EPA-600/R-06/008 

February 2006 

Characterization of 

Mercury-Enriched Coal 

Combustion Residues 

from Electric Utilities 

Using Enhanced Sorbents 

for Mercury Control 
EPA-600/R-06/008 

February 2006 

Characterization of Mercury-Enriched

Coal Combustion Residues from Electric

Utilities Using Enhanced Sorbents for

Mercury Control

by 

F. Sanchez1

, R. Keeney2, D. Kosson1, and R. Delapp1 

1

Vanderbilt University 2ARCADIS G&M, Inc. 

Department of Civil and Environmental Engineering 4915 Prospectus Drive, Suite F 

Nashville, TN 37235 Durham, NC 27713 

Contract No. EP-C-04-023, Work Assignment 1-31

EPA Project Officer: Ms. Susan Thorneloe

Office of Research and Development (ORD)

National Risk Management Research Laboratory (NRMRL)

Air Pollution Prevention and Control Division (APPCD)

 Research Triangle Park, North Carolina.

U.S. Environmental Protection Agency

Office of Research and Development

Washingtion, DC 20460
Characterization of Coal Combustion Residues 

Abstract 

This report evaluates changes that may occur to coal-fired power plant air pollution control residues from the use 

of activated carbon and other enhanced sorbents for reducing air emissions of mercury and evaluates the potential for captured pollutants leaching during the disposal or use of these residues. Leaching of mercury, arsenic, 

and selenium during land disposal or beneficial use of coal combustion residues (CCRs) is the environmental 

impact pathway evaluated in this report. Coal combustion residues refer collectively to fly ash and other air 

pollution control solid residues generated during the combustion of coal collected through the associated air 

pollution control system. This research is part of an on-going effort by U.S. Environmental Protection Agency 

(EPA) to use a holistic approach to account for the fate of mercury and other metals in coal throughout the lifecycle stages of CCR management. 

The specific objectives of the research reported here are to: 

1. Evaluate the potential for leaching to groundwater of mercury, arsenic, and selenium removed from coalfired power plant air emissions by air pollution control technology and, as a result, are contained in CCRs; 

2. Provide the foundation for assessing the impact of enhanced mercury and multi-pollutant control technology on leaching of mercury and other constituents of potential concern from CCRs during the lifecycle of 

CCR management, including storage, beneficial use, and disposal; and 

3. Perform these assessments using the most appropriate evaluation methods currently available. 

Air pollution control residues were obtained from coal combustion electric utility facilities with a representative 

range of facility configurations (including air pollution controls) and coal types combusted. Each of the residues 

sampled has been analyzed for selected physical properties, and for total content and leaching characteristics. 

Results of laboratory leaching tests were used to develop estimates of constituent release under field management scenarios. Laboratory leaching test results also were compared to field observations of leaching. 

This report focuses on facilities that use injected sorbents for mercury control. It includes four facilities with 

activated carbon injection (ACI) and two facilities using brominated ACI. Fly ash has been obtained from each 

facility with and without operation of the sorbent injection technology for mercury control. Each fly ash sampled 

was evaluated in the laboratory for leaching as a function of pH and liquid-to-solid ratio. Mercury, arsenic and 

selenium were the primary constituents of interest; results for these elements are presented here. 

ii
Characterization of Coal Combustion Residues 

Foreword 

The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the Nation’s 

land, air, and water resources. Under a mandate of national environmental laws, the Agency strives to 

formulate and implement actions leading to a compatible balance between human activities and the 

ability of natural systems to support and nurture life.To meet this mandate, EPA’s research program is 

providing data and technical support for solving environmental problems today and building a science 

knowledge base necessary to manage our ecological resources wisely, understand how pollutants 

affect our health, and prevent or reduce environmental risks in the future. 

The National Risk Management Research Laboratory (NRMRL) is the Agency’s center for 

investigation of technological and management approaches for preventing and reducing risks from 

pollution that threaten human health and the environment. The focus of the Laboratory’s research 

program is on methods and their cost-effectiveness for prevention and control of pollution to air, land, 

water, and subsurface resources; protection of water quality in public water systems; remediation of 

contaminated sites, sediments and ground water; prevention and control of indoor air pollution; and 

restoration of ecosystems. NRMRL collaborates with both public and private sector partners to foster 

technologies that reduce the cost of compliance and to anticipate emerging problems. NRMRL’s research 

provides solutions to environmental problems by: developing and promoting technologies that protect 

and improve the environment; advancing scientific and engineering information to support regulatory 

and policy decisions; and providing the technical support and information transfer to ensure 

implementation of environmental regulations and strategies at the national, state, and community levels. 

This publication has been produced as part of the Laboratory’s strategic long-term research plan. 

It is published and made available by EPA’s Office of Research and Development to assist the user 

community and to link researchers with their clients. 

Sally Gutierrez, Director 

National Risk Management Research Laboratory 

iii
Characterization of Coal Combustion Residues 

EPA Review Notice 

The U.S. Environmental Protection Agency through its Office of Research and Development funded and managed the research described here under Contract EP-C-04-023 to ARCADIS Geraghty & MIller, Inc. It has been 

subjected to Agency review and has been approved for publication as an EPA document. Mention of trade names 

or commercial products does not constitute endorsement or recommendation for use. 

This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161. 

iv
Characterization of Coal Combustion Residues 

Table of Contents 

Section Page 

Abstract ............................................................................................................................................................. ii

Foreword .......................................................................................................................................................... iii

EPA Review Notice ......................................................................................................................................... iv

List of Figures ................................................................................................................................................. vii

List of Tables ................................................................................................................................................. viii

Glossary of Terms ............................................................................................................................................ ix

Acknowledgments ........................................................................................................................................... xi

Executive Summary ........................................................................................................................................ xii

1 Introduction ................................................................................................................................................1

1.1 Regulatory Context..............................................................................................................................2

1.1.1 Waste Management .....................................................................................................................2

1.1.2 Air Pollution Control ..................................................................................................................3

1.2 Configurations of U.S. Coal Fired Power Plants and Multi-pollutant Control Technologies .............3

1.2.1 Current Air Pollution Control Technologies ............................................................................... 5

1.2.2 Enhancement of Controls for Mercury Removal: Sorbent Injection ..........................................6

1.2.3 Mercury Control by Conventional PAC Injection ......................................................................8

1.2.4 Mercury Control by Halogenated PAC Injection .......................................................................8

1.3 Coal Combustion Residues..................................................................................................................9

1.4 Residue Management Practices ...........................................................................................................9

1.4.1 Beneficial Use ..........................................................................................................................10

1.4.2 Land Disposal ........................................................................................................................... 11

1.5 Leaching Protocol .............................................................................................................................. 11

2 Materials and Methods .............................................................................................................................15

2.1 CCR Materials for Evaluation ...........................................................................................................15

2.1.1 Reference Fly Ash ....................................................................................................................15

2.1.2 Facilities Using Injection of Standard Activated Carbon .........................................................15

2.1.2.1 Brayton Point ................................................................................................................15

2.1.2.2 Pleasant Prairie .............................................................................................................19

2.1.2.3 Salem Harbor ................................................................................................................20

2.1.2.4 Facility C ......................................................................................................................20

2.1.3 Facilities Using Injection of Brominated Activated Carbon.....................................................20

2.1.3.1 St. Clair .........................................................................................................................20

2.1.3.2 Facility L ......................................................................................................................20

2.2 Leaching Assessment Protocols.........................................................................................................21

2.2.1 Alkalinity, Solubility and Release as a Function of pH (SR002.1) ..........................................21

2.2.2 Solubility and Release as a Function of LS Ratio (SR003.1)...................................................21

2.3 Analytical Methods ...........................................................................................................................21

2.3.1 Surface Area and Pore Size Distribution ..................................................................................21

2.3.2 pH and Conductivity.................................................................................................................22

2.3.3 Moisture Content ......................................................................................................................22

2.3.4 Carbon Content: Organic Carbon/Elemental Carbon Analyzer................................................22

v
Characterization of Coal Combustion Residues 

Table of Contents (concluded)

Section Page 

2.3.5 Mercury (CVAA, Method 3052, and Method 7473) ................................................................22

2.3.6 Other Metals (ICP-MS, Method 3052 and Method 6020)........................................................22

2.3.6.1 ICP-MS Analysis at Vanderbilt.....................................................................................23

2.3.6.2 Severn Trent Laboratories, Inc. (STL)..........................................................................23

2.3.7 X-Ray Fluorescence (XRF) ......................................................................................................23

2.3.8 MDL and ML for Analytical Results........................................................................................23

2.4 Quality Assurance Validation ............................................................................................................24

2.4.1 Homogenization of Individual CCR Samples and Aliquots for Analyses ................................24

2.4.2 Leaching Test Methods and Analytical QA/QC .......................................................................24

2.4.3 Laboratory Mass Balance Verification for Leaching Test Methods .........................................24

2.4.4 Improving QA/QC Efficiency ..................................................................................................27

2.5 Interpretation and Presentation of Laboratory Leaching Data ..........................................................27

2.6 Long-Term Release Assessment ........................................................................................................29

3 Results and Discussion.............................................................................................................................35

3.1 Leaching Characteristics from Field Observations of CCR Landfills and Impoundments ...............35

3.2 Quality Assurance for Laboratory Leaching Tests ............................................................................39

3.2.1 Mass Balance using EPA Reference Fly Ash............................................................................39

3.2.2 Analytical Quality Control/Quality Assurance .........................................................................39

3.3 Laboratory Test Results .....................................................................................................................40

3.1.1 Mercury Results........................................................................................................................43

3.3.2 Arsenic Results .........................................................................................................................45

3.3.3 Selenium Results ......................................................................................................................47

3.4 Long-Term Release Assessment ........................................................................................................48

3.3.4 Long-Term Release Estimates for Mercury ..............................................................................49

3.3.4 Long-Term Release Estimates for Arsenic ...............................................................................50

3.3.4 Long-term Release Estimates for Selenium .............................................................................50

4 Conclusions and Recommendations ........................................................................................................55

4.1 Assessment of CCRs Without and With Activated Carbon Injection ................................................55

4.2 Implementation of Leaching Test Methods .......................................................................................56

5 References ................................................................................................................................................57

Appendix A U.S. EPA Science Advisory Board Consultation Summary .......................................................59

Appendix B DOE NETL Full-Scale Test Site Flow Diagrams.......................................................................73

Appendix C Quality Assurance Project Plan ..................................................................................................79

Appendix D Brayton Point Fly Ashes .......................................................................................................... 116

Appendix E Pleasant Prairie Fly Ashes ........................................................................................................131

Appendix F Salem Harbor Fly Ashes ...........................................................................................................146

vi
Characterization of Coal Combustion Residues 

List of Figures 

Figure Page 

1 Coal-Fired Boiler with Sorbent Injection and Spray Cooling ....................................................................7

2 Flow Diagram for Power Plant with a Hot ESP, Carbon Injection, and a COHPAC .................................7

3 Life-Cycle Evaluation of Coal Combustion Residues ...............................................................................9

4 Uses of CCRs Based on 2003 Industry Statistics.....................................................................................10

5 Mixing Fly Ash Prior to Obtaining Aliquots for Laboratory Analyses ....................................................24

6 Flow Diagram for Mass Balance and Quality Control on Laboratory Leaching Procedures ..................26

7 Example of Extract Concentrations as a Function of pH from SR002.1 .................................................28

8 Leachate pH Distribution: Scenario of Disposal in a Combustion Waste Landfill ..................................30

9 LS Ratio Distribution: Scenario of Disposal in a Combustion Waste Landfill ........................................31

10 Example of Variability of Hg Concentrations as a Function of pH from SR002.1 ..................................31

11 Example of Regression Fits and Corresponding Equations for Solubility as a Function of pH ..............32

12 Example of Cumulative Probability Distribution for Release of Selenium from Brayton Point CCR ....32

13 Example of Comparison of 100 Yr Cumulative Release Estimates for Arsenic ......................................33

14 Range of pH Observed in Field Leachate at Landfills and Impoundments Used for

Disposal of CCRs .....................................................................................................................................36

15 Arsenic Concentrations Observed in Field Leachate at Landfills and Impoundments Used for

Disposal of CCRs .....................................................................................................................................37

16 Selenium Concentrations Observed in Field Leachate at Landfills and Impoundments Used

or Disposal of CCRs ................................................................................................................................38

17 STL Versus Vanderbilt Analytical Results for Arsenic and Selenium from Sr002.1................................41

18 Example Results from SR002.1 ...............................................................................................................42

19 Example Results from SR002.1 and SR003.1 for Selenium in Fly Ashes from Salem Harbor

with Enhanced Hg Control .......................................................................................................................43

20 Comparison of Total Mercury Content in Baseline Cases and with Sorbent Injection for

CCRs from Different Facilities ................................................................................................................44

21 Ranges of Laboratory and Field Leachate Mercury Concentrations Compared with the

Drinking Water Maximum Contaminant Level........................................................................................45

22 Comparison of Total Arsenic Content in Baseline Cases and with Sorbent Injection for

CCRs from Different Facilities ................................................................................................................46

23 Ranges of Laboratory and Field Leachate Arsenic Concentrations Compared with the

Drinking Water Maximum Contaminant Level........................................................................................47

24 Comparison of Total Selenium Content in Baseline Cases and with Sorbent Injection for

CCRs from Different Facilities ................................................................................................................48

25 Ranges of Laboratory and Field Leachate Selenium Concentrations Compared with the

Drinking Water Maximum Contaminant Level........................................................................................49

26 Example Regression Curves of Experimental Data of Arsenic Solubility as a Function

of pH for Brayton Point ...........................................................................................................................49

27 Example 100-Year Arsenic Release Estimates for Brayton Point as a Function of the

Cumulative Probability for the Scenario of Disposal in a Combustion Waste Landfill ...........................50

28 Upper Bound of 100 yr Mercury Release Estimates for Landfill Scenario Without and

With Activated Carbon Injection..............................................................................................................51

29 Upper Bound of 100 yr Arsenic Release Estimates for Landfill Scenario Without and

With Activated Carbon Injection..............................................................................................................52

30 Upper Bound of 100 yr Selenium Release Estimates for Landfill Scenario Without and

With Activated Carbon Injection..............................................................................................................53

vii
Characterization of Coal Combustion Residues 

List of Tables 

Table Page 

1 List of CCRs collected to date for evaluation of under this research program ..........................................4

2 General Characteristics of Coals Burned in U.S. Power Plants .................................................................5

3 Projected Coal-Fired Capacity by APC Configuration ..............................................................................6

4 Beneficial Uses of CCRs .......................................................................................................................... 11

5 Characteristics of Coal Combusted and Facilities Sampled and Reported Here......................................16

6 Fly Ashes from Brayton Point, Pleasant Prairie, Salem Harbor, and Facility C: Elemental

Composition (by x-ray fluorescence) and Other Characteristics. ............................................................16

7 Fly Ashes from St. Clair and Facility L: Elemental Composition (by x-ray fluorescence)

and Other Characteristics .........................................................................................................................17

8 CCRs from Facilities with Electrostatic Precipitators: Total Content of Mercury, Arsenic,

Cadmium, Lead and Selenium. ................................................................................................................18

9 Detection Limits and Quality Control Information for ICP-MS Analysis for As, Pb, and

Se at Vanderbilt ........................................................................................................................................23

10 Total Content Analysis Results for Reference Fly Ash after Mixing .......................................................25

11 Composition of Combustion Waste Landfill Leachate ............................................................................28

12 Distribution of pH and Concentrations of Arsenic and Selenium from Field CCR

Management Facilities from the U.S. EPA Database ...............................................................................35

13 Distribution of pH and Concentrations of Arsenic, Selenium, and Mercury from Field

CCR Management Facilities ....................................................................................................................39

14 Leaching (Method SR002.1) and Mass Balance Results for the EPA-Reference Fly Ash ......................40

viii
Characterization of Coal Combustion Residues 

Glossary of Terms 

Term Definition 

ACAA American Coal Ash Association 

ACI activated carbon injection 

APC air pollution control 

APPCD Air Pollution Prevention and Control Division 

ASTM American Society for Testing and Materials 

BET Brunauer, Emmett, and Teller (method for quantification of surface area) 

B-PAC Brominated Powdered Activated Carbon (product name from Sorbent Technologies Corp, 

Twinsburg, OH) 

BPB Brayton Point baseline 

BPT Brayton Point test (with ACI) 

BML below method limit 

CAIR Clean Air Interstate Rule 

CAMR Clean Air Mercury Rule 

CCRs coal combustion residues 

CCV continuous calibration verification 

COHPAC Compact Hybrid Particulate Collector 

CS-ESP cold-side electrostatic precipitator 

CVAA cold vapor atomic adsorption 

DAFs dilution and attenuation factors 

DOE U.S. Department of Energy 

DI deionized (i.e., deionized water) 

DRC dynamic reaction chamber 

EPA U.S. Environmental Protection Agency 

EPRI Electric Power Research Institute 

ESP electrostatic precipitator 

FF fabric filter (baghouse) 

FGD flue gas desulfurization 

FID flame ionization detector 

GAB Facility C baseline 

GAT Facility C test (with ACI) 

HCl hydrogen chloride 

Hg0 elemental mercury 

Hg2+ oxidized or ionic mercury 

HS-ESP hot-side electrostatic precipitator 

ICP-MS inductively coupled plasma-mass spectroscopy 

ICV internal calibration verification 

JAB St. Clair facility baseline 

JAT St. Clair facility test (with B-PAC) 

kd CCR linear partition coefficient 

ix
Characterization of Coal Combustion Residues 

Glossary of Terms (concluded)

Term Definition 

LOI loss on ignition 

LS liquid-to-solid (LS ratio) 

MC mechanical collector 

MCL maximum concentration limit (for drinking water) 

MDL method detection limit 

ML minimum quantification limit 

NETL National Energy Technology Laboratory 

NOX nitrogen oxides 

NSPS New Source Performance Standard 

OC/EC organic carbon/elemental carbon 

ORD EPA’s Office of Research and Development 

OSW EPA’s Office of Solid Waste 

PAC powdered activated carbon 

PJFF pulse jet fabric filter 

PM particulate matter 

PPB Pleasant Prairie baseline 

PPT Pleasant Prairie test (with ACI) 

PRB sub-bituminous coal mined in Wyoming’s Powder River Basin 

QA/QC quality assurance/quality control 

RCRA Resource Conservation and Recovery Act 

RFA reference fly ash 

PS particulate scrubber 

SAB EPA’s Science Advisory Board 

SCA specific collection area 

SCR selective catalytic reduction 

SDA spray dryer absorber 

SGLP synthetic ground leaching procedure 

SHB Salem Harbor baseline 

SHT Salem Harbor test (with ACI) 

SNCR selective non-catalytic reduction 

SOX oxides of sulfur 

SPLS synthetic precipitation leaching procedure 

S/S stabilization/solidification 

SWDA Solid Waste Disposal Act 

TCLP toxicity characteristic leaching procedure 

TOXECON toxic emissions control 

WS wet scrubber 

XRF X-ray fluorescence 

x
Characterization of Coal Combustion Residues 

Acknowledgments 

Extensive input on the research program design was provided by G. Helms, U.S. EPA, Office of Solid Waste 

(Washington, DC). Additional technical support was provided by B. Ghorishi, formerly of ARCADIS, and J. 

Kilgroe, formerly of U.S. EPA, National Risk Management Research Laboratory. 

Laboratory testing described herein was carried out by ARCADIS with technical support from Vanderbilt University. R. Delapp was responsible for the chemical analyses carried out at Vanderbilt University. Technical 

assistance also was provided by A. Garrabrants and V. Laohom. 

K. Ladwig and EPRI are gratefully acknowledged for assistance in obtaining coal combustion residue samples 

and providing information from the EPRI database on coal combustion residues. 

C. Senior also is gratefully acknowledged for her assistance in obtaining coal combustion residue samples and 

related background information for this project. 

xi
Characterization of Coal Combustion Residues 

Executive Summary 

This report evaluates changes that may occur to coal-fired power plant air pollution control residues from the use 

of activated carbon and other enhanced sorbents for reducing air emissions of mercury and evaluates the potential for captured pollutants leaching during the disposal or use of these residues. Leaching of mercury, arsenic, 

and selenium during land disposal or beneficial use of coal combustion residues (CCRs) is the environmental 

impact pathway evaluated in this report. Coal combustion residues refer collectively to fly ash and other air 

pollution control solid residues generated during the combustion of coal collected through the associated air 

pollution control system. This research is part of an on-going effort by U.S. Environmental Protection Agency 

(EPA) to use a holistic approach to account for the fate of mercury and other metals in coal throughout the lifecycle stages of CCR management. 

The specific objectives of the research reported here are to: 

1. Evaluate the potential for leaching to groundwater of mercury, arsenic, and selenium removed from coalfired power plant air emissions by air pollution control technology and, as a result, are contained in CCRs; 

2. Provide the foundation for assessing the impact of enhanced mercury and multi-pollutant control technology on leaching of mercury and other constituents of potential concern from CCRs during the lifecycle of 

CCR management, including storage, beneficial use, and disposal; and 

3. Perform these assessments using the most appropriate evaluation methods currently available. This involved use of a laboratory leach testing approach developed by Kosson, et al. (2002), which considers the 

effects of varying environmental conditions on waste constituent leaching. Effective use of this approach 

required technology transfer to the U.S. EPA National Risk Management Laboratory, and development of 

a quality assurance/quality control (QA/QC) framework to help evaluate and verify test results. 

Air pollution control residues were obtained from coal combustion electric utility facilities with a representative 

range of facility configurations (including air pollution controls) and coal types combusted. Each of the residues 

sampled has been analyzed for selected physical properties, and for total content and leaching characteristics. 

Results of laboratory leaching tests were used to develop estimates of constituent release under field management scenarios. Laboratory leaching test results also were compared to field observations of leaching. 

This report focuses on facilities that use injected sorbents for mercury control. It includes four facilities with 

activated carbon injection (ACI) and two facilities using brominated ACI. Fly ash has been obtained from each 

facility with and without operation of the sorbent injection technology for mercury control. Each fly ash sampled 

was evaluated in the laboratory for leaching as a function of pH and liquid-to-solid ratio. Mercury, arsenic and 

selenium were the primary constituents of interest; results for these elements are presented here. 

This testing approach was chosen for use because it evaluates leaching over a range of values for two key 

variables (pH and liquid:solid ratio) that both vary in the environment and affect the rate of constituent release 

from waste. The range of values used in the laboratory testing encompasses the range of values expected to be 

found in the environment for these parameters. Because the effect of these variables on leaching is evaluated in 

the laboratory, prediction of leaching from the waste in the field is expected to be done with much greater 

reliability. 

xii
Characterization of Coal Combustion Residues 

Application of this leach testing approach to mercury leaching involved an extensive QA/QC program. This 

included conducting a mass balance of mercury and other metals using a reference fly ash to ensure that unacceptable losses of mercury in lab equipment or glassware or due to volatilization did not occur. If mercury was 

not found to be leaching, it was critical to ensure that this result was real and not due to mercury losses during 

handing or processing of the samples. 

In addition, results from laboratory leaching evaluation were compared to field leachate concentrations from 

CCR management facilities available from a U.S. EPA database and an Electric Power Research Institute (EPRI) 

database to determine if laboratory testing results reasonably represented field observations. 

Constituent release estimates projected to occur over a 100 year period were developed to evaluate the potential 

cumulative impacts of different CCR management scenarios. Disposal in a combustion waste landfill was examined using Monte Carlo simulation based on reported field conditions and for three hypothetical default landfill 

scenarios. 

Summary of Conclusions 

Assessment of CCRs with and without Use of Activated Carbon Injection and Brominated Carbon Injection. 

Analysis has been completed for CCRs from four coal combustion facilities using powdered activated carbon 

injection and from two facilities using brominated powdered activated carbon injection to control mercury emissions. For each facility, the evaluation included assessments of CCRs generated both with and without use of the 

activated carbon injection. None of these facilities had scrubbers as part of their air pollution control technology. 

The following conclusions are drawn for this class of facilities: 

• Application of activated carbon injection substantially increased the total mercury content in the resulting 

CCRs for five of the six facilities evaluated. Substantially increased arsenic and selenium content in the 

CCRs was observed at the one facility that employed compact hybrid particulate collector (COHPAC1

) 

fabric filter particulate control technology. This may have resulted from additional arsenic and selenium 

adsorption onto the CCR while retained in the fabric filters. Significant increase in the selenium content of 

one additional facility was noted. 

• Mercury is strongly retained by the CCR and unlikely to be leached at levels of environmental concern. 

Leaching that did occur did not depend on total mercury content in the CCR, leaching pH, or liquid to solid 

ratio, and mercury concentrations in laboratory extracts appeared to be controlled by non-linear adsorption equilibrium. Laboratory extract concentrations ranged from less than the minimul detection level 

(0.01 μg/L) to 0.2 μg/L. 

• Arsenic and selenium may be leached at levels of potential concern from CCRs generated at some facilities both with and without enhanced mercury control technology. Further evaluation of leaching of arsenic 

and selenium from CCRs that considers site specific conditions is warranted. 

• Leachate concentrations and the potential release of mercury, arsenic and selenium do not correlate with 

total content. For many cases, leachate concentrations observed are a function of final pH over the range of 

field conditions, and the observed leaching behavior implies that solubility in the leachate or aqueous 

extract controls observed liquid concentration rather than linear adsorption equilibrium. For these cases, 

use of linear partition coefficients (Kd

) in modeling leaching phenomena does not reflect the underlying 

processes. In addition, for many cases, the amount of mercury, arsenic, and selenium estimated to be 

released over a 100 year interval is a small fraction (< 0.1% – 5%) of the total content. For selenium, 

release from less than 5% up to the total content of selenium can be anticipated over the 100 year period. 

1

 For the COHPAC air pollution control configuration, combustion gasses pass through an electrostatic precipitator; then 

activated carbon is injected into the gas stream before it passes through a fabric filter for particulate collection. 

xiii
Characterization of Coal Combustion Residues 

Therefore, it is not recommended to base landfill management decisions on total content of constituents in 

CCRs since total content does not consistently relate to quantity released. 

• Results of this assessment also suggest management conditions (e.g., by control of infiltration and pH) 

that may result in reduction releases of arsenic and selenium by as much as two orders of magnitude in 

comparison to upper bound estimated releases. 

• Use of the leaching framework facilitated understanding the variations in anticipated leaching behavior 

under the anticipated field landfill disposal conditions, including expected ranges of constituent concentrations in leachate and cumulative release over a defined time interval. In addition, insights into the 

mechanisms controlling constituent leaching were obtained. This depth of understanding would not have 

been possible using leaching tests focused on a single extraction condition (e.g., toxicity characteristic 

leaching procedure, synthetic precipitation leaching procedure, or synthetic groundwater leaching procedure). 

• This study provides baseline data which allows using a reduced set of laboratory testing conditions as a 

screening leaching assessment for CCRs from coal combustion facilities employing similar air pollution 

control technology. For mercury, extraction only at the material’s natural pH at a liquid-to-solid ratio (LS) 

of 10 is adequate. For arsenic, extraction at four conditions is warranted to define the range of expected 

leachate concentrations and release: (i) pH 5.5–6.0 at LS=10, (ii) pH 7.5–8.5 at LS=10, (iii) pH 12.0–12.5 

at LS=10 and (iv) natural pH at LS=2. For selenium, either the total content or the same conditions as 

recommended for arsenic can be used. At least duplicate extractions should be used. Results from this 

more limited testing can be evaluated in comparison with the results presented in this report to determine 

if more extensive evaluation is warranted. 

Implementation of Leaching Test Methods 

The leaching assessment approach published by Kosson et al. (2002) and implemented in this report was selected because, after internal EPA review (Office of Research and Development, Office of Solid Waste) and 

consultation with the Environmental Engineering committee of the EPA Science Advisory Board, it was considered the only available, peer reviewed, and published approach that allowed consideration of the range of potential field management scenarios expected for CCRs and provided a fundamental foundation for extrapolation of 

laboratory testing to field scenarios. Additional development and validation of the leaching assessment approach 

through this project provides the following conclusions: 

• Laboratory leaching test results were consistent with observations of ranges of field leachate pH and 

mercury, arsenic, and selenium concentrations. Thus, the leaching test methods employed in this study 

provide an appropriate basis for evaluating leaching under the range of anticipated field management 

scenarios. 

• Leaching test methods SR002.1 (Solubility and Release as a Function of pH) and SR003.1 (Solubility and 

Release as a Function of LS ratio) have been successfully implemented at the EPA National Risk Management Research Laboratory. The use of these methods is now considered near routine methodology for the 

laboratory. 

• QA/QC methodology conforming with EPA Category 3 requirements has been developed and demonstrated for the leaching test methods SR002.1 and SR003.1. 

• Further efficiency in implementation of the QA/QC methodology may be obtained, based on the results 

from testing the initial set of CCRs, by reducing the number of replicates and control analyses required 

under the initial QA/QC plan. These improved project efficiencies are being implemented for evaluation 

of additional CCRs under this project. 

• A mass balance around the laboratory leaching test procedures has been completed for mercury and selected metals of potential concern. These results indicate that recoveries were between 60% and 91% for 

mercury during the leaching tests and subsequent analytical procedures, which is within the uncertainty 

resulting from heterogeneity within the CCR. Additional mass balance verification may be warranted if 

future samples have significantly different characteristics that may result in greater volatility of the constituents of interest than in the reference sample evaluated. 

xiv
Characterization of Coal Combustion Residues 

This is the first of a series of reports that will address the potential for leaching of constituents of potential 

concern from CCRs. Subsequent reports will address: 

• CCRs from coal-fired power plants that use SO2 scrubbers as a part of their air pollution control technology 

• CCRs from coal-fired power plants that use air pollution control technologies other than evaluated in 

earlier reports necessary to span the range of coal-types and air pollution configurations. 

• Assessment of leaching for constituents of potential concern under additional management scenarios, 

including impoundments and beneficial use. 

• Broader correlation of CCR leaching characteristics to coal type, combustion facility characteristics and 

geochemical speciation within CCRs supported by information and analysis on additional trace elements 

and primary constituents. 

xv
Characterization of Coal Combustion Residues 

xvi
Characterization of Coal Combustion Residues 

1. Introduction 

Congress has directed EPA to document that the Clean Air 

Act regulations are not trading one environmental burden 

for another. The Air Pollution Prevention and Control Division (APPCD) of EPA’s Office of Research and Development (ORD) is conducting the research to help identify 

any potential leaching with unacceptable impacts resulting from land disposal or beneficial use of mercury-enriched CCRs. The research results presented in this report 

are part of that effort. 

The focus of this report is to present an evaluation of 

changes to air pollution control residues that may result 

from the use of sorbent injection as enhanced mercury control technology at coal-fired power plants and to document 

the potential for transfer of pollutants from the resulting 

residues to water resources or other environmental systems 

(e.g., soils, sediments). The residues studied for this report 

were fly ashes generated using activated carbon and other 

enhanced sorbents for reducing air emissions of mercury 

from the power plants and fly ashes from the same power 

plants without use of sorbent injection. The potential for 

leaching of mercury and other constituents of potential 

concern during land disposal or beneficial use of the coal 

combustion residues (CCRs) is the more narrow focus of 

this assessment. This research is part of an on-going effort 

by EPA to use a holistic approach to account for the fate of 

mercury and other metals in coal throughout the life-cycle 

stages of CCR management. 

CCRs include bottom ash, boiler slag, fly ash, scrubber 

sludge, and other miscellaneous solids generated during 

the combustion of coal. The boiler slag and bottom ash are 

not of interest in this study because enhanced mercury 

emission controls will not change their composition. Fly 

ash characteristics are expected to change from implementation of enhanced mercury emission controls. Fly ash includes unburned and inorganic materials in coal that do 

not burn, such as oxides of silicon, aluminum, iron, and 

calcium. Fly ash is light enough to be entrained in the flue 

gas stream and captured in the air pollution control equipment. Scrubber sludge is the by-product of the SO2 wet 

scrubbing process resulting from neutralization of acid 

gases. Air pollution control can concentrate or partition 

metals to fly ash and scrubber sludge. 

When coal is burned in an electric utility boiler, the resulting high combustion temperatures vaporize the Hg in the 

coal to form gaseous elemental mercury (Hg0). Subsequent 

cooling of the combustion gases and interaction of the gaseous Hg0

 with other combustion products result in a portion of the Hg being converted to gaseous oxidized forms 

of mercury (Hg2+) and particle-bound mercury. The specific chemical form—known as the speciation—has a 

strong impact on the capture of mercury and other metals 

by boiler air pollution control (APC) equipment. 

Sorbents, typically finely ground powdered activated carbon, can be used to capture mercury. The sorbent is typically injected upstream of the particulate control device, 

where both the sorbent and adsorbed mercury are collected. 

Depending upon the type of sorbent, gas conditioning, and 

other air pollution control technology in use, there may be 

changes occurring to the fly ash that may affect the stability and mobility of mercury and other metals in the CCRs. 

In response to increasingly stricter requirements to reduce 

air emissions of mercury and other pollutants from coalfired power plants, additional advanced air pollution control technology is being introduced. Activated carbon injection (ACI) or brominated powdered activated carbon 

injection (B-PAC) are two technologies being considered 

for widespread use. This research is evaluating changes to 

air pollution control residues as a result of these technologies, and the impacts of land disposal or commercial use 

of the residues. 

The specific objectives of the research reported here are 

to: 

1 Evaluate the potential for leaching to groundwater of 

mercury, arsenic, and selenium removed from coal1
Characterization of Coal Combustion Residues 

fired power plant air emissions by air pollution control technology and, as a result, contained in CCRs; 

2 Provide the foundation for assessing the impact of enhanced mercury and multi-pollutant control technology on leaching of mercury and other constituents of 

potential concern from CCRs during the lifecycle of 

CCR management, including storage, beneficial use 

and disposal; and 

3 Perform these assessments using the most appropriate 

evaluation methods currently available. This has involved use of a laboratory leach testing approach developed by Kosson, et al. (2002), which considers the 

effects of varying environmental conditions on waste 

constituent leaching. Effective use of this approach 

required technology transfer to the U.S. EPA National 

Risk Management Laboratory and development of a 

quality assurance/quality control (QA/QC) framework 

to help evaluate and verify test results. 

The approach to satisfying these objectives was to obtain 

samples of air pollution control residues from a variety of 

coal-fired power plants, each under operating conditions 

with and without use of enhanced mercury control technology. 

This report focuses on facilities that employ electrostatic 

precipitators (ESPs) but do not have SO2 scrubbers for air 

pollution control. Enhanced mercury control technology 

consisted of activated carbon injection for four facilities 

(Brayton Point, Pleasant Prairie, Salem Harbor, and Facility C1

) and injection of brominated activated carbon for 

two facilities (St. Clair and Facility L1). This is the first of 

a series of reports that will address the potential for crossmedia transfer of constituents of potential concern from 

CCRs. Subsequent reports will address: 

• CCRs from coal-fired power plants that use scrubbers 

as a part of their air pollution control technology (report 2); 

• CCRs from coal-fired power plants that use air pollution control technologies other than evaluated in earlier reports necessary to span the range of coal-types 

and air pollution configurations (report 3); 

• Assessment of leaching for constituents of potential 

concern under additional management scenarios, including impoundments and beneficial use on the land 

(report 4); and, 

• Broader correlation of CCR leaching characteristics 

to coal type, combustion facility characteristics and 

geochemical speciation within CCRs supported by in1 These facilities have requested to remain anonymous. 

formation and analysis on additional trace elements 

and primary constituents (report 4). 

Table 1 provides a summary of facilities sampled to date 

and indicates which of the reports will present an evaluation of which samples. 

Sampled CCRs were subjected to multiple leaching conditions according to the designated leaching assessment approach. Leaching conditions included batch equilibrium2 

extractions at acidic, neutral, and alkaline conditions at a 

liquid-to-solid ratio (LS) of 10 mL/g, and LS ratio from 

0.5 to 10 mL/g using distilled water as the leachant. The 

results of this testing are being used to evaluate the likely 

range of leaching characteristics under a variety of CCR 

management scenarios. Results of the laboratory leaching 

tests were compared to the range of observed constituent 

concentrations in field leachates reported in a U.S. EPA 

database (EPA, 2000) and an Electric Power Research Institute (EPRI) database (EPRI, 2005). A probabilistic assessment approach considered leaching estimates over the 

observed range of field pH and LS from the U.S. EPA database to develop 100 yr release estimates for constituents 

of interest from the CCRs tested. 

As part of this research program, a QA/QC plan consistent 

with EPA requirements was developed for the leaching 

assessment approach. The QA/QC methodology included 

verification of acceptable mercury retention during laboratory testing through evaluation of a mass balance around 

testing procedures. Laboratory testing for leaching assessment was carried out at the EPA National Risk Management Laboratory (Research Triangle Park, North Carolina) 

with technical assistance from Vanderbilt University. 

1.1. Regulatory Context 

1.1.1. Waste Management 

Management of coal combustion residues is subject to the 

Resource Conservation and Recovery Act (RCRA), which 

is the federal law regulating both solid and hazardous 

wastes. Subtitle C under the RCRA pertains to hazardous 

waste; other solid, non-hazardous wastes fall under Subtitle D. Subtitle C wastes are federally regulated while Subtitle D wastes are regulated primarily at the state level. The 

2

 In the context of leaching tests, the term “equilibrium” is used 

to indicate that the test method result is a reasonable approximation of chemical equilibrium conditions even though thermodynamic equilibrium may not be approached for all constituents. 

2
Characterization of Coal Combustion Residues 

original version of the RCRA did not specify whether CCRs 

were Subtitle C or D wastes. In 1980, the Solid Waste Disposal Act (SWDA) amendments to RCRA conditionally 

excluded CCRs from Subtitle C regulation pending completion of a study of CCR hazards. Since that time, CCRs 

have been regulated at the state level under Subtitle D. 

The SWDA amendments to RCRA required EPA to prepare a report to Congress identifying CCR hazards and recommending a regulatory approach for CCRs. In this report 

(EPA, 1988), EPA recommended that CCRs generated by 

electric utilities continue to be regulated under Subtitle D 

(See 58 FR 42466, August 9, 1993). 

Other residues generated at coal-fired electric utilities were 

not included in this 1993 decision. EPA conducted a follow-up study specifically aimed at low-volume, co-managed wastes3

 and issued another Report to Congress (EPA, 

1999) with a similar recommendation. In April 2000, EPA 

issued a regulatory determination exempting these wastes 

from hazardous waste regulations (See 65 FR 32214, May 

22, 2000). However, concern was expressed over the use 

of CCR as backfill for mining operations, and it was decided that this practice be regulated under a federal Subtitle D rule. It was also decided by EPA that federal regulations under Subtitle D are needed for CCR when they are 

disposed in surface impoundments and landfills. Currently, 

the Agency is in the process of developing these regulations. The results presented in this report, and subsequent 

reports, will help provide the information needed to identify the release potential of mercury and other metals that 

have been removed from stack gases into air pollution control residues, over a range of plausible management options. These data will help identify those conditions that 

will either reduce or enhance releases to the land so that 

the effects of different management conditions can be factored into any controls developed under the regulations. 

1.1.2. Air Pollution Control 

On March 10, 2005, EPA announced the Clean Air Interstate Rule (CAIR; FR 25162, May 2005), which is expected 

to increase the use of wet scrubbers and selective catalytic 

reduction (SCR) units to help reduce sulfur dioxide and 

nitrogen oxides from coal-fired power plants. On March 

15, 2005, EPA announced the Clean Air Mercury Rule 

(CAMR; FR 28606, May 2005) for reducing mercury emissions through the use of a cap and trade program. Power 

plants are the largest remaining source of anthropogenic 

3

 Co-managed wastes are low-volume wastes that are co-managed with the high-volume CCRs. 

mercury emissions in the county. When fully implemented, 

a reduction of 70% is projected to occur (from 48 tons to 

15 tons annually). 

The Clean Air Mercury Rule establishes “standards of performance” that limit mercury emissions from new— 

through new source performance standards (NSPS)—and 

existing (through emission guidelines) coal-fired power 

plants by creating a market-based cap-and-trade program 

that will reduce mercury emissions in two phases. The first 

phase caps national annual mercury emissions at 38 tons 

through co-benefit reductions achieved by controlling sulfur dioxide (SO2) and nitrogen oxides (NOX) emissions 

under CAIR. In the second phase, due in 2018, coal-fired 

power plants will be subject to a second cap, which will 

reduce emissions to 15 tons per year upon full implementation. 

Congress has directed EPA to document that the Clean Air 

Act regulations are not trading one environmental burden 

for another. The Air Pollution Prevention and Control Division (APPCD) of EPA’s Office of Research and Development (ORD) is conducting the current research to help 

identify any potential pollutant transfers resulting from land 

disposal or beneficial use of mercury-enriched CCRs. The 

research results presented in this report are part of that effort. 

