SEPA
Leaching Environmental
Assessment Framework
(LEAF) How-To Guide
Understanding the LEAF Approach and
How and When to Use It
SW-846 Update VII
Revision 1
May 2019
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NOTICE/DISCLAIMER
The United States Environmental Protection Agency (U.S. EPA, or the Agency), through its Office of Land
and Emergency Management and Office of Research and Development, funded the preparation of this
report under EPA Contract Nos. EP-D-11-006 and EP-W-10-055. This report was subjected to the Agency's
peer and administrative review and was approved for publication as an EPA document. Any opinions,
findings, conclusions, or recommendations do not change or substitute for any statutory or regulatory
provisions. This document does not impose legally binding requirements, nor does it confer legal rights,
impose legal obligations, or implement any statutory or regulatory provisions. Mention of trade names or
commercial products is not intended to constitute endorsement or recommendation for use.
ACKNOWLEDGEMENTS
Authors
This document was prepared for the U.S. EPA Office of Land and Emergency Management and Office of
Research and Development. This document was prepared and edited by Eastern Research Group, Inc.
(ERG) for EPA under EPA Contracts EP-D-11-006 and EP-W-10-055.
The authors of this guide are David S. Kosson (Vanderbilt University), Andrew Garrabrants (Vanderbilt
University), Susan Thorneloe (EPA, Office of Research and Development), Daniel Fagnant (EPA, Office of
Land and Emergency Management), Greg Helms (EPA, Office of Land and Emergency Management), Katie
Connolly (ERG), and Molly Rodgers (ERG).
In addition to input we received from the peer review process, contributors and reviewers of this guide
include Hans van der Sloot (Hans van der Sloot Consultancy, The Netherlands), Schatzi Fitz-James (EPA,
Office of Land and Emergency Management), Paul Lemieux (EPA, Office of Research and Development),
Ken Ladwig (Electric Power Research Institute), Connie Senior (ADA-ES), and Craig Benson (University of
Virginia).
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Notice/Disclaimer & Acknowledgements
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Table of Contents
NOTICE/DISCLAIMER i
ACKNOWLEDGEMENTS i
List of Tables v
List of Figures vi
List of Highlight Boxes viii
Acronyms and Abbreviations ix
Abstract x
Key Definitions xi
1. An Introduction to LEAF and this Guide 1-1
1.1 What is the Purpose of this Guide? 1-1
1.2 Who Can Benefit from this Guide? 1-2
1.3 What is LEAF? 1-2
1.3.1 Why was LEAF Developed? 1-3
1.3.2 Why Perform Leaching Tests? 1-6
1.3.3 When Can LEAF be Used? 1-6
1.4 What Topics Are Covered in this Guide? 1-7
2. Understanding the Leaching Process 2-1
2.1 What is Leaching? 2-1
2.2 What is a Source Term? 2-1
2.3 What is the Available Content of a CO PC? 2-2
2.4 How Does Leaching Occur? 2-2
2.4.1 The Extent of Leaching Through Liquid-Solid Partitioning (LSP) 2-4
2.4.2 The Rate of Leaching (Mass Transport) 2-7
2.4.3 Leachability of a Material in the Field 2-7
3. An Overview of LEAF 3-1
3.1 Analytical Leach Test Methods 3-1
3.1.1 U.S. EPA Method 1313: pH-Dependent LSP 3-3
3.1.2 U.S. EPA Method 1314: Percolation Column 3-5
3.1.3 U.S. EPA Method 1315: Rates of Mass Transfer 3-8
3.1.4 U.S. EPA Method 1316: L/S-Dependent LSP 3-10
3.1.5 Validation of LEAF Tests 3-12
3.1.6 Relationship between LEAF and Single Point Tests (e.g., TCLP, SPLP) 3-13
3.2 Building a Testing Program 3-14
3.2.1 Material Collection for Leaching Tests 3-15
3.2.2 Analytical Parameters 3-15
3.2.3 Suggested Best Practices for Conducting LEAF Tests 3-16
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Table of Contents (Continued)
3.2.4 Quality Assurance/Quality Control 3-17
3.2.5 Testing and Analytical Costs 3-21
3.2.6 Processing Time 3-23
3.3 LEAF Data Management Tools 3-24
3.3.1 Laboratory Data and Import Templates 3-24
3.3.2 Data Management with LeachXS™ Lite 3-25
3.3.3 Pre-Existing Leaching Data 3-27
4. Developing Leaching Evaluations using LEAF 4-1
4.1 Applications of LEAF 4-2
4.1.1 Material Characterization 4-2
4.1.2 Beneficial Use Evaluation 4-3
