Response to Public Review Comments: 

Human and Ecological Risk Assessment 

for Coal Combustion Residuals 

Final 

December 2014 

U.S. Environmental Protection Agency 

Office of Solid Waste and Emergency Response 

Office of Resource Conservation and Recovery 

Regulation Identifier Number: 2050-AE81 
Submitted to: 

Office of Resource Conservation and Recovery 

Office of Solid Waste and Emergency Response 

U.S. Environmental Protection Agency 

Submitted by: 

RTI International 

EPA Work Assignment 4-25 

EPA Contract No. EP-W-09-004 
Response to Public Review Comments

i 

Table of Contents 

1. Introduction and Background ............................................................................................. 1-1

2. Fate and Transport Modeling .............................................................................................. 2-1

2.1. 10,000-Year Ground Water Modeling Time ............................................................. 2-1

2.2. Ground Water Transport Modeling Approach ........................................................... 2-2

2.3. Site-Specific Analysis and Comparisons with Measured Data .................................. 2-8

2.4. Receptor Wells and Surface Water Interception ...................................................... 2-10

3. Source Modeling ................................................................................................................. 3-1

3.1. Use of TCLP and LEAF Data .................................................................................... 3-1

3.2. Facility Data, WMU Data, and Liner Scenarios ........................................................ 3-5

3.3. Alternative Waste/Codisposal Scenarios ................................................................... 3-7

3.4. Liner Leakage ............................................................................................................ 3-9

3.5. Treatment of Non-detect Values ................................................................................ 3-9

3.6. Effect of Waste Compaction .................................................................................... 3-10

3.7. HELP Infiltration Rates, Liner and Cover Assumptions ......................................... 3-11

3.8. Water Table above the Disposal Unit ...................................................................... 3-12

3.9. Impact of Increased Mercury Capture with New Future Air Emission Control 

Regulations .............................................................................................................. 3-13

3.10. Use of Pore Water Data for Impoundment Source Concentrations ......................... 3-14

3.11. Modeling Surface Impoundments Only Pre-Closure ............................................... 3-18

3.12. Modeling of Landfills Only Post-Closure................................................................ 3-20

4. Public Comments on Exposure Scenarios .......................................................................... 4-1

4.1. Direct Surface Impoundment Exposure ..................................................................... 4-1

4.2. Indirect Exposure through Game Species .................................................................. 4-1

4.3. Exposure to Surface Impoundment Effluent.............................................................. 4-1

4.4. Exposure to Fugitive Dust during Landfill Operation (Before Closure) ................... 4-2

4.5. Elimination of Pathways during Screening Analysis................................................. 4-5

4.6. Exposure to Additional Constituents ......................................................................... 4-7

5. Comments Related to Human Exposure and Toxicity ........................................................ 5-1

5.1. Combined Chemical Effects, Additive Risk, and Multiple Pathway Exposures ....... 5-1

5.2. Toxicity and Associated Benchmark Values ............................................................. 5-3

5.3. Target Cancer and Non-Cancer Risk Criteria ............................................................ 5-6

5.4. Defining the Exposed Population .............................................................................. 5-7

5.5. Exposure Factor Assumptions ................................................................................... 5-8

5.6. Child/Infant Exposure Assumptions ........................................................................ 5-10

5.7. Correlations in Input Variables ................................................................................ 5-11

5.8. Bioconcentration Factors ......................................................................................... 5-11

6. Comments Related to Ecological Exposure and Toxicity .................................................. 6-1

6.1. Cumulative Ecological Risk ...................................................................................... 6-1

6.2. Sensitive Habitats/Sensitive Species.......................................................................... 6-2

6.3. Indirect Effects ........................................................................................................... 6-3

6.4. Ecological Benchmarks, Ecological Toxicity ............................................................ 6-3
Response to Public Review Comments Table of Contents 

ii 

7. Comments Related to the Monte Carlo Analysis Approach ............................................... 7-1

7.1. Use of Conservative Parameter Estimates ................................................................. 7-1

7.2. Variability versus Uncertainty ................................................................................... 7-2

7.3. Calculation of Percentile Probabilities as Opposed to an Overall Probability .......... 7-3

7.4. The Numerical Stability of Monte Carlo Results ...................................................... 7-3

7.5. Impacts on Ground water as a Resource .................................................................... 7-3

8. Comments on Documentation and Miscellaneous Comments ........................................... 8-1

8.1. Insufficient Documentation to Reproduce Analysis Independently .......................... 8-1

8.2. Graphical Presentation of Input / Output Distributions, Truncation Values ............. 8-2

8.3. Documentation of Sensitivity Analysis ..................................................................... 8-3

8.4. Discussion of General Risk-Susceptibility Patterns such as Climate-Specific 

Risk ............................................................................................................................ 8-4

8.5. Discussion of Worst-Case Scenarios ......................................................................... 8-4

8.6. Discussion of Sulfate, Phosphate, and Chloride ........................................................ 8-4

8.7. Background Concentrations ....................................................................................... 8-4

9. References .......................................................................................................................... 9-1

List of Tables 

Table 2-2. Comments Related to the Ground Water Transport Modeling Approach .................. 2-3

Table 2-3. Comments Related to Site-Specific Analysis and Comparisons with 

Measured Data .......................................................................................................... 2-9

Table 2-4. Comments Related to Receptor Wells and Surface Water Interception ................... 2-11

Table 3-1. Comments Related to Use of TCLP and LEAF Data ................................................. 3-2

Table 3-2. Comments Related to Facility Data, WMU Data and Liner Scenarios ...................... 3-5

Table 3-3. Public Comments Related to Alternative Waste/Codisposal Scenarios ..................... 3-7

Table 3-4. Public Comments Related to Liner Leakage .............................................................. 3-9

Table 3-5. Public Comments Related to Treatment of Non-detect Values ................................ 3-10

Table 3-6. Public Comments Related to Effect of Waste Compaction...................................... 3-11

Table 3-7. Public Comments Related to HELP Infiltration Rates/Cover Assumptions ............ 3-12

Table 3-8. Public Comments Related to Water Table Above the Disposal Unit ....................... 3-13

Table 3-9. Comments Related to Impact of Increased Mercury Capture with New 

Future Air Emission Control Regulations .............................................................. 3-14

Table 3-10. Comments Related to the Use of Pore Water Data for Impoundment Source 

Concentrations. ....................................................................................................... 3-15

Table 3-11. Comments Related to Modeling Surface Impoundments Only Pre-Closure .......... 3-19
Response to Public Review Comments Table of Contents 

iii 

Table 3-12. Public Comments Related to Modeling of Landfills Only Post-Closure ............... 3-20

Table 4-1. Comments Related to Exposure to Surface Impoundment Effluent .......................... 4-2

Table 4-3. Comments Related to Elimination of Pathways During Screening Analysis ............. 4-6

Table 4-4. Comments Related to Exposure to Additional Constituents ...................................... 4-7

Table 5-1. Public Comments Related to Combined Chemical Effects, Additive Risk, 

and Multiple Pathway Exposures ............................................................................. 5-2

Table 5-2. Public Comments Related to Toxicity Values............................................................ 5-3

Table 5-3. Public Comments Related to Target Cancer Risk ...................................................... 5-6

Table 5-4. Public Comments Related to Defining the Exposed Population ................................ 5-7

Table 5-5. Public Comments Related to Exposure Factor Assumptions ..................................... 5-9

Table 5-6. Public Comments Related to Child/Infant Exposure Assumptions .......................... 5-10

Table 5-7. Public Comments Related to Bioconcentration Factors ........................................... 5-11

Table 6-1. Comments Related to Cumulative Ecological Risk ................................................... 6-1

Table 6-2. Comments Related to Sensitive Habitats/Sensitive Species ...................................... 6-2

Table 6-3. Comments Related to Ecological Benchmarks, Ecological Toxicity ......................... 6-3

Table 7-1. Comments Related to the Use of Conservative Parameter Estimates ........................ 7-1

Table 7-2. Comments Related to Variability versus Uncertainty ................................................ 7-2

Table 8-1. Comments Related to Insufficient Documentation to Reproduce the Analysis ......... 8-1

Table 8-2. Comments Related to the Graphical Presentation of Input/Output 

Distributions, Truncation Values ............................................................................. 8-2

Table 8-3. Public Comments Related to Documentation of Sensitivity Analysis ....................... 8-3
Response to Public Review Comments Table of Contents 

iv 

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Response to Public Review Comments

1-1 

1. Introduction and Background 

To ensure protection of human health and the environment, the U.S. Environmental Protection Agency 

(EPA) has completed a risk assessment to evaluate potential risks to human health and the environment 

from exposure to coal combustion residuals (CCRs), also formerly known as coal combustion wastes 

(CCW), in landfills and surface impoundments (U.S. EPA, 2014a). The data associated with the current 

risk assessment have been provided in a series of Notices of Data Availability (NODAs) published by 

EPA to seek additional information from the public on CCRs to help inform EPA’s regulatory 

determination.1 This document responds to public comments received from the following NODAs: 

 August 2007 – New information and data contained in three documents were published that concern 

the management of CCW in landfills and surface impoundments: 

- A joint U.S. Department of Energy (DOE) and EPA report entitled Coal Combustion Waste 

Management at Landfills and Surface Impoundments, 1994-2004; 

- A draft risk assessment conducted by EPA on the management of CCRs in landfills and surface 

impoundments; and 

- EPA's damage case assessment. 

 June 2010 – The proposed CCR rule was issued for public comment. 

 October 2010 – Additional information was published on the structural integrity of CCRs in surface 

impoundments. 

 October 2011 – Additional information was published on chemical constituent data from CCRs, 

facility and WMU data, damage cases, the adequacy of state programs, and beneficial use. 

 August 2013 – Additional data supplementing the Regulatory Impact Analysis and risk assessment 

were published, as well as information on large scale fill, and data on the surface impoundment 

structural integrity assessments. 

EPA established multiple dockets for this action on www.regulations.gov. The public can view the 

comments in their entirety on the docket Web sites. The docket is located at the EPA Docket Center, 

Public Reading Room, EPA West Building, 1301 Constitution Avenue, NW, Washington, D.C. 

The draft risk assessment (U.S. EPA, 2010) was independently peer reviewed after the 2007 NODA. The 

purpose of the peer review is to enhance scientific and technical work products so that the subsequent

decision or position taken by the EPA has a sound, credible basis. Based on the comments provided by 

the peer reviewers, the document Response to External Peer Review Comments: Human and Ecological 

Risk Assessment for Coal Combustion Residuals (U.S. EPA, 2014b) was prepared by the EPA. For 

consistency, all comment categories from the peer review are included in this document. For each 

comment category, EPA prepared a table that summarizes the docket ID, commenter name and affiliation 

 

1 The Proposed Rule and all NODAs from 2010 to present are available online at: 

www.epa.gov/solidwaste/nonhaz/industrial/special/fossil/ccr-rule/index.htm. 
Response to Public Review Comments Introduction and Background

 1-2 

(e.g. advocacy group), and year. Following this table, EPA prepared a summary of the major comments. 

Lastly, an EPA response is provided that addresses the major comment themes for each subsection, and 

points readers to where the comments are addressed in the revised risk assessment report. In instances that 

no public comments were received on a given category, the relevant section will simply state “no public 

comments.” Four additional comment categories beyond those in the peer review appeared in the public 

comments, and have been added to the end of the relevant sections (e.g., Section 3.4: Receptor Wells and 

Surface Water Interception, Section 4.12: Modelling Landfills Only After Closure; Section 6.8: 

Bioconcentration Factors). Additionally, some comment category names have been expanded to account 

for a broader range of public comments (e.g. Section 4.2 was modified from “2006 DOE Facility Data...” 

to “Facility Data...”). 

EPA received numerous comments discussing the following non-technical or non-risk-related categories: 

beneficial reuse, regulatory comments including Subtitle C versus D listing, legal comments, monitoring 

requirements, the Regulatory Impact Analysis, cost considerations and population risk, direct discharge 

and associated permitting, structural integrity, environmental remediation, sand and gravel pits, coal

mining, and the receipt of site-specific data. Because these comments are not germane to the risk 

assessment, no responses are provided in this document. In addition, EPA received numerous, general 

comments on both the draft risk assessment and subsequent NODAs. These comments tended to express 

general support or disapproval for the risk assessment methodology, data, or results. However, these 

comments did not provide any specific technical recommendations or data that could be used to improve 

the risk assessment. EPA appreciates the overwhelming interest of the public regarding the Agency’s risk 

assessment. However, without any substantive critique that could be acted upon, EPA could not alter the 

risk assessment in response to these more general comments. To the extent that any commenter mentioned

substantive issues regarding a specific aspect of the risk assessment, these comments are further addressed 

in subsequent sections of this document. Table 1-1 on the next page summarizes the comments by 

commenter and major category. If the same commenter commented on the same topic in more than one 

rulemaking or NODA, it is only counted as one subcategory comment in the totals. 
Response to Public Review Comments Introduction and Background

 1-3 

Table 1-1. Summary of Public Comments by Major Category

Commenter Name Commenter ID 

Fate and Transport 

Modeling 

Source Modeling 

Exposure Scenarios 

Human Exposure 

and Toxicity 

Ecological Exposure 

and Toxicity 

Monte Carlo 

Analysis Approach 

Documentation and 

Miscellaneous 

Comments 

Thomas Adams, American Coal 

Ash Association (ACAA) 

EPA-HQ-RCRA-2012-

0028-0108 – ● – – – – – 

Andrew Aho, Geosynthetic 

Materials Association (GMA) 

EPA-HQ-RCRA-2011-

0392-0204 – ● – – – – – 

Paul Allen, Constellation Energy EPA-HQ-RCRA-2011-

0392-0264 – ● ● – – – – 

Alliant Energy EPA-HQ-RCRA-2012-

0028-0078 ● – – ● – – – 

Lauren P. Alterman, Saint-Gobain 

Corp./CertainTeed Corp. 

EPA-HQ-RCRA-2009-

0640-06555 – ● ● – – – – 

Ameren Missouri EPA-HQ-RCRA-2012-

0028-0069 – ● – – – – – 

Sharon Anderson, Powder River 

Basin Resource Council 

EPA-HQ-RCRA-2009-

0640-06192 – – – ● – – – 

EPA-HQ-RCRA-2006-

0796-0057 and 0242 – – ● – – – – 

Anonymous EPA-HQ-RCRA-2006-

0796-0045 – – – ● ● – – 

Anonymous EPA-HQ-RCRA-2009-

0640-06410 – ● – – – – – 

Anonymous EPA-HQ-RCRA-2009-

0640-05774 – – ● – – – –

Traci L. Barkley, Prairie Rivers 

Network, Illinois Chapter of the 

Sierra Club, American Bottom 

Conservancy 

EPA-HQ-RCRA-2009-

0640-06886 – – – ● – – – 

Basin Electric Power Cooperative 

(Basin Electric) 

EPA-HQ-RCRA-2012-

0028-0065 – ● – – – – – 

Mary Arlis Bates, Private Citizen 

EPA-HQ-RCRA-2009-

0640-06959 – – – ● – – – 
Response to Public Review Comments Introduction and Background

 1-4 

Table 1-1. Summary of Public Comments by Major Category

Commenter Name Commenter ID 

Fate and Transport 

Modeling 

Source Modeling 

Exposure Scenarios 

Human Exposure 

and Toxicity 

Ecological Exposure 

and Toxicity 

Monte Carlo 

Analysis Approach 

Documentation and 

Miscellaneous 

Comments 

Robert Bessette, Council of 

Industrial Boiler Owners (CIBO) 

EPA-HQ-RCRA-2006-

0796-0431 – ● – – – – – 

Joyce Blumenshine, Heart of 

Illinois Group Sierra Club 

EPA-HQ-RCRA-2009-

0640-06886 – – – ● – – – 

Jim Brown, Georgia Department 

of Natural Resources (DNR) 

EPA-HQ-RCRA-2009-

0640-07791 ● – – – – – – 

James Burch, Ph.D, Private Citizen EPA-HQ-RCRA-2009-

0640-04005 – – ● – – – 

Daniel J. Casiraro, Salt River 

Project (SRP) 

EPA-HQ-RCRA-2009-

0640-10017 ● – – – – – – 

Michael J. Churchman, AL Envr. 

Council 

EPA-HQ-RCRA-2009-

0640-07002 – – ● ● – – – 

Stephen A. Cobb, Association of 

State and Territorial Solid Waste 

Management Officials 

(ASTSWMO) 

EPA-HQ-RCRA-2009-

0640-08787 ● ● ● – – – 

Basil Constantelos, Edison 

Mission Energy 

EPA-HQ-RCRA-2009-

0640-08244 ● ● – ● – – ● 

EPA-HQ-RCRA-2011-

0392-0237 ● ● ● – – – – 

Terry Coss, Xcel Energy EPA-HQ-RCRA-2009-

0640-08253 – ● ● – – – – 

Art Covi, Wisconsin Electric 

Power Company (We Energies) 

EPA-HQ-RCRA-2009-

0640-06251 – – ● – – – – 

Darren Daboda, Moapa Band of 

Paiutes 

EPA-HQ-RCRA-2009-

0640-06809 – – – ● – – – 

Gary Dawson, Consumers Energy EPA-HQ-RCRA-2012-

0028-0068 ● – – ● – – – 

Edward Dexter, MD Dept. of the 

Environment 

EPA-HQ-RCRA-2011-

0392-0270 – ● – – – – – 

Eva Dillard, Black Warrior 

Riverkeeper, Inc. 

EPA-HQ-RCRA-2009-

0640-08261 ● – – – – – – 
Response to Public Review Comments Introduction and Background

 1-5 

Table 1-1. Summary of Public Comments by Major Category

Commenter Name Commenter ID 

Fate and Transport 

Modeling 

Source Modeling 

Exposure Scenarios 

Human Exposure 

and Toxicity 

Ecological Exposure 

and Toxicity 

Monte Carlo 

Analysis Approach 

Documentation and 

Miscellaneous 

Comments 

Earthjustice EPA-HQ-RCRA-2006-

0796-0446 ● ● ● ● ● – – 

Scott Edwards, Waterkeeper 

Alliance 

EPA-HQ-RCRA-2009-

0640-09633 ● – – ● – – – 

Lisa Evans, Earthjustice 

EPA-HQ-RCRA-2009-

0640-06311 ● ● ● ● ● ● 

EPA-HQ-RCRA-2009-

0640-06313 – – ● – – ● ● 

EPA-HQ-RCRA-2009-

0640-10495 – – ● – – – – 

EPA-HQ-RCRA-2011-

0392-0239 – ● ● – – – – 

Pamela Faggert, Dominion 

Resources Services 

EPA-HQ-RCRA-2011-

0392-0254 – ● ● – – – – 

Jon A. Finlinson, Intermountain 

Power Service Corporation (IPSC) 

EPA-HQ-RCRA-2009-

0640-09728 – ● – – – – – 

Jeffery A. Fornan, Earthjustice EPA-HQ-RCRA-2006-

0796-0446 – – – – ● – – 

Mary A. Fox, Ph.D, MPH, Private 

Citizen 

EPA-HQ-RCRA-2009-

0640-09533 ● – – ● – – – 

Matthew Frank, Wisconsin 

Department of Natural Resources 

(WI DNR) and Eric Callisto, Public 

Service Commission of Wisconsin 

(WI PSC) 

EPA-HQ-RCRA-2009-

0640-06416 – ● – – – – – 

Mollie Freebairn, Private Citizen 

EPA-HQ-RCRA-2009-

0640-06349 – – ● ● – – – 

Michael Gardner, Gypsum Assoc. 

. 

