### EPA-600/R-0 8 /0 77

Jul y 200 8 

# Characterization of

Coal Combustion

Residues from Electric

Utilities Using Wet

Scrubber s for M ulti-Pollutant

ControlEPA/600/R-08/077 July 2008



# Characterization of Coal Combustion Residues from Electric Utilities Using Wet Scrubbers for
Multi-Pollutant Control

F. Sanchez 1 

### , D. Kosson 1



### , R. Keeney 2 

### , R. Delapp 1 

### , L. Turner 3 

### , and P. Kariher 2

1 

### Vanderbilt University Department of Civil and Environmental Engineering
Nashville, TN 37235

2 

### ARCADIS 4915 Prospectus Drive, Suite F
Durham, NC 27713

3 

### Turner Technology
Nashville, TN 37235

Category III / Applied Research

Contract No. EP-C-04-023 Work Assignment No. 4- 26 Project No. RN990234.0026



### U.S. Environmental Protection Agency Office of Research and Development National Risk Management Research Laboratory

Air Pollution Preventio n and Control Division Cincinnati, Ohio

### Notice

The U.S. Environmental Protection Agency (EPA) through its Office of Research and Development funded the research described here under Work Assignment No. 4-26 of Contract Number EP-C-04-023 to Vanderbilt University. It has been subjected to the Agency’s peer and administrative review and has been cleared for publicationas an EPA document. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement or recommendation. The views and opinions of authors expressed herein do not necessarily state

or refl ect those of EPA or any agency thereof.

ii

### 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 en vironmental problems today and building a science knowledge base necessary to manage our ecological r esources 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. Th e focus of the Laboratory's research program is on methods and their cost-effectiveness for prevention an d control of pollution to air, land, water, and subsurface resources; protection of water quality in pu blic water systems; remediation of contaminated sites, sediments and ground water; prevention and co ntrol 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 engineer ing information to support regulatory and policy decisions; and providing the technical support and in formation 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 Labo ratory'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 II



## ACKNOWLEDGMENTS

Extensive input on the research program design wa s provided by G. Helms, U.S. EPA, Office of Solid Waste (Washington, D.C.).

Laboratory testing described here in was carried out by ARCADIS with technical support from Vanderbilt University. R. Delapp was responsibl e for the chemical analyses carried out at Vanderbilt University. Technical assistan ce also was provided by A. Garrabrants.

K. Ladwig and the Electric Power Research Institute (EPRI) are gratefully acknowledged for assistance in obtaining coal combustion residu e samples and providing information from the

EPRI database on coal combustion residues.

S. Thorneloe is the U.S. EPA pr oject officer for this research.

Note: R. Keeney substantially participated in the work reported here and the preparation of this report but left employment of ARCADIS prior to the completion of this study and report.

iv

### Characterization of Coal Combustion Residues II



## TABLE OF CONTENTS

Acknowledgments

................................................................................................................ .......... iv

Abstract

....................................................................................................................... .................... v

Glossary of terms

.............................................................................................................. ............. vi

Executive Summary

.............................................................................................................. ......... ix

Table of Contents

.............................................................................................................. ............ xii

List of Tables

................................................................................................................................ xv

List of Figures

.............................................................................................................................. xvi

1. Introduction

................................................................................................................................. 1

1.1. Regulatory Context

............................................................................................................... 6

1.1.1. Waste Management

....................................................................................................... 6

1.1.2. Air Pollution Control

................................................................................................... . 6

1.2. Configurations of U.S. Coal Fired Po wer Plants and Multi-pollutant Control Technologies

................................................................................................................................ 7

1.2.1. Current Air Pollution Control Technologies

................................................................. 8

1.2.2. Wet Scrubbers, NOx Controls and Multi-pollutant Controls

..................................... 11

1.3. Coal Combustion Residues

................................................................................................. 12

1.4. Residue Management Practices

.......................................................................................... 13

1.4.1. Beneficial Use

............................................................................................................. 13

1.4.2. Land Disposal

............................................................................................................. 14

1.5. Leaching Protocol

......................................................................................................... ...... 16

2. Materials and Methods

....................................................................................................... ....... 20

2.1. CCR Materials for Evaluation

............................................................................................ 20

2.1.1. Facilities Using Inhibited or Natural Oxidation of Scrubber Residues (Producing Scrubber Sludge or Fixated Scrubber Sludge)

...................................................................... 24

2.1.1.1. Facility A (Natural Oxidation and SNCR)

........................................................... 24

2.1.1.2. Facility B (Natural Oxidation and SCR)

.............................................................. 24

2.1.1.3. Facility K (Natural Oxidation and SCR)

............................................................. 25

2.1.1.4. Facility M (Inhibited Oxidation and SCR)

.......................................................... 25

2.1.2. Facilities Using Forced Oxidation of Scrubber Residues (Producing FGD Gypsum) 26

2.1.2.1. Facility N (Forced Oxidation)

.............................................................................. 26

2.1.2.2. Facility O (Forced Oxidation and SCR)

.............................................................. 26

2.1.2.3. Facility P (Forced Oxidation and SCR and SNCR)

............................................. 26

2.1.2.4. Facility Q (Forced Oxidation and SCR)

.............................................................. 27

v

### Characterization of Coal Cumbustion Residues II



### 2.2. Leaching Assessment Protocols

.......................................................................................... 27

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

............................ 27

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

..................................... 28

2.3. Analytical Methods

............................................................................................................. 28

2.3.1. Surface Area and Pore Size Distribution

.................................................................... 28

2.3.2. pH and Conductivity

................................................................................................... 28

2.3.3. Moisture Content

........................................................................................................ 28

2.3.4. Carbon Content Organic Carbon/Elemental Carbon Analyzer

................................... 28

2.3.5. Dissolved Inorganic Carbon (DIC) a nd Dissolved Organic Carbon (DOC)

.............. 29

2.3.6. Mercury (CVAA, Method 3052, and Method 7473)

.................................................. 29

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

......................................... 30

2.3.7.1. ICP-MS Analysis

................................................................................................. 30

2.3.8. X-Ray Fluorescence (XRF)

........................................................................................ 32

2.3.9. MDL and ML for Analytical Results

......................................................................... 32

2.4. Quality Assurance ASSESSMENT

.................................................................................... 33

2.4.1. Homogenization of Individual CCR Samp les and Aliquots for Analyses

.................. 33

2.4.2. Leaching Test Methods and Analytical QA/QC

......................................................... 33

2.4.3. Improving QA/QC efficiency

..................................................................................... 34

2.5. Interpretation and Presentation of Laboratory Leaching Data

............................................ 35

2.5.1. Interpretation of Mechanisms C ontrolling Constituent Leaching

.............................. 36

2.6. Field pH probability distribution

........................................................................................ 38

2.7. Estimated leachate concentration as a function of pH

........................................................ 41

3. Results and Discussion

............................................................................................................. 43

3.1. Total elemental content by digestion

.................................................................................. 43

3.2. total elemental content by xrf

............................................................................................ . 51

3.3. Laboratory Leaching Test Results

...................................................................................... 57

3.3.1. Typical Characteristic Leaching Behavi or as a Function of pH and LS

..................... 58

3.3.2. Comparisons of the Ranges of Constituent Concentrations from Laboratory Testing with Measurements of Field Samples and the EPA Risk Report Database

.......................... 77

4. Summ ary of Results, Conclusions and Recommendations

....................................................... 87

5. References

................................................................................................................................. 94

Appendices

.................................................................................................................................... 97

A. Quality Assurance Project Plan

..................................................................................... A-1

B. Total Elemental Content by Digestion

............................................................................. B-1

vi

### Characterization of Coal Combustion Residues II



### C. Elemental Total Content (by XRF), Carbon, Loss on Ignition and Specific Surface Area

...................................................................................................... C-1

D. pH Titration and Constituent Leaching as a Function of pH (SR002 test results)

......... D-1

E. pH and Constituent Leaching as a Function of LS (SR003 test results)

.......................... E-1

F. Curve Fits

................................................................................................................. ........ F-1

G. Additional Facility Information

..................................................................................... G-1

vii

### Characterization of Coal Cumbustion Residues II



## LIST OF TABLES

Table 1. Summary of facility c onfigurations and sample identific ation contained in this report. Facilities are identified by c ode letter only (e.g., “Faci lity A”) to preserve the confidentiality of the CCR source. All fly ash samples are ASTM Class F.

.................................................... 5

(EPA, 2005). CCR samples evaluated in this repo rt are from configur ations indicated by shaded (light gray) rows. Current cap acity re flects date of data collection for EPA report

Table 4. Beneficial uses of CCRs (ACAA, 2007). Total production of CCRs during 2006 was

Table 6. Method detection limits (MDLs) and mi nimum level of quantification (ML) for ICPTable 7. Comparison of summary statistics for fi eld pH data and pH probability distributions Table 2. General Characteristics of Coals Bu rned in U. S. Power Plants (EPA, 2005).

............... 7

Table 3. Projected Coal-Fired Capacity by APC Configuration as per data collection in 1999

(EPA, 2005).

........................................................................................................................... 10

124,795,124 short tons

............................................................................................................ 15

Table 5. MDL and ML of analysis of DIC and DOC.

................................................................. 29

MS analysis on liquid samples

................................................................................................ 31

used in Report 1 and this report.

............................................................................................. 4 1

Table 8. Fly Ash. Summary of results.

....................................................................................... 9 0

Table 9. FGD Gypsum. Summary of results

............................................................................... 91

Table 10. Scrubber Sludge. Summary of results

......................................................................... 92

Table 11. Fixated Scrubber Sl udge. Summary of results

............................................................ 93

viii

### Characterization of Coal Combustion Residues II



## LIST OF FIGURES

Figure 1. Flow diagram descri bing processing and nomenclature of FGD scrubber residues and samples included in this study.

................................................................................................ . 2

Figure 5. Fly ash (FA) comparisons (CFA, AFA, DFA, etc refer to sample identification codes;

Figure 6. Gypsum (Gyp-U, Gyp-W) comparisons (NAU, NAW, OAU, etc. are sample

Figure 7. Scrubber sludge (ScS) comparisons (CGD, AGD, DGD, etc. are sample identification

Figure 8. Fixated scrubber sludge (FSS) and fixated scrubber sludge with lime (FSSL)

Figure 9. Coefficient of variation (C.V.) from XRF elemental analysis of 10 subsamples of Figure 2. Multi-pollutant control syst ems in coal fired power plants

.......................................... 12

Figure 3. Life-cycle evaluation of coal combustion residues (EPA, 2002)

................................. 13

Figure 4. Uses of CCRs based on 2006 Industry Statistics (ACAA, 2007)

................................. 16

see Table 1). Shorthand is used for when SCR is in use (“on”) or not in use (“off”)

............ 20

identification codes; see Table 1).

.......................................................................................... 21

codes; see Table 1). Shorthand is used for wh en SCR is in use (“on”) or not in (“off”)

....... 22

comparisons (DCC, BCC, KCC, etc. are samp le identification codes; see Table 1)

.............. 23

FSSL sample MAD after mixing by coning and quartering

................................................... 33

Figure 10. An example of extract concentra tions as a function of pH from SR002.1

................. 38

Figure 11. Probability dist ributions for field pH used in Re port 1 (LogLogistic) and this report (BetaGeneral). Summary statistics f or the fiel d data and the probability distribution used in this report (BetaGeneral) are provide d to the right of the graph

............................................. 40

Figure 12. Example of regression fit and corresponding coefficients for a 5 th 

### order polynomial equation used to represent solubility and rel ease as a function of pH (antimony for fly ash from Facility B with SCR bypassed (DFA)).

......................................................................... 42

Figure 13 and Figure 14. Mercury and Aluminum. Comp arison of total elemental content by digestion

.................................................................................................................................. 45

Figure 15 and Figure 16. Antimony and Arsenic. Comparison of total elemental content by

Figure 17 and Figure 18. Barium and Cadmium. Comparison of total elemental content by

Figure 19 and Figure 20. Chromium and Cobalt. Comparison of total elemental content by

F igure 21 and Figure 22. Lead and Molybdenum. Comparison of total elemental content by

Figure 23 and Figure 24. Selenium and Thallium. Comparison of total elemental content by digestion

.................................................................................................................................. 46

digestion

.................................................................................................................................. 47

digestion

.................................................................................................................................. 48

digestion

.................................................................................................................................. 49

digestion

.................................................................................................................................. 50

Figure 25. Fly Ash - Total content by XRF

................................................................................. 52

Figure 26. Gypsum – Total content by XRF

................................................................................ 53

Figure 27. Scrubber Sludge – Total content by XRF

................................................................... 54

ix

### Characterization of Coal Cumbustion Residues II



### Figure 28. Fixated Scrubber Sludge – Total content by XRF

...................................................... 55

Figure 30. Mercury - Examples of characteristic leaching behavior as a function of pH (SR002.1

Figure 47 and Figure 48. Mercury and Aluminum . Comparison of maximum, minimum and natural pH concentrations observed in SR 02 and SR03 extracts over the pH domain 5.4 ≤

Figure 49 and Figure 50. Antimony and Arsenic. Comparison of maximum, minimum and natural pH concentrations observed in SR 02 and SR03 extracts over the pH domain 5.4 ≤

Figure 51 and Figure 52. Barium and Boron. Co mparison of maximum, minimum and natural pH concentrations observed in SR02 a nd SR03 extracts over the pH domain 5.4 ≤ pH ≤ 12.4.

Figure 53 and Figure 54. Cadmium and Chromium . Comparison of ma ximum, minimum and natural pH concentrations observed in SR 02 and SR03 extracts over the pH domain 5.4 ≤

Figure 55 and Figure 56. Cobalt a nd Lead. Comparison of maximu m, minimum and natural pH

Figure 57 and Figure 58. Molybdenum and Seleni um. Comparison of maximum, minimum and natural pH concentrations observed in SR 02 and SR03 extracts over the pH domain 5.4 ≤ Figure 29. Fixated Scrubber Sludge with Lime – Total content by XRF

.................................... 56

results)

..................................................................................................................................... 61

Figure 31. Aluminum. Examples of characterist ic leaching behavior as a function of pH.

....... 62

Figure 32. Antimony. Examples of characteristic leaching behavior as a function of pH.

........ 63

Figure 33. Arsenic. Examples of characteristic leaching beha vior as a function of pH

............. 64

Figure 34. Barium. Examples of characteristic leaching behavi or as a function of pH.

............ 65

Figure 35. Boron. Examples of characteristic leaching behavior as a function of pH.

.............. 66

Figure 36. Cadmium. Examples of characterist ic leaching behavior as a function of pH

.......... 67

Figure 37. Chromium. Examples of characterist ic leaching behavior as a function of pH.

....... 68

Figure 38. Chromium. Examples of characterist ic leaching behavior as a function of pH.

....... 69

Figure 39. Cobalt. Examples of characteristi c leaching behavior as a function of pH

............... 70

Figure 40. Lead. Examples of characteristic leaching behavior as a function of pH.

................ 71

Figure 41. Molybdenum. Examples of characteris tic leaching behavior as a function of pH

.... 72

Figure 42. Molybdenum. Examples of characteris tic leaching behavior as a function of pH

.... 73

Figure 43. Selenium. Examples of characterist ic leaching behavior as a function of pH.

......... 74

Figure 44. Selenium. Examples of characterist ic leaching behavior as a function of pH.

......... 75

Figure 45. Thallium. Examples of characterist ic leaching behavior as a function of pH

........... 76

Figure 46. Natural pH (pH in distilled wate r at LS=10) observed in SR02 extracts.

.................. 79

pH ≤ 12.4

.. ............................................................................................................................... 80

pH ≤ 12.4

.. ............................................................................................................................... 81

............................................................................................................................... .................. 82

pH ≤ 12.4

.. ............................................................................................................................... 83

concentrations observed in SR02 and SR03 extracts over the pH domain 5.4 ≤ pH ≤ 12.4. . 84

pH ≤ 12.4

.. ............................................................................................................................... 85

x

### Characterization of Coal Combustion Residues II



### Figure 59. Thallium. Comparison of maximum, minimum and natural pH concentrations observed in SR02 and SR03 extracts over the pH domain 5.4 ≤ pH ≤ 12.4............................. 86

xi

### Characterization of Coal Cumbustion Residues II



## ABSTRACT

This report evaluates leaching characteristics of air pollution control residues from coal-fired power plants that use acid gas scrubbers, whic h may also reduce air emissions of mercury and other pollutants. Leaching of mercury and othe r constituents of pot ential concern (COPCs) during land disposal of coal combustion residues (CCRs) 1 

### is evaluated in this report. The data presented in this report will be used in a future report to evaluate the fate of mercury and other COPCs from the management of CCRs resulti ng from the use of multi-pollutant control technologies. 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 life-cycle stag es of CCR management including disposal and beneficial use.

The specific objectives of the research reported here are to:

1. Evaluate the potential for leaching to ground water of mercury and other COPCs (i.e., aluminum, antimony, arsenic, barium, boron, cadmium, chromium, cobalt, lead, molybdenum, selenium, and thallium) removed from the flue gas of coal -fired power plants by facilities that use wet scrubbe rs as part of a multi-pollutant control strategy to reduce air

emissions.

2. Provide the foundation for assessing the impact of enhanced mercury and multi-pollutant control technology on leaching of mercury and other COPCs from CCR management including storage, beneficial use, and disposal; and,

3. Perform these assessments using the most appropriate evaluation methods currently available. The laboratory leach testing follo wed the approach developed by Kosson, et al. (2002), which considers the effects of varyi ng environmental conditions on waste constituent leaching.

Air pollution control residues (fly ash, gypsum , and scrubber sludge samples) were obtained

from coal combustion electric utility facilities using wet scrubbers. A range of facility configurations was selected representing di fferences in air pollu tion control technology configurations and coal rank. E ach of the residues sampled has been analyzed for selected physical properties, and for total content and leaching characteristic s of selected COPCs. Results of laboratory leaching tests were used to deve lop estimates of constituent release under field management scenarios. Laboratory leaching test re sults also were compared to field observations of leaching.

This report includes results for 23 CCRs (5 fly ashes, 6 gypsum samples, 5 scrubber sludges, 7 fixated scrubber sludges) sampled from eight fac ilities. Each CCR sampled was evaluated in the laboratory for leaching as a function of pH and liquid-to-solid ratio. Results are presented for mercury, aluminum, antimony, arsenic, barium, boron, cadmium, chromium, cobalt, lead, molybdenum, selenium and thallium.

1 

### Coal combustion residues (CCRs) refer collectively to fly ash, scrubber residues and other air pollution control solid residues generated during the combustion of coal collected through the associated air pollution control system. Resultant CCRs may be managed as separate or combined residue streams, depending on individual facility configuration.



### xii

### Characterization of Coal Combustion Residues II



## GLOSSARY OF TERMS

ACI Activated Carbon Injection

Al Aluminum

APC Air Pollution Control

APPCD Air Pollution Preven tion and Control Division

As Arsenic

ASTM American Society fo r Testing and Materials

B Boron

Ba Barium

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

BML Below Method Limit

CAIR Clean Air Interstate Rule

CAMR Clean Air Mercury Rule

Cd Cadmium

CCRs Coal Combustion Residues

CCV Continuing Calibration Verification

Co Cobalt

COPCs Constituents of Potential Concern

Cr Chromium

C.V. Coefficient of Variation

CVAA Cold Vapor Atomic Adsorption

DIC Dissolved Inorganic Carbon

DOC Dissolved Organic Carbon

DOE United States Department of Energy

DI Deionized (i.e., deionized water)

DRC Dynamic Reaction Chamber

dw dry weight basis

DWEL Drinking Water Equivalent Level

EPA United States Environmental Protection Agency

EPRI Electric Power Research Institute

ESP Electrostatic Precipitator

ESP-CS Cold-side Electrostatic Precipitator

ESP-HS Hot-side Electrostatic Precipitator

xiii

### Characterization of Coal Cumbustion Residues II



### FF Fabric Filter (bag house)

FGD Flue Gas Desulfurization

FID Flame Ionization Detector

FO Forced Oxidation

FSS Fixated Scrubber Sludge

FSSL Fixated Scrubber Sludge with Lime

Gyp-U Unwashed Gypsum

Gyp-W Washed Gypsum

Hg Mercury

HHV Higher Heating Value

Ho Holmium

ICP-MS Inductively Coupled Plasma-Mass Spectrometry

ICV Initial Calibration Verification

In Indium

IO Inhibited Oxidation

I.Ox. Inhibited Oxidation (this abbrevia tion used in some figures to improve clarity)

LOI Loss On Ignition

LS Liquid-to-Solid Ratio (LS ratio)

M Molar

Max Maximum

MCL Maximum Contaminant Level (for drinking water)

MDL Method Detection Limit

Mg Lime Magnesium Enriched Lime (oft en also referred to as “mag-lime”)

Min Minimum

ML Minimum Level of Quantification

Mo Molybdenum

NETL National Energy Tec hnology Laboratory (DOE)

NIOSH National Institute of Occupational Safety and Health

NO Natural Oxidation

NOx Nitrogen Oxides

NSPS New Source Performance Standards

OC/EC Organic Carbon/Elemental Carbon

ORD Office of Research and Development (EPA)

xiv

### Characterization of Coal Combustion Residues II



### OSWER Office of Solid Waste and Emergency Response

PAC Powdered Activated Carbon

Pb Lead

PM Particulate Matter

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

PS Particulate Scrubber

QA/QC Quality Assurance/Quality Control

RCRA Resource Conservation and Recovery Act

RFA Reference Fly Ash

SAB U.S. EPA Science Advisory Board

SCA Specific Collection Area

Sb Antimony

ScS Scrubber Sludge

SCR Selective Catalytic Reduction

SNCR Selective Non-Catalytic Reduction

SDA Spray Dryer Absorber

Se Selenium

SO 2 

### Sulfur Dioxide

SPLP Synthetic Precipitation Leaching Procedure

SRM Standard Reference Material

S/S Stabilization/Solidification

SWDA Solid Waste Disposal Act

TC Toxicity Characteristic

TCLP Toxicity Characteristic Leaching Procedure

Tl Thallium

XRF X-Ray Fluorescence

xv

### Characterization of Coal Cumbustion Residues II



## EXECUTIVE SUMMARY

This report evaluates cha nges that may occur to coal combustion residues (CCRs) 2 

### in response to changes in air pollution control technology at coal-fired power plan ts, which will reduce emissions from the flue gas stack by transferring pollutants to fly ash and other air pollution control residues. Congress has directed EPA to document that the Clean Air Act regulations do

not have the net effect of tr ading one environmental burden for another. The Air Pollution Prevention and Control Division (APPCD) of EPA’s Office of Research and Development (ORD) is conducting research to evaluate poten tial leaching and cross media transfers of mercury and other constituents of potential con cern (COPCs) resulting from land disposal or beneficial use of CCRs. The focus of this report is to present data that will be used to evaluate the fate of mercury and other metals from the us e of wet scrubbers at co al-fired power plants. Leaching tests are being conducte d on the residues to determine the potential transfer of pollutants from the residues to water resources or other environmental systems (e.g., soils, sediments).

The specific objectives of the research reported here are to:

1. Evaluate the potential for leaching to gr oundwater of mercury and other COPCs (i.e., aluminum, antimony, arsenic, barium, bor on, cadmium, chromium, cobalt, lead, molybdenum, selenium, and thallium) removed from the flue gas of coal-fired power plants by facilities that use wet scrubbers as part of a multi-pollutant control strategy to

reduce air emissions.

2. Provide the foundation for assessing the impact of enhanced mercury and multi-pollutant control technology on leaching of mercury and other COPCs from CCR management including storage, beneficial use, and disposal; and,

3. Perform these assessments using the most appropriate evaluation methods currently available. The laboratory leach testing follo wed the approach developed by Kosson, et al. (2002), which considers the effects of va rying environmental conditions on waste constituent leaching.

Air pollution control residues were obtained from co al combustion electric ut ility facilities using wet scrubbers. A range of facility configurations was selected representing differences in air pollution control technol ogy configurations and coal rank. 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.

2 

### Coal combustion residues (CCRs) refer collectively to fly ash and other air pollution control solid residues generated during the combustion of coal co llected through the associated air pollution control system. Resultant CCRs may be managed as separ ate or combined residue streams, depending on individual facility configuration.



### xvi

### Characterization of Coal Combustion Residues II



### This report includes results for 23 CCRs (5 fly ashes, 6 gypsum samples, 5 scrubber sludges, 7 fixated scrubber sludges) samp led from eight facilities. 3 

### The samples are considered to be representative of likely facility configurations indicative of 84 and 74 percent, respectively, of the current and future facility configuration types with acid ga s scrubbers based on generating capacity; however, only a limited number of facilit ies representing each configuration type have been sampled. A range of coal ranks typically combusted is also represented. Each CCR sampled was evaluated in the laboratory for leaching as a function of pH and liquid- to-solid ratio. Results are presented for mercury, aluminum, antimon y, arsenic, barium, boron, cadmium, chromium, cobalt, lead, molybdenum, selenium and thallium.

The selected testing approach was chosen for us e because it evaluates leaching over a range of values for two key variables [pH and liquid-to-solid ratio (LS)] 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 variab les 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.

In addition, results from laboratory leaching evaluation were compared to field leachate concentrations from CCR manage ment 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.

Summary of Conclusions

The data presented in this report will be used in a future report that provides a probabilistic assessment of plausible management practices to ev aluate the fate of merc ury and other COPCs. Leach results contained in this report are compared to health-based values to identify where there may be potential concerns. The intende d use of these results is to suggest that for values less than MCLs or DWELs there is unlikely a potential for environmental concern. The thresholds used here for preliminary screening do not account for additional dilution and attenuation processes that may occur under field management scenarios 4 

### . Therefore the results are considered environmentally conservative and actual release ra tes would be less. For values greater than MCLs or DWELs, additional research is needed to determine potential release rates.

Based on the results of testing a nd evaluations in this study, the fo llowing conclusions are drawn:

1. For each CCR type, the following constitu ents exceeded either the maximum contaminant level (MCL) or drinking water eq uivalent level (DWEL) in at least one laboratory leaching test condition over the ra nge of pH and LS ratios considered, and therefore potentially may present unacc eptable environmental risks under some management scenarios. These cases warra nt more detailed evaluation, including consideration of site-specific conditions.