4.1.3 Treatment Effectiveness 4-3
4.1.4 Miscellaneous Uses 4-3
4.2 Developing an Assessment Framework 4-3
4.2.1 A Stepwise Assessment Approach 4-4
4.2.2 Assessment Objectives 4-5
4.2.3 Comparing Test Results to Threshold Values 4-6
4.2.4 Screening Level Assessments 4-11
4.2.5 Scenario Based Assessments 4-18
4.3 Accounting for Environmental Processes That Can Influence Leaching 4-23
4.3.1 Reducing and Oxidizing Conditions 4-24
4.3.2 Carbonation of Alkaline Materials 4-27
4.3.3 Microbial Activity 4-27
4.3.4 Complexation with Dissolved Organic Matter 4-28
4.3.5 Co-precipitation of Arsenic with Calcium 4-28
4.3.6 Chemical Interactions 4-29
4.4 Performing Common Analyses in Leaching Assessments 4-32
4.4.1 Determining the Available Content from Method 1313 Data 4-32
4.4.2 Interpolating Method 1313 Data to Endpoint Target pH 4-36
4.4.3 Calculating Water Contact and Assessment Time: Liquid-Solid Ratio (L/S, percolation
mode) and Liquid-Area Ratio (L/A, flow around mode) 4-37
4.4.4 Interpreting Observed Liquid Solid Partitioning (LSP) Behavior 4-38
4.4.5 Identifying Solubility- and Available Content-Limited Leaching 4-44
4.4.6 Understanding Mass Transport Parameters (Low Permeability Materials) 4-46
4.4.7 Considering Dilution and Attenuation in an Assessment Ratio 4-49
4.4.8 Integrating Source Terms into Models 4-50
5. Case Studies of Using LEAF for Assessments 5-1
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Table of Contents (Continued)
5.1 Screening Assessment: Evaluating Coal Combustion Fly Ash for Use as Structural Fill
Material 5-1
5.1.1 Definition of the Assessment Scenario 5-2
5.1.2 Testing Program and Results 5-3
5.1.3 Total and Available Content Screening 5-5
5.1.4 Equilibrium-pH Screening (Method 1313) 5-6
5.1.5 Full LSP Screening (Method 1313 and Method 1314) 5-8
5.1.6 Consideration of an Alternate Coal Combustion Fly Ash 5-11
5.2 Scenario Assessment: Evaluating Treatment Effectiveness of a Cement-Based
Stabilization/Solidification (SS) Process 5-13
5.2.1 Definition of the Assessment Scenario 5-14
5.2.2 Testing Plan 5-15
5.2.3 Material Characterization and Environmental Conditions 5-15
5.2.4 Mass Transport Assessment 5-18
5.2.5 LSP Considerations 5-20
5.2.6 Treatment Effectiveness 5-22
5.2.7 Comparison to Reference Thresholds 5-24
6. Test Your Knowledge 6-1
6.1 Paula's First Assignment 6-1
6.2 Characterizing the Fly Ash 6-2
6.3 Preliminary Available Content Evaluation 6-5
6.4 Paula's Plausible Range of pH Dependent Leaching 6-8
6.5 Confirming Solubility Limited Leaching 6-10
6.6 Conclusions on Use for Structural Fill 6-11
7. Useful Resources 7-1
8. References 8-1
Appendix A: Leaching Methods in the U.S. and European Union A-l
Appendix B: Graphical and Tabular LEAF Results for Case Study (Section 5) B-l
Leaching Environmental Assessment Framework (LEAF) How-To Guide
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List of Tables
Table 1-1. Overview of Topics in the How-To Guide 1-7
Table 3-1. Comparison of Test Parameters for LEAF Leaching Methods 3-2
Table 3-2. Potential Applications of Method 1313 Data 3-5
Table 3-3. Potential Applications of Method 1314 Data 3-7
Table 3-4. Potential Applications of Method 1315 Data 3-10
Table 3-5. Potential Applications of Method 1316 Data 3-11
Table 3-6. Precision Data for LEAF Test Methods based on Interlaboratory Validation Studies 3-12
Table 3-7. Example Analytical Method Detection Limit [MDL] and Lower Limit of Quantitation
(LLOQ) Values Compared to U.S. Drinking Water Standards 3-20
Table 3-8. Estimated Laboratory Costs for Method 1313 3-22
Table 3-9. Estimated Laboratory Costs for Method 1314 3-22
Table 3-10. Estimated Laboratory Costs for Method 1315 3-23
Table 3-11. Estimated Laboratory Costs for Method 1316 3-23
Table 3-12. Processing Time 3-24
Table 4-1. Summary of Suggested Test Methods and Analyses for Screening Assessments 4-9
Table 4-2. Summary of Suggested Test Methods and Analyses for Scenario-Based Assessments 4-10
Table 4 3. Summary of Observed pH and Redox Conditions for Field Scenarios 4-20
Table 4-4. Comparison of Method 1313 Eluate Concentrations atpH 2, 9,13 and Reported
Available Content: Contaminated smelter site soil (CFS), coal combustion fly ash (EaFA) and
