboratory study demonstrated that diet can be an important source of trace element

exposure in aquatic snakes and potentially other amphibians [Hopkins et al., 2002]. Hopkins

reported that the snakes accumulated significant concentrations of the trace elements, most

notably selenium. This study also revealed that amphibian prey species are able to migrate 

considerable distances and can therefore be exposed to toxic levels of selenium even if they do 

not inhabit a contaminated site. Because of bioaccumulation and biomagnification, seleniumrelated environmental impacts can linger for years even after exposure to steam electric power 

plant wastewater has ceased [Rowe et al., 2002]. 

Selenium-related impacts observed by 

scientists include lethal effects such as fish kills, 

sublethal effects such as histopathological 

changes and damage to reproductive and 

developmental success, and the impacts of these 

effects on aquatic populations and communities. 

In a 1991 study, Sorensen found that dissolved 

selenium levels as low as 3 to 8 micrograms per 

liter (μg/L) in aquatic environments can be lifethreatening to fish [NPS, 1997]. Section 3.3.1 

presents further details regarding the lethal and

sublethal effects on aquatic organisms caused by 

selenium from steam electric power plant 

wastewater. 

In addition to ecological impacts, EPA 

has documented numerous damage cases where 

selenium in steam electric power plant 

wastewater discharges resulted in fish 

consumption advisories being issued for surface 

waters and selenium MCLs being exceeded in

ground water, suggesting that selenium 

concentrations in power plant wastewater have the potential to impact human health [NRC, 

2006; U.S. EPA, 2014a through 2014e]. Short-term exposure at levels above the MCL, 0.05 

mg/L [U.S. EPA, 2009e], can cause hair and fingernail changes, damage to the peripheral 

nervous system, and fatigue and irritability in humans. Long-term exposure can damage the

kidney, liver, and nervous and circulatory systems.

3-5
Toxic Pollutant Impacts to Human 

Receptors

 Pregnant women exposed to mercury

can pass the contaminant to their 

developing fetus, leading to possible 

mental retardation and damage to 

other parts of the nervous system. 

 Inorganic arsenic is a carcinogen 

(i.e., causes cancer). Cadmium is a 

probable carcinogen.

 Human exposure to high

concentrations of lead in drinking

water can cause serious damage to 

the brain, kidneys, nervous system, 

and red blood cells, especially in 

children. 

Section 3—Environmental And Human Health Concerns

Mercury 

Mercury is a volatile metal and highly toxic compound that represents an environmental 

and human health threat even in small concentrations. One of the primary environmental 

concerns regarding mercury concentrations in steam electric power plant wastewater is the 

potential for methylmercury to form in combustion residual surface impoundments and 

constructed wetlands prior to discharge and in surface waters following discharge. 

Methylmercury is an organic form of mercury that readily bioaccumulates in fish and other 

organisms and is associated with high rates of reproductive failure [WHO, 1976]. Bacteria found 

in anaerobic conditions, such as those that may be present in sediments found on the bottom of 

combustion residual surface impoundments or in river sediments, convert mercury to 

methylmercury through a process called methylation [WHO, 1976]. Microbial methylation rates 

increase in acidic and anoxic environments with 

high concentrations of organic matter. Sublethal 

effects from mercury exposure include reduced 

growth and reproductive success, metabolic 

changes, and abnormalities of the liver and kidneys.

Human exposure at levels above the MCL, 0.002 

mg/L [U.S. EPA, 2009e], for relatively short periods

of time can result in kidney and brain damage. 

Pregnant women who are exposed to mercury can 

pass the contaminant to their developing fetus, 

leading to possible mental retardation and damage 

to other parts of the nervous system [ATSDR, 

1999]. Studies have documented fish and 

invertebrates exposed to mercury from steam 

electric power plant wastewater exhibiting elevated 

levels of mercury in their tissues and developing 

sublethal effects such as reduced growth and 

reproductive success [Rowe et al., 2002]. 

Arsenic

Arsenic, like selenium, is of concern because it is soluble in near-neutral pH and in 

alkaline conditions, which are commonly associated with steam electric power plant wastewater. 

As a soluble pollutant, arsenic leaches into ground water and is highly mobile. Arsenic is 

frequently observed at elevated concentrations at sites located downstream from combustion 

residual surface impoundments [NRC, 2006]. Inorganic arsenic, a carcinogen, is found in natural 

and drinking waters mainly as trivalent arsenite (As(III)) or pentavalent arsenate (As(V)) [WHO,

2001]. Both the arsenite and arsenate forms are highly soluble in water. 

Arsenic is also of concern due to its tendency to bioaccumulate in aquatic communities

and potentially impact higher-trophic-level organisms in the area. For example, studies have 

documented water snakes, which feed on fish and amphibians, with arsenic tissue concentrations

higher than their prey [Rowe et al., 2002]. Elevated arsenic tissue concentrations are associated 

with several biological impacts such as liver tissue death, developmental abnormalities,

behavioral impairments, metabolic failure, reduced growth, and appetite loss [NRC, 2006; Rowe 

et al., 2002; U.S. EPA 2011f]. 

3-6
 

Section 3—Environmental And Human Health Concerns

Humans are exposed to arsenic primarily by ingesting contaminated drinking water 

[WHO, 2001]. Humans are also exposed to arsenic by consuming contaminated fish. Of greatest 

concern is inorganic arsenic, which can cause cancer in humans. Several studies have shown that 

most arsenic in fish is organic and not harmful to humans. Inorganic arsenic typically accounts

for 4 percent or less of the total arsenic that accumulates in fish.9 The highest potential exposure 

is for individuals whose diet is high in fish and particularly shellfish [U.S. EPA, 1997b]. 

As discussed in Section 3.3.4, EPA has documented several damage cases where arsenic 

levels exceeded drinking water standards in ground water near combustion residual surface 

impoundments [U.S. EPA, 2014b through 2014e]. Arsenic contamination of ground water at the 

levels documented represents a potential human health threat, if either the aquifer is used as a 

drinking water source or the ground water contaminates a downstream drinking water source. 

Cadmium

The speciation and toxicity of cadmium in water depends on the water’s salinity, 

hardness, temperature, and organic content [WHO, 1992]. Cadmium tends to bioaccumulate 

readily in mollusks, soil invertebrates, and microorganisms. Due to its chemical similarity to 

calcium, it can also interfere with calcium uptake in aquatic organisms, which can cause 

sublethal effects in fish such as skeletal malformation. Divalent cadmium (Cd(II)) is the species 

most commonly found in an aquatic environment, but depending on the quality of the water, 

cadmium can also occur as cadmium carbonate, hydroxide, sulfite, sulfate, or chlorides. 

EPA determined that cadmium is a probable human carcinogen. Studies found lung 

cancer in humans and rats exposed to cadmium via inhalation. In humans, chronic low-level 

exposure to cadmium from contaminated air, drinking water, or food can cause kidney failure. 

Chronic low-level exposure from contaminated drinking water or food can also lead to fragile 

bones. Exposure via inhalation at high levels can damage lungs and exposure via food and 

drinking water can irritate the stomach, leading to vomiting and diarrhea [ATSDR, 2012]. 

Thallium

Thallium typically exists as the monovalent or trivalent thallium ion [WHO, 1996]. It is

soluble in most waters and is readily available to aquatic life. Thallium can bioaccumulate in fish 

and vegetation in fresh and marine waters, as well as marine invertebrates, which suggests that 

thallium may be a potential threat to higher order organisms in vulnerable ecosystems [U.S. 

EPA, 2011a]. Studies in humans and animals indicate that thallium compounds are readily 

absorbed through ingestion of food and water and maternal transfer [WHO, 1996]. 

In humans, elevated thallium concentrations can lead to neurological symptoms (e.g., 

weakness, sleep disorders, muscular problems), alopecia (i.e., loss of hair from the head and 

body), and gastrointestinal effects (e.g., diarrhea and vomiting). Long-term exposures at levels 

above the MCL, 0.002 mg/L [U.S. EPA, 2009e], lead to changes in blood chemistry, damage to 

liver, kidney, and intestinal and testicular tissues, and hair loss. Thallium exposure can also cause 

reproductive and developmental damage [U.S. EPA, 2009a]. 

9

 Based on a 1996 literature review of toxicity and exposure concerns related to arsenic in seafood prepared for U.S. 

EPA Region 10, inorganic arsenic comprised higher than four percent total arsenic for three species (shark, sturgeon, 

and sucker). Inorganic arsenic for all other species accounted for less than 4 percent of the total arsenic [U.S. EPA, 

1997b].

3-7
Section 3—Environmental And Human Health Concerns

Lead

Neither metallic lead nor many of its common mineral forms are soluble in water,

although it can be soluble in some acids or water with low pH; thus, lead is commonly present in 

precipitate form in water. Therefore, steam electric power plant wastewater may initially have 

high concentrations of lead, but later sampling of the wastewater can show decreased

concentrations because the lead settles out quickly. Lead will accumulate in aquatic organisms, 

but depends on the species. Studies have shown lead to delay embryonic development, suppress 

reproduction, and inhibit growth rate among fish, crab, and several other aquatic organisms [U.S. 

EPA, 1984]. Human exposure to high concentrations of lead in drinking water can seriously 

damage the brain, kidneys, nervous system, and red blood cells, especially in children. 

Boron

Boron is primarily found in the environment combined with oxygen in compounds called 

borates [ATSDR, 2010b]. Boron concentrations in North American waters are typically below 

0.1 mg/L [WHO, 1998], although areas with natural boron-rich deposits may have ground water 

levels as high as 300 mg/L [ATSDR, 2010b]. The World Health Organization (WHO) suggests 

that the potential of adverse effects of boron on the aquatic ecosystem is low because the noeffect concentration (1 mg/L) is much greater than levels found in the ambient environment. 

Boron does not magnify through the food chain, but does accumulate in aquatic and terrestrial 

plants. While it is an essential micronutrient for higher plants, there is a small range between 

deficiency and toxicity in some plants. Studies of acute exposure in fish yielded toxicity values 

ranging from approximately 10 to 300 mg/L with rainbow trout and zebra fish being the most

sensitive. Mallard duckling growth was impacted at dietary levels of 30 and 300 milligrams per 

kilogram (mg/kg), while survival was reduced at 1,000 mg/kg [WHO, 1998]. 

EPA has not set a numerical criterion under the National Recommended Water Quality 

Criteria (NRWQC) for aquatic life, but it has issued a narrative criterion of 0.75 mg/L for 

sensitive crops that receive long-term irrigation. 

EPA has not set a NRWQC for human health. Very few human studies have examined 

health effects resulting from boron exposure through oral ingestion. However, one study 

documents nausea, vomiting, and diarrhea in an adult male who ingested 85 mg/kg of boron (30 

g as boric acid) [ATSDR, 2010b]. In addition, animal experiments indicate that boron in the form

of boric acid and borate affects reproductive and developmental processes at levels that are 

approximately 100 to 1,000 times greater than normal exposure levels, approximately 1.2 

milligrams per day (mg/day) [WHO, 1998]. 

Manganese

In water, manganese tends to attach to particles or settle into the sediment [ATSDR, 

2008b]. It occurs in both dissolved and suspended forms, depending on the water chemistry (e.g., 

pH) [WHO, 2011]. Manganese can bioaccumulate in lower organisms, such as phytoplankton,

algae, mollusks, and some fish, but not in higher organisms. Studies suggest that 

biomagnification up the food chain is not significant [ATSDR, 2008b]. 

Due to a high bioaccumulation factor and concentrations in mollusks, EPA established a 

criterion to protect consumers of marine mollusks—100 micrograms per liter (μg/L) for marine 

3-8
Section 3—Environmental And Human Health Concerns

waters [U.S. EPA, 1986]. Although high levels can be toxic to humans, manganese is an 

essential nutrient required to maintain health and is generally not considered to be toxic when 

ingested [WHO, 2011]. EPA did not set a primary MCL for manganese in drinking water; 

however, EPA did set secondary (nonenforceable) standards at 50 μg/L to minimize

objectionable qualities in the drinking water that cause laundry stains and objectionable tastes in 

beverages [U.S. EPA, 2009e]. 

3.1.2 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 low oxygen in surface waters (hypoxia) and harmful algal blooms. 

These are primarily problems for estuaries, such as the Chesapeake Bay, and coastal waters, such

as the Gulf of Mexico. Nutrient concentrations present in steam electric power plant wastewater 

are primarily attributed to the fuel composition and air pollution controls in the combustion 

process. 

Total nitrogen loadings from coal-fired power plants could potentially increase 

significantly in the future as air pollution limits become stricter and air pollution control use 

increases. While wastewater from an individual steam electric power plant can have a relatively

low nitrogen concentration the total nitrogen loadings from a single plant can be significant due

to high wastewater discharge flow rates. Total nutrient loadings from multiple power plants are

especially a concern for waterbodies that are nutrient-impaired or in watersheds that contribute to 

downstream nutrient problems. High nutrient loadings to surface waters can affect the ecological 

stability of freshwater and saltwater aquatic systems. For example, excessive 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, 2015a]. These aquatic changes can potentially kill bottom-dwelling aquatic 

plants. Cyanobacterial blooms can also produce toxic secondary metabolites, known as 

cyanotoxins, that can have negative impacts to humans and wildlife that consume water 

contaminated with cyanobacteria. The presence of high levels of cyanotoxins in recreational and 

drinking water may cause fever, headaches, abdominal pain, and other symptoms in humans. 

Severe human impacts include seizures, liver failure, respiratory arrest, and (rarely) death [U.S. 

EPA, 2012d]. 

3.1.3 TDS 

TDS, a reflection of water’s salinity level, is a measure of the amount of dissolved matter 

in water. TDS comprises primarily inorganic salts and dissolved metals, as well as a small

amount of organic matter. 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, chlorides, and bromides. Dissolved metals and other TDS constituents are found in 

wastewater particularly at acidic pH levels when they exhibit high solubilities. The specific 

constituents in TDS in steam electric power plant wastewater cause the negative impacts.

3-9
Section 3—Environmental And Human Health Concerns

Bromides

Bromide is the anion of bromine; it commonly exists as salts with potassium and other 

cations, which are usually very soluble in water. In water, bromide reacts to form hydrobromic 

acid (HBr) and hypobromous (HOBr), bromous (HBrO2), and bromic (HBrO3) oxyacids. 

Bromide is commonly found in nature, with levels ranging from trace amounts to 0.5 mg/L in 

fresh water and levels ranging from 65 to over 80 mg/L in seawater. The bromide ion has a low 

degree of toxicity, and animal testing suggests very low acute toxicity upon oral administration 

[WHO, 2009]. 

While bromide itself is not thought to be toxic at levels present in the environment, its 

reaction with other constituents in water may be cause for concern now and into the future. The

bromide ion in water can form brominated disinfection by-products (DBPs) when drinking water 

plants use certain processes including chlorination and ozonation to disinfect the incoming 

source water. Bromide can react with the ozone, forming bromates, or with chlorine or chlorinebased disinfectants used at drinking water treatment plants, to form brominated and mixed 

chloro-bromo DBPs, such as trihalomethanes (THMs) or haloacetic acids (HAAs) [WHO, 2009].

EPA has set MCLs for the following DBPs in chlorinated water: 

 0.010 mg/L for bromate due to increased cancer risk from long-term exposure. 

 0.060 for HAAs due to increased cancer risk from long-term exposure HAAs include 

dichloroacetic acid, trichloroacetic acid, chloracetic acid, bromoacetic acid, and

dibromoacetic acid. 

 0.080 mg/L for total trihalomethanes (TTHMs) due to increased cancer risk and liver, 

kidney, or central nervous system problems from long-term exposure [U.S. EPA, 

2009e]. TTHMs include the brominated trihalomethanes (bromodichloromethane, 

bromoform, dibromochloromethane) and chloroform. MCL goals for the individual 

trihalomethanes include 0 (zero) for bromodichloromethane and bromoform. 

Studies indicate that exposure to THMs and other DBPs from chlorinated water are 

associated with human bladder cancer [Villanueva et al., 2004; Cantor et al., 2010]. Brominesubstituted DBPs are generally thought to have higher risks of cancer and other adverse human

health effects compared to DBPs containing chlorine instead of bromine [Cantor et al., 2010]. 

EPA has determined that bromodichloromethane and bromoform are likely to be carcinogenic to 

humans by all exposure routes and there is suggestive evidence of dibromocloromethane 

carcinogencity. Excess cancer risk (based on increased risk to 1-in-a-million) occurs at 

concentrations above 0.001 mg/L for bromodichloromethane, 0.008 mg/L for bromoform, and 

0.0008 mg/L for dibromochlormethane [U.S. EPA, 2005c]. 

DBP formation and the individual form of the DBP are influenced by factors such as 

bromide ion concentration, pH of the source water, the disinfectant dose (ozone or chlorine), 

reaction or contact time, and organic matter concentration and reactivity [Liang and Singer, 

2003; U.S. EPA, 2005c]. Studies have shown that higher bromide levels in source waters shift 

the distribution of the TTHMs towards brominated species [Krasner et al., 1989] and the types of

HAAs from chlorinated to brominated and mixed chloro-bromo haloacetic acids [HellerGrossman, 1993; Cowman and Singer, 1996]. 

3-10
 

Section 3—Environmental And Human Health Concerns

Under the Safe Drinking Water Act (SDWA), drinking water treatment plants must 

reduce DBPs in their treated water and reduce exposure to customers. EPA conducted a 

nationwide survey that showed that bromide levels in source water above 400 μg/L corresponded 

with increased levels of DBPs in the treated water [Weinberg, 2002]. Due to increased bromide 

concentrations in surface water, drinking water treatment plants have found increased difficulty 

meeting regulatory limits on DBPs [U.S. EPA, 2012a; Handke, 2009; Fiske et al., 2011; States et 

al., 2013; Wilson et al., 2013]. In general, drinking water produced using surface water had 

higher concentrations of the DBPs than drinking water produced using ground water [U.S. EPA, 

2005c]. 

The city of Pittsburgh, in cooperation with the University of Pittsburgh, completed a

multiyear study on the Allegheny River to determine the major sources of bromide discharges, 

including coal-fired power plants. Typically, bromide concentrations are very low in the river,

but there are increased levels near industrial sites. The bromide concentration in the source water 

provided a linear correlation to bromination in the drinking water. At a concentration of 0.050 

mg/L in the source water, 62 percent of the TTHMs were the three brominated trihalomethane 

species. At a concentration of 0.150 mg/L, 83 percent of the TTHMs were the three brominated 

trihalomethane species [States et al., 2013]. 

The California Urban Water Agencies (CUWA) evaluated costs associated with increased 

bromide levels in the source water for baseline and potential future DBP controls. CUWA

developed virtual water treatment plants (WTPs) to represent their different source water areas 

and treatment needs, with virtual WTP design capacities ranging from 40 to 800 million gallons

per day. To achieve potential future standards on currently regulated pollutants, including DBPs, 

CUWA estimated costs for capital improvements and added annual operation and maintenance 

costs. On the low end, CUWA anticipated spending between $46 million to $923 million in 

capital improvements and $1 million to $59 million on annual operation and maintenance costs

to each virtual WTP (costs vary based on the characteristics of the virtual WTP). On the high

end, CUWA anticipated spending between $98 million and almost $2 billion in capital 

improvements and between $2 million and $127 million in annual operation and maintenance 

costs for each virtual WTP [CUWA, 2011]. 

Bromide is naturally present in coal at trace levels and becomes part of the flue gas air 

emissions following combustion at steam electric power plants. Combusting coal with higher 

levels of bromide is known to improve removal of mercury from air emissions at steam electric 

power plants that operate wet FGD scrubbers. Accordingly, steam electric power plant operators 

might add bromide-containing salts (e.g., calcium bromide) during coal combustion to improve

mercury removal efficiency. The bromide-containing salts convert the mercury Hg0

 form into the

more water soluble Hg2+ form. Bromide is not typically removed from steam electric power plant 

wastewaters prior to discharge to surface waters. As discussed earlier, bromides in surface waters 

can react with organic matter in the surface water to form DBPs at drinking water treatment 

plants. A recent study identified four drinking water treatment plants that experienced increased 

levels of bromide in their source water, and corresponding increases in the formation of 

brominated DBPs, after upstream steam electric power plants installed wet FGD scrubbers

[McTigue et al., 2014]. Bromide loadings into surface waters from coal-fired steam electric 

power plants could potentially increase in the future as more plant operators add bromide to help 

control mercury emissions. 

3-11
Pollutant Loadings: How Does the

Steam Electric Power Generating 

Industry Compare?

EPA estimates that discharges from

steam electric power plants alone 

contribute approximately one-third of 

the toxic weighted pound equivalent 

(TWPE) pollutant loadings to the 

environment among all industrial 

categories that report discharges under 

NPDES permits. 

 

Section 3—Environmental And Human Health Concerns

Chlorides 

Studies have found that combustion residual leachate reaching ground water has caused 

chloride levels to exceed secondary MCLs [NRC, 2006]. Chlorides contribute to the high TDS 

levels typical of steam electric power plant wastewater, as do calcium and magnesium. Both

chlorides and TDS levels affect the availability and toxicity of other steam electric power plant 

wastewater constituents, including metals. As TDS and chlorides levels fluctuate, so do the 

amounts of other metals that dissolve due to solubility characteristics. 

EPA recommends the following for chlorides: criterion maximum concentration of

860 mg/L (acute effects) and criterion continuous concentration of 230 mg/L (chronic effects) 

[U.S. EPA, 2009d]. Exceeding these chlorides levels in wastewater discharges can be harmful to

animals and plants in nonmarine surface waters and can disrupt ecosystem structure. It can also

adversely affect biological wastewater treatment processes. Furthermore, excessively high 

chlorides concentrations in surface waters can impair their use as source waters for potable water 

supplies. If sodium is the predominant cation present, the water will have an unpleasant taste due 

to the corrosive action of chloride ions. 

3.2 LOADINGS ASSOCIATED WITH STEAM ELECTRIC POWER PLANT WASTEWATER 

As discussed above, the pollutants 

commonly found in steam electric power plant 

wastewater such as metals, nutrients, and TDS 

(including bromides and chlorides) can cause 

considerable harm to surface waters, aquatic life, 

wildlife, and human health. EPA estimated pollutant 

loadings for the steam electric power plant 

wastestreams evaluated and considered as part of the 

revision to the steam electric ELGs (i.e., FGD 

wastewater, fly ash transport water, bottom ash 

transport water, and combustion residual leachate).

The total pollutant loadings for the evaluated 

wastestreams are significant, with these discharges 

accounting for over one-third of the toxic pollutants reported to be discharged in industrial 

National Pollutant Discharge Elimination System (NPDES) permits [ERG, 2015a]. EPA 

estimated the amount of pollutants (i.e., loadings) discharged by steam electric power plants 

throughout the United States for the evaluated wastestreams as almost 3 million toxic-weighted

pound equivalents (TWPE) annually.10 EPA uses TWFs as a way to better understand how

treatment technologies and industry discharges compare to one another [U.S. EPA, 2012b]. 

Although EPA uses TWFs and the estimated TWPE as an indicator of a pollutant’s relative 

potential to cause harm, EPA does not use TWPE to represent actual aquatic or human health 

impacts that may have occurred at specific locations due to these pollutant loadings. To assess

10 To calculate the TWPE, EPA multiplies a mass loading of a pollutant in pounds per year (lb/yr) by a pollutantspecific weighting factor, called the toxic weighting factor (TWF), to derive a "toxic equivalent" loading (lbequivalent/yr), or TWPE. TWFs account for differences in toxicity across pollutants and allow mass loadings of

different pollutants to be compared on the basis of their toxic potential. EPA has developed TWFs for more than

1,000 pollutants based on aquatic life and human health toxicity data, as well as physical/chemical property data 

[U.S. EPA, 2012b]. 

3-12
Pollutant Loadings from Steam

Electric Power Plants Evaluated 

Wastestreams

 2,210,000,000 pounds of pollutants 

per year.

 2,680,000 pounds of TWPE per 

year.

 

 

 

Section 3—Environmental And Human Health Concerns

impacts to aquatic life or human health, EPA uses the amount of pollutant loadings discharged to 

the surface water and the resulting concentrations in the surface waters.

When coupled with the types of impacts associated with the pollutants, the magnitude of

the loadings raises concern about the risks that these discharges present to the aquatic 

environment and the surrounding ecosystem. This section presents the annual baseline11 pollutant 

loadings associated with the evaluated wastestreams and compares steam electric discharges to

those of other industries to provide perspective on the magnitude of the loadings and subsequent 

potential impact these wastestreams pose to the environment. 

3.2.1 Annual Baseline Pollutant Loadings

In support of the final rule, EPA estimated the pollutant loadings discharged from steam 

electric power plants for the evaluated wastestreams, as described in Section 10 of the TDD.12

Table 3-2 presents the baseline annual pollutant loadings discharged for select pollutants 

considered for analysis in the EA.13 EPA presents these loadings in terms of pounds and TWPE 

and lists the TWF where applicable. The pollutants with the highest annual TWPE discharges are 

manganese, cadmium, boron, thallium, mercury, selenium, and arsenic. Although the total 

pounds discharged of arsenic, cadmium, mercury, and 

thallium are lower than other pollutants, their relative 

toxicity (as represented by the TWF) results in a large 

TWPE. Other pollutants, such as boron and 

manganese, are relatively low in toxicity but have a 

high TWPE due to the fairly high amount of these 

pollutants in steam electric power plant wastewater 

discharges. The high TWPE for selenium results from 

a combination of its quantity discharged in steam 

electric power plant wastewaters and its TWF. 

11 The analyses presented in this report incorporate some adjustments to current conditions in the industry. See 

Section 1 for further details.

12 Prior to finalizing the rulemaking, EPA revised the datasets used to calculate pollutant loadings for bottom ash

transport water and fly ash transport water. The final industry loadings calculated using these revised datasets are 

presented in the TDD. The total industry loadings presented in Section 3.2 reflect the revised datasets. However,

EPA did not rerun the EA models and other analyses to reflect the final loadings dataset. EA analyses used

previously calculated version of the steam electric power plant pollutant loadings that were derived following the 

same methodology. The EA pollutant loadings are included in DCN SE05620. Pollutant-specific loadings and 

removals presented in this report are based on the previously calculated version. Appendix J presents the results of a

sensitivity analysis that evaluated the potential for these loadings revisions to affect the EA analyses. 

13 EPA selected the pollutants listed in Table 3-2 (which represent a subset of all steam electric pollutants of 

concern) for analysis in the EA based on the following factors for each pollutant: presence of the pollutant in the 

evaluated wastestreams (see Table 2-1); 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.

3-13
 

 

 

 

 

 

Section 3—Environmental And Human Health Concerns

Table 3-2. Annual Baseline Pollutant Discharges from Steam Electric Power Plants 

(Evaluated Wastestreams) 

Pollutant a TWF b

Annual Discharge,

pounds (lbs) c

Annual TWPE, 

pound-equivalent 

(lb-eq) c

Metals and Toxic Bioaccumulative Pollutants

Manganese 0.103 7,530,000 773,000

Cadmium 22.8 13,300 303,000 

Boron 0.00834 31,300,000 261,000 

Thallium 2.85 63,700 182,000 

Mercury 110.0 1,490 164,000

Selenium 1.12 140,000 157,000

Arsenic 3.47 29,600 103,000 

Aluminum 0.0647 1,410,000 91,500 

Lead 2.24 19,700 44,100 

Copper 0.623 31,200 19,500 

Vanadium 0.280 66,000 18,500 

Iron 0.00560 2,740,000 15,400 

Nickel 0.109 120,000 13,100 

Zinc 0.0469 174,000 8,160 

Chromium VI 0.517 156 80.5 

Nutrients

Total Nitrogen d Not applicable 16,900,000 Not applicable 

Total Phosphorus Not applicable 214,000 Not applicable 

Other

Chlorides 2.435 X 10-5 930,000,000 22,600 

Total dissolved solids Not applicable 

Total Pollutants e 2,210,000,000 2,680,000 

Sources: Abt, 2008; ERG, 2015a; ERG, 2015b; ERG, 2015f; U.S. EPA, 2012c. 

Note: Numbers are rounded to three significant figures. 

a – The list of pollutants included in this table is only a subset of pollutants included in the loadings analysis (see 

Section 10 of the TDD).

b – TWFs for the following metals apply to all metal compounds: arsenic, chromium, copper, lead, manganese, 

mercury, nickel, selenium, thallium, vanadium, and zinc. EPA updated TWFs for arsenic, cadmium, copper, 

manganese, mercury, thallium, and vanadium for the steam electric ELGs pollutant loadings analysis. 

c – These loadings reflect adjustments to current conditions in the industry. See Section 1 for further details. Data 

source for pollutant specific loadings is DCN SE05620. 

d – Total nitrogen is the sum of total Kjeldahl nitrogen and nitrate/nitrite as N. 

e – The totals represent the pollutant loadings in discharges of the evaluated wastestreams – specifically, FGD 

wastewater, fly ash transport wastewater, bottom ash transport wastewater, and combustion residual leachate (see

Section 10 of the TDD). Loadings presented are based on the final loadings analysis presented in the TDD. The 

totals exclude loadings for pollutants not identified as POCs and for biochemical oxygen demand (BOD), chemical

oxygen demand (COD), total organic carbon (TOC), total dissolved solids (TDS), and total suspended solids (TSS). 

3-14
 

 

Section 3—Environmental And Human Health Concerns

3.2.2 Comparison of Steam Electric Power Plant Loadings to Other Industries

The total TWPE discharges from the steam electric power generating industry are higher 

than the TWPEs estimated for many other industries. As part of the Preliminary 2010 Effluent

Guidelines Program Plan published on October 30, 2009 (74 FR 68599), EPA identified 10 point 

source categories, out of 56, that represented the bulk of the estimated toxic wastewater 

discharges (as measured by TWPE) from existing industrial point source categories. EPA ranked 

each point source category by the amount of toxic pollutants in its discharges and identified the 

Steam Electric Power Generating Point Source Category (40 CFR 423) as the category with the 

highest TWPE. Table 3-3 presents the total TWPE estimated as part of the 2010 Effluent

Guidelines Planning Process for the remaining nine point source categories with the highest

TWPE [U.S. EPA, 2011d]. The TWPE estimated for the 2010 Effluent Guidelines Planning 

Process includes pollutant loadings estimated from discharge monitoring reports (DMRs) and 

Toxic Release Inventory (TRI) reporting. Therefore, the industry totals may include doublecounting of certain chemical discharges (i.e., a facility must report a chemical on both its DMR 

and its TRI reporting form). 

Table 3-3. Pollutant Loadings for the Final 2010 Effluent Guidelines Planning Process: 

Top 10 Point Source Categories

40 CFR Part Point Source Category 

Total TWPE a

(lb-eq/yr) 

423 Steam Electric Power Generating 2,680000 b

430 Pulp, Paper, And Paperboard 1,030,000

419 Petroleum Refining 1,030,000

421 Nonferrous Metals Manufacturing 994,000 

418 Fertilizer Manufacturing 826,000 

414 Organic Chemicals, Plastics, And Synthetic Fibers 649,000

440 Ore Mining And Dressing 448,000 

415 Inorganic Chemicals Manufacturing 299,000

444 Waste Combustors 254,000

410 Textile Mills 250,000 

Source: U.S. EPA, 2011d. 

a – Only TWPE totals for the steam electric power generating industry include updates to TWFs for arsenic, 

cadmium, copper, manganese, mercury, thallium, and vanadium. The TWPE for all other point source categories is 

estimated from DMRs and TRI reporting and may include double-counting of certain pollutant discharges (i.e., a 

facility must report a pollutant on both its DMR and its TRI reporting form). Loadings are rounded to three 

significant figures.

b –EPA calculated the steam electric power generating industry (40 CFR 423) discharges for the final rule as total

2,680,000 TWPE annually (see Section 10 of the TDD). These loadings reflect adjustments to current conditions in

the industry. See Section 1 for further details. 

EPA estimated that the total baseline TWPE from steam electric power plant wastewater 

is almost three times the amount estimated for the pulp, paper, and paperboard industry, 

petroleum refining industry, and nonferrous metals manufacturing (second, third, and fourth 

highest ranking), and it is over five times the TWPE for four of the six other industries identified 

as the top TWPE dischargers in the Final 2010 Effluent Guidelines Program Plan [U.S. EPA, 

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Section 3—Environmental And Human Health Concerns

2011d].14 This suggests that the loadings from the subset of evaluated wastestreams represent a 

greater environmental concern within the context of all industrial dischargers across the United

States. 

3.2.3 Comparison of Steam Electric Power Plant Loadings to Publicly Owned Treatment 

Works

To provide additional perspective on the magnitude of the pollutant loadings from steam 

electric power plants, EPA compared loadings for the evaluated wastestreams to those of an

average publicly owned treatment works (POTW). EPA selected POTWs for comparison

because, for point sources, POTWs and steam electric power plants dwarf all other point source 

discharges in terms of total TWPE of metals discharged to waters in the United States [U.S. 

EPA, 2010c].15 In addition, the more than 16,000 POTWs are located across the United States

and provide a common metric to use for point source evaluations. 

EPA calculated the average pollutant loadings discharged from a typical POTW using 

EPA’s Effluent Guidelines Program Plan DMR database, DMRLoadsAnalysis2009_v02.mdb. 

EPA assumed that a typical POTW discharges wastewater at a rate of 3 to 5 million gallons per 

day (MGD)16 based on the number of facilities by discharge flow rate reported in Metcalf and 

Eddy, 2003 [ERG, 2015a]. EPA developed queries in the DMRLoadsAnalysis2009_v02.mdb to 

do the following: 1) select POTWs that discharge between 3 and 5 MGD, and 2) calculate the 

average DMR loadings (in pounds and TWPE per year) for each pollutant [ERG, 2015a]. Table 

3-4 compares the average steam electric pollutant loadings by wastestream17 to the pollutant

14 Data sources for the other industry discharges include DMRs and TRI reports. EPA recognizes that the DMR and 

TRI data have limitations (e.g., only a subset of facilities and a subset of pollutants might be included in the 

estimated loadings); however, these are the most readily available data sets that represent discharges across the 

United States. 

15 Based on metal loadings (total TWPE) calculated by EPA’s DMR Pollutant Loading Tool, 2010 data, by Standard

Industrial Classification (SIC) code. The top two industries are SIC 4952 – Sewerage Systems (i.e., POTWs) and 

SIC 4911 – Electrical Services. EPA’s DMR Pollutant Loading Tool is an online tool (http://cfpub.epa.gov/dmr/) 

that calculates pollutant loadings from permit and DMR data from EPA’s Permit Compliance System (PCS) and

Integrated Compliance Information System for the National Pollutant Discharge Elimination System (ICISNPDES). The tool also ranks dischargers, industries, and watersheds based on pollutant mass and toxicity, and

presents “top 10” lists to help users determine which facilities and industries are producing these discharges and 

which watersheds are impacted. Facilities report pollutant discharge monitoring data in their DMR as mass-based

quantities (e.g., pounds per day) and/or concentrations (e.g., mg/L). The DMR Pollutant Loading Tool allows users 

to gather annual loadings data. For this EA, EPA reviewed the 2010 loadings reported in DMRs. 

The use of the DMR data has its limitations. Only pollutants included in the facility’s NPDES permit are included in 

the PCS and ICIS-NPDES databases; therefore, if a facility does not have mercury limitations, mercury discharges 

from that facility will not be included in the total for industrial discharges. States (or other permitting authority) have

some discretion as to which data they make available (or enter) to PCS and ICIS-NPDES. For example, permitting

authorities enter DMR and permit information for facilities that are considered major dischargers. However, they do

not necessarily enter DMR or permit information into PCS for minor dischargers or facilities covered by a general

permit. 

16 For comparison, the average discharge flow rates for the evaluated wastestreams are 0.45 MGD for FGD 

wastewater; 3.5 MGD for fly ash transport water; 2.1 MGD for bottom ash transport water; and 0.08-0.09 MGD for

leachate [see Section 6 of the TDD]. 

17 EPA calculated the average pollutant loadings for each wastestream by dividing the total pollutant loadings for the

wastestream by the number of steam electric power plants discharging the wastestream [ERG, 2015a]. 

3-16
Section 3—Environmental And Human Health Concerns

loadings from an average POTW assumed to discharge 3 to 5 MGD. The results of the analysis 

demonstrate the following: 

 Average FGD wastewater discharges contain over 200 times more boron and 

manganese, over 75 times more selenium, and approximately 20 times more cadmium 

and nickel than average POTW discharges. 

 Average fly ash transport water discharges contain over 10 times more boron, 

cadmium and thallium and over five times more arsenic, nickel, and selenium than 

average POTW discharges. 

 Average bottom ash transport water discharges contain 30 times more thallium;

approximately 10 times more manganese and nickel; and five times more cadmium 

than average POTW discharges. 

 Average combustion residual leachate wastewater discharges contain more boron, 

iron, manganese, and selenium than average POTW discharges. 

Nutrient loadings (total nitrogen and 

total phosphorus) from the average steam 

electric wastestreams are generally lower than 

the nutrient loadings from an average POTW. 

Total nitrogen loadings from an average FGD 

wastestream are approximately equal to those 

of an average POTW. Nitrogen loadings from 

average fly ash and bottom ash transport 

waters are less than the total nitrogen

discharges from an average POTW

(approximately 20 percent). The amount of 

total phosphorus discharged by an average 

POTW is over 20 times higher than that in the 

average fly ash transport water, bottom ash

transport water discharges, and FGD 

wastewater. EPA did not calculate nutrient 

loadings for combustion residual leachate. 

For chlorides, EPA found that average 

FGD wastewater discharges contain 

approximately six times greater chlorides 

Loadings of the Evaluated Wastestreams 

Compared to POTWs

 FGD wastewater discharges contain: 

- 200 times more manganese 

- 200 times more boron 

- 75 times more selenium 

- 20 times more nickel 

- 20 times more cadmium

 Bottom ash transport water discharges 

contain 30 times more thallium and 10 

times more manganese and nickel. 

 Fly ash transport water discharges contain 

five times more arsenic, nickel, and 

selenium and 10 times more boron, 

cadmium, and thallium.

 Combustion residual leachate contains over 

four times more boron and iron.

loadings than an average POTW discharge. The average discharges of fly ash transport water, 

bottom ash transport water, and combustion residual leachate from a steam electric power plant 

contain less chlorides than a typical POTW discharge (less than 10 percent). EPA’s DMR data 

did not include pollutant loadings for TDS from POTWs; therefore, EPA could not compare

these pollutant loadings between steam electric and POTW discharges. 

3-17
Section 3—Environmental An

Table 3-4. Comparison of Average Pollutant Loadings in the Evaluated Wastestreams to an Aver

Pollutant 

Average Plant FGD 

Wastewater Discharge a,b

Average Plant Fly Ash 

Transport Water 

Discharge a,c

Average Plant Bottom 

Ash Transport Water

Discharge a,d

Average Plant 

Combustion Residual 

Leachate Discharge a,e

Loadings

(lbs/yr)

TWPE 

(lb-eq/yr) 

Loadings

(lbs/yr)

TWPE 

(lb-eq/yr) 

Loadings

(lbs/yr)

TWPE 

(lb-eq/yr) 

Loadings

(lbs/yr)

TWPE 

(lb-eq/yr) 

Aluminum 1,530 99.1 8,490 549 4,240 274 837 54.1 

Arsenic 9.54 33.1 312 1,080 66.5 231 10.8 37.5 

Boron 334,000 2,790 17,900 149 2,190 18.3 6,530 54.5 

Cadmium 81.2 1,850 47.7 1,090 19.1 435 2.87 65.3 Chromium VI (g) (g) 2.62 1.35 0.136 0.070 (g) (g) Copper 17.9 11.1 263 164 89.0 55.5 2.16 1.34 Iron 1,150 6.42 5,140 28.8 7,610 42.6 10,400 58.4 

Lead 5.71 12.8 152 340 63.4 142 (g) (g) Manganese 74,500 7,650 486 49.9 4,770 490 790 81.1 

Mercury 5.50 605 7.85 864 3.19 351 0.298 32.8 

Nickel 620 67.6 180 19.6 301 32.7 13.1 1.43 

Selenium 1,410 1,580 134 150 32.4 36.3 31.2 35.0 

Thallium 16.7 47.7 137 392 302 863 0.338 0.964 

Vanadium 20.8 5.82 220 61.7 11.4 3.21 538 151 

Zinc 983 46.1 734 34.4 247 11.6 59.1 2.77 

Total Nitrogen 128,000 -- 23,400 -- 24,600 -- (g) -- 

Total Phosphorus 457 -- 864 -- 715 -- (g) -- 

Chlorides 10,200,000 248 83,500 2.03 96,700 2.35 120,000 2.93 

TDS 40,400,000 -- 1,760,000 -- 2,560,000 -- 1,020,000 -- 

Note: Numbers are rounded to three significant figures. a – TWPE presented in the table include updates to TWFs for arsenic, cadmium, copper, manganese, mercury, thallium, and vanadiumb – Average loadings based on 88 plants assumed to discharge FGD wastewater under baseline conditions [ERG, 2015a]. c – Average loadings based on 50 plants assumed to discharge fly ash transport water under baseline conditions [ERG, 2015a]. d – Average loadings based on 183 plants assumed to discharge bottom ash transport water under baseline conditions [ERG, 2015a]. e – Average loadings based on 95 plants assumed to discharge combustion residual leachate under baseline conditions [ERG, 2015a].f – Average loadings based on average loadings calculated for POTWs discharging 3 to 5 MGD of wastewater (see DCN SE01961). 

g – EPA did not calculate loadings for this pollutant and wastestream. See the Costs and Loads Report (DCN SE05831). 

3-18 
 

 

Section 3—Environmental And Human Health Concerns

To provide additional perspective on the magnitude of the loadings, EPA calculated the 

equivalent number of typical POTWs that would discharge loadings equal to the 202 steam 

electric power plants18 included in the baseline loadings analysis. Table 3-5 presents total 

pollutant loadings for the evaluated wastestreams (for the 202 plants) and the number of typical 

POTWs that would discharge equivalent loadings. The results demonstrate that the magnitude of 

the total loadings from 202 steam electric power plants is equivalent to a significantly larger 

number of typical POTWs for many of the pollutants commonly known to cause environmental

harm. For example, EPA estimated that the total loadings in discharges of the evaluated 

wastestreams from these 202 plants are equivalent to approximately 20,000 POTW discharges of 

boron and manganese; over 7,500 POTW discharges of selenium; over 6,000 POTW discharges

of thallium; over 3,500 POTW discharges of cadmium and nickel; over 1,000 POTW discharges

of iron; and over 500 POTW discharges of arsenic and chlorides. This suggests that, for the 

evaluated wastestreams, 202 steam electric power plants contribute substantial pollutant loadings 

to the environment. 

Table 3-5. Estimated Number of POTW Equivalents for Total Pollutant Loadings from the 

Evaluated Wastestreams 

Pollutant 

Annual Discharge

pounds (lbs) 

Equivalent Number of Average

POTWs a

Aluminum 1,410,000 394

Arsenic 29,600 646 

Boron 31,300,000 20,300 

Cadmium 13,300 3,760

Chromium VI 156 8.81

Copper 31,200 203 

Iron 2,740,000 1,080

Lead 19,700 406 

Manganese 7,530,000 21,300 

Mercury 1,490 <1 

Nickel 120,000 3,920

Selenium 140,000 7,560

Thallium 63,700 6,410

Vanadium 66,000 No values for comparison

Zinc 174,000 384 

Total Nitrogen 16,900,000 138 

Total Phosphorus 214,000 12.0

Chlorides 930,000,000 578 

TDS 4,210,000,000 No values for comparison

Source: ERG, 2015a. 

Note: Numbers are rounded to three significant figures. 

a – Equivalent number of POTWs is estimated by dividing the total annual pollutant loadings from the 202 steam

electric power plants by the average POTW loadings presented in Table 3-4 for a 4-MGD POTW.

18 The count of 202 steam electric power plants includes seven indirect dischargers that discharge wastewater to a 

POTW and do not discharge any of the evaluated wastestreams directly to surface waters. EPA included these

indirect dischargers to protect confidential business information.

3-19 
 

Section 3—Environmental And Human Health Concerns

3.3 ENVIRONMENTAL IMPACTS FROM STEAM ELECTRIC POWER PLANT WASTEWATER

EPA identified environmental impacts from EPA’s assessment of damage cases and 

literature sources (“other documented site impacts”) caused by steam electric power plant 

wastewater and combustion residuals. EPA found over 150 steam electric power plants causing 

environmental impacts to surface water and ground water environments following exposure to

steam electric power plant wastewater. Impacts identified in the damage cases and other

documented site impacts include lethal and sublethal impacts on fish, impacts on the diversity 

and size of populations in the ecosystem, and impacts on drinking water quality. While these 

impacted sites are often assumed to be anomalies, mounting evidence indicates that the

characteristics contributing to the documented impact (e.g., magnitude of the pollutant loadings,

type of pollutant present, plant operations, and wastewater handling techniques) are common 

among steam electric power plant receiving water locations [Cherry et al., 2000; NRC, 2006; 

Rowe et al., 2002]. 

Section 3.3.1 presents a qualitative discussion of the lethal and sublethal ecological 

effects of pollutants in steam electric power plant wastewater. Section 3.3.2 summarizes

documented instances where steam electric power plant wastewater discharges have caused fish 

advisories or exceeded MCLs presenting a potential human health concern. Section 3.3.3 and 

Section 3.3.4 summarize the damage cases and other documented site impacts to surface water 

and ground water, respectively. Section 3.3.5 discusses the potential for these environmental 

impacts to occur at other locations. 

3.3.1 Ecological Impacts

Documented ecological impacts associated with exposure to steam electric power plant 

wastewater include acute effects (e.g., fish kills) and chronic effects (e.g., malformations, and 

metabolic, hormonal, and behavioral disorders) upon biota within the receiving water and 

surrounding environment. Effects have included reduced growth and reduced survival of aquatic 

organisms and changes to the local habitat [Carlson and Adriano, 1993; Rowe et al., 2002]. 

This section provides examples of the lethal and sublethal effects on organisms exposed 

to steam electric power plant wastewater pollutants (e.g., arsenic, cadmium, chromium, copper, 

mercury, and selenium) in surface waters and sediment. Scientific studies reported in the 

literature included: 

 Field studies in which organisms collected from known contaminated sites were 

compared to those collected from uncontaminated sites.

 Laboratory experiments in which organisms intentionally exposed to steam electric 

power plant wastewater were compared to those unexposed. 

Many of the scientific studies documented in the literature focused on selenium as a key 

pollutant of environmental concern within steam electric power plant wastewater. However, due 

to the complex nature of the wastewater, many studies evaluated the environmental effects of 

metals in steam electric power plant wastewater in aggregate.

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Section 3—Environmental And Human Health Concerns

Lethal and Sublethal Effects of Selenium

Selenium can bioaccumulate to toxic levels in organisms inhabiting environments with 

low selenium concentrations. For example, Lemly conducted a field study that investigated the 

patterns of selenium biomagnification and toxicity in aquatic organisms inhabiting a cooling 

water reservoir that received effluent from a power plant’s surface impoundment [Lemly, 

1985a]. Throughout the study, selenium concentrations in the reservoir averaged 10 μg/L; 

however, Lemly reported that fish tissue concentrations reached levels ranging from 500 to 4,000 

times the average reservoir water selenium concentration. The results of the study indicated that 

the extent of selenium bioaccumulation depended on the trophic level of the fish present in the

reservoir. Lemly observed that the selenium accumulation increased as the trophic level 

increased, which potentially correlated with the observed elimination of multiple higher-tropiclevel fish species. Therefore, these findings suggest that—even at low concentration within a 

surface water—selenium can accumulate and biomagnify to toxic levels in aquatic organisms 

and pose a lethal threat to fish at the top of the trophic structure [Lemly, 1985a]. Predicting the 

impacts of selenium in aquatic ecosystems can be particularly challenging, because impacts to 

the ecosystem cannot be determined solely on the selenium concentration in the receiving water 

as demonstrated in this study. 

Selenium discharges also impact species diversity in receiving waters. In 1977, two years 

after the initial operation of the Belews Creek Steam Station in North Carolina, the fish 

community inhabiting the plant’s cooling water reservoir (a lake) underwent rapid decline, and 

species diversity drastically altered [Lemly, 1985a]. Lemly observed that 17 of the 20 fish 

species originally present in the lake were eliminated after the power plant began operation,

including all game species (temperate perch [Percichthyidae], true perch and pike perch 

[Percidae], and sunfish [Centrarchidae]). Lemly reported significant levels of selenium 

accumulation in the eliminated species and statistically unchanged levels of selenium 

accumulation in the surviving species, relative to levels before the power plant began operation.

Only three species maintained reproducing populations in the reservoir: one native species 

(mosquitofish) and two introduced non-native species of minnows (fathead minnows and red 

shiners) [Lemly, 1985a]. 

A number of scientific studies express concern over selenium exposure within lakes and 

reservoirs where longer residence times allow for further bioaccumulation and a greater potential

to reach lethal concentrations. This is demonstrated by a series of major fish kills that occurred in

1978 and 1979 at Martin Creek Lake (Texas) due to the elevated concentrations of selenium in 

the water and fish tissue [U.S. EPA, 2014b]. In particular, studies concluded that elevated 

selenium concentrations were likely the primary contributor to fish kills in lakes and reservoirs, 

decreasing population density and community diversity [Coughlan and Velte, 1989; Crutchfield, 

2000b; Crutchfield and Ferguson, 2000a; Cumbie and Van Horn, 1978]. 

The sublethal effects of selenium vary widely and can impact growth, reproduction, and 

survival of susceptible organisms. Scientists have demonstrated that various fish and amphibian 

species are sensitive to elevated selenium concentrations such as those found in steam electric 

power plant wastewater. In addition to lethal effects described above, 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 

3-21 
Section 3—Environmental And Human Health Concerns

growth, changes in weight, abnormal morphology, and reduced hatching success [Coughlan and 

Velte, 1989; Lemly, 1993; Sager and Colfield, 1984; Sorensen, 1988; Sorensen and Bauer, 

1984a; Sorensen et al., 1982, 1983, 1984b]. 

The literature indicates that the extent of selenium accumulation in fish tissue varies by 

species, and selenium accumulates most significantly in the liver and reproductive tissues in 

most species [Baumann and Gillespie, 1986; Sager and Colfield, 1984; Sorensen, 1988]. Other 

studies have reported accumulation in the skeletal muscle, kidneys, gills, and hearts of fish, 

resulting in pathological lesions, morphological changes, increased organ weight, and decreased 

growth [Coughlan and Velte, 1989; Lemly, 2002; Sorensen and Bauer, 1984b]. Aquatic 

organisms exposed to steam electric power plant wastewater have exhibited elevated selenium 

concentrations in organs such as kidneys, liver, and gonads, resulting in abnormalities that hinder 

growth and survival [Rowe et al., 2002]. 

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, 1997b; Maier and Knight, 1994]. Selenium is known to 

bioaccumulate in the reproductive organs of fish and amphibian species. In one study, ovarian

selenium concentrations in bluegill fish were observed at levels 1,000 times greater than the 

surrounding surface water [Baumann and Gillespie, 1986]. Multiple studies have documented 

reproductive failure or diminished reproductive success in both fish and amphibians inhabiting

ponds, lakes, and reservoirs contaminated with selenium from steam electric power plant 

wastewater discharges [Baumann and Gillespie, 1986; Crutchfield, 2000b; Cumbie and Van 

Horn, 1978; Gillepsie et al., 1986; Hopkins et al., 2002; Nagle et al., 2001]. For example, 

Hopkins et al. [2006] observed reduced hatching success, abnormal swimming, and 

abnormalities in the face and skull in the offspring of selenium-contaminated female toads. Field

and captive feeding studies also show reproductive impairment (reduced hatchability of eggs) 

among waterfowl exposed to elevated levels of selenium [Adams et al., 2003; Ohlendorf, 2003 

and 2007; Beckon et al., 2008; U.S. DOI, 1998; Smith et al., 1998]. 

Histopathological effects (i.e., observable changes in tissue), increased metabolic rate, 

and decreased growth rates are effects typically caused by contamination from steam electric 

power plant wastewater. Water and fish samples collected before and after the discharge of 

power plant wastewater from the surface impoundment to the Texas Utilities Martin Creek Lake

found that selenium concentrations were significantly elevated in the reservoir and in fish livers, 

kidneys, and gonads. In 1984, Garrett and Inman reported that elevated selenium concentrations 

persisted in the livers and kidneys of several species of fish for up to 3 years after the power 

plant wastewater discharges ceased. Additionally, a 1988 study by Sorensen found that red ear 

sunfish native to the reservoir exhibited ovary abnormalities related to elevated selenium 

concentrations up to 8 years following an 8-month exposure to power plant wastewater 

discharges. Although the surface impoundment discharge was short-lived, many of the 

histopathological effects persisted for years after the discharge had ceased [Rowe et al., 2002]. 

These sublethal effects of selenium, while not directly resulting in the mortality of 

exposed aquatic wildlife, can ultimately cause the types of population-level impacts described

under lethal impacts above. The available scientific evidence indicates that reproductive 

success—specifically, offspring mortality and severe development abnormalities that affect the 

3-22 
Section 3—Environmental And Human Health Concerns

ability of fish to swim, feed, and successfully avoid predation—is the critical assessment 

endpoint when evaluating the potential for selenium exposure to result in population-level 

impacts to resident fish species.

For a summary of the impacts of selenium on surface water, refer to Table A-10 in 

Appendix A. 

Lethal Effects of Other Pollutants

Scientific studies have confirmed that both acute and chronic exposure to pollutants in 

steam electric power plant wastewater can be lethal to a wide range of aquatic organisms. For 

example, Guthrie and Cherry [1976] found that shrimp darters and salamanders were highly 

sensitive to acute exposures of steam electric power plant wastewater and experienced nearly 

100 percent mortality following a five-day exposure to power plant wastewater discharges. 

Invertebrates and fish also evaluated in the study were less sensitive to the acute exposure to 

power plant wastewater and reported lower rates of mortality [Guthrie and Cherry, 1976]. 

Chronic exposures to power plant wastewater are also of concern; however, studies show 

extreme differences in species sensitivity [Rowe et al., 2002]. For example, juvenile chubsuckers 

(a benthic fish) exposed for 45 days to sediments, water, and food contaminated with power 

plant wastewater experienced a 75 percent mortality rate [Hopkins et al., 2001]. In another study, 

bullfrogs exposed to sediment and water from a combustion residual surface impoundment for 

34 days demonstrated an 87 percent mortality rate (which was 41 percent greater than the 

mortality rate of bullfrogs included in control group) [Rowe et al., 2002]. A third study reported 

no lethal effects for banded snakes exposed for 2 years to fish collected from combustion 

residual surface impoundments [Hopkins et al., 2002]. 

Other studies examined lethal effects of sediments contaminated with combustion 

residuals. For example, eggs and hatchlings of fish and reptiles raised in contaminated sediment 

reported higher mortality rates (16 to 94 percent) than eggs and hatchlings from control groups 

[Hopkins et al., 2000; Nagle et al., 2001; Roe et al., 2006; Rowe et al., 1998a, 1998b, 2001; 

Snodgrass et al., 2004]. Each of the studies observed elevated mortality rates in conjunction with 

higher concentrations of steam electric power plant wastewater pollutants (e.g., arsenic, 

cadmium, chromium, copper, selenium) in the exposed sediment. 

Three studies evaluated the lethal effects of specific pollutants in steam electric power

plant wastewater on a variety of organisms (i.e., insects, fish, and amphibians) and determined 

the median lethal concentration (LC50) for each pollutant-organism combination. LC50 is the

concentration expected to be lethal to 50 percent of a group of organisms exposed for a given 

time duration. Table 3-6 summarizes the results from the three experiments and Table 3-7 

presents the LC50 concentrations reported in the studies. Overall, the LC50 studies report speciesspecific differences, particularly among species living downstream of fly ash surface 

impoundment discharges. The downstream species developed resistance to pollutants compared

to those living in unpolluted ponds. Because the LC50 concentrations were much higher than 

actual aquatic concentrations, there was no evidence in these experiments of acute lethal effects,

though long-term (1 to 3 months) lethal effects could not be ruled out [Benson and Birge, 1985; 

Birge, 1978; Specht et al., 1984]. 

3-23 
 

Section 3—Environmental And Human Health Concerns

Sublethal Effects of Other Pollutants

Although the majority of sublethal effects documented in the literature primarily focus on 

selenium concentrations in steam electric power plant wastewater, several studies discussed the 

sublethal effects of other pollutants, such as arsenic, cadmium, chromium, copper, and lead 

[Rowe et al., 2002]. 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., swimming ability, ability to catch prey, ability to escape from predators), and 

metabolism that can negatively affect long-term survival. For example, a study of larval 

bullfrogs living in combustion residual surface impoundments found that more than 95 percent 

of individuals had abnormal oral structures, such as the absence of grazing teeth or entire rows of 

teeth, which altered feeding habits and subsequently reduced growth rates in the affected

bullfrogs [Rowe et al., 1996]. In another study, tail malformations in larval bullfrogs attributed to 

power plant wastewater exposure caused abnormal swimming behavior, and the affected 

bullfrogs were preyed upon more frequently than bullfrogs from unpolluted sites [Raimondo et

al., 1998]. 

Several studies have demonstrated increased metabolic rates and decreased growth rates

in aquatic organisms exposed to steam electric power plant wastewater. Increased metabolism 

causes organisms to waste energy during normal metabolic processes, which can affect growth. 

In a 1998 study by Rowe, grass shrimp caged in a surface impoundment for eight months 

experienced a 51 percent increase in standard metabolic rate. Similarly, crayfish captured near 

the impoundment experienced increased metabolic rates and decreased growth rates—effects that 

were also observed in crayfish collected from unpolluted sites and exposed to contaminated 

sediments from the combustion residual surface impoundment [Rowe et al., 2002]. 