EPA-HQ-RCRA-2009-

0640-08227 – – ● – – – – 

EPA-HQ-RCRA-2011-

0392-0259 – ● – – – – – 
Response to Public Review Comments Introduction and Background

 1-6 

Table 1-1. Summary of Public Comments by Major Category

Commenter Name Commenter ID 

Fate and Transport 

Modeling 

Source Modeling 

Exposure Scenarios 

Human Exposure 

and Toxicity 

Ecological Exposure 

and Toxicity 

Monte Carlo 

Analysis Approach 

Documentation and 

Miscellaneous 

Comments 

Myra Glover, Entergy Services, 

Inc. (Entergy) 

EPA-HQ-RCRA-2011-

0392-0227 – ● – – – – – 

Jonathon Gray, Private Citizen EPA-HQ-RCRA-2009-

0640-06331 – – – ● ● – – 

Great River Energy (GRE) EPA-HQ-RCRA-2012-

0028-0071 – ● – – – – – 

Larry Jensen, People in Need of 

Environmental Safety (PINES) TRANS-CHI-0002-1 – – – ● – – – 

Douglas Green, Utility Solid 

Waste Activities Group (USWAG) 

EPA-HQ-RCRA-2012-

0028-0060 – – ● – – – – 

Emily Greenlee, Earthjustice EPA-HQ-RCRA-2009-

0640-10496 – – ● – – – – 

Tim Gregori, Southern Montana 

Electric 

EPA-HQ-RCRA-2006-

0796-0046 – ● – – – – ● 

Jody Harlan, Sierra Club 

Oklahoma 

EPA-HQ-RCRA-2009-

0640-02401 – – – ● – – – 

Harlan Hatfield, Headwaters 

Resources Inc. (Headwaters) 

EPA-HQ-RCRA-2012-

0028-0061 – ● – – – – – 

Anthony Hatton, Comm. of KY 

EPA-HQ-RCRA-2011-

0392-0219 ● ● ● – – – – 

EPA-HQ-RCRA-2012-

0028-0059 ● ● – ● – – – 

Brad Heavner, Environment 

Maryland Research & Policy 

EPA-HQ-RCRA-2009-

0640-04041 – – – ● – – – 

Dale Helmers, Northern Indiana 

Public Service Company (NIPSCO) 

EPA-HQ-RCRA-2011-

0392-0225 – ● – – – – – 

Chris Hobson, Southern Company 

EPA-HQ-RCRA-2011-

0392-0238 – ● ● – – – – 

EPA-HQ-RCRA-2012-

0028-0044 ● – – ● – – – 
Response to Public Review Comments Introduction and Background

 1-7 

Table 1-1. Summary of Public Comments by Major Category

Commenter Name Commenter ID 

Fate and Transport 

Modeling 

Source Modeling 

Exposure Scenarios 

Human Exposure 

and Toxicity 

Ecological Exposure 

and Toxicity 

Monte Carlo 

Analysis Approach 

Documentation and 

Miscellaneous 

Comments 

Gene Iannazzo, Harsco Minerals 

EPA-HQ-RCRA-2009-

0640-10489 – – – ● – – – 

Kristina Keeling, Private Citizen 

EPA-HQ-RCRA-2009-

0640-06554 – – – ● – – – 

Barbara Gottlieb, Physicians for 

Social Responsibility TRANS-KNX-0069-1 – – ● – ● – – 

Chris Korleski, Ohio 

Environmental Protection Agency 

(EPA) 

EPA-HQ-RCRA-2009-

0640-08226 – ● – – – – – 

Michael J. Kosnett, University of 

Colorado School of Medicine 

EPA-HQ-RCRA-2009-

0640-08869 – – – ● – – – 

TRANS-DEN-0037-1 – – – ● – – – 

William L. Kovacs, U.S. Chamber 

of Commerce 

EPA-HQ-RCRA-2009-

0640-06356 – – – ● – – – 

Carrie La Seur, Plains Justice EPA-HQ-RCRA-2009-

0640-06516 – – – ● – – – 

Ken Ladwig, Electric Power 

Research Institute (EPRI) 

EPA-HQ-RCRA-2006-

0796-0441 ● ● ● ● – ● ● 

EPA-HQ-RCRA-2009-

0640-09765 ● ● ● ● – ● ● 

EPA-HQ-RCRA-2011-

0392-0198 ● ● ● – – – – 

EPA-HQ-RCRA-2012-

0028-0102 ● ● – – – – – 

Dennis Leonard, DTE Energy Co. EPA-HQ-RCRA-2012-

0028-0089 – ● – – – – – 

John McManus, American Electric 

Power (AEP) 

EPA-HQ-RCRA-2012-

0028-0067 – ● – – – – – 

Jeff A. McNelly, ARIPPA EPA-HQ-RCRA-2009-

0640-06360 – – ● – – – – 
Response to Public Review Comments Introduction and Background

 1-8 

Table 1-1. Summary of Public Comments by Major Category

Commenter Name Commenter ID 

Fate and Transport 

Modeling 

Source Modeling 

Exposure Scenarios 

Human Exposure 

and Toxicity 

Ecological Exposure 

and Toxicity 

Monte Carlo 

Analysis Approach 

Documentation and 

Miscellaneous 

Comments 

Dana G. Meier, Indianapolis 

Power & Light (IPL) 

EPA-HQ-RCRA-2009-

0640-09713 ● ● – – – – – 

Richard Meiers, Duke Energy 

Business Services, LLC (Duke 

Energy) 

EPA-HQ-RCRA-2011-

0392-0215 ● ● ● – – – – 

EPA-HQ-RCRA-2012-

0028-0095 – ● – – – – – 

Pamela K. Miller and Sarah B. 

Petras, Alaska Community Action 

on Toxics (ACAT) 

EPA-HQ-RCRA-2009-

0640-06340 – – – ● – – – 

Brian H. Moeck, Large Public 

Power Council (LPPC) 

EPA-HQ-RCRA-2009-

0640-06541 – – – ● – – – 

John W. Myers, TVA EPA-HQ-RCRA-2009-

0640-09536 – – ● – – – 

Jodi Perras EPA-HQ-RCRA-2009-

0640-06829 – – – ● – – – 

Sarah B. Petras, Alaska 

Community Action on Toxics 

EPA-HQ-RCRA-2009-

0640-06307 – – – ● – – – 

Richard C. Phelps, Private Citizen EPA-HQ-RCRA-2009-

0640-05768 – ● – – – – – 

Paul Pike, Ameren EPA-HQ-RCRA-2011-

0392-0223 – ● – – – – – 

G. Preschle, Foothills Group of 

the Sierra Club 

EPA-HQ-RCRA-2009-

0640-05752 – – – ● – – – 

Bruce Ramme, We Energies EPA-HQ-RCRA-2011-

0392-0234 – ● – – – – – 

Renee Reber, Private Citizen 

EPA-HQ-RCRA-2009-

0640-06556 – – – ● – – – 

Farren Richard, Otter Tail Power 

Company 

EPA-HQ-RCRA-2009-

0640-09431 ● – – – – – – 
Response to Public Review Comments Introduction and Background

 1-9 

Table 1-1. Summary of Public Comments by Major Category

Commenter Name Commenter ID 

Fate and Transport 

Modeling 

Source Modeling 

Exposure Scenarios 

Human Exposure 

and Toxicity 

Ecological Exposure 

and Toxicity 

Monte Carlo 

Analysis Approach 

Documentation and 

Miscellaneous 

Comments 

Jim Roewer, USWAG 

EPA-HQ-RCRA-2006-

0796-0432 ● ● – ● – ● ● 

EPA-HQ-RCRA-2009-

0640-06526 ● ● ● ● ● – – 

EPA-HQ-RCRA-2009-

0640-10483 ● ● – ● – – ● 

EPA-HQ-RCRA-2011-

0392-0211 ● ● ● ● ● – – 

EPA-HQ-RCRA-2009-

0640-10791_DA-022-3 – – – – ● – –

Natalie Roy, Clean Water 

Network 

EPA-HQ-RCRA-2009-

0640-06305 – – – ● – – – 

Laura S. Ruhl, Ph.D., Private 

Citizen 

EPA-HQ-RCRA-2009-

0640-09769 ● – – – – – – 

Ruth Santiago, Comite Dialogo 

Ambiental 

EPA-HQ-RCRA-2009-

0640-06196 – – – ● – – – 

Eric Schaeffer, Environmental 

Integrity Project (EIP) 

EPA-HQ-RCRA-2011-

0392-0259 – ● – – – – – 

Abel Russ, EIP 

TRANS-KNX-0048-1 – – – – ● – – 

EPA-HQ-RCRA-2009-

0640-11736_K-162-3 – – – – ● – – 

Rae Schnapp, Citizens Coal 

Council (CCC) and Wabash 

Riverkeeper 

EPA-HQ-RCRA-2012-

0028-0099 ● – – – – – – 

Patricia Schuba, CCC and Labadie 

Environmental Organization 

(LEO) 

EPA-HQ-RCRA-2012-

0028-0097 ● – – – – – – 

R. Bruce Scott, Kentucky 

Department of Environmental 

Resources (KY DER) 

EPA-HQ-RCRA-2009-

0640-06260 ● ● – ● – – – 

Paul L. Sloan, Tennessee 

Department of Environmental 

Conservation (TDEC) 

EPA-HQ-RCRA-2009-

0640-06298 ● – ● – – – – 
Response to Public Review Comments Introduction and Background

 1-10 

Table 1-1. Summary of Public Comments by Major Category

Commenter Name Commenter ID 

Fate and Transport 

Modeling 

Source Modeling 

Exposure Scenarios 

Human Exposure 

and Toxicity 

Ecological Exposure 

and Toxicity 

Monte Carlo 

Analysis Approach 

Documentation and 

Miscellaneous 

Comments 

Rosemary G. Spalding and 

Kathryn A. Watson, Spalding & 

Hilmes, PC 

EPA-HQ-RCRA-2009-

0640-10019 – – ● – – – – 

Kelly Spencer, Private Citizen 

EPA-HQ-RCRA-2009-

0640-06346 – – – ● – – – 

Jeff Stant, CCC EPA-HQ-RCRA-2012-

0028-0046 – ● – – – – – 

Jeffrey A. Steers, Virginia 

Department of Environmental 

Quality (VDEQ) 

EPA-HQ-RCRA-2009-

0640-09284 – – ● – – – – 

Glen Suter II, Ph.D, Private Citizen EPA-HQ-RCRA-2011-

0392-0181 – – – – ● – – 

Richard B. Tedder, Florida 

Department of Environmental 

Protection (FDEP) 

EPA-HQ-RCRA-2009-

0640-06846 – ● – – – – – 

Tennessee Valley Authority (TVA) EPA-HQ-RCRA-2012-

0028-0073 ● ● – ● – – – 

Chet Thompson, CME 

Engineering 

EPA-HQ-RCRA-2012-

0028-0105 ● ● – ● – – – 

Grant Tolley, Earthjustice EPA-HQ-RCRA-2012-

0028-0111 ● ● – – – – – 

Avner Vengosh, Duke University EPA-HQ-RCRA-2009-

0640-07785 – – – – ● – – 

John Veranth, Utah Physicians for 

a Healthy Environment 

EPA-HQ-RCRA-2009-

0640-06068 – ● ● – – – – 

Dr. Conrad Daniel Volz, 

U.Pittsburgh Dept. of Public 

Health 

EPA-HQ-RCRA-2009-

0640-06548 ● – – – ● – – 

Robert J. Waldrop, Full Circle 

Solutions 

EPA-HQ-RCRA-2009-

0640-09951 – – ● – – – – 

Barbara A. Walz, Tri-State 

Generation & Transmission 

EPA-HQ-RCRA-2009-

0640-06956 – – ● – – – – 

Richard Wasserstrom, American 

Forest & Paper Association 

(AF&PA) 

EPA-HQ-RCRA-2006-

0796-0423 – ● – – – – – 
Response to Public Review Comments Introduction and Background

 1-11 

Table 1-1. Summary of Public Comments by Major Category

Commenter Name Commenter ID 

Fate and Transport 

Modeling 

Source Modeling 

Exposure Scenarios 

Human Exposure 

and Toxicity 

Ecological Exposure 

and Toxicity 

Monte Carlo 

Analysis Approach 

Documentation and 

Miscellaneous 

Comments 

Cynthia Water, Saint Vincent 

College 

EPA-HQ-RCRA-2006-

0796-0425 – ● – – – – – 

Shari T. Wilson, Maryland 

Department of the Environment 

(MDE) 

EPA-HQ-RCRA-2009-

0640-08218 – ● – – – – – 

Cathy Woollums, MidAmerican 

Energy Holdings 

EPA-HQ-RCRA-2011-

0392-0233 – ● – – – – – 

Jean-Claude Younan, SCANA Corp EPA-HQ-RCRA-2011-

0392-0274 ● ● ● ● ● – – 

Ian Zabarte, Native Community 

Action Council (NCAC) 

EPA-HQ-RCRA-2009-

0640-06823 – – – ● – – – 

Total Number of Commenters (99 total) 28 48 27 43 9 3 5

 
Response to Public Review Comments Introduction and Background

 1-12 

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Response to Public Review Comments

2-1 

2. Fate and Transport Modeling 

The comments relating to exposure scenarios were grouped into five subcategories, which are 

summarized in the following bulleted list: 

 Section 2.1: 10,000-year maximum ground water modeling time 

 Section 2.2: Ground water transport modeling approach 

 Section 2.3: Site-specific analysis and comparisons with measured data 

 Section 2.4: Receptor Wells and Surface Water Interception. 

2.1. 10,000-Year Ground Water Modeling Time 

Comment Summary 

Commenters wondered how realistic results may be using a risk assessment model that assumes 

current conditions will be maintained for 10,000 years. Specifically, commenters were concerned 

about the assumption that constituent concentrations in the leachate remain constant throughout 

that timeframe. In addition, commenters questioned the assumption that well use and climate 

conditions will remain constant for 10,000 years. The specific comments related to the 10,000-

year ground water modeling time and associated reference information are listed in Table 2-1. 

Table 2-1. Public Comments Related to 10,000-Year Ground Water Modeling Time 

EPA Commenter 

ID Commenter Type Commenter Name Commenter Organization Year 

EPA-HQ-RCRA2011-0392-0211 Trade Association Jim Roewer USWAG 2011 

EPA-HQ-RCRA2009-0640-06526 Trade Association Jim Roewer USWAG 2010 

EPA-HQ-RCRA2009-0640-09533 Private Citizen Mary A. Fox, Ph.D, 

MPH Private Citizen 2010 

EPA-HQ-RCRA2009-0640-09765 Trade Association Ken Ladwig EPRI 2010 

EPA Response 

EPA acknowledges that the 10,000-year ground water modeling time horizon required further 

clarification in the revised risk assessment. Thus, the text in the revised risk assessment has been 

updated to make it clear that the selection of a maximum 10,000-year time horizon does not mean 

that all model simulations continue for the full 10,000 years. Specifically, Section 4 states: 
Response to Public Review Comments Fate and Transport Modeling 

2-2 

EPA ran the model until either the observed ground water concentration of a 

constituent at the receptor point reached a peak and then fell below a modelspecified minimum concentration (10-16 mg/L), or the model had been run for a time 

period of 10,000 years. 

Although ground water concentrations are modeled beyond the observed peak or maximum 

average concentrations, these post-peak or post-maximum average predictions are not used in 

estimates of risk. In many cases the leachate plume reaches the receptor point much sooner than 

10,000 years. As discussed in Section 5 and Appendix K of the revised risk assessment, on a 

national scale, both unlined and clay-lined surface impoundments consistently pose peak risks 

within 100 years. Meanwhile, composite liners show much longer peak arrival times, close to 

10,000 years for most surface impoundment runs. Peak arrival times are longer for landfills, and 

more than 10,000 years for composite-lined landfills. Under such timeframes, EPA acknowledges 

that surface conditions may change significantly, compounding the uncertainty associated with the 

predicted exposures and risks. However, EPA also notes that the time to first exceedance of 

selected risk criteria is typically considerably less than the time to the greatest exceedance. 

EPA acknowledges that future ground water use patterns may shift as the number and location of 

receptors changes, and that it is unknown whether future changes in receptor locations and other 

surface conditions would result in greater, lesser, or the same risk as predicted in this analysis. 

However, no known data exist that would allow EPA to do more than speculate about future 

population dynamics. Thus, the Agency relied on the best available data on the current population 

to conduct the revised risk assessment. The approach used to place residential ground water wells 

is further discussed in Section 4 and Appendix B of the revised risk assessment, and the associated 

uncertainties are discussed in Section 5. 

2.2. Ground Water Transport Modeling Approach 

Comment Summary 

Comments related to the specifics of the ground water transport modeling were received from 

commenters. Issues covered in their comments included the following: 

Geochemical Modeling: 

 The way that soil and aquifer Kd values were determined and used, including the fact that the 

risk assessment did not explicitly model oxidation/reduction reactions and precipitationdissolution processes that may influence the chemical fate and transport. 

 Whether hydrogeologic settings were assigned correctly. 

Selection of Sorbents: 

 The selection of iron oxides, and dissolved (DOM) and particulate organic matter (POM) to 

represent all sorbents in soil and aquifer materials. 

 The selection of goethite as the iron oxide mineral to use to estimate sorption to vadose zone 

and aquifer materials. 
Response to Public Review Comments Fate and Transport Modeling 

2-3 

 The treatment of POM and DOM in the MINTEQA2 modeling used to generate the Kd values 

(sorption isotherms) used in the analysis. 

 The adequacy of sensitivity and uncertainty analyses for the MINTEQA2 modeling. 

Kd Values: 

 The approach used to determine the value of pH in the aquifer for selecting Kd. 

 The subsequent calculation of the retardation factor. 

Arsenic Speciation: 

 The assumption that arsenic III is the only or dominant form of arsenic is too conservative, 

as arsenic III readily converts to the less mobile arsenic V species under aerobic conditions. 

 A commenter requested time to exceedance results for arsenic species and other constituents, 

as well as distance versus concentration output from EPACMTP. 

EPACMTP Assumptions and Simplifications: 

 The appropriateness of EPACMTP and its various assumptions and simplifications for 

ground water modeling, including: 

- Not altering the chemistry of the aquifer receiving leachate. 

- Not simulating variable oxidation-reduction potential conditions or multiple chemical 

species during a model run. 

- Not evaluating the potential mobilization of non-waste related metals from soils when 

exposed to leachate with potentially different geochemistry compared to ambient 

conditions. 

- Not considering the potential occupation of adsorption sites by naturally occurring metals 

or competition from multiple contaminants. 

- Not considering mounding-induced reduction of the unsaturated zone thickness or other 

cases where the ground water table is in direct contact with the bottom of the WMU. 

- Not considering fractured rock, karst, and other complex hydrogeologic settings. 

The comments also addressed the general need for more transparency in the data and methods used 

in the analysis and the need for validation and/or comparison of model inputs and results to sitespecific field data. The specific comments related to the Ground Water Transport Modeling 

Approach and associated reference information are detailed in Table 2-2. 

Table 2-2. Comments Related to the Ground Water Transport Modeling Approach 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2012-0028-0105 Electric Utility 

Company Chet Thompson CME Engineering LP 2013 
Response to Public Review Comments Fate and Transport Modeling 

2-4 

Table 2-2. Comments Related to the Ground Water Transport Modeling Approach 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2012-0028-0111 Advocacy Group Grant Tolley Earthjustice 2013 

EPA-HQ-RCRA2011-0392-0211 Trade Association Jim Roewer USWAG 2011 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-06526 Trade Association Jim Roewer USWAG 2010 

EPA-HQ-RCRA2009-0640-09765 Trade Association Ken Ladwig EPRI 2010 

EPA-HQ-RCRA2009-0640-10017 Electric Utility 

Company Daniel J. Casiraro SRP 2010 

EPA-HQ-RCRA2009-0640-08244 Electric Utility 

Company 

Basil G. 

Constantelos 

Edison Mission 

Energy, LLC 2010 

EPA-HQ-RCRA2006-0796-0446 Consulting Charles Norris and 

Mark Hutson Geo-Hydro, Inc. 2007 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA-HQ-RCRA2006-0796-0432 Trade Association Jim Roewer USWAG 2007 

EPA Response 

Geochemical Modeling: EPA recognizes that explicit reactive/geochemical modeling would be 

more realistic than using linear and nonlinear partitioning coefficients. EPA considered the use of 

the Objects Representing Chemical Speciation and Transport (ORCHESTRA) model during 

revisions to the risk assessment because it can account for geochemical interactions, such as 

aqueous complexation, precipitation, surface complexation, and ion exchange (Meeussen, 2003). 

However, such modeling is not a practical approach for a nationwide analysis because the data 

collection effort necessary to populate such a model on a nationwide, location-based level would 

be prohibitively expensive. Even assuming such data were available to populate ORCHESTRA or 

a similar model, the complexity of the algorithms necessary to account for highly variable 

geochemical and hydrogeologic conditions nationwide and the time required to run such a model 

would also be impractical. Furthermore, the use of Kd as a surrogate for dilution/sorption/ 

precipitation processes is a widely used and accepted method in both the scientific literature and 

the ground water modeling community, provided the values of Kd used are appropriate to account 
Response to Public Review Comments Fate and Transport Modeling 

2-5 

for the range of potential attenuation processes (U.S. EPA, 1999a). Therefore, for a nationwide 

analysis, the use of Kd is a practical and necessary simplification. EPA has added discussion to the 

risk assessment to clarify Kd-related issues raised by the commenters. Appendix H of the revised 

risk assessment displays select percentiles of the Kd values used in the analysis. These values were 

derived from the isotherm sampling performed by EPACMTP and used in the modeling (including 

effective Kd values for the unsaturated zone). A listing of all individual Kd values available in the 

MINTEQA2 isotherms used in these analyses would not be practicable. Instead, the full input and 

output files are available to the public in the docket. 

Some commenters suggested that EPA should focus on the effect of redox potential in the ground 

water on fate and transport. While this is possible, it would take significant effort to set up this 

type of approach for every inorganic constituent considered in the risk assessment, and it was 

determined not to be necessary. EPA did indirectly account for some of the major effects of redox 

potential when modeling arsenic and other constituents for which speciation is known to have a 

significant impact on mobility. For these constituents, a model run was conducted for each species 

under the assumption that all of the constituent mass was present as that speciation. Therefore, 

EPA did not evaluate redox, and acknowledges this is a source of uncertainty for the ground water 

transport modeling approach. Commenters expressed concern about the assumption of a single 

speciation, noting that it is likely that constituents will be present as some combination of the 

different species. EPA acknowledges that this approach is a simplification of real world conditions; 

however, the Agency believes this approach is useful because it provide bounding estimates that 

can inform the risk assessment. 

Regarding the concern that there were possible errors in hydrogeological assignments, these 

assignments have been updated in the revised risk assessment based on a more robust and accurate 

dataset for waste management unit (WMU) and facility locations. These data are discussed in 

Section 3 and Appendix B of the revised risk assessment. Because these assignments were based 

on more complete GIS coverages of soils and aquifers across the U.S., they are more consistent 

and reliable than the previous ones in representing the spatial variability in hydrogeologic 

environments needed by the EPACMTP model. 

Selection of Sorbents: In recent years, databases of equilibrium sorption reactions have been 

compiled in the literature for several of the dominant potential sorbents in the environment, 

including two common iron oxide minerals: hydrous ferrous oxides (HFO) and goethite (Dzombak 

and Morel, 1990; Mathur, 1995). Because of the availability of these data and their prevalence in 

the environment, these are the sorbent types available for MINTEQ2 modeling used to develop 

constituent sorption isotherms. Other common hydrous oxides that can sorb chemicals include 

hydrous oxides of aluminum, manganese, and silicon (Dzombak and Morel, 1990); however, there 

were insufficient data on these to consider their use. To determine the most appropriate iron oxide 

sorbent, EPA chose goethite as the most appropriate form of hydrous iron oxide for the risk 

assessment to avoid an underestimation of risk. While both goethite and HFO are common forms 

of iron oxide in soils, goethite is a much poorer adsorbent than HFO, thereby leading to relatively 

greater ground water plume concentrations. EPA acknowledges that HFOs are common as well 
Response to Public Review Comments Fate and Transport Modeling 

2-6 

and there is the potential for HFOs with greater sorption affinities than goethite to be present at 

some CCR disposal sites. In reaching this conclusion, EPA consulted experts who published on 

this subject (specifically, Dr. David Dzombak, Dr. Samir Mathur and Dr. Jerry Allison), developer 

of MINTEQA2. EPA agrees that this was a necessary assumption. 