solidified waste form (SWA) 4-34
Table 5-1. Total Content and LEAF Testing Results for EaFA Coal Combustion Fly Ash 5-4
Table 5-2. Initial Screening Values for EaFA Fly Ash Using LEAF Leaching Estimates 5-6
Table 5-3. Equilibrium-pH Assessment of Fly Ash 5-7
Table 5-4. Full LSP Screening Assessment of EaFA Fly Ash Fill Material 5-10
Table 5-5. LEAF Coal Fly Ash CaFA Total Content Analysis and LEAF Leaching Test Results 5-12
Table 5-6. Leaching Assessment Ratios for Alternative Coal Combustion Fly Ash CaFA 5-13
Table 5-7. Total Content Analysis of Contaminated Field Soil (CFS) and Monolithic Material (S/S-
CFS) 5-16
Table 5-8. Precipitation data for Nashville, TN 5-18
Table 5-9. Comparison of leaching assessment results to reference thresholds 5-24
Leaching Environmental Assessment Framework (LEAF) How-To Guide
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List of Figures
Figure 1-1. LEAF test methods in leaching evaluations and the chemical factors influencing
leaching estimated by each test method. Leaching analyses presented in this guide(left column)
utilize the test methods in the boxes to the right of the analysis. Methods in grey are optional
depending on the specifics of a scenario. A red X indicates the leaching analysis does not use test
for the environmental parameter 1-5
Figure 1-2. LEAF testing can estimate leaching from a material with varying environmental
factors. A source term to represent leaching in the environment can be developed from LEAF
testing 1-6
Figure 2-1. Various environmental assessment scenarios showing a source term for leaching with
transport to the water table and through the groundwater to a point of compliance. Note that the
point of compliance may be at the unit boundary of the material for some applications 2-2
Figure 2-2. Solubility of metal hydr(oxides) in water as a function of pH 2-5
Figure 2-3. Illustration of the changes in LSP leaching behavior as the system L/S increases 2-6
Figure 3-1. Experimental scheme of U.S. EPA Method 1313 as a parallel batch extraction test 3-3
Figure 3-2. Example results from Method 1313 for leaching from a coal combustion fly ash
(EaFA): Titration curve (top), chromium eluate concentration (lower, left) and chromium release
with available content displayed (lower, right) 3-4
Figure 3-3. Experimental scheme of U.S. EPA Method 1314 as a percolation column test 3-6
Figure 3-4. Example results from Method 1314 for lead as a function of L/S from a contaminated
smelter site soil (CFS): Concentration (top, left), eluate pH (top, right) and cumulative release on
Cartesian axis (lower, left) and logarithmic axis (lower, right) 3-7
Figure 3-5. Experimental scheme of U.S. EPA Method 1315 as a tank leaching test 3-8
Figure 3-6. Example results from Method 1315 for selenium shown as a function of leaching time
from a solidified waste form (SWA): Eluate pH (upper, left), eluate concentration (upper, right),
mean interval flux (lower, left) and cumulative release (lower, right) 3-9
Figure 3-7. Experimental scheme of U.S. EPA Method 1316 as a parallel batch extraction test 3-10
Figure 3-8. Example arsenic results for Method 1316 from a contaminated smelter site soil (CFS):
Eluate pH (top), eluate concentration (lower, left) and release (lower, right) 3-11
Figure 3-9. Comparison of TCLP (pink square) and SPLP (green triangle) results to pH-dependent
leaching from Method 1313 for a contaminated smelter site soil (CFS; top), a solidified waste form
(SWA; center) and a coal combustion fly ash (EaFA; bottom) 3-14
Figure 3-10. Example of a Microsoft Excel® data template for recording and archiving laboratory
and analytical information from LEAF tests 3-25
Figure 3-11. LeachXS™ Lite program structure showing data inputs, databases and outputs 3-26
Figure 3-12. LeachXS™ Lite interface for comparison of granular materials showing the approach
for comparing pH-dependent arsenic data for three CCR materials 3-27
Figure 4-1. Example assessment hierarchy presenting options for progressively working from
more bounding assessments to less bounding assessments based on levels of leaching
information 4-5