3-24 
 

 

 

Section 3—Environmental And Human Health Concerns

Table 3-6. Summary of Studies Evaluating Lethal Effects of 

Pollutants in Steam Electric Power Plant Wastewater 

Citation Studied Organism 

Test 

Performed 

Trace Elements 

Studied Summary of Results

Birge, 

1978 

Eggs from goldfish, trout,

and toads

7- to 28-day

lethal effects

22 elements Among the 22 elements tested, 

cadmium, chromium, mercury, nickel, 

lead, and silver were the most toxic to 

all three species, with most LC50 being 

0.1 milligrams per liter (mg/L) or less. 

Benson

and Birge,

1985

Minnows (fish) living in fly 

ash-polluted ponds in

Kentucky compared to those 

living in uncontaminated

ponds 

Acute (96­

hour) toxicity

Cadmium 

Copper 

Zinc

The study found a higher tolerance to 

cadmium and copper in the exposed 

fish compared to the fish from

unpolluted ponds. However, both

exposed and unexposed populations

exhibited similar tolerance to zinc. See

Table 3-7 for LC50 values.

Specht et 

al., 1984 

Insects (coleopterans, 

mayflies, and other insects)

exposed to fly ash surface 

impoundment effluent from

the Appalachian Power 

Plant in Giles County, 

Virginia, compared to those 

living in an uncontaminated 

pond 

Acute (96­

hour) toxicity

Cadmium 

Copper 

Zinc

The study observed a higher tolerance 

to pollutants in exposed insects 

compared to those living in unpolluted 

ponds. See Table 3-7 for LC50 values.

3-25 
Section 3—Environmental An

Table 3-7. Median Lethal Concentrations (LC50) for Pollutants in Steam Electric Power Plant W

Pollutant 

LC50, mg/L 

7- to 28-Day Exposure 96-Hour Exposure

Trout 

[Birge, 1978] 

Goldfish

[Birge, 1978] 

Toad

[Birge, 1978] 

Exposed 

Minnows 

[Benson and

Birge, 1985] 

Control 

Minnows 

[Benson and

Birge, 1985] 

Mayflies 

[Specht et a

1984] 

Aluminum 0.56 0.15 0.05

Arsenic 0.54 0.49 0.04Cadmium 0.13 0.17 0.04 3.89 a

9.55 b

3.06 a

7.16 b

0.27 

Chromium 0.18 0.66 0.03

Cobalt 0.47 0.81 0.05Copper 0.09 5.2 0.04 0.36 a

0.41 b

0.21 a

0.39 b

0.18 

Lead 0.18 1.66 0.04

Mercury 0.005 0.12 0.001Nickel 0.05 2.14 0.05Selenium 4.18 8.78 0.09Silver 0.01 0.03 0.01Vanadium 0.16 4.6 0.25Zinc 1.06 2.54 0.01 6.14 a

5.96 b

6.09 a

7.45 b

18.44 

Acronyms: mg/L – milligrams per liter. Shaded cells indicate that the pollutant was not evaluated. a – Nominal water hardness of 100 mg/L calcium carbonate (CaCO3).

b – Nominal water hardness of 250 mg/L calcium carbonate (CaCO3).

3-26 
 

Section 3—Environmental And Human Health Concerns

3.3.2 Human Health Effects

Exposure to pollutants can cause noncancer effects in humans, including damage to 

the circulatory, respiratory, or digestive systems

and neurological and developmental effects. 

Steam electric power plant wastewater includes

toxic pollutants and known or suspected 

carcinogens (e.g., arsenic and cadmium). In the 

literature review, EPA identified potential 

human impacts from consuming fish in 

contaminated waters and from ingesting 

drinking water contaminated by pollutants from 

combustion residuals.19

During the late 1970s, three power plant 

cooling water reservoirs in Texas received 

discharges from surface impoundments 

containing elevated selenium levels, resulting in 

a series of fish kills. The reservoirs included Brandy Branch Reservoir, located in Harrison 

County; Welsh Reservoir, located in Titus County; and Martin Creek Lake, located in Rusk 

County. Investigations at the reservoirs implicated elevated selenium levels in the fish tissue as 

the cause. In 1992, the Texas Department of Health issued a fish consumption advisory for the 

three reservoirs after determining that the level of selenium in fish could pose a potential health 

risk to humans, especially children 6 years or younger and pregnant women. 

Ground water and drinking water supplies can be degraded by pollutants in steam electric 

power plant wastewater and combustion residual leachate [Cross, 1981]. Combustion residual 

leachate can migrate from the site in the ground water at concentrations that could contaminate 

public or private drinking water wells and surface waters, even years following disposal of

combustion residuals [NRC, 2006], as exemplified in the following example. The Wisconsin 

Electric Power Company (WEPCO) plant in Port Washington, Wisconsin, had disposed of fly 

ash in a quarry for over 20 years (1943-1971) at a depth of 40 to 60 feet, with some of the

disposed ash below the water table. The disposal site is located in an upland area where downgradient ground water is used as a source of drinking water. The Wisconsin Department of 

Natural Resources was notified in January 1980 and November 1990 that elevated levels of 

sulfates, selenium, and boron were found in a private drinking water well located 250 feet downgradient from the coal-fired power plant waste disposal site. The impacted private well was

replaced with a deeper well to avoid further contamination [U.S. EPA, 2014c]. 

19 In this EA, EPA evaluated the threats to human health and the environment associated with pollutants leaching 

into ground water from surface impoundments and landfills containing combustion residuals. If these leached 

pollutants do not constitute the discharge of a pollutant to surface waters, then they are not controlled under the 

steam electric ELGs. While the CCR rulemaking is the major controlling action for these pollutant releases to

ground water, the ELGs could indirectly reduce impacts to ground water. These secondary improvements are 

discussed in Section 7.8.

Numerous damage cases show exceedances of 

drinking water standards at ground water and 

drinking water wells due to leachate from 

nearby impoundments and landfills.

3-27 
 

Section 3—Environmental And Human Health Concerns

As discussed in Section 3.3.4 and Appendix A, there have been documented exceedances 

of MCL drinking water standards at off-site ground water and drinking water wells. Exceedances 

of MCLs in the ground water indicate potential human health impacts if the pollutants enter 

private drinking water wells. Section 3.3.4 outlines three documented instances where

combustion residual leachate contamination caused impacts to private drinking water wells. 

Drinking water standards can also be exceeded in surface waters. For example, Duke 

Energy's Riverbend Plant discharges surface impoundment effluent into Mountain Island Lake,

which supplies drinking water to 700,000 people. The county detected arsenic and zinc 

concentrations above state standards in an area near the surface impoundment discharge pipe

[Charlotte Observer, 2010]. While most of the pollutants in the surface water would likely be

reduced to safe levels during drinking water treatment, elevated levels of pollutants in source

water can impact the effectiveness of drinking water treatment processes and the ability of 

drinking water treatment plants to meet MCLs. Section 3.4.6 presents further details on drinking 

water resources near steam electric power plants.

3.3.3 Damage Cases and Other Documented Surface Water Impacts

Changes in surface water chemistry due to contamination from steam electric power plant 

wastewater can negatively impact all levels of an ecosystem, including lower food chain 

organisms, which affect the ecosystem’s food web; fish inhabiting the surface water; and wildlife 

and humans when they bathe in or drink the water. As described in earlier sections, pollutants in 

surface water can accumulate 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. Documented 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. Impacts that 

affect humans include exceedances of 

NRWQC, fish consumption advisories, and 

designation of surface waters as impaired

(limiting recreational activities). 

EPA’s damage case assessment found

26 proven damage case sites and 31 potential 

damage case sites with surface water impacts 

[U.S. EPA, 2014a through 2014e]. Including 

documented site impacts from the literature

review, EPA identified impacts to surface

waters at nearly 70 steam electric power plants

following exposure to wastewater (more than 

140 documented site impacts) [ERG, 2015m]. 

Some of the documented impact sites are the 

same locations identified by EPA as damage 

case sites. Table 3-8 highlights several damage 

case and other documented impact sites where 

Some wastewater surface impoundments are 

located in, or near, large river floodplains. 

Failure of the embankments of surface 

impoundments can release catastrophic 

amounts of pollutants into surrounding 

ecosystems. 

3-28 
Section 3—Environmental And Human Health Concerns

negative surface water impacts from steam electric power plant wastewater discharges have been

studied. In most cases, negative impacts have been studied and documented in multiple articles

and reports. Tables A-6 and A-7 in Appendix A summarize the damage cases from combustion 

residual surface impoundments and landfills, respectively.

3-29 
Section 3—Environm

Table 3-8. Summary of Select Sites with Documented Surface Water Impacts from Steam Electric Po

Site Name and 

Location

Number of 

Documents that

Discuss Surface 

Water Impacts 

at the Site

EPA 

Damage 

Case

Assessment Summary of Surface Water Impacts

Belews Lake, 13 Proven In 1970, Duke Power Company constructed Belews Lake as a cooling water reserv

NC damage case 

[U.S. EPA, 2014b]

Steam Station. Almost immediately after surface impoundment effluent began disc

populations experienced morphological changes, reproductive failure, and eventuaCreek Steam Station converted to a dry-ash transport system, ending the surface im

lake. However, even 11 years after the discharges ceased, reproductive abnormalitpopulations. Due to selenium concentrations, 16 of the 20 populations originally pentirely eliminated, including all primary sport fish [Lemly, 1997a; U.S. EPA, 201

Brandy Branch 1 Proven Brandy Branch Reservoir serves as a cooling water reservoir for Pirkey Power Pla

Reservoir, TX damage case 

[U.S. EPA, 2014b]

Parks and Wildlife Department's) reported increases in the selenium concentrationreceiving water. As a result, the Texas Department of Health issued a fish consumbecause of the potential health impact due to the levels of selenium in fish. Since tSouthwestern Electric Power Company has worked cooperatively to monitor fish twhich have decreased since the late 1980s [ATSDR, 1998a].

Euharlee Creek, GA

1 Proven

damage case [U.S. EPA, 2014b]

On July 28, 2002, a sinkhole developed in the surface impoundment at the Georgia 

GA. The sinkhole expanded to 4 acres, and an estimated 2.25 million gallons of astributary of the Euharlee Creek. Approximately 80 tons of ash entered Euharlee Crpipe. This discharge deposited an ash blanket in the creek up to 8 inches deep over bottom. Sampling at the ash discharge site found that concentrations of certain me

copper, lead, mercury, and nickel) exceeded EPA Region IV ecological sediment s

indicating a potential for adverse impacts to aquatic life. Sediment concentrations weight–over five times the toxic threshold. Biological sampling indicated that benash deposition zone of Euharlee Creek were either killed by contaminants or physicommunity, which consisted of at least 25 species, was displaced due to the irritat

plume as it moved through during the spill. One month after the spill, concentratio

elevated in crayfish, clams, mollusks, and insects at a Euharlee Creek site downstr

3-30 
Section 3—Environm

Table 3-8. Summary of Select Sites with Documented Surface Water Impacts from Steam Electric Po

Site Name and 

Location

Number of 

Documents that

Discuss Surface 

Water Impacts 

at the Site

EPA 

Damage 

Case

Assessment Summary of Surface Water Impacts

Gibson Lake, IN

4 Proven

damage case [U.S. EPA, 2014b]

Gibson Lake is a man-made, shallow impoundment that receives surface impoundGenerating Station. Starting in 1986, least terns, an endangered species of migratoGibson Lake as a nesting ground for breeding. To protect the birds from potential cooperative program with the Indiana Department of Natural Resources to protect nearby alternative habitat, known as Cane Ridge Wildlife Management Area (WMfrom Gibson Lake. In April 2007, Duke Energy closed access to the lake for recre

selenium levels. A year later, the U.S. Fish and Wildlife Service (USFWS) becamin the water and fish in the Cane Ridge WMA. The USFWS stopped the flow of wRidge, discouraged least terns from using the refuge, removed the contaminated firedistribute and bury the selenium in the soil. Subsequently, the USFWS stopped tLake into Cane Ridge and piped water from Wabash River instead. Cane Ridge w

migratory birds. As of 2010, fish populations in Gibson Lake still had selenium lev[U.S. EPA, 2014b]. 

Glen Lyn, VA 5 Proven

damage case [U.S. EPA, 2014b]

Glen Lyn Plant discharged fly ash transport water from a surface impoundment intNew River. A 1984 study reported that the local insect diversity and density remai(reference site) and downstream of the surface impoundment when the impoundmHowever, as the settling impoundment reached its capacity, the insect density and After closure of the surface impoundment, it took up to 10 months for the insect p

al., 1984]. 

Hyco Lake, NC 8 Proven

damage case [U.S. EPA, 2014b]

Hyco Lake is a large cooling water reservoir that received effluent from a power p

residual leachate and fly ash transport water discharges containing high levels of skill occurred in the reservoir, prompting numerous scientific studies to examine thenvironmental damage. Multiple studies detected selenium concentrations in the wthe reservoir, while other trace elements were within normal concentration ranges. 

fish in the lake, impacting reproduction and causing declines in fish populations in fish consumption advisory was issued in 1988 for this lake due to selenium contam

3-31 
Section 3—Environm

Table 3-8. Summary of Select Sites with Documented Surface Water Impacts from Steam Electric Po

Site Name and 

Location

Number of 

Documents that

Discuss Surface 

Water Impacts 

at the Site

EPA 

Damage 

Case

Assessment Summary of Surface Water Impacts

Martin Creek 8 Proven Martin Creek Lake is a cooling water reservoir that also receives steam electric po

Lake, TX damage case 

[U.S. EPA, 2014b]

In 1978 and 1979, a series of major fish kills occurred due to the elevated concentand fish tissue. Numerous studies conducted throughout the 1980s documented hisdamage in the fish populations inhabiting the lake. In addition, the studies determidischarge ceased, the overall health of the aquatic populations near the discharge sthe selenium pollution. In 1992, a fish consumption advisory was issued for the laksteam electric power plant [U.S. EPA, 2014b]. 

McCoy Branch, TN 

3 Proven

damage case [U.S. EPA, 2014b]

In 1986, coal ash slurry discharges from the Department of Energy’s (DOE’s) CheMcCoy Branch were found to contain elevated concentrations of trace elements, w

Quality Act. A 1992 report written by DOE documented bioaccumulation of contadiversity in benthic macroinvertebrate communities, and increased fish mortality a

DOE, 1992].

Mountain 5 Location not Duke Energy's Riverbend Plant discharges surface impoundment effluent into MoIsland Lake, assessed drinking water to 700,000 people. The county staff has detected arsenic and zinc c

NC standards in an area near the surface impoundment discharge pipe [Charlotte Obse

to extensively monitor metal concentrations in Mountain Island Lake surrounding 2011]. 

North Carolina Not applicable, Location not A study of receiving waters (including lakes and rivers) for 10 steam electric powe

(Multiple multiple sites assessed evaluated the environmental and ecological impacts that wastewater discharges ha

Locations) found that the receiving waters at the 10 plants contain high levels of contaminant

discharges. From the data collected between 2010 and 2012, contaminant levels at 

drinking water standards and/or NRWQC. For example, arsenic concentrations at μg/L and 92 μg/L, respectively (the drinking water MCL for arsenic is 10 μg/L). Wpollutant concentrations at the 10 North Carolina locations, data showed elevated boron, chromium, selenium, bromine, arsenic, and thallium. Elevated pollutant conlake sediments (arsenic and selenium) and pore water near lake bottoms (including bromine). The study found elevated levels of arsenic and selenium in fish tissues fand Mayo Lake). A report on fish in Mayo Lake found deformities consistent with [Ruhl et al., 2012].

3-32 
Section 3—Environm

Table 3-8. Summary of Select Sites with Documented Surface Water Impacts from Steam Electric Po

Site Name and 

Location

Number of 

Documents that

Discuss Surface 

Water Impacts 

at the Site

EPA 

Damage 

Case

Assessment Summary of Surface Water Impacts

Rocky Run 5 Proven Rocky Run Creek, a tributary of the Wisconsin River, receives effluent from Colu

Creek, WI damage case 

[U.S. EPA, 2014b]

impoundments. After the power station began operation in 1975, the aquatic macroin the area. Two studies conducted at this site concluded that population density deto coal ash toxicity, but because the aquatic macroinvertebrate populations avoided alterations in the creek. Studies found increased TDS and total suspended solids (Tmetals, downstream from the discharge. Some species of macroinvertebrates were 

discharges began. 

Savannah River 23 Proven The Savannah River Site, which is owned by DOE, is divided into several areas, bSite, SC damage case 

[U.S. EPA, 2014b]

other related characteristics. The D-area, a site utilized by numerous ecologists to power plant waste, houses a coal-fired power plant that discharges ash into a serie

swamp that ultimately drains into the Savannah River. Numerous studies observed accumulated high concentrations of trace elements in their tissues and exhibited vaand developmental effects. Sediments, water, and biota in the disposal system havelements and heavy metals derived from bottom ash and fly ash deposited in the bseveral impacts to amphibians, reptiles, and fish, including five species of fish that 

TVA’s 6 Proven On December 22, 2008, the retaining wall of a surface impoundment at TVA’s Ki

Kingston Fossil damage case released billions of gallons of coal ash slurry into the Emory, Clinch, and Tenness

Plant, TN [U.S. EPA, 

2014b]

of Environment and Conservation found exceedances of the more stringent criteria aquatic life at least once in January 2009 for several metals (e.g., aluminum, cadmafter the spill, all fish collected had concentrations of selenium above a toxic threscontaminated at that level 14 months after the spill. Twenty-one months after the sfound with lesions, deformities, and infections, all symptoms of extreme stress. In elevated levels of arsenic and mercury in sediments near the ash spill, as well as sein three wells underneath the Kingston’s coal ash disposal area, ash processing are

[U.S. EPA, 2014b].

3-33 
Section 3—Environm

Table 3-8. Summary of Select Sites with Documented Surface Water Impacts from Steam Electric Po

Site Name and 

Location

Number of 

Documents that

Discuss Surface 

Water Impacts 

at the Site

EPA 

Damage 

Case

Assessment Summary of Surface Water Impacts

WelshReservoir, TX

2 Proven

damage case [U.S. EPA, 2014b]

Welsh Reservoir serves as a cooling water reservoir for Welsh Power Plant. From 

Wildlife Department reported increases in the selenium concentrations of the fish a result, the Texas Department of Health (TDH) issued a fish consumption advisorpotential health impact due to the levels of selenium in fish. In 1998, TDH collecteobserved an average selenium concentration in the fish above the reported nationa

for Toxic Substances and Disease Registry (ATSDR) concluded in a report that thoverall change in selenium fish tissue concentrations over the 12 years [ATSDR, 1

Sources: ATSDR, 1998a; ATSDR, 1998b; Charlotte Observer, 2010; ERG, 2013b; Lemly, 1997a; NCDENR, 2011; Ruhl et al., 2012; 

1992; U.S. EPA, 2014b. 

3-34 
Section 3—Environmental And Human Health Concerns

3.3.4 Damage Cases and Other Documented Ground Water Impacts

Pollutants in combustion residuals can leach into ground water from surface 

impoundments and landfills at the site. 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 ground water contamination. 

Combustion residuals held in unlined surface impoundments can enter the subsurface and 

contaminate ground water. Pollutants in unlined landfills, used for the dry disposal of 

combustion residuals, can also leach as precipitation flows through the residuals pile and 

dissolves pollutants; the combustion residual leachate can eventually migrate into ground water. 

New plants are increasingly installing liners in surface impoundments and landfills, but 

pollutants can also enter the ground water when liners fail or when a disposal site is situated such 

that natural ground water fluctuations come into contact with the disposed waste. Furthermore, 

state regulation on leachate collection systems and impermeable liners is not uniform [EPRI, 

1997; 65 FR 32214-32237, 2000]. 

Numerous damage cases and other documented site impacts demonstrate the toxic effects 

of steam electric power plant wastewater contamination to ground water and the potential to 

impact off-site sources due to combustion residual leachate migrating from landfills and surface 

impoundments (often unlined). EPA’s damage case assessment found 24 proven damage case

sites and 110 potential damage case sites with ground water impacts [U.S. EPA, 2014a through 

2014e]. EPA identified impacts to ground water quality caused by combustion residual leachate

from 140 steam electric power plants (more than 130 documented site impacts) [ERG, 2015m]. 

Some of these documented site impacts are caused by ash contributions from multiple plants

(e.g., a landfill that stores ash from multiple plants). EPA identified some of the documented 

impact sites as also being damage case sites. The majority of the damage cases and documented

site impacts reported ground water pollutant levels in on-site wells above regulatory levels; 

however, only a portion of the cases indicated off-site contamination. Documented impacts to 

off-site ground water resources may be lower due to long migration times within the subsurface 

until the combustion residual leachate reaches a known monitoring point [NRC, 2006]. Further,

the limited number of studies documenting off-site contamination might reflect less extensive

monitoring of off-site ground water wells for evidence of impacts from combustion residual 

leachate, which suggests off-site impacts may be underrepresented in the documented ground 

water impacts [Cherry, 2000]. 

In surface impoundments, combustion residuals are in constant contact with water,

allowing toxic pollutants to leach into and eventually contaminate ground water. From an

environmental impact perspective, combustion residual surface impoundments are generally 

considered less desirable than landfills for disposal because they provide constant saturated or

nearly saturated conditions and a relatively large hydraulic driving force to move combustion 

residual leachate into the subsurface [Theis and Gardner, 1990]. Table A-4 in Appendix A 

summarizes documented ground water damage cases from combustion residual surface 

impoundments [U.S. EPA, 2014a through 2014e]. 

Although more desirable than surface impoundments, landfills pose their own ground 

water contamination risks. If the landfills are not properly lined, the pollutants in combustion 

residuals can leach into the soil during precipitation. In areas with acid rain, the precipitation’s 

3-35 
Section 3—Environmental And Human Health Concerns

low pH can accelerate the leaching of contaminants into ground water. In addition, heavy 

precipitation can not only accelerate leaching, but also carry pollutants in stormwater runoff,

potentially contaminating ground water or surface water resources [Andersen and Madsen, 

1983]. Table A-5 in Appendix A summarizes documented ground water damage cases from 

combustion residual landfills [MDNRE, 2010; U.S. EPA, 2014a through 2014e]. 

While many damage cases document elevated pollutant levels in ground water wells, it is 

unclear how many of these are private drinking water wells (as opposed to monitoring wells). 

However, the fact that many sites reported MCL exceedances in ground water testing suggests 

that potential impacts to drinking water resources are a realistic concern. The following three 

damage cases are documented instances where uncollected combustion residual leachate 

contaminated ground water and resulted in impacts to private drinking water wells. 

Constellation Ash Disposal at Waugh Chapel and Turner Pits – Anne Arundel County, 

Maryland 

For over a decade, Constellation Energy Group (Constellation) supplied fly ash for 

structural fill at the B.B.S.S. Inc. (BBSS) sand and gravel mines in Anne Arundel County, 

Maryland. Fly ash from Constellation’s Brandon Shores and Wagner plants was used to reclaim

portions of BBSS’s Turner Pit starting in 1995 and the Waugh Chapel Pit starting in 2000. In the

fall of 2006, Anne Arundel County Health Department officials documented concentrations of 

sulfate and metals (i.e., antimony, beryllium, cadmium, manganese, and nickel) exceeding the

state’s screening criteria for potable aquifers in residential wells located downgradient from 

Waugh Chapel and Turner Pits [MDNR, 2007]. 

An independent study of the contamination confirmed that the elevated concentrations of 

sulfate and metals observed in the wells directly resulted from precipitation infiltrating the fly 

ash deposited in the BBSS sand and gravel mines [MDNR, 2007]. In October 2007, the

Maryland Department of the Environment (MDE) fined Constellation and BBSS $1 million for 

the ground water contamination and required the companies to restore the local aquifer water 

quality [MDE, 2008]. In addition, Anne Arundel homeowners impacted by the contamination

filed a class action lawsuit against Constellation and were awarded a $45 million settlement. The 

settlement required Constellation to pay the costs for converting 84 homes from well water to 

public water; cease future deliveries of new coal ash to the quarry; and to establish trust funds to

compensate impacted property owners, enhance the neighborhood, and remediate and restore a 

former quarry site [Schultz, 2008]. 

Gibson Generating Station Plant – Gibson County, Indiana

The Gibson Generating Station Plant has six unlined surface impoundments (four surface

impoundments and two settling/decant basins) and a landfill for combustion residuals. The 

landfill consists of a 94-acre older portion built in the late 1970s that is unlined and a 43-acre 

portion built in 2002 with a composite liner and leachate collection system. Additionally, the 

plant has a 400-acre landfill (South Landfill), permitted in 2005, which also has a composite

liner and leachate collection system. 

Samples from monitoring wells downgradient from the older landfill show high levels of 

arsenic, boron, iron, and manganese. Leaching from the landfill has contaminated 12 drinking

water wells in the hamlet of East Mount Carmel, Indiana, with boron, manganese, iron, sulfate, 

3-36 
 

 

Section 3—Environmental And Human Health Concerns

sodium, and TDS. Sampling performed by Duke Energy in 2007 and by the Natural Resources 

Defense Council in 2008 show drinking water contamination from boron, iron, and manganese in 

at least nine off-site private residential wells [U.S. EPA, 2014b]. 

Ground Water Violations Near North Carolina Power Plants With Surface 

Impoundments – North Carolina

The North Carolina Department of Environment and Natural Resources reported ground 

water contamination near combustion residual surface impoundments at all 14 of the state’s coalfired power plants. Duke Energy and Progress Energy each own seven of the plants and perform 

ground water monitoring as required by the state. Manganese and lead concentrations exceeded 

state ground water standards at all 14 locations and TDS and chromium concentrations exceeded 

state standards at seven locations. Boron levels at six plants exceeded state ground water 

standards, and some plants had elevated levels of arsenic, selenium, thallium, antimony, 

chlorides, and nickel. The state and plants have not identified the source of the contamination but 

noted that the exceedances occurred at newly located wells. Drilling the wells may have affected

the concentration of naturally occurring elements such as lead and manganese [Ballard, 2012].20

3.3.5 Potential for Impacts to Occur in Other Locations

Key environmental characteristics that contributed to the impacts documented in Sections 

3.3.3 and 3.3.4, such as chronic exposure to large pollutant loadings, plants discharging to waters 

with long residence times, and unlined surface impoundments or landfills, are common at steam 

electric power plants. This suggests that the impacts documented above indicate the greater 

potential threat that steam electric power plant wastewater discharges pose to the environment.

Although substantial events such as fish kills are well documented, the extent to which more 

subtle damages, such as histopathological changes, morphological deformities, and damage to 

reproductive success, occur elsewhere is not known due to the limited extent of monitoring

programs. 

Some of the documented environmental impacts discussed above occurred following 

discharges of steam electric power plant wastewater under normal operations. Although the 

actual amounts of pollutant loadings discharged may vary among steam electric power plants, 

documented site impacts under normal operations do not indicate that the pollutant loadings

associated with the impacts are unusual for steam electric power plants. This suggests that 

chronic exposure to typical steam electric power plant wastewater pollutant loadings can impact 

the environment at other sites not documented in the literature. 

The residence time of steam electric power plant wastewater pollutants in surface water is 

a major factor in determining the impact to the environment and the length of the recovery time. 

Many documented impact sites are lentic waterbodies such as lakes (i.e., still waters) where 

pollutants can reside for long periods of time. These types of surface waters are at particular risk

to impacts from steam electric power plant wastewater discharges. Steam electric power plants

that discharge to a pond, lake, or reservoir may experience similar environmental effects as those 

observed in the documented impacts from analogous aquatic systems [ERG, 2015j]. 

20 EPA notes that the impacts reported at North Carolina plants have not been documented in a peer-reviewed 

literature source; however, the information shows that elevated levels of metal contamination can occur near ash

ponds. 

3-37 
 

 

Section 3—Environmental And Human Health Concerns

3.4 DISCHARGE TO SENSITIVE ENVIRONMENTS

The pollutant loadings, ecological impacts, and human health concerns discussed in 

Section 3.2 and Section 3.3 are also of concern due to the proximity of many steam electric 

power plants to sensitive environments where the characteristics of steam electric power plant 

wastewater may impair water quality (e.g., 303(d)-listed waters and waters with fish advisories) 

or pose a threat to threatened and endangered species.21 EPA identified the number of surface 

waters that receive discharges of the evaluated wastestreams and are located in close proximity 

to the following sensitive environments: 

 Great Lakes watershed (Section 3.4.1). 

 Chesapeake Bay watershed (Section 3.4.2). 

 Impaired waters (Section 3.4.3). 

 Fish consumption advisory waters (Section 3.4.4). 

 Threatened and endangered species habitats (Section 3.4.5). 

 Drinking water resources (Section 3.4.6). 

Table 3-9 summarizes the number and percentage of immediate receiving waters located 

in sensitive environments. 

Table 3-9. Number and Percentage of Immediate 

Receiving Waters Identified as Sensitive Environments

Sensitive Environment 

Number (Percentage) of Immediate

Receiving Waters Identified a

Great Lakes watershed 25 (11%)

Chesapeake Bay watershed 13 (6%)

Impaired water 111 (50%)

Surface water impaired for a subset of pollutants associated with the 

evaluated wastestreams b 59 (27%)

Fish consumption advisory water 140 (63%)

Surface water with a fish consumption advisory for a subset of 

pollutants associated with the evaluated wastestreams c 93 (42%)

Drinking water resource within 5 miles 199 (90%)

a – For the sensitive environment proximity analysis, EPA evaluated 222 immediate receiving waters that receive

discharges of the evaluated wastestreams [ERG, 2015c; ERG, 2015d].

b – Table B-1 in Appendix B contains a complete list of the impairment categories identified in EPA’s 303(d)­

listed waters and designates the subset of pollutants evaluated.

c – Table B-2 in Appendix B contains a complete list of the types of advisories identified under the sensitive 

environment proximity analysis, including pollutants that are not associated with the evaluated wastestreams.

3.4.1 Pollutant Loadings to the Great Lakes Watershed

The Great Lakes watershed includes hundreds of tributaries, thousands of smaller lakes, 

and extensive mineral deposits. The watershed provides a unique habitat that supports a wide 

range of flora and fauna, including over 200 globally rare plants and animals and more than 40 

species found only in the Great Lakes watershed. Rare species include the white catspaw pearly 

mussel, the copper redhorse fish, and the Kirtland’s warbler. The watershed provides a habitat

21 See the ERG memorandum “Proximity Analysis Methodology” (DCN SE04448) for a description of the

methodology used to evaluate the proximity of steam electric power plants to sensitive environments. 

3-38 
Annual Discharges to the Great Lakes

Watershed from the Evaluated 

Wastestreams

 1.15 million pounds of total nitrogen 

 9,570 pounds of thallium

 8,730 pounds of zinc 

 5,020 pounds of selenium 

 2,170 pounds of arsenic 

 1,900 pounds of lead 

Section 3—Environmental And Human Health Concerns

and food web for an estimated 180 species of native fish, including small- and large-mouth bass, 

muskellunge, northern pike, lake herring, whitefish, walleye, and lake trout [Great Lakes 

Restoration Initiative, 2010]. 

The Great Lakes provide humans with transportation, power, and recreational 

opportunities including fishing and boating. Between the United States and Canada, the Great 

Lakes have more than 10,000 miles of coastline and 30,000 islands. The watershed is home to 

more than 30 million people. Recreational spending directly supports 107,000 jobs and nearly

250,000 jobs when secondary impacts are taken into consideration [Great Lakes Restoration 

Initiative, 2010]. 

Environmental impacts documented in the Great Lakes are associated with a range of 

stressors, including toxic and nutrient pollutants, invasive species, and habitat degradation. EPA 

and Environment Canada have focused their Great Lakes Binational Toxics Strategy on 

persistent toxic substances such as mercury [U.S. EPA and Environment Canada, 1997; Great 

Lakes Restoration Initiative, 2010]. Mercury is a concern in all of the Great Lakes due to its 

bioaccumulation in fish and wildlife and potential impacts on humans. For example, in a study of 

65 hair samples from fish-eating and non-fish-eating women, average mercury concentrations in 

hair were significantly greater (i.e., 128 to 443 

percent higher concentration) for women who ate 

several meals of sport-caught fish from the Great 

Lakes. EPA and Environment Canada have 

documented a range of wildlife impacts from 

mercury in the Great Lakes such as an increase of 

physiological abnormalities in herring gulls [U.S. 

EPA and Environment Canada, 2009]. 

As part of the EA, EPA wanted to determine 

the extent of impacts to the Great Lakes watershed

that might be caused by discharges of the evaluated 

wastestreams. The primary source of mercury in the Great Lakes watershed is atmospheric 

deposition from sources around the Great Lakes watershed (e.g., fuel combustion, incineration, 

and manufacturing) emitting approximately 70,000 pounds of mercury annually [Evers et al., 

2011]. When compared to atmospheric deposition, mercury contributions from point source 

discharges are less of a concern. Due to the bioaccumulative nature of mercury, EPA has placed 

strict controls (e.g., mixing zones are not allowed in permits) to limit the total amount of mercury 

entering the Great Lakes watershed. Monitoring within the Great Lakes watershed has indicated 

a decrease in mercury point source discharges, primarily because of implemented control 

strategies. EPA identified 23 steam electric power plants discharging to the Great Lakes 

watershed with the majority discharging to Lake Michigan (11 plants) and Lake Erie (6 plants) 

[ERG, 2015a]. In the Lake Erie Management Plan, EPA identified steam electric discharges as

contributing 57 percent of the mercury to Lake Erie from wastewater sources [U.S. EPA, 2008b]. 

The potential for bioaccumulative pollutant retention in still or slow-moving water, such 

as the Great Lakes, is a particular concern. Many pollutants in steam electric power plant 

wastewater can bioaccumulate in fish and then affect higher trophic levels and terrestrial 

environments. Table 3-10 presents total pollutant loadings for the evaluated wastestreams

discharging to the Great Lakes watershed. 

3-39 
 

 

 

 

 

Section 3—Environmental And Human Health Concerns

Table 3-10. Pollutant Loadings to the Great Lakes Watershed from the Evaluated 

Wastestreams

Pollutant 

Annual Discharge to the Great Lakes 

Watershed (lbs) 

Annual TWPE Discharge to the 

Great Lakes Watershed (lb-eq) 

Arsenic 2,170 7,510

Boron 997,000 8,310 

Cadmium 648 14,700 

Chromium VI 0.548 0.283

Copper 2,550 1,590 

Lead 1,900 4,250

Manganese 242,000 24,900 

Mercury 82.8 9,110 

Nickel 9,840 1,070

Selenium 5,020 5,630

Thallium 9,570 27,300 

Zinc 8,730 409

Total Nitrogen 1,150,000 --

Total Phosphorus 23,100 --

Chlorides 31,900,000 778 

Total Dissolved Solids 186,000,000 --

Source: ERG, 2015a. 

Note: Numbers are rounded to three significant figures. 

3.4.2 Pollutant Loadings to the Chesapeake Bay Watershed

The Chesapeake Bay is the largest estuary in the United States and is a complex 

ecosystem that provides habitats and food webs for diverse groups of animals and plants. A 

variety of fish either live in the Chesapeake Bay and its tributaries year-round or visit its waters 

as they migrate along the East Coast. The Chesapeake Bay Watershed covers 64,000 square 

miles, with 11,684 miles of shoreline, and includes areas in six states: Delaware, Maryland, New 

York, Pennsylvania, Virginia, and West Virginia, plus Washington, DC. The watershed includes 

approximately 284,000 acres of tidal wetlands that provide critical habitats for fish, birds, crabs, 

and other species [Chesapeake Bay Program, 2015a and 2015b].

The Chesapeake Bay and its tributaries

provide recreational and commercial opportunities, 

with more than 100,000 streams, creeks, and rivers

in the watershed. Fishers commonly catch striped 

bass and white perch and seafood production from 

the Bay totals approximately 500 million pounds per 

year [Chesapeake Bay Program, 2015]. 

The Chesapeake Bay was the first estuary in

the nation to be selected for restoration as an 

integrated watershed and ecosystem. The watershed supports over 2,700 species of plants and 

animals, including 348 species of finfish and 173 species of shellfish. Other aquatic life includes 

algae, bay grasses, and other invertebrates. The watershed provides habitats for at least 29 

species of waterfowl, with a population of nearly one million during the winter (representing 

Annual Discharges to the Chesapeake 

Bay from the Evaluated Wastestreams

 993,000 pounds of total nitrogen

 6,560 pounds of selenium 

 5,830 pounds of zinc 

 5,280 pounds of thallium

2,510 pounds of arsenic

3-40 
 

 

 

 

 

Section 3—Environmental And Human Health Concerns

approximately one-third of the Atlantic Coast’s migratory population) [Chesapeake Bay 

Program, 2015]. 

Most of the Chesapeake Bay and its tidal waters are listed as impaired for excess

nitrogen, phosphorus, and sediment. These pollutants cause oxygen-consuming algae blooms and 

create “dead zones” where fish and shellfish cannot survive, block sunlight that is needed for

underwater grasses, and smother aquatic life on the bottom of the Bay. To restore water quality 

in the Bay, EPA established Total Maximum Daily Load (TMDL) limits for the Chesapeake Bay 

watershed in December 2010. These limits are 186 million pounds of nitrogen, 12.5 million

pounds of phosphorus, and 6.45 billion pounds of sediment each year, reducing the discharges to 

the watershed by 25 percent for nitrogen, 24 percent for phosphorus, and 20 percent for 

sediment. Pollutant loadings to the Chesapeake Bay watershed come from both point sources and 

nonpoint sources. Point sources include municipal wastewater treatment facilities, industrial 

discharge facilities (e.g., steam electric power plants and concentrated animal feeding 

operations), NPDES permitted stormwater (municipal separate storm sewer systems (MS4) and 

construction and industrial sites), and other sources. Nonpoint sources include agricultural land 

runoff, atmospheric deposition, forest land runoff, nonregulated stormwater runoff, stream banks

and tidal shorelines, tidal resuspension, the ocean, wildlife, and natural background [U.S. EPA, 

2010d].

EPA identified nine steam electric power plants discharging to the Chesapeake Bay 

watershed and estimated that these plants discharge almost one million pounds of nitrogen and

over 16,000 pounds of phosphorus to the Bay annually [ERG, 2015a]. Table 3-11 presents the 

baseline pollutant loadings for the evaluated wastestreams. 

Table 3-11. Pollutant Loadings to the Chesapeake Bay Watershed from the Evaluated 

Wastestreams

Pollutant 

Annual Discharge to the Chesapeake

Bay Watershed (lbs) 

Annual TWPE Discharge to the 

Chesapeake Bay Watershed (lb-eq) 

Arsenic 2,510 8,720

Boron 1,390,000 11,600 

Cadmium 513 11,700 

Chromium VI 16.7 8.62

Copper 2,210 1,380 

Lead 1,560 3,490

Manganese 148,000 15,200 

Mercury 88.8 9,770 

Nickel 5,280 575 

Selenium 6,560 7,360

Thallium 5,280 15,100 

Zinc 5,830 273

Total Nitrogen 993,000 --

Total Phosphorus 16,800 --

Chlorides 43,000,000 1,050 

Total Dissolved Solids 186,000,000 --

Source: ERG, 2015a. 

Note: Numbers are rounded to three significant figures. 

3-41 
 

 

Section 3—Environmental And Human Health Concerns

3.4.3 Proximity to Impaired Waters

A surface water is classified as a 303(d) impaired water when pollutant concentrations

exceed water quality standards and the surface water can no longer meet its designated uses (e.g., 

drinking, recreation, and aquatic habitat). Based on that definition, half of the immediate 

receiving waters included in the EA are impaired waters.22 EPA reviewed the identified 303(d) 

impairment categories and determined that approximately 27 percent of the immediate receiving

waters are impaired for a pollutant associated with the evaluated wastestreams, as shown in 

Table 3-12. Figure 3-1, Figure 3-2, and Figure 3-3 illustrate the geographical location of plants 

that directly discharge wastewater to a water classified as impaired by high concentrations of 

mercury, metals (other than mercury), and nutrients. 

Table 3-12. Number and Percentage of Immediate Receiving Waters Classified as

Impaired for a Pollutant Associated with the Evaluated Wastestreams

Pollutant Causing Impairment 

Number (Percentage) of Immediate

Receiving Waters Identified a

Mercury 30 (14%) 

Metals, other than mercury b 28 (13%)

Nutrients 19 (9%)

TDS, including chlorides 4 (2%)

Total for Any Pollutant c 70 (32%)

a – For the impaired waters proximity analysis, EPA evaluated 222 immediate receiving waters that receive 

discharges of the evaluated wastestreams [ERG, 2015c; ERG, 2015d].

b – The EPA impaired water database listed 28 immediate receiving waters as impaired based on the “metal, other 

than mercury” impairment category. Of those 28 immediate receiving waters, 13 receiving waters are also listed as

impaired for one or more specific metals in the EA analysis (arsenic, cadmium, chromium, copper, lead, manganese, 

selenium, and zinc). One additional immediate receiving water is impaired for boron (but not included in the 

“metals, other than mercury” impairment category). 

c – Total does not equal the sum of the immediate receiving waters listed in the table. Some immediate receiving 

waters are impaired for multiple pollutants. 

22 Table B-1 in Appendix B lists the impairment categories identified under the sensitive environments proximity 

analysis, including pollutants that are not associated with the evaluated wastestreams. 

3-42 
Figure 3-1. Location of Plants that Directly Discharge the Evaluated Wastestreams 

to a Surface Water Impaired due to Mercury

Figure 3-2. Location of Plants that Directly Discharge the Evaluated Wastestreams

to a Surface Water Impaired due to Metals, Other than Mercury

Section 3—Environmental And Human Health Concerns

3-43 
Figure 3-3. Location of Plants that Directly Discharge the Evaluated Wastestreams

to a Surface Water Impaired due to Nutrients 

 

Section 3—Environmental And Human Health Concerns

3.4.4 Proximity to Fish Consumption Advisory Waters

States, territories, and authorized tribes issue fish consumption advisories when pollutant 

concentrations in fish tissue are considered unsafe for consumption [U.S. EPA, 2011e]. EPA 

determined that 140 of the immediate receiving waters included in the EA (63 percent) are under 

fish consumption advisories; 93 of the immediate receiving waters (42 percent) are under an 

advisory for a pollutant associated with the evaluated wastestreams.23 All of these 93 immediate 

receiving waters are under a fish consumption advisory for mercury and one of the receiving 

waters is also under a fish consumption advisory for lead. EPA also reviewed fish consumption 

advisories for arsenic, cadmium, and selenium but did not identify any immediate receiving 

waters under advisories for these pollutants. Figure 3-4 illustrates the geographical location of 

plants that directly discharge steam electric power plant wastewater to surface waters with a fish

consumption advisory for lead or mercury. 

23 Table B-2 in Appendix B lists the types of advisories identified under the sensitive environment proximity

analysis, including pollutants that are not associated with the evaluated wastestreams.

3-44 
Figure 3-4. Location of Plants that Directly Discharge to a Surface Water with a Fish 

Consumption Advisory 

 

 

Section 3—Environmental And Human Health Concerns

3.4.5 Proximity to Threatened and Endangered Species Habitats

Under the Endangered Species Act (ESA), endangered species are those in danger of 

extinction throughout all or a significant portion of its range. Threatened species are those 

species that are likely to become endangered within the foreseeable future. A species may be

listed solely on the basis of their biological status and threats to their existence. The USFWS 

considers five factors for listing: 1) damage to, or destruction of, a species’ habitat; 2)

overutilization of the species for commercial, recreational, scientific, or education purposes; 3) 

disease or predation; 4) inadequacy of existing protection; and 5) other natural or man-made 

factors that affect the continued existence of the species. 

EPA evaluated the extent to which the estimated range and critical habitats of currently 

listed threatened and endangered species, or those in consideration for listing under the ESA (as

of December 2014), overlap with surface waters that are potentially affected by the final rule. As 

described in the Benefits and Cost Analysis (EPA-821-R-15-005), these “affected areas” are 

receiving waters that do not meet water quality metrics recognized to cause harm in organisms 

under baseline conditions, but which do meet these metrics under the most stringent regulatory

option EPA analyzed (Option E). EPA identified 138 threatened and endangered species whose 

habitats overlap with, or are located within, an “affected” surface water under baseline 

conditions.24

24 The habitat locations evaluated for this analysis include waters downstream from steam electric power plant 

discharges and reflect changes in the industry as a result of the Clean Power Plan [Clean Air Act Section 111(d)]. 

3-45 
 

 

Section 3—Environmental And Human Health Concerns

In addition, EPA assessed the vulnerability of each species identified to changes in water 

quality and developed the following categories:

 High vulnerability: species living in aquatic habitats for several life history stages 

and/or species that obtain a majority of their food from aquatic sources. 

 Moderate vulnerability: species living in aquatic habitats for one life history stage 

and/or species that obtain some of their food from aquatic sources. 

 Low vulnerability: species whose habitats overlap bodies of water, but whose life

history traits and food sources are terrestrial. 

EPA classified 54 percent of the species (75 of 138 species) with habitats located within 

an “affected” surface water as highly vulnerable to changes in water quality. The habitats of

these highly vulnerable species overlap a total of 145 affected stream reaches. For further details 

on the threatened and endangered species analysis and results, see the Benefits and Cost Analysis

(EPA-821-R-15-005). 

3.4.6 Proximity to Drinking Water Resources

EPA also evaluated the potential for steam electric power plants to pose a threat to public 

sources of drinking water. Although many of the pollutants (e.g., selenium, mercury, arsenic, 

nitrates) in the evaluated wastestreams would likely be reduced to safe levels during drinking 

water treatment, these pollutants could potentially impact the effectiveness of the treatment

processes, which could increase public drinking water treatment costs.25 EPA evaluated the 

proximity of steam electric power plants to the following sensitive environments for drinking

water resources: 

 Drinking water intakes – drinking water sources that collect surface water through a 

public water system. Intakes are protected under the SDWA of 1974 and its 1986 and 

1996 amendments, which require delegated states and tribes to perform routine 

testing to ensure that they meet state drinking water standards. 

 Public wells – drinking water sources that collect ground water through a public 

water system. Public wells are protected under the SDWA, which requires delegated 

states and tribes to perform routine testing to ensure that they meet state drinking

water standards. 

 Sole-source aquifers – drinking water sources that supply at least 50 percent of the

drinking water consumed in the area overlying the aquifer. These areas can have no 

reasonably available alternative drinking water source(s) if the aquifer were to 

become contaminated. 

Table 3-13 summarizes the number and percentages of plants included in the nationalscale proximity analysis that are located within five miles of the evaluated drinking water 

resources. The table also presents the number of drinking water resources that are located within

this five-mile buffer zone. For example, 67 steam electric power plants are located within 5 miles

25 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 ERG memorandum “Drinking

Water Treatment Technologies that Can Reduce Metal and Selenium Concentrations Associated with Discharges

from Steam Electric Power Plants” (DCN SE02154). 

3-46 
Section 3—Environmental And Human Health Concerns

of a drinking water system intake or drinking water reservoir. Within 5 miles of these 67 plants 

are 113 drinking water system intakes or reservoirs. 

Table 3-13. Comparison of Number and Percentage of Steam Electric Power Plants 

Located within 5 Miles of a Drinking Water Resource 

Type of Drinking Water 

Resource

Number of Drinking Water 

Resources within 5 Miles of a Steam 

Electric Power Plant 

Number (Percentage) of Steam 

Electric Power Plants

Located within 5 Miles of a 

Drinking Water Resource a

Intakes and reservoirs 113 67 (33%)

Public wells b 2,057 157 (81%)

Sole-source aquifers 8 7 (4%)

Sources: ERG, 2015c; ERG, 2015d 

a – For the drinking water resource proximity analysis, EPA evaluated 222 immediate receiving waters that receive

discharges of the evaluated wastestreams from 195 steam electric power plants.

b – Counts include two springs and 29 wellheads.

3.5 LONG ENVIRONMENTAL RECOVERY TIMES ASSOCIATED WITH POLLUTANTS IN STEAM 

ELECTRIC POWER PLANT WASTEWATER

Recovery of the environment from exposure to steam electric power plant wastewater is 

affected by continued cycling of contaminants within the ecosystem, bioaccumulation, and the 

potential alterations to ecological processes, such as population and community dynamics in the

surrounding ecosystems. The ability of aquatic and adjacent terrestrial environments to recover 

from even short periods of exposure to steam electric power plant wastewater depends on the 

distance from discharge, the pollutant concentrations, pollutant residence time, and the time

elapsed since exposure. In particular, accumulation of metals and other bioacummulative 

pollutants in sediments can slow recovery of aquatic systems following exposure to power plant 

wastewater due to the potential for resuspension

in the water column and for benthic organisms to 

provide a pathway for exposure long after power 

plant wastewater discharges have ended. For 

example, Lemly [1985a, 1997a, 1999] 

documented that benthic pathways can continue to 

provide toxic doses of selenium to wildlife even

10 years after water column selenium 

concentrations are below levels of concern. Ruhl 

et al. [2012] documented elevated levels of power 

plant wastewater pollutants (including arsenic and 

selenium) in pore water, even in cases where the 

water column concentrations are not elevated.

This study found that arsenic is retained in lake 

sediments and pore water through a cycle of 

adsorption and desorption, likely in response to 

seasonal changes in the lake water chemistry 

[Ruhl et al., 2012]. 

Short Exposures to Steam Electric Power 

Plant Wastewater Can Equate to Lasting 

Ecological Effects 

In Martin Creek Lake, ecological effects

persisted for at least 8 years following 8 

months of fly ash discharges into the lake. 

Ash pond discharges to Belews Lake in 

North Carolina resulted in elevated levels of 

arsenic, selenium, and zinc in the water and 

impacts to fish populations. Even 11 years 

after discharges ceased, selenium levels in 

the sediments still posed a risk to wildlife 

that feed on benthic organisms. 

As discussed in Section 3.1, many of the pollutants in steam electric power plant 

wastewater (e.g., arsenic, mercury, selenium) readily bioaccumulate in exposed biota. The 

3-47 
Section 3—Environmental And Human Health Concerns

bioaccumulation of these pollutants 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. As a result, the benthic 

invertebrate population, which graze on detrital 

material, declined as did benthic fish that prey 

upon small invertebrates because of the 

reduced available resources [Magnuson et al., 

1980]. 

Belews Lake, a 1,500-hectare cooling 

reservoir constructed to support the Belews 

Creek Steam Station in Stokes County, North 

Carolina, is a well-documented site that

highlights the effects that steam electric power 

plant wastewater can have on fish populations 

and the subsequent long recovery time. In 

1970, Duke Energy began monitoring the fish 

populations in Belews Lake prior to any 

discharges of steam electric power plant 

wastewater. From 1974 to 1985, Duke Energy discharged surface impoundment effluent into

Belews Lake. Almost immediately after these discharges began, rapid and dramatic changes in 

the fish populations were observed [Lemly, 1993]. By 1975, morphological abnormalities (e.g., 

partial fin loss, head deformities, cataracts) were reported for all 19 fish species monitored in the

lake. Within 2 years after surface impoundment effluent was released into the lake, several 

species stopped reproducing, leaving only four species by 1978 (i.e., 4 years after discharges

began). Water samples collected in the lake reported elevated levels of arsenic, selenium, and 

zinc. Large predatory fish were some of the first species to die out completely, due to the lethal

and sublethal effects of exposure to surface impoundment effluent. Because a top predator was 

gone, some fish that exhibited developmental abnormalities were able to survive, despite their 

otherwise high susceptibility to predation [Lemly, 1993]. The study eventually correlated the 

observed fish abnormalities with high selenium whole-body concentrations, and identified the 

planktonic community as the key source of selenium to the impacted fish. In 1985, the Belews 

Creek Steam Station switched to disposing of the coal ash in a dry landfill and ended the surface

impoundment discharges to the lake. In a 1997 study, Lemly determined that there was evidence 

that the lake was recovering; however, even 11 years after the discharges ceased, selenium levels

in the sediments still posed a risk to wildlife that feed on benthic organisms. Lemly also 

Studies have linked historical discharges of 

selenium from the Belews Creek Steam Station 

with persistent ecological impacts in the plant’s 

cooling reservoir. 

3-48 
 

Section 3—Environmental And Human Health Concerns

observed that despite the reduction in the selenium concentration in fish ovaries, reproductive 

abnormalities remained persistent, highlighting the long ecological recovery time observed in

Belews Lake. 

In addition to population density effects, the diversity of species in the communities in

both field and experimental studies exposed to steam electric power plant wastewater has altered, 

which can further prolong ecosystem recovery [Benson and Birge, 1985; Guthrie and Cherry, 

1976; Rowe et al., 2001; Specht et al., 1984]. In a study of fish populations in Martin Creek 

Lake following a short 8-month period in which the lake received fly ash surface impoundment 

discharges, both planktivorous (i.e., diet primarily consists of plankton) and carnivorous (i.e., 

diet primarily consists of meat) fish populations were severely reduced [Garrett and Inman, 

1984]. Three years after the effluent release was halted, planktivorous fish populations remained 

extremely low, while carnivorous fish populations had nearly recovered. Carnivorous fish have a 

more diverse diet than planktivorous fish and therefore benefited from an increase in food 

availability as the aquatic system recovered; however, the size of carnivorous fish in the lake 

suggested that surviving adults continued to have reproductive impairments [Garrett and Inman, 

1984]. Sorensen (1988) documented that ecological impacts in the lake remained evident even up 

to 8 years after the 8-month exposure to fly ash transport water discharges, with sunfish 

populations continuing to exhibit tissue damage to the liver, kidneys, gills, and ovaries and

impaired overall reproductive health. Fish samples taken in 1996 and 1997 showed that the 

selenium concentration (2.3 parts per million (ppm) average for all sample fish) remained well 

above the national average range of between 0.1 and 1.5 ppm [ATSDR, 1998a].

3-49 
Section 4—Assessment of Exposure Pathways 

SECTION 4

ASSESSMENT OF 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. 

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. 

EPA identified four primary exposure 

pathways of concern for steam electric power

plant wastewater entering the environment: 1) 

discharges entering surface waters, 2) 

uncollected combustion residual leachate 

infiltrating through soil to nearby surface 

water, 3) uncollected combustion residual leachate entering ground water, and 4) direct contact 

with steam electric power plant wastewater stored in surface impoundments. This section 

describes the factors that control the magnitude of impacts to water quality, wildlife, and human 

health associated with exposure to steam electric power plant discharges and presents an 

overview of EPA’s environmental assessment (EA) of the steam electric power generating

industry, in which EPA evaluated the national-scale effects of power plant wastewater pollutants 

on the environment. Table 4-1 presents the environmental pathways, routes of exposure, and 

environmental concerns identified during the literature review and the types of analyses 

conducted to determine the impacts under baseline conditions and regulatory options. 

Pollutants from steam electric power plant 

wastewater stored in surface impoundments can 

reach receptor populations (such as wildlife or 

people) through various exposure pathways.

4-1 
 

 

 

Section 4—Assessment of Exposure Pathways

Table 4-1. Steam Electric Power Plant Wastewater Environmental Pathways and 

Routes of Exposure Evaluated in the EA

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 

organisms a

Water quality impacts 

analysis (quantitative) –

see Section 4.1.2 Ingestion of surface water Degradation of surface

water quality used as intake

to drinking water plants 

Direct contact with 

sediment 

Toxic effects on benthic 

organisms 

Wildlife impacts 

analysis (quantitative) –

see Section 4.1.2 Consumption of aquatic

organisms 

Bioaccumulation of 

contaminants and resulting 

toxic effects on wildlife 

Toxic effects on humans 

consuming contaminated 

fish

Human health impacts 

analysis (quantitative) –

see Section 4.1.2 

Uncollected combustion residual 

leachate infiltration to nearby 

surface waters from combustion 

residual surface impoundment or 

landfill 

Direct contact with 

surface water or sediment 

Toxic effects on humans 

and aquatic wildlife 

Ground water quality 

impacts analysis 

(qualitative) – see 

Section 4.2.2

Uncollected combustion residual 

leachate entering ground water 

from combustion residual

surface impoundment or landfill 

Ingestion of ground water Changes in ground water

quality 

Contaminated private 

drinking water wells

Combustion residual surface 

impoundment

Direct contact with or 

ingestion of surface water 

Toxic effects on wildlife Attractive nuisances 

analysis (qualitative) –

see Section 4.3 Bioaccumulation of 

contaminants in wildlife 

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.

4.1 DISCHARGE AND LEACHING TO SURFACE WATERS

Steam electric power plants commonly discharge wastewater directly to surface waters

following storage and treatment (e.g., particulate settling) in surface impoundments. In addition

to effluent discharges, uncollected combustion residual leachate can migrate through the soil and 

into the surface water. Section 4.2 further discusses the impacts of uncollected combustion 

residual leachate. 

4.1.1 Factors Controlling Environmental Impacts in Surface Waters

One of the primary factors controlling the environmental impact of steam electric power 

plant wastewater on surface waters is the residence time of the pollutants once they enter an

4-2 
 

 

 

Section 4—Assessment of Exposure Pathways

aquatic system. Residence times are often determined by the flow rate of the receiving water and

type of ecosystem it supports. The potential for pollutant retention in lentic aquatic systems (i.e., 

still or slow-moving water, such as lakes or ponds) and the creation of hot spots in lotic aquatic 

systems (i.e., flowing water, such as streams and rivers) are of particular concern when

bioaccumulative pollutants are present. Many of the pollutants in steam electric power plant 

wastewater discharges bioaccumulate, complicating estimates of potential impacts in surface 

waters because the pollutants can affect higher trophic levels, local terrestrial environments, and 

transient species, in addition to the aquatic organisms directly exposed to the wastewater. 

