# 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-AE81Submitted 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-09-004Response 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 Measure d 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 Assumption s ......................................... 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 Conce ntrations ......................... 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 Multi ple 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 Toxicit y ................................................. . 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 ........

................................................... . 6-3Response to Public Review Comments Table of Contents

ii 7. Comments Related to the Monte Carlo Analysis Approa ch ............................................... 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 Comment s ........................................... 8-1 8.1. Insufficient Documentation to Reproduce Analysis In dependently .......................... 8-1 8.2. Graphical Presentation of Input / Output Distributi ons, 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 Tra nsport Modeling Approach .................. 2-3 Table 2-3. Comments Related to Site-Specific Analys is and Comparisons with

Measured Data .....................................

................................................... .................. 2-9 Table 2-4. Comments Related to Receptor Wells and S urface 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 D ata and Liner Scenarios ...................... 3-5
Table 3-3. Public Comments Related to Alternative W aste/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 Was te Compaction...................................... 3-11 Table 3-7. Public Comments Related to HELP Infiltra tion Rates/Cover Assumptions ............ 3-12
Table 3-8. Public Comments Related to Water Table A bove 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 Wat er Data for Impoundment Source

Concentrations. ...................................

................................................... ................. 3-15 Table 3-11. Comments Related to Modeling Surface Im poundments Only Pre-Closure .......... 3-19Response 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 Pathw ays During Screening Analysis ............. 4-6 Table 4-4. Comments Related to Exposure to Addition al Constituents ................................... ... 4-7

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

and Multiple Pathway Exposures ....................

................................................... ...... 5-2 Table 5-2. Public Comments Related to Toxicity Valu es................................................. ........... 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 Fact or Assumptions .................................... . 5-9 Table 5-6. Public Comments Related to Child/Infant Exposure Assumptions .......................... 5-1 0 Table 5-7. Public Comments Related to Bioconcentrat ion Factors ....................................... .... 5-11

Table 6-1. Comments Related to Cumulative Ecologica l Risk ............................................ ....... 6-1
Table 6-2. Comments Related to Sensitive Habitats/S ensitive Species .................................. .... 6-2 Table 6-3. Comments Related to Ecological Benchmark s, Ecological Toxicity ......................... 6- 3

Table 7-1. Comments Related to the Use of Conservat ive Parameter Estimates ........................ 7- 1 Table 7-2. Comments Related to Variability versus U ncertainty ........................................ ........ 7-2

Table 8-1. Comments Related to Insufficient Documen tation to Reproduce the Analysis ......... 8-1 Table 8-2. Comments Related to the Graphical Presen tation of Input/Output

Distributions, Truncation Values ..................

................................................... ........ 8-2 Table 8-3. Public Comments Related to Documentation of Sensitivity Analysis ....................... 8- 3Response to Public Review Comments Table of Contents

iv [This page intentionally left blank.]Response to Public Review Comments

1-1 

# 1. Introduction and Background

To ensure protection of human health and the enviro nment, the U.S. Environmental Protection Agency (EPA) has completed a risk assessment to evaluate p otential 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 N otices 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 impo undments:

- A joint U.S. Department of Energy (DOE) and EPA rep ort entitled Coal Combustion Waste Management at Landfills and Surface Impoundments, 1 994-2004;

- A draft risk assessment conducted by EPA on the man agement of CCRs in landfills and surface impoundments; and

- EPA's damage case assessment.

 June 2010 – The proposed CCR rule was issued for pu blic 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 o f state programs, and beneficial use.

 August 2013 – Additional data supplementing the Reg ulatory Impact Analysis and risk assessment were published, as well as information on large sca le 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 Consti tution Avenue, NW, Washington, D.C. The draft risk assessment (U.S. EPA, 2010) was inde pendently 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 an d Ecological Risk Assessment for Coal Combustion Residuals (U.S. EPA, 2014b) was prepared by the EPA. For consistency, all comment categories from the peer r eview are included in this document. For each comment category, EPA prepared a table that summari zes the docket ID, commenter name and affiliation

1 The Proposed Rule and all NODAs from 2010 to presen t are available online at: www.epa.gov/solidwaste/nonhaz/industrial/special/fo ssil/ccr-rule/index.htm

.Response to Public Review Comments Introduction and Background

1-2 (e.g. advocacy group), and year. Following this tab le, 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 categor y, the relevant section will simply state “no publi c comments.” Four additional comment categories beyon d those in the peer review appeared in the public comments, and have been added to the end of the rel evant sections (e.g., Section 3.4: Receptor Wells a nd Surface Water Interception, Section 4.12: Modelling Landfills Only After Closure; Section 6.8: Bioconcentration Factors). Additionally, some comme nt category names have been expanded to account for a broader range of public comments (e.g. Sectio n 4.2 was modified from “2006 DOE Facility Data...” to “Facility Data...”). EPA received numerous comments discussing the follo wing non-technical or non-risk-related categories: beneficial reuse, regulatory comments including Sub title C versus D listing, legal comments, monitorin g requirements, the Regulatory Impact Analysis, cost considerations and population risk, direct discharg e and associated permitting, structural integrity, en vironmental remediation, sand and gravel pits, coal mining, and the receipt of site-specific data. Beca use these comments are not germane to the risk assessment, no responses are provided in this docum ent. In addition, EPA received numerous, general comments on both the draft risk assessment and subs equent NODAs. These comments tended to express general support or disapproval for the risk assessm ent methodology, data, or results. However, these comments did not provide any specific technical rec ommendations or data that could be used to improve the risk assessment. EPA appreciates the overwhelmi ng interest of the public regarding the Agency’s ri sk assessment. However, without any substantive critiq ue that could be acted upon, EPA could not alter th e risk assessment in response to these more general c omments. To the extent that any commenter mentioned substantive issues regarding a specific aspect of t he risk assessment, these comments are further addr essed 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 subca tegory comment in the totals.Response to Public Review Comments Introduction and Background

1-3 Table 1-1. Summary of Public Comments by Major Cate gory

**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 Cate gory

**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 Cate gory

**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 Cate gory

**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 Cate gory

**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 Cate gory

**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 Cate gory

**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 Cate gory

**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 Cate gory

**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 5Response to Public Review Comments Introduction and Background

1-12 [This page intentionally left blank.]Response to Public Review Comments

2-1 

# 2. Fate and Transport Modeling

The comments relating to exposure scenarios were gr ouped 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 measu red 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 us ing a risk assessment model that assumes current conditions will be maintained for 10,000 ye ars. Specifically, commenters were concerned about the assumption that constituent concentration s 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. T he specific comments related to the 10,000- year ground water modeling time and associated refe rence 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 Transpo rt Modeling

2-2 EPA ran the model until either the observed ground water concentration of a constituent at the receptor point reached a peak an d 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 be yond the observed peak or maximum average concentrations, these post-peak or post-max imum 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 Appendi x 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. Pea k arrival times are longer for landfills, and more than 10,000 years for composite-lined landfill s. Under such timeframes, EPA acknowledges that surface conditions may change significantly, c ompounding the uncertainty associated with the predicted exposures and risks. However, EPA also no tes that the time to first exceedance of selected risk criteria is typically considerably le ss than the time to the greatest exceedance. EPA acknowledges that future ground water use patte rns may shift as the number and location of receptors changes, and that it is unknown whether f uture 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 t o 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 approac h 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 wat er transport modeling were received from commenters. Issues covered in their comments includ ed the following: Geochemical Modeling:

 The way that soil and aquifer K d values were determined and used, including the fac t that the risk assessment did not explicitly model oxidation/reduction reactions and precipitationdissolution processes that may influence the chemic al fate and transport.

 Whether hydrogeologic settings were assigned correc tly.

Selection of Sorbents:

 The selection of iron oxides, and dissolved (DOM) a nd particulate organic matter (POM) to represent all sorbents in soil and aquifer material s.

 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 Transpo rt Modeling

2-3  The treatment of POM and DOM in the MINTEQA2 modeli ng used to generate the K d values (sorption isotherms) used in the analysis.

 The adequacy of sensitivity and uncertainty analyse s for the MINTEQA2 modeling.

K d Values:

 The approach used to determine the value of pH in t he aquifer for selecting K d
.

 The subsequent calculation of the retardation facto r. Arsenic Speciation:

 The assumption that arsenic III is the only or domi nant 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 fo r arsenic species and other constituents, as well as distance versus concentration output fro m EPACMTP.
EPACMTP Assumptions and Simplifications:

 The appropriateness of EPACMTP and its various assu mptions and simplifications for ground water modeling, including:

- Not altering the chemistry of the aquifer receiving leachate.

- Not simulating variable oxidation-reduction potenti al conditions or multiple chemical species during a model run.

- Not evaluating the potential mobilization of non-wa ste related metals from soils when exposed to leachate with potentially different geoc hemistry compared to ambient conditions.