Figure 4-2. Method 1313 LSP results over an applicable pH domain compared to total content,
available content and a reference threshold 4-6
Figure 4-3. Screening level assessments, test methods and assumed leaching conditions 4-12
Leaching Environmental Assessment Framework (LEAF) How-To Guide
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List of Figures (Continued)
Figure 4-4. Maximum concentration over an applicable scenario pH domain for cadmium (left)
and selenium (right) from Method 1313 testing of a coal combustion fly ash (CaFA), a
contaminated soils (CFS) and a solidified waste form (SWA) 4-16
Figure 4-5. Full LSP screening data showing examples where pH effects dominate LSP (barium in
solidified waste form, SWA) and where L/S-dependence influences maximum LSP concentration
(boron in coal fly ash, EaFA) 4-18
Figure 4-6. Flowchart for using LEAF for leaching assessments based on water contact 4-21
Figure 4-7. Comparison of geochemical simulation of iron leaching at various pH/redox
conditions (pH + pE) to laboratory test results for mixed municipal solid waste (MSW) landfill
material 4-27
Figure 4-8. Method 1314 (left) and Method 1313 (right) for eluate pH, calcium, and arsenic 4-29
Figure 4-9. Comparison of Method 1313 and Method 1316 for calcium, arsenic and chromium
leaching from low-calcium fly ash (EaFA) and high-calcium fly ash (CaFA) 4-31
Figure 4-10. Relationship between total content, available content and measured pH-dependent
release for a cationic metal 4-33
Figure 4-11. Comparison of eluate concentrations at specified pH values of 2, 9, and 13 used to
determine the available content: Contaminated smelter site soil (CFS; left), coal combustion fly
ash (EaFA; middle) and solidified waste form (SWA; right) 4-35
Figure 4-12. Comparison of measured Method 1313 eluate data (red dots) for a contaminated
smelter site soil (CFS) with interpolated test results (green squares) using linear interpolation of
log-transformed concentration data 4-37
Figure 4-13. Statistical distribution of time to reach L/S=2 L/kg-dry or L/S=10 L/kg-dry based on
national distributions of precipitation and infiltration for CCR landfills 4-38
Figure 4-14. LSP patterns for classical pH-dependence leaching behaviors 4-40
Figure 4-15. LSP behavior for different example waste forms: coal combustion fly ash (CaFA and
EaFA), smelter site soil (CFS) and solidified waste (SWA) 4-42
Figure 4-16. LSP behavior for different example waste forms: coal combustion fly ash (CaFA and
EaFA), smelter site soil (CFS) and solidified waste (SWA) 4-43
Figure 4-17. Available content-limited leaching of boron and solubility-limited leaching of
chromium from a coal combustion fly ash (EaFA) based on the results of Method 1313 (left) and
Method 1316 (right) 4-45
Figure 4-18. Comparison of mass transport data (green triangles, Method 1315) to equilibrium
data shown as a function of pH (red circles, Method 1313) for a contaminated lead smelter soil
(CFS) 4-48
Figure 5-1. COPC concentrations as a function of pH (left) and L/S (right) for a coal combustion fly
ash (EaFA) for full LSP screening assessment: Method 1313 interpolated), Method 1314, and
Method 1316 5-9
Figure 5-2. pH characterization of contaminated field soil (CFS) and monolithic material (S/S-CFS) 5-17
Figure 5-3. Method 1315 test results for arsenic and selenium release 5-19
Figure 5-4. Method 1313 and 1314 test results for CFS and SS-CFS 5-21
Figure 5-5. Mass transport limited leaching of arsenic, cadmium, lead, selenium, chloride, and
nitrate 5-23
Leaching Environmental Assessment Framework (LEAF) How-To Guide
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List of Highlight Boxes
Leaching Key Terms 1-2
LEAF Leaching Tests 3-1
LEAF Key Terms 3-3
Water Contact Key Terms 3-5
Analytical QA/QC Solutions 3-19
Key Attributes of the Beneficial Use Case Study 5-2
Key Attributes of the Treatment Effectiveness Case Study 5-15
Leaching Environmental Assessment Framework (LEAF) How-To Guide
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Acronyms and Abbreviations
Acronym
Definition
ANC
acid neutralization capacity
CaFA
material specimen code for a coal combustion fly ash