3 

### Fly ash is collected by the particulate collection device, such as an electrostatic precipitator; gypsum is

dewatered material collected from forced oxidation fl ue gas desulfurization; scrubber sludge is collected from natural or inhibited oxidation flue gas desulfur ization; and fixated scrubber sludge is a mixture of scrubber sludge, fly ash and often with additional lime added.

4 

### Dilution and attenuation factors are specific to i ndividual sites and management scenarios and may range from less than 10 to greater than 100.



### xvii

### Characterization of Coal Cumbustion Residues II



### (i) Fly ash – antimony, arsenic, bor on, cadmium, chromium, molybdenum,

selenium and thallium.

(ii) FGD gypsum – boron, cadmium, molybdenum, selenium and thallium.

(iii) Scrubber sludge – mercury, antimony, ar senic, boron, chromium, lead, molybdenum, selenium and thallium.

(iv) Fixated scrubber sludge – mercury, an timony, arsenic barium , boron, cadmium, chromium, lead, molybdenum, selenium and thallium.

However, (i) typically, evaluation results fr om only a subset of samples of a given material type exceeded the indi cated criteria, and (i i) never did the full range reported

exceed the indicated threshold.

2. Leaching of individual constituents may vary over several orders of magnitude, depending on the conditions of the management scenario. Thus, these results can be used to suggest design conditions that would redu ce or minimize constituent release (e.g., pH, and other conditions).

3. Leaching concentrations do not correlate w ith total content ex cept for specific

constituents in selected materials where the constituent (i) is weakly retained, and (ii) leaching concentrations have a low variability relative to pH. Thus, total content is not a good indicator of leaching.

4. Results of this study suggest that it appears that Cr leachability is associated with the use of post-combustion NOx controls . This is based on a limited set of paired samples from the same facility operating with and with SC R or SNCR in use. This finding will be

further evaluated as additional data are collected.

5. The systematic leaching behavior of COPCs observed in the range of samples evaluated suggests that the geochemical mechanisms controlling leaching can be discerned and quantified using geochemical speciation modeli ng, which in turn, can serve as the basis for evaluating and improving design of CCR management scenarios. Development of generalized geochemical speciation models fo r the CCR materials eval uated in this study

is recommended.

The new information reported here provides an expanded basis for future assessments and may impact risk evaluations. Ranges of concentratio ns of some constituents in laboratory leaching

test extracts and field data incl uded in this study suggest diffe rent applicable concentration ranges for risk evaluation other than used in th e recent risk assessment on coal combustion waste found in docket # EPA-HQ-RCRA-2006-0796
( 

### http://www.regulations.gov/ fdmspublic/component/mai n ).

This is the second of a series of reports that will evaluate the potential for leaching of COPCs from CCRs from coal-fired power plants that use wet scrubbers. The first report focused on the use of sorbents for enhancing mercury capture at coal-fired power plants. (Sanchez et al., 2006) The third report will evaluate CCRs from fac ilities with different air pollution control configurations and coal ranks th at were not previously covered in the first two reports. The fourth and final report will provide a probabi listic assessment of the leaching potential of mercury and other COPCs based on plausible management strategies. The data will be used to correlate leaching characterist ics to coal rank, air pollution control configurations, and combustion facility characteristics.

xviii

### Characterization of Coal Cumbustion Residues II



## 1. INTRODUCTION

Changes are occurring to air pollution control t echnology at coal-fired power plants which will reduce emissions from the flue gas stack by tr ansferring pollutants to fly ash and other air pollution control residues. Congr ess has directed EPA to document that the Clean Air Act regulations do not have th e net effect of tradi ng one environmental burden for another. The Air Pollution Prevention and Control Division (A PPCD) of EPA’s Office of Research and Development (ORD) is conducting research to evaluate potential leaching and cross media transfers of Constituents of Potential Concern (COPCs) resulting from land disposal or beneficial use of coal combustion residues (CCRs). This report is part of a series of reports being prepared to document the fate of mercury and other metals found in coal that are being controlled at the power plant stack through implementati on of multi-pollutant control technology.

The focus of this report is to present an eval uation of air pollution control residues that may

result from the use of SO 2 

### scrubbers as mercury control technology at coal-fired power plants, and the potential for transfer of pollutants from th e resulting residues to water resources or other environmental systems (e.g., soils, sediments). The residues studied for this report were unwashed and washed flue gas desulfurization (FGD) gypsum, scrubber sl udge, fixated scrubber sludge, and fly ashes generated fr om power plants that have SO 2 

### scrubbers. This report compares the impact of NOx control technology [selectiv e catalytic reduction (S CR) and selective noncatalytic reduction (SNCR)] on characteristics of CCRs obtained from the same facilities during periods when the NOx control was and was not in use.

The potential for leaching of mercury and other CO PCs during land disposal or beneficial use of

the CCRs is the more narrow focus of this assessme nt. This research is part of an on-going effort by EPA to use an integrated, comprehensive appr oach to account for the fate of mercury and other metals in coal throughout the life-cycle stages of CCR manageme nt (Thorneloe et al., 2008; Sanchez et al., 2006). Re lated research and assessment on environmental fate of constituents during CCR management includes conducting thermal stability studies, leach testing, and probabilistic assessment modeling to determine fate of mercury and other metals that are in coal combustion residues resulting fro m implementation of multi-pollutant control technology (Kilgroe et al., 2001; EPA, 2002).

CCRs include bottom ash, boiler slag, fly ash, scr ubber residues and other miscellaneous solids generated during the combustion of coal. Air pollution control can concentrate or partition metals to fly ash and scrubber residues. The boiler slag and bottom ash are not of interest in this study because enhanced mercury emission controls are not expected to change their composition. Use of multi-pollutant controls minimizes air emissions of mercury and other metals by the transfer of the metals to the fly ash and other CCRs. Th is research will help determine the fate of mercury and other COPCs from the management of CCRs through either dispos al or reuse. Fly ash may include unburned carbonaceous materials a nd 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 capture d in the air pollution control equipment.

The type and characteristics of FGD scrubber resi due produced is primaril y a function of (i) the scrubber sorbent used (i.e., limestone, lime, magnes ium enriched lime referred to as Mg lime, or alkaline fly ash), (ii) the ex tent of oxidation during scrubbing (i.e., forced oxidation, natural oxidation, or inhibited oxidati on), (iii) post-scrubber processi ng, including possibly dewatering or thickening, drying, water rinsing, or blendi ng with other materials, and (iv) coal rank

1

### Characterization of Coal Combustion Residues II



### combusted. The presence and leaching characteristic s of the constituents of potential concern in scrubber residues is a consequence of the coal combusted, process sequence employed, process conditions, process additives and us e or disposal scenario. Figure 1 illustrates the processes used in the production of materials that were samp led for this study, sample nomenclature, and the typical management pathways for each material. FGD gypsum is defined here as the by-product

of the SO 2 

### wet scrubbing process when the scrubber resi due is subjected to forced oxidation. In forced oxidation systems, nearly all of the by-product is calcium sulfate dihydrate (CaSO 4 

### •H 2 

### O). The resulting wet gypsum is partially dewatere d and then either disposed in a landfill ( unwashed

gypsum ; Gyp-U ) or water rinsed (in some cases) and dried to produce washed gypsum ( washed gypsum; Gyp-W ) that then potentially can be used in wallboard manufactur ing or agricultural applications. Scrubber sludge ( ScS ) is the by-product of the SO 2 

### wet scrubbing process resulting

from neutralization of acid gases at facilities that use either inhibi ted oxidation or natural

oxidation of scrubber residue. In inhibited oxida tion systems, nearly all of the by-product is calcium sulfite hemihydrates (CaSO 3 

### •1⁄2H 2 

### O). In natural oxidation systems, the by-product is a

mixture of CaSO 3 

### •1⁄2H 2 

### O and CaSO 4 

### •H 2 

### O. Scrubber sludge typically will be either partially dewatered in a thickener and then disposed in a surface impoundment, or after thickening, further dewatered and mixed with fly ash to form fixated scrubber sludge ( FSS ). In most cases,

additional lime is also blended with th e scrubber sludge and fly ash to form fixated scrubber sludge with lime ( FSSL ). The blend of fly ash and scrubber sludge is typically between 0.5 to 1.5 parts fly ash to 1 part scrubber sludge on a dry weight basis, w ith 0 or 2-4% additional lime added (FSS or FSSL, respectively). Fixated scrubbe r sludge typically is either disposed in a landfill or supplied to a beneficial use (e.g., fill in mining applications). Th is report evaluates the characteristics of fly ash, FGD gypsum, scr ubber sludge, and fixated scrubber sludge (as produced with or without lime) from several coal combustion facilities.

Absorber (Forced Oxidation) Facilities N, O, P, Q Facilities A, B, K, M

Wet Gypsum 

### Absorber (Inhibited Oxidation

or Natural Oxidation)

Thickener Impoundment Dewatering (Scrubber Sludge; ScS)



### Landfill (Agriculture?)

(Unwashed Gypsum; Gyp

‐ U) 

### Drying

Rinsing Mixing of Scrubber Sludge

& Drying Fly Ash and Lime

(Fixated Scrubber Sludge) (Washed Gypsum; Gyp

‐ W) (FA+ScS; FSS) (FA+ScS+lime; FSSL)



### Wallboard Landfill or
Beneficial Use



### Figure 1. Flow diagram descri bing processing and nomenclature of FGD scrubber residues and samples included in this study.

2

### Characterization of Coal Cumbustion Residues II



### When coal is burned in an electric utility bo iler, the resulting high combustion temperatures vaporize the Hg in the coal to fo rm gaseous elemental mercury (Hg 0 

### ). Subsequent cooling of the combustion gases and interaction of the gaseous Hg 0 

### with other combustion products result in a portion of the Hg being converted to gaseous oxidized forms of mercury (Hg 2+ 

### ) and particlebound mercury. The specific chemical form — know n as the speciation — has a strong impact on the capture of mercury and other metals by boiler air pollution control (APC) equipment. (EPA, 2001)

Mercury and other elements parti tion between the combustion gas, fly ash and scrubber residues. Depending upon the gas conditioning, presence or absence of NOx control and other air pollution control technology in use, there may be ch anges occurring to the fly ash that may affect the stability and mobility of mercury and other metals in the CCRs. Similarly, NOx control and

SO 2 

### scrubber technology may affect the content, stability and mobility of mercury and other

metals in scrubber residues.

In response to wider use of multi-pollutant control, changes are occurring in air pollution control at coal-fired power plants to reduce emissions of nitrogen oxides, sulfur oxides, and mercury. How these changes in air pollution c ontrol is the focus of this resear ch. The fate of mercury and other COPCs in fly ash and scrubber residues is of interest as part of the overall lifecycle evaluation of impact of air pollution control technology and the management of CCRs either through disposal or beneficial us e. This research is evaluating changes to air pollution control residues as a result of more widespread impl ementation of these multi-pollutant 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 of merc ury and other COPCs removed from coalfired power plant air emissions by different types of air pollution control technology that includes acid gas scrubbers , particulate, and sorbents;

2. Provide information to be used in separate reports to assess the fate of mercury and other COPCs from enhanced or expanded us e multi-pollutant control technologies. This will include consideration of potenti al leaching of mercury and other COPCs during the life-cycle management of CCRs during storage, beneficial use and disposal; and

3. Perform these assessments using the most appropriate evaluation methods currently available. The laboratory leach testing followed the approach developed by Kosson, et al. (2002), which considers the effect s of varying environmental conditions on waste constituent leaching.

This is the second of a series of reports that will address the poten tial for cross-media transfer of COPCs from CCRs. The first report focused on the use of sorbent inj ection (activated carbon and brominated activated carbon) for enhan ced mercury control (Sanchez et al., 2006). Subsequent reports will address:

 

### CCRs from coal-fired power plants that use air pollution control t echnologies other than evaluated in earlier reports necessary to span the range of coal-types and air pollution control technology configurat ions (report 3);

 

### Assessment of leaching for COPCs under add itional management scenarios, including impoundments and beneficial use on the land (re port 4); and,

3

### Characterization of Coal Combustion Residues II

 

### Broader correlation of CCR leaching characte ristics to coal rank, combustion facility characteristics and geochemical speciation within CCRs supported by information and analysis on additional trace elements a nd primary constituents (report 4).

Table 1 provides a summary of facility conf igurations, including samples and sample identification for testing, describe d in this report. Fo r simplicity in presentation, the use of NOx

controls is indicated as either “off” or “on” (i.e., SNCR Off, SNCR On, SCR Off, SCR On), recognizing that SCR not in us e (SCR Off) reflects that eith er the system was bypassed or ammonia was not added, and SNCR not in use (S NCR Off) indicates th at urea was not added.

Sampled CCRs were subjected to multiple le aching conditions according to the designated leaching assessment approach. Leaching conditions included batch equilibrium 5 

### extractions at acidic, neutral and alkaline conditions at an LS of 10 mL/g, and LS from 0.5 to 10 mL/g using

distilled water as the leachant. The leach testing results are used to evaluate the likely range of leaching characteristics during land disposal (i .e., landfill or surface im poundment). Results of the laboratory leaching tests carried out in this study were compared to the range of observed

constituent concentrations in field leachates re ported in a U.S. EPA database (EPA, 2007) and an Electric Power Research Institute (EPRI) databa se (EPRI, 2006). The test ing results presented

here will be used for evaluati ng disposal and beneficial use s cenarios in subsequent reports.

As part of this research program, a QA/QC plan consistent with EPA requirements was developed for the leaching assessment approach and reported earlier (Sanchez et al., 2006). The QA/QC methodology included initia l verification of acceptable mercury retention during laboratory testing through evalua tion of a mass balance around te sting procedures (Sanchez et al., 2006). Modifications to the QA/QC program to reduce the experime ntal and analytical burden while maintaining confidence in the resulti ng data, based on program results to date, are presented in this report.

Laboratory testing for leaching assessment wa s carried out at the EPA National Risk Management Research Laboratory (Research Tr iangle Park, North Carolina) with technical assistance from Vanderbilt University and ARCADIS.

5 

### 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.



### 4Characterization of Coal Cumbustion Residues II5Table 1. Summary of facility configurations and sample identification contained in this report.Facilities are identified by code letteronly (e.g., “Facility A”) to preserve the confidentiality of the CCR source. All fly ash samples are ASTM Class F.1Bit – bituminous; Sub-Bit – sub-bituminous2SNCR – selective non-catalytic reduction; SNCR-BP – SNCR by-passed during winter months; SCR & SNCR – residues combinedfrom facility with both SCR and SNCR3ESP-CS – cold-side electrostatic precipitator;ESP-HS – hot-side electrostatic precipitator.4FA – fly ash; Gyp-U – unwashed gypsum;Gyp-W – washed gypsum; ScS – scrubber sludge; FSS – fixated scrubber sludge (amixture of fly ash and scrubber sludge);FSSL – fixated scrubber sludge with lime (amixture of fly ash and scrubber sludge withadditional lime added). The three-letter identification codes are shown for each facility and sample type (e.g., CFA, CGD).FGD Scrubber TypeSample Types and Identification4FacilityCodeCoalRank1PostCombustionNOx Control2ParticulateControl3LimeorMg LimeOxidationFAGyp-UGyp-WScSFSSFSSLABitSNCR-BP (off)Fabric FilterLimestoneNaturalCFACGDCCCABitSNCR (on)Fabric FilterLimestoneNaturalAFAAGDACCBBitSCR-BP (off)ESP-CSMg LimeNaturalDFADGDDCCBBitSCR (on)ESP-CSMg LimeNaturalBFABGDBCCKSub-BitSCR (on)ESP-CSMg LimeNaturalKFAKGDKCCMBitSCR-BP (off)ESP-CSLimestoneInhibitedMADMBitSCR (on)ESP-CSLimestoneInhibitedMASNBitNoneESP-CSLimestoneForcedNAUNAWOBitSCR (on)ESP-CSLimestoneForcedOAUOAWPBitSCR & SNCRESP-CSLimestoneForcedPADQSub-BitnoneESP-HSLimestoneForcedQAU

### Characterization of Coal Combustion Residues II



## 1.1. REGULATORY CONTEXT

1.1.1. Waste Management
The management of coal combustion residues is subject to the Resource Conservation and Recovery Act (RCRA), which is the federal la w regulating both solid and hazardous wastes, as well as state regulatory requirements. Subtitle C of RCRA pertains to hazardous waste; other solid, non-hazardous wastes fall under RCRA Sub title D. Subtitle C wastes are federally regulated while Subtitle D wastes are regulated primarily at the state level. The original version of RCRA did not specify whether CCRs were S ubtitle 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 appro ach for CCRs. In this report (EPA, 1988) and the subsequent regulatory determination, EPA recommended that CCRs generated by electric

utilities continue to be re gulated under RCRA 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 wastes 6 

### and issued another Report to Congress (EPA, 1999) with a similar recommendation. In April 2000, EPA issued a regulatory determination exempti ng these wastes from h azardous waste regulations (see 65 FR 32214, May 22, 2000). However, concern wa s expressed over the use of CCRs as backfill for mine reclamation operations, and it wa s determined that this practice should be regulated under a federal Subtitle D rule. It wa s 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 th e process of developing these regulations ( http://www.epa.gov/epaoswer/other/fossil/noda07.htm ). The results presented in this report, and subsequent reports, will help provide the informa tion needed to identify the release potential of mercury and other metals that have been remove d 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 develope d under the regulations.

1.1.2. Air Pollution Control

On March 10, 2005, EPA announced the CAIR (FR 25612, May 2005) which is expected to

increase the use of wet scrubbe rs and selective catal ytic reduction (SCR) un its to help reduce sulfur dioxide and nitrogen oxi des emissions from coal-fired power plants. On March 15, 2005, EPA announced the 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 mercury emissions in the county. The CAMR established “standard s of performance” that limit mercury emissions from new [through new sour ce performance standard s (NSPSs)] and existing (through emission guidelines) coal-f ired power plants through th e creation of a market-based cap-and-trade program that will reduce mercury emissions in two phases. The first phase caps

6 

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



### 6

### Characterization of Coal Cumbustion Residues II



### national annual mercury emissions at 38 tons through co-benefit reducti ons achieved through controlling sulfur dioxide (SO 2 

### ) and nitrogen oxides (NOx) emi ssions under CAIR. In the second phase, due in 2018, coal-fired power plants will be subject to a second cap, which will reduce mercury emissions to 15 tons per year upon fu ll implementation. On February 8, 2008, the D.C. Circuit vacated EPA's rule removing power plants from the Clean Air Act list of sources of hazardous air pollutants. At the same time, the court vacated the CAMR. EPA is reviewing the court's decisions and evaluating its impacts. ( http://www.epa.gov/mercuryrule/ ) On July 11, 2008, the D.C. Circuit vacated EPA’s Clean Air In terstate Rule. EPA is reviewing the court’s decisions and evaluating its impacts.

Congress has directed EPA to doc ument that the Clean Air Act re gulations are not trading one

environmental burden for another. The Air Pollu tion Prevention and Control Division (APPCD) of EPA’s Office of Research and Development (ORD ) is conducting the curre nt research to help identify any potential pollutant transfers resul ting from land disposal or beneficial use of mercury-enriched CCRs. The research results presen ted 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 CONT ROL TECHNOLOGIES

In the U.S., there are approximately 1,100 units at approximately 500 coal-fired electricity generating facilities. These facilities represen t a range of coal ranks, boiler types, and air pollution control technologies. The current combined capacity of U.S. coal-fired pow er plants is 307 GW (DOE-EIA, 2007). The coal rank burned and facility design characteristics affect the effectiveness of multi-pollutant control technologies that are or could be used at these plants. The

U.S. coal-fired power plants ty pically burn one of three types of fuel: (1) bituminous coal (also referred to as “high rank” coal ), (2) sub-bituminous coal, and (3) and lignite (sub-bituminous coal and lignite are referred to as “low rank” co als). Some of the characteristics of interest related to the possible e nvironmental impacts of burning these different coal ranks are given in Table 2 (EPA, 2005).

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

Mercury Chlorine Sulfur Ash HHV a 

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

Coal Range Avg Range Avg Range Avg Range Avg Range Avg

Bitu- 0.036 - 0.113 48 - 1033 0.55 - 1.69 5.4 - 11.1 8646 - 13203

minous 0.279 2730 4.10 27.3 14014

Sub- 0.025 - 0.071 51 - 158 0.22 - 0.50 4.7 - 8.0 8606 - 12005

bitu- 0.136 1143 1.16 26.7 13168

minous 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 

### Higher Heating Value.

7

### Characterization of Coal Combustion Residues II



### 1.2.1. Current Air Pollution Control Technologies
The key air pollutants of concern released by co al fired power plants include particulates, SO 2 

### , NOx, mercury and other metals 7 

### . A range of pollution control te chnologies is used to reduce particulate, SO 2 

### , and NOx and these technologies also im pact the emission of mercury and other metals. The pollution control technology type and configurations va ry across facilities.

7 

### Concerns regarding carbon dioxide emissions from coal fired power plants are beyond the scope of this

report.



### 8

### Characterization of Coal Cumbustion Residues II



### Table 3 shows the current and projected coal-f ired capacity by air po llution control technology configuration. This report emphasizes wet scrubbe rs since their use is expected to double or triple in response to implementa tion of CAIR. Post-combustion pa rticulate matter controls used at coal-fired utility boilers in the United States can include electrostatic precipitators (ESPs), fabric filters (FFs), particulate scrubbers (PSs), or mechanical collectors (MCs). Post-combustion

SO 2 

### controls can consist of a wet scrubber (WS), spray dryer adsorb er (SDA), or duct injection.

Post-combustion NOx controls can involve selective catalyti c reduction (SCR) or selective noncatalytic reduction (SNCR).

In response to current and proposed NOx and SO 2 

### control requirements, additional NOx control and flue gas desulfurization (FGD) systems for SO 2 

### control are expected to be installed and more widely used in the future. Some estimates proj ect a doubling or tripling of the number of wet scrubbers as a result of CAIR implementation. Ov er half of the U.S. coal-fired 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 be heavily dependent on the partitioning of mercury between th e particulate and vapor phases and the distribution of mercury species (e.g., elemental or oxidi zed) in the vapor phase. In gene ral, ESPs and FFs which are designed for particulate control ar e quite efficient at removing me rcury 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 the observed differences in mercury removal effici ency, such as the mercury oxidation state. Differences in mercury contents of U.S. coals also result in a range of me rcury 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). Further, the chlorine content of the coal may have an impact on mercury removal because the oxidation state of mercury is strongly affected by the presence of halides in the flue gas. In general, the higher the chlorine content of the coal, the more likely the mercury will be present in its oxidized state, enhancing the

likelihood of its removal from the gas stream. The addition of NO

x 

### controls may improve the mercury capture efficiency of particulate collection devices for some cases. (EPA, 2001)

9

### Characterization of Coal Combustion Residues II



### Table 3. Projected Coal-Fired Capacity by AP C Configuration as per data collection in 1999 (EPA, 2005). CCR samples evaluated in this report are from configurations indicated by shaded (light gray) rows. Current capacity reflects date of data collection for EPA report (EPA, 2005).

Air Pollution Control Configuration Current Capacity, MW 2010 Capacity,

MW 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 Existing or Planned Retrofit Units 304,955 298,263 297,161

New Builds of Coal Steam Units Current Capacity, MW 2010 Capacity,

MW 2020 Capacity,

MW

Fabric Filter + SCR + Wet Scrubber

- 221 17,292

Total All Units 304,955 298,484 314,453
Note: IGCC units are not included as part of this list. Note: Current capacity includes some SCR and FG D projected to be built in 2005 and 2006. Note: 2010 and 2020 is capacity projected for final CAIR rule. Note: IPM projects some coal retiremen ts and new coal in 2010 and 2020.



### 10

### Characterization of Coal Cumbustion Residues II



### 1.2.2. Wet Scrubbers, NOx Controls and Multi-pollutant Controls

Wet FGD scrubbers are the most widely used technology for SO 2 

### control. Scrubbe rs are typically installed downstream of particul ate control (i.e., ESP or FF). Re moval of PM from the flue gas

before it enters the wet scrubber reduces solids in the scrubbing soluti on and minimizes impacts to the fly ash that might affect its beneficial use.

FGD technology uses sorbents and chemical reacta nts such as limestone (calcium carbonate) or lime (hydrated to form calcium hydroxide) to re move sulfur dioxide from the flue gas created from coal combustion. Limestone is ground into a fine powder and then co mbined with water to spray the slurry into co mbustion gases as they pass through a scrubber vessel. The residues are collected primarily as calcium sulfite (a chem ically reduced material produced in natural

oxidation or inhibited oxidation sc rubbers), or can be oxidized to form calcium sulfate or FGD gypsum (using forced oxidation). The most widely used FGD systems use either forced oxidation scrubbers with limestone addition, or natural/inhi bited oxidation scrubbers with lime or Mg-lime

addition 8 

### . Wet scrubbers that use forced oxidati on produce calcium sulfate (gypsum) and are expected to be the most preval ent technology because of the poten tial beneficial use of gypsum and easier management and handling of the resi dues. There are also dry FGD systems that include spray dryer absorbers, usually in comb ination with a FF (EPA, 2001; Srivastava et al., 2001).

NOx emissions are controlled through the use of low NOx producing burners and use of a selective catalytic reduction (SCR) system in the flue gas that is capable of a 90% reduction of flue gas NOx emissions. SCR is typically in stalled upstream of the PM control device. Sometimes selective non-catalytic reduction (SNCR) is used fo r NOx control, although use of SNCR is less frequent.

Figure 2 illustrates options for multi-pollutant control at power plants.

8 As of 1999: Total FGD units – 151; limestone forced ox idation (FO) - 38 units (25%); limestone natural/inhibited oxidation - 65 (43%); lime FO (all forms other than Mg-Lime) - 1 (<1%); lime natural/inhibited oxidation (all forms other than Mg-lime) - 23 (15%); Mg-lime FO - 0 (0%); Mg-lime natural/inhibited oxidation - 25 (17%) It is estimated that the numbers of natural/inhibited systems has remained nearly the same since 1999, and the limestone FO units have increased significantly. In the futu re, limestone FO units will increase significantly, and all types of natural/inhibited units w ill likely decrease (Ladwig, 2007).