Based on industry responses to EPA’s 2010 Questionnaire for the Steam Electric Power 

Generating Effluent Guideline (Steam Electric Survey),26 EPA determined that 18 percent of the

222 receiving waters included in the scope of the EA, all of which receive steam electric power 

plant wastewater discharges, are lentic systems such as lakes, ponds, reservoirs, and estuaries 

(Table 4-2). The majority of ecological studies on the impact of power plant wastewater in

aquatic environments have focused on lentic systems [Rowe et al., 2002]. In lentic aquatic

systems, the hydraulic residence time, or the amount of time it takes for the water in the aquatic 

system to be replaced by inflowing streams or precipitation is relatively long, allowing pollutants 

to build up over time and making these systems more vulnerable to impacts from power plant 

wastewater. In addition, aquatic organisms are limited in their ability to avoid areas of high 

pollutant concentrations and are restricted to the food supply available only within the 

waterbody. 

Table 4-2. Receiving Water Types for Steam Electric Power Plants Evaluated in the EA 

Receiving Water Type

Number (Percentage) of Immediate

Receiving Waters a

River/Stream 183 (82%)

Lake/Pond/Reservoir 26 (12%)

Great Lakes 11 (5%)

Estuary and others (bay) 2 (1%)

Total Receiving Waters 222 (100%)

Source: ERG, 2015d. 

a – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power 

plants (some of which discharge to multiple receiving waters). The immediate receiving water (IRW) model, 

which excludes the Great Lakes and estuaries, encompasses a total of 209 immediate receiving waters and 

loadings from 188 steam electric power plants. 

Based on responses to EPA’s Steam Electric Survey, EPA determined that 82 percent of 

aquatic environments that receive discharges of the evaluated wastestreams are lotic systems 

such as rivers and streams [ERG, 2015j]. Lotic systems dilute discharges more quickly than 

lentic systems. The moving water in lotic systems also provides a transport mechanism to 

disperse pollutants greater distances from the power plant, and enables aquatic organisms to 

move away from the areas contaminated by steam electric power plant discharges [Rowe et al., 

26 Results presented in this report are based on plant responses to the Steam Electric Survey, which represent 2009

data. However, the analyses presented in this report incorporate some adjustments to current conditions in the 

industry. See Section 1 for further details.

4-3 
 

 

Section 4—Assessment of Exposure Pathways

2002]. Although power plant wastewater discharges into a lotic system can distribute pollutants 

across a greater spatial area, changes in flow velocity may result in the concentration of

pollutants at a single location further downstream [Rowe et al., 2002]. For example, power plant 

wastewater discharged to a river may encounter areas of slower moving water downstream 

where pollutants would fall out of suspension and concentrate in a limited area. These pockets of 

higher pollutant concentrations, or hot spots, could be vulnerable to continued resuspension as 

stream velocities are affected by rainfall, resulting in the aquatic organisms being exposed to 

pollutants over much longer periods of time [Lemly, 1997a; Rowe et al., 2002]. 

4.1.2 Assessment of the Surface Water Exposure Pathway

EPA developed and executed models to quantify the water quality, wildlife, and human

health impacts resulting from discharges of the evaluated wastestreams to surface waters. These 

models consist of the following: 1) a national-scale IRW model that evaluates the discharges

from 186 steam electric power plants and focuses on impacts within the immediate surface 

water27 where discharges occur, and 2) case study models that perform more sophisticated and 

extensive modeling of selected waterbodies that receive, or are downstream from, steam electric 

power plant wastewater discharges. Section 5 describes the IRW model and Section 8 describes 

the case study models. In addition, as part of the benefits and cost analysis, EPA also evaluated 

surface water concentrations downstream from steam electric discharges using EPA’s RiskScreening Environmental Indicators (RSEI) model; see the Benefits and Cost Analysis (EPA821-R-15-005). 

The remainder of this section discusses the scope of EPA’s environmental assessment of 

the steam electric power generating industry in terms of evaluated pollutants, evaluated 

waterbody types, and evaluated environmental impacts. 

Evaluated Pollutants

The EA quantitative analyses focused on the environmental impacts associated with 

discharges of toxic, bioaccumulative pollutants to surface waters. A key factor in determining the 

pollutants to include in the quantitative analyses was the potential for pollutant loadings to be

diluted in the receiving waters following discharge. For example, EPA determined that the rivers

and streams included in the IRW model had a median average annual flow of 2,808 cubic feet 

per second (cfs) and that 57 percent had an average annual flow greater than 1,000 cfs. Due to 

the potential for dilution, EPA focused the quantitative analyses on pollutants where the total 

mass loadings and not the concentration are critical factors in determining the potential for

environmental impact. Section 5.1.2 lists the pollutants selected for quantitative analyses and 

how they were selected.

27 The length of the immediate receiving water, as represented in the national-scale IRW model, ranges from 

between 1 to 5 miles from the steam electric power plant outfall. See the ERG memorandum “Water Quality

Module: Plant and Receiving Water Characteristics” (DCN SE04513) for details on the immediate discharge zone

and length of stream reach represented. 

4-4 
 

 

Section 4—Assessment of Exposure Pathways

The EA quantitative analyses did not focus on water quality impacts associated with 

discharges of nutrients (total nitrogen and total phosphorus).28 While discharges of large amounts 

of nutrients to surface waters can cause environmental problems (e.g., eutrophication), EPA 

focused the EA quantitative analyses on 10 toxic pollutants that can bioaccumulate in fish and

impact wildlife and human receptors via fish consumption. Additionally, nutrient-related impacts 

tend to be site-specific depending on environmental factors (e.g., water-body temperature, the 

limiting nutrient in the system, algal species in the waterbody, and availability of oxygen in the 

water). 

While the EA quantitative analyses did not address nutrient-related impacts, EPA did 

include nutrient loadings in the Benefits and Cost Analysis. EPA estimated total nitrogen and

total phosphorus concentrations in receiving waters using dilution equations as input values to

analyze benefits related to improvements in water quality. EPA used the SPARROW (SPAtially 

Referenced Regressions On Watershed attributes) model to provide baseline concentrations, as 

well as concentrations under each regulatory option. EPA used these concentrations to develop 

subindices for a water quality index (WQI), a value that translates water quality measurements, 

gathered for multiple parameters that represent various aspects of water quality, into a single

numerical indicator. Total nitrogen and total phosphorous are only two of the subindices 

included in the WQI; the others are dissolved oxygen, biochemical oxygen demand, fecal 

coliform, total suspended solids (TSS), and heavy metals. EPA then used the WQI as a basis for 

calculating a willingness to pay for an increase in water quality as a result of the different 

regulatory options. See the Benefits and Cost Analysis for further details on the analysis and the 

results.

EPA identified total dissolved solids (TDS) and chlorides as the pollutants with the 

largest loadings under baseline conditions (see Table 3-2); however, EPA did not perform 

quantitative analyses of these pollutants for several reasons. TDS from the evaluated

wastestreams consists largely of dissolved metals that are already captured in the analysis.

Therefore, estimates of potential environmental impacts from TDS would double-count many of 

the environmental impacts and potential improvements assessed. Chlorides lack partition 

coefficient data (which are necessary for the water quality modeling performed in this EA) and 

have limited numeric threshold criteria data for comparison. 

Evaluated Waterbody Types

In selecting the appropriate methodologies for the quantitative analyses, EPA considered 

the types of receiving waters commonly impacted by steam electric power plants and the

pollutants typically found in the evaluated wastestreams. The IRW model and the selected case 

study models quantify the environmental risks within rivers/streams and lakes/ponds (including 

reservoirs), based on the determination that 94 percent of the final outfall receiving water 

designations fell within these two categories.

The EA quantitative analyses did not evaluate pollutant concentrations in the Great Lakes 

and estuarine systems, which represented 6 percent of all final outfall receiving waters. The 

28 EPA evaluated the nutrient impacts to the Great Lakes and Chesapeake Bay systems from a total mass loadings 

perspective, discussed in Section 3.4.

4-5 
 

 

Section 4—Assessment of Exposure Pathways

specific hydrodynamics and scale of the analysis required to appropriately model and quantify 

receiving water concentrations in the Great Lakes and estuarine systems are more complex than 

the IRW model.29 In selecting the receiving waters to evaluate in the case study analyses, EPA 

focused primarily on rivers and streams based on the following: 1) the determination that 82 

percent of the final outfall receiving water designations fell within this category, and 2) the 

relative simplicity of the hydrodynamics in river and stream case study models. This allowed 

EPA to develop and execute a larger set of case studies. EPA also developed one case study to 

represent the impacts of steam electric discharges to a lake. Refer to Section 8 for discussion of 

the receiving waters selected for case study analyses. 

Evaluated Environmental Impacts

EPA focused the evaluation of environmental impacts on four key areas resulting from

discharges of harmful pollutants to surface waters (rivers, streams, lakes, ponds, and reservoirs): 

 Water Quality Impacts: 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. 

 Wildlife Impacts: Potential toxic effects on benthic organisms based on changes in 

sediment quality within surface waters—specifically, exceedances of chemical 

stressor concentration limits (CSCL) for sediment biota. 

 Wildlife Impacts: Bioaccumulaton of contaminants and potential toxic effects on 

wildlife from consuming contaminated aquatic organisms, specifically: 

- Risk of adverse reproductive impacts in fish and waterfowl that consume aquatic 

organisms with elevated levels of selenium (as determined by the ecological risk 

modeling methodology described in Section 5.2). 

- Potential risk of reduced reproduction rates in piscivorous wildlife, based on 

exceedances of no effect hazard concentration (NEHC) benchmarks. 

 Human Health Impacts: Potential toxic effects to human health from consuming 

contaminated fish and water, specifically: 

- Exceedances of the human health NRWQC based on two standards: 1) standard 

for the consumption of water and organisms and 2) standard for the consumption 

of organisms. 

- Exceedances of drinking water maximum contaminant levels (MCLs). Although 

MCLs apply to drinking water produced by public water systems and not surface 

waters themselves, EPA identified immediate receiving waters that exceeded a 

MCL as an indication of the degradation of the overall water quality following 

exposure to the evaluated wastestreams. 

29 EPA evaluated the impacts to the Great Lakes and Chesapeake Bay systems from a total mass loadings

perspective, discussed in Section 3.4. See the ERG memorandum “Site-Specific Estuary Dilution Analysis” (DCN 

SE02152) for details on EPA’s initial screening analysis of the modeled receiving water concentrations in the Great

Lakes and estuary systems compared to water quality benchmarks. 

4-6 
 

 

 

Section 4—Assessment of Exposure Pathways

- Risk of cancer and non-cancer threats (e.g., reproductive or neurological impacts)

due to consuming fish caught from contaminated receiving waters.

4.2 LEACHING TO GROUND WATER

Combustion residual landfills and surface impoundments can impact local ground water 

through leaching.30 Once in ground water, pollutants can migrate from the site and contaminate 

public or private drinking water wells and surface waters [NRC, 2006]. Contamination of 

drinking water wells is of particular concern because more than one-third of the U.S. population 

relies on ground water for drinking water. According to the U.S. Geological Survey (USGS), one

in every five samples of ground water used as a source for drinking contains at least one 

contaminant at a level of concern for human health [USGS, 2015]. 

The fate of pollutants that leach from combustion residuals to ground water is controlled 

by many biological and geochemical (e.g., adsorption, desorption, and precipitation reactions 

with aquifer materials) processes that can vary over large spatial and temporal scales [NRC, 

2006]. This section describes the pollutant concentrations, chemical characteristics (e.g., 

solubility, leachability, persistence, and mobility), and fate and transport processes that influence 

the potential environmental impact of uncollected combustion residual leachate. 

4.2.1 Factors Controlling Environmental Impacts to Ground Water

Environmental impacts to ground water are determined by the pollutant concentrations in 

the combustion residual leachate and the rate of pollutant transport in the ground water. The 

pollutant concentrations in the combustion residual leachate depend on factors such as 

characteristics of the combustion residuals, site conditions (e.g., rainfall amount and pH of the 

pore water in the surface impoundment or landfill), and combustion residual residence time in 

the surface impoundment or landfill.31 The rate of pollutant transport in ground water depends on 

factors such as the biogeochemical characteristics of the subsurface (e.g., soil pH and oxidationreduction potentials), local rates of ground water recharge, and unsaturated and saturated ground 

water flow velocities.

Pollutant Concentrations in Combustion Residual Leachate

Combustion residual characteristics include the mineralogy of the waste (e.g., lime, 

gypsum, iron, and aluminum oxide content) and pollutant solubility in the pore water. The 

mobility of pollutants may be altered due to changes in pH, carbon and chloride content, and 

interaction with other wastes from steam electric power plants [Thorneloe et.al., 2010]. The

waste mineralogy can vary based on the chemical composition in the fuel source (e.g., the 

30 In this EA, EPA evaluated the threats to human health and the environment associated with pollutants leaching 

into ground water from surface impoundments and landfills containing combustion residuals. If these leached 

pollutants do not constitute the discharge of a pollutant to surface waters, then they are not controlled under the 

steam electric ELGs. While the Coal Combustion Residuals (CCR) rulemaking is the major controlling action for 

these pollutant releases to ground water, the ELGs could indirectly reduce impacts to ground water. These

secondary improvements are discussed in Section 7.8.

31 Leaching experiments indicate that the chemistry of leachates is based on both the chemical composition of the

waste and other factors such as site conditions [Thorneloe et al., 2010]. Thorneloe [2010] specifically looked at fly

ash and bottom ash waste from coal-fired power plants. 

4-7
 

 

Section 4—Assessment of Exposure Pathways

specific coal seam and geographic location of the mine) and operational characteristics at the 

plant. Many laboratory investigations have examined the solubility characteristics of various 

pollutants associated with fly ash [Prasad et al., 1996; Thorneloe et.al., 2010]. The results of 

these investigations largely depend on multiple factors, and they tend to be more applicable 

qualitatively rather than quantitatively (e.g., results from investigations can be used to determine 

the likelihood of a pollutant to dissolve in the combustion residual leachate, but not the amount). 

Concentrations of inorganic pollutants derived from calcium, sodium, magnesium, potassium, 

iron, sulfur, and carbon are relatively high in aqueous solution of fly ash because of their high

total concentrations in the ash [Prasad et al., 1996]. 

The pH level of pore water in surface 

impoundments can strongly influence the 

concentration of pollutants in leachate from 

impoundments to ground water. 

The pH of the pore water is a dominant 

factor in the leaching of pollutants from 

unlined surface impoundments and landfills.

Because most pollutants in combustion 

residuals exhibit weak acidic or weak basic 

behavior in aqueous solution, the pore water 

pH strongly influences the concentrations of 

pollutants in the combustion residual leachate. 

Steam electric power plants generate 

combustion residuals in high-temperature 

processes, and many acids and acidic 

precursors (e.g., carbon dioxide, hydrogen 

sulfide, hydrochloric acid) are volatilized prior 

to waste collection. Therefore, combustion 

residuals typically yield an alkaline reaction in 

water, but acidic reactions have also been

observed [Theis and Gardner, 1990]. Acidic 

pore water allows pollutants from the 

combustion residuals to remain in solution, increasing their mobility and the potential for ground

water contamination. The results of a study of three power plants in Turkey indicated that 

combustion residuals in the deeper layers of landfills and on the bottoms of the surface 

impoundments may continue to leach if the pH value drops in the surrounding environment

[Baba and Kaya, 2004].32

Table 4-3 presents data collected by EPA’s Steam Electric Survey regarding pollutant 

concentrations in the combustion residual leachate under acidic, neutral, and basic (or alkaline) 

conditions. Arsenic exceeded its MCL for more than 60 percent of the samples in both acidic and

basic combustion residual leachate. Similarly, the majority of manganese samples exceeded its

secondary MCL under all pH conditions, with 95 percent of the samples exceeding the MCL in

32 This conclusion was based on a comparison of ash extraction procedures used. The study examined how the 

concentration of trace elements in the ash can vary based on the procedure used, comparing the EPA-developed EP 

(extraction procedure) and its replacement method, TCLP (toxicity characteristic leaching procedure), and the 

ASTM (American Society for Testing and Materials) Method D-3987. A comparison of the results revealed that the

ASTM procedure indicated much lower dissolved metal concentrations than the EP and TCLP procedures. These 

results indicate that pH is an important parameter affecting the leaching rate of metals from ash deposits. The lower 

pH values in the EP and TCLP methods increase the leaching rate of inorganic constituents of fly ash and bottom 

ash [Fleming et al., 1996]. 

4-8
 

 

Section 4—Assessment of Exposure Pathways

acidic conditions. Selenium had varying concentrations under all pH conditions, but exceeded its

MCL more frequently under basic conditions. Overall, the results support the conclusion that pH

levels influence the concentrations of pollutants in the combustion residual leachate. 

Table 4-3. Exceedances of MCLs in Leachate Under Acidic, Neutral, and Basic 

Conditions

Pollutant 

MCL

(mg/L)

Total Number of Samples

Percentage of Total Samples

Exceeding MCL 

Acidic Neutral Basic Acidic Neutral Basic 

Arsenic 0.01 21 64 90 62% 30% 71%

Boron 7 a 21 64 91 14% 31% 31%

Cadmium 0.005 21 63 90 29% 3% 29%

Chromium 0.1 21 64 90 0% 0% 18%

Copper 1.3 21 64 91 0% 0% 0%

Lead 0.015 21 62 86 5% 0% 2%

Manganese 0.05 b 21 64 89 95% 81% 54%

Mercury 0.002 21 64 89 5% 16% 8%

Nickel No MCL 21 64 87 NC NC NC

Selenium 0.05 21 64 90 14% 17% 31%

Thallium 0.002 21 62 86 52% 10% 14%

Zinc 5 b 21 63 86 0% 0% 0%

Source: ERG, 2015d. 

Acronyms: mg/L (milligrams per liter); MCL (Maximum contaminant level); NC (not calculated; no MCL for 

comparison). 

Note: Data are for untreated leachate collected in leachate collection systems at steam electric landfills and surface 

impoundments. 

a – The drinking water equivalent level, used for noncarcinogenic endpoints, is listed rather than the MCL.

b – MCL is a secondary (nonenforceable) standard. 

In addition to the pH of the pore water, amounts of precipitation can affect pollutant 

concentrations in the combustion residual leachate. Although landfills are dry disposal sites, 

rainfall and frozen precipitation infiltrate through the waste, dissolving pollutants that can then

leach from the landfill. Landfills in drier climates generate less combustion residual leachate than

landfills in wetter climates.

The last factor affecting pollutant concentrations in the combustion residual leachate is

the combustion residual residence time in the surface impoundment or landfill. In a study of 

metals (calcium, copper, iron, lead, magnesium, manganese, potassium, sodium, and zinc)

leaching from fly ash and bottom ash, all pollutants decreased in concentration with time of 

leaching, except for calcium, which released at a constant rate [Kopsick and Angino, 1981]. The 

most commonly noted leachate release curve is an initial flush curve, where the highest 

concentrations of pollutants are released as the leachate initially forms, with rapidly decreasing 

concentrations over time. Therefore, active surface impoundments receiving fresh combustion 

residuals will produce a leachate with elevated concentrations of pollutants that have a greater 

potential to contaminate drinking water sources and surface waters. Most inactive surface 

impoundments where pollutants have initially already leached from the combustion residuals 

4-9
 

 

Section 4—Assessment of Exposure Pathways

should produce a leachate with decreasing concentrations of pollutants [Kopsick and Angino, 

1981]. 

Thorneloe et al. [2010] studied the leaching behavior of coal combustion residuals in 

landfills, performing tests using a range of pH conditions and liquid-solid ratios expected during 

management via landfills or beneficial use. Combustion residual leachate concentrations for most 

pollutants were variable over a range of coal types, plant configurations, and combustion residual 

types (i.e., fly ash or flue gas desulfurization (FGD) gypsum). The study showed significantly 

different leaching results (liquid-solid partitioning [equilibrium] as a function of pH) for similar 

combustion residual types and plants. The variability in pollutant leaching results was several 

orders of magnitude higher than the variability in the pollutant concentrations in the combustion 

residuals; this indicates that the pollutant

concentrations alone cannot predict the 

leaching of metals, as noted above. Table 4-4

presents pollutant concentrations in

combustion residual samples across a pH 

range of 5.4 to 12.4 and the range of pollutant 

concentrations in the combustion residual 

leachate. The table also includes indicator 

values for each pollutant: toxicity 

characteristic (TC) values for Resource 

Conservation and Recovery Act (RCRA)

hazardous waste regulatory determination and 

drinking water MCLs for combustion residual 

leachate concentrations. As shown in the table, 

the maximum combustion residual leachate

pollutant concentrations: 

 Exceed the TC values for RCRA hazardous waste determinations for arsenic, barium,

chromium, and selenium (in fly ash).

 Exceed the TC values for RCRA hazardous waste determinations for selenium (in

FGD gypsum).

 Exceed the MCLs for nine metals (in fly ash and FGD gypsum): antimony, arsenic,

barium (fly ash only), boron, cadmium, chromium, molybdenum, selenium, and

thallium.

The higher pollutant concentrations in the combustion residual leachate indicate greater 

mobility of the pollutant from the solid/slurry residual to the liquid phase. The concentration of

the pollutants in the combustion residual leachate can be hundreds to thousands of times greater 

than the MCL. 

Most surface impoundments are unlined, 

allowing pollutants to infiltrate into ground 

water and eventually into surface waters.

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Section 4—Assessment of Exposure Pathways

Table 4-4. Range of Fly Ash and FGD Gypsum Total Content and Combustion Residual 

Leaching Test Results (Initial Screening Concentrations) for Trace Metals

Pollutant 

Range of Combustion 

Residual Content

Range of Leaching Test

Results: Concentration in the 

Combustion Residual 

Leachate Indicator Values 

Fly Ash 

(mg/kg)

FGD 

Gypsum 

(mg/kg)

Fly Ash 

(μg/L)

FGD 

Gypsum 

(μg/L)

TC Value for 

Hazardous Waste 

Designation

(μg/L)

Drinking

Water 

MCL

(μg/L)

Antimony 3.0-14 0.14-8.2 <0.3-11,000 <0.3-330 -- 6

Arsenic 17-510 0.95-10 0.32-18,000 0.32-1,200 5,000 10

Barium 50-7,000 2.4-67 50-670,000 30-560 100,000 2,000

Boron NA NA 210-270,000 12-270,000 -- 7,000 a

Cadmium 0.3-1.8 0.11-0.61 <0.1-320 <0.2-240 1,000 5

Chromium 66-210 1.2-20 <0.3-7,300 <0.3-240 5,000 100

Mercury 0.1-1.5 0.01-3.1 <0.01-0.50 <0.01-0.66 200 2

Molybdenum 6.9-77 1.1-12 <0.5-130,000 0.36-1,900 -- 200 a

Selenium 1.1-210 2.3-46 5.7-29,000 3.6-16,000 1,000 50

Thallium 0.72-13 0.24-2.3 <0.3-790 <0.3-1,100 -- 2

Source: Thorneloe et al., 2010. 

Acronyms: Acronyms: MCL (maximum contaminant level); mg/kg (milligrams per kilogram); TC (Toxicity 

Characteristics); μg/L (micrograms per liter); NA (Not Available). 

a – The drinking water equivalent level, used for noncarcinogenic endpoints, is listed rather than the MCL.

Transporting Pollutants in the Ground Water

Predicting the movement of combustion residual pollutants in ground water can be 

challenging due to the wide range of biogeochemical characteristics between sites and within a

given site. Pollutant transport times can vary, and combustion residual pollutants can take many 

years to reach local drinking water wells and surface waters [NRC, 2006]. For example, in the 

damage case at the Virginia Power Yorktown Power Station Chisman Creek Disposal Site in 

Yorktown, Virginia, fly ash had been disposed of in abandoned, unlined sand and gravel pits at

the site for almost 20 years, from 1957 to 1974. However, ground water contamination was not 

discovered until 1980, when nearby shallow residential wells became contaminated with nickel 

and vanadium. Sampling also showed elevated levels of other heavy metals and toxic pollutants: 

arsenic, beryllium, chromium, copper, molybdenum, and selenium [U.S. EPA, 2014b]. 

Natural mechanisms, such as soil buffering capacity, attenuation of trace pollutants in 

certain soil types, amount of organic matter, and low soil permeability, can limit the transport of

combustion residual pollutants in the subsurface environment. The mobility of pollutants in the

subsurface strongly depends on soil-specific characteristics. Soil can have a buffering influence 

over the leachate by raising or lowering the pH. As noted previously, the solubility of most trace 

pollutants (the notable exceptions being arsenic and selenium) tends to decrease with increased

pH (i.e., alkaline conditions). In general, trace pollutants are less mobile in alkaline soils because 

the pollutants will precipitate and/or adsorb onto hydrous iron and aluminum oxides. Theis and 

Richter [1979] attempted to assess the factors influencing the attenuation of trace metals in 

4-11
Section 4—Assessment of Exposure Pathways 

soil/ground water. Results show that the major solubility control for cadmium, nickel, and zinc is

adsorption by iron and manganese oxides while chromium, copper, and lead are controlled by 

precipitation. In some cases, particles in leachate may seal a surface impoundment or landfill,

reducing the amount of leachate entering the ground water. Simsiman et al. [1987] and Kopsick 

and Angino [1981] both reported evidence of some sealing and reduced permeability of

combustion residual surface impoundments, reducing seepage. 

4.2.2 Assessment of the Ground Water Exposure Pathway

The EA focused on the discharges of toxic, bioaccumulative pollutants to surface waters 

from the evaluated wastestreams. While Section 3.3 provides qualitative discussion of ground 

water impacts based on a review of damage cases and other documented site impacts, the EA did 

not quantify the environmental and human health impacts resulting from pollutants leaching into

the ground water from combustion residual surface impoundments and landfills. Additionally,

the models used for this EA did not consider pollutant loadings to surface waters caused by

combustion residual pollutants migrating through the soil and into surface waters, even though 

this may be occurring at many of the plants. As shown in Tables A-4 and A-5 in Appendix A, 

several damage cases have documented impacts to surface waters due to ground water 

contamination from combustion residual surface impoundments and landfills. The EA may 

therefore underestimate the number of cases where water quality standards are being exceeded in 

immediate receiving waters (see Section 6).

On April 17, 2015, EPA published a RCRA rule that regulates the disposal of CCRs from

steam electric power plants (80 FR 21302). As part of the final CCR rulemaking, EPA’s Office 

of Solid Waste and Emergency Response (OSWER) evaluated ground water contamination 

associated with combustion residuals in surface impoundments and landfills. The ground water 

impact analysis for the CCR rule identified and quantified human health risks to private drinking 

water wells due to potential ground water contamination from current CCR management 

practices. The analysis determined that human health risks were primarily from exposures to 

arsenic and molybdenum in ground water used as a source of drinking water. EPA identified 

additional human health risks from exposures to boron, cadmium, cobalt, fluoride, mercury, 

lithium, and thallium in ground water used as drinking water at certain sites based on the CCR 

disposal practices. Refer to the Regulatory Impact Analysis: EPA’s 2015 RCRA Final Rule 

Regulating Coal Combustion Residual (CCR) Landfills and Surface Impoundments at Coal-Fired

Electric Utility Power Plants (EPA-HQ-RCRA-2009-0640-12034) for the results of the nationalscale analysis of ground water impacts. 

4.3 COMBUSTION RESIDUAL SURFACE IMPOUNDMENTS AS ATTRACTIVE NUISANCE

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. As an attractive nuisance, a surface

impoundment can impact 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].

4-12 
Section 4—Assessment of Exposure Pathways 

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, 1997a; Pruitt, 2000]. 

Organisms that frequent attractive nuisance sites at steam electric power plants, such as 

surface impoundments, risk exposure to elevated pollutant concentrations. Several studies have 

shown that terrestrial fauna nesting near combustion residual 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]. Table A-8 in Appendix A 

summarizes documented examples of impacts to wildlife associated with attractive nuisances at 

steam electric power plants.

In several of these instances, histopathological effects (i.e., changes in pollutant tissue 

concentrations) were observed. For example, birds nesting near a combustion residual surface 

impoundment produced eggs with higher selenium concentrations than eggs found at the 

reference site. Although egg selenium concentrations near combustion residual surface 

impoundments exceeded thresholds that 

signify adverse effects on reproduction, the 

study did not observe any reduction in 

reproductive success [Bryan et al., 2003]. In a 

study conducted by Hopkins et al. [1998], 

sediment from a contaminated combustion 

residual surface impoundment had arsenic 

levels more than 100 times higher than the 

levels found in reference site sediments. Adult 

toads captured in the contaminated surface 

impoundment reported a sevenfold difference

in arsenic levels between those from reference 

sites [Hopkins et al., 1998]. Although the 

study did not measure any indicators of 

reduced survival or reproductive success in the 

toads, the results indicate that exposure to 

combustion residual surface impoundments are 

a potential threat [Hopkins et al., 1998]. 

Surface impoundments and constructed 

wetlands can act as attractive nuisances by 

attracting wildlife and exposing them to 

elevated pollutant levels.

Multiple studies have linked attractive nuisance areas at steam electric power plants to 

diminished reproductive success. Field studies have documented adverse effects on reproduction 

for turtles and toads living near selenium-laden combustion residual surface impoundments 

[Hopkins et al., 2006; Nagle et al., 2001]. In another study, an interior least tern (Sternula 

antillarum), an endangered migratory bird, began nesting at Gibson Lake, an artificial shallow 

pond that receives combustion residual surface impoundment effluent from the Gibson 

Generating Station in Indiana. Within several years, nearby combustion residual surface 

impoundments at the Gibson Generating Station were also attracting nesting least terns, placing 

these sensitive species in direct contact with steam electric power plant wastewater. To address 

the attractive nuisance problem presented by the surface impoundments, the Gibson Generating 

Station began a cooperative program with the Indiana Department of Natural Resources to 

4-13 
Section 4—Assessment of Exposure Pathways 

protect the nesting birds by creating a nearby alternative habitat known as the Cane Ridge 

Wildlife Management Area (WMA) [Pruitt, 2000]. Cane Ridge WMA received water from 

Gibson Lake and, in 2008, the U.S. Fish and Wildlife Service became concerned about selenium 

levels in the water and fish present in the Cane Ridge WMA [USFWS, 2008]. Accordingly, the

bottom of Cane Ridge was plowed to redistribute and bury the selenium in the soil and the water 

flowing from Gibson Lake into Cane Ridge was stopped and replaced with water piped from the 

Wabash River. Duke Energy paid to stock the Cane Ridge WMA ponds with fathead minnows to 

lure back migratory birds. As of June 2009, avocets, dunlins, black terns, Forster’s terns, Caspian 

terns, and 50 endangered least terns have returned to Cane Ridge [USFWS, 2012]. 

Other well-documented cases of attractive nuisance settings with characteristics (e.g., 

elevated concentrations of specific pollutants) similar to those associated with steam electric 

power plants provide further support that combustion residual surface impoundments have the 

potential to pose a threat to wildlife. For example, exposed organisms in attractive nuisance 

settings affected by urban and agricultural wastes have exhibited elevated tissue concentrations 

of pollutants, with some organisms experiencing a combination of reproductive or sublethal 

effects that adversely impact their survival [Clark, 1987; Hofer et al., 2010; King et al., 1994; 

Ohlendorf et al., 1986, 1988a, 1988b, 1989, 1990; Tsipoura et al., 2008]. Although these 

examples do not directly relate to steam electric power plants, they highlight the potential 

dangers of attractive nuisances and ability for pollutants to bioaccumulate in the surrounding

wildlife [Ohlendorf et al., 1986, 1989, 1990]. Table A-9 in Appendix A summarizes documented 

examples of impacts to wildlife associated with attractive nuisances that are not specific to steam 

electric power plants. 

4-14 
 

 

Section 5—Surface Water Modeling 

SECTION 5

SURFACE WATER MODELING 

Based on the documented environmental impacts discussed in the literature, EPA 

identified several key environmental and human health concerns and pathways of exposure to 

evaluate in the environmental assessment (EA). Environmental concerns include degradation of

surface water, sediment, and ground water quality; toxic effects on aquatic and benthic

organisms; bioaccumulation of contaminants and resultant toxic effects on wildlife; toxic effects

on humans consuming contaminated fish; and contamination of drinking water resources. 

EPA focused its quantitative analyses on discharges of the evaluated wastestreams to 

surface water – one of the primary exposure pathways of concern discussed in Section 4. To

quantify baseline impacts and improvements under the final steam electric effluent limitations 

guidelines and standards (ELGs), EPA developed models to determine pollutant concentrations 

in the immediate receiving waters, pollutant concentrations in fish tissue, and exposure doses to 

ecological and human receptors from consuming aquatic organisms. This section describes the 

immediate receiving water (IRW) model and the ecological risk model used in developing this 

EA. Section 8 describes the development and execution of case study models using EPA’s Water 

Quality Analysis Simulation Program (WASP) to supplement the results of the IRW model. 

5.1 IMMEDIATE RECEIVING WATER (IRW) MODEL

EPA developed the IRW model33 to quantify the environmental impacts to surface

waters, wildlife, and human health from the wastestreams evaluated for the regulatory options. 

As part of this national assessment, EPA determined impacts in the immediate surface water 

where steam electric power generating industry discharges occur, between 1 and 5 miles from 

the outfall depending on the stream reach.34 As part of the benefits and cost analysis, EPA also 

evaluated surface water concentrations downstream from steam electric discharges using EPA’s

Risk-Screening Environmental Indicators (RSEI) model; see the Benefits and Cost Analysis 

(EPA-821-R-15-005). The IRW model framework focused on four key areas of impacts: 

 Impacts to aquatic life based on reduction in water quality from discharges of the 

evaluated wastestreams. 

 Impacts to aquatic life based on reduction in sediment quality from discharges of the

evaluated wastestreams. 

 Impacts to wildlife from the bioaccumulation of contaminants in aquatic organisms 

and fish, including piscivorous (fish-eating) wildlife.

 Impacts to human health from consuming contaminated fish. 

33 The IRW model is the same model that EPA used for the national-scale analyses in support of the proposed ELGs.

EPA assigned the “IRW model” label to help distinguish the national-scale model from the case study models 

developed in support of the final ELGs.

34 See the ERG memorandum “Water Quality Module: Plant and Receiving Water Characteristics” (DCN SE04513) 

for details on the immediate discharge zone and length of stream reach represented. 

5-1 
 

Section 5—Surface Water Modeling 

As discussed in Section 4.1.2, EPA considered the type of receiving waters commonly 

impacted by steam electric power plants and the pollutants typically found in the evaluated 

wastestreams in selecting the appropriate methodologies for the quantitative analysis. The IRW 

model quantified the environmental risks within rivers/streams and lakes/ponds/reservoirs, and 

evaluated impacts from 10 toxic, bioaccumulative pollutants: arsenic, cadmium, copper, 

hexavalent chromium (chromium VI), lead, mercury, nickel, selenium, thallium, and zinc. EPA’s 

IRW model includes three interrelated modules: 

 Water quality module—calculates immediate-receiving-water-specific pollutant 

concentrations in the water column and sediment and evaluates the impacts that 

receiving water concentrations pose to aquatic life and human health. 

 Wildlife module—evaluates the impact that sediment concentrations pose to aquatic 

life, calculates the pollutant concentrations in exposed fish populations, and evaluates 

the potential adverse effects to minks and eagles from consuming fish. 

 Human health module—calculates non-cancer and cancer risks to human populations 

from consuming fish. 

Additionally, EPA used the selenium outputs from the IRW water quality module to 

evaluate the risks to fish and waterfowl that consume aquatic organisms with elevated levels of 

selenium (see Section 5.2). This ecological risk analysis expands on the results of the IRW 

wildlife module described in this section.

The IRW water quality module uses plant-specific input data (plant-specific pollutant 

loadings and cooling water flow rate),35 surface-water-specific characteristic data (e.g., receiving

water flow rate, lake volume), and representative environmental parameters (e.g., partition 

coefficients) to quantify the environmental impacts of the evaluated wastestreams to surface 

waters. The module calculates pollutant concentrations in the surface water and sediment. These

concentrations are inputs to the IRW wildlife module, which calculates the bioaccumulation of 

pollutants in fish tissue and determines impacts to wildlife. The fish tissue concentration 

calculated in the IRW wildlife module becomes an input to the IRW human health module. This 

section provides overviews of each module. Appendices C through E describe the IRW model 

equations, input data, and assumed environmental parameters in further detail. The appendices 

also describe the limitations and assumptions of the IRW model. 

Figure 5-1 provides an overview of the IRW model inputs and the connections among the 

three modules to support EPA’s national-scale modeling framework. 

35 EPA calculated annual pollutant loadings for the evaluated wastestreams and excluded any pollutants discharged

with other wastewaters (e.g., coal pile runoff). EPA incorporated cooling water flow rates into the IRW water 

quality module on a site-by-site basis. EPA assumed no pollutant loadings were associated with cooling water 

discharges to surface waters and used cooling water flow rates only to evaluate dilution effects. 

5-2 
Figure 5-1. Overview of IRW Model 

 

Section 5—Surface Water Modeling 

5.1.1 Water Quality Module

EPA selected the steady-state equilibrium-partitioning model described in EPA’s 

Methodology for Assessing Health Risks Associated with Indirect Exposure to Combustor

Emissions (EPA 600-R-98-137) for the IRW water quality module. This selection was based on

three factors: 1) the model’s ability to represent pollutants in the aquatic environment; 2) the 

model’s complexity, which EPA judged to be appropriate for a national-scale evaluation;36 and 

3) the level of previous Agency and external peer reviews performed on the modeling 

methodology. 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. 

36 For a national-scale environmental assessment of over 200 receiving waters, data limitations inhibit the feasibility 

of using more complex fate and transport receiving water models (dynamic or hydrodynamic) to estimate surface

water concentrations. 

5-3 
Section 5—Surface Water Modeling 

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

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

Table 5-1 lists the pollutants commonly found in the evaluated wastestreams with known 

environmental impacts (see Section 3.1, Table 3-1). EPA selected a subset of these pollutants for 

the water quality model based on the following criteria: 

 The pollutant is known to be present in the evaluated wastestreams (i.e., identified as 

a pollutant of concern). 

 Scientific literature documents elevated levels observed in surface waters or wildlife

from exposure to steam electric power plant wastewater. 

 Partition coefficient data are available for the water quality model.

 Benchmarks are available to evaluate potential threats to wildlife or human health. 

For the immediate receiving water quality analysis, EPA modeled 10 of the pollutants 

shown in Table 5-1: arsenic, cadmium, chromium VI, copper, lead, mercury, nickel, selenium, 

thallium, and zinc. 

5-4 
Section 5

Table 5-1. Pollutants Considered for Analysis in the Immediate Receiving Water Mode

Pollutant POC a

Literature 

Review b

Partition

Coefficient c NRWQC d

Maximum Contaminant

Level (MCL) 

Wildlife 

Benchmark e

Human Healt

Benchmark 

Aluminum   Arsenic h        

Boron   

Cadmium        

Chromium i        

Copper        

Iron   

Lead      

Manganese   

Mercury j        

Nickel       

Selenium k        

Thallium      

Vanadium    

Zinc      

a – A check mark indicates that the pollutant is a pollutant of concern (POC) for one or more of the evaluated wastestreams (see Section 

Development Document (TDD) (EPA-821-R-15-007)).b – Literature review identified documented cases of elevated pollutant levels in surface waters or wildlife near steam electric power pl

2015m].c – Partition coefficients for modeling analysis identified in U.S. EPA, 1999, and U.S. EPA, 2005a. d – National Recommended Water Quality Criteria (NRWQC) are available at http://water.epa.gov/scitech/swguidance/standards/curre

e – No effect hazard concentration (NEHC) identified in USGS, 2008, for minks and bald eagles. f – Reference dose (RfD) identified in EPA’s Integrated Risk Information System (IRIS) for all pollutants except copper and thallium (http://www.epa.gov/iris/); RfD for copper is the intermediate oral minimal risk level (MRL) [ATSDR, 2010a]; and RfD for thallium is 

chloride provided in U.S. EPA, 2010a. Cancer slope factor for arsenic identified in EPA’s Integrated Risk Information System (IRIS) dg – Pollutant is included in the quantitative modeling analysis discussed in this section. h – Arsenic exists in two primary forms: arsenic III (arsenite) and arsenic V (arsenate). A check mark indicates that total arsenic, arsenisatisfied the criterion in the table header. i – Chromium exists in two primary forms: chromium III and chromium VI. A check mark indicates that total chromium and/or chromicriterion in the table header. j – A check mark indicates that mercury and/or methylmercury satisfied the criterion in the table header. k – Selenium exists in two primary forms: selenium IV (selenite) and selenium VI (selenate). A check mark indicates that total seleniumsatisfied the criterion in the table header. 

5-5 
Section 5—Surface Water Modeling 

EPA developed the IRW water quality module in Microsoft AccessTM using the 

equilibrium-partition equations presented in Appendix C. The IRW water quality module is a 

mathematical model used to represent the partitioning of pollutants through the surface water 

after the wastestream has been discharged. The module output provides site-specific pollutant 

concentrations in the water column (total, dissolved, and suspended) and sediment for 188 steam 

electric power plants located across the United States that discharge to a river or stream or to a

lake, pond, or reservoir. Figure 5-2 depicts the pollutant concentrations calculated in the IRW 

water quality module. EPA implemented this modeling approach through the following steps: 

1. Characterize the immediate receiving water characteristics (e.g., depth of water 

column, depth of waterbody, receiving water width, and flow independent mixing 

value) using site-specific inputs. See the ERG memorandum “Water Quality Module: 

Plant and Receiving Water Characteristics” (DCN SE04513). 

2. Using the immediate receiving water characteristics, determine the fraction of 

pollutant in the benthic sediment and in the water column and determine fraction of

pollutant in the water column that is dissolved. 

3. Using the immediate receiving water characteristics and assumed input values, 

calculate the water column volatilization rate constant, for volatile pollutants only 

(i.e., mercury). 

4. Calculate the water concentration dissipation rate (zero for nonvolatile pollutants). 

5. Based on site-specific pollutant loadings (converting annual loadings to an average 

daily loading), cooling water flow rates (for a subset of plants), and immediate 

receiving water characteristics, calculate the total pollutant concentrations (e.g., total 

arsenic) in the immediate receiving water, including the concentration in the water

column and in the benthic sediment. 

6. Calculate the concentration of dissolved pollutant in the water column. Section 10 of

the TDD details the pollutant loadings methodology; the ERG memorandum “Water 

Quality Module: Plant and Receiving Water Characteristics” (DCN SE004513)

describes the use of cooling water flow rates. Note that the pollutant loadings

included in the module do not represent the total pollutant loadings from steam 

electric power plants; several wastestreams were not evaluated (e.g., stormwater 

runoff, metal cleaning wastes, coal pile runoff). In addition, the module uses an 

annual average discharge rate, assuming no seasonal or daily variation. 

7. Quantify the number of sites that exceed the NRWQC and drinking water maximum 

contaminant levels (MCLs) to evaluate the potential exposure of ecological receptors 

(i.e., aquatic biota) and human receptors to toxic pollutants in the environment from

the evaluated wastestreams. 

5-6 
Source: Adapted from U.S. EPA, 1998b. 

Figure 5-2. Water Quality Module: Pollutant Fate in the Waterbody 

Section 5—Surface Water Modeling 

As an indicator of potential impacts, EPA compared the immediate receiving water 

concentrations (under baseline and regulatory options) to the following NRWQCs: 

 Freshwater acute and chronic aquatic life NRWQC. 

 Human health NRWQC for the consumption of water and organisms. 

 Human health NRWQC for the consumption of organisms. 

EPA also compared immediate receiving water concentrations to drinking water MCLs. 

EPA identified immediate receiving waters that exceeded a NRWQC or MCL as an indication of 

the degradation of the overall water quality following exposure to the evaluated wastestreams. 

Section 6.3 summarizes the NRWQC and MCL exceedances under baseline pollutant loadings. 

Section 7.2 presents the percent reduction in number of immediate receiving waters that

potentially impact water quality under the final rule. 

As with any modeling, EPA recognizes that model limitations exist and certain 

assumptions need to be made. EPA used average annual pollutant loadings and normalized 

effluent flow rates, which do not take into account temporal variability (e.g., variable plant 

operating schedules, storm flows, low-flow events, catastrophic events). The IRW water quality

module does not account for ambient background pollutant concentrations or contributions from 

other point and nonpoint sources, and assumes a constant flow rate in the receiving water based 

on the annual average reported in National Hydrography Dataset Plus (NHDPlus). Appendix C 

discusses these and additional module-specific limitations and assumptions and Section 6 and

5-7 
 

 

Section 5—Surface Water Modeling 

Section 7 present the results of the IRW water quality module under baseline and regulatory 

options. 

5.1.2 Wildlife Module

As shown in Figure 5-1, the IRW wildlife module builds off the IRW water quality 

module by using the calculated immediate receiving water and sediment concentrations to

calculate pollutant concentrations in fish populations exposed to the evaluated wastestreams and 

to assess the potential to impact wildlife for the following categories:

 Impact to aquatic organisms from contact with sediment contaminated by the 

evaluated wastestreams. To do this, the model quantifies the number of sites with 

potential exposure of ecological receptors (i.e., sediment biota) to the pollutant in the 

environment. 

 Impact to piscivorous wildlife (i.e., wildlife that habitually feeds on fish) from

consuming fish impacted by the evaluated wastestreams. To do this, the model 

quantifies the number of sites with potential exposure of ecological receptors (i.e., 

piscivorous wildlife) to the pollutant in the environment. 

EPA developed the wildlife model in Microsoft AccessTM to calculate pollutant 

concentrations in fish populations exposed to the evaluated wastestreams and estimate daily 

contaminant dose for wildlife receptors (i.e., minks and eagles) using equations presented in 

Appendix D. EPA determined potential impacts to wildlife by comparing the concentration in the 

contaminated media (i.e., water, sediment, or fish) to concentrations known to be protective of

negative impacts (i.e., benchmark). Benchmarks, which are pollutant- and endpoint-specific and 

sometimes are species-specific, are an expression of the concentration level in contaminated

media that is protective against a specific endpoint (e.g., mortality). Endpoints frequently 

reflected in benchmark values include sublethal effects (e.g., reduced reproduction, neurological 

effects) and lethal effects. EPA implemented the wildlife modeling approach through the 

following steps: 

1. Compare the concentration of the contaminant in benthic sediment to the benchmark 

for sediment biota. 

2. Calculate the pollutant concentration in fish for trophic level three (T3) or trophic

level four (T4),37 using the calculated pollutant concentration in the water column and 

the bioaccumulation factor (BAF) or bioconcentration factor (BCF).38 For mercury, 

calculate the concentration of methylmercury in the fish. See Appendix D for details 

on the IRW wildlife module and calculation of methylmercury concentration in fish. 

3. Compare the concentration of the contaminant in the fish to the wildlife benchmarks

for ecological receptors (i.e., mink and eagle). 

37 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.

38 BCFs are more appropriate for use with pollutants where the primary pathway entering fish tissue is via the water, 

whereas BAFs are more appropriate for pollutants where the primary pathway entering fish tissue is through a food

source (takes into account both water and diet). Where available, EPA used pollutant-specific BAFs.

5-8 
Section 5—Surface Water Modeling 

4. Compare the baseline and regulatory option results (i.e., number of sites with 

potential exposure of ecological receptors to concentrations above protective

benchmarks). 

Adverse Effects to Aquatic Organisms from Contact with Sediment

EPA compared the concentration in the benthic sediment to benchmarks protective of 

benthic organisms. EPA used threshold effects level (TEL) benchmarks provided in the National 

Oceanic and Atmospheric Administration (NOAA) 2008 Screening Quick Reference Tables 

(SQuiRTs), referred to as the chemical stressor concentration limit (CSCL), for the sediment

biota adverse impacts analysis. The CSCL is a chemical-specific media concentration that is 

protective of ecological receptors of concern. The CSCL benchmark is species-specific, but can

be used to represent a community of organisms, such as amphibians or fish. Usually the most 

sensitive (or lowest) CSCL for a species is used to represent the community. Table D-1 in 

Appendix D presents the benchmarks used for sediment exposure analysis. Section 6.2 discusses 

the results of this analysis for baseline pollutant loadings.

Assessment of Pollutant Bioconcentration in Fish

EPA calculated fish tissue concentrations based on the following: 1) total water column

concentrations (i.e., dissolved plus sorbed) calculated in the IRW water quality module, and 2)

trophic-level-specific BAFs or BCFs. BAFs and BCFs are based on field and laboratory study 

results compiled to develop a single factor or ratio for estimating the amount of pollutant 

transferred into fish tissue at a given trophic level (i.e., rank in the food chain) based on the 

pollutant concentration in the waterbody. EPA estimated fish tissue concentrations in milligrams

per kilogram (mg/kg) for T3 and T4 fish to account for the variability in fish likely consumed by 

both wildlife and human receptors included in the IRW model. 

Although using the total water column concentration in the bioaccumulation analysis may 

overestimate the level of pollutants in the fish, it provides for a more environmentally protective 

estimate of risk in the subsequent human health model because it assumes that all pollutants

within the waterbody (both dissolved and sorbed) are bioavailable to the exposed fish. The

exception to this methodology is mercury, where EPA based the fish tissue concentration 

calculation on the dissolved concentration of methylmercury in the waterbody [U.S. EPA, 

2005b]. Appendix D presents the BCFs and model equations for the analysis of pollutant 

bioconcentration in fish tissue for T3 and T4 fish. EPA used the fish tissue concentrations to

evaluate impacts to piscivorous wildlife (see next section) and impacts to human health receptors

(see Section 5.1.3). 

Impact to Piscivorous Wildlife

EPA based the piscivorous wildlife impact analysis on the methodology outlined in the

2008 U.S. Geological Survey (USGS) study Environmental Contaminants in Freshwater Fish 

and Their Risk to Piscivorous Wildlife Based on a National Monitoring Program. The study 

examined the impacts to minks and eagles from eating contaminated fish. Minks and eagles are 

commonly used in ecological risk assessments as indicator species for potential impacts to fisheating mammals and birds in areas contaminated with bioaccumulative pollutants [USGS, 2008]. 

Minks and eagles are appropriate receptors for the steam electric power plant wildlife impact 

5-9 
 

 

Section 5—Surface Water Modeling 

analysis because their habitats span most of the country and their diet largely consists of adult 

fish from the two trophic levels (i.e., T3 and T4 fish) included in the IRW wildlife module. 

According to the literature [U.S. EPA, 1998a], minks consume mostly T3 fish, while eagles 

consume mostly T4 fish. EPA evaluated the potential adverse effects to minks and eagles for 

nine pollutants commonly found in the wastestreams of interest: arsenic, cadmium, chromium, 

copper, mercury, nickel, lead, selenium, and zinc.39 The USGS method [USGS, 2008] is a

wildlife impact analysis using NOAELs (no-observed-adverse-effect levels), which were derived 

from adult dietary exposure or tissue concentration studies based primarily on reproductive 

endpoints. The study calculated a NEHC benchmark, which is based on the NOAEL, the food 

consumption rate, and/or the biomagnification factor of each receptor. The report states that 

piscivorous wildlife may be at an elevated risk for reduced reproduction rates if the measured 

pollutant concentration in fish exceeds the NEHC. Therefore, EPA compared the mink-specific 

and eagle-specific NEHC values from the USGS study with the T3 and T4 fish tissue 

concentrations, respectively, to identify potential adverse impacts to the ecological receptors. In

the piscivorous wildlife analysis, a benchmark exceedance indicates that piscivorous mammals

or birds exposed to fish in the immediate receiving water of interest are at an elevated risk for 

reduced reproduction rates or other health effects. 

Table D-3 in Appendix D presents the NEHC values used to evaluate potential adverse 

effects to wildlife. The text of Appendix D presents the equations used to compare model outputs 

to benchmarks (NEHCs), along with model-specific limitations and assumptions. The results of 

the IRW wildlife module under baseline conditions and the final rule are included in Section 6 

and Section 7, respectively. 

5.1.3 Human Health Module

As shown in Figure 5-1, the IRW human health module builds off the IRW wildlife 

module, using the calculated T3 and T4 fish tissue concentrations. Its purpose is to evaluate the 

cancer risk and potential to cause non-cancer health effects from consuming fish within the 

following age and consumption categories: 

 Child recreational fishers (six cohorts covering different age ranges).40

 Child subsistence fishers (six cohorts covering different age ranges). 

 Adult recreational fishers. 

 Adult subsistence fishers.

In addition, EPA evaluated potential impacts to different race populations using these 

same cohorts as part of its environmental justice analysis. See the Regulatory Impact Analysis for 

the Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating 

Point Source Category (RIA) (EPA-821-R-15-004). 

39 Because there are no benchmarks for chromium VI or methylmercury, EPA used the total chromium and total 

mercury benchmarks, respectively, which may underestimate the risk to wildlife. 

40 The child cohort age ranges correspond to the ranges provided in the 2008 Child-Specific Exposure Factors 

Handbook (EPA-600-R-06-096F) for body weights. 

5-10 
 

 

Section 5—Surface Water Modeling 

EPA developed the IRW human health module in Microsoft AccessTM to estimate the

daily pollutant doses for human receptors as a result of eating T3 and T4 contaminated fish. EPA 

used a mathematical model to estimate the potential threats to human receptors from pollutant 

exposure. EPA estimated the average concentration of pollutants in a fish fillet consumed by

humans based on a consumption diet of 36 percent T3 and 64 percent T4 fish (see Appendix E). 

The IRW human health module then calculates the daily dose of pollutants from fish 

consumption for each cohort included in the analysis. EPA varied the fish consumption rate 

based on the specific cohort using two factors: 1) type of fisher (recreational or subsistence) and 

2) age (adult and six child cohorts). EPA first evaluated human health impacts based on type of

fisher and age of cohort using national-level consumption rates. For the environmental justice 

analysis, EPA determined fish consumption rates using the race population in addition to the 

other two factors. See Appendix E for further details. Using the fish consumption rate, EPA 

determined an average daily pollutant dose for each human cohort evaluated. Table E-2 in 

Appendix E presents the cohorts included in the IRW human health module and the

corresponding fish consumption rates used in the module. EPA implemented the human health 

modeling approach through the following steps: 

1. Calculate the pollutant concentration in a fish fillet.

2. Calculate the average daily dose of pollutant from fish consumption by each receptor

cohort (used for comparison to reference dose [RfD] values). 

3. Calculate the lifetime average daily dose (LADD) for carcinogenic pollutants only, by

each receptor cohort (used to determine cancer risk). 

4. Calculate the lifetime excess cancer risk (LECR) for carcinogenic pollutants only, by 

each receptor cohort, using the LADD. 

5. Compare the exposure doses of human receptor cohorts to appropriate benchmarks 

(RfD and selected cancer benchmark: 1-in-a-million). 

6. Compare the baseline and regulatory option results: reduction in the number of 

immediate receiving waters with exposure doses from consuming fish that pose a 

potential threat to human receptors. 

Non-Cancer Threat to Human Receptors

EPA evaluated the non-cancer threat (e.g., reproductive or neurological impacts) to each

cohort by comparing the pollutant-specific average daily dose values for fish consumption to the 

corresponding RfDs. EPA evaluated non-cancer risks for the following pollutants: inorganic 

arsenic,41 cadmium, chromium VI, copper, methylmercury, nickel, selenium, thallium, and zinc.

Table E-3 in Appendix E presents the RfD values used in the non-cancer threat analysis. RfD 

values are an expression of the consumption dose that is protective against a specific endpoint. 

41 For this analysis, EPA used only the concentration of inorganic arsenic for the human health impact assessment. 

Based on the literature review, arsenic in fish is mostly in the organic form and is not considered harmful. The

wildlife model calculates a total arsenic fish tissue concentration. To convert this number to inorganic arsenic, EPA 

assumed that 4 percent of the total arsenic is inorganic based on EPA’s 1997 document Arsenic and Fish 

Consumption (EPA-822-R-97-003). The 1997 document reported that the inorganic arsenic concentration in fish is 

between 0.4 and 4 percent of the total arsenic accumulating in fish [U.S. EPA, 1997b]. 

5-11 
 

 

Section 5—Surface Water Modeling 

Endpoints frequently reflected in RfDs include various immunological, reproductive, 

neurological, and other non-cancer effects. In the IRW human health module, when the RfD is 

exceeded, it indicates a potential threat to humans for the endpoint associated with the RfD. For

example, exceeding the RfD for selenium indicates that the exposure dose from fish consumption 

can cause non-cancer health effects, such as selenium-induced liver dysfunction or selenosis 

(hair or nail loss, morphological changes of the nails, etc.) [U.S. EPA, 2011c]. 

Cancer Risk to Human Receptors 

Arsenic is the only pollutant included in the IRW model for which EPA has derived a 

cancer slope factor for ingestion exposures.42 The IRW human health module calculates the 

LADD for each receptor cohort based on an exposure duration (i.e., length of time a receptor is

in contact with the carcinogen) averaged over a lifetime (i.e., 70 years). For this analysis, EPA 

assumed the exposure duration to be equal to the number of years represented by each cohort.

Using these exposure durations is appropriate for screening-level estimates of cancer risk and for 

comparing changes between baseline and regulatory options.43 The model then multiplies the

LADD by the cancer slope factor to calculate the LECR from arsenic. LECR is an estimate of the

increase in cancer risk resulting from an exposure (i.e., consumption of contaminated fish). EPA 

used the benchmark value for evaluating cancer risk of 1-in-a-million people. Therefore, a 

calculated LECR greater than 1 × 10-6 indicates an increased cancer risk for humans that 

consume fish exposed to discharges of evaluated wastestreams. 

5.2 ECOLOGICAL RISK MODELING

Selenium bioaccumulation in aquatic organisms occurs primarily from ingesting food 

rather than through direct exposure to dissolved selenium in the water column [Fan et al., 2002; 

Ohlendorf et al., 1986; Saiki and Lowe, 1987; Presser and Ohlendorf, 1987; Luoma et al., 1992; 

Presser et al., 1994; Chapman et al., 2009]. Unlike other bioaccumulative contaminants such as 

mercury, the single largest step in selenium accumulation in aquatic environments occurs in

aquatic organisms at the base of the food web; algae, particulates, and microorganisms can 

accumulate selenium to levels far greater than the concentration in the water column.