CCR
coal combustion residue
CERCLA
Comprehensive Environmental Response, Compensation, and Liability Act
CFS
material specimen code for a contaminated smelter site soil
COPC(s)
constituent(s) of potential concern
DAF(s)
dilution and attenuation factor(s)
DOC
dissolved organic carbon
EaFA
material specimen code for a coal combustion fly ash
EC
electrical conductivity [mV]
EDD
electronic data deliverable
EPACMTP
EPA Composite Model for Leachate Migration with Transformation Products
IWEM
Industrial Waste Management Evaluation Model
L/A
liquid-to-surface area ratio [mL/cm3]
L/S
liquid-to-solid ratio [mL/g-dry]
LDR
Land Disposal Restrictions
LEAF
Leaching Environmental Assessment Framework
LLOQ
lower limit of quantification
LSP
liquid-solid partitioning
MCL
maximum contaminant level
MDL
method detection limit
MSWI
municipal solid waste incinerator
ORCHESTRA
Objects Representing Chemical Speciation and Transport
ORP
oxidation/reduction potential
QAPP
Quality Assurance Project Plan
QA/QC
quality assurance/quality control
POC
point of compliance
RCRA
Resource Conservation and Recovery Act
redox
reduction/oxidation
RSDr
replicate standard deviation for repeatability
RSDr
replicate standard deviation for reproducibility
RSL
Regional Screening Level
SAB
Science Advisory Board
SPLP
Synthetic Precipitation Leaching Procedure
SWA
material specimen code for a solidified waste form
TCLP
Toxicity Characteristic Leaching Procedure
U.S. EPA
United States Environmental Protection Agency
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Acronyms and Abbreviations
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Abstract
This document provides guidance on the use and application of the Leaching Environmental Assessment
Framework (LEAF) published by the United States Environmental Protection Agency (U.S. EPA or the
Agency). The purpose of this guide is to provide an understanding of LEAF to facilitate its broader use in
environmental assessment. LEAF is a leaching evaluation framework, which consists of four leaching tests
(i.e., U.S. EPA Methods 1313, 1314, 1315 and 1316), data management tools, and approaches for
estimating constituent release from solid materials. The LEAF tests consider the effect on leaching of key
environmental conditions and waste properties known to significantly affect constituent release. This
document provides background on the LEAF tests as well as information on how to perform the tests and
how to understand the test results. This document also provides guidance on the application of LEAF to
assess leaching potential of COPCs from solid waste matrices for beneficial use, disposal, treatment, and
remediation applications. In addition, this document addresses frequently asked questions about the four
LEAF test methods, data management and reporting using freely-available software, and potential
applications of the LEAF approach.
The approach to testing and evaluation presented in this guide is progressive in that each of the different
methods provide information on the effect of different environmental parameters on leaching. Therefore,
investment in each increment of additional testing and evaluation may reward the user with increasingly
refined estimates of leaching. Traditionally, the potential for environmental impact through leaching of
COPCs from a solid material disposed or otherwise in contact with the land into ground water or surface
water can be estimated using one or more single-point leaching tests that represent a specific scenario or
set of environmental conditions. Alternatively, LEAF testing may provide more reliable release estimates
by assessing the impact on leaching of environmental factors and waste properties that are known to
significantly affect constituent leaching and which vary in the environment and across waste forms. By
testing over a range of values for release-controlling factors, the LEAF approach allows for flexibility in
that a single data set can be used to evaluate multiple potential management scenarios for a material
(e.g., disposal or beneficial use) under varied or site-specific environmental conditions.