### 11

### Characterization of Coal Combustion Residues II



### OxidizingOxidizing Wet Scrubber Stack Wet Scrubber

Coal & Air

Oxidizing

Chemicals SCR Catalysts

Residue Ash PM Control

Coal & Air

Oxidizing

Chemicals SCR Catalysts

Residue Ash PM Control

Figure 2. Multi-pollutant control sy stems in coal fired power plants.

Improvements in wet scrubber performance to enhance mercury capture depend on oxidizing elemental mercury (Hg 0 

### ) to Hg 2+ 

### by using additives to the flue gas or scrubber. A DOE-funded study found that wet scrubbers remove about 90% of the oxidized gaseous mercury (Hg 2+ 

### ) in the flue gas but none of the elemental mercury (Pav lish et al., 2003). The per centage of total Hg removed by multi-pollutant controls (particulate and scrubber devices) is influenced by coal chlorine content, which determines the Hg oxida tion status exiting the particulate control and entering the scrubber. Mercury re moval efficiency by wet scrubbe rs ranges from 30 to 60% for cold-side ESPs as coal chlorine content is increased from 50 to 1000 mg kg -1 

### . Mercury removal efficiency for hot-side ESPs is less effective ra nging from 20 to 50% as co al chlorine content is increased from 200 to 1000 mg kg -1 

### (Pavlish et al., 2003). Other factors that influence mercury capture are the amount of carbon and chlorine in the fly ash. Fuel blendi ng, addition of oxidizing chemicals, controlling unburned carbon content in the fly ash, and addition of a mercury-specific oxidizing catalyst downstream of the particul ate matter control can help improve mercury capture (Thorneloe, 2006; EPA, 2005).



## 1.3. COAL COMBUSTION RESIDUES

The range of air pollution contro l technologies and configurations determines the characteristics of the coal combustion residues. In 2006, 125 m illion tons of coal combustion residues were produced with ~53 million tons being used in commercial, engineering, and agricultural applications. (ACAA, 2007). CCRs result from unburned carbon and inor ganic materials in coals that do not burn, such as oxides of silicon, aluminum, iron, and calcium. 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 APC equipment. APC can concentrate or partition metals in fly ash and scrubber sludge. Bottom ash and boiler slag are not affected by APC technology and, therefore, these materials are not being evaluated as part of this study. Bottom ash is the unburned material that is too heavy to be entrained in the flue gas

12

### Characterization of Coal Cumbustion Residues II



### stream 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.

Changes in multi-pollutant control in re sponse to CAIR implementation, voluntary improvements by facilities, and changes in stat e requirements, will reduce air emissions of mercury and other pollutants that will be transferred from the flue gas to the APC residues. The purpose of this research is to evaluate the impact of these ch anges on CCRs, with a focus on changes in metals concentrations in CCRs, and the potential for subsequent release of these metals to the environment under different plausi ble management (disposal or reuse) conditions (Figure 3). The properties of fly ash and scrubber residues are likely to change as a result of changes in air pollution control to reduce emissions of concern from coal-fired power plants. Changes in CCRs that may occur include increase d content of mercury and other metals (e.g., arsenic, selenium, chromium) The chemical and physical properties ma y also change as a results of sorbents and other additives being used to improve air po llution control.

Figure 3. Life-cycle evaluation of coal combustion residues (EPA, 2002).



## 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 to groundwater. Research on the impact of CCR di sposal on the environment has been conducted by many researchers and has been summarized by 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 40% per cent (49.6 million tons) of all CCRs produced are reused in commercial applications or other us es that are considered beneficial and avoid

13

### Characterization of Coal Combustion Residues II



### landfilling. Forty-eight percen t (23.8 million tons) of CCRs is fly ash which is used in commercial applications such as making concrete /grout, cement, structur al fill, and highway construction (ACAA, 2005; Thorneloe, 2003). Ei ght million tons of the FGD gypsum that was produced (or 68%) was used in making wall board (ACAA, 2005). Table 4 and Figure 4 present the primary commercial uses of CCRs, and a breakdown of U.S. production and usage by CCR

type.

Some of the beneficial uses may have the poten tial to release mercury from the CCRs by several pathways. Of particular concern are high-temperature processes. In ce ment manufacturing, for example, CCRs are inputs to the cement kiln. Virtually all mercury will be volatilized from

CCRs when CCRs are used as feedstock to cement kilns. Even where mercury can be captured by the controls on cement kilns, approximately tw o-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 filler for asphalt, or when FGD material is used in wallboard manufacturing. A se parate report is being prepared to document the finding on the thermal stability of Hg and other metals when used in high-temperature processes.

The fate of mercury and other metals is also a potential concern when CCRs are used on the land (mine reclamation, building highways, soil amendments, agriculture a nd in making concrete, cement) or to make products that are subseque ntly disposed (e.g., disposal of wallboard in unlined landfill).

For several commercial uses, it ap pears less likely that mercur y in CCRs will be reintroduced into the environment, at leas t during the lifetime of the product. However, the impact of advanced mercury emissions cont rol technology (e.g., activ ated carbon injection) on beneficial use applications is uncertain. Th ere is concern that the presence of increased concentrations of mercury, certain other metals, or high carbon content may reduce the suitability of CCRs for use in some applications (e.g., carbon content ca n limit use in Portland cement concrete).

1.4.2. Land Disposal
There are approximately 600 land-based CCR wast e disposal units (landfills or surface impoundments) being used by the approximately 500 co al-fired power plants in the United States (EPA, 1999). About 60% of the 122 million tons of CCRs generated annually are land disposed. Landfills may be located either on-site or off-s ite while surface impoundments are almost always located on-site with the combustion operations. Although the distribution of units is about equal between landfills and surface impoundments, there is a trend toward increased use of landfills as the primary disposal method.

14Characterization of CoalCumbustion ResiduesReportTable 4. Beneficial uses of CCRs (ACAA, 2007).Total production of CCRs during 2006 was 124,795,124 short tons.CCR Categories (Short Tons)FlyAshBottomAshFGDGypsumFGD WetScrubbersBoilerSlag1FGD DryScrubbers1FGDOtherCCR Production Category Totals272,400,00018,600,00012,100,00016,300,0002,026,0661,488,951299,195CCR Used Category Totals332,423,5698,378,4949,561,489904,3481,690,999136,63929,341CCR Use By Application4FlyAshBottomAshFGDGypsumFGD WetScrubbersBoilerSlag1FGD DryScrubbers1FGDOther1. Concrete/Concrete Products/Grout15,041,335597,3871,541,930009,66002. Cement/Raw Feed for Clinker4,150,228925,888264,568017,773003. Flowable Fill109,35700009,843 04. Structural Fills/Embankments7,175,7843,908,5610131,821126,280005. Road Base/Sub-base/Pavement379,020815,5200060249 06. Soil Modification/Stabilization648,551189,5870002991,5037. Mineral Filler in Asphalt26,72019,2500045,000008. Snow and Ice Control0331,1070041,549009. Blasting Grit/Roofing Granules081,2420232,7651,445,9330010. Mining Applications942,04879,6360201,0110115,696 011. Wallboard007,579,187000012. Waste Stabilization/Solidification2,582,125105,052000027,83813. Agriculture81,2121,527168,19000846 84614. Aggregate271,098647,274004160015. Miscellaneous/Other1,016,091676,4637,614338,75113,9884646CCR Category Use Tools32,423,5698,378,4949,561,489904,3481,690,999136,639 29,341Application Use to Production Rate44.8%45.0%79.0%5.5%83.5%9.2%9.8%1As submitted based on 54 percent coal burn.2CCR Production totals for Fly Ash, Bottom Ash, FGD Gypsum, and Wet FGD are extrapolated estimatesrounded off to nearest 50,000 tons.3CCR Used totals for Fly Ash, Bottom Ash, FGD Gypsum, and Wet FGD are per extrapolation calculations (not rounded off).4CCR Uses by application for Fly Ash, Bottom Ash, FGD Gypsum, and Wet FGD are calculated per proportioning the CCR Used CategoryTotals by the same percentage as each ofthe individual application types' raw data contributions to the as-submitted raw datasubmittal total(not rounded off).15

### Characterization of Coal Combustion Residues II

0 2 4 6 8 10 12 14 16 18

Con c ret

e / G

r o ut Structu r al

Fill

Wa

ll b

oar

d

Cement

Waste Stabiliz at

ion/Sol i dif

i cat

i o n

Mi

s cellan e o u s /O

t h

er

B lastin g Grit/Roofing G

ra

n ules

Road Base/Pavem e nt Mining Applications

Soil Modification/Stabilization

A

g gregate

Snow an

d

Ice

Con t rol Agricult u r e

Mi

ner

al

Filler i n A

s p ha

lt Flow abl

e

F i l lQuantityofCCRs(milliontons)

FG D Dr y Sc r u b b e r s

Bo i l e r Sla g

FG D We t Sc r u b b e r s

FG D G y ps um

Bo t t o m As h

Fl y As h



### Figure 4. Uses of CCRs based on 20 06 Industry Statistics (ACAA, 2007).



## 1.5. LEACHING PROTOCOL

One of the major challenges initially facing this research was identification of an appropriate test protocol for evaluating the leachi ng potential of CCRs that may have increased levels of several metals, particularly mercury. The goal of this re search is to develop the most accurate estimates of likely constituent leaching when CCRs are land di sposed. These estimates of leaching need to be appropriate for assessing at a national level the likely impacts through leaching of pollutants from CCRs that is a consequence of installatio n of 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 result s can be appropriately extrapolated to a national assessment. A large pa rt of the approach to achieving this goal has been to identify and evaluate CCR samples collect ed from the most prevalent combinations of power plant design (with a focus on air polluti on control technology configurations) and coal rank used. In addition, the resulti ng data set is expected to serve as foundation for evaluation of CCR management options for different types of CCRs at specific sites.

Data have been collected on the disposal cond itions for CCRs. The conditions will vary over

time which need to be cons idered when evaluating leaching. (EPA, 1999, 202, 2007). When

16

### Characterization of Coal Cumbustion Residues II



### disposed, CCRs are typically monofilled or disposed with othe r CCRs. However, CCR composition can change over time, due to reactions with the atmosphere (e.g., carbonation and oxidation), changes in the source of coal or coal rank burned, or due to installation of additional pollution control equipment.

Many leaching tests have been developed by regul atory agencies, researchers, or third-party technical standards organizations, and are described in th e published literature. States and others have expressed concern with the variety of leachi ng 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 conditio ns. There is also limited or no quality assurance (QA) information for many of these tests. Leaching tests such as the Toxicity Characterization Leaching Procedure (TCLP) 9 

### (which reflects municipal solid waste co-disposal conditions) or the synthetic precipitation leachi ng procedure (SPLP), or any numb er of deionized water based tests may be inappropriate, or are at least no t optimal for evaluating the leaching potential of CCRs as they are actually managed (i.e., monofilled or codisposed with ot her CCRs). These tests either presume a set of prevailing landfill co nditions (which may or may not exist at CCR disposal sites; e.g., TCLP), try to account for an environmental fact or considered to be important in leaching (e.g., SPLP), or presume that the waste as tested in the laboratory will define the disposal conditions (such as deionized (DI) wa ter tests). Most existing leaching tests are empirical, in that results are presented simply as the contaminant concentrations leached when using the test, and without measuring or reporti ng values for factors that may affect waste leaching, or that provide insight into the chemistr y 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 10



### . In searching for a reliable procedure to charac terize the leaching potential of metals from the management of CCRs, EPA sought an approach that (i) considers key asp ects of the range of known CCR chemistry and management conditions (including re-use); and (ii) permits development of data that are comparable acros s U.S. coal and CCR types. Because the data resulting from this research will be used to s upport regulations, scrutiny of the data is expected.

9 

### The Toxicity Characterization Leaching Procedure (T CLP) was not included as part of this study for two reasons. First, EPA previously made a waste st atus 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 re gulation 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 flex ibility to consider the effects of actual management conditions on these wa stes, and so will be more accurate in this case.

10 

### Many factors are known or may reasonably be exp ected 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 th e leaching rate, and also affect leaching chemistry and equilibrium.



### 17

### Characterization of Coal Combustion Residues II



### Therefore, the use of a published, peer-reviewed prot ocol is also considered to be an essential

element of this work.

EPA ORD has worked closely with EPA’s Office of Solid Waste and Emergency Response (OSWER) to identify an appropriate leaching pr otocol for evaluating CCRs . The protocol that has been adopted is the “Integrated Framewor k for Evaluating Leaching in Waste Management and Utilization of Secondary Materials” (Kosson et al., 2002) and referred to here as the “leaching framework.” The leaching framework c onsists of a tiered approach to leaching assessment. The general approach under the leachi ng 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 estimat e constituent release by leaching under specific management scenarios (e.g., landfilling). Unlike 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 leaching framework has focused on assessing metals leaching, and this work includes equilibrium batch testi ng (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 es timate release for specifi c management scenarios based on testing results from a common set of leaching conditions . EPA OSWER and ORD believe that this approach successf ully addresses the concerns identif ied above, in that it seeks to consider the effect of key di sposal conditions on constituent leaching, and to understand the leaching chemistry of wastes tested.

The following attributes of the leaching framewor k were considered as part of the selection

process:

 

### The leaching framework will permit development of data that are comparable across U.S. coal and CCR types;

 

### The leaching framework will permit comparison with existing laboratory and field leaching data on CCRs;

 

### The leaching framework was published in the peer -reviewed scientific literature (Kosson et al., 2002);

 

### On consultation with EPA’s OSWER, it was reco mmended as the approp riate protocol based on review of the range of available test methods and assessment approaches; and

 

### On consultation with the Environmental Engi neering Committee of the Science Advisory Board (June 2003), the committee considered the leaching framework responsive to earlier SAB criticisms of EPA’s approach to leaching evaluation, and also was considered broadly applicable and appropriate for this study

For this study, the primary leaching tests used fr om the leaching framework were Solubility and Release as a Function of pH (SR002.1) and Solub ility and Release as a Function of the LiquidSolid Ratio (LS) (SR003.1) 11 

### . These tests represent equilibrium-based leaching characterization

11 

### 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



### 18

### Characterization of Coal Cumbustion Residues II



### (Kosson et al., 2002). 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-c hemical mechanisms controlling constituent leaching. When used in conjunction with mass tr ansfer and geochemical speciation modeling, the results can provide conservative 12 

### but realistic estimates of c onstituent 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 Research Laboratory (Research Tria ngle Park, NC) with technical assistance from Vanderbilt University.

deionized water at LS= 0.5, 1, 2, 5 and 10. Under fi eld conditions, LS refers to the cumulative amount of water passing through the total mass of CCR subject to leaching.

12 

### In this report, “conservative” implies that the cons tituent release estimates are eq ual to or greater than actual expected release under field conditions.



### 19

### Characterization of Coal Combustion Residues II



## 2. MATERIALS AND METHODS

2.1. CCR MATERIALS FOR EVALUATION

The 23 CCR materials tested in this study in clude five fly ash, four unwashed gypsum, two washed gypsum, five scrubber sludges, two fixa ted scrubber sludges and five fixated scrubber sludges with lime obtained from eight coal fired power plants (Tab le 1). The facilities and CCRs that were sampled were selected to allow comparisons

(i) between different CCR types from a give n facility (Facilities A, B and K),

(ii) between CCRs of the same type from th e same facility without and with postcombustion NOx control, either by SNCR (Facility A) or SCR (Facility B),

(iii) the impact of different FGD scrubber types on scrubber sludge and “as managed” FSS or FSSL (Facilities A, B, K and M),

(iv) the influence of coal rank (bituminous vs. s ub-bituminous) being combusted in facilities with similar APC technology configurations (Facility B and K with SCR on),

(v) unwashed and washed gypsum from the same facility (Facilities N and O), and

(vi) unwashed gypsum from four fac ilities (Facilities N, O, P a nd Q). This set of 23 CCRs reflects 84 and 74 percent, respectively, of the current and expected future facility configuration types with aci d gas scrubbers based on generating capacity, but only a

limited number of facilities within each configuration type. Figure 5, Figure 6,

(vii) Figure 7, and Figure 8 diagram the layout of comparisons that will be used in presentation of data for fly ash, gypsum, scrubber sludge, fixated scrubber sludge and fixated scrubber sludge w ith lime, respectively.



## Facility A
Coal: low sulfur bituminous

APC: NO+SNCR+FF

Facility B
Coal: low sulfur bituminous APC: NO+SCR+ESP(CS) [Mg lime]

Facility K
Coal: sub

- bituminous APC: NO+SCR+ESP(CS) [Mg lime] 

# BFA
(SCR On) 

# DFA
(SCR Off) 

# AFA
(SNCR On) 

# CFA
(SNCR Off)



# KFA
(SCR On)

Figure 5. Fly ash (FA) comparisons (CFA, AFA, DFA, etc refer to sample identification codes; see Table 1). Shorthand is used for when S CR is in use (“on”) or not in use (“off”).

20

## Facility N

Coal: bituminous APC: FO+ESP(CS)

Facility O

Coal: bituminous APC: FO+SCR+ESP(CS) 

# Gyp-U

OAU
(unwashed) 

# NAU
(unwashed) 

# Gyp-W

OAW
(washed)



# NAW
(washed)



## Facility P

Coal: bituminous APC: FO+ SCR & SNCR +ESP(CS) 

# PAD (U)
(unwashed) 

# QAU
(unwashed)



## Facility Q

Coal: sub-bituminous APC: FO+SCR+ESP(CS) Characterization of Coal Cumbustion Residues II



### Figure 6. Gypsum (Gyp-U, Gyp-W) comparis ons (NAU, NAW, OAU, etc. are sample identification codes; see Table 1).

Errata: Subsequent tables and figures indicate the Facility N has SCR in use. That is not correct. This will be corrected in Report 4 and doe s not change the leach testing results.

21

## Facility A

Coal: low sulfur bituminous

APC: NO+SNCR+FF

Facility B

Coal: low sulfur bituminous APC: NO+SCR+ESP(CS) [Mg lime] 

# BGD
(SCR On) 

# DGD
(SCR Off) 

# AGD
(SNCR On) 

# CGD
(SNCR Off)



# KGD
(SCR On) 

## Facility K

Coal: sub- bituminous APC: NO+SCR+ESP(CS) [Mg lime] Characterization of Coal Combustion Residues II



### Figure 7. Scrubber sludge (ScS ) comparisons (CGD, AGD, DGD, et c. are sample identification codes; see Table 1). Shorthand is used for when SCR is in use (“on”) or not in (“off”).

22

## FSS: Fly Ash + Scrubber Sludge (FA+ScS)

Facility A ( FSS )

Coal: low sulfur bituminous

APC: NO+SNCR+FF 

# ACC
(SNCR On) 

# CCC
(SNCR Off)



## FSSL: Fly Ash + Scrubber Sludge + Lime (FA+ScS+lime)

Facility B ( FSSL )

Coal: low sulfur bituminous APC: NO+SCR+ESP(CS) [Mg lime]

Facility K ( FSSL )

Coal: sub-bituminous APC: NO+SCR+ESP(CS) [Mg lime]

Facility M ( FSSL )

Coal: bituminous 

# MAD MAS
APC: IO+SCR+ESP(CS) (SCR Off) (SCR On) 

# BCC
(SCR On) 

# DCC
(SCR Off)



# KCC
(SCR On) Characterization of Coal Cumbustion Residues II



### Figure 8. Fixated scrubber sl udge (FSS) and fixated scrubbe r sludge with lime (FSSL) comparisons (DCC, BCC, KCC, etc. are samp le identification codes; see Table 1).

23

### Characterization of Coal Combustion Residues II



### 2.1.1. Facilities Using Inhibited or Natural Ox idation of Scrubber Residues (Producing Scrubber Sludge or Fixated Scrubber Sludge)

2.1.1.1. Facility A (Natural Oxidation and SNCR)

Facility A is a 440-MW coal-fired power plant with a reverse-ai r fabric filter followed by a wet FGD system. The unit burns ~1 percent sulfur eastern bituminous coal. The unit operated at nominally full load for the duration of the testprogram. The unit is equipped with a pulverizedcoal boiler and in-furnace selective SNCR; urea wa s injected into the boile r during the course of operations within the duration of the initial part of this test program. However, urea was not injected into the boiler for the final comparis on test (“SNCR off”). Gas exiting the furnace is split between two flues equipped with comparable control equipm ent. Particulate is removed with a reverse-air fabric filter. Flue gas is then scrubbed through a multiple tower wet FGD unit; FGD is a limestone natural-oxidation design. The two flues are joined pr ior to exhausting to a

common stack. The annular stack rises 308 feet above the top of the incomi ng flue. The stack is operated in a saturated condition with no reheat . The fly ash and FGD waste are combined and then dewatered before landfill disposal.

Facility A was sampled in September 2003. Thr ee samples were collected in September 2003 when the SCR was operating: one fresh fly ash sample collected from the ash hopper (sample AFA), one scrubber sludge filter cake sample co llected after the centrifuge but before mixing

with other materials in the pug mill (sample AGD), and one fi xated scrubber sludge sample collected after mixing the scrubbe r sludge with fly ash and magnesium-enhanced lime in the pug mill (sample ACC). Three additional samples were co llected from the same locations in February 2004 when the SCR was not in use (samples CFA, CGD and CCC, respectively). Each sample consisted of two 5-gallon pails of the materi al, and all were collected by plant personnel.

2.1.1.2. Facility B (Natural Oxidation and SCR)

Facility B is a 640 MW coal-fired power plan t with cold side ESP followed by a wet FGD system with Mg-lime. The unit burns medium to high sulfur eastern bituminous coals. The unit is equipped with a pulverized coal bo iler and selective catalytic re duction composed of vanadium pentoxide (V 2 

### O 5 

### ) and tungsten trioxide (WO 3 

### ), on titanium dioxide (TiO 2 

### ) supporting matrix. One set of samples was collected during the season of elevated ozone, when ammonia is injected into the ductwork in front of the SCR catalyst, resulting in a flue gas mixture with a concentration of 320 ppm ammonia as it enters the catalyst. Samp les were also collected during

the winter when ammonia was not being injected (“SCR off”). Particulate is removed with a cold-side ESP. Flue gas is then scrubbed th rough a wet FGD unit; FGD is an inhibited mag-lime design. The FGD sludge is thickened and then mi xed with fly ash and magnesium-enhanced lime before landfill disposal in a clay-lined site. Refer to appendix G for a process flow-diagram for facility A.

Three samples were collected in September, 2003 when the SCR was opera ting: one give gallon bucket of the fly ash (BFA) from the hoppe rs, partially dewatered scrubber sludge by centrifuging (BGD), and centrate cake (BCC) or scrubber sludge fixated with fly ash and Mg lime (MgO). Three additional samp les were collected from the sa me locations in February, 2004 when the SCR was not in use (samples DFA, DGD, and DCC, respectively). Each sample consisted of one 5-gallon bucket of the materi al, and all were collected a Natural Resource Technology contractor to EPRI.

24

### Characterization of Coal Cumbustion Residues II



### Coal analysis information for facility B was provided by EPRI. Results of the analysis on the medium to high sulfur bituminous coal for su lfur was 3.24% by weight, ash was 12.4%, moisture was 6.1%, heat of combustion was 12,000 BTU/l b, chloride was 615 ug/g, and mercury was 0.08 ug/g.

2.1.1.3. Facility K (Natural Oxidation and SCR)

Facility K is two tangentially fired 400 MW coal-f ired boilers with cold side ESP followed by a wet flue gas desulfurization system with wet Mg-lime natural oxidation. These units burn

medium sulfur eastern bituminous coals from Ohi o, Pennsylvania and West Virginia. Flue gas is scrubbed through a common wet FGD unit; FGD is a wet Mg-lime natural oxidation design. FGD sludge is mixed with fly ash and quickli me for stabilization prior to disposal.

Two samples were collected on November 29, 2004: one scrubber sludge filter cake before mixing in the pug mill (sample KGD), and one fixa ted scrubber sludge collected after mixing the scrubber sludge with fly ash and 2-3% lime in the pugmill (sample KCC). On January 12, 2005, one fly ash sample was collecte d directly from the ESP before the ash storage silo (sample KFA). Each sample consisted of four 5-gallon pa ils of the material, and all were collected by plant personnel.

2.1.1.4. Facility M (Inhibited Oxidation and SCR)

Facility M is a 1,000+ MW power plant. The plant burns bituminous coal in a dry-bottom pulverizer boiler. Cold-side ESPs are used on all units for particulate control, and wet FGD systems are used to reduce SO 2 

### emissions on two units. The wet FGD systems utilize limestone slurry and an inhibited oxida tion process. The FGD sludge, c onsisting primarily of calcium sulfite, is pumped from the absorber to a thic kener. Liquid overflow from the thickener is recycled back into the FGD system, and the thickened sludge is pumped to a series of drum vacuum filters for further dewatering. Water re moved by the drum vacuum filters is recycled back into the FGD system, and th e filter cake is take n by conveyor belt to a pug mill, where it is mixed with dry fly ash and dry quicklime for st abilization. The resulting scrubber FGD solids are taken by conveyor to a temporar y outdoor stockpile, and then tr ansported by truck either to a

utilization site or to an on-site landfill. The currently active portion of the landfill is lined and

includes leachate collection. An older inactive portion of the landf ill is clay-lined but does not

have leachate collection.