EPA also recognizes that limiting MINTEQA2 to two types of sorptive materials (iron oxide and 

organic matter [DOM and POM]) is a simplification given the wide range or soil and aquifer 

materials that actually adsorb metals (e.g., clay and other soil minerals). However, given that the 

extensive sorption databases needed to perform MINTEQA2 are available for POM, DOM, and 

goethite, we believe that they are the best representation of subsurface sorption processes active in 

soils and aquifer materials. This decision and the actual approaches used to model DOM, POM, 

and goethite are described in detail in MINTEQA2 background documents and the associated 

Response to Peer Review Comments for those documents. 

Finally, with respect to the adequacy of sensitivity and uncertainty analyses for MINTEQA2, EPA 

notes that the 2009 sensitivity analysis showed that only results for strongly sorbing constituents 

were sensitive to the Kd values output from MINTEQA2. In contrast, the three risk drivers 

identified in the revised risk assessment (arsenic, lithium, and molybdenum) all tend to be weakly 

sorbing, with the exception of arsenic in the pentavalent state. Furthermore, to the extent Kd affects

the risks, Section 5 of the revised risk assessment evaluated these effects by examining alternate 

speciation (e.g., trivalent and pentavalent arsenic) as well as the effect of waste type and waste pH.

For these reasons, EPA finds that sufficient sensitivity and uncertainty analyses were conducted. 

Kd Values: The approach adopted in the risk assessment to determine the value of pH in the aquifer 

(used to select Kd) and the subsequent calculation of the retardation factor assumed that, after 

entering the aquifer, the leachate plume would thoroughly mix with the ambient, uncontaminated 

ground water. One commenter stated that the mixing zone would only be present at the periphery 

of the ground water plume. This is consistent with the general conceptual model used in this risk 

assessment of uniform subsurface flow with recharge. However, EPACMTP requires a constant 

ground water pH in each model run to model transport with nonlinear sorption isotherms. EPA 

assumed full mixing as a more conservative approach to selecting pH because, for most metals, 

sorption/precipitation tends to increase (i.e., Kd goes up) with higher pH, which is characteristic of 

much CCR leachate (i.e., assuming full mixing lowers the ground water pH and, thus, decreases 

sorption). To characterize the potential effect of this simplifying assumption on calculated risk 

results, EPA conducted an uncertainty analysis that is presented in Section 5 of the revised risk 

assessment. 

EPA considered comparing the modeled Kd values to available estimates in the published 

literature, but did not do so for three reasons. First, there are many individual values within each 

Kd isotherm that depend both on constituent concentrations and MINTEQA2 master variables, 

such as pH, organic carbon, and iron oxide concentrations. Second, measured values are limited 

to specific sites where conditions that may not be fully documented, and because such variables 

can vary from site to site, it can be very difficult to determine exactly how well the collected values 
Response to Public Review Comments Fate and Transport Modeling 

2-7 

represent conditions across the country. Third, field and laboratory methods for measuring Kd vary 

greatly and are not easy to compare, adding a significant measurement uncertainty to the variability 

issues mentioned above. Therefore, not only would this comparison be complicated to perform, it 

would also be subject to its own numerous uncertainties and unknown biases, making it unlikely 

to provide a basis for definitive conclusions about the representativeness of the current approach. 

With respect to comments on the calculation of the retardation factor, EPA points commenters to 

U.S. EPA (2003b) which discusses how EPA uses Kd values to model sorption in the subsurface 

environment. 

Arsenic Speciation: Commenters also pointed out that literature on arsenic V often shows that it 

is orders of magnitude less soluble than arsenic III, which appears inconsistent with the results of 

the 2010 Draft Risk Assessment. The draft assessment found similar exposure concentrations for 

both arsenic species. As a result of a combination of different updates to the revised risk 

assessment, the modeled concentrations of arsenic III and V are now generally an order of 

magnitude different, although the specific results vary between pathways. One cause of this 

difference is likely the increased distances to receptors in the revised risk assessment. The 

increased distance would lead to additional arsenic V attenuation because this species sorbs more 

readily (i.e., has greater Kd values) than arsenic III. Section 5 of the revised risk assessment 

discusses the uncertainty associated with modeling both species of arsenic. For the specific 

concentrations at various distances, EPA directs the commenter to review the input and output files 

available in the docket. 

EPA did not model the time to first exceedance of risk criteria, but did conduct a sensitivity 

analysis for the time to peak ground water concentration. The time to peak results for arsenic 

species and other select other constituents are presented in Section 5 of the revised risk assessment.

The distance to nearest well receptors is also discussed in Section 5 of the revised risk assessment. 

The relation of distance versus concentration was not explicitly evaluated on a per simulation basis, 

rather all receptor well locations within one mile from the WMU footprint were included in the 

analysis to provide a conservative risk estimate. 

EPACMTP Assumptions and Simplifications: Comments on the treatment of dispersivity 

within EPACMTP highlighted the need for greater transparency about the model’s underlying 

assumptions and input data sources. The documentation for the 2010 Draft Risk Assessment did 

not include comprehensive tables detailing model input parameters, their values or distributional 

characteristics, and the sources of the data used. These values are, in many cases, publicly available

in the EPACMTP Background and Parameters/Data Background documents (U.S. EPA, 2003a,b). 

EPA still finds it inappropriate to duplicate this large amount of data. Instead, the revised risk 

assessment includes an increase in the number of references to these documents, and directs 

readers to refer to these documents for further information. Additionally, the full input and output 

files are available to the public in the docket. 

With respect to the fundamental questions raised about the assumptions and simplifications built 

into EPACMTP, EPA acknowledges some limitations within the model. Some simplifications are 
Response to Public Review Comments Fate and Transport Modeling 

2-8 

necessary to complete a large, national scale risk assessment, and the model provides the most 

appropriate available tool to complete this type of analysis. As discussed in Section 5 of the revised

risk assessment, EPACMTP has been thoroughly peer reviewed and tested for application in largescale risk assessments. This section also provides additional documentation on these internal and 

external reviews of the model, its limitations, and the associated uncertainties. With respect to 

particular criticisms levied: 

• EPA alters the chemistry of the aquifer receiving leachate by changing the aquifer pH in 

response to full mixing. Alternatively, EPA conducts an analysis in Section 5 using the 

alternate assumption of partial mixing; 

• EPA evaluates alternative species in separate model runs. As described in the revised risk 

assessment, EPA believes that presentation of these two results bound the range of possible 

risks from a constituent. To the extent that EPA does not model oxidation-reduction 

potential, EPA notes that this would require geochemical modeling, which was not feasible 

for the reasons discussed above; 

• Full mixing of the leachate plume did not demonstrate significant potential to affect aquifer 

pH. Thus, since pH is one of the most significant factors affecting constituent mobilization 

EPA does not believe significant constituent from the underlying soils will be mobilized in 

most cases. Instead, it is a site-specific consideration that is not possible to include in a 

nationwide risk assessment. 

• A discussion of sorbent competition as a limitation of the analysis is discussed in 

Attachment H-1 of Appendix H in the revised risk assessment. 

EPA did not consider ground water mounding, ground water in contact with the waste management 

unit, fractured rock, karst, and other complex hydrogeologic settings as these are site-specific 

considerations that could not be accommodated in a nationwide risk assessment. 

Additional Comments: The comments provided on the topics discussed above also touched on 

other topics, which are addressed in greater detail elsewhere in this document. Thus, EPA does not 

provide a response to these additional topics here. Comments relating to the general need for more 

transparency in the data and methods used in the analysis are discussed in Section 8.1 of this 

document. Comments regarding the need for validation and/or comparison of model inputs and 

results to site-specific field data are discussed in Section 2.3 of this document. 

2.3. Site-Specific Analysis and Comparisons with 

Measured Data 

Comment Summary 

Several commenters discuss the use of site-specific analysis to increase confidence in the risk 

assessment results. They expressed concern that the results are difficult to evaluate given the 

significant variability and uncertainty associated with the national scope of the analysis, and that 
Response to Public Review Comments Fate and Transport Modeling 

2-9 

validation or calibration of EPACMTP results with actual data is needed, including the potential 

use of damage cases. The specific public comments related to the site-specific analysis and 

comparisons with measured data, and associated reference information are detailed in Table 2-3. 

Table 2-3. Comments Related to Site-Specific Analysis and Comparisons with 

Measured Data 

EPA Commenter 

ID Commenter Type Commenter Name Commenter Organization Year 

EPA-HQ-RCRA2009-0640-06298 State Government Paul L. Sloan TDEC 2010 

EPA-HQ-RCRA2009-0640-06526 Trade Association Jim Roewer USWAG 2010 

EPA-HQ-RCRA2009-0640-08244 Electric Utility 

Company 

Basil G. 

Constantelos 

Edison Mission Energy, 

LLC 2010 

EPA-HQ-RCRA2009-0640-09431 Electric Utility 

Company Farren Richard Otter Tail Power Company 2010 

EPA-HQ-RCRA2009-0640-09633 Advocacy Group Scott Edwards Waterkeeper Alliance 2010 

EPA-HQ-RCRA2009-0640-09765 Trade Association Ken Ladwig EPRI 2010 

EPA-HQ-RCRA2009-0640-08261 Advocacy Group Eva Dillard Black Warrior 

Riverkeeper, Inc. 2010 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-09769 Private Citizen Laura S. Ruhl, Ph.D. Private Citizen 2010 

EPA-HQ-RCRA2009-0640-06548 Academia Dr. Conrad Daniel 

Volz 

University of 

Pittsburgh Department 

of Public Health 

2010 

EPA-HQ-RCRA2006-0796-0432 Trade Association Jim Roewer USWAG 2007 

EPA Response 

Commenters expressed concern about validation of the EPACMTP model with actual field data 

and some commenters suggested that EPA should use actual monitoring data rather than modeling 

to assess potential risks. EPA recognizes the importance of monitoring data in characterizing 

specific sites. EPA agrees with the commenters that confidence in the results of an environmental 

fate and transport model increase significantly when model predictions can be compared favorably 

with measured field results. However, site-specific modeling involves extensive data collection 

and detailed modeling (representing site-specific conditions and processes), which was not 
Response to Public Review Comments Fate and Transport Modeling 

2-10 

possible for this large, national-scale risk assessment. Available site-specific data are limited to a

relatively small fraction of locations and settings. This risk assessment was intended to represent 

a broad range of potential conditions. Consequently, EPA validated the model results with actual 

field data by comparing the results of the national probabilistic, Monte Carlo analysis to 

proven/potential damage cases from across the United States. These damage cases represent realworld instances of contamination from CCR WMUs that provide the best available comparison 

for the results of the risk assessment. This comparison is presented in Section 5 of the revised risk 

assessment. EPA also provided extensive EPACMTP validation results relative to theoretical 

models and field data in Appendix D of the EPACMTP technical background document (U.S. 

EPA, 2003a,b). 

2.4. Receptor Wells and Surface Water Interception 

Comment Summary 

Comments relating to the number of wells contaminated, the realistic risk of exposure, well 

placement within the plume, distance to receptor wells, identification of surface water receptors, 

surface water interception modeling, the appropriateness of receiving water reaches (e.g. the 

nearest surface water body), and other receptor or well-related issues were received from public 

commenters. 

Surface Water Interception Modeling: Regarding surface water interception, many comments

were supportive of EPA’s approach for simulating the interception of ground water by surface 

water bodies, which has been added to the revised risk assessment. However, some commenters 

indicated that a meaningful allocation of the ground water plume between a surface water body 

and a downgradient well receptor can only be determined reliably with assessment of the system 

at a local scale. 

Commenters also raised questions regarding the specific surface water interception methodology, 

including the base data and algorithms used to calculate stream base flow, net ground water flow, 

and the contaminant mass loss to ground water. Concern was expressed about the large range of 

possible values used for Monte Carlo sampling without calibrating models to site specific 

conditions and the potential to mismatch parameters. Additionally, concerns were raised that the 

assessment assumed transport directly to the nearest water body without reflecting complexities 

that are often present and could lead to longer transport pathways or to pathways to water bodies 

other than the nearest. 

Commenters noted that the vicinity of many WMUs is serviced by a municipal water supply, and; 

therefore, there would be no drinking water receptors associated with these WMUs. Comments 

were also received that the one mile distance considered by the transport model is not sufficient, 

because actual receptor wells in many cases are further than one mile from facilities. Comments 

also highlighted the possibility that modeled receptor well concentrations may incorrectly 

represent actual exposures by sampling from a single aquifer depth. Comments on dispersivity 

noted the need for greater transparency in the report. 
Response to Public Review Comments Fate and Transport Modeling 

2-11 

Placement of Receptor Wells, EPACMTP Well Inputs and Assumptions: Additional 

comments related to the risk assessment’s use of water well distances from municipal solid waste 

(MSW) landfills and the Agency’s belief that these distances would be protective for CCR WMUs. 

Additional comments focused on the assumption that the wells used in this assessment are 

contaminated (i.e., located within the plume), even if the well location used reflects a deeper well 

that may be screened in an uncontaminated aquifer; the manner in which the assessment handles 

uncontaminated wells, plume characteristics, ground water–surface water interactions, vertical 

contaminant concentration across a screened interval in an aquifer; and the values used for plume 

dispersivity. The specific comments related to receptor well and surface water interception related 

issues, and associated reference information are detailed in Table 2-4. 

Table 2-4. Comments Related to Receptor Wells and Surface Water Interception 

EPA Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2012-0028-0044 Electric Utility 

Company Chris Hobson Southern Company 2013 

EPA-HQ-RCRA2012-0028-0068 Electric Utility 

Company Gary Dawson Consumers Energy Company 2013 

EPA-HQ-RCRA2012-0028-0097 Advocacy Group Patricia Schuba CCC and LEO 2013 

EPA-HQ-RCRA2012-0028-0099 Advocacy Group Rae Schnapp CCC and Wabash 

Riverkeeper 2013 

EPA-HQ-RCRA2012-0028-0102 Trade Association Ken Ladwig EPRI 2013 

EPA-HQ-RCRA2012-0028-0105 Electric Utility 

Company Chet Thompson CME Engineering LP 2013 

EPA-HQ-RCRA2012-0028-0111 Advocacy Group Grant Tolley Earthjustice 2013 

EPA-HQ-RCRA2012-0028-0059 State Government Anthony Hatton Commonwealth of 

Kentucky 2013 

EPA-HQ-RCRA2012-0028-0073 Electric Utility 

Company 

Tennessee Valley 

Authority (TVA) TVA 2013 

EPA-HQ-RCRA2012-0028-0078 Electric Utility 

Company 

Alliant Energy 

Corporate Services, 

Inc. 

Alliant Energy Corporate 

Services, Inc. 2013 

EPA-HQ-RCRA2011-0392-0198 Trade Association Ken Ladwig EPRI 2011 

EPA-HQ-RCRA2011-0392-0211 Trade Association James Roewer USWAG 2011 
Response to Public Review Comments Fate and Transport Modeling 

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Table 2-4. Comments Related to Receptor Wells and Surface Water Interception 

EPA Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2011-0392-0219 State Government Anthony Hatton Commonwealth of 

Kentucky 2011 

EPA-HQ-RCRA2011-0392-0274 Electric Utility 

Company Jean-Claude Younan SCANA Corp. 2011 

EPA-HQ-RCRA2011-0392-0237 Electric Utility 

Company Basil Constantelos Edison Mission Energy, LLC 2011 

EPA-HQ-RCRA2011-0392-0215 Electric Utility 

Company Richard Meiers Duke Energy 2011 

EPA-HQ-RCRA2009-0640-06260 State Government R. Bruce Scott KY DEP 2010 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-10483 Trade Association James Roewer USWAG 2010 

EPA-HQ-RCRA2009-0640-08787 State Government Stephen A. Cobb ASTSWMO 2010 

EPA-HQ-RCRA2009-0640-09765 Trade Association Ken Ladwig EPRI 2010 

EPA-HQ-RCRA2009-0640-07791 State Government Jim Brown Georgia DNR 2010 

EPA-HQ-RCRA2009-0640-08244 Electric Utility 

Company 

Basil G. 

Constantelos 

Edison Mission Energy, 

LLC 2010 

EPA-HQ-RCRA2009-0640-09713 Electric Utility 

Company Dana G. Meier IPL 2010 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA Response 

Surface Water Interception Modeling: In cases where receptor wells are located downgradient 

from a surface water body that intersects the ground water table, some or all of the ground water, 

along with the mass of constituents contained therein, is intercepted by the water body before it 

can reach the well. This interception was not modeled in the 2010 Draft Risk Assessment. 

However, a review of the input database for the 2010 Draft Risk Assessment found that such a 

water body was present in approximately two-thirds of the Monte Carlo runs. Furthermore, 
Response to Public Review Comments Fate and Transport Modeling 

2-13 

ignoring the loss of constituent mass had the effect of overestimating exposures. Thus, in the 

revised risk assessment an EPACMTP model post-processor was created to account for surface 

water interception by removing constituent mass flowing into the water body from the ground 

water plume, and leaving only the remaining ground water available to migrate to a drinking water 

receptor. The approach used to account for interception is discussed in further detail in Section 4 

and Appendix J of the revised risk assessment. 

While commenters were generally supportive of the proposed approach, some indicated that a 

meaningful allocation of constituent mass from ground water into a surface water body required 

site-specific data. Concerns were raised about the assumption that transport occurred directly to 

the nearest water body without reflecting complexities that are often present and could lead to 

longer transport pathways or to pathways to water bodies other than the nearest. EPA 

acknowledges that local conditions can make ground water flow conditions complex, and detailed, 

local-scale assessments would be required to describe these conditions accurately. While EPA 

agrees that local-scale conditions must be considered for precise estimation for specific systems, 

it was impractical for EPA to characterize, simulate, and calibrate models for the numerous 

locations across the nation. Discussion of the uncertainties associated with this approach has been 

added to Section 5 of the revised risk assessment. 

Several questions about the surface water interception methodology were raised by the public. The 

qBaseflow input parameter was derived from the NHDplus mean recharge parameter 

(MEAN_RCHRG; USGS, 2002) and the size of the water body catchment and reach (see 

Appendix B of the revised risk assessment). The approach assumes that all streams intersect the 

shallow aquifer and that all streams either gain water from the aquifer or do not interact with the 

aquifer at all (for simplicity and conservatism). As the commenter indicates, qNetflow is a key 

result calculated by subtracting the stream baseflow from the average ground water flow 

upgradient of the stream. The qNetflow value becomes the adjusted ground water flow beyond the 

stream, reflecting ground water losses to the stream. One commenter raised a specific question 

about how the methodology handles cases where qNetflow is less than zero, but greater than the 

average ground water flow. This case does not occur with the methodology adopted by EPA, 

because qNetflow is always equal to or less than the average ground water flow (i.e. streams are 

assumed not to be losing). If qNetflow is negative (i.e., a losing stream), all of the ground water is

assumed to migrate to any wells on the opposite side of the stream. 

Model Validation/Calibration: Concern was expressed about the large range of possible values 

used in the probabilistic analysis for certain parameters and the potential for this to result in a 

mismatch of input parameters without proper site-specific calibration. EPA notes that the revised 

risk assessment is not intended to capture the exact risks at each disposal site. Instead, the revised

assessment combines the best resolution of site-based, regional and national data available to 

provide an estimate of potential risks that may occur from current disposal practices. While the 

assigned data for any given model iteration may not reflect the exact conditions at a real-world 

site, the resulting sum of all model iterations reflect the range of potential conditions near each 

WMU, weighted by prevalence, across the conterminous United States. 
Response to Public Review Comments Fate and Transport Modeling 

2-14 

Placement of Receptor Wells, EPACMTP Well Inputs and Assumptions: Comments 

regarding placement of receptor wells in the probabilistic analysis (also known as the 

appropriateness of receiving water reaches) are the result of a fundamental misinterpretation 

regarding the constraints placed on ground water receptor location to be, as described in the 2010 

Draft Risk Assessment, “within the contaminant plume.” This constraint is more fully explained 

in Section 4.4.3.6 of the EPACMTP technical background document (U.S. EPA, 2003a,b). A 

citation referring readers to that document has been placed in Section 4 of the revised risk 

assessment. Because the comment resulted from a misunderstanding, EPA does not believe the 

sensitivity analysis suggested by the commenter is necessary. 

Some commenters were concerned that many residents in the vicinity of some WMUs may be 

serviced by a municipal water supply. Because these residents would not be exposed to ground 

water, the risk assessment could overestimate exposures. EPA acknowledges that there may be a 

large percentage of the population that does not rely on ground water as a source of potable water; 

however, the aim of the risk assessment is to estimate the magnitude of potential risk to the exposed 

population. Thus, this does not represent a significant source of uncertainty in the risk assessment. 

Comments were also received that the one-mile distance considered by the transport model is not 

sufficient, because actual receptor wells in many cases are further distant than one mile from 

facilities. EPA conducted a sensitivity analysis, discussed in Section 5 of the revised risk 

assessment, which indicates that risks beyond the one-mile distance are appreciably lower than 

risks within one mile. Given that the highly exposed population was adequately captured by a onemile radius, the significant additional effort required to extend the analysis further downgradient 

was unjustified. 