The four LEAF test methods presented in this document have undergone interlaboratory validation for
use with inorganic constituents of potential concern (COPCs), such as metals and radionuclides, and have
been incorporated into the U.S. EPA compendium of laboratory methods, SW-846 (see
https://www.epa.gov/hw-sw846/sw-846-compendium). The Agency recognizes that the leaching of
organic constituents will follow the same principles (i.e., that key environmental conditions or waste
properties that significantly affect leaching can be identified) but may require different testing methods
to address controlling properties. Therefore, the next steps for the Agency are to adapt these methods or
develop new methods applicable to evaluating the potential release of organic COPCs from waste or other
materials.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Abstract
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Key Definitions
Term Definition
Assessment Ratio
The estimated maximum leaching concentration for a COPC divided by the
threshold value for a scenario.
Available Content
The fraction of the total concentration of a constituent in the solid phase
(mg/kg-dry) that potentially may leach over a reasonably near-term
timeframe (e.g., 100 y).
Available Content-
Limited Leaching
A liquid-solid partitioning endpoint at which the available content of a
constituent in the solid phase limits the amount leached into aqueous phase
(i.e., the aqueous phase is less than the saturation concentration and the
solid phase is depleted of the constituent's available content).
Chemical Species
Particular forms of a chemical element or compound (e.g., ions, molecules,
molecule fragments, etc.) that contribute to the measured concentration of
a constituent in a given liquid or solid phase.
Constituent
A chemical element or species in the liquid or solid phase, typically
chemically analyzed based on total content of chemical species or
compound.
Constituent of
Potential Concern
(COPC)
A constituent that may be present at concentrations of regulatory,
environmental, or human health significance due to their toxicity or other
properties.
Eluant
The water or aqueous solution used to contact or extract constituents from a
material during a laboratory test.
Eluate
The aqueous solution, analyzed as part of a laboratory test, which results
from contact of an eluant with the tested material.
Equilibrium Limited
Leaching
A liquid-solid partitioning endpoint at which the leaching of constituents is
limited by the amount of material leached at equilibrium conditions (e.g.,
available content limited leaching, solubility-limited leaching.)
Flow-through
The water contact scenario when precipitation, infiltrating water, or
groundwater flows around the external surface area of a low-permeability
material (e.g., cement-treated wastes, compacted materials) and release
occurs at the interface between the flowing water and the material.
Leachant
The water or aqueous solution contacting a material under field conditions
(e.g., infiltrating water, groundwater).
Leachate
The aqueous solution resulting from leachant contact with a material under
field conditions.
Mass Transport
(diffusion) - Limited
Leaching
The release from solid material when leaching potential is less than
equilibrium liquid-solid partitioning, typically constrained by the rate of
diffusion through the material being leached.
Percolation
The water contact scenario in which precipitation, infiltrating water, or
groundwater, moves through the contiguous voids of a porous material and
leaching occurs at the solid-liquid interface between the percolating fluid
and the solid material.
Solubility-Limited
Leaching
A liquid-solid partitioning endpoint at which the solubility of a constituent in
the aqueous phase or eluant limits the leaching process (i.e., the aqueous
phase concentration is at saturation yet available constituent remains in the
solid phase).
Sorption-Controlled
Leaching
A liquid-solid partitioning endpoint at which neither the solid nor the
aqueous phase limits leaching, but sorption to mineral or organic matter
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Key Definitions
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surfaces controls the concentration measured in the aqueous phase or
eluant.
Source Term
A numerical or model-based estimate of constituent release used to
represent leaching from material in a field application and which may also be
used for subsequent fate and transport modeling.
Total Content
The concentration of a constituent in the solid material (mg/kg-dry)
accounting for all species.
Washout
A rapid release of constituents resulting from highly soluble species rapidly
dissolving in water percolating through a material; usually indicated during
Method 1314 by a decrease in leaching concentration of approximately one
order of magnitude or more from L/S = 0.2 mL/g-dry to 2.0 mL/g-dry.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Key Definitions
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1. An Introduction to LEAF and this Guide