Three samples were obtained from the Pug Mill Ar ea by the EPRI contractor during the week of March 6, 2006 when the SCR was not operating: fly ash, vacuum drum filter cake, and fixated scrubber sludge with lime (only FSSL was evaluated as part of this study, sample MAD). In each case, the samples were collected daily duri ng the four day sample collection (four daily samples of each), for compositing in the laboratory. All of the samples were collected into clean 5 gallon plastic pails. Excess sample was containe rized and discharged back into the appropriate system. The drum filter cake was sampled daily fr om the conveyor belt leading into the pug mill. Two of the three drum filters were running simultaneously; both were feeding the conveyor belt. The same drums were running each day of sampling. Each 5 gallon bucket was sealed immediately after collection and the lid secure d with duct tape. The dry fly ash sample was obtained directly from the day tank via a hos e connected to a sampling port. Each 5 gallon bucket was sealed immediately after collection and the lid secured with duct tape. FSS was

25

### Characterization of Coal Combustion Residues II



### sampled from the conveyor belt on the outlet side of the pug mill on the first, third and fourth days. A clean, short handled spade was used to collect sample from the conveyor belt into a 2 gallon bucket. The sample in the bucket was pl aced on a clean piece of 3 mm plastic sheeting; then more sample was collected from the conveyor belt into the bucket and added to the sheet until at least 6 gallons of sample was collect ed. Each sample was homogenized on the sheet using the spade and placed into a 5 gallon bucket, sealed immediately, and the lid secured with duct tape. A similar process was used to collect three more samples the week of May 9 when the SCR was in use (FSSL sample MAS).

2.1.2. Facilities Using Forced Oxidation of Scrubber Residues (Producing FGD Gypsum)

2.1.2.1. Facility N (Forced Oxidation)

Facility N is a wall fired 715 MW coal-fired pow er plant with cold side ESP followed by a wet FGD system with wet limestone forced oxidation. The unit burns medium to high sulfur eastern bituminous coals approximately 3% sulfur. The gyps um is washed, dried and then sold to the wallboard industry.

Facility N was sampled on June 1, 2006. Five gallon buckets of the washed and unwashed gypsum were collected by RMB Consulting & Research Inc. (Raleigh, NC) personnel and provided for analysis.

2.1.2.2. Facility O (Forced Oxidation and SCR)

Facility O is a tangentially fire d 500 MW coal-fired plant with cold side ESP followed by a wet FGD system with wet limestone forced oxidati on. The unit is equipped with a pulverized coal

boiler and ammonia based SCR. This unit burns high sulfur eastern bituminous coals. Slurry from the absorber goes to a primary hydrocyclone for initial dewatering. The gypsum (hydrocyclone underflow) is dried on a vacuum belt and washed to remove chlorides, before use

in wallboard.

Two samples were collected from the FGD gyps um drying facility by compositing samples collected on June 10, 11, and 12, 2006 when the SCR was operating. On each day, two gallon pails of unwashed gypsum and washed/dried gyp sum were collected. The unwashed gypsum was collected from the vacuum belt prior to the chlo ride spray wash. The washed/dried gypsum was

collected from the end of the vacuum belt. The three daily samples were sent to Arcadis for compositing to form sample OAU (unwashed gypsum) and sample OAW (washed gypsum). All samples were collected by plant personnel.

2.1.2.3. Facility P (Forced Oxidation and SCR and SNCR)

Facility P is two wall fired 200 MW coal-fired boilers with cold side ESP followed by a wet FGD system with wet limestone forced oxidation. Unit 1 is equipped with SNCR and Unit 2 is equipped with SCR. These units burn medium sulfur eastern b ituminous coals. Particulate is removed with a cold-side ESP. Flue gas is then scrubbed through a common wet FGD unit; FGD

is a wet limestone forced oxidation desi gn. The gypsum provided was not washed.

Facility P was sampled in October 2006 when both SCR and SNCR were operating and the residues from Unit 1 and Unit 2 were commingled during collection. A five gallon bucket of the washed gypsum was collected by plant personnel.

26

### Characterization of Coal Cumbustion Residues II



### 2.1.2.4. Facility Q (Forced Oxidation and SCR)

Facility Q is a 1800 MW coal fired plant with hot side ESP followed by a wet flue gas desulfurization system with wet limestone forced oxidation. This unit burns sub-bituminous

coals. Particulate is removed w ith a hot-side ESP. Flue gas is then scrubbed through a wet FGD unit; FGD is a wet limestone forced oxidation design that includes the addition of dibasic acid to

the absorber 13 

### . The gypsum provided was not washed and was sampled on Oct. 30, 2006 by an EPRI contractor (Natural Re source Technology). A five gall bucket of the unwashed gypsum was shipped to ARCADIS for analysis on May 4, 2007.



## 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 test set is cons idered Tier 2 testing (equilibrium-based) for detailed characterization, which was selected to develop a comprehensive data set of 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 releas e as a function of pH were de termined according to method SR002.1 (Kosson et al., 2002). This protocol consists of 11 parallel extractio ns of particle size reduced material, at a LS ratio of 10 mL extractant/g dry sample. In this method, particle-size reduction is used to prepare larg e-grained samples for extraction so that the approach toward liquid-solid equilibrium is enha nced and mass transport through la rge particles is minimized. For the samples evaluated in this study, minima l size reduction was required. Each extraction condition was carried out in triplicate using 40 g of material for each material evaluated. In addition, three method blanks were included, c onsisting of the DI water, nitric acid and potassium hydroxide used for extractions. Typical pa rticle size of the test ed materials was less than 300 μm using standard sieves according to ASTM E-11-70(1995). 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 is adjusted ba sed on the nature of the material; however, the range of pH values includes 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-overend fashion at 28 ± 2 rpm for 24 hours followed by filtration separa tion 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 behavi or of the materials is 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 is plotte d as a function of extract final pH to provide liquid-solid partitioning equilibrium as a function of pH. Initially, the SR002.1 test was carried out in triplicate; however, replication was reduced to two replicates of the test

13 

### Dibasic acid (DBA) is a commercial mixture of glutaric, succinic, and adipic acids: HOOC(CH 2 

### ) 2-4 

### COOH.



### 27

### Characterization of Coal Combustion Residues II



### method for later samples based on good replicati on and consistency amongst the early results (Sanchez et al., 2006).

2.2.2. Solubility and Release as a Function of LS Ratio (SR003.1)
Solubility and release as a func tion of LS ratio was determin ed according to method SR003.1 (Kosson et al., 2002). This protocol consists of fi ve 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 ex tractant with aliquots of material that has been partic le size reduced. Typical particle si ze of the material tested was less than 300 μm. Between 40 and 200 g of material were used for each extraction, based on the

desired LS ratio. All extractions are conducted at room te mperature (20 ± 2 ° C) in leak-proof

vessels that are tumbled in an end-over-end fa shion at 28 ± 2 rpm for 24 hours. Following gross separation of the solid and liquid phases by cen trifuge or settling, leachate pH and conductivity measurements are taken and the phases are se parated by pressure filtration using 0.45-μm polypropylene filter membrane. The five leachates ar e collected, and preserved as appropriate for chemical analysis. Initia lly, the SR003.1 test was carried out in triplica te; however, replication was reduced to two replicates of the test method for later sa mples based on good replication and consistency amongst the early results.



## 2.3. ANALYTICAL METHODS

2.3.1. Surface Area and Pore Size Distribution
A Quantachrome Autosorb-1 C-MS chemisorption mass spectrometer was used to perform 5- point Brunauer, Emmett, and Teller (BET) met hod surface area, pore volume, and pore size distribution analysis on each as-received and si ze-reduced CCR. A 200 mg sample was degassed

under vacuum at 200 oC for at leas t one hour in the sample preparat ion manifold prior to analysis

with N 2 

### as the analysis gas. Standard materials w ith known surface area were routinely run as a QC check.

2.3.2. pH and Conductivity
pH and conductivity 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 daily using pH buffer solutions at pH 4.0, 7.0 and

10.0. Conductivity of the leachates was measur ed using a standard conductivity probe. The conductivity probe was calibrated using appropri ate 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 re ceived” CCRs was determined usi ng American Society for Testing and Materials (ASTM) D 2216-92. This procedure supersedes the method indicated in the version of the leaching procedure published by Kosson et al. (2002).

2.3.4. Carbon Content Organic Carbon /Elemental Carbon Analyzer
Organic carbon (OC) and elemental carbon (EC) c ontent of each CCR tested was measured using a Sunset Lab thermal-optical EC/OC analyzer using the thermal/optical method (NIOSH Method 5040). The sample collected on quar tz fiber filters is heated under a completely oxygen-free

28

### Characterization of Coal Cumbustion Residues II



### helium atmosphere in a quartz oven in four in creasing temperature steps (375 °C, 540 °C, 670 °C and 870 °C) at 60 second ramp times for the firs t three temperatures and a ramp time of 90 seconds for the final temperature. The heating process removes all organic carbon on the filter. As the organic compounds are vaporized, they are immediately oxidized to carbon dioxide in an oxidizer oven which follows the sample oven. The flow of helium c ontaining the produced carbon dioxide then flows to a quartz methanator oven where the carbon dioxide is reduced to methane. The methane is then detected by a flam e ionization detector (FID). After the sample oven is cooled to 525 oC, the pure helium eluent is switched to an oxygen/helium mixture in the sample oven. At that time, the sample oven temp erature is stepped up to 850 oC. During this phase, both the original elemental carbon and th e residual carbon produced by the pyrolysis of organic compounds during the first phase are oxidi zed to carbon dioxide due to the presence of oxygen in the eluent. The carbon dioxide is then c onverted to methane and detected by the FID.

After all carbon has been oxidized from the sample, a known volume and concentration of methane is injected into the sample oven. Thus, each sample is calibrated to a known quantity of carbon as a means of checking the operation of the instrument.

The calibration range for these analyses was from 10 to 200 μg/cm 2 

### of carbon using a sucrose

solution as the standard. The detection limit of this instrument is approximately 100 ng/cm 2 

### with a linear dynamic range from 100 ng/cm 2 

### to 1 g/cm 2



### .

2.3.5. Dissolved Inorganic Carbon (DIC) and Dissolved Organic Carbon (DOC)
Analyses of total organic carbon and inorgani c carbon were performed on a Shimadzu model TOC-V CPH/CPN. Five-point ca libration curves, for both dissolv ed inorganic carbon (DIC) and non-purgeable dissolved organic ca rbon (DOC) analyses, were generated for an analytical range between 5 ppm and 100 ppm and are accepted with a correlation coefficien t of at least 0.995. An analytical blank and check standard at approxi mately 10 ppm were run every 10 samples. The standard was required to be within 15% of the specified value. A volume of approximately 16 mL of undiluted sample is loaded for analysis. DI C analysis is performed first for the analytical blank and standard and then the samples. DOC analysis is carried out separately after completion of DIC analysis. DOC analysis begins with a ddition of 2 M (mole/L) of hydrochloric acid to achieve a pH of 2 along with a sparge gas flow rate of 50 mL /min to purge inorganic carbon prior to analysis. Method detection limit (MDL ) and minimum level of quantification (ML) are

shown in Table 5.

Table 5. MDL and ML of analysis of DIC and DOC.

MDL (μg/L) ML (μg/L)

DIC 70 200

DOC 90 200

2.3.6. Mercury (CVAA, Method 3052, and Method 7473)
Liquid samples were preserved fo r mercury analysis by additions of nitric acid and potassium permanganate and then prepared prior to an alysis according to the following method. For each 87 mL of sample, 3 mL of concentrated nitr ic acid and 5 mL of 5 wt% aqueous potassium permanganate solution were adde d prior to storage. Immediatel y before cold vapor atomic absorption (CVAA) analysis, 5 mL of hydroxylamin e were added to clear the sample and then the sample was digested according to ASTM Met hod D6784-02 (Ontario Hydro) as described for

29

### Characterization of Coal Combustion Residues II



### the permanganate fraction (ASTM, 2002). On co mpletion 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 desc ribed above prior to CVAA analysis.

Sample preparation of the solids and filters was carried out by HF/HNO 3 

### microwave digestion according to Method 3052 (EPA, 1996) followed by CVAA analysis as indicated above. No additional preservation or digestion was carried out prior to CVAA analysis.

Mercury analysis of each dige st, extract and leachate was car ried out by CVAA according to EPA SW846 Method 7470A “Mercury in Liquid Wa ste (Manual Cold Vapor Technique)” (EPA, 1998a). 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 μ g/L mercury.

Solids also were analyzed by Method 7473 “Mer cury in Solids and Solutions by Thermal Decomposition, Amalgamation, and Atomic Ab sorption Spectrophotometry” (EPA, 1998b). A Nippon MD-1 mercury system was used for this an alysis. The instrument was calibrated with known standards ranging from 1 to 20 ng of me rcury. The method detection limit for mercury in solids is 0.145 μg/kg.

2.3.7. Other Metals (ICP-MS, Method 3052, and Method 6020)
Liquid samples for ICP-MS analysis were preser ved through addition of 3 mL of concentrated nitric acid (trace metal grade) per 97 mL of sample. Known quant ities of each analyte were also added to sample aliquots for analytical matrix spikes. Solid samples were digested by EPA Method 3052 (EPA, 1996) prior to ICP-MS analysis.

2.3.7.1. ICP-MS Analysis

ICP-MS analyses of aqueous samples from la boratory leaching tests were carried out at Vanderbilt University (Department of Civil a nd Environmental Engineering) using a Perkin

Elmer model ELAN DRC II in both standard and dynamic reaction chamber (DRC) modes. Standard analysis mode was used for all analyt es except for As and Se, which were run in DRC mode with 0.5 mL/min of oxygen as the reaction gas. Seven-point st andard curves were used for an analytical range between approximately 0.5 μg/L and 500 μg/L and completed before each analysis. Analytical blanks and analytical check standards at approximately 50 μg/L were run every 10 samples and required to be within 15% of the specified value. Samples for analysis were diluted gravimetrically to within the target ed analytical range usi ng 1% v/v Optima grade nitric acid (Fisher Scientific). Initially, analys es for 10:1 dilutions were performed to minimize total dissolved loading to the instrument. Additional dilutions at 100:1 and 1000:1 were analyzed if the calibration range was exceeded with the 10:1 dilution. 50 μL of a 10 mg/L internal standard consisting of indium (In) (for mass range below 150) and holmium (Ho) (for mass range over 150) was added to 10 mL of sample ali quot prior to analysis. An alytical matrix spikes were completed for one of each of the replic ate extracts from SR00 2.1. For each analytical matrix spike, a volume between 10 μL and 100 μL of a 10 mg/L standard solution was added to 10 mL of sample aliquot. Table 6 provides the element analyzed, method detection limit (MDL) and minimum level of quantification (ML). Analyt e concentrations measured that are less than the ML and greater than the MDL are reported as estimated value using the instrument response.

The values reflect the initial 10:1 dilution used for samples from laboratory leaching tests.

30

### Characterization of Coal Cumbustion Residues II



### Table 6. Method detection limits (MDLs) and mi nimum level of quantification (ML) for ICPMS analysis on liquid samples.*

Symbol Units MDL ML

Al μg/L 1.25 2.00

Sb μg/L 0.60 2.00

As μg/L 1.09 2.00

Ba μg/L 0.75 2.00

Be μg/L 0.85 2.00

B μg/L 0.63 2.00

Cd μg/L 0.40 1.00

Ca μg/L 1.86 5.00

Cs μg/L 0.60 2.00

Cr μg/L 0.47 1.00

Co μg/L 0.51 2.00

Cu μg/L 0.87 2.00

Fe μg/L 1.55 5.00

Pb μg/L 0.28 1.00

Li μg/L 0.80 2.00

Mg μg/L 1.17 2.00

Mn μg/L 0.47 1.00

Mo μg/L 0.75 2.00

Ni μg/L 0.90 2.00

K μg/L 1.86 5.00

Re μg/L 0.30 1.00

Rb μg/L 0.70 2.00

Se μg/L 0.78 2.00

Si μg/L 1.85 5.00 Ag μg/L 2.10 5.00

Na μg/L 1.12 2.00

Sr μg/L 0.47 1.00

Tl μg/L 0.63 2.00

Sn μg/L 0.87 2.00

Ti μg/L 0.61 2.00

U μg/L 0.36 1.00

V μg/L 0.79 2.00

Zn μg/L 1.15 2.00

Zr μg/L 0.60 2.00



### * All elements indicated in Table 6 have been analyzed, however, only elements indicated in bold are reported as part of the leaching studies. The elements that were included in the leaching studies were selected based on input from EP A program offices due to potential concern for

human health and the environment.

31

### Characterization of Coal Combustion Residues II



### 2.3.8. X-Ray Fluorescence (XRF)
XRF analysis was performed on each CCR to pr ovide additional information on each CCR total elemental composition. For each CCR two pellets we re prepared as follows. 3000 mg of material was weighed and mixed with 1.5 mL (100 mg dr y solids) of liquid bi nder to give a 32 mm diameter pellet weighing 3150 mg with a ma terial-to-diluent ratio of 0.05. For high carbon content samples 3.0 ml (100 mg dry solids) of li quid binder was used to give a 32 mm diameter pellet weighing 3300 mg with a material to diluen t 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 “standardle ss” data analysis software. The UQ/Fly ash calibration was used to analyze the samples. The pellets were evaluated as oxides. Known fly ash Standard Reference Materials (SRMs) were also run to assess the accuracy of the analysis. This information is useful in supplementing CVAA and ICP results.

2.3.9. MDL and ML for Analytical Results
The MDL is defined by 40 CFR Part 136, Appendi x 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 gr eater 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 14 

### and verified by the analysis of calibration standards near the calculated MDL according to EPA (2003). The MD L then was determined by multiplying the standard deviation of the replicate measuremen ts by the appropriate Students t value for a 99% confidence level (two tailed) and n-1 (six) de grees 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 5x10 n



### , where n is an integer) to 10 ti mes the standard deviation observe d for determination of the MDL. This value is also multiplied by the minimum dilution factor required for preservation and analysis of the sample matrix to obtain the ML reported here.

Mercury, as measured by CVAA, required modifi cation of the calculati on 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 de viation 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 instrume nt detection limit and rounded to the nearest integer value as above. The resulting ML was 0.01 μg/L.

14 

### Establishing spikes in an actual leaching extract matrix is not possible because the sample being extracted dictates the matrix composition by virtue of the constituents that partition into the resulting aqueous extract, which varies by test position and materi al being tested. However, the extract aliquots are diluted at least 10:1 with 1% nitric acid (prepared from Optima grade nitric acid, Fisher Scientific), and the COPCs are dilute in the resulting analytical sample. Therefore, the 1% nitric acid solution was used

as the matrix for MDL and ML determinations.



### 32

### Characterization of Coal Cumbustion Residues II



## 2.4. QUALITY ASSURANCE ASSESSMENT

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 as described in Sanchez et al. (2006) . Scrubber sludges that we re flowable slurries were mixed using a paddle mixer. Gypsum and fixated scrubber sludge samples were mixed by repetitively coning 15 

### and quartering while passing thr ough a mesh screen. After mixing, ten Subsamples were taken from FSSL sample MAD and analyzed by XRF to evaluate the homogeneity of the resultant mate rial; Figure 9 presents the coe fficient of variation for the XRF

results. These results indicate that total c ontent variability for primary and most trace constituents is less than 20% for this set of samples.

0 5 10 15 20 25 30 35 40

C.V. (%)

K P S V Y

F Si Ti

Al Cl Ni Sr Zr

As Br Cr Fe La Sc Se W Zn

Ba Ca Cd Ce Co Cu Ga Ge Na Nb Pb Rb

Mg

Mn Mo 

### Fac. M, SCR off, FSSL (MAD)

Figure 9. Coefficient of varia tion (C.V.) from XRF elemental analysis of 10 subsamples of FSSL sample MAD after mixing by coning and quartering.

2.4.2. Leaching Test Methods and Analytical QA/QC
One of the requirements of this project was to establish a QA/QC framework for the leaching assessment approach developed by Kosson et al. (2002). The devel oped QA/QC framework incorporates the use of blanks, spiked samp les, and replicates. Appendix A provides the complete Quality Assurance Project Plan, as updated for this phase of the study. For each designated leaching test condition (i .e., acid or base addition to establish end-point pH values and LS value), triplicate leaching test extractions were completed (i.e., thr ee separate aliquots of

CCR were each extracted at the designated test condition) for early samples, while duplicate

extractions were used after evaluation of initial results. The three types of method blanks were the deionized water case, the most concentrated nitric acid addition case, and the most

15 

### "Coning and quartering" is a term used to describe ho w the material is mixed. The approach is to pass the material through a screen so that a "cone" forms in the collection container. Then the cone is bisected twice into quarters (quarter sections of the cone) a nd each section then is passed sequentially through the screen again to form a new cone. This sequence is repeated several times to achieve desired mixing.



### 33

### Characterization of Coal Combustion Residues II



### concentrated potassium hydroxide addition case. Each method blank was carried through the entire protocol, including tumbling and filtra tion, except an aliquot of CCR was not added.

During analysis for mercury and elemental sp ecies by ICP-MS, analytical spikes for the

constituents of interest were ca rried out for one replicate of each test case to assess analytical recoveries over the complete ra nge of pH and liquid matrix c onditions. Multipoint calibration curves using at least seven standards and an init ial calibration verification (ICV) using a standard

obtained from a different source than the calibra tion standards were completed daily or after every 50 samples, whichever was more frequent. In addition, instrument blanks and continuing calibration verification (CCV) sta ndards were analyzed after every 10 analytical samples and required to be within 10 percent of the expected value. Samples are rerun if they are not within 10 percent of the expected value. CCV standards and instrument blanks al so 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 concentr ation of the element of interest. The “spike recovery” was require d to be within 80 – 120% of the expected value for an acceptable analytical result.

2.4.3. Improving QA/QC efficiency
Throughout the study, the approach to QA/QC was regularly reviewed to seek out opportunities

for increased evaluation efficien cy without unacceptable degradati on of precision or accuracy in

results. Based on evaluation of results from the first several facilities (Sanchez et al, 2006), the number of replicates for Method SR002.1 (solub ility as a function of pH) and Method SR003.1 (solubility as a function of liqui d/solid ratio) was reduced from three to two. Results from this study (Sanchez et al., 2006 and this report) show that the precision between duplicate analyses is acceptable and that the triplicate set does not significantly increase the quality of the data set. This finding follows from recognition that (i ) the data sets genera ted by Method SR002.1 and SR003.1 must provide both consiste ncy 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 unde r evaluation and representative sub-sampling, rather than by the intrin sic variability of the leaching test methods. There were a total of 11,743 observations for the 14 parameters evaluated in detail in this report (pH and 13 constituents of interest). Review of the resul ting data sets indicated 15 outlier pH values of 846 measurements 16



### and an additional 19 outliers ou t of 10,897 measurements of spec ific constituents. Thus, the overall error rate was less than 2%. Implementa tion of a reduction in th e number of replicates has greatly improved laboratory efficien cy without compromising data quality.

Data were screened for outliers based on compar ison of individual data points (i) relative to replicate extractions (i.e., para llel extractions of aliquots of the same material under the same extraction conditions), and (ii) relative to the ot her data points in the ex traction series (i.e., parallel extractions of aliquots of the same mate rial at different pH (SR02) and LS conditions

16 

### When a pH measurement is determined to be an outlier, then all constituent measurements associated with the particular extract sample are also consider ed outliers because they would be incorrectly evaluated as release as a function of pH. This resulted in excluding (15) × (13)=195 individual constituent

measurements.



### 34

### Characterization of Coal Cumbustion Residues II



### (SR03)) because of the expected systematic re sponse behavior. The pH was considered an outlier when the final pH of the extract deviated from the other replicates by more than 0.5 pH units and corresponding constituen t analyses did not follow systematic behavior indicated by other extracts across multiple constituents. Individual constituents were considered outliers when results of constituent analyses deviated from the systematic behavior indicated by results in the extraction series (as a function of pH or as a f unction of LS) by more than one-half to one order of magnitude. Results were screened through in spection of the appropria tely plotted results.

Data quality indicators (DQIs) were measured for all parameters continuously during the leaching experiments and during analytical tasks. Chemical (ICP, CVAA, XRF, IC, EC/OC) and physical (surface area, pore size distribution and density) characterization data were reduced and reports were generated automatically by the inst rument software. The primary analyst reviewed 100% of the report data for completeness to ensu re that quality control checks met established criteria. Sample analysis was repeated for any results not meeting acceptance criteria. A secondary review was performed by the Inorganic Laboratory Manager to validate the analytical report. A data quality report for the CCR leach tes ting results will be provi ded in the fourth and final report of this resear ch. The data quality report will cove r the leach test re sults documented in Report 1 (Sanchez et al., 2006), Report 2 (this re port), and a third report (in preparation). The fourth report summarizes the data from th e first three reports an d provides probabilistic assessment of the potential release rates of mercury and other metals based on plausible management practices.



## 2.5. INTERPRETATION AND PRES ENTATION OF LABORATORY

LEACHING DATA

Complete laboratory leaching results for each CCR type and test method are presented in Appendices D and E. Appendix D pres ents results for Solubility a nd Release as a Function of pH (SR002.1). Appendix E presents results for Solubi lity and Release as a Function of LS ratio (SR003.1). Results are organized by CCR type (fly ash, gypsum, scrubber sludge, fixated scrubber sludge), with pH results followed by mercury and then other constituents of interest (aluminum, antimony, arsenic, barium, boron, ca dmium, chromium, cobalt, lead, molybdenum, selenium and thallium). For SR002.1, pH results ar e a titration curve of pH as a function of milliequivalents of acid or base, with acid additions considered positive (+) and base additions considered negative (-). For SR 003.1, pH results are a curve of pH as a function of LS ratio.

For Solubility and Release as a Function of pH (SR002.1), results for each CCR type are grouped as described in Figure 5 through Figure 8. Results are presented as extract concentrations as a function of pH. The “natural” pH 17 

### of the system is indicated as a vertical line to the average pH and a horizontal line to the y- axis indicating the co rresponding extract concentration. Included with each figure are horizontal lines at the dr inking water maximum concentration level (MCL) or drinking water equi valent level (DWEL) 18 

### , and analytical limits (M L and MDL) to provide a frame of reference for the results. Also included with each figure are the 5 and 95 percentile for pH (vertical lines) from field observations of leachate from landfills and surface impoundments

17 

### “Natural pH” or “own 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.

18 

### MCL and DWEL values used are as reported in (EPA, 2006).



### 35

### Characterization of Coal Combustion Residues II



### for combustion residues (see Section 2.5.1). An annot ated example of the results is provided as Figure 10.

For Solubility and Release as a Function of LS ratio (SR003.1), results ar e presented as extract

concentrations as a func tion of LS ratio. Also indicated are the relevant MCL, ML and MDL or

DWEL.