In response to the evolving implementation of advanced 

air pollution control technology for coal-fired power plants, 

this research is directed towards understanding changes in 

CCR characteristics that may increase environmental burdens from land disposal of CCRs or impact CCR usage in 

commercial applications. 

1.2. Configurations of U.S. Coal Fired 

Power Plants and Multi-pollutant Control Technologies 

The approximately 450 coal-fired electricity generating 

facilities in the United States uses a range of coals and 

plant configurations. The coal type burned and facility 

design characteristics affect the effectiveness of various 

mercury control methods that are or could be used at these 

plants. The U.S. coal-fired power plants typically burn one 

of three types of fuel: (1) bituminous coal (also referred to 

as “high rank” coal), (2) subbituminous coal, and (3) and 

lignite (subbituminous coal and lignite are referred to as 

“low rank” coals). Some of the characteristics of interest 

related to the possible environmental impacts of burning 

these different coal types are given in Table 2 (EPA, 2005). 

3
Facility Coal Type APC Configuration CCR/Ash Type 

(CCR pHa

)

Report 1: ACI and B-PAC (this report) 

Brayton Point low-sulfur bituminous CS-ESPb with and without ACI Class F

(12.2, 9.5) 

Salem Harbor low-sulfur bituminous CS c -ESP with and without ACI; with SNCR /urea Class F

(11.7, 10.3) 

PRBd Pleasant Prairie subbituminous CS-ESP with and without ACI Class C

(11.2, 11.9) 

Facility C low-sulfur bituminous HS-ESPe with and without ACI; with COHPACf Class F

(11.1, 8.4) 

PRB subbituminous/ low-sulfur St. Clair butuminous blend (85:15) CS-ESP with and without B-PAC Class C/F 

(12.1, 12.2) 

g,h Facility L low-sulfur bituminous 

HS-ESP with and without B-PAC; with SOFAi 

ports "on" for NOX

j control. 

Class F

(5.8, 6.0) 

Report 2: Facilities with scrubbers 

Facility Ak low-sulfur bituminous

fabric filter, limestone wet scrubber with and

without SNCR/urea 

Class F 

(10.3, 10.5) 

Facility B low-sulfur bituminous CS-ESP, magnesium-enhanced lime scrubber;

with SCRl/ammonia 

Class F 

(10.3, 9.5) 

m Facility H high-sulfur bituminous CS-ESP, limestone wet scrubber Class F 

(8.5) 

n Facility I high-sulfur bituminous CS-ESP, limestone wet scrubber with forced

oxidation; SCR not in use when sample taken 

Class F 

(NTo) 

Facility Kp medium-sulfur bituminous CS-ESP, magnesium-enhanced lime wet 

scrubber, natural oxidation 

Class F 

(9.2) 

Report 3: Miscellaneous configurations 

Facility E (Unit 1) medium-sulfur bituminous CS-ESP SCR operating Class F 

(4.8) 

Facility E (Unit 2) medium-sulfur bituminous CS-ESP SCR off Class F 

(4.3) 

Facility E (Unit 3) low-sulfur bituminous CS-ESP SCR operating Class F 

(4.8) 

Facility E (Unit 4)q low-sulfur bituminous HS-ESP SCR operating Class F 

(NTo

) 

Facility F low-sulfur bituminous CS-ESP Class F 

(4.2) 

Facility G low-sulfur bituminous CS-ESP, SNCR operating Class F 

(4.3) 

Characterization of Coal Combustion Residues 

Table 1. List of CCRs collected to date for evaluation of under this research program. [Some facilities are identified by 

code letter only (e.g., “Facility C”) to preserve the confidentiality of the CCR source.] 

a The pH of the CCR (with and without ACI or B-PAC injection, as applicable) when mixed in distilled water at a ratio of 1g 

CCR per 10 mL water. b CS-ESP = cold-side electrostatic precipitator. 

SNCR = selective non-catalytic reduction. d PRB = Powder River Basin. e HS-ESP = hot-side electrostatic precipitator. f COHPAC = compact hybrid particulate collector. 

continued 

4

c 
Characterization of Coal Combustion Residues 

Table 1 (concluded). List of CCRs collected to date for evaluation of under this research program. [Some facilities are 

identified by code letter only (e.g., “Facility C”) to preserve the confidentiality of the CCR source.] 

g This facility has HS-ESP for particulate control. The fly ash undergoes pneumatic control. Collected fly ash with and without 

use of B-PAC. h Two samples were collected from this facility. The only difference between the two samples (Run #1 and Run #2) was the 

Run #1 sample was allowed to accumulate in the hopper for 4 hours and the Run #2 sample for 30 minutes prior to 

collection. Not enough fly ash was collected with 30 minutes of accumulation to evaluate leaching potential. Therefore, the 

sample that was allowed to accumulate in hopper from HS-ESP for about 4 hours prior to collection was used for leaching 

evaluation. A concern is that mercury may have partially desorped from fly ash prior to collection because of the high 

temperature in the collection hopper. Total mercury analyses were used to evaluate the change in mercury content for fly ash 

with and without brominated carbon injection after being collected over 4 hours and 30 minutes. i SOFA = separated overfire air. j NOX = oxides of nitrogen. k CCR samples obtained when SNCR was in use (during summer months) and not in use. l SCR = selective catalytic reduction. m For Facility H, sludge is first collected in the absorber at 12–15% solids, then goes through cyclone to achieve 50% solids, and 

finally is dewatered using a belt press to >90% solids. While on belt, gypsum is "sprayed" to remove excess soluble salts. For 

this facility, samples have been obtained of (1) prepared gypsum (which is used for wall board production) and (2) fly ash from 

the CS-ESP. n Facility I has a 500 MW tangential-fired boiler. Samples from this facility include (1) fly ash when the SCR was operating, (2) fly 

ash when SCR was not operating, and (3) raw FGD sludge when the SCR was not operating. Scrubber sludge from this 

facility is used in making gypsum for producing wallboard. The samples from this facility were gypsum and FGD sludge. There 

was not enough sludge to test for leaching, so the pH was not tested. o NT = not tested. p Facility K is an 800 MW facility with two 400 MW units (tangential fired). APC includes CS-ESP, magnesium-enhanced lime 

wet scrubber with natural oxidation. There is no SCR. Samples received from Facility K, are (1) partially dewatered FGD 

sludge, (2) fly ash sample, and (3) fly ash stabilized sludge. q Fly ash found to have low mercury and selenium content and, therefore, was not included in the leaching evaluation. 

Table 2. General Characteristics of Coals Burned in U.S. Power Plants (EPA, 2005). 

Mercury Chlorine Sulfur Ash HHVa 

Coal ppm (dry) ppm (dry) %(dry) %(dry) BTU/lb (dry) 

Range Avg Range Avg Range Avg Range Avg Range Avg 

Bituminous 0.036–0.279 0.113 48–2730 1033 0.55–4.10 1.69 5.4–27.3 11.1 8646–14014 13203 

Subbituminous 0.025–0.136 0.017 51–1143 158 0.22–1.16 0.50 4.7–26.7 8.0 8606–13168 12005 

Lignite 0.080–0.127 0.107 133–233 188 0.8–1.42 1.30 12.2–24.6 19.4 9487–10702 10028 

a HHV = higher heating value. 

1.2.1. Current Air Pollution Control Technologies 

The current combined capacity of U.S. coal-fired power 

plants is just over 300 GW and includes a wide range of 

combinations of installed air pollution control (APC) devices. 

Table 3 shows the current and projected coal-fired capacity by APC configuration. Several of the air pollution control devices described here will remove some mercury (cobenefit control) from stack gases as they perform their main 

function. Current APC devices are designed primarily to 

control particulates, oxides of sulfur (SOX), and NOX. 

Post-combustion particulate matter controls used at coalfired utility boilers in the United States can include ESPs, 

fabric filters (FF), particulate scrubbers (PS), or mechanical collectors (MC). Post-combustion SO2 controls can 

consist of a wet scrubber (WS), spray dryer adsorber (SDA), 

or duct injection. Post-combustion NOX controls can involve SCR or selective noncatalytic reduction (SNCR). 

In response to current and proposed NOX and SO2 control 

requirements, additional NOX control and flue gas desulfurization (FGD) systems are expected to be installed and 

more widely used in the future. Over half of the U.S. coalfired capacity is projected to be equipped with SCR and/or 

FGD technology by 2020. 

The mercury capture efficiency of existing ESPs and FFs 

appears to heavily depend on the partitioning of mercury 

between the particulate and vapor phases and the distribu5
Table 3. Projected Coal-Fired Capacity by APC Configuration (EPA, 2005). 

Current Capacityb 2010 Capacityc 

APC C a onfiguration (MW) (MW) 

c 2020 Capacity

(MW) 

Cold-Side ESP 111,616 75,732 48,915 

Cold-Side ESP + Wet Scrubber 41,745 34,570 33,117 

Cold-Side ESP + Wet Scrubber + ACI --- 379 379 

Cold-Side ESP + Dry Scrubber 2,515 3,161 5,403 

Cold-Side ESP + SCR 45,984 35,312 22,528 

Cold-Side ESP + SCR + Wet Scrubber 27,775 62,663 98,138 

Cold-Side ESP + SCR + Dry Scrubber --- 11,979 13,153 

Cold-Side ESP + SNCR 7,019 4,576 2,534 

Cold-Side ESP + SNCR + Wet Scrubber 317 2,830 6,088 

Fabric Filter 11,969 10,885 7,646 

Fabric Filter + Dry Scrubber 8,832 8,037 9,163 

Fabric Filter + Wet Scrubber 4,960 4,960 4,960 

Fabric Filter + Dry Scrubber +ACI --- 195 195 

Fabric Filter + SCR 2,210 2,950 1,330 

Fabric Filter + SCR + Dry Scrubber 2,002 2,601 4,422 

Fabric Filter + SCR + Wet Scrubber 805 805 2,363 

Fabric Filter + SNCR 267 267 345 

Fabric Filter + SNCR + Dry Scrubber 559 557 557 

Fabric Filter + SNCR + Wet Scrubber 932 932 1,108 

Hot-Side ESP 18,929 11,763 10,160 

Hot-Side ESP + Wet Scrubber 8,724 10,509 10,398 

Hot-Side ESP + Dry Scrubber --- 538 538 

Hot-Side ESP + SCR 5,952 3,233 1,847 

Hot-Side ESP + SCR + Wet Scrubber 688 6,864 9,912 

Hot-Side ESP + SNCR 684 1,490 1,334 

Hot-Side ESP + SNCR + Wet Scrubber 474 474 627 

Total Existing Units 304,955 298,263 297,161 

New Builds of Coal Steam Units 

Fabric Filter + SCR + Wet Scrubber --- 221 17,292 

Total All Units 304,955 298,484 314,453 a Integrated gasification combined cycle units are not included in this list. b Current capacity includes some SCR and FGD units projected to be built in 2005 and 2006. c 2010 and 2020 is capacity projected for final CAIR rule; Integrated Planning Model projects some coal retirements and some 

new coal in 2010 and 2020. 

Characterization of Coal Combustion Residues 

tion of mercury species (e.g., elemental or oxidized) in the 

vapor phase. In general, ESPs and FFs are quite efficient 

at removing mercury in the particulate phase; however, the 

overall mercury removal efficiency in these devices may 

be low if most of the mercury entering the device is in the 

vapor phase (MTI, 2001). Many factors contribute to this 

range of performance. Differences in mercury contents of 

U.S. coals result in a range of mercury concentrations in 

the flue gas from the boiler. In general, it is easier to achieve 

higher mercury percent removal with higher mercury inlet 

concentrations (MTI, 2001). The addition of NOX controls 

may improve the mercury capture efficiency of particulate 

collection devices for some cases. 

1.2.2. Enhancement of Controls for Mercury 

Removal: Sorbent Injection 

Unlike the technologies described earlier, where mercury 

removal was incidental and achieved as a co-benefit with 

removal of other pollutants, controls are under development that target mercury removal by injecting sorbent 

6
Characterization of Coal Combustion Residues 

materials into the gas stream of coal-fired boilers. Injection of dry sorbents, such as powdered activated carbon 

(PAC), has been used for control of mercury emissions from 

waste combustors and has been tested at numerous utility 

units in the United States. However, sorbent injection experience on waste combustors may not be directly transferable to coal-fired electric utility boilers due to differences in facility sizes and mercury content and speciation 

in the combustion gases. 

Figure 1 presents a coal-fired boiler with sorbent injection 

and spray cooling. Figure 2 presents a power plant with a 

hot-side ESP (HS-ESP), carbon injection, and a compact 

hybrid particle collector. Dry sorbent is typically injected 

into the ductwork upstream of a particulate matter (PM) 

control device—normally either an ESP or FF. Usually the 

sorbent is pneumatically injected as a powder, and the injection location is determined by the existing plant configuration. Another approach, designed to segregate colFigure 1. Coal-Fired Boiler with Sorbent Injection and Spray Cooling (Senior et al., 2003a). 

Figure 2. Flow Diagram for Power Plant with a Hot ESP, Carbon Injection, and a COHPAC 

(Senior et al., 2003a). 

7
Characterization of Coal Combustion Residues 

lected fly ash from collected sorbent, would be to retrofit a 

pulse-jet FF (PJFF) downstream of an existing ESP and 

inject the sorbent between the ESP and the PJFF. This type 

of particulate removal configuration is called a Compact 

Hybrid Particle Collector (COHPAC) by its manufacturer 

and, when combined with sorbent injection, is called Toxic 

Emission Control (TOXECON). The TOXECON configuration can be useful because it avoids commingling the 

larger flyash stream with mercury recovered on the injected 

sorbent. Implementation of sorbent injection for mercury 

control will likely entail either: 

• Injection of powdered sorbent upstream of the existing PM control device (ESP or FF); or 

• Injection of powdered sorbent downstream of the existing ESP and upstream of a retrofit PJFF, the 

TOXECON option; or 

• Injection of powdered sorbent between ESP fields 

(TOXECON-II approach). 

In general, factors that affect the performance of sorbent 

technology for mercury methods include: 

• Injection concentration of the sorbent measured in lb/ 

MMacf ;4 

• Flue gas conditions, including temperature and concentrations of hydrogen chloride (HCl) and sulfur trioxide (SO3); 

• The air pollution control configuration; 

• The characteristics of the sorbent; and 

• The method of injecting the sorbent. 

1.2.3. Mercury Control by Conventional PAC 

Injection 

The most widely tested sorbent for mercury control at utility boilers is PAC. 

In general, the efficacy of mercury capture using standard 

PAC increases with the amount of oxidized or ionic mercury (Hg2+) in flue gas relative to elemental mercury (Hg0

),5 

the number of active sites in the PAC,6 and lower tempera4

 Sorbent injection concentration is expressed in lb/MMacf (i.e., 

pounds of sorbent used for each million actual cubic feet of gas). 

For a 500 MW boiler, a sorbent rate of 1.0 lb/MMacf will correspond to approximately 120 lb/hour of sorbent. 

5

 Standard PAC binds mercury via physical (i.e., weak) bonds, 

which are formed more easily with Hg2+. There have been results that show a similar removal for both elemental and oxidized mercury. However, the results do not account for surface 

catalyzed oxidation of Hg0 followed by sorption on the carbon 

(EPA, 2005). 

ture. The amount of Hg2+ in flue gas is usually directly 

influenced by the amount of chlorine present in the flue 

gas, with higher chlorine content enhancing Hg2+ formation. Based on these factors, standard PAC injection appears to be generally effective for mercury capture on lowsulfur bituminous coal applications, but less effective for 

the following applications: 

• Low-rank coals with ESP (current capacity of greater 

than 150 GW; the capacity with this configuration is 

not expected to increase significantly in the future). 

Lower chlorine and higher calcium contents in coal 

lead to lower levels of chlorine in flue gas, which results in reduced oxidation of mercury and, therefore, 

lower Hg2+ in flue gas; 

• Low-rank coals with SDA and FF (current capacity of 

greater than 10 GW. These number of facilities with 

this configuration is expected to increase significantly 

in the future). Similar effect as above, except lime reagent from the SDA scavenges even more chlorine from 

flue gas; 

• High-sulfur coal (current capacity with wet FGD of 

approximately 100 GW. The number of facilities with 

this configuration is likely to increase to more than 

150 GW capacity by 2015). Relatively high levels of 

SO3 compete for active sites on PAC, which reduces 

the number of sites available for mercury. Generally, 

plants will use wet FGD and, in many cases, SCR; 

PAC injection may be needed as a trim application; 

and 

• Hot-side ESPs (current capacity of approximately 30 

GW. The number of facilities with this configuration 

is not likely to increase.). Weak (physical) bonds get 

ruptured at higher temperatures resulting in lower sorption capacity. 

1.2.4. Mercury Control by Halogenated PAC 

Injection 

Some situations, as described above, may not have adequate 

chlorine present in the flue gas for good mercury capture 

by standard PAC. Pre-halogenated PAC sorbents have been 

developed to overcome some of the limitations associated 

with PAC injection for mercury control in power plant applications (Nelson et al., 2004; Nelson, 2004). Two halogenated PAC sorbents have been tested extensively in the 

field. They are Sorbent Technologies Corp. brominatedPAC (B-PAC) and Norit America’s halogenated PAC 

(DARCO HG-LH, formerly known as E-3). 

6 These are collection of atoms/radicals such as oxygen, chlorine, 

and hydroxyls that provide binding sites. 

8
Characterization of Coal Combustion Residues 

Halogenated PACs offer several potential benefits. Relative to standard PAC, halogenated PAC use: 

• may expand the usefulness of sorbent injection to many 

situations where standard PAC may not be as effective; 

• may avoid the need for installation of downstream FF, 

thereby improving cost-effectiveness of mercury capture; 

• would, in general, be at lower injection rates, which 

potentially will lead to fewer plant impacts and a lower 

carbon content in the captured fly ash; 

• may result in somewhat better performance with lowsulfur (including low-rank) coals because of less competition from SO3; and, 

• may be a relatively inexpensive and attractive control 

technology option for technology transfer to developing countries as it does not involve the capital intensive FF installation. 

Performance of a halogenated sorbent such as B-PAC appears to be relatively consistent regardless of coal type and 

appears to be mostly determined by whether or not the capture is in-flightCas in upstream of a cold-side ESP (CSESP)Cor on a fabric filter. 

1.3. Coal Combustion Residues 

Fossil fuel combustion (burning of coal, natural gas, or 

oil) is the primary source of energy in the United States— 

providing approximately 67% of the total demand in 1997. 

Coal-fired utilities provide more than 50% of all electric 

power generated using fossil fuels (EPA, 1999). In 1994 

there were approximately 1,250 separate coal-fired boilers 

in operation at 450 different utilities throughout the United 

States (EPA, 1999). These boilers used approximately 900 

million tons of coal and produced approximately 105 million tons of high-volume coal combustion residues—fly 

ash, bottom ash, boiler slag, and FGD wastes (EPA, 1999). 

Regulations that require the reduction of mercury air emissions from coal-fired power plants will result in changes 

to coal combustion residues including increasing the concentration of mercury and other trace metals (Figure 3; EPA, 

2002). 

CCRs result from unburned carbon and inorganic materials in coal that do not burn, such as oxides of silicon, aluminum, iron, and calcium. Air pollution control can concentrate or partition metals in fly ash and scrubber sludge. 

Bottom ash and boiler slag are not affected by air pollution 

control technology, and therefore, these materials are not 

examined in this report. Bottom ash is the unburned material that is too heavy to be entrained in the flue gas stream 

Figure 3. Life-Cycle Evaluation of Coal Combustion 

Residues (EPA, 2002). 

and drops out in the furnace. Boiler slag, unburned carbon 

or inorganic material in coal that does not burn, falls to the 

bottom of the furnace and melts. 

Fly ash and scrubber sludge are the two types of CCRs of 

interest in this report. Fly ash is the unburned material from 

coal combustion that is light enough to be entrained in the 

flue gas stream, carried out of the process, and collected as 

a dry material in the air pollution control equipment. Seventy million tons of fly ash were produced in 2003. 

FGD wastes (or scrubber sludge) result from a SO2 wet 

scrubbing process and generally contain 5% to 10% solids. The quantity of FGD material produced depends on 

the sulfur content of the coal and the amount of coal being 

combusted. Thirty million tons of FGD wastes were generated in 2003. 

The properties of fly ash and scrubber residues from many 

facilities are likely to change as a result of enhanced air 

pollution controls for reducing mercury stack emissions. 

Changes in CCR properties will include increased content 

of mercury and other co-collected metals (e.g., arsenic, 

selenium) and the presence of injected sorbent or other 

chemical modifiers to improve mercury removal. In several prevalent APC configurations, the sorbent will be commingled with either fly ash or other residue streams, modifying both chemical and physical properties of the CCR. 

1.4. Residue Management Practices 

CCRs can be disposed in landfills or surface impoundments 

or used in commercial applications to produce concrete 

and gypsum wallboard, among other products. The major 

pathway of concern for release from land disposal and some 

beneficial use applications is leaching. Research on the 

impact of CCR disposal on the environment has been conducted by many researchers and has been summarized by 

9
Characterization of Coal Combustion Residues 

the EPA (1988, 1999). However, most of the existing CCR 

data are for CCRs prior to implementation of mercury or 

multi-pollutant controls. 

1.4.1. Beneficial Use 

In the United States, approximately 31% of all CCRs produced are reused in commercial applications or other beneficial uses. Thirty-two percent of fly ash is used in commercial applications such as making concrete/grout, structural fill, and highway construction (ACAA, 2000; 

Thorneloe, 2003). Six million tons of the scrubber sludge 

(or 26%) was used in making wall board (ACAA, 2000; 

Thorneloe, 2003). In Europe, use of CCRs for commercial 

applications/beneficial uses is much higher (over 50%). 

Table 4 ACCA, 2003) and Figure 4 present the primary 

commercial uses of CCRs, and a breakdown of U.S. production and usage by CCR type. The primary commercial 

applications or commercial uses of CCRs are shown. 

Some of the beneficial uses may have the potential to release mercury from the CCRs, particularly in high-temperature processes. In cement manufacturing, for example, 

CCRs are inputs to the cement kiln. It is expected that virtually all mercury will be volatilized from CCRs in this 

application. Even where mercury can be captured by the 

controls on cement kilns, approximately two-thirds of cement kiln dust captured by the control devices is reintroduced into the kiln. Therefore, a significant fraction of the 

mercury in CCRs introduced into cement kilns may be 

emitted to the air at the cement plant. Some mercury may 

also be revolatilized when CCRs are used as a filler for 

asphalt or when FGD material is used in wallboard manufacturing. A separate report will present the results from a 

study conducted to evaluate the thermal stability of mercury and other metals during application of these hightemperature processes. 

The fate of mercury and other metals is a potential concern 

when CCRs are used on the land (mine reclamation, building highways, soil amendments, agriculture and in making 

concrete, cement) or to make products that are subsequently 

disposed (e.g., disposal of wall board in unlined landfill). 

For several commercial uses, it appears less likely that 

mercury in CCRs will be reintroduced into the environment, at least during the lifetime of the product. For example, mercury appears unlikely to be volatilized from 

confined uses such as concrete, flowable fill, or structural 

fill. The potential for leaching of mercury in these applications also seems limited, in part due to the relative impermeability of concrete and flowable fill; however, special 

applications such as those involving continuous immerFigure 4. Uses of CCRs Based on 2003 Industry Statistics (ACAA, 2003). 

10
CCPa Categories Fly Ash Bottom 

Ash 

FGD 

Gypsum 

FGD 

Material 

Wet 

Scrubbers 

Boiler 

Slagb 

FGD 

Material 

Dry 

Scrubbersb 

FGD 

Otherb 

FBC

Ashb,c 

CCP Production Category Totalsd 70,150,000 18,100,000 11,900,000 17,350,000 1,836,235 1,444,273 167,345 796,718

CCP Production Total 121,744,571

CCP U e se Category Totals 27,136,524 8,247,273 8,299,060 484,412 1,756,004 197,509 0 263,623 

All CCP Used Total 46,384,405 

CCP Use by Applicationf 

Concrete/Concrete Products/Grout 12,265,169 298,181 65,693 0 15,907 34,284 0 0 

Cement/Raw Feed for Clinker 3,024,930 493,763 420,043 0 15,766 2,469 0 0 

Flowable Fill 136,618 20,327 0 0 0 9,184 0 0 

Structural Fills/Embankments 5,496,948 2,443,206 0 224,100 11,074 12,141 0 0 

Road Base/Sub-base/Pavement 493,487 1,138,101 0 0 29,800 0 0 0 

Soil Modification/Stabilization 515,552 67,998 0 704 0 114 0 188,708 

Mineral Filler in Asphalt 52,608 0 0 0 31,402 0 0 0 

Snow and Ice Control 1,928 683,556 0 0 102,700 0 0 0 

Blasting Grit/Roofing Granules 0 42,604 0 0 1,455,140 0 0 0 

Mining Applications 683,925 1,184,927 0 259,608 59,800 130,723 0 11,049 

Wallboard 0 0 7,780,906 0 0 0 0 0 

Waste Stabilization/Solidification 3,919,898 30,508 0 0 0 0 0 49,217 

Agriculture 12,140 3,534 32,518 0 0 2,295 0 0 

Aggregate 137,171 512,769 0 0 31,600 6,299 0 0 

Miscellaneous/Other 396,150 1,327,797 0 0 2,815 0 0 14,649 

CCP Category Use Totals 27,136,524 8,247,273 8,299,060 484,412 1,756,004 197,509 0 263,623 

Application Use to Production Rate 38.68% 45.57% 69.74% 2.79% 95.63% 13.68% 0.00% 33.09% 

Overall CCP Utilization Rate 38.10% 

a The American Coal Ash Association uses CCP (coal combustion products) to refer to CCRs. b As submitted based on 60% coal burn. c FBC = fluidized-bed combustion. d CCP Production totals for Fly Ash, Bottom Ash, FGD Gypsum, and Wet FGD are extrapolated estimates rounded off to the 

nearest 50,000 tons. e CCP Used totals for Fly Ash, Bottom Ash, FGD Gypsum, and Wet FGD are per extrapolation calculations (not Rounded off). f CCP Uses by application for Fly Ash, Bottom Ash, FGD Gypsum, and Wet FGD are calculated per proportioning the CCP Used 

Category Totals by the same percentage as each of the individual types' raw data contributions to the as-cubmitted raw data 

submittal total (not rounded off). 

Characterization of Coal Combustion Residues 

Table 4. Beneficial Uses of CCRs (ACAA, 2003). 

sion in water may produce different results. The impact of ments are almost always located on-site with the combusadvanced mercury emissions control technology (e.g., ACI) tion operations. Although the distribution of units is about 

on beneficial use applications is uncertain. There is con- equal between landfills and surface impoundments, there 

cern that the presence of increased concentrations of mer- is a trend toward increased use of landfills as the primary 

cury, certain other metals, or high carbon content may re- disposal method. 

duce the suitability of CCRs for use in some applications 

(e.g., in Portland cement concrete). 1.5. Leaching Protocol 

One of the major challenges facing this research was iden- 1.4.2. Land Disposal tification of an appropriate test protocol for evaluating the

There are approximately 600 land-based CCR waste dis- leaching potential of CCRs that may have increased levels

posal units (landfills or surface impoundments) being used of several metals, particularly mercury. The goal of this 

by the 450 coal-fired power plants in the United States research is to develop the most accurate estimates of likely

(EPA, 1999). About 70% of the 122 million tons of CCRs constituent leaching when CCRs are land disposed. These 

generated annually are land disposed. Landfills may be estimates of leaching need to be appropriate for assessing

located either on-site or off-site while surface impound- at a national level the likely impacts through leaching of 

11
Characterization of Coal Combustion Residues 

pollutants from CCRs that is a consequence of installing 

enhanced mercury and/or multi-pollutant controls. To 

achieve this goal requires that U.S. EPA evaluate leaching 

potential for CCRs as-managed (to the degree this is known) 

and that the leach testing results can be appropriately extrapolated to a national assessment. A large part of the approach to achieving this has been to identify and evaluate 

CCR samples collected from the most prevalent combinations of power plant design (with a focus on air pollution 

control configurations) and coal type used. U.S. EPA and 

EPRI have also examined and collected data on the actual 

disposal conditions for CCRs because these conditions will 

affect leaching and will also vary over time. When disposed, CCRs are typically monofilled or disposed with 

other CCRs. However, CCR composition can change over 

time, due to changes in the source of coal or coal type 

burned or due to installation of additional pollution control equipment, so the conditions of leaching created by 

the CCRs will also change over time. 

Many leaching tests have been developed by regulatory 

agencies, researchers, or third-party technical standards 

organizations and are described in the published literature. 

States and others have expressed concern with the variety 

of leaching protocols in use, the lack of correlation of test 

results with field conditions and actual leaching, and lack 

of comparability of available data because of incomplete 

reporting of test conditions. There is also limited or no 

quality assurance (QA) information for many of these tests. 

Leaching tests such as the toxicity characteristic leaching 

procedure (TCLP),7 which reflects municipal solid waste 

co-disposal conditions; the synthetic precipitation leaching procedure (SPLP); or any number of deionized-water 

based tests may be inappropriate or are at least not optimal 

for evaluating the leaching potential of CCRs as they are 

7 TCLP was not included as part of this study for two reasons. 

First, EPA previously made a waste status determination under 

RCRA that coal combustion residues are non-hazardous (65 FR 

32214, May 22, 2000). Therefore, use of TCLP was not required 

as indicated under the RCRA toxicity characteristic regulation 

for determination of whether or not CCRs were hazardous. Second, TCLP was developed to simulate co-disposal of industrial 

waste with municipal solid waste as a mismanagement scenario 

and to reflect conditions specific to this scenario. However, the 

vast majority of CCRs are not being managed through co-disposal with municipal solid waste, and the test conditions for 

TCLP are different from the actual management practices for 

most CCRs. In seeking a tailored, “best-estimate” of CCR leaching, the leaching framework provides the flexibility to consider 

the effects of actual management conditions on these wastes, 

and so will be more accurate in this case. 

actually managed. These tests either presume a set of prevailing landfill conditions that may or may not exist at CCR 

disposal sites (e.g., TCLP), try to account for an environmental factor considered to be important in leaching (e.g., 

SPLP), or presume that the waste tested will define the 

disposal conditions—such as deionized (DI) water tests. 

Most existing leaching tests are empirical in that results 

are presented simply as the contaminant concentrations 

leached when using the test and presented without measuring or reporting values for factors that may affect waste 

leaching or that provide insight into the chemistry that is 

occurring in leaching. Most tests are performed as a single 

batch test and so do not consider the effect of variations in 

conditions on waste constituent leaching.8 

In searching for a leach testing approach that will produce 

the most reliable results for this waste and that can be used 

to predict leaching nationally, EPA sought an approach that 

(1) considers the range of known CCR chemistry and management conditions (including re-use) and (2) permits development of data that are comparable across U.S. coal 

and CCR types. Because the data resulting from this research will be used to support regulations, careful scrutiny 

of the data is expected. Therefore, the use of a published, 

peer-reviewed protocol is also considered to be an essential element of this work. 

EPA’s Office of Research and Development (ORD) has 

worked closely with EPA’s Office of Solid Waste (OSW) 

to identify an appropriate leaching protocol for evaluating 

CCRs. The protocol that has been adopted is the “Integrated Framework for Evaluating Leaching in Waste Management and Utilization of Secondary Materials” (Kosson 

et al., 2002) and referred to here as the “Leaching Framework,” or Framework. The Leaching Framework consists 

of a tiered approach to leaching assessment. The general 

approach under the Leaching Framework is to use laboratory testing to measure intrinsic leaching characteristics of 

a material (i.e., liquid-solid equilibrium partitioning as a 

function of pH and LS ratio, mass transfer rates) and then 

use this information in conjunction with mass transfer 

models to estimate constituent release by leaching under 

specific management scenarios (e.g., landfilling). Unlike 

8

 Many factors are known or may reasonably be expected to 

affect waste constituent leaching. The solubility of many metal 

salts is well known to vary with pH; adsorption of metals to the 

waste matrix varies with pH; redox conditions may determine 

which metal salts are present in wastes; temperature may affect 

reaction rates; water infiltration can affect the leaching rate and 

also affect leaching chemistry and equilibrium. 

12
Characterization of Coal Combustion Residues 

other laboratory leaching tests, under this approach, laboratory testing is not intended to directly simulate or mimic 

field conditions. Development work to-date on the Framework has focused on assessing metals leaching, and it includes equilibrium batch testing (over a range of pH and 

LS ratio values), diffusion-controlled mass transfer, and 

percolation-controlled (column) laboratory test methods in 

conjunction with mass transfer models to estimate release 

for specific management scenarios based on testing results 

from a common set of leaching conditions. EPA’s OSW 

and ORD believe that this approach successfully addresses 

the concerns identified above because it seeks to consider 

the effect of key disposal conditions on constituent leaching and to understand the leaching chemistry of wastes 

tested. 

The following attributes of the Leaching Framework were 

considered as part of the selection process: 

• It will permit development of data that are comparable 

across U.S. coal and CCR types; 

• It will permit comparison with existing laboratory and 

field leaching data on CCRs; 

• It was published in the peer-reviewed scientific literature; 

• On consultation with EPA’s OSW, it was recommended 

as the appropriate protocol based on review of the range 

of available test methods and assessment approaches; 

and 

• On consultation with the Environmental Engineering 

Committee of the Science Advisory Board (June 2003), 

the Committee considered the Leaching Framework 

to be responsive to earlier SAB criticisms of EPA’s 

approach to leaching evaluation and to be broadly applicable and appropriate for this study. The complete 

summary of the SAB consultation is provided as Appendix A. 

For this study, the primary leaching tests used from the 

Leaching Framework were Solubility and Release as a 

Function of pH (SR002.1) and Solubility and Release as a 

Function of the Liquid-Solid Ratio (LS) (SR003.1).9

 These 

tests represent equilibrium-based leaching characterization. 

9

 LS refers to liquid to solid ratio (mL water/g CCR or L water/ 

kg CCR) occurring during laboratory leaching tests or under 

field conditions. SR002.1 is carried out at LS=10 with several 

parallel batch extractions over a range of pH, while SR003.1 is 

carried out using several parallel batch extractions with deionized water at LS= 0.5, 1, 2, 5 and 10. Under field conditions, LS 

refers to the cumulative amount of water passing through the 

total mass of CCR subject to leaching. 

The range of pH and LS ratio used in the leaching tests 

includes the range of conditions (pH and LS ratio) observed 

for current CCR management practices. Results of these 

tests provide insights into the physical-chemical mechanisms controlling constituent leaching. When used in conjunction with mass transfer and geochemical speciation 

modeling, the results can provide conservative but realistic estimates of constituent leaching under a variety of environmental conditions (pH, redox, salinity, carbonation) 

and management scenarios. 

Laboratory testing for leaching assessment was carried out 

at the U.S. EPA National Risk Management Laboratory 

(Research Triangle Park, NC) with technical assistance 

from Vanderbilt University. 

13
Characterization of Coal Combustion Residues 

14
Characterization of Coal Combustion Residues 

2. Materials and Methods 

2.1. CCR Materials for Evaluation 

The CCR materials tested in this study include a reference 

fly ash and fly ashes collected by ADA-Environmental 

Solutions from designated coal combustion facilities under contract for the Department of Energy’s National Energy Technology Laboratory (NETL) field evaluation program of sorbent injection upstream of existing particulate 

control devices. This program represents the first time that 

PAC has been injected on a large scale for a period of several weeks as enhanced mercury control technology. All 

six of the facilities evaluated in this report burn either lowsulfur bituminous coal (Brayton Point, Salem Harbor, Facility C, Facility L), sub-bituminous coal (Pleasant Prairie) or a sub-bituminous/low-sulfur bituminous coal blend 

(St. Clair) and have particulate control devices only (no 

SO2 scrubbers). This facility configuration is representative of 75% of the coal-fired utilities in the U.S. The same 

commercial sorbent (Norit Americas FGD Carbon )10 was 

used for all of the tests using ACI. This sorbent has a surface area of approximately 600 m2

/g and a mass-mean diameter of 18 μm. The tests using B-PAC used sorbent obtained from Sorbent Technologies Corp., with a surface 

area of 700 to 1070 m2/g and a mass-mean diameter of 19 

μm. Samples of fly ash were collected from each facility 

under conditions with the enhanced mercury control technology turned off and in use. 

The facilities and associated CCRs reported here are described below. Appendix B provides a schematic flow diagram for each facility. Table 5 provides characteristics of 

the low-sulfur bituminous coal combusted at Brayton Point, 

Salem Harbor, Facility C and Facility L, the sub-bituminous coal combusted at Pleasant Prairie and the sub-bituminous/low-sulfur bituminous coal blend combusted at St. 

Clair. Elemental composition by x-ray fluorescence and 

additional characteristics of the fly ashes from baseline 

10 DARCO FGD carbon is currently sold under the trade name 

DARCO-HG. 

testing and testing with enhanced mercury control are provided in Table 6 and Table 7. For samples from Salem 

Harbor, the loss on ignition (LOI) is more than twice the 

total carbon content because of a relatively high fraction 

of uncombusted particulate in the CCR. Total content analyses for mercury, arsenic, cadmium, lead and selenium results are provided in Table 8. 

2.1.1. Reference Fly Ash 

The reference fly ash was obtained from the EPA, National 

Risk Management Research Laboratory (Research Triangle 

Park, NC). X-Ray Fluorescence (XRF) analysis shown in 

Table 6 is typical of a Class F fly ash from an eastern bituminous coal. This fly ash was selected for this program 

because it was available in large quantities (approximately 

two 55-gallon drums) and it contained low mercury levels. 

The large quantity allows for inter-laboratory comparisons 

at a later date. The low mercury content was important to 

test the laboratories’ ability to close the mercury mass-balance around the leaching and thermal desorption studies 

in the limit case of very low mercury content. 

2.1.2. Facilities Using Injection of Standard 

Activated Carbon 

2.1.2.1. Brayton Point 

Brayton Point Station (Somerset, MA) is operated by 

PG&E National Energy Group. This facility is composed 

of four fossil fuel fired units designated as Units 1, 2, 3, 

and 4. The test unit selected, unit 1, has a tangentially fired 

boiler rated at 245 MW. Brayton Point Unit 1 was chosen 

for this evaluation because of its combination of firing lowsulfur bituminous coal with a cold-side ESP. This configuration represents a wide range of coal-fired power plants 

located in the eastern U.S. (Senior et al., 2003a). 

The primary particulate control equipment consists of two 

CS-ESPs in series, with an EPRICON flue gas conditioning system that provides SO3 for fly ash resistivity control. 

15
Reference Brayton Point Pleasant Prairie Salem Harbor Facility C 

Element Fly 

(Average%) 

(Average%)

a (Average%) (Average%) (Average%) 

Baseline with ACI Baseline with ACI Baseline with ACI Baseline with ACI 

Al 14.700 13.430 12.400 10.050 10.220 9.523 7.623 12.25 8.96 

As 0.010 BMLb BML BML BML BML BML BML BML 

Ba 0.110 0.010 0.095 0.695 0.647 0.091 0.099 0.206 0.148 

Br BML 0.005 0.065 BML BML BML BML 0.0025 0.0097 

Ca 0.860 6.080 2.030 18.430 16.640 1.298 0.803 2.07 1.92 

Cl 0.026 0.030 0.440 BML .0.045 0.101 0.203 0.0373 0.0790 

Cr 0.017 0.022 0.018 0.016 0.013 0.011 0.012 0.0177 0.0134 

Cu 0.018 0.022 0.020 0.022 0.022 0.007 0.008 0.0247 0.0179 

Fe 5.110 4.650 2.500 4.310 4.280 4.870 3.630 7.43 5.90 

I BML BML 0.014 BML BML BML BML BML BML 

K 2.460 1.853 1.500 0.371 0.455 1.250 0.977 1.84 1.34 

Mg 0.637 0.800 0.641 2.810 2.460 1.785 0.420 1.679 0.586 

Mn 0.015 0.041 0.020 0.057 0.020 0.045 0.021 0.0196 0.0179 

Parameter 

Brayton 

Point 

Pleasant 

Prairie 

Salem 

Harbor 

Facility C St. Clair Facility L 

Coal Low-sulfur 

Bituminous 

(2002)

a 

PRBb Sub

bituminous

(2002) 

Low-sulfur 

Bituminous 

(2002) 

Low-sulfur 

Bituminous 

PRB Subbitu

minous/Low-sulfur 

Bituminous 

(85:15) Blend 

Low-sulfur 

bituminous 

Sulfur, wt% 0.7 0.3 0.67 1.24 NTc NT 

Ash, wt% 10.8 5.1 6.48 14.78 NT NT 

Moisture, wt 4.7 30.7 9.05 6.85 NT NT 

HHVd , Btu/lb 12,780 8,385 12,420 11,902 NT NT 

Hg, :g/g 0.044 0.109 0.0617 0.136 NT NT 

Cl, :g/g 1475 8.1 64.3 169 NT NT 

As, :g/g 5.68 NT 2.4 NT NT NT 

Cd, :g/g 0.055 NT 0.14 NT NT NT 

Pb, :g/g 8.9 NT 3.8 NT NT NT 

Se, :g/g 3 NT 4.8 NT NT NT 

Particulate 

Control Device 

2 CS-ESPs 

in series CS-ESP CS-ESP HS-ESP + COHPAC CS-ESP HS-ESP 

Sorbent 

Injection Point 

Between the 

2 ESPs 

Before ESP Before ESP Between HS-ESP 

and COHPAC 

Before South 

Side ESP 

Before B-Side

ESP 

SOX and NOX 

Control NAe NA SNCR NA NA Separated Overfire Air Ports 

Sampling 

Location 

Ash Hopper 

Row C 

ESP Hopper 1 

and 2 Composite 

ESP Hopper 

A B-Side Hopper 

North and South 

side Hoppers 

A- and B-side 

Hoppers a Year over which coal sampled to obtain average values. b PRB = Powder River Basin. c NT = not tested. d HHV = higher heating value. e NA = not applicable.