Bioaccumulation and transfer through aquatic food webs constitute the major selenium exposure

pathway in aquatic ecosystems. 

Macrophytes, algae, phytoplankton, zooplankton, and macroinvertebrates at the base of 

the food web easily bioaccumulate selenite and selenate and incorporate selenium in tissues as 

selenomethionine, an organo-selenide. This selenomethionine is then released back to the water 

42 Although EPA determined that lead and lead compounds can be “reasonably anticipated to be human

carcinogens,” no numeric value has been determined to quantify the cancer risk. As stated on the IRIS website,

“quantifying lead’s cancer risk involves many uncertainties, some of which may be unique to lead. Age, health, 

nutritional state, body burden, and exposure duration influence the absorption, release, and excretion of lead. In

addition, current knowledge of lead pharmacokinetics indicates that an estimate derived by standard procedures 

would not truly describe the potential risk. Thus, the Carcinogen Assessment Group recommends that a numerical 

estimate not be used.” (See http://www.epa.gov/iris/subst/0277.htm#reforal.) 

43 To completely assess risk to an individual, EPA recommends that risks should be calculated by integrating

exposures throughout all life stages (i.e., adding multiple cohort risks from screening analysis). For example, the 

exposure duration may be equal to the length of time a person lives in an area [U.S. EPA, 2011b]. 

5-12 
Section 5—Surface Water Modeling 

column as these plants and organisms die or are consumed [U.S. EPA, 2014f]. In general, 

selenium concentrations in particulates (e.g., sediment, detritus, and primary producers such as 

algae and biofilm) are 100 to 500 times higher than dissolved concentrations in selenatedominated environments such as streams and rivers. Where selenite or organo-selenide is 

proportionately more abundant, such as in lakes, wetlands, some estuaries, and oceans, the ratio 

can be much higher (1,000 to 10,000 times higher than dissolved concentrations). This variability 

of particulate concentrations relative to dissolved concentrations across different aquatic 

environments makes it difficult to develop a simple relationship between the concentration of

selenium in water and the concentration of selenium in organisms [Presser and Luoma, 2010]. 

The scientific community has devoted significant effort to understanding the mechanisms

of selenium bioaccumulation. The preferred approach, as described in Presser and Luoma 

[2010], accounts for the variability in particulate concentrations described above by applying 

site-specific enrichment factors (EFs) that represent the ratio of the concentration of selenium at 

the base of the food web (i.e., particulates) to the dissolved concentration in water. Subsequent 

bioaccumulation by aquatic organisms is described through a series of empirically derived, 

species-specific trophic transfer factors (TTFs) that link the selenium concentrations in 

particulates and invertebrates to higher trophic-level organisms such as fish and birds. TTFs can 

be derived from laboratory experiments or from field data. TTFs differ from traditional BCFs 

(described in Section 5.1.2) in that they are the ratio of the selenium concentration in each animal

to the selenium concentration in its food, whereas BCFs represent the ratio of the selenium

concentration in an animal to the selenium concentration in the water of its environment. Using 

TTFs therefore more accurately predicts selenium bioaccumulation in aquatic organisms because 

it accounts for the significant role of dietary exposure. 

Selenium toxicity among exposed fish and birds primarily is transferred to the eggs and 

demonstrated via subsequent reproductive effects. Many studies and expert panels have shown 

that reproductive effects, linked to egg-ovary selenium concentrations, are of greatest concern 

and likely have led to observed reductions in sensitive fish species populations in waterbodies 

having excessive selenium concentrations [Chapman et al., 2009]. 

EPA developed and applied a probabilistic ecological risk model, based on the 

bioaccumulation concepts described above, to assess the risk of adverse reproductive impacts 

among fish and birds exposed to selenium in waterbodies that receive discharges of the evaluated 

wastestreams. Figure 5-3 provides a general schematic of the approach, which follows these 

general steps: 

1. Apply a distribution of site-specific EFs (with separate distributions for lentic and 

lotic systems) to the predicted dissolved selenium concentration from the IRW

water quality module, resulting in a distribution of predicted selenium

concentrations in particulates and primary producers for each receiving water.

2. Apply a TTF distribution for invertebrates (TTFinvert) to the outputs from Step 1, 

resulting in a distribution of predicted selenium concentrations in invertebrates 

that inhabit each receiving water.

3. To predict the bioaccumulation and reproductive risk among fish: 

5-13 
 

Section 5—Surface Water Modeling 

a. Apply a TTF distribution for fish (TTFfish) to the outputs from Step 2, 

resulting in a distribution of predicted selenium concentrations in the eggs 

and ovaries of fish that inhabit each receiving water (some of the TTFs 

incorporate tissue conversion factors to translate the outputs from whole

body or muscle concentrations into fish egg-ovary concentrations). 

b. Apply an exposure-response function for fish (ERfish) to the outputs from 

Step 3a, resulting in a distribution showing the probability of a decline in

reproductive success across exposed fish populations. 

4. To predict the bioaccumulation and reproductive risk among birds (specifically, 

mallards): 

a. Apply a TTF distribution for mallards (TTFmallard) to the outputs from Step 

2, resulting in a distribution of predicted selenium concentrations in the 

eggs of mallards that forage and/or breed in each receiving water.

b. Apply an exposure-response function for mallards (ERmallard) to the 

outputs from Step 4a, resulting in a distribution showing the probability of 

a decline in reproductive success across exposed mallard populations.

This modeling approach is consistent with the approach taken in developing the External

Peer Review Draft Aquatic Life Ambient Water Quality Criterion for Selenium – Freshwater

[U.S. EPA, 2014f] (referred to as the external peer review draft selenium criterion) and is based 

on the same data sets and studies for EF, TTFinvert, TTFfish, and ERfish. For this EA, EPA 

expanded the model to include data sets for TTFmallard and ERmallard and to include several 

additional data sets and studies for EF, TTFinvert, TTFfish, and ERfish that were eventually 

incorporated into the Draft Aquatic Life Ambient Water Quality Criterion for Selenium – 

Freshwater [U.S. EPA, 2015b]. 

5-14 
 

Figure 5-3. Flowchart of Selenium Ecological Risk Model 

Section 5—Surface Water Modeling 

5-15 
 

Section 5—Surface Water Modeling 

Detailed information for some of the factors that influence selenium bioaccumulation at a

particular site, such as the form of selenium in the environment (e.g., selenate, selenite, and 

organo-selenide) and the structure of the aquatic food web, is not available across the 209 

immediate receiving waters modeled in this EA. The ecological risk model accounts for these 

unknowns by applying distributions of EFs and TTFs based on data representing a wide variety 

of lentic and lotic waterbodies and freshwater invertebrate and fish species, rather than relying 

on a single statistical measure (e.g., mean or median) for those parameters. This approach 

accounts for the variability across aquatic systems and captures the full range of food web 

constructs that could occur in these receiving waters.

The remainder of this section further discusses EPA’s development of the EFs, TTFs, and 

ER functions in the ecological risk model and use of those functions to calculate risk of adverse 

reproductive effects (performed using Oracle Crystal Ball software). Appendix F provides 

additional details regarding data sources, data acceptance criteria, statistical methods, and

assumptions and limitations of the ecological risk model. 

Enrichment Factors

EPA compiled a database of empirical measurements of selenium concentration (water, 

sediment, biofilm, algae, phytoplankton, and detritus) from relevant field studies across a range 

of aquatic systems. EPA then calculated EFs for a set of aquatic systems and applied statistical 

methods to distinguish categories with similar bioaccumulation characteristics, consistent with 

the approach followed in developing the external peer review draft selenium criterion [U.S. EPA, 

2014f]. The key factor distinguishing EFs across systems is whether the data were collected from

lentic systems (e.g., lakes, reservoirs, and ponds) or lotic systems (e.g., rivers, creeks, and 

streams). Therefore, the EPA developed EF distributions separately for lentic and lotic systems. 

This effort produced EF distributions for both systems that are well described by 

lognormal distributions with means (standard deviations) of 1,738 (2,499)44 for lentic systems 

and 692 (787) for lotic systems. 

Trophic Transfer Factors for Invertebrates and Fish

EPA compiled a database of empirical measurements of selenium concentration in 

particulates, invertebrates, and fish from relevant field studies. EPA arranged the data by 

developing data pairs representing the concentration in the consumer organism (invertebrate or 

fish) and the concentration in the consumed material or lower-trophic-level organism (particulate 

or invertebrate). The ratio between these two values defines the TTF for the consumer organism. 

EPA limited these data pairs to measurements collected from the same aquatic site. EPA further

limited the data pairs by excluding measurements of material or lower-trophic-level organisms

deemed unlikely to be ingested by the higher-trophic-level organism. Many of the fish 

concentration measurements required a further conversion to the concentration of selenium in 

eggs, requiring a whole-body-to-egg/ovary conversion factor. This factor (egg/ovary 

concentration = whole body concentration × 1.9) is based on paired measurements from 

44 The EF incorporates a multiplier of 1,000. A mean EF of 1,738 for lentic systems indicates that, on average, the

concentration of selenium at the base of the food web is 1.738 times greater than the dissolved concentration in

water.

5-16 
Section 5—Surface Water Modeling 

individual fish and is consistent with the value used to develop the external peer review draft 

selenium criterion [U.S. EPA, 2014f]. 

This effort resulted in a TTFinvert distribution with a mean (standard deviation) of 2.84 

(2.49) and a TTFfish distribution with a mean (standard deviation) of 1.6 (1.08). 

Trophic Transfer Factors for Mallards

EPA selected the mallard (Anas platyrhynchos) as the representative bird species for the 

ecological risk analysis. The mallard has been extensively evaluated in both field and laboratory 

studies and has been shown to be relatively sensitive to selenium. Mallards are ubiquitous, 

occurring in every state at specific times during the year, and are the species with the highest

probability of being found at any of the 209 modeled receiving waters. Dabbling ducks such as 

mallards contribute important ecosystem services, such as transferring eggs and seeds of aquatic

organisms between isolated wetlands and maintaining the biodiversity of other organisms 

[Bengtsson et al., 2014; Green and Elmberg, 2014]. 

Based on a review of Ohlendorf [2003], EPA developed a database of field measurements 

of mallards and their likely food sources, expressed as a ratio of measured egg concentrations to 

dietary concentrations. Many studies across a wide variety of species have shown that selenium 

concentrations in bird eggs range from roughly equal to or three or four times the concentrations 

in the diet of the female at the time of egg-laying [Ohlendorf and Heinz, 2011]. The resulting 

TTFmallard distribution is best described by a triangular distribution, with a likeliest value of 2.5, a 

minimum value of 0.4, and a maximum value of 4.1. 

Exposure-Response Function for Fish

Larval mortality and reproductive teratogenesis (i.e., deformities in offspring) from 

maternal transfer of selenium to eggs represent the most sensitive endpoints in fish. Deformities 

in fish that affect feeding or respiration can be lethal shortly after hatching. Deformities that are not 

directly lethal, but that distort the spine and fins, can affect larval survival by reducing swimming

ability and overall fitness. EPA therefore selected larval mortality and deformities as the target

endpoints for this analysis. 

This approach is consistent with the approach taken to develop the external peer review

draft selenium criterion, and used the same extensively peer-reviewed exposure-response 

function (i.e., curve) as was used in that analysis [U.S. EPA, 2014f]. Appendix F provides the 

exposure-response function for fish, which translates the modeled egg-ovary concentration into 

the probability of adverse reproductive effects. 

Exposure-Response Function for Mallards

To derive the exposure-response function for mallards, EPA used the same set of six 

progressive studies used to develop the TTFmallard distribution [Ohlendorf, 2003]. This approach 

ensures consistency in the predicted bioaccumulation and reproductive response across different 

selenium exposure levels. 

5-17 
Section 5—Surface Water Modeling 

The mallard exposure-response function in Ohlendorf [2003] is based on a regression 

meta-analysis of six different laboratory studies that evaluated the effect of selenium on mallard 

egg hatchability [Heinz et al., 1987, 1989; Heinz and Hoffman, 1996, 1998; Stanley et al., 1994, 

1996]. This function formed the basis of the water quality criterion adopted by the Utah Water 

Quality Board for Lake Gilbert, and underwent peer review by EPA Region 8. For this analysis, 

EPA fit a logistic curve to the combined, control normalized data from the six mallard studies.

Appendix F provides the resulting exposure-response function for mallards. 

Calculation of Reproductive Risk

In this analysis, risk is defined as the probability of a percentage reduction in 

reproductive capacity based on larval mortality and deformity in fish and hatching success in

mallards. For any given exposure concentration to selenium predicted from the EF-TTF model, 

the exposure-response function provides the probability of the effect occurring, termed a joint 

probability model. 

The EF-TTF models provide the predicted exposure distributions in fish and mallard 

eggs. For each concentration, the probability of exposure occurring is compared to the 

probability of effect at that exposure level. The resulting functions provide the probability of 

larval mortality and deformities in fish and hatching failure in mallards.

5-18 
Section 6—Current Impacts from Steam Electric Power Generating Industry 

SECTION 6

CURRENT IMPACTS FROM STEAM ELECTRIC POWER 

GENERATING INDUSTRY 

EPA developed the immediate receiving water (IRW) model and ecological risk model 

described in Section 5 to quantify the current national-scale environmental impacts of direct 

surface water discharges of the evaluated wastestreams (i.e., flue gas desulfurization (FGD) 

wastewater, fly ash transport water, bottom ash transport water, and combustion residual 

leachate) from steam electric power plants. This section presents the baseline results of the 

modeled pollutant concentrations in surface waters and fish tissue and their potential impacts to

aquatic life, wildlife, and human health. 

6.1 WATER QUALITY IMPACTS

The quality of a surface water is defined by its chemical, physical, and biological 

characteristics and is measured to evaluate a water’s potential to harm aquatic life and human 

health. EPA assessed 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). Based on the modeling results for surface water quality impacts, 

approximately 62 percent of the lakes, ponds, and reservoirs (16 out of 26) and 43 percent of the 

rivers and streams (78 out of 183) that receive discharges of the evaluated wastestreams have 

estimated pollutant concentrations that exceed these water quality benchmarks and may have 

quantifiably impaired water quality due to those discharges. Based on the modeling results, 

human health criteria exceedances are more prevalent among the immediate receiving waters 

than aquatic life criteria exceedances. Approximately 17 to 45 percent of the immediate 

receiving waters had modeled pollutant concentrations that exceed a human health criterion,

while approximately 4 to 17 percent of the immediate receiving waters had modeled pollutant 

concentrations that exceed an aquatic life criterion. The difference between exceedances for 

human health and aquatic life criteria is due to the human health criteria for arsenic and thallium, 

which are significantly lower than the aquatic life criteria for most of the modeled pollutants. 

Due to data limitations at the national scale, EPA did not include other pollutant sources 

(e.g., naturally -occurring pollutants, nonpoint source discharges, or other point source 

discharges) in the IRW model. Quantified exceedances estimated by the IRW model represent 

environmental impacts due entirely to the pollutant loadings in discharges of the evaluated 

wastestreams from steam electric power plants. Table 6-1 presents the number and percentage of 

immediate receiving waters with estimated pollutant concentrations that exceed each water 

quality criterion under baseline conditions. 

EPA identified arsenic, thallium, cadmium, and selenium as the primary pollutants

contributing to the water quality exceedances, as shown in Table 6-1. Humans are primarily at 

risk for exposure to arsenic and thallium. Out of the 209 modeled immediate receiving waters: 

 94 exceed the human health NRWQC for the consumption of arsenic-contaminated 

water and organisms (0.018 micrograms per liter (μg/L)).

6-1 
 

 

 

Section 6—Current Impacts from Steam Electric Power Generating Industry 

 65 exceed the arsenic NRWQC for consumption of organisms only (0.14 μg/L). 

 49 exceed the human health NRWQC for the consumption of thallium-contaminated

water and organisms (0.24 μg/L). 

 45 exceed the thallium NRWQC for consumption of organisms only (0.47 μg/L). 

Therefore, humans consuming water and/or organisms inhabiting these waters are more 

at risk of arsenic-related effects (skin damage, cardiovascular disease, and cancer in the skin, 

lungs, bladder, and kidney) and thallium-related effects (changes in blood chemistry; damage to

liver, kidney, and intestinal and testicular tissues; hair loss; and reproductive and developmental

damage). 

Aquatic organisms are primarily at risk due to exposure to cadmium and selenium. 

Estimated pollutant concentrations in approximately 15 percent of the immediate receiving

waters (29 and 33 out of 209, respectively) exceed the aquatic life criterion for chronic exposure 

to cadmium- and selenium-contaminated waters (0.25 and 5 μg/L, respectively). Therefore, 

aquatic organisms inhabiting these waters are under a greater threat for cadmium-related effects 

(tissue damage and organ abnormalities) and selenium-related effects (reproductive failure, 

deformities, reduced growth, increased metabolic rates, and death). Sublethal and lethal impacts 

from chronic selenium exposure are frequently cited in literature. For more information on these 

impacts, refer to Section 3.1.1. 

Table 6-1. Number and Percentage of Immediate Receiving Waters with Estimated 

Water Concentrations that Exceed the Water Quality Criteria at Baseline 

Evaluation Criterion

Number of Immediate Receiving Waters Exceeding a 

Criterion a

Number of 

Rivers and 

Streams

Number of 

Lakes, Ponds,

and

Reservoirs

Total Immediate Receiving 

Waters b

Number

Exceeding 

Percentage

Exceeding 

Aquatic 

Life 

Criteria 

Freshwater Acute NRWQC 9 0 9 4%

Freshwater Chronic NRWQC 30 5 35 17%

Human 

Health

Criteria 

Human Health Water and

Organism NRWQC 78 16 94 45%

Human Health Organism Only

NRWQC 55 11 66 32%

Drinking Water MCL 31 5 36 17%

Total Number of Unique Immediate 

Receiving Waters c 78 16 94 45%

Sources: ERG, 2015d; ERG, 2015h; ERG, 2015i. 

Acronyms: NRWQC (National Recommended Water Quality Criteria); MCL (maximum contaminant level). 

a – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power 

plants (some of which discharge to multiple receiving waters). The IRW model, which excludes the Great Lakes and 

estuaries, encompasses a total of 209 immediate receiving waters (183 rivers and streams; 26 lakes, ponds, and 

reservoirs) and loadings from 188 steam electric power plants. 

b – These values are the sum and percentage of rivers, streams, lakes, ponds, and reservoirs impacted. 

c – This represents the number of unique immediate receiving waters that exceeded at least one criterion. 

6-2 
Section 6—Current Impacts from Steam Electric Power Generating Industry 

Table H-1 in Appendix H presents additional details on the number and percentage of 

immediate receiving waters that are exceeding each water quality criterion by pollutant. For

more detailed information on the modeled immediate receiving water concentrations under 

baseline conditions, see Figures H-1 to H-10 and Tables H-2 to H-11 in Appendix H. 

6.2 WILDLIFE IMPACTS

As part of the national-scale wildlife impacts analysis, EPA assessed the impacts of the

evaluated wastestreams on the following categories:

 Impacts to wildlife indicator species (i.e., mink and eagle) due to consuming 

contaminated fish (using the wildlife component of the IRW model). 

 Impacts to fish and waterfowl due to dietary exposure and trophic transfer of 

selenium (using the ecological risk model in combination with the water quality 

component of the IRW model). 

 Impacts to benthic organisms due to contact with contaminated sediment (using the 

wildlife component of the IRW model). 

The results of these analyses are described in the following sections.

6.2.1 Impacts to Wildlife Indicator Species

As described in Section 5.1.2, EPA assessed the potential impact to piscivorous wildlife

from the evaluated wastestreams by modeling fish tissue pollutant concentrations and comparing 

these concentrations to no effect hazard concentrations (NEHC) for minks and eagles developed 

by the U.S. Geological Survey (USGS). Based on the estimated fish tissue concentrations, 

approximately 34 percent (71 out of 209) and 28 percent (58 out of 209) of the immediate

receiving waters pose a potential threat to eagles and minks, respectively, through the 

consumption of contaminated fish. This result demonstrates that estimated pollutant 

concentrations in fish that inhabit receiving waters immediately downstream from steam electric 

power plant wastewater discharges pose a potential reproductive threat to surrounding minks and 

eagles and indicates the potential broader impacts that steam electric power plant wastewater 

discharges may pose to the greater environment as pollutants transfer from the aquatic

environment and begin to accumulate in terrestrial food webs. 

As expected, based on documented environmental impacts, modeling results indicate that 

pollutant concentrations in fish inhabiting lakes, ponds, and reservoirs are more likely to exceed 

the NEHC benchmarks than pollutant concentrations in fish inhabiting rivers and streams. The

estimated fish tissue pollutant concentrations pose a potential reproductive threat to minks and 

eagles in approximately 46 percent of modeled lakes, ponds, and reservoirs (12 out of 26) and in 

32 percent of rivers and streams (59 out of 183) that were evaluated. These results are expected, 

since fish populations inhabiting lake environments cannot travel to uncontaminated waters and 

therefore continue to bioaccumulate pollutants.

Table 6-2 presents the number and percentage of immediate receiving waters that exceed

the USGS wildlife fish consumption NEHC for minks and eagles. 

6-3 
 

Section 6—Current Impacts from Steam Electric Power Generating Industry 

Table 6-2. Number and Percentage of Immediate Receiving Waters That Exceed Wildlife 

Fish Consumption NEHCs for Minks and Eagles (by Waterbody Type) at Baseline 

Evaluation Criterion

Number of 

Rivers and 

Streams

Number of 

Lakes, Ponds,

and Reservoirs

Total Receiving Waters a,b

Number

Exceeding 

Percentage

Exceeding 

Mink fish consumption NEHC 47 11 58 28%

Eagle fish consumption NEHC 59 12 71 34%

Total Number of Unique

Immediate Receiving Waters c 59 12 71 34%

Sources: ERG, 2015d; ERG, 2015h; ERG, 2015i. 

Acronyms: NEHC (No Effect Hazard Concentration). 

a – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power 

plants (some of which discharge to multiple receiving waters). The IRW model, which excludes the Great Lakes and 

estuaries, encompasses a total of 209 immediate receiving waters (183 rivers and streams; 26 lakes, ponds, and 

reservoirs) and loadings from 188 steam electric power plants. 

b – These values are the sum and percentage of rivers, streams, lakes, ponds, and reservoirs impacted. 

c – This represents the number of unique immediate receiving waters that exceed a criterion. 

The pollutants found to present the greatest threat to minks and eagles from fish 

consumption were mercury and selenium. The modeled concentrations of mercury in fish tissue 

exceeded the NEHC benchmarks for minks and eagles in 26 and 34 percent of the modeled 

immediate receiving waters, respectively. Approximately 20 percent of the immediate receiving 

waters contained fish with modeled selenium concentrations exceeding a fish consumption 

NEHC benchmark for minks and eagles. 

Table 6-3 presents the number and percentage of immediate receiving waters that exceed

a USGS wildlife fish consumption NEHC for minks and eagles by pollutant. 

6.2.2 Impacts to Fish and Waterfowl due to Dietary Selenium Exposure

As discussed in Section 5.2, EPA expanded upon the piscivorous wildlife benchmark 

analysis to include ecological risk modeling of the reproductive risks among fish and waterfowl 

that consume aquatic organisms contaminated with elevated levels of selenium. Selenium is of 

particular concern in aquatic environments because it can accumulate in sediment and 

biomagnify to toxic levels in fish inhabiting selenium-contaminated waters (even at relatively 

low concentrations), potentially eliminating piscivorous (fish-eating) wildlife higher in the food 

chain [Ohlendorf et al., 1988a]. Impacts to fish populations are well documented in the literature 

[Garrett and Inman, 1984; Lemly, 1985a; Sorensen et al., 1982]. While exposed fish populations 

may not experience lethal impacts, the sublethal damage to their reproductive systems can 

eventually impact the survivability of fish populations near steam electric power plants. The 

documented impacts at Belews Lake illustrate this is especially an issue in lakes, ponds, and 

reservoirs, where healthy fish populations cannot migrate and seek out alternative food sources. 

Decreased fish populations may cause cascading effects within the food web that can adversely 

affect other organisms in the ecosystem. 

6-4 
 

 

 

 

 

 

 

Section 6—Current Impacts from Steam Electric Power Generating Industry 

Table 6-3. Number and Percentage of Immediate Receiving Waters That Exceed Wildlife 

Fish Consumption NEHCs for Minks and Eagles (by Pollutant) at Baseline 

Pollutant 

Mink Eagle

Fish 

Consumption

NEHC

(μg/g) a

Immediate Receiving 

Waters

Fish 

Consumption

NEHC

(μg/g) a

Immediate Receiving 

Waters

Number

Exceeding b

Percentage

Exceeding 

Number

Exceeding b

Percentage

Exceeding 

Arsenic 7.65 0 0% 22.4 0 0%

Cadmium 5.66 6 3% 14.7 4 2%

Chromium VI 17.7 c

 0 0% 26.6 c 0 0%

Copper 41.2 1 <1% 40.5 1 <1% 

Lead 34.6 1 <1% 16.3 2 1%

Mercury 0.37 55 26% 0.5 71 34%

Nickel 12.5 0 0% 67.1 0 0%

Selenium 1.13 42 20% 4 42 20%

Thallium ID NC NC ID NC NC 

Zinc 904 1 <1% 145 5 2%

Sources: ERG, 2015d; ERG, 2015h; ERG, 2015i. 

Acronyms: ID (Insufficient data; no benchmarks were identified in the wildlife analysis for thallium); NC (Not

calculated); NEHC (No Effect Hazard Concentration); μg/g (micrograms/gram). 

a – The wildlife fish consumption NEHC represents the maximum pollutant concentration in the fish that will result 

in no observable adverse effects in wildlife (i.e., minks or eagles) [USGS, 2008].

b – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power 

plants (some of which discharge to multiple receiving waters). The IRW model, which excludes the Great Lakes and 

estuaries, encompasses a total of 209 immediate receiving waters (183 rivers and streams; 26 lakes, ponds, and 

reservoirs) and loadings from 188 steam electric power plants. 

c – An NEHC benchmark is not available for chromium VI; therefore, EPA used the total chromium benchmark.

The results of the ecological risk model indicate that, under baseline conditions, 

discharges of selenium from steam electric power plants elevate the risk of adverse reproductive 

impacts among fish and mallards that inhabit, forage, or breed in the immediate receiving waters. 

These reproductive impacts include larval mortality and deformities among fish and reduced egg

hatchability among mallards. 

The ecological risk modeling results indicate that 15 percent of the lakes, ponds, and 

reservoirs (four out of 26) and 11 percent of the rivers and streams (20 out of 183) that receive 

discharges of the evaluated wastestreams present an elevated risk of negative reproductive 

impacts to fish. For mallards, the counts are slightly higher, with 19 percent of the lakes, ponds, 

and reservoirs (five out of 26) and 14 percent of the rivers and streams (26 out of 183) presenting 

these risks. These results support the conclusion that lentic systems, which have higher potential 

for pollutant retention due to longer residence times, are more likely to experience ecological 

impacts due to discharges from steam electric power plants.

The results described above represent those immediate receiving waters whose median 

modeled egg/ovary concentration is predicted to impact reproduction among at least 10 percent 

of the exposed fish or mallard population. As described below, however, adjusting these criteria 

reveals additional perspective regarding the prevalence of immediate receiving waters that may 

be causing reproductive impacts due to selenium exposure. 

6-5 
Section 6—Current Impacts from Steam Electric Power Generating Industry 

Selecting the 90th percentile modeled egg/ovary concentration, meaning there is a 10 

percent probability that the egg/ovary concentrations are greater than the selected concentration,

reveals that 20 percent of the immediate receiving waters (42 out of 209) present reproductive 

risks to at least 10 percent of the exposed fish population. The results for mallards (21 percent) 

are very similar. These counts are considerably higher than the results obtained using the median 

modeled egg/ovary concentration, indicating the potential for more widespread ecological 

impacts among those waterbodies and food webs that tend to experience higher bioaccumulation 

of selenium. 

The results of the ecological risk model indicate that sublethal effects from dietary 

exposure to selenium (from discharges of the evaluated wastestreams) can lead to hidden 

population-level effects among exposed fish and waterfowl by reducing reproductive success. 

The results for mallards illustrate the broader effects throughout the food web that can result 

from exposure to waterbodies contaminated with selenium. These results also indicate that 

impacts to aquatic-dependent wildlife are not limited to piscivorous wildlife such as mink and 

eagles.

The ecological risk model accounts only for those reproductive effects associated with

exposure to selenium. There might be more immediate receiving waters whose pollutant levels

result in elevated reproductive risk because they contain other pollutants at concentrations that 

are harmful to wildlife. 

For more information on the potential environmental impacts from selenium exposure, 

refer to the selenium discussion in Section 3.1. For more detailed information on baseline 

modeled fish tissue concentrations in the immediate receiving water for selenium and other 

pollutants evaluated in the EA, see Figures H-11 to H-21 and Tables H-12 to H-22 in 

Appendix H.

6.2.3 Impacts to Benthic Organisms

EPA also assessed the potential impact to wildlife exposed to sediments in surface waters 

that receive discharges of the evaluated wastestreams by comparing estimated pollutant

concentrations in the sediment to chemical stressor concentration limit (CSCL) benchmarks for

sediment biota published by MacDonald, et. al. (2000) in Archives of Environmental 

Contamination and Toxicology. Table 6-4 presents the number and percentage of immediate 

receiving waters with sediment pollutant concentrations that exceed a CSCL. EPA calculated 

that 22 percent of rivers and streams (40 out of 183) and 35 percent of lakes, ponds, and 

reservoirs (9 out of 26) had estimated sediment pollutant concentrations that may be toxic to 

wildlife. 

Benthic organisms are at risk primarily due to exposure to mercury, nickel, and cadmium. 

Estimated sediment pollutant concentrations in 13 to 23 percent of the immediate receiving

waters (27 to 49 out of 209) exceed the sediment biota CSCL benchmarks for exposure to

cadmium-contaminated, nickel-contaminated, and mercury-contaminated waters. Therefore,

benthic organisms inhabiting these waters are under a greater threat for sublethal effects such as

skeletal malformation and reduced growth and reproductive success. For more information on 

these impacts, refer to Section 3.1.1. 

6-6 
 

 

 

 

 

 

Section 6—Current Impacts from Steam Electric Power Generating Industry 

As expected, based on documented environmental impacts, modeling results indicate that 

pollutant concentrations in the benthic sediment in lakes, ponds and reservoirs are more likely to 

exceed the sediment biota CSCL benchmarks than pollutant concentrations in the benthic 

sediment of rivers and streams. Several publications in the literature confirm that sediment 

impacts are more likely to occur in lakes where pollutants can accumulate in sediments over time

[Hopkins et al., 2000, 2003; Lemly, 1997a]. 

Table 6-4. Number and Percentage of Immediate Receiving Waters with Sediment 

Pollutant Concentrations Exceeding CSCLs for Sediment Biota at Baseline

Pollutant 

Sediment 

Benchmark 

(mg/kg)

Number of Immediate Receiving Waters Exceeding CSCLs for 

Sediment Biota 

Rivers and 

Streams

Lakes, Ponds,

and Reservoirs

Total Immediate Receiving 

Waters

Number a Percent 

Arsenic 5.90 7 0 7 3%

Cadmium 0.596 22 5 27 13%

Chromium VI b 37.3 0 0 0 0%

Copper 35.7 6 1 7 3%

Lead 35 5 1 6 3%

Mercury 0.174 40 9 49 23% 

Nickel 18.0 29 5 34 16%

Selenium ID NC NC NC NC 

Thallium ID NC NC NC NC 

Zinc 123 14 1 15 7%

Total Number of Unique Immediate

Receiving Waters 40 9 49 23%

Sources: ERG, 2015d; ERG, 2015h; ERG, 2015i. 

Acronyms: CSCL (Chemical stressor concentration limit); ID (Insufficient data; no benchmarks were identified); 

NC (Not calculated).a – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 

steam electric power plants (some of which discharge to multiple receiving waters). The IRW model, which 

excludes the Great Lakes and estuaries, encompasses a total of 209 immediate receiving waters (183 rivers and 

streams; 26 lakes, ponds, and reservoirs) and loadings from 188 steam electric power plants. 

b – No benchmark for chromium VI. EPA used the total chromium benchmark, which may underestimate the impact

to wildlife. 

6.3 HUMAN HEALTH IMPACTS

In addition to assessing water quality impacts on human health as discussed in Section 

3.3.2, EPA expanded the analysis to evaluate human health impacts from consuming fish in 

immediate receiving waters downstream from discharges of the evaluated wastestreams. The 

purpose of this analysis was to evaluate the broader bioaccumulative effects of pollutants in

steam electric power plant discharges to see whether average daily doses of pollutants from fish 

consumption could potentially exceed human health thresholds where water concentrations may 

not indicate an issue. EPA evaluated multiple human cohorts (i.e., recreational and subsistence 

fishers, children and adults) by calculating the average daily dose of pollutants from fish 

consumption using the estimated fish tissue concentrations calculated in the model. EPA varied

the fish consumption rate of each cohort (based on age) to determine the average and long-term

daily doses for each pollutant. EPA calculated the lifetime excess cancer risk (LECR) based on 

6-7 
 

Section 6—Current Impacts from Steam Electric Power Generating Industry 

estimated fish tissue concentrations of inorganic arsenic and calculated non-cancer threats by 

comparing the average daily doses to threshold values for all pollutants with published reference

doses. EPA first evaluated human health impacts based on type of fisher and age of cohort using 

national-level consumption rates. For the environmental justice analysis, EPA determined fish 

consumption rates using the race population in addition to the other two factors. For more 

information on how EPA identified potential impacts to human receptors, see Section 5.1.3 and 

Appendix E. 

The human health module presents the risk results for each age group individually to 

allow for further manipulation in the benefits analysis. The true cancer risk to a child would

depend on the amount of time the child consumed fish from locations downstream from steam 

electric power plant discharges. For example, the cancer risk for a 6-year-old child who was born 

and raised in the same place would be the sum of the LECRs from the 1 to <2 years, 2 to <3 

years, and 3 to <6 years cohort groups. 

A limitation of the national-scale IRW modeling that may underestimate the cancer risk 

is the use of an average annual pollutant loading rate as the basis for the risk estimation; as 

described earlier, the model does not consider the potential for pollutants to accumulate over 

time in the environment. The model estimates a minimal cancer risk from consuming fish in 

lakes, ponds, and reservoirs that receive discharges of the evaluated wastestreams. The cancer 

risk is likely greater in a lake, where fish are limited in their food sources and can bioaccumulate 

pollutants over a longer exposure period than is represented in the model. 

6.3.1 National-Scale Cohort Analysis

Table 6-5 presents the number and percentage of immediate receiving waters where the 

estimated LECR for the national-scale human receptor exceeds the selected threshold, 1-in-amillion cancer risk for arsenic. Inorganic arsenic concentrations in fish result in an estimated

cancer risk greater than 1-in-a-million to adult subsistence fishers in approximately 12 percent of

the immediate receiving waters (25 out of 209) and to adult recreational fishers in approximately 

6 percent of the immediate receiving waters (12 out of 209). Cancer risks for the child cohorts 

are lower, with LECRs exceeding the cancer risk threshold in 2 to 4 percent of the immediate 

receiving waters. Even given the limitations of the modeling framework discussed in Section 6.3, 

the inorganic arsenic concentrations in fish can pose a cancer risk to adult subsistence fishers in

12 percent of the lakes and to adult recreational fishers in 8 percent of the lakes. 

6-8 
 

 

 

Section 6—Current Impacts from Steam Electric Power Generating Industry 

Table 6-5. Number and Percentage of Immediate Receiving Waters That Exceed Human 

Health Evaluation Criteria (Lifetime Excess Cancer Risk) for Inorganic Arsenic at 

Baseline

Receptor Cohort

Exposure 

Duration 

(Years)

Number of Immediate Receiving Waters Where

Lifetime Excess Cancer Risk Exceeds 1-in-a-Million a,b

Number of 

Rivers and 

Streams

Number of 

Lakes, Ponds,

and Reservoirs

Total Receiving Waters c

Number

Exceeding 

Percentage

Exceeding 

Child

recreational 

fisher

1 to <2 years 1 4 0 4 2%

2 to <3 years 1 4 0 4 2%

3 to <6 years 3 6 0 6 3%

6 to <11 years 5 6 0 6 3%

11 to <16 years 5 6 0 6 3%

16 to <21 years 5 6 0 6 3%

Adult recreational fisher 49 10 2 12 6%

Child

subsistence 

fisher

1 to <2 years 1 6 0 6 3%

2 to <3 years 1 6 0 6 3%

3 to <6 years 3 7 0 7 3%

6 to <11 years 5 8 1 9 4%

11 to <16 years 5 6 0 6 3%

16 to <21 years 5 6 0 6 3%

Adult subsistence fisher 49 22 3 25 12%

Sources: ERG, 2015d; ERG, 2015h; ERG, 2015i. 

a – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power 

plants (some of which discharge to multiple receiving waters). The IRW model, which excludes the Great Lakes and 

estuaries, encompasses a total of 209 immediate receiving waters (183 rivers and streams; 26 lakes, ponds, and 

reservoirs) and loadings from 188 steam electric power plants. 

b – Inorganic arsenic cancer slope factor of 1.5 per milligrams per kilogram (mg/kg) per day.

c – These values are the sum and percentage of rivers, streams, lakes, ponds, and reservoirs impacted. 

Based on the estimated fish tissue concentrations and average daily pollutant doses by 

cohort, subsistence fishers (adults and children) have the greatest threat for non-cancer health 

effects. This is because the average daily doses (for one or more pollutant) exceed the oral 

reference dose values in 49 to 56 percent of the immediate receiving waters, depending on the 

age group evaluated. Recreational fishers (adult or child) have less of a threat, with average daily 

doses exceeding oral reference doses in 41 to 48 percent of the immediate receiving waters. 

These results suggest that fish downstream from discharges of the evaluated wastestreams pose a

non-cancer health threat to surrounding fisher populations. Given the modeling limitations 

described above, these results may underestimate these non-cancer health impacts. 

Table 6-6 presents the number and percentage of immediate receiving waters where the 

average daily dose of one or more pollutant exceeds an oral reference dose for non-carcinogens. 

6-9 
 

 

 

 

 

 

 

 

 

Section 6—Current Impacts from Steam Electric Power Generating Industry 

Table 6-6. Number and Percentage of Immediate Receiving Waters

That Exceed Non-Cancer Oral Reference Dose Values at Baseline

Receptor Cohort

Exposure 

Duration 

(Years)

Number of Immediate Receiving Waters where Estimated 

Exposure Doses Exceed Non-Cancer Reference Doses a

Number of 

Rivers and 

Streams

Number of 

Lakes, Ponds,

and Reservoirs

Total Receiving Waters b

Number

Exceeding 

Percentage

Exceeding 

Child

recreational 

fisher

1 to <2 years 1 82 18 100 48%

2 to <3 years 1 82 18 100 48%

3 to <6 years 3 80 18 98 47%

6 to <11 years 5 76 16 92 44%

11 to <16 years 5 72 14 86 41%

16 to <21 years 5 72 14 86 41%

Adult recreational fisher 49 72 14 86 41%

Child

subsistence 

fisher

1 to <2 years 1 98 20 118 56%

2 to <3 years 1 98 20 118 56%

3 to <6 years 3 92 19 111 53%

6 to <11 years 5 87 19 106 51%

11 to <16 years 5 84 18 102 49%

16 to <21 years 5 84 18 102 49%

Adult subsistence fisher 49 85 18 103 49%

Sources: ERG, 2015d; ERG, 2015h; ERG, 2015i. 

a – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power 

plants (some of which discharge to multiple receiving waters). The IRW model, which excludes the Great Lakes and 

estuaries, encompasses a total of 209 immediate receiving waters (183 rivers and streams; 26 lakes, ponds, and 

reservoirs) and loadings from 188 steam electric power plants. 

b – These values are the sum and percentage of rivers, streams, lakes, ponds, and reservoirs impacted. 

According to the exposure doses calculated from the estimated fish tissue concentrations, 

methylmercury poses the greatest threat to cause non-cancer health effects in humans from fish 

consumption. Mercury concentrations in fish pose a non-cancer threat to humans in 

approximately 52 percent of the immediate receiving waters. Therefore, humans who consume

fish inhabiting these waters are at risk for developing mercury-related effects, which could 

include neurological symptoms (e.g., affecting fine motor function, language skills, verbal 

memory) and cardiovascular disease if exposed at high enough doses. In addition, thallium 

concentrations in fish pose a non-cancer threat to humans in approximately 45 percent of

immediate receiving waters.45 Therefore, humans who consume thallium-contaminated fish

inhabiting these waters are more likely to develop neurological symptoms (e.g., weakness, sleep 

disorders, muscular problems), alopecia (i.e., loss of hair from the head and body), and 

gastrointestinal effects (e.g., diarrhea and vomiting). 

Table 6-7 presents the number and percentage of immediate receiving waters where 

average daily doses exceed an oral reference dose for non-carcinogens by pollutant. 

45 EPA used the chronic oral exposure value cited in U.S. EPA, 2010a for thallium chloride as the reference dose. 

6-10 
 

 

 

Section 6—Current Impacts from Steam Electric Power Generating Industry 

Table 6-7. Number and Percentage of Immediate Receiving Waters That Exceed NonCancer Oral Reference Dose Values at Baseline by Pollutant 

Pollutant 

Oral

Reference Dose

(mg/kg/day)

Number of Immediate Receiving Waters where Estimated 

Exposure Doses Exceed Non-Cancer Reference Doses a

Number Exceeding Percentage Exceeding 

Inorganic arsenic 0.0003 b

 3 1%

Cadmium 0.001 b

 32 15%

Chromium VI 0.003 b

 0 0%

Copper 0.01 c

 6 3%

Lead ID NC NC 

Mercury (as methylmercury) 0.0001 b

 109 52% 

Nickel (soluble salts) 0.02 b

 0 0%

Selenium 0.005 b

 55 26%

Thallium (soluble salts) 0.00001 d

 94 45%

Zinc 0.3 b

 9 4%

Sources: ERG, 2015d; ERG, 2015h; ERG, 2015i. 

Acronyms: NC (Not calculated); ID (Insufficient data; there is no current reference dose for lead). 

a – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power 

plants (some of which discharge to multiple receiving waters). The IRW model, which excludes the Great Lakes and 

estuaries, encompasses a total of 209 immediate receiving waters (183 rivers and streams; 26 lakes, ponds, and 

reservoirs) and loadings from 188 steam electric power plants. 

b – U.S. EPA, 2011c.

c – ATSDR, 2010a. 

d – U.S. EPA, 2010a.

States, territories, and authorized tribes have the primary responsibility to protect 

residents from the health risks of consuming contaminated noncommercially caught fish. They 

inform the general population, including recreational and subsistence fishers, typically by issuing 

advisories that notify the public that chemical contamination found in local fish may present a 

public health hazard. 

EPA modeled concentrations in T4 fish tissue and compared them 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 hazard. Based on the modeling 

results, up to 48 percent of the immediate receiving waters evaluated may contain fish with 

contamination levels that could trigger advisories for recreational and subsistence fishers. 

Mercury and selenium are the pollutants most likely to exceed screening values. This result 

indicates that steam electric power plants are contributing to the already widespread

concentrations of mercury and selenium in fish throughout the country. 

Table 6-8 presents the number and percentage of immediate receiving waters where the 

modeled T4 fish tissue concentrations exceed screening values used for fish advisories. 

6-11 
 

 

 

 

 

Section 6—Current Impacts from Steam Electric Power Generating Industry 

Table 6-8. Comparison of T4 Fish Tissue Concentrations at Baseline to 

Fish Advisory Screening Values 

Pollutant 

Recreational Fishers Subsistence Fishers

Screening 

Value (ppm)a

Number

Exceeding b

Percentage

Exceeding 

Screening 

Value (ppm) a

Number

Exceeding b

Percentage

Exceeding 

Inorganic arsenic 

(noncarcinogen) 1.2 0 0% 0.147 3 1%

Inorganic arsenic 

(carcinogen) 0.026 4 2% 0.00327 9 4%

Cadmium 4.0 8 4% 0.491 22 11%

Mercury (as 

methylmercury) 0.4 76 36% 0.049 101 48%

Selenium 20 22 11% 2.457 46 22%

Sources: ERG, 2015d; ERG, 2015h; ERG, 2015i. 

Acronyms: ppm (parts per million).

a – Screening values are defined as concentrations of target analytes in fish or shellfish tissue that are of potential 

public health concern and that are used as threshold values against which levels of contamination in similar tissue 

collected from the ambient environment can be compared. Exceedance of these screening values indicates that more 

intensive site-specific monitoring and/or evaluation of human health risk should be conducted [U.S. EPA, 2000a,

Table 5-3].

b – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power 

plants (some of which discharge to multiple receiving waters). The IRW model, which excludes the Great Lakes and 

estuaries, encompasses a total of 209 immediate receiving waters (183 rivers and streams; 26 lakes, ponds, and 

reservoirs) and loadings from 188 steam electric power plants. 

6.3.2 Environmental Justice Analysis

As part of the EA, EPA evaluated whether the impacts from steam electric power plant 

wastewater discharges disproportionately impact minority groups. This environmental justice 

(EJ) analysis included looking at impacts based on race or Hispanic origin. Table 6-9 presents 

the number and percentage of immediate receiving waters where the estimated LECR for the 

human receptor exceeds the selected threshold, 1-in-a-million cancer risk for arsenic. Inorganic

arsenic concentrations in fish result in an estimated cancer risk greater than 1-in-a-million to 

adult subsistence, minority fishers in approximately 12 to 15 percent of the immediate receiving 

waters (26 to 32 out of 209) and to adult recreational fishers in approximately 7 to 9 percent of 

the immediate receiving waters (14 to 19 out of 209). 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 (especially among the recreational fisher population). 

6-12 
 

 

 

 

Section 6—Current Impacts from Steam Electric Power Generating Industry 

Table 6-9. Number and Percentage of Immediate Receiving Waters That Exceed Human 

Health Evaluation Criteria (Lifetime Excess Cancer Risk) for Inorganic Arsenic at 

Baseline, by Race or Hispanic Origin 

Receptor

Race or Hispanic 

Origin 

Number of Immediate Receiving Waters Where

Lifetime Excess Cancer Risk Exceeds 1-in-a-Million a,b

1 to <2

years

2 to <3

years

3 to <6

years

6 to <11 

years

11 to <16 

years

16 to <21 

years Adult 

Recreational

Non-Hispanic White 3 3 4 6 6 6 12

Non-Hispanic Black 3 3 5 6 6 6 14

Mexican-American 4 4 6 6 6 6 18

Other Hispanic 4 4 6 6 6 6 16

Other, including 

Multiple Races 

4 4 6 6 6 6 19

Subsistence 

Non-Hispanic White 4 4 6 7 7 7 25

Non-Hispanic Black 5 5 6 7 7 7 26

Mexican-American 6 6 6 8 8 8 28

Other Hispanic 6 6 6 7 7 7 28

Other, including 

Multiple Races 

6 6 7 10 10 10 32

Sources: ERG, 2015d; ERG, 2015h; ERG, 2015i. 

a – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power 

plants (some of which discharge to multiple receiving waters). The IRW model, which excludes the Great Lakes and 

estuaries, encompasses a total of 209 immediate receiving waters (183 rivers and streams; 26 lakes, ponds, and 

reservoirs) and loadings from 188 steam electric power plants. 

b – Inorganic arsenic cancer slope factor of 1.5 per milligrams per kilogram (mg/kg) per day.

Based on the estimated fish tissue concentrations and average daily pollutant doses by 

cohort, subsistence fishers (adults and children) have the greatest threat for non-cancer health 

effects. This is because the average daily doses (for one or more pollutant) exceed the oral 

reference dose values in 49 to 56 percent of the immediate receiving waters, depending on the 

age group evaluated. Recreational fishers (adult or child) have less of a threat, with average daily 

doses exceeding oral reference doses in 41 to 48 percent of the immediate receiving waters. 

These results suggest that fish downstream from discharges of the evaluated wastestreams pose a

non-cancer health threat to surrounding fisher populations. Given the modeling limitations 

described above, these results may underestimate these non-cancer health impacts. 

Table 6-10 presents the number and percentage of immediate receiving waters where the 

average daily dose of one or more pollutant exceeds an oral reference dose for non-carcinogens. 

6-13
Section 6—Current Impacts from Steam Electric P

Table 6-10. Number and Percentage of Immediate Receiving Waters That Exceed Non-Cancer Oral Refer

Baseline, by Race or Hispanic Origin 

Receptor Race or Hispanic Origin 

Number of Immediate Receiving Waters Where Pollutant Exceeds a Non-

Inorganic 

Arsenic Cadmium Copper Mercury b Selenium T

Recreational, 

Child Fisher 

Non-Hispanic White 0 (0%) 10 (5%) 3 (1%) 81 (39%) 32 (15%) 

Non-Hispanic Black 0 (0%) 12 (6%) 4 (2%) 84 (40%) 33 (16%) 

Mexican-American 0 (0%) 14 (7%) 4 (2%) 86 (41%) 33 (16%) 

Other Hispanic 0 (0%) 13 (6%) 4 (2%) 84 (40%) 33 (16%) 

Other, including Multiple Races 0 (0%) 14 (7%) 4 (2%) 88 (42%) 34 (16%) 

Subsistence, Child Fisher 

Non-Hispanic White 3 (1%) 21 (10%) 5 (2%) 98 (47%) 42 (20%) 

Non-Hispanic Black 3 (1%) 22 (11%) 5 (2%) 98 (47%) 43 (21%) 

Mexican-American 3 (1%) 25 (12%) 6 (3%) 100 (48%) 46 (22%) 

Other Hispanic 3 (1%) 25 (12%) 5 (2%) 100 (48%) 46 (22%) 

Other, including Multiple Races 3 (1%) 29 (14%) 6 (3%) 104 (50%) 48 (23%) 

Recreational, 

Adult Fisher 

Non-Hispanic White 0 (0%) 10 (5%) 3 (1%) 81 (39%) 32 (15%) 

Non-Hispanic Black 0 (0%) 12 (6%) 4 (2%) 84 (40%) 33 (16%) 

Mexican-American 0 (0%) 14 (7%) 4 (2%) 86 (41%) 33 (16%) 

Other Hispanic 0 (0%) 13 (6%) 4 (2%) 84 (40%) 33 (16%) 

Other, including Multiple Races 0 (0%) 14 (7%) 4 (2%) 88 (42%) 34 (16%) 

Subsistence, 

Adult Fisher 

Non-Hispanic White 3 (1%) 21 (10%) 5 (2%) 98 (47%) 42 (20%) 

Non-Hispanic Black 3 (1%) 22 (11%) 5 (2%) 98 (47%) 43 (21%) 

Mexican-American 3 (1%) 25 (12%) 6 (3%) 100 (48%) 46 (22%) Other Hispanic 3 (1%) 25 (12%) 5 (2%) 100 (48%) 46 (22%) 

Other, including Multiple Races 3 (1%) 29 (14%) 6 (3%) 104 (50%) 48 (23%) 

Sources: ERG, 2015d; ERG, 2015h; ERG, 2015i. a – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power plants (some of which receiving waters). The IRW model, which excludes the Great Lakes and estuaries, encompasses a total of 209 immediate receiving wat

streams; 26 lakes, ponds, and reservoirs) and loadings from 188 steam electric power plants. 

b – Mercury, as methylmercury. c – Reference dose based on thallium (soluble salts).

6-14
 

 

Section 7—Environmental Improvements Under the Final Rule 

SECTION 7

ENVIRONMENTAL IMPROVEMENTS UNDER 

THE FINAL RULE 

In Section 6, EPA presented the environmental impacts to surface water quality, wildlife, 

and human health estimated with EPA’s immediate receiving water (IRW) model and ecological 

risk model resulting from baseline discharges of the evaluated wastestreams. Under the final 

steam electric effluent limitations guidelines and standards (ELGs), EPA evaluated six regulatory 

options (Options A, B, C, D, E, and F). As part of this quantitative environmental assessment 

(EA), EPA evaluated the environmental improvements associated with the reduction in pollutant

loadings from the evaluated wastestreams (i.e., flue gas desulfurization (FGD) wastewater, fly 

ash transport water, bottom ash transport water, and combustion residual leachate) under Options 

A, B, C, D, and E, described in Table 7-1.46

In the remainder of this document, EPA presents the results only for Options A through E 

for existing sources. During development of the final rule, EPA decided not to base the final rule 

on Option F for existing sources due primarily to the high cost of that Option, particularly in 

light of the costs associated with other rulemakings expected to impact the steam electric 

industry (see Section VIII.C.1 of the preamble). As a result, EPA chose not to conduct particular 

analyses for Option F to the same extent that it did for some of the other options considered. 

Section 8 of the Technical Development Document (TDD) (EPA-821-R-15-007) details the 

technology options for all wastestreams evaluated under each regulatory option for the final rule. 

As described in Section 8 of the TDD, EPA selected Option D as the technology basis for the 

best available technology economically achievable (BAT) and for pretreatment standards for 

existing sources (PSES). See Section 12 of the TDD for further information on the limitations

and standards of the final rule. This section presents the improvements to surface water quality, 

wildlife, and human health under the final rule as quantified by EPA’s IRW model and 

ecological risk model. 

Based on the quantitative and qualitative analyses performed for the EA, EPA estimated 

that a variety of environmental improvements would result from the pollutant loading removals

associated with the regulatory options. In particular, the EA evaluated the following: 1) 

improvements in water quality, 2) reduction in threats to wildlife, 3) reduction in human health 

cancer risks, 4) reduction in threats for non-cancer human health effects, and 5) other

unquantified environmental improvements. Table 7-2 lists the quantified and unquantified 

environmental improvements estimated to result from the final rule’s regulatory options and 

designates which quantified improvements were monetized in the benefits analysis described in

the Benefits and Cost Analysis (EPA-821-R-15-005). 

46 In addition to the wastestreams listed in Table 7-1, EPA evaluated technology options associated with flue gas 

mercury control (FGMC) wastewater, gasification wastewater, and nonchemical metal cleaning wastes as part of 

the regulatory options. However, no plants currently discharge FGMC wastewater, all existing gasification plants are 

operating the technology used as the basis for the regulatory option, and EPA will continue to reserve

BAT/NSPS/PSES/PSNS for nonchemical metal cleaning wastes, as previously established regulations do.

Therefore, EPA estimated zero compliance costs and zero pollutant reductions associated with these wastestreams

and did not include these three wastestreams in the EA. 

7-1 
Section 7—Environmental Improvements Under the Final Rule 

Table 7-1. Regulatory Options for the Wastestreams Evaluated in the EA 

Evaluated 

Wastestream a

Option

A 

Option

B 

Option

C 

Option

D 

Option

E 

FGD wastewater Chemical

precipitation

Chemical

precipitation + 

biological 

treatment

Chemical

precipitation + 

biological 

treatment

Chemical

precipitation + 

biological 

treatment

Chemical

precipitation + 

biological 

treatment

Fly ash transport 

water 

Dry handling Dry handling Dry handling Dry handling Dry handling 

Bottom ash 

transport water

Impoundment 

(equal to BPT)

Impoundment 

(equal to BPT)

Dry handling/ 

closed loop

(for units >400 

MW); 

impoundment 

(equal to BPT) for 

units ≤400 MW 

Dry handling/ 

closed loop

Dry handling/ 

closed loop

Combustion 

residual leachate

Impoundment 

(equal to BPT)

Impoundment 

(equal to BPT)

Impoundment 

(equal to BPT)

Impoundment 

(equal to BPT)

Chemical

precipitation

Acronyms: BPT (Best practicable control technology currently available); MW (Megawatt). 

a – The evaluated wastestreams and regulatory options listed in the table are a subset of regulatory options for the 

steam electric ELGs. See Section 8 of the TDD for the full list of regulatory options. 