With respect to comments related to the placement of wells within deeper aquifers, EPA has a 

policy of addressing uncertainty by erring in favor of the protection of human health and 

environmental quality. Consistent with this practice, wells screened within vulnerable, surficial 

aquifers (i.e., the top 10 meters of the saturated zone) continue to be the primary focus of the 

Agency’s national-scale modeling efforts. Comments also highlighted the possibility that modeled 

receptor well concentrations may incorrectly represent actual exposures by sampling from a single 

aquifer depth. Wells are typically screened across an extended depth, and may capture both 

contaminated and pristine ground water. Due to the constraints of EPACMTP, EPA maintained 

the current approach of modeling exposures at a single depth. A discussion of the uncertainties 

associated with this approach has been added to Section 5 of the revised risk assessment. 

In response to comments on the use of MSW landfill data to predict the distance to private wells, 

EPA did not use the MSW data in the revised risk assessment. Instead, EPA used synthetic 

population representations of U.S. Census data to place each household and its occupants at 

discrete points across the landscape surrounding CCR WMUs. Synthetic populations are realistic 

representations of households and individual residents and their attributes in a given census area, 

and are based on methods that identify realistic locations within each block by using LandScan 

90-meter night-time population distributions to place each household across the landscape 
Response to Public Review Comments Fate and Transport Modeling 

2-15 

(Bhaduri, 2007). From these households, a distribution of the distances to the nearest well was 

created. This approach is discussed in more detail in Appendix B of the revised risk assessment. 

Some commenters suggested that EPA develop site-specific estimates of actual populations around 

facilities rather than relying on synthetic populations to determine potential receptor locations. The

synthetic approach provides the maximum spatial resolution possible for publically available 

population data from the U.S. Census. More site-specific estimates would be costly, but not 

necessarily more accurate. 

Some commenters were also concerned that the assessment did not consider direct discharges from 

surface impoundments to surface water. This pathway was outside the scope of the assessment, 

because it is regulated by the NPDES program. However, this pathway was evaluated in 

Environmental Assessment for the Proposed Effluent Limitation Guidelines and Standards for the 

Steam Electric Power Generating Point Source Category (U.S. EPA, 2013), which will be revised 

in support of final effluent limitation guidelines due to be released in September of 2015. 

Additional Comments: The comments provided on the topics discussed above also touched on 

other topics, which are addressed in greater detail elsewhere in this document. Thus, EPA does not 

provide a response to these additional topics here. Comments relating to the conservative inputs to 

the fate and transport models are discussed in Section 7.1 of this document. 
Response to Public Review Comments

3-1 

3. Source Modeling 

The comments relating to source modelling were grouped into twelve subcategories, which are 

summarized in the following bulleted list. 

 Section 3.1: The use of leachate concentrations based on toxicity characteristic leaching 

procedure (TCLP) data and the availability of more representative results from EPA’s 

research with Vanderbilt University 

 Section 3.2: The use of facility data, WMU data and liner scenarios 

 Section 3.3: Alternative waste disposal/codisposal scenarios 

 Section 3.4: Updates on liner leakage assumptions 

 Section 3.5: Treatment of nondetect CCR constituent values 

 Section 3.6: The effect of waste compaction on infiltration and leaching 

 Section 3.7: Hydrologic Evaluation of Landfill Performance (HELP) model infiltration rates, 

liner and landfill cover assumptions 

 Section 3.8: Scenarios where the water table is above the disposal unit 

 Section 3.9: The impact of increased mercury capture under future air emission control 

regulations 

 Section 3.10: The use of pore water data for surface impoundment source concentrations 

 Section 3.11: Modeling surface impoundments only before closure

 Section 3.12: Modeling landfills only after closure. 

3.1. Use of TCLP and LEAF Data 

Comment Summary 

The majority of the public commentary in this subcategory was dominated by the assertion that 

Toxicity Characteristic Leaching Procedure (TCLP), Synthetic Precipitation Leaching Procedure 

(SPLP) and other laboratory leachate test data are not applicable to CCR wastes. Comments 

specifically regarding the use of Leaching Environmental Assessment Framework (LEAF) data for 

modeling leaching behavior noted that the data should be applied appropriately and pointed out 

the following: (1) that the range of conditions (i.e., range of pH) encompassed by the LEAF data 

is broader than those conditions found in the field for CCR disposal; (2) high pH limits the mobility 

of leaching constituents; (3) the need for validating LEAF leachate concentrations against field 

data if available; and (4) the reliability of the LEAF data is questionable as a result of 

inconsistencies identified in the LeachXS LiteTM database. The specific public comments related 

to use of TCLP data and the availability of the Vanderbilt study and associated reference 

information are detailed in Table 3-1.
Response to Public Review Comments Source Modeling 

3-2 

Table 3-1. Comments Related to Use of TCLP and LEAF Data 

EPA Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2006-0796-0431 Trade Association Robert Bessette CIBO 2007 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA-HQ-RCRA2006-0796-0046 Electric Utility 

Company Tim Gregori Southern Montana Electric 2007 

EPA-HQ-RCRA2006-0796-0432 Trade Association Jim Roewer USWAG 2007 

EPA-HQ-RCRA2009-0640-08787 State Government Stephen A. Cobb ASTSWMO 2010 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-08244 Electric Utility 

Company 

Basil G. 

Constantelos 

Edison Mission 

Energy, LLC 2010 

EPA-HQ-RCRA2009-0640-09765 Trade Association Ken Ladwig EPRI 2010 

EPA-HQ-RCRA2009-0640-06260 State Government R. Bruce Scott KY DEP 2010 

EPA-HQ-RCRA2009-0640-08218 State Government Shari T. Wilson MDE 2010 

TRANS-KNX-0069-1 Advocacy Group Barbara Gottlieb Physicians for Social 

Responsibility 2010 

EPA-HQ-RCRA2009-0640-05768 Private Citizen Richard C. Phelps Private Citizen 2010 

EPA-HQ-RCRA2009-0640-06555 Beneficial User Lauren P. Alterman 

Saint-Gobain 

Corporation/Certain

Teed Corporation 

2010 

EPA-HQ-RCRA2009-0640-06526 Trade Association Jim Roewer USWAG 2010 

EPA-HQ-RCRA2009-0640-06068 Advocacy Group John Veranth 

Utah Physicians for 

a Healthy 

Environment 

2010 

EPA-HQ-RCRA2009-0640-08253 Electric Utility 

Company Terry Coss Xcel Energy 2010 
Response to Public Review Comments Source Modeling 

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Table 3-1. Comments Related to Use of TCLP and LEAF Data 

EPA Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2011-0392-0223 Electric Utility 

Company Paul Pike Ameren Corporation 2011 

EPA-HQ-RCRA2011-0392-0219 State Government Anthony Hatton Commonwealth of 

Kentucky 2011 

EPA-HQ-RCRA2011-0392-0264 Electric Utility 

Company Paul Allen Constellation Energy 2011 

EPA-HQ-RCRA2011-0392-0254 Electric Utility 

Company Pamela Faggert 

Dominion 

Resources Services, 

Inc. 

2011 

EPA-HQ-RCRA2011-0392-0215 Electric Utility 

Company Richard Meiers Duke Energy 2011 

EPA-HQ-RCRA2011-0392-0239 Advocacy Group Lisa Evans Earthjustice 2011 

EPA-HQ-RCRA2011-0392-0259 Advocacy Group Eric Schaeffer EIP 2011 

EPA-HQ-RCRA2011-0392-0227 Electric Utility 

Company Myra Glover Entergy 2011 

EPA-HQ-RCRA2011-0392-0198 Trade Association Ken Ladwig EPRI 2011 

EPA-HQ-RCRA2011-0392-0259 Trade Association Michael Gardner Gypsum Association 2011 

EPA-HQ-RCRA2011-0392-0233 Electric Utility 

Company Cathy Woollums 

MidAmerican 

Energy Holdings 

Company 

2011 

EPA-HQ-RCRA2011-0392-0225 Electric Utility 

Company Dale Helmers NIPSCO 2011 

EPA-HQ-RCRA2011-0392-0211 Trade Association Jim Roewer USWAG 2011 

EPA-HQ-RCRA2011-0392-0234 Electric Utility 

Company Bruce Ramme We Energies 2011 

EPA-HQ-RCRA2012-0028-0108 Trade Association Thomas Adams ACAA 2013 

EPA-HQ-RCRA2012-0028-0065 Electric Utility 

Company Basin Electric Basin Electric 2013 
Response to Public Review Comments Source Modeling 

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Table 3-1. Comments Related to Use of TCLP and LEAF Data 

EPA Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2012-0028-0105 Electric Utility 

Company Chet Thompson CME Engineering LP 2013 

EPA-HQ-RCRA2012-0028-0059 State Government Anthony Hatton Commonwealth of 

Kentucky 2013 

EPA-HQ-RCRA2012-0028-0111 Advocacy Group Grant Tolley Earthjustice 2013 

EPA-HQ-RCRA2012-0028-0102 Trade Association Ken Ladwig EPRI 2013 

EPA-HQ-RCRA2012-0028-0061 Beneficial User Harlan Hatfield Headwaters 2013 

EPA-HQ-RCRA2012-0028-0073 Electric Utility 

Company TVA TVA 2013 

EPA Response 

Only pore water and impoundment water data were used to characterize surface impoundments. 

Therefore, the comments received on the use of laboratory leachate data are not relevant for the 

surface impoundment scenario. For landfills, EPA agrees that TCLP, SPLP and other single pH 

test methods may not be the most appropriate leachate extraction methods for all waste streams 

and all disposal scenarios. The 2010 Draft Risk Assessment relied on a hierarchy of dissolved 

concentration data to characterize leaching from landfills, ranging in order of preference from field 

leachate data to TCLP. However, new data collected using the LEAF test methods have been made 

available through a series of EPA reports (U.S. EPA 2006, 2008a, 2009a). LEAF were collected 

with three LEAF methods, specifically: 

 SW-846 Method 1313 (and its predecessor, Method SR02); 

 SW-846 Method 1314; and 

 SW-846 Method 1316 (and its predecessor, Method SR03).2

With the availability of the LEAF data, EPA no longer relied on other data sources to model 

landfills because the inability to identify trends in leaching behavior from single pH tests made it 

impossible to link these data together with the LEAF data in the probabilistic analysis. The LEAF 

data provide information on the leaching behavior of CCRs for a range of pH values observed in 

CCR landfills, as well as the liquid-to-solid ratio of the pore water. The data from these three 

methods were used in conjunction to characterize landfill leaching. While the natural pH range for 

any individual sample may be narrower than the full range analyzed with the LEAF methods, many 

 

2 Methods SR02 and SR03 are predecessor methods to SW-846 Methods 1313 and 1316. 
Response to Public Review Comments Source Modeling 

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facilities burn a range of coal types under varying operating conditions, and co-dispose with other 

materials, so the range of pH for a specific CCR sample may be exposed to is wider than the pH 

estimated based on one sample alone. 

EPA agrees that appropriate use of the data is needed to ensure that data represent likely conditions 

of leaching occurring at range of facilities nationwide taking into account local specific 

environmental conditions, the geometry of monofill, type of coal, air pollution control, and other 

factors that affect leaching. Since the NODAs were released, a report comparing leachate from 

field and laboratory analyses has been completed. The report includes the use of geochemical 

speciation modeling as needed to reflect site-specific factors affecting leaching, and shows that 

LEAF methods provide realistic predictions of environmental releases across the range of pH. 

All three LEAF methods are summarized in Appendix C, with the leachate data provided in 

Attachment C-5 of the revised risk assessment. Additionally, the inter-laboratory validation for 

these methods are described in U.S. EPA (2012a,b) while Kosson et al. (2002) provides the 

detailed test methodology for the predecessor methods, SR02 and SR03. The noted discrepancies 

and classification errors within LeachXS Lite have been corrected. 

3.2. Facility Data, WMU Data, and Liner Scenarios 

Comment Summary 

Public comments focused on the general relevance of the facility data based on age and noted that 

newer data should be used to more accurately reflect the current state of CCR management. Related 

comments cited that the grouping of waste and liner types by facility is not representative of current

conditions. Another commenter suggested that the outcomes for different liner types were not 

comparable and should not be used to make relative conclusions about liner performance. It was 

also suggested that the assumed three-foot clay layer underlying composite liners is too thick, and 

two feet would be more representative of current practice. Commenters also described existing 

management controls required in some geographical locations that mitigate potential risks (e.g., 

liners, leachate collection) and requested that EPA reflect the existence of those controls in their 

analysis, as well as mismanagement scenarios when these controls are not in place. The specific 

public comments related to facility data, WMU data and liner scenarios, as well as associated 

reference information, are detailed in Table 3-2. 

Table 3-2. Comments Related to Facility Data, WMU Data and Liner Scenarios 

Commenter ID Commenter Type Commenter Name Commenter 

Organization YEAR 

EPA-HQ-RCRA2012-0028-0069 Electric Utility 

Company Ameren Missouri Ameren Missouri 2013 

EPA-HQ-RCRA2012-0028-0071 Electric Utility 

Company GRE GRE 2013 
Response to Public Review Comments Source Modeling 

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Table 3-2. Comments Related to Facility Data, WMU Data and Liner Scenarios 

Commenter ID Commenter Type Commenter Name Commenter 

Organization YEAR 

EPA-HQ-RCRA2012-0028-0111 Advocacy Group Grant Tolley Earthjustice 2013 

EPA-HQ-RCRA2011-0392-0211 Trade Association Jim Roewer USWAG 2011 

EPA-HQ-RCRA2011-0392-0234 Electric Utility 

Company Bruce Ramme We Energies 2011 

EPA-HQ-RCRA2009-0640-06526 Trade Association Jim Roewer USWAG 2010 

EPA-HQ-RCRA2009-0640-08787 State Government Stephen A. Cobb ASTSWMO 2010 

EPA-HQ-RCRA2009-0640-10483 Trade Association Jim Roewer USWAG 2010 

EPA-HQ-RCRA2009-0640-06260 State Government R. Bruce Scott KY DEP 2010 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-08226 State Government Chris Korleski Ohio EPA 2010 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA-HQ-RCRA2006-0796-0423 Advocacy Group Richard 

Wasserstrom AF&PA 2007 

EPA-HQ-RCRA2006-0796-0431 Trade Association Robert Bessette CIBO 2007 

EPA-HQ-RCRA2006-0796-0446 Advocacy groups Earthjustice Earthjustice 2007 

EPA-HQ-RCRA2006-0796-0425 Academia Cynthia Water Saint Vincent College 2007 

EPA-HQ-RCRA2006-0796-0432 Trade Association Jim Roewer USWAG 2007 

EPA Response 

Since the purpose of the risk assessment was to evaluate risks for the universe of currently 

operating facilities and WMUs, EPA generally agrees with the commenter that the 1995 EPRI and 
Response to Public Review Comments Source Modeling 

3-7 

2006 DOE survey data relied on in the 2010 Draft Risk Assessment may be outdated. Thus, EPA 

collected data from several new sources of information on the facilities, WMUs, and liners that 

are present at the time of this analysis. Further discussion of these data sources is available in 

Section 2 and Appendix A of the revised risk assessment. 

Regarding the inclusion of mismanagement scenarios, EPA reviewed the high-end pore water 

concentrations and determined that these data represent actual CCR samples and therefore 

represent possible high-end risks from current management practices. To better understand which 

practices may lead to the highest risks, EPA conducted sensitivity analyses that consider the 

influence of liner type, liner design, waste type and other variables on model results. The results 

of these analyses are presented in Section 5 of the revised risk assessment. 

Several commenters described existing management controls required in some geographical 

locations that mitigate potential risks (e.g., liners, leachate collection) and requested that EPA 

reflect the existence of those controls in the final risk analysis. The Agency’s analysis reflects the

presence of different management scenarios at WMUs to the extent the available data allowed 

(e.g., WMUs were assumed to have liners if the information indicated such). A key objective of 

the analysis was to compare the effectiveness of management options (e.g., liners; surface 

impoundments versus landfills) at preventing potential releases and exposures. Because the 

population of WMUs considered in the analysis included a range of management controls, the 

analysis does provide such comparative results between management options. The uncertainties 

associated with the updated facility, WMU and liner data are discussed in Section 5 of the revised 

risk assessment. 

3.3. Alternative Waste/Codisposal Scenarios 

Comment Summary 

One commenter suggested that the risk assessment applied risk results for fly ash to bottom ash, 

FGD sludge, and other CCR wastes, which may result in an incorrect estimate of risks for these 

other wastes. Other commenters called for EPA to evaluate each CCR waste independently. A 

public commenter expressed concern about whether the risk assessment adequately considered 

alternative CCR disposal scenarios. Specifically, it was noted that CCRs codisposed with coal 

refuse generate more acidic conditions (i.e., lower pH) due to higher-levels of sulfide minerals, 

which may significantly impact the mobility of metals. The specific public comments related to 

alternative waste/codisposal scenarios and associated reference information are detailed in 

Table 3-3. 

Table 3-3. Public Comments Related to Alternative Waste/Codisposal Scenarios 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2011-0392-0237 Electric Utility 

Company Basil Constantelos Edison Mission Energy, LLC 2011 
Response to Public Review Comments Source Modeling 

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Table 3-3. Public Comments Related to Alternative Waste/Codisposal Scenarios 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2011-0392-0211 Trade Association Jim Roewer USWAG 2011 

EPA-HQ-RCRA2009-0640-08227 Trade Association Michael Gardner Gypsum Association 2010 

EPA-HQ-RCRA2009-0640-08244 Electric Utility 

Company Basil Constantelos Edison Mission Energy, LLC 2010 

EPA-HQ-RCRA2009-0640-09728 Electric Utility 

Company Jon A. Finlinson IPSC 2010 

EPA-HQ-RCRA2009-0640-09713 Electric Utility 

Company Dana G. Meier IPL 2010 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2006-0796-0046 Electric Utility 

Company Tim Gregori Southern Montana Electric 2007 

EPA Response 

In the revised risk assessment, EPA modeled a combined ash waste types for the majority of 

surface impoundments and all landfills. Although commenters are correct that different CCR 

wastes may behave differently when monofilled, the 2009/2010 EPA survey data indicates that the 

CCRs are codiposed in a majority of units. Thus, EPA believes this approach appropriately reflects 

current disposal practices. 

With regard to the evaluation of CCRs codisposed with coal refuse, EPA notes that the pore water 

data used to characterize surface impoundments were broken out separately for this waste type 

evaluation. These data reflect samples collected in the field and are representative of the pH at 

which these samples are managed. While some ash and coal refuse samples are highly acidic, 

others are more neutral or slightly basic (full pH range of 1.7 to 8.2). The development and 

application of these waste types is discussed in Section 3, Section 4 and Appendix H of the revised 

risk assessment, while the associated uncertainties are discussed in Section 5. For landfills, waste 

pH, which is the major driver of variations in Kd values used to distinguish waste types, was known 

with great accuracy for CCRs nationwide because U.S. EPA (2009a) compiled a full, nationwide 

distribution of CCR pH. In this distribution, disposal of ash with coal refuse is reflected is the 

acidic tail of the distribution. For the national probabilistic analysis, EPA aggregated model runs 

for ash and coal refuse (surface impoundments) and acidic waste (landfills) with other wastes so 

that risks reflected the prevalence of these disposal practices. However, EPA also performed 

sensitivity analyses to understand the extent that the lower pH of co-managed wastes could affect 

risks, which is discussed in Section 5 of the revised risk assessment. 
Response to Public Review Comments Source Modeling 

3-9 

3.4. Liner Leakage 

Comment Summary 

Commenters stated that it is unclear why EPA chose to approximate infiltration through composite 

liner systems based on leak detection system flow rates from industrial landfills that use a different

construction design than projected for CCR landfills. The specific comments related to liner 

leakage and associated reference information are detailed in Table 3-4. 

Table 3-4. Public Comments Related to Liner Leakage

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2011-0392-0204 Trade Association Andrew Aho GMA 2011 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA Response 

The composite liner leakage rates used for this risk assessment correspond to leakage rates 

developed for the peer-reviewed Industrial Waste Management Evaluation Model (IWEM) (U.S. 

EPA, 2002). The types of synthetic liners used are likely to be the same, regardless of the type of 

waste present. EPA is unaware of any factors specific to CCRs that would exacerbate leakage 

rates, nor did the commenter provide any. Thus, in the absence of any information to the contrary, 

EPA finds these to be the best available data. 

Because there is currently no approach for differentiating between flow from unimpacted water 

released by the consolidation of clay and from contaminated leakage through the liner, EPA 

excluded data on the subset of composite liners constructed with natural clay from the distribution 

of composite liner leakage rates. EPA did consider the potential impact of incorporating these 

additional data into the risk assessment as part of sensitivity analysis, presented in Section 5 of the 

revised risk assessment. 

3.5. Treatment of Non-detect Values 

Comment Summary 

Concerning the treatment of non-detect values in the risk assessment, one commenter recognized 

that the use of one half the detection limit in calculations has become an accepted protocol. 

However, it was suggested that this approach may not be appropriate in all cases, and that newer 

or more straightforward methods can be applied to improve precision and minimize biasing of the 

dataset. Another commenter noted that mercury was excluded from the analysis due to the high 

number of non-detects. The specific public comments related to treatment of non-detect values 

and associated reference information are detailed in Table 3-5. 
Response to Public Review Comments Source Modeling 

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Table 3-5. Public Comments Related to Treatment of Non-detect Values 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2011-0392-0219 State Government Anthony Hatton Commonwealth of 

Kentucky 2011 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-09765 Trade Association Ken Ladwig EPRI 2010 

EPA-HQ-RCRA2006-0796-0046 Electric Utility 

Company Tim Gregori Southern Montana Electric 2007 

EPA Response

Additional constituent data measured with lower detection limits have been made available to EPA 

since completion of the 2010 Draft Risk Assessment. However, the overall CCR constituent 

database still contains a large number of non-detect data for some constituents. EPA continues to 

incorporate all available with the use half the reported detection limit as the most appropriate 

method to account for these non-detects. The commenter is correct that much of the pre-2010 

mercury data has high detection limits and a large proportion of non-detects. In this one instance, 

EPA relied only on the newer data made available to the Agency since the 2010 Risk Assessment, 

which was collected through newer methods with significantly lower detection limits. A more 

detailed rationale for this approach is provided in Section 3 of the revised risk assessment, along 

with further discussion of the uncertainty in Section 5. 