2.5.1. Interpretation of Mechanisms Controlling Constituent Leaching
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 define d here as the flux or amount of constituent released from the waste or secondary material (e.g., CCRs). Factors controlling consti tuent release an d transport in

and within the near field of the CCRs are of ten distinctly different from the factors and mechanisms which 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 either as adsorbed species, co-precipitated as amorphous or cr ystalline solid phases, or incor porated as trace components in solid phases. If chemical equilibrium conditions are approached (as is the approximate case for the laboratory and field sample c onditions discussed in th is report), then the functional behavior of the aqueous solution concentratio n reflects the nature of the cons tituent species in the waste or secondary material, the presen ce of any co-constituents in the aqueous phase influencing aqueous solution speciation (e.g., effects of high ionic strength, chel ating 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 intere st is present at very low concentration in the waste or secondary material, re latively weakly adsorbed, and th e presence of complexing and, or, competing species in solution is at a constant con centration. 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 partiti oning function, where the critical constant of proportionality is the partitioning coefficient, commonly known as K d 

### . Linear partitioning and

use of K d 

### values is a common approach for mathema tically modeling contaminant transport at low contaminant concentrations in soils. Assumpti on of linear partitioning is a valid and useful approach when the necessary conditions (discussed above) are fulfilled 19



### . For mercury adsorbed on activated carbon or char particles in fly ash, a complex combination of adsorption mechanisms is indicated. During laborato ry leaching tests, mercury concentrations in the leaching test extracts are relatively constant over the pH range and LS ratio of interest, and

19 

### Often specific K d 

### values are a function of pH because of co mpetition for adsorption sites by hydrogen ions. However, often a single K d 

### or range of K d 

### values are used in contaminant fate and transport models, without specific relationship between pH and K d 

### which can result in misrepresentation of actual

contaminant behavior.



### 36MDL ML 10.3 46.8

MCL

0.1

1 10 100 1000 10000

2 4 6 8 10 12 14As [μg/L]

pH

SR2 DFA A SR2 DFA - B

SR2 DFA C 

### SR2-DFA-A

SR2=SR002.1
Sample name Replicate A Characterization of Coal Cumbustion Residues II



### independent of total mercury content in the CCR. In addition, the total mercury content in the CCR is very low. These results are indicative of adsorption phenomena wher e, in the adsorbed state, interactions between ad sorbed mercury species are str onger (thermodynamically) than the

interactions between th e adsorbed mercury species and carbon surface 20 

### . This observation has been supported by the observation of mercury di mer formation during sorption (Munro et al, 2001) and the occurrence of chemisorption as the dominant adsorption mechanism at temperatures above 75 oC (consistent with cond itions in air pollution c ontrol devices; Vidic, 2002). In other studies, this ph enomenon has been observed as the formation of molecular

clusters on the adsorbent surf ace (Ruthven, 1984; Duong, 1998; Rudz inski et al., 1997). For this case, use of a K d 

### approach would underestimate release because desorption is be st represented as

a constant aqueous concentra tion until depletion occurs.

A third case is encountered when the constituent of interest is present in the waste or secondary material (e.g., CCR) as a primary or trace constituent in either an amorphous or crystalline solid phase and there may be complexing or chelating co-constituents 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 sp ecies of interest under the given conditions (pH, co-constituents). For these cases, an approximation of field c onditions can be made empirically based on laboratory testing and observed sa turation over the relevant domain (as applied in this report) or geochemical speciation modeling c oupled with mass transfer modeling can be used to assess release under specific field scenarios (the subject of a future report). Use of a K d 

### approach would not be appropriate for these cases because co nstituent concentrations will remain relatively constant at a given pH until the controlling solid pha se is depleted and control is shifted to a new solid phase or mechanism.

- ­ -

- ­ 

### 95 th 

### %tile for field pH 5 th 

### %tile for field pH

Own pH Concentration
at own pH MCL

MDL ML

20 

### 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 [see Sanchez et al. (2006) for further discussion].



### 37 Figure 10. An example of extract concentr ations as a function of pH from SR002.1.

### Characterization of Coal Combustion Residues II



### 38 

## 2.6. FIELD pH PROBABILITY DISTRIBUTION

A probability distribution of field leachate pH values from coal combustion waste landfills was derived, as described below, from the set of field pH observations in cluded in the EPA Risk Report (EPA, 2007). The pH probability distribution used in this report considers additional data beyond the pH probability distribution used in Report 1 (Sanchez et al, 2006), which was based solely on relevant data from th e EPA Office of Solid Waste da tabase (EPA, 2000) and included 158 observations from six CCR disposal facilities. The data set developed for the EPA Risk Report included (i) observations from the comprehensive database of landfill leachate characteristics developed by the EPA’s Offi ce of Solid Waste (EPA, 2000), (ii) field observations from literature, primarily from EPRI reports, (iii) additional data reported to EPA, and (vi) pH observations from laboratory leachi ng tests. Only pH meas urements from field samples (i.e., leachate, pore water) were selected for use in development of the resulting pH probability distribution. The resulting data se t included 580 observations from 42 CCR landfill disposal facilities and was highly unbalanced, with some sites ha ving only a few (e.g., less than five) observations and some sites having many observations (e.g., greater than 20). To prevent the unbalanced data from skewing the resultin g probability distribution, the minimum, 25 th 

### , 50 th



### , 75 th 

### percentile, and maximum values of observations for each individual facility were compiled into a single data set. For facilities with fewe r than five observations, all observations for that facility were included. This data set then served as the basis for fitting a statistical distribution function. For each data set, different distribution f unctions 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 was truncated and norma lized to the pH range of the field data.

The resulting pH probability dist ribution developed in this report is compared in Figure 11 and Table 7 to the pH probability di stribution used in Report 1. The new pH probability distribution reflects a similar range of pH, but has a more alkaline median value, and in general, has greater weighting in the pH range between 8 and 12. The pr obability distribution used in this report is considered more representative than what was us ed in Report 1 because of a larger dataset using results from recent studies by EP A and EPRI. (EPA, 2006; EPRI, 2006)

Field pH observations were also evaluated fo r surface impoundments receiving CCRs from coal

combustion facilities with FGD scrubbers in use. Pore water pH values measured in samples

obtained fr om within the settled CCRs were se lected from the EPRI database. Resulting pH observations were across the same range as the landfill field pH observations, but were insufficient to develop an independent pH proba bility distribution. Therefore, the same pH probability distribution was used for landfill and surface impoundment faciliti es in this report.

### Characterization of Coal Cumbustion Residues II



### 39 0 0.2 0.4 0.6 0.8

1

2 3 4 5 6 7 8 9 10 11 12 13
pHProbability

EPA leach 2000 Fitted distribution (LogLogistic, (1))

EPA Risk database & EPA leach 2000 Fitted distribution (BetaGeneral, (2)) (1)

(2)

Distributions LogLogistic(4.7386, 2.9538, 3.4815) BetaGeneral(9.0369, 1.5076, -7.4214, 12.814) pH Field data Fitted

distribution Simulated

Min 2.75 -7.42 2.76 5th percentile 5.40 5.84 5.85 50th percentile 10.53 10.38 10.24 90th percentile 12.20 12.18 11.94 95th percentile 12.40 12.43 12.43

Max 12.80 12.81 12.43



### Figure 11. Probability distributions for field pH used in Report 1 (LogLogistic) and this report (BetaGeneral). Summary statistics for the field da ta and the probability di stribution used in this report (BetaGeneral) are provide d to the right of the graph..

Table 7. Comparison of summary statistics for field pH data and pH probability distributions used in Report 1 and this report.

Field Data Distribution

Estimates Used in Release

Report 1 This Report Report 1 This Report

Minimum 5.40 2.75 4.92 2.76

5 th 

### percentile 5.80 5.40 5.97 5.85

50 th 

### percentile 7.70 10.53 7.63 10.24

90 th 

### percentile NR 12.20 NR 11.94

95 th 

### percentile 12.09 12.40 10.63 12.43

Maximum 12.80 12.80 12.50 12.43

NR=not reported.



## 2.7. ESTIMATED LEACHATE CONCENTRA TION AS A FUNCTION OF pH

For each CCR tested, results from SR002.1 (Alkalinit y, Solubility and Release as a Function of pH) were used to develop an empirical functiona l relationship between solution pH and expected

concentration for each constituent of interest . For each constituent within each CCR case, a polynomial function was regressed to the resu lts from SR002.1 (Alkalinity, Solubility and

### Characterization of Coal Combustion Residues II



### 40 Release as a Function of pH) to provide the expected leachate concentration as a function of solution pH. Up to a fifth order polynomial wa s used for the regression. An example of a regression fit and corresponding equation for sol ubility and release as a function of pH is presented in Figure 12. The coeffi cients provided in the table re flect the order of the polynomial used. For all cases, the lowest order polynomia l possible based on the R-square (no further increase for higher order) was used . Also included with each figure of regression fit is the 5 th



### and 95 th 

### percentile for pH (vertical line) from field observations of leachate from landfills and surface impoundments for combustion residues. Re gression fit results are provided in Appendix F for each case examined (i.e., for each constituent in each CCR tested).

Antimony
log (μg/L) Number of points pH range of validity

0.0000 pH 5 33 2.2-12.4

0.0008 pH 4

-0.0399 pH 3

0.5519 pH 2

-2.7978 pH

6.031866 pH 0

0.97 R 2

5% 95% 0.001

0.01

0.1

1 10 100 1000 10000 100000

2 4 6 8 10 12 14 pHSb [μg/L]

SR2-DFA - A SR2-DFA - B

SR2-DFA - C Fit curve



### Figure 12. Example of regression fit and corresponding coefficients for a 5 th 

### order polynomial equation used to represent solubility and releas e as a function of pH (antimony for fly ash from Facility B with SCR bypassed (DFA)).

### Characterization of Coal Cumbustion Residues II



## 3. RESULTS AND DISCUSSION

The EPA Risk Report (EPA, 2007) identified the following COPC s based on the potential for either human health or ecological impacts using a screening risk assessment: aluminum (Al), arsenic (As), antimony (Sb), barium (Ba), boron (B ), cadmium (Cd), cobalt (Co), chromium (Cr), lead (Pb), mercury (Hg), molybdenum (M o), selenium (Se), and thallium (Tl). 21 

### Thus, the evaluation provided here focuses on the same thirteen constituents and can be used in future risk

and environmental assessments.



## 3.1. TOTAL ELEMENTAL CONT ENT BY DIGESTION

Total elemental compositions using digestion 22 

### , on a dry weight basis, for COPCs for the CCRs evaluated are compared by constituent in Figures 13 through 24; tabular results are provided in Appendix B. Boron was not analyzed because it is used in the digestion process and therefore analysis would not yiel d meaningful results.

Mercury. Mercury content exhibite d a similar range (0.01 to 1.0 μ g/g) for all CCR types. Use of SNCR (Facility A) resulted in increased mercur y content in the fly ash and decreased mercury content in the scrubber sludge, compared to when the SNCR was not in use. In contrast, use of SCR (Facility B) resulted in decreased mercur y content in the fly as h and increased mercury content in the scrubber sludge, compared to when the SCR was bypassed. For all three comparative cases (Facilities A, B and M) use of the NOx control increased the total mercury

content in the fixated scrubber sl udge. Mercury content in gypsum was significantly lower in the washed gypsum than in the unwashed gypsum for comparative cases (Facilities N and O).

Aluminum. Aluminum content was approximately an order of magnitude gr eater in the fly ash samples than in the scrubber sludge samples fr om facilities without SCR and than in gypsum samples with and without SCR. Facilities with SCR operating (samples BGD, KGD) had greater aluminum content in scrubber sludge than th e other scrubber sludges, likely because of the addition of aluminum with the SCR catalyst. Fi xated scrubber sludge samples had intermediate Al content, reflective of the ble nding of fly ash with scrubber sludge.

Antimony. Antimony content ranged over similar leve ls for fly ash, scrubber sludge and fixated scrubber sludge; gypsum had lower antimony conten t except for the sample from Facility Q. Samples from both Facilities K and Q had greater antimony content than comparative FGD

residues from other facilities (scrubber sludges and fixated sc rubber sludges for Facility K, gypsum for Facility Q) perhaps as a consequenc e of greater antimony content in sub-bituminous coal burned by these facilities than bituminous coal burned by the other facilities. The SNCR samples had higher antimony contents in the fly ash, scrubber sludge and fixated scrubber sludge for Facility A than the samples collected with SNCR off. The SCR samples had higher antimony contents in the fly ash from Fac ility B and the fixated scrubber sludges from Facilities A, B and

21 

### The database used in the EPA Risk Report (EPA, 2007) for the assessment was based on both measurements of field samples (e.g., leachate, pore wa ter) and single point laboratory leaching tests (e.g., TCLP, SPLP). The database was sparse with respect to measurements of field samples for many

constituents.

22 

### Digestion Method 3052 and ICP-MS analysis by Method 6020; see Section 2.3.7.



### 4 1

### Characterization of Coal Combustion Residues II



### M, although the reason for the high level of antimony in sample BCC cannot be explained by the relative antimony content in samples BFA and BGD.

Arsenic. Gypsum had very low arsenic content (<5 μg/g) compared to the other residue types. Arsenic content in scrubber sludge was significantly le ss than in fly ash for residue from the same facility. Use of NOx controls resulted in decreased arsenic content in the fly ash, increased content in the scrubber sludge (Fac ilities A and B) and decreased content in the fixated scrubber sludge (Facilities A, B and M; reflecting the relative contributions of fly ash and scrubber sludge in fixated scrubber sludge) for comparative samples.

Barium. Barium content was similar in scrubber sludge and gypsum for all facilities except for sample BGD (unexplained), and lowe r than barium content in fly ash by approximately an order of magnitude. The relatively low barium conten t in unwashed gypsum from Facility O is also unexplained.

Cadmium. Cadmium content was low in the gypsum (<0.69 ng/g) and scrubber sludges (<1.72 ug/g) and generally total content of the gypsum was half that in fly ash (<1.51 ng/g). The greater cadmium content in sample BGD relative to sa mple DGD may be a conse quence of the use of post-combustion NOx control using SCR.

Chromium. Chromium content in gypsum (< 19.3 ng/ g) and scrubber sludges (< 139 ng/g) was low and approximately an order of magnitude le ss than in fly ash sa mples (<194). Scrubber sludge samples without SCR in ope ration also had chromium conten t similar to that of gypsum. Scrubber sludge samples without SCR in use also had chromium content similar to that of gypsum. Elevated chromium content in scru bber sludge samples BGD and KGD may be associated with the use of post-co mbustion NOx control using SCR.

Cobalt. Cobalt content in gypsum wa s low and approximately an or der of magnitude less than in fly ash samples. Scrubber sludge samples w ithout SCR in operation also had cobalt content similar to that of gypsum. Elev ated cobalt content in scrubb er sludge samples BGD and KGD may be associated with SCR catalyst addition. The relatively low cobalt content in fixated scrubber sludge samples BCC and KCC relative to corresponding fly as h and scrubber sludge samples is unexplained.

Lead. Lead content in gypsum was low and less than one third of the lead content in fly ash samples. Scrubber sludge samples without SCR in operation also had lead content similar to that of gypsum. The relatively low l ead content in fixated scrubber sludge samples BCC and KCC in relationship to corresponding fly ash and scrubber sludge samples is unexplained.

Molybdenum. A similar range in molybdenum conten t was found in fly ash, scrubber sludge

and fixated scrubber slu dge samples, with lower content by approximately one third in gypsum samples, with the exception of gypsum sample QAU.

Selenium . All samples were less than 5 μg/g, except for samples for fly ash and fixated scrubber sludge from Facility A and unwashed gypsum from Facilities P and Q. The upper bound for these samples was less than 30 μg/g.

Thallium . All gypsum samples had thallium content less than 3 μg/g. Fly ash, scrubber sludge, and fixated scrubber sludge samples all had a si milar range of thallium content between 2 and 5 μg/g, except scrubber sludge and fixated scrubber sludge from Facility B with SCR and fly ash and fixated scrubber sludge from Facility K. Bo th of these observations of greater thallium content (between 5 and 13 μg/g) may re sult from the SCR catalyst addition.

4 2

### Characterization of Coal Cumbustion Residues II



### 43 0.001

0.01

0.1

1Fac.A(CFA)‐Fac.A(AFA)+Fac.B(DFA)‐Fac.B(BFA)+Fac.K(KFA)+Fac.A(CGD)‐Fac.A(AGD)+Fac.B(DGD)‐Fac.B(BGD)+Fac.K(KGD)+Fac.N(NAU)+UFac.N(NAW)+WFac.O(OAU)+UFac.O(OAW)+WFac.P(PAD)+UFac.Q(QAU)+UFac.A(CCC)‐Fac.A(ACC)+Fac.B(DCC)‐Fac.B(BCC)+Fac.K(KCC)+Fac.M(MAD)‐Fac.M(MAS)+μg/g 

## Mercury (Hg)

I. Ox. Nat. Ox. Forced Ox. Nat. Ox. Nat. Ox.

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge

100 1,000 10,000 100,000 1,000,000Fac.A(CFA)‐Fac.A(AFA)+Fac.B(DFA)‐Fac.B(BFA)+Fac.K(KFA)+Fac.A(CGD)‐Fac.A(AGD)+Fac.B(DGD)‐Fac.B(BGD)+Fac.K(KGD)+Fac.N(NAU)+UFac.N(NAW)+WFac.O(OAU)+UFac.O(OAW)+WFac.P(PAD)+UFac.Q(QAU)+UFac.A(CCC)‐Fac.A(ACC)+Fac.B(DCC)‐Fac.B(BCC)+Fac.K(KCC)+Fac.M(MAD)‐Fac.M(MAS)+μg/g 

## Aluminum (Al)

I. Ox. Nat. Ox. Forced Ox. Nat. Ox. Nat. Ox.

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge



### Figure 13 and Figure 14. Mercury and Aluminum. Comparison of total elemental content by digestion (key: - = NOx control off; + = NOx control on; U = unwashed gypsum; W = washed gypsum; Nat. Ox. = natural oxidation; Forced Ox. = forced oxidation; I.Ox. = inhibited oxidation).

### Characterization of Coal Combustion Residues II

0 5 10 15 20Fac.A(CFA)‐Fac.A(AFA)+Fac.B(DFA)‐Fac.B(BFA)+Fac.K(KFA)+Fac.A(CGD)‐Fac.A(AGD)+Fac.B(DGD)‐Fac.B(BGD)+Fac.K(KGD)+Fac.N(NAU)+UFac.N(NAW)+WFac.O(OAU)+UFac.O(OAW)+WFac.P(PAD)+UFac.Q(QAU)+UFac.A(CCC)‐Fac.A(ACC)+Fac.B(DCC)‐Fac.B(BCC)+Fac.K(KCC)+Fac.M(MAD)‐Fac.M(MAS)+μg/g 

## Antimony (Sb)

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge I. Ox. Nat. Ox. Forced Ox. Nat. Ox. Nat. Ox.

0 20 40 60 80 100Fac.A(CFA)‐Fac.A(AFA)+Fac.B(DFA)‐Fac.B(BFA)+Fac.K(KFA)+Fac.A(CGD)‐Fac.A(AGD)+Fac.B(DGD)‐Fac.B(BGD)+Fac.K(KGD)+Fac.N(NAU)+UFac.N(NAW)+WFac.O(OAU)+UFac.O(OAW)+WFac.P(PAD)+UFac.Q(QAU)+UFac.A(CCC)‐Fac.A(ACC)+Fac.B(DCC)‐Fac.B(BCC)+Fac.K(KCC)+Fac.M(MAD)‐Fac.M(MAS)+μg/g 

## Arsenic (As)

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge I. Ox. Nat. Ox. Forced Ox. Nat. Ox. Nat. Ox.



### 44 Figure 15 and Figure 16. Antimony and Arsenic. Comparison of total elemental content by digestion (key: - = NOx control off; + = NOx control on; U = unwashed gypsum ; W = washed gypsum; Nat. Ox. = natural oxidation; Forced Ox. = forced oxidation; I.Ox. = inhibited oxidation).

### Characterization of Coal Cumbustion Residues II



### 45 1 10 100 1,000 10,000Fac.A(CFA)‐Fac.A(AFA)+Fac.B(DFA)‐Fac.B(BFA)+Fac.K(KFA)+Fac.A(CGD)‐Fac.A(AGD)+Fac.B(DGD)‐Fac.B(BGD)+Fac.K(KGD)+Fac.N(NAU)+UFac.N(NAW)+WFac.O(OAU)+UFac.O(OAW)+WFac.P(PAD)+UFac.Q(QAU)+UFac.A(CCC)‐Fac.A(ACC)+Fac.B(DCC)‐Fac.B(BCC)+Fac.K(KCC)+Fac.M(MAD)‐Fac.M(MAS)+μg/g 

## Barium (Ba)

I. Ox. Nat. Ox. Forced Ox. Nat. Ox. Nat. Ox.

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge

0.0 0.5 1.0 1.5 2.0Fac.A(CFA)‐Fac.A(AFA)+Fac.B(DFA)‐Fac.B(BFA)+Fac.K(KFA)+Fac.A(CGD)‐Fac.A(AGD)+Fac.B(DGD)‐Fac.B(BGD)+Fac.K(KGD)+Fac.N(NAU)+UFac.N(NAW)+WFac.O(OAU)+UFac.O(OAW)+WFac.P(PAD)+UFac.Q(QAU)+UFac.A(CCC)‐Fac.A(ACC)+Fac.B(DCC)‐Fac.B(BCC)+Fac.K(KCC)+Fac.M(MAD)‐Fac.M(MAS)+μg/g 

## Cadmium (Cd)

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge I. Ox. Nat. Ox. Forced Ox. Nat. Ox. Nat. Ox.



### Figure 17 and Figure 18. Barium and Cadmium. Comparison of total elemental content by digestion (key: - = NOx control off; + = NOx control on; U = unwashed gypsum; W = washed gypsum; Nat. Ox. = natural oxidation; Forced Ox. = forced oxidation; I.Ox. = inhibited oxidation).

### Characterization of Coal Combustion Residues II



### 46 0 100 200 300 400Fac.A(CFA)‐Fac.A(AFA)+Fac.B(DFA)‐Fac.B(BFA)+Fac.K(KFA)+Fac.A(CGD)‐Fac.A(AGD)+Fac.B(DGD)‐Fac.B(BGD)+Fac.K(KGD)+Fac.N(NAU)+UFac.N(NAW)+WFac.O(OAU)+UFac.O(OAW)+WFac.P(PAD)+UFac.Q(QAU)+UFac.A(CCC)‐Fac.A(ACC)+Fac.B(DCC)‐Fac.B(BCC)+Fac.K(KCC)+Fac.M(MAD)‐Fac.M(MAS)+μg/g 

## Chromium (Cr)

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge I. Ox. Nat. Ox. Forced Ox. Nat. Ox. Nat. Ox.

0 20 40 60 80Fac.A(CFA)‐Fac.A(AFA)+Fac.B(DFA)‐Fac.B(BFA)+Fac.K(KFA)+Fac.A(CGD)‐Fac.A(AGD)+Fac.B(DGD)‐Fac.B(BGD)+Fac.K(KGD)+Fac.N(NAU)+UFac.N(NAW)+WFac.O(OAU)+UFac.O(OAW)+WFac.P(PAD)+UFac.Q(QAU)+UFac.A(CCC)‐Fac.A(ACC)+Fac.B(DCC)‐Fac.B(BCC)+Fac.K(KCC)+Fac.M(MAD)‐Fac.M(MAS)+μg/g 

## Cobalt (Co)

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge I. Ox. Nat. Ox. Forced Ox. Nat. Ox. Nat. Ox.



### Figure 19 and Figure 20. Chromium and Cobalt. Comparison of total elemental content by digestion (key: - = NOx control off; + = NOx control on; U = unwashed gypsum; W = washed gypsum; Nat. Ox. = natural oxidation; Forced Ox. = forced oxidation; I.Ox. = inhibited oxidation).

### Characterization of Coal Cumbustion Residues II



### 47 0 20 40 60 80 100 120Fac.A(CFA)‐Fac.A(AFA)+Fac.B(DFA)‐Fac.B(BFA)+Fac.K(KFA)+Fac.A(CGD)‐Fac.A(AGD)+Fac.B(DGD)‐Fac.B(BGD)+Fac.K(KGD)+Fac.N(NAU)+UFac.N(NAW)+WFac.O(OAU)+UFac.O(OAW)+WFac.P(PAD)+UFac.Q(QAU)+UFac.A(CCC)‐Fac.A(ACC)+Fac.B(DCC)‐Fac.B(BCC)+Fac.K(KCC)+Fac.M(MAD)‐Fac.M(MAS)+μg/g 

## Lead (Pb)

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge I. Ox. Nat. Ox. Forced Ox. Nat. Ox. Nat. Ox.

0 10 20 30 40Fac.A(CFA)‐Fac.A(AFA)+Fac.B(DFA)‐Fac.B(BFA)+Fac.K(KFA)+Fac.A(CGD)‐Fac.A(AGD)+Fac.B(DGD)‐Fac.B(BGD)+Fac.K(KGD)+Fac.N(NAU)+UFac.N(NAW)+WFac.O(OAU)+UFac.O(OAW)+WFac.P(PAD)+UFac.Q(QAU)+UFac.A(CCC)‐Fac.A(ACC)+Fac.B(DCC)‐Fac.B(BCC)+Fac.K(KCC)+Fac.M(MAD)‐Fac.M(MAS)+μg/g 

## Molybdenum (Mo)

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge I. Ox. Nat. Ox. Forced Ox. Nat. Ox. Nat. Ox.



### Figure 21 and Figure 22. Lead and Molybdenum. Comparison of total elemental content by digestion (key: - = NOx control off; + = NOx control on; U = unwashed gypsum; W = washed gypsum; Nat. Ox. = natural oxidation; Forced Ox. = forced oxidation; I.Ox. = inhibited oxidation).