7-2 
 

 

 

 

 

 

 

Section 7—Environmental Improvements Under the Final Rule 

Table 7-2. Description of Environmental Improvements 

Associated with the Final Rule 

Assessment 

Category

Description of Environmental 

Improvement 

Improvement 

Quantified

Improvement 

Monetized More Information

Water 

Quality 

Reduced number of immediate 

receiving waters exceeding an acute 

or chronic aquatic life NRWQC 



Section 7.2 

Section 7.3

Reduced number of immediate 

receiving waters exceeding a human 

health NRWQC 



Section 7.2 

Section 7.3

Reduced number of immediate 

receiving waters exceeding MCLs  Section 7.2 

Section 7.3

Increased aesthetic benefits, such as 

enhancement of adjoining site 

amenities (e.g., residing, working,

traveling, and owning property near

water)

 

Benefits and Cost 

Analysis a

Improved water-based recreation,

including swimming, fishing,

boating, and near-water activities 

from improved water quality 

 

Benefits and Cost 

Analysis a

Improved quality of source water 

used for drinking, irrigation, and

industrial use 

Qualitative 

Discussion (Benefits 

and Cost Analysis) 

Increased property values from water 

quality improvements 

Qualitative 

Discussion (Benefits 

and Cost Analysis) 

Increased tourism and participation in

water-based recreation 

Qualitative 

Discussion (Benefits 

and Cost Analysis) 

Pollutant removals to impaired

waters

 Section 7.4

Pollutant removals to the Great Lakes 

and Chesapeake Bay 

 Section 7.5

Pollutant removals of toxic 

contaminants, chlorides, and TDS to

receiving waters



Section 7.1

Nutrient removals to receiving waters

 

Section 7.1 and 

Benefits and Cost 

Analysis a

Reduced risk of surface 

impoundment failures 

  Benefits and Cost 

Analysis a

Reduced sediment contamination Qualitative 

Discussion (Benefits 

and Cost Analysis) 

Increased availability of ground 

water resources 

  Benefits and Cost 

Analysis a

7-3
 

 

 

 

 

 

 

 

 

 

Section 7—Environmental Improvements Under the Final Rule 

Table 7-2. Description of Environmental Improvements 

Associated with the Final Rule 

Assessment 

Category

Description of Environmental 

Improvement 

Improvement 

Quantified

Improvement 

Monetized More Information

Wildlife Reduced exposure among minks to

pollutants that bioaccumulate in fish  Section 7.2 

Section 7.3

Reduced exposure among eagles to

pollutants that bioaccumulate in fish  Section 7.2 

Section 7.3

Reduced selenium concentrations in

fish and waterfowl and associated 

reduced reproductive risk 



Section 7.2 

Section 7.3

Improved aquatic and wildlife habitat

and improved protection of

threatened and endangered species 

 

Section 7.4 and 

Benefits and Cost 

Analysis a

Improved commercial fisheries yield 

due to aquatic habitat improvement 

Qualitative 

Discussion (Benefits 

and Cost Analysis) 

Enhanced existence, option, and 

bequest values from improved

ecosystem health 

 

Benefits and Cost 

Analysis a

Reduced risks to aquatic life from

exposure to steam electric pollutants 

 Benefits and Cost 

Analysis a

Reduced exposure to pollutants 

associated with the wastestreams of 

concern in surface impoundments 

that serve as attractive nuisances 

Qualitative 

Discussion (Section 

7.7)

Human 

Health 

Reduced exposure to non-cancer 

pollutants for recreational and 

subsistence fishers 

Section 7.2 

Section 7.3

Benefits and Cost 

Analysis a

Reduced cancer risk in recreational

and subsistence fishers  

Section 7.2 

Section 7.3

Benefits and Cost 

Analysis a

Reduced incidences of cardiovascular 

disease from reduced arsenic and lead 

exposure

 

Benefits and Cost 

Analysis a

Reduced adverse health effects from

reduced in-utero mercury exposure 

from maternal fish consumption

 

Benefits and Cost 

Analysis a

Reduced IQ loss and specialized 

education from reduced childhood

exposure to lead from fish 

consumption 

 

Benefits and Cost 

Analysis a

Reduced adult mortality from air 

pollutant emissions

  Benefits and Cost 

Analysis a

Avoided climate change impacts 

from carbon dioxide emissions 

  Benefits and Cost 

Analysis a

Reduced exposure to pollutants from

recreational water uses 

Qualitative 

Discussion (Benefits 

and Cost Analysis) 

7-4
Section 7—Environmental Improvements Under the Final Rule 

Table 7-2. Description of Environmental Improvements 

Associated with the Final Rule 

Assessment 

Category

Description of Environmental 

Improvement 

Improvement 

Quantified

Improvement 

Monetized More Information

Reduced injury associated with

impoundment failures

Qualitative 

Discussion (Benefits 

and Cost Analysis) 

Reduced number of immediate 

receiving waters exceeding fish 

consumption advisory screening

values



Section 7.4

Acronyms: MCL (maximum contaminant level); NRWQC (National Recommended Water Quality Criteria); TDS 

(total dissolved solids).

a – The Benefits and Cost Analysis quantifies and monetizes individual environmental improvements for Options A, 

B, C, D, and E. See Benefits and Cost Analysis for more detail.

7.1 POLLUTANT REMOVALS UNDER THE REGULATORY OPTIONS

EPA estimates that the regulatory options would significantly reduce pollutant loadings 

to receiving waters for the 10 pollutants modeled in the EA and for other pollutants that can

adversely affect surface waters, such as boron, manganese, nutrients, chlorides, and TDS. Table 

7-3 and Table 7-4 present the pollutant removals under the regulatory options for the evaluated

wastestreams.

Under the final rule (Option D), EPA estimates that pollutant loadings from existing 

sources will decrease by over 95 percent for copper, lead, mercury, nickel, selenium, thallium,

and zinc and over 90 percent for arsenic and cadmium. In turn, these pollutant removals will 

reduce the negative impacts on the environment as well as the potential exposure of these 

contaminants to ecological and human receptors. The selenium removals will significantly

improve the water quality around the steam electric power plant discharge locations. Mercury 

removals will improve human health as mercury has been linked to decreased IQs in children

whose pregnant mothers have been exposed to mercury by consuming fish. 

Manganese and boron, while not generally considered toxic at levels seen in the aquatic 

environment, have the highest and third highest toxic-weighted pound equivalents (TWPEs), 

respectively, under baseline conditions for pollutants evaluated in the EA (see Section 3.2). As 

discussed in Section 3, boron can negatively impact fish and ducks and manganese can be toxic 

to humans at high levels. Under the final rule, the pollutant loadings for manganese and boron 

will decrease by 80 and 15 percent, respectively. 

As discussed in Section 3, nutrients (i.e., nitrogen and phosphorus) in excess quantities 

can adversely affect surface waters by causing oxygen-consuming harmful algae blooms and 

creating “dead zones” where fish and shellfish cannot survive. Under the final rule, EPA 

calculated that nitrogen loadings will decrease by 16.8 million pounds per year (99 percent) and 

phosphorus loadings will decrease by 174,000 pounds per year (81 percent). The nutrient

removals will improve hypoxic areas (i.e., low-oxygen surface waters) such as the Chesapeake 

Bay and the Gulf of Mexico (via reduced loadings to the Mississippi River Basin).

7-5
 

 

Section 7—Environmental Improvements Under the Final Rule 

Excess chlorides levels in wastewater discharges can be harmful to animals and plants in 

nonmarine surface waters and can disrupt ecosystem structure. Under the final rule, annual 

chlorides loadings to surface waters will decrease by 21.8 million pounds (two percent).

The pollutant parameter, TDS, comprises dissolved solids such as chloride and metals. 

Under the final rule, EPA calculated that annual TDS loadings to surface waters will decrease by 

more than 1.32 billion pounds (31 percent). This decrease is at least partially due to the reduction 

in total and dissolved metals discharged to receiving waters.47

47 EPA’s estimated TDS removals do not account for additional removals that may be achieved as a result of steam

electric power plants opting to participate in the voluntary incentives program, in which they would be subject to

effluent limitations based on evaporation technology, including for TDS.

7-6
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Section 7—Environmental Improvements Under the Final Rule 

Table 7-3. Steam Electric Power Generating Industry Pollutant Removals for Metals, 

Bioaccumulative Pollutants, Nutrients, Chlorides, and TDS Under Regulatory Options 

Pollutant 

Pollutant Removals, lbs/yr (Percent Reduction) a

Option A Option B Option C Option D Option E

Arsenic 15,700 

(53%)

15,700 

(53%)

23,200 

(78%)

27,900 

(94%)

28,500 

(96%)

Boron 4,230,000

(14%)

4,230,000

(14%)

4,480,000

(14%)

4,630,000

(15%)

4,630,000

(15%)

Cadmium 9,020

(68%)

9,020

(68%)

11,200 

(84%)

12,500 

(94%)

12,600 

(95%)

Chromium VI 131 

(84%)

131 

(84%)

147 

(95%)

156 

(>99%)

156 

(>99%)

Copper 14,300 

(46%)

14,300 

(46%)

24,300 

(78%)

30,500 

(98%)

30,600 

(98%)

Lead 7,670

(39%)

7,670

(39%)

14,800 

(75%)

19,200 

(98%)

19,200 

(98%)

Manganese 5,120,000

(68%)

5,120,000

(68%)

5,650,000

(75%)

5,990,000

(80%)

5,990,000

(80%)

Mercury 858 

(58%)

868 

(58%)

1,230

(83%)

1,450

(97%)

1,470

(99%)

Nickel 62,300 

(52%)

62,600 

(52%)

96,200 

(80%)

117,000

(98%)

118,000

(99%)

Selenium 29,300 

(21%)

130,000

(93%)

134,000

(96%)

136,000

(97%)

136,000

(97%)

Thallium 7,180

(11%)

7,180

(11%)

40,900 

(64%)

62,300 

(98%)

62,300 

(98%)

Zinc 120,000

(69%)

120,000

(69%)

148,000

(85%)

166,000

(95%)

169,000

(97%)

Nitrogen, total b 1,980,000

(12%)

12,300,000 

(73%)

15,100,000 

(89%)

16,800,000 

(99%)

16,800,000 

(99%)

Phosphorus, total 43,100 

(20%)

43,100 

(20%)

123,000

(57%)

174,000

(81%)

174,000

(81%)

Chlorides 4,160,000

(<1%)

4,160,000

(<1%)

14,900,000 

(2%)

21,800,000 

(2%)

21,800,000 

(2%)

TDS 849,000,000 

(20%)

849,000,000 

(20%)

1,130,000,000 

(27%)

1,320,000,000 

(31%)

1,320,000,000 

(31%)

Source: ERG, 2015a. 

Acronyms: TDS (Total Dissolved Solids); lbs/yr (pounds per year).

Note: Pollutant removals are rounded to three significant figures. 

a – .>0 to 15 percent reduction; 16 to 30 percent reduction; 31 to 45 percent reduction; 46 to 60 percent reduction; 

>60 percent reduction.

b – Total nitrogen loadings are the sum of total Kjeldahl nitrogen and nitrate/nitrite as N loadings.

7-7
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Section 7—Environmental Improvements Under the Final Rule 

Table 7-4. Steam Electric Power Generating Industry TWPE Removals for Metals, 

Bioaccumulative Pollutants, Nutrients, Chlorides, and TDS Under Regulatory Options 

Pollutant 

Pollutant Removals, TWPE/year (Percent Reduction) a

Option A Option B Option C Option D Option E

Arsenic 54,600 

(53%)

54,600 

(53%)

80,400 

(78%)

96,700 

(94%)

98,900 

(96%)

Boron 35,300 

(13%)

35,300 

(13%)

37,300 

(14%)

38,600 

(15%)

38,600 

(15%)

Cadmium 205,000

(68%)

205,000

(68%)

254,000

(84%)

285,000

(94%)

287,000

(95%)

Chromium VI 6\7.5

(84%)

67.5

(84%)

76.1

(94%)

80.4

(>99%)

80.4

(>99%)

Copper 8,890

(46%)

8,890

(46%)

15,100 

(78%)

19,000 

(98%)

19,100 

(98%)

Lead 17,200 

(39%)

17,200 

(39%)

33,100 

(75%)

43,100 

(98%)

43,100 

(98%)

Manganese 526,000

(68%)

526,000

(68%)

580,000

(75%)

615,000

(80%)

615,000

(80%)

Mercury 94,400 

(58%)

95,500 

(58%)

136,000

(83%)

160,000

(97%)

162,000

(99%)

Nickel 6,790

(52%)

6,820

(52%)

10,500 

(80%)

12,800 

(98%)

12,900 

(99%)

Selenium 32,900 

(21%)

146,000

(93%)

150,000

(96%)

152,000

(97%)

152,000

(97%)

Thallium 20,500 

(11%)

20,500 

(11%)

117,000

(64%)

178,000

(98%)

178,000

(98%)

Zinc 5,650

(69%)

5,650

(69%)

6,950

(85%)

7,770

(95%)

7,940

(97%)

Nitrogen, total N/A N/A N/A N/A N/A

Phosphorus, total N/A N/A N/A N/A N/A

Chlorides 101 

(<1%)

101 

(<1%)

364 

(2%)

531 

(2%)

531 

(2%)

TDS N/A N/A N/A N/A N/A

Source: ERG, 2015a. 

Acronyms: TDS (Total Dissolved Solids); TWPE (Toxic Weighted Pound Equivalents).

Note: Pollutant removals are rounded to three significant figures. 

N/A – The TWPE/year is not provided for total nitrogen, total phosphorus, and TDS because EPA has not 

established a toxic weighting factor (TWF) for these pollutants. 

a – >0 to 15 percent reduction; 16 to 30 percent reduction; 31 to 45 percent reduction; 46 to 60 percent reduction; 

>60 percent reduction.

7-8
Section 7—Environmental Improvements Under the Final Rule 

7.2 KEY ENVIRONMENTAL IMPROVEMENTS

As part of this EA, EPA conducted modeling of the expected environmental 

improvements under Options A through E. EPA estimates the environmental improvements 

under Option F, which were not modeled, to be incrementally greater than those under Option E 

based on the pollutant reductions calculated. 

Table 7-5 summarizes the key environmental improvements within the immediate 

receiving waters due to the pollutant removals under the final rule (Option D) and other 

evaluated regulatory options. The numbers of immediate receiving waters with water quality,

wildlife, and human health exceedances would: 

 Decrease under Options A and B by no more than 33 percent, with most exceedances

being reduced by less than 15 percent.

 Decrease under Option C by 17 to 56 percent, with most exceedances being reduced

by less than 40 percent.

 Decrease under Option D by 45 to 83 percent, with most exceedances being reduced

by at least 56 percent.

 Decrease under Option E by 51 to 84 percent, with most exceedances being reduced

by at least 61 percent.

The final rule (Option D) will substantially improve water quality, wildlife, and human 

health. Under the final rule, EPA estimates that: 

 Receiving water exceedances of the NRWQC will decrease by 45 to 67 percent.

 Receiving water exceedances of the MCL benchmarks will decrease by 83 percent.

 The number of receiving waters with fish tissue concentrations exceeding the no

effect hazard concentration (NEHC) for selenium for eagles and minks will decrease

by 63 and 62 percent, respectively.

 Human exposures via fish consumption to pollutants with the potential to cause noncancer health effects will decrease by up to 56 percent.

 Human exposures to pollutants that present a cancer risk will decrease by up to 75

percent.

Results for the final rule are discussed in further detail in the sections following Table 

7-5.

7.2.1 Improvements in Water Quality Under the Final Rule

EPA estimates that pollutant removals to surface waters associated with the final rule will 

significantly improve water quality by reducing exceedances of the NRWQC and MCLs by up to

83 percent. The largest reductions in NRWQC exceedances are attributed to reduced loadings of

cadmium, selenium, arsenic, and thallium. Due to the substantial pollutant removals, EPA

projects that aquatic organisms will be less susceptible to chronic impacts such as: 

7-9
 

Section 7—Environmental Improvements Under the Final Rule 

 Skeletal malformations;

 Organ damage;

 Developmental abnormalities;

 Behavioral impairments;

 Reproductive failure;

 Metabolic failure;

 Neurological effects;

 Gastrointestinal effects; and

 Fish kills.48

EPA estimates that up to 45 percent of the 209 evaluated immediate receiving waters 

currently exceed NRWQC for the protection of human health, primarily due to arsenic and 

thallium. EPA estimates that these arsenic and thallium removals will lower the number of 

immediate receiving waters that exceed NRWQC designed to protect public health by 45 to 50

percent. By reducing MCL exceedances by 83 percent, the final rule will improve the quality of

source water available to drinking water treatment plants downstream from steam electric power 

plants. 

In addition to reducing NRWQC and MCL exceedances, the final rule will quantifiably 

improve overall water quality – in the immediate receiving waters and downstream from steam

electric power plants. EPA calculates that, on average, receiving water concentrations of the 10 

toxic, bioaccumulative pollutants evaluated in the EA will decrease by 57 percent.

48 Impacts documented in ATSDR, 2008a; Coughlan and Velte, 1989; Lemly, 1985b; Nagle et al., 2001; NRC,

2006; Rowe et al., 2002; U.S. EPA, 2009a; and U.S. EPA, 2011f. 

7-10
Section 7—Environmental Improvem

Table 7-5. Key Environmental Improvements Under the Regulatory Options

Evaluation Benchmark

Modeled Immediate Receiving 

Waters Exceeding Benchmark 

Under Baseline Conditions a

Number of Immediate Receiving Waters E

(Percent Reduction from Baseline Condition

Options b

Number Percentage Option A Option B Option C 

Water Quality Results Freshwater Acute NRWQC 9 4% 6 

(33%)

6 

(33%)

6 

(33%)

Freshwater Chronic NRWQC 35 17% 34

(3%)

27

 (23%)

21

(40%)

Human Health Water and Organism NRWQC 94 45% 90

(4%)

90

(4%)

69

(27%)

Human Health Organism Only NRWQC 66 32% 62

(6%)

62

(6%)

46

(30%)

Drinking Water MCL 36 17% 34

(6%)

33

(8%)

16

(56%)

Wildlife Results Fish Ingestion NEHC for Minks 58 28% 57

 (2%) 

51

 (12%)

32

 (45%)

Fish Ingestion NEHC for Eagles 71 34% 65

 (8%) 

61

 (14%)

44

 (38%)

Human Health Results—Non-Cancer Non-Cancer Reference Dose for Child (recreational)

100 48 92

(8%)

90

 (10%)

68

 (32%)

Non-Cancer Reference Dose for Adult (recreational)

86 41% 77

 (10%)

74

(14%)

56

 (35%)

Non-Cancer Reference Dose for Child (subsistence) 

118 56% 107 

 (9%) 

104 

 (12%)

79

 (33%)

Non-Cancer Reference Dose for Adult (subsistence) 

103 49% 94

 (9%) 

93

 (10%)

71

 (31%)

7-11
Section 7—Environmental Improvem

Table 7-5. Key Environmental Improvements Under the Regulatory Options

Evaluation Benchmark

Modeled Immediate Receiving 

Waters Exceeding Benchmark 

Under Baseline Conditions a

Number of Immediate Receiving Waters E

(Percent Reduction from Baseline Condition

Options b

Number Percentage Option A Option B Option C 

Human Health Results—Cancer Arsenic Cancer Risk for Child (recreational) 6 3% 5 

 (17%)

5 

 (17%)

5 

 (17%)

Arsenic Cancer Risk for Adult (recreational) 12 6% 9 

(25%)

9 

 (25%)

6 

 (50%)

Arsenic Cancer Risk for Child (subsistence) 8 4% 7 

(13%)

7 

(13%)

6 

(25%)

Arsenic Cancer Risk for Adult (subsistence) 25 12% 23

(8%)

23

(8%)

15

(40%)

Source: ERG, 2015d; ERG, 2015h; ERG, 2015i.Acronyms: MCL (maximum contaminant level); NEHC (No Effect Hazard Concentration); NRWQC (National Recommended Water Qa – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power plants (some of which 

receiving waters). The IRW model, which excludes the Great Lakes and estuaries, encompasses a total of 209 immediate receiving wat

streams; 26 lakes, ponds, and reservoirs) and loadings from 188 steam electric power plants. 

b – >0 to 15 percent reduction; 16 to 30 percent reduction; 31 to 45 percent reduction; 46 to 60 percent reduction; >60 percent reductio

7-12
Section 7—Environmental Improvements Under the Final Rule 

7.2.2 Reduced Threat to Wildlife Under the Final Rule

In the EA, EPA evaluated multiple threats to wildlife, including impacts to wildlife

indicator species by consuming contaminated fish; impacts to fish and waterfowl due to dietary 

exposure to selenium; and exposure of benthic aquatic organisms to contaminated sediments. 

The combination of lethal and sublethal effects (e.g., changes to morphology, behavior, and 

metabolism) of exposure to steam electric power plant wastewater can cause cascading effects 

through the food web. 

As discussed in Section 7.2.1, the number of immediate receiving waters that can 

potentially pose an acute or chronic threat to wildlife will decrease under the final rule,

improving wildlife populations and communities surrounding steam electric power plants (e.g., 

reduced impacts to population density and species diversity as discussed in Section 3). EPA 

estimates that average fish tissue concentrations of the pollutants evaluated in the EA will 

decrease by an average of 57 percent. EPA projects that these lower pollutant concentrations will 

significantly improve the health of fish populations and the quality of fish available for 

consumption by both humans and wildlife near steam electric power plants. 

Based on the threats to minks and eagles from consuming fish contaminated by steam 

electric power plant wastewater, pollutants can bioaccumulate and impact higher order species in 

the food chain. Under the final rule, EPA estimates that exceedances of the NEHC for eagles and 

minks will decrease by approximately 70 percent. See Section 7.3.3 for discussion of the reduced

risk of adverse reproductive effects among aquatic wildlife (fish and mallards) resulting from

dietary exposure to selenium. 

EPA estimates that pollutant removals to surface waters associated with the final rule will 

decrease the exposure of aquatic organisms to pollutants in the sediment, as shown in Table 7-6. 

As discussed in Section 6.2.3, benthic organisms are at risk primarily due to exposure to 

mercury, nickel, and cadmium. Under the final rule, the number of immediate receiving waters

with pollutant concentration in the sediment above chemical stressor concentration limits 

(CSCL) will decrease by over 60 percent. 

7-13
Section 7—Environmental Improvem

Table 7-6. Number of Immediate Receiving Waters with Sediment Pollutant Concentrations Exceedin

Sediment Biota Under the Regulatory Options

Pollutant 

Modeled Immediate

Receiving Waters 

Exceeding CSCLs Under

Baseline Conditions a

Number of Immediate Receiving Waters Exceeding Benchm

(Percent Reduction from Baseline Conditions) Under the Regulator

Option A Option B Option C Option D 

Arsenic 7 (3%) 6 (14%) 6 (14%) 6 (14%) 3 (57%) 

Cadmium 27 (13%) 21 (22%) 21 (22%) 14 (48%) 10 (63%) 

Chromium VI c 0 (0%) 0 (N/A) 0 (N/A) 0 (N/A) 0 (N/A) 

Copper 7 (3%) 5 (29%) 5 (29%) 5 (29%) 2 (71%) 

Lead 6 (3%) 4 (33%) 4 (33%) 4 (33%) 1 (83%) 

Mercury 49 (23%) 45 (8%) 44 (10%) 26 (47%) 19 (61%) 

Nickel 34 (16%) 28 (18%) 28 (18%) 16 (53%) 11 (68%) 

Selenium NC NC NC NC NC 

Thallium NC NC NC NC NC Zinc 15 (7%) 9 (40%) 9 (40%) 9 (40%) 6 (60%) 

Total 49

(23%) 

45

(8%)

44

(10%) 

27

(45%) 

20

(59%) 

Source: ERG, 2015d;ERG, 2015h; ERG, 2015i.Acronyms: CSCL (Chemical stressor concentration limit); N/A (Not Applicable, no exceedances at baseline conditions to compare opti

calculated; no benchmark for comparison).a – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power plants (some of which 

receiving waters). The IRW model, which excludes the Great Lakes and estuaries, encompasses a total of 209 immediate receiving wat

streams; 26 lakes, ponds, and reservoirs) and loadings from 188 steam electric power plants. 

b – >0 to 15 percent reduction; 16 to 30 percent reduction; 31 to 45 percent reduction; 46 to 60 percent reduction; >60 percent reduction

c – EPA used the total chromium benchmark for this analysis.

7-14
 

Section 7—Environmental Improvements Under the Final Rule 

7.2.3 Reduced Human Health Cancer Risk Under the Final Rule

Under baseline conditions, EPA estimates that 25 immediate receiving waters (12 

percent) could contain fish contaminated with inorganic arsenic that present cancer risks above 

the 1-in-a-million threshold for the most sensitive, national-scale cohort. EPA calculates that the 

number of immediate receiving waters whose fish exceed this cancer risk threshold will decrease

by at least 56 percent for all national-scale cohorts under the final rule. 

7.2.4 Reduced Threat of Non-Cancer Human Health Effects Under the Final Rule

Chronic exposure to toxic, bioaccumulative pollutants in steam electric power plant 

wastewater can potentially compromise neurological and developmental functions and affect the 

circulatory, respiratory, and digestive systems of exposed populations. EPA estimates that the 

number of immediate receiving waters whose fish pose non-cancer health risks will decrease by 

at least 52 percent for all national-scale cohorts under the final rule. As discussed in Section 

7.2.2, EPA found that the pollutant concentrations in fish tissue will decrease, improving the 

quality of fish available to recreational and subsistence fishers and subsequently lowering 

exposures to toxic, bioaccumulative pollutants and the potential for humans to develop noncancer health effects (e.g., nausea, abdominal pain, sleep disorders, muscular problems, and 

cardiovascular disease). 

The pollutants that cause the potential for non-cancer health effects are selenium, 

cadmium, mercury (as methylmercury), and, to a lesser degree, thallium. EPA calculates that the 

final rule will decrease the number of immediate receiving waters with fish that, if consumed, 

would exceed the reference doses for these pollutants, by the following amounts: 

 Selenium: decrease by at least 51 percent for all national-scale cohorts.

 Cadmium: decrease by at least 53 percent for all national-scale cohorts.

 Methylmercury: decrease by at least 52 percent for all national-scale cohorts.

 Thallium: decrease by at least 62 percent for all national-scale cohorts.

Although the EA did not directly assess the potential non-cancer health effects posed by 

lead,49 the final rule will lower the total annual loadings of lead to the environment by 19,000 

pounds (98 percent), thus reducing the potential threat of hypertension, coronary heart disease, 

and impaired cognitive function in exposed populations. For children in particular, lead exposure 

can cause additional negative impacts, such as hyperactivity, behavioral and attention 

difficulties, delayed mental development, and motor and perceptual skill deficits. The benefits to 

adults and children from the reduced lead discharges are discussed in the Benefits and Cost 

Analysis. 

7.2.5 Reduced Human Health Risk for Environmental Justice Analysis

As discussed in Section 6.3.2, EPA evaluated the impacts that steam electric power plant 

discharges have on environmental justice (EJ) cohorts in addition to the national-scale cohorts.

Under baseline conditions, EPA estimates that 32 immediate receiving waters (15 percent) could 

49 Currently, there is no reference dose for lead—there is no safe level for ingestion of lead (see EPA’s Integrated 

Risk Information System (IRIS) website: http://www.epa.gov/IRIS/). 

7-15
 

Section 7—Environmental Improvements Under the Final Rule 

contain fish contaminated with inorganic arsenic that present cancer risks above the 1-in-amillion threshold for the most sensitive minority cohort. EPA estimates that the number of 

immediate receiving waters whose fish exceed this cancer risk threshold will decrease by at least 

46 percent for the average recreational fisher minority cohort and at least 51 percent for the

average subsistence fisher minority cohort under the final rule.50 These improvements are similar 

to those for non-minority recreational and subsistence fisher cohorts (at least 33 and 50 percent, 

respectively) under the final rule. 

EPA estimates that the number of immediate receiving waters whose fish pose noncancer health risks will decrease by 56 percent for all recreational fisher minority cohorts and 53 

percent for all subsistence fisher minority cohorts under the final rule. These improvements are 

similar to those for non-minority recreational and subsistence fisher cohorts (56 and 52 percent, 

respectively) under the final rule. The pollutants that cause the potential for non-cancer health 

effects are selenium, cadmium, mercury (as methylmercury), and, to a lesser degree, thallium. 

7.3 POLLUTANT-SPECIFIC IMPROVEMENTS

EPA identified several key pollutants (i.e., arsenic, mercury, selenium, cadmium, and 

thallium) whose pollutant removals would primarily be responsible for the improvements in 

water quality, wildlife, and human health attributed to the final rule. This section highlights the

environmental improvements associated with these five pollutants. 

7.3.1 Arsenic

Under the final rule, EPA estimates 27,900 pounds per year of arsenic removals from 

steam electric power plant discharges – a 94 percent reduction in annual loadings. The final rule 

will decrease the number of immediate receiving waters exceeding human health NRWQC for 

arsenic by up to 49 percent. The arsenic removals will reduce negative effects on aquatic 

organisms, such as liver tissue death, developmental abnormalities, behavioral impairments,

metabolic failure, growth reduction, and appetite loss [NRC, 2006; Rowe et al., 2002; U.S. EPA, 

2011f]. As a result, the final rule will decrease human exposure to arsenic through fish 

consumption and thus lower the potential for exposed populations to develop arsenic-related 

cancer and non-cancer health effects such as dermal, cardiovascular, and respiratory effects. The 

final rule will decrease the number of immediate receiving waters exceeding the human health

cancer risk threshold for arsenic by up to 75 percent, depending on the evaluated cohort. Table 

7-7 presents the key environmental improvements resulting from arsenic removals under the

regulatory options evaluated in the EA.

EPA did not see a reduction in the number of immediate receiving waters exceeding the 

arsenic NEHCs for minks or eagles because there are no exceedances modeled at baseline. The 

final rule, however, will still reduce the bioaccumulation of arsenic in the food web. 

50 These values represent the average percentage improvements across the four race populations that comprise the 

minority cohorts. 

7-16
Section 7—Environmental Improvem

Table 7-7. Key Environmental Improvements for Arsenic Under the Regulatory Option

Evaluation Benchmark

Modeled Immediate

Receiving Waters Exceeding 

Benchmark Under Baseline 

Conditions a

Number of Immediate Receiving Waters Exce

(Percent Reduction from Baseline Conditions) Under 

b

Number Percentage Option A Option B Option C Op

Water Quality Results Freshwater Acute NRWQC 3 1% 2 

(33%)

2 

(33%)

2 

(33%)

(

Freshwater Chronic NRWQC 4 2% 3 

(25%)

3 

(25%)

3 

(25%)

(

Human Health Water and OrganismNRWQC

94 45% 90

(4%)

90

(4%)

69

(27%)

(

Human Health Organism Only NRWQC 65 31% 61

(6%)

61

(6%)

45

(31%)

(

Drinking Water MCL 12 6% 9 

(25%)

9 

(25%)

6 

(50%)

(

Wildlife Results Fish Ingestion NEHC for Minks 0 0% 0 

(N/A)

0 

(N/A)

0 

(N/A)

(

Fish Ingestion NEHC for Eagles 0 0% 0 

(N/A)

0 

(N/A)

0 

(N/A)

(

Human Health Results—Non-Cancer Non-Cancer Reference Dose for Child (recreational)

2 1% 1 

(50%)

1 

(50%)

1 

(50%)

(

Non-Cancer Reference Dose for Adult (recreational)

0 0% 0 

(N/A)

0 

(N/A)

0 

(N/A)

(

Non-Cancer Reference Dose for Child (subsistence) 

3 1% 2 

(33%)

2 

(33%)

2 

(33%)

(

Non-Cancer Reference Dose for Adult (subsistence) 

3 1% 2 

(33%)

2 

(33%)

2 

(33%)

(

7-17
Section 7—Environmental Improvem

Table 7-7. Key Environmental Improvements for Arsenic Under the Regulatory Option

Evaluation Benchmark

Modeled Immediate

Receiving Waters Exceeding 

Benchmark Under Baseline 

Conditions a

Number of Immediate Receiving Waters Exce

(Percent Reduction from Baseline Conditions) Under 

b

Number Percentage Option A Option B Option C Op

Human Health Results—Cancer Arsenic Cancer Risk for Child(recreational)

6 3% 5 

(17%)

5 

(17%)

5 

(17%)

(

Arsenic Cancer Risk for Adult(recreational)

12 6% 9 

(25%)

9 

(25%)

6 

(50%)

(

Arsenic Cancer Risk for Child(subsistence) 

8 4% 7 

(13%)

7 

(13%)

6 

(25%)

(

Arsenic Cancer Risk for Adult(subsistence) 

25 12% 23

(8%)

23

(8%)

15

(40%)

(

Source: ERG, 2015d; ERG, 2015h; ERG, 2015i.Acronyms: MCL (Maximum contaminant level); N/A (Not Applicable, no exceedances at baseline conditions to compare option result

Hazard Concentration); NRWQC (National Recommended Water Quality Criteria). a – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power plants (some of which 

receiving waters). The IRW model, which excludes the Great Lakes and estuaries, encompasses a total of 209 immediate receiving wat

streams; 26 lakes, ponds, and reservoirs) and loadings from 188 steam electric power plants. 

b – >0 to 15 percent reduction; 16 to 30 percent reduction; 31 to 45 percent reduction; 46 to 60 percent reduction; >60 percent reduction

7-18
Section 7—Environmental Improvements Under the Final Rule 

7.3.2 Mercury

Under the final rule, EPA estimates 1,450 pounds per year of mercury removals from 

steam electric power plant discharges – a 97 percent reduction in annual loadings. As discussed

in Section 6.2, estimated fish tissue concentrations for mercury (and selenium) exceed levels that 

can affect reproduction in exposed mink and eagle populations. EPA estimates that the final rule 

will decrease the number of immediate receiving waters with fish tissue concentrations that

exceed the mercury NEHC for eagles and minks by 62 and 64 percent, respectively. These 

reductions also represent the potential improvement in exposure to mercury above effects 

thresholds in other wildlife that consume fish from these receiving waters. 

Under baseline pollutant loadings, EPA estimates that fish methylmercury concentrations

pose a non-cancer threat to subsistence fishers and recreational fishers in up to 52 and 46 

percent, respectively, of immediate receiving waters. EPA calculates that fish tissue

concentrations of methylmercury will decrease under the final rule and, as a result, the number of 

immediate receiving waters with exposure doses from fish consumption that exceed the 

methylmercury reference dose will decrease by up to 57 percent. Because there are over 80

addressed by this final rule discharge to receiving waters that are under a fish advisory for 

mercury (see Section 3.4.4), the final rule will reduce mercury loadings to those receiving waters 

(see Section 7.4). Table 7-8 presents the key environmental improvements resulting from

mercury removals under the regulatory options. 

7-19
Section 7—Environmental Improvem

Table 7-8. Key Environmental Improvements for Mercury Under the Regulatory Optio

Evaluation Benchmark

Modeled Immediate

Receiving Waters Exceeding 

Benchmark Under Baseline 

Conditions a

Number of Immediate Receiving Waters Exce

(Percent Reduction from Baseline Conditions) Under 

b

Number Percentage Option A Option B Option C Op

Water Quality Results Freshwater Acute NRWQC 1 0% 0 

(100%) 

0 

(100%) 

0 

(100%) 

(1

Freshwater Chronic NRWQC 1 0% 0 

(100%) 

0 

(100%) 

0 

(100%) 

(1

Human Health Water and OrganismNRWQC

No benchmark for comparison N/A N/A N/A 

Human Health Organism Only NRWQC No benchmark for comparison N/A N/A N/A Drinking Water MCL 5 2% 4 

(20%)

4 

(20%)

4 

(20%)

(

Wildlife Results Fish Ingestion NEHC for Minks 55 26% 50

(9%)

49

(11%)

30

(45%)

(

Fish Ingestion NEHC for Eagles 71 34% 61

(14%)

61

(14%)

44

(38%)

(

Human Health Results—Non-Cancer Non-Cancer Reference Dose for Child (recreational)

96 46% 87

(9%)

84

(13%)

63

(34%)

(

Non-Cancer Reference Dose for Adult (recreational)

82 39% 71

(13%)

69

(16%)

52

(37%)

(

Non-Cancer Reference Dose for Child (subsistence) 

109 52% 97

(11%)

96

(12%)

75

(31%)

(

Non-Cancer Reference Dose for Adult (subsistence) 

99 47% 89

(10%)

87

(12%)

66

(33%)

(

Source: ERG, 2015d; ERG, 2015h; ERG, 2015i.Acronyms: MCL (Maximum contaminant level); N/A (Not Applicable, no exceedances at baseline conditions to compare option resultsHazard Concentration); NRWQC (National Recommended Water Quality Criteria). a – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power plants (some of which 

receiving waters). The IRW model, which excludes the Great Lakes and estuaries, encompasses a total of 209 immediate receiving wat

streams; 26 lakes, ponds, and reservoirs) and loadings from 188 steam electric power plants. 

b – >0 to 15 percent reduction; 16 to 30 percent reduction; 31 to 45 percent reduction; 46 to 60 percent reduction; >60 percent reduction

7-20 
Selenium is known to cause fish deformities at

high levels, such as these from Belews Lake,

NC.

Section 7—Environmental Improvements Under the Final Rule 

7.3.3 Selenium

Under the final rule, EPA estimates 136,000 pounds per year of selenium removals from 

steam electric power plant discharges – a 97 percent reduction in annual loadings. Selenium is 

one of the primary pollutants identified in the literature and by EPA as causing documented 

environmental impacts to fish and wildlife from steam electric power plant discharges. EPA 

estimates that immediate receiving water concentrations of total selenium will decrease under the 

final rule by 71 percent on average, decreasing the amount of selenium that would bioaccumulate 

or persist in the aquatic environment. Under the final rule, the number of immediate receiving 

waters exceeding chronic aquatic life NRWQC will decrease by 55 percent and the number of 

immediate receiving waters exceeding a drinking water MCL for selenium will decrease by 75 

percent.

Reducing selenium loadings and 

subsequent bioaccumulation will decrease by 52

percent the number of immediate receiving

waters with fish tissue concentrations exceeding

the NEHC for selenium for both eagles and 

minks. These reductions also represent the 

potential health improvements in other wildlife 

that consume fish from these receiving waters, as

well as the potential decrease in bioaccumulation 

of toxic pollutants in the broader food web near 

steam electric power plants. 

The results of the ecological risk model 

further support these predicted reductions in the 

bioaccumulative impact of selenium throughout 

the food web. Under the final rule, the ecological 

risk modeling results indicate that: 

 The risk of negative reproductive impacts among fish and/or mallards will be reduced 

to less than one percent in each of the 26 modeled lentic immediate receiving waters.

 The number of immediate receiving waters that present a risk of reproductive impacts 

among at least 10 percent of the exposed population will be reduced by 67 percent 

(for fish) and 61 percent (for mallards). 

 The number of immediate receiving waters that present a risk of reproductive impacts 

among at least 50 percent of the exposed population will be reduced by 70 percent 

(for fish) and 74 percent (for mallards). 

These results are based on the median modeled egg/ovary selenium concentration in 

exposed fish and mallards. Use of the 90th percentile modeled egg/ovary concentration, which 

results in a higher predicted risk of reproductive impacts, shows similar improvements under the 

final rule: 

7-21 
Section 7—Environmental Improvements Under the Final Rule 

 The risk of negative reproductive impacts among fish will be reduced to less than one 

percent in all but one of the 26 modeled lentic immediate receiving waters. 

 The number of immediate receiving waters that present a risk of reproductive impacts 

among at least 10 percent of the exposed population will be reduced by 55 percent 

(for fish) and 52 percent (for mallards). Under the final rule, none of the lentic 

immediate receiving waters will pose this reproductive risk to fish or mallards.

 The number of immediate receiving waters that present a risk of reproductive impacts 

among at least 50 percent of the exposed population will be reduced by 53 percent 

(for fish) and 59 percent (for mallards). 

Under the final rule, EPA estimates that fish selenium concentrations that pose a noncancer threat to subsistence fishers and recreational fishers will decrease in up to 53 and 56 

percent of immediate receiving waters, respectively. This reduces the risk of developing noncancer health effects associated with selenium, such as pulmonary edema and lesions of the lung; 

cardiovascular effects such as tachycardia; gastrointestinal effects including nausea, vomiting, 

diarrhea, and abdominal pain; effects on the liver; and neurological effects such as aches, 

irritability, chills, and tremors [U.S. EPA, 2000b]. Table 7-9 presents the key environmental

improvements resulting from selenium removals under the regulatory options. 

7-22 
Section 7—Environmental Improvem

Table 7-9. Key Environmental Improvements for Selenium Under the Regulatory Optio

Evaluation Benchmark

Modeled Immediate

Receiving Waters Exceeding 

Benchmark Under Baseline 

Conditions a

Number of Immediate Receiving Waters Exce

(Percent Reduction from Baseline Conditions) Under 

b

Number Percentage Option A Option B Option C Op

Water Quality Results Freshwater Acute NRWQC No benchmark for comparison N/A N/A N/A 

Freshwater Chronic NRWQC d 33 16% 30

(9%)

20

(39%)

18

(45%)

(

Human Health Water and OrganismNRWQC

8 4% 7 

(13%)

3 

(63%)

3 

(63%)

(

Human Health Organism Only NRWQC 1 0% 1 

(0%)

1 

(0%)

1 

(0%)

Drinking Water MCL 12 6% 10

(17%)

5 

(58%)

5 

(58%)

(

Wildlife Results Fish Ingestion NEHC for Minks 42 20% 40

(5%)

29

(31%)

23

(45%)

(

Fish Ingestion NEHC for Eagles 42 20% 40

(5%)

29

(31%)

23

(45%)

(

Negative Reproductive Effects in Fish c 24 11% 19

(21%)

10

(58%)

10

(58%)

(

Negative Reproductive Effects inMallards c

31 15% 26

(16%)

16

(48%)

14

(55%)

(

7-23 
Section 7—Environmental Improvem

Table 7-9. Key Environmental Improvements for Selenium Under the Regulatory Optio

Evaluation Benchmark

Modeled Immediate

Receiving Waters Exceeding 

Benchmark Under Baseline 

Conditions a

Number of Immediate Receiving Waters Exce

(Percent Reduction from Baseline Conditions) Under 

b

Number Percentage Option A Option B Option C Op

Human Health Results—Non-Cancer Non-Cancer Reference Dose for Child (recreational)

41 20% 39

(5%)

29

(29%)

23

(44%)

(

Non-Cancer Reference Dose for Adult (recreational)

32 15% 29

(9%)

18

(44%)

17

(47%)

(

Non-Cancer Reference Dose for Child (subsistence) 

55 26% 51

(7%)

39

(29%)

33

(40%)

(

Non-Cancer Reference Dose for Adult (subsistence) 

43 21% 40

(7%)

30

(30%)

23

(47%)

(

Source: ERG, 2015d; ERG, 2015h; ERG, 2015i.Acronyms: MCL (Maximum contaminant level); N/A (Not Applicable, no exceedances at baseline conditions to compare option resultHazard Concentration); NRWQC (National Recommended Water Quality Criteria). a – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power plants (some of which 

receiving waters). The IRW model, which excludes the Great Lakes and estuaries, encompasses a total of 209 immediate receiving wat

streams; 26 lakes, ponds, and reservoirs) and loadings from 188 steam electric power plants. 

b – >0 to 15 percent reduction; 16 to 30 percent reduction; 31 to 45 percent reduction; 46 to 60 percent reduction; >60 percent reduction

c – These rows indicate the number of immediate receiving waters whose median modeled egg/ovary concentration is predicted to resu

among at least 10 percent of the exposed fish or mallard population, as determined using the ecological risk model.d – The EA analyses use the EPA recommended water quality criteria for selenium in the water column of 5 μg/L -- in effect at the timboth for the proposed rule in 2012, and the final rule in 2015. EPA used this criterion in its modeling for the final rule to allow for consbetween the modeling done for the proposed rule and that done for the final rule. All modeling was done prior to EPA publishing new fselenium on July 27, 2015. The new final draft criteria, which EPA now recommends, of 3.1 μg/L in freshwater flowing systems (riverlakes and reservoirs, are lower than the criteria EPA used in these analyses. Had EPA conducted the modeling with these new recomme

have resulted in slightly greater estimated impacts (more exceedances of the new selenium criteria) than that revealed using the old crit

would have led to slightly greater potential improvements due to control of selenium discharges under the final rule. Therefore, the estiselenium impacts, and potential improvements of the final ELG, are conservative and tend, if anything, to underestimate both the impac

7-24 
Section 7—Environmental Improvements Under the Final Rule 

7.3.4 Cadmium

Under the final rule, EPA estimates 9,020 pounds per year of cadmium removals from

steam electric power plant discharges – a 68 percent reduction in annual loadings. At baseline 

conditions, discharges of cadmium are the second largest toxic-weighted pollutant discharges 

from the steam electric power generating industry among those pollutants evaluated in the EA 

(see Section 3.2). The final rule will decrease the number of immediate receiving waters that 

exceed acute and chronic NRWQC by up to 67 and 59 percent, respectively. The number of 

immediate receiving waters with fish tissue concentrations that exceed NEHCs for minks and 

eagles will decrease by 67 and 50 percent, respectively. Under the final rule, the number of 

immediate receiving waters with fish containing cadmium concentrations that pose a risk of noncancer health effects will decrease by 53 to 70 percent, depending on the cohort. Table 7-10

presents the key environmental improvements resulting from cadmium removals under the 

regulatory options. 

7.3.5 Thallium

Under the final rule, EPA estimates 62,300 pounds per year of thallium removals from

steam electric power plant discharges – a 98 percent reduction in annual loadings. EPA estimates 

that the final rule will decrease the number of immediate receiving waters exceeding human 

health NRWQC and MCLs for thallium by up to 85 percent. Under the final rule, the number of 

immediate receiving waters with fish containing thallium concentrations that can potentially 

cause non-cancer health effects in humans (e.g., neurological symptoms, alopecia, 

gastrointestinal effects, and reproductive and developmental damage) will decrease by up to 69 

percent, depending on the cohort. Table 7-11 presents the key environmental improvements

resulting from thallium removals under the regulatory options.

7-25 
Section 7—Environmental Improvem

Table 7-10. Key Environmental Improvements for Cadmium Under the Regulatory Opti

Evaluation Benchmark

Modeled Immediate

Receiving Waters Exceeding 

Benchmark Under Baseline 

Conditions a

Number of Immediate Receiving Waters Excee

(Percent Reduction from Baseline Conditions) Under 

Number Percentage Option A Option B Option C Op

Water Quality Results Freshwater Acute NRWQC 9 4% 6 

(33%)

6 

(33%)

6 

(33%)

(

Freshwater Chronic NRWQC 29 14% 23

(21%)

23

(21%)

16

(45%)

(

Human Health Water and OrganismNRWQC

No benchmark for comparison N/A N/A N/A 

Human Health Organism Only NRWQC No benchmark for comparison N/A N/A N/A 

Drinking Water MCL 11 5% 7 

(36%)

7 

(36%)

6 

(45%)

(

Wildlife Results Fish Ingestion NEHC for Minks 6 3% 5 

(17%)

5 

(17%)

5 

(17%)

(

Fish Ingestion NEHC for Eagles 4 2% 3 

(25%)

3 

(25%)

3 

(25%)

(

Human Health Results—Non-Cancer Non-Cancer Reference Dose for Child (recreational)

16 8% 12

(25%)

12

(25%)

9 

(44%)

(

Non-Cancer Reference Dose for Adult (recreational)

10 5% 7 

(30%)

7 

(30%)

6 

(40%)

(

Non-Cancer Reference Dose for Child (subsistence) 

32 15% 26

(19%)

26

(19%)

19

(41%)

(

Non-Cancer Reference Dose for Adult (subsistence) 

22 11% 17

(23%)

17

(23%)

11

(50%)

(

Source: ERG, 2015d; ERG, 2015h; ERG, 2015i.Acronyms: MCL (Maximum contaminant level); N/A (Not Applicable, no exceedances at baseline conditions to compare option results

Hazard Concentration); NRWQC (National Recommended Water Quality Criteria). a – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power plants (some of which 

receiving waters). The IRW model, which excludes the Great Lakes and estuaries, encompasses a total of 209 immediate receiving wat

streams; 26 lakes, ponds, and reservoirs) and loadings from 188 steam electric power plants. 

b – >0 to 15 percent reduction; 16 to 30 percent reduction; 31 to 45 percent reduction; 46 to 60 percent reduction; >60 percent reduction

7-26 
Section 7—Environmental Improvem

Table 7-11. Key Environmental Improvements for Thallium Under the Regulatory Opti

Evaluation Benchmark

Modeled Immediate

Receiving Waters Exceeding 

Benchmark Under Baseline 

Conditions a

Number of Immediate Receiving Waters Excee

(Percent Reduction from Baseline Conditions) Under 

Number Percentage Option A Option B Option C Op

Water Quality Results Freshwater Acute NRWQC No benchmark for comparison N/A N/A N/A 

Freshwater Chronic NRWQC No benchmark for comparison N/A N/A N/A 

Human Health Water and OrganismNRWQC

49 23% 46

(6%)

46

(6%)

27

(45%)

(

Human Health Organism Only NRWQC 45 22% 42

(7%)

42

(7%)

23

(49%)

(

Drinking Water MCL 34 16% 32

(6%)

32

(6%)

15

(56%)

(

Wildlife Results Fish Ingestion NEHC for Minks No benchmark for comparison N/A N/A N/A 

Fish Ingestion NEHC for Eagles No benchmark for comparison N/A N/A N/A 

Human Health Results—Non-Cancer Non-Cancer Reference Dose for Child (recreational)

74 35% 73

(1%)

73

(1%)

46

(38%)

(

Non-Cancer Reference Dose for Adult (recreational)

54 26% 51

(6%)

51

(6%)

31

(43%)

(

Non-Cancer Reference Dose for Child (subsistence) 

94 45% 90

(4%)

90

(4%)

63

(33%)

(

Non-Cancer Reference Dose for Adult (subsistence) 

77 37% 76

(1%)

76

(1%)

49

(36%)

(

Source: ERG, 2015d; ERG, 2015h; ERG, 2015i.Acronyms: MCL (Maximum contaminant level); N/A (Not Applicable, no exceedances at baseline conditions to compare option resultsHazard Concentration); NRWQC (National Recommended Water Quality Criteria). a – The EA encompasses a total of 222 immediate receiving waters and loadings from 195 steam electric power plants (some of which 

receiving waters). The IRW model, which excludes the Great Lakes and estuaries, encompasses a total of 209 immediate receiving wat

streams; 26 lakes, ponds, and reservoirs) and loadings from 188 steam electric power plants. 

b – >0 to 15 percent reduction; 16 to 30 percent reduction; 31 to 45 percent reduction; 46 to 60 percent reduction; >60 percent reduction

7-27
 

 

Section 7—Environmental Improvements Under the Final Rule 

7.4 IMPROVEMENTS TO SENSITIVE ENVIRONMENTS

As discussed in Section 3.4, EPA evaluated pollutant discharges to sensitive 

environments (i.e., impaired waters, threatened and endangered species, and fish consumption 

advisory waters) and sensitive watersheds (the Great Lakes and Chesapeake Bay). The purpose

was to assess if steam electric power plants discharge to receiving waters with existing

impairments or fish advisories and assess if discharges of the evaluated wastestreams increase 

stress on threatened and endangered species. This section presents EPA’s estimated pollutant

removals under five regulatory options to the evaluated sensitive environments. 

The final rule will decrease pollutant loadings to sensitive environments, which will help

impaired waters to recover; decrease the bioaccumulation of toxic pollutants in fish, thereby 

reducing the number of fish advisories; and reduce stress on threatened and endangered species 

and sensitive watersheds such as Chesapeake Bay and the Great Lakes (see Section 7.5).

7.4.1 Impaired Waters

EPA determined that 59 of the immediate receiving waters are 303(d)-listed waterbodies, 

designated as impaired for one or more pollutants found in the evaluated wastestreams.51

Mercury (30 immediate receiving waters), nutrients (19 immediate receiving waters), and 

phosphorus (11 immediate receiving waters) are the most frequently identified impairment 

categories among the surface waters that directly receive the evaluated wastestreams. Table 7-12 

presents the pollutant removals to impaired waters (by impairment category) as a result of the 

regulatory options. 

Under the final rule, EPA estimates the following pollutant removals: 

 Mercury removals of 168 pounds per year to mercury-impaired waters (decrease of

99 percent).

 Phosphorus removals of 4,100 pounds per year to nutrient-impaired waters (decrease

of 78 percent).

 Nitrogen removals of 471,000 pounds per year to nutrient-impaired waters (decrease

of 96 percent).

 Pollutant removals to receiving waters impaired for a metal (except mercury) include

4,100 pounds per year of arsenic (decrease of 95 percent); 1,770 pounds per year of

cadmium (decrease of 93 percent); 2,630 pounds per year of lead (decrease of 97

percent); 21,500 pounds per year of selenium (decrease of 97 percent); and 7,130

pounds per year of thallium (decrease of 97 percent).52

51 The count of impaired waters excludes the general impairment category “metals (not mercury)” and includes

receiving waters impaired for arsenic, boron, cadmium, chromium, copper, lead, manganese, mercury, selenium,

zinc, phosphorous, nutrients, TDS, or chlorides.

52 EPA presents pollutant loadings and removals for metals, other than mercury, for immediate receiving waters

designated as impaired for the general impairment category “metals (not mercury)” to protect confidential business 

information. See all results in Table 7-12. 

7-28
Section 7—Environmental Improvem

Table 7-12. Pollutant Removals to Impaired Waters by Impairment Type 

Impairment 

Type/Number of 

Receiving Waters b Pollutant 

Baseline 

Loadings

(lbs/yr)

Pollutant Removals (lbs/yr) to Impaired Waters Under the Regula

Reduction) a

Option A Option B Option C Option 

Mercury-Impaired Receiving Waters

30 Mercury 170 89.7 90.2 139 168 

(53%) (53%) (81%) (99%) 

Metals (Not Mercury)-Impaired Receiving Waters

28

Arsenic 4,320 2,800 2,800 3,690 4,110 

(65%) (65%) (85%) (95%) 

Boron 4,900,000 316,000 316,000 349,000 361,000 

(6%) (6%) (7%) (7%) 

Cadmium 1,900 1,380 1,380 1,650 1,770 

(73%) (73%) (87%) (93%) 

Chromium

VI 27.2 23.4 23.4 26.9 27.2 

(86%) (86%) (99%) (>99%

Copper 4,420 2,490 2,490 3,790 4,320 

(56%) (56%) (86%) (98%) 

Lead 2,700 1,360 1,360 2,240 2,630 

(50%) (50%) (83%) (97%) 

Manganese 1,080,000 718,000 718,000 780,000 810,000 

(66%) (66%) (72%) (75%) 

Nickel 15,600 9,270 9,320 13,300 15,200 

(59%) (60%) (85%) (97%) 

Selenium 22,100 3,320 20,900 21,300 21,500 

(15%) (94%) (96%) (97%) 

Thallium 7,330 1,260 1,260 5,220 7,130 

(17%) (17%) (71%) (97%) 

Zinc 24,700 18,600 18,600 21,900 23,500 

(75%) (75%) (89%) (95%) 

7-29
Section 7—Environmental Improvem

Table 7-12. Pollutant Removals to Impaired Waters by Impairment Type 

Impairment 

Type/Number of 

Receiving Waters b Pollutant 

Baseline 

Loadings

(lbs/yr)

Pollutant Removals (lbs/yr) to Impaired Waters Under the Regula

Reduction) a

Option A Option B Option C Option 

Nutrient-Impaired Receiving Waters

19

Total 

Nitrogen 492,000 7,250 341,000 395,000 471,000 

(1%) (69%) (80%) (96%) 

Total 

Phosphorous 5,280 406 406 1,930 4,090 

(8%) (8%) (37%) (78%) 

TDS and Chlorides-Impaired Receiving Waters

4 

Chlorides CBI CBI CBI CBI CBI 

TDS CBI CBI CBI CBI CBI 

Source: ERG, 2015c. Acronyms: CBI (Confidential business information); lbs/yr (pounds per year).Note: Loadings and pollutant reductions are rounded to three significant figures. a – >0 to 15 percent reduction; 16 to 30 percent reduction; 31 to 45 percent reduction; 46 to 60 percent reduction; >60 percent reduction

b – For the impaired waters proximity analysis, EPA evaluated 222 immediate receiving waters that receive discharges of the evaluated 

c – The EPA impaired water database listed 28 immediate receiving waters as impaired based on the “metal, other than mercury” impai

28 immediate receiving waters, 13 receiving waters are also listed as impaired for one or more specific metals (arsenic, cadmium, chromanganese, selenium, and zinc). One additional immediate receiving water is impaired for boron (but not included in the “metals, other 

impairment category). d – Total phosphorous and total nitrogen loadings are presented with this impairment category. Total nitrogen loadings are the sum of t

nitrate/nitrite as N loadings. 

7-30
 

 

 

Section 7—Environmental Improvements Under the Final Rule 

7.4.2 Threatened and Endangered Species

As discussed in Section 3.4.5, EPA identified 138 threatened and endangered species

whose habitats overlap with, or are located within, surface waters that exceeded NRWQC for the 

protection of aquatic life under baseline conditions.53 To assess the potential improvements to

threatened and endangered species under the final rule, EPA initially selected only those species

identified as highly vulnerable to changes in water quality (75 of the 138 species) for evaluation. 

EPA further excluded species from the analysis based on the following criteria: the species is 

already presumed extinct, species habitat is unlikely to be affected by discharges of the evaluated

wastestreams (e.g., isolated headwaters), species listing status is due to habitat destruction 

unrelated to steam electric power plant discharges (e.g., damming, stream channelization), and 

other criteria. Based on the analysis, EPA identified 15 species out of the 75 that are highly 

vulnerable to changes in water quality and whose recovery may be enhanced by the final rule.

Four of these 15 species inhabit waters that will no longer exceed NRWQC for the protection of 

aquatic life following implementation of the final rule. The species may therefore experience

increases in population growth rates as a result of the final rule. See the Benefits and Cost 

Analysis for further details on the methodology and results of EPA’s threatened and endangered 

species analysis. 

7.4.3 Fish Advisory Waters

States, territories, and authorized tribes issue fish advisories to notify the public 

(including recreational and subsistence fishers) of waterbodies containing fish with elevated and 

potentially unhealthy contamination levels. Mercury is the most common pollutant found in 

steam electric power plant wastewater for which fish advisories are issued to the surface waters

that receive the evaluated wastestreams (see Section 3.4.4). EPA determined that 88 of the 222 

immediate receiving waters included in the EA are under a fish advisory for mercury. Under the 

final rule, the number of immediate receiving waters with fish that exceed EPA’s mercury 

screening value for recreational fishers (based on steam electric power plant discharges only) 

will decrease by 63 percent, thereby reducing the potential threat to human health from 

consuming contaminated fish. 

7.5 IMPROVEMENTS TO WATERSHEDS

As discussed in Section 3.4, both the Great Lakes and Chesapeake Bay watersheds have a 

history of receiving pollutant discharges that negatively affect water quality, wildlife, and human 

health. Both are well-studied, sensitive environments that are affected by pollutants commonly 

found in steam electric power plant wastewater. Mercury is one of the primary pollutants of

concern in the Great Lakes,54 and nutrients are the primary pollutants of focus in the Chesapeake

Bay. 