3.6. Effect of Waste Compaction 

Comment Summary 

Comments received related to the effect of waste compaction in landfills focused on changes to 

hydrologic properties of waste materials, such as porosity and hydraulic conductivity. These 

changes may result from compaction, consolidation, hydration or geochemical changes, and have 

the potential to result in either an underestimation or overestimation of risks. The specific public 

comments related to effect of waste compaction and associated reference information are detailed 

in Table 3-6. 
Response to Public Review Comments Source Modeling 

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Table 3-6. Public Comments Related to Effect of Waste Compaction 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-08244 Electric Utility 

Company 

Basil G. 

Constantelos 

Edison Mission 

Energy, LLC 2010 

EPA-HQ-RCRA2006-0796-0431 Trade Association Robert Bessette CIBO 2007 

EPA Response 

EPA acknowledges that the landfill source model does not consider the compaction of CCR waste 

that may occur over time as a result of anthropogenic activities, gravity or infiltrating water. 

However, no data on either the rate or degree to which these processes may occur were provided 

by commenters or identified elsewhere. EPA considered the impacts of this uncertainty in Section 

5 of the revised risk assessment. 

3.7. HELP Infiltration Rates, Liner and Cover 

Assumptions 

Comment Summary 

Public comments focused on assumptions relating to the variability of unlined landfill design, 

landfill clay liner materials, and construction of landfill cover materials and construction. Specific

comments emphasized that the clay liner and cover thickness assumptions (three feet) were too 

conservative and not conservative enough, respectively. Commenters also questioned why 

composite covers and leachate collection systems were not considered for clay-lined landfills. 

Additionally, commenters stated that there was a high degree of variability in the material and 

design and construction for unlined landfills that was not accounted for in the HELP modeling. 

One commenter also pointed out that the assessment may overestimate percolation rates from 

landfills by underestimating the use of engineering controls. In addition, a commenter stated that 

the assessment assumes that States will require liners in all cases which may not be the case, 

thereby weakening the regulation. The specific public comments related to HELP infiltration 

rates/cover assumptions and associated reference information are detailed in Table 3-7. 
Response to Public Review Comments Source Modeling 

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Table 3-7. Public Comments Related to HELP Infiltration Rates/Cover Assumptions 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2011-0392-0211 Trade Association Jim Roewer USWAG 2011 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-06416 State Government Matthew Frank and 

Eric Callisto WI DNR and WI PSC 2010 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA Response 

For both unlined and clay-lined landfills, EPA used Hydrologic Evaluation of Landfill 

Performance (HELP) model-derived infiltration rates. These infiltration rates assume that the cap 

placed on top of the landfill at the end of its useful life will remain intact for the duration of the

risk assessment, up to a maximum 10,000 years of modeling. A commenter pointed out that 

hydraulic conductivity of a clay liner is likely to increase by orders of magnitude due to desiccation

resulting from natural temperature cycles. Additionally, commenters stated that there was a high 

degree of variability in the material and design and construction for unlined landfills that was not 

accounted for in the HELP modeling. EPA has adopted the use of the HELP model, which was 

subject to both peer and administrative review, as the source of unlined and clay-lined infiltration 

rates for landfill for nearly two decades. EPA acknowledges that there are limitations in using 

HELP. However, the model has been tested and verified as discussed in the EPACMTP 

Parameter/Data Background Document (U.S. EPA, 2003a). To the extent that the performance of 

the cap will decrease over time, EPA acknowledges that unlined and clay-lined infiltration rates 

calculated by HELP may be underestimated, however the degree of that underestimate is unknown. 

Discussion of this uncertainty has been added to Section 5 of the revised risk assessment. 

3.8. Water Table above the Disposal Unit 

Comment Summary 

One commenter expressed concern over the fact that the assessment modeled all disposal sites 

above the water table. The commenter indicated that many surface impoundments and landfills are 

deep and can come in direct contact with the water table. This will result in an underestimation of 

peak concentrations, arrival times and risks for these WMUs. Furthermore, the commenter 

emphasized that the use of the unsaturated zone flow module to calculate infiltration from the 

bottom of impoundments underestimates true risks in the consolidated sediment, and noted that 

clogged soil layers should be treated as saturated rather than unsaturated. The specific comments 
Response to Public Review Comments Source Modeling 

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related to water table above the disposal unit and associated reference information are detailed in 

Table 3-8 and presented below. 

Table 3-8. Public Comments Related to Water Table Above the Disposal Unit 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA Response 

EPA acknowledges that EPACMTP is not designed to handle scenarios where the water table is 

above the bottom of the landfill. However, EPACMTP can accommodate surface impoundments 

in direct contact with the water table. If unit geometry and the selected depth to the water table 

create a scenario where the bottom of the unit is in contact with the water table, then the entire soil 

column is considered saturated. Otherwise, even for very high infiltration rates, regions beneath 

impoundments will remain partially saturated when there is sufficient distance between the unit 

and the water table EPA has added a discussion of the uncertainties associated with WMU source 

terms and EPACMTP in Section 5 of the revised risk assessment. 

EPA believes the commenter misunderstood how the sediments were modeled for surface 

impoundments. The EPACMTP unsaturated zone module assumes that the 0.2 m of consolidated 

sediments at the bottom of a surface impoundment are always saturated whereas the 0.5 m of 

clogged native soil are assumed to be unsaturated when the bottom of the surface impoundment is 

above the water table. 

3.9. Impact of Increased Mercury Capture with 

New Future Air Emission Control Regulations 

Comment Summary 

Public commenters recommended that EPA address the future increase in mercury and NOx 

compounds levels in CCR that will result from mercury capture from flue gas under new emission 

control regulations. Commentary pointed out that the recent Vanderbilt study should provide data 

that could be used to expand the risk assessment in this area. The specific public comments related 

to impact of increased mercury capture with new future air emission control regulations and 

associated reference information are detailed in Table 3-9 and presented below. 
Response to Public Review Comments Source Modeling 

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Table 3-9. Comments Related to Impact of Increased Mercury Capture with New 

Future Air Emission Control Regulations 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-06846 State Government Richard B. Tedder FDEP 2010 

EPA Response 

The risk assessment was designed to evaluate the risks associated with current management 

practices and, as such, draws no conclusions about the potential for future air pollution 

technologies to alter the composition or leaching behavior of CCR wastes. However, it has been 

shown that newer mercury pollution control technologies currently in place have the potential to 

affect leaching behavior (U.S. EPA, 2006, 2008, 2009). Thus, EPA conducted a sensitivity analysis 

to evaluate the risks associated with existing units that dispose of this waste; however the data 

were too few to allow EPA to draw conclusions about the effect of pollution control technologies 

on the risks. This sensitivity analysis is presented in Section 5 of the revised risk assessment. 

3.10. Use of Pore Water Data for Impoundment 

Source Concentrations 

Comment Summary 

Multiple public commenters noted that additional pore water will improve the risk assessment, but 

TCLP and SPLP data are not appropriate for use as source concentrations. Additionally, 

commenters stated that EPA applies the LEAF data to pH conditions that are not realistic to CCR 

disposal scenarios. Although LEAF provides a more representative and scientifically sound 

approach, it must be correctly adapted. Alternative statistical methods to represent the input data 

as a range is certainly feasible and could enhance the risk assessment if the range of data is used 

as an input to the risk assessment. 

Commenters agree that the LEAF data does provide useful information, but point out that it is 

associated with the potential for leaching and does not represent actual leaching of a specific CCR 

under actual field conditions. Commenters argues that field leaching data should not be mixed with 

laboratory data, and that EPA's field leachate dataset (for landfills and impoundments) is not 

adequate for use in the CCR risk assessment. Specific efforts recommended to properly utilize the 

LEAF data include: Use of probability density functions for leachate concentrations based on pH 

and/or L/S ratios in the Monte Carlo process; Selection of leachate concentrations based on pH 

and L/S and tied to the geographic location of the WMU and CCR type; and geochemical modeling 

to incorporate reactions once leachate impacts groundwater. 

A few commenters pointed out that the pore water data are generally representative, although 

concerns were raised about the highest arsenic concentration (81 mg/L) in the dataset. One 
Response to Public Review Comments Source Modeling 

3-15 

commenter believed that although the addition of new data is an improvement, EPA could greatly 

improve the accuracy of the model’s results by removing the extreme and unsubstantiated outlier 

data driving its high risk cases. Another commenter believed the assumption that concentration of 

contaminants in the sediment pores (applicable to a post closure scenario) would be equal to the 

concentration assigned to in the impoundment water would result in underestimated risks. 

Additionally, commenters noted that EPA should classify the data according to CCR type and coal 

type. 

Overall, commenters support updates to the pore water data and the use of statistical method to 

normalize the data curve. However, one commenter noted that EPA should not use commentersubmitted CCR pore water data unless it meets requisite applicable data quality requirements. 

Another commenter stated that EPA needs to provide better clarity on these solicited comments 

(on the use of older pore water data) and provide these documents in the docket. Without these 

documents, the reader does not have a complete understanding of co-managed material containing 

CCRs. Another comment noted that properly collected field pore water (freely draining) samples 

should take priority over any of the laboratory generated data and freely draining pore water is 

more representative of leachate releases than tightly held pore water. The specific public comments 

related to the use of pore water data for impoundment source concentrations and associated 

reference information are detailed in Table 3-10. 

Table 3-10. Comments Related to the Use of Pore Water Data for Impoundment Source 

Concentrations.

EPA Comment ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2012-0028-0111 Advocacy Group Grant Tolley Earthjustice 2013 

EPA-HQ-RCRA2012-0028-0046 Advocacy Group Jeff Stant Citizens Coal 

Council 2013 

EPA-HQ-RCRA2012-0028-0089 Electric Utility 

Company Dennis Leonard DTE Energy Company 2013 

EPA-HQ-RCRA2012-0028-0095 Electric Utility 

Company Richard Meiers Duke Energy 2013 

EPA-HQ-RCRA2012-0028-0067 Electric Utility 

Company John McManus AEP 2013 

EPA-HQ-RCRA2011-0392-0198 Trade Association Ken Ladwig EPRI 2011 

EPA-HQ-RCRA2011-0392-0211 Trade Association James Roewer USWAG 2011 

EPA-HQ-RCRA2011-0392-0219 State Government Anthony Hatton Commonwealth of 

Kentucky 2011 
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Table 3-10. Comments Related to the Use of Pore Water Data for Impoundment Source 

Concentrations.

EPA Comment ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2011-0392-0233 Electric Utility 

Company Cathy Woollums 

MidAmerican 

Energy Holdings 

Company 

2011 

EPA-HQ-RCRA2011-0392-0237 Electric Utility 

Company Basil Constantelos Edison Mission Energy, LLC 2011 

EPA-HQ-RCRA2011-0392-0238 Electric Utility 

Company Chris Hobson Southern Company 2011 

EPA-HQ-RCRA2011-0392-0270 State Government Edward Dexter MDE 2011 

EPA-HQ-RCRA2011-0392-0274 Electric Utility 

Company Jean-Claude Younan SCANA Corporation 2011 

EPA-HQ-RCRA2011-0392-0227 Electric Utility 

Company Myra Glover Entergy 2011 

EPA-HQ-RCRA2011-0392-0239 Advocacy Group Lisa Evans Earthjustice 2011 

EPA-HQ-RCRA2009-0640-06260 State Government R. Bruce Scott KY DEP 2010 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-06410 Anonymous Anonymous N/A 2010 

EPA-HQ-RCRA2009-0640-06526 Trade Association Jim Roewer USWAG 2010 

EPA-HQ-RCRA2009-0640-10483 Trade Association Jim Roewer USWAG 2010 

EPA-HQ-RCRA2009-0640-08244 Electric Utility 

Company 

Basil G. 

Constantelos 

Edison Mission 

Energy, LLC 2010 

EPA-HQ-RCRA2009-0640-09765 Trade Association Ken Ladwig EPRI 2010 

EPA Response 

The use of pore water data is still considered the most appropriate approach to estimate constituent 

fluxes to ground water for CCR surface impoundments. This is because pore water better 

represents the leachate seeping from the bottom of the impoundment than impoundment water 
Response to Public Review Comments Source Modeling 

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samples. EPA did not use available LEAF data for surface impoundments because a national 

distribution of pH was not available to allow the Agency to probabilistically assign LEAF 

concentrations to these units, and because there was no way to account for partitioning of the 

leachate into wastewater versus porewater. Thus, EPA has continued to rely on pore water data, 

supplemented with data from the 2010 comments. EPA appreciates commenter support on the use 

of pore water data and statistical methods for data analysis for surface impoundments. EPA agrees 

that data available for minefill sites may not be representative of disposal in surface 

impoundments. Thus, these data were not considered in the revised risk assessment. The specific 

handling of pore water concentration data with site quartiles, rather than site averages, is discussed

in Section 4 and Section 5 of the revised risk assessment report. 

EPA agrees that TCLP and SPLP data are less appropriate for CCR disposal scenarios and no 

longer uses these data in the revised risk assessment. EPA adapted the LEAF methods and data for 

landfills, as this is the best available approach and data to represent CCR landfill leachates, and 

does not mix or use field data with LEAF laboratory results for landfill leachate. The LEAF data 

are considered the most robust and technically defensible data available. As noted in the 2010 

Environmental Science and Technology publication (Thorneloe et al., 2010), the data represents 

the largest collection of comprehensive characteristic leaching data to date. 

A commenter noted that the LEAF data provide the potential for leaching and not actual leaching 

of a specific CCR under actual field conditions. The commenter suggests using probability 

distribution of key factors affecting leaching behavior [i.e., pH and liquid/solid ratio (L/S)] and 

site specific data tied to the geographic location of the management unit and the type of CCR being 

managed. In the revised risk assessment, pH is expressed as a national distribution for selecting 

leachate concentrations developed to represent CCR nationally, and L/S is considered in estimating 

washout leachate concentrations based on field data observations. The use of the pH distribution 

developed in U.S. EPA (2009) does capture the range of potential variability in pH conditions at 

CCR sites nationwide and is the best approach possible given the current availability of 

information on site-specific coal ash chemistry. Although leachate concentrations were selected 

considering pH and L/S conditions that are nationally representative, EPA does not have the 

detailed and extensive site-specific measurements that would be needed to tie CCRs and leachate 

concentrations to specific WMU locations. Instead, EPA adopted a national probabilistic approach 

that is site-based and representative of risks to human and ecological health across the country. 

The revised risk assessment also provides details regarding how the LEAF data are used in 

combination of geographical specific data such as hydrology, precipitation, fill configuration, CCR 

type, pH, L/S ratio, and other factors that take the leaching potential as an input to fate and transport 

models accounting for attenuation and dilution. Additionally, an effort was made to collect CCR 

samples that characterize the range and quantity of coal usage in the U.S. along with likely air 

pollution control configurations. While the data is not statistically representative on a site-specific 

basis, it is adequate to identify trends in leaching behavior that relate to differences in materials 

types, APC technology, and coal rank. Geochemical speciation modeling was not conducted 

because the source term as measured and interpreted is conservative, provided that oxidizing 

conditions occur. 
Response to Public Review Comments Source Modeling 

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Regarding the number and concentration of pore water samples, EPA reviewed the high-end pore 

water concentrations and determined that these represent actual CCR samples that therefore 

represent possible high-end risks if CCR is inadequately regulated and managed. EPA recognizes 

that more pore water data would potentially improve the representativeness of the dataset, but is 

convinced that the current dataset adequately captures the possible high end risks that are of most 

interest in the rulemaking, including risks from the mismanagement of CCR through codisposal 

with coal refuse. 

The assumption that saturated contaminant concentrations in surface impoundment sediments are 

at equilibrium with the impoundment waters is a conservative assumption that is unlikely to 

significantly underestimate risks. This assumption is further discussed in Section 5 of the revised 

risk assessment report. 

Regarding commenter-submitted pore water data, EPA conducted a review of the additional 

datasets provided by the commenters with respect to relevance and data quality. Based on the 

available information, EPA determined that the selected datasets were relevant and acceptable in 

terms of data quality requirements. However, EPA does not have sufficient data to distinguish 

between freely draining and tightly bound pore water data at this time. Overall, EPA agrees that 

the use of these data introduces some uncertainty into the analysis, which is discussed in Section 

5 of the revised risk assessment. 

3.11. Modeling Surface Impoundments Only PreClosure 

Comment Summary 

One commenter questioned the assumption that there will be no net addition of waste into a surface 

impoundment during and after the operational life, noting that impoundments are frequently 

deepened. Additionally, many surface impoundment wastes are left in place at the time of closure, 

so that the waste behaves more as a landfill than a surface impoundment (and increasingly, with 

new landfills being constructed on top of previous surface impoundments). Another commenter 

questioned why the conceptual model assumes that impoundments are always full during their 

operating life, which overestimates releases to the subsurface. Additionally, a commenter noted 

that the assumption of only 0.2 m of sediment accumulation underestimates the amount of 

sedimentation and subsequently overestimates the amount of percolation to the subsurface. The 

commenter stated that in actual operation, ash thickness can increase up to 30 feet or more, 

eventually filling the impoundment, which results in a significant decrease in percolation through 

the base. Furthermore, the commenter questioned the assumption that post-closure percolation 

continues at the same rate as during active operations. The specific comments related to modeling 

surface impoundments only before closure and associated reference information are detailed in 

Table 3-11 and presented below. 
Response to Public Review Comments Source Modeling 

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Table 3-11. Comments Related to Modeling Surface Impoundments Only Pre-Closure

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2011-0392-0198 Trade Association Ken Ladwig EPRI 2011 

EPA-HQ-RCRA2011-0392-0211 Trade Association Jim Roewer USWAG 2011 

EPA-HQ-RCRA2011-0392-0237 Electric Utility 

Company Basil Constantelos Edison Mission Energy, LLC 2011 

EPA-HQ-RCRA2011-0392-0274 Electric Utility 

Company Jean-Claude Younan SCANA Corporation 2011 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA Response 

Based on the 2009/2010 EPA surveys, it was assumed that the majority of the surface 

impoundments are storage impoundments, which are continuously dredged. Because these 

facilities have other units (whether onsite or offsite) established for disposition, it likely that the 

majority of waste in the dredged impoundments would be removed by the end of the unit’s 

operating life. Regardless, an uncertainty analysis provided in Appendix K demonstrates that the 

risks during the operating life of surface impoundments are greater because the higher hydraulic 

head drives leachate into underlying soils with greater force than gravity alone post-closure. 

Therefore, EPA did not explicitly model the post-closure phase of surface impoundments. The 

uncertainties resulting from this decision are discussed in Section 5 of the revised risk assessment. 

EPA acknowledges that EPACMTP is restricted to modeling flow as steady state with the 

assumption that an impoundment always has a fixed depth of wastewater. EPA further 

acknowledges that such an assumption may overestimate infiltration. The surface impoundment 

conceptual model assumes that sediments are periodically dredged and removed and that the longterm average thickness of the sediment is approximately 0.4 m, with half of that layer consolidated. 

EPA has used EPACMTP and its predecessor model versions for a longstanding time period and 

it has undergone multiple rounds of internal and external review. The reviews associated with 

EPACMTP and its limitations are further discussed in Section 5 of the revised risk assessment 

report. 
Response to Public Review Comments Source Modeling 

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3.12. Modeling of Landfills Only Post-Closure 

Comment Summary 

Public commenters suggested that risks from operating landfills should be considered along with 

those that occur post-closure. These commenters questioned whether greater risks may occur 

during site operations when wastes are uncovered and exposed directly to precipitation. Additional 

commenters noted that complete leaching of all constituent mass at a constant concentration is 

overly conservative. The specific public comments related to modeling landfills only after closure 

and associated reference information are detailed in Table 3-12. 

Table 3-12. Public Comments Related to Modeling of Landfills Only Post-Closure

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2011-0392-0198 Trade Association Ken Ladwig EPRI 2011 

EPA-HQ-RCRA2011-0392-0211 Trade Association Jim Roewer USWAG 2011 

EPA-HQ-RCRA2011-0392-0237 Electric Utility 

Company Basil Constantelos Edison Mission Energy, LLC 2011 

EPA-HQ-RCRA2011-0392-0238 Electric Utility 

Company Chris Hobson Southern Company 2011 

EPA-HQ-RCRA2011-0392-0274 Electric Utility 

Company Jean-Claude Younan SCANA Corporation 2011 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA Response 

The landfill source model used in this risk assessment is not able to address landfills during 

operation because the non-linear sorption isotherms used require a constant, annualized infiltration 

rate throughout the duration of leaching. Instead, the revised risk assessment assumed that the full 

footprint of the landfill is filled to capacity with a cap no less permeable than the soil or liner 

underlying the WMU is present at the start of leaching. EPA acknowledges that this approach 

introduces some uncertainty into the analysis, the potential impacts of which are discussed in 

Section 5 of the revised risk assessment. 

With respect to comments that complete leaching of all constituent mass is overly conservative, 

EPA now models landfills using leachable mass as discussed in Section 4 and Appendix C of the 
Response to Public Review Comments Source Modeling 

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revised risk assessment. Alternatively, EPA presents a sensitivity analysis of these results 

compared with the results generated using total mass in Section 5. 
Response to Public Review Comments

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4. Public Comments on Exposure 

Scenarios

The comments relating to exposure scenarios were grouped into six subcategories, which are 

summarized in the following bulleted list. Subcategories with no public comments are included 

for consistency with the peer review response to comments (U.S. EPA, 2014b).