- Not considering the potential occupation of adsorpt ion sites by naturally occurring metals or competition from multiple contaminants.

- Not considering mounding-induced reduction of the u nsaturated zone thickness or other cases where the ground water table is in direct con tact with the bottom of the WMU.

- Not considering fractured rock, karst, and other co mplex hydrogeologic settings. The comments also addressed the general need for mo re 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 d etailed in Table 2-2

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

Commenter ID Commenter Type Commenter Name Commenter Organization Year

EPA-HQ-RCRA2012-0028-0105 Electric Utility Company Chet Thompson CME Engineering LP 2013Response to Public Review Comments Fate and Transpo rt Modeling

2-4 Table 2-2. Comments Related to the Ground Water Tra nsport 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 m odeling would be more realistic than using linear and nonlinear part itioning coefficients. EPA considered the use of the Objects Representing Chemical Speciation and Tr ansport (ORCHESTRA) model during revisions to the risk assessment because it can acc ount for geochemical interactions, such as aqueous complexation, precipitation, surface comple xation, 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 mode l 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 n ecessary 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 K d as a surrogate for dilution/sorption/ precipitation processes is a widely used and accept ed method in both the scientific literature and the ground water modeling community, provided the v alues of K d used are appropriate to accountResponse to Public Review Comments Fate and Transpo rt Modeling

2-5 for the range of potential attenuation processes (U .S. EPA, 1999a). Therefore, for a nationwide analysis, the use of K d is a practical and necessary simplification. EPA h as added discussion to the risk assessment to clarify K d -related issues raised by the commenters. Appendix H of the revised risk assessment displays select percentiles of the K d values used in the analysis. These values were derived from the isotherm sampling performed by EPA CMTP and used in the modeling (including effective K d values for the unsaturated zone). A listing of all individual K d 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 doc ket. 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 co nsidered 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 constitue nts for which speciation is known to have a significant impact on mobility. For these constitue nts, a model run was conducted for each species under the assumption that all of the constituent ma ss was present as that speciation. Therefore, EPA did not evaluate redox, and acknowledges this i s a source of uncertainty for the ground water transport modeling approach. Commenters expressed c oncern about the assumption of a single speciation, noting that it is likely that constitue nts will be present as some combination of the different species. EPA acknowledges that this appro ach is a simplification of real world conditions; however, the Agency believes this approach is usefu l because it provide bounding estimates that can inform the risk assessment. Regarding the concern that there were possible erro rs in hydrogeological assignments, these assignments have been updated in the revised risk a ssessment based on a more robust and accurate dataset for waste management unit (WMU) and facilit y locations. These data are discussed in Section 3 and Appendix B of the revised risk assess ment. Because these assignments were based on more complete GIS coverages of soils and aquifer s 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 domin ant potential sorbents in the environment, including two common iron oxide minerals: hydrous f errous oxides (HFO) and goethite (Dzombak and Morel, 1990; Mathur, 1995). Because of the avai lability of these data and their prevalence in the environment, these are the sorbent types availa ble for MINTEQ2 modeling used to develop constituent sorption isotherms. Other common hydrou s 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 u se. 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. Whi le both goethite and HFO are common forms of iron oxide in soils, goethite is a much poorer a dsorbent than HFO, thereby leading to relatively greater ground water plume concentrations. EPA ackn owledges that HFOs are common as wellResponse to Public Review Comments Fate and Transpo rt Modeling

2-6 and there is the potential for HFOs with greater so rption affinities than goethite to be present at some CCR disposal sites. In reaching this conclusio n, 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 a ssumption. EPA also recognizes that limiting MINTEQA2 to two t ypes of sorptive materials (iron oxide and organic matter [DOM and POM]) is a simplification g iven the wide range or soil and aquifer materials that actually adsorb metals (e.g., clay a nd other soil minerals). However, given that the extensive sorption databases needed to perform MINT EQA2 are available for POM, DOM, and goethite, we believe that they are the best represe ntation 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 ba ckground documents and the associated Response to Peer Review Comments for those document s. Finally, with respect to the adequacy of sensitivit y and uncertainty analyses for MINTEQA2, EPA notes that the 2009 sensitivity analysis showed tha t only results for strongly sorbing constituents were sensitive to the Kd values output from MINTEQA 2. 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 penta valent 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 sensit ivity and uncertainty analyses were conducted.

K d Values: The approach adopted in the risk assessment to dete rmine the value of pH in the aquifer (used to select K d ) and the subsequent calculation of the retardation factor assumed that, after entering the aquifer, the leachate plume would thor oughly 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 transpor t 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., K d goes up) with higher pH, which is characteristic o f much CCR leachate (i.e., assuming full mixing lower s 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 K d values to available estimates in the published literature, but did not do so for three reasons. Fi rst, there are many individual values within each K d isotherm that depend both on constituent concentra tions and MINTEQA2 master variables, such as pH, organic carbon, and iron oxide concentr ations. 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 difficul t to determine exactly how well the collected value sResponse to Public Review Comments Fate and Transpo rt Modeling

2-7 represent conditions across the country. Third, fie ld and laboratory methods for measuring K d vary greatly and are not easy to compare, adding a signi ficant measurement uncertainty to the variability issues mentioned above. Therefore, not only would t his comparison be complicated to perform, it would also be subject to its own numerous uncertain ties 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 va lues to model sorption in the subsurface environment. Arsenic Speciation: Commenters also pointed out that literature on arse nic V often shows that it is orders of magnitude less soluble than arsenic II I, which appears inconsistent with the results of the 2010 Draft Risk Assessment. The draft assessmen t 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 I II 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 rec eptors 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 K d 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 th e commenter to review the input and output files available in the docket.

EPA did not model the time to first exceedance of r isk criteria, but did conduct a sensitivity analysis for the time to peak ground water concentr ation. The time to peak results for arsenic species and other select other constituents are pre sented in Section 5 of the revised risk assessment. The distance to nearest well receptors is also disc ussed in Section 5 of the revised risk assessment. The relation of distance versus concentration was n ot 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 tra nsparency about the model’s underlying assumptions and input data sources. The documentati on for the 2010 Draft Risk Assessment did not include comprehensive tables detailing model in put 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 Backg round 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 re ferences to these documents, and directs readers to refer to these documents for further inf ormation. Additionally, the full input and output files are available to the public in the docket. With respect to the fundamental questions raised ab out the assumptions and simplifications built into EPACMTP, EPA acknowledges some limitations wit hin the model. Some simplifications areResponse to Public Review Comments Fate and Transpo rt 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 r eviewed 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 l eachate by changing the aquifer pH in response to full mixing. Alternatively, EPA conduct s 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 do es not model oxidation-reduction potential, EPA notes that this would require geoche mical modeling, which was not feasible for the reasons discussed above;

• Full mixing of the leachate plume did not demonstra te significant potential to affect aquifer pH. Thus, since pH is one of the most significant f actors affecting constituent mobilization EPA does not believe significant constituent from t he underlying soils will be mobilized in most cases. Instead, it is a site-specific consider ation 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 as sessment. EPA did not consider ground water mounding, ground water in contact with the waste management unit, fractured rock, karst, and other complex hydr ogeologic 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 an alysis are discussed in Section 8.1 of this document. Comments regarding the need for validatio n and/or comparison of model inputs and results to site-specific field data are discussed i n 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 thatResponse to Public Review Comments Fate and Transpo rt Modeling

2-9 validation or calibration of EPACMTP results with a ctual data is needed, including the potential use of damage cases. The specific public comments r elated to the site-specific analysis and comparisons with measured data, and associated refe rence information are detailed in Table 2-3

. Table 2-3. Comments Related to Site-Specific Analys is 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 2 010

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 Citize n 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 th e EPACMTP model with actual field data and some commenters suggested that EPA should use a ctual monitoring data rather than modeling to assess potential risks. EPA recognizes the impor tance 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 whe n model predictions can be compared favorably with measured field results. However, site-specific modeling involves extensive data collection and detailed modeling (representing site-specific c onditions and processes), which was notResponse to Public Review Comments Fate and Transpo rt Modeling

2-10 possible for this large, national-scale risk assess ment. 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 Unite d 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 compar ison is presented in Section 5 of the revised risk assessment. EPA also provided extensive EPACMTP val idation 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 contaminat ed, the realistic risk of exposure, well placement within the plume, distance to receptor we lls, identification of surface water receptors, surface water interception modeling, the appropriat eness 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 th e interception of ground water by surface water bodies, which has been added to the revised r isk assessment. However, some commenters indicated that a meaningful allocation of the groun d water plume between a surface water body and a downgradient well receptor can only be determ ined reliably with assessment of the system at a local scale. Commenters also raised questions regarding the spec ific surface water interception methodology, including the base data and algorithms used to calc ulate stream base flow, net ground water flow, and the contaminant mass loss to ground water. Conc ern was expressed about the large range of possible values used for Monte Carlo sampling witho ut calibrating models to site specific conditions and the potential to mismatch parameters . Additionally, concerns were raised that the assessment assumed transport directly to the neares t water body without reflecting complexities that are often present and could lead to longer tra nsport 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 recepto rs associated with these WMUs. Comments were also received that the one mile distance consi dered by the transport model is not sufficient, because actual receptor wells in many cases are fur ther than one mile from facilities. Comments also highlighted the possibility that modeled recep tor well concentrations may incorrectly represent actual exposures by sampling from a singl e aquifer depth. Comments on dispersivity noted the need for greater transparency in the repo rt.Response to Public Review Comments Fate and Transpo rt Modeling

2-11 Placement of Receptor Wells, EPACMTP Well Inputs an d Assumptions: Additional comments related to the risk assessment’s use of wa ter 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 interva l in an aquifer; and the values used for plume dispersivity. The specific comments related to rece ptor well and surface water interception related issues

, and associated reference information are detailed i n Table 2-4

. Table 2-4. Comments Related to Receptor Wells and S urface 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 2011Response to Public Review Comments Fate and Transpo rt Modeling

2-12 Table 2-4. Comments Related to Receptor Wells and S urface 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 downgradi ent from a surface water body that intersects the groun d water table, some or all of the ground water, along with the mass of constituents contained there in, is intercepted by the water body before it can reach the well. This interception was not model ed in the 2010 Draft Risk Assessment. However, a review of the input database for the 201 0 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 Transpo rt Modeling

2-13 ignoring the loss of constituent mass had the effec t of overestimating exposures. Thus, in the revised risk assessment an EPACMTP model post-proce ssor was created to account for surface water interception by removing constituent mass flo wing 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 intercep tion is discussed in further detail in Section 4 and Appendix J of the revised risk assessment. While commenters were generally supportive of the p roposed approach, some indicated that a meaningful allocation of constituent mass from grou nd 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 complexit ies that are often present and could lead to longer transport pathways or to pathways to water b odies 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 descri be these conditions accurately. While EPA agrees that local-scale conditions must be consider ed for precise estimation for specific systems, it was impractical for EPA to characterize, simulat e, and calibrate models for the numerous locations across the nation. Discussion of the unce rtainties associated with this approach has been added to Section 5 of the revised risk assessment. Several questions about the surface water intercept ion methodology were raised by the public. The qBaseflow input parameter was derived from the NHDp lus 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 app roach assumes that all streams intersect the shallow aquifer and that all streams either gain wa ter from the aquifer or do not interact with the aquifer at all (for simplicity and conservatism). A s the commenter indicates, qNetflow is a key result calculated by subtracting the stream baseflo w from the average ground water flow upgradient of the stream. The qNetflow value become s the adjusted ground water flow beyond the stream, reflecting ground water losses to the strea m. One commenter raised a specific question about how the methodology handles cases where qNetf low 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 th e 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 sid e of the stream.

Model Validation/Calibration: Concern was expressed about the large range of poss ible values used in the probabilistic analysis for certain para meters and the potential for this to result in a mismatch of input parameters without proper site-sp ecific calibration. EPA notes that the revised risk assessment is not intended to capture the exac t risks at each disposal site. Instead, the revised assessment combines the best resolution of site-bas ed, regional and national data available to provide an estimate of potential risks that may occ ur 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 ref lect the range of potential conditions near each WMU, weighted by prevalence, across the conterminou s United States.Response to Public Review Comments Fate and Transpo rt Modeling

2-14 Placement of Receptor Wells, EPACMTP Well Inputs an d Assumptions: Comments regarding placement of receptor wells in the probab ilistic analysis (also known as the appropriateness of receiving water reaches) are the result of a fundamental misinterpretation regarding the constraints placed on ground water re ceptor location to be, as described in the 2010 Draft Risk Assessment, “within the contaminant plum e.” This constraint is more fully explained in Section 4.4.3.6 of the EPACMTP technical backgro und document (U.S. EPA, 2003a,b). A citation referring readers to that document has bee n placed in Section 4 of the revised risk assessment. Because the comment resulted from a mis understanding, 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 expos ures. EPA acknowledges that there may be a large percentage of the population that does not re ly on ground water as a source of potable water; however, the aim of the risk assessment is to estim ate the magnitude of potential risk to the exposed population. Thus, this does not represent a signifi cant source of uncertainty in the risk assessment.

Comments were also received that the one-mile dista nce considered by the transport model is not sufficient, because actual receptor wells in many c ases are further distant than one mile from facilities. EPA conducted a sensitivity analysis, d iscussed in Section 5 of the revised risk assessment, which indicates that risks beyond the o ne-mile distance are appreciably lower than risks within one mile. Given that the highly expose d population was adequately captured by a onemile radius, the significant additional effort requ ired to extend the analysis further downgradient was unjustified. With respect to comments related to the placement o f 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 practic e, 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 repres ent 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 sin gle depth. A discussion of the uncertainties associated with this approach has been added to Sec tion 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 as sessment. Instead, EPA used synthetic population representations of U.S. Census data to p lace each household and its occupants at discrete points across the landscape surrounding CC R WMUs. Synthetic populations are realistic representations of households and individual reside nts and their attributes in a given census area, and are based on methods that identify realistic lo cations within each block by using LandScan 90-meter night-time population distributions to pla ce each household across the landscapeResponse to Public Review Comments Fate and Transpo rt Modeling

2-15 (Bhaduri, 2007). From these households, a distribut ion 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-spe cific estimates of actual populations around facilities rather than relying on synthetic populat ions to determine potential receptor locations. The synthetic approach provides the maximum spatial res olution possible for publically available population data from the U.S. Census. More site-spe cific estimates would be costly, but not necessarily more accurate.

Some commenters were also concerned that the assess ment 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. Howev er, this pathway was evaluated in Environmental Assessment for the Proposed Effluent Limitation Guidelines and Standards for the Steam Electric Power Generating Point Source Catego ry (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 grou ped into twelve subcategories, which are summarized in the following bulleted list.

 Section 3.1 : The use of leachate concentrations based on toxic ity 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 scen arios

 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 an d leaching

 Section 3.7 : Hydrologic Evaluation of Landfill Performance (HE LP) model infiltration rates, liner and landfill cover assumptions

 Section 3.8 : Scenarios where the water table is above the disp osal unit

 Section 3.9 : The impact of increased mercury capture under fut ure air emission control regulations

 Section 3.10 : The use of pore water data for surface impoundmen t 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 subca tegory 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 shou ld 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 validati ng LEAF leachate concentrations against field data if available; and (4) the reliability of the L EAF data is questionable as a result of inconsistencies identified in the LeachXS LiteTM dat abase. The specific public comments related to use of TCLP data and the availability of the Van derbilt 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 2 010

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 2010Response to Public Review Comments Source Modeling

3-3 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 Associatio n 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 2013Response to Public Review Comments Source Modeling

3-4 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 use d to characterize surface impoundments. Therefore, the comments received on the use of labo ratory leachate data are not relevant for the surface impoundment scenario. For landfills, EPA ag rees that TCLP, SPLP and other single pH test methods may not be the most appropriate leacha te extraction methods for all waste streams and all disposal scenarios. The 2010 Draft Risk Ass essment relied on a hierarchy of dissolved concentration data to characterize leaching from la ndfills, 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 SR0 2);

 SW-846 Method 1314; and

 SW-846 Method 1316 (and its predecessor, Method SR0 3). 2 With the availability of the LEAF data, EPA no long er 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 LEA F data in the probabilistic analysis. The LEAF data provide information on the leaching behavior o f 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 la ndfill 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

3-5 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 sa mple may be exposed to is wider than the pH estimated based on one sample alone. EPA agrees that appropriate use of the data is need ed to ensure that data represent likely conditions of leaching occurring at range of facilities nation wide 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. T he report includes the use of geochemical speciation modeling as needed to reflect site-speci fic factors affecting leaching, and shows that LEAF methods provide realistic predictions of envir onmental 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. Addi tionally, the inter-laboratory validation for these methods are described in U.S. EPA (2012a,b) w hile Kosson et al. (2002) provides the detailed test methodology for the predecessor metho ds, 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 reflec t 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 ou tcomes 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 lay er underlying composite liners is too thick, and two feet would be more representative of current pr actice. Commenters also described existing management controls required in some geographical l ocations 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 t hese 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 D ata 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 2013Response to Public Review Comments Source Modeling

3-6 Table 3-2. Comments Related to Facility Data, WMU D ata 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 eva luate risks for the universe of currently operating facilities and WMUs, EPA generally agrees with the commenter that the 1995 EPRI andResponse to Public Review Comments Source Modeling

3-7 2006 DOE survey data relied on in the 2010 Draft Ri sk Assessment may be outdated. Thus, EPA collected data from several new sources of informat ion on the facilities, WMUs, and liners that are present at the time of this analysis. Further d iscussion of these data sources is available in Section 2 and Appendix A of the revised risk assess ment. Regarding the inclusion of mismanagement scenarios, EPA reviewed the high-end pore water concentrations and determined that these data repre sent actual CCR samples and therefore represent possible high-end risks from current mana gement practices. To better understand which practices may lead to the highest risks, EPA conduc ted sensitivity analyses that consider the influence of liner type, liner design, waste type a nd 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 co ntrols required in some geographical locations that mitigate potential risks (e.g., line rs, leachate collection) and requested that EPA reflect the existence of those controls in the fina l 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 info rmation indicated such). A key objective of the analysis was to compare the effectiveness of ma nagement options (e.g., liners; surface impoundments versus landfills) at preventing potent ial releases and exposures. Because the population of WMUs considered in the analysis inclu ded a range of management controls, the analysis does provide such comparative results betw een 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 ap plied 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 ev aluate each CCR waste independently. A public commenter expressed concern about whether th e risk assessment adequately considered alternative CCR disposal scenarios. Specifically, i t 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 meta ls. The specific public comments related to alternative waste/codisposal scenarios and associat ed reference information are detailed in Table 3-3

. Table 3-3. Public Comments Related to Alternative W aste/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 2011Response to Public Review Comments Source Modeling

3-8 Table 3-3. Public Comments Related to Alternative W aste/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 Associatio n 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 combi ned ash waste types for the majority of surface impoundments and all landfills. Although co mmenters 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, EP A believes this approach appropriately reflects current disposal practices. With regard to the evaluation of CCRs codisposed wi th 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 Se ction 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 K d 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, dispo sal of ash with coal refuse is reflected is the acidic tail of the distribution. For the national p robabilistic 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 dispos al 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 revis ed 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 r ates from industrial landfills that use a different construction design than projected for CCR landfill s. The specific comments related to liner leakage and associated reference information are de tailed 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 ris k assessment correspond to leakage rates developed for the peer-reviewed Industrial Waste Ma nagement 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 specif ic 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 differen tiating between flow from unimpacted water released by the consolidation of clay and from cont aminated leakage through the liner, EPA excluded data on the subset of composite liners con structed 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 th e revised risk assessment. 

# 3.5. Treatment of Non-detect Values Comment Summary Concerning the treatment of non-detect values in th e risk assessment, one commenter recognized that the use of one half the detection limit in cal culations has become an accepted protocol. However, it was suggested that this approach may no t be appropriate in all cases, and that newer or more straightforward methods can be applied to i mprove precision and minimize biasing of the dataset. Another commenter noted that mercury was e xcluded 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 i n Table 3-5

.Response to Public Review Comments Source Modeling

3-10 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 det ection 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-detec t data for some constituents. EPA continues to incorporate all available with the use half the rep orted detection limit as the most appropriate method to account for these non-detects. The commen ter 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 sign ificantly 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 Secti on 5. 

# 3.6. Effect of Waste Compaction Comment Summary Comments received related to the effect of waste co mpaction in landfills focused on changes to hydrologic properties of waste materials, such as p orosity and hydraulic conductivity. These changes may result from compaction, consolidation, hydration or geochemical changes, and have the potential to result in either an underestimatio n 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

3-11 Table 3-6. Public Comments Related to Effect of Was te 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 doe s not consider the compaction of CCR waste that may occur over time as a result of anthropogen ic activities, gravity or infiltrating water. However, no data on either the rate or degree to wh ich these processes may occur were provided by commenters or identified elsewhere. EPA consider ed 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 t hickness assumptions (three feet) were too conservative and not conservative enough, respectiv ely. Commenters also questioned why composite covers and leachate collection systems we re not considered for clay-lined landfills. Additionally, commenters stated that there was a hi gh 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 lin ers in all cases which may not be the case, thereby weakening the regulation. The specific publ ic comments related to HELP infiltration rates/cover assumptions and associated reference in formation are detailed in Table 3-7

.Response to Public Review Comments Source Modeling

3-12 Table 3-7. Public Comments Related to HELP Infiltration R ates/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 use ful life will remain intact for the duration of the risk assessment, up to a maximum 10,000 years of mo deling. 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. Addition ally, commenters stated that there was a high degree of variability in the material and design an d 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 ackn owledges that there are limitations in using HELP. However, the model has been tested and verifi ed 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 t hat unlined and clay-lined infiltration rates calculated by HELP may be underestimated, however t he degree of that underestimate is unknown. Discussion of this uncertainty has been added to Se ction 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 th ese WMUs. Furthermore, the commenter emphasized that the use of the unsaturated zone flo w 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 commentsResponse to Public Review Comments Source Modeling

3-13 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 t he 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 ha ndle 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 geo metry and the selected depth to the water table create a scenario where the bottom of the unit is i n contact with the water table, then the entire soi l column is considered saturated. Otherwise, even for very high infiltration rates, regions beneath impoundments will remain partially saturated when t here is sufficient distance between the unit and the water table EPA has added a discussion of t he uncertainties associated with WMU source terms and EPACMTP in Section 5 of the revised risk assessment.

EPA believes the commenter misunderstood how the se diments were modeled for surface impoundments. The EPACMTP unsaturated zone module a ssumes that the 0.2 m of consolidated sediments at the bottom of a surface impoundment ar e always saturated whereas the 0.5 m of clogged native soil are assumed to be unsaturated w hen 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 mercu ry capture from flue gas under new emission control regulations. Commentary pointed out that th e 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 fut ure air emission control regulations and associated reference information are detailed in Table 3-9 and presented below.Response to Public Review Comments Source Modeling

3-14 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 ri sks 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 b ehavior of CCR wastes. However, it has been shown that newer mercury pollution control technolo gies currently in place have the potential to affect leaching behavior (U.S. EPA, 2006, 2008, 200 9). Thus, EPA conducted a sensitivity analysis to evaluate the risks associated with existing unit s 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 presente d 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 po re water will improve the risk assessment, but TCLP and SPLP data are not appropriate for use as s ource 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 r epresentative 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 us eful 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 th at field leaching data should not be mixed with laboratory data, and that EPA's field leachate data set (for landfills and impoundments) is not adequate for use in the CCR risk assessment. Specif ic efforts recommended to properly utilize the LEAF data include: Use of probability density funct ions for leachate concentrations based on pH and/or L/S ratios in the Monte Carlo process; Selec tion 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 grou ndwater. A few commenters pointed out that the pore water da ta are generally representative, although concerns were raised about the highest arsenic conc entration (81 mg/L) in the dataset. OneResponse to Public Review Comments Source Modeling

3-15 commenter believed that although the addition of ne w data is an improvement, EPA could greatly improve the accuracy of the model’s results by remo ving 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 clas sify the data according to CCR type and coal type. Overall, commenters support updates to the pore wat er data and the use of statistical method to normalize the data curve. However, one commenter no ted that EPA should not use commentersubmitted CCR pore water data unless it meets requi site 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 t hese documents in the docket. Without these documents, the reader does not have a complete unde rstanding 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 gen erated data and freely draining pore water is more representative of leachate releases than tight ly held pore water. The specific public comments related to the use of pore water data for impoundme nt source concentrations and associated reference information are detailed in Table 3-10

. Table 3-10. Comments Related to the Use of Pore Water Dat a 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 2011Response to Public Review Comments Source Modeling

3-16 Table 3-10. Comments Related to the Use of Pore Water Dat a 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 waterResponse to Public Review Comments Source Modeling

3-17 samples. EPA did not use available LEAF data for su rface impoundments because a national distribution of pH was not available to allow the A gency to probabilistically assign LEAF concentrations to these units, and because there wa s no way to account for partitioning of the leachate into wastewater versus porewater. Thus, EP A 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 r epresentative 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 asse ssment report. EPA agrees that TCLP and SPLP data are less appropr iate for CCR disposal scenarios and no longer uses these data in the revised risk assessme nt. EPA adapted the LEAF methods and data for landfills, as this is the best available approach a nd 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 defe nsible data available. As noted in the 2010 Environmental Science and Technology publication (T horneloe et al., 2010), the data represents the largest collection of comprehensive characteris tic leaching data to date. A commenter noted that the LEAF data provide the po tential for leaching and not actual leaching of a specific CCR under actual field conditions. Th e commenter suggests using probability distribution of key factors affecting leaching beha vior [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 expr essed 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 possi ble given the current availability of information on site-specific coal ash chemistry. Al though leachate concentrations were selected considering pH and L/S conditions that are national ly representative, EPA does not have the detailed and extensive site-specific measurements t hat 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 h uman and ecological health across the country. The revised risk assessment also provides details r egarding how the LEAF data are used in combination of geographical specific data such as h ydrology, precipitation, fill configuration, CCR type, pH, L/S ratio, and other factors that take th e leaching potential as an input to fate and transp ort models accounting for attenuation and dilution. Add itionally, 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-specifi c basis, it is adequate to identify trends in leachin g behavior that relate to differences in materials types, APC technology, and coal rank. Geochemical s peciation 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

3-18 Regarding the number and concentration of pore wate r samples, EPA reviewed the high-end pore water concentrations and determined that these repr esent actual CCR samples that therefore represent possible high-end risks if CCR is inadequ ately 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 captu res the possible high end risks that are of most interest in the rulemaking, including risks from th e mismanagement of CCR through codisposal with coal refuse. The assumption that saturated contaminant concentra tions in surface impoundment sediments are at equilibrium with the impoundment waters is a con servative 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 sele cted datasets were relevant and acceptable in terms of data quality requirements. However, EPA do es not have sufficient data to distinguish between freely draining and tightly bound pore wate r data at this time. Overall, EPA agrees that the use of these data introduces some uncertainty i nto 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 wa stes 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 im poundments 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 accum ulation underestimates the amount of sedimentation and subsequently overestimates the am ount of percolation to the subsurface. The commenter stated that in actual operation, ash thic kness can increase up to 30 feet or more, eventually filling the impoundment, which results i n 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 operati ons. The specific comments related to modeling surface impoundments only before closure and associ ated reference information are detailed in Table 3-11 and presented below.Response to Public Review Comments Source Modeling

3-19 Table 3-11. Comments Related to Modeling Surface Im poundments 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 co ntinuously dredged. Because these facilities have other units (whether onsite or offs ite) established for disposition, it likely that th e 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 impoundm ents are greater because the higher hydraulic head drives leachate into underlying soils with gre ater force than gravity alone post-closure. Therefore, EPA did not explicitly model the post-cl osure phase of surface impoundments. The uncertainties resulting from this decision are disc ussed in Section 5 of the revised risk assessment. EPA acknowledges that EPACMTP is restricted to mode ling flow as steady state with the assumption that an impoundment always has a fixed d epth of wastewater. EPA further acknowledges that such an assumption may overestima te infiltration. The surface impoundment conceptual model assumes that sediments are periodi cally dredged and removed and that the longterm average thickness of the sediment is approxima tely 0.4 m, with half of that layer consolidated. EPA has used EPACMTP and its predecessor model vers ions for a longstanding time period and it has undergone multiple rounds of internal and ex ternal review. The reviews associated with EPACMTP and its limitations are further discussed i n Section 5 of the revised risk assessment report.Response to Public Review Comments Source Modeling

3-20 

# 3.12. Modeling of Landfills Only Post-Closure Comment Summary Public commenters suggested that risks from operati ng landfills should be considered along with those that occur post-closure. These commenters que stioned whether greater risks may occur during site operations when wastes are uncovered an d exposed directly to precipitation. Additional commenters noted that complete leaching of all cons tituent mass at a constant concentration is overly conservative. The specific public comments r elated to modeling landfills only after closure and associated reference information are detailed i n 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 assessm ent 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 wit h a cap no less permeable than the soil or liner underlying the WMU is present at the start of leach ing. 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 di scussed in Section 4 and Appendix C of theResponse to Public Review Comments Source Modeling

3-2 revised risk assessment. Alternatively, EPA present s a sensitivity analysis of these results compared with the results generated using total mas s in Section 5.Response to Public Review Comments

4-1 

# 4. Public Comments on Exposure Scenarios

The comments relating to exposure scenarios were gr ouped into six subcategories, which are summarized in the following bulleted list. Subcateg ories with no public comments are included for consistency with the peer review response to co mments (U.S. EPA, 2014b).

 Section 4.1 : Direct surface impoundment exposure (no public co mments)

 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 landfi ll 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 d oes not consider direct discharges to ground and surface water systems other than ground water i nfiltration (e.g., direct injection to ground water, point and nonpoint discharges to surface wat er 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 grou nd water and surface water systems. The commenter continues by suggesting that the use of l iners 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

4-2 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 wate rs because they are regulated as permitted point source discharges under the Clean Water Act b y EPA’s Office of Water. Since this pathway is outside the scope of the risk assessment, the re vised risk assessment does not consider these releases. However, this pathway was evaluated in th e Environmental Assessment for the Proposed Effluent Limitation Guidelines and Standards for th e 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 ev aluate it. 

# 4.4. Exposure to Fugitive Dust during Landfill Operation (Before Closure) Comment Summary Public comments were received on the methodology ap plied to evaluate exposure to fugitive dust during landfill operations (before closure). The ma jority 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 ini tial 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 met hodology for refining the fugitive dust analysis that was applied in the revised risk asses sment. 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 act ive portions of the landfills are significantly smaller than the landfills identified in the 1995 E PRI survey. Several comments were received that pointed out that the application of AERSCREEN and A ERMOD is appropriate if representative or realistic inputs are used including meteorologic al 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, AERSCREENResponse 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 note d that consideration of deposition impacts and constituent-specific modeling is appropriate. One c ommenter recommended that EPA should conduct a full-scale assessment that considers fugi tive dust as well as emissions from landfills and emissions of diesel particulate matter from haul tr ucks, 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 t he transportation route and at the landfill. Another commenter expressed concern over the lack o f 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 pr ovided 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 re lated to exposure during landfill operation and associated reference information are detailed i n Table 4-2

. Table 4-2. Comments Related to Exposure During Land fill 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 2011Response to Public Review Comments Exposure Scenarios

4-4 Table 4-2. Comments Related to Exposure During Land fill 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 Associatio n 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 2010Response to Public Review Comments Exposure Scenarios

4-5 

### EPA Response The majority of the comments received concerning ex posures 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 c onsidered releases from windblown emissions and the potential to excee d national ambient air quality standards (NAAQS) for particulate matter. Based on the comments received, EPA updated the scr eening analysis of fugitive dust. EPA agrees that there are potential risks posed by fugitive em issions 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. Emi ssions 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 per formed with a combination of AERSCREEN and AERMOD to estimate dus t dispersion and deposition rates. Model inputs were selected to be representative of current landfills, environmental settings (e.g., meteorological conditions) and common dust manageme nt 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 downgradi ent media. This was done for all relevant metal species. In contrast, EPA did not evaluate em issions 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 a nalysis 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 appr opriateness of a screening analysis to eliminate pathways from consideration in the full-s cale probabilistic analysis. One commenter pointed out that the EPA conducted a very conservat ive, but appropriate, screen to identify constituents to include in the full-scale probabili stic analysis. Another commenter emphasized that a full scale risk assessment should be conducted th at assesses exposures concurrently through all pathways (e.g., including surface pathways with inh alation exposure) for all chemical constituents. In particular, they emphasized that inhalation expo sures to human carcinogens, such as hexavalent chromium, as well as non-carcinogens may occur thro ugh the aboveground pathway. Although disagreed over the use of a screening approach, bot h commenters expressed concerns over the use of risk attenuation factors to scale screening risk s 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 theResponse to Public Review Comments Exposure Scenarios

4-6 omitted constituents and that the use of a simplist ic, attenuation factor is not an appropriate way to estimate risk. The specific public comments rela ted to elimination of pathways during screening and associated reference information are detailed i n Table 4-3

. Table 4-3. Comments Related to Elimination of Pathw ays 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 presente d in Section 3 of the revised risk assessment, EPA was able to focus available resources on the ch aracterization of risks for exposure routes and constituents with the greatest potential to pose ri sks. The screening analysis conducted for the revised risk assessment considered all of the poten tial exposure routes identified in the conceptual models for surface impoundments and landfills, whic h included aboveground exposures to ambient air, soil, sediment, produce and animal pro ducts. Each exposure pathway was evaluated for all constituents (and individual species, as ap propriate) for which both concentration and toxicity data were available. The screening analysis was developed to be protecti ve of highly exposed individuals. Due to the conservative nature of the screening, the calculate d 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 asses sment did not rely on risk attenuation factors to screen out constituents. All constituents that resu lted in screening-level risks above human health or ecological criteria, and for which characterizat ion of fate and transport could be refined, were carried forward for further consideration in the pr obabilistic analysis, described in Section 4 of the revised risk assessment. It is possible that consid eration 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. H owever, it is highly unlikely that these additionalResponse to Public Review Comments Exposure Scenarios

4-7 constituents would remain risk drivers once more re alistic dilution and attenuation in the environment is considered. 

# 4.6. Exposure to Additional Constituents Comment Summary Multiple commenters noted that there may be additio nal constituents present in CCR wastes beyond those quantitatively evaluated in the risk a ssessment. In particular, multiple commenters referenced organics and radionuclides. Some comment ers called on EPA to quantify the risks associated with these additional constituents. Othe rs claimed that these constituents are present in low levels and do not pose risk to receptors. The s pecific public comments related to exposure to additional constituents are detailed in Table 4-4

. Table 4-4. Comments Related to Exposure to Addition al 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 F ossil 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 an alytical 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 compos ition of CCR wastes have markedly changed, EPA continues to rely on these findings. EPA acknowledges that, like other inorganic constit uents, 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 concentratio ns for individual radionuclides, a quantitativeResponse to Public Review Comments Exposure Scenarios

4-8 evaluation of risk was not conducted. To address th is data gap, EPA has included radionuclides in the list of constituents for ground water monitorin g. Furthermore, potential transport of these constituents downgradient by windblown dust and sto rm 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 toxicit y 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 respo nse to comments (U.S. EPA, 2014b).

 Section 5.1 : Combined chemical effects, additive risk, and mul tiple 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 commen ts)

 Section 5.8 : Bioconcentration Factors. 

# 5.1. Combined Chemical Effects, Additive Risk, and Multiple Pathway Exposures Comment Summary Some commenters argued that EPA underestimated risk s by not considering combined chemical effects, additive risk and concurrent exposures thr ough multiple pathways. One commenter indicated that EPA should conduct a full scale asse ssment 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 a nd may affect the same body organ or system, resulting in greater risks than predicted through t he consideration of each constituent separately.

One commenter noted that the combination of risks f rom different constituents would not change the overall results of the risk assessment. Constit uents concentrations found to result in an HQ less than 1 in the screening analysis are unlikely to ma ke a meaningful contribution to overall risk regardless of whether multiple compounds share the same toxicological endpoints. Additionally, the commenter expressed that it would be inappropri ate to add the risks from different constituents as modeled because the constituents do not all arri ve at a hypothetical receptor at the same time, due to differing mobility in the subsurface environ ment. The specific public comments related to combined chemical effects, additive risk, and multi ple pathway exposures, and associated reference information are detailed in Table 5-1

.Response to Public Review Comments Human Exposure a nd Toxicity

5-2 Table 5-1. Public Comments Related to Combined Chem ical 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 consider ed potential risks to human health from individual constituents and individual pathways. EP A 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 ris ks from drinking contaminated ground water, as well as eating contaminated fish from a local surfa ce water body, it is unlikely that these two exposure pathways would occur simultaneously with a ny appreciable frequency in the real world. It is even more unlikely that a receptor would be e xposed 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 possib le for an individual to be exposed to multiple constituents through a single pathway. This is a mo re likely scenario because, as demonstrated by the available data, CCRs typically leach multiple i norganic constituents. Where exposure to multiple constituents is likely to occur, EPA polic y is to assume that the risks resulting from these exposures are additive (U.S. EPA, 2000). The curren t 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 theResponse to Public Review Comments Human Exposure a nd Toxicity

5-3 high-end risks modeled in this risk assessment, is unlikely alter the principal results of the probabilistic analysis. Similarly, because the risk s 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 ri sk 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 inconsiste nt reporting of toxicity benchmark values and recommended conducting a thorough review of literat ure 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 underes timates 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 [c hromium (VI)] published by the New Jersey Department of Environmental Protection (NJDEP). Con cerning lead, one commenter supported a peer reviewer’s recommendation to use the Integrate d Exposure Uptake Biokinetic (IEUBK) model to calculate human health risks, especially f or 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 woul d provide an uncertainty discussion regarding toxicity values, facilitate communication with the public, and provide a balanced perspective on risk. The specific public comments r elated to toxicity values and associated reference information are detailed in Table 5-2

. Table 5-2. Public Comments Related to Toxicity Valu es

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 2010Response to Public Review Comments Human Exposure a nd Toxicity

5-4 Table 5-2. Public Comments Related to Toxicity Valu es

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 2010Response to Public Review Comments Human Exposure a nd Toxicity

5-5 Table 5-2. Public Comments Related to Toxicity Valu es

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 20 10

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 2 010

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 2011Response to Public Review Comments Human Exposure a nd Toxicity

5-6 

### EPA Response Human health benchmarks were chosen based on the Of fice 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 append ix provide further information on the potential adverse effects and derivation of toxicity criteria

. For lead, EPA used the drinking water maximum conta minant level (MCL) to estimate risks from drinking water exposure in the draft risk assessmen t. In the revised risk assessment EPA continued to rely on the MCL, but also used IEUBK model for l ead 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 part icular, 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 suggeste d that non-cancer risks should be report as follows: Worst Case – Assume maximum exposure scena rios including exposure 24 hours/day, 365 days/year for 70 years; High End – 95th percent ile based on national human activity pattern distributions; Central Tendency – 50th percentile ( or median) risk based on national human activity pattern distributions. Furthermore, another comment er believed that it is more appropriate to consider 95th percentiles, rather than 90th percent ile, of exposure and risk estimates for humans and ecological receptors. The specific public comme nts 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 2010Response to Public Review Comments Human Exposure a nd 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 assessme nt. A citation to the where “point of departure” was originally defined is provided for reference. T he rationale for use of 90 th 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 re asonable maximum exposure scenario. Specifically, it was noted that the receptor placem ent downgradient of an unlined management unit does not represent the entire population expos ure distribution. One commenter suggested that EPA clearly define the exposed population of intere st. The specific public comments related to defining the exposed population and associated refe rence 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 2010Response to Public Review Comments Human Exposure a nd 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 und er 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 protect ive 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 fis h from impacted water bodies are not available. EPA believes that consideration of RME is a reasona ble and protective alternative, given the available data. Uncertainties associated with the r evised 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 variou s exposures, because more current data are currently available. Commenters recommended that EP A 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 commen ters 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 commen ter suggested that a sensitivity analysis of human health exposure factors be conducted to add t o the sensitivity analysis conducted by EPA in 2009. Regarding fish consumption rates, commenters questi oned 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 te sts to demonstrate how well the fish consumption rate data fit a log normal distribution. Additional ly, it was suggested that fish consumption rates should be determined from other studies and more ro bust data sets. One commenter suggested the incorporation of fish consumption rates representat ive 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 a nd Toxicity

5-9 Regarding drinking water ingestion rates, one comme nter voiced concern about the assumption that ground water is the source of all drinking wat er. 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, s ports 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 Fact or 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 199 7 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 fo r the U.S. population. The 2011 Exposure Factors Handbook

(U.S. EPA, 2011) has been completed and updates so me of the data from the 1997 EFH. During the finalization of this risk asse ssment, 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 anglersResponse to Public Review Comments Human Exposure a nd Toxicity

5-10 from Maine that fished from streams, rivers, and po nds. 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 Ame rican subsistence fishers are currently limited and can vary widely geographically, to the point th at 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 rev ised risk assessment. 

# 5.6. Child/Infant Exposure Assumptions Comment Summary Commenters emphasized the need to update exposure f actors for childhood exposures and recommended that updates include data from the 2011 EFH. One commenter stated that the risk assessment appropriately considered the potential f ish exposures for children. However, they pointed out that the fish consumption rates for chi ldren should be lower than those applied for adults. Another commenter suggested that the risk a ssessment 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 wer e truncated at the end of each age cohort or aged through the different cohorts. The specific pu blic comments related to child/infant exposure assumptions and associated reference information ar e 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 E FH (U.S. EPA, 1997a,b,c) and the 2008 CSEFH (U.S. EPA, 2008b) for information on human ex posure 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 inf ant exposures that may occur from formula mixed with contaminated ground water. These data ar e presented in Appendix D of the revised risk assessment. Consistent with the commenter’s re commendation for cohort aging, the risk assessment aged receptors through each age cohort u sing age-specific data for exposure factors and physical characteristics that were weighted pro portionally by the corresponding time periodResponse to Public Review Comments Human Exposure a nd Toxicity

5-11 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 w ith more current references. One commenter questioned why bioconcentration factors w ere zero for some constituents that are essential nutrients (i.e., cobalt and copper). Anot her 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 docume nts) indicates that BCFs are poor predictors of tissue metal concentrations due to wide variatio n 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 asse ssment adhere to the EPA policy of using dissolved metals in the calculating the bioconcentr ation of metals in fish, or should provide the rationale for using a different approach. The speci fic public comments related to bioconcentration factors and associated reference information are de tailed in Table 5-7

. Table 5-7. Public Comments Related to Bioconcentrat ion 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 2007Response to Public Review Comments Human Exposure a nd Toxicity

5-12 

### EPA Response EPA recognizes that the use of BCFs may not represe nt 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 us eful in a screening-level assessment and EPA believes they are also appropriate for a nation al-level risk assessment, where site-specific data are not available and collection of site-speci fic 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. Regar ding the concern expressed with respect to zero BCF values, the commenter did not provide alternati ve BCFs that EPA could consider for the constituents at issue. Additionally, EPA agrees tha t given the latest scientific information, distributions of BAFs/BCFs may be better than singl e BAFs/BCFs because they account for changes in bioaccumulation/bioconcentration at diff erent water concentrations. EPA is working to develop BAF/BCF distributions for several CCR pollu tants of concern but does not yet have a robust enough dataset for use for the final CCR Rul e. In lieu of this, EPA is proceeding with the single BAF/BCF approach for the current analysis. E PA does recognize this issue as a limitation for the BCF calculations and considers it as an unc ertainty in the risk characterization. Overall, EPA agrees that the use of this older data introduc es some uncertainty into the analysis. These uncertainties are discussed in greater detail in Se ction 5 of the revised risk assessment. With the exception of mercury, EPA evaluated biocon centration based on water column concentrations that include contributions from diss olved and solid phases because available BCFs represent contributions from both. Because a BAF ba sed only on dissolved-phase concentrations was available for mercury, EPA evaluated this const ituent using only dissolved concentrations. Applying this conservative approach for most consti tuents ensured protection of human health. Even with this conservative assumption, the 90th pe rcentile risks for the probabilistic analysis (Section 4) did not exceed risk criteria for the fi sh 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 a vailable literature and identified BCFs for additional constituents that previously had no valu es. 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 che mical (Eisler, 1989; Kumada et al., 1973; Lemly, 1985; Murphy et al., 19 78) 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 Ban k (HSDB; U.S. NLM, 2011). EPA also finds that the references provided by comm enters provided primarily phytotoxicity and accumulation data for terrestrial plants, and were therefore not relevant to EPA’s explicitResponse to Public Review Comments Human Exposure a nd Toxicity

5-13 solicitation on whether the bioconcentration factor s drawn from Baes et al. (1984) should be considered in the final risk assessment.Response to Public Review Comments Human Exposure a nd Toxicity

5-14 [This page intentionally left blank.]Response to Public Review Comments

6-1 

# 6. Comments Related to Ecological Exposure and Toxicity

The comments relating to ecological exposure and to xicity 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 respo nse 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 importan ce of cumulative ecological risk, whereby an ecological receptor may be exposed to multiple c onstituents and/or pathways concurrently. For example, amphibians may be subject to both dermal a nd ingestion exposure. Public commenters noted that ecological risks were underestimated bec ause the following scenarios were not considered for ecological receptors: aboveground pa thways, contaminant transport to nearby uncontaminated environments, and the inclusion of f ield 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 Ecologica l 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 2007Response to Public Review Comments Ecological Expos ure and Toxicity

6-2 

### EPA Response EPA acknowledges that cumulative effects can be imp ortant for ecological receptors. However, just as EPA did not consider cumulative human healt h risks from exposures to ground water (discussed in Section 6.1 of this document), they were not modeled for ecolo gical receptors. In the national, probabilistic analysis (Section 4 of the revised risk assessment), risks for all constituent s fell below the ecological criteria. Even the sum of modeled risks for all constituents fell below the ecological criteria. In sensitivity analyses (Secti on 5 of the revised risk assessment), which considered different subsets of national disposal p ractices 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 acknow ledges that ecological risk could be underestimated to some degree. However, these uncer tainties are unlikely to affect the principal findings of the risk assessment. In addition, EPA a lso notes that all surface water risks are orders of magnitude lower than the risks resulting from di rect discharges modeled in U.S. EPA (2013). In contrast to the surface water and sediment expos ures, ecological risks for individual constituents were appreciably above risk criteria for direct exp osure to impoundment wastewater. As a result, it is clear that CCR disposal in surface impoundmen ts 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 d oes not consider sensitive habitats or species. Commenters requested additional consideration of th reatened and endangered species and the inclusion of ecological field data. The specific co mments related to sensitive habitats/species and associated reference information are detailed in Table 6-2

. Table 6-2. Comments Related to Sensitive Habitats/S ensitive 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 s ensitive/endangered ecological receptors because the presence these are inherently site-spec ific issues for which data on potential impacts are often not available and can be difficult to qua ntify, even on a site-specific basis. EPA acknowledges that the inability to quantitatively e valuate the potential for these adverse effects represents a source of uncertainty. Discussion of t hese uncertainties is presented in Section 5 of the revised risk assessment.Response to Public Review Comments Ecological Expos ure 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 conser vative approach was needed to derive the ecological benchmarks. Multiple commenters also sta ted that the use of risk attenuation factors to scale the screening risks to full-scale risks was i nappropriate. Several commenters noted that the ecological boron benchmark used for surface water e xposures contained incorrect units based on an incorrect transcription in the peer-reviewed art icle. Another commenter noted that the ecological cadmium benchmark used for direct contac t with surface water was incorrect. The specific public comments related to ecological benc hmarks, ecological toxicity and associated reference information are detailed in Table 6-3

. Table 6-3. Comments Related to Ecological Benchmark s, 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 constit uents when available and compared with the modeled media concentrations (e.g., surface wat er, sediment) to estimate the HQs used to characterize ecological risk. These benchmarks repr esent the best available estimates of receptor responses based “no effects” (NOAEL) or “lowest eff ects” (LOAEL) study data. In someResponse to Public Review Comments Ecological Expos ure and Toxicity

6-4 scenarios, these benchmarks may represent species n ot actually present in the field. In others, these benchmarks may not capture the most sensitive possi ble 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 thes e 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. Considera tion of any additional sensitive species not captured by the current benchmarks may result in so me additional constituents above risk criteria in the probabilistic analysis. EPA notes that ecolo gical 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 assessm ent. Regarding incorrect benchmark values, an updated bo ron 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 concen tration (CCC) was used for the cadmium surface water benchmark in the revised risk assessment, rep lacing the previous value. The updated values are presented in Appendix E of the revised risk ass essment 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 w ere grouped into five subcategories, which are summarized in the following bulleted list. Subc ategories with no public comments are included for consistency with the peer review response to co mments (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 op posed to an overall probability (no public comments)

 Section 7.4 : Comments related to the numerical stability of Mo nte 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 c onservative 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 ac tual risk and associated uncertainty rather than weighting the results conservatively. The specific public comments related to the use of conservative parameter estimates and associated ref erence information are detailed in Table 7-1

. Table 7-1. Comments Related to the Use of Conservat ive 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 2007Response to Public Review Comments Monte Carlo Anal ysis Approach

7-2 

### EPA Response The revised risk assessment conducted full-scale pr obabilistic 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, s oil type, WMU data, climate data, distance to ground water wells, distance to surface water bodie s, 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 p rotective 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 assessm ent 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, includin g 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 refer ence information are detailed in Table 7-2

. Table 7-2. Comments Related to Variability versus U ncertainty

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 vari ability from uncertainty when possible in a probabilistic risk assessment. EPA was able to redu ce a substantial number of the uncertainties in the revised risk assessment through the acquisition of additional data on facilities, environmental parameters, and constituent concentrations. Variabi lity and uncertainty are still comingled in a large number of cases due to remaining data gaps; h owever, EPA conducted multiple sensitivity analyses to determine the potential for different i nputs to affect risk results. Additional discussion of the differences between parameter variability, d ata uncertainty, and model error, as well as discussions of the sensitivity and uncertainty anal yses, is presented in Section 5 of the revised risk
assessment.Response to Public Review Comments Monte Carlo Anal ysis Approach

7-3 EPA disagrees that there are wide risk distribution s. While the commenter correctly points to other risk assessments that had closer central tendency a nd high-end results, those were either sitespecific assessments or involved no fate or transpo rt modeling. National-scale risk assessments will necessarily have wider variability in their re sults compared to risk assessments that are specific to a single site. Thus, the “wider” risk d istributions simply reflect the fact that different sites with different CCRs can have very disparate i mpacts 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 Anal ysis Approach

7-4 [This page intentionally left blank.]Response to Public Review Comments

8-1 

# 8. Comments on Documentation and Miscellaneous Comments

The comments related to documentation and other mis cellaneous comments were grouped into seven subcategories (subcategories with no public c omments are included for consistency with the peer review response to comments):

 Section 8.1 : Insufficient documentation to reproduce the analy sis 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 pattern s (e.g., climate-specific risk) (no public comments)

 Section 8.5 : Discussion of worst-case scenarios (no public com ments)

 Section 8.6 : Discussion of sulfate, phosphate, and chloride (n o 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 in complete 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 c omments related to insufficient documentation to reproduce the analysis independently and associa ted reference information are detailed in Table 8-1

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

**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 2007Response to Public Review Comments Documentation an d Miscellaneous Comments

8-2 

### EPA Response EPA acknowledges that the documentation of the inpu ts 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 directl y 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 discussion s of inputs in the document were not sufficient for complete duplication of the results. Thus, the input and output files for the draft risk assessmen t were made available in the docket of the proposed r ule 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 p resentation of risk results. Additionally, commenters requested further explanation of the min imum and maximum truncating values, as truncated values may reduce risk estimates. The spe cific public comments related to graphical presentation of input/output distributions, truncat ion values and associated reference information are detailed in Table 8-2

. Table 8-2. Comments Related to the Graphical Presen tation 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 output s files, see the responses in Section 8.1 above. With regard to truncation, EPA no longer ma nually truncates input distributions for the human exposur e 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-residuesResponse to Public Review Comments Documentation an d Miscellaneous Comments

8-3 NY), 4 as described in Appendix D. EPA has also added fur ther 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 fac tor variables to the sensitivity analysis, and to conduct additional sensitivity analyses on differen t topics (e.g. well distance distribution). The specific public comments related to documentation o f 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 sensi tivity 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 th e revised risk assessment. This sensitivity analysis was placed in the docket for the proposed rule. Human health exposure factor variables were not eva luated in the sensitivity analysis. Human exposure factor variables have well-established, pe er-reviewed, national distributions that are regularly used in probabilistic risk analyses condu cted by EPA based on Agency policy. Therefore, the contribution of variability in the exposure fac tors to the variability in risk was not particularl y useful for understanding the aspects of CCR disposa l practices that may drive risk. Additional sensitivity analyses such as leachate duration vers us leachable content and liner performance by thickness were conducted in the revised risk assess ment 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 docum ent. Thus, EPA does not provide a response to

4 Available online at: www.palisade.com/risk/Response to Public Review Comments Documentation an d 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 Regi stry). 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. 19 80. Bioconcentration and elimination of selected water pollutants by bluegill sunfish (Lepo mis macrochirus). In: Haque R, ed. Dynamics, exposure and hazard assessment of toxic c hemicals. Ann Arbor, Michigan, U.S.A.: American Chemical Society. p. 379-392. Bhaduri, B., Bright, E., Coleman, P., Urban, M. 200 7. LandScan USA: A high resolution geospatial and temporal modeling approach for popul ation 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 Invertebr ates: A Synoptic Review

. Contaminant Hazard Reviews, Report No. 19, Biologic al Report 85(1.19). Laurel, MD. August.
Hamilton, S.J. 1995. Hazard assessment of inorganic s 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 manageme nt 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 freshwa ter 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 Goeth ite using Surface Complexation Modeling. M.S. Thesis, Department of Civil and Environmental Engineering, 1995.Response to Public Review Comments References

9-2 Meeussen, J.C.L. 2003. ORCHESTRA: An Object-Oriente d 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. 197 8. Cadmium and zinc in muscle of bluegill (Lepomis macrochirus) and largemouth bass (Micropte rus salmoides) from an industrially contaminated lake. Environmental Pollution 17:253–257.
Stephan, C.E. 1993. Derivation of Proposed Human He alth and Wildlife Bioaccumulation Factors for the Great Lakes Initiative. Draft. Environmenta l Research Laboratory, Office of Research and Development, U.S. Environmental Protec tion 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 Biot a 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 Source s (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 Rese arch 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 Res earch 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 Environm ent . EPA 452/R-97/005. Office of Air Quality Planning and Standards and Office of Resear ch and Development, Washington, DC.
U.S. EPA (Environmental Protection Agency). 1999a. Understanding Variation in Partition Coefficient, Kd, Values Volume I: The Kd Model, Met hods of Measurement, and Application of Chemical Reaction Codes. EPA 402-R-9 9-004A. OAR. Washington, DC. August. Available online at: www.epa.gov/rpdweb00/cleanup/402-r-99-004.html

.Response to Public Review Comments References

9-3 U.S. EPA (Environmental Protection Agency). 1999b. Report to Congress: Wastes from the Combustion of Fossil Fuels: Volume 2 – Methods, Fin dings, and Recommendations (EPA 530-R-99-010). Office of Solid Waste and Emergency Response. Washington, DC. U.S. EPA (Environmental Protection Agency). 2000. S upplementary Guidance for Conducting Health Risk Assessment of Chemical Mixtures. Risk A ssessment Forum, Washington, DC. August. U.S. EPA (Environmental Protection Agency). 2002. I ndustrial 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 Migration with Transformation Products (EPACMTP): P arameters/Data Background Document. Office of Solid Waste, Washington, DC. Ap ril. Available at www.epa.gov/epaoswer/non-hw/industd/tools/cmtp/epac mtp.htm#data. U.S. EPA (Environmental Protection Agency). 2003b. EPACMTP Technical Background Document. Office of Solid Waste, Washington, DC. U.S. EPA (Environmental Protection Agency). 2003c. Human Health Toxicity Values in Superfund Risk Assessments . Office of Solid Waste and Emergency Response Dire ctive 9285.7-53. December. U.S. EPA (Environmental Protection Agency). 2006. C haracterization of Mercury-Enriched Coal Combustion Residues from Electric Utilities Using E nhanced Sorbents for Mercury Control. EPA 600/R-06/008. Office of Research and D evelopment. Research Triangle Park, NC. January. U.S. EPA (Environmental Protection Agency). 2008a. Characterization of Coal Combustion Residues from Electric Utilities Using Wet Scrubber s for Multi-Pollutant Control. EPA600/R-08/077. Office of Research and Development, N ational Risk Management Research Laboratory, Air Pollution Prevention and Control Di vision. Cincinnati, Ohio. July. U.S. EPA (Environmental Protection Agency). 2008b. Child-Specific Exposure Factors Handbook. EPA/600/R-06-096F. National Center for En vironmental Assessment, Cincinnati, OH. U.S. EPA (Environmental Protection Agency). 2009a. Characterization of Coal Combustion Residues from Electric Utilities – Leaching and Cha racterization Data. EPA-600/R09/151. Office of Research and Development, Nationa l Risk Management Research Laboratory, Research Triangle Park, NC. December. U.S. EPA (Environmental Protection Agency). 2009b. EC OTOX User Guide: ECOTOXicology Database System . Version 4.0. Available online at www.epa.gov/ecotox/

.Response to Public Review Comments References

9-4 U.S. EPA (Environmental Protection Agency). 2009c. Sensitivity Analysis for the Coal Combustion Waste Risk Assessment. Prepared by RTI I nternational for U.S. EPA, Office of Solid Waste, Washington, DC. U.S. EPA (Environmental Protection Agency). 2010. I nhalation of Fugitive Dust: A Screening Assessment of the Risks Posed by Coal Combustion Wa ste Landfills. Prepared by the Office of Solid Waste, Washington, DC. U.S. EPA (Environmental Protection Agency). 2010b. Human and Ecological Risk Assessment of Coal Combustion Wastes . Draft

. Office of Resource Conservation and Recovery, Washington, DC. April. U.S. EPA (Environmental Protection Agency). 2011. Exposure Factors Handbook: 2011 Edition. EPA/600/R-090/052F. National Center for Environment al Assessment, Office of Research and Development, Washington, DC. September U.S. EPA (Environmental Protection Agency). 2012a. Interlaboratory Validation of the Leaching Environmental Assessment Framework (LEAF) Method 13 14 and Method 1315. EPA/600/R-12/624. Prepared by A.C. Garrabrant s, D.S. Kosson, R. DeLapp, P. Kariher, P.F.A.B. Seignette, H.A. van der Sloot, L. Stefanski, and M. Baldwin for the U.S. EPA Office of Research and Development, Air Polluti on Control Division. September. U.S. EPA (Environmental Protection Agency). 2012b. Interlaboratory Validation of the Leaching Environmental Assessment Framework (LEAF) Method 13 13 and Method 1316. EPA/600/R-12/623. Prepared by A.C. Garrabrant s, D.S. Kosson, L. Sefanski, R. DeLapp, P.F.A.B. Seignette, H.A. van der Sloot, P. Kariher, and M. Baldwin for the U.S. EPA Office of Research and Development, Air Polluti on Control Division. September. U.S. EPA (Environmental Protection Agency). 2013. Environmental Assessment for the Proposed Effluent Limitation Guidelines and Standards for th e Steam Electric Power Generating Point Source Category. Office of Water. Washington, DC. 20460. April. EPA -821-R-13- 003. U.S. EPA (Environmental Protection Agency). 2014a. Human and Ecological Risk Assessment for Coal Combustion Residuals. Office of Solid Waste and Emergency Response. Wash ington, DC. 20460. December. EPA530-R-15-001. U.S. EPA (Environmental Protection Agency). 2014b. Response to External Peer Review Comments: Human and Ecological Risk Assessment for Coal Combustion Residuals

. Office of Solid Waste and Emergency Response. Washi ngton, DC. 20460. December. EPA530-R-15-002. U.S. EPA (Environmental Protection Agency). 2014c . Human Health Evaluation Manual, Supplemental Guidance: Update of Standard Default E xposure Factors . OSWER Directive 9200.1-120. February.Response to Public Review Comments References

9-5 USGS (U.S. Geological Survey). 2002. Attributes for NHDPlus Catchments (Version 1.1) for the Conterminous United States: Estimated Mean Annual N atural Groundwater Recharge, 2002. Available online at: water.usgs.gov/GIS/metadata/usgswrd/XML/nhd_recharg e.xml U.S. NLM (National Library of Medicine). 2011. Hazardous Substances Data Bank (HSDB). Available online at: toxnet.nlm.nih.gov/cgi-bin/sis/htmlgen?HSDB

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