EPA identified 23 steam electric power plants that discharge into the Great Lakes 

watershed. Table 7-13 presents the pollutant reductions to the Great Lakes watershed under the 

53 The habitat locations evaluated for this analysis include waters downstream from steam electric power plant 

discharges and reflect changes in the industry as a result of the Clean Power Plan [Clean Air Act Section 111(d)]. 54 One of the main environmental pathways for mercury in the Great Lakes is from atmospheric deposition, which is

not in the scope of the final rule.

7-31
Section 7—Environmental Improvements Under the Final Rule 

regulatory options considered by EPA. Under the final rule, EPA estimates the following 

pollutant removals to the Great Lakes watershed: 

 2,070 pounds of arsenic annually (96 percent reduction). 

 612 pounds of cadmium annually (95 percent reduction). 

 1,880 pounds of lead annually (99 percent reduction). 

 80.6 pounds of mercury annually (97 percent reduction). 

 4,800 pounds of selenium annually (96 percent reduction). 

 9,510 pounds of thallium annually (99 percent reduction). 

 1.15 million pounds of total nitrogen annually (>99 percent reduction).

 21,800 pounds of total phosphorus annually (94 percent reduction). 

EPA identified nine steam electric power plants that discharge to the Chesapeake Bay

watershed. Under the final rule, EPA estimates the following pollutant removals to the 

Chesapeake Bay watershed: 

 2,430 pounds of arsenic annually (97 percent reduction). 

 476 pounds of cadmium annually (93 percent reduction). 

 1,540 pounds of lead annually (99 percent reduction). 

 87.1 pounds of mercury annually (98 percent reduction). 

 6,380 pounds of selenium annually (97 percent reduction). 

 5,220 pounds of thallium annually (99 percent reduction). 

 990,000 pounds of total nitrogen annually (>99 percent reduction). 

 14,900 pounds of total phosphorus annually (89 percent reduction). 

7-32 
Section 7—Environmental Improvem

Table 7-13. Pollutant Removals to the Great Lakes Watershed Under the Regulatory Optio

Pollutant 

Baseline Loadings

to the Great

Lakes Watershed

(lbs/yr)

Pollutant Removals (lbs/yr) to Great Lakes Watershed Under the Regulato

(Percent Reduction) a

Option A Option B Option C Option D 

Arsenic 2,170 47.5 (2%) 47.5 (2%) 513 (24%) 2,070 (96%) 

Boron 997,000 9,190 (1%) 9,190 (1%) 22,600 (2%) 66,800 (7%) 

Cadmium 648 53.6 (8%) 53.6 (8%) 183 (28%) 612 (95%) 

Chromium VI 0.548 0.471 (86%) 0.471 (86%) 0.548 (>99%) 0.548 (>99%) 

Copper 2,550 34.5 (1%) 34.5 (1%) 608 (24%) 2,510 (99%) 

Lead 1,900 19.4 (1%) 19.4 (1%) 449 (24%) 1,880 (99%) 

Manganese 242,000 35,500 (15%) 35,500 (15%) 70,500 (29%) 188,000 (77%) 

Mercury 82.8 4.56 (6%) 4.91 (6%) 22.6 (27%) 80.6 (97%) 

Nickel 9,840 402 (4%) 413 (4%) 2,550 (26%) 9,720 (99%) 

Selenium 5,020 126 (3%) 3,780 (75%) 4,010 (80%) 4,800 (96%) 

Thallium 9,570 23.5 (<1%) 23.5 (<1%) 2,200 (23%) 9,510 (95%) 

Zinc 8,730 658 (8%) 658 (8%) 2,410 (28%) 8,270 (95%) 

Nitrogen, total b 1,150,000 2,420 (<1%) 380,000 (33%) 556,000 (48%) 1,150,000 (>99%) 

Phosphorus, total 23,100 135 (1%) 135 (1%) 5,110 (22%) 21,800 (94%) 

Chlorides 31,900,000 11,400 (<1%) 11,400 (<1%) 698,000 (2%) 3,000,000 (9%) 

TDS 186,000,000 3,890,000 (2%) 3,890,000 (2%) 22,300,000 (12%) 83,900,000 (45%) 

Source: ERG, 2015a; ERG, 2015c. Acronyms: lbs/yr (pounds per year).Note: Loadings and pollutant removals are rounded to three significant figures. 

a – >0 to 15 percent reduction; 16 to 30 percent reduction; 31 to 45 percent reduction; 46 to 60 percent reduction; >60 percent reductionb – Total nitrogen loadings are the sum of total Kjeldahl nitrogen and nitrate/nitrite as N loadings. 

7-33 
 

Section 7—Environmental Improvements Under the Final Rule 

7.6 ENVIRONMENTAL AND HUMAN HEALTH IMPROVEMENTS IN DOWNSTREAM SURFACE

WATER

EPA estimates that the environmental and human health improvements in the immediate

receiving waters expected from the final rule will translate into considerable improvements in 

water quality further downstream from steam electric power plant discharges. EPA calculated 

downstream receiving water pollutant concentrations using EPA’s Risk-Screening

Environmental Indicators (RSEI) model55 and compared these concentrations to the same

NRWQC and MCL water quality benchmarks used in the IRW model national-scale analysis. 

EPA also evaluated the wildlife (mink and eagle NEHC benchmarks) and human health (cancer 

and non-cancer) improvements in downstream surface waters using a simplified version of the 

IRW model national-scale analysis. This approach involved calculating the water pollutant 

concentrations that would result in exceedances if used as inputs to the wildlife and human 

health modules in the IRW model; EPA then compared the downstream receiving water pollutant

concentrations in RSEI to these “threshold” concentrations to identify the downstream reaches 

that would have at least one exceedance of a particular wildlife or human health benchmark.56

EPA used this approach to estimate the extent (in river miles) of environmental and human 

health impacts in downstream surface waters under baseline conditions and the improvements

under the modeled regulatory options (Options A, B, C, D, and E). Table 7-14 presents the

results of this downstream analysis. 

Based on the results of the downstream modeling, thousands of downstream river miles

are impacted by steam electric power plant discharges. Pollutant concentrations exceed NRWQC 

for human health (water and organism) in 4,400 river miles downstream from immediate 

receiving waters. However, under the final rule, this drops by 2,390 river miles (54 percent). The 

final rule reduces the number of downstream exceedances for each of the NRWQCs and MCLs 

evaluated. This reduction improves the water quality and aquatic habitats available to wildlife 

and human populations located outside of the immediate vicinity of steam electric power plants. 

In addition, pollutant removals under the final rule also reduce impacts to wildlife that rely on 

downstream aquatic habitats as a food source. Up to 1,040 miles of surface waters downstream 

from steam electric power plant discharges will no longer contain fish populations that exceed an 

NEHC benchmark for minks or eagles. The final rule also decreases potential exposure of 

humans to pollutants that can cause non-cancer health effects from consumption of contaminated 

fish in up to 5,470 river miles. These results demonstrate that steam electric power plant 

discharges are impacting surface waters beyond the immediate receiving waters. Pollutant 

removals associated with the final rule will substantially improve the environmental and human 

health for communities beyond the area immediately surrounding steam electric power plants.

55 EPA used pollutant loadings discharged to each receiving reach by steam electric power plants to estimate 

concentrations in downstream reaches. The RSEI model uses a simple dilution and first-order decay equation to 

calculate receiving water concentrations (metals are treated as conservative substances). The RSEI model assumes

that the plant’s annual discharge is released at a constant rate throughout the year. In addition, EPA included

pollutant loadings from EPA’s Toxics Release Inventory (TRI) database for other industries to represent background

pollutant concentrations in the downstream receiving waters. For further details on the RSEI model methodology 

and assumptions, see the Benefits and Cost Analysis. 

56 See the ERG memorandum “Downstream EA Modeling Methodology and Supporting Documentation” (DCN

SE04455) regarding the calculation of these water pollutant concentration thresholds. 

7-34 
Section 7—Environmental Improvem

Table 7-14. Key Environmental Improvements for Downstream Waters Under the Regulatory 

Evaluation Criteria

Number of RiverMiles Exceeding 

Criteria Under 

Baseline Conditions 

Number of River-Miles Exceeding Criteria 

(Percent Reduction from Baseline Conditions) Under the Reg

Option A Option B Option C Option 

Water Quality Results Freshwater Acute NRWQC 417 396 

(5%)

396 

(5%)

394 

(5%)

390 

(7%)

Freshwater Chronic NRWQC 628 612 (3%) 569 (9%) 547 (13%) 518 (18%) 

Human Health Water andOrganism NRWQC

4,400 3,670

(17%)

3,670

(17%)

2,620

(40%)

2,010

(54%)

Human Health Organism-onlyNRWQC 1,560 1,300 (16%) 1,300 (16%) 1,070 (31%) 782 (50%) 

Drinking WaterMCL 

759 731 

(4%)

726 

(4%)

630 

(17%)

487 

(36%)

Wildlife Results Fish Ingestion NEHC for Minks 1,180 917 

(23%)

892 

(25%)

723 

(39%)

527 

(56%)

Fish Ingestion NEHC for Eagles 2,000 1,730

(13%)

1,720

(14%)

1,390

(30%)

959 

(52%)

Human Health Results—Non-Cancer Non-cancer reference dose forchild (recreational) 

6,350 4,900

(23%)

4,890

(23%)

3,130

(51%)

2,310

(64%)

Non-cancer reference dose foradult (recreational) 

3,760 2,960

(21%)

2,950

(21%)

2,050

(46%)

1,470

(61%)

Non-cancer reference dose forchild (subsistence) 

10,100 8,380

(17%)

8,350

(17%)

6,150

(39%)

4,630

(54%)

Non-cancer reference dose foradult (subsistence) 

7,110 5,580

(22%)

5,570

(22%)

3,720

(48%)

2,770

(61%)

7-35 
Section 7—Environmental Improvem

Table 7-14. Key Environmental Improvements for Downstream Waters Under the Regulatory 

Evaluation Criteria

Number of RiverMiles Exceeding 

Criteria Under 

Baseline Conditions 

Number of River-Miles Exceeding Criteria 

(Percent Reduction from Baseline Conditions) Under the Reg

Option A Option B Option C Option 

Human Health Results—Cancer Cancer risk for child (recreational)

231 216 

(7%)

216 

(7%)

211 

(9%)

210 

(9%)

Cancer risk for adult (recreational)

286 263 

(8%)

263 

(8%)

251 

(12%)

246 

(14%)

Cancer risk for child (subsistence) 

262 241 

(8%)

241 

(8%)

239 

(9%)

235 

(10%)

Cancer risk for adult (subsistence) 

446 383 

(14%)

383 

(14%)

358 

(20%)

328 

(27%)

Source: ERG, 2015i; ERG, 2015l. Note: River miles are rounded to three significant figures. a – >0 to 15 percent reduction; 16 to 30 percent reduction; 31 to 45 percent reduction; 46 to 60 percent reduction; >60 percent reduction

b – EPA evaluated a total of 73,000 river-miles in the downstream receiving water analysis for toxic, bioaccumulative pollutants. Downconcentrations are calculated until one of three conditions occurs: 1) the discharge travels 300 kilometers (km) downstream; 2) the disc

for a week; or 3) the concentration reaches 1 x 10-9 milligrams per liter (mg/L). 

7-36 
Section 7—Environmental Improvements Under the Final Rule 

7.7 ATTRACTIVE NUISANCES

EPA projects that the final rule will also decrease the environmental impact to wildlife

exposed to pollutants through direct contact with surface impoundments and constructed 

wetlands at steam electric power plants. Multiple studies show that wildlife living near steam 

electric surface impoundments exhibit elevated levels of arsenic, cadmium, chromium, lead,

mercury, selenium, strontium, and vanadium [Burger et al., 2002; Bryan et al., 2003; Hopkins et 

al., 1997, 1998, 2000, 2002, 2006; Nagle et al., 2001; Rattner et al., 2006]. Multiple studies have 

linked attractive nuisance areas at steam electric power plants to diminished reproduction 

[Hopkins et al., 2002, 2006; Nagle et al., 2001]. While the final rule does not control pollutants 

within surface impoundments or constructed wetlands prior to their discharge to surface waters, 

EPA estimates that the final rule will decrease pollutant loadings to these waterbodies (e.g., 

through plants converting to dry handling their fly ash). These pollutant removals will decrease 

the exposure of wildlife populations to toxic pollutants and decrease the threat that combustion 

residual surface impoundments pose to surrounding wildlife. 

7.8 OTHER SECONDARY IMPROVEMENTS

In addition to the improvements discussed above, other secondary, or ancillary, other 

resources will see improvements that are associated directly or indirectly with the final rule.

Pollutant removals not only improve water quality in surface waters but enhances their aesthetic 

(e.g., by improving clarity and decreasing odor and discoloration). Cleaner surface water 

improves the source of drinking water for both surface water treatment plants and wells that are 

influenced by surface water; water used for irrigation; and water used for industrial uses (less 

contaminants). 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

clean-up and treatment costs for contamination or impoundment failures, reduced injury 

associated with surface impoundment failures, reduced water usage, reduced potential for algal 

blooms, and decreased air emissions. 

The Benefits and Cost Analysis monetizes benefits of implementing the final rule 

(increased aesthetics, recreational improvements, increased availability of ground water 

resources, reduced risk of surface impoundment failures, and air quality improvements). In 

addition, the document also qualitatively discusses improvements to the quality of source water 

for drinking, irrigation, and industrial use; quantity and quality of recreational opportunities; 

improved commercial fisheries yields; increased property values; and reduced sediment

contamination within receiving waters. 

While the final rule does not control pollutants leaching to ground water from surface

impoundments and landfills containing combustion residuals, EPA estimates that the final rule 

will decrease pollutant loadings to surface impoundments (e.g., through plants converting to dry 

handling their fly ash). These pollutant removals will decrease pollutants leaching from 

combustion residual surface impoundments to ground water and decrease the potential human

health impacts associated with exposure to contaminated drinking water wells (see Section 

3.3.4). EPA, however, did not quantify or monetize the benefits associated with this

improvement to ground water quality. 

7-37 
 

Section 7—Environmental Improvements Under the Final Rule 

7.9 UNRESOLVED DRINKING WATER IMPACTS DUE TO BROMIDE DISCHARGES

As discussed in Section 3.1.3, bromide in water can form brominated disinfection byproducts (DBPs), some potentially carcinogenic, when drinking water plants use certain 

processes including chlorination and ozonation to disinfect the incoming source water. The 

national effluent limitations guidelines and standards under the final rule (regulatory Option D)

do not directly control TDS levels (including bromides) in FGD wastewater discharges from all 

steam electric power plants.57 Coal-fired steam electric power plants can discharge bromide due

to its natural presence in coal (which is released when burned and/or captured in particulates by 

baghouses and FGD controls) or through bromide addition to flue gas control processes to reduce 

mercury emissions. Steam electric power plant discharges occur close to more than 100 public 

drinking water intakes on rivers and other waterbodies and there is evidence that bromide 

discharges are already having adverse effects on the quality of drinking water sources. 

While bromide itself is not thought to be toxic at levels present in the environment, its 

reaction with other constituents in water may be of concern now and into the future. Drinking 

water utilities should be concerned about bromides affecting drinking water sources, as bromide 

loadings into surface waters could potentially increase in the future as more coal-fired steam 

electric power plant operators add bromide to help control mercury emissions. Although EPA 

decided not to finalize BAT requirements based on evaporation for treating FGD wastewater at 

all steam electric power plants in the final rule, evaporation technology is potentially available 

and may be appropriate for achieving water quality-based effluent limitations, depending on sitespecific conditions, where drinking water supplies need to be protected. 

57 They do, however, directly control TDS in cases where steam electric power plants opt into the voluntary 

incentives program, in which they would be subject to effluent limitations based on evaporation technology.

7-38 
 

Section 8—Case Study Modeling

SECTION 8

CASE STUDY MODELING 

EPA developed dynamic water quality models of selected case study locations to 

supplement the water quality component of the national-scale immediate receiving water (IRW)

model. EPA performed the case study modeling to provide additional resolution regarding the

baseline impacts and the expected environmental and human health improvements under the 

final rule, while encompassing a broader temporal and spatial scope than what is included in the

IRW model. The case study models also validate and provide additional perspective on the 

results of the IRW model for those waterbodies included in both models. The case study 

modeling improves upon the IRW model in the following ways: 

 Accounts for long-term pollutant loadings from steam electric power plants (under 

both baseline conditions and the final rule) and estimates the resultant accumulation 

of pollutants within the water column and sediments of the receiving water. These 

models can more accurately assess baseline pollutant concentrations and the time 

frame and magnitude of environmental improvements associated with the final rule. 

 Accounts for fluctuations in receiving water flow rates by using daily stream flow 

monitoring data instead of one annual average flow rate for the receiving water. This 

approach better reflects the varying influence of dilution (or lack thereof) within the

receiving water during high-flow and low-flow conditions. 

 Accounts for pollutant transport and accumulation within receiving water reaches that 

are downstream from the discharge location. This approach can more accurately

estimate the river distance showing environmental impacts under baseline conditions 

and improvements under the final rule.58

 Accounts for pollutant contributions from other point, nonpoint, and background 

sources, to the extent practical, using available data sources. Incorporating nonsteam-electric pollutant sources and available water quality data provides a more 

complete illustration of the compounding impacts of background pollutant 

concentrations, steam electric power plant pollutant loadings, and other point source 

dischargers. 

This section describes EPA’s methodology for developing and running the case study 

models (Section 8.1); presents the results of the case study models for the selected case study 

locations (Section 8.2); and compares the case study and IRW model results (Section 8.3). 

58 The case study downstream modeling described in this section is separate from the downstream modeling EPA

performed using the Risk-Screening Environmental Indicators (RSEI) model and the SPARROW (SPAtially

Referenced Regressions On Watershed attributes) model. EPA used the national-scale RSEI and SPARROW models

to quantify changes in water quality in support of the benefits analysis for the final rule. See the Benefits and Cost

Analysis for the Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating Point 

Source Category (EPA-821-R-15-005).

8-1 
Section 8—Case Study Modeling

8.1 CASE STUDY MODELING METHODOLOGY

The case studies use EPA’s Water Quality Analysis Simulation Program (WASP), a 

dynamic compartment-modeling program for aquatic systems that simulates pollutant fate and 

transport within both the water column and the benthic sediment. The WASP model helps users 

interpret and predict water quality responses to natural phenomena and man-made pollution for 

various pollutant management decisions. EPA’s approach also relies on U.S. Geological Survey 

(USGS) daily stream flow data downloaded through EPA’s Better Assessment Science 

Integrating Point and Nonpoint Sources (BASINS) interface to provide input time series flow 

data for use in the WASP model. 

This section is organized as follows: 

 Section 8.1.1 discusses EPA’s approach for selecting case study locations (i.e., steam 

electric power plants and receiving waters) for case study modeling, including the 

differences in selection criteria for lotic, lentic, and estuarine water systems. 

 Section 8.1.2 summarizes the scope and general technical approach for the case study 

modeling, including the selection of pollutants and wastestreams for modeling; the 

data sources evaluated for non-steam-electric pollutant contributions; and approaches 

for modeling pollutant levels before and after the assumed final rule compliance date.

 Section 8.1.3 explains the development and execution of the case study models using 

WASP. Appendix G provides additional information regarding the specific input 

parameters (e.g., background pollutant concentrations, USGS time series flow data) 

and model settings (e.g., solids transport parameters) for each of the WASP models.

For additional documentation regarding the selection and calculation of the input 

parameters and settings, refer to the ERG memorandum, “Technical Approach for 

Case Study Water Quality Modeling of Aquatic Systems in Support of the Final

Steam Electric Power Generating Industry Environmental Assessment” (DCN 

SE05570) (Case Study Water Quality Modeling Memorandum). 

 Section 8.1.4 describes the use of the case study model outputs to determine impacts 

to aquatic life based on changes in water quality; impacts to aquatic life based on 

changes in sediment quality; impacts to wildlife from consuming contaminated 

aquatic organisms; and impacts to human health from consuming contaminated fish. 

 Section 8.1.5 lists some of the limitations and assumptions involved with EPA’s case

study modeling. 

8.1.1 Selection of Case Study Locations for Modeling

To select locations for detailed case study modeling, EPA developed site-selection 

criteria to identify a collection of steam electric power plants and receiving waters that, when 

evaluated as a group: 

 Represent a reasonable cross-section of the range of receiving waters evaluated in the

environmental assessment (EA). 

 Illustrate pollutant removals across the regulatory options evaluated by EPA. 

8-2 
Figure 8-1. Overview of Case Study Modeling Locations 

Section 8—Case Study Modeling

 Encompass discharges of all four wastestreams evaluated in the EA. 

 Demonstrate pollutant loadings that are representative of those discharged by steam 

electric power plants evaluated in the EA (i.e., discharges are typical of steam electric 

power plants and not outlier values). 

EPA evaluated 195 steam electric power plants that discharge directly to aquatic systems

with lotic characteristics (rivers and streams), lentic characteristics (lakes, ponds, and reservoirs), 

or that are estuarine systems. Through the site-selection process described below, EPA identified

six representative case study locations (five lotic sites and one lentic site) that capture 

improvements across multiple regulatory options, represent all four evaluated wastestreams (flue 

gas desulfurization (FGD) wastewater, fly ash transport water, bottom ash transport water, and

combustion residual leachate), and represent both lentic and lotic aquatic environments. Figure 

8-1 and Table 8-1 present the six receiving waters that EPA selected for case study modeling. 

8-3 
Sectio

Table 8-1. Locations Selected for Case Study Modeling 

Case Study 

Location

Waterbody

Type 

Steam Electric 

Power Plant(s)

Modeled

Evaluated Wastestreams Discharged 

Regulatory Options 

Demonstrating Removals

FGD Fly Ash

Bottom

Ash Leachate A B C D 

Black Creek, MS Lotic R.D. Morrow Sr. Generating Site       

Etowah River,GA Lotic Plant Bowen      

Lick Creek & White River, IN Lotic Petersburg Generating Station      

Ohio River, PA/WV/OH Lotic 

Bruce Mansfield Plant & W.H.Sammis Plant 

       

Mississippi River, MO/IL Lotic Rush Island b     

Lake Sinclair,GA Lentic Plant Harllee Branch c        

Acronym: FGD (flue gas desulfurization); N/A (Not applicable). a – The modeling periods start at 1982 (the year of the last revision to the steam electric effluent limitations guidelines and standards (E

installation of the most recent generating unit impacted by the final rule (if after 1982). The duration of the modeling period is influenc

periods covered by USGS time series flow data and by the assumed date upon which the steam electric power plant would achieve the lrule, as determined based on the plant’s National Pollutant Discharge Elimination System (NPDES) permitting cycle. b – EPA identified another steam electric power plant, Meramec, that discharges upstream of the Rush Island plant. EPA incorporated tthe Meramec plant to account for the upstream pollutant contributions. EPA did not evaluate the water quality, wildlife, or human healt

discharges from the Meramec plant because this plant was not selected using the case study selection methodology described in this secc – This steam electric power plant has decertified and retired all of its steam electric generating units. EPA selected this plant to repres

of discharges of the evaluated wastestreams to lentic waterbodies because it meets all of the case study selection criteria.

8-4 
Section 8—Case Study Modeling

Selection of Lotic Case Study Locations

To select lotic receiving waters to model using WASP, EPA reviewed all combinations of 

steam electric power plants and their receiving waters evaluated in the EA for factors that would 

negatively influence the ability to use WASP for case study water quality modeling or the ability 

to discuss the case study modeling results in a public document. EPA completed an assessment 

using industry responses to the 2010 Questionnaire for the Steam Electric Power Generating 

Effluent Guidelines (the Steam Electric Survey), EPA’s BASINS tool, National Hydrography 

Dataset Plus (NHDPlus Version 1) hydrography layers, and USGS National Water Information 

System (NWIS) data sources to identify and eliminate the lotic receiving waters that met one or

more of the following criteria from consideration for case study modeling: 

 Confidential Business Information (CBI). EPA identified and eliminated steam 

electric power plants with CBI claims on discharge flow rate data for any of the four

evaluated wastestreams. EPA eliminated these plants as potential case study locations 

because CBI data, including modeled water concentrations based on CBI data, cannot 

be discussed in a public document such as this EA report. 

 Stream gage flow data. EPA identified and eliminated receiving waters that lack 

sufficient stream gage flow data. Availability of a long-term, continuous stream flow 

record for both the receiving water being modeled and any significant downstream 

tributaries was a major factor in selecting case study locations because these data are 

needed to construct the hydrodynamics in WASP. The primary considerations when 

reviewing the sufficiency of stream gage flow data for use in WASP were the

following: 

- Location of USGS stream gage stations (the ideal location is within the vicinity of

the immediate receiving water being evaluated, plus additional locations within 

the model area).

- A continuous stream flow record covering a time period that matches or exceeds 

the length of the desired modeling period. 

- Age of the stream gage flow data (data sets without data from within the previous 

30 years were considered potentially unrepresentative of current flow conditions). 

 Downstream waterbody characteristics. WASP’s ability to accurately model water 

quality using USGS stream gage flow data can be affected by flow control structures 

such as dams that affect the linear flow and circulation of water, and thus influence 

the transport of pollutants. EPA identified and eliminated receiving waters whose 

downstream waterbodies exhibit these characteristics, unless the areas of concern 

were sufficiently downstream to allow for modeling of a reasonable distance (i.e., at 

least 25 miles) before encountering the area of concern. 

 Influence by other point source dischargers that could not be modeled. EPA identified

receiving waters that could be significantly influenced by discharges from other point 

sources (including other steam electric power plants) and evaluated whether those 

point sources would meet the criteria listed above for case study modeling. If EPA 

determined that a receiving water would be significantly influenced by other point 

source discharges that could not be modeled (e.g., an upstream steam electric power

8-5 
 

 

Section 8—Case Study Modeling

plant exercising CBI claims) or represented in the model by STORET monitoring 

data (see Section 8.1.3), EPA eliminated the receiving water from consideration. If 

EPA deemed the pollutant loadings from the other point source discharges to be 

insignificant compared to the steam electric power plant pollutant loadings being 

evaluated, EPA included the receiving water in the analysis.59

Next, EPA assessed the representativeness of the steam electric power plants and 

receiving waters that were not eliminated based on the criteria above. EPA selected the receiving 

water flow rate, magnitude of pollutant loadings from the evaluated wastestreams, and water

column concentrations output calculated based on these values as the primary factors in 

determining whether it considered a particular receiving water representative. EPA reviewed the

average annual flow rates (as defined in NHDPlus Version 1), baseline loadings of the modeled 

pollutants, and water column concentrations output from the IRW model of each of the steam 

electric power plants and receiving waters that were not eliminated after application of the 

acceptance criteria. EPA assessed how each plant and receiving water compared to the general 

population in the EA and eliminated plant and receiving water combinations that did not 

reasonably represent typical conditions. From the population of lotic receiving waters that EPA

determined would be suitable for WASP modeling and representative of typical pollutant 

loadings from discharges of the evaluated wastestreams, the Agency selected a collection that,

when evaluated as a group, demonstrated pollutant removals across all modeled regulatory 

options and all four evaluated wastestreams. As a result, EPA identified five case study locations

as the best candidates for modeling as part of a representative set of steam electric power plants 

that discharge to lotic systems. The selected case study locations are further described in Section 

8.2.60 Additional information about EPA’s methodology for selecting plants and receiving waters

that are representative and suitable for WASP modeling is further described in the Case Study 

Water Quality Modeling Memorandum (DCN SE05570). 

Selection of Lentic and Estuarine Case Study Locations

Water quality modeling of lentic systems (lakes, ponds, and reservoirs) or estuarine 

systems involves more complex hydrodynamics that would not be adequately represented by 

stream gage flow data. Modeling steam electric power plants that discharge to lentic or estuarine 

systems requires using existing EPA-developed WASP models (or more specifically, the 

underlying hydrodynamic data) for the specific waterbodies of interest. Accordingly, EPA 

considered the availability of existing models a primary factor in selecting lentic and estuarine 

systems for case study water quality modeling. 

59 EPA considered receiving water flow rate, distance between outfalls, and relative magnitude of pollutant loadings 

when assessing whether the discharges from upstream or downstream plants or point sources could significantly

affect the water quality modeling results for the selected case study location. EPA applied best professional

judgment using these criteria, but did not apply numeric thresholds.

60 Because of the level of effort required to design, execute, and evaluate the outputs for case study modeling, EPA 

did not complete case study modeling for all candidates that met all acceptance criteria and were determined to be

representative. EPA used best professional judgment in determination of which five case study locations were the 

best candidates for modeling and represent a reasonable cross-section of the range of receiving waters evaluated in

the EA. 

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Section 8—Case Study Modeling

EPA identified one preexisting WASP model for a lake (Lake Sinclair, GA) that receives

steam electric power plant discharges from Georgia Power Company’s Plant Harllee Branch. As 

of April 16, 2015, this plant has decertified and retired all four of its coal-fired generating units. 

Based on a review of the water concentration outputs generated by the IRW model in support of 

the proposed ELGs (which were developed prior to the announcement of plans to retire Plant 

Harllee Branch), EPA determined that Lake Sinclair remains a representative illustration of

lentic waterbodies that receive discharges of the evaluated wastestreams. As discussed in Section 

3, pollutant loadings to lentic systems often more strongly affect water quality and ecosystem 

health (compared to lotic systems) due to the longer residence times and associated long-term

accumulation of pollutants in these systems. Accordingly, and despite the retirement of Plant 

Harllee Branch, EPA proceeded with case study modeling of Lake Sinclair to represent the 

potential impacts of steam electric power plant discharges on lentic waterbodies (including the 

26 lake, pond, and reservoir receiving waters evaluated in this EA) and the potential 

environmental improvements under the final rule in other lentic waterbodies that receive

discharges of the evaluated wastestreams. 

EPA also identified one preexisting water WASP model for an estuary (Hillsborough 

Bay, FL) that receives steam electric power plant discharges. However, due to the hydrologic

complexity of the model, and because estuarine systems represent less than 2 percent of the 

receiving waters evaluated in the EA, EPA elected to develop only freshwater river and lake

WASP models for this case study analysis. Additionally, the ecological risk modeling approach 

described in Section 5.2 is based on selenium bioaccumulation within freshwater environments 

and would not be appropriate to apply to estuarine or marine aquatic systems, which would limit 

EPA’s ability to analyze the ecological effects for the estuarine case study. 

8.1.2 Scope and Technical Approach for Case Study Modeling

This section describes the scope and technical approach used for EPA’s detailed case 

study modeling, including the selection of pollutants and wastestreams evaluated, the inclusion 

of other point and nonpoint sources, the development of a historical baseline for the case study 

location, and the prediction of decreased water and sediment pollutant concentrations under the 

regulatory options evaluated for the final rule. 

Selection of Pollutants for Modeling

EPA approached the case study modeling with the goal of modeling the same 10 

pollutants included in the IRW model, which are listed in Section 5.1. As described later in this

section, however, EPA was unable to perform case study modeling for chromium VI and 

mercury. EPA performed case study water quality modeling for the following eight pollutants (or 

“toxicants” as defined in the WASP model), which were also included in the IRW model: 

 Arsenic (As). 

 Cadmium (Cd). 

 Copper (Cu). 

 Lead (Pb).

 Nickel (Ni).

 Selenium (Se). 

8-7 
Section 8—Case Study Modeling

 Thallium (Tl).

 Zinc (Zn). 

These pollutants can be modeled using the Simple Toxicant module within WASP. 

Similar to the water quality module of the IRW model, the Simple Toxicant module applies 

pollutant-specific partition coefficients to estimate the degree to which pollutants in the water 

column will adsorb to benthic sediments and suspended solids. Unlike the IRW model, the 

Simple Toxicant module does not incorporate separate partition coefficients to define the benthic 

sediment/pore water equilibrium and the suspended sediment/water column equilibrium.

Therefore, EPA selected only the suspended sediment-water (Kdsw) partition coefficient for each

pollutant (see Table C-4 in Appendix C). 

EPA also considered using WASP to perform water quality modeling for chromium VI 

and mercury. These pollutants, however, require using more data-intensive modules within 

WASP. Accurately modeling chromium VI requires using the META4 module within WASP to 

accurately predict pollutant speciation and depends on the availability of extensive site-specific 

monitoring data. Modeling mercury (and methylmercury, a bioaccumulative organic form of 

mercury) requires using the MERC7 module within WASP to account for transformation 

processes such as methylation. Using the more data-intensive modules requires site-specific data

that were not available for all locations. 

Evaluated Wastestreams

The case study models quantified the water quality impacts resulting from discharges of 

the same four evaluated wastestreams included in the IRW model: 

 Fly ash transport water. 

 Bottom ash transport water.

 FGD wastewater. 

 Combustion residual leachate. 

As with the IRW model, EPA performed the WASP water quality modeling using 

average daily pollutant loadings derived from average annual pollutant loadings and normalized 

effluent flow rates. This assumption of a static loadings rate does not account for temporal

variability in the loadings to receiving waters due to factors such as variable plant operating

schedules, storm flows, low-flow events, and catastrophic events. 

Inclusion of Other Point and Nonpoint Sources

Accounting for pollutant contributions from non-steam-electric point sources and 

nonpoint sources, to the extent practical using available data, can improve the accuracy of the 

case study water quality models. EPA identified the following data sources that provide pollutant 

loadings and/or concentration data for these other sources potentially affecting water quality in

the case study location: 

 Discharge Monitoring Reports (DMR). Point source dischargers are required to report 

certain wastewater monitoring data through the submittal of DMRs. However, they

are required to report only for the pollutants that are listed in the facility’s National 

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Section 8—Case Study Modeling

Pollutant Discharge Elimination System (NPDES) permit.61 EPA evaluated 2011 

pollutant loadings data for direct dischargers including publicly owned treatment 

works (POTWs) and industrial facilities. 

 Toxics Release Inventory (TRI). TRI collects facility-reported estimates of 

wastewater loadings data for both direct and indirect dischargers. The TRI database

does not include loadings from facilities with total annual chemical releases of less 

than 500 pounds and incorporates assumptions regarding plants with annual releases

of less than 1,000 pounds. The point source loadings from smaller facilities, therefore, 

may not be well represented in the TRI database.62 EPA evaluated 2011 pollutant 

loadings data for industrial facilities with indirect discharges of a modeled pollutant. 

EPA also evaluated TRI direct pollutant loadings data for these facilities and 

pollutants if the facilities are not also required to report this pollutant in their DMRs 

(to avoid double-counting direct discharges). 

 STORET Monitoring Data. EPA’s STORET database is a repository for water

quality, biological, and physical data compiled from many data sources and locations 

throughout the country. The STORET database contains water quality and sediment 

quality monitoring data for all eight modeled pollutants and other input parameters

for WASP including total organic carbon (TOC) and total suspended solids (TSS). 

EPA reviewed these publicly available data sources to identify pollutant contributions 

from non-steam-electric point sources and nonpoint sources that may impact the case study water 

quality model. EPA also used available STORET monitoring data to help calibrate the modeled 

outputs. For additional documentation regarding EPA’s collection and use of these data, refer to

the Case Study Water Quality Modeling Memorandum (DCN SE05570). 

Modeling of Pollutant Loadings Prior to the Final Rule

EPA developed and executed WASP models (as described in Section 8.1.3) for the

selected case study locations to predict the baseline accumulation of pollutants in the receiving

water and sediment leading up to implementation of the final rule. 

The modeling periods start at 1982 (the year of the last revision to the steam electric

ELGs) or the date of installation of the most recent generating unit impacted by this rulemaking 

(if after 1982), and extend to the assumed compliance date.63 If the available stream gage flow 

61 In addition, states (or other permitting authorities) have some discretion as to which data they make available (or 

enter) to the national database (i.e., Permit Compliance System (PCS) and Integrated Compliance Information 

System for the National Pollutant Discharge Elimination System (ICIS-NPDES)). For example, permitting

authorities enter DMR and permit information for facilities that are considered major dischargers. However, they do

not necessarily enter DMR or permit information into PCS for minor dischargers or facilities covered by a general

permit.

62 Other limitations of the data collected in TRI include the following: small establishments are not required to 

report, nor are facilities that do not meet reporting thresholds; releases reported are based on estimates, not

measurements; certain chemicals are reported as a class, not as individual compounds; facilities are identified by

North American Industrial Classification System (NAICS) code, not point source category; and TRI requires 

facilities to only report certain chemicals and therefore all pollutants discharged from a facility may not be captured. 63 For each steam electric power plant in the case study modeling, EPA assumed a plant-specific date, derived from

the plant’s permitting cycle, that the plant would achieve the limitation under the final rule. 

8-9 
Section 8—Case Study Modeling

data did not cover the desired modeling period, EPA extrapolated the available data, 

incorporating another partial cycle of the flow data to reach the total desired modeling period. 

Historical pollutant loadings data for the evaluated wastestreams and non-steam-electric 

point sources are very limited and difficult to obtain, so EPA used Steam Electric Survey data 

(representing plant operations in 2009), STORET monitoring data, and 2011 TRI and DMR 

loadings data as a representative set of discharge conditions. EPA acknowledges that these data 

may not reflect the actual pollutant loadings over the entire modeling period; however, they 

represent an appropriate estimation of annual pollutant loadings and how discharges may affect

individual aquatic systems over time. 

For each case study location, EPA assumed that the annual, historical pollutant loadings

associated with fly ash transport water, bottom ash transport water, and combustion residual

leachate discharges were equal to the baseline pollutant loadings calculated for these 

wastestreams (i.e., the same annual pollutant loadings used to represent baseline conditions in the 

national-scale IRW model). The impoundment and discharge of these wastestreams has been a 

standard technique practiced since before 1982. EPA did not attempt to determine whether a 

modeled plant had historical discharges of an evaluated wastestream that are not represented in 

the baseline pollutant loadings. For example, for a plant that does not have fly ash transport 

water pollutant loadings under baseline conditions, EPA did not attempt to determine whether 

the plant had historical discharges of fly ash transport water. 

In estimating the annual, historical pollutant loadings associated with FGD wastewater, 

EPA accounted for the fact that steam electric power plants may have installed FGD systems

after the start of the modeling period. EPA used the FGD system installation dates, based on 

industry responses to the Steam Electric Survey, to determine how to incorporate FGD 

wastewater pollutant loadings into the case study model. If a plant installed multiple FGD 

systems during the modeling period, EPA assumed that the annual, historical FGD wastewater

pollutant loadings associated with each individual system were proportional to that system’s flow 

rate contribution compared to the total FGD wastewater flow rate under baseline conditions. The 

procedure for calculating and incorporating the proportional loadings for each FGD system is 

further described in the Case Study Water Quality Modeling Memorandum (DCN SE05570). 

EPA accounted for pollutant loadings from non-steam-electric point sources within the 

modeling boundary by using 2011 TRI and DMR data. EPA assumed that the annual, historical 

pollutant loadings for these point sources throughout the modeling period were equal to the 

pollutant loadings reported in the 2011 TRI and DMR data sets. To account for contributions 

from nonpoint sources, EPA evaluated STORET water quality monitoring data collected 

upstream of the modeling boundary. The Agency used these monitoring data to represent the 

pollutant contributions from all point, nonpoint, and background sources upstream of the

monitoring location, potentially avoiding the need to collect TRI and DMR pollutant loadings 

data and perform WASP modeling of those upstream or tributary reaches. The Case Study Water 

Quality Modeling Memorandum (DCN SE05570) further discusses how EPA incorporated DMR 

pollutant loadings data, TRI pollutant loadings data, and STORET monitoring data into the

WASP water quality models. 

8-10 
 

 

 

Section 8—Case Study Modeling

The results of this baseline modeling provided initial receiving water and sediment

concentrations for modeling discharges after the assumed compliance date, discussed in the 

following section. 

Modeling of Pollutant Loadings Under the Final Rule

EPA developed and executed WASP water quality models (as described in Section 8.1.3) 

for the selected case study locations to predict the decreases of receiving water and sediment 

pollutant concentrations (relative to baseline conditions) following implementation of the final 

rule.

EPA executed separate models for continued baseline pollutant loadings and regulatory 

option pollutant loadings (Options A through D)64. These modeling periods started at the 

assumed compliance date, as determined by each steam electric power plant’s permitting cycle,

and continued for at least 10 years after the assumed compliance date. EPA used the pollutant 

loadings calculated under the regulatory options to represent the annual steam electric pollutant 

loadings for each year of the period following implementation of the final rule. EPA assumed 

that the pollutant contributions from non-steam-electric point sources (based on TRI and DMR 

data) and from nonpoint sources (based on STORET monitoring data) would remain constant 

and would be equal to those used to model the period leading up to implementation of the final 

rule.

8.1.3 Development and Execution of WASP Models

EPA built each case study model using the BASINS setup tool for WASP, known as the 

WASP Model Builder, which allows the user to open WASP directly from the BASINS

interface. As described in Section 8.1.2, EPA’s approach used the Simple Toxicant module 

within WASP for the eight modeled pollutants. The Simple Toxicant module puts stretches of 

the modeled receiving water into segments based on the hydrologic characteristics. The WASP 

model calculates the water column and benthic pollutant concentrations using user-defined 

parameters and default assumption values. The process described in this section is based on 

using WASP Version 7.52 and BASINS Version 4.1. Both represent the most current versions

available for EPA’s analysis.

EPA followed the general approach described below in developing the WASP models for 

each of the lotic case study locations: 

 WASP calculates receiving water and sediment concentrations by dividing the

waterbody into segments and performing calculations for each segment. EPA used 

NHDPlus Flowlines as the basis for defining waterbody segments. To maintain 

reasonable model runtimes and reduce system instability, EPA further refined these 

segments by combining short segments such that the flow time through each segment 

is at least a tenth of a day. In some cases, segment travel times were shorter than the 

64 Case study modeling omitted Option E because EPA determined that the additional pollutant removals for Option 

E are only marginally better than Option D. Under Option E, only R.D. Morrow Generating Station and W.H.

Sammis plant would have additional removals. 

8-11 
Section 8—Case Study Modeling

desired minimum because the segment was located between an upstream and 

downstream tributary of some significance. 

 EPA used USGS stream gage flow data to represent inflows at the upstream end of 

the case study location, as well as any significant tributary with a USGS stream gage 

station. In all cases, EPA scaled the stream gage flow data to account for the

difference in drainage area between the actual gage location and the point where the 

contributing flow enters the model. 

 For those tributaries without available USGS stream gage flow data for the simulation 

period, EPA set the flow rate equal to the average annual flow rate as per NHDPlus 

Version 1. 

 To simplify the geographic extent of the modeling area, EPA did not model any 

tributaries with mean annual flow rates of less than 5 cubic feet per second (cfs) as 

per NHDPlus Version 1. 

 EPA used stream gage flow data from the actual time period (e.g., 1982 – 2014) to 

represent the baseline flow rate in the modeling area. EPA reused the historical flow

data to the extent necessary to complete the modeling period through the assumed

compliance date (e.g., 2015 – 2020), preferentially selecting flow data from periods 

that excluded years of particularly high or low flow rates. Then EPA reused the 

historical flow data to represent the period through the end of the model run (e.g., 

2020 – 2036). This approach ensured that the modeling periods before and after the

assumed compliance date were based on similar flow data. 

 To represent non-steam-electric point sources within the modeling area, EPA 

assigned the TRI and DMR pollutant loadings to the stream reach (as represented in 

NHDPlus Version 1) that was closest to the location of the point source. 

 EPA used STORET monitoring data, where available, to represent pollutant 

contributions flowing into the modeling area from upstream point sources, nonpoint 

sources, and background sources. Prior to incorporation into the WASP model, EPA 

converted the pollutant concentrations to mass loadings (for all pollutants except 

TOC and TSS) using the annual average flow rate for the stream segment where the

sample was collected (as represented in NHDPlus Version 1). This approach ensured 

that the modeled pollutant concentrations flowing into the modeling area would vary 

with changes in the stream flow rate. 

 To define initial concentrations for the organic solids, sands, and silts/fines 

parameters, EPA used TOC and TSS concentrations derived from STORET 

monitoring data collected within the modeling area. 

 EPA calibrated the WASP water quality models by modifying the solids transport 

input parameters until the modeled pollutant concentrations in the benthic segments 

closely matched the sediment concentrations derived from STORET monitoring data. 

The existing WASP model used for Lake Sinclair already divides the waterbody into 

segments and an existing Environmental Fluid Dynamics Code (EFDC) model provides 

hydrodynamics for the lentic system. Using an existing model of a lentic system was a 

reasonable approach to investigate the regulatory options without developing a detailed model 

8-12 
Section 8—Case Study Modeling

from scratch. However, this approach does limit the modeling period to the period simulated in

the existing EFDC model. Other than these differences, the approach for developing the WASP 

model for the lentic system was similar to the approach described above for lotic systems. 

EPA developed the WASP water quality models (for both lotic and lentic systems) to 

provide output data for pollutant concentration (total, dissolved, and sorbed) in the water column

and benthic segments on a daily output time step. The WASP models generate these outputs for 

both the immediate receiving water and every downstream segment. As described in Section 

8.1.2, EPA then executed the models to represent conditions before and after implementation of 

the final rule. 

Appendix G provides additional information regarding the specific input parameters (e.g., 

background pollutant concentrations, USGS time series flow data) and model settings (e.g., 

solids transport parameters) for each of the WASP water quality models. For additional 

documentation regarding the use or bypassing of specific WASP model features, incorporating 

stream gage flow and pollutant loadings data, and default settings and assumptions, refer to the 

Case Study Water Quality Modeling Memorandum (DCN SE05570). 

8.1.4 Use of WASP Water Quality Model Outputs

For each modeled segment, EPA used the water column and benthic sediment pollutant 

concentration outputs (for baseline and Option D, both from the WASP model run representing 

the time period after the assumed compliance date) to perform the following environmental and

human health analyses: 

 EPA compared the modeled pollutant concentrations in the water column (daily 

outputs) to the water quality benchmarks listed in Table C-7 of Appendix C and 

calculated the frequency of exceedances over the entire modeling period (i.e., the 

percentage of days that have a modeled exceedance).

 EPA compared the modeled pollutant concentrations in the benthic sediment (daily 

outputs) to the sediment biota chemical stressor concentration limit (CSCL)

benchmarks listed in Table D-2 of Appendix D and calculated the frequency of 

exceedances over the entire modeling period (i.e., the percentage of days with a 

modeled exceedance).

 EPA compared the modeled pollutant concentrations in the water column (averaged 

over the entire modeling period) to the water pollutant concentrations that would

result in exceedances if used as inputs to the wildlife and human health modules in 

the IRW model (as described in Section 7.6). 

For the Black Creek case study, which had relatively high concentrations of selenium 

compared to the other selected case studies, EPA also performed ecological risk modeling 

following the methodology described in Section 5.2. 

Using the WASP water quality outputs in these analyses allowed EPA to evaluate, with

greater focus and accuracy, the potential for additional environmental and human health impacts

that were not reflected in the IRW model outputs. These included impacts associated with peak 

pollutant concentrations during low-flow periods; long-term accumulation of pollutants in

8-13 
Section 8—Case Study Modeling

benthic sediment; impacts in downstream receiving waters; and pollutant contributions from

non-steam-electric sources. 

8.1.5 Limitations of Case Study Modeling

The results of the case study models are intended to illustrate the types and magnitudes of 

environmental impacts that are likely to have occurred, and which may continue to occur, in 

surface waters that receive discharges of the evaluated wastestreams from steam electric power 

plants. Similarly, the case study modeling results provide valuable information regarding the 

relative magnitude of water quality improvements predicted for each of the regulatory options.

In developing the case study models, EPA found it necessary to incorporate several 

assumptions that simplified the modeling approach while introducing uncertainty into the model 

results. For example, due to a lack of data regarding temporal variability in point source 

loadings, EPA assumed that the pollutant loadings from steam electric power plants and other 

point sources are static loadings (i.e., a constant daily average loading rate). This approach does 

not account for temporal variability in the loadings to receiving waters due to factors such as 

variable plant operating schedules, storm flows, low-flow events, and catastrophic events. In

actuality, steam electric power plants and other point sources could adjust wastewater discharge 

rates based on stream flow conditions or other considerations. For instance, a plant could reduce

discharges during periods of low flow in the receiving water and increase discharges during 

periods of high flow, resulting in surface water concentrations that differ from what is predicted

by the case study model. These assumptions influence the relationship between modeled and 

actual surface water concentrations at specific locations and times. 

Appendix G further discusses the limitations and assumptions made in developing the 

case study models and describes in more detail the development of each case study model, 

including input parameters (e.g., pollutant loadings) and model settings. Refer to the Case Study 

Water Quality Modeling Memorandum (DCN SE05570) for discussion of EPA’s technical

approach and data acceptance criteria to incorporate DMR, TRI, and STORET monitoring data. 

8.2 QUANTIFIED ENVIRONMENTAL IMPACTS AND IMPROVEMENTS FROM CASE STUDY 

MODELING

As described in Section 8.1.1, EPA identified six representative case study locations that 

would capture the types of impacts to surface waters associated with steam electric power plant 

discharges, capture the improvements expected across the regulatory options, represent the four 

wastestreams evaluated in the EA, and represent both lentic and lotic systems. Figure 8-1 and 

Table 8-1 present the six receiving waters that EPA selected for case study modeling. 

Section 8.2 introduces each of the six selected case study locations and presents the 

scope, inputs, and modeling results. For each case study, EPA presents: 

 Potential impacts to aquatic life, wildlife, and human health under baseline

conditions; 

 Improvements to aquatic life, wildlife, and human health following compliance with 

the final rule; and

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Section 8—Case Study Modeling

 Comparison of the case study and IRW model results for the case study location. 

Although EPA modeled the expected environmental improvements under Options A 

through D, this section primarily presents the water quality, wildlife, and human health 

improvements under the final rule (Option D). Appendix G of this report includes figures 

illustrating the water column concentrations output for the immediate receiving water both for 

baseline conditions and following compliance with the final rule, for those modeled pollutants 

that exceed one or more water quality benchmarks based on modeling results. These figures

present the National Recommended Water Quality Criteria (NRWQC) and Maximum 

contaminant level (MCL) benchmarks for the modeled pollutant and the steady-state water 

column concentration results from the IRW model. Appendix G also includes the average total 

water column concentration for each of the modeled pollutants in WASP model segments

downstream of the modeled case study plants. 

8.2.1 Black Creek Case Study

Black Creek flows south-southeast through southern Mississippi from Hattiesburg 

through the De Soto National Forest until it converges with the Pascagoula River. Black Creek is 

Mississippi’s only designated National Wild and Scenic River (for 21 miles) under the National 

Wild and Scenic Rivers System Act. South Mississippi Electric Power Association’s R.D. 

Morrow, Sr. (Morrow) Generating Site (Plant ID 1185) is a 400-megawatt (MW) coal-fired 

power plant operating alongside Black Creek near Purvis, Mississippi. Morrow’s two standalone steam turbine generating units reported producing more than 2,000,000 megawatt-hours 

(MWh) of electricity in 2009. Based on data obtained from the Steam Electric Survey, Morrow

Generating Site discharges FGD wastewater, bottom ash transport water, and combustion 

residual leachate directly into Black Creek. Table 8-2 contains some general information on the 

two steam electric generating units at Morrow Generating Site. 

Table 8-2. Summary of Morrow Generating Site Operations

SE Unit Fuel 

Capacity

(MW) Fly Ash Bottom Ash 

FGD 

(Year Installed) 

1 Bituminous coal and

No. 2 fuel oil

200 Dry conveyed Wet handled to 

impoundment

Wet system

(1978) 

2 Bituminous coal and

No. 2 fuel oil

200 Dry conveyed Wet handled to 

impoundment

Wet system

(1978) 

Source: ERG, 2015j. 

Acronyms: FGD (Flue gas desulfurization); MW (Megawatt); SE (steam electric). 

Modeling Area

The Black Creek WASP model encompasses a 95-mile reach of Black Creek, extending 

from the Morrow Generating Site discharge outfall on Black Creek to the confluence of Black 

Creek and Red Creek. The immediate receiving water that Morrow Generating Site discharges to 

is approximately 1.6 miles long, as defined in the WASP model. This modeling area includes the 

21-mile span of the waterway, from Moody’s Landing to Fairley Bridge Landing, that is 

8-15 
Figure 8-2. Black Creek WASP Modeling Area 

Section 8—Case Study Modeling

protected under the National Wild and Scenic River Systems Act. Figure 8-2 illustrates the 

location and extent of the Black Creek WASP model. 

Identified Point Sources and Background Concentrations

As discussed below, EPA reviewed available pollutant loadings (DMR and TRI) and 

monitoring data (STORET) for potential incorporation into the Black Creek WASP model to 

represent pollutant contributions from background and non-steam-electric point sources, and for 

use in calibrating the model results.

 Upstream pollutant contributions. EPA did not identify sufficient STORET 

monitoring data to represent pollutant contributions from upstream of the Morrow 

Generating Site immediate receiving water. EPA did not identify any upstream nonsteam-electric point sources with loadings for the eight modeled pollutants. EPA 

therefore assumed pollutant concentrations of zero within the water column at the 

upstream boundary of the modeling area. 

 Downstream pollutant contributions. EPA incorporated STORET data from eight 

monitoring stations to represent the pollutant contributions flowing into the modeling 

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Section 8—Case Study Modeling

area downstream of the Morrow Generating Site immediate receiving water (i.e., 

tributaries flowing into Black Creek). EPA did not identify any non-steam-electric 

point sources whose pollutant loadings would significantly influence the model 

results in the downstream modeling area. 

 Monitoring data within the modeling area. EPA compiled STORET data from two 

monitoring stations located within the modeling area and used these data to calibrate 

the WASP model. 

Modeling Period

The modeling period starts in 1982 (the year of the last revision to the steam electric 

ELGs) and extends through 2036, covering a period of 55 years. Based on Morrow Generating 

Site’s NPDES permitting cycle, EPA assumes that the plant will achieve the limitations under 

the final rule by 2019. 

Modeling Results - Water Quality

Under baseline conditions, the modeled pollutant concentrations in the immediate 

receiving water and downstream reaches exceed the NRWQC water quality benchmarks for four 

modeled pollutants, indicating that pollutant loadings from the Morrow Generating Site may 

quantifiably reduce water quality in the modeled portions of Black Creek. The reduced water 

quality is primarily attributed to arsenic, cadmium, selenium, and thallium. Intervals of higher 

pollutant concentrations occur during periods of low flow in Black Creek for all eight modeled 

pollutants. 

The baseline modeled pollutant concentrations exceed human health criteria primarily for 

arsenic, thallium, and selenium, as discussed below: 

 Arsenic concentrations in the immediate receiving water exceed the water quality

benchmark for consumption of water and organisms (0.018 micrograms per liter

(μg/L)) for 99 percent of the modeling period. These exceedances continue

downstream, generally at a reduced frequency, throughout the entire 95-mile-long 

modeling area downstream of the plant. 

 Arsenic concentrations in the immediate receiving water also exceed the higher water 

quality benchmark for consumption of organisms only (0.14 μg/L) for 16 percent of

the modeling period. These exceedances continue downstream, at a reduced

frequency, throughout the entire 95-mile-long modeling area downstream of the plant. 

 Thallium concentrations in the immediate receiving water exceed the water quality 

benchmark for consumption of water and organisms (0.24 μg/L) for 17 percent of the 

modeling period. These exceedances continue downstream, at a reduced frequency,

throughout the entire 95-mile-long modeling area downstream of the plant. 

 Thallium concentrations in the immediate receiving water also exceed the higher

water quality benchmark for consumption of organisms only (0.47 μg/L) for 1 percent

of the modeling period. These exceedances continue downstream throughout the 

entire 95-mile-long modeling area downstream of the plant. The frequency of 

8-17 
Section 8—Case Study Modeling

exceedances downstream ranges from less than 1 percent to 3 percent of the modeling 

period. 

 On rare occasions (less than 1 percent of the modeling period), selenium

concentrations in reaches downstream of the immediate receiving water exceed the 

water quality benchmark for consumption of water and organisms (170 μg/L). These 

exceedances occur in 5.3 miles of the modeling area downstream of the plant and up

to 88 miles downstream of the plant. 

These case study modeling results indicate that, under baseline conditions, humans 

consuming water and/or organisms inhabiting these modeled portions of Black Creek could be at 

an elevated risk of the negative effects associated with oral exposure to these pollutants (see 

Section 3.1.1). 

Aquatic organisms may be at risk for exposure to cadmium and selenium under baseline 

conditions, as discussed below: 

 Cadmium concentrations in the immediate receiving water exceed the freshwater

aquatic life criteria for chronic exposure (0.25 μg/L) for 39 percent of the modeling 

period. These exceedances continue downstream, at a reduced frequency, throughout 

28 miles of the modeling area downstream of the plant. 

 Selenium concentrations in the immediate receiving water exceed the freshwater 

aquatic life criteria for chronic exposure (5.0 μg/L) for 43 percent of the modeling 

period. These exceedances continue downstream throughout the entire 95-mile-long 

modeling area downstream of the plant. The frequency of exceedances downstream 

ranges from 2 percent to 51 percent of the modeling period. 

These case study modeling results indicate that, under baseline conditions, aquatic 

organisms inhabiting these modeled portions of Black Creek could be at an elevated risk of the 

negative effects associated with oral exposure to these pollutants (see Section 3.1.1). 

Under baseline conditions, the modeled pollutant concentrations in the immediate 

receiving water and downstream reaches occasionally exceed the MCL drinking water 

benchmarks for three modeled pollutants. The baseline modeled pollutant concentrations exceed 

drinking water criteria for cadmium, selenium, and thallium, as discussed below: 

 On rare occasions (less than 1 percent of the modeling period), cadmium 

concentrations in the immediate receiving water exceed the MCL benchmark (5

μg/L). These exceedances continue downstream throughout the entire 95- mile-long 

modeling area downstream of the plant. The frequency of exceedances downstream 

ranges from less than 1 percent to 5 percent of the modeling period. 