### Characterization of Coal Combustion Residues II



### 48 0 5 10 15 20 25 30Fac.A(CFA)‐Fac.A(AFA)+Fac.B(DFA)‐Fac.B(BFA)+Fac.K(KFA)+Fac.A(CGD)‐Fac.A(AGD)+Fac.B(DGD)‐Fac.B(BGD)+Fac.K(KGD)+Fac.N(NAU)+UFac.N(NAW)+WFac.O(OAU)+UFac.O(OAW)+WFac.P(PAD)+UFac.Q(QAU)+UFac.A(CCC)‐Fac.A(ACC)+Fac.B(DCC)‐Fac.B(BCC)+Fac.K(KCC)+Fac.M(MAD)‐Fac.M(MAS)+μg/g 

## Selenium (Se)

I. Ox. Nat. Ox. Forced Ox. Nat. Ox. Nat. Ox.

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge

0 5 10 15Fac.A(CFA)‐Fac.A(AFA)+Fac.B(DFA)‐Fac.B(BFA)+Fac.K(KFA)+Fac.A(CGD)‐Fac.A(AGD)+Fac.B(DGD)‐Fac.B(BGD)+Fac.K(KGD)+Fac.N(NAU)+UFac.N(NAW)+WFac.O(OAU)+UFac.O(OAW)+WFac.P(PAD)+UFac.Q(QAU)+UFac.A(CCC)‐Fac.A(ACC)+Fac.B(DCC)‐Fac.B(BCC)+Fac.K(KCC)+Fac.M(MAD)‐Fac.M(MAS)+μg/g 

## Thallium (Tl)

I. Ox. Nat. Ox. Forced Ox. Nat. Ox. Nat. Ox.

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge



### Figure 23 and Figure 24. Selenium and Thallium. Comparison of total elemental content by digestion (key: - = NOx control off; + = NOx control on; U = unwashed gypsum; W = washed gypsum; Nat. Ox. = natural oxidation; Forced Ox. = forced oxidation; I.Ox. = inhibited oxidation).

### Characterization of Coal Cumbustion Residues II



## 3.2. TOTAL ELEMENTAL CONTENT BY XRF

Total elemental compositions, on a dry weight basi s, for major and some trace constituents in each of the CCRs evaluated are compared in grouping by CCR type (i.e., fly ash, gypsum, scrubber sludge, fixated scrubber sludge) in Fi gure 25 through Figure 29; tabular results are provided in Appendix C. Major elemental constitu ents present in CCRs but not detected by XRF analysis include oxygen and carbon. Elements that may be analyzed by XRF but were below the detection limit are indicated in the figures on the x-axis but without any reported value represented. Separate analyses were carried out for carbon and are also included in Appendix C.

Fly Ash. Elemental constituents typically present in fly ash at concentrations greater than 1 percent (10,000 mg/kg) are aluminum, calcium , iron, potassium, and silicon. Elemental constituents typically present at concentrations between 0.1 and 1 percent are barium, chloride, magnesium, sodium, phosphorus, stro ntium, sulfur, and titanium.

Gypsum. Elemental constituents typi cally present in gypsum at concentrations greater than 1 percent (10,000 mg/kg) are calcium and sulfur. Elemental constituents typically present at

concentrations between 0.1 and 1 percent are chloride (unwashed gypsum), fluoride (unwashed gypsum), iron, magnesium, sodium (unwashed gypsum) and silicon.

Scrubber Residue. Elemental constituents typically present in scrubber residue at concentrations greater than 1 percent (10,000 mg/kg) are aluminum (SCR on), calcium, iron (SCR on), magnesium, silicon (SCR on) and sulfur. Elemental constituents typically present at

concentrations between 0.1 and 1 percent are aluminum (except wi th SCR on), chloride, fluoride, iron (except with SCR on), potas sium, sodium (SCR on), silic on (except with SCR on), and titanium (SCR on).

Fixated Scrubber Sludge. Elemental constituents typically present in fi xated scrubber sludge at concentrations greater than 1 percent (10,000 mg /kg) are aluminum, calcium, iron, potassium, silicon and sulfur. Elemental constituents typica lly present at concentr ations between 0.1 and 1 percent are barium, chloride, so dium, phosphorus and strontium.

Fixated Scrubber Sludge with Lime. Elemental constituents typically present in fixated scrubber sludge with lime at concentrations grea ter than 1 percent (10,000 mg/kg) are aluminum, calcium, iron, magnesium (Mg lime scrubbers), silicon, and sulfur. Elemental constituents typically present at concentr ations between 0.1 and 1 per cent are chloride, potassium, magnesium (non-Mg lime scrubbers), sodium, and titanium.

49

### Characterization of Coal Combustion Residues II



### 5 0 1 10 100 1,000 10,000 100,000 1,000,000AlAsBaBrCaCdCeClCoCrCuFFeGaGeKLaMgMnMoNaNbNiPPbRbScSeSiSrSTiVWYZnZrμg/g

CFA (SNCR Off) AFA (SNCR On) 

### Fac. A. (NO+SNCR+FF)

‐ Fly Ash

1 10 100 1,000 10,000 100,000 1,000,000AlAsBaBrCaCdCeClCoCrCuFFeGaGeKLaMgMnMoNaNbNiPPbRbScSeSiSrSTiVWYZnZrμg/g

DFA (SCR Off) BFA (SCR On) 

### Fac. B. (NO+SCR+ESP, Mg lime)

‐ Fly Ash

1 10 100 1,000 10,000 100,000 1,000,000AlAsBaBrCaCdCeClCoCrCuFFeGaGeKLaMgMnMoNaNbNiPPbRbScSeSiSrSTiVWYZnZrμg/g

KFA (SCR On) 

### Fac. K. (NO+SCR+ESP, Mg lime)

‐ Fly Ash 

### a)

b)

c)

Figure 25. Fly Ash - Total content by XRF.

### Characterization of Coal Cumbustion Residues II



### 51 1 10 100 1,000 10,000 100,000 1,000,000AlAsBaBrCaCdCeClCoCrCuFFeGaGeKLaMgMnMoNaNbNiPPbRbScSeSiSrSTiVWYZnZrμg/g

NAU (Unwashed) NAW (Washed) 

### Fac. N. (FO+SCR+ESP)

‐ Gypsum

1 10 100 1,000 10,000 100,000 1,000,000AlAsBaBrCaCdCeClCoCrCuFFeGaGeKLaMgMnMoNaNbNiPPbRbScSeSiSrSTiVWYZnZrμg/g

OAU (Unwashed) OAW (Washed) 

### Fac. O. (FO+SCR+ESP)

‐ Gypsum

1 10 100 1,000 10,000 100,000 1,000,000AlAsBaBrCaCdCeClCoCrCuFFeGaGeKLaMgMnMoNaNbNiPPbRbScSeSiSrSTiVWYZnZrμg/g

PAD (U) (Unwashed) QAU (Unwashed) 

### Fac. P. (FO+SCR & SNCR +ESP)

‐ Gypsum

Fac. Q. (FO+SCR+ESP)
‐ Gypsum 

### a)

b)

c)

Figure 26. Gypsum – Total content by XRF.

### Characterization of Coal Combustion Residues II



### 52 1 10 100 1,000 10,000 100,000 1,000,000AlAsBaBrCaCdCeClCoCrCuFFeGaGeKLaMgMnMoNaNbNiPPbRbScSeSiSrSTiVWYZnZrμg/g

CGD (SNCR Off) AGD (SNCR On) 

### Fac. A. (NO+SNCR+FF)

‐ Scrubber Sludge

1 10 100 1,000 10,000 100,000 1,000,000AlAsBaBrCaCdCeClCoCrCuFFeGaGeKLaMgMnMoNaNbNiPPbRbScSeSiSrSTiVWYZnZrμg/g

DGD (SCR Off) BGD (SCR On) 

### Fac. B. (NO+SCR+ESP, Mg lime)

‐ Scrubber Sludge

1 10 100 1,000 10,000 100,000 1,000,000AlAsBaBrCaCdCeClCoCrCuFFeGaGeKLaMgMnMoNaNbNiPPbRbScSeSiSrSTiVWYZnZrμg/g

KGD (SCR On) 

### Fac. K. (NO+SCR+ESP, Mg lime)

‐ Scrubber Sludge 

### a)

b)

c)

Figure 27. Scrubber Sludge – Total content by XRF.

### Characterization of Coal Cumbustion Residues II



### 53 1 10 100 1,000 10,000 100,000 1,000,000AlAsBaBrCaCdCeClCoCrCuFFeGaGeKLaMgMnMoNaNbNiPPbRbScSeSiSrSTiVWYZnZrμg/g

CCC (SNCR Off) ACC (SNCR On)



### Fac. A. (NO+SNCR+FF)

‐ Fixated Scrubber Sludge



### Figure 28. Fixated Scrubber Sl udge – Total content by XRF.

### Characterization of Coal Combustion Residues II



### 54 1 10 100 1,000 10,000 100,000 1,000,000AlAsBaBrCaCdCeClCoCrCuFFeGaGeKLaMgMnMoNaNbNiPPbRbScSeSiSrSTiVWYZnZrμg/g

DCC (SCR Off) BCC (SCR On) 

### Fac. B. (NO+SCR+ESP, Mg lime)

‐ FSSL

1 10 100 1,000 10,000 100,000 1,000,000AlAsBaBrCaCdCeClCoCrCuFFeGaGeKLaMgMnMoNaNbNiPPbRbScSeSiSrSTiVWYZnZrμg/g

KCC (SCR On)



### Fac. K. (NO+SCR+ESP, Mg lime)

‐ FSSL

1 10 100 1,000 10,000 100,000 1,000,000AlAsBaBrCaCdCeClCoCrCuFFeGaGeKLaMgMnMoNaNbNiPPbRbScSeSiSrSTiVWYZnZrμg/g

MAD (SCR Off) MAS (SCR On) 

### Fac. M. (IO+SCR+ESP)

‐ FSSL 

### a)

b)

c)

Figure 29. Fixated Scrubber Sludge w ith Lime – Total content by XRF.

### Characterization of Coal Cumbustion Residues II



## 3.3. LABORATORY LEACHING TEST RESULTS

Appendix D and Appendix E provide graphical pres entation of the results of Solubility and Release as a Function of pH (SR002.1) and Solubility and Re lease as a Function of LS (SR003.1), respectively, for the 13 constituents of interest in th is report. Within each appendix, results are grouped by CCR type (fly ash, gyps um, scrubber sludge, FSS, FSSL) and with each CCR type grouping, comparisons are made by constitu ent of interest. First discussed below are typical characteristic results for pH and each of the 13 constituents of interest (Section 3.3.1) followed by a discussion (Section 3.3.2) comparing the ranges of observed constituent concentrations (from both test methods) with m easurements reported elsewhere on field leachate and pore water samples for CCR dis posal sites and the database used in the EPA Risk Report (EPA, 2007). Complete data also have been developed for other constituents to facilitate evaluation of geochemical speciation of constitu ents of concern and provide more thorough evaluation of leaching under alternative manage ment scenarios in the future if warranted.

For each CCR evaluated, results of the leachi ng tests provide the following information:

 

### Leachate concentrations for the constituents of in terest as a function of pH over the range of reported field management conditio ns (from test method SR002.1);

 

### pH titration curves (from test method SR002.1). Th is information is useful in characterizing the CCR and assessing how it will respond to envir onmental stresses and material aging (e.g., carbon dioxide uptake, acid precipitation, co-d isposal, mixing with other materials); and,

 

### Leachate concentrations for the constituents of interest, pH a nd electrical conductivity as a

function of LS ratio when c ontacted with distil led water (from test method SR003.1). This information provides insight into the initial leachate concentrations expected during land disposal and effects of pH and ionic strength at low LS ratio. Often these concentrations can be either greater than or less than concentrat ions observed at higher LS ratio (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 water well contamination resulting from the release. Dilu tion and attenuation factor s for metals (DAFs) have been estimated to be poten tially as low as 2 to 10 on a nati onal basis or as high as 8,000 at a particular site with hydrogeology that indicated low transport potential 23 

### . Therefore, comparison with thresholds greater than the MCL and deve loped for specific scenarios may be appropriate.

23 

### See 60 FR 66372, Dec. 21, 1995, for a discussion of model parameters leading to low DAFs, particularly the assumption of a continuous source landf ill. 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 in 65 FR 55703, September 14, 2000.



### 5 5

### Characterization of Coal Combustion Residues II



### 3.3.1. Typical Characteristic Leaching Beh avior as a Function of pH and LS
Figure 30 through Figure 45 provide comparisons of typical leaching behavi or as a function of pH for each constituent, as examples reproduced from Appendix D. These comparisons illustrate on an empirical basis some of the differences in leaching behavior for different CCRs that result

from the combination of the coal rank co mbusted, combustion c onditions and specific combustion facility design and operation. Also noted but not shown is the observed behavior for

each constituent as a function of LS at the ma terial’s natural pH (see Appendix E). Elements with predominantly oxyanionic species (e.g., boron, molybdenum, selenium, etc.) typically exhibited non-linearly incr easing extract concentrations as LS was decreased from 10 mL/g to

0.5 mL/g, in many cases increasing by a factor of 5 or 10 or greater.

These figures illustrate that for a particular constituent, the chemistry controlling release or aqueous-solid equilibrium may be similar within a material type (i.e., mercury behavior for fly ash or scrubber sludge) or across material types (i.e., the same be havior for aluminum in fly ash and fixated scrubber sludge) but that there are not necessarily generalized behaviors present for each constituent across all samples within a material type or betw een material types. The most robust groupings of leaching behavior will re sult from the development of geochemical speciation models of the materials that accoun t for the underlying solid phase speciation (e.g., solid phases, adsorption behavior ) and modifying solution characte ristics (e.g., dissolved organic matter, pH, ionic strength, co-di ssolved constituents). Developm ent of the needed geochemical speciation models, and associated leaching beha vior groupings as a function of coal rank, combustion facility design, and CCR type, will be th e basis of a subsequent report. The resulting models and groupings, in turn, are expected to allow for more detailed constituent release predictions based on limited testing for a broader set of facilities.

Mercury. Figure 30 (a, b) compares the impact of SNCR usage (Facility A) on the release behavior of mercury from fly ash. The increased mercury release, reaching a maximum at pH~8, when SNCR is in use, is likely a consequence of additional ammonium present and consequent formation of an ammonium mercury complex in solution (Wang, 2007). For all fly ash samples except AFA (Facility A, SNCR[+]), the mercury re lease indicated apparently random scatter with solution concentrations ranging from 0.01 to 0.1 μg/L. This behavior is similar to that reported earlier in this study (Sanchez et al., 2006) and is indicat ive of adsorption of elemental mercury as the primary release mechanism. For gypsum samples, mercury release was either (i) similar to that observed for fly ash (Figure 30d, Facil ity P), (ii) at very low concentration near or below the MDL (Facility O, unwashed and washed; Facility N washed) potentially indicative of adsorption onto carbon char, or (i ii) had increased release at pH <6 potentially indicative of adsorbed ionic mercury being displaced by hydr ogen ions at acidic pH (Facility A, unwashed; Facility Q). For scrubber sludge, mercury release wa s either (i) similar to that observed for fly ash, (ii) had increasing release concurrent with decreasing pH at pH<8 (Facility B, Figure 30c), or (iii) had increased release at pH~8 (local peak, indicative of ammonium complexation) and then increasing release with decreasing pH at pH<6 (Facility K). For FSS, behavior was either (i) analogous to that observed for fl y ash (Facility A), or (ii) analogous to that observed for scrubber sludge illustrated in Figure 30c (Facilities B, K, M). Mercury extract concentrations were not significantly affected by LS.

Aluminum. Figure 31 (a, b) compares the impact of SNCR usage (Facility A) on the release behavior of aluminum from fly ash and illustrates one of the three types of aluminum behavior observed across the CCR types. One type of observed aluminum behavior was amphoteric

5 6

### Characterization of Coal Cumbustion Residues II



### behavior (minimum release at pH~6-8, with in creasing release as pH decreases and increases outside of this range) with a local maximum of approximate ly 10,000 μg/L at pH~12 and a maximum of ca. 100,000 to 1,000,000 μg/L at pH~3. The concentration of the minimum at 6<pH<8 is typically influenced by the amoun t of DOC complexing aluminum in solution (increased complexation increases dissolved alum inum). This behavior was present for fly ash from Facilities A and K. Other samples exhibited increasing aluminum release with decreasing pH at pH<8 but without substant ially increased release at pH>8 (fly ash from facility B; scrubber sludge from facilities B, K). Several samples exhi bited increasing release with decreasing pH for pH<6 and a local maximum at pH~10 (Figure 31c, scrubber sludge fro m Facility A; FSS from Facility B). In addition, several samples exhibited relatively consta nt release (ca. 100 μg/L) at pH>8 with increasing release with decreasing pH at pH<8 (Figure 31d, scrubber sludge for facility B with SCR[-]; FSS from facilities A, B, K). Aluminum extract concentrations typically were either relatively constant or decreasing (salting out) with de creasing LS. The notable exception was the scrubber sludge from facility B with SCR off (DGD) and FSS from facility M with SCR on (MAS), where aluminum con centration increased with decreasing LS.

Antimony. Figure 32a illustrates antimony behavior with local maxima at pH~8 and pH<3, which was observed for fly ash from facilities A and B, and FSS from facility A. Figure 32b illustrates behavior that was observed for gypsum from Facility Q and scrubber sludge from Facility A. For gypsum samples other than from Facility Q, antimony release appeared random at concentrations of <MDL to 3 μg/L at pH>4 with a general slight increas e in concentration at pH<4. Figure 32c and d illustrates behavior that was observed for the remaining CCR samples. For some samples, antimony concentrations in ex tracts increased by up to a factor of 5 with decreasing LS, while it remained consta nt or decreased for other samples.

Arsenic. Figure 33 illustrates the four typical release behaviors obser ved for arsenic release as a function of pH. Each of these f our behaviors was observed for a least one of the samples from each material type (fly ash, gypsum, scrubbe r sludge, FSS). Leaching from gypsum generally was less than 10 μg/L for pH>6 and reached a maximum of approximately 30-100 μg/L at pH<5.

Arsenic concentrations in extracts were either cons tant or increased by up to a factor of 2 with decreasing LS.

Barium. Figure 34 illustrates the four typical releas e behaviors observed for barium. For fly ash, barium was either relatively cons tant at approximately 100 μg/L as a function of pH or exhibited increases at pH< 4 (Figure 34a) and pH>9 to approximately 1000 μg/L (i.e., facility K). For gypsum, Figure 35d illustrates the typical behavior. Behaviors illu strated by Figure 34b and c are typical of that observed for scrubber sludge and FSS, with both behaviors observed for both material types. Barium extract concentrations remained constant with decreasing LS, with the exception of fly ash from facility A, where barium concentrations increased by up to a factor of 5 with decreasing LS.

Boron. Figure 35 (a, b, c) illustrate s the three typical release beha viors for boron: (i) decreasing concentration with increasing pH for pH>8 (Figur e 35a, fly ash from faci lities A, B; scrubber sludge from facility K; FSS from f acilities A, M), (ii) relatively constant concentration with a slight decrease at 8<pH<10 (Figure 35b, scrubber sludge from facility B, FS S from facility K), (iii) relatively constant or with a slight in crease at pH>10 (Figure 35d). Comparison of Figure

35c and d illustrates the reduction in leachable boron achieved through the washing step (facility N, unwashed and washed). Boron concentrations in extracts were either constant or increased by up to a factor of 10 with decreasing LS.

5 7

### Characterization of Coal Combustion Residues II



### Cadmium. Figure 36 illustrates typical release behavior for cadmium, which is similar for all cases. The maximum concentration at pH<4 reflects the total content in the sample, and the slope and pH shift in the increasing cadmium concentr ation with decreasing pH typically reflects the presence or absence of complexa nts in solution (e.g., chloride or DOC). Cadmium concentrations

in extracts were either constant or increasing with decreasing LS.

Chromium. Figure 37 and Figure 38 illustrate typical release behavior for chromium. Comparison of the pairs Figure 37a and b, Figure 37c and d, and Figure 38a and b illustrate the

effect of NOx control on chromium release fro m fly ash, scrubber sludge, and FSS respectively for Facility B. Use of SCR at this facility appears to result in a larger fraction of the chromium in the residue being oxidized (Cr +6 

### ), forming chromate, which is more soluble at neutral pH. The SCR catalyst used for Facility B may have cont ributed to increased overall total chromium present in the CCRs from that facility when SCR was in use. Increased l eachability of chromium as a consequence of NOx control was also observed for Facility A (comparing results for SNCR[-] with SNCR[+]), even t hough total chromium content was similar for cases with and without NOx control. Figure 38c and d illustrate s the typical amphoteric behavior for reduced chromium (Cr +3 

### ), which was observed for gypsum samples. Chromium concentra tions in extracts were either constant (for cases with low leachabl e chromium), or increasing by up to a factor of 10 (cases with Cr +6 

### as the apparently dominant ch romium form) with decreasing LS.

Cobalt. Figure 39 illustrates typica l release behavior fo r cobalt, which is similar for all CCRs tested. Cobalt release increases with decreasing pH at pH<8, with the maximum concentration reflecting the total leachable content and the slope and relative pH shift in the slope typically reflecting the presence or absence of complexants in solution. Cobalt concentrations in extracts (where greater than the MDL) were typically in creasing by up to a factor of 5 with decreasing

LS.

Lead. Figure 40 illustrates typical release behavior for lead, which generally is expected to be amphoteric (Figure 40a, c). However, many sample s did not have sufficient lead content or complexants present in solution to produce amphot eric behavior at pH<12 (Figure 40b, d). Lead

concentrations in extracts were not significantly changed at decreasing LS.

Molybdenum. Figure 41 and Figure 42 illustrate t ypical release behaviors for molybdenum. Figure 41a illustrates increased concentration p eaking at pH~8 most likely from complexation with ammonium present from use of SNCR (Faci lity A). Note the similar release behavior observed for fly ash, FSS and gypsum illustrated by Figure 41b and Figure 42b, c, albeit at different orders of magnitude in concentra tion. Figure 41c, d and Figure 42b, d illustrate three additional observed behaviors, present across multiple CCR types. Molybdenum concentrations typically increased with decreasi ng LS, in some cases by a factor much greater than 10 (e.g., FSS from Facility A).

Selenium. Figure 43 and Figure 44 illustrate typical selenium release behaviors observed for fly ash, scrubber sludge and FSS. For gypsum, selenium release was either cons tant as a function of pH (facilities O, P) or amphoteric (facilities N, Q). Selenium concentrations in extracts typically increased by up to a factor of 6 with decreasing LS.

Thallium. Figure 45 illustrates typical release behavior for thalliu m. Most cases were either analogous to Figure 45a or Figure 45 c (increasing concentration with decreasing pH at pH<9) or Figure 45d (relatively constant as a function of pH). For gypsum, wa shing resulted in at least an

58

### Characterization of Coal Cumbustion Residues II



### 59 order of magnitude reduction in the observed lea ching concentrations (facilities N, O). Thallium concentrations typically increased by up to a factor of 5 with decreasing LS.

MDL ML 10.3 0.044 MCL

0.001

0.01

0.1

1

2 4 6 8 10 12 14Hg [μg/L]

pH

SR2-CFA - A SR2-CFA - B

SR2-CFA - C

Fly Ash ‐ Fac. A. (NO+SNCR[

‐ ]+FF) MDL ML 10.5 0.116 MCL

0.001

0.01

0.1

1

2 4 6 8 10 12 14Hg [μg/L]

pH

SR2-AFA - A SR2-AFA - B

SR2-AFA - C

Fly Ash ‐ Fac. A. (NO+SNCR[+]+FF )

MDL ML 9.1 0.040 MCL

0.001

0.01

0.1

1 10

2 4 6 8 10 12 14Hg [μg/L]

pH

SR2-DGD - A SR2-DGD - B

SR2-DGD - C

Scrubber Sludge ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 6.7 0.029 MCL

0.001

0.01

0.1

1 10

2 4 6 8 10 12 14Hg [μg/L]

pH

SR2-PAD - A SR2-PAD - B

Gypsum

‐ Fac. P. (FO+SCR[+]&SNCR[+]+ESP) 

### a) b)

c) d)

Figure 30. Mercury - Examples of characteristic leaching be havior as a function of pH (SR002.1 results).

### Characterization of Coal Combustion Residues II



### 60 MDL 1000000

100000

10000 1804]L 1000/g [μ 100Al 10

1

0.1 10.3 2 4 6 8 10 12 14

ML pH

SR2-CFA - A SR2-CFA - B

SR2-CFA - C

Fly Ash ‐ Fac. A. (NO+SNCR[

‐ ]+FF ) MDL 1000000

100000

13427 10000]L 1000/g [μ 100Al 10

1

0.1 10.5 2 4 6 8 10 12 14

ML pH

SR2-AFA - A SR2-AFA - B

SR2-AFA - C

Fly Ash ‐ Fac. A. (NO+SNCR[+]+FF )

MDL 1000000

100000

10000]L 1000/g 496[μ 100Al 10

1

0.1 7.3 2 4 6 8 10 12 14

ML pH

SR2-CGD - A SR2-CGD - B

SR2-CGD - C

Scrubber Sludge ‐ Fac. A. (NO+SNCR[

‐ ]+FF) MDL 1000000

100000

10000]L 1000/g [μ 100 37.0Al 10

1

0.1 9.1 2 4 6 8 10 12 14

ML pH

SR2-DGD - A SR2-DGD - B

SR2-DGD - C

Scrubber Sludge ‐ Fac. B. (NO+SCR[

‐ ]+ESP) 

### a) b)

c) d)

Figure 31. Aluminum. Examples of characteri stic leaching behavior as a function of pH.