 Section 4.1: Direct surface impoundment exposure (no public comments) 

 Section 4.2: Indirect exposure through game species (no public comments) 

 Section 4.3: Exposure to surface impoundment effluent 

 Section 4.4: Exposure to fugitive dust emissions during landfill operation (before closure) 

 Section 4.5: Elimination of pathways during screening analysis. 

 Section 4.6: Exposure to additional constituents. 

4.1. Direct Surface Impoundment Exposure 

Comment Summary 

No public comments. 

4.2. Indirect Exposure through Game Species 

Comment Summary 

No public comments. 

4.3. Exposure to Surface Impoundment Effluent 

Comment Summary 

The commenter emphasized that the risk assessment does not consider direct discharges to ground 

and surface water systems other than ground water infiltration (e.g., direct injection to ground 

water, point and nonpoint discharges to surface water systems). It was recommended that EPA 

consider combining contributions from these sources with CCR ground water leaching impacts to 

calculate the full load of CCR constituents to ground water and surface water systems. The 

commenter continues by suggesting that the use of liners in impoundments does not reduce overall 

hazards if direct discharges are considered in the risk assessment. The specific public comments 

related to exposure to surface impoundment effluent and associated reference information are 

detailed in Table 4-1. 
Response to Public Review Comments Exposure Scenarios 

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Table 4-1. Comments Related to Exposure to Surface Impoundment Effluent 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA Response 

Resource Conservation and Recovery Act (RCRA) waste disposal risk assessments do not address 

direct discharges from impoundments to surface waters because they are regulated as permitted 

point source discharges under the Clean Water Act by EPA’s Office of Water. Since this pathway 

is outside the scope of the risk assessment, the revised risk assessment does not consider these 

releases. However, this pathway was evaluated in the Environmental Assessment for the Proposed 

Effluent Limitation Guidelines and Standards for the Steam Electric Power Generating Point 

Source Category (U.S. EPA, 2013), which will be revised in support of final effluent limitation 

guidelines (ELG) due to be released in September of 2015. The revised risk assessment was 

updated to note this fact. 

EPA is not aware of any CCR disposal where waste is directly injected into ground water aquifers, 

and absent any data on this practice declines to evaluate it. 

4.4. Exposure to Fugitive Dust during Landfill 

Operation (Before Closure) 

Comment Summary 

Public comments were received on the methodology applied to evaluate exposure to fugitive dust 

during landfill operations (before closure). The majority of these comments focused on the fugitive 

analysis as presented in Inhalation of Fugitive Dust: A Screening Assessment of the Risks Posed 

by Coal Combustion Waste Landfills (U.S. EPA, 2010a), and EPA’s proposed approach for

refining the analysis. Comments received on the initial fugitive dust analysis methodology and 

modeling ranged from emphasizing that the approach was overly conservative in some cases to 

underestimating risk in other cases. 

Multiple comments were provided on the proposed methodology for refining the fugitive dust 

analysis that was applied in the revised risk assessment. One commenter recommended that 

2010/2011 EPA survey data should be used to refine the fugitive dust analysis for landfills. 

Specifically, the current OW data indicate that active portions of the landfills are significantly 

smaller than the landfills identified in the 1995 EPRI survey. Several comments were received that 

pointed out that the application of AERSCREEN and AERMOD is appropriate if representative 

or realistic inputs are used including meteorological data, material silt content, source areas for 

subcells of ash management units and consideration of common operating and control practices, 

which are in some cases defined by the states (e.g., Virginia). However, one commenter expressed 

concern that no previous or current EPA regulatory model, including SCREEN3, AERSCREEN 
Response to Public Review Comments Exposure Scenarios 

4-3 

or AERMOD, has been rigorously tested and evaluated for performance in modeling fugitive 

emissions associated with CCR landfills. 

In general, the commenters supported or recommended the use of appropriate AP-42 factors and 

other techniques to estimate emissions. Others noted that consideration of deposition impacts and 

constituent-specific modeling is appropriate. One commenter recommended that EPA should 

conduct a full-scale assessment that considers fugitive dust as well as emissions from landfills and 

emissions of diesel particulate matter from haul trucks, on-site heavy-duty landfill equipment, and 

diesel-powered pumps and generators, with potential receptors of interest as residents and sensitive 

subpopulations living near the power plant, along the transportation route and at the landfill. 

Another commenter expressed concern over the lack of metal speciation data, while another 

comment concerned gas emissions from the landfills (e.g., hydrogen sulfide). One final commenter 

voiced concern that insufficient information was provided on the modeling approach and the model 

inputs to support evaluation and allow comments on the overall validity or propriety of the 

suggested modeling. The specific public comments related to exposure during landfill operation 

and associated reference information are detailed in Table 4-2. 

Table 4-2. Comments Related to Exposure During Landfill Operation 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2012-0028-0060 Trade Association Douglas Green USWAG 2013 

EPA-HQ-RCRA2011-0392-0198 Trade Association Ken Ladwig EPRI 2011 

EPA-HQ-RCRA2011-0392-0211 Trade Association James Roewer USWAG 2011 

EPA-HQ-RCRA2011-0392-0215 Electric Utility 

Company Richard Meiers Duke Energy 2011 

EPA-HQ-RCRA2011-0392-0219 State Government Anthony Hatton Commonwealth of 

Kentucky 2011 

EPA-HQ-RCRA2011-0392-0237 Electric Utility 

Company Basil Constantelos Edison Mission Energy, LLC 2011 

EPA-HQ-RCRA2011-0392-0238 Electric Utility 

Company Chris Hobson Southern Company 2011 

EPA-HQ-RCRA2011-0392-0254 Electric Utility 

Company Pamela Faggert Dominion Resources Services Inc. 2011 

EPA-HQ-RCRA2011-0392-0264 Electric Utility 

Company Paul Allen Constellation Energy 2011 

EPA-HQ-RCRA2011-0392-0274 Electric Utility 

Company Jean-Claude Younan SCANA Corporation 2011 
Response to Public Review Comments Exposure Scenarios 

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Table 4-2. Comments Related to Exposure During Landfill Operation 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-06068 Advocacy Group John Veranth Utah Physicians for a 

Healthy Environment 2010 

EPA-HQ-RCRA2009-0640-06251 Electric Utility 

Company Art Covi We Energies 2010 

EPA-HQ-RCRA2009-0640-06298 State Government Paul L. Sloan TDEC 2010 

EPA-HQ-RCRA2009-0640-06313 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-10495 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-06360 Trade Association Jeff A. McNelly ARIPPA 2010 

EPA-HQ-RCRA2009-0640-06526 Trade Association James Roewer USWAG 2010 

EPA-HQ-RCRA2009-0640-06956 Electric Utility 

Company Barbara A. Walz Tri-State Generation & Transmission 2010 

EPA-HQ-RCRA2009-0640-07002 Advocacy Group Michael J. 

Churchman 

Alabama 

Environmental 

Council 

2010 

EPA-HQ-RCRA2009-0640-08227 Trade Association Michael Gardner Gypsum Association 2010 

EPA-HQ-RCRA2009-0640-08253 Electric Utility 

Company Terry Coss Xcel Energy 2010 

EPA-HQ-RCRA2009-0640-09284 State Government Jeffrey A. Steers VDEQ 2010 

EPA-HQ-RCRA2009-0640-09536 Electric Utility 

Company John W. Myers Tennessee Valley Authority 2010 

EPA-HQ-RCRA2009-0640-09765 Trade Association Ken Ladwig EPRI 2010 

EPA-HQ-RCRA2009-0640-09951 Beneficial User Robert J. Waldrop Full Circle Solutions, 

Inc. 2010 

EPA-HQ-RCRA2009-0640-10019 Law Firm 

Rosemary G. 

Spalding and 

Kathryn A. Watson 

Spalding & 

Hilmes, PC 2010 

EPA-HQ-RCRA2009-0640-10496 Advocacy Group Emily Greenlee Earthjustice 2010 
Response to Public Review Comments Exposure Scenarios 

4-5 

EPA Response 

The majority of the comments received concerning exposures during landfill operation (before 

closure) focused on the assessment of fugitive dust. EPA acknowledges that the 2010 Draft Risk 

Assessment did not evaluate the inhalation pathway, relying instead on the findings of a previous 

evaluation, Inhalation of Fugitive Dust: A Screening Assessment of the Risks Posed by Coal 

Combustion Waste Landfills (U.S. EPA, 2010a). This previous evaluation only considered releases 

from windblown emissions and the potential to exceed national ambient air quality standards 

(NAAQS) for particulate matter. 

Based on the comments received, EPA updated the screening analysis of fugitive dust. EPA agrees 

that there are potential risks posed by fugitive emissions from sources beyond wind and revised 

the analysis to consider emissions from a range of activities, such as vehicular activity, unloading 

operations and spreading/compacting operations. Emissions from these sources were calculated 

using techniques that have undergone extensive peer-review, including AP-42: Compilation of Air 

Pollutant Emission Factors (U.S. EPA, 1985). Screening level modeling was performed with a 

combination of AERSCREEN and AERMOD to estimate dust dispersion and deposition rates. 

Model inputs were selected to be representative of current landfills, environmental settings (e.g., 

meteorological conditions) and common dust management practices. Estimated air concentrations 

were used to screen acute and chronic health risks from inhalation, as well as the potential to 

exceed NAAQS standards. Furthermore, EPA considered exposures that may result from the 

offsite deposition on and accumulation in downgradient media. This was done for all relevant 

metal species. In contrast, EPA did not evaluate emissions of hydrogen sulfide to air as EPA has 

no data on the extent to which this constituent is present in CCRs or released into the surrounding 

environment. Further discussion of this screening analysis is presented in Section 3 and Appendix 

F of the revised risk assessment. 

4.5. Elimination of Pathways during Screening 

Analysis

Comment Summary 

Comments both supported and disagreed with the appropriateness of a screening analysis to 

eliminate pathways from consideration in the full-scale probabilistic analysis. One commenter 

pointed out that the EPA conducted a very conservative, but appropriate, screen to identify 

constituents to include in the full-scale probabilistic analysis. Another commenter emphasized that 

a full scale risk assessment should be conducted that assesses exposures concurrently through all 

pathways (e.g., including surface pathways with inhalation exposure) for all chemical constituents. 

In particular, they emphasized that inhalation exposures to human carcinogens, such as hexavalent 

chromium, as well as non-carcinogens may occur through the aboveground pathway. Although 

disagreed over the use of a screening approach, both commenters expressed concerns over the use 

of risk attenuation factors to scale screening risks to the full-scale risks for the subset of 

constituents that did not pass the screen and were not evaluated under the full scale assessment. 

Both commenters believe that this approach ignores the unique fate and transport properties of the 
Response to Public Review Comments Exposure Scenarios 

4-6 

omitted constituents and that the use of a simplistic, attenuation factor is not an appropriate way 

to estimate risk. The specific public comments related to elimination of pathways during screening 

and associated reference information are detailed in Table 4-3. 

Table 4-3. Comments Related to Elimination of Pathways During Screening Analysis 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA-2011-

0392-0211 Trade Association Jim Roewer USWAG 2011 

EPA-HQ-RCRA-2009-

0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA-2009-

0640-06526 Trade Association Jim Roewer USWAG 2010 

EPA-HQ-RCRA-2009-

0640-08787 State Government Stephen A. Cobb ASTSWMO 2010 

EPA-HQ-RCRA-2009-

0640-06555-13 Beneficial User Lauren P. Alterman Saint-Gobain Corporation / CertainTeed Corporation 2010 

EPA-HQ-RCRA-2006-

0796-0446 Advocacy Group Jeffery A. Fornan Earthjustice 2007 

EPA-HQ-RCRA-2006-

0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA Response 

By first conducting the screening analysis presented in Section 3 of the revised risk assessment, 

EPA was able to focus available resources on the characterization of risks for exposure routes and 

constituents with the greatest potential to pose risks. The screening analysis conducted for the 

revised risk assessment considered all of the potential exposure routes identified in the conceptual 

models for surface impoundments and landfills, which included aboveground exposures to 

ambient air, soil, sediment, produce and animal products. Each exposure pathway was evaluated 

for all constituents (and individual species, as appropriate) for which both concentration and 

toxicity data were available. 

The screening analysis was developed to be protective of highly exposed individuals. Due to the 

conservative nature of the screening, the calculated risks represent a protective, but unlikely, 

combination of conditions that most likely reflect an upper bond on potential exposures for each 

individual constituent. The revised screening assessment did not rely on risk attenuation factors to 

screen out constituents. All constituents that resulted in screening-level risks above human health 

or ecological criteria, and for which characterization of fate and transport could be refined, were 

carried forward for further consideration in the probabilistic analysis, described in Section 4 of the

revised risk assessment. It is possible that consideration of exposure to multiple constituents 

through a single pathway or to the same constituent through multiple pathways may have resulted 

in the retention of some additional constituents. However, it is highly unlikely that these additional
Response to Public Review Comments Exposure Scenarios 

4-7 

constituents would remain risk drivers once more realistic dilution and attenuation in the 

environment is considered. 

4.6. Exposure to Additional Constituents 

Comment Summary 

Multiple commenters noted that there may be additional constituents present in CCR wastes 

beyond those quantitatively evaluated in the risk assessment. In particular, multiple commenters 

referenced organics and radionuclides. Some commenters called on EPA to quantify the risks 

associated with these additional constituents. Others claimed that these constituents are present in 

low levels and do not pose risk to receptors. The specific public comments related to exposure to 

additional constituents are detailed in Table 4-4. 

Table 4-4. Comments Related to Exposure to Additional Constituents 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA-2006-

0796-0057 and 0242 Advocacy Group Shannon Anderson Powder River Basin Council 2006 

EPA-HQ-RCRA-2009-

0640-05774 Private Citizen Anonymous Anonymous 2009 

EPA-HQ-RCRA-2009-

0640-06349 Private Citizen Mollie Freebairn N/A 2009 

EPA-HQ-RCRA-2009-

0640-06298 State Government Paul L. Sloan TDEC 2009 

EPA-HQ-RCRA-2009-

0640-06068 Advocacy Group John Veranth Utah Physicians for a Healthy Environment 2009 

TRANS-CHI-0002-1 Advocacy Group Larry Jensen PINES 2010 

EPA-HQ-RCRA-2011-

0392-0239 Advocacy Group Lisa Evans Earthjustice 2011 

EPA Response 

In the Report to Congress: Wastes from the Combustion of Fossil Fuels: Volume 2 - Methods, 

Findings, and Recommendations (U.S. EPA, 1999b), EPA reviewed the available data on organic 

constituents, such as polyaromatic hydrocarbons and dioxins. These data indicated that 

concentrations of all organics are near or below analytical detection limits both in CCRs and in the 

leachate released from CCRs. Based on the findings of this report, the Agency concluded that 

organic constituents were not risk drivers and did not require further evaluation. In the absence of 

additional data that demonstrate the organic composition of CCR wastes have markedly changed, 

EPA continues to rely on these findings. 

EPA acknowledges that, like other inorganic constituents, naturally-occurring radionuclides may 

be concentrated in CCR waste through the combustion of coal. However, due to a lack of data that 

could be used to characterize leachate concentrations for individual radionuclides, a quantitative 
Response to Public Review Comments Exposure Scenarios 

4-8 

evaluation of risk was not conducted. To address this data gap, EPA has included radionuclides in 

the list of constituents for ground water monitoring. Furthermore, potential transport of these 

constituents downgradient by windblown dust and storm runoff are addressed through 

requirements for fugitive dust controls and run-on/run-off controls. 
Response to Public Review Comments

5-1 

5. Comments Related to Human 

Exposure and Toxicity 

The comments relating to human exposure and toxicity were grouped into eight subcategories, 

which are summarized in the following bulleted list. Subcategories with no public comments are 

included for consistency with the peer review response to comments (U.S. EPA, 2014b).

 Section 5.1: Combined chemical effects, additive risk, and multiple pathway exposures 

 Section 5.2: Toxicity and associated benchmark values 

 Section 5.3: Target cancer and non-cancer risk criteria 

 Section 5.4: Defining the exposed population 

 Section 5.5: Exposure factor assumptions 

 Section 5.6: Child/infant exposure assumptions 

 Section 5.7: Correlations in input variables (no public comments) 

 Section 5.8: Bioconcentration Factors. 

5.1. Combined Chemical Effects, Additive Risk, 

and Multiple Pathway Exposures 

Comment Summary 

Some commenters argued that EPA underestimated risks by not considering combined chemical 

effects, additive risk and concurrent exposures through multiple pathways. One commenter 

indicated that EPA should conduct a full scale assessment that considers concurrent exposure from 

ingestion of fish and ground water. Commenters also raised concerns that some chemical 

constituents share a common mechanism of toxicity and may affect the same body organ or system, 

resulting in greater risks than predicted through the consideration of each constituent separately. 

One commenter noted that the combination of risks from different constituents would not change 

the overall results of the risk assessment. Constituents concentrations found to result in an HQ less 

than 1 in the screening analysis are unlikely to make a meaningful contribution to overall risk 

regardless of whether multiple compounds share the same toxicological endpoints. Additionally, 

the commenter expressed that it would be inappropriate to add the risks from different constituents 

as modeled because the constituents do not all arrive at a hypothetical receptor at the same time, 

due to differing mobility in the subsurface environment. The specific public comments related to 

combined chemical effects, additive risk, and multiple pathway exposures, and associated 

reference information are detailed in Table 5-1. 
Response to Public Review Comments Human Exposure and Toxicity 

5-2 

Table 5-1. Public Comments Related to Combined Chemical Effects, Additive Risk, 

and Multiple Pathway Exposures 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2006-0796-0446 Advocacy Group Jeffery A. Fornan Earthjustice 2007 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA-HQ-RCRA2006-0796-0045 N/A Anonymous N/A 2007 

EPA-HQ-RCRA2006-0796-0425 Academia Cynthia Water Saint Vincent 

College 2007 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

TRANS-KNX-0048-1 Advocacy Group Abel Russ EIP 2010 

EPA-HQ-RCRA2009-0640-09765 Trade Association Ken Ladwig EPRI 2010 

TRANS-KNX-0069-1 Advocacy Group Barbara Gottlieb Physicians for Social 

Responsibility 2010 

EPA-HQ-RCRA2009-0640-09533 Private Citizen Mary A. Fox, Ph.D, 

MPH Private Citizen 2010 

EPA Response 

EPA acknowledges that this risk assessment considered potential risks to human health from 

individual constituents and individual pathways. EPA acknowledges that not explicitly evaluating 

cumulative risk is a source of uncertainty that may result in some underestimation of risks. It is 

possible that an individual could be exposed to risks from drinking contaminated ground water, as 

well as eating contaminated fish from a local surface water body, it is unlikely that these two 

exposure pathways would occur simultaneously with any appreciable frequency in the real world. 

It is even more unlikely that a receptor would be exposed to both media at the high-end 

concentrations modeled. Therefore, the magnitude of the uncertainty introduced into the risk 

assessment is likely to be small. It is also possible for an individual to be exposed to multiple 

constituents through a single pathway. This is a more likely scenario because, as demonstrated by 

the available data, CCRs typically leach multiple inorganic constituents. Where exposure to 

multiple constituents is likely to occur, EPA policy is to assume that the risks resulting from these 

exposures are additive (U.S. EPA, 2000). The current probabilistic analysis identified individual 

constituents above risk criteria. Many of the other constituents modeled resulted in risks an order 

of magnitude or more below risk criteria. Thus, the consideration of additive risk, even with the 
Response to Public Review Comments Human Exposure and Toxicity 

5-3 

high-end risks modeled in this risk assessment, is unlikely alter the principal results of the 

probabilistic analysis. Similarly, because the risks for individual constituents were found to be 

above levels of concern, consideration of additive risk is unlikely to meaningfully change the 

results of the analysis. EPA updated the revised risk assessment to include a discussion of the 

associated uncertainties in Section 5. 

5.2. Toxicity and Associated Benchmark Values 

Comment Summary 

Some commenters identified incorrect and inconsistent reporting of toxicity benchmark values and 

recommended conducting a thorough review of literature to ensure the use of the most current 

values were used. Some commenters expressed concern over the use of the current IRIS value for 

arsenic carcinogenic effects and believe it underestimates risk. Other commenters emphasized that 

it would be inappropriate for EPA to consider using the draft oral cancer slope factor (CSF) for 

arsenic and the oral CSF for hexavalent chromium [chromium (VI)] published by the New Jersey 

Department of Environmental Protection (NJDEP). Concerning lead, one commenter supported a 

peer reviewer’s recommendation to use the Integrated Exposure Uptake Biokinetic (IEUBK) 

model to calculate human health risks, especially for young children. Additionally, a commenter 

requested chemical-specific information on toxicity criteria derivation, as well as information on 

the relationship between environmental exposures to specific chemicals and adverse health effects. 

The commenter emphasized that this information would provide an uncertainty discussion 

regarding toxicity values, facilitate communication with the public, and provide a balanced 

perspective on risk. The specific public comments related to toxicity values and associated 

reference information are detailed in Table 5-2. 

Table 5-2. Public Comments Related to Toxicity Values 

Commenter ID Commenter 

Type 

Commenter 

Name 

Commenter 

Organization Year 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA-HQ-RCRA2006-0796-0045 N/A Anonymous N/A 2007 

EPA-HQ-RCRA2006-0796-0432 Trade Association Jim Roewer USWAG 2007 

EPA-HQ-RCRA2009-0640-06340 Advocacy Group Pamela K. Miller 

and Sarah B. Petras ACAT 2010 

EPA-HQ-RCRA2009-0640-07002 Advocacy Group Michael J. 