 On rare occasions (less than 1 percent of the modeling period), selenium

concentrations in the immediate receiving water exceed the MCL benchmark (50 

μg/L). These exceedances continue downstream, generally at a reduced frequency, in

93 miles of the modeling area downstream of the plant. 

 On rare occasions (less than 1 percent of the modeling period), thallium 

concentrations in downstream reaches of the modeling area exceed the MCL (2 

8-18 
Section 8—Case Study Modeling

μg/L). These exceedances occur in 8.9 miles of the modeling area downstream of the 

plant and up to 92 miles downstream of the plant. 

Modeling results do not indicate any exceedances of NRWQC or MCL criteria for the 

other modeled pollutants (copper, nickel, lead, and zinc). Appendix G of this report includes 

figures that illustrate the water column pollutant concentration output for the immediate

receiving water for arsenic, cadmium, selenium, and thallium. These figures also present the

NRWQC and MCL benchmarks for the pollutant and the steady-state water column pollutant 

concentrations predicted by the IRW model. 

The final rule modeling results show significantly decreased concentrations of all 

modeled pollutants in the immediate receiving water, which will greatly improve water quality.

These pollutant removals result in fewer exceedances of NRWQC and MCL benchmarks 

compared to those estimated in the baseline modeling. Case study modeling results for Black 

Creek reveal the following water quality improvements under the final rule: 

 For arsenic: 

- Exceedances of the human health water quality benchmark for consumption of 

water and organisms reduce in frequency from 99 percent to 94 percent of the 

modeling period in the immediate receiving water. Additionally, the exceedances 

of this benchmark reduce in frequency in all remaining sections of the 

downstream modeling area following compliance with the final rule. Despite the 

continued exceedances of this human health criteria, reducing the pollutant 

concentrations in the water column may decrease the risk to humans consuming 

contaminated water and organisms. 

- Exceedances of the human health water quality benchmark for consumption of 

organisms reduce in frequency from 16 percent to 6 percent of the modeling 

period in the immediate receiving water. Additionally, the exceedances of this 

benchmark reduce in frequency in all remaining sections of the downstream

modeling area following compliance with the final rule. Despite the continued 

exceedances of this human health criteria, reducing the pollutant concentrations in 

the water column may decrease the risk to humans consuming contaminated 

organisms. 

 For cadmium:

- Exceedances of the aquatic life water quality criteria for chronic impacts are 

eliminated throughout the entire modeling area. 

- Exceedances of the MCL benchmark are eliminated throughout the entire 

modeling area. 

 For selenium:

- Exceedances of the human health water quality benchmark for consumption of 

water and organisms are eliminated throughout the entire modeling area. 

- Exceedances of the MCL benchmark are eliminated throughout the entire 

modeling area. 

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Section 8—Case Study Modeling

- Exceedances of the aquatic life water quality criteria for chronic impacts are 

eliminated in 13 miles of the modeling area, including the immediate receiving 

water. The exceedances of this benchmark reduce in frequency to less than 4 

percent in all remaining sections of the downstream modeling area following 

compliance with the final rule. Most of these exceedances occur within the first 

year following compliance with the final rule (due to the gradual recovery of the 

system following the pollutant loading removals). Despite the continued 

exceedances of these human health criteria, reducing the pollutant concentrations 

in the water column may decrease risk to humans consuming contaminated water 

and/or organisms. 

 For thallium:

- Exceedances of the MCL benchmark are eliminated throughout the entire 

modeling area. 

- Exceedances of the human health water quality benchmark for consumption of 

water and organisms reduce in frequency from 17 percent to less than 1 percent of

the modeling period in the immediate receiving water. Additionally, the 

exceedances of this benchmark reduce in frequency in all remaining sections of 

the downstream modeling area following compliance with the final rule. Despite 

the continued exceedances of this human health criteria, reducing the pollutant 

concentrations in the water column may decrease the risk to humans consuming 

contaminated water and organisms. 

- Exceedances of the human health water quality benchmark for consumption of 

organisms are eliminated in 6.2 miles of the modeling area, including the 

immediate receiving water. Additionally, the exceedances of these benchmarks 

reduce in frequency in all remaining sections of the downstream modeling area 

following compliance with the final rule. Despite the continued exceedances of 

this human health criteria, reducing the pollutant concentrations in the water 

column may decrease risk to humans consuming contaminated organisms. 

Modeling Results – Wildlife

EPA assessed the potential threat to piscivorous wildlife from the evaluated wastestreams 

by modeling the average pollutant concentrations in the water column and comparing these to the 

concentrations that would trigger exceedances of no effect hazard concentrations (NEHC) for

minks and eagles developed by the USGS. Under baseline conditions, Black Creek may pose a

risk to minks and eagles that consume fish contaminated with selenium. The average modeled 

selenium concentrations in 90 miles of the Black Creek modeling area are greater than the

concentration that would translate to NEHC exceedances for minks and eagles, demonstrating 

that the fish inhabiting these portions of Black Creek may pose a potential reproductive threat to 

terrestrial food webs. 

EPA also assessed the potential impact to wildlife exposed to sediments in surface waters 

by comparing estimated pollutant concentrations in the sediment to sediment biota CSCL 

benchmarks. Modeling results demonstrate that cadmium concentrations in the upper benthic 

sediment of the immediate receiving water exceed the CSCL criteria (0.596 mg/kg) during 36 

8-20 
Section 8—Case Study Modeling

percent of the modeling period. These exceedances continue downstream for 36 miles of the total 

modeling area. 

Ecological risk modeling results indicate that baseline selenium loadings also present an

elevated risk of widespread negative reproductive impacts (larval mortality and deformities) 

among fish that inhabit the immediate receiving water of Black Creek. The results illustrate the

significant increase in risk that can result from minor variations in selenium bioaccumulation 

patterns and toxicity responses within the organisms that inhabit a particular waterbody. 

Specifically: 

 The median (50th percentile) of the model outputs indicates that selenium

concentrations in the fish eggs and ovaries would cause reproductive impacts in less

than 1 percent of the exposed fish population. 

 However, there is a 35 percent probability that these concentrations are high enough 

to cause reproductive impacts in more than 30 percent of the exposed fish population. 

 There is a 25 percent probability that these concentrations are high enough to cause 

reproductive impacts in more than 80 percent of the exposed fish population. 

Ecological risk modeling results also indicate an elevated risk of widespread negative

reproductive impacts (hatching failure) among mallards that forage or breed in the immediate 

receiving water of Black Creek. Specifically: 

 There is a 50 percent probability that selenium concentrations in the mallard eggs are

high enough to cause reproductive impacts in at least 9 percent of the exposed 

mallard population. 

 There is a 35 percent probability that these concentrations are high enough to cause 

reproductive impacts in more than 20 percent of the exposed mallard population. 

 There is a 10 percent probability that these concentrations are high enough to cause 

reproductive impacts in more than 70 percent of the exposed mallard population. 

Elevated risks of reproductive impacts to fish and mallards continue downstream from 

the immediate receiving water. Ecological risk modeling results indicate that the entire 95-mile 

modeled length of Black Creek has selenium concentrations that lead to a 10 percent or greater

probability of negative reproductive impacts among at least 17 percent of the exposed fish or 

mallard populations. Additionally, several downstream segments of Black Creek (totaling 29

miles) have selenium concentrations that lead to a 25 percent or greater probability of negative

reproductive impacts among at least 10 percent of the exposed mallard population. 

The case study modeling results demonstrate that the final rule will significantly reduce 

pollutant concentrations and the associated impacts to wildlife that inhabit Black Creek. The 

final rule will eliminate selenium exceedances of the NEHC benchmarks for minks and eagles in

all modeled reaches of Black Creek. The final rule will also eliminate CSCL benchmark 

exceedances for cadmium in 27 miles of the modeling area, including the immediate receiving

water. The exceedances of this benchmark reduce in frequency to 3 percent or less in all 

remaining sections of the downstream modeling area following compliance with the final rule. 

Most of these remaining exceedances occur within the first year following compliance with the 

8-21 
Section 8—Case Study Modeling

final rule. Ecological risk modeling results also indicate that the final rule will eliminate the risk

of selenium-related adverse reproductive impacts among exposed fish and mallards in all 

modeled reaches of Black Creek (i.e., the risk to fish and mallards is less than 0.1 percent at the 

95th percentile egg/ovary concentration). 

Modeling Results – Human Health

EPA evaluated the potential threat to human receptors due to consumption of 

contaminated fish from Black Creek. EPA modeled the average pollutant concentrations in the 

water column and compared these to the concentrations that would trigger exceedances of either 

the non-cancer reference dose or the 1-in-a-million lifetime excess cancer risk (LECR). Under 

baseline conditions, the average water column concentration of arsenic throughout the modeling 

area downstream of the plant does not result in an estimated cancer risk greater than 1-in-amillion for any of the national-scale cohorts. See Appendix E for details on the human health 

module of the IRW model and national-scale cohorts. 

Based on the average pollutant concentrations in the water column under baseline 

conditions, cadmium, selenium, and thallium pose the greatest threat to cause non-cancer health 

effects in humans from fish consumption, as discussed below:

 Average thallium concentrations in the water column throughout the entire 95-milelong modeling area are greater than the concentration that would translate to 

exceedance of the reference doses for at least one child subsistence fisher cohort 

(with all child subsistence cohorts impacted by 59 or more miles of the modeling area

downstream of the plant), while the concentrations in 90 miles of the modeling area

are high enough to trigger exceedance of the reference dose for adult subsistence 

fishers. Additionally, the average thallium concentrations in 59 miles of the modeling 

area are high enough to trigger exceedance of the reference dose for at least one child 

recreational fisher cohort. 

 Average selenium concentrations in the water column throughout the entire 95-milelong modeling area are greater than the concentration that would translate to 

exceedance of the reference dose for the adult subsistence fisher cohorts and at least 

one child subsistence fisher cohort (with all child subsistence cohorts impacted by 90 

or more miles). Additionally, the average selenium concentrations are high enough to 

trigger exceedances of the reference doses for adult recreational fishers and at least 

one child recreational fisher cohort in 13 miles and 90 miles of the modeling area, 

respectively.

 Average cadmium concentrations in the water column in 38 miles of the modeling 

area are greater than the concentration that would translate to exceedance of the 

reference dose for at least one child subsistence fisher cohort. 

Therefore, humans who consume cadmium-, selenium-, or thallium-contaminated fish 

inhabiting these waters may be at greater risk for developing the negative health effects 

associated with these pollutants, which are discussed in Section 3.1.1. 

8-22 
Section 8—Case Study Modeling

The modeling results demonstrate significant reductions in average water column 

concentrations of cadmium, selenium, and thallium under the final rule, which would reduce 

average cadmium and selenium concentrations enough to eliminate the risk for non-cancer health 

effects for all cohorts throughout the entire modeling area. These loadings reductions would also 

reduce the thallium concentrations enough to eliminate the risk for non-cancer health effects for

adult subsistence and child recreational fishers. While the case study model continues to show 

average thallium concentrations that may pose non-cancer health effects for at least one child 

subsistence cohort, the total area of impact is reduced by up to 37 miles (with some child 

subsistence cohort non-cancer risks being eliminated throughout the entire modeling period 

downstream of the plant). 

Interpretation of Black Creek Results

Case study modeling results for Black Creek indicate greater water quality, wildlife, and 

human health impacts to the immediate receiving water under baseline conditions than predicted

by the IRW model. Case study modeling results for Black Creek also demonstrate water quality 

benchmark exceedances and risks to wildlife and humans sustaining beyond Morrow Generating 

Site’s immediate receiving water. In some instances, the average water column concentrations

can increase in some portions of the downstream modeling area, posing a greater threat to 

humans, aquatic organisms, and terrestrial ecosystems. This phenomenon is most pronounced for

modeled pollutants with the largest partition coefficients (i.e., lead, zinc, cadmium, and copper) 

suggesting that sediment transport has significant influence in this small receiving water. Under 

baseline conditions, significant water quality, wildlife, and human health impacts are identified 

in the modeled area corresponding with 21-mile span of the waterway that is protected under the 

National Wild and Scenic River Systems Act. 

Ecological risk modeling results for the Black Creek case study indicate that the risk of 

negative reproductive effects among fish and mallards exposed to selenium may be significantly 

greater than predicted using water quality outputs from the IRW model. Use of the case study 

water quality outputs, which include extended periods of elevated selenium concentrations that 

are not reflected in the IRW model outputs, reveals the potential for widespread ecological 

impacts among wildlife that inhabit, forage, or breed in the immediate receiving water of Black 

Creek and its downstream waters. 

The USGS stream gage flow data used in the case study model indicate that flow rates in 

Black Creek are typically lower than the annual average flow rate used in the IRW model, while 

greatly exceeding the annual average flow rate during occasional high-flow events. During the 

frequent periods of below-average flow, the pollutant concentrations in the modeling area

quickly climb to levels associated with negative impacts to fish, wildlife, and humans. 

The exceedances identified in the Black Creek WASP model are based solely on 

discharges of the evaluated wastestreams from the steam electric power plant because EPA did 

not identify any STORET monitoring data or point sources suggesting any other sources were 

contributing pollutant discharges to the modeling area. The Black Creek WASP model may be

underestimating the pollutant concentrations actually present if there are other discharges that 

were not captured in the DMR and TRI data sets. Under the final rule, case study modeling of 

Black Creek indicates that the waterbody will exhibit fewer exceedances of water quality

8-23 
 

Section 8—Case Study Modeling

benchmarks; will no longer pose reproductive risks to higher trophic-level wildlife; will pose less 

risk to benthic organisms; and will pose less risk to humans consuming fish. The extent of

improvements identified by the case study model is greater than what was projected by the IRW 

model. The decrease of the average pollutant concentrations within the immediate receiving 

water occurs very quickly after compliance with the final rule; however, some downstream 

reaches of the modeling area take up to a year to reach equilibrium. 

8.2.2 Etowah River Case Study

The Etowah River is a 164-mile-long waterway north of Atlanta, Georgia. The river 

flows west-southwest from Amicalola Creek, the primary tributary, to Rome, Georgia, where it 

meets the Oostanaula River and forms the Coosa River at their confluence. Once estimated to

have 91 native fish species, the Etowah watershed is biologically one of the richest river systems 

in North America. Eight imperiled fish species, 

three of which are federally listed as endangered 

or threatened, are known to inhabit the Etowah 

watershed, and five mollusk species are believed 

to have been decimated [Etowah Aquatic 

Habitat Conservation Plan, 2015]. 

The Etowah River serves as a source of 

cooling water for, and receives steam electric 

wastewater discharges from, Southern 

Company’s Plant Bowen (Plant ID 2244), 

located in Cartersville, Georgia. In commercial 

operation since 1975, Plant Bowen is bordered 

on two sides by the Etowah River and Euharlee 

Creek. Plant Bowen’s four stand-alone steam

turbine generating units have a total nameplate

capacity of 3,499 MW. As the nation’s ninthlargest power plant in net generation of electricity, Plant Bowen reported producing almost 

23,000,000 MWh of electricity in 2009 [Georgia Power, 2014]. Based on data EPA obtained in 

responses to the Steam Electric Survey, Plant Bowen discharges two of the evaluated 

wastestreams, FGD wastewater and bottom ash transport water, directly to the Etowah River. 

Table 8-3 contains general information on the four steam electric generating units at Plant

Bowen. 

In estimating the historical pollutant loadings associated with Plant Bowen’s four FGD 

systems, EPA incorporated the pollutant loadings from FGD wastewater as the systems were 

installed, between 2008 and 2011. EPA did not model any FGD wastewater pollutant loadings 

before the installation of Plant Bowen’s first FGD system. 

Georgia Power Company’s Plant Bowen

8-24 
 

 

 

 

Section 8—Case Study Modeling

Table 8-3. Summary of Plant Bowen Operations 

SE Unit Fuel Capacity (MW) Fly Ash Bottom Ash FGD 

(Year Installed) 

1 Bituminous coal and

No. 2 fuel oil

806 Dry conveyed Wet handled to 

impoundment

Wet system

(2010) 

2 Bituminous coal and

No. 2 fuel oil

789 Dry conveyed Wet handled to 

impoundment

Wet system

(2009) 

3 Bituminous coal and

No. 2 fuel oil

952 Dry conveyed Wet handled to 

impoundment

Wet system

(2008) 

4 Bituminous coal and

No. 2 fuel oil

952 Dry conveyed Wet handled to 

impoundment

Wet system

(2008) 

Source: ERG, 2015j. 

Acronyms: FGD (Flue gas desulfurization); MW (Megawatt); SE (steam electric). 

Modeling Area

The Etowah River WASP model encompasses a 35-mile segment of the Etowah River, 

extending from the immediate receiving water to the confluence of the Etowah River and Silver 

Creek. The immediate receiving water to which Plant Bowen discharges is approximately 3.6 

miles long, as defined in the WASP model. Figure 8-3 illustrates the location and extent of the 

Etowah River WASP model. 

8-25 
Figure 8-3. Etowah River WASP Modeling Area 

Section 8—Case Study Modeling

Identified Point Sources and Background Concentrations

As discussed below, EPA reviewed available pollutant loadings (DMR and TRI) and 

monitoring data (STORET) for potential incorporation into the Etowah River WASP model to

represent pollutant contributions from background and non-steam-electric point sources, and for 

use in calibrating the model results.

 Upstream pollutant contributions. EPA incorporated STORET data from four 

monitoring stations to represent the pollutant contributions from upstream of the Plant 

Bowen immediate receiving water. EPA also identified two upstream non-steamelectric point sources whose pollutant loadings (from DMR and TRI data sets) could 

influence the model results; however, EPA assumed that the STORET data from the 

four monitoring stations (which encompass all of the modeled pollutants except for

selenium) adequately reflect the pollutant contributions from upstream point sources. 

Therefore, EPA did not incorporate pollutant loadings from the two identified 

upstream non-steam-electric point sources. 

8-26 
 

Section 8—Case Study Modeling

 Downstream pollutant contributions. EPA incorporated STORET data from 10 

monitoring stations to represent the pollutant concentrations flowing into the 

modeling area downstream of the Plant Bowen immediate receiving water (i.e., 

tributaries flowing into the Etowah River). EPA did not identify any non-steamelectric point sources whose pollutant loadings would significantly influence the

model results in the downstream modeling area. 

 Monitoring data within the modeling area. EPA compiled STORET data from six 

monitoring stations located within the modeling area and used these data to calibrate 

the WASP model. 

The contributions of arsenic, cadmium, copper, lead, and thallium from upstream sources 

have a much greater influence on the modeled pollutant concentrations in the Etowah River than 

the pollutant loadings from Plant Bowen. The contributions of nickel and zinc from upstream

sources also strongly influence the modeled pollutant concentrations in the Etowah River. 

The Etowah River case study model did not account for the documented surface water 

impacts from Plant Bowen that are discussed in Section 3.3.3. In 2002, a sinkhole developed in 

the surface impoundment at Plant Bowen that released 2.25 million gallons of ash/water mixture,

estimated to contain 80 tons of ash, to Euharlee Creek, which immediately flows into the Etowah

River [U.S. EPA, 2014b]. Additionally, an extreme rainfall event in 2008 caused a dry ash 

stockpile to collapse, depositing approximately two tons of ash in Euharlee Creek. The surface

water quality impacts resulting from these events are not reflected in this model; therefore, the

case study modeling could under-represent the actual baseline impacts of Plant Bowen on the 

Etowah River. 

Modeling Period

The modeling period starts in 1982 (the year of the last revision to the steam electric 

ELGs) and extends through 2032, covering a period of 51 years. Based on Plant Bowen’s 

NPDES permitting cycle, EPA assumes that the plant will achieve the limitations under the final 

rule by 2021. 

Modeling Results – Water Quality

Under baseline conditions, the modeled pollutant concentrations in the immediate 

receiving water and downstream reaches exceed the NRWQC water quality benchmarks for five 

modeled pollutants, indicating that pollutant loadings from Plant Bowen may contribute to a 

quantifiable reduction in water quality in the modeled portions of the Etowah River. The reduced 

water quality is primarily attributed to arsenic, cadmium, selenium, thallium, and lead.

The baseline modeled water concentrations exceed human health criteria primarily for 

arsenic and thallium, as discussed below: 

 Arsenic concentrations in the immediate receiving water exceed the water quality

benchmark for consumption of water and organisms (0.018 μg/L) for the entire 

modeling period. These exceedances continue downstream, at the same frequency,

throughout the entire 35-mile-long modeling area downstream of the plant. 

8-27 
Section 8—Case Study Modeling

 Arsenic concentrations in the immediate receiving water also exceed the higher water 

quality benchmark for consumption of organisms only (0.14 μg/L) for the entire 

modeling period. These exceedances continue downstream, at the same frequency,

throughout the entire 35-mile-long modeling area downstream of the plant. 

 Thallium concentrations in the immediate receiving water exceed the water quality 

benchmarks for consumption of water and organisms (0.24 μg/L) for more than 99 

percent of the modeling period. These exceedances continue downstream, at an 

increased frequency, throughout the entire 35-mile-long modeling area downstream 

of the plant. 

 Thallium concentrations in the immediate receiving water also exceed the higher

water quality benchmark for consumption of organisms only (0.47 μg/L) for 90 

percent of the modeling period. These exceedances continue downstream, at an 

increased frequency, throughout the entire 35-mile-long modeling area downstream 

of the plant. 

These case study modeling results indicate that, under baseline conditions, humans 

consuming water and/or organisms inhabiting these modeled portions of the Etowah River may 

be more at risk of the negative effects associated with oral exposure to arsenic and thallium (see 

Section 3.1.1). 

Aquatic organisms may be at risk for exposure to cadmium and selenium under baseline 

conditions, specifically: 

 Cadmium concentrations in the immediate receiving water exceed the freshwater

aquatic life criteria for chronic exposure (0.25 μg/L) for 52 percent of the modeling 

period. These exceedances continue downstream throughout the 35-mile-long 

modeling area downstream of the plant. The frequency of exceedances downstream 

ranges from 33 percent to 55 percent of the modeling period. 

 On rare occasions (less than 1 percent of the modeling period), selenium

concentrations in downstream reaches of the modeling area exceed the freshwater 

aquatic life criteria for chronic exposure (5 μg/L). These exceedances occur in 4.7 

miles of the downstream modeling area downstream of the plant and up to 35 miles 

downstream of the plant. 

These modeling results indicate that, under baseline conditions, aquatic organisms 

residing in the portions of the Etowah River with modeled exceedances may be more at risk to 

negative impacts from chronic exposure to cadmium and selenium. 

Under baseline conditions, the modeled pollutant concentrations in the immediate 

receiving water and downstream reaches exceed the MCL drinking water benchmarks for four 

modeled pollutants. The baseline modeled pollutant concentrations exceed drinking water 

criteria for thallium, arsenic, cadmium and lead as discussed below: 

 Thallium concentrations in the immediate receiving water exceed the MCL 

benchmark (2 μg/L) for 29 percent of the modeling period. These exceedances 

8-28 
Section 8—Case Study Modeling

continue downstream, at a reduced frequency, throughout the entire 35-mile-long 

modeling area downstream of the plant. 

 On rare occasions (less than 1 percent of the modeling period), arsenic concentrations

in the immediate receiving water exceed the MCL benchmark (10 μg/L). These 

exceedances do not occur beyond the 3.6-mile-long immediate receiving water.

 On rare occasions (less than 1 percent of the modeling period), cadmium 

concentrations in downstream reaches of the modeling area exceed the MCL 

benchmark (5 μg/L). These exceedances occur in 5.1 miles of the downstream

modeling area downstream of the plant and up to 35 miles downstream of the plant. 

 On rare occasions (less than 1 percent of the modeling period), lead concentrations in 

downstream reaches of the modeling area exceed the MCL benchmark (15 μg/L).

These exceedances occur in 5.1 miles of the downstream modeling area downstream 

of the plant and up to 35 miles downstream of the plant. 

Modeling results do not indicate any exceedances of NRWQC or MCL criteria for the 

other modeled pollutants (copper, nickel, and zinc). Appendix G of this report includes figures 

that illustrate the water column pollutant concentration output for the immediate receiving water 

for arsenic, cadmium, selenium, and thallium. These figures also present the NRWQC and MCL

benchmarks for the pollutant and the steady-state water column pollutant concentrations

predicted by the IRW model. 

The final rule modeling results show a significant reduction in selenium concentrations

and moderately decreased concentrations of cadmium, nickel, and zinc within the Etowah River, 

which will improve water quality. These pollutant removals result in fewer exceedances of

NRWQC and MCL benchmarks compared to those estimated in the baseline modeling. Case 

study modeling results for the Etowah River reveal the following water quality improvements 

under the final rule: 

 Exceedances of the cadmium aquatic life water quality criteria for chronic impacts 

reduce in frequency (by 13 percent) in the immediate receiving water. Additionally, 

the exceedances of these benchmarks reduce in frequency in all remaining sections of 

the downstream modeling area following compliance with the final rule. Despite 

continued exceedances of these aquatic life criteria, reducing the pollutant

concentrations in the water column may decrease the risk to aquatic life in the Etowah 

River. 

 Exceedances of the selenium aquatic life water quality criteria for chronic impacts are 

eliminated throughout the entire modeling area. 

While case study modeling results continue to show exceedances for NRWQC 

benchmark exceedances of arsenic and thallium and MCL benchmark exceedances of arsenic, 

cadmium, lead, and thallium, the final rule will reduce loading contributions of these pollutants 

from Plant Bowen. 

8-29 
Section 8—Case Study Modeling

Modeling Results – Wildlife

Based on the average pollutant concentrations in the water column under baseline 

conditions, the modeled portion of the Etowah River does not exceed the concentrations that 

would translate to NEHC exceedances and does not pose a risk to minks and eagles that consume 

contaminated fish. Despite the modeling not being able to quantify any improvements to minks 

and eagles under the final rule, the pollutant loading removals will decrease bioaccumulation of

toxic pollutants in the terrestrial food chains. 

Modeling results do not indicate that there are any pollutant concentrations in the upper 

benthic sediment that exceed CSCL benchmarks of for any of the eight modeled pollutants;

therefore, the Etowah River does not pose a threat to benthic organisms in contact with 

contaminated sediment. Despite the modeling not being able to quantify any improvements to 

benthic organisms under the final rule, the pollutant loading removals will decrease the

concentrations of toxic pollutants in benthic sediment and decrease the exposure of organisms to 

these pollutants. 

Modeling Results – Human Health

EPA modeled the average pollutant concentrations in the water column and compared

these to the concentrations that would trigger exceedances of either the non-cancer reference 

dose or the 1-in-a-million lifetime excess cancer risk (LECR). Under baseline conditions, the

average water column concentration of arsenic in the immediate receiving water over the

modeling period results in an estimated cancer risk greater than 1-in-a-million for adult 

subsistence fishers. These exceedances do not occur beyond the 3.6-mile-long immediate 

receiving water. Therefore, adults who frequently consume arsenic-contaminated fish inhabiting 

the immediate receiving water may be at greater risks for development of cancer. Modeling 

results demonstrate no reduction in the cancer risk from inorganic arsenic under the final rule.

Based on the average pollutant concentrations in the water column under baseline 

conditions, selenium and thallium pose the greatest threat to cause non-cancer health effects in 

humans from fish consumption, as discussed below: 

 Average selenium concentrations in the immediate receiving water are greater than 

the concentrations that would translate to exceedance of the reference doses for the

child (younger than 11 years old) subsistence fisher cohorts. The average selenium 

concentrations throughout the entire 35-mile-long modeling area downstream of the 

plant are greater than the concentration that would translate to an exceedance of the 

reference dose for least one child subsistence cohort.

 Average thallium concentrations in the water column throughout the entire 35-milelong modeling area downstream of the plant are greater than the concentrations that 

would translate to exceedance of the reference doses for adult and children 

recreational and subsistence fishers (all national-scale cohorts evaluated). 

Therefore, humans who consume selenium- or thallium-contaminated fish inhabiting the

modeled area of the Etowah River may be at greater risk for developing the negative health 

effects associated with these pollutants, which are discussed in Section 3.1.1. 

8-30 
Section 8—Case Study Modeling

The final rule modeling results demonstrate significant reductions in selenium

concentrations in the Etowah River, which will eliminate selenium exceedances of the noncancer health effects reference dose for all cohorts. While the modeling results continue to show 

thallium water concentrations that would translate to exceedances of the non-cancer health 

effects reference dose, the final rule will reduce thallium loading contributions from Plant 

Bowen. 

Interpretation of Etowah River Results

Case study modeling results for the Etowah River indicate greater water quality and 

human health impacts than predicted by the IRW model (IRW modeling results did not indicate 

any quantifiable impacts in the immediate receiving water of Plant Bowen). By accounting for 

background pollutant contributions from upstream sources and other boundaries (for all modeled 

pollutants except selenium), case study modeling predicts higher pollutant concentrations under 

baseline conditions. For arsenic and thallium, and to a lesser extent cadmium, the projected

exceedances are driven by the background concentrations flowing into the Etowah River

modeling area. Plant Bowen’s discharges of the evaluated wastestreams may be further 

impairing the degraded waterway. 

Case study modeling results for the Etowah River also demonstrate water quality 

benchmark exceedances and risks to humans occur beyond Plant Bowen’s immediate receiving

water. In some instances, the average water column concentrations can increase in some portions 

of the downstream modeling area, posing a greater threat to humans and aquatic life. This

phenomenon is most pronounced for modeled pollutants with the largest partition coefficients 

(i.e., lead, zinc, cadmium, and copper), suggesting that sediment transport has moderate 

influence in the Etowah River. 

Case study modeling of the Etowah River indicates that, under the final rule, the Etowah

River will exhibit fewer exceedances of water quality benchmarks and pose less risk to humans 

consuming fish that inhabit these waters. The improvements identified by the case study model 

are more extensive than what was projected by the IRW model. This is due in part to the greater

water quality and human health impacts under baseline conditions, which created additional 

opportunities for modeled improvements, and in part to the identified improvements in 

downstream reaches of the Etowah River that were not evaluated as part of the IRW model. The 

average pollutant concentrations throughout the entire modeling area reduce promptly after 

compliance with the final rule.

8.2.3 Lick Creek & White River Case Study

The White River is a two-forked river that primarily flows southwest through central and 

southern Indiana. The two forks, the West Fork and the East Fork, are nearly equal in size when 

they converge in Daviess Country, just north of Petersburg, Indiana. From this confluence, the 

White River flows west-southwest for 50 river-miles until it joins the Wabash River at the 

Illinois-Indiana state border. Located on the banks of the lower White River, Indianapolis Power 

& Light’s (IPL) Petersburg Generating Station (Plant ID 3997) has four stand-alone steam 

turbine units with a nameplate capacity of 1,864 MW. The plant reported that these four coalfired generating units produced more than 12,000,000 MWh of electricity in 2009 in the Steam 

8-31 
 

 

 

 

 

Section 8—Case Study Modeling

Electricity Survey. Petersburg Generating Station also operates three minor oil-burning internal 

combustion units, which are exempt from the requirements of the final rule. Based on data 

obtained in responses to the Steam Electric Survey, this power plant discharges FGD wastewater 

and bottom ash transport water. Table 8-4 

contains general information on the four coalfired generating units at Petersburg Generating 

Station. 

In estimating the historical pollutant

loadings associated with Petersburg Generating 

Station’s four FGD systems, EPA incorporated

the pollutant loadings from FGD wastewater as 

the systems were installed, between 1977 and 

1996. EPA included the pollutant loadings from 

the FGD systems on units 3 and 4 at the start of 

the historical modeling period (1986).

Table 8-4. Summary of Petersburg Generating Station Operations

IPL’s Petersburg Generating Station 

SE Unit Fuel 

Capacity

(MW) Fly Ash a Bottom Ash 

FGD 

(Year Installed) 

1 Subbituminous coal

and No. 2 fuel oil 

255 Dry conveyed Wet handled to 

impoundment

Wet system

(05/1996) 

2 Subbituminous coal

and No. 2 fuel oil 

445 Dry conveyed Wet handled to 

impoundment

Wet system

(05/1996) 

3 Subbituminous coal

and No. 2 fuel oil 

580 Dry conveyed Wet handled to 

impoundment

Wet system

(11/1977) 

4 Subbituminous coal

and No. 2 fuel oil 

584 Dry conveyed Wet handled to 

impoundment

Wet system

(04/1986) 

Source: ERG, 2015j. 

Acronyms: FGD (Flue gas desulfurization); MW (Megawatt); SE (steam electric). 

a – Based on EPA projections, Petersburg Generating Station will convert to dry ash handling to comply with the 

CCR rulemaking. 

Modeling Area

Based on data obtained in responses to the Steam Electric Survey, Petersburg Generating 

Station discharges FGD wastewater and bottom ash transport water to Lick Creek, a 1.8-milelong tributary emptying into the White River. The White River WASP model encompasses Lick 

Creek and a 52-mile reach of the White River, 49 miles of which is downstream of Lick Creek. 

The immediate receiving water, Lick Creek, is the first of three upstream modeling boundaries 

for this WASP model. The other upstream model boundaries are on the West Fork White River 

and East Fork White River approximately one mile upstream of their confluence. EPA extended 

the modeling area upstream of Lick Creek to capture and incorporate available STORET 

monitoring data as further described below. The Lick Creek and White River WASP model ends 

8-32 
Figure 8-4. Lick Creek and White River WASP Modeling Area 

Section 8—Case Study Modeling

at the confluence of the White River with the Wabash River. Figure 8-4 illustrates the location 

and extent of the White River WASP model. 

Identified Point Sources and Background Concentrations

As discussed below, EPA reviewed available pollutant loadings (DMR and TRI) and 

monitoring data (STORET) for potential incorporation into the Lick Creek and White River

WASP model to represent pollutant contributions from background and non-steam-electric point 

sources, and for use in calibrating the model results. 

 Upstream pollutant contributions (Lick Creek). EPA did not identify sufficient

STORET monitoring data to represent pollutant contributions from upstream of the

Petersburg Generating Station immediate receiving water (Lick Creek). EPA did not

identify any upstream non-steam-electric point sources with loadings for the eight

modeled pollutants on Lick Creek. EPA therefore assumed pollutant concentrations

of zero within the water column at the upstream boundary of the modeling area.

 Upstream pollutant contributions (West Fork White River). EPA incorporated

STORET data from three monitoring stations to represent the pollutant contributions

8-33
Section 8—Case Study Modeling

from upstream on the west fork of the White River. EPA also identified three 

upstream non-steam-electric point sources whose pollutant loadings (from DMR and 

TRI data sets) could influence the model results; however, EPA assumed that the

STORET monitoring data (which include all of the modeled pollutants except for

thallium) adequately reflect the pollutant contributions from upstream point sources. 

Similarly, EPA identified that a steam electric power plant, Edwardsport Generating 

Station (Plant ID 8544), has historically discharged to the west fork of the White

River 30 miles upstream of the start boundary. Edwardsport Generating Station 

discontinued operation of all steam electric generating units in 2011 to construct a 

new integrated gasification combined cycle power plant. EPA assumed that the 

STORET monitoring data adequately reflect the pollutant contributions from this 

point source. Therefore, EPA did not incorporate pollutant loadings from the three 

identified upstream non-steam-electric point sources or Edwardsport Generating 

Station into the WASP model. 

 Upstream pollutant contributions (East Fork White River). EPA incorporated 

STORET data from one monitoring station to represent the pollutant contributions 

from upstream on the east fork of the White River. EPA also identified one upstream 

non-steam-electric point source whose pollutant loadings (from DMR and TRI data

sets) could influence the model results; however, EPA assumed that the STORET

monitoring data (which include all of the modeled pollutants) adequately reflect the 

pollutant contributions from upstream point sources. Therefore, EPA did not 

incorporate pollutant loadings from this identified upstream non-steam-electric point 

source in the WASP model.

 Downstream pollutant contributions. EPA incorporated STORET data from four

monitoring stations to represent the pollutant concentrations flowing into the 

modeling area downstream of the Petersburg Generating Station immediate receiving 

water, Lick Creek (i.e., tributaries flowing into the White River). EPA did identify

one non-steam-electric point source that discharges one or more of the modeled 

pollutants within the modeling area. EPA incorporated the pollutant loadings from the

identified non-steam-electric point source into the model. 

 Monitoring data within the modeling area. EPA compiled STORET data from 12 

monitoring stations located within the modeling area and used these data to calibrate 

the WASP model. 

The contributions of arsenic, cadmium, copper, nickel, lead, and zinc from upstream 

sources have a much greater influence on the modeled pollutant concentrations in White River

than the pollutant loadings from Petersburg Generating Station. 

Due to the lack of pollutant loadings data, the White River case study model did not 

account for the ground water impacts from Petersburg Generating Station associated with the 

damage case listed in Appendix A. In 1997, the catastrophic release of coal combustion residuals 

degraded the quality of ground water and surface water around the plant. 

The White River case study model does not account for pollutant loadings from Hoosier 

Energy’s Frank E. Ratts (Ratts) Generating Station (Plant ID 2314), a 232-MW steam electric 

power plant located less than a mile downstream of Petersburg Generating Station. Based on 

8-34 
Section 8—Case Study Modeling

information obtained in responses to the Steam Electric Survey, Ratts Generating Station 

discharged one or more of the evaluated wastestreams directly to the White River. This plant,

however, has publicly announced plans to retire all of its steam generating units prior to 

implementation of the final rule. EPA therefore excluded pollutant loadings from the Ratts 

Generating Station so that the changes in pollutant loadings during the modeling period, and the 

associated environmental improvements, reflect only those attributable to the final rule.

Modeling Period

The modeling period starts in 1986 (the year the last generating unit at Petersburg 

Generating Station began operating) and extends through 2034, covering a period of 49 years. 

Based on Petersburg Generating Station’s NPDES permitting cycle, EPA assumes that the plant 

will achieve the limitations under the final rule by 2019. 

Modeling Results – Water Quality

Under baseline conditions, the modeled pollutant concentrations in Lick Creek, the

immediate receiving water exceed NRWQC water quality benchmarks for five modeled 

pollutants, indicating that pollutant loadings from the Petersburg Generating Station may 

quantifiably reduce water quality in the modeled portions of Lick Creek. Additionally, the

modeled pollutant concentrations in portions of the White River downstream of Lick Creek 

exceed NRWQC water quality benchmarks for four of the modeled pollutants, indicating that the

water quality downstream of Lick Creek may also be reduced by the pollutant loadings form 

Petersburg Generating Station. 

The baseline modeled pollutant concentrations exceed human health criteria primarily for 

arsenic, thallium, and selenium, as discussed below: 

 Arsenic concentrations in Lick Creek exceed the water quality benchmark for 

consumption of water and organisms (0.018 μg/L) for the entire modeling period. 

These exceedances continue downstream in the White River, at the same frequency,

throughout the entire 50-mile-long modeling area downstream of the plant. 

 Arsenic concentrations in Lick Creek also exceed the higher water quality benchmark 

for consumption of organisms only (0.14 μg/L) for the entire modeling period. These 

exceedances continue downstream in the White River, generally at the same

frequency, throughout the entire 50-mile-long modeling area downstream of the plant. 

 Thallium concentrations in Lick Creek exceed the water quality benchmarks for

consumption of water and organisms (0.24 μg/L) for the entire modeling period. 

These exceedances continue downstream in the White River, at a much lower 

frequency (less than 2 percent of the modeling period), throughout the entire 50-milelong modeling area downstream of the plant. 

 Thallium concentrations in Lick Creek also exceed the higher water quality

benchmark for consumption of organisms only (0.47 μg/L) for the entire modeling 

period. On rare occasions (less than 1 percent of the modeling period), thallium 

concentrations in reaches downstream in the White River also exceed this benchmark.

8-35 
Section 8—Case Study Modeling

These downstream exceedances occur in 26 miles of the modeling area downstream 

of the plant and up to 31 miles downstream of the plant. 

 On rare occasions (less than 1 percent of the modeling period), selenium

concentrations in Lick Creek exceed the water quality benchmark for consumption of 

water and organisms (170 μg/L). These exceedances do not occur downstream after 

the confluence of the Lick Creek and White River. 

These case study modeling results indicate that, under baseline conditions, humans 

consuming water and/or organisms inhabiting these modeled portions of Lick Creek and the 

White River may be more at risk of the negative effects associated with oral exposure to these 

pollutants (see Section 3.1.1). 

Aquatic organisms may be at risk for exposure to copper, selenium, and cadmium under 

baseline conditions, as discussed below: 

 Copper concentrations in Lick Creek exceed the freshwater aquatic life criteria for 

chronic exposure (9.0 μg/L) for 45 percent of the modeling period. These 

exceedances do not occur downstream after the confluence of the Lick Creek and 

White River. 

 Copper concentrations in Lick Creek also exceed the higher freshwater aquatic life 

criteria for acute exposure (13 μg/L) for 25 percent of the modeling period. These 

exceedances do not occur downstream after the confluence of the Lick Creek and 

White River. 

 Selenium concentrations in Lick Creek exceed the freshwater aquatic life criteria for 

chronic exposure (5.0 μg/L) for 99 percent of the modeling period. On rare occasions 

(less than 1 percent of the modeling period), selenium concentrations in reaches 

downstream in the White River also exceed this benchmark. These downstream 

exceedances occur in 21 miles of the modeling area downstream of the plant and up

to 32 miles downstream of the plant. 

 Cadmium concentrations in Lick Creek exceed the freshwater aquatic life criteria for 

chronic exposure (0.25 μg/L) for 86 percent of the modeling period. On rare

occasions (less than 1 percent of the modeling period), cadmium concentrations in

reaches downstream in the White River also exceed this benchmark. These 

downstream exceedances occur in 18 miles of the modeling area downstream of the 

plant. 

These modeling results indicate that, under baseline conditions, aquatic organisms 

residing in the portions of Lick Creek and the White River with modeled exceedances may be 

more at risk to negative impacts from chronic exposure to cadmium and selenium. Additionally,

the copper loadings from Petersburg Generating Station may pose a threat from chronic or acute 

exposure. 

Under baseline conditions, the modeled pollutant concentrations in Lick Creek and 

downstream reaches in the White River exceed the MCL drinking water benchmarks for five

8-36 
Section 8—Case Study Modeling

modeled pollutants. The baseline modeled pollutant concentrations exceed drinking water 

criteria for thallium, selenium, arsenic, lead, and cadmium as discussed below: 

 Thallium concentrations in Lick Creek exceed the MCL benchmark (2 μg/L) for 96 

percent of the modeling period. These exceedances do not occur downstream after the

confluence of the Lick Creek and White River. 

 Selenium concentrations in Lick Creek exceed the MCL benchmark (50 μg/L) for 38 

percent of the modeling period. These exceedances do not occur downstream after the

confluence of the Lick Creek and White River. 

 Arsenic concentrations in Lick Creek exceed the MCL benchmark (10 μg/L) for 34 

percent of the modeling period. These exceedances occur in 8.0 miles of the modeling 

area downstream of the plant and up to 35 miles downstream of the plant. 

 On rare occasions (less than 1 percent of the modeling period), lead concentrations in 

Lick Creek exceed the MCL benchmark (15 μg/L). These exceedances continue to 

occur downstream in 24 miles of the White River as far as the end of the model (50 

miles downstream of the plant discharge). 

 On rare occasions (less than 1 percent of the modeling period), cadmium 

concentrations in Lick Creek exceed the MCL benchmark (0.25 μg/L). These 

exceedances do not occur downstream after the confluence of the Lick Creek and 

White River. 

Modeling results do not indicate any exceedances of NRWQC or MCL criteria for nickel 

or zinc. Appendix G of this report includes figures that illustrate the water column pollutant

concentration output for the immediate receiving water for arsenic, cadmium, copper, lead, 

selenium, and thallium. These figures also present the NRWQC and MCL benchmarks for the

pollutant and the steady-state water column pollutant concentrations predicted by the IRW

model. 

The final rule modeling results show significantly decreased concentrations of all 

modeled pollutants in the immediate receiving water (Lick Creek), which will greatly improve 

water quality. The final modeling results also demonstrate that the reduction of pollutant 

loadings from Petersburg Generating Station will significantly reduce the concentrations of

selenium and thallium in the White River, downstream of Lick Creek. These pollutant removals 

result in fewer exceedances of NRWQC and MCL benchmarks compared to those estimated in 

the baseline modeling. Case study modeling results for Lick Creek and the White River reveal 

the following water quality improvements under the final rule: 

 For arsenic: 

- Exceedances of the MCL benchmark are eliminated in Lick Creek. Despite the 

continued exceedances of this benchmark, at the same frequency, downstream in 

the White River, reducing the pollutant concentrations in the water column may 

decrease the human health risk.

- Exceedances of the human health water quality benchmark for consumption of 

organisms reduce in frequency from 100 percent to 87 percent of the modeling 

8-37 
Section 8—Case Study Modeling

period in Lick Creek. Despite the continued exceedances of this human health 

criteria, at the same frequency, downstream in the White River, reducing the 

pollutant concentrations in the water column may decrease the risk to humans 

consuming contaminated organisms. 

 For cadmium:

- Exceedances of the aquatic life water quality criteria for chronic impacts are 

eliminated throughout the entire modeling area. 

- Exceedances of the MCL benchmark (observed only in Lick Creek under baseline 

conditions) are eliminated throughout the entire modeling area. 

 For copper: 

- Exceedances of the aquatic life water quality criteria for chronic and acute 

impacts (observed only in Lick Creek under baseline conditions) are eliminated 

throughout the entire modeling area. 

 For lead: 

- Exceedances of the MCL benchmark are eliminated in Lick Creek. Despite the 

continued exceedances of this benchmark, at the same frequency, downstream in 

the White River, reducing the pollutant concentrations in the water column may 

decrease the human health risk.

 For selenium:

- Exceedances of the aquatic life water quality criteria for chronic impacts are 

eliminated throughout the entire modeling area. 

- Exceedances of the human health water quality benchmark for consumption of 

water and organisms (observed only in Lick Creek under baseline conditions) are 

eliminated throughout the entire modeling area. 

- Exceedances of the MCL benchmark (observed only in Lick Creek under baseline 

conditions) are eliminated throughout the entire modeling area. 

 For thallium:

- Exceedances of the MCL benchmark reduce in frequency from 96 percent to less 

than 1 percent of the modeling period in Lick Creek. 

- Exceedances of the human health water quality benchmark for consumption of 

water and organisms reduce in frequency from 100 percent to 84 percent of the 

modeling period in Lick Creek. Exceedances of this benchmark are eliminated 

through the modeling area downstream of the immediate receiving water (after 

the confluence of the Lick Creek and White River). 

- Exceedances of the human health water quality benchmark for consumption of 

organisms reduce in frequency from 100 percent to 61 percent of the modeling 

period in Lick Creek. Exceedances of this benchmark are eliminated through the 

modeling area downstream of the immediate receiving water (after the confluence 

of the Lick Creek and White River). 

8-38 
Section 8—Case Study Modeling

The final rule modeling results demonstrate that, due to background concentrations of 

arsenic from upstream sources, there will still be exceedances of the human health water quality 

benchmark for consumption of water and organisms throughout the entire modeling area 

downstream of the plant; however, the final rule will reduce the arsenic loadings that the

Petersburg Generating Station contributes to the White River.

Modeling Results – Wildlife

Under baseline conditions, Lick Creek may pose a risk to minks and eagles that consume

fish contaminated with selenium. The average modeled selenium concentration in Lick Creek is

more than 18 times greater than the concentration that would translate to NEHC exceedances for 

minks and eagles, demonstrating that this portion of the immediate receiving water may pose a

potential reproductive threat to terrestrial food webs. The water concentrations downstream after

the confluence of the Lick Creek and White River do not pose a threat to these indicator species. 

Modeling results indicate that on rare occasions (less than 1 percent of the modeling 

period), nickel concentrations in benthic sediment downstream reaches exceed the CSCL

benchmark (18 mg/kg). These exceedances occur in 3.0 miles of the modeling area downstream

of the plant and up to 35 miles downstream of the plant. 

The case study modeling results demonstrate that the final rule will significantly reduce 

pollutant concentrations and the associated impacts to wildlife that inhabit Lick Creek. The final 

rule will eliminate selenium exceedances of the NEHC benchmarks for minks and eagles in all 

modeled reaches of Lick Creek. Despite the modeling not being able to quantify any 

improvements to benthic organisms under the final rule, the pollutant loading removals will 

decrease the concentrations of toxic pollutants in benthic sediment and decrease the exposure of

organisms to these pollutants. 

Modeling Results – Human Health

EPA modeled the average pollutant concentrations in the water column and compared

these to the concentrations that would trigger exceedances of either the non-cancer reference 

dose or the 1-in-a-million LECR. Under baseline conditions, the average water column

concentration of arsenic in the immediate receiving water over the modeling period results in an 

estimated cancer risk of approximately 3-in-a-million for adult subsistence fishers. Therefore, 

adults who frequently consume arsenic-contaminated fish inhabiting the immediate receiving

water may be at greater risks for development of cancer. 

Based on the average pollutant concentrations in the water column under baseline 

conditions, cadmium, selenium, and thallium pose the greatest threat to cause non-cancer health 

effects in humans from fish consumption, as discussed below:

 Average thallium concentrations in Lick Creek are significantly greater than the

concentrations that would translate to exceedances of the reference doses for adult

and children recreational and subsistence fishers (all national-scale cohorts 

evaluated), with some cohorts potentially being exposed to concentrations more than 

200 times the reference dose. The water concentrations downstream after the 

8-39 
Section 8—Case Study Modeling

confluence of the Lick Creek and White River do not pose a threat to any of the 

evaluated cohorts. 

 Average selenium concentrations in Lick Creek are greater than the concentration that 

would translate to exceedances of the reference doses for adult and children 

recreational and subsistence fishers (all national-scale cohorts evaluated). The water 

concentrations downstream after the confluence of the Lick Creek and White River 

do not pose a threat to any of the evaluated cohorts. 

 Average cadmium concentrations in Lick Creek are greater than the concentration

that would translate to exceedances of the reference doses for the child (younger than 

11 years old) subsistence fisher cohorts. The water concentrations downstream after

the confluence of the Lick Creek and White River do not pose a threat to any of the 

evaluated cohorts. 

Therefore, humans who consume thallium-, selenium-, or cadmium-contaminated fish 

inhabiting Lick Creek may be at greater risk for developing the negative health effects associated

with these pollutants, which are discussed in Section 3.1.1. 

The final rule modeling results demonstrate significant reductions in selenium and 

cadmium concentrations in Lick Creek, which will eliminate exceedances of the non-cancer 

health effects reference dose for all cohorts for these pollutants. While the modeling results 

continue to show thallium water concentrations that would translate to exceedances of the noncancer health effects reference doses for all cohorts, the final rule will reduce the magnitude of 

the human health impacts and reduce thallium loading contributions from Petersburg Generating 

Station. 

Interpretation of Lick Creek and White River Results

Case study modeling results for Lick Creek indicate that there are severe water quality, 

wildlife, and human health impacts in Lick Creek. Case study modeling of Lick Creek reveals 

more exceedances of water quality and human health benchmarks than the IRW model; however,

the IRW model predicts more impacts to benthic organisms than the case study modeling results. 

The exceedances identified in Lick Creek are based solely on discharges of the evaluated 

wastestreams from Petersburg Generating Station because EPA did not identify any STORET 

monitoring data or point sources suggesting any other sources were contributing pollutant 

discharges on this small tributary.

The pollutant loadings discharged by Petersburg Generating Station contribute to the 

overall concentrations in the White River, along with other upstream sources. Case study 

modeling indicates that some of the water quality impacts identified in Lick Creek for arsenic,

cadmium, selenium, thallium, and lead can occur in the White River, far downstream of where 

Lick Creek flows into it. For thallium, these downstream impacts are solely caused by the 

discharges of the evaluated wastestreams from the plant because EPA did not identify any other 

sources of thallium within the modeling period. For arsenic and lead, the projected exceedances

are driven by the background concentrations flowing into the White River modeling area. 

Pollutant loadings from Petersburg Generating Station may be further impairing the degraded 

waterway for arsenic and lead. For lead and zinc, the average water column concentrations are

8-40 
Section 8—Case Study Modeling

highest downstream in the White River, indicating that pollutants with high partition coefficients 

may pose a greater threat to humans and aquatic life in the White River than in Lick Creek. The 

case study modeling results suggest that while high concentrations of toxic pollutants may dilute 

once Lick Creek empties into the White River, there are still impacts downstream that are not

captured by the IRW model. 

Under the final rule, case study modeling of Lick Creek and the White River indicate that

both these waterbodies will exhibit fewer exceedances of water quality benchmarks. 

Additionally, Lick Creek will no longer pose reproductive risks to higher trophic-level wildlife 

and will pose less risk to humans consuming fish for cancer and non-cancer impacts. Case study 

modeling predicts more water quality improvements in the modeling area than the IRW model. 

This is due in part to the greater water quality impacts under baseline conditions, which created

additional opportunities for modeled improvements, and in part to the identified improvements in 

downstream reaches of the White River that were not evaluated as part of the IRW model. Case

study modeling predict fewer human health improvements than the IRW model. The average 

pollutant concentrations throughout the entire modeling area reduce promptly after compliance 

with the final rule.

8.2.4 Ohio River Case Study

The 948-mile Ohio River flows westward from Pittsburgh, Pennsylvania, to Cairo,

Illinois, where it meets the Mississippi River. According to 2013 TRI reporting, 23 million 

pounds of chemicals were discharged into the Ohio River, more than any other surface water in 

the TRI database [U.S. EPA, 2013a]. EPA identified that 24 steam electric power plants 

evaluated in the EA discharge one or more of the evaluated wastestreams to the Ohio River or to 

tributaries that flow into the Ohio River in under five miles. FirstEnergy Corp. (FirstEnergy) 

owns and operates several of the coal-fired power plants that discharge to the Ohio River. 

The Bruce Mansfield plant (Plant ID 2269) is FirstEnergy’s largest coal-fired power plant 

by nameplate capacity. The plant is located in Shippingport, Pennsylvania, along the Ohio River, 

approximately 25 miles northwest of Pittsburgh. This plant operates three stand-alone steam

turbines, each with a nameplate capacity of 914 MW. These three generating units have a total 

capacity of 2,741 MW and reported producing approximately 19,000,000 MWh of electricity in 

2009 [ERG, 2015j]. The Bruce Mansfield plant discharges FGD wastewater and bottom ash 

transport water directly to the Ohio River from the Little Blue Run surface impoundment, which

straddles the border of Pennsylvania and West Virginia. Table 8-5 contains general information 

about the three coal-fired generating units at the Bruce Mansfield plant. 

Located along the Ohio River in Stratton, Ohio, FirstEnergy’s W.H. Sammis plant (Plant 

ID 103) is the largest coal-fired power plant in Ohio. W.H. Sammis Plant’s seven stand-alone 

steam turbine generating units have a total nameplate capacity of 2,460 MW. Based on data EPA

obtained in responses to the Steam Electric Survey, the W.H. Sammis plant reported generating 

more than 9,500,000 MWh of energy with these seven coal-fired generating units in 2009. The 

W.H. Sammis plant discharges three of the evaluated wastestreams (FGD wastewater, bottom 

ash transport water, and combustion residual leachate) directly to the Ohio River. Table 8-6 

contains general information about each of the seven steam electric generating units at the W.H.

Sammis plant. 

8-41 
 

 

 

 

Section 8—Case Study Modeling

Table 8-5. Summary of Bruce Mansfield Operations

SE Unit Fuel 

Capacity

(MW) Fly Ash Bottom Ash 

FGD 

(Year Installed) 

1 Bituminous coal and 914 Wet scrubber a Wet handled to Wet system

No. 2 fuel oil impoundment (1975) 

2 Bituminous coal and 914 Wet scrubber a Wet handled to Wet system

No. 2 fuel oil impoundment (1977) 

3 Bituminous coal and 914 Dry conveyed Wet handled to Wet system

No. 2 fuel oil impoundment (1980) 

Source: ERG, 2015j. 

Acronyms: FGD (Flue gas desulfurization); MW (Megawatt); SE (steam electric). 

a – EPA does not consider the ash collected by venturi-type wet scrubbers as fly ash, and therefore, the water 

generated by these systems is not considered fly ash transport water. 

Table 8-6. Summary of W.H. Sammis Operations 

SE Unit Fuel Capacity (MW) Fly Ash Bottom Ash FGD 

(Year Installed) 

1 Bituminous coal, 

subbituminous coal, 

and No. 2 fuel oil 

190 Dry conveyed Wet handled to 

impoundment

Wet system

(2010)

2 Bituminous coal, 

subbituminous coal, 

and No. 2 fuel oil 

190 Dry conveyed Wet handled to 

impoundment

Wet system

(2010) 

3 Bituminous coal, 

subbituminous coal, 

and No. 2 fuel oil 

190 Dry conveyed Wet handled to 

impoundment

Wet system

(2010)

4 Bituminous coal, 

subbituminous coal, 

and No. 2 fuel oil 

190 Dry conveyed Wet handled to 

impoundment

Wet system

(2010) 

5 Bituminous coal, 

subbituminous coal, 

and No. 2 fuel oil 

334 Dry conveyed Wet handled to 

impoundment

Wet system

(2010) 

6 Bituminous coal, 

subbituminous coal, 

and No. 2 fuel oil 

680 Dry conveyed Wet handled to 

impoundment

Wet system

(2010) 

7 Bituminous coal, 

subbituminous coal, 

and No. 2 fuel oil 

680 Dry conveyed Wet handled to 

impoundment

Wet system

(2010) 

Source: ERG, 2015j. 

Acronyms: FGD (Flue gas desulfurization); MW (Megawatt); SE (steam electric). 

In estimating the historical pollutant loadings associated with W.H. Sammis’ three FGD 

systems, EPA incorporated the pollutant loadings for FGD wastewater as the systems were 

installed, between March and May 2010. EPA did not model any FGD wastewater pollutant

loadings in the model prior to the installation of W.H. Sammis plant’s first FGD system. 

8-42 
Figure 8-5. Ohio River WASP Modeling Area 

Section 8—Case Study Modeling

Modeling Area

The Ohio River WASP model encompasses a 49-mile-long reach of the Ohio River, 37 

miles of which is downstream of one or both of the two modeled steam electric power plant 

immediate receiving waters. Located furthest upstream, the Bruce Mansfield plant discharges 

approximately 12 miles downstream of the start of the modeling area. The immediate receiving

water that the Bruce Mansfield plant discharges to is approximately 3.3 miles long, as defined in 

the WASP model. W.H. Sammis plant discharges 13 miles downstream of the Bruce Mansfield 

plant’s immediate receiving water. The immediate receiving water that W.H. Sammis plant 

discharges to is approximately 3.4 miles long, as defined in the WASP model. The modeling area 

ends just upstream of the discharges from another steam electric power plant, the Cardinal plant 

(Plant ID 3265). EPA did not model the pollutant loadings from the Cardinal plant because of

CBI claims on one or more of the evaluated wastestream flow rates. Figure 8-5 illustrates the 

location and extent of the Ohio River WASP model. 

8-43
Section 8—Case Study Modeling

Identified Point Sources and Background Concentrations

As discussed below, EPA reviewed available pollutant loadings (DMR and TRI) and 

monitoring data (STORET) for potential incorporation into the Ohio River WASP model to

represent pollutant contributions from background and non-steam-electric point sources, and for 

use in calibrating the model results.

 Upstream pollutant contributions. EPA identified many upstream non-steamelectric point sources whose pollutant loadings could influence the model results.

EPA identified STORET data from one monitoring station on the Ohio River

(approximately 28 river-miles upstream of Bruce Mansfield plant’s immediate

receiving water). EPA incorporated the monitoring data (which encompass five of the

modeled pollutants) to represent the pollutant contributions flowing into the modeling

area. EPA identified additional STORET monitoring data from one station on a

tributary to the Ohio River; EPA incorporated these data to represent pollutant

contributions flowing in from that tributary. EPA also incorporated the pollutant

loadings, based on DMR and TRI data, from seven non-steam-electric point sources

upstream of the Bruce Mansfield plant’s immediate receiving water to account for the

pollutant contributions not captured by the STORET monitoring data.

 Downstream pollutant contributions. EPA incorporated STORET data from eight

monitoring stations to represent TSS concentrations flowing into the modeling area

downstream of both steam electric power plant immediate receiving waters (i.e.,

tributaries flowing into the Ohio River). These monitoring stations all represent one

tributary that flows into the Ohio River near the downstream end of the modeling

area. EPA identified 29 non-steam-electric point sources whose pollutant loadings

could influence the model results downstream of the Bruce Mansfield plant

immediate receiving water and incorporated these pollutant loadings into the Ohio

River WASP model.

 Monitoring data within the modeling area. EPA compiled STORET data from

seven monitoring stations located within the modeling area and used these data to

calibrate the WASP model.

The contributions of copper, lead, nickel, and zinc from upstream sources are 

significantly greater than the pollutant loadings from the Bruce Mansfield and W.H. Sammis 

plants. 

The Ohio River case study model did not account for the documented surface water and 

ground water impacts from Bruce Mansfield or Little Blue Run that are listed in Appendix A. In 

1993, a catastrophic release of steam electric power plant wastewater compromised the quality of

ground water and surface water around the Bruce Mansfield plant and Little Blue Run 

impoundment. Due to the lack of pollutant loadings data, surface water quality impacts resulting

from this event are not reflected in this model; therefore, the case study modeling could 

underrepresent the actual baseline impacts of the Bruce Mansfield plant on the Ohio River. 

8-44
Section 8—Case Study Modeling

Modeling Period

The modeling period starts in 1982 (year of the last revision to the steam electric ELGs)

and extends through 2036, covering a period of 55 years. Based on their NPDES permitting 

cycles, EPA assumes that the Bruce Mansfield and W.H. Sammis plants will achieve the 

limitations under the final rule by 2020 and 2021, respectively. EPA focused the assessment of 

the improvements under the final rule on the period after the 2021 assumed compliance date. 

Modeling Results – Water Quality

Under baseline conditions, the modeled pollutant concentrations in the modeled portion 

of the Ohio River exceed a human health NRWQC water quality benchmark for one modeled 

pollutant (arsenic), indicating that arsenic loadings from the two steam electric power plants may 

contribute to a quantifiable reduction in water quality in the modeled portions of the Ohio River. 

Arsenic concentrations in 33 miles of the modeling area downstream of the Bruce Mansfield 

plant exceed the human health water quality benchmark for consumption of water and organisms 

(0.018 μg/L). These exceedances begin several miles downstream of the Bruce Mansfield plant 

due to the pollutant loadings from a non-steam-electric point source. This area of exceedances 

continues downstream of the W.H. Sammis plant for 24 miles (including the W.H. Sammis

plant’s immediate receiving water) and exceeds the arsenic benchmark during 30 percent of the 

modeling period. In some portions of the modeling area, the frequency of these exceedances 

increases due to arsenic contributions from other non-steam-electric point sources. These case 

study modeling results indicate that, under baseline conditions, humans consuming water and/or 

organisms inhabiting these modeled portions of the Ohio River may be more at risk of the 

negative effects associated with oral exposure to arsenic (see Section 3.1.1). On rare occasions 

(less than 1 percent of the modeling period), the modeled pollutant concentrations exceed the 

MCL drinking water benchmark for one pollutant (lead), indicating that lead loadings from the 

two steam electric power plants may contribute to a quantifiable reduction in water quality in the

modeled portions of the Ohio River. These rare lead exceedances occur in 15 miles of the 

modeling area downstream of the Bruce Mansfield plant, of which 13 miles are also downstream 

of the W.H. Sammis plant (including the immediate receiving water). 

Modeling results do not indicate any exceedances of human health NRWQC criteria for

the other modeled pollutants (cadmium, copper, nickel, selenium, thallium, and zinc) and do not 

indicate any exceedances of aquatic life NRWQC or MCL criteria for any of the eight modeled 

pollutants. Appendix G of this report includes figures that illustrate the water column pollutant

concentration output for the immediate receiving water for arsenic and lead. These figures also

present the NRWQC and MCL benchmarks for the pollutant and the steady-state water column 

pollutant concentrations predicted by the IRW model. 

The final rule modeling results show significantly decreased concentrations of four of the 

modeled pollutants (arsenic, cadmium, selenium, and thallium) in the modeled portion of the 

Ohio River, which will improve water quality. These pollutant removals result in less frequent 

exceedances of human health NRWQC benchmarks compared to those estimated in the baseline 

modeling. Arsenic exceedances of human health water quality benchmarks for consumption of 

water and organisms reduce in frequency from 30 percent to 6 percent of the modeling period in 

the W.H. Sammis plant’s immediate receiving water. Additionally, the exceedances of these 

8-45
Section 8—Case Study Modeling

benchmarks reduce in frequency in all remaining sections of the downstream modeling area 

following compliance with the final rule. Despite the continued exceedances of the arsenic 

human health criteria and the lead MCL benchmark, reducing the pollutant concentrations in the 

water column may decrease the risk to humans. 

Modeling Results – Wildlife

Based on the average pollutant concentrations in the water column under baseline 

conditions, the modeled portion of the Ohio River does not exceed the concentrations that would 

translate to NEHC exceedances and does not pose a risk to minks and eagles that consume 

contaminated fish. Despite the modeling not being able to quantify any improvements to minks 

and eagles under the final rule, the pollutant loading removals will decrease bioaccumulation of

toxic pollutants in the terrestrial food chains. 

Modeling results do not indicate that there are any pollutant concentrations in the upper 

benthic sediment that exceed CSCL benchmarks for any of the eight modeled pollutants;

therefore, the modeled portion of the Ohio River does not pose a threat to benthic organisms in 

contact with contaminated sediment. Despite the modeling not being able to quantify any 

improvements to benthic organisms under the final rule, the pollutant loading removals will 

decrease the concentrations of toxic pollutants in benthic sediment and decrease the exposure of

organisms to these pollutants. 

Modeling Results – Human Health

Under baseline conditions, the average concentration of arsenic in fish over the modeling 

period does not result in an estimated cancer risk greater than 1-in-a-million for any of the

national-scale cohorts. 

Based on the average pollutant concentrations in the water column under baseline 

conditions, thallium poses the greatest threat to cause non-cancer health effects in humans from 

fish consumption. Average thallium concentrations in the W.H. Sammis plant’s immediate 

receiving water are greater than the concentration that would translate to exceedances of the 

reference doses for the child (younger than 11 years old) subsistence fisher cohorts. Average 

thallium concentrations in 24 miles of the modeling area downstream of the W.H. Sammis plant

are high enough to trigger exceedances of the reference dose for at least one subsistence cohort. 

Therefore, humans who consume fish inhabiting these waters may be at greater risk for

developing the negative health effects associated with thallium, which are discussed in Section 

3.1.1. 

The final rule modeling results demonstrate significant reductions in thallium, 

eliminating thallium exceedances of the non-cancer health effects reference dose throughout the 

entire modeling area. 

Interpretation of Ohio River Results

Case study modeling results for the Ohio River indicate greater water quality and human 

health impacts under baseline conditions than predicted by the IRW model. The impacts 

identified in the Ohio River by case study modeling are more extensive than the IRW model 

8-46
Section 8—Case Study Modeling

because EPA has accounted for pollutant contributions from upstream on the Ohio River, other 

waterways flowing into the Ohio River, and non-steam electric point sources. Modeled alone, the 

Bruce Mansfield plant and W.H. Sammis plant would not cause any quantifiable impacts over 

the modeling period; however the modeled potion of the Ohio River is heavily industrialized. 

EPA identified 34 non-steam electric point sources that discharge one or more of the modeled 

pollutants and report to DMR or TRI. The pollutant contributions from the Bruce Mansfield 

plant, W.H. Sammis plant, and these other non-steam electric point sources modeled accumulate 

in the waterbody, increasing the overall water column concentrations to a degree that adversely 

affects water quality and human health. EPA identified exceedances of human health 

benchmarks that indicate that consuming water and/or organisms from the modeled portion of 

the Ohio River, including the W.H. Sammis plant’s immediate receiving water and areas 

downstream, can cause health problems related to arsenic, lead, or thallium. The Ohio River case

study model results exemplify that, by not accounting for non-steam-electric point sources 

discharging to the same waterbodies as steam electric power plants, the IRW model may be 

under-representing the total number of receiving waters with impacts that are caused, in part, by

pollutant contributions from the steam electric power generating industry. The case modeling 

results also suggest that the discharges of the evaluated wastestreams from Bruce Mansfield 

plant and W.H. Sammis plant may be further impairing the degraded waterway. 

Case study modeling of the Ohio River indicates that, under the final rule, the Ohio River 

will exhibit less frequent exceedances of water quality benchmarks and will eliminate risk to 

humans consuming fish that inhabit these waters. The human health non-cancer impacts and 

improvements under the final rule are solely caused by the reduction in steam electric plant 

pollutant loadings (there are no other input sources of thallium in the Ohio River WASP 

model).The improvements identified by the case study model are more extensive than what was 

projected by the IRW model for either of Bruce Mansfield plant or W.H. Sammis plant. This is 

due in part to the greater water quality and human health impacts under baseline conditions, 

which created additional opportunities for modeled improvements, and in part to the identified 

improvements in downstream reaches of the Ohio River that were not evaluated as part of the 

IRW model. The average pollutant concentrations throughout the entire modeling area reduce 

within a year after compliance with the final rule.

8.2.5 Mississippi River Case Study

The Mississippi River watershed is the largest in North America, covering about 40 

percent of the lower 48 states. The 190-mile stretch of the Mississippi River between the 

confluence with the Missouri River at St. Louis, Missouri, and the confluence with the Ohio

River at Cairo, Illinois, is known as the Middle Mississippi River. South of St. Louis along this 

stretch of the river, Ameren Corporation operates the Rush Island steam electric power plant 

(Plant ID 5038) on the west bank of the Mississippi River. The Rush Island plant operates two

stand-alone steam turbine units with a nameplate capacity of 670 MW each. Together, these two 

coal-fired generating units have a capacity of 1,340 MW and reported producing over 8,500,000 

MWh of electricity in 2009 in the Steam Electric Survey. The Rush Island plant discharges fly 

ash and bottom ash transport water directly to the Mississippi River. Table 8-7 contains general 

information on the two coal-fired units at the Rush Island plant. 

8-47
 

 

 

Section 8—Case Study Modeling

Table 8-7. Summary of Rush Island Operations

SE Unit Fuel 

Capacity

(MW) Fly Ash Bottom Ash 

FGD 

(Year Installed) 

1 Subbituminous coal

and No. 2 fuel oil 

670 Dry conveyance & wet 

handled to impoundment

Wet handled to 

impoundment

No FGD system 

2 Subbituminous coal

and No. 2 fuel oil 

670 Dry conveyance & wet 

handled to impoundment

Wet handled to 

impoundment

No FGD system 

Source: ERG, 2015j. 

Acronyms: FGD (Flue gas desulfurization); MW (Megawatt); SE (steam electric). 

Modeling Area

The Mississippi River WASP model encompasses a 46-mile-long reach of the 

Mississippi River, 23 miles of which is downstream of the Rush Island plant immediate 

receiving water. The model has two start boundaries that are on the Meramec River and 

Mississippi River shortly upstream of their confluence. The immediate receiving water that the 

Rush Island plant discharges to is approximately 1.5 miles long, as defined in the WASP model. 

This model ends at the confluence of the Mississippi River and Kaskaskia River. Figure 8-6

illustrates the location and extent of the Mississippi River WASP model. 

Identified Point Sources and Background Concentrations

As discussed below, EPA reviewed available pollutant loadings (DMR and TRI) and 

monitoring data (STORET) for potential incorporation into the Mississippi River WASP model 

to represent pollutant contributions from background and non-steam-electric point sources, and 

for use in calibrating the model results. 

 Upstream pollutant contributions from non-steam-electric point sources. EPA

identified several upstream non-steam-electric point sources whose loadings could

influence the model results. EPA therefore extended the modeling area upstream to

model these point sources and incorporate upstream monitoring data. EPA identified

STORET data from four monitoring stations on the Mississippi River prior to the

confluence with the Meramec River (approximately 24 river-miles upstream of Rush

Island’s immediate receiving water). EPA incorporated the monitoring data (which

encompass all of the modeled pollutants except for thallium) to represent the pollutant

contributions in the Mississippi River prior to where it converges with the Meramec

River. EPA assumed that the monitoring data adequately reflect the pollutant

contributions from upstream of this confluence. EPA incorporated the pollutant

loadings from three non-steam-electric point sources downstream of the convergence

to account for the pollutant contributions not captured by the STORET monitoring

data.

 Upstream pollutant contributions from steam electric sources. EPA identified one

steam electric power plant, Ameren’s Meramec plant (Plant ID 1435), whose loadings

could influence the model results at the Rush Island immediate receiving water and

other downstream locations. EPA incorporated the loadings from the Meramec plant

into the extended Mississippi River model, as discussed further below.

8-48
Figure 8-6. Mississippi River WASP Modeling Area 

Section 8—Case Study Modeling

 Downstream pollutant contributions. EPA incorporated STORET data from two

monitoring stations to represent pollutant concentrations flowing into the modeling

area downstream of the Rush Island immediate receiving water (i.e., tributaries

flowing into the Mississippi River). EPA did not identify any non-steam-electric point

sources whose pollutant loadings would significantly influence the model results in

the downstream modeling area.

 Monitoring data within the modeling area. EPA compiled STORET data from four

monitoring stations located within the modeling area and used these data to calibrate

the WASP model.

The Meramec plant discharges approximately 24 river miles upstream of the Rush Island 

plant’s immediate receiving water. EPA did not identify STORET monitoring data between the 

two plants to represent the pollutant concentrations from the Meramec plant; therefore, EPA 

incorporated the pollutant loadings from the Meramec plant (as calculated for this rulemaking) 

into the Mississippi River model. The Meramec plant operates four coal-fired generating units

with a total nameplate capacity of 923 MW. All pollutant loadings from the evaluated 

wastestreams are from bottom ash transport water. EPA assumed that the Meramec plant will 

8-49
Section 8—Case Study Modeling

comply with the standards of the final rule by 2019. EPA did not evaluate the water quality, 

wildlife, or human health impacts associated with discharges from the Meramec plant because

this plant did not meet the case study location selection criteria described in Section 8.1.1. EPA 

incorporated the loadings from Meramec plant solely to account for the upstream pollutant 

contributions flowing into the Rush Island plant’s immediate receiving water from upstream, 

under baseline conditions and the final rule. 

The contributions of arsenic, cadmium, copper, lead, nickel, and zinc from upstream 

sources are significantly greater than the pollutant loadings from the Rush Island plant.

Modeling Period

The modeling period starts in 1982 (year of the last revision to the steam electric ELGs)

and extends through 2036, covering a period of 55 years. Based on their NPDES permitting 

cycles, EPA assumes that the Meramec and Rush Island plants will achieve the limitations under 

the final rule by 2019 and 2023, respectively. For the Rush Island plant’s immediate receiving 

water and downstream reaches, EPA focused the assessment of the baseline impacts and

improvements under the final rule on the period after the 2023 assumed compliance date. 

Modeling Results – Water Quality

Under baseline conditions, the modeled pollutant concentrations in the Rush Island 

plant’s immediate receiving water and downstream reaches exceed human health NRWQC water 

quality benchmarks for one modeled pollutant (arsenic), indicating that loadings from Rush

Island may contribute to a quantifiable reduction in water quality in the modeled portions of the 

Mississippi River. Arsenic concentrations in the Rush Island plant’s immediate receiving water 

exceed the human health water quality benchmark for consumption of water and organisms 

(0.018 μg/L) and the human health water quality benchmark for consumption organisms (0.14 

μg/L) for the entire modeling period. These exceedances continue downstream, at the same

frequency, throughout the entire 23-mile-long modeling area downstream of the plant. The case 

study modeling results indicate that, under baseline conditions, humans consuming water and/or 

organisms that inhabit these modeled portions of the Mississippi River may be more at risk of the 

negative effects associated with oral exposure to arsenic (see Section 3.1.1). 

Modeling results do not indicate any exceedances of human health NRWQC benchmarks

for the other modeled pollutants (cadmium, copper, nickel, lead, selenium, thallium, and zinc). In 

addition, modeling results do not indicate any exceedances of aquatic life NRWQC or MCL

criteria for any of the eight modeled pollutants. Appendix G of this report includes figures that 

illustrate the water column pollutant concentration output for the immediate receiving water for 

arsenic. This figure also presents the NRWQC and MCL benchmarks for the pollutant and the 

steady-state water column pollutant concentrations predicted by the IRW model. 

The final rule modeling continues to show human health NRWQC benchmark 

exceedances for arsenic within the Mississippi River due to additional arsenic contributions from 

other sources (i.e., Mississippi River background concentrations and non-steam electric point 

sources). However, under the final rule, both the Meramec and Rush Island plants will no longer 

8-50
Section 8—Case Study Modeling

discharge any of the evaluated wastestreams and will therefore no longer contribute to the

arsenic or lead impairment of the Mississippi River. 

Modeling Results – Wildlife

Based on the average pollutant concentrations in the water column under baseline 

conditions, the modeled portion of the Mississippi River does not exceed the concentrations that 

would translate to NEHC exceedances and does not pose a risk to minks and eagles that consume 

contaminated fish. Despite the modeling not being able to quantify any improvements to minks 

and eagles under the final rule, the pollutant loading removals will decrease bioaccumulation of

toxic pollutants in the terrestrial food chains. 

Modeling results do not indicate that there are any pollutant concentrations in the upper 

benthic sediment that exceed CSCL benchmarks of for any of the eight modeled pollutants;

therefore, the modeled portion of the Mississippi River does not pose a threat to benthic 

organisms in contact with contaminated sediment. Despite the modeling not being able to 

quantify any improvements to benthic organisms under the final rule, the pollutant loading 

removals will decrease the concentrations of toxic pollutants in benthic sediment and decrease

the exposure of organisms to these pollutants. 

Modeling Results – Human Health

EPA modeled the average pollutant concentrations in the water column and compared

these to the concentrations that would trigger exceedances of either the non-cancer reference 

dose or the 1-in-a-million LECR. Under baseline conditions, the average water column

concentration of arsenic throughout the modeling area downstream of the plant results in an 

estimated cancer risk greater than 1-in-a-million for adult subsistence fishers. Therefore, humans 

who consume arsenic-contaminated fish inhabiting the immediate receiving water may be at

greater risks for development of cancer. Modeling results demonstrate no reduction in the cancer 

risk from inorganic arsenic under the final rule. 

Under baseline conditions, the average pollutant concentrations over the modeling period 

does not pose the threat to cause non-cancer health effects for adult and children recreational and 

subsistence fishers (all national-scale cohorts evaluated). 

Interpretation of Mississippi River Results

Case study modeling results for the Mississippi River indicate greater water quality and 

human health impacts under baseline conditions than predicted by the IRW model. By 

accounting for pollutant contributions from background and upstream sources, the case study 

model predicts higher pollutant concentrations under baseline conditions. For arsenic, the

projected exceedances are driven by the pollutant contributions entering the Mississippi River 

upstream of the Rush Island plant. Alone, the steam electric discharges of the evaluated 

wastestreams would not cause any quantifiable impacts, which is consistent with the IRW model 

results; however, the pollutant loadings from the Rush Island plant may be further exacerbating

the impairment of the degraded waterway. 

8-51
Section 8—Case Study Modeling

The case study modeling of the Mississippi River indicates that, under the final rule, it 

will continue to exceed all of the water quality and human health benchmarks observed at 

baseline, with little to no reduction in frequency. Under the final rule, the Rush Island plant will 

no longer discharge any fly ash or bottom ash transport water. After compliance with the final 

rule, the modeled steam electric power plants will no longer contribute to the impairment of the 

Mississippi River and the overall magnitude of the pollutant concentrations in the aquatic system

will decrease. 

8.2.6 Lake Sinclair Case Study

Lake Sinclair is a reservoir located in central Georgia. The lake was created in 1953 when 

the waters of the Oconee River were dammed by Georgia Power, a subsidiary of Southern 

Company, to create a hydroelectric generating station. Georgia Power also owns and operates 

Plant Harllee Branch (Plant ID 5762), a steam electric power plant situated on the northern shore 

of Lake Sinclair. Based on 2009 data obtained in responses to the Steam Electric Survey, Plant 

Harllee Branch operated four coal-fired generating units with a total nameplate capacity of 1,750 

MW and produced more than 6,800,000 MWh of electricity in 2009. As of April 16, 2015 (the

date by which the plant would be required to comply with the U.S. EPA’s Clean Power Plan

[Clean Air Act Section 111(d)]), this plant has decertified and retired all four of its coal-fired

generating units. Georgia Power cited several factors, including the cost to comply with existing 

and future environmental regulations, recent and future economic conditions, and lower natural 

gas prices, in the decision to close the plant. Plant Harllee Branch discharged FGD wastewater, 

fly ash transport water, and bottom ash transport water directly to Lake Sinclair. Table 8-8 

contains general information on the four coal-fired units at Rush Island Plant. 

Despite the retirement of all coal-fired generating units at this plant, EPA proceeded with 

case study modeling of Lake Sinclair to represent the potential impacts of steam electric 

discharges on lentic waterbodies (including the 26 lake, pond, and reservoir receiving waters 

evaluated in this EA) and the potential environmental improvements that could reasonably be 

expected under the final rule in other lentic waterbodies that receive discharges of the evaluated 

wastestreams. EPA did not include Plant Harllee Branch or Lake Sinclair in the other 

quantitative and qualitative analyses in this EA for the final rule (e.g., the IRW model). 

In estimating the historical pollutant loadings associated with Plant Harllee Branch, EPA 

incorporated the loadings only from generating unit IDs 3 and 4 because generating unit IDs 1 

and 2 were flagged for retirement at the time of the proposed revised ELGs. EPA incorporated 

the loadings with the FGD wastewater as the systems were installed (starting in 2013). EPA did 

not model any FGD wastestream loadings in the historical model prior to the installation of Plant 

Harllee Branch’s first FGD system. 

8-52
 

Section 8—Case Study Modeling

Table 8-8. Summary of Plant Harllee Branch Operations

SE Unit Fuel 

Capacity

(MW) Fly Ash Bottom Ash 

FGD 

(Year Installed) 

1 a Bituminous coal and

No. 2 fuel oil

299 Wet handled to

impoundment

Wet handled to 

impoundment

Wet system

(2014) 

2 a Bituminous coal and

No. 2 fuel oil

359 Wet handled to

impoundment

Wet handled to 

impoundment

Wet system

(2014) 

3 Bituminous coal and

No. 2 fuel oil

544 Wet handled to

impoundment

Wet handled to 

impoundment

Wet system

(2013) 

4 Bituminous coal and

No. 2 fuel oil

544 Wet handled to

impoundment

Wet handled to 

impoundment

Wet system

(2013) 

Source: ERG, 2015j. 

Acronyms: FGD (Flue gas desulfurization); MW (Megawatt); SE (steam electric). 

a – EPA did not model any pollutant loadings associated with these generating units.

Modeling Area

As discussed in Section 8.1.1, EPA relied upon the availability of existing models to 

perform case study modeling of lentic systems: an existing WASP model that divided the 

waterbody into segments and EFDC model that provided hydrodynamics and simulated the 

aquatic system in three dimensions. The EFDC model uses stretch or sigma vertical coordinates 

and Cartesian coordinates to represent the physical characteristics of Lake Sinclair. 

The three-dimensional EFDC model, which provides the hydrodynamic foundation for

the WASP model, divides the waterbody into 1,235 segments; each segment represents a unique 

location and stratum within Lake Sinclair. The model accounts for a total volume of

approximately 340 million cubic meters. In contrast to the WASP models that EPA developed to 

model lotic systems, the Lake Sinclair model is not set up to quantify the pollutant

concentrations in the benthic sediment; therefore, EPA was unable to assess whether pollutant 

accumulation in the sediment was occurring over prolonged discharge periods. Figure 8-7

illustrates the location and extent of the Lake Sinclair modeling area.

8-53
Section 8—Case Study Modeling

Figure 8-7. Lake Sinclair WASP and EDFC Modeling Area 

Identified Point Sources and Background Concentrations

As discussed below, EPA reviewed available pollutant loadings (DMR and TRI) and 

monitoring data (STORET) for potential incorporation into the Lake Sinclair water quality model 

to represent pollutant contributions from background and non-steam-electric point sources, and 

for use in validating and calibrating the model results. 

 Upstream pollutant contributions. EPA incorporated STORET data from three

monitoring stations to represent TOC and TSS contributions from upstream of Lake

Sinclair on the Oconee River. EPA did not identify sufficient STORET monitoring

data to represent the pollutant contributions of the eight modeled pollutants or any

upstream non-steam-electric point sources with loadings for the eight modeled

pollutants. EPA therefore assumed pollutant concentrations of zero within the water

column flowing into Lake Sinclair from the Oconee River.

 Other pollutant contributions. EPA incorporated STORET data from 15 monitoring

stations to represent the modeled pollutants, TOC, and TSS concentrations flowing

into Lake Sinclair from other streams. EPA did not identify any non-steam-electric

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Section 8—Case Study Modeling

point sources whose pollutant loadings would significantly influence the model 

results. 

 Monitoring data within the modeling area. EPA compiled STORET data from six

monitoring stations located within the modeling area and used these data to calibrate

the Lake Sinclair water quality model.

The pollutant concentrations entering the modeling area for arsenic, copper, lead, and 

thallium which EPA calculated using monitoring data, are much greater than the pollutant

loadings from Lake Sinclair plant. The concentrations entering the modeling area for cadmium, 

nickel, and zinc also strongly influence the model outputs. 

Modeling Period

As discussed earlier in this section, EPA adopted the preexisting Lake Sinclair EFDC 

model. The preexisting model was designed with seven years of hydrodynamic and flow input, 

limiting the length of the period EPA could model. Based on Plant Harllee Branch’s NPDES 

permitting cycle, EPA assumed that the plant would have achieved the limitations under the final 

rule by 2019 if it continued to operate. The modeling period begins in February 2012 

(approximately seven years before the assumed compliance date) and extends through November 

2025 (approximately seven years after the assumed compliance date). 

Modeling Results – Water Quality

EPA selected three portions of Lake Sinclair to evaluate the modeled pollutant 

concentrations: 1) the immediate receiving water (a 720,000-cubic-meter cell of the lake); 2) the 

average of all segments in the reach of the lake where Plant Harllee Branch discharges, including

subsurface water segments (hereafter referred to as the “receiving branch”), and 3) the average of

all segments included in the Lake Sinclair model, including subsurface water segments (hereafter 

referred to as the “entire modeling area”). 

Under baseline conditions, the modeled pollutant concentrations in Lake Sinclair, 

including the immediate receiving water and the receiving reach, exceed NRWQC water quality

benchmarks for three modeled pollutants, indicating that pollutant loadings from Plant Harllee

Branch may quantifiably reduce water quality in the modeled portions of Lake Sinclair. The 

reduced water quality is primarily attributed to arsenic, cadmium, and thallium.

The baseline modeled pollutant concentrations exceed human health criteria primarily for 

arsenic and thallium, as discussed below: 

 Arsenic concentrations exceed the water quality benchmark for consumption of water

and organisms (0.018 μg/L):

- In the immediate receiving water for the entire modeling period.

- In all modeled segments of the receiving branch for more than 99 percent of the

modeling period.

- In 97 percent of the entire modeling area for 10 percent or more of the modeling

period.

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Section 8—Case Study Modeling

 Arsenic concentrations also exceed the higher water quality benchmark for

consumption of organisms (0.14 μg/L):

- In five of the six modeled segments of the receiving branch for up to 19 percent of

the modeling period.

- In 54 percent of the entire modeling area for 10 percent or more of the modeling

period.

 Thallium concentrations exceed the water quality benchmark for consumption of

water and organisms (0.24 μg/L):

- In three of the six modeled segments of the receiving branch for up to 6 percent of

the modeling period.

- In 14 percent of the entire modeling area for 10 percent or more of the modeling

period.

 Thallium concentrations also exceed the higher water quality benchmark for

consumption of organisms (0.47 μg/L):

- In two of the six modeled segments of the receiving branch for less than 1 percent

of the modeling period.

- In 11 percent of the entire modeling area for 10 percent or more of the modeling

period.

The case study modeling results indicate that, under baseline conditions, humans 

consuming water and/or organisms that inhabit these modeled portions of Lake Sinclair may be 

more at risk of the negative effects associated with oral exposure to arsenic and thallium (see 

Section 3.1.1). 

Aquatic organisms may be at risk for exposure to cadmium under baseline conditions. 

Specifically, cadmium concentrations exceed the freshwater aquatic life criteria for chronic 

exposure (0.25 μg/L) in 4 percent of the entire modeling area for 10 percent or more of the

modeling period. These case study modeling results indicate that, under baseline conditions, 

aquatic organisms inhabiting these modeled portions of Lake Sinclair could be at an elevated risk

of the negative effects associated with oral exposure to cadmium (see Section 3.1.1). 

Under baseline conditions, the modeled pollutant concentrations in Lake Sinclair 

occasionally exceed the MCL drinking water benchmarks for two of the modeled pollutants

(arsenic and thallium), as discussed below: 

 Arsenic concentrations exceed the MCL drinking water criteria (10 μg/L) in less than

1 percent of the segments for 10 percent or more of the modeling period.

 Thallium concentrations exceed the MCL drinking water criteria (2 μg/L) in 5 percent

of the segments for 10 percent or more of the modeling period.

Modeling results do not indicate any exceedances of NRWQC or MCL criteria for the 

other modeled pollutants (copper, lead, nickel, selenium, and zinc). Appendix G of this report 

includes figures that illustrate the average water column pollutant concentration output for the 

8-56
Section 8—Case Study Modeling

entire lake for arsenic, cadmium, and thallium. These figures also present the NRWQC and MCL 

benchmarks for the pollutant and the steady-state water column pollutant concentrations

predicted by the IRW model. 

The final rule modeling results show significantly decreased average concentrations of 

two of the modeled pollutants (nickel and selenium) in the modeled portion of Lake Sinclair. 

Case study modeling results for Lake Sinclair reveal the water quality improvements for arsenic 

under the final rule. Specifically, arsenic exceedances of the human health NRWQC benchmark 

for consumption of water and organisms reduce in frequency from the entire modeling period to 

23 percent of the modeling period in the immediate receiving water and reduce from above 99 

percent of the modeling period to as low as 23 percent of the modeling period in the receiving

branch. Additionally, slightly less (2 percent of the modeling area) of Lake Sinclair will exceed

this benchmark under the final rule. Arsenic exceedances of the higher human health NRWQC 

benchmark for consumption of organisms also reduce throughout the entire lake as 12 percent 

less of the modeling area exceed this benchmark for more than 10 percent of the modeling 

period. 

While the modeling results demonstrate continuing arsenic, cadmium, and thallium 

exceedances of NRWQC and MCL benchmarks in the receiving reach and the entire modeling 

area, the pollutant loading contributions to the lake would be reduced under the final rule (if 

Plant Harllee Branch did not retire all generating units).

Modeling Results – Wildlife

For the analysis of wildlife impacts and improvements, EPA assumed that aquatic life

travel freely throughout Lake Sinclair and do not confine themselves within particular segments 

of the lake. EPA calculated the average fish tissue concentrations of all segments within the Lake

Sinclair model (i.e., entire modeling area) for purposes of the wildlife assessment. 

Based on the average pollutant concentrations in the water column under baseline 

conditions, the modeled portion of Lake Sinclair does not exceed the concentrations that would 

translate to NEHC exceedances and does not pose a risk to minks and eagles that consume 

contaminated fish. Despite the modeling not being able to quantify any improvements to minks 

and eagles under the final rule, the pollutant loading removals will decrease bioaccumulation of

toxic pollutants in the terrestrial food chains (if Plant Harllee Branch did not retire all generating 

units).

The Lake Sinclair EFDC model is not set up to quantify the pollutant concentrations in 

the benthic sediment; therefore, EPA was unable to assess whether pollutant concentrations in 

the sediment exceeded CSCL benchmarks and pose a threat to benthic organisms. 

Modeling Results – Human Health

For the analysis of human health impacts and improvements, EPA also assumed that fish 

travel freely throughout Lake Sinclair and do not confine themselves within particular segments 

of the lake. EPA calculated the average fish tissue concentrations of all segments within the Lake

Sinclair model (i.e., entire modeling area) for purposes of the human health assessment. 

8-57
Section 8—Case Study Modeling

Under baseline conditions, the average water column concentration of arsenic in Lake 

Sinclair over the modeling period does not result in an estimated cancer risk greater than 1-in-amillion for any of the national-scale cohorts.

Based on the average pollutant concentrations in the water column under baseline 

conditions, thallium poses the greatest threat to cause non-cancer health effects in humans from 

fish consumption. Average thallium concentrations in the water column of the entire Lake 

Sinclair modeling area are greater than the concentrations that would translate to exceedance of

the reference doses for adult and children recreational and subsistence fishers (all national-scale

cohorts evaluated). Therefore, humans who consume thallium-contaminated fish inhabiting the 

modeled area of Lake Sinclair may be at greater risk for developing the negative health effects

associated with these pollutants, which are discussed in Section 3.1.1. 

While the modeling results continue to show thallium water concentrations that would 

translate to exceedances of the non-cancer health effects reference dose, the final rule will reduce 

thallium loading contributions from Plant Harllee Branch (if Plant Harllee Branch did not retire 

all generating units).

Interpretation of Lake Sinclair Results

The case study modeling results indicate that the water quality impacts are greater in the 

receiving branch (closest portion of the lake to the Plant Harllee Branch discharge) of Lake

Sinclair compared to the rest of the lake. EPA identified that the receiving branch of Lake 

Sinclair also exhibited more quantifiable improvements (i.e., reduced NRWQC and MCL 

benchmark exceedances) under the final rule than the average of all Lake Sinclair model 

segments. Despite the model not indicating any wildlife or human health impacts in Lake

Sinclair, the reduction of pollutant loadings under the final rule would lessen the contribution of 

steam electric power plant discharges on the entire aquatic and terrestrial ecosystems. 

8.3 COMPARISON OF CASE STUDY AND IRW MODELING RESULTS

In general, the case study modeling results from the six case study models support the 

overall conclusions of the IRW model. 

Case study modeling of smaller receiving waters, such as Black Creek and Lick Creek,

indicate that more severe water quality, wildlife, and human health impacts are occurring at

baseline conditions than the IRW model predicted. Since flow rates in small receiving waters

fluctuate significantly, the case study modeling demonstrates impacts that can occur during

periods when the flow is lower than the annual average used in the IRW model. During the 

frequent periods of low flow in smaller rivers and streams, the case study modeling shows that 

pollutant concentrations quickly climb to levels that will negatively affect fish, wildlife, and

humans. The Black Creek and Lick Creek case study model also suggests the potential for

additional improvements under the final rule than the IRW model predicts. Case study modeling 

therefore indicates that small receiving waters with highly variable flow rates may benefit from 

the final rule more than the IRW model results suggest. 

The case study modeling also demonstrates that the impacts from steam electric power 

plant discharges can propagate much further downstream than the immediate receiving water

8-58 
Section 8—Case Study Modeling

used in the IRW modeling. In four of the six case study models, results illustrate that the 

pollutant loadings from steam electric power plant discharges of the evaluated wastestreams may 

contribute to water quality impacts up to 95 miles downstream of the plant discharge. These 

additional impacts, as well as additional improvements under the final rule, are not represented in 

the IRW modeling results. 

Additionally, case study modeling of smaller water bodies revealed that downstream 

reaches may be heavily influenced by the sediment transport and exhibit much higher water 

column concentrations than the immediate receiving water. In the Black Creek, Etowah River, 

and White River results, “hot spots” with higher pollutant concentrations were observed and

posed a greater risk to humans, aquatic life, and terrestrial food chains than reaches closer to the 

steam electric power plants.

EPA performed one case study model of a representative lentic receiving water to assess 

the potential impact on similar lakes or reservoirs that receive steam electric power plant 

discharges of the evaluated wastestreams. Case study modeling of Lake Sinclair showed that 

impacts are occurring in the lake, and these are more severe in the immediate area of the steam 

electric discharge as compared to the lake average. The water quality improvements 

demonstrated by the reduced exceedances of water quality benchmarks indicate that other lentic 

receiving waters may also exhibit similar improvements. Although the case study modeling of 

Lake Sinclair was unable to quantify the accumulation of pollutant concentrations in benthic

sediment, lower concentrations of pollutants under the final rule should reduce pollutant longterm accumulation and consequential resuspension. 

Each of the case study models demonstrated at least one exceedance of a water quality,

wildlife, or human health benchmark for a modeled pollutant discharged from stream electric 

power plants. Under the final rule, the steam electric power plant(s) will contribute a reduced 

loading of the pollutant(s), thereby improving water quality in these receiving waters. As

demonstrated by the Black Creek, Etowah River, Lick Creek and White River, Ohio River, and

Lake Sinclair case study modeling results, pollutant removals will result in quantifiable 

improvements through reduced exceedances of environmental benchmarks. 

8-59 
 

 

Section 9—Conclusions

SECTION 9

CONCLUSIONS 

Based on evidence in the literature, damage cases, other documented impacts, and 

modeled receiving water pollutant concentrations, it is clear that current wastewater discharge

practices at steam electric power plants are impacting the surrounding aquatic and terrestrial 

environments and pose a human health threat to nearby communities. EPA estimates that

discharges from steam electric power plants contribute over one-third of the toxic-weighted 

pollutant loadings of the combined discharges of all industrial categories currently required to 

report discharges to U.S. waters. These discharges add large quantities of toxic bioaccumulative 

pollutants (e.g., selenium, arsenic, and mercury) to the aquatic environment. Substantial evidence

exists that pollutants from steam electric power plant wastewater discharges are transferring from

the aquatic environment to terrestrial food webs; this indicates the potential for broader impacts 

to ecological systems by altering population diversity and community dynamics in the areas

surrounding steam electric power plants. Ecosystem recovery from exposure to steam electric 

power plant wastewater discharges 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. The strong

bioaccumulative properties and long residence times of pollutants in immediate receiving waters 

reinforce the threat of these wastes to the local environment, and many of the impacts may not be 

fully realized for years to come. 

In addition, EPA’s modeling demonstrates that pollutant loadings from discharges of the

evaluated wastestreams are impacting areas beyond the immediate receiving waters and pose a 

threat to wildlife and human populations in thousands of river-miles downstream from steam 

electric power plants under current discharge practices. Furthermore, EPA predicts that the 

recently promulgated Clean Air Act requirements (i.e., Clean Power Plan) and other state and 

local regulations may lead to additional air pollution controls (and resulting wastestreams) that 

will increase the pollutant loadings to surface waters in the future. These additional pollutant

loadings above current baseline conditions will increase the number of immediate receiving

waters exceeding water quality, wildlife, and human health benchmarks in the future.65

Steam electric power plants discharge wastewater into waterbodies used for recreation, 

and these discharges can present a potential threat to human health. Documented fish kills have

resulted in states issuing fish advisories to protect the public from exposure to fish with elevated 

pollutant concentrations in recreational waters that receive these discharges. Combustion residual 

leachate from surface impoundments and landfills is known to impact off-site ground water and 

drinking water wells at concentrations above Maximum contaminant level (MCL) drinking water 

standards and pose a potential threat to human health. 

65 The analyses presented in this report incorporate some adjustments to current conditions in the industry. For 

example, these analyses account for publicly announced plans from the steam electric power generating industry to 

retire or modify steam electric generating units at specific power plants. These analyses also account for changes to

the industry that are expected to occur as a result of the recent Coal Combustion Residuals (CCR) rulemaking by

EPA’s Office of Solid Waste and Emergency Response (OSWER). These analyses, however, do not reflect changes

in the industry that may occur as a result of the proposed Clean Power Plan [Clean Air Act section 111(d)].

9-1 
 

 

Section 9—Conclusions

The final steam electric effluent limitations guidelines and standards (ELGs) will result in

quantifiable improvements in ecological and human health by reducing immediate receiving 

water pollutant concentrations, on average, by 57 percent.66 The final rule will result in the

following environmental improvements as estimated by the national-scale immediate receiving 

water (IRW) model: 

 A 51 to 67 percent reduction in the number of immediate receiving waters exceeding 

National Recommended Water Quality Criteria (NRWQC) for the protection of

aquatic life.

 A 45 to 50 percent reduction in the number of immediate receiving waters exceeding 

an NRWQC for the protection of human health. 

 A 63 to 64 percent reduction in the number of immediate receiving waters that 

support fish whose tissue pollutant concentrations exceed benchmarks for the 

protection of piscivorous wildlife (represented by minks and eagles). 

 A 61 to 67 percent reduction in the number of immediate receiving waters where 

selenium contamination in the food web presents reproductive risks67 to aquatic

wildlife (represented by fish and mallards). 

 A 56 to 75 percent reduction in the number of immediate receiving waters that 

support fish whose tissue pollutant concentrations pose a cancer risk to exposed 

populations. 

 A 52 to 56 percent reduction in the number of immediate receiving waters that 

support fish whose tissue pollutant concentrations pose a risk of non-cancer health 

effects in exposed populations. 

The results of the case study modeling for selected plants and receiving waters indicate

that the environmental and human health impacts associated with steam electric power plant 

discharges, and the corresponding improvements under the final rule, could be even more

extensive than those predicted by the IRW model. Case study modeling results demonstrate that 

the impacts from steam electric power plant discharges of the evaluated wastestreams can 

propagate much further downstream of the immediate receiving water. While the steam electric

power plant discharges may not cause these impacts in isolation, case study modeling reveals 

that the discharges contribute to the further impairment of such waterways. Case study modeling 

results identified a larger increase in baseline impacts and improvements under the final rule in 

small receiving waters with variable flow than larger receiving waters. The analyses presented in

the environmental assessment (EA) focus on quantifying the environmental improvements within 

rivers and lakes from post-compliance pollutant removals for metals, bioaccumulative pollutants, 

and nutrients. 

66 Reductions apply to the subset of pollutants evaluated in the environmental assessment (i.e., arsenic, cadmium, 

chromium VI, copper, lead, mercury, nickel, selenium, thallium, and zinc). 

67 For this statistic, reproductive risk is indicated by a 50-percent (or higher) probability that adverse reproductive 

effects will occur in at least 10 percent of the exposed population of fish and mallards. 

9-2 
 

 

Section 9—Conclusions

While extensive, the environmental improvements quantified above do not encompass 

the full range that will result from the final rule, such as the following improvements that are not 

quantified (or have only limited analysis) in this EA: 

 Reducing the loadings of bioaccumulative pollutants to the broader ecosystem, 

decreasing long-term exposures and sublethal ecological effects.

 Reducing sublethal chronic effects of toxic pollutants on aquatic life not captured by 

the NRWQC. 

 Reducing loadings of pollutants for which EPA did not perform water quality 

modeling in support of the EA (e.g., boron, manganese, aluminum, vanadium, and

iron).

 Mitigating impacts to aquatic and aquatic-dependent wildlife population diversity and 

community structures.68

 Reducing wildlife exposure to pollutants through direct contact with combustion

residual impoundments and constructed wetlands built as treatment systems at steam 

electric power plants.

 Reducing water withdrawals from surface waters and aquifers, leading to greater 

availability of groundwater supplies for alternative uses and reducing fish 

impingement and entrainment mortality due to surface water intake structures.

 Reducing the potential of harmful algal blooms to form. 

Data limitations prevented EPA from 

appropriately modeling the scale and 

complexity of the ecosystem processes 

potentially impacted by steam electric power 

plant wastewater and therefore did not fully 

quantify the improvements listed above.

However, damage cases and other documented

impacts in the literature reinforce that these

impacts are common in the environments 

surrounding steam electric power plants and 

fully support the conclusion that pollutant 

removals will improve overall environmental 

and wildlife health. 

Although the EA quantifies some

impacts to wildlife that consume fish 

contaminated with pollutants from steam 

electric power plant wastewater, it does not 

capture the full range of exposure pathways through which bioaccumulative pollutants can enter

the surrounding food web. Wildlife can encounter bioaccumulative pollutants from steam electric 

power plant wastewater discharges through direct exposure, drinking water, consuming

68 EPA did evaluate impacts to aquatic and aquatic-dependent wildlife from selenium contamination as part of the 

ecological risk modeling. EPA did not quantify impacts that might occur due to other pollutant contamination.

As surface impoundments accumulate fly ash, 

bottom ash and flue gas desulfurization 

sludges, they can begin to fill up and lose their 

treatment capability.

9-3 
Section 9—Conclusions

contaminated vegetation, and consuming contaminated prey other than fish. Therefore, the 

quantified improvements underestimate the complete loadings of bioaccumulative pollutants that 

can impact wildlife in the ecosystem. EPA did quantify improvements to aquatic and aquaticdependent wildlife due to reduced selenium exposure via the food web. The reduced selenium 

loadings under the final rule will significantly reduce the risk of negative reproductive effects to 

wildlife in waterbodies that receive discharges from steam electric power plants. In addition to 

the improvements resulting from reduced selenium loadings, EPA estimates that the postcompliance pollutant removals under the final rule will lower the total amount of 

bioaccumulative pollutants entering the food web in immediate receiving waters and downstream 

waters. 

EPA estimates that pollutant removals will also decrease sublethal effects associated with 

many of the pollutants in steam electric power plant wastewater that may not be captured by 

comparisons with NRWQC for aquatic life. Well-documented studies suggest that organisms in 

aquatic environments near steam electric power plants exhibit chronic effects such as changes in 

metabolic rates, decreased growth rates, changes in morphology (e.g., fin erosion, oral 

deformities), and changes in behavior (e.g., decreased ability to swim, catch prey, or escape from 

predators) that can negatively affect long-term survival [Raimondo et al., 1998; Rowe et al., 

1996, 2002]. However, these effects are not fully quantified in the EA due to data limitations, 

and therefore improvements to wildlife health and survival from the final rule may be

underestimated. Reduced organism survival rates from chronic effects such as abnormalities can 

alter interspecies relationships (e.g., declines in the abundance or quality of prey) and prolong 

ecosystem recovery. EPA was unable to quantify changes to aquatic and wildlife population 

diversity and community dynamics; however, population effects (i.e., decline in number and type 

of organisms present) attributed to exposure to steam electric power plant wastewater are well 

documented in the literature [Lemly, 1985a; Garrett and Inman, 1984; Sorensen et al., 1982]. 

Changes in aquatic populations can alter the structure of aquatic communities and cause

cascading effects within the food web that have long-term impacts to ecosystem dynamics. EPA 

estimates that post-compliance pollutant removals associated with the final rule will lower the 

stressors that can alter population and community dynamics and will improve the overall 

function of ecosystems surrounding steam electric power plants. 

9-4 
Section 10—References

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U.S. EPA. 2010b. Human and Ecological Risk Assessment of Coal Combustion Wastes (CCW)

(Draft). Washington, DC. (April). DCN SE01834. 

U.S. EPA. 2010c. Discharge Monitoring Report (DMR) Pollutant Loading Tool: 2010 Data. 

Available online at: http://cfpub.epa.gov/dmr/. DCN SE01959. 

U.S. EPA. 2010d. Chesapeake Bay Total Maximum Daily Load for Nitrogen, Phosphorus and 

Sediment. Washington, DC. (December). DCN SE01910. 

10-12 
Section 10—References

U.S. EPA. 2011a. Technical Factsheet on: THALLIUM. National Primary Drinking Water 

Regulations. Available online at: 

http://water.epa.gov/drink/contaminants/basicinformation/historical/upload/ArchivedTechnical-Fact-Sheet-on-Thallium.pdf. DCN SE01911. 

U.S. EPA. 2011b. Exposure Factors Handbook: 2011 Edition. EPA/600/R-09/052F. 

Washington, DC. (September). DCN SE01912. 

U.S. EPA, 2011c. Integrated Risk Information System (IRIS). National Center for Environmental 

Assessment. Washington, DC. Available online at: http://www.epa.gov/IRIS/. DCN 

SE01960. 

U.S. EPA. 2011d. Technical Support Document for the 2010 Effluent Guidelines Program Plan.

EPA-821-R-09-006. Washington, DC. (October). DCN SE02135. 

U.S. EPA. 2011e. Office of Science & Technology Annual Report, Calendar Year 2011. EPA 

820-R-12-006. Washington, DC. DCN SE01951. 

U.S. EPA. 2011f. Ecological Toxicity Information (website). EPA Region 5. (December). 

Available online at: http://www.epa.gov/R5Super/ecology/toxprofiles.htm. DCN SE01913. 

U.S. EPA. 2012a. “EPA Weighs Setting Possible First-Time Water Quality Criteria for 

Bromide.” Inside EPA. (January 4). DCN SE01949. 

U.S. EPA. 2012b. Toxic Weighting Factors Methodology. EPA-820-R-12-005. Washington, DC. 

(March). DCN SE04470. 

U.S. EPA. 2012c. TWF Database (EPA-HQ-OW-2008-0517-0713). MS ExcelTM. Washington, 

DC. DCN SE04465. 

U.S. EPA. 2012d. Cyanobacteria and Cyanotoxins: Information for Drinking Water Systems. 

EPA-810-F-11-001. Washington, DC. (July). DCN SE04466. 

U.S. EPA. 2012e. Final Determination of Identified Proven Damage and Recently Alleged 

Damage Cases. SE01966. 

U.S. EPA. 2013a. DMR & TRI Loadings Database for Case Study Modeling. DCN SE05589. 

U.S. EPA. 2013b. Impact Case Study Analysis Database. Washington, DC. DCN SE02156. 

U.S. EPA. 2014a. CCR Damage Cases Database. Office of Solid Waste and Emergency 

Response (OSWER)/Office of Resource Conservation and Recovery (ORCR). Washington, 

DC. DCN SE04457. 

U.S. EPA. 2014b. Damage Case Compendium Technical Support Document, Volume I: Proven 

Damage Cases. OSWER/ORCR. Washington, DC. DCN SE04458. 

U.S. EPA. 2014c. Damage Case Compendium Technical Support Document, Volume IIa: 

Potential Damage Cases. OSWER/ORCR. Washington, DC. DCN SE04459. 

U.S. EPA. 2014d. Damage Case Compendium Technical Support Document, Volume IIb Part 

One: Potential Damage Cases. OSWER/ORCR. Washington, DC. DCN SE04460. 

U.S. EPA. 2014e. Damage Case Compendium Technical Support Document, Volume IIb Part 

Two: Potential Damage Cases. OSWER/ORCR. Washington, DC. DCN SE04461. 

U.S. EPA. 2014f. External Peer Review Draft Aquatic Life Ambient Water Quality Criterion for 

Selenium – Freshwater. EPA 822-P-14-001. Washington, DC. (May). DCN SE06438. 

10-13 
Section 10—References

U.S. EPA. 2014g. Human and Ecological Risk Assessment of Coal Combustion Residuals. 

(December) DCN SE06442. 

U.S. EPA. 2014h. National Fish Consumption Advisories NHD Indexed Dataset. Reach Address 

Database (RAD). Extracted on July 7. Available online at: http://epamap32.epa.gov/radims/. 

DCN SE04545. 

U.S. EPA. 2014i. National 303(d) Listed Impaired Waters National Hydrography Data (NHD) 

Indexed Dataset. RAD. Extracted on August 4. Available online at: 

http://www.epa.gov/waters/data/downloads.html. DCN SE04544. 

U.S. EPA. 2015a. Preventing Eutrophication: Scientific Support for Dual Nutrient Criteria. EPA 

820-S-15-001. Washington, DC. (February). DCN SE04505. 

U.S. EPA. 2015b. Draft Aquatic Life Ambient Water Quality Criterion for Selenium – 

Freshwater. EPA 822-P-15-001. Washington, DC. (July). DCN SE06439. 

U.S. EPA and Environment Canada. 1997. Great Lakes Binational Toxics Strategy. DCN 

SE01942. 

U.S. EPA and Environment Canada. 2009. State of the Great Lakes 2009. EPA 905-R-09-031. 

DCN SE01939. 

USFWS. 2008. U.S. Fish and Wildlife Service. “Steps Taken to Address Selenium Concerns at 

Cane Ridge Wildlife Management Area.” News Release. (June 13). DCN SE02150. 

USFWS. 2012. “Selenium Threat Averted.” News Release. (June 19). DCN SE01943. 

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. DCN SE01893. 

USGS. 2015. The Quality of the Nation’s Groundwater. Barbara Mahler and Jon Campbell. 

(January 21). DCN SE04639. 

VanBriesen, Jeane M. 2013. Potential Drinking Water Effects of Bromide Discharges from CoalFired Electric Power Plants. EPA-HQ-OW-2009-0819-4687-A10. 

Vengosh, A. 2009. The Tennessee Valley Authority's Kingston Ash Slide: Potential Water 

Quality Impacts of Coal Combustion Waste Storage. A Testimony to the Subcommittee on 

Water Resources and Environment, U.S. House of Representatives. Available online at: 

http://transportation.house.gov/Media/file/water/20090331/Vengosh%20Testimony.pdf. 

DCN SE01864. 

Villanueva, C.M., K.P. Cantor, S. Cordier, J.J.K. Jaakkola, W.D. King, D.F. Lynch, S. Porru, 

and M. Kogevinas. 2004. Disinfection byproducts and bladder cancer: a pooled analysis. 

Epidemiology, 15(3):357-367. DCN SE01983. 

Vogel, et. al., 1999. R.M. Vogel, I.W. Wilson, and C. Daly. Regional Regression Models of 

Annual Streamflow for the United States. Journal of Irrigation and Drainage Engineering. 

125 (3): 148-157. (As cited in the NHD Plus User’s Guide). 

Weinberg. 2002. H.S. Weinberg, S. W. Krasner, et al. The Occurrence of Disinfection ByProducts (DBPs) of Health Concern in Drinking Water: Results of a Nationwide DBP 

Occurrence Study (EPA/600/R-02/068) Athens, GA. (As cited in VanBriesen, 2013). 

10-14 
Section 10—References

WHO. 1976. World Health Organization. Environmental Health Criteria 1: Mercury. 

International Programme on Chemical Safety. Geneva, Switzerland. DCN SE01914. 

WHO. 1987. Environmental Health Criteria 58: Selenium. International Programme on Chemical 

Safety. Geneva, Switzerland. DCN SE01915. 

WHO. 1992. Environmental Health Criteria 135: Cadmium. International Programme on 

Chemical Safety. Geneva, Switzerland. DCN SE01916. 

WHO. 1996. Environmental Health Criteria 182: Thallium. International Programme on 

Chemical Safety. Geneva, Switzerland. DCN SE01917. 

WHO. 1998. Environmental Health Criteria 204: Boron. International Programme on Chemical 

Safety. Geneva, Switzerland. DCN SE01918. 

WHO. 2001. Arsenic in Drinking Water. Available online at: 

http://www.who.int/mediacentre/factsheets/fs210/en/. (20 January). DCN SE01919. 

WHO. 2009. Bromide in Drinking-Water. Background Document for Development of WHO 

Guidelines for Drinking-Water Quality. WHO/HSE/WSH/09.01/6. Geneva, Switzerland. 

DCN SE01920. 

WHO. 2011. Manganese in Drinking-Water. Background Document for Development of WHO 

Guidelines for Drinking-Water Quality. WHO/HSE/WSH/03.04/104/Rev/1. Geneva, 

Switzerland. DCN SE01921. 

Wilson et al. 2013. J.M. Wilson, Y. Wang, et al. Sources of high total dissolved solids to 

drinking water supply in Southwestern Pennsylvania. ASCE Journal of Environmental 

Engineering. (As cited in VanBriesen, 2013). 

10-15