1.1 What is the Purpose of this Guide?
The purpose of this document is to provide information that improves understanding and supports
application of the Leaching Environmental Assessment Framework (LEAF) published by the United States
Environmental Protection Agency1 (U.S. EPA, or the Agency) and, thereby, facilitate its broader use. LEAF
is a leaching evaluation framework consisting of four leaching tests (i.e., U.S. EPA Methods 1313, 1314,
1315 and 1316; U.S. EPA, 2012f, 2013a, 2013b, 2013c) data management tools, and scenario assessment
approaches that are designed to work together to provide an estimate of the release of constituents of
potential concern (COPCs) from a wide range of solid materials. This document provides background and
technical support for implementing LEAF to assess leaching potential of COPCs from solid waste matrices
for beneficial use,2 disposal, treatment and remediation applications. In addition, this document is
designed to address frequently asked questions about the four EPA LEAF leaching test methods, data
management and reporting using the freely available LeachXS™ Lite software,3 and potential applications
of the LEAF approach. For detailed information on EPA's SW-846 Methods, see https://www.epa.gov/hw-
sw846/sw-846-compendium.
The LEAF test methods presented in this document have been validated for inorganic COPCs (U.S. EPA,
2012c, 2012d). The Agency believes the methodology in this guide is applicable to the leaching of heavy
metals, and by extension, inorganic radionuclides.4 Next steps for the Agency are to adapt these methods
or develop new tests for estimating the leaching of organic COPCs. Although these leaching tests for
organic COPCs will be based on the LEAF principles (i.e., testing protocols addressing identified
environmental parameters having the greatest effect on COPC release), the specifics of organic COPC
leaching may require development of different testing methods (i.e., different environmental factors may
determine leaching behavior of organic COPC than for inorganic COPC). Every effort will be made to
ensure the organic COPC test methods are compatible with the methods for inorganic COPC leaching, with
the overall goal of creating an integrated set of tests that can be reliably used to evaluate the leaching
potential of a broad range of wastes containing inorganic and/or organic COPCs.
1 EPA worked collaboratively with parallel efforts in the European Union to develop and harmonize test methods to support
data comparisons. (Appendix A of this document identifies analogous leaching tests)
2 EPA's Methodology for Evaluating Beneficial Uses of Industrial Non-Hazardous Secondary Materials presents a voluntary
approach for evaluating the potential adverse impacts to humans and the environment from a wide range of industrial non-
hazardous secondary materials and their associated beneficial uses. Prior to beneficially using secondary materials in any
projects, interested individuals or organizations should consult with the relevant state and federal environmental agencies to
ensure proposed uses are consistent with state and federal requirements.
3 LeachXS™ Lite is a free, limited capability version of the LeachXS™ decision support software. As a data management tool for
use with LEAF data, LeachXS™ Lite is available for licensing at no cost at www.vanderbilt.edu/leaching.
4 Chemically, inorganic radionuclides behave similarly to inorganic species that are not radionuclides. Therefore, the LEAF
leaching test methods may be applicable to estimating radionuclide leaching release provided appropriate modifications are
taken to ensure adequate worker protection and materials management and disposal during and after testing. LEAF can be
applied to radionuclides for the purposes of evaluating leaching potential; however, LEAF does not address radiological risks
associated with radionuclides.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Introduction to LEAF and this Guide
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1.2 Who Can Benefit from this Guide?
The intended audience for this guide includes waste generators; decision-makers for waste management,
such as beneficial use of non-hazardous industrial secondary materials, waste treatment effectiveness,
and site remediation; risk assessors; technical consultants; state environmental agency officials; analytical
laboratories; and other interested stakeholders to the degree that their use is consistent with existing
federal and state regulations and policies.
1.3 What is LEAF?
Leaching of COPCs from solid materials to surrounding
soils, groundwater, or surface water can occur in the
environment whenever a material is placed on or in the
ground. A leaching assessment provides an estimate of
the extent and rate of COPC release to the environment
through waterborne pathways. In addition, leaching
assessments can provide insights into material durability
under environmental conditions based on the
dissolution and transport of the primary constituents
that comprise the solid matrix. Laboratory leaching tests
provide the basis for estimating which constituents will
leach, the rate at which they will leach, and the factors
that control leaching. In addition, the data obtained
from leaching tests can be used to develop a
quantitative description of the leaching behavior of a
material, referred to as a leaching source term,
representing the release of COPCs from a material under
defined management scenario conditions.
LEAF is an integrated framework that includes four
laboratory methods for characterizing the leaching
behavior of solid materials under specified release
conditions. It also provides data management tools for
collecting leaching data, comparing leaching behavior
between materials, reporting graphical and tabular results, and suggesting approaches for