Churchman 

Alabama 

Environmental Council 2010 

EPA-HQ-RCRA2009-0640-06307 Advocacy Group Sarah B. Petras Alaska Community 

Action on Toxics 2010 
Response to Public Review Comments Human Exposure and Toxicity 

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Table 5-2. Public Comments Related to Toxicity Values 

Commenter ID Commenter 

Type 

Commenter 

Name 

Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-06305 Advocacy Group Natalie Roy Clean Water Network 2010

EPA-HQ-RCRA2009-0640-06196 Advocacy Group Ruth Santiago Comite Dialogo 

Ambiental 2010 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-04041 Advocacy Group Brad Heavner 

Environment Maryland 

Research & Policy 

Center 

2010 

EPA-HQ-RCRA2009-0640-05752 Advocacy Group G. Preschle Foothills Group of the 

Sierra Club 2010 

EPA-HQ-RCRA2009-0640-10489 Beneficial User Gene Iannazzo 

Harsco Minerals 

International 2010 

EPA-HQ-RCRA2009-0640-06886 Advocacy Group Joyce Blumenshine Heart of Illinois Group 

Sierra Club 2010 

EPA-HQ-RCRA2009-0640-06829 Advocacy Group Jodi Perras Improving Kids' 

Environment 2010 

EPA-HQ-RCRA2009-0640-06541 Trade Association Brian H. Moeck LPPC 2010 

EPA-HQ-RCRA2009-0640-06809 Tribal Government Darren Daboda Moapa Band of 

Paiutes 2010 

EPA-HQ-RCRA2009-0640-06823 Advocacy Group Ian Zabarte NCAC 2010 

EPA-HQ-RCRA2009-0640-06516 Advocacy Group Carrie La Seur Plains Justice 2010 

EPA-HQ-RCRA2009-0640-06192 Advocacy Group Sharon Anderson Powder River Basin 

Resource Council 2010 

EPA-HQ-RCRA2009-0640-06959 Advocacy Group Traci L. Barkley 

Prairie Rivers Network, 

Illinois Chapter of the 

Sierra Club, American 

Bottom Conservancy 

2010 

EPA-HQ-RCRA2009-0640-04005 Private Citizen James Burch, Ph.D Private Citizen 2010 
Response to Public Review Comments Human Exposure and Toxicity 

5-5 

Table 5-2. Public Comments Related to Toxicity Values 

Commenter ID Commenter 

Type 

Commenter 

Name 

Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-06331 Private Citizen Jonathon Gray Private Citizen 2010 

EPA-HQ-RCRA2009-0640-06346 Private Citizen Kelly Spencer Private Citizen 2010 

EPA-HQ-RCRA2009-0640-06349 Private Citizen Mollie Freebairn Private Citizen 2010 

EPA-HQ-RCRA2009-0640-06545 Private Citizen Mary Arlis Bates Private Citizen 2010 

EPA-HQ-RCRA2009-0640-06554 Private Citizen Kristina Keeling Private Citizen 2010 

EPA-HQ-RCRA2009-0640-06556 Private Citizen Renee Reber Private Citizen 2010 

EPA-HQ-RCRA2009-0640-02401 Advocacy Groups Jody Harlan Sierra Club Oklahoma 2010 

EPA-HQ-RCRA2009-0640-06356 Trade Association William L. Kovacs U.S. Chamber of 

Commerce 2010 

TRANS-DEN-0037-1 Academia Michael J. Kosnett 

University of Colorado 

School of Medicine, 

and Colorado School 

of Public Health 

2010 

EPA-HQ-RCRA2009-0640-06311 Academia Michael J. Kosnett 

University of Colorado 

School of Medicine, 

and Colorado School 

of Public Health 

2010 

EPA-HQ-RCRA2009-0640-06526 Trade Association Jim Roewer USWAG 2010 

EPA-HQ-RCRA2009-0640-09633 Advocacy Group Scott Edwards Waterkeeper Alliance 2010 

EPA-HQ-RCRA2011-0392-0274 Electric Utility 

Company Jean-Claude Younan SCANA Corporation 2011 

EPA-HQ-RCRA2009-0640-

11736_K-162-3 

Advocacy Group Abel Russ EIP 2010 

EPA-HQ-RCRA2011-0392-0211 Trade Association Jim Roewer USWAG 2011 
Response to Public Review Comments Human Exposure and Toxicity 

5-6 

EPA Response 

Human health benchmarks were chosen based on the Office of Solid Waste and Emergency 

Response hierarchy (OSWER Directive 9285.7-53; U.S. EPA, 2003c). EPA reviewed the 

benchmarks to confirm their accuracy and determine whether newer values have become available 

from EPA or other sources used by EPA since the CCR draft risk assessment was conducted. The 

current, updated list of human health benchmarks is provided in Appendix E of the revised risk 

assessment, and the references cited in that appendix provide further information on the potential 

adverse effects and derivation of toxicity criteria. 

For lead, EPA used the drinking water maximum contaminant level (MCL) to estimate risks from 

drinking water exposure in the draft risk assessment. In the revised risk assessment EPA continued 

to rely on the MCL, but also used IEUBK model for lead in children as described in Section 5 of 

the revised risk assessment. While lead failed the screening assessment, risks from lead exposure 

in the probabilistic assessment were well below the risk criterion, and did not drive risks in either 

the probabilistic or any sensitivity analyses. 

5.3. Target Cancer and Non-Cancer Risk Criteria 

Comment Summary 

The commenters questioned why the cancer benchmark of 1×10-5 was selected while the typical 

range used by OSWER and EPA guidance is a range of 1×10-4 to 1×10-6. The commenters 

suggested that an explanation is necessary. In particular, one commenter requests clarification on 

the phrase “point of departure” when supporting the use of the cancer benchmark of 1×10-5

. 

Concerning noncancer criteria, a commenter suggested that non-cancer risks should be report as 

follows: Worst Case – Assume maximum exposure scenarios including exposure 24 hours/day, 

365 days/year for 70 years; High End – 95th percentile based on national human activity pattern 

distributions; Central Tendency – 50th percentile (or median) risk based on national human activity 

pattern distributions. Furthermore, another commenter believed that it is more appropriate to 

consider 95th percentiles, rather than 90th percentile, of exposure and risk estimates for humans 

and ecological receptors. The specific public comments related to target cancer risk and associated 

reference information are detailed in Table 5-3. 

Table 5-3. Public Comments Related to Target Cancer Risk 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2006-0796-0446 Advocacy Group Jeffery A. Fornan Earthjustice 2007 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 
Response to Public Review Comments Human Exposure and Toxicity 

5-7 

Table 5-3. Public Comments Related to Target Cancer Risk 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-

10791_DA-022-3 

Electric Utility 

Company Jim Roewer USWAG 2010

EPA Response 

The rationale for the selected cancer and noncancer risk criteria, based on Agency policy, is 

discussed in Section 2 of the revised risk assessment. A citation to the where “point of departure” 

was originally defined is provided for reference. The rationale for use of 90th percentile risk 

generated by a Monte Carlo simulation is discussed in Section 4 of the revised risk assessment. 

5.4. Defining the Exposed Population 

Comment Summary 

Commenters questioned the evaluation of only the reasonable maximum exposure scenario. 

Specifically, it was noted that the receptor placement downgradient of an unlined management 

unit does not represent the entire population exposure distribution. One commenter suggested that 

EPA clearly define the exposed population of interest. The specific public comments related to 

defining the exposed population and associated reference information are detailed in Table 5-4. 

Table 5-4. Public Comments Related to Defining the Exposed Population 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2012-0028-0059 State Government Anthony Hatton Commonwealth of 

Kentucky 2013 

EPA-HQ-RCRA2012-0028-0068 Electric Utility 

Company Gary Dawson Consumers Energy Company 2013 

EPA-HQ-RCRA2012-0028-0073 Electric Utility 

Company TVA TVA 2013 

EPA-HQ-RCRA2012-0028-0078 Electric Utility 

Company 

Alliant Energy 

Corporate Services, 

Inc. 

Alliant Energy 

Corporate Services, 

Inc. 

2013 

EPA-HQ-RCRA2012-0028-0105 Electric Utility 

Company Chet Thompson CME Engineering LP 2013 

EPA-HQ-RCRA2011-0392-0211 Trade Association Jim Roewer USWAG 2011 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 
Response to Public Review Comments Human Exposure and Toxicity 

5-8 

Table 5-4. Public Comments Related to Defining the Exposed Population 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-06526 Trade Association Jim Roewer USWAG 2010 

EPA-HQ-RCRA2006-0796-0432 Trade Association Jim Roewer USWAG 2007 

EPA Response 

In risk assessments used to develop regulations under RCRA, EPA has historically assessed 

potential risks resulting from a reasonable maximum exposure (RME) scenario in order to ensure 

that the resulting regulation is adequately protective of human health without being excessively 

conservative. The types of data necessary to define the exact population that relied on ground water 

wells as a source of drinking water or consumes fish from impacted water bodies are not available. 

EPA believes that consideration of RME is a reasonable and protective alternative, given the 

available data. Uncertainties associated with the revised risk assessment are further discussed in 

Section 5 of the revised risk assessment. 

5.5. Exposure Factor Assumptions 

Comment Summary 

The commenters questioned the use of data from the 1997 Exposure Factors Handbook in the 

development of intake rate distributions for various exposures, because more current data are 

currently available. Commenters recommended that EPA make updates to these parameters using 

more current sources of information, including the recently released 2011 Exposure Factors 

Handbook (U.S. EPA, 2011). In addition, some commenters pointed out the potential for the 

available exposure factor data to underestimate or overestimate exposures. One commenter noted 

that the risk assessment did not fully account for the dependence of input variables (e.g., the 

interdependence of body weight and water ingestion rates for children and link between the rate 

of fish consumed from a water body). Another commenter suggested that a sensitivity analysis of 

human health exposure factors be conducted to add to the sensitivity analysis conducted by EPA 

in 2009. 

Regarding fish consumption rates, commenters questioned the representativeness of a fixed fish 

consumption rate drawn from a single study. It was suggested for transparency that the risk 

assessment provide the results of the chi-square tests to demonstrate how well the fish consumption 

rate data fit a log normal distribution. Additionally, it was suggested that fish consumption rates 

should be determined from other studies and more robust data sets. One commenter suggested the 

incorporation of fish consumption rates representative of subsistence fishers, such as Native 

American populations that harvest and consume fish as part of their native traditions and culture. 
Response to Public Review Comments Human Exposure and Toxicity 

5-9 

Regarding drinking water ingestion rates, one commenter voiced concern about the assumption 

that ground water is the source of all drinking water. The commenter indicated that this is an overly 

conservative and atypical assumption, as a majority of individuals will consume liquids from other 

sources (e.g., milk, juice, sodas, bottled water, sports and energy drinks). The specific public 

comments related to exposure factor assumptions and associated reference information are detailed 

in Table 5-5. 

Table 5-5. Public Comments Related to Exposure Factor Assumptions 

EPA Commenter Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2011-0392-0211 Trade Association Jim Roewer USWAG 2011 

EPA-HQ-RCRA2011-0392-0274 Electric Utility 

Company Jean-Claude Younan SCANA Corporation 2011 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-08244 Electric Utility 

Company 

Basil G. 

Constantelos 

Edison Mission 

Energy, LLC 2010 

EPA-HQ-RCRA2009-0640-10483 Trade Association Jim Roewer USWAG 2010 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA-HQ-RCRA2006-0796-0432 Trade Association Jim Roewer USWAG 2007 

EPA-HQ-RCRA2009-0640-06260 State Government R. Bruce Scott KY DEP 2010 

EPA Response 

This revised risk assessment relied on both the 1997 Exposure Factors Handbook (EFH) (U.S. 

EPA, 1997a,b,c) and the 2008 Child-Specific Exposure Factors Handbook (CSEFH) (U.S. EPA, 

2008b) for information on human exposure factors for the U.S. population. The 2011 Exposure 

Factors Handbook (U.S. EPA, 2011) has been completed and updates some of the data from the 

1997 EFH. During the finalization of this risk assessment, EPA released OSWER Directive 9200.1-

120 (U.S. EPA, 2014c). Although this document provides default exposure factors to use for point 

estimates, EPA is still in the process of updating the full distributions necessary for probabilistic 

analysis. Therefore, this risk assessment does not incorporate the data from the 2011 EFH. 

Exposure data used for the fish ingestion rates are described in Appendix D of the revised risk 

assessment. Data on site-specific fish consumption rates were not available for use in this analysis. 

Instead, the full distribution of fish consumption rates were drawn from a study of adult anglers 
Response to Public Review Comments Human Exposure and Toxicity 

5-10 

from Maine that fished from streams, rivers, and ponds. Because age-specific data for children 

were not available, all child cohorts were assumed to consume fish at the same rate as the adult 

cohort. Data on fish ingestion rates for Native American subsistence fishers are currently limited 

and can vary widely geographically, to the point that the 2011 EFH makes no recommendation for 

representative values. EPA acknowledges that these issues introduce uncertainty into the analysis, 

which are further discussed in Section 5 of the revised risk assessment. 

5.6. Child/Infant Exposure Assumptions 

Comment Summary 

Commenters emphasized the need to update exposure factors for childhood exposures and 

recommended that updates include data from the 2011 EFH. One commenter stated that the risk 

assessment appropriately considered the potential fish exposures for children. However, they 

pointed out that the fish consumption rates for children should be lower than those applied for 

adults. Another commenter suggested that the risk assessment should provide a clear description 

of how the exposure duration of child cohorts were used in the risk calculations. Specifically, the 

commenter questioned whether exposure durations were truncated at the end of each age cohort or 

aged through the different cohorts. The specific public comments related to child/infant exposure 

assumptions and associated reference information are detailed in Table 5-6. 

Table 5-6. Public Comments Related to Child/Infant Exposure Assumptions 

Commenter ID Commenter 

Type 

Commenter 

Name 

Commenter 

Organization Year 

EPA-HQ-RCRA2011-0392-0211 Trade Association Jim Roewer USWAG 2011 

EPA-HQ-RCRA2011-0392-0274 Electric Utility 

Company Jean-Claude Younan SCANA Corporation 2011 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA Response 

The revised risk assessment makes use of the 1997 EFH (U.S. EPA, 1997a,b,c) and the 2008 

CSEFH (U.S. EPA, 2008b) for information on human exposure factors for the U.S. population. 

Although, as discussed in Section 5.6 of this document, the revised risk assessment does not 

incorporate data from the recent 2011 EFH (U.S. EPA. 2011), all child data included in this 

document was derived from the 2008 EFH. In addition to child ingestion of drinking water, EPA’s 

evaluation has been revised to also account for infant exposures that may occur from formula 

mixed with contaminated ground water. These data are presented in Appendix D of the revised 

risk assessment. Consistent with the commenter’s recommendation for cohort aging, the risk 

assessment aged receptors through each age cohort using age-specific data for exposure factors 

and physical characteristics that were weighted proportionally by the corresponding time period 
Response to Public Review Comments Human Exposure and Toxicity 

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and then summed. Specific discussion of truncation values is provided in Section 8.2 of this 

document. 

5.7. Correlations in Input Variables 

Comment Summary 

 No public comments. 

5.8. Bioconcentration Factors 

Comment Summary 

Public commenters recommended updating BCF values with more current references. One 

commenter questioned why bioconcentration factors were zero for some constituents that are 

essential nutrients (i.e., cobalt and copper). Another commenter voiced concern that EPA had not 

fully considered the appropriateness of using BCFs to describe metals bioaccumulation, suggesting 

that current science (including EPA guidance documents) indicates that BCFs are poor predictors 

of tissue metal concentrations due to wide variation in uptake patterns governed by several 

chemical and biological factors. Another commenter recommended the use of an approach that 

would be more robust than the single BCF approach, establishing and applying distributions of 

BCFs. This commenter also recommended that the assessment adhere to the EPA policy of using 

dissolved metals in the calculating the bioconcentration of metals in fish, or should provide the 

rationale for using a different approach. The specific public comments related to bioconcentration 

factors and associated reference information are detailed in Table 5-7. 

Table 5-7. Public Comments Related to Bioconcentration Factors 

Commenter ID Commenter 

Type 

Commenter 

Name 

Commenter 

Organization Year 

EPA-HQ-RCRA2012-0028-0059 State Government Anthony Hatton Commonwealth of 

Kentucky 2013 

EPA-HQ-RCRA2012-0028-0044 Electric Utility 

Company Chris Hobson Southern Company 2013 

EPA-HQ-RCRA2012-0028-0073 Electric Utility 

Company 

Tennessee Valley 

Authority 

Tennessee Valley 

Authority 2013 

EPA-HQ-RCRA2012-0028-0105 Electric Utility 

Company Chet Thompson CME Engineering LP 2013 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 
Response to Public Review Comments Human Exposure and Toxicity 

5-12 

EPA Response 

EPA recognizes that the use of BCFs may not represent the most current approaches available to 

estimate metal bioaccumulation at individual sites, where fish tissue data can be collected. 

However, as noted by public commenters, BCFs are useful in a screening-level assessment and 

EPA believes they are also appropriate for a national-level risk assessment, where site-specific 

data are not available and collection of site-specific data is not viable. 

In some cases, insufficient data to determine a BCF value meant that these constituents could not 

be quantitatively evaluated for this pathway. Regarding the concern expressed with respect to zero 

BCF values, the commenter did not provide alternative BCFs that EPA could consider for the 

constituents at issue. Additionally, EPA agrees that given the latest scientific information, 

distributions of BAFs/BCFs may be better than single BAFs/BCFs because they account for 

changes in bioaccumulation/bioconcentration at different water concentrations. EPA is working to 

develop BAF/BCF distributions for several CCR pollutants of concern but does not yet have a 

robust enough dataset for use for the final CCR Rule. In lieu of this, EPA is proceeding with the 

single BAF/BCF approach for the current analysis. EPA does recognize this issue as a limitation 

for the BCF calculations and considers it as an uncertainty in the risk characterization. Overall, 

EPA agrees that the use of this older data introduces some uncertainty into the analysis. These 

uncertainties are discussed in greater detail in Section 5 of the revised risk assessment. 

With the exception of mercury, EPA evaluated bioconcentration based on water column 

concentrations that include contributions from dissolved and solid phases because available BCFs 

represent contributions from both. Because a BAF based only on dissolved-phase concentrations 

was available for mercury, EPA evaluated this constituent using only dissolved concentrations. 

Applying this conservative approach for most constituents ensured protection of human health. 

Even with this conservative assumption, the 90th percentile risks for the probabilistic analysis 

(Section 4) did not exceed risk criteria for the fish ingestion pathway. Therefore, this approach is 

unlikely to have affected the principal findings of the risk assessment. 

For the revised risk assessment, EPA reviewed the available literature and identified BCFs for 

additional constituents that previously had no values. As noted in Appendix G of the revised risk 

assessment, the following source hierarchy was used for fish BCFs: 

 Primary literature: These are generally papers focused on a single chemical (Eisler, 1989; 

Kumada et al., 1973; Lemly, 1985; Murphy et al., 1978) or may contain data on multiple 

chemicals (Barrows et al., 1980; Stephan, 1993). 

 U.S. EPA databases/publications: These included ECOTOX (U.S. EPA, 2009b) and the 

Mercury Report to Congress (U.S. EPA, 1997d). 

 Other government agency resources: These included ATSDR Toxicological Profiles 

(ATSDR, 2008) and the Hazardous Substances Data Bank (HSDB; U.S. NLM, 2011). 

EPA also finds that the references provided by commenters provided primarily phytotoxicity and 

accumulation data for terrestrial plants, and were therefore not relevant to EPA’s explicit 
Response to Public Review Comments Human Exposure and Toxicity 

5-13 

solicitation on whether the bioconcentration factors drawn from Baes et al. (1984) should be 

considered in the final risk assessment. 
Response to Public Review Comments Human Exposure and Toxicity 

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Response to Public Review Comments

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6. Comments Related to Ecological 

Exposure and Toxicity

The comments relating to ecological exposure and toxicity were grouped into four subcategories, 

which are summarized in the following bulleted list. Subcategories with no public comments are 

included for consistency with the peer review response to comments (U.S. EPA, 2014b).

 Section 6.1: Cumulative ecological risk 

 Section 6.2: Sensitive habitats/sensitive species 

 Section 6.3: Indirect effects (no public comments) 

 Section 6.4: Eco benchmarks, eco toxicity. 

6.1. Cumulative Ecological Risk 

Comment Summary 

Public commenters emphasized the potential importance of cumulative ecological risk, whereby 

an ecological receptor may be exposed to multiple constituents and/or pathways concurrently. For 

example, amphibians may be subject to both dermal and ingestion exposure. Public commenters 

noted that ecological risks were underestimated because the following scenarios were not 

considered for ecological receptors: aboveground pathways, contaminant transport to nearby 

uncontaminated environments, and the inclusion of field data in the analysis. The specific public 

comments related to cumulative ecological risk and associated reference information are detailed 

in Table 6-1. 

Table 6-1. Comments Related to Cumulative Ecological Risk 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-06548 Academia Dr. Conrad Daniel 

Volz 

University of 

Pittsburgh Department 

of Public Health 

2010 

EPA-HQ-RCRA2009-0640-07785 Academia Avner Vengosh 

Nicholas School of the 

Environment, Duke 

University 

2010 

EPA-HQ-RCRA2009-0640-06331 Private Citizen Jonathon Gray Private Citizen 2010 

EPA-HQ-RCRA2006-0796-0446 Advocacy Group Jeffery A. Fornan Earthjustice 2007 
Response to Public Review Comments Ecological Exposure and Toxicity 

6-2 

EPA Response 

EPA acknowledges that cumulative effects can be important for ecological receptors. However, 

just as EPA did not consider cumulative human health risks from exposures to ground water 

(discussed in Section 6.1 of this document), they were not modeled for ecological receptors. In the 

national, probabilistic analysis (Section 4 of the revised risk assessment), risks for all constituents 

fell below the ecological criteria. Even the sum of modeled risks for all constituents fell below the 

ecological criteria. In sensitivity analyses (Section 5 of the revised risk assessment), which 

considered different subsets of national disposal practices that may drive risks, boron and cadmium 

were the two constituents found to result in risks above ecological criteria. To the extent that 

cumulative exposures were not evaluated, EPA acknowledges that ecological risk could be 

underestimated to some degree. However, these uncertainties are unlikely to affect the principal 

findings of the risk assessment. In addition, EPA also notes that all surface water risks are orders 

of magnitude lower than the risks resulting from direct discharges modeled in U.S. EPA (2013). 