### Characterization of Coal Cumbustion Residues II



### 61 MDL ML 10.3 6.43 MCL

0.1

1 10 100 1000

2 4 6 8 10 12 14Sb [μg/L]

pH

SR2-DFA - A SR2-DFA - B

SR2-DFA - C

Fly Ash ‐ Fac. B. (NO+SNCR[

‐ ]+FF) MDL ML 6.9 2.53 MCL

0.1

1 10 100

2 4 6 8 10 12 14Sb [μg/L]

pH

SR2-QAU - A SR2-QAU - B

Gypsum

‐ Fac. Q. (FO+SCR[+]+ESP)

MDL ML 9.1 5.44 MCL

0.1

1 10 100 1000

2 4 6 8 10 12 14Sb [μg/L]

pH

SR2-DGD - A SR2-DGD - B

SR2-DGD - C

Scrubber Sludge ‐ Fac. B. (NO+SCR[

‐ ]+ESP, Mg Lime ) MDL ML 12.2 1.76 MCL

0.1

1 10 100 1000

2 4 6 8 10 12 14Sb [μg/L]

pH

SR2-DCC - A SR2-DCC - B

SR2-DCC - C

FSSL ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) 

### a) b)

c) d)

Figure 32. Antimony. Examples of characterist ic leaching behavior as a function of pH.

### Characterization of Coal Combustion Residues II



### 62 MDL ML 10.3 46.8

MCL

0.1

1 10 100 1000 10000

2 4 6 8 10 12 14As [μg/L]

pH

SR2-DFA - A SR2-DFA - B

SR2-DFA - C

Fly Ash ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 10.1 29.0

MCL

0.1

1 10 100 1000 10000

2 4 6 8 10 12 14As [μg/L]

pH

SR2-BFA - A SR2-BFA - B

SR2-BFA - C

Fly Ash ‐ Fac. B. (NO+SCR[+]+ESP,Mg Lime)

MDL ML 9.1 0.545 MCL

0.1

1 10 100 1000

2 4 6 8 10 12 14As [μg/L]

pH

SR2-DGD - A SR2-DGD - B

SR2-DGD - C

Scrubber Sludge ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 12.2 2.09 MCL

0.1

1 10 100 1000 10000

2 4 6 8 10 12 14As [μg/L]

pH

SR2-DCC - A SR2-DCC - B

SR2-DCC - C

FSSL ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) 

### d)

b) a)

c)

Figure 33. Arsenic. Examples of characteristic leaching be havior as a function of pH.

### Characterization of Coal Cumbustion Residues II



### 63 MDL ML 10.3 192 MCL

0.1 1 10 100 1000 10000

2 4 6 8 10 12 14Ba [μg/L]

pH

SR2-DFA - A SR2-DFA - B

SR2-DFA - C

Fly Ash ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 11.0 113 MCL

0.1 1 10 100 1000 10000

2 4 6 8 10 12 14Ba [μg/L]

pH

SR2-KGD - A SR2-KGD - B

Scrubber Sludge ‐ Fac. K. (NO+SCR[+]+ESP,Mg Lime)

MDL ML 12.2 2286 MCL

0.1 1 10 100 1000 10000

2 4 6 8 10 12 14Ba [μg/L]

pH

SR2-DCC - A SR2-DCC - B

SR2-DCC - C

FSSL ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 7.3 80.0 MCL

0.1 1 10 100 1000 10000

2 4 6 8 10 12 14Ba [μg/L]

pH

SR2-OAW - A SR2-OAW - B

Gypsum (Gyp

‐ W)

‐ Fac. O. (FO+SCR[+]+ESP) 

### d) b) a)

c)

Figure 34. Barium. Examples of characteristic leaching be havior as a function of pH.

### Characterization of Coal Combustion Residues II



### 64 MDL ML 10.3 3551 DWEL

0.1

1 10 100 1000 10000 100000

2 4 6 8 10 12 14B [μg/L]

pH

SR2-DFA - A SR2-DFA - B

SR2-DFA - C

Fly Ash ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 9.1 3331 DWEL

0.1 1 10 100 1000 10000 100000

2 4 6 8 10 12 14B [μg/L]

pH

SR2-DGD - A SR2-DGD - B

SR2-DGD - C

Scrubber Sludge ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime)

MDL ML 7.2 2214 DWEL

0.1 1 10 100 1000 10000 100000

2 4 6 8 10 12 14B [μg/L]

pH

SR2-NAU - A SR2-NAU - B

Gypsum (Gyp

‐ U)

‐ Fac. N. (FO+SCR[+]+ESP) MDL ML 7.1 48.6 DWEL

0.1 1 10 100 1000 10000 100000

2 4 6 8 10 12 14B [μg/L]

pH

SR2-NAW - A SR2-NAW - B

Gypsum (Gyp

‐ W)

‐ Fac. N. (FO+SCR[+]+ESP) 

### d) c) b) a)

Figure 35. Boron. Examples of characteristi c leaching behavior as a function of pH.

### Characterization of Coal Cumbustion Residues II



### 65 MDL ML 10.3 0.795 MCL

0.1

1 10 100

2 4 6 8 10 12 14Cd [μg/L]

pH

SR2-DFA - A SR2-DFA - B

SR2-DFA - C

Fly Ash ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 11.0 0.200 MCL

0.1

1 10 100

2 4 6 8 10 12 14Cd [μg/L]

pH

SR2-KGD - A SR2-KGD - B

Scrubber Sludge ‐ Fac. K. (NO+SCR[+]+ESP,Mg Lime)

MDL ML 6.9 6.03 MCL

0.1

1 10 100

2 4 6 8 10 12 14Cd [μg/L]

pH

SR2-QAU - A SR2-QAU - B

Gypsum (Gyp

‐ U)

‐ Fac. Q. (FO+SCR[+]+ESP) MDL ML 8.4 0.634 MCL

0.1

1 10 100

2 4 6 8 10 12 14Cd [μg/L]

pH

SR2-ACC - A SR2-ACC - B

SR2-ACC - C

FSSL

‐ Fac. B. (NO+SCR[+]+ESP,Mg Lime) 

### d) c) b) a)

Figure 36. Cadmium. Examples of characteri stic leaching behavior as a function of pH.

### Characterization of Coal Combustion Residues II



### 66 MDL ML 10.3 132 MCL

0.1

1 10 100 1000 10000

2 4 6 8 10 12 14Cr [μg/L]

pH

SR2-DFA - A SR2-DFA - B

SR2-DFA - C

Fly Ash ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 10.1 851

MCL

0.1

1 10 100 1000 10000

2 4 6 8 10 12 14Cr [μg/L]

pH

SR2-BFA - A SR2-BFA - B

SR2-BFA - C

Fly Ash ‐ Fac. B. (NO+SCR[+]+ESP,Mg Lime)

MDL ML 9.1 2.98 MCL

0.1

1 10 100 1000 10000

2 4 6 8 10 12 14Cr [μg/L]

pH

SR2-DGD - A SR2-DGD - B
SR2-DGD - C

Scrubber Sludge ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 10.1 228 MCL

0.1

1 10 100 1000 10000

2 4 6 8 10 12 14Cr [μg/L]

pH

SR2-BGD - A SR2-BGD - B

SR2-BGD - C

Scrubber Sludge ‐ Fac. B. (NO+SCR[+]+ESP,Mg Lime)



### d) c) b) a)

Figure 37. Chromium. Examples of characteri stic leaching behavior as a function of pH.

### Characterization of Coal Cumbustion Residues II



### 67 MDL ML 12.2 11.2 MCL

0.1

1 10 100 1000 10000

2 4 6 8 10 12 14Cr [μg/L]

pH

SR2-DCC - A SR2-DCC - B
SR2-DCC - C

FSSL ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 8.0 715

MCL

0.1

1 10 100 1000 10000

2 4 6 8 10 12 14Cr [μg/L]

pH

SR2-BCC - A SR2-BCC - B

SR2-BCC - C

FSSL ‐ Fac. B. (NO+SCR[+]+ESP,Mg Lime)

MDL ML 7.2 2.87 MCL

0.1 1 10 100 1000 10000

2 4 6 8 10 12 14Cr [μg/L]

pH

SR2-NAU - A SR2-NAU - B

Gypsum (Gyp

‐ U)

‐ Fac. N. (FO+SCR[+]+ESP) MDL ML 7.1 0.235 MCL

0.1 1 10 100 1000 10000

2 4 6 8 10 12 14Cr [μg/L]

pH

SR2-NAW - A SR2-NAW - B

Gypsum (Gyp

‐ W)

‐ Fac. N. (FO+SCR[+]+ESP) 

### d) c) b) a)

Figure 38. Chromium. Examples of characteri stic leaching behavior as a function of pH.

### Characterization of Coal Combustion Residues II



### 68 MDL ML 10.3 0.255

0.1 1 10 100 1000

2 4 6 8 10 12 14Co [μg/L]

pH

SR2-CFA - A SR2-CFA - B
SR2-CFA - C

Fly Ash ‐ Fac. A. (NO+SNCR[

‐ ]+FF) MDL ML 10.5 7.72

0.1

1 10 100 1000

2 4 6 8 10 12 14Co [μg/L]

pH

SR2-AFA - A SR2-AFA - B

SR2-AFA - C

Fly Ash ‐ Fac. A. (NO+SNCR[+]+FF)

MDL ML 9.1 0.255

0.1 1 10 100 1000

2 4 6 8 10 12 14Co [μg/L]

pH

SR2-DGD - A SR2-DGD - B

SR2-DGD - C

Scrubber Sludge ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 7.5 1.65

0.1

1 10 100 1000

2 4 6 8 10 12 14Co [μg/L]

pH

SR2-OAU - A SR2-OAU - B

Gypsum (Gyp

‐ U)

‐ Fac. O. (FO+SCR[+]+ESP) 

### d) c) b) a)

Figure 39. Cobalt. Examples of characteris tic leaching behavior as a function of pH.

### Characterization of Coal Cumbustion Residues II



### 69 MDL ML 10.5 0.339 MCL

0.1

1 10 100 1000

2 4 6 8 10 12 14Pb [μg/L]

pH

SR2-AFA - A SR2-AFA - B

SR2-AFA - C

Fly Ash ‐ Fac. A. (NO+SNCR[+]+FF) MDL ML 6.8 0.354 MCL

0.1

1 10 100 1000

2 4 6 8 10 12 14Pb [μg/L]

pH

SR2-AGD - A SR2-AGD - B

SR2-AGD - C

Scrubber Sludge ‐ Fac. A. (NO+SNCR[+]+FF)

MDL ML 8.4 0.569 MCL

0.1

1 10 100 1000

2 4 6 8 10 12 14Pb [μg/L]

pH

SR2-ACC - A SR2-ACC - B

SR2-ACC - C

FSSL

‐ Fac. A. (NO+SCR[+]+ESP,Mg Lime) MDL ML 7.5 0.140 MCL

0.1

1 10 100 1000

2 4 6 8 10 12 14Pb [μg/L]

pH

SR2-OAU - A SR2-OAU - B

Gypsum (Gyp

‐ U)

‐ Fac. O. (FO+SCR[+]+ESP) 

### d) c) b) a)

Figure 40. Lead. Examples of characterist ic leaching behavior as a function of pH.

### Characterization of Coal Combustion Residues II



### 70 MDL ML 10.5 587 DWEL

0.1 1 10 100 1000 10000

2 4 6 8 10 12 14Mo [μg/L]

pH

SR2-AFA - A SR2-AFA - B

SR2-AFA - C

Fly Ash ‐ Fac. A. (NO+SNCR[+]+FF) MDL ML 10.3 1956

DWEL

0.1 1 10 100 1000 10000

2 4 6 8 10 12 14Mo [μg/L]

pH

SR2-DFA - A SR2-DFA - B

SR2-DFA - C

Fly Ash ‐ Fac. B. (NO+SCR[

‐ ]+FF)

MDL ML 7.3 10.2 DWEL

0.1 1 10 100 1000

2 4 6 8 10 12 14Mo [μg/L]

pH

SR2-CGD - A SR2-CGD - B

SR2-CGD - C

Scrubber Sludge ‐ Fac. A. (NO+SNCR[

‐ ]+FF) MDL ML 9.1 135 DWEL

0.1 1 10 100 1000

2 4 6 8 10 12 14Mo [μg/L]

pH

SR2-DGD - A SR2-DGD - B

SR2-DGD - C

Scrubber Sludge ‐ Fac. B. (NO+SCR[

‐ ]+ESP, Mg Lime )



### d) c) b) a)

Figure 41. Molybdenum. Examples of character istic leaching behavior as a function of pH.

### Characterization of Coal Cumbustion Residues II



### 71 MDL ML 8.4 241 DWEL

0.1 1 10 100 1000 10000

2 4 6 8 10 12 14Mo [μg/L]

pH

SR2-ACC - A SR2-ACC - B

SR2-ACC - C

FSSL

‐ Fac. A. (NO+SCR[+]+ESP,Mg Lime) MDL ML 12.2 138 DWEL

0.1 1 10 100 1000 10000

2 4 6 8 10 12 14Mo [μg/L]

pH

SR2-DCC - A SR2-DCC - B

SR2-DCC - C

FSSL ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime)

MDL ML 7.5 18.8 DWEL

0.1 1 10 100 1000 10000

2 4 6 8 10 12 14Mo [μg/L]

pH

SR2-OAU - A SR2-OAU - B

Gypsum (Gyp

‐ U)

‐ Fac. O. (FO+SCR[+]+ESP) MDL ML 6.9 14.3 DWEL

0.1 1 10 100 1000 10000

2 4 6 8 10 12 14Mo [μg/L]

pH

SR2-QAU - A SR2-QAU - B

Gypsum (Gyp

‐ U)

‐ Fac. Q. (FO+SCR[+]+ESP) 

### d) c) b) a)

Figure 42. Molybdenum. Examples of character istic leaching behavior as a function of pH.

### Characterization of Coal Combustion Residues II



### 72 MDL ML 10.3 9.27 MCL

0.1 1 10 100 1000

2 4 6 8 10 12 14Se [μg/L]

pH

SR2-DFA - A SR2-DFA - B

SR2-DFA - C

Fly Ash ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 9.2 123

MCL

0.1 1 10 100 1000

2 4 6 8 10 12 14Se [μg/L]

pH

SR2-KFA - A SR2-KFA - B

Fly Ash ‐ Fac. K. (NO+SCR[+]+ESP,Mg Lime)

MDL ML 9.1 21.9 MCL

0.1 1 10 100 1000

2 4 6 8 10 12 14Se [μg/L]

pH

SR2-DGD - A SR2-DGD - B

SR2-DGD - C

Scrubber Sludge ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 10.1 2.31 MCL

0.1 1 10 100 1000

2 4 6 8 10 12 14Se [μg/L]

pH

SR2-BGD - A SR2-BGD - B

SR2-BGD - C

Scrubber Sludge ‐ Fac. B. (NO+SCR[+]+ESP,Mg Lime)



### d) c) b) a)

Figure 43. Selenium. Examples of characteri stic leaching behavior as a function of pH.

### Characterization of Coal Cumbustion Residues II



### 73 MDL ML 12.2 16.3 MCL

0.1

1 10 100 1000

2 4 6 8 10 12 14Se [μg/L]

pH

SR2-DCC - A SR2-DCC - B

SR2-DCC - C

FSSL ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 8.2 22.6 MCL

0.1

1 10 100 1000

2 4 6 8 10 12 14Se [μg/L]

pH

SR2-KCC - A SR2-KCC - B

FSSL ‐ Fac. K. (NO+SCR[+]+ESP,Mg Lime)

MDL ML 7.2 18.5 MCL

0.1

1 10 100 1000 10000

2 4 6 8 10 12 14Se [μg/L]

pH

SR2-NAU - A SR2-NAU - B

Gypsum (Gyp

‐ U)

‐ Fac. N. (FO+SCR[+]+ESP) MDL ML 6.9 325

MCL

0.1

1 10 100 1000 10000

2 4 6 8 10 12 14Se [μg/L]

pH

SR2-QAU - A SR2-QAU - B

Gypsum (Gyp

‐ U)

‐ Fac. Q. (FO+SCR[+]+ESP) 

### d) c) b) a)

Figure 44. Selenium. Examples of characteri stic leaching behavior as a function of pH.

### Characterization of Coal Combustion Residues II



### 74 MDL ML 10.3 0.773 MCL

0.1

1 10 100 1000

2 4 6 8 10 12 14Tl [μg/L]

pH

SR2-DFA - A SR2-DFA - B

SR2-DFA - C

Fly Ash ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 9.2 38.0

MCL

0.1

1 10 100 1000

2 4 6 8 10 12 14Tl [μg/L]

pH

SR2-KFA - A SR2-KFA - B

Fly Ash ‐ Fac. K. (NO+SCR[+]+ESP,Mg Lime)

MDL ML 12.2 15.6

MCL

0.1

1 10 100 1000

2 4 6 8 10 12 14Tl [μg/L]

pH

SR2-DCC - A SR2-DCC - B

SR2-DCC - C

FSSL ‐ Fac. B. (NO+SCR[

‐ ]+ESP,Mg Lime) MDL ML 8.2 2.98 MCL

0.1

1 10 100 1000

2 4 6 8 10 12 14Tl [μg/L]

pH

SR2-KCC - A SR2-KCC - B

FSSL ‐ Fac. K. (NO+SCR[+]+ESP,Mg Lime) 

### d) c) b) a)

Figure 45. Thallium. Examples of characteri stic leaching behavior as a function of pH

.

### Characterization of Coal Cumbustion Residues II



### 3.3.2. Comparisons of the Ranges of Constituent Concentrations from Laboratory Testing with Measurements of Field Samples and the EPA Risk Report Database
Figure 46 through Figure 59 present comparisons of the range of constituent concentrations observed in laboratory extracts from testing as a function of pH and LS (SR002.1 and SR003.1) over the pH range from 5.4 to 12.4 and LS ratios from 0.5 to 10. Th is pH range represents the 5 th



### and 95 th 

### percentiles of pH observed in field samples from CCR landfills and surface impoundments, as discussed in Section 2.6. For la boratory leaching test ex tracts, the presented data represent the observed minimum, natural pH, and maximum concentration, considering all

results from both test methods. Including results from testing as a function of LS allows consideration of potentially higher concentrations observed for initial releases that may occur at

low LS ratios in the field. The MCL or DWEL is included in each figure as a dashed horizontal line to provide a reference value. However, the concentration ranges indicated in the figures as results of this study are direct measurements of laboratory extracts and do not consider attenuation that may occur in the field. Ranges of field observations are included for comparison as derived from the EPRI database, considering only observations from dis posal sites associated

with facilities that have wet FGD scrubbers. The 5 th 

### , median, and 95 th 

### percentile of field data is presented for surface impoundments [“Surface Im p. (EPRI)”] and landfills [“Landfill (EPRI)”]. Surface impoundment data are compared with sc rubber sludge results because scrubber sludges are most likely to be disposed in this manner (see Section 1). Landfill data are compared with

FSS and FSSL because these blended materials are th e likely to be disposed in landfills. Also included for comparison is the 5 th 

### , median, and 95 th 

### percentile of the data base used to carry out human and ecological hea lth risk evaluations in the EPA Risk Report (EPA, 2007) (“CCW Ash,” “CCW FGD,” and “CCW Ash and Coal Waste” referring to monofilled fly ash, disposed FGD scrubber sludge, and combined CCR disposal, respectively).

pH. The natural pH of the fly ash sample s evaluated in this report was alkaline 24 

### , scrubber sludge samples were neutral to alkaline, gypsum samples were neutral and FSS samples were mildly alkaline (pH ~8) to very alkaline (pH>11 ), most likely depending on the amount of lime

added.

Mercury. Laboratory extract concentration ranges for two of the scrubber sludge samples (Facility B) and four of the FSS samples (facilities B, K, M) exceeded the MCL for mercury. The mercury concentration ranges indicate that the greatest leaching concen trations are expected from scrubber sludge and blending with fly ash and lime to pr oduce FSS does not substantially decrease, and may increase, mercury leaching. All natural pH samples were less than the MCL, most by more than an order of magnitude. All fly ash and gypsum data were less than the MCL, regardless of pH. Mercury fiel d data were very sparse.

Aluminum. There was no reference limit available for aluminum. The range of laboratory

extract concentrations from scr ubber sludge samples agreed well with field observations. The range of field observations for la ndfills tended to be similar to somewhat lower than the values observed for laboratory extracts. However, the range used in the EPA Risk Report (EPA, 2007) had an upper bound approximately one order of magn itude greater than the field data and the laboratory extracts.

24 

### Some fly ash samples reported on in Sanchez et al. (2006) were acidic.



### 7 5

### Characterization of Coal Combustion Residues II



### Antimony. Fly ash and FSS had the hi ghest concentrations of antimony in la boratory extracts. The range of field observations for surface impoundments (EPRI) was much greater than for laboratory extracts of scrubber sludge, but also likely reflects co-disposal of fly ash with scrubber sludge in surface impoundments. If the fi eld data includes co-disposal data, then the concentration range reported for field observati ons is entirely consistent with the laboratory testing. The range of field observation for landf ills (EPRI) was lower than observed in laboratory extracts. This comparison suggests the potential for attenuation or immobilization under field conditions, many of which may be reducing in contrast to the oxi dizing conditions used in the laboratory testing. For gypsum, all natural pH results were less than the MCL.

Arsenic. Leachable arsenic appears to be distri buted between fly ash and scrubber sludge. Results for Facility A (fly ash, scrubber sludge, and FSS), Facility B (scrubber sludge and FSS) and Facility M (FSS) suggest that NOx controls increase the leachability of arsenic at the material’s natural pH. Results from field observa tions indicate narrower ranges than laboratory testing. Ranges used in the EPA Risk report (E PA, 2007) appear to be much higher than the laboratory testing results, except for Facility M. All results for gypsum were less than the MCL.

Barium. Laboratory testing results i ndicate a much broader range of concentrations than field observations. Two samples of FSS, both with NOx controls off (Facility B and Facility M), had much greater laboratory extract concentrations th an the other samples. All natural pH results were less than the MCL for fly ash, scrubber sludge and gypsum.

Boron. Most notable for boron is a reduction of approximately an order of magnitude in leachable boron from gypsum as a consequence of washing (facilities N, O). There is no clear trend amongst the material types for boron. Labor atory results are cons istent with field observations. All gypsum natural pH re sults were less than the DWEL.

Cadmium. Cadmium concentrations in laboratory extracts were generally lower for the scrubber sludge than for the other materials. For scrubber sludge, cadmium concentrations observed in laboratory extracts were less than th e concentrations reported for field observations for surface impoundments. For all cases, cadmium concentrations in laboratory extracts were

consistent with field observati ons for landfills. In addition, th e measured concentrations in laboratory extracts from this st udy and reported for field results are approximately an order of magnitude less than the upper bound reported for CC W and coal waste in the Risk Report (EPA 2007).

Chromium. The range of field observa tions appears low in comparison to the laboratory testing results. The increase in chromium leaching, appa rently as a consequence of NOx controls, is evident for facilities A, B and M. Six cases exceed the MCL by greater than one order of magnitude. Test results for all of the gypsum samples are well below the MCL. The field observations for both surface impoundments and landf ills are up to two orders of magnitude less than the laboratory testing results.

Cobalt. The use of NOx controls appears to incr ease cobalt leaching from fly ash based results for facilities A and B. The data range used by the EPA risk report (EPA, 2007) for combined management of ash and coal waste is one to two orders of magnit ude greater than the observations for laboratory ex tracts and field observations.

7 6

### Characterization of Coal Cumbustion Residues II



### 77 Lead. Laboratory test results indi cate concentration ranges genera lly lower than or consistent with field observations for surface impoundments a nd landfills and m uch lower than the values used in the EPA risk report (EPA, 2007). All fl y ash and gypsum samples were less than the

MCL.

Molybdenum. Leachate molybdenum concentrations exceeding the DWEL by up to two orders of magnitude were observed for fly ash and FSS. Leachate molybdenum concentrations generally less than the DWEL were observed for gypsum.

Selenium. Similar ranges of selenium concentr ations are expected for all materials.

Thallium. Laboratory test results i ndicate a concentration range in excess of two orders of

m agnitude for all ma terials and the observed co ncentration can exceed the MCL for thallium by more than one order of magnitude. Wash ed gypsum had significantly lower extract concentrations of thallium than unwashed gypsum.

4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0Fac. A (CFA) -Fac. A (AFA) +Fac. B (DFA) -Fac. B (BFA) +Fac. K (KFA) +CCW Ash [EPA]Fac. A (CGD) -Fac. A (AGD) +Fac. B (DGD) -Fac. B (BGD) +Fac. K (KGD) +Surface Imp. [EPRI]Fac. N (NAU) +UFac. N (NAW) +WFac. O (OAU) +UFac. O (OAW) +WFac. P (PAD) +UFac. Q (QAU) +UFac. A (CCC) -Fac. A (ACC) +Fac. B (DCC) -Fac. B (BCC) +Fac. K (KCC) +Fac. M (MAD) -Fac. M (MAS) +Landfill [EPRI]CCW FGD [EPA]Ash & Coal Waste [EPA]pH (SI)

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge Nat. Ox. Nat. Ox. | I. Ox. Nat. Ox. Forced Ox.



### Figure 46. Natural pH (pH in distilled wa ter at LS=10) observed in SR02 extracts.

### Characterization of Coal Combustion Residues II



### 78 0.001 0.010 0.100 1.000 10.000Fac. A (CFA) -Fac. A (AFA) +Fac. B (DFA) -Fac. B (BFA) +Fac. K (KFA) +CCW Ash [EPA]Fac. A (CGD) -Fac. A (AGD) +Fac. B (DGD) -Fac. B (BGD) +Fac. K (KGD) +Surface Imp. [EPRI]Fac. N (NAU) +UFac. N (NAW) +WFac. O (OAU) +UFac. O (OAW) +WFac. P (PAD) +UFac. Q (QAU) +UFac. A (CCC) -Fac. A (ACC) +Fac. B (DCC) -Fac. B (BCC) +Fac. K (KCC) +Fac. M (MAD) -Fac. M (MAS) +Landfill [EPRI]CCW FGD [EPA]Ash & Coal Waste [EPA]Hg (μg/L)

Max

Min

own pH MCL = 2 μ g/L Nat. Ox. Nat. Ox. | I. Ox. Nat. Ox. Forced Ox.

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge

0.1 1.0 10.0 100.0 1,000.0 10,000.0 100,000.0 1,000,000.0Fac. A (CFA) -Fac. A (AFA) +Fac. B (DFA) -Fac. B (BFA) +Fac. K (KFA) +CCW Ash [EPA]Fac. A (CGD) -Fac. A (AGD) +Fac. B (DGD) -Fac. B (BGD) +Fac. K (KGD) +Surface Imp. [EPRI]Fac. N (NAU) +UFac. N (NAW) +WFac. O (OAU) +UFac. O (OAW) +WFac. P (PAD) +UFac. Q (QAU) +UFac. A (CCC) -Fac. A (ACC) +Fac. B (DCC) -Fac. B (BCC) +Fac. K (KCC) +Fac. M (MAD) -Fac. M (MAS) +Landfill [EPRI]CCW FGD [EPA]Ash & Coal Waste [EPA]Al (μg/L)

Max

Min

own pH Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge Nat. Ox. Nat. Ox. | I. Ox. Nat. Ox. Forced Ox.



### Figure 47 and Figure 48. Mercury and Alumin um. Comparison of maxi mum, minimum and natural pH concentrations observed in SR 02 and SR03 extracts over the pH domain 5.4 ≤ pH ≤ 12.4. (key: - = NOx control off; + = NOx c ontrol on; U = unwashed gypsum; W = washed gypsum; Nat. Ox. = natural oxidation; Forced Ox. = forced oxidation; I.Ox. = inhibited oxidation).

### Characterization of Coal Cumbustion Residues II



### 79 0.1 1.0 10.0 100.0 1,000.0Fac. A (CFA) -Fac. A (AFA) +Fac. B (DFA) -Fac. B (BFA) +Fac. K (KFA) +CCW Ash [EPA]Fac. A (CGD) -Fac. A (AGD) +Fac. B (DGD) -Fac. B (BGD) +Fac. K (KGD) +Surface Imp. [EPRI]Fac. N (NAU) +UFac. N (NAW) +WFac. O (OAU) +UFac. O (OAW) +WFac. P (PAD) +UFac. Q (QAU) +UFac. A (CCC) -Fac. A (ACC) +Fac. B (DCC) -Fac. B (BCC) +Fac. K (KCC) +Fac. M (MAD) -Fac. M (MAS) +Landfill [EPRI]CCW FGD [EPA]Ash & Coal Waste [EPA]Sb (μg/L)

Max

Min

own pH MCL = 6 μ g/L

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge Nat. Ox. Nat. Ox. | I. Ox. Nat. Ox. Forced Ox.

0.1 1.0 10.0 100.0 1,000.0 10,000.0 100,000.0Fac. A (CFA) -Fac. A (AFA) +Fac. B (DFA) -Fac. B (BFA) +Fac. K (KFA) +CCW Ash [EPA]Fac. A (CGD) -Fac. A (AGD) +Fac. B (DGD) -Fac. B (BGD) +Fac. K (KGD) +Surface Imp. [EPRI]Fac. N (NAU) +UFac. N (NAW) +WFac. O (OAU) +UFac. O (OAW) +WFac. P (PAD) +UFac. Q (QAU) +UFac. A (CCC) -Fac. A (ACC) +Fac. B (DCC) -Fac. B (BCC) +Fac. K (KCC) +Fac. M (MAD) -Fac. M (MAS) +Landfill [EPRI]CCW FGD [EPA]Ash & Coal Waste [EPA]As (μg/L)

Max

Min

own pH MCL = 10 μ g/L

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge Nat. Ox. Nat. Ox. | I. Ox. Nat. Ox. Forced Ox.



### Figure 49 and Figure 50. Antim ony and Arsenic. Comparis on of maximum, m inimum and natural pH concentrations observed in SR 02 and SR03 extracts over the pH domain 5.4 ≤ pH ≤ 12.4. (key: - = NOx control off; + = NOx c ontrol on; U = unwashed gypsum; W = washed gypsum; Nat. Ox. = natural oxidation; Forced Ox. = forced oxidation; I.Ox. = inhibited oxidation).

### Characterization of Coal Combustion Residues II



### 80 1 10 100 1,000 10,000 100,000Fac. A (CFA) -Fac. A (AFA) +Fac. B (DFA) -Fac. B (BFA) +Fac. K (KFA) +CCW Ash [EPA]Fac. A (CGD) -Fac. A (AGD) +Fac. B (DGD) -Fac. B (BGD) +Fac. K (KGD) +Surface Imp. [EPRI]Fac. N (NAU) +UFac. N (NAW) +WFac. O (OAU) +UFac. O (OAW) +WFac. P (PAD) +UFac. Q (QAU) +UFac. A (CCC) -Fac. A (ACC) +Fac. B (DCC) -Fac. B (BCC) +Fac. K (KCC) +Fac. M (MAD) -Fac. M (MAS) +Landfill [EPRI]CCW FGD [EPA]Ash & Coal Waste [EPA]Ba (μg/L)

Max

Min

own pH MCL = 2000 μ g/L Nat. Ox. Nat. Ox. | I. Ox. Nat. Ox. Forced Ox.

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge

1 10 100 1,000 10,000 100,000 1,000,000Fac. A (CFA) -Fac. A (AFA) +Fac. B (DFA) -Fac. B (BFA) +Fac. K (KFA) +CCW Ash [EPA]Fac. A (CGD) -Fac. A (AGD) +Fac. B (DGD) -Fac. B (BGD) +Fac. K (KGD) +Surface Imp. [EPRI]Fac. N (NAU) +UFac. N (NAW) +WFac. O (OAU) +UFac. O (OAW) +WFac. P (PAD) +UFac. Q (QAU) +UFac. A (CCC) -Fac. A (ACC) +Fac. B (DCC) -Fac. B (BCC) +Fac. K (KCC) +Fac. M (MAD) -Fac. M (MAS) +Landfill [EPRI]CCW FGD [EPA]Ash & Coal Waste [EPA]B (μg/L)

Max

Min

own pH DWEL= 7000

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge Nat. Ox. Nat. Ox. | I. Ox. Nat. Ox. Forced Ox.



### Figure 51 and Figure 52. Barium and Boron. Co mparison of maximum, mi nimum and natural pH concentrations observed in SR02 a nd SR03 extracts over the pH domain 5.4 ≤ pH ≤ 12.4. (key: - = NOx control off; + = NOx contro l on; U = unwashed gypsum; W = washed gypsum; Nat. Ox. = natural oxidation; Forced Ox. = fo rced oxidation; I.Ox. = inhibited oxidation).

### Characterization of Coal Cumbustion Residues II



### 81 0.01

0.1

1 10 100Fac. A (CFA) -Fac. A (AFA) +Fac. B (DFA) -Fac. B (BFA) +Fac. K (KFA) +CCW Ash [EPA]Fac. A (CGD) -Fac. A (AGD) +Fac. B (DGD) -Fac. B (BGD) +Fac. K (KGD) +Surface Imp. [EPRI]Fac. N (NAU) +UFac. N (NAW) +WFac. O (OAU) +UFac. O (OAW) +WFac. P (PAD) +UFac. Q (QAU) +UFac. A (CCC) -Fac. A (ACC) +Fac. B (DCC) -Fac. B (BCC) +Fac. K (KCC) +Fac. M (MAD) -Fac. M (MAS) +Landfill [EPRI]CCW FGD [EPA]Ash & Coal Waste [EPA]Cd (μg/L)

Max

Min

own pH MCL = 5 μ g/L Nat. Ox. Nat. Ox. | I. Ox. Nat. Ox. Forced Ox.

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge

0.1 1.0 10.0 100.0 1,000.0 10,000.0Fac. A (CFA) -Fac. A (AFA) +Fac. B (DFA) -Fac. B (BFA) +Fac. K (KFA) +CCW Ash [EPA]Fac. A (CGD) -Fac. A (AGD) +Fac. B (DGD) -Fac. B (BGD) +Fac. K (KGD) +Surface Imp. [EPRI]Fac. N (NAU) +UFac. N (NAW) +WFac. O (OAU) +UFac. O (OAW) +WFac. P (PAD) +UFac. Q (QAU) +UFac. A (CCC) -Fac. A (ACC) +Fac. B (DCC) -Fac. B (BCC) +Fac. K (KCC) +Fac. M (MAD) -Fac. M (MAS) +Landfill [EPRI]CCW FGD [EPA]Ash & Coal Waste [EPA]Cr (μg/L)

Max

Min

own pH MCL = 100 μ g/L

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge Nat. Ox. Nat. Ox. | I. Ox. Nat. Ox. Forced Ox.



### Figure 53 and Figure 54. Cadmium and Chromi um. Comparison of maxi mum, minimum and natural pH concentrations observed in SR 02 and SR03 extracts over the pH domain 5.4 ≤ pH ≤ 12.4. (key: - = NOx control off; + = NOx c ontrol on; U = unwashed gypsum; W = washed gypsum; Nat. Ox. = natural oxidation; Forced Ox. = forced oxidation; I.Ox. = inhibited oxidation).

### Characterization of Coal Combustion Residues II



### 82 0.1 1.0 10.0 100.0 1,000.0 10,000.0Fac. A (CFA) -Fac. A (AFA) +Fac. B (DFA) -Fac. B (BFA) +Fac. K (KFA) +CCW Ash [EPA]Fac. A (CGD) -Fac. A (AGD) +Fac. B (DGD) -Fac. B (BGD) +Fac. K (KGD) +Surface Imp. [EPRI]Fac. N (NAU) +UFac. N (NAW) +WFac. O (OAU) +UFac. O (OAW) +WFac. P (PAD) +UFac. Q (QAU) +UFac. A (CCC) -Fac. A (ACC) +Fac. B (DCC) -Fac. B (BCC) +Fac. K (KCC) +Fac. M (MAD) -Fac. M (MAS) +Landfill [EPRI]CCW FGD [EPA]Ash & Coal Waste [EPA]Co (μg/L)

Max

Min

own pH Nat. Ox. Nat. Ox. | I. Ox. Nat. Ox. Forced Ox.

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge

0.01 0.10 1.00 10.00 100.00Fac. A (CFA) -Fac. A (AFA) +Fac. B (DFA) -Fac. B (BFA) +Fac. K (KFA) +CCW Ash [EPA]Fac. A (CGD) -Fac. A (AGD) +Fac. B (DGD) -Fac. B (BGD) +Fac. K (KGD) +Surface Imp. [EPRI]Fac. N (NAU) +UFac. N (NAW) +WFac. O (OAU) +UFac. O (OAW) +WFac. P (PAD) +UFac. Q (QAU) +UFac. A (CCC) -Fac. A (ACC) +Fac. B (DCC) -Fac. B (BCC) +Fac. K (KCC) +Fac. M (MAD) -Fac. M (MAS) +Landfill [EPRI]CCW FGD [EPA]Ash & Coal Waste [EPA]Pb (μg/L)

Max

Min

own pH MCL = 15 μ g/L

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge Nat. Ox. Nat. Ox. | I. Ox. Nat. Ox. Forced Ox.



### Figure 55 and Figure 56. Cobalt and Lead. Comparison of ma ximum, mi nimum and natural pH

concentrations observed in SR02 and SR 03 extracts over the pH domain 5.4 ≤ pH ≤ 12.4. (key: - = NOx control off; + = NOx c ontrol on; U = unwashed gypsum; W = washed gypsum; Nat. Ox. = natural oxidation; Forced Ox. = forced oxidation; I.Ox. = inhibited oxidation).

### Characterization of Coal Cumbustion Residues II



### 83 0.1 1.0 10.0 100.0 1,000.0 10,000.0 100,000.0Fac. A (CFA) -Fac. A (AFA) +Fac. B (DFA) -Fac. B (BFA) +Fac. K (KFA) +CCW Ash [EPA]Fac. A (CGD) -Fac. A (AGD) +Fac. B (DGD) -Fac. B (BGD) +Fac. K (KGD) +Surface Imp. [EPRI]Fac. N (NAU) +UFac. N (NAW) +WFac. O (OAU) +UFac. O (OAW) +WFac. P (PAD) +UFac. Q (QAU) +UFac. A (CCC) -Fac. A (ACC) +Fac. B (DCC) -Fac. B (BCC) +Fac. K (KCC) +Fac. M (MAD) -Fac. M (MAS) +Landfill [EPRI]CCW FGD [EPA]Ash & Coal Waste [EPA]Mo (μg/L)

Max

Min

own pH DWEL= 200 μ g/L Nat. Ox. Nat. Ox. | I. Ox. Nat. Ox. Forced Ox.

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge

1.0 10.0 100.0 1,000.0 10,000.0Fac. A (CFA) -Fac. A (AFA) +Fac. B (DFA) -Fac. B (BFA) +Fac. K (KFA) +CCW Ash [EPA]Fac. A (CGD) -Fac. A (AGD) +Fac. B (DGD) -Fac. B (BGD) +Fac. K (KGD) +Surface Imp. [EPRI]Fac. N (NAU) +UFac. N (NAW) +WFac. O (OAU) +UFac. O (OAW) +WFac. P (PAD) +UFac. Q (QAU) +UFac. A (CCC) -Fac. A (ACC) +Fac. B (DCC) -Fac. B (BCC) +Fac. K (KCC) +Fac. M (MAD) -Fac. M (MAS) +Landfill [EPRI]CCW FGD [EPA]Ash & Coal Waste [EPA]Se (μg/L)

Max

Min

own pH MCL = 50 μ g/L

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge Nat. Ox. Nat. Ox. | I. Ox. Nat. Ox. Forced Ox.



### Figure 57 and Figure 58. Molybdenum and Seleni um. Comparison of maximum, minimum and natural pH concentrations observed in SR 02 and SR03 extracts over the pH domain 5.4 ≤ pH ≤ 12.4. (key: - = NOx control off; + = NOx c ontrol on; U = unwashed gypsum; W = washed gypsum; Nat. Ox. = natural oxidation; Forced Ox. = forced oxidation; I.Ox. = inhibited oxidation).

### Characterization of Coal Combustion Residues II



### 84 0.1 1.0 10.0 100.0 1,000.0Fac. A (CFA) -Fac. A (AFA) +Fac. B (DFA) -Fac. B (BFA) +Fac. K (KFA) +CCW Ash [EPA]Fac. A (CGD) -Fac. A (AGD) +Fac. B (DGD) -Fac. B (BGD) +Fac. K (KGD) +Surface Imp. [EPRI]Fac. N (NAU) +UFac. N (NAW) +WFac. O (OAU) +UFac. O (OAW) +WFac. P (PAD) +UFac. Q (QAU) +UFac. A (CCC) -Fac. A (ACC) +Fac. B (DCC) -Fac. B (BCC) +Fac. K (KCC) +Fac. M (MAD) -Fac. M (MAS) +Landfill [EPRI]CCW FGD [EPA]Ash & Coal Waste [EPA]Tl (μg/L)

Max

Min

own pH MCL = 2 μ g/L

Fly Ash | Scrubber Sludge | Gypsum | Fixated Scrubber Sludge Nat. Ox. Nat. Ox. | I. Ox. Nat. Ox. Forced Ox.



### Figure 59. Thallium. Compar ison o f maximum, minimum a nd natural pH concentrations

observed in SR02 and SR03 ex tracts over the pH domain 5.4 ≤ pH ≤ 12.4. (key: - = NOx control off; + = NOx contro l on; U = unwashed gypsum; W = washed gypsum; Nat. Ox. = natural oxidation; Forced Ox. = fo rced oxidation; I.Ox. = inhibited oxidation).

### Characterization of Coal Cumbustion Residues II



## 4. SUMMARY OF RESULTS, CONCLUS IONS AND RECOMMENDATIONS

The following sections present conclusions fr om the results presented in this report.

Tables 8 through 11 summarize the results obtained from this study for fly ash, FGD gypsum, scrubber sludge, and FSS, respectively. The set of 23 CCRs evaluated in this report reflects 84 and 74 percent, respectively, of the current and future facility c onfiguration types with acid gas scrubbers based on generating capacity, but only a limited number of facilities within each configuration type. Each table provides the follo wing attributes, and associ ated ranges, related to each material type and constituent examined:

1. Total content (mg/kg, dw) from acid digestion.

2. The minimum and maximum elemental concentr ations measured in laboratory leaching

test extracts over the domain of 5.4 ≤ pH ≤ 12.4 from leaching evaluation as a function of pH at LS=10 mL/g (SR002.1) and as a function of 0.5 ≤ LS ≤ 10 mL/g dw (SR003.1). This range is intended to represent the potential ra nge of leachate concentr ations expected to be observed in the field from management of each of the material types in monofilled management conditions. Concentration ranges for individual samples of each material type are compared in Section 3.3.2.

3. The minimum and maximum elemental concentr ations measured in laboratory leaching

test extracts when extracted with de ionized water only (“natural pH”) and 0.5 ≤ LS ≤ 10 mL/g dw (SR003.1). The resulting pH range is also indicated.

4. The MCL or DWEL and TC (as available) for each constituent to provide reference

concentrations for evaluation of the concentratio n results summarized as described above. However, the expected leachate concentrati on ranges derived directly from laboratory testing and probabilistic assessm ents do not include any diluti on and attenuation that may occur prior to impacting water resources. Pr evious studies have indicated dilution and

attenuation factors of as low as 2 to 10 on a national basis or as high as 8,000 at a particular site 25 

### . Thus, comparisons with the MCL, DWEL or TC for any constituent

must be done with caution.

5. Variability in extract concentration as a f unction of pH based on results from laboratory leaching testing (SR002.1). Classification of variability is as follows: (a) Low = concentration range ≤ 1 order of magnitude, (b) Med. = concentration range of 1 to 2 orders of magnitude, (c) High = concentra tion range of >2 orders of magnitude.

In addition, results are emphasized through coding as follows:

1. Expected concentration values that exceed either the MCL or DWEL for the given

constituent are in red bold typeface

.

2. Constituents are underlined in the column heading (e.g., Cd in Table 9) when one of the expected concentration ranges ex ceeds either the MCL or DWEL.

25 

### See Section 3.3.



### 8 5

### Characterization of Coal Combustion Residues II



### Based on the results of testing a nd evaluations in this study, the fo llowing conclusions are drawn:

1. For each CCR type the following constituents exceeded either the maximum contaminant level (MCL) or drinking water equivalent level (DWEL) in at least one laboratory leaching test condition over the range of pH and LS ratios considered, and therefore potentially may present unacceptable envi ronmental risks under some management

scenarios. These cases warrant more detailed evaluation, including consideration of sitespecific conditions.

a. Fly ash – antimony, arsenic, boron, cadmiu m, chromium, molybdenum, selenium

and thallium.

b. FGD gypsum – boron, cadmium, molybdenum, selenium and thallium.

c. Scrubber sludge – mercury, antimony, arsenic, boron, chromium, lead, molybdenum, selenium and thallium.

d. Fixated scrubber sludge – mercury, an timony, arsenic barium, boron, cadmium, chromium, lead, molybdenum, selenium and thallium.

However, (i) typically, evaluation results fr om only a subset of samples of a given material type exceeded the indicated criter ia, (ii) never did the full range reported exceed the indicated threshold, and (iii) this analysis does not account for additional dilution and attenuation processes that may occur under field management scenarios. These results suggest that (i ) consideration of dilution and attenuation factors for specific management scenarios may indicate that release concentrations may be higher than exposure concentr ations, and that release concentrations above the MCL or DWEL may not result in e xposure concentrations above those levels; (ii) linear partition coefficients (Kds) are not appropriate for representing source term release from CCRs for a range of constituents a nd materials; and, (iii) evaluation of individual CCR sources may indicate that th e environmental compatibility of specific types of CCRs with general management scenarios will depend on the source (reflected through leaching charac teristics) of the material.

2. Leaching of individual constituents may vary over several orders of magnitude, depending on the conditions of the management scenario. Thus, these results can be used to suggest design conditions that would redu ce or minimize constituent release (e.g., pH, and other conditions).

3. Leaching concentrations do not correlate w ith total content ex cept for specific

constituents in selected materials where the constituent (a) is weakly retained, and (b) leaching concentrations have a low variability relative to pH. Thus, total content is not a good indicator of leaching.

4. Results of this study suggest that it appears that Cr leachability is associated with the use of post-combustion NOx controls . This is based on a limited set of paired samples from the same facility operating with and with SC R or SNCR in use. This finding will be

further evaluated as additional data are collected.

5. The systematic leaching behavior of COPCs observed in the range of samples evaluated suggests that the geochemical mechanisms controlling leaching can be discerned and

8 6

### Characterization of Coal Cumbustion Residues II



### quantified using geochemical speciation modeli ng, which in turn, can serve as the basis for evaluating and improving design of CCR management scenarios. Development of generalized geochemical speciation models for the materials evaluated in this study is

recommended.

6. Ranges of concentrations of some constituents in laboratory leaching test extracts and field data included in this study suggest applicable concentration ranges for risk

evaluation are different from the concentra tion ranges used in a recent report by USEPA (EPA, 2007). The new information reported here will help provide a more up-to-date and comprehensive dataset for future risk assessments.

8 7Characterization of Coal Combustion Residues IITable 8. Fly Ash. Summary of results.HgSbAsBaBCdCrCoPbMoSeTlTotal in Material(mg/kg)0.04 -0.63 - 1570 - 90600 -1,500NA0.71.5-100 -20020 - 5040 - 9010 - 202 - 303 - 13Leaching test and assessment resultsConc. Rangefor5.4≤pH≤12.4<0.01- 0.5<0.3 -2007 -30090 -4,000200 -300,000<0.230-1 -4,000<0.3 -200<0.2 -2100 -40,0007 -400<0.3 -300(μg/L)Conc. range atnatural pH(7.7≤pH≤11.1)<0.01– 0.4<0.3 -507 -7590 –4,000300 –300,000<0.230-20 –4,000<0.3 -20<0.2 –0.7400 –40,0007 -400<0.3 -300MCL (or DWEL)(μg/L)26102,0007,000DWEL5100-15200DWEL502TC (μg/L)200-5,000100,0006,5001,0005,0005,0005,000-1,000-Variabilityrelative to pHLowtoHighMed.ToHighLow toMed.LowMed. toHighHighLow toMed.HighMed.Low toMed.Low toMed.Med.NA – not analyzed (total content for boron estimated based on leaching test results); ND – not determined.88Characterization of Coal Cumbustion Residues IITable 9. FGD Gypsum. Summary of results.HgSbAsBaBCdCrCoPbMoSeTlTotal inMaterial(mg/kg)0.01 -0.52 - 62 - 43 - 60NA0.30.5-6 -201 - 41 -122 - 122 - 300.6 - 2Leaching test and assessment resultsConc. Rangefor5.4≤pH≤12.4(μg/L)<0.01- 0.1<0.3 -9<0.5 -1040 -40040 -70,000<0.250-<0.3 -50<0.6 -50<0.2 -101 -4004 -3,000<0.3 -20Conc. rangeat natural pH(3.8≤pH≤8.1)<0.01– 0.1<0.3 -15<0.5 -940 -15040 –70,000<0.215-<0.3 -201 - 50<0.2 -123 -4004 –3,000<0.3 -20MCL (orDWEL whereindicated)(μg/L)26102,0007,000DWEL5100-15200DWEL502TC (μg/L)200-5,000100,0006,5001,0005,0005,0005,000-1,000-Variabilityrelative to pHLow -Med.LowLow -Med.LowLow -Med.HighMed. -HighLowLowLowLow -Med.LowNA – not analyzed (total content for boron estimated based on leaching test results); ND – not determined.89Characterization of Coal Combustion Residues IITable 10. Scrubber Sludge. Summary of results.HgSbAsBaBCdCrCoPbMoSeTlTotal in Material(mg/kg)0.04 –0.64 - 154 - 4080 –2,500NA0.3 –1.59 - 3501 - 402 - 309 - 302 - 42- 12Leaching test and assessment resultsConc. Rangefor5.4≤pH≤12.4(μg/L)<0.01-9<0.3 -200.6 -10020 –2,00020 –200,000<0.2 -4<0.8 -800<0.3 -250<0.2 -250.4 –1,5002 -300<0.3 -100Conc. range atnatural pH(6.5≤pH≤11.0)<0.01– 0.07<0.3 -100.6 -2030 -95020 –200,000<0.2 -42 -800<0.3 -60<0.2 -2510 –1,5002 -2002 -90MCL (or DWELwhere indicated)(μg/L)26102,0007,000DWEL5100-15200DWEL502TC (μg/L)200-5,000100,0006,5001,0005,0005,0005,000-1,000-Variabilityrelative to pHLow -HighLow -Med.Med. -HighLow -Med.Low -HighHighLowHighLowLow -HighMed.HighNA – not analyzed (total content for boron estimated based on leaching test results); ND – not determined.90Characterization of Coal Cumbustion Residues IITable 11. Fixated Scrubber Sludge. Summary of results.HgSbAsBaBCdCrCoPbMoSeTlTotal in Material(mg/kg)0.02 -1.05 - 203 - 7080 -1,000NA0.7 - 240 -1502 - 504 - 1009 - 302 - 300.8 - 8Leaching test and assessment resultsConc. Rangefor5.4≤pH≤12.4(μg/L)<0.01-30<0.3 -2000.5 -4,0009 -10,0006 -200,000<0.2 -20<0.3 -2,000<0.3150-<0.2 -5010 -40,0009 -1,0002 -100Conc. range atnatural pH(5.8≤pH≤12.3)<0.01– 0.7<0.3 -600.5 –4,00015 –10,000100 –200,000<0.2 -20<0.3 –2,000<0.350-<0.2 -5010 –40,0009 -5003 - 50MCL (or DWELwhere indicated)(μg/L)26102,0007,000DWEL5100-15200DWEL502TC (μg/L)200-5,000100,0006,5001,0005,0005,0005,000-1,000-Variabilityrelative to pHLow -HighLow -HighMed -HighLow -Med.HighLow -HighLowHighLowLowLow -Med.Low -Med.NA – not analyzed (total content for boron estimated based on leaching test results); ND – not determined.91

### Characterization of Coal Combustion Residues II



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