Characterization of Coal Combustion Residues 

Table 5. Characteristics of Coal Combusted and Facilities Sampled and Reported Here (Senior et al., 2003a, Senior et 

al., 2003b, Senior et al., 2004). 

­ ­

Table 6. Fly Ashes from Brayton Point, Pleasant Prairie, Salem Harbor, and Facility C: Elemental Composition (by x-ray 

fluorescence) and Other Characteristics. 

continued 

16
Reference Brayton Point Pleasant Prairie Salem Harbor Facility C 

Element Fly (Average%)a (Average%) (Average%) (Average%) 

(Average%) Baseline with ACI Baseline with ACI Baseline with ACI Baseline with ACI 

Reference St. Clair Facility C 

Element Fly 

(Average%) 

(Average%)

a (Average%) 

Baseline with BPAC Baseline with BPAC 

Al 14.700 10.63 10.16 13.19 13.15 

As 0.010 BMLb BML BML BML 

Ba 0.110 1.20 1.01 0.0652 0.0632 

Br BML BML 0.0962 BML 0.0061 

Ca 0.860 12.06 11.35 0.328 0.319 

Cl 0.026 0.0156 0.0412 0.0389 0.0339 

Cr 0.017 0.0116 0.0109 0.0147 0.0147 

Cu 0.018 0.0170 0.0148 0.0100 0.0093 

Fe 5.110 5.35 5.52 2.39 2.36 

I BML BML 0.014 BML BML 

K 2.460 0.794 0.768 2.27 2.22 

Characterization of Coal Combustion Residues 

Table 6 (concluded). Fly Ashes from Brayton Point, Pleasant Prairie, Salem Harbor, and Facility C: Elemental Composition 

(by x-ray fluorescence) and Other Characteristics. 

Na 0.346 0.511 0.242 1.660 1.310 0.270 0.293 0.374 0.287 

Ni 0.011 0.015 0.016 0.006 0.006 0.009 0.009 0.0173 0.0149 

Pb 0.008 BML 0.010 BML BML 0.005 BML 0.0066 0.0037 

pX 

c 0.087 0.161 0.042 0.056 0.508 0.086 0.057 0.303 0.184 

Se BML 0.005 0.020 BML BML 0.005 0.005 0.0157 0.0487 

Si 26.400 23.080 23.240 16.600 16.250 21.898 23.468 17.48 12.92 

Sr 0.089 0.124 0.083 0.369 0.341 0.042 0.032 0.143 0.104 

Sd BML BML BML BML BML BML BML BML BML 

SX 

e 0.174 0.351 0.582 0.635 0.971 0.335 0.761 0.544 1.18 

Ti 0.897 1.015 0.100 0.964 0.943 0.453 0.407 0.709 0.574 

V 0.031 0.043 0..32 0.030 0.033 0.029 0.030 0.0411 0.0322 

Zn 0.023 0.021 0.011 0.009 0.010 0.013 0.013 0.0139 0.0105 

Zr 0.050 0.031 0.031 0.035 0.035 0.019 0.019 0.0245 0.0202 

Physical Parameters 

Total 

Carbon 0.76 2.3 13 0.25 3.6 7.8 11 10.9 24.44 

Surface 

Areaf 1.36 6.5 92 1.8 23 28 36 14.10 36.55 

(m2/g) 

LOI (wt%) 0.85 5.5 12 0.60 3.5 21 25 18.0 36.26 a Unless otherwise noted. b BML = below method limit (As<0.009%, I<0.006%, Pb<0.003%, Se<0.003%). c PX = phosphorus in oxidized form such as phosphate. d S = sulfur in elemental form. e SX = sulfur in oxidized form such as sulfate. f Brunauer, Emmett, and Teller method for quantifying surface area. 

Table 7. Fly Ashes from St. Clair and Facility L: Elemental Composition (by x-ray fluorescence) and Other Characteristics. 

continued 

17
Table 7 (concluded). Fly Ashes from St. Clair and Facility L: Elemental Composition (by x-ray fluorescence) and Other 

Characteristics. 

Reference St. Clair Facility C a Element Fly (Average%) (Average%) 

(Average%) Baseline with BPAC Baseline with BPAC 

Sample ID Mercury 

(ng/g) 

Mercury

(thermal) 

(ng/g) 

Arsenic 

(:g/g) 

Cadmium 

(:g/g) 

Lead 

(:g/g) 

Selenium 

(:g/g) 

Brayton Point Baseline 650.6!6.8 582.2!2.1 80.5!1.9 BMLa 117.3!4.9 51.4!1.7 

Brayton Point with ACI 1529.6!1.1 1414.1!43.7 27.9!2.1 BML 82.9!2.3 151.9!6.2 

Pleasant Prairie Baseline 157.7!0.2 146.9!3.9 21.3!0.3 BML 41.6!0.8 BML 

Pleasant Prairie with ACI 1180!1.2 1176.8!16.4 24.0!0.8 BML 47.0!0.3 BML 

Salem Harbor Baseline 528.5!5.3 573.8!8.7 25.9!0.0 NTb 24.9!1.4 41.9!0.1 

Salem Harbor with ACI 411.5!12.6 454.0!12.1 26.0!0.0 NT 24.0!0.0 44.0!0.0 

Facility C Baseline 15.8!0.9 10.5!0.7 93.6!5.5 NT 55.8!0.7 BML 

Facility C with ACI 1150.7!14 1090.1!24.1 506.3!28.7 NT 114.4!5.8 206.3!0.9 

Characterization of Coal Combustion Residues 

Mg 0.637 3.07 2.92 0.584 0.580 

Mn 0.015 0.0350 0.0314 0.0088 0.0085 

Na 0.346 4.66 4.09 0.134 0.132 

Ni 0.011 0.0074 0.0064 0.0109 0.0109 

Pb 0.008 0.0045 0.0040 0.0046 0.0046 

pX 

c 0.087 0.219 0.169 0.0262 0.0240 

Se BML BML 0.0024 BML BML 

Si 26.400 16.65 17.00 24.75 24.8 

Sr 0.089 0.565 0.517 0.0322 0.0322 

Sd BML BML BML BML BML 

SX 

e 0.174 1.23 1.03 BML BML 

Ti 0.897 0.759 0.713 0.882 0.878 

V 0.031 0.0292 0.0257 0.0232 0.0233 

Zn 0.023 0.0104 0.0077 0.0075 0.0065 

Zr 0.050 0.0274 0.0283 0.0284 0.0277 

Physical Parameters 

Total 

Carbon 0.76 0.16 2.65 5.56 5.92 

Surface 

Areaf 1.36 2.50 24.86 8.23 27.01 

(m2/g) 

LOI (wt%) 0.85 0.41 3.19 12.28 12.38 a Unless otherwise noted. b BML = below method limit (As<0.009%, I<0.006%, Pb<0.003%,

Se<0.003%). c PX = phosphorus in oxidized form such as phosphate. d S = sulfur in elemental form. e SX = sulfur in oxidized form such as sulfate. f Brunauer, Emmett, and Teller method for quantifying surface area.

Table 8. CCRs from Facilities with Electrostatic Precipitators: Total Content of Mercury, Arsenic, Cadmium, Lead and 

Selenium. [All analyses are according to EPA Method 3052, except for mercury (thermal), which is by EPA Method 7473 

(EPA, 1998b)]. 

continued 

18
St. Clair Baseline 110.9!5.8 NT 43.4!2.6 1.4!0.1 46.3!17.9 10.7!0.1 

St. Clair with B-PAC 1163.0!8.9 NT 40.8!1.1 1.3!0.1 34.9!1.7 12.6!0.9 c Facility L (Run 1) Baseline 13.0!0.2 NT 20.0!1.1 0.4!0.0 44.8!0.7 4.1!0.1 c Facility L (Run 1) with B-PAC 37.7!1.3 NT 18.7!0.7 0.3!0.0 42.2!0.3 4.3!0.2 

Facility L (Run 2) Baselined 20.3!0.14 NT 44.4!1.1 0.6!0.1 60.2!3.8 3.0!0.3 

Facility L (Run 2) with B-PACd 71.4!0.03 NT 44.3!1.4 0.9!0.2 63.0!2.8 4.3!0.0 

MDL 0.2 ng/g 0.145 ng/g 1.12 1.0 0.18 0.72 

Minimum Quantification Limit 0.72 ng/g 1.0 ng/g 4.0 10.0 0.6 4.0 a BML = below method limit. b NT = not tested. c Pneumatic controls were turned off for 4 hr to collect fly ash. d Pneumatic controls were turned off for 30 min to collect fly ash. Not tested for leaching. 

Characterization of Coal Combustion Residues 

Table 8 (concluded). CCRs from Facilities with Electrostatic Precipitators:Total Content of Mercury, Arsenic, Cadmium, 

Lead, and Selenium. [All analyses are according to EPA Method 3052, except for mercury (thermal), which is by EPA 

Method 7473 (EPA, 1998b)]. 

Sample ID M

(

e

n

r

g

c

/

u

g

r

)

y (

M

th

e

e

r

r

c

m

ur

a

y

l) A

(

r

:

s

g

e

/

n

g

i

)

c Ca

(:

d

g

m

/g

iu

)

m 

(

L

:

e

g

a

/g

d

) 

Se

(:

le

g

n

/g

iu

)

m 

(ng/g) 

The EPRICON system is not used continuously, but on an 

as-needed basis. The first ESP (“Old ESP”) in this particular configuration was designed and manufactured by 

Koppers. The Koppers ESP has a weighted wire design 

and a specific collection area (SCA) of 156 ft2/1000 acfm. 

The second ESP (“New ESP”) in the series configuration 

was designed and manufactured by Research-Cottrell. The 

second ESP has a rigid electrode design and an SCA of 

403 ft2/1000 acfm. Total SCA for the unit is 559 ft2/1000 

acfm. The precipitator inlet gas temperature is nominally 

280 EF at full load (Senior et al., 2003a). 

Hopper ash is combined between both precipitators in the 

dry ash-pull system. The ash is processed by an on-site 

Separation Technology Inc. (STI) carbon separation system, to reduce the carbon content. This processed ash is 

sold as base for concrete and the remainder of the higher 

carbon ash is land disposed (Senior et al., 2003a). 

The injection rate of the PAC was 20 lb of sorbent used for 

each million actual cubic feet of gas (lb/MMacf) at the 

time when the CCR with ACI in use was collected from 

this facility. 

The baseline and post-control ashes used for this study were 

collected as composite samples from the C-row ash hoppers of the new ESP before processing for carbon separation.11 The baseline ash was collected on 6 June 2002. The 

post-control fly ash was collected on 21 July 2002. Both 

11 Ash for this study was collected before processing for carbon 

separation because not all facilities do this processing. 

fly ashes were stored in covered five gallon buckets in the 

onsite trailer at ambient temperatures. 

2.1.2.2. Pleasant Prairie 

Wisconsin Electric Power Company, a subsidiary of Wisconsin Energy, owns and operates Pleasant Prairie Power 

Plant located near Kenosha, WI. The plant has two 600 

MW balanced-draft coal-fired boilers designated Units 1 

and 2. Unit 2 is the test unit. This site was of key interest 

because it was the only plant in the NETL program that 

burns a variety of Powder River Basin (PRB) low sulfur, 

sub-bituminous coals. In addition, this facility has the ability to isolate one ESP chamber (1/4 of the unit) (Starns et 

al., 2002). 

The primary particulate control equipment consists of CSESPs of weighted wire design with a Wahlco gas conditioning system that provides SO3 for fly ash resistivity control. The precipitators were designed and built by ResearchCottrell. The design flue gas flow was 2,610,000 acfm. 

The precipitator inlet gas temperature is nominally 280 EF 

at full load (Starns et al., 2002). 

Precipitator #2 is comprised of four electrostatic precipitators that are arranged piggyback style and designated 2-1, 

2-2, 2-3, and 2-4. Each of the four precipitators is two chambers wide and four mechanical fields deep with eight electrical fields in the direction of gas flow. The SCA is 468 

ft2

/kacfm (Starns et al., 2002). 

Hopper ash is combined from all four precipitators in the 

dry ash-pull system and sold as base for concrete (Starns 

et al., 2002). 

19
Characterization of Coal Combustion Residues 

The PAC injection rate was 10 lb/MMacf at the time when 

the CCR with ACI in use was collected from this facility. 

The baseline ash was collected as a composite sample from 

ash hoppers 7-1 and 7-2 of ESP 2-4. The post-control ash 

was collected as a grab sample from ash hopper 7-2 of 

ESP 2-4 (see Appendix B for flow diagram). The baseline 

ash was collected on 11 September 2001, and the postcontrol fly ash was collected on 13 November 2001. Both 

fly ashes were stored in covered five gallon buckets in the 

onsite trailer at ambient temperatures. 

2.1.2.3. Salem Harbor 

PG&E National Energy Group owns and operates Salem 

Harbor Station located in Salem, MA. There are four fossil 

fuel fired units at the facility designated as Units 1, 2, 3, 

and 4. Units 1–3 fire a low sulfur, bituminous coal and use 

oil for startup. Unit 4 fires #6 fuel oil. Unit 1, the test unit, 

is a B&W single-wall-fired unit with twelve DB Riley CCV90 burners. It is rated at 88 gross MW. Salem Harbor Unit 

1 was chosen for this evaluation because of its combination of firing low-sulfur bituminous coal with urea-based 

SNCR, high LOI, and a CS-ESP. The opportunity to quantify the impact of SNCR on mercury removal and sorbent 

effectiveness is unique in this program. In addition, test 

results from prior mercury tests have indicated 87% to 94% 

mercury removal efficiency on this unit without sorbent 

injection (Senior et al., 2003a). However, fly ash from this 

facility has a relatively high percentage of total carbon 

without carbon injection (7.8%, see Table 6), which likely 

serves as a sorbent for mercury. 

The particulate control equipment consists of a two-chamber CS-ESP (chambers designated 1-1 and 1-2), which provides two separate gas flow paths from the outlet of the 

tubular air heaters to the ID fan inlets. This Environmental 

Elements ESP has a rigid electrode design and a SCA of 

474 ft2

/1000 acfm. The precipitator inlet gas temperature 

is nominally 255 EF at full load. Typical LOI or carbon 

content of the Unit 1 ash is about 25%. This ash is landfilled. 

The PAC injection rate was 10 lb/MMacf at the time when 

the CCR with ACI in use was collected from this facility. 

The baseline and post-control ashes used for this study were 

collected as grab samples from the first ash hopper (hopper A) of row 1-1 of the ESP. The baseline ash was collected on 6 June 2002, and the post-control fly ash was 

collected on 7 July 2002. Both fly ashes were stored in 

covered five gallon buckets in an onsite trailer at ambient 

temperatures. 

2.1.2.4. Facility C 

This plant has four 270 MW balanced draft coal-fired boilers designated as Units 1–4. All of these units fire a variety 

of low-sulfur, washed, Eastern bituminous coals. Unit #3 

was used for the ACI studies. 

All of the units at this plant employ HS-ESP as the primary particulate control equipment. The HS-ESP of unit 

#3 is followed by COHPAC. The COHPAC system is a 

pulse-jet cleaned baghouse designed to treat flue gas volumes of 1,070,000 acfm at 290 EF. The COHPAC baghouse 

consist of two sides, with the A-side being the control and 

the B-side being the side where activated carbon was injected after the HS-ESP but before the COHPAC. An ESP 

followed by COHPAC and combined with sorbent injection is referred to as the TOXECON configuration. 

The injection rate of the PAC was 1.5 lb/MMacf at the 

time when the CCR with ACI in use was collected from 

this facility. 

2.1.3. Facilities Using Injection of Brominated Activated Carbon 

2.1.3.1. St. Clair 

Detroit Energy St. Clair Power Plant Unit #1 is a 160 MW 

boiler that typically burns a 85:15 blend of PRB and bituminous coals.12 The flue gas from the boiler splits and is 

directed into two parallel CS-ESPs (designated the “South 

ESP” and the “North ESP”, each treating half of the flue 

gas). The flue gas is then recombined before exiting the 

stack. During testing, B-PAC was injected upstream of the 

South ESP. The unit has no NOX or SO2 controls. 

The injection rate of the B-PAC was 5 lb/MMacf at the 

time when the CCR with B-PAC in use was collected from 

this facility. 

2.1.3.2. Facility L 

This facility is configured similarly to St. Clair except that 

it used one HS-ESP with two compartments rather than 

two CS-ESPs, and it uses separated overfired air (SOfA) 

ports for NOX control. As a result, the fly ash collection 

temperature is between 300 and 450 EF. Samples were collected from hoppers which were evacuated under negative 

12 The unit sometimes switches to 100% PRB on the weekends. 

However, during our flue gas/fly ash sampling, the unit was 

burning the PRB/bituminous blend. 

20
Characterization of Coal Combustion Residues 

pressure. The pneumatic hopper controls were turned off 

to allow enough samples to collect for the leaching evaluation. The controls were off for about 4 hr. There is concern that because of the high temperature within the fly 

ash collection hoppers, some mercury may have desorbed 

prior to sampling. Therefore, the samples obtained for 

evaluation may have a lower metal content. Because of the 

concern about mercury desorbing from the fly ash, additional fly ash was collected by turning off the pneumatic 

transfer for 30 min (2 weeks after the original samples were 

collected). Total metal content determinations were completed for all samples, which includes with and without BPAC for fly ash collected after accumulation in the hopper 

for 4 hr (first sampling) and 30 min (second sampling). 

The leaching evaluation was conducted only on the samples 

collected over 4 hr intervals since this provided adequate 

sample size (5 gallons). 

2.2. Leaching Assessment Protocols 

Laboratory testing for this study focused on leaching as a 

function of pH and LS ratio as defined by the Leaching 

Framework. This is considered Tier 2 testing (equilibriumbased) for detailed characterization, which was selected to 

establish baseline CCR characteristics. Mass transfer rate 

testing (Tier 3, detailed characterization) may be carried 

out in the future for specific cases where results from equilibrium-based characterization indicate a need for detailed 

assessment. 

2.2.1. Alkalinity, Solubility and Release as a 

Function of pH (SR002.1) 

Alkalinity, solubility, and release as a function of pH were 

determined according to method SR002.1 (Kosson et al., 

2002). This protocol consists of 11 parallel extractions of 

particle size reduced material at a liquid-to-solid ratio of 

10 mL extractant/g dry sample. Particle size reduction facilitates achieving equilibrium, but minimal size reduction 

was required for the samples evaluated in this study. Each 

extraction condition was carried out in triplicate using 40 

g of material for each material evaluated. In addition, three 

method blanks were included, consisting of the deionized 

water, nitric acid and potassium hydroxide used for extractions. Typical particle size of the tested materials was 

less than 300 μm. An acid or base addition schedule is 

formulated based on initial screening for eleven extracts 

with final solution pH values between 3 and 12, through 

addition of aliquots of nitric acid or potassium hydroxide 

as needed. The exact schedule was adjusted based on the 

nature of the material; however, the range of pH values 

included the natural pH of the matrix that may extend the 

pH domain (e.g., for very alkaline or acidic materials). The 

final LS ratio is 10 mL extractant/g dry sample, which includes DI water, the added acid or base, and the amount of 

moisture that is inherent to the waste matrix as determined 

by moisture content analysis. The eleven extractions were 

tumbled in an end-over-end fashion at 28±2 rpm for 24 hr 

followed by filtration separation of the solid phase from 

the extract using a 0.45 μm polypropylene filter. Each extract then was analyzed for constituents of interest. The 

acid and base neutralization behavior of the materials was 

evaluated by plotting the pH of each extract as a function 

of equivalents of acid or base added per gram of dry solid. 

Concentration of constituents of interest for each extract 

was plotted as a function of extract final pH to provide 

liquid-solid partitioning equilibrium as a function of pH. 

2.2.2. Solubility and Release as a Function 

of LS Ratio (SR003.1) 

Solubility and release as a function of LS ratio was determined according to method SR003.1 (Kosson et al., 2002). 

This protocol consists of five parallel batch extractions over 

a range of LS ratios (i.e., 10, 5, 2, 1, and 0.5 mL/g dry 

material), using DI water as the extractant with aliquots of 

material that has been particle size reduced. Typical particle size of the material tested was less than 300 μm. Between 40 and 200 g of material, based on the desired LS 

ratio, were used for each extraction. All extractions were 

conducted at room temperature (20 ± 2 EC) in leak-proof 

vessels that were tumbled in an end-over-end fashion at 

28±2 rpm for 24 hr. Following gross separation of the solid 

and liquid phases by centrifugation or settling, leachate 

pH and conductivity measurements were taken, and the 

phases were separated by pressure filtration using 0.45 μm 

polypropylene filter membrane. The five leachates were 

collected and preserved, as appropriate, for chemical analysis. Each extraction condition was carried out in triplicate 

and a method blank consisting of the DI water used for 

extraction was included. 

2.3. Analytical Methods 

2.3.1. Surface Area and Pore Size Distribution 

A Quantachrome Autosorb IC-MS was used to perform 5­

point Brunauer, Emmett, and Teller (BET) method surface 

area, pore volume, and pore size distribution analysis on 

each as-received and size-reduced CCR. A 200 mg sample 

was degassed under vacuum at 200 EC for at least 1 hr in 

the sample preparation manifold prior to analysis with N2 

as the analysis gas. Standard materials with known surface 

area were routinely run as a QC check. 

21
Characterization of Coal Combustion Residues 

2.3.2. pH and Conductivity 

Conductivity and pH were measured for all aqueous extracts using an Accumet 925 pH/ion meter. The pH of the 

leachates was measured using a combined pH electrode 

accurate to 0.1 pH units. A 3-point calibration was performed using pH buffer solutions at pH 4.0, 7.0, and 10.0. 

Conductivity of the leachates was measured using a standard conductivity probe. The conductivity probe was calibrated using appropriate standard conductivity solutions 

for the conductivity range of concern. Conductivity meters 

typically are accurate to ±1% and have a precision of ±1%. 

2.3.3. Moisture Content 

Moisture content of the “as received” CCRs, was determined using American Society for Testing and Materials 

(ASTM) method D 2216-92. This method supercedes the 

one indicated in the published version of the leaching procedure. 

2.3.4. Carbon Content: Organic Carbon/ 

Elemental Carbon Analyzer 

Organic carbon (OC) and elemental carbon (EC) content 

of each CCR tested was measured using a Sunset Lab thermal-optical EC/OC analyzer using NIOSH Method 5040. 

The sample, collected on quartz fiber filters, was heated 

under a completely oxygen-free helium atmosphere in a 

quartz oven in four increasing temperature steps (375, 540, 

670, and 870 EC) at 60 s ramp times for the first three 

temperatures and a 90 s ramp time for the final temperature. This removed all organic carbon on the filter. As the 

organic compounds were vaporized, they were immediately oxidized to carbon dioxide in an oxidizer oven that 

followed the sample oven. The flow of helium containing 

the produced carbon dioxide then went to a quartz 

methanator oven where the carbon dioxide was reduced to 

methane, which was then detected by a flame ionization 

detector (FID). After the sample oven was cooled to 525 

EC, the pure helium eluent was switched to an oxygen/ 

helium mixture in the sample oven. At that time, the sample 

oven temperature was stepped up to 850 EC. During this 

phase, both the original elemental carbon and the residual 

carbon produced by the pyrolysis of organic compounds 

during the first phase were oxidized to carbon dioxide by 

the presence of oxygen in the eluent. The carbon dioxide 

was then converted to methane and detected by the FID. 

After all carbon had been oxidized from the sample, a 

known volume and concentration of methane was injected 

into the sample oven, so each sample was calibrated to a 

known quantity of carbon. This also provided a means of 

checking the operation of the instrument. 

The calibration range for these analyses was from 10 to 

200 μg/cm2

 of carbon using a sucrose solution as the standard. The detection limit of this instrument is approximately 

100 ng/cm2 with a linear dynamic range from 100 ng/cm2 

to 1 g/cm2. 

2.3.5. Mercury (CVAA, Method 3052, and 

Method 7473) 

Liquid samples were preserved for mercury analysis by 

additions of nitric acid and potassium permanganate and 

then prepared prior to analysis according to the following 

method. For each 87 mL of sample, 3 mL of concentrated 

nitric acid and 5 mL of 5 wt% aqueous potassium permanganate solution were added prior to storage. Immediately 

before cold vapor atomic absorption (CVAA) analysis, 5 

mL of hydroxylamine were added to clear the sample, and 

the sample was then digested according to ASTM Method 

D6784-02 (Ontario Hydro) as described for the permanganate fraction. On completion of the digestion, the sample 

was analyzed for mercury by CVAA. Samples with known 

additions of mercury for matrix analytical spikes also were 

digested as described above prior to CVAA analysis. 

Sample preparation of the solids and filters was carried 

out by HF/HNO3 microwave digestion according to Method 

3052 followed by CVAA analysis as indicated above. No 

additional preservation or digestion was carried out prior 

to CVAA analysis. 

Mercury analysis of each digest, extract, and leachate was 

carried out by CVAA according to EPA SW846 Method 

7470A “Mercury in Liquid Waste (Manual Cold Vapor 

Technique).” A Perkin Elmer FIMS 100 Flow Injection 

Mercury System was used for this analysis. The instrument was calibrated with known standards ranging from 

0.025 to 1 μg/L mercury. 

Solids also were analyzed by Method 7473 “Mercury in 

Solids and Solutions by Thermal Decomposition, Amalgamation, and Atomic Absorption Spectrophotometry” 

(EPA, 1998b). A Nippon MD-1 mercury system was used 

for this analysis. The instrument was calibrated with known 

standards ranging from 1 to 20 ng of mercury. The method 

detection limit for mercury in solids is 0.145 mg/kg. 

2.3.6. Other Metals (ICP-MS, Method 3052 

and Method 6020) 

Inductively coupled plasma-mass spectroscopy (ICP-MS) 

analyses for other elements of interest were carried out by 

Vanderbilt and STL laboratories. These two laboratories 

22
Element Mode 

Internal 

Standard 

MDL 

(:g/L) 

ML

(:g/L) 

As DRC 20 :g/L In 0.64 3.0 

Pb Standard 20 :g/L Ho 0.31 1.0 

Se DRC 20 :g/L In 0.52 2.0 

Characterization of Coal Combustion Residues 

were used to provide inter-laboratory comparison for selected analyses. 

Liquid samples for ICP-MS analysis were preserved by 

addition of 3 mL of concentrated nitric acid (trace metal 

grade) per 97 mL of sample. Solid samples were digested 

by EPA Method 3052 prior to ICP-MS analysis. Known 

quantities of arsenic, selenium, cadmium, and lead were 

also added to sample aliquots for analytical matrix spikes. 

2.3.6.1. ICP-MS Analysis at Vanderbilt 

ICP-MS analyses carried out at Vanderbilt University (Department of Civil and Environmental Engineering) were 

completed using a Perkin Elmer model ELAN DRC II in 

both standard and dynamic reaction chamber (DRC) modes. 

Standard analysis mode was used for Pb, and DRC mode 

with 0.6 mL/min of methane as the reaction gas was used 

for As and Se. Nine-point standard curves were used for 

an analytical range between approximately 0.1 and 500 

μg/L and completed daily. Analytical blanks and analytical check standards at approximately 50 μg/L were run 

every 10 samples and required to be within 10% of the 

specified value. Samples for analysis were diluted gravimetrically to within the targeted analytical range using 1% 

v/v Optima grade nitric acid (Fisher Scientific). Typically, 

analysis for As, Pb, and Se required 10:1 dilution. Twenty 

microliters of a 10 mg/L internal standard consisting of 

indium (In) (for As and Se) and holmium (Ho) (for Pb) 

was added to 10 mL of sample aliquot prior to analysis. 

Analytical matrix spikes were completed for As, Pb, and 

Se on one of each of the three replicate extracts from 

SR002.1. For each analytical matrix spike, 20 μL of a 10 

mg/L standard solution was added to 10 mL of sample aliquot (effective concentration addition of 200 μg/L). Table 

9 provides the element analyzed, analytical mode, corresponding internal standard, method detection limit (MDL), 

and minimum level of quantification (ML). 

2.3.6.2. Severn Trent Laboratories, Inc. (STL) 

STL (Savannah, GA) was selected as a commercial laboratory to carry out some of the ICP-MS analyses for this 

project. Analyses for As, Cd, Se, and Pb were performed 

Table 9. Detection Limits and Quality Control Information 

for ICP-MS Analysis for As, Pb, and Se at Vanderbilt. 

on an Agilent ICP-MS with octopole reaction system 

(ORS). Mixed calibration standards were prepared for each 

metal at five levels ranging from 0.5 μg/L to 100 μg/L. 

2.3.7. X-Ray Fluorescence (XRF) 

XRF analysis was performed on each CCR to provide additional information on its total elemental composition. For 

each CCR, two pellets were prepared as follows. Three 

grams of material was weighed and mixed with 1.5 mL 

(100 mg dry solids) of liquid binder to give a 32 mm diameter pellet weighing 3150 mg with a material-to-diluent 

ratio of 0.05. For high carbon content samples, 3.0 ml (100 

mg dry solids) of liquid binder was used to give a 32 mm 

diameter pellet weighting 3300 mg with a material to diluent 

ratio of 0.1. XRF intensities were collected on each side of 

each pellet using Philips SuperQ data collection software 

and evaluated using Omega Data System’s UniQuant 4 

XRF “standardless” data analysis software. The UQ/Flyash 

calibration was used to analyze the samples. The pellets 

were evaluated as oxides. Known flyash Standard Reference Materials (SRMs) were also run to assess the accuracy of the analysis. This information is useful in supplementing CVAA and ICP results. 

2.3.8. MDL and ML for Analytical Results 

The MDL is defined by 40 CFR Part 136, Appendix B, 

July 1, 1995, Revision 1.11 as “the minimum concentration of a substance that can be measured and reported with 

99% confidence that the analyte concentration is greater 

than zero and is determined from analysis of a sample in a 

given matrix containing the analyte.” 

The MDL was determined statistically from data generated by the analysis of seven or more aliquots of a spiked 

reagent matrix and verified by the analysis of calibration 

standards near the calculated MDL according to EPA 

(2003). The MDL then was determined by multiplying the 

standard deviation of the replicate measurements by the 

appropriate Students t value for a 99% confidence level 

(two tailed) and n-1 (six) degrees of freedom and also 

multiplying by the minimum dilution factor required for 

matrix preservation and analysis. 

The ML is defined by 40 CFR Part 136, 1994 as “the lowest level at which the entire analytical system must give a 

recognizable signal and acceptable calibration point for the 

analyte.” According to EPA (2003), the ML is intended to 

be the nearest integer value (i.e., 1, 2 or 5×10n, where n is 

an integer) to 10 times the standard deviation observed for 

determination of the MDL. This value is also multiplied 

by the minimum dilution factor required for preservation 

23
Characterization of Coal Combustion Residues 

and analysis of the sample matrix to obtain the ML reported here. 

Mercury, as measured by CVAA, required modification of 

the calculation of the MDL and ML because very consistent replication resulted in calculation of a MDL lower than 

the instrument detection limit. For this case, the standard 

deviation of seven replicate analyses of 0.025 μg/L was 

0.00069. Therefore, the MDL was set equal to the instrument detection limit of 0.001 μg/L times the minimum dilution factor from sample preparation (3.59) to result in an 

MDL of 0.0036 μg/L. The ML was set to 10 times the 

instrument detection limit and rounded to the nearest integer value as above. The resulting ML was 0.01 μg/L. 

2.4. Quality Assurance Validation 

2.4.1. Homogenization of Individual CCR 

Samples and Aliquots for Analyses 

To ensure sample homogeneity the fly ashes were mixed 

using a Morse single can tumbler model 1-305 (Figure 5). 

This tumbler is designed to provide aggressive corner-overcorner mixing at 23 RPM. Because the sample is tumbled 

at an angle it yields superior mixing to a conventional tumbler. Briefly, each fly ash was mixed by filling a 5 gal bucket 

to the half way mark and tumbled for 1 hr. The bucket was 

then inverted and tumbled for another hour. 

At the beginning of this program a series of test were conducted to ensure that the samples were being adequately 

Figure 5. Mixing Fly Ash Prior to Obtaining Aliquots for 

Laboratory Analyses. 

mixed. The reference fly ash was mixed as outlined above 

and 3 sub-samples taken from the top, middle and bottom 

respectively and XRF pellets prepared. The XRF results 

showed that the concentrations of 28 elements including 

calcium and silicon were consistent from sub-sample to 

sub-sample (Table 10) 

2.4.2. Leaching Test Methods and Analytical 

QA/QC 

One of the objectives of this project was to establish a QA/ 

QC framework for the leaching assessment approach developed by Kosson et al. (2002). The developed QA/QC 

framework incorporates the use of blanks, spiked samples, 

and replicates, and Appendix C provides the complete 

Quality Assurance Project Plan. For each designated leaching test condition, triplicate leaching test extractions were 

obtained (i.e., three separate aliquots of CCR were each 

extracted at the designated test condition). The three types 

of method blanks were the deionized water case, the most 

concentrated nitric acid addition case, and the most concentrated potassium hydroxide addition case. Each method 

blank was carried through the entire protocol, including 

tumbling and filtration, except an aliquot of CCR was not 

added. 

During analysis for mercury and elemental species by ICPMS, analytical spikes for the constituents of interest were 

carried out for one replicate of each test case to assess analytical recoveries over the complete range of pH and liquid matrix conditions. Using a standard obtained from a 

source different from the calibration standards, multipoint 

calibration curves using at least 7 standards and an initial 

calibration verification (ICV) were completed daily or after every 50 samples, whichever was more frequent. In 

addition, instrument blanks and continuing calibration verification (CCV) standards were analyzed after every 10 

analytical samples and required to be within 10 percent of 

the expected value. CCV standards and instrument blanks 

also were run at the end of each batch of samples. 

For both ICP-MS and CVAA analyses, each sample was 

analyzed along with a matrix spike, which is an aliquot of 

the sample plus a known spike concentration of the element of interest. The “spike recovery” should be within 

80–120% of the expected value. 

2.4.3. Laboratory Mass Balance Verification 

for Leaching Test Methods 

Mass balance analysis around the SR002.1 Solubility and 

Release as a Function of pH leaching test procedure was 

used to demonstrate retention of Hg, As, Se, Cd, and Pb 

24
Element #1 

(%)

a 

#2 

(%)

a 

#3 

(%)

a 

Mean

(%)

a 

Standard

Deviation 

(%)

a 

%RSD 

Si 26.41 26.41 26.43 26.4167 0.011547 0.04 

Al 14.62 14.64 14.52 14.5933 0.064291 0.44 

Fe 5.31 5.29 5.38 5.3267 0.047258 0.89 

K 2.43 2.44 2.46 2.4433 0.015275 0.63 

Ti 0.871 0.871 0.877 0.8730 0.003464 0.40 

Ca 0.834 0.847 0.835 0.8387 0.007234 0.86 

Mg 0.638 0.645 0.645 0.6427 0.004041 0.63 

Na 0.351 0.352 0.34 0.3477 0.006658 1.92 

S b 

X 0.172 0.164 0.172 0.1693 0.004619 2.73 

P c 

X 0.0834 0.0854 0.0881 0.0856 0.002359 2.75 

Ba 0.107 0.106 0.112 0.1083 0.003215 2.97 

Sr 0.0846 0.0846 0.085 0.0847 0.000231 0.27 

Zr 0.0509 0.0486 0.052 0.0505 0.001735 3.44 

V 0.0243 0.0236 0.0234 0.0238 0.000473 1.99 

Zn 0.0219 0.0243 0.025 0.0237 0.001626 6.85 

Er 0.0224 0.0248 0.024 0.0237 0.001222 5.15 

Cu 0.0173 0.0173 0.0205 0.0184 0.001848 10.06 

Cr 0.0144 0.0122 0.0122 0.0129 0.00127 9.82 

Y 0.0162 0.0153 0.0154 0.0156 0.000493 3.16 

Mn 0.0125 0.0099 0.0108 0.0111 0.00132 11.93 

Ga 0.0073 0.0073 0.0057 0.0068 0.000924 13.65 

As 0.007 0.0072 0.0072 0.0071 0.000115 1.62 

Rb 0.008 0.0079 0.0091 0.0083 0.000666 7.99 

Co 0.0064 0.0072 0.009 0.0075 0.001332 17.68 

Ni 0.0057 0.007 0.008 0.0069 0.001153 16.71 

Pb 0.0059 0.0044 0.007 0.0058 0.001305 22.63 

Sc 0.0033 0.0028 0.0025 0.0029 0.000404 14.10 

Hg 51ng/g 61ng/g 66 ng/g 59.3333 ng/g 7.637626 ng/g 12.87 

a Unless otherwise noted. b Sulfur in oxidized form such as sulfate. c Phosphorus in oxidized form such as phosphate.

Characterization of Coal Combustion Residues 

Table 10. Total Content Analysis Results for Reference Fly Ash after Mixing (mercury analysis by Method 3052 followed 

by analysis with CVAA). 

during testing through the analysis of the EPA reference 

fly ash. Six extraction conditions reflecting six different 

extraction pHs were completed in triplicate. Figure 6 provides a flow diagram of the approach used to carry out a 

mass balance analysis. This flow indicates the steps used 

for completing the necessary analysis of one leaching test 

condition (pH, LS ratio, and CCR) to assess the mass balance for mercury and other species of interest. The steps 

indicated in solid lines were already incorporated in the 

leaching assessment approach by Kosson et al. (2002). The 

steps indicated in dotted lines were added during this project 

to complete mass balance evaluation. 

After the samples for each evaluated leaching condition 

had been tumbled for the appropriate amount of time, they 

were each filtered and then divided into three fractions: 

liquid, solid, and filter. In addition, glass containers used 

in the procedure were rinsed with nitric acid after use, and 

25
Liquid 87% Leachate 3% HNO3 5% KMnO4 Clear Solution with Hydroxylamine (5% of total volume) Spike Digest in with 0.2 triplicate by ppb Hg OH method 

for KMnO4 

ICP 

CVAA

 Solid Lines - Standard Procedure Dashed Lines - Additional Analyses for Mass Balance

One pH Sample at One

LS Ratio of One CCR

Solid 

97% Leachate Thermal Digest by D

3% HNO Analysis for Method 

3 

Hg by 3052B 

Method

7473

CVAA ICP CVAA 

Spike with 2 

ppm of As, Se,

Pb, Cd 

Spike with 0.2 ppb of 

Hg 

Spike with 0.2 ppb 

As, Se, Pb, Cd 

level

Spike 

Hg a

As, 

Digest by 

OH method 

Digest by

OH method 

for KMnO4 for KMno4

ICP CVAA ICP CVAA 

Figure 6. Flow Diagram for Mass Balance and Quality Control on Laboratory Leaching Procedures. 

26
mL + mS + mF %R = × 100 

mT

Characterization of Coal Combustion Residues 

the resulting rinse was analyzed to verify that there were 

no significant constituent losses to container walls. Each 

fraction was independently analyzed to evaluate the mass 

balance. Aliquots of each liquid sample were preserved 

separately for mercury analysis and for analysis by ICPMS as described earlier. For the solid, an aliquot was 

sampled for each case and digested according to EPA 

Method 3052 (EPA, 1996). For the filter, the entire filter 

with any retained solids was digested according Method 

3052. Each digest and liquid sample was then analyzed in 

triplicate for mercury using CVAA as described earlier. 

Each digest and liquid sample also was analyzed in triplicate for As, Se, Cd, and Pb by ICP-MS. In addition to each 

liquid or digest sample analyzed, matrix spikes were used 

to determine matrix effects on the analytes of interest (Hg, 

As, Se, Cd, and Pb). For mercury spikes, the spiked solution then was digested by ASTM method D6784-02 prior 

to analysis by CVAA. 

The mass balance recovery was calculated for each test 

case according to 

where %R is the percent recovery and mL, mS, mF, and mT

are the masses of the species of interest in the liquid phase, 

solid phase, filter, and the total content initially in the 

sample (based on independent analysis of the “as received” 

EPA reference fly ash), respectively. 

2.4.4. Improving QA/QC Efficiency 

Throughout the study, the approach to QA/QC was regularly reviewed for opportunities to increase evaluation efficiency without unacceptably degrading precision or accuracy in results. Based on evaluation of results from 

the first several facilities, the number of replicates for 

Method SR002.1 (solubility as a function of pH) and 

Method SR003.1 (solubility as a function of LS ratio) were 

reduced from three to two. Study results have shown that 

the precision between duplicate analyses is acceptable and 

that a triplicate set does not significantly increase the quality of the data set. This finding follows from (i) the data 

sets generated by Method SR002.1 and SR003.1 must provide both consistency between replicate extractions and 

analyses and internal consistency between results at different pH and LS ratio and (ii) precision is controlled primarily by the degree of homogeneity of the CCR under 

evaluation and representative sub-sampling, rather than by 

the intrinsic variability of the leaching test methods. Reducing the number of replicates has greatly improved laboratory efficiency without compromising data quality. 

2.5. Interpretation and Presentation of 

Laboratory Leaching Data 

Complete laboratory leaching results for Brayton Point, 

Pleasant Prairie, Salem Harbor, Facility C, and St. Clair 

are presented in Appendices D through H, respectively. For 

each facility, a common format is used for presenting results. First, a titration curve of pH as a function of 

milliequivalents of acid or base added is presented, with 

acid additions considered positive (+) and base additions 

considered negative (-). The titration figure is then followed 

by a curve of pH as a function of LS ratio. The pH curves 

are then followed by a series of figures for each species of 

interest (i.e., mercury, arsenic, and selenium). The results 

from Solubility and Release as a Function of pH (SR002.1) 

are presented first, followed by the results from Solubility 

and Release as a Function of LS ratio (SR003.1). 

For Solubility and Release as a Function of pH (SR002.1), 

results for the baseline case are presented side by side with 

the results from the case with enhanced mercury control. 

Results are presented as extract concentrations as a function of pH. Total content of the species of interest is provided above the first figure for that species. The natural 

pH13 of the system is indicated as a vertical line to the average pH and a horizontal line to the y-axis indicating the 

corresponding extract concentration. Included with each 

figure are horizontal lines at the drinking water maximum 

concentration level (MCL) and ML and MDL analytical 

limits to provide a frame of reference for the results. Also 

included with each figure is the 5 and 95 percentile for pH 

(vertical lines) and for constituent concentration (horizontal lines) from field observations of leachate from landfills 

for combustion residues (Table 11; EPA, 200014; EPRI 

2005), forming a rectangular box that encloses the corresponding domain of field leachate observations. An annotated example of the results is provided as Figure 7. Figures with corresponding analytical recoveries are provided 

below the concentration results. 

For Solubility and Release as a Function of LS ratio 

(SR003.1), results are presented as extract concentrations 

13 “Natural pH” of a material refers to the equilibrium pH when 

the material is placed in deionized water at a ratio of 10 g CCR 

per 100 mL of water. 

14 The EPA data represent six ash landfills for which data were 

available. These data were not collected as nationally representative although they do portray the range of pH values also found 

in the EPRI data. 

27
As [

μg/L] 

5th %tile for pH 95th %tile for pH 

10000 

95th %tile for As 

1000 

Concentration 95% 

at natural pH 100 

MCL ML

10 

4.8 5% 1 

95th %tile for As concentration 

0.1 

0.01 

SR2-BPT-0001-A MDL

SR2-BPT-0001 - A 

SR2-BPT-0001 - B 

SR2-BPT-0001 - C 

0.001 SR2=SR002.1 Replicate A 5% 9.5 95%

2 4 6 8 10 12 14 Sample name

ML pH Natural pH

MDL 

Parameter 5% 95% MCLs 

pH 5.8 12.09 --

Mercury (:g/L) 0.0021 0.0498 2 

Arsenic (:g/L) 2 140 10 

Selenium (:g/L) 2.4 170 50 

Characterization of Coal Combustion Residues 

Figure 7. Example of Extract Concentrations as a Function of pH from SR002.1. 

Table 11. Composition of Combustion Waste Landfill 

Leachate—LEACH 2000 database for Arsenic and 

Selenium (EPA, 2000), EPRI Database for Mercury (EPRI, 

2005) and MCL Values. 

­

as a function of LS ratio. Also indicated are the relevant 

MCL, ML, and MDL. A separate figure with analytical 

recoveries corresponding to the figure with concentration 

results are provided as an indicator of analytical quality 

assurance. 

Constituent (e.g., mercury, arsenic, and selenium) concentrations observed in laboratory leach test extracts and in 

field leachate samples may be the result of several mechanisms and factors. The discussion presented here focuses 

on constituent leaching and source term modeling approaches. Source term is defined here as the flux or amount 

released from the waste or secondary material (e.g., CCRs). 

Factors controlling constituent release and transport in and 

within the near field of the CCRs are often distinctly different than factors and mechanisms that are important for 

subsequent vadose zone or groundwater transport outside 

of the near-field area. 

In general, constituents are present in the waste or secondary material (e.g., CCR) either as adsorbed species, coprecipitated as amorphous or crystalline solid phases, or 

incorporated as trace components in solid phases. If chemical equilibrium conditions are approached (as is the approximate case for the laboratory and field sample conditions discussed in this report), then the functional behavior 

of the aqueous solution concentration reflects the nature 

of the constituent species in the waste or secondary material, the presence of any co-constituents in the aqueous 

phase influencing aqueous solution speciation (e.g., effects 

of high ionic strength, chelating or complexing constituents), and the presence of species in the solution that may 

compete for adsorption sites if adsorption is the controlling solid phase mechanism. If the constituent is present in 

the waste or secondary material as an adsorbed species, 

many different adsorption/desorption characteristic patterns 

are possible (Ruthven, 1984; Duong, 1998). 

The simplest case is when the constituent of interest is 

present at very low concentration in the waste or second28
⎛ L ⎞ Pore Volum eL ( )

3 () 2 LSsite . ⎝

⎜

kg⎠

⎟ = ρ(kg m )⋅ Hfill m ⋅ A fill( ) m

Characterization of Coal Combustion Residues 

ary material, relatively weakly adsorbed, and the presence 

of complexing and/or competing species in solution are at 

a constant concentration. For this case, leaching test results will indicate a constant concentration as a function of 

pH at a fixed LS ratio and linearly increasing concentration as LS ratio decreases at constant pH. This case is represented mathematically as a linear equilibrium partitioning function, where the critical constant of proportionality 

is the partitioning coefficient, Kd. Linear partitioning and 

use of Kd values is a common approach for mathematically 

modeling contaminant transport at low contaminant concentrations in soils. It is a valid and useful approach when 

the necessary conditions (discussed above) are fulfilled.15 

For mercury adsorbed on activated carbon, a complex combination of adsorption mechanisms is indicated. During 

laboratory leaching tests, mercury concentrations in the 

leaching test extracts are relatively constant over the pH 

range and LS ratio of interest and independent of total 

mercury content in the CCR. In addition, the total mercury 

content in the CCR is very low. These results indicate adsorption phenomena where, in the adsorbed state, interactions between adsorbed mercury species are stronger (thermodynamically) than the interactions between the adsorbed 

mercury species and carbon surface.16 This observation has 

been supported by the observation of mercury dimmer formation during sorption (Munro et al., 2001) and the occurrence of chemisorption as the dominant adsorption mechanism at temperatures above 75 EC (consistent with conditions in air pollution control devices; Vidic, 2002). In other 

studies, this phenomenon has been observed as the formation of molecular clusters on the adsorbent surface 

(Ruthven, 1984; Duong, 1998; Rudzinski et al., 1997). For 

this case, use of a Kd approach would underestimate release because desorption is best represented as a constant 

aqueous concentration until depletion occurs. 

A third case is when the constituent of interest is present in 

the waste or secondary material (e.g., CCR) as a primary 

15 Often specific Kd values are a function of pH because of competition for adsorption sites by hydrogen ions. However, a single 

Kd or range of Kd values are often used in contaminant fate and 

transport models without specific relationship between pH and 

Kd. 

16 For this case, the first mercury molecule is adsorbed more 

weakly than subsequent mercury molecules because the adsorbed 

mercury-mercury interaction is stronger than the adsorbed mercury-carbon surface interaction. 

or trace constituent in either an amorphous or crystalline 

solid phase and there may be complexing or chelating coconstituents in the aqueous phase. Observed aqueous concentrations are a non-linear function of pH and LS ratio 

and reflect aqueous saturation with respect to the species 

of interest under the given conditions (pH, co-constituents). 

For these cases, an approximation of field conditions can 

be made empirically based on laboratory testing and observed saturation over the relevant domain (as applied in 

this report), or geochemical speciation modeling coupled 

with mass transfer modeling can be used to assess release 

under specific field scenarios (the subject of a future report). Use of a Kd approach would not be appropriate for 

these cases because constituent concentrations will remain 

relatively constant at a given pH until the controlling solid 

phase is depleted and control is shifted to a new solid phase 

or mechanism. 

2.6. Long-Term Release Assessment 

Long-term constituent release estimates were developed 

to evaluate the potential cumulative impacts of different 

CCR management scenarios. A scenario of disposal in a 

combustion waste landfill and three default scenarios were 

examined. These scenarios were selected to provide upper 

bounding estimates of release considering: 

• the range of field observations (pH and LS ratio15) for 

analogous impoundments or landfills of combustion 

wastes, 

• constituent release if occurring at the material’s natural pH, and, 

• constituent release if occurring at extreme acidic or 

alkaline pH. 

A 100-year time interval was selected as a convenient reference period because it is beyond a lifetime but within a 

comprehendible period. Cumulative release estimates are 

provided on the basis of mass of constituent released per 

17 For field scenarios, LS is directly a function of time (t), infiltration rate (inf), landfill depth (Hfill), and fill density (r) accord-

⎛ L ⎞ L ⎞⎡ inf cm yr t ⎤ ⋅ year LSsite ⎜

⎝ kg⎟⎠ = 10⎝

⎜

⎛

cm ⋅ m ⎠

⎟⎢

⎢

⎣ρ(kg m 3 )⋅ H fill(m 

⎥

⎥

⎦

( ) ( )

ing to ) . Alternatively, LS can be related to pore volumes of water passing 

through the CCRs (where Afill is the fill area) according to 

29
 Probability 

1 

0.8 

0.6 

0.4 

0.2 

0 

5 6 7 8 9 10 11 12 13 14

 pH

(2) (1) 

Field data 

Fitted distribution (Logistic, (1)) 

Simulated (2) 

Fitted 

pH Field data distribution Simulated 

pH min 5.40 4.74 4.92 

pH - 5% 5.80 6.00 5.97 

pH - 50% 7.7 7.69 7.63 

pH - 95% 12.09 11.62 10.63 

pH max 12.80 +infinity 12.50 

Characterization of Coal Combustion Residues 

mass of CCR disposed (μg X/kg CCR).18 These estimates 

are not intended to be absolute predictions of release, but 

rather, an initial assessment of whether further evaluation 

is warranted. These estimates for the monofill disposal scenario assume local equilibrium, which is a conservative 

assumption (i.e., estimated release is greater than actual 

expected release). A more refined assessment can be made 

using results from column leaching tests or diffusion controlled leaching tests that will allow consideration of release kinetics in developing field release estimates. The 

mass of constituent (e.g., As) that would be released if all 

of the leachate percolating through the landfill for the given 

scenario were at the MCL is provided as a reference value. 

The estimates presented here are only for constituent release from the waste and do not account for any dilution or 

attenuation that would occur in the vadose zone or groundwater or for the impact of a landfill liner. 

For the scenario of disposal in a combustion waste landfill, a historical data set of typical leachate generated from 

this landfill type was taken from the comprehensive database of landfill leachate characteristics developed by the 

EPA’s Office of Solid Waste (EPA, 2000). Cumulative release estimates were developed according to the methodology developed by Sanchez and Kosson (2005), and values of leachate pH were used to derive the probability distribution function of the field pH. Annual leachate generation quantities observed for industrial co-disposal landfills 

were used to derive the probability distribution function 

LS ratio that may be expected to contact the fill over the 

estimated time period of 100 years. For each data set (field 

pH and LS ratio), different distribution functions were used 

to fit the data, and the one providing the best data fit based 

on the chi-square test was selected. The resulting field pH 

probability distribution then was truncated and normalized 

to the pH range of the field data (Figure 8). The distribution for field pH was the result of over 158 sample observations from coal combustion residue disposal facilities at 

six sites. The probability distribution for the LS ratio was 

the result of over 41 sample observations from Industrial 

D landfill facilities at 17 sites. (Figure 9). 

For each CCR tested, results from SR002.1 (Alkalinity, 

Solubility and Release as a Function of pH) were used to 

develop an empirical functional relationship between solution pH and expected concentration for mercury, arsenic, 

and selenium. Laboratory results of mercury concentra18 These release estimates can be converted to the amount released per unit area according to 

Mt [mg/m2] = Mt [mg/kg] C ρ [kg/m3] C Hfill [m]. 

Figure 8. Leachate pH Distribution: Scenario of Disposal 

in a Combustion Waste Landfill. 

tions typically showed a high degree of variability between 

measured and non-detected values in the laboratory leaching test extracts (Figure 10). This was likely due to microscale sample heterogeneity with respect to carbon distribution. However, the values of the measured mercury concentrations for a specific CCR typically did not vary significantly as a function of pH. Therefore, as an upper bounding approximation for each specific CCR, the expected 

mercury concentration over the expected field pH range 

was set to the maximum observed extract concentration 

over the anticipated field pH range for that CCR. As a result of this approach, all expected release of mercury should 

be viewed as less than or equal to the indicated value at the 

indicated percentile. 

For arsenic and selenium, a polynomial function was regressed to the results from SR002.1 (Alkalinity, Solubility 

and Release as a Function of pH) with each CCR case to 

provide the expected leachate concentration as a function 

of solution pH (Figure 11). The regression fits and corresponding equations for solubility as a function of pH are 

provided in the appendices for each case examined (i.e., 

for each constituent in each CCR tested). 

30
1 

0.9 

0.8 

(2) (1) 

 Probability 0.7 

0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

0 

0 0.5 1 1.5 2 2.

Field data 

Fitted distribution (Gamma, (1)) 

Simulated (2) 

 LS ratio [L/kg year]

Fitted 

LS 1 year Field data distribution Simulated 

LS min 1.0E-05 3.3E-04 3.3E-04 

LS - 5% 5.5E-04 4.9E-04 4.4E-04 

LS - 50% 0.06 0.08 0.08 

LS - 95% 1.50 1.07 1 

LS max 2.50 +infinity 1.99 

10 

MCL 

1 

Hg [μg/L] 

0.1 

95% 

0.01 

0.006 

5% 

0.001 

5% 9.5 95% 2 4 6 8 10 12 14

pH 

ML 

MDL SR2-BPT-0001 - A 

SR2-BPT-0001 - B 

SR2-BPT-0001 - C 

Characterization of Coal Combustion Residues 

A Monte Carlo simulation was then carried out using randomly selected pH and LS ratio values from the field data

set distributions and the expected constituent equilibrium

concentration at the designated pH based on laboratory

leaching test results as indicated above. Thus, the relative 

weight of leachate solution concentration at each pH is

based on the frequency of that pH occurring in the field

observations. Solution concentration values from these

equations then were used in conjunction with the randomly

selected LS ratio values from the field LS ratio probability

distribution as input parameters for the percolation/equilibrium release model. Thus, the final resulting probability 

distribution for constituent release reflects expected concentration at a given pH from laboratory testing results and 

weighting from the distributions of field pH, and field LS 

ratio. 

5

For the three default scenarios, an infiltration rate of 20 

cm/yr, a fill depth of 1 m and a fill density of 1.6 g/cm3 

were assumed. Three different field pHs were considered: 

the natural pH of the material (i.e., case of a monofill) and 

two “extreme” pHs, a pH of 3 and a pH of 12.5. The LS 

ratio that may be expected to contact the fill over the estimated time period of 100 years was estimated from the 

assumed geometry, infiltration rate, and time frame. The 

LS ratio obtained for this scenario was 12.5 L/kg over 100 

years. Leachate concentration was assumed to be constant 

over the release interval at the concentration interpolated 

from laboratory test results (SR002.1) for the corresponding pH. Assuming constant leachate concentration is considered a first order assumption because, for very soluble 

constituents, leachate concentration is expected to decrease 

with increasing LS ratio; but for constituents where solubility increases as pH becomes less alkaline, leachate concentration is expected to increase over time. Using this 

approach, several of the ash samples would be fully depleted of Se over the 100 year leaching period.

Figure 9. LS Ratio Distribution: Scenario of Disposal in a 

Combustion Waste Landfill. 

Results of the long-term release estimates, based on the

Monte Carlo simulation results accounting for both pH and 

LS ratio as random variables, are presented as cumulative 

release probability curves and as a bar chart, comparing

total content of the constituent evaluated and cumulative 

release for each case. Annotated example results figures 

are provided as Figure 12 and Figure 13. 

Figure 10. Example of Variability of Hg Concentrations as 

a Function of pH from SR002.1. 

31
100000 100000 

10000 10000 

1000 1000 

5% 95%

95% 100 95% 100 

5% 95%

As [

μg/L] 

10 

1 5% 

As [

μg/L] 

10 

1 5% 

0.1 0.1 

0.01 0.01 

0.001 0.001 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

SR2-BPT-0001-A 

SR2-BPT-0001-B 

SR2-BPT-0001-C 

Fit curve 

SR2-BPB-0001-A 

SR2-BPB-0001-B 

SR2-BPB-0001-C 

A) Fit curve B)

Material log As (μg/L) pH range of R2 Number of 

validity points 

BPB 0.0004 pH5 -0.0135 pH4 0.1634 pH3 3-14 0.77 27 

-0.8130 pH2 1.1609 pH 2.7085 

BPT 0.0005 pH5 -0.0207 pH4 0.3035 pH3 3-12.5 0.98 33 

-2.0113 pH2 5.4552 pH -2.7126 

Selenium 

100000 

Mt = Cumulative

release of selemium 10000

over 100 years

1000 

100 

10 

BPT = Case with 

1 

enhanced mercury 

5% 50% 95% control 

0.1 

0 20 40 60 80 100 

100-year Mt [μ

(:g Se/kg CCR) 

g/kg] 

BPB = Baseline case 

Percentile 

BPB BPT 

Characterization of Coal Combustion Residues 

Figure 11. Example of Regression Fits and Corresponding Equations for Solubility as a Function of pH. 

Figure 12. Example of Cumulative Probability Distribution for Release of Selenium from Brayton Point CCR. 

32
100 yr cumulative release for 

default case of leaching at pH 3 

80500 μg/kg 

BPB - Arsenic (in :g As/kg CCR and as % of 

100% total As content in CCR) 

100000 

2095 μg/kg 2439 μg/kg 

2.6% 3.0% 

105 μg/kg 83 μg/kg 

0.1% 0.1% 

Assuming the 95th 

percentile LS from 

10000 field data 

1000 MCL = 1000 :g/kg LS 95%

MCLLS 12.5 = 125 :g/kg 100 

10 Cumulative mass 

released over 100 

years if release occurs 

at MCL concentration 1 

for given LS Total content Combustion Default - pH 3 Default -pH Default ­

Waste Landfill - 12.5 Natural pH

95% confidence 12.2 A) 

Based on Monte Carlo simulation 

using field pH and pH dependent 

leaching results 

100-year arsenic release [μg/kg] 

Characterization of Coal Combustion Residues 

Figure 13. Example of Comparison of 100 yr Cumulative Release Estimates for Arsenic. 

33
Characterization of Coal Combustion Residues 

34
Parameter pH (:g/L) (:g/L) 

median 7.7 8.15 19.5 

5th % 5.8 2.0 2.4 

95th % 12.09 140.0 170.0 

Characterization of Coal Combustion Residues 

3. Results and Discussion 

3.1. Leaching Characteristics from 

Field Observations of CCR Landfills 

and Impoundments 

In response to concerns raised by U.S. EPA Science Advisory Board regarding leaching tests, observations of pH, 

and concentrations of mercury, arsenic, and selenium from 

field CCR management facilities were evaluated for comparison with laboratory results. Landfills and impoundments were the types of CCR management facilities considered. Information was available from a U.S. EPA database (EPA, 2000) and an EPRI database (EPRI, 2005). 

The U.S. EPA database (EPA, 2000) compiled by OSW 

included data on six CCR monofills. Data included measurements of pH, mercury, arsenic, selenium and other 

constituents as self reported by facilities to Office of Solid 

Waste (OSW).19 Data in this database was not coded to 

allow association of different parameters (e.g., pH, mercury, arsenic, selenium) from the same field sample. Therefore, data from this database was evaluated based only on 

the distribution of measurements for each parameter for 

the class of CCR monofills (Table 12). Mercury data were 

carefully reviewed, including re-evaluating the primary 

Table 12. Distribution of pH and Concentrations of Arsenic 

and Selenium from Field CCR Management Facilities from 

the U.S. EPA Database (EPA, 2000). 

As Se

source data, and were not considered to be reliable and, 

therefore, not included.20 

The EPRI database (EPRI, 2005) included measurements 

of samples obtained from CCR landfills and impoundments. 

Samples were from leachate collection points, lysimeters, 

and pore water. For some facilities, multiple observations 

were obtained from different locations within the facility 

and over several years. Results from a recent sampling and 

analysis program were observations from a range of facilities (considered representative of management practices, 

combustion facility configurations, and coal types) but with 

only one or two samples per facility. Data included measurements of pH, mercury, arsenic, selenium, and other 

constituents. Data on selenium were more limited than data 

on pH and arsenic. Data on mercury were limited to the 

recent sampling and analysis program from multiple facilities. Data was coded to allow association of different 

parameters. Only CCR management facilities that receive 

residues from utilities that do not include scrubbers as part 

of the air pollution control technology are considered here. 

Information on pH from field observations is presented in 

Figure 14. For landfills, the range of data in the U.S. EPA 

database (5th–95th percentile) was consistent with the data 

reported in the EPRI database. In addition, the range of pH 

reported in the EPRI database for individual facilities with 

multiple observations was similar to the range reported for 

multiple facilities with limited numbers of observations. 

Therefore, it is considered reasonable to use the pH range 

of 5.8 to 12.09 (5th–95th percentile) reported in the U.S. 

EPA database as the basis for extrapolating from laboratory leaching test results to field estimates of leaching from 

landfills. 

20 Inconsistent methodologies were used, and most values were 19 As noted previously, data from six coal combustion ash land- either qualified results (e.g., estimated values) or below detecfills were collected based on their availability and are not neces- tion limits (with relatively high corresponding detection limits

sarily representative of all coal combustion ash landfills. reported). 

35
Characterization of Coal Combustion Residues 

Landfills 

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 

Field pH 

Facility 1 

(subbit., 

western) 

Facility 2 

(subbit., 

Wyoming) 

Facility 3 

(subbit., 

Wyoming) 

Multiple sites 

(single 

observations) 

EPA data (5th95th percentile) 

Impoundments 

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 

Field pH 

Facility 4 (subbit., 

Wyoming) 

Facility 5 (bit., 

Kentucky) 

Facility 6 (bit., 

eastern w/pyrite) 

Facility 7 (bit., 

Kentucky western) 

Facility 8 (subbit., 

Western) 

Facility 9 (bit., 

Kentucky eastern) 

Facility 10 (bit. 

w/pyrite) 

Multiple sites (single 

observations) 

Figure 14. Range of pH Observed in Field Leachate at Landfills and Impoundments Used for Disposal of CCRsCfrom 

EPRI Database. Also included is the range (5th–95th percentile) of pH values for CCR landfills reported in the EPA 

database (EPA, 2000). Facilities 6 and 10 have co-disposal of pyrite from mill rejects with CCRs. Data does not include 

facilities with scrubbers. Primary data from EPRI (EPRI, 2005). 

Information on pH in impoundments from the EPRI data- observations of very acidic pH (pH < 3), presumably as a 

base indicates two general groupings of data—impound- consequence of acid-forming pyrite oxidation. 

ments without and with co-disposal of pyrite from coal 

mill tailings. Facilities without co-disposal of pyrite from Information on arsenic from field observations is presented 

coal mill tailings (Figure 14, all except Facilities 6 and 10) in Figure 15. For landfills, most of the data from the EPRI 

fall within the same pH range as the landfill data. Facili- database falls within the range (5th–95th percentile) of pH 

ties with co-disposal of pyrite (Facilities 6 and 10) include and arsenic concentration reported in the U.S. EPA data36
Characterization of Coal Combustion Residues 

base. However, the uppermost bound of arsenic concentration in the EPRI database exceeds the U.S. EPA data 

range illustrated. In addition, the range of arsenic concentrations reported for individual facilities with multiple observations was similar to the range reported for multiple 

facilities with limited numbers of observations. The greatest arsenic concentrations are reported in the pH range between 7 and 10. 

For impoundments, the upper range of arsenic concentrations is substantially greater than reported for landfills. A 

significant number of reported arsenic concentrations are 

between 1,000 and 10,000 :g/L for impoundments, whereas 

all reported concentrations are less than 1,000 :g/L for 

landfills. Greater observed concentrations may be from 

leaching of arsenic naturally associated with pyrite in coal 

mill tailings co-disposed with CCRs rather than from the 

Landfills 

0.1 

1 

10 

100 

1000 

10000 

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 

pH 

As (ug/L) 

Facility 1 (subbit., 

western) 

Facility 2 (subbit., 

Wyoming) 

Facility 3 (subbit., 

Wyoming) 

Multiple sites 

(single 

observations) 

Impoundments 

0.1 

1 

10 

100 

1000 

10000 

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 

pH 

As (ug/L) 

Facility 4 (subbit., 

Wyoming) 

Facility 5 (bit., 

Kentucky) 

Facility 6 (bit., 

eastern w/pyrite) 

Facility 7 (bit., 

Kentucky, western) 

Facility 8 (subbit., 

western) 

Facility 9 (bit., 

Kentucky, eastern) 

Facility 10 (bit. 

w/pyrite) 

Multiple sites (single 

observations) 

Figure 15. Arsenic Concentrations Observed in Field Leachate at Landfills and Impoundments Used for Disposal of 

CCRs—from EPRI database. Also indicated by dashed lines is the range (5th–95th percentile) of pH and arsenic values 

for CCR landfills reported in the EPA database (EPA, 2000). Facilities 6 and 10 have co-disposal of pyrite from mill rejects 

with CCRs. Data does not include facilities with scrubbers. Primary data from EPRI (EPRI, 2005). 

37
Characterization of Coal Combustion Residues 

CCRs. Alternatively, the significantly lower pH in the pyrite co-disposal impoundments (Figure 14) may be causing the higher As concentrations (see Figure 13, leaching 

at pH 3). EPRI has recommended alternative management 

practices for coal mill tailings containing pyrite, and this 

practice is diminishing (EPRI, 1999). 

Information on selenium from field observations is presented in Figure 16. For landfills, the EPRI database includes a wider range (greater than and less than) of reported concentrations than the U.S. EPA database. For 

impoundments, the reported range of selenium concentrations is within the same range as reported for landfills. For 

Landfills 

0.1 

1 

10 

100 

1000 

10000 

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 

pH 

Se (ug/L) 

Facility 1 (subbit., 

western) 

Facility 2 (subbit., 

Wyoming) 

Facility 3 (subbit., 

Wyoming) 

Multiple sites 

(single 

observations) 

Impoundments 

0.1 

1 

10 

100 

1000 

10000 

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 

pH 

Se (ug/L) 

Facility 4 (subbit., 

Wyoming) 

Facility 5 (bit., 

Kentucky) 

Facility 8 (subbit., 

western) 

Facility 10 (bit. 

w/pyrite) 

Multiple sites 

(single 

observations) 

Figure 16. Selenium Concentrations Observed in Field Leachate at Landfills and Impoundments Used for Disposal of 

CCRs—from EPRI database. Also indicated by dashed lines is the range (5th–95th percentile) of pH and arsenic values 

for CCR landfills reported in the EPA database (EPA, 2000). Facilities 6 and 10 have co-disposal of pyrite from mill rejects 

with CCRs. Data does not include facilities with scrubbers. Primary data from EPRI (EPRI, 2005). 

38
Parameter 

Landfills Impoundments 

As 

(:g/L) 

Se 

(:g/L) 

Hg 

(:g/L) 

As 

(:g/L) 

Se 

(:g/L) 

Hg 

(:g/L) 

Average 48.1 265.9 0.0179 381.4 50.6 0.0019 

Median 21.2 57.0 0.0102 55.0 18.5 0.0014 

Min 2.2 0.3 0.0021 4.0 0.2 0.0002 

5th

% 3.0 1.7 0.0021 4.2 0.6 0.0003 

95th

% 179.1 1733.0 0.0498 852.8 278.6 0.0056 

Max 238.0 1760.0 0.0606 5223.0 315.0 0.0059 

Characterization of Coal Combustion Residues 

both landfills and impoundments, the range of data reported 

for a single facility (Facility 2) is fairly wide. 

To balance the assessment of the EPRI data in comparison 

with the EPA data and laboratory leaching test results, the 

following data reduction steps were taken. For the facilities with more than three observations, the mean value of 

the observations from the individual facility was taken to 

be representative of that facility. The mean value then was 

included with the data of single observations from multiple facilities. The MDL was used in the data set when the 

data were reported as less than the MDL. The resulting 

data set then was evaluated to obtain distribution statistics 

for the EPRI data evaluated (Table 13). The median, 5th 

and 95th percentiles for arsenic, selenium, and mercury then 

were used to for comparison with the EPA data set and 

laboratory results, as described later in this report. 

3.2. Quality Assurance for Laboratory 

Leaching Tests 

3.2.1. Mass Balance using EPA Reference 

Fly Ash 

The results of the Reference fly ash analysis are provided 

in Table 14. These results show that the mass balance was 

closed reasonably well for mercury, arsenic, cadmium, lead, 

and selenium with a majority of the mass for each analyte 

remaining in the solid. The mass balance closure is well 

within the expected range, especially considering the measurement of very small changes in the analyte mass in the 

solid phase relative to the total content present. These results also indicate that large losses of mercury do not occur as a consequence of the leaching test methods and subsequent analysis. However, additional mass balance verification may be required for implementation when testing 

materials with more volatile components or for validation 

of laboratories newly implementing the procedures. 

3.2.2. Analytical Quality Control/Quality 

Assurance 

Implementation of the developed QA/QC plan facilitated 

analysis of data quality and identification of testing uncertainties. The coefficient of variation for calibration standards and continuing calibration standards and blanks was 

within 5% for metals analysis by inductively coupled 

plasma-mass spectroscopy (ICP-MS) (Vanderbilt). Spike 

recoveries for metals had a mean of 101% with a coefficient of variation within 5%. Typical inter-laboratory comparisons for arsenic and selenium analyses are presented 

in Figure 17. Good agreement generally was obtained between the two laboratories except for cases of arsenic analyses when the concentration was less than 100 :g/L. For 

this condition, the Vanderbilt analysis typically resulted in 

greater values than the commercial laboratory. This result 

was most likely from the differences in analytical ICP-MS 

technology, where dynamic reaction chamber (DRC) measurements (Vanderbilt) are considered more sensitive and 

less susceptible to interferences. For all of these cases, the 

spike recoveries for Vanderbilt analyses were within ±10% 

of the expected value, with most cases within ±5% of the 

expected value. However, the analytical results, including 

repeating analysis when necessary, demonstrated the importance of including a matrix spike to verify recovery for 

each test condition. In contrast to the analytical uncertainty, 

the mean (for different test conditions, i.e., pH values) coefficient of variation for replicate tests on each fly ash type 

(resulting from variation in the subsamples of the solids 

tested) varied between 5% and 25%. Thus, the primary 

source of uncertainty in the leaching test results is a consequence of sampling, homogenization, and inherent heterogeneity of the primary material to be tested. 

Table 13. Distribution of pH and Concentrations of Arsenic, Selenium, and Mercury from Field CCR Management 

Facilities—from the EPRI database (EPRI, 2005) for landfills and impoundments (including impoundments co-disposing 

mill rejects with CCRs). 

39
Metal As

Received 

Leaching at pH of 1.95 (position 1) Leaching at pH of 2.5 (position 2)

Exposed Leachate Recovery Filter Solid solution % 

Exposed Leachate Recovery Filter Solid solution % 

Hg (ng/g) 59!8 0.369! 0.279! 48!2 76S91 0.011 0.233

0.106! 0.155! 50!11 76S92 0.184 0.083 

Pb (:g/g) 84!2.5 a 87!1.8 BD 8!11.2 94S132 93!13.5 BD 2!2.2 84S136 

Se (:g/g) 2!0.3 3!0.3 BD BD 117S194 2!0.2 BD BD 78S129 

Cd (:g/g) 1!0 1!0 BD BD 100 1!0 BD BD 100 

As (:g/g) 87!2.6 89!1.3 BD 2!0.7 99S110 94!4.1 BD 1!0.6 103S115 

Metal Received 

Leaching at pH of 4.0 (position 3) Leaching at Natural pH (position 4) 

Exposed Leachate Recovery Filter Solid solution % Exposed Leachate Recovery Filter Solid solution % 

Hg (ng/g) 59!8 0.124! 0.045! 39!0.5 60S75 0.215 0.015 

0.122! 0.030! 46!8 75S81 0.212 0.003 

Pb (:g/g) 84!2.5 89!3.4 BD 0!0.2 99S114 89!6.3 BD 2!1.2 97S121 

Se (:g/g) 2!0.3 2!0.1 BD BD 83S124 3!0.3 BD BD 117S194 

Cd (:g/g) 1!0 1!0 BD BD 100 1!0 BD BD 100 

As (:g/g) 87!2.6 91!2.6 BD 1!0.1 106S112 90!3.4 BD 2!1.5 97S115 

Metal Received 

Leaching at pH of 10.0 (position 5) Leaching at pH of 12 (position 6) 

Exposed Leachate Recovery Filter Solid solution % Exposed Leachate Recovery Filter Solid solution % 

Hg (ng/g) 59!8 44!2 0.115!

0.199 

0.019!

0.008 70S82 42!0.4 BD 0.031!

0.013 63S82

Pb (:g/g) 84!2.5 87!2.6 BD 20!28 88S169 84!1.5 BD 6!6.6 95S120 

Se (:g/g) 2!0.3 2!0.4 BD BD 70S141 1!0.1 BD BD 39S59 

Cd (:g/g) 1!0 1!0 BD BD 100 1!0 BD BD 100 

As (:g/g) 87!2.6 92!0.6 BD 4!3.2 103S118 86!0.8 BD 4!1.2 98S121 a BD = below detection limit. 

Characterization of Coal Combustion Residues 

Table 14. Leaching (Method SR002.1) and Mass Balance Results for the EPA-Reference Fly Ash. 

3.3. Laboratory Test Results 

The constituents of interest in this evaluation, based on 

input from EPA-OSW and EPA-OAQPS, are mercury (Hg), 

arsenic (As), cadmium (Cd), lead (Pb), and selenium (Se). 

Initial screening indicated low content and leaching concentrations below levels of concern for lead and cadmium. 

As a result, although complete data have been developed 

for lead and cadmium, the results are not provided in this 

report. Complete data also have been developed for other 

constituents to facilitate evaluation of geochemical speciation of constituents of concern and to provide more thorough evaluation of leaching under alternative management 

scenarios in the future, if warranted. Screening of leaching 

results against drinking water maximum contaminant levels (MCLs) indicates that antimony (Sb) may be a concern 

for some cases and is being considered for inclusion in 

future research. Complete results for pH titration, mercury, 

arsenic and selenium for each CCR reported here are presented in Appendices D through I. 

For each CCR evaluated, results of the leaching tests provide the following information: 

• Leachate concentrations for the constituents of interest as a function of pH over the range of reported field 

management conditions (from test method SR002.1; 

example results provided in Figure 18 and Figure 19A). 

• pH titration curves (from test method SR002.1). This 

information is useful in characterizing the CCR and 

assessing how it will respond to environmental stresses 

and material aging (e.g., carbon dioxide uptake, acid 

precipitation, mixing with other materials). 

• Leachate concentrations for the constituents of interest, pH and electrical conductivity as a function of LS 

ratio when contacted with distilled water (from test 

method SR003.1; example results are in Figure 19B). 

This information provides insight into the initial 

leachate concentrations expected during land disposal 

and the effects of pH and ionic strength at low LS ratios. Often these concentrations can be either greater 

40
Baseline Fly Ash Fly Ash with Enhanced Hg Control 

10000 10000

1000 1000

As 

Rep A 

Rep B 

Rep C 

As 

Rep A 

Rep B 

Rep C 

STL Conc. [

μg/L] 

100

10

STL Conc. [

μg/L] STL Conc. [μg/L] 

100

10

1 

1 10 100 1000 10000 1 10 100 1000 10000 

VU Conc. [μg/L] VU Conc. [μg/L] 

1 

A) 

10000 Se 

Rep A 

Rep B 

Rep C 

10000

1000 

100 

10 

Se 

Rep A 

Rep B 

Rep C 

STL Conc. [μg/L] 

1000

100

10

1 1 

1 10 100 1000 10000 1 10 100 1000 10000 

B) VU Conc. [μg/L] VU Conc. [μg/L] 

Characterization of Coal Combustion Residues 

Figure 17. STL Versus Vanderbilt Analytical Results for Arsenic and Selenium from Sr002.1. Baseline Fly Ash and Fly 

Ash with Enhanced Hg Control from Brayton Point Are Shown. 

than or less than concentrations observed at higher LS 

ratios (i.e., LS=10 mL/g as used in SR002.1) because 

of ionic strength and co-constituent concentration effects. 

The MCL is used as a reference threshold for the constituent of interest. However, releases identified here are estimates of concentrations potentially leaching from landfills. 

Any assessment of the environmental impact of these releases needs to consider the dilution and attenuation of these 

constituents in ground water and the plausibility of drinking well-water contamination resulting from the release. 

Dilution and attenuation factors for metals (DAFs) have 

been estimated to be potentially as low as 2 to 10 on a 

national basis or as high as 8,000 at a particular site with 

hydrogeology that indicates low transport potential.21 

Therefore, comparison with thresholds greater than the 

MCL and developed for specific scenarios may be appropriate. The following comparisons are included for each 

CCR in Appendices D through I: 

• Laboratory leachate concentrations as a function of pH 

for each CCR are compared to (i) the constituent MCL; 

21 See 60 FR 66372, Dec. 21, 1995, for a discussion of model 

parameters leading to low DAFs, particularly the assumption of 

a continuous source landfill. Implied DAFs for the metals of 

interest here can be found at 60 FR 66432-66438 in Table C-2. 

Site specific high-end DAFs are discussed at 65 FR 55703, September 14, 2000. 

41
Baseline Fly Ash Fly Ash with ACI 

10 Total Hg content: 650.6!6.8 ng/g 10 Total Hg content: 1529.6!1.1 ng/g 

MCL MCL 

1 1 

0.01 0.01 

0.006 

5% 5%

0.001 0.001 

5% 95% 12.2 5% 9.5 95% 2 4 6 8 10 12 14 2 4 6 8 10 12 14

pH pH

ML ML

MDL SR2-BPB-0001 - A 

SR2-BPB-0001 - B 

SR2-BPB-0001 - C 

MDL SR2-BPT-0001 - A 

SR2-BPT-0001 - B 

SR2-BPT-0001 - C 

0.1 

Hg [μg/L] 

95%

As [μg/L] 

Hg [μg/L] As [μg/L] 

0.1

95% 0.035 

Total As content: 27.9!2.1 :g/g 10000 Total As content: 80.5!1.9 :g/g 10000 

1000 

 95% 100 

1000 

95% 100 

4.8 5%

0.01 0.01 

0.001 0.001 95% 12.2 5% 9.5 95%

2 4 6 8 10 12 14 2 4 6 8 

5% 

10 12 14 

pH ML pH ML

MDL

10 

SR2-BPB-0001 - A 

SR2-BPB-0001 - B 

SR2-BPB-0001 - C 

MDL SR2-BPT-0001 - A 

SR2-BPT-0001 - B 

SR2-BPT-0001 - C 

MCL MCL 10

6.67 

5% 1 1

0.1 0.1

Characterization of Coal Combustion Residues 

Figure 18. Example Results from SR002.1. Brayton Point fly ashes—mercury (top) and arsenic (bottom) release as a 

function of pH for the baseline fly ash and the fly ash with enhanced Hg control. 5th and 95th percentiles of mercury and 

arsenic concentrations observed in typical CCR monofill leachate are shown for comparison. Replicate A for mercury 

results likely reflects sample heterogeneity (i.e., more activated carbon in sub-sample). ML=method limit (for quantification); 

MDL=method detection limit; less than MDL reported at 1⁄2 MDL. 

42
10000 5000 

1497 1000 

 95% 4000 

100 MCL 

3000 

0.1 

1000 0.01 

MCL 0.001 0 5% 10.3 95% 2 4 6 8 10 12 14 0 2 4 6 8 10 12 

ML pH ML LS ratio [mL/g] 

MDL MDL 

SR2-SHT-0001 - A 

SR2-SHT-0001 - B 

SR2-SHT-0001 - C 

SR3-SHT-0001 - A 

SR3-SHT-0001 - B 

SR3-SHT-0001 - C 

10 

5% 1

Se [

μg/L] 

Se [

μg/L] 

2000 

A. SR002.1 B. SR003.1 

Characterization of Coal Combustion Residues 

Figure 19. Example Results from SR002.1 and SR003.1 for Selenium in Fly Ashes from Salem Harbor with Enhanced 

Hg Control. 

(ii) the observed field leachate concentrations (5th and 

95th percentiles of reported concentrations) over the 

observed pH range for field leachates based on the U.S. 

EPA database (5th and 95th percentiles of pH), forming 

a “box” on the results figures (Figure 18); and, (iii) 

results for CCRs from the same combustion facility 

with and without the air pollution control technology 

specifically being evaluated (e.g., with and without 

activated carbon injection); 

• Laboratory leachate concentrations and pH as a function of LS ratio for each CCR are compared to the 

leachate concentrations as a function of pH at LS=10 

to evaluate whether expected initial leachate concentrations under land disposal conditions will be the same, 

less than, or greater than the concentrations used in 

comparison to field data and for cumulative release 

estimates. Figure 19 illustrates a case where initial selenium concentrations in leachate at low LS ratio (Figure 19B, SR003.1) are expected to be greater than indicated by the evaluation of concentration as a function of pH at LS=10 (Figure 19A, SR002.1). 

3.3.1. Mercury Results 

A comparison of total content and range of laboratory extract mercury concentrations as a function of pH and LS 

ratio for CCRs from different facilities is provided in Figures 20 and 21, respectively. Total content, especially for 

mercury, has exhibited considerable variability for reported 

values from the same facility, most likely resulting from 

sample heterogeneity and variations in operating conditions. Values reported here are those measured as part of 

this study. For each facility, the baseline case and the case 

with enhanced air pollution control treatment—either activated carbon injection or brominated activated carbon injection (for the St. Clair facility and Facility L)—are compared. Also, note that Facility C uses COHPAC air pollution control configuration. For each case in Figure 21, the 

range of laboratory extract concentrations was based on 

the CCR’s natural pH at LS=10 from SR002.1, and the 

minimum and maximum concentrations observed over 5.8 

# pH # 12.09 in results from testing over the range of pH 

(SR002.1) and LS ratio (SR003.1). For most cases, the 

minimum value indicated is the MDL (0.004 :g/L). As 

indicated previously, this pH range is based on the 5th and 

95th percentiles of pH in field leachate samples from CCR 

landfills reported in the EPA database. The MCL is included 

to provide a reference basis, but consideration must be given 

to appropriate dilution and attenuation factors when making determinations for specific cases. Also included in Figure 21 are the ranges of mercury concentrations observed 

in field leachates for landfills from the U.S. EPA database 

and for landfills and surface impoundments from the EPRI 

database. For field observations, the symbol with error bars 

represents the median (50th percentile), 5th and 95th percentiles of applicable observations in the respective database. 

The full range of values was not included to avoid bias 

from outlier data points. 

43
Characterization of Coal Combustion Residues 

0.01 

0.1 

1 

10 

Hg (mg/kg) 

BPB BPT PPB PPT SHB SHT GAB GAT JAB JAT FLB FLT FLB2 FLT2 

Brayton Pleasant Salem Facility C St. Clair Facility L Facility L

Point Prairie Harbor (Run #1) (Run #2)

Figure 20. Comparison of Total Mercury Content in Baseline Cases and with Sorbent Injection for CCRs from Different 

Facilities. (Facility code suffixes B = baseline and T = treated with sorbent injection; for example, PPB = Pleasant Prairie 

baseline, and PPT = Pleasant Prairie treated) 

Considering the results provided in Appendices D through • Although the use of ACI substantially increases the 

I, and comparisons in Figure 20 and Figure 21, the follow- total mercury content in the CCRs, the range of laboing observations for mercury are made: ratory leaching extract concentrations in the baseline 

• Use of sorbent injection increased the total mercury cases and cases with sorbent injection are either uncontent for the fly ash to ca. 1–2 mg/kg except for Sa- changed or the maximum leaching concentration is 

lem Harbor. This value may represent the maximum reduced as a consequence of activated carbon injecpractical capacity for the sorbent entrained with the tion. The exceptions are Facility C and Facility L, 

fly ash. The total content of mercury in fly ash from which have an increased maximum extract concentraSalem Harbor may be relatively unchanged or slightly tion for the case with sorbent injection. 

lower because of the high content of uncombusted car- • The expected range of mercury leachate concentrations 

bon (LOI = 21 wt%) for the baseline case, which acts based on these results is from < 0.004 (below MDL) 

a sorbent similar to activated carbon; in this case, in- to 0.2 :g/L over the range of pH conditions expected 

jection of activated carbon serves to dilute the total in coal ash landfill leachate. 

mercury content in the CCR. • The range of mercury concentrations observed from 

• For Facility L, accumulation of the fly ash for sam- laboratory extracts is consistent with the range reported 

pling for 4 hours (Run #1) resulted in loss of mercury for field leachates from landfills in the EPRI database. 

from the fly ash when compared to fly ash accumu- Reliable data on mercury concentrations in leachates 

lated for 30 minutes (Run #2), most likely by volatil- from landfills was not available in the EPA database. 

ization at the elevated temperatures within the accu- A lower range of field concentrations is reported for 

mulation hopper. Fly ash obtained from Run #1 was impoundments in the EPRI database, possibly resultused for leaching evaluation because of the limited ing from a combination of dilution or volatilization 

sample quantity available from Run #2. occurring during management in impoundments. 

44
Characterization of Coal Combustion Residues 

10 

MCL 

1 

0.1 

0.01 

0.001 

0.0001 

BPB BPT PPB PPT SHB SHT GAB GAT JAB JAT LAB LAT LF IMP 

max 

* min 

Natural pH 

95th% 

50th% 

5th% 

* * * * * * * * * *

* Indicates <MDL 

Brayton Pleasant Salem Facility C St. Clair Facility L EPRI 

Point Prairie Harbor 

/L) H (

Hg (:g/L) 

Figure 21. Ranges of Laboratory and Field Leachate Mercury Concentrations Compared with the Drinking Water Maximum 

Contaminant Level (MCL). [For laboratory data, symbol represents the concentrations at the natural pH of the CCR 

tested, and the error bars represent the minimum and maximum concentrations within the relevant field pH range of 5.8 

to 12.09, inclusive. For field data, symbol and error bars represent the 5th, 50th and 95th percentiles of reported values (LF 

= landfills from EPRI database; IMP = impoundments from EPRI database). Reliable data for mercury was not available 

in the EPA database.] 

• All concentrations observed in laboratory leach test 

extracts over 5.8 # pH # 12.09 were at least an order 

of magnitude less than the MCL. 

• For all cases of laboratory extracts, mercury concentrations in extracts were consistent without any significant effect of total mercury content, pH, or LS ratio observed. Mercury leaching appears to be controlled 

by adsorption from the aqueous phase with strong interaction between adsorbed mercury molecules, indicating that use of a linear partition coefficient (Kd) approach to model source term mercury leaching would 

not be appropriate. Variability observed in concentrations observed within individual cases is likely the result of sampling and CCR heterogeneity at the particle 

scale (i.e., resulting from mercury adsorption specifically onto carbon surfaces and relatively more or less 

carbon particles in a specific subsample used for extraction). 

3.3.2. Arsenic Results 

A comparison of total content and of the range of laboratory extract arsenic concentrations as a function of pH and 

LS ratio for CCRs from different facilities is provided in 

Figures 22 and 23, respectively. The approach used and 

comparisons made in Figure 23 are the same as for mercury in Figure 21. For the presentation of field leachate 

concentrations from impoundments, facilities co-disposing CCRs with coal mill rejects containing pyrite are presented along with impoundments not receiving pyrite. 

Considering the results provided in Appendices D through 

H, and comparisons in Figures 22 and 23, the following 

observations for arsenic are made: 

• Use of ACI resulted in a substantial increase in total 

arsenic content in CCR from Facility C (COHPAC facility), but there was not a corresponding increase in 

laboratory leaching test extract concentrations. 

45
Characterization of Coal Combustion Residues As (mg/kg) 

1000 

100 

10 

BPB BPT PPB PPT SHB SHT GAB GAT JAB JAT FLB FLT FLB2 FLT2 

Brayton 

Point 

Pleasant 

Prairie 

Salem 

Harbor 

Facility C St. Clair Facility L 

Run #1 

Facility L 

Run #2 

Figure 22. Comparison of Total Arsenic Content in Baseline Cases and with Sorbent Injection for CCRs from Different

Facilities. (Facility code suffixes B = baseline and T = treated with sorbent injection; for example, PPB = Pleasant Prairie

baseline, and PPT = Pleasant Prairie treated) 

• Use of ACI resulted in a substantial decrease in total 

arsenic content in CCR for Brayton Point. 

• There was not a consistent pattern with respect to the 

effect of ACI on the range of laboratory extract concentrations. For Salem Harbor and slightly for Pleasant Prairie facilities, the cases with ACI had an increase 

in the upper bound of extract concentrations compared 

to the same facility without ACI. For Facility C and 

the Brayton Point and St. Clair facilities, a corresponding decrease was observed. 

• Very low extract concentrations were observed for the 

St. Clair facility without and with B-PAC, even though 

the total arsenic content was comparable to several of 

the other cases. Conversely, relatively high extract 

concentrations were observed for Facility L without 

and with B-PAC, even though the total arsenic concentration was low compared to the other cases. Thus, 

the presence of other constituents in the CCRs or the 

formation conditions appears to have a strong influence on the release of arsenic. 

• The range of arsenic concentrations observed in the 

laboratory extracts is consistent with the range of values reported for field leachates from landfills and impoundments. For some cases, both laboratory (Salem 

Harbor, Facility C, Facility L) and field concentrations 

exceeded the MCL by more than a factor of 10. The expected range of arsenic concentrations under field conditions is less than 10 :g/L to approximately 1000 :g/L. 

• Arsenic leachate concentrations typically are strongly 

a function of pH over the entire pH range examined 

and within the pH range observed for field conditions 

(for example, see Figure 18). For some cases (for example, see St. Clair, Appendix H), measured concentrations of arsenic are strongly a function of LS ratio 

at the material’s natural pH, with much greater concentrations observed at low LS ratio. Therefore, testing at a single extraction final pH or LS ratio would 

not provide sufficient information to characterize the 

range of expected leachate concentrations under field 

conditions. Furthermore, for some of the CCRs a shift 

from the CCR’s natural pH within the range of anticipated conditions (e.g., Facility L, Brayton Point with 

ACI, Salem Harbor baseline, Facility C baseline) can 

result substantial increases in leachate concentrations. 

Therefore, co-disposal of these CCRs with other materials should be carefully evaluated. 

46
* Indicates < MDL 

As (:g/L) 

10000 

1000 

100 

10 MCL 

1 

0.1 

BPB BPT PPB PPT SHB SHT GAB GAT JAB JAT LAB LAT EPA LF IMP 

* * 

min 

max 

Natural pH 95th% 

50th% 

5th% 

Brayton Pleasant Salem Facility C St. Clair Facility L EPRI 

Point Prairie Harbor 

Characterization of Coal Combustion Residues 

Figure 23. Ranges of Laboratory and Field Leachate Arsenic Concentrations Compared with the Drinking Water Maximum 

Contaminant Level (MCL). [For laboratory data, symbol represents the concentrations at the natural pH of the CCR 

tested, and the error bars represent the minimum and maximum concentrations within the relevant field pH range of 5.8 

to 12.09, inclusive. For field data, symbol and error bars represent the 5th, 50th and 95th percentiles of reported values 

(EPA = EPA database; LF = landfills from EPRI database; IMP = impoundments from EPRI database). Reliable data for 

mercury was not available in the EPA database.] 

• For several cases (Brayton Point, Salem Harbor, Facility C without ACI, Facility L), arsenic concentrations in laboratory extracts appear to be controlled by 

solid phase solubility, whereas adsorption processes 

appear to play a more important role for other cases 

(Pleasant Prairie, Facility C with ACI, St. Clair). 

3.3.3. Selenium Results 

A comparison of total content and of the range of laboratory leach test extract selenium concentrations as a function of pH and LS ratio for CCRs from different facilities 

is provided in Figures 24 and 25, respectively. The approach 

used and comparisons made in Figure 25 are the same as 

for mercury in Figure 21. 

Considering the results provided in Appendices D through 

I, and comparisons in Figures 24 and 25, the following 

observations for selenium are made: 

• For two cases (Brayton Point, Facility C), use of ACI 

resulted in a substantial increase in the total selenium 

content of the CCR in comparison to the same case 

without ACI. For Facility C, this is likely a direct consequence of the COHPAC configuration when ACI is 

in use. For the other cases, the change in total selenium content resulting from application of ACI or BPAC was minor but increased in all cases. 

• The range of selenium concentration in laboratory leach 

test extracts is not correlated with total selenium content in the CCRs. For example, Brayton Point with ACI 

had much greater total selenium content than the other 

cases except Facility C with ACI, but it had only the 

fifth highest selenium concentration under the laboratory leaching conditions. Conversely, Facility C 

baseline had one of the lowest selenium total content 

(less than MDL), but it had second greatest selenium 

concentration under the laboratory leaching conditions. 

• The range of selenium concentrations observed in laboratory leach test extracts for Facility C are much greater 

than the concentrations observed for other cases and 

for field conditions. This is a COHPAC facility, and 

field leachate composition data for CCRs from this type 

of facility was not available in the EPA or EPRI databases. For all other facilities, the range of concentrations observed from laboratory testing is consistent with 

47
Characterization of Coal Combustion Residues Se (mg/kg) 

1000 

100 

10 

1 

* * * * 

* Indicates < MDL 

BPB BPT PPB PPT SHB SHT GAB GAT JAB JAT FLB FLT FLB2 FLT2 

Brayton 

Point 

Pleasant 

Prairie 

Salem 

Harbor 

Facility C St. Clair Facility L 

(Run #1) 

Facility L 

(Run #2) 

Figure 24. Comparison of Total Selenium Content in Baseline Cases and with Sorbent Injection for CCRs from Different

Facilities. (Facility code suffixes B = baseline and T = treated with sorbent injection; for example, PPB = Pleasant Prairie

baseline, and PPT = Pleasant Prairie treated) 

the range reported in the EPRI database for landfills. 

The concentration range reported in the EPA database 

for CCR landfills has a much lower upper bound than 

reported in the EPRI database. 

• The concentration range for laboratory extracts and 

field observations exceeded the MCL for all cases except Facility L. For 5 out of 12 of the cases used for 

laboratory evaluation and for some field observations, 

the MCL is exceeded by more than a factor of 10. 

• Selenium concentrations in laboratory leach test extracts typically are strongly a function of pH over the 

entire pH range examined and within the pH range 

observed for field conditions (for example, see Brayton 

Point, Salem Harbor, Facility C). For some cases (for 

example, see Figure 19 or Brayton Point, Salem Harbor, St. Clair in Appendices D, F, and H, respectively), 

measured concentrations of selenium are strongly a 

function of LS ratio at the material’s natural pH, with 

much greater concentrations observed at low LS ratio. 

Therefore, testing at a single extraction final pH or LS 

ratio would not provide sufficient information to characterize the range of expected leachate concentrations 

under field conditions. 

• For several cases (Brayton Point, Salem Harbor, Facility C, Facility L), selenium concentrations in laboratory extracts appears to be controlled by solid phase 

solubility, whereas adsorption processes appear to play 

a more important role for other cases (Pleasant Prairie, 

St. Clair). 

3.4. Long-Term Release Assessment 

Cumulative release estimates for CCRs from each facility, 

both for the baseline case and the case with enhanced mercury recovery, are presented in Appendices D through I. 

One hundred year release estimates of mercury, arsenic 

and selenium are presented. One example of long-term release assessment results for arsenic and selenium is provided in Figures 26 and 27. For each case, first the polynomial curve fits for solubility as a function of pH are presented along with the corresponding data from laboratory 

leaching test results (SR002.1) and the 5th and 95th percentile of pH and constituent concentration from the U.S. EPA 

database. Next, the cumulative probability distribution for 

cumulative constituent release is provided from the Monte 

Carlo simulation for both the baseline and test cases. Finally, a bar chart, comparing total content of the constitu48
100000 

10000 

1000 

5% 95%

 5% 

95% 

As [

μg/L] 

100 

10 

1 

0.1 

0.01 

0.001 

2 4 6 8 10 12 14 

pH 

B) 

SR2-BPT-0001-A 

SR2-BPT-0001-B 

SR2-BPT-0001-C 

Fit curve 

Characterization of Coal Combustion Residues 

MCL 

S ( /L) 

0.1 

1 

10 

100 

1000 

10000 

100000 

max 

Natural pH 

min 

95th% 

50th% 

5th% 

Se (:g/L) 

BPB BPT PPB PPT SHB SHT GAB GAT JAB JAT LAB LAT EPA LF IMP 

Brayton Pleasant Salem Facility C St. Clair Facility L EPRI 

Point Prairie Harbor 

Figure 25. Ranges of Laboratory and Field Leachate Selenium Concentrations Compared with the Drinking Water 

Maximum Contaminant Level (MCL). [For laboratory data, symbol represents the concentrations at the natural pH of the 

CCR tested, and the error bars represent the minimum and maximum concentrations within the relevant field pH range 

of 5.8 to 12.09, inclusive. For field data, symbol and error bars represent the 5th, 50th and 95th percentiles of reported 

values (EPA = EPA database; LF = landfills from EPRI database; IMP = impoundments from EPRI database). Reliable 

data for mercury was not available in the EPA database.] 

ent evaluated, estimated cumulative release over 100 years, 

and percent of total content released is provided for the 

baseline and test cases. Similar results are not provided for 

mercury because of the simplification used for the assessment based on results and underlying mechanism (see section 2.5.1). 

3.4.1. Long-term Release Estimates for 

Mercury 

A comparison of the long-term (100 yr) mercury release 

estimates from the Monte Carlo simulation for each case is 

presented in Figure 28A on a mass basis (micrograms of 

Hg released per kilogram of CCR) and Figure 28B as a 

percent of total mercury released. Figure 28A also includes 

the total mercury content for each case. 

Considering the results provided in Appendices D through 

I, and comparisons in Figure 28, the following observations for mercury are made: Figure 26. Example Regression Curves of Experimental 

• The estimated mass of mercury released over the as- Data of Arsenic Solubility as a Function of pH for Brayton 

sessment period does not correlate with the total mer- Point. 

49
μg/kg % μg/kg % 

Mt min 0.2 0.0003 0.1 0.0003 

Mt - 5% 0.9 0.0011 0.1 0.0005 

Mt - 50% 152 0.2 22 0.0772 

Mt - 95% 2095 2.6 338 1.2 

Mean Mt 468 0.6 90 0.3 

Mt max 4693 5.8 10157 36.4 

BPB BPT 

5% 95% 0.1 

1 

10 

100 

1000 

10000 

0 20 40 60 80 100

Percentile 

100-year Mt [

μg/kg] 

BPB BPT 

Arsenic 

50% 

Characterization of Coal Combustion Residues 

Figure 27. Example 100-Year Arsenic Release Estimates 

for Brayton Point as a Function of the Cumulative Probability 

for the Scenario of Disposal in a Combustion Waste Landfill. 

(Mt refers to the cumulative release over the 100-year 

interval.) 

cury content of the CCR. This is a consequence of the 

relatively constant leaching test extract concentrations 

independent of the total mercury content in the CCR. 

For all cases, the median expected release over 100 

years is less than or equal to 1 :g/kg, with the 5th and 

95th percentiles less than or equal to 0.005 and 15 :g/ 

kg, respectively. 

• The percentage of total mercury estimated to be released over 100 years ranges from a very small percentage (less than 0.002%) to less than 5% for most 

cases. From less than a very small percentage (less than 

0.03%) to less than 80% of the total mercury may be 

released from cases Facility C baseline and Facility L. 

The higher percentages for these three cases reflects 

the lower total mercury content present in the CCR. 

3.4.2. Long-Term Release Estimates for 

Arsenic 

A comparison of the long-term (100 yr) arsenic release 

estimates from the Monte Carlo simulation for each case is 

presented in Figure 29A on a mass basis (micrograms As 

released per kilogram CCR) and Figure 29B as a percent 

of total arsenic released. Figure 29A also includes the total 

arsenic content for each case and MCLLS95% for reference. 

MCLLS95% is the amount of arsenic that would be released 

(1,000 :g/kg) if the leachate concentration was equal to 

the MCL for arsenic (10 :g/L) for the entire 100 year period and if the infiltration rate was at the 95th percentile of 

reference cases for landfills in the U.S. EPA database. For 

the purposes of this study, values that exceed this threshold may warrant further examination as to whether or not 

additional management controls should be considered. 

Considering the results provided in Appendices D through 

I, and comparisons in Figure 29, the following observations for arsenic are made: 

• The estimated mass of arsenic released over the assessment period does not correlate with the total arsenic content of the CCR. For all cases except Salem 

Harbor, Facility C, and Facility L, less than 0.1% to 

5% of the total arsenic content is anticipated to be released. 

• Salem Harbor, Facility C baseline, and Facility L are 

cases where up to a very high percentage (more than 

30%) of the total arsenic content may be released under some management conditions. 

• The cases of Salem Harbor, Facility C, and Facility L 

are examples of where more detailed release evaluation is warranted, considering site specific management 

practices, infiltration rates, and dilution and attenuation factors. 

3.4.3. Long-term Release Estimates for 

Selenium 

A comparison of the long-term (100 yr) selenium release 

estimates from the Monte Carlo simulation for each case is 

presented in Figure 30A on a mass basis (micrograms Se 

released per kilogram CCR) and Figure 30B as a percent 

of total arsenic released. The presentation in Figure 30 is 

analogous to the presentation used for arsenic release estimates in Figure 29 and discussed previously. 

Considering the results provided in Appendices D through 

I, and comparisons in Figure 30, the following observations for selenium are made: 

• For all cases except Brayton Point, from 40% up to 

the total content of selenium in the CCR is anticipated 

to be released at the 95th percentile, with between 3% 

and 20% for the median case (except Facility C 

baseline, where the median case is 100% of the total). 

For Brayton Point, from 1% to 30% of the total con50
H ( /k ) 

0.0001 

0.001 

0.01 

0.1 

1 

10 

100 

1000 

10000 

Median 

Total Content 

95th% 

50th% 

5th% 

Hg (:g/kg)

BPB BPT PPB PPT SHB SHT GAB GAT JAB JAT LAB LAT 

Brayton Pleasant Salem Facility C St. Clair Facility L 

A) Point Prairie Harbor 

Hg ( of Total) 

0.00001 

0.0001 

0.001 

0.01 

0.1 

1 

10 

100 

Median 

95th% 

50th% 

5th% 

Hg (% of Total) 

BPB BPT PPB PPT SHB SHT GAB GAT JAB JAT LAB LAT 

Brayton Pleasant Salem Facility C St. Clair Facility L 

B) Point Prairie Harbor 

Characterization of Coal Combustion Residues 

Figure 28. Upper Bound of 100 yr Mercury Release Estimates for Landfill Scenario Without and with Activated Carbon 

Injection. (A) mass released in :g of mercury released per kg of CCR and total content in :g of mercury per kg of CCR, 

(B) percent of total mercury content released. Symbol with error bars represents 5th, 50th and 95th percentiles from Monte 

Carlo simulation. (Facility code suffixes B = baseline and T = treated with sorbent injection; for example, PPB = Pleasant 

Prairie baseline, and PPT = Pleasant Prairie treated) 

51
t As (:g/kg)

1000000

100000

10000

1000

100

10

1

0.1 

0.01 

0.001

BPB BPT PPB PPT SHB SHT GAB GAT JAB JAT LAB LAT

Brayton Pleasant Salem Facility C St. Clair Facility L

A) Point Prairie Harbor

/k )A (

BPB BPT PPB PPT SHB SHT GAB GAT JAB JAT LAB LAT 

Brayton Pleasant Salem Facility C St. Clair Facility L

B) Point Prairie Harbor

MCL 

LS 95% 

=1000μg/kg 

Median 

Total Content 

5th% 

50th% 

95th% 

5th% 

A (% f T l) 

0.00001 

0.0001 

0.001 

0.01 

0.1 

1 

10 

100 

Median 

95th% 

50th% 

5th% 

As (% of Total) 

Characterization of Coal Combustion Residues 

Figure 29. Upper Bound of 100 yr Arsenic Release Estimates for Landfill Scenario Without and with Activated Carbon 

Injection. (A) mass released in :g of arsenic released per kg of CCR and total content in :g of arsenic per kg of CCR, (B) 

percent of total arsenic content released. Symbol with error bars represents 5th, 50th and 95th percentiles from Monte 

Carlo simulation. (Facility code suffixes B = baseline and T = treated with sorbent injection; for example, PPB = Pleasant 

Prairie baseline, and PPT = Pleasant Prairie treated) 

52
Se (:g/kg)

1000000 

100000 

10000 

1000 

100 

/k( ) S

MCL 

LS 95% 

=5000μg/kg 

Median 

Total Content 

5th% 

50th% 

95th% 

10 

1 

0.1

BPB BPT PPB PPT SHB SHT GAB GAT JAB JAT LAB LAT

Brayton Pleasant Salem Facility C St. Clair Facility L

A) Point Prairie Harbor

BPB BPT PPB PPT SHB SHT GAB GAT JAB JAT LAB LAT 

Brayton Pleasant Salem Facility C St. Clair Facility L

B) Point Prairie Harbor

S (% f T l) 

0.001 

0.01 

0.1 

1 

10 

100 

Median 

5

th% 

50th% 

95th% 

Se (% of Total) 

Characterization of Coal Combustion Residues 

Figure 30. Upper Bound of 100 yr Selenium Release Estimates for Landfill Scenario Without and with Activated Carbon 

Injection. (A) mass released in :g of selenium released per kg of CCR and total content in :g of selenium per kg of CCR, 

(B) percent of total selenium content released. Symbol with error bars represents 5th, 50th and 95th percentiles from 

Monte Carlo simulation. (Facility code suffixes B = baseline and T = treated with sorbent injection; for example, PPB = 

Pleasant Prairie baseline, and PPT = Pleasant Prairie treated) 

53
Characterization of Coal Combustion Residues 

tent is anticipated to be released for more than half of 

the anticipated conditions. 

• Low fractional releases of selenium (less than 0.1%, 

except for Facility C baseline) at the 5th percentile suggest management scenarios where anticipated release 

can be substantially reduced for each CCR case, either 

through control of pH or infiltration. 

• All cases are examples of where more detailed release 

evaluation is warranted, considering site specific management practices, infiltration rates, and dilution and 

attenuation factors. 

54
Characterization of Coal Combustion Residues 

4. Conclusions and Recommendations

4.1. Assessment of CCRs Without 

and With Activated Carbon Injection 

Analysis has been completed for CCRs from six coal combustion facilities that control mercury emissions by sorbent injection; four using powdered activated carbon injection and two using brominated powdered activated carbon injection. For each facility, the evaluation included 

assessments of CCRs generated both with and without use 

of the activated carbon injection. None of these facilities 

had scrubbers as part of their air pollution control technology. The following conclusions are drawn for this class of 

facilities: 

• Application of activated carbon injection substantially 

increased the total mercury content in the resulting 

CCRs for five of the six facilities evaluated. Substantially increased arsenic and selenium content in the 

CCRs was observed at the one facility that employed 

COHPAC fabric filter particulate control technology. 

This may have resulted from additional arsenic and 

selenium adsorption onto the CCR while retained in 

the fabric filters. Significant increase in the selenium 

content of one additional facility was noted. 

• Mercury is strongly retained by the CCR and unlikely 

to be leached at levels of environmental concern. 

Leaching that did occur did not depend on total mercury content in the CCR, leaching pH, nor liquid to 

solid ratio, and mercury concentrations in laboratory 

extracts appeared to be controlled by non-linear adsorption equilibrium. Laboratory extract concentrations 

ranged between less than the MDL (0.01 :g/L) and 

0.2 :g/L. 

• Arsenic and selenium may be leached at levels of potential concern from CCRs generated at some facilities both with and without enhanced mercury control 

technology. Further evaluation of leaching of arsenic 

and selenium from CCRs that considers site specific 

conditions is warranted. 

• Leachate concentrations and the potential release of 

mercury, arsenic and selenium do not correlate with 

total content. For many cases, leachate concentrations 

observed are a function of final pH over the range of 

field conditions, and the observed leaching behavior 

implies that solubility in the leachate or aqueous extract controls observed liquid concentration rather than 

linear adsorption equilibrium. For these cases, use of 

linear partition coefficients (Kd) in modeling leaching 

phenomena does not reflect the underlying processes. 

In addition, for many cases, the amount of mercury, 

arsenic and/or selenium estimated to be released over 

a 100 year interval is a small fraction (less than 0.1% 

to 5%) of the total content. For selenium, release from 

less than 5% up to the total content of selenium can be 

anticipated over the 100 year period. Therefore, it is 

not recommended to base landfill management decisions on total content of constituents in CCRs since 

total content does not consistently relate to quantity 

released. 

• Results of this assessment also suggest management 

conditions (e.g., through control of infiltration and pH) 

that may result in reduction releases of arsenic and 

selenium by as much as two orders of magnitude in 

comparison to upper bound estimated releases. 

• Use of the Leaching Framework facilitated understanding the variations in anticipated leaching behavior under the anticipated field landfill disposal conditions, 

including expected ranges of constituent concentrations 

in leachate and cumulative release over a defined time 

interval. In addition, insights into the mechanisms controlling constituent leaching were obtained. This depth 

of understanding would not have been possible using 

leaching tests focused on a single extraction condition 

(e.g., TCLP, SPLP, or SGLP). 

• This study provides baseline data which allows using 

a reduced set of laboratory testing conditions as a 

screening leaching assessment for CCRs from coal 

combustion facilities employing similar air pollution 

control technology. For mercury, extraction only at the 

material’s natural pH at LS=10 is adequate. For arsenic, extraction at four conditions is warranted to de55
Characterization of Coal Combustion Residues 

fine the range of expected leachate concentrations and 

release: (i) pH 5.5–6.0 at LS=10, (ii) pH 7.5–8.5 at 

LS=10, (iii) pH 12.0–12.5 at LS=10 and (iv) natural 

pH at LS=2. For selenium, either the total content or 

the same conditions as recommended for arsenic can 

be used. At least duplicate extractions should be used. 

Results from this more limited testing can be evaluated in comparison with the results presented in this 

report to determine if more extensive evaluation is 

warranted. 

4.2. Implementation of Leaching Test 

Methods 

The leaching assessment approach published by Kosson et 

al. (2002) and implemented in this report was selected because after internal EPA review (Office of Research and 

Development, Office of Solid Waste) and consultation with 

the Environmental Engineering committee of the EPA Science Advisory Board, it was considered the only available 

peer reviewed and published approach that allowed consideration of the range of potential field management scenarios expected for CCRs and that provided a fundamental foundation for extrapolation of laboratory testing to field 

scenarios. Additional development and validation of the 

leaching assessment approach through this project provides 

the following conclusions: 

• Laboratory leaching test results were consistent with 

observed ranges of field leachate pH and with mercury, arsenic, and selenium concentrations. Thus, the 

leaching test methods employed in this study provide 

an appropriate basis for evaluating leaching under the 

range of anticipated field management scenarios. 

• Leaching test methods SR002.1 (Solubility and Release as a Function of pH) and SR003.1 (Solubility 

and Release as a Function of LS ratio) have been successfully implemented at the EPA National Risk Management Research Laboratory. The use of these methods is now considered near routine methodology for 

the laboratory. 

• QA/QC methodology conforming with EPATier 3 requirements has been developed and demonstrated for 

the leaching test methods SR002.1 and SR003.1. 

• Further efficiency in implementation of the QA/QC 

methodology may be obtained, based on the results 

from testing the initial set of CCRs, by reducing the 

number of replicates and control analyses required 

under the initial QA/QC plan. These improved project 

efficiencies are being implemented for evaluation of 

additional CCRs under this project. 

• A mass balance around the laboratory leaching test procedures has been completed for mercury and selected 

metals of potential concern. These results indicate that 

recoveries were between 60% and 91% for mercury 

during the leaching tests and subsequent analytical 

procedures, which is within the uncertainty resulting 

from heterogeneity within the CCR. Additional mass 

balance verification may be warranted if future samples 

have significantly different characteristics that may 

result in greater volatility of the constituents of interest than in the reference sample evaluated. 

56
Characterization of Coal Combustion Residues 

5. References 

ACAA (American Coal Ash Association), 2000. 1999 Coal Combustion Product (CCP) Production and Use (Short Tons), 

available at http://www.acaa-usa.org/whatsnew/ccp_surveys.htm (accessed March 2001). 

ACAA (American Coal Ash Association), 2003. 2003 Coal Combustion Product (CCP) Production and Use Survey, ACAA, 

Alexandria, VA, available at http://www.acaa-usa.org/PDF/2003_CCP_Survey(10-1-04).pdf (accessed January 2006). 

Clean Air Mercury Rule: 70 FR 28606; May 18, 2005. 

Clean Air Interstate Rule: 70 FR 25162; May 12, 2005. 

Duong D. Do., 1998. Adsorption Analysis: Equilibria and Kinetics. Imperial College Press, London, 892 p. 

EPA, 1988. Report to Congress–Wastes from the Combustion of Coal by Electric Utility Power Plants. EPA/530/SW-88/002, U.S. 

EPA, Office of Solid Waste and Emergency Response, Washington, DC. 

EPA, 1996. Method 3052 “Microwave Assisted Acid Digestion of Siliceous and Organically Based Matrices,” Test Methods for 

Evaluating Solid Waste, Physical/Chemical Methods (SW-846), available at http://www.epa.gov/sw-846/main.htm (accessed 

January 2006). 

EPA, 1998. Method 7473 “Mercury in Solids and Solutions by Thermal Decomposition, Amalgamation, and Atomic Absorption 

Spectrophotometry,” Test Methods for Evaluating Solid Waste, Physical/Chemical Methods (SW-846), available at 

http://www.epa.gov/sw-846/main.htm (accessed January 2006). 

EPA, 1999. Report to Congress-Wastes from the Combustion of Fossil Fuels: Volume 2-Methods, Findings and 

Recommendations. EPA/530/R-99/010. U.S. EPA, Office of Solid Waste and Emergency Response, Washington, DC. 

EPA, 2000. Characterization and evaluation of landfill leachate. EPA, Draft Report. 68-W6-0068, September 2000. 

EPA, 2002. Characterization and Management of Residues from Coal-Fired Power Plants, Interim Report. EPA/600/R-02/083, 

December. 

EPA, 2003. Technical Support Document for the Assessment of Detection and Quantitation Approaches. EPA/821/R-03/005. U.S 

EPA, Office of Water, Washington, DC, available at (http://epa.gov/waterscience/methods/det/index.html) [Superceded by 

Revised Assessment of Detection and Quantitation Approaches, EPA/821/B-004/005, available at 

http://www.epa.gov/waterscience/methods/det/rad/rad.pdf (accessed January 2006)]. 

EPA, 2005. Control of Mercury Emissions from Coal Fired Electric Utility Boilers: An Update, U.S. EPA, Office of Research and 

Development, Research Triangle Park, NC, Feb 18, available at 

http://www.epa.gov/ttn/atw/utility/ord_whtpaper_hgcontroltech_oar-2002-0056-6141.pdf accessed January 2006. 

EPRI, 1999. Guidance for Co-management of Mill Rejects at Coal-Fired Power Plants. Report TR-108994. 

EPRI, 2005. Personal communication of EPRI leaching database (as of June 2005) summary information from K. Ladwig to D. 

Kosson. 

57
Characterization of Coal Combustion Residues 

Kosson, D.S., van der Sloot, H.A., Sanchez, F., and Garrabrants, A.C., 2002. An Integrated Framework for Evaluating Leaching 

in Waste management and Utilization of Secondary Materials, Environmental Engineering Science 19:3, 159–204. 

MTI (McDermott Technology, Inc.), 2001. Mercury Emissions Predictions, available at 

http://www.mtiresearch.com/aecdp/mercury.html#Coal%20Analyses%20and%20Mercury%20Emissions%20Predictions, 

accessed November 2002. 

Munro, L.J., Johnson, K.J., and Jordan, K.D., 2001. An Interatomic Potential for Mercury Dimmer, J. of Chemical Physics, 

114:13, 5545–5551. 

Nelson, S., 2004. “Advanced Utility Sorbent Field Testing Program,” DOE/NETL Mercury Control Technology R&D Program 

Review, Pittsburgh, PA, July 14–15, 2004. 

Nelson, S., Landreth, R., Zhou, Q., Miller, J., 2004. “Accumulated Power-Plant Mercury-Removal Experience with Brominated 

PAC Injection”, Joint EPRI DOE EPA Combined Utility Air Pollution Control Symposium, The Mega Symposium, Washington, 

D.C., August 30–September 2. 

Rudzinski, W., W.A. Steele, and G. Zgrablich, 1997. Equilibria and Dynamics of Gas Adsorption on Heterogeneous Solid 

Surfaces. Elsevier, Amsterdam. 

Ruthven, D.M., 1984. Principles of Adsorption and Adsorption Processes. Wiley, New York, 433 p. 

SAB (EPA Science Advisory Board, Environmental Engineering Committee), 2003. TCLP Consultation Summary, presented at 

the SAB Environmental Engineering Committee consultation with EPA, Washington, D.C., June 17–18. 

Sanchez, F., Kosson, D.S., 2005. Probabilistic Approach for Estimating the Release of Contaminants under Field Management 

Scenarios, Waste Management, 25:5, 643–472. 

Senior, C, Bustard, C.J., Baldrey, K., Starns, T. Durham, M., 2003a. “Characterization of Fly Ash From Full-Scale Demonstration 

of Sorbent Injection for Mercury Control on Coal-Fired Power Plants,” presented at the Combined Power Plant Air Pollutant 

Control Mega Symposium, Washington D.C., May 19–22. 

Senior, C., Bustard, C.J., Durham, M., Starns, T., Baldrey, K, 2003b. “Characterization of Fly Ash From Full-Scale 

Demonstration of Sorbent Injection for Mercury Control on Coal-Fired Power Plants,” presented at the Air Quality IV 

Conference and Exhibition, Washington D.C, September 22–27. 

Senior, C., Bustard, C.J., Durham, M., Baldrey, K., Michaud, D., 2004. Characterization of Fly Ash From Full-Scale 

Demonstration of Sorbent Injection For Mercury Control on Coal-Fired Power Plants, Fuel Processing Technology, 85:6–7, 601– 

612. 

Starns, T., Bustard, J., Durham, M., Lindsey, C., Martin, C., Schlager, R., Donnelly, B., Sjostrom, S., Harrington, P., 

Haythornthwaite, S., Johnson, R., Morris, E., Change, R., Renninger, S., 2002. “Full-Scale Test of Mercury Control with Sorbent 

Injection and an ESP at Wisconsin Electric’s Pleasant Prairie Power Plant,” presented at the Air & Waste Management 

Association 95th Annual Conference and Exhibition, Baltimore, MD, June 23–27. 

Thorneloe, S., 2003. Presentation to EPA Science Advisory Board (Environmental Engineering Committee), Washington, D.C., 

June 17th. 

Vidic, R.D., 2002. Combined Theoretical and Experimental Investigation of Mechanisms and Kinetics of Vapor-Phase Mercury 

uptake by Carbonacoues Surfaces. Final Report, Grant No. DE-FG26-98FT40119 to U.S. DOE, National Energy Technology 

Laboratory. 

58
Characterization of Coal Combustion Residues 

Appendix A 

U.S. EPA Science Advisory Board Consultation Summary 

This summary was prepared at the close of the June 2003 U.S. EPA OSW and ORD consultation with the Science 

Advisory Board, Environmental Engineering Committee Review Panel. These comments do not represent formal consensus of the panel, and no consensus recommendations to the U.S. EPA were prepared. These comments do present 

panel members views, with informal consensus on many points. 

59
Characterization of Coal Combustion Residues 

TCLP CONSULTATION SUMMARY

Environmental Engineering Committee

Science Advisory Board

U.S. Environmantal Protection Agency

Washington, DC

June 18, 2003

FOCUS

• Alternatives to TCLP test for use in waste and 

site situations where TCLP test is not 

required by regulation 

• Focus Areas: contaminated site remediation; 

waste material reuse; waste delisting 

60
Characterization of Coal Combustion Residues 

OVERVIEW

• Five specific consultation issues 

• Two general consultation issues 

• Key findings and recommendations 

SPECIFIC CONSULTATION ISSUE 1

Laboratory testing conditions should, to the 

degree possible, anticipate the plausible 

range of field conditions affecting waste 

leaching in disposal and reuse situations. 

These conditions will be most realistically 

represented by a distribution of values for 

factors affecting leaching, and testing should 

reflect this range of values to the degree 

possible 

61
Characterization of Coal Combustion Residues 

COMMENTS

SPECIFIC CONSULTATION ISSUE 1

• Agree with statement; comments that follow represent 

consensus of committee 

• Statement should be related to some contextual use of 

leaching test 

• Could expand probabilistic approach to include distributions 

for field property parameters 

• Range of conditions considered depends on the intended 

use of the information; need context 

• Need to define what the target problems are. What are we 

trying to fix? Might be short list. 

• EPA needs to define better what the objectives are for the 

broader leaching framework 

COMMENTS

SPECIFIC CONSULTATION ISSUE 1

• Unclear what is the cost of making no change. 

• Unclear to what extent overly conservative 

classification affects beneficial reuse 

• Also need to consider waste material properties, 

e.g., physical form, presence of oil, etc. 

• Need to consider organics as well as metals 

• Perhaps can group waste materials, consider 

categories 

62
Characterization of Coal Combustion Residues 

SPECIFIC CONSULTATION ISSUE 2

Conditions present at the end of a test (rather 

than initial test conditions) should be the 

basis for comparison with field conditions. 

COMMENTS

SPECIFIC CONSULTATION ISSUE 2

• Statement indicates application is to dissolution of solids, 

and to assessment of max aqueous phase conc of released 

species for purposes other than waste classification 

• To the extent that the test aims to achieve equil conditions, 

end measurement is appropriate 

• Issue motivated by the TCLP test, where final solution pH is 

not measured. 

• Conditions in a reactor at equilibrium or at the end of a fixed 

period of time are more relevant to the leaching measured in 

the reactor at the time of sampling than the initial condition. 

63
Characterization of Coal Combustion Residues 

SPECIFIC CONSULTATION ISSUE 3

For assessing metals leaching, pH is the strongest 

predictor of leaching potential in most cases. 

Other important factors include infiltration rate, 

liquid/solid ratio, redox environment, effect of 

common ions and ionic strength, effects of 

external factors (co-disposed waste, biological 

activity, etc.), and exposure to ambient air. The 

relative importance of these factors is likely to vary 

for different wastes. 

COMMENTS

SPECIFIC CONSULTATION ISSUE 3

• Redox condition (Eh), organic matter, aging-afterdisposal are important factors not in current tests 

• Microbes important, but not in current tests; 

biotransformation can render solid phase metals soluble 

• Inclusion of microbes difficult for standard tests 

• pH important; not clear it is “strongest” predictor 

• Depends on constituent; pure metals, organics 

influenced by different factors 

• R&D needed to be able to rank parameters 

• Again, need to define objectives better 

64
Characterization of Coal Combustion Residues 

SPECIFIC CONSULTATION ISSUE 4

The development of multiple leaching tests, or a 

flexible testing framework is required. Selection of 

a suitable leaching test should be made based on a 

number of factors: anticipated use of test results, 

waste characterization, the range of plausible 

disposal or reuse conditions, and previously 

available information on the subject waste or similar 

wastes. ... 

COMMENTS

SPECIFIC CONSULTATION ISSUE 4

• Framework of Kosson et al. is flexible tiered approach that encompasses 

equilibrium and kinetics and includes a suite of tests to address both, and 

allows for site-specific and generic release estimates using mass transfer 

modeling 

• Framework of Kosson et al. is broad and potentially applicable to broad range 

of wastes and disposal scenarios 

• Framework is open ended; it is a huge step beyond a single leach test; the 

manner in which it will be implemented by decisionmakers needs to be clarified 

• Establishment of the framework for implementation will be resource intensive; 

EPA needs to justify the value of the information for decisionmaking, as 

balanced against other waste regulation needs. 

• Need systematic approach for applying framework 

• Need well-defined objectives for framework in order to develop step-by-step 

guidance for use 

65
Characterization of Coal Combustion Residues 

SPECIFIC CONSULTATION ISSUE 5

Modeling may also play an important role in 

relating laboratory and field conditions to one 

another, and in using leach test results to 

assess the leaching potential of waste. 

COMMENTS

SPECIFIC CONSULTATION ISSUE 5

• Concerned about use of deterministic models for prediction of leaching 

potential; probabilistic modeling will be more appropriate in some cases, but 

is resource intensive 

• Concern about incorporating modeling into leaching test protocol; 

connecting model to field difficult 

• Modeling of leaching test may be useful for better understanding leach 

mechanisms, and connection of test with field 

• For certain wastes, coupling of leach tests with a model should be 

considered to predict solubilization over time, especially for organics 

(Multiple equil. states may exist) 

• Usefulness of modeling depends on question to be answered; goals for 

leach eval. need to be defined 

66
Characterization of Coal Combustion Residues 

GENERAL CONSULTATION ISSUE 1

EPA requests SAB reaction to current research, 

and the potential to apply it to improve particular 

programs, specifically programs that do not now 

require the use of TCLP. 

COMMENTS

GENERAL CONSULTATION ISSUE 1

• Capability to address organics, oily wastes, long-term 

reliability need to be incorporated 

• Framework of Kosson et al. is broadly applicable; more 

development work yet needed (guidance for specific 

applications, database for field conditions and waste types, 

data quality criteria, data interpretation/decisionmaking) 

• Framework of Kosson et al. is responsive to the 1999 SAB 

commentary, but to this point is limited to inorganics 

• Current research proceeding without clear definition of 

problem to be addressed by alternatives to TCLP 

• EPA should invest in identifying areas where alternative to 

TCLP is vitally needed 

67
Characterization of Coal Combustion Residues 

COMMENTS

GENERAL CONSULTATION ISSUE 1

• Leaching-related research inside/outside EPA 

could be exploited more 

COMMENTS

GENERAL CONSULTATION ISSUE 1

• Tiered structure of framework: enables tradeoffs in value of 

information 

• EPA should prioritize R&D efforts based on assessment of 

the problem most in need of alternatives to the TCLP, e.g., 

S If going to do evaluation of problems driving TCLP

 alternatives, try to ascertain value of making a change,

 i.e., economic analysis of problem 

S Evaluate waste generation and management trends an

 projections as well as current situation 

S Cost-benefit analysis may be difficult; try to assess

 opportunity cost of not pursuing alt. to TCLP 

68
Characterization of Coal Combustion Residues 

GENERAL CONSULTATION ISSUE 2

EPA requests SAB reaction to the direction for longterm research work to further develop fundamental

understanding of leaching that would improve the

predictive capability of test suites or testing

frameworks. 

COMMENTS

GENERAL CONSULTATION ISSUE 2

• Goals for long-term research not well defined 

• Increased fundamental knowledge will yield long-term 

advancement in assessment of leaching 

• Funding priority for leaching research clearly is low. 

• Long-term ORD research should be better coordinated with 

efforts inside/outside EPA, including DOD, FHWA, DOE 

• Long-term ORD research is responsive to 1999 SAB 

commentary in science factors under study, but is focused on 

inorganics only and will benefit from clearer objectives 

69
Characterization of Coal Combustion Residues 

COMMENTS

GENERAL CONSULTATION ISSUE 2

• Problem definition has two components 

S determine waste categories and field situations

 most in need of TCLP alternatives 

S determine research priorities for the most

 important waste/field situations

COMMENTS

GENERAL CONSULTATION ISSUE 2

• Organics, manufacturing process wastes, end-oflife product wastes need to be considered 

• Industry/government/academic research 

consortium on leashing issues would be useful 

• Industry may be willing to co-fund leaching 

evaluation R&D 

• EPA should investigate collaborative efforts with 

European, Canadian, and Japanese researchers 

70
Characterization of Coal Combustion Residues 

KEY FINDINGS AND RECOMMENDATIONS

• Alternatives to TCLP for evaluation of leach potential are 

needed for some waste and site situations 

• Not clear if there is large or small number of waste and site 

situations for which alternative approach is needed 

• Framework of Kosson et al. is broadly applicable; more 

development work yet needed (guidance for specific 

applications, database for field conditions and waste types, data 

quality criteria, data interpretation/decisionmaking) 

• Framework of Kosson et al. is responsive to the 1999 SAB 

commentary, but to this point is limited to inorganics 

KEY FINDINGS AND RECOMMENDATIONS

• Current research needs clear definition of problem 

to be addressed by alternative to TCLP 

• EPA should invest in identifying areas where 

alternative to TCLP is vitally needed 

• The 1999 SAB commentary focused on sciencebased issues in leaching: EPA has been 

responsive within resource limitations. 

• Organic waste constituents need to be considered, 

and a broader framework should include 

assessment or organic constituent leaching 

71
Characterization of Coal Combustion Residues 

KEY FINDINGS AND RECOMMENDATIONS

• Research and development should focus on most 

applicable waste/site situations, and possible 

beneficial reuse scenarios 

• Given limited R&D resources, EPA should 

prioritize research efforts and leverage DOD, 

DOE, FHWA interest in leaching through crossgovt coordination, as well as industrial and 

international collaboration 

• EPA intra-agency efforts should be more closely 

linked 

72
Characterization of Coal Combustion Residues 

Appendix B

DOE NETL Full-Scale Test Site Flow Diagrams

73 
Characterization of Coal Combustion Residues 

Brayton Point Unit 1 

• Carbon injected upstream of second ESP (Research Cottrell). Only 1⁄2 of the unit was treated, or carbon was injected 

into one of the two new ESPs (Research Cottrell ESPs). 

• Hopper IDs also shown. Samples from C-row are from the first row of hoppers in the second ESP. 

74 
Characterization of Coal Combustion Residues 

• Bird’s eye view of second ESP. 

• Samples taken from C-raw hoppers. 

75 
Characterization of Coal Combustion Residues 

Pleasant Prairie Unit 2 

Carbon injected upstream of cold-side ESP. Only 1⁄4 of the unit was treated. Test ESP was ESP 2-4. 

ESP 2-4 

Spray Cooling 

Carbon Injection 

SCEM Inlet 

SCEM Outlet 

on vertical drop 

ESP 2-4 

Spray Cooling

Carbon Injection

SCEM Inlet

SCEM Outlet

on vertical drop

76 
Characterization of Coal Combustion Residues 

Salem Harbor Unit 1 

Carbon injected upstream of cold-side ESP. Row-A hoppers were the front hoppers. 

Long Air 

Heater 

Short Air 

Heater 

I.D. 

Fan 

F.D. 

Steam Coils Fan

ESP 

Boiler 

Long Air

Heater

Short Air

Heater

Lo I.D.

Fan

F.D.

Steam Coils Fan

ESP

Boiler

ng Air

Heater

Short Air

Heater

I.D.

Fan

F.D.

Steam Coils Fan

ESP

Boiler

Carbon 

Injection Point 

Facility C 

Carbon injected upstream of Unit 3B COHPAC baghouse (in between hot-side ESP and baghouse) 

77 
Characterization of Coal Combustion Residues 

St. Clair

Total flow from 

boiler/econimizer 

Total Flow to 

Stack 

North-Side CS-ESP (ESP B) 

South-Side CS-ESP (ESP A) 

B-PAC injection 

Facility L 

B-PAC injection 

Total flow from 

boiler/econimizer 

B-Side HS-ESP (ESP B) To B Stack 

To A Stack 

A-side HS-ESP (ESP A) 

78 
Characterization of Coal Combustion Residues 

Appendix C

Quality Assurance Project Plan

7 9
Characterization of Coal Combustion Residues 

8 0
Characterization of Coal Combustion Residues 

8 1
Characterization of Coal Combustion Residues 

8 2
Characterization of Coal Combustion Residues 

8 3
Characterization of Coal Combustion Residues 

8 4
Characterization of Coal Combustion Residues 

8 5
Characterization of Coal Combustion Residues 

8 6
Characterization of Coal Combustion Residues 

8 7
Characterization of Coal Combustion Residues 

8 8
Characterization of Coal Combustion Residues 

8 9
Characterization of Coal Combustion Residues 

9 0
Characterization of Coal Combustion Residues 

9 1
Characterization of Coal Combustion Residues 

9 2
Characterization of Coal Combustion Residues 

9 3
Characterization of Coal Combustion Residues 

9 4
Characterization of Coal Combustion Residues 

9 5
Characterization of Coal Combustion Residues 

9 6
Characterization of Coal Combustion Residues 

9 7
Characterization of Coal Combustion Residues 

9 8
Characterization of Coal Combustion Residues 

9 9
Characterization of Coal Combustion Residues 

100
Characterization of Coal Combustion Residues 

101
Characterization of Coal Combustion Residues 

102
Characterization of Coal Combustion Residues 

103
Characterization of Coal Combustion Residues 

104
Characterization of Coal Combustion Residues 

105
Characterization of Coal Combustion Residues 

106
Characterization of Coal Combustion Residues 

107
Characterization of Coal Combustion Residues 

108
Characterization of Coal Combustion Residues 

109
Characterization of Coal Combustion Residues 

110
Characterization of Coal Combustion Residues 

111
Characterization of Coal Combustion Residues 

112
Characterization of Coal Combustion Residues 

113
Characterization of Coal Combustion Residues 

114
Characterization of Coal Combustion Residues 

115
Characterization of Coal Combustion Residues 

Appendix D

Brayton Point Fly Ashes

116
Characterization of Coal Combustion Residues 

List of Figures 

Figure Page 

D-1 pH Titration Curves for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control ............................................... 118

D-2 pH as a Function of LS Ratio for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control ................................. 118

D-3 Mercury Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 119

D-4 Mercury Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and

the Fly Ash with Enhanced Hg Control .............................................................................................................................. 120

D-5 Arsenic Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 121

D-6 Arsenic Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash

and the Fly Ash with Enhanced Hg Control ....................................................................................................................... 122

D-7 Selenium Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 123

D-8 Selenium Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash

and the Fly Ash with Enhanced Hg Control ....................................................................................................................... 124

D-9 Regression Curves of Experimental Data of Arsenic Solubility as a Function of pH. ......................................................... 125

D-10 Regression Curves of Experimental Data of Selenium Solubility as a Function of pH ........................................................ 126

D-11 100-Year Arsenic Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal

in a Combustion Waste Landfill .......................................................................................................................................... 127

D-12 100-Year Selenium Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal

in a Combustion Waste Landfill .......................................................................................................................................... 127

D-13 100-Year Arsenic Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI ................................................... 128

D-14 100-year Selenium Release Estimates fromA) Baseline Fly Ash and B) Fly Ash with ACI ................................................. 129

117
6 

pH Titration Curves 

Baseline Fly Ash Fly Ash with ACI 

14 14

12.2

12 12 

10 9.5 10

8 8

pH

pH 

6 

4 4

2 

-12 -10 -8 -6 -4 -2 0 2 4 6 8 -2 -1.5 -1 -0.5 0 0.5 1 1.5 

meq Acid/g dry meq Acid/g dry 

2 

SR2-BPB-0001 - A 

SR2-BPB-0001 - B 

SR2-BPB-0001 - C 

SR2-BPT-0001 - A 

SR2-BPT-0001 - B 

SR2-BPT-0001 - C 

14 

Baseline Fly Ash 

14 

Fly Ash with ACI 

12 12 

10 10 

6 6 

4 4 

2 2 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

SR3-BPB-0001 - A 

SR3-BPB-0001 - B 

SR3-BPB-0001 - C 

SR3-BPT-0001 - A 

SR3-BPT-0001 - B 

SR3-BPT-0001 - C 

pH

8

pH

8

Characterization of Coal Combustion Residues 

Figure D-1. pH Titration Curves for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control. 

pH as a Function of LS Ratio 

Figure D-2. pH as a Function of LS Ratio for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control. 

118
Mercury Release as a Function of pH 

Baseline Fly Ash Fly Ash with ACI 

*Total content as determined by digestion using method 3052. 

MDL 

ML 

9.5 

0.006 

MCL 

0.001 

0.01 

1 

10 

2 4 6 8 10 12 14 

pH 

SR2-B PT-0001 - A 

SR2-B PT-0001 - B 

SR2-B PT-0001 - C 

5% 95% 

5%

Hg total content*: 1529.6!1.1 ng/g 

MDL 

ML 

12.2 

MCL 

0.001 

0.01 

1 

10 

2 4 6 8 10 12 14 

pH 

SR2-BP B-0001 - A 

SR2-BP B-0001 - B 

SR2-BP B-0001 - C 

5% 95% 

5%

 95% 

Hg total content*: 650.6!6.8 ng/g 

140 

150 

140 

150 

Hg [ μg/ L] 

Hg [μ g/L] Hg spike recovery [%] 

0.1 0.1 

 95% 0.035 

Hg spike recovery [%]

130

120

110

100

90

80

70

130

120

110

100

90

80

70

60 60

2 4 6 8 10 12 14 2 4 6 8 10 12 14

pH pH

SR2-BPB-0001 - A SR2-BPT-0001 - A 

Characterization of Coal Combustion Residues 

Figure D-3. Mercury Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the Fly 

Ash with Enhanced Hg Control. 5th and 95th percentiles of mercury concentrations observed in typical combustion waste 

landfill leachate are shown for comparison. 

119
Baseline Fly Ash Fly Ash with ACI 

MCL 0.02 MCL 0.02 

0.015 0.015 

Hg spike recovery [%] Hg [

μg/L] 

Hg spike recovery [%] Hg [

μg/L] 

0.01 0.01

0.005 0.005 

0 0 

ML 0 2 4 6 8 10 12 0 2 4 6 8 10 12 

MDL LS ratio [mL/g] 

SR3-BPB-0001 - A 

SR3-BPB-0001 - B 

SR3-BPB-0001 - C 

150

140

ML

MDL

150 

140 

LS ratio [mL/g] 

SR3-BPT-0001 - A 

SR3-BPT-0001 - B 

SR3-BPT-0001 - C 

130

120

110

100

90

80

70

130

120

110

100

90

80

70

60

50

60 40 

50 30 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

SR3-BPB-0001 - A SR3-BPT-0001 - A 

Characterization of Coal Combustion Residues 

Mercury Release as a Function of LS Ratio 

Figure D-4. Mercury Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

120
Baseline Fly Ash Fly Ash with ACI 

140 

150 

MDL 

ML 

9.5 

MCL 

0.001 

0.01 

10 

100 

1000 

10000 

2 4 6 8 10 12 14 

pH 

SR2-BPT-0001 - A 

SR2-BPT-0001 - B 

SR2-BPT-0001 - C 

5% 95%

 95% 

As total content*: 27.9!2.1 :g/g 

MDL 

ML 

12.2 

MCL 

0.001 

0.01 

1 

10 

100 

1000 

10000 

2 4 6 8 10 12 14 

pH 

SR2-BPB-0001 - A 

SR2-BPB-0001 - B 

SR2-BPB-0001 - C 

5% 95%

 5%

 95% 

As total content*: 80.5!1.9 :g/g 

*Total content as determined by digestion using method 3052. 

140 

150 

As [

μg/L] 

As [

μg/L] As spike recovery [%] 

6.67 4.8 5% 1

0.1 0.1

As spike recovery [%] 

130

120

110

100

90

80

70

130

120

110

100

90

80

70

60

2 4 6 8 10 12 14 2 4 6 8 10 12 14

pH pH

60

SR2-BPB-0001 - A SR2-BPT-0001 - A 

Characterization of Coal Combustion Residues 

Arsenic Release as a Function of pH 

Figure D-5. Arsenic Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the Fly 

Ash with Enhanced Hg Control. 5th and 95th percentiles of arsenic concentrations observed in typical combustion waste 

landfill leachate are shown for comparison. 

121
Baseline Fly Ash Fly Ash with ACI 

MCL 

0 

5 

10 

15 

20 

25 

30 

35 

40 

As [

μg/L] 

MCL 

0 

5 

10 

15 

20 

25 

30 

35 

40 

As [

μg/L] 

0 2 4 6 8 10 12 0 2 4 6 8 10 12

ML LS ratio [mL/g] ML LS ratio [mL/g] 

MDL MDL 

SR3-BPB-0001 - A 

SR3-BPB-0001 - B 

SR3-BPB-0001 - C 

SR3-BPT-0001 - A 

SR3-BPT-0001 - B 

SR3-BPT-0001 - C 

150 150 

140 140 

As spike recovery [%] 

130

120

110

100

90

80

70

As spike recovery [%] 

130

120

110

100

90

80

70

60 60 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

SR3-BPB-0001 - A SR3-BPT-0001 - A 

Characterization of Coal Combustion Residues 

Arsenic Release as a Function of LS Ratio 

Figure D-6. Arsenic Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

122
Baseline Fly Ash Fly Ash with ACI 

Se total content*: 51.4!1.7 :g/g Se total content*: 51.4!1.7 :g/g 10000 10000 

1000 1000 

 95% 164.3 95% 100 100 MCL 57 MCL 

0.01 0.01 

0.001 

2 4 5%6 8 10 95%12

12.2 

14 

0.001 

5% 9.5 95% 2 4 6 8 10 12 14 

ML pH 

ML pH

MDL SR2-BPB-0001 - A 

SR2-BPB-0001 - B 

SR2-BPB-0001 - C 

MDL SR2-BPT-0001 - A 

SR2-BPT-0001 - B 

SR2-BPT-0001 - C 

*Total content as determined by digestion using method 3052. 

150 150 

140 140 

10 

Se [

μg/L] 

10

Se [

μg/L] Se spike recovery [%] 

1 5% 5% 1

0.1 0.1

130

120

110

100

90

80

70

130

120

110

100

90

80

70

Se spike recovery [%] 

60 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

60 

SR2-BPB-0001 - A SR2-BPT-0001 - A 

Characterization of Coal Combustion Residues 

Selenium Release as a Function of pH 

Figure D-7. Selenium Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the 

Fly Ash with Enhanced Hg Control. 5th and 95th percentiles of selenium concentrations observed in typical combustion 

waste landfill leachate are shown for comparison. 

123
Baseline Fly Ash Fly Ash with ACI 

600 600 

500 500 

400 400 Se spike recovery [%] Se [

μg/L] 

Se spike recovery [%] Se [

μg/L] 

300 300

200 200

100 100 MCL MCL 0 0 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

ML LS ratio [mL/g] 

ML LS ratio [mL/g] 

MDL 

MDL 

SR3-BPB-0001 - A 

SR3-BPB-0001 - B 

SR3-BPB-0001 - C 

SR3-BPT-0001 - A 

SR3-BPT-0001 - B 

SR3-BPT-0001 - C 

150 150 

140 140 

130

120

110

100

90

80

70

130

120

110

100

90

80

70

60 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

60 

SR3-BPB-0001 - A SR3-BPT-0001 - A 

Characterization of Coal Combustion Residues 

Selenium Release as a Function of LS Ratio 

Figure D-8. Selenium Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

124
Baseline Fly Ash Fly Ash with ACI 

100000 100000 

10000 10000 

1000 1000 

0.1 0.1 

0.01 0.01 

5% 95% 5% 95%

95% 95%

5%

100 100

As [

μg/L] 

As [

μg/L] 

10 10

5% 1 1

0.001 0.001

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

SR2-BPB-0001-A SR2-BPT-0001-A 

SR2-BPB-0001-B SR2-BPT-0001-B 

SR2-BPB-0001-C SR2-BPT-0001-C 

A) Fit curve B) Fit curve 

Material log As (μg/L) pH range of R2 Number of 

validity points 

BPB 0.0004 pH5 -0.0135 pH4 0.1634 pH3 3-14 0.77 27 

-0.8130 pH2 1.1609 pH 2.7085 

BPT 0.0005 pH5 -0.0207 pH4 0.3035 pH3 3-12.5 0.98 33 

-2.0113 pH2 5.4552 pH -2.7126 

Characterization of Coal Combustion Residues 

Arsenic Solubility 

Figure D-9. Regression Curves of Experimental Data of Arsenic Solubility as a Function of pH. 

125
Baseline Fly Ash Fly Ash with ACI 

100000 100000 

10000 10000 

1000 1000 

95% 95%

5%

100 100

Se [

μg/L] 

Se [

μg/L] 

10 10

5% 1 1

0.1 0.1 

0.01 0.01 

0.001 0.001 

5% 95% 5% 95% 2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

SR2-BPB-0001-A 

SR2-BPB-0001-B 

SR2-BPB-0001-C 

A) Fit curve B)

SR2-BPT-0001-A 

SR2-BPT-0001-B 

SR2-BPT-0001-C 

Fit curve 

Material log Se (μg/L) pH range of R2 Number of 

validity points 

BPB -0.0006 pH5 0.0262 pH4 -0.4379 pH3 3-14 0.81 27 

3.3856 pH2 -12.0291 pH 17.7907 

BPT -0.0006 pH5 0.0229 pH4 -0.3475 pH3 3-12.5 0.93 33 

2.4521 pH2 -7.9388 pH 11.4439 

Characterization of Coal Combustion Residues 

Selenium Solubility 

Figure D-10. Regression Curves of Experimental Data of Selenium Solubility as a Function of pH. 

126
10000 

1000 

Mt min 

Mt - 5% 

Mt - 50% 

100 

10 Mt - 95% 

Mean Mt 

1 Mt max 

0.1 

5% 50% 95%

0 20 40 60 80 100

Percentile

100-year Mt [

μg/kg] 

BPB BPT 

μg/kg % μg/kg 

0.2 0.0003 0.1 

0.9 0.0011 0.1 

152 0.2 22 

2095 2.6 338 

468 0.6 90 

4693 5.8 10157 

% 

0.0003 

0.0005 

0.0772 

1.2 

0.3 

36.4 

BPB BPT 

100000

BPB BPT 10000 

100-year Mt [μg/kg] 

μg/kg % μg/kg % 

Mt min 1.5 0.003 5.9 0.004 1000

Mt - 5% 

Mt - 50% 100 

Mt - 95% 

10 Mean Mt 

Mt max 

1 

0.1 

5% 50% 95% 

0 20 40 60 80 100

Percentile

BPB BPT 

7.6 

1031 

16681 

3573 

45169 

0.015 

2.0 

32.5 

7.0 

87.9 

10.0 

1661 

23931 

6038 

151900 

0.007 

1.1 

15.8 

4.0 

100.0 

Characterization of Coal Combustion Residues 

100-Year Arsenic Release Estimates 

Figure D-11. 100-Year Arsenic Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal 

in a Combustion Waste Landfill. 

100-Year Selenium Release Estimates 

Figure D-12. 100-Year Selenium Release Estimates as a Function of the Cumulative Probability for the Scenario of 

Disposal in a Combustion Waste Landfill. 

127
BPB - Arsenic 

80500 μg/kg 

100% 

2095 μg/kg 

2.6% 

2439 μg/kg 

3.0% 

105 μg/kg 

0.1% 

83 μg/kg 

0.1% 

1 

10 

100 

1000 

10000 

100000 

100-year arsenic release [μg/kg] 

MCLLS 95% = 1000 :g/kg 

MCLLS 12.5 = 125 :g/kg 

Total content Combustion Default - pH 3 Default -pH Default ­

Waste Landfill - 12.5 Natural pH 

95% confidence 12.2 A) 

BPT - Arsenic 

60 μg/kg 

0.2% 

999 μg/kg 

3.6% 

1981 μg/kg 

7.1% 

338 μg/kg 

1.2% 

27900 μg/kg 

100% 

1 

10 

100 

1000 

10000 

100000 

100-year arsenic release [μg/kg] 

MCLLS 95% = 1000 :g/kg 

MCLLS 12.5 = 125 :g/kg 

Total content Combustion Default - pH 3 Default -pH Default ­

Waste Landfill ­ 12.5 Natural pH 

95% confidence 9.5 

B) 

Characterization of Coal Combustion Residues 

100-Year Arsenic Release Estimates 

Figure D-13. 100-Year Arsenic Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI. Release estimates 

for percolation controlled scenario are compared to release estimate based on total content.The amount of the arsenic that 

would be released if the release concentration was at the MCL is also shown for comparison (LSdefault scenario = 12.5 L/kg and 

LS95% = 100 L/kg). 

128
BPB - Selenium 

51400 μg/kg 

MCLLS 95% = 5000 :g/kg 

MCLLS 12.5 = 625 :g/kg 

713 μg/kg 

1.4% 

3226 μg/kg 

6.3% 

2667 μg/kg 

5.2% 

16681 μg/kg 

32.5% 

100% 

1 

10 

100 

1000 

10000 

100000 

100-year selenium release [μg/kg] 

Total content Combustion Default - pH 3 Default -pH Default ­

Waste Landfill ­ 12.5 Natural pH 

95% confidence 12.2 

A) 

BPT - Selenium 

151900 μg/kg 

2054 μg/kg 

1.4% 

43479 μg/kg 

28.6% 

1347 μg/kg 

0.9% 

23931 μg/kg 

15.8% 

100% 

1 

10 

100 

1000 

10000 

100000 

1000000 100-year selenium release [μg/kg] 

MCLLS 95% = 5000 :g/kg 

MCLLS 12.5 = 625 :g/kg 

Total content Combustion Default - pH 3 Default -pH Default ­

Waste Landfill ­ 12.5 Natural pH 

95% confidence 9.5 

B) 

Characterization of Coal Combustion Residues 

100-Year Selenium Release Estimates 

Figure D-14. 100-year Selenium Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI. Release estimates 

for percolation controlled scenario are compared to release estimate based on total content.The amount of the selenium 

that would be released if the release concentration was at the MCL is also shown for comparison (LSdefault scenario = 12.5 L/kg 

and LS95% = 100 L/kg). 

129
Characterization of Coal Combustion Residues 

Comments 

Figure D-3: 

• The fly ash from the test case had greater total Hg 

content than the fly ash from the baseline case (by 

about 2.5 times). 

• Hg release is low (but poor replication) for both baseline 

and test cases. 

Figure D-5: 

• The fly ash from the test case had lower total As content than the fly ash from the baseline case (by about a 

factor of 3). 

• The laboratory measurements fit within the 5-95% confidence intervals of the field observations. 

• As release is most frequently worse in baseline case 

than test case and exceeds MCL for many possible 

conditions. 

Figure D-7: 

• The fly ash from the test case had greater total Se 

content than the fly ash from the baseline case (by 

about a factor of 3). 

• The laboratory measurements fit within the 5% to 95% 

confidence intervals of the field observations. 

• Se release substantially exceeds MCL for both baseline 

and test cases and is generally worse for test cases. 

• The fly ash from the test case resulted in greater Se 

concentration at the natural pH of the material than 

the baseline case (by about 3 times). 

Figures D-11. and D-12: 

• The fly ash from the test case would result in As release less than expected from the baseline case, with a 

95% probability to be less than 338 and 2095 :g/kg, 

respectively. 

• No significant difference in Se release is expected from 

both baseline and test cases. 

Figure D-13: 

• For the 95% probability scenario, arsenic release from 

the baseline case would be greater than the amount 

that would be released if the release concentration was 

at the MCL. 

• For the 95% probability scenario, a lower arsenic release would be expected from the test case. However, 

the fly ash from the test case had lower total As content than the fly ash from the baseline case (by about a 

factor of 3). 

• For the default scenario corresponding to disposal in a 

monofill (leachate pH controlled by the material being 

disposed), no significant difference in arsenic release 

between the baseline and the test cases would be expected. Additionally, arsenic release would be less than 

the amount that would be released if the release concentration was at the MCL. 

• For the default scenario corresponding to the “extreme” 

pH of 3, arsenic release would be greater than the 

amount that would be released if the release concentration was at the MCL, for both the baseline and the 

test cases. 

• For the default scenario corresponding to the “extreme” 

pH of 12.5, arsenic release is expected to be greater 

for the test case than the baseline case. 

Figure D-14: 

• For the 95% probability case, selenium release would 

be greater than the amount that would be released if 

the release concentration was at the MCL for both the 

baseline and the test cases. 

• For the default scenario corresponding to disposal in a 

monofill (leachate pH controlled by the material being 

disposed), a greater selenium release would be expected from the test case. 

• For the default scenario corresponding to the “extreme” 

pH of 12.5, selenium release is expected to be greater 

for the test case than the baseline case. Selenium release from the test case would be greater than the 

amount that would be released if the release concentration was at the MCL. 

130
Characterization of Coal Combustion Residues 

Appendix E

Pleasant Prairie Fly Ashes

131
Characterization of Coal Combustion Residues 

List of Figures 

Figure Page 

E-1 pH Titration Curves for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control ............................................... 133

E-2 pH as a Function of LS Ratio for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control ................................. 133

E-3 Mercury Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 134

E-4 Mercury Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and

the Fly Ash with Enhanced Hg Control .............................................................................................................................. 135

E-5 Arsenic Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 136

E-6 Arsenic Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash

and the Fly Ash with Enhanced Hg Control ....................................................................................................................... 137

E-7 Selenium Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 138

E-8 Selenium Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash

and the Fly Ash with Enhanced Hg Control ....................................................................................................................... 139

E-9 Regression Curves of Experimental Data of Arsenic Solubility as a Function of pH. ......................................................... 140

E-10 Regression Curves of Experimental Data of Selenium Solubility as a Function of pH ........................................................ 141

E-11 100-Year Arsenic Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal

in a Combustion Waste Landfill .......................................................................................................................................... 142

E-12 100-Year Selenium Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal

in a Combustion Waste Landfill .......................................................................................................................................... 142

E-13 100-Year Arsenic Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI ................................................... 143

E-14 100-year Selenium Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI ................................................. 144

132
pH Titration Curves 

Baseline Fly Ash Fly Ash with ACI 

14 14

12 12 

11.2 11.9 

10 10 

8 8

pH

pH 

6 

4 

2 

-2 0 2 4 6 8 10 

meq Acid/g dry 

SR2-PPB-0001 - A 

SR2-PPB-0001 - B 

SR2-PPB-0001 - C 

6 

4 

2 

-4 -2 0 2 4 6 

meq Acid/g dry 

SR2-PPT-0001 - A 

SR2-PPT-0001 - B 

SR2-PPT-0001 - C 

8 

pH as a Function of LS Ratio 

Baseline Fly Ash 

14

12

10

Fly Ash with ACI 

14 

12 

10 

4 4 

2 2 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

SR3-PPB-0001 - A 

SR3-PPB-0001 - B 

SR3-PPB-0001 - C 

SR3-PPT-0001 - A 

SR3-PPT-0001 - B 

SR3-PPT-0001 - C 

pH

8

pH

6

8

6

Characterization of Coal Combustion Residues 

Figure E-1. pH Titration Curves for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control. 

Figure E-2. pH as a Function of LS Ratio for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control. 

133
Baseline Fly Ash Fly Ash with ACI 

Hg total content*: 157.7!0.2 ng/g Hg total content*: 1180.1!1.2 ng/g 10 10

MCL MCL 

1 1

11.2 

0.011 

2 4 6 8 10 12 14 

5% 95% 

95% 

11.9 95%

5% 5% Hg [μg/L] Hg spike recovery [%] 

Hg [μg/L] 

0.1 0.1 95% 

0.011 

0.01 0.01

0.001 0.001 5% 2 4 6 8 10 12 14 

pH pH 

ML ML

SR2-PPT-0001 - A 

SR2-PPT-0001 - B 

SR2-PPT-0001 - C 

SR2-PPB-0001 - A 

SR2-PPB-0001 - B 

SR2-PPB-0001 - C 

MDL 

MDL 

*Total content as determined by digestion using method 3052. 

150 150 

140 140 

130

120

110

100

90

80

70

130

120

110

100

90

80

Hg spike recovery [%] 

70

60 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

60 

SR2-PPB-0001 - A SR2-PPT-0001 - A 

Mercury Release as a Function of pH 

Characterization of Coal Combustion Residues 

Figure E-3. Mercury Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the Fly 

Ash with Enhanced Hg Control. 5th and 95th percentiles of mercury concentrations observed in typical combustion waste 

landfill leachate are shown for comparison. 

134
Mercury Release as a Function of LS Ratio 

Baseline Fly Ash Fly Ash with ACI 

MCL 0.02 MCL 0.02 

0.015 0.015 

Hg spike recovery [%] Hg [

μg/L] 

Hg spike recovery [%] Hg [

μg/L] 

0.01 0.01

0.005 0.005 

0 0 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

ML LS ratio [mL/g] MDL 

SR3-PPB-0001 - A 

SR3-PPB-0001 - B 

SR3-PPB-0001 - C 

150

140

130

120

110

100

90

80

70

LS ratio [mL/g] 

SR3-PPT-0001 - A 

SR3-PPT-0001 - B 

SR3-PPT-0001 - C 

ML

MDL

150

140

130

120

110

100

90

80

70

60 60

0 2 4 6 8 10 12 0 2 4 6 8 10 12

LS ratio [mL/g] LS ratio [mL/g]

SR3-PPB-0001 - A SR3-PPT-0001 - A 

Characterization of Coal Combustion Residues 

Figure E-4. Mercury Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

135
Arsenic Release as a Function of pH 

Baseline Fly Ash Fly Ash with ACI 

As total content*: 21.3!0.3 :g/g As total content*: 24.0!0.8 :g/g 10000 10000 

1000 

 95% 100 

1000 

 95% 100 

MCL MCL 

4.2 5%

0.01 0.01 

0.001 0.001 

5% 11.2 95% 5% 11.9 95%

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH ML pH ML

MDL SR2-PPB-0001 - A 

SR2-PPB-0001 - B 

SR2-PPB-0001 - C 

MDL SR2-PPT-0001 - A 

SR2-PPT-0001 - B 

SR2-PPT-0001 - C 

*Total content as determined by digestion using method 3052. 

150 150

140 140 

10 10

4 

As [

μg/L] As spike recovery [%] 

As [

μg/L] 

1 5% 1

0.1 0.1

2 4 6 8 10 12 14 

pH 

2 4 6 8 10 12 14 

pH 

130

120

110

100

90

80

70

130

120

110

100

90

80

70

60

As spike recovery [%] 

60

SR2-PPB-0001 - A SR2-PPT-0001 - A 

Characterization of Coal Combustion Residues 

Figure E-5. Arsenic Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the Fly 

Ash with Enhanced Hg Control. 5th and 95th percentiles of arsenic concentrations observed in typical combustion waste 

landfill leachate are shown for comparison. 

136
Arsenic Release as a Function of LS Ratio 

Baseline Fly Ash Fly Ash with ACI

20 20

15 15

0 2 4 6 8 10 12 

LS ratio [mL/g] 

5 5

0 

ML 

ML MDL 

MDL 

0 

0 2 4 6 8 10 12 

LS ratio [mL/g] 

SR3-PPB-0001 - A 

SR3-PPB-0001 - B 

SR3-PPB-0001 - C 

SR3-PPT-0001 - A 

SR3-PPT-0001 - B 

SR3-PPT-0001 - C 

150 150

140 140 As spike recovery [%] As [

μg/L] 

As spike recovery [%] As [

μg/L] 

MCL MCL 

10 10

130 130

120 120

110 110

100 100

90 90

80 80

70 70

60 60 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

SR3-PPB-0001 - A SR3-PPT-0001 - A 

Characterization of Coal Combustion Residues 

Figure E-6. Arsenic Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

137
Selenium Release as a Function of pH 

Baseline Fly Ash Fly Ash with ACI 

Se total content*: <4.0 :g/g Se total content*: <4.0 :g/g 10000 10000 

1000 1000 

110.9 95% 95% 100 100 MCL MCL 

11.2 

2 4 6 8 10 12 14 

5% 95%

0.01 0.01 

25.3 10 10

Se [

μg/L] 

Se [

μg/L] 

5% 5% 1 1

0.1 0.1

0.001 0.001

5% 11.9 95%

2 4 6 8 10 12 14

ML pH ML pH 

SR2-PPB-0001 - A 

SR2-PPB-0001 - B 

SR2-PPB-0001 - C 

MDL MDL 

B) 

SR2-PPT-0001 - A 

SR2-PPT-0001 - B 

SR2-PPT-0001 - C 

*Total content as determined by digestion using method 3052. 

150 150 

140 140 

130

120

110

100

90

80

70

Se spike recovery [%] 

130

120

110

100

90

80

70

Se spike recovery [%] 

60 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

60 

SR2-PPB-0001 - A SR2-PPT-0001 - A 

Characterization of Coal Combustion Residues 

Figure E-7. Selenium Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the 

Fly Ash with Enhanced Hg Control. 5th and 95th percentiles of selenium concentrations observed in typical combustion 

waste landfill leachate are shown for comparison. 

138
Selenium Release as a Function of LS Ratio 

Baseline Fly Ash Fly Ash with ACI

160 160 

140 140 

120 120 

MCL 

0 2 4 6 8 10 12 

LS ratio [mL/g] 

MCL 40 40

20 20 

0 0 

0 2 4 6 8 10 12 

LS ratio [mL/g] ML ML 

MDL 

Se [

μg/L] 

SR3-PPB-0001 - A 

SR3-PPB-0001 - B 

SR3-PPB-0001 - C 

MDL SR3-PPT-0001 - A 

SR3-PPT-0001 - B 

SR3-PPT-0001 - C 

150

140

150 

140 

100 100 Se [

μg/L] 

80 80

60 60

Se spike recovery [%] Se spike recovery [%] 

130

120

110

100

90

80

70

130

120

110

100

90

80

70

60 60 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

SR3-PPB-0001 - A SR3-PPT-0001 - A 

Characterization of Coal Combustion Residues 

Figure E-8. Selenium Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

139
Arsenic Solubility 

Baseline Fly Ash Fly Ash with ACI

5% 95%

 5% 

95% 

0.001 

0.01 

0.1 

1 

10 

100 

1000 

10000 

100000 

As [

μg/L] 

5% 95%

 5% 

95% 

0.001 

0.01 

0.1 

1 

10 

100 

1000 

10000 

100000 

As [

μg/L] 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

SR2-PPT-0001-A 

SR2-PPT-0001-B 

SR2-PPT-0001-C 

A) Fit curve 

SR2-PPB-0001-A 

SR2-PPB-0001-B 

SR2-PPB-0001-C 

Fit curve B) 

Material log As (μg/L) pH range of R2 Number of 

validity points 

PPB 0.0003 pH5 -0.0117 pH4 0.1674 pH3 3-12.5 0.47 33 

-1.1600 pH2 3.8716 pH -4.2743 

PPT 0.0006 pH5 -0.0238 pH4 0.3460 pH3 3-13 0.84 33 

-2.3840 pH2 7.7036 pH -8.6786 

Characterization of Coal Combustion Residues 

Figure E-9. Regression Curves of Experimental Data of Arsenic Solubility as a Function of pH. 

140
Selenium Solubility 

Baseline Fly Ash Fly Ash with ACI

100000 

10000 

1000 

100 

10 

5% 

5% 

95% 

0.001 

0.01 

0.1 

1 

14 

0.001 

0.01 

0.1 

1 

10 

100 

1000 

10000 

100000 

14 

Se [

μg/L] 

95%

Se [

μg/L] 

5%

95% 12 5% 95% 2 4 6 8 10 2 4 6 8 10 12

pH pH 

SR2-PPB-0001-A 

SR2-PPB-0001-B 

SR2-PPB-0001-C 

A) Fit curve B) 

SR2-PPT-0001-A 

SR2-PPT-0001-B 

SR2-PPT-0001-C 

Fit curve 

Material log Se (μg/L) pH range of R2 Number of 

validity points 

PPB 0.0006 pH5 -0.0234 pH4 0.3605 pH3 3-12.5 0.54 33 

-2.6711 pH2 9.4536 pH -10.6432 

PPT 0.0012 pH5 -0.0440 pH4 0.6379 pH3 3-13 0.81 33 

-4.3855 pH2 14.2483 pH -15.6626 

Characterization of Coal Combustion Residues 

Figure E-10. Regression Curves of Experimental Data of Selenium Solubility as a Function of pH. 

141
100-Year Selenium Release Estimates 

Selenium

100000

10000 PPB PPT 

% μg/kg 

100-year Mt [μg/kg] 

Mt min 

Mt - 5% 

100 

1000 

Mt - 50% 

Mt - 95% 

10 Mean Mt 

Mt max 

1 

0.1 

5% 50% 95% 

0 20 40 60 80 100

Percentile

μg/kg 

3.0 

4.4 

733 

4000 

2254 

4000 

0.1 

0.1 

18.3 

100.0 

56.4 

100.0 

0.9 

3.3 

516 

4000 

1599 

4000 

% 

0.0 

0.1 

12.9 

100.0 

40.0 

100.0 

PPB PPT 

100-Year Arsenic Release Estimates 

Arsenic

10000

PPB PPT 

% μg/kg 

100-year Mt [

μg/kg] 

1000 

Mt min 

100 Mt - 5% 

Mt - 50% 

Mt - 95% 10 Mean Mt 

Mt max 

1 

0.1 

5% 50% 95% 

0 20 40 60 80 100

Percentile

μg/kg 

0.1 

0.2 

36 

473 

107 

1188 

0.0006 

0.0010 

0.2 

2.2 

0.5 

5.6 

0.1 

0.2 

27 

358 

81 

1049 

% 

0.0004 

0.0007 

0.1 

1.5 

0.3 

4.4 

PPB PPT 

Characterization of Coal Combustion Residues 

Figure E-11. 100-Year Arsenic Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal 

in a Combustion Waste Landfill. 

Figure E-12. 100-Year Selenium Release Estimates as a Function of the Cumulative Probability for the Scenario of 

Disposal in a Combustion Waste Landfill. 

142
100-Year Arsenic Release Estimates 

PPB - Arsenic 

21300 μg/kg 

MCLLS 12.5 = 125 :g/kg 

MCLLS 95% = 1000 :g/kg 

50 μg/kg 

0.2% 

104 μg/kg 

0.5% 45 μg/kg 

0.2% 

473 μg/kg 

2.2% 

100% 

1 

10 

100 

1000 

10000 

100000 

100-year arsenic release [μg/kg] 

Total content Combustion Default - pH 3 Default -pH Default ­

Waste Landfill ­ 12.5 Natural pH 

95% confidence 11.2 

A) 

PPT - Arsenic 

24000 μg/kg 

52 μg/kg 

0.2% 

96 μg/kg 

0.4% 44 μg/kg 

0.2% 

358 μg/kg 

1.5% 

100% 

1 

10 

100 

1000 

10000 

100000 

100-year arsenic release [μg/kg] 

MCLLS 95% = 1000 :g/kg 

MCLLS 12.5 = 125 :g/kg 

Total content Combustion Default - pH 3 Default -pH Default ­

Waste Landfill ­ 12.5 Natural pH 

95% confidence 11.9 

B) 

Characterization of Coal Combustion Residues 

Figure E-13. 100-Year Arsenic Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI. Release estimates 

for percolation controlled scenario are compared to release estimate based on total content.The amount of the arsenic that 

would be released if the release concentration was at the MCL is also shown for comparison (LSdefault scenario = 12.5 L/kg and 

LS95% = 100 L/kg). 

143
100-Year Selenium Release Estimates 

PPB - Selenium 

<4000 μg/kg 4000 μg/kg 4000 μg/kg 

MCLLS 12.5 = 625 :g/kg 

MCLLS 95% = 5000 :g/kg 1386 μg/kg 

34.7% 

100% 

565 μg/kg 

14.1% 

100% 100%

1 

10 

100 

1000 

10000 

100-year selenium release [μg/kg] 

Total content Combustion Default - pH 3 Default -pH Default ­

Waste Landfill ­ 12.5 Natural pH 

95% confidence 11.2 

A) 

PPT - Selenium 

<4000 μg/kg 4000 μg/kg 

MCLLS 95% = 5000 :g/kg 

MCLLS 12.5 = 625 :g/kg 

316 μg/kg 

7.9% 

740 μg/kg 

448 μg/kg 18.5% 

11.2% 

100% 100%

1 

10 

100 

1000 

10000 

100-year selenium release [μg/kg] 

Total content Combustion Default - pH 3 Default -pH Default ­

Waste Landfill ­ 12.5 Natural pH 

95% confidence 11.9 

B) 

Characterization of Coal Combustion Residues 

Figure E-14. 100-year Selenium Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI. Release estimates 

for percolation controlled scenario are compared to release estimate based on total content.The amount of the selenium 

that would be released if the release concentration was at the MCL is also shown for comparison (LSdefault scenario = 12.5 L/kg 

and LS95% = 100 L/kg). 

144
Characterization of Coal Combustion Residues 

Comments 

Figure E-3: 

• Fly ash from the test case had greater total Hg content 

than the fly ash from the baseline case (by about 7.5 

times). 

• Hg release is well below levels of potential concern 

(but poor replication) for both baseline and test cases. 

Figure E-5: 

• The fly ash from the test case had similar total As 

content than that from the baseline case. 

• As release was below the MCL for both the baseline 

and the test cases for most pH conditions. 

Figure E-7: 

• Total selenium content was below detection limits for 

Method 3052 for both fly ashes while significant selenium release (ranging from around 30 :g/L to around 

1000 :g/L) as a function of pH was observed. This 

result is a consequence of the dilution effects of the 

digestion method and analytical requirements. 

• Selenium release from both the baseline and the test 

cases was close to or exceeded the MCL (50 :g/L) 

for most pH conditions. 

Figures E-11 and E-12: 

• The fly ash from the test case would result in As release slightly less than expected from the baseline case, 

with a 95% probability to be less than 358 and 473 :g/ 

kg, respectively. 

• The fly ash from the test case would result in Se release less than expected from the baseline case, with a 

95% probability to be less than 4000 :g/kg (total content) in both cases and a 5% possibility that the total 

content will be released. 

Figure E-13: 

• For all scenarios examined, no significant difference in 

arsenic release would be observed between the fly ash 

from the baseline case and the fly ash from the test 

case. 

• For the 95% probability scenario, arsenic release from 

both cases would be less than the amount that would 

be released if the release concentration was at the MCL 

and the LS ratio was the resultant LS ratio for the 95% 

case (i.e., about 100 L/kg). However, arsenic release 

would be greater than the amount that would be released if the release concentration was at the MCL 

and the LS ratio was the LS ratio of the default scenario considered (i.e., 12.5 L/kg). 

• For the three default scenarios considered, arsenic release would most likely be less than the amount that 

would be released if the release concentration was at 

the MCL. 

Figure E-14: 

• For scenarios at alkaline pH, lower Se release would 

be expected for the test case compared to the baseline 

case. 

• For the 95% probability scenario, selenium release from 

both cases would be greater than the amount that would 

be released if the release concentration was at the 

MCL. 

• In conclusion, Se release will most likely be greater 

than the MCL based on solubility and cumulative release. Without controls appears worse than with controls. 

145
Characterization of Coal Combustion Residues 

Appendix F

Salem Harbor Fly Ashes

146
Characterization of Coal Combustion Residues 

List of Figures 

Figure Page 

F-1 pH Titration Curves for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control ............................................... 148

F-2 pH as a Function of LS Ratio for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control ................................. 148

F-3 Mercury Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 149

F-4 Mercury Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and

the Fly Ash with Enhanced Hg Control .............................................................................................................................. 150

F-5 Arsenic Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 151

F-6 Arsenic Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash

and the Fly Ash with Enhanced Hg Control ....................................................................................................................... 152

F-7 Selenium Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 153

F-8 Selenium Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash

and the Fly Ash with Enhanced Hg Control ....................................................................................................................... 154

F-9 Regression Curves of Experimental Data of Arsenic Solubility as a Function of pH. ......................................................... 155

F-10 Regression Curves of Experimental Data of Selenium Solubility as a Function of pH ........................................................ 156

F-11 100-Year Arsenic Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal

in a Combustion Waste Landfill .......................................................................................................................................... 157

F-12 100-Year Selenium Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal

in a Combustion Waste Landfill .......................................................................................................................................... 157

F-13 100-Year Arsenic Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI ................................................... 158

F-14 100-year Selenium Release Estimates fromA) Baseline Fly Ash and B) Fly Ash with ACI ................................................. 159

147
6 

pH Titration Curves 

Baseline Fly Ash Fly Ash with ACI 

14 14 

12 12

11.7 10.3 

10 10

8 8

pH

pH 

6 

4 4

2 

-1 -0.5 0 0.5 1 1.5 2 -2 -1.5 -1 -0.5 0 0.5 1 1.5 

meq Acid/g dry meq Acid/g dry 

2 

SR2-SHB-0001 - A 

SR2-SHB-0001 - B 

SR2-SHB-0001 - C 

SR2-SHT-0001 - A 

SR2-SHT-0001 - B 

SR2-SHT-0001 - C 

pH as a Function of LS Ratio 

14 

Baseline Fly Ash 

14 

Fly Ash with ACI 

12 12 

10 10 

6 6

4 4

2 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

2 

SR3-SHB-0001 - A 

SR3-SHB-0001 - B 

SR3-SHB-0001 - C 

SR3-SHT-0001 - A 

SR3-SHT-0001 - B 

SR3-SHT-0001 - C 

pH

8

pH

8

Characterization of Coal Combustion Residues 

Figure F-1. pH Titration Curves for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control. 

Figure F-2. pH as a Function of LS Ratio for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control. 

148
Mercury Release as a Function of pH 

Baseline Fly Ash Fly Ash with ACI 

Hg total content*: 650.6!6.8 ng/g Hg total content*: 1529.6!1.1 ng/g 10 10 

MCL MCL 

1 1 

5% 5% 

0.001 0.001 95% 5% 11.7 95% 5% 10.3 2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

ML ML

MDL SR2-SHB-0001 - A 

SR2-SHB-0001 - B 

SR2-SHB-0001 - C 

MDL SR2-SHT-0001 - A 

SR2-SHT-0001 - B 

SR2-SHT-0001 - C 

*Total content as determined by digestion using method 3052. 

150

140

150 

140 

Hg [μg/L] 

Hg spike recovery [%] Hg [μg/L] 

0.1 0.1 95% 95% 

0.032 

0.011 

0.01 0.01 

130

120

110

100

90

80

70

130

120

110

100

90

80

70

Hg spike recovery [%] 

60 60 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

SR2-SHB-0001 - A SR2-SHT-0001 - A 

Characterization of Coal Combustion Residues 

Figure F-3. Mercury Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the Fly 

Ash with Enhanced Hg Control. 5th and 95th percentiles of mercury concentrations observed in typical combustion waste 

landfill leachate are shown for comparison. 

149
Mercury Release as a Function of LS Ratio 

Baseline Fly Ash Fly Ash with ACI 

MCL 0.1 MCL 0.1 

0.08 0.08 

0.02 

0 2 4 6 8 10 12 

LS ratio [mL/g] 

0.02 

0 2 4 6 8 10 12 

LS ratio [mL/g] 

0 0

ML 

ML 

MDL MDL 

SR3-SHB-0001 - A 

SR3-SHB-0001 - B 

SR3-SHB-0001 - C 

SR3-SHT-0001 - A 

SR3-SHT-0001 - B 

SR3-SHT-0001 - C 

150 150

140 140

Hg [

μg/L] Hg spike recovery [%] 

Hg spike recovery [%] Hg [

μg/L] 

0.06 

0.04 

0.06

0.04

130

120

110

100

90

80

70

130

120

110

100

90

80

70

60

0 2 4 6 8 10 12 0 2 4 6 8 10 12

LS ratio [mL/g] LS ratio [mL/g]

60

SR3-SHB-0001 - A SR3-SHT-0001 - A 

Characterization of Coal Combustion Residues 

Figure F-4. Mercury Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

150
Arsenic Release as a Function of pH 

Baseline Fly Ash Fly Ash with ACI 

As total content*: 25.9!0.04 :g/g As total content*: 26.0!0.03 :g/g 10000 10000 

1000 

156 

1000 

 95% 95% 100 100 

19.30 

0.01 0.01 

0.001 0.001 5% 11.7 95% 5% 10.3 95%

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH ML ML

MDL SR2-SHB-0001 - A 

SR2-SHB-0001 - B 

SR2-SHB-0001 - C 

MDL SR2-SHT-0001 - A 

SR2-SHT-0001 - B 

SR2-SHT-0001 - C 

*Total content as determined by digestion using method 3052. 

150

140

150 

140 

MCL 10 MCL 10

As [

μg/L] 

As spike recovery [%] As [

μg/L] 

5% 5% 1 1

0.1 0.1

130 130

As spike recovery [%] 

120 120

110 110

100 100

90 90

80 80

70 70

60 60

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

SR2-SHB-0001 - A SR2-SHT-0001 - A 

Characterization of Coal Combustion Residues 

Figure F-5. Arsenic Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the Fly 

Ash with Enhanced Hg Control. 5th and 95th percentiles of arsenic concentrations observed in typical combustion waste 

landfill leachate are shown for comparison. 

151
Arsenic Release as a Function of LS Ratio 

Baseline Fly Ash Fly Ash with ACI

250

40

50 

200 

50 

0 

As spike recovery [%] As [

μg/L] 

30

20

MCL 10 

MCL 

0 

0 2 4 6 8 10 12 

150

100

As [

μg/L] As spike recovery [%] 

SR3-SHB-0001 - A SR3-SHT-0001 - A 

0 2 4 6 8 10 12 

LS ratio [mL/g] 

SR3-SHT-0001 - A 

SR3-SHT-0001 - B 

SR3-SHT-0001 - C 

ML LS ratio [mL/g] 

MDL 

SR3-SHB-0001 - A 

SR3-SHB-0001 - B 

SR3-SHB-0001 - C 

150

140

130

120

110

100

90

80

70

ML

MDL

150 

140

130

120

110

100

90

80

70

60 60 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

Characterization of Coal Combustion Residues 

Figure F-6. Arsenic Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

152
Selenium Release as a Function of pH 

Baseline Fly Ash Fly Ash with ACI 

Se total content*: 41.9!0.06 :g/g Se total content*: 44.0!0.04 :g/g 10000 10000 

1217 1497 1000 1000 

 95% 95% 100 100 

MCL MCL 

0.01 0.01 

0.001 0.001 5% 11.7 95% 5% 10.3 95% 2 4 6 8 10 12 14 2 4 6 8 10 12 14 

ML pH ML pH

MDL SR2-SHB-0001 - A 

SR2-SHB-0001 - B 

SR2-SHB-0001 - C 

MDL SR2-SHT-0001 - A 

SR2-SHT-0001 - B 

SR2-SHT-0001 - C 

*Total content as determined by digestion using method 3052. 

150 150

140 140 

5% 1 

10 10

Se [

μg/L] 

Se spike recovery [%] Se [

μg/L] 

5% 1

0.1 0.1

130

120

110

100

90

80

70

130

120

110

100

90

80

70

Se spike recovery [%] 

60 60 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

SR2-SHB-0001 - A SR2-SHT-0001 - A 

Characterization of Coal Combustion Residues 

Figure F-7. Selenium Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the 

Fly Ash with Enhanced Hg Control. 5th and 95th percentiles of selenium concentrations observed in typical combustion 

waste landfill leachate are shown for comparison. 

153
Selenium Release as a Function of LS Ratio 

Baseline Fly Ash Fly Ash with ACI

5000 5000

4000 4000

1000

0 2 4 6 8 10 12 

LS ratio [mL/g] 

1000

MCL MCL 0 0 

ML ML 

MDL 

0 2 4 6 8 10 12 

LS ratio [mL/g] 

SR3-SHB-0001 - A 

SR3-SHB-0001 - B 

SR3-SHB-0001 - C 

MDL 

SR3-SHT-0001 - A 

SR3-SHT-0001 - B 

SR3-SHT-0001 - C 

150 150

140 140

Se [

μg/L] 

Se [

μg/L] Se spike recovery [%] 

3000

2000

3000

2000

Se spike recovery [%]

130

120

110

100

90

80

70

130

120

110

100

90

80

70

60 60

0 2 4 6 8 10 12 0 2 4 6 8 10 12

LS ratio [mL/g] LS ratio [mL/g]

SR3-SHB-0001 - A SR3-SHT-0001 - A 

Characterization of Coal Combustion Residues 

Figure F-8. Selenium Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

154
Arsenic Solubility 

Baseline Fly Ash Fly Ash with ACI

100000 100000 

10000 10000 

1000 1000 

5% 95%

0.1 0.1 

0.01 0.01 

5% 95%

95%

5%

100 95% 100 As [

μg/L] 

As [ 

μg/L]

10 10

1 5% 1

0.001 0.001

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

SR2-SHB-0001-A SR2-SHT-0001-A 

SR2-SHB-0001-B SR2-SHT-0001-B 

SR2-SHB-0001-C SR2-SHT-0001-C 

A) Fit curve B) Fit curve 

Material log As (μg/L) pH range of R2 Number of 

validity points 

SHB 0.0000 pH5 0.0011 pH4 -0.0428 pH3 3-12.5 0.96 33 

0.4859 pH2 -2.2393 pH 5.6031 

SHT 0.0003 pH5 -0.0106 pH4 0.1194 pH3 3-13 0.92 33 

-0.5142 pH2 0.4220 pH 3.3432 

Characterization of Coal Combustion Residues 

Figure F-9. Regression Curves of Experimental Data of Arsenic Solubility as a Function of pH. 

155
Selenium Solubility 

Baseline Fly Ash Fly Ash with ACI

100000 100000 

10000 10000 

1000 1000 

95% 95%

5%

100 100

Se [

μg/L] 

Se [

μg/L]

10 10

5% 1 1

0.1 0.1 

0.01 0.01 

0.001 0.001 5% 95% 5% 95% 2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

A) B) 

SR2-SHB-0001-A 

SR2-SHB-0001-B 

SR2-SHB-0001-C 

Fit curve 

SR2-SHT-0001-A 

SR2-SHT-0001-B 

SR2-SHT-0001-C 

Fit curve 

Material log Se (μg/L) pH range of R2 Number of 

validity points 

SHB -0.0001 pH5 0.0061 pH4 -0.1107 pH3 3-12.5 0.93 33 

0.9490 pH2 -3.5922 pH 6.8613 

SHT 0.0001 pH5 -0.0020 pH4 0.0141 pH3 3-13 0.98 33 

0.0589 pH2 -0.6849 pH 3.3216 

Characterization of Coal Combustion Residues 

Figure F10. Regression Curves of Experimental Data of Selenium Solubility as a Function of pH. 

156
100-Year Arsenic Release Estimates 

Arsenic

100000

SHB SHT 

10000 μg/kg % μg/kg % 

100-year Mt [

μg/kg] 

Mt min 

1000 Mt - 5% 

Mt - 50% 

100 Mt - 95% 

Mean Mt 

10 Mt max 

1 

0.1 

0 5% 20 40 50% 60 80 

95%

100

Percentile

SHB SHT 

0.8 

3.6 

546 

7922 

1749 

18969 

0.003 

0.014 

2.1 

30.6 

6.8 

73.2 

2.7 

6.1 

968 

13374 

3013 

26000 

0.01 

0.02 

3.7 

51.4 

11.6 

100.0 

100-Year Selenium Release Estimates 

Selenium

100000

10000 SHB SHT 

% μg/kg 

100-year Mt[μg/kg]

Mt min 

Mt - 5% 

100 

1000 

Mt - 50% 

Mt - 95% 

10 Mean Mt 

Mt max 

1 

0.1 

5% 50% 95%

0 20 40 60 80 100

Percentile

SHB SHT 

μg/kg 

6.6 

34.5 

5011 

41900 

17623 

41900 

0.02 

0.08 

12.0 

100.0 

42.1 

100.0 

4.7 

24.3 

3650 

44000 

14240 

44000 

% 

0.01 

0.06 

8.3 

100.0 

32.4 

100.0 

Characterization of Coal Combustion Residues 

Figure F-11. 100-Year Arsenic Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal 

in a Combustion Waste Landfill. 

Figure F-12. 100-Year Selenium Release Estimates as a Function of the Cumulative Probability for the Scenario of 

Disposal in a Combustion Waste Landfill. 

157
100-Year Arsenic Release Estimates 

SHB - Arsenic 

25900 μg/kg 

241 μg/kg 

0.9% 

360 μg/kg 

1.4% 

1967 μg/kg 

7.6% 

7922 μg/kg 

30.6% 

100% 

1 

10 

100 

1000 

10000 

100000 

100-year arsenic release [μg/kg] 

MCLLS 95% = 1000 :g/kg 

MCLLS 12.5 = 125 :g/kg 

Total content Combustion Default - pH 3 Default -pH Default ­

Waste Landfill - 12.5 Natural pH 

95% confidence 11.7 A) 

SHT - Arsenic 

26000 μg/kg 

1950 μg/kg 

7.5% 

2590 μg/kg 

10% 

3326 μg/kg 

12.8% 

13374 μg/kg 

51.4% 

100% 

1 

10 

100 

1000 

10000 

100000 

100-year arsenic release [μg/kg] 

MCLLS 95% = 1000 :g/kg 

MCLLS 12.5 = 125 :g/kg 

Total content Combustion Default - pH 3 Default -pH Default ­

Waste Landfill ­ 12.5 Natural pH 

95% confidence 10.3 

B) 

Characterization of Coal Combustion Residues 

Figure F-13. 100-Year Arsenic Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI. Release estimates 

for percolation controlled scenario are compared to release estimate based on total content.The amount of the arsenic that 

would be released if the release concentration was at the MCL is also shown for comparison (LSdefault scenario = 12.5 L/kg and 

LS95% = 100 L/kg). 

158
100-Year Selenium Release Estimates 

SHB - Selenium 

41900 μg/kg 41900 μg/kg 

MCLLS 95% = 5000 :g/kg 

MCLLS 12.5 = 625 :g/kg 

15208 μg/kg 

36.3% 

20296 μg/kg 

48.4% 

1572 μg/kg 

3.8% 

100% 100% 

1 

10 

100 

1000 

10000 

100000 

100-year selenium release [ 

μg/kg] 

A) 

SHT - Selenium 

44000 μg/kg 44000 μg/kg 24978 μg/kg 100000 100% 100% 56.8% 

Total content Combustion Default - pH 3 Default -pH Default ­

Waste Landfill - 12.5 Natural pH 

95% confidence 11.7 

18708 μg/kg 

42.5% 

1337 μg/kg 10000 3% 

MCLLS 95% = 5000 :g/kg 

100-year selenium release [ 

μg/kg] 

MCLLS 12.5 = 625 :g/kg 

B) 

1000 

100 

10 

1 

Total content Combustion Default - pH 3 Default -pH Default ­

Waste Landfill - 12.5 Natural pH 

95% confidence 10.3 

Characterization of Coal Combustion Residues 

Figure F-14. 100-year Selenium Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI. Release estimates 

for percolation controlled scenario are compared to release estimate based on total content.The amount of the selenium 

that would be released if the release concentration was at the MCL is also shown for comparison (LSdefault scenario = 12.5 L/kg 

and LS95% = 100 L/kg). 

159
Characterization of Coal Combustion Residues 

Comments 

Figure F-3: 

• The fly ash from the test case had similar total Hg 

content to that from the baseline case. 

• Hg release is greater in baseline than test case, but 

both were below MCL. 

Figure F-5: 

• The fly ash from the test case had similar total As 

content than that from the baseline case. 

• The laboratory measurements fit within the 5–95% confidence intervals of the field observations. 

• Arsenic release is less in baseline than test case, but 

both are about 10 times greater than the MCL. Arsenic release at pH higher than 9 is much greater for 

the test case than the baseline case. 

Figure F-6: 

• Initial landfill leachate As concentrations will likely be 

about 20–30 :g/L for the baseline case but at least 100 

:g/L for the test case. 

Figure F–7: 

• The fly ash from the test case had similar total Se content to that from the baseline case. 

• Se release is similar in baseline and test cases, but significantly above MCL for both cases. The observed 

concentrations are greater than reported in the EPA 

database but consistent with the EPRI database. 

Figure F-8: 

• Initial landfill leachate Se concentrations are expected 

to be around 200 :g/L for the baseline case and increasing with increasing LS ratio, but the initial concentrations for the test case are expected to be around 

3000 :g/L and decreasing with increasing LS ratio. 

Figures F-11 and F-12: 

• The fly ash from the test case would result in As release greater than expected from the baseline case, 

with a 95% probability to be less than 13,375 and 7,925 

:g/kg, respectively. 

• The fly ash from the test case would result in Se release less than expected from the baseline case. At 

the 95th percentile the total content of Se will be released (41,900 and 44,000 :g/kg, respectively, for the 

baseline case and the test case). 

• 10–100% of the Se can be anticipated to be leached 

from the fly ash for both cases under the projected 

landfill conditions. 

Figure-13: 

• Greater As release would be expected for the test case 

compared to the baseline case, for all scenarios examined. 

• For all scenarios examined, Arsenic release from the 

test case fly ash would be greater than the amount that 

would be released if the release concentration was at 

the MCL. 

Figure F-14: 

• At the 95th percentile, Se release estimate exceeds total 

content for both the baseline and the test cases. This is 

not physically possible. However, this result indicates 

that there is 5% possibility that 100% of the total Se 

content would be released. 

• For all scenarios examined, Se release would most likely 

be greater than the amount that would be released if 

the release concentration was at the MCL. 

160
Characterization of Coal Combustion Residues 

Appendix G

Facility C Fly Ashes

161
Characterization of Coal Combustion Residues 

List of Figures 

Figure Page 

G-1 pH Titration Curves for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control ............................................... 163

G-2 pH as a Function of LS Ratio for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control ................................. 163

G-3 Mercury Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 164

G-4 Mercury Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and

the Fly Ash with Enhanced Hg Control .............................................................................................................................. 165

G-5 Arsenic Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 166

G-6 Arsenic Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash

and the Fly Ash with Enhanced Hg Control ....................................................................................................................... 167

G-7 Selenium Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 168

G-8 Selenium Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash

and the Fly Ash with Enhanced Hg Control ....................................................................................................................... 169

G-9 Regression Curves of Experimental Data of Arsenic Solubility as a Function of pH. ......................................................... 170

G-10 Regression Curves of Experimental Data of Selenium Solubility as a Function of pH ........................................................ 171

G-11 100-Year Arsenic Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal

in a Combustion Waste Landfill .......................................................................................................................................... 172

G-12 100-Year Selenium Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal

in a Combustion Waste Landfill .......................................................................................................................................... 172

G-13 100-Year Arsenic Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI ................................................... 173

G-14 100-year Selenium Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI ................................................. 174

162
6 

pH Titration Curves 

Baseline Fly Ash Fly Ash with ACI 

14 14

12 12

11.3 

10 10 

8.1 

8 8

pH

pH 

6 

4 4

2 

-0.5 0 0.5 1 1.5 2 -0.5 0 0.5 1 1.5 2 

meq Acid/g dry meq Acid/g dry 

2 

SR2-GAT - A SR2-GAT - B 

SR2-GAB - A SR2-GAB - B 

SR2-GAB - C 

pH as a Function of LS Ratio 

14 

Baseline Fly Ash 

14 

Fly Ash with ACI 

12 12 

10 10 

6 6 

4 4 

2 2 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

SR3-GAB - A SR3-GAB - B 

SR3-GAB - C 

SR3-GAT - A SR3-GAT - B 

pH

8 

pH

8 

Characterization of Coal Combustion Residues 

Figure G-1. pH Titration Curves for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control. 

Figure G-2. pH as a Function of LS Ratio for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control. 

163
Mercury Release as a Function of pH 

Baseline Fly Ash Fly Ash with ACI 

Hg total content*: 15.8!0.9 ng/g Hg total content*: 1150.7!14.4 ng/g 10 10 

MCL MCL 

1 1 

0.001 0.001 

5% 11.3 95% 5% 8.1 95% 2 4 6 8 10 12 14 2 4 6 8 10 12 14 

ML pH ML pH 

MDL 

SR2-GAB - A SR2-GAB - B 

SR2-GAB - C

MDL 

S R2-GAT - A S R2-GAT - B

*Total content as determined by digestion using method 3052. 

150 150

140 140 

0.01 

5% 5%

Hg [μg/L] 

Hg spike recovery [%] Hg [μg/L]

0.1 0.1 95% 95% 

0.014 0.016 

0.01 

Hg spike recovery [%] 

130

120

110

100

90

80

70

130

120

110

100

90

80

70

60 60 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

SR2-GAB - A SR2-GAT - A 

Characterization of Coal Combustion Residues 

Figure G-3. Mercury Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the Fly 

Ash with Enhanced Hg Control. 5th and 95th percentiles of mercury concentrations observed in typical combustion waste 

landfill leachate are shown for comparison. 

164
Mercury Release as a Function of LS Ratio 

Baseline Fly Ash Fly Ash with ACI 

0.1 0.1 

0.08 0.08 

0.02 0.02 

0 0

0 2 4 6 8 10 12

ML ML LS ratio [mL/g] 

MDL 

0 2 4 6 8 10 12 

LS ratio [mL/g] 

SR3-GAB - A SR3-GAB - B 

SR3-GAB - C 

MDL 

SR3-GAT - A SR3-GAT - B 

150 150

140 140 

Hg spike recovery [%] Hg [μg/L] 

0.06

Hg spike recovery [%] Hg [μg/L] 

0.06

0.04 0.04

130

120

110

100

90

80

70

130

120

110

100

90

80

70

60 60 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

SR3-GAB - A SR3-GAT - A 

Characterization of Coal Combustion Residues 

Figure G-4. Mercury Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

165
Arsenic Release as a Function of pH 

Baseline Fly Ash Fly Ash with ACI 

*Total content as determined by digestion using method 3052. 

MDL 

ML 

11.3 

237.37 

MCL 

0.001 

0.01 

0.1 

1 

10 

100 

1000 

10000 

2 4 6 8 10 12 14 

pH 

As [μg/L] 

SR2-GAB - A SR2-GAB - B 

SR2-GAB - C 

5% 95% 

 95% 

As total content*: 93.6!5.5 :g/g 

MDL 

ML 

8.1 

119.67 

0.001 

0.01 

100 

1000 

10000 

2 4 6 8 10 12 14 

pH 

SR2-GAT - A SR2-GAT - B 

5% 95% 

 95% 

As total content*: 506.3!28.7 :g/g 

140 

150 

140 

150 

MCL 10

As spike recovery [%] As [μg/L]

5% 5% 1

0.1 

60 60

2 4 6 8 10 12 14 2 4 6 8 10 12 14

pH pH

As spike recovery [%] 

130 130

120 120

110 110

100 100

90 90

80 80

70 70

SR2-GAB - A SR2-GAT - A 

Characterization of Coal Combustion Residues 

Figure G-5. Arsenic Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the Fly 

Ash with Enhanced Hg Control. 5th and 95th percentiles of arsenic concentrations observed in typical combustion waste 

landfill leachate are shown for comparison. 

166
Arsenic Release as a Function of LS Ratio 

Baseline Fly Ash Fly Ash with ACI

400 400

350 350

300 300

50

0 2 4 6 8 10 12 

LS ratio [mL/g] 

50

MCL MCL 0 0

ML ML 

0 2 4 6 8 10 12 

LS ratio [mL/g] 

MDL SR3-GAB - A SR3-GAB - B 

SR3-GAB - C 

MDL 

SR3-GAT - A SR3-GAT - B 

150 150

140 140

250 250

200

As spike recovery [%] As [μg/L] 

As [μg/L] As spike recov ery [%] 

200

150

100

150

100

0 2 4 6 8 10 12 

LS ratio [mL/g] 

130 130

120

110

100

120

110

100

90 90

80 80

70 70

60 60

0 2 4 6 8 10 12

LS ratio [mL/g]

SR3-GAB - A SR3-GA T - A 

Characterization of Coal Combustion Residues 

Figure G-6. Arsenic Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

167
Selenium Release as a Function of pH 

Baseline Fly Ash Fly Ash with ACI

Se total content*: <4.0 :g/g Se total content*: 206.3!0.9 :g/g 10000 10000 

2851.88 3288.09 

1000 1000 

 95% 95% 100 100 MCL MCL 

0.01 0.01 

0.001 

5% 11.3 95% 5% 8.1 

0.001 

95% 2 4 6 8 10 12 14 2 4 6 8 10 12 14 

ML pH ML pH

MDL

SR 2-GAB - A SR 2-GAB - B 

SR 2-GAB - C 

MDL 

SR2-GAT - A SR2-GAT - B 

*Total content as determined by digestion using method 3052. 

150 150

140 140 

5% 1 

10 10

Se [μ g/L] 

Se spike recovery [%] Se [μ g/L]

5% 1 

0.1 0.1 

130 

120 

110 

100 

90 

80 

70 

130 

120 

110 

100 

90 

80 

70

Se spike recovery [%] 

60 60 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

SR2-GAB - A SR2-GAT - A 

Characterization of Coal Combustion Residues 

Figure G-7. Selenium Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the 

Fly Ash with Enhanced Hg Control. 5th and 95th percentiles of selenium concentrations observed in typical combustion 

waste landfill leachate are shown for comparison. 

168
Selenium Release as a Function of LS Ratio 

Baseline Fly Ash Fly Ash with ACI

8000 8000 

7000 7000 

6000 6000 

5000 5000 Se [μ g/L] 

Se spike recovery [%] Se [μg/L] 

4000 4000 

3000 3000 

2000 2000 

1000 1000 

MC L 0 MCL 0

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

ML LS rat io [mL/g] ML LS ratio [ mL/g] 

MDL MDL 

SR3-GAB - A S R3-GAB - B 

SR3-GAB - C 

SR3-GAT - A SR 3-GAT - B 

150 150 

140 140 Se spike recovery [%] 

130 

120 

110 

100 

90 

80 

70 

130 

120 

110 

100 

90 

80 

70 

60 60 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [m L/g] LS ratio [mL/g] 

SR3-GAB - A SR3-GA T - A 

Characterization of Coal Combustion Residues 

Figure G-8. Selenium Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

169
A) 

Arsenic Solubility 

Baseline Fly Ash Fly Ash with ACI

As [μg/L] 

100000 

10000 

1000 

100 

10 

1 

0.1 

0.01 

0.001 5% 95%

 5% 

95% 

2 4 6 8 10 12 14 

5% 95%

 5% 

95% 

0.001 

0.01 

0.1 

1 

10 

100 

1000 

10000 

100000 

2 4 6 8 10 12 14 

As [μg/L] 

pH 

B) 

pH 

SR2-GAT - A 

SR2-GAT - B 

Fit curve 

Material log As (μg/L) pH range of 

validity 

R2 Number of 

points 

SR2-GAB - A 

SR2-GAB - B 

SR2-GAB - C 

Fit curve 

GAB 0.0012 pH5 -0.0416 pH4 0.5236 pH3 3-12.5 0.78 33 

-3.0400 pH2 8.0912 pH -5.3943 

GAT -0.0008 pH5 0.0304 pH4 -0.4500 pH3 3-12.5 0.75 22 

3.1407 pH2 -10.1848 pH 14.1412 

Characterization of Coal Combustion Residues 

Figure G-9. Regression Curves of Experimental Data of Arsenic Solubility as a Function of pH. 

170
Selenium Solubility 

Baseline Fly Ash Fly Ash with ACI

100000 

10000 

1000 

100000 

10000 

1000 

95% 100 

10 

5% 1 

0.1 

0.01 

0.001 

5% 95% 12 14 2 4 Se [μg/L] 

95% 

5% 

100 

10

Se [μg/L] 

1 

0. 1 

0. 01 

0. 001 

pH pH 

SR2-GAB - A 

SR2-GAB - B 

SR2-GAB - C 

Fit curve B) A) 

5% 

SR2-GAT - A 

SR2-GAT - B 

Fit curve 

95% 

2 4 6 8 10 6 8 10 14 12 

Material log Se (μg/L) pH range of R2 Number of 

validity points 

GAB -0.0003 pH5 0.0092 pH4 -0.1259 pH3 3-12.5 0.98 33 

0.8035 pH2 -2.2208 pH 4.5849 

GAT -0.00002 pH5 0.0021 pH4 -0.0530 pH3 3-12.5 0.96 22 

0.5431 pH2 -2.2226 pH 5.8084 

Characterization of Coal Combustion Residues 

Figure G-10. Regression Curves of Experimental Data of Selenium Solubility as a Function of pH. 

171
100-Year Arsenic Release Estimates Arsenic 

100000 

10000 

1000 Mt min 

Mt - 5% 

100 Mt - 50% 

Mt - 95% 

10 Mean Mt 

Mt max 

1 

95% 0.1

GAB GAT 

μg/kg 

5.8 

27.5 

4086 

59706 

13789 

93600 

% μg/kg % 

0.0062 4.1 0.0008 

0.0294 7.0 0.0014 

4.4 1142 0.2 

63.8 15411 3.0 

14.7 3485 0.7 

100.0 48499 9.6

100-year Mt [μg/kg] 

5% 50% 

0 20 40 60 80 100

Percentile 

GAB GAT 

100-Year Selenium Release Estimates 

Selenium

1000000

100000

10000 Mt min 

95% 

GAB GAT 

μg/kg % μg/kg %

100-year Mt [μg /kg] 

24.8 0.6 31.1 0.02 

Mt - 5% 

Mt - 50% 

1000 

100 Mt - 95% 

Mean Mt 10 

Mt max 

1 

69.6 

4000 

4000 

4000 

4000 

1.7 

100.0 

100.0 

100.0 

100.0 

142.5 

21033 

206300 

78816 

206300 

0.1 

10.2 

100.0 

38.2 

100.0 

0.1

5% 50% 0 20 40 60 80 100

P ercentile 

GAB GAT 

Characterization of Coal Combustion Residues 

Figure G-11. 100-Year Arsenic Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal 

in a Combustion Waste Landfill. 

Figure G-12. 100-Year Selenium Release Estimates as a Function of the Cumulative Probability for the Scenario of 

Disposal in a Combustion Waste Landfill. 

172
100-Year Arsenic Release Estimates 

GAB - Arsenic 

93600 μg/kg 93600 μg/kg 

100% 59706 μg/kg 100% 

2967 μg/kg 

3.2% 

4855 μg/kg 

5.2% 

63.8% 

1 

10 

100 

1000 

10000 

100000 

100-y ear arsenic releas e [μ g/kg] 

MCLLS 95% = 1000 :g/kg 

MCLLS 12.5 = 125 :g/kg 

Total content Combustion Default - pH 3 Default - pH Default ­

Waste Landfill ­ 12.5 Natural pH 

95% confidence 11.3 A) 

GAT - Arsenic 

506300 μg/kg 

1496 μg/kg 

0.3% 

2413 μg/kg 

1178 μg/kg 0.5% 

0.2% 

15411 μg/kg 

3.0% 

100% 

1 

10 

100 

1000 

10000 

100000 

1000000 

100-year arsenic release [μg/kg] 

MCLLS 95% = 1000 :g/kg 

MCLLS 12.5 = 125 :g/kg 

B) 

Total content Combustion Default - pH 3 Default - pH Default ­

Waste Landfill ­ 12.5 Natural pH 

95% confidence 8.1 

Characterization of Coal Combustion Residues 

Figure G-13. 100-Year Arsenic Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI. Release estimates 

for percolation controlled scenario are compared to release estimate based on total content.The amount of the arsenic that 

would be released if the release concentration was at the MCL is also shown for comparison (LSdefault scenario = 12.5 L/kg and 

LS95% = 100 L/kg). 

173
100-Year Selenium Release Estimates 

GAB - Selenium 

<4000 μg/ kg 4000 μg/kg 

100% 100% 3447.2 μg/kg 

86. 2% 

100% 100% 

1 

10 

100 

1000 

10000 

Total content Com bustion 

Waste Landfill ­

95% confidence 

Default - pH 3 Default - pH 

12.5 

Default - Natural 

pH 

100-year selenium release [ μg/ kg] 

11.3 

MCLLS 95% = 5000 :g/kg 

MCLLS 12.5 = 625 :g/kg 

4000 μg/ kg 4000 μg/kg 

A) 

GAT - Selenium 

41101.1 μg/kg 

19. 9% 

206300 μg/kg 

100% 

7191.3 μg/ kg 

3.5% 

206300 μg/ kg 

100% 

206300 μg/kg 

100% 

1 

10 

100 

1000 

10000 

100000 

1000000 100-year selenium release [μ g/kg] 

MCLLS 95% = 5000 :g/kg 

MCLLS 12.5 = 625 :g/kg 

Total content Combustion Default - pH 3 Default - pH Default ­

Waste Landfill - 12.5 Natural pH

B) 8.1 95% confidence 

Characterization of Coal Combustion Residues 

Figure G-14. 100-year Selenium Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI. Release estimates 

for percolation controlled scenario are compared to release estimate based on total content.The amount of the selenium 

that would be released if the release concentration was at the MCL is also shown for comparison (LSdefault scenario = 12.5 L/kg 

and LS95% = 100 L/kg). 

174
Characterization of Coal Combustion Residues 

Comments 

Figure G-1: 

• All extract Hg concentrations are well below levels of 

potential concern. 

Figure G-5: 

• Arsenics extract concentrations for the baseline case 

peak between pH 7 and 9, with maximum concentrations significantly greater than the range reported for 

field landfill leachates in the EPA database but consistent with the range of concentrations for field landfill 

leachates reported in the EPRI database. 

• Arsenic extract concentrations for the test case indicate somewhat lower concentrations than for the 

baseline case over the range of pH examined, even 

though the test case as around 5 times as much total 

As as the baseline case. These results also suggest 

different chemistry controlling the aqueous-solid equilibrium for the two cases. 

Figure G-7: 

• Se extract concentrations as a function of pH exhibit 

similar behavior for the baseline and test cases, even 

though the test case has greater than 50 times the 

amount of total As than the baseline case. 

Figure G-8: 

• Initial leachate concentrations for Se are likely to be 

ca. 1000–4000 :g/L (at LS=2), which is much greater 

than reported in the EPA database but consistent with 

values reported in the EPRI database for landfill 

leachates. 

Figures G-11and G-12: 

• A much greater percentage and quantity of As can be 

anticipated to be released from the baseline case than 

for the test case under the scenarios examined. 

Figure G13: 

• Arsenic release from the base case warrants further 

examination. 

Figure G-14: 

• Se release from the test case warrants further examination. 

175
Characterization of Coal Combustion Residues 

Appendix H

St. Clair Fly Ashes

176
Characterization of Coal Combustion Residues 

List of Figures 

Figure Page 

H-1 pH Titration Curves for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control ............................................... 178

H-2 pH as a Function of LS Ratio for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control ................................. 178

H-3 Mercury Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 179

H-4 Mercury Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and

the Fly Ash with Enhanced Hg Control .............................................................................................................................. 180

H-5 Arsenic Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 181

H-6 Arsenic Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash

and the Fly Ash with Enhanced Hg Control ....................................................................................................................... 182

H-7 Selenium Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 183

H-8 Selenium Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash

and the Fly Ash with Enhanced Hg Control ....................................................................................................................... 184

H-9 Regression Curves of Experimental Data of Arsenic Solubility as a Function of pH. ......................................................... 185

H-10 Regression Curves of Experimental Data of Selenium Solubility as a Function of pH ........................................................ 186

H-11 100-Year Arsenic Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal

in a Combustion Waste Landfill .......................................................................................................................................... 187

H-12 100-Year Selenium Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal

in a Combustion Waste Landfill .......................................................................................................................................... 187

H-13 100-Year Arsenic Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI ................................................... 188

H-14 100-year Selenium Release Estimates fromA) Baseline Fly Ash and B) Fly Ash with ACI ................................................. 189

177
pH as a Function of LS Ratio 

14 

Baseline Fly Ash 

14 

Fly Ash with B-PAC 

12 12 

10 10 

6 6 

4 4 

2 2 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

pH

8 

pH

8 

SR3-JAB - A SR3-JAB - B SR3-JAT - A SR3-JAT - B 

Characterization of Coal Combustion Residues 

pH Titration Curves 

Baseline Fly Ash Fly Ash with B-PAC 

14 14 

12.1 12.2 

12 12 

10 10 

8 8

pHpH 

6 6 

4 4 

2 2 

-1 0 1 2 3 4 5 6 7 -1 0 1 2 3 4 5 6 7 

meq Acid/g dry meq Acid/g dry 

SR2-JAB - A SR2-JAB - B SR2-JAT - A SR2-JAT - B 

Figure H-1. pH Titration Curves for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control. 

Figure H-2. pH as a Function of LS Ratio for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control. 

178
Mercury Release as a Function of pH 

Baseline Fly Ash Fly Ash with B-PAC 

Hg total content*: 110.9!5.8 ng/g Hg total content*: 1163.0!8.9 ng/g 10 10 

MCL MCL 

1 1 

] ] 

LL

//

g

0.1 g0.1 

μ μ 

 [ [

HgHg ] % [yrvecoe rekispg H

 95% 95% 0.030 

0.01 0.01 

 5% 5%

0.001 0.001 

5% 95% 12.1 5% 95% 12.2 2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH ML ML

MDL 

SR2-JAB - A 

MDL 

SR2-JAB - B SR2-JAT - A SR2-JAT - B 

0.020 

*Total content as determined by digestion using method 3052. 

150 150 

140 140 

] %

130 130

y [r

120 120

ve

110 110

coe r

100 100

eki

90 90

 sp

80 80

gH

70 70

60 60 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

SR2-JAB - A SR2-JAT - A 

Figure H-3. Mercury Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the Fly 

Ash with Enhanced Hg Control. 5th and 95th percentiles of mercury concentrations observed in typical combustion waste 

landfill leachate are shown for comparison. 

Characterization of Coal Combustion Residues 

179
Mercury Release as a Function of LS Ratio 

Baseline Fly Ash Fly Ash with B-PAC 

0.1 0.1 

0.08 0.08 

] 

]

/L

0.06

/L

0.06

g [μ

 [μg

gH

0.04

gH

0.04

0.02 

0 

0 2 4 6 8 10 

ML LS ratio [mL/g] 

MDL 

] ] 

%[%[

yy

rr

veve

oo

cc

ee

rr

ee

kiki

 sp sp

gg

HH

12 

0.02 

0 

0 2 4 6 8 10 12 

ML LS ratio [mL/g] 

MDL 

SR3-JAB - A SR3-JAB - B 

150

140

SR3-JAT - A SR3-JAT - B 

150

140

60 60 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

130 130

120 120

110 110

100 100

90 90

80 80

70 70

SR3-JAB - A SR3-JAT - A 

Figure H-4. Mercury Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

Characterization of Coal Combustion Residues 

180
Arsenic Release as a Function of pH 

Baseline Fly Ash Fly Ash with B-PAC 

10000 As total content*: 43.4!2.6 :g/g As total content*: 40.8!1.1 :g/g 10000

1000 1000 

 95% 95% 100 100 

MCL MCL 10 10

As [μg/L] As [μg/L] As spike recovery [%] 

5% 5% 1 1 

0.92 0.54 

0.1 0.1

0.01 0.01 

0.001 0.001 5% 95% 12.1 5% 95% 12.2 2 4 6 8 10 12 14 2 4 6 8 10 12 14 

ML pH ML pH 

MDL MDL 

SR2-JAB - A SR2-JAB - B SR2-JAT - A SR2-JAT - B 

*Total content as determined by digestion using method 3052. 

150 150 

140 140 

60 60 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

As spike recovery [%] 

130 130

120 120

110 110

100 100

90 90

80

70

80

70

SR2-JAB - A SR2-JAT - A 

Characterization of Coal Combustion Residues 

Figure H-5. Arsenic Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the Fly 

Ash with Enhanced Hg Control. 5th and 95th percentiles of arsenic concentrations observed in typical combustion waste 

landfill leachate are shown for comparison. 

181
Arsenic Release as a Function of LS Ratio 

Baseline Fly Ash Fly Ash with B-PAC 

350 350 

300 300 

250 250 

MCL 

200

150

100 

50 

MCL 0 

0 2 4 6 8 10 

LS ratio [mL/g] ML 

MDL 

12 

SR3-JAB - A SR3-JAB - B 

150 

140 

200

150

100 

50 

0 

0 2 4 6 8 10 12 

LS ratio [mL/g] 

ML 

MDL 

SR3-JAT - A SR3-JAT - B 

150 

140 

As spike recovery [%] As [μg/L] As spike recovery [%] As [μg/L]

SR3-JAB - A SR3-JAT - A 

130 

120 

110 

100 

90 

80 

70 

130 

120 

110 

100 

90 

80 

70 

60 60 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

Characterization of Coal Combustion Residues 

Figure H-6. Arsenic Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

182
Selenium Release as a Function of pH 

Baseline Fly Ash Fly Ash with B-PAC 

Se total content*: 10.7!0.1 :g/g Se total content*: 12.6!0.9 :g/g 10000 10000 

1000 1000 

 95% 95% 100 100 MCL 50.80 MCL 58.85 

10 

5%

12.2 2 4 6 8 10 12 14 5% 95% 

Se [μg/L] 

Se spike recovery [%] Se [μg/L] 

10 

1 

0.1 

0.01 

0.001 

5% 1 

0.1 

0.01 

0.001 

5% 95% 12.1 

2 4 6 8 10 12 14

ML pH ML pH 

MDL 

SR2-JAB - A SR2-JAB - B 

MDL 

SR2-JAT - A SR2-JAT - B 

*Total content as determined by digestion using method 3052. 

150 150 

140 140 

Se spike recovery [%] 

130 

120 

110 

100 

90 

80 

70 

130 

120 

110 

100 

90 

80 

70 

60 60 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

SR2-JA B - A SR2-JAT - A 

Characterization of Coal Combustion Residues 

Figure H-7. Selenium Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the 

Fly Ash with Enhanced Hg Control. 5th and 95th percentiles of selenium concentrations observed in typical combustion 

waste landfill leachate are shown for comparison. 

183
Selenium Release as a Function of LS Ratio 

Baseline Fly Ash Fly Ash with B-PAC 

Se [μg/L] Se spike recovery [%] 

800 800 

700 700 

600 600 

500

400

300

200 

100 

MCL 

0 

0 2 4 6 8 10 

ML LS ratio [mL/g] 

MDL 

12 

SR3-JAB - A SR3-JAB - B 

150

140

Se [μg/L] Se spike recovery [%] 

SR3-JAB - A SR3-JAT - A 

500

400

300

200 

100 

MCL 

0 

0 2 4 6 8 10 12 

MDL 

ML LS ratio [mL/g] 

SR3-JAT - A SR3-JAT - B 

150

140

130

120

110

100

90

80

70

130

120

110

100

90

80

70

60 60 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

Characterization of Coal Combustion Residues 

Figure H-8. Selenium Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

184
Arsenic Solubility 

Baseline Fly Ash Fly Ash with B-PAC 

5% 95%

 5% 

95% 

0.001 

0.01 

0.1 

1 

10 

100 

1000 

10000 

100000 

As [μg/L] 

5% 95%

 5% 

95% 

0.001 

0.01 

0.1 

1 

10 

100 

1000 

10000 

100000 

As [μg/L] 

2 4 6 8 10 12 14 2 4 6 8 10 12 14

pH pH 

SR2-JAT - A 

SR2-JAT - B 

Fit curve 

SR2-JAB - A 

SR2-JAB - B 

A) Fit curve B)

Material log As (μg/L) pH range of R2 Number of 

validity points 

JAB 0.0010 pH5 -0.0324 pH4 0.4137 pH3 3-12.5 0.62 22 

-2.4547 pH2 6.7105 pH -6.6563 

JAT 0.0025 pH5 -0.0973 pH4 1.4698 pH3 4-12.5 0.81 22 

-10.6792 pH2 37.2419 pH -50.3673 

Characterization of Coal Combustion Residues 

Figure H-9. Regression Curves of Experimental Data of Arsenic Solubility as a Function of pH. 

185
Selenium Solubility 

Baseline Fly Ash Fly Ash with B-PAC 

100000 100000 

10000 10000 

1000 1000 

5% 95% 

0.1 0.1 

0.01 0.01 

5% 1 

100 95% 100 95%

Se [μg/L] 

Se [μg/L] 

10 10

5% 1

0.001 0.001

5% 95% 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

SR2-JAT - A 

SR2-JAT - B 

Fit curve 

SR2-JAB - A 

SR2-JAB - B 

A) Fit curve B)

Material log Se (μg/L) pH range of R2 Number of 

validity points 

JAB 0.0002 pH5 -0.0070 pH4 0.0761 pH3 3-12.5 0.75 22 

-0.2648 pH2 -0.3724 pH 4.6460 

JAT 0.0005 pH5 -0.0201 pH4 0.2890 pH3 3-12.5 0.61 22 

-1.9155 pH2 5.6877 pH -3.7128 

Characterization of Coal Combustion Residues 

Figure H-10. Regression Curves of Experimental Data of Selenium Solubility as a Function of pH. 

186
1000

100-Year Arsenic Release Estimates 

Arsenic 

10000 

JAB JAT 

100-year Mt [μg/kg] 

μg/kg % μg/kg % 

Mt min 0.01 0.00003 0.01 0.00001 

100 Mt - 5% 

Mt - 50% 

Mt - 95% 10 

Mean Mt 

Mt max 1 

0.1 

5% 50% 95% 

0 20 40 60 80 100

Percentile

0.05 

8 

110 

25 

836 

0.0001 

0.02 

0.3 

0.1 

1.9 

0.01 

2 

29 

7 

346 

0.00003 

0.01 

0.1 

0.02 

0.8 

JAB JAT 

100-Year Selenium Release Estimates 

Selenium

100000 100-year Mt [μg/kg] 10000 

Mt min 

Mt - 5% 

100 

1000 

Mt - 50% 

Mt - 95% 

10 Mean Mt 

Mt max 

1 

0.1 

5% 50% 95% 

0 20 40 60 80 100

Percentile

JAB JAT 

μg/kg 

1.8 

4.5 

748 

10028 

2270 

10700 

% 

0.02 

0.04 

7.0 

93.7 

21.2 

100.0 

μg/kg 

1.9 

4.3 

710 

9602 

2172 

12600 

% 

0.01 

0.03 

5.6 

76.2 

17.2 

100.0 

JAB JAT 

Characterization of Coal Combustion Residues 

Figure H-11. 100-Year Arsenic Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal 

in a Combustion Waste Landfill. 

Figure H-12. 100-Year Selenium Release Estimates as a Function of the Cumulative Probability for the Scenario of 

Disposal in a Combustion Waste Landfill. 

187
100-Year Arsenic Release Estimates 

JAB - Arsenic 

43400 μg/kg 100000 

100% 

100-year arsenic release [μg/kg] 

10000 

1000

110 μg/kg

0.3%

100 

10 

1 

Total content Combustion 

Waste Landfill ­

95% confidence 

A) 

18 μg/kg 

0.04% 

110 μg/kg 

0.3% 

12 μg/kg 

0.03% 

MCLLS 95% = 1000 :g/kg 

MCLLS 12.5 = 125 :g/kg 

Default - pH 3 Default - pH 

12.5 

Default ­

Natural pH 

12.1 

100-year arsenic release [μg/kg] 

JAT - Arsenic 

100000 40800 μg/kg 

100% 

10000 

1000 

0.1 μg/kg 

0.0001%

MCLLS 95% = 1000 :g/kg 

29 μg/kg 47 μg/kg MCLLS 12.5 100 = 125 :g/kg 0.1% 0.1% 7 μg/kg 

0.02% 10

1

0.1 

0.01 

Total content Combustion Default - pH 3 Default - pH Default ­

Waste Landfill - 12.5 Natural pH

B) 

95% confidence 12.2

Characterization of Coal Combustion Residues 

Figure H-13. 100-Year Arsenic Release Estimates from A) Baseline Fly Ash and B) Fly Ash with B-PAC. Release estimates 

for percolation controlled scenario are compared to release estimate based on total content.The amount of the arsenic that 

would be released if the release concentration was at the MCL is also shown for comparison (LSdefault scenario = 12.5 L/kg and 

LS95% = 100 L/kg). 

188
100-Year Selenium Release Estimates 

JAB - Selenium 

100000 

MCLLS 95% = 5000 :g/kg 10700 μg/kg 

100% 

10028 μg/kg 

93.7% 

1 

10 

100 

1000 

10000 

100-year selenium release [μg/kg] 

6070 μg/kg 

56.7% MCLLS 12.5 = 625 :g/kg 

727 μg/kg 635 μg/kg 

6.8% 5.9% 

Total content Combustion Default - pH 3 Default - pH Default ­

Waste Landfill - 12.5 Natural pH 

A) 95% confidence 12.1 

JAT - Selenium 

100000 

MCLLS 95% = 5000 :g/kg 12600 μg/kg 9602 μg/kg 

100-year selenium release [μg/kg] 

100% 

10000 

25.7% MCLLS 12.5 = 625 :g/kg 

778 μg/kg 736 μg/kg 

6.2% 5.8% 1000 

100 

10 

1

Total content Combustion Default - pH 3 Default - pH Default ­

Waste Landfill - 12.5 Natural pH

95% confidence 12.2 

76.2% 3243 μg/kg 

B) 

Characterization of Coal Combustion Residues 

Figure H-14. 100-year Selenium Release Estimates from A) Baseline Fly Ash and B) Fly Ash with B-PAC. Release 

estimates for percolation controlled scenario are compared to release estimate based on total content.The amount of the 

selenium that would be released if the release concentration was at the MCL is also shown for comparison (LSdefault scenario = 

12.5 L/kg and LS95% = 100 L/kg). 

189
Characterization of Coal Combustion Residues 

Comments 

Figure H-3: 

• All extract concentrations for Hg are well below levels of potential concern. 

• Scatter in the extract concentrations for the cased with 

enhanced Hg control most likely results from the material heterogeneity associated with addition of particulate activated carbon. 

Figure H-5: 

• All extract concentrations for As are well below levels 

of potential concern. 

Figure H-6: 

• Initial As leachate concentrations from landfills are expected to be substantially greater (i.e., equal to 50 :g/ 

L at LS=2) than indicated by SR002 (LS=10) because 

of other ionic species at higher concentrations present 

at low LS ratio typical of landfill scenarios. These anticipated concentrations are consistent with landfill 

leachate concentrations reported in the EPRI database. 

Figure H-7: 

• Extract concentrations of selenium are greater than 

the MCL but within the range reported in the EPA and 

EPRI databases. 

Figure H-8: 

• Initial Se leachate concentrations from landfills are expected to be substantially greater (i.e., more than 200– 

300 :g/L at LS=2) than indicated by SR002 (LS=10) 

because of other ionic species at higher concentrations present at low LS ratio typical of landfill scenarios. These anticipated concentrations are consistent with landfill leachate concentrations reported in 

the EPRI database. 

Figures H-11 and H-12: 

• A much greater percentage and quantity of As can be 

anticipated to be released from the baseline case than 

for the test case under the scenarios examined. 

Figure H-13: 

• For the three default scenarios considered and the 95% 

probability scenario, arsenic release would most likely 

be less than the amount that would be released if the 

release concentration was at the MCL. 

Figure H-14: 

• For the 95% probability scenario, selenium release from 

baseline and test cases would be greater than the 

amount that would be released if the release concentration was at the MCL. 

• For the default scenario corresponding to disposal in a 

monofill (leachate pH controlled by the material being 

disposed) and the default scenario corresponding to 

the “extreme” pH of 12.5, no significant difference in 

selenium release between the baseline and test cases 

would be expected. 

• For the default scenario corresponding to the “extreme” 

pH of 3, selenium release is expected to be greater for 

the baseline case than the test case. In both cases, 

selenium release would be at or greater than the amount 

that would be released if the release concentration was 

at the MCL. 

• Se release from the baseline and test cases warrants 

further examination. 

190
Characterization of Coal Combustion Residues 

Appendix I

Facility L Fly Ashes

191
Characterization of Coal Combustion Residues 

List of Figures 

Figure Page 

I-1 pH Titration Curves for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control ............................................... 193

I-2 pH as a Function of LS Ratio for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control ................................. 193

I-3 Mercury Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 194

I-4 Mercury Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and

the Fly Ash with Enhanced Hg Control .............................................................................................................................. 195

I-5 Arsenic Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 196

I-6 Arsenic Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash

and the Fly Ash with Enhanced Hg Control ....................................................................................................................... 197

I-7 Selenium Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the

Fly Ash with Enhanced Hg Control .................................................................................................................................... 198

I-8 Selenium Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash

and the Fly Ash with Enhanced Hg Control ....................................................................................................................... 199

I-9 Regression Curves of Experimental Data of Arsenic Solubility as a Function of pH. ......................................................... 200

I-10 Regression Curves of Experimental Data of Selenium Solubility as a Function of pH ........................................................ 201

I-11 100-Year Arsenic Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal

in a Combustion Waste Landfill .......................................................................................................................................... 202

I-12 100-Year Selenium Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal

in a Combustion Waste Landfill .......................................................................................................................................... 202

I-13 100-Year Arsenic Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI ................................................... 203

I-14 100-year Selenium Release Estimates from A) Baseline Fly Ash and B) Fly Ash with ACI ................................................. 204

192
pH Titration Curves 

Baseline Fly Ash Fly Ash with Enhanced Hg Control 

14 14 

12 12 

10 10 

8 

6 

5.8 

4 

2 

8 

6 

5.0 

4 

2 

pHpH 

-0.5 -0.25 0 0.25 0.5 -0.5 -0.25 0 0.25 0.5 

meq Acid/g dry meq Acid/g dry 

SR2-LAB - A SR2-LAB - B SR2-LAT - A SR2-LAT - B 

pH as a Function of LS Ratio 

Baseline Fly Ash Fly Ash with Enhanced Hg Control 

14 14 

12 12 

10 10 

pH

8 

6 

4 

2 

pH

8 

6 

4 

2 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

SR3-LAB - A SR3-LAB - B SR3-LAT - A SR3-LAT - B 

Characterization of Coal Combustion Residues 

Figure I-1. pH Titration Curves for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control. 

Figure I-2. pH as a Function of LS Ratio for the Baseline Fly Ash and the Fly Ash with Enhanced Hg Control. 

193
Mercury Release as a Function of pH 

Baseline Fly Ash Fly Ash with Enhanced Hg Control 

10 Hg total content*: 13!0.2 ng/g 10 Hg total content*: 37.7!1.3 ng/g 

MCL 

1 

MCL 

1 

Hg [μg/L] 

Hg [μg/L] Hg spike recovery [%] 

0.1

95% 

0.010 

0.1 95% 

0.01 0.01 

0.009 

5% 5% 

0.001 0.001 5.8 5% 95% 5.0 5% 95%

2 4 6 8 10 12 14 2 4 6 8 10 12 14

ML pH pH

MDL ML 

MDL 

SR2-LAB - A SR2-LAB - B SR2-LAT - A SR2-LAT - B 

*Total content as determined by digestion using method 3052. 

150 150

140 140

Hg spike recovery [%] 

130

120

110

100

90

130

120

110

100

90

80 80

70 70

60 60 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

SR2-LAB - A SR2-LAT - A 

Characterization of Coal Combustion Residues 

Figure I-3. Mercury Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the Fly 

Ash with Enhanced Hg Control. 5th and 95th percentiles of mercury concentrations observed in typical combustion waste 

landfill leachate are shown for comparison. 

194
Mercury Release as a Function of LS Ratio 

Baseline Fly Ash 

0.1 

Fly Ash with Enhanced Hg Control 

0.1 

0.08 0.08 

Hg spike recovery [%] Hg [μg/L] 

0.06

0.04 

0.02 

0 

0 2 4 6 8 10 

ML LS ratio [mL/g] 

MDL 

12 

SR3-LAB - A SR3-LAB - B 

150

140

130

120

110

100

90

80

70

Hg [μg/L] Hg spike recovery [%] 

0.06

0.04 

0.02 

0 

0 2 4 6 8 10 12 

ML LS ratio [mL/g] 

MDL 

SR3-LAT - A SR3-LAT - B 

150

140

130

120

110

100

90

80

70

60 60 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

SR3-LAB - A SR3-LAT - A 

Characterization of Coal Combustion Residues 

Figure I-4. Mercury Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

195
Arsenic Release as a Function of pH 

Fly Ash with Enhanced Hg Control 

MDL 

ML 

5.0 

24.96 

0.001 

0.01 

100 

1000 

10000 

2 4 6 8 10 12 14 

pH 

SR2-LAT - A SR2-LAT - B 

5% 95%

 95% 

As total content*: 18.7!0.7 :g/g 

Baseline Fly Ash 

MDL 

ML 

5.8 

25.95 

0.001 

0.01 

100 

1000 

10000 

2 4 6 8 10 12 14 

pH 

SR2-LAB - A SR2-LAB - B 

5% 95%

 95% 

As total content*: 20!1.1 :g/g 

MCL 10 MCL 10

As [μg/L] 

As [μg/L] As spike recovery [%] 

5% 5% 1 1

0.1 0.1

*Total content as determined by digestion using method 3052. 

150 150 

140 140 

As spike recovery [%] 

130

120

110

100

90

80

70

130

120

110

100

90

80

70

60 60 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

SR2-LAB - A SR2-LAT - A 

Characterization of Coal Combustion Residues 

Figure I-5. Arsenic Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the Fly 

Ash with Enhanced Hg Control. 5th and 95th percentiles of arsenic concentrations observed in typical combustion waste 

landfill leachate are shown for comparison. 

196
Arsenic Release as a Function of LS Ratio 

Baseline Fly Ash Fly Ash with Enhanced Hg Control 

MCL 

0 

10 

20 

30 

40 

50 

As [μg/L] 

MCL 

0 

10 

20 

30 

40 

50 

As [μg/L] 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

ML LS ratio [mL/g] ML LS ratio [mL/g] 

MDL MDL 

SR3-LAB - A SR3-LAB - B SR3-LAT - A SR3-LAT - B 

150 150 

140 140 

As spike recovery [%] 

130

120

110

100

90

80

70

As spike recovery [%] 

130

120

110

100

90

80

70

60 60 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

SR3-LAB - A SR3-LAT - A 

Characterization of Coal Combustion Residues 

Figure I-6. Arsenic Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

197
Selenium Release as a Function of pH 

Baseline Fly Ash Fly Ash with Enhanced Hg Control 

MDL 

ML 

5.8 

MCL 

0.001 

0.01 

100 

1000 

10000 

2 4 6 8 10 12 14 

pH 

SR2-LAB - A SR2-LAB - B 

5% 95%

 95% 

Se total content*: 4.1!0.1 :g/g 

MDL 

ML 

5.0 

MCL 

0.001 

0.01 

100 

1000 

10000 

2 4 6 8 10 12 14 

pH 

SR2-LAT - A SR2-LAT - B 

5% 95%

 95% 

Se total content*: 4.3!0.2 :g/g 

10 

8.29 

10

Se spike recovery [%] 

Se [μg/L] 

Se [μg/L]

5.85 5% 5% 1 1

0.1 0.1

*Total content as determined by digestion using method 3052. 

150 150 

140 140 

60 60 

2 4 6 8 10 12 14 2 4 6 8 10 12 14 

pH pH 

Se spike recovery [%] 

130 130

120 120

110 110

100 100

90 90

80 80

70 70

SR2-LAB - A SR2-LAT - A 

Characterization of Coal Combustion Residues 

Figure I-7. Selenium Release (top) and Spike Recoveries (bottom) as a Function of pH for the Baseline Fly Ash and the Fly 

Ash with Enhanced Hg Control. 5th and 95th percentiles of selenium concentrations observed in typical combustion waste 

landfill leachate are shown for comparison. 

198
Selenium Release as a Function of LS Ratio

Baseline Fly Ash Fly Ash with Enhanced Hg Control 

MCL 50 MCL 50 

40 40 

Se [μg/L] Se spike recovery [%] 

30

20

10 

0 

0 2 4 6 8 10 

ML LS ratio [mL/g] 

MDL 

12 

SR3-LAB - A SR3-LAB - B 

150

140

130

120

110

100

90

80

70

Se [μg/L] Se spike recovery [%] 

30

20

10 

MDL 

ML 

0 

0 2 4 6 8 

LS ratio [mL/g] 

10 12 

SR3-LAT - A SR3-LAT - B 

150

140

130

120

110

100

90

80

70

60 60 

0 2 4 6 8 10 12 0 2 4 6 8 10 12 

LS ratio [mL/g] LS ratio [mL/g] 

SR3-LAB - A SR3-LAT - A 

Characterization of Coal Combustion Residues 

Figure I-8. Selenium Release (top) and Spike Recoveries (bottom) as a Function of LS Ratio for the Baseline Fly Ash and 

the Fly Ash with Enhanced Hg Control. 

199
Arsenic Solubility 

Baseline Fly Ash Fly Ash with Enhanced Hg Control 

100000 100000 

10000 10000 

1000 1000 

0.1 

5% 95%

0.1 

0.01 0.01 

5% 95%

95% 95%

5%

100 100

As [μg/L] 

As [μg/L] 

10 10

5% 1 1

0.001 0.001

2 4 6 8 10 12 14 2 4 6 8 10 12 14

pH pH 

SR2-LAT - A 

SR2-LAT - B 

A) Fit curve 

SR2-LAB - A 

SR2-LAB - B 

Fit curve B) 

Material log As (μg/L) pH range of R2 Number of 

validity points 

LAB 0.0004 pH5 -0.0120 pH4 0.0966 pH3 3-12.5 0.92 22 

0.0151 pH2 -2.4406 pH 7.2162 

LAT 0.0000 pH5 0.0040 pH4 -0.1157 pH3 3-12.5 0.92 22 

1.2681 pH2 -5.5708 pH 9.6784 

Characterization of Coal Combustion Residues 

Figure I-9. Regression Curves of Experimental Data of Arsenic Solubility as a Function of pH. 

200
A) 

Selenium Solubility 

Baseline Fly Ash Fly Ash with Enhanced Hg Control 

Se [μg/L] 

100000 

10000 

1000 

100 

10 

95% 0.001 

0.01 

0.1 

1 

10 

100 

1000 

10000 

100000 

12 14 

Se [μg/L] 

5% 95% 

5% 

95% 95%

1 

0.1 

0.01 

0.001 

5%

2 4 6 8 10 12 14

5% 2 4 6 8 10 

pH pH 

SR2-LAB - A 

SR2-LAB - B 

Fit curve B) 

SR2-LAT - A 

SR2-LAT - B 

Fit curve 

Material log Se (μg/L) pH range of R2 Number of 

validity points 

LAB 0.0007 pH5 -0.0239 pH4 0.3133 pH3 3-12.5 0.94 22 

-1.8284 pH2 4.4667 pH -1.9621 

LAT 0.0007 pH5 -0.0230 pH4 0.2978 pH3 3-12.5 0.81 22 

-1.7038 pH2 4.0275 pH -1.4335 

Characterization of Coal Combustion Residues 

Figure I-10. Regression Curves of Experimental Data of Selenium Solubility as a Function of pH. 

201
100-Year Arsenic Release Estimates Arsenic 

100000 

10000 LAB LAT 

% μg/kg 

100-year Mt [μg/kg] 

Mt min 

Mt - 5% 

100 

1000 

Mt - 50% 

Mt - 95% 

10 Mean Mt 

Mt max 

1 

0.1 

5% 50% 95%

0 20 40 60 80 100

Percentile

μg/kg 

0.83 

13.36 

2049 

20000 

10541 

20000 

0.00413 

0.0668 

10.25 

100.0 

52.7 

100.0 

1.50 

17.38 

2471 

18700 

10090 

18700 

% 

0.00800 

0.09296 

13.22 

100.0 

53.96 

100.0 

LAB LAT 

100-Year Selenium Release Estimates 

Selenium

100000

μg/kg 

10000 

Mt min 

Mt - 5% 

100 

1000 

Mt - 50% 

Mt - 95% 

10 Mean Mt 

Mt max 

1 

0.1 

5% 50% 95% 

0 20 40 60 80 100

Percentile

100-year Mt [μg/kg] 

LAB LAT 

μg/kg 

0.3 

1.0 

143 

2113 

484 

4100 

% 

0.01 

0.02 

3.5 

51.5 

11.8 

100.0 

0.3 

1.0 

141 

2041 

466 

4300 

% 

0.007 

0.02 

3.3 

47.5 

10.8 

100.0 

LAB LAT 

Characterization of Coal Combustion Residues 

Figure I-11. 100-Year Arsenic Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal 

in a Combustion Waste Landfill. 

Figure I-12. 100-Year Selenium Release Estimates as a Function of the Cumulative Probability for the Scenario of Disposal 

in a Combustion Waste Landfill. 

202
100-Year Arsenic Release Estimates 

LAB - Arsenic 

100000 

20000 μg/kg 20000 μg/kg 20000 μg/kg 

100% 100% 100% 

100-year arsenic release [μg/kg] 

10000 

729.3 μg/kg 

3.7% 324.3 μg/kg 1000 MCLLS 95% = 1000 :g/kg 1.6% 

MCLLS 12.5 100 = 125 :g/kg

10 

1

Total content Combustion Default - pH 3 Default - pH Default ­

Waste Landfill - 12.5 Natural pH

95% confidence 5.8 A) 100-year arsenic release [μg/kg] 

B) 

LAT - Arsenic 

100000 18700 μg/kg 18700 μg/kg 18700 μg/kg

100% 100% 100%

10000 

468 μg/kg 312 μg/kg 1000 MCLLS 95% = 1000 :g/kg 2.5% 1.7% 

MCLLS 12.5 100 = 125 :g/kg

10 

1

Total content Combustion Default - pH 3 Default - pH Default ­

Waste Landfill - 12.5 Natural pH

95% confidence 5.0

Characterization of Coal Combustion Residues 

Figure I-13. 100-Year Arsenic Release Estimates from A) Baseline Fly Ash and B) Fly Ash with Enhanced Hg Control. 

Release estimates for percolation controlled scenario are compared to release estimate based on total content. The 

amount of the arsenic that would be released if the release concentration was at the MCL is also shown for comparison 

(LSdefault scenario = 12.5 L/kg and LS95% = 100 L/kg). 

203
100-Year Selenium Release Estimates 

LAB - Selenium 

4100 μg/kg 10000 100% 

2112.6 μg/kg MCLLS 95% = 5000 :g/kg 

100-year selenium release [μg/kg] 

51.5% 587.9 μg/kg 989.7 μg/kg 

14.3% 24.1% 

1000 

MCLLS 12.5 = 625 :g/kg 

103.6 μg/kg 

2.5%

100

10 

1 

Total content Combustion Default - pH 3 Default - pH Default - Natural

Waste Landfill - 12.5 pH

A) 95% confidence 5.8 100-year selenium release [μg/kg] 

B) 

LAT - Selenium 

4300 μg/kg

100% 10000 

2040.9 μg/kg 947.6 μg/kg 47.5% 22% 

559.4 μg/kg 1000 

13.0% 

100 

10 

1 

Total content Combustion Default - pH 3 Default - pH 

Waste Landfill - 12.5 

95% confidence 

73.1 μg/kg 

1.7% 

MCLLS 95% = 5000 :g/kg 

MCLLS 12.5 = 625 :g/kg 

Default - Natural 

pH 

5.0 

Characterization of Coal Combustion Residues 

Figure I-14. 100-year Selenium Release Estimates from A) Baseline Fly Ash and B) Fly Ash with Enhanced Hg Control. 

Release estimates for percolation controlled scenario are compared to release estimate based on total content. The 

amount of the selenium that would be released if the release concentration was at the MCL is also shown for comparison 

(LSdefault scenario = 12.5 L/kg and LS95% = 100 L/kg). 

204
Characterization of Coal Combustion Residues 

Comments 

Figure I-3: 

• Fly ash from the test case had greater total Hg content 

than the fly ash from the baseline case (by about 3 

times). 

• Hg release is low (but poor replication) for both baseline 

and test cases. 

Figure I-5: 

• The fly ash from the test case had lower total As content than that from the baseline case (by about 4.5 

times). 

• Arsenic release was close to or exceeded the MCL 

(10 :g/L) for both the baseline and the test cases for 

all pH conditions. 

Figure I-7: 

• Fly ash from the test case had greater total Se content 

than the fly ash from the baseline case (by about 4.5 

times). 

• Selenium release from both the baseline and the test 

cases was close to the MCL (50 :g/L) for most pH 

conditions. 

Figures I-11 and I-12: 

• The fly ash from the test case would result in similar 

As release than expected from the baseline case, with 

a 95% probability to be less than 18700 and 20000 :g/ 

kg, respectively. 

• The fly ash from the test case would result in similar 

Se release than expected from the baseline case, with 

a 95% probability to be less than 2115 and 2045 :g/kg, 

respectively. 

Figure I-13: 

• For the 95% probability scenario, arsenic release from 

both cases would exceed the amount that would be 

released if the release concentration was at the MCL. 

• For two of the three default scenarios considered (i.e., 

pH 3 and natural pH), arsenic release would most likely 

be less than the amount that would be released if the 

release concentration was at the MCL. However, for 

the default scenario at pH 12.5, arsenic release would 

most likely exceed the amount that would be released 

if the release concentration was at the MCL. 

Figure I-14: 

• Similar Se release would be expected for the test case 

compared to the baseline case for all scenarios examined. 

• For the 95% probability scenario, selenium release from 

both cases would be less than the amount that would 

be released if the release concentration was at the MCL 

and the LS ratio was the resultant LS ratio for the 95% 

case (i.e., around 100 L/kg). However, selenium release would be greater than the amount that would be 

released if the release concentration was at the MCL 

and the LS ratio was the LS ratio of the default scenario considered (i.e., 12.5 L/kg). 

205