In contrast to the surface water and sediment exposures, ecological risks for individual constituents 

were appreciably above risk criteria for direct exposure to impoundment wastewater. As a result, 

it is clear that CCR disposal in surface impoundments have the potential to pose risk to ecological 

receptors, even without consideration of cumulative exposures. 

6.2. Sensitive Habitats/Sensitive Species

Comment Summary 

Public commenters stated that the risk assessment does not consider sensitive habitats or species. 

Commenters requested additional consideration of threatened and endangered species and the 

inclusion of ecological field data. The specific comments related to sensitive habitats/species and 

associated reference information are detailed in Table 6-2. 

Table 6-2. Comments Related to Sensitive Habitats/Sensitive Species 

Comment ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2006-0796-0446 Advocacy Group Jeffery A. Fornan Earthjustice 2007 

EPA Response 

EPA did not evaluate these sensitive habitats and sensitive/endangered ecological receptors 

because the presence these are inherently site-specific issues for which data on potential impacts 

are often not available and can be difficult to quantify, even on a site-specific basis. EPA 

acknowledges that the inability to quantitatively evaluate the potential for these adverse effects 

represents a source of uncertainty. Discussion of these uncertainties is presented in Section 5 of 

the revised risk assessment. 
Response to Public Review Comments Ecological Exposure and Toxicity 

6-3 

6.3. Indirect Effects

Comment Summary 

No public comments. 

6.4. Ecological Benchmarks, Ecological Toxicity

Comment Summary 

Public commenters were concerned that a more conservative approach was needed to derive the 

ecological benchmarks. Multiple commenters also stated that the use of risk attenuation factors to 

scale the screening risks to full-scale risks was inappropriate. Several commenters noted that the 

ecological boron benchmark used for surface water exposures contained incorrect units based on 

an incorrect transcription in the peer-reviewed article. Another commenter noted that the 

ecological cadmium benchmark used for direct contact with surface water was incorrect. The 

specific public comments related to ecological benchmarks, ecological toxicity and associated 

reference information are detailed in Table 6-3. 

Table 6-3. Comments Related to Ecological Benchmarks, Ecological Toxicity 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2011-0392-0181 Private Citizen Glen Suter II, Ph.D Private Citizen 2011 

EPA-HQ-RCRA2011-0392-0211 Trade Association Jim Roewer USWAG 2011 

EPA-HQ-RCRA2011-0392-0274 Electric Utility 

Company Jean-Claude Younan SCANA Corporation 2011 

EPA-HQ-RCRA2009-0640-06526 Trade Association Jim Roewer USWAG 2010 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2006-0796-0446 Advocacy Group Jeffery A. Fornan Earthjustice 2007 

EPA-HQ-RCRA2006-0796-0045 N/A Anonymous N/A 2007 

EPA Response 

Ecological benchmarks were obtained for CCR constituents when available and compared with 

the modeled media concentrations (e.g., surface water, sediment) to estimate the HQs used to 

characterize ecological risk. These benchmarks represent the best available estimates of receptor 

responses based “no effects” (NOAEL) or “lowest effects” (LOAEL) study data. In some 
Response to Public Review Comments Ecological Exposure and Toxicity 

6-4 

scenarios, these benchmarks may represent species not actually present in the field. In others, these 

benchmarks may not capture the most sensitive possible receptor at every site or for each 

constituent. While some benchmarks have factors of safety included to account for these or other 

uncertainties, there remains the potential for these ecological benchmarks to underestimate risks 

for the specific species and communities that live in surface waters impacted by CCR WMUs. The 

magnitude of this uncertainty is unknown. Consideration of any additional sensitive species not 

captured by the current benchmarks may result in some additional constituents above risk criteria 

in the probabilistic analysis. EPA notes that ecological risks to some of these additional sensitive 

receptors may be reflected in damage cases. However, this site-specific uncertainty is unlikely to 

affect the national conclusions of the risk assessment. 

Regarding incorrect benchmark values, an updated boron benchmark was used in the revised risk 

assessment. The units in the fish study from which the previous SCV was derived (Hamilton, 1995) 

had been erroneously transcribed in Suter and Tsao (1996) as μg/L instead of mg/L. The updated 

SCV was recalculated using the corrected units. The revised value has been corroborated with the 

authors. Additionally, a continuous criteria concentration (CCC) was used for the cadmium surface 

water benchmark in the revised risk assessment, replacing the previous value. The updated values 

are presented in Appendix E of the revised risk assessment report. 
Response to Public Review Comments

7-1 

7. Comments Related to the Monte 

Carlo Analysis Approach

The comments relating to the Monte Carlo approach were grouped into five subcategories, which 

are summarized in the following bulleted list. Subcategories with no public comments are included 

for consistency with the peer review response to comments (U.S. EPA, 2014b).

 Section 7.1: Use of conservative parameter estimates 

 Section 7.2: Variability versus uncertainty 

 Section 7.3: The calculation of percentile probabilities as opposed to an overall probability 

(no public comments) 

 Section 7.4: Comments related to the numerical stability of Monte Carlo results 

 Section 7.5: Impacts on ground water as a resource (no public comments). 

7.1. Use of Conservative Parameter Estimates 

Comment Summary 

While some public commenters stated that the human health probability distributions appeared 

appropriate, others expressed concern regarding a conservative bias in input parameter probability 

distributions used and the resulting potential for overestimation of risks. These commenters noted 

that the ideal approach would be to estimate the actual risk and associated uncertainty rather than 

weighting the results conservatively. The specific public comments related to the use of 

conservative parameter estimates and associated reference information are detailed in Table 7-1. 

Table 7-1. Comments Related to the Use of Conservative Parameter Estimates 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-06313 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-09765 Trade Association Ken Ladwig EPRI 2010 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA-HQ-RCRA2006-0796-0046 Electric Utility 

Company Tim Gregori Southern Montana Electric 2007 

EPA-HQ-RCRA2006-0796-0432 Trade Association Jim Roewer USWAG 2007 
Response to Public Review Comments Monte Carlo Analysis Approach 

7-2 

EPA Response 

The revised risk assessment conducted full-scale probabilistic Monte Carlo analysis to quantify 

human and ecological risks. EPA agrees it would be ideal to produce best estimates of actual risk. 

All input data distributions (e.g., aquifer data, soil type, WMU data, climate data, distance to 

ground water wells, distance to surface water bodies, constituent concentrations, water flow data, 

human exposure factors) were developed in line with this objective. However, these distributions 

were developed from available data and are subject to the limitations of these data. In cases where 

data were not sufficient to fully characterize the input distribution, conservative values and 

assumptions were used to fill data gaps to remain protective of human health and the environment. 

Further discussion of these uncertainties has been added to Section 5 of the revised risk assessment. 

7.2. Variability versus Uncertainty

Comment Summary 

Public commenters pointed out that the risk assessment does not formally differentiate variability 

from uncertainty or show confidence limits for risk results, which makes it challenging to identify 

opportunities to reduce uncertainty. One commenter requested that EPA discuss the implications 

of the relatively wide risk distributions, including the reasons why some risk distributions are 

larger than others based on the Monte Carlo results. The specific public comments related to 

variability versus uncertainty and associated reference information are detailed in Table 7-2. 

Table 7-2. Comments Related to Variability versus Uncertainty 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-06313 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-09765 Trade Association Ken Ladwig EPRI 2010 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA Response 

EPA acknowledges it would be ideal to separate variability from uncertainty when possible in a 

probabilistic risk assessment. EPA was able to reduce a substantial number of the uncertainties in 

the revised risk assessment through the acquisition of additional data on facilities, environmental 

parameters, and constituent concentrations. Variability and uncertainty are still comingled in a 

large number of cases due to remaining data gaps; however, EPA conducted multiple sensitivity 

analyses to determine the potential for different inputs to affect risk results. Additional discussion

of the differences between parameter variability, data uncertainty, and model error, as well as 

discussions of the sensitivity and uncertainty analyses, is presented in Section 5 of the revised risk

assessment. 
Response to Public Review Comments Monte Carlo Analysis Approach 

7-3 

EPA disagrees that there are wide risk distributions. While the commenter correctly points to other 

risk assessments that had closer central tendency and high-end results, those were either sitespecific assessments or involved no fate or transport modeling. National-scale risk assessments 

will necessarily have wider variability in their results compared to risk assessments that are 

specific to a single site. Thus, the “wider” risk distributions simply reflect the fact that different

sites with different CCRs can have very disparate impacts on human health and the environment. 

7.3. Calculation of Percentile Probabilities as 

Opposed to an Overall Probability

Comment Summary 

No public comments. 

7.4. The Numerical Stability of Monte Carlo 

Results

Comment Summary 

No public comments. 

7.5. Impacts on Ground water as a Resource

Comment Summary 

No public comments. 
Response to Public Review Comments Monte Carlo Analysis Approach 

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Response to Public Review Comments

8-1 

8. Comments on Documentation 

and Miscellaneous Comments

The comments related to documentation and other miscellaneous comments were grouped into 

seven subcategories (subcategories with no public comments are included for consistency with the 

peer review response to comments): 

 Section 8.1: Insufficient documentation to reproduce the analysis independently 

 Section 8.2: Graphical input/output distributions, truncation values 

 Section 8.3: Documentation of sensitivity analysis 

 Section 8.4: Discussion of general risk-susceptibility patterns (e.g., climate-specific risk) (no 

public comments) 

 Section 8.5: Discussion of worst-case scenarios (no public comments) 

 Section 8.6: Discussion of sulfate, phosphate, and chloride (no public comments) 

 Section 8.7: Background concentrations (no public comments). 

8.1. Insufficient Documentation to Reproduce 

Analysis Independently 

Comment Summary 

Some commenters stated that the documentation is incomplete and that an independent reviewer 

could not reproduce the analysis. Another commenter performed an independent review and 

cancer risk estimate and noted that the EPA used a reasonable approach for calculating cancer 

cases in the risk assessment. The specific public comments related to insufficient documentation 

to reproduce the analysis independently and associated reference information are detailed in 

Table 8-1. 

Table 8-1. Comments Related to Insufficient Documentation to Reproduce the Analysis 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-08244 Electric Utility 

Company Basil G. Constanelos Edison Mission Energy, LLC 2010 

EPA-HQ-RCRA2006-0796-0432 Trade Association Jim Roewer USWAG 2007 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 
Response to Public Review Comments Documentation and Miscellaneous Comments 

8-2 

EPA Response 

EPA acknowledges that the documentation of the inputs and intermediate outputs could have been 

more transparent for the 2010 Draft Risk Assessment (U.S. EPA, 2010b). In the revised risk 

assessment, many of the inputs EPA used are directly discernible from the appendices. A summary 

of the data available in each appendix is presented in Section 1 of the revised risk assessment. EPA 

also acknowledges that the additions and discussions of inputs in the document were not sufficient 

for complete duplication of the results. Thus, the input and output files for the draft risk assessment 

were made available in the docket of the proposed rule via an FTP site,3

 and final input and output 

files are being placed in the docket for the final rule concurrently with this response to comments 

document. 

8.2. Graphical Presentation of Input / Output 

Distributions, Truncation Values

Comment Summary 

Commenters requested improvement on the graphical presentation of risk results. Additionally, 

commenters requested further explanation of the minimum and maximum truncating values, as 

truncated values may reduce risk estimates. The specific public comments related to graphical 

presentation of input/output distributions, truncation values and associated reference information 

are detailed in Table 8-2. 

Table 8-2. Comments Related to the Graphical Presentation of Input/Output 

Distributions, Truncation Values 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-10483 Trade Association Ken Ladwig EPRI 2010 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA Response 

While EPA did not provide a graphical presentation of the risk results, this information is more 

clearly discernible from the full input and output files. For discussion of the full inputs and outputs 

files, see the responses in Section 8.1 above. With regard to truncation, EPA no longer manually 

truncates input distributions for the human exposure factors. Instead, exposure factor distributions 

in the revised risk assessment were generated with the @Risk software (Palisade Co., Newfield, 

 

3 Available online at: ftp://ftp.epa.gov/coal-combustion-residues 
Response to Public Review Comments Documentation and Miscellaneous Comments 

8-3 

NY),4 as described in Appendix D. EPA has also added further discussion of the cohorts to revised 

risk assessment, with tables comparing each cohort’s risk presented in Section 5 of the revised risk 

assessment. 

8.3. Documentation of Sensitivity Analysis

Comment Summary 

Commenters requested more complete documentation of the sensitivity analysis. Other comments 

included a request to add human health exposure factor variables to the sensitivity analysis, and to 

conduct additional sensitivity analyses on different topics (e.g. well distance distribution). The 

specific public comments related to documentation of sensitivity analysis and associated reference 

information are detailed in Table 8-3. 

Table 8-3. Public Comments Related to Documentation of Sensitivity Analysis 

Commenter ID Commenter Type Commenter Name Commenter 

Organization Year 

EPA-HQ-RCRA2009-0640-06311 Advocacy Group Lisa Evans Earthjustice 2010 

EPA-HQ-RCRA2009-0640-09765 Trade Association Ken Ladwig EPRI 2010 

EPA-HQ-RCRA2006-0796-0441 Trade Association Ken Ladwig EPRI 2007 

EPA Response 

EPA acknowledges the omission of the original sensitivity analysis from the docket. EPA updated 

the sensitivity analysis (U.S. EPA, 2009c) so that it clearly describes the methodology that 

underlies the results summarized in Section 5 of the revised risk assessment. This sensitivity 

analysis was placed in the docket for the proposed rule. 

Human health exposure factor variables were not evaluated in the sensitivity analysis. Human 

exposure factor variables have well-established, peer-reviewed, national distributions that are 

regularly used in probabilistic risk analyses conducted by EPA based on Agency policy. Therefore, 

the contribution of variability in the exposure factors to the variability in risk was not particularly 

useful for understanding the aspects of CCR disposal practices that may drive risk. Additional 

sensitivity analyses such as leachate duration versus leachable content and liner performance by 

thickness were conducted in the revised risk assessment and are summarized in Section 5. 

Additional Comments: 

The comments provided on the topics discussed above also touched on other topics, which are 

addressed in greater detail elsewhere in this document. Thus, EPA does not provide a response to 

 

4 Available online at: www.palisade.com/risk/ 
Response to Public Review Comments Documentation and Miscellaneous Comments 

8-4 

these additional topics here. Comments relating to the conservative inputs to the fate and transport 

models are discussed in Section 7.1 of this document. 

8.4. Discussion of General Risk-Susceptibility 

Patterns such as Climate-Specific Risk

Comment Summary 

No public comments. 

8.5. Discussion of Worst-Case Scenarios

Comment Summary 

No public comments. 

8.6. Discussion of Sulfate, Phosphate, and Chloride

Comment Summary 

No public comments. 

8.7. Background Concentrations

Comment Summary 

No public comments. 
Response to Public Review Comments

9-1 

9. References 

ATSDR (Agency for Toxic Substances and Disease Registry). 2008. Minimal Risk Levels (MRLs) 

for Hazardous Substances. Available at www.atsdr.cdc.gov/mrls.html. 

Baes, C.F., R.D. Sharp, A.L. Sjoreen, and R.W. Shor. 1984. A Review and Analysis of Parameters 

for Assessing Transport of Environmentally Released Radionuclides Through Agriculture. 

ORNL-5786. Prepared for U.S. Department of Energy. Oak Ridge National Laboratory, Oak 

Ridge, TN. September. 

Barrows ME, Petrocelli SR, Macek KJ, Carroll JJ. 1980. Bioconcentration and elimination of 

selected water pollutants by bluegill sunfish (Lepomis macrochirus). In: Haque R, ed. 

Dynamics, exposure and hazard assessment of toxic chemicals. Ann Arbor, Michigan, 

U.S.A.: American Chemical Society. p. 379-392. 

Bhaduri, B., Bright, E., Coleman, P., Urban, M. 2007. LandScan USA: A high resolution 

geospatial and temporal modeling approach for population distribution and 

dynamics. GeoJournal 69:103–117. 

Dzombak, D.A and Morel, F.M.M. 1990. Surface Complexation Modeling: Hydrous Ferric Oxide. 

Wiley-Interscience, New York, 393 pp.Eisler, 1989. 

Eisler, R. 1989. Molybdenum Hazards to Fish, Wildlife, and Invertebrates: A Synoptic Review. 

Contaminant Hazard Reviews, Report No. 19, Biological Report 85(1.19). Laurel, MD. 

August. 

Hamilton, S.J. 1995. Hazard assessment of inorganics to three endangered fish in the Green River, 

Utah. Ecotoxicol Environ Saf 30:134-142. 

Kosson, D.S., H.A. van der Sloot, F. Sanchez and A.C. Garrabrants. 2002. An integrated 

framework for evaluating leaching in waste management and utilization of secondary 

materials. Environmental Engineering Science 19(3):159–204. 

Kumada, H., et al. 1973. Acute and chronic toxicity, uptake and retention of cadmium in freshwater 

organisms. Bull. Freshwater Fish. Res. Lab. 22: 157. 

Lemly AD. 1985. Toxicology of selenium in a freshwater reservoir: implications for 

environmental hazard evaluation and safety. Ecotoxicology and Environmental Safety. 

10(3): 314-338. 

Mathur, Samir S. 1995. Development of a Database for Ion Sorption on Goethite using 

Surface Complexation Modeling. M.S. Thesis, Department of Civil and Environmental

Engineering, 1995. 
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Meeussen, J.C.L. 2003. ORCHESTRA: An Object-Oriented Framework for Implementing 

Chemical Equilibrium Models. Environmental Science & Technology 37 (6) 1175-1182. 

Available online at: www.meeussen.nl/orchestra/ 

Murphy, B.R., G.J. Atchison, and A.W. McIntosh. 1978. Cadmium and zinc in muscle of bluegill 

(Lepomis macrochirus) and largemouth bass (Micropterus salmoides) from an industrially 

contaminated lake. Environmental Pollution 17:253–257. 

Stephan, C.E. 1993. Derivation of Proposed Human Health and Wildlife Bioaccumulation Factors 

for the Great Lakes Initiative. Draft. Environmental Research Laboratory, Office of 

Research and Development, U.S. Environmental Protection Agency, Duluth, MN. March. 

Suter, G.W. II, and C.L. Tsao. 1996. Toxicological Benchmarks for Screening of Potential 

Contaminants of Concern for Effects on Aquatic Biota on Oak Ridge Reservation: 1996 

Revision. Oak Ridge National Laboratory, Oak Ridge, TN. 104 pp. ES/ER/TM-96/R2. 

Thornloe, S.; Kosson, D.; Sanchez, F.; Garrabrants, A.; Helms, G. 2010. Evaluating the Fate of 

Metals in Air Pollution Control Residues from Coal-Fired Power Plants, Environ. Sci. 

Technol. 2010, 44, 7351-7356. 

U.S. EPA (Environmental Protection Agency). 1985. Compilation of Air Pollutant Emission 

Factors. Volume I: Stationary Point and Area Sources (Fourth Edition). AP-42. U.S. 

Environmental Protection Agency, Office of Air and Radiation and Office of Air Quality 

Planning and Standards, Research Triangle Park, NC. September. 

U.S. EPA (Environmental Protection Agency). 1997a. Exposure Factors Handbook, Volume I, 

General Factors. EPA/600/P-95/002Fa. Office of Research and Development, Washington, 

DC. August. 

U.S. EPA (Environmental Protection Agency). 1997b. Exposure Factors Handbook, Volume II, 

Food Ingestion Factors. EPA/600/P-95/002Fa. Office of Research and Development, 

Washington, DC. August. 

U.S. EPA (Environmental Protection Agency). 1997c. Exposure Factors Handbook, Volume III, 

Activity Factors. EPA/600/P-95/002Fa. Office of Research and Development, 

Washington, DC. August. 

U.S. EPA (Environmental Protection Agency). 1997d. Mercury Study Report to Congress. Volume 

III - Fate and Transport of Mercury in the Environment. EPA 452/R-97/005. Office of Air 

Quality Planning and Standards and Office of Research and Development, Washington, 

DC. 

U.S. EPA (Environmental Protection Agency). 1999a. Understanding Variation in Partition 

Coefficient, Kd, Values Volume I: The Kd Model, Methods of Measurement, and 

Application of Chemical Reaction Codes. EPA 402-R-99-004A. OAR. Washington, DC. 

August. Available online at: www.epa.gov/rpdweb00/cleanup/402-r-99-004.html. 
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U.S. EPA (Environmental Protection Agency). 1999b. Report to Congress: Wastes from the 

Combustion of Fossil Fuels: Volume 2 – Methods, Findings, and Recommendations (EPA 

530-R-99-010). Office of Solid Waste and Emergency Response. Washington, DC. 

U.S. EPA (Environmental Protection Agency). 2000. Supplementary Guidance for Conducting 

Health Risk Assessment of Chemical Mixtures. Risk Assessment Forum, Washington, DC. 

August. 

U.S. EPA (Environmental Protection Agency). 2002. Industrial Waste Management Evaluation 

Model (IWEM) Technical Background Document. EPA530-R-02-012. Office of Solid 

Waste, Washington, DC. August. 

U.S. EPA (Environmental Protection Agency). 2003a. EPA’s Composite Model for Leachate 

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EPA530-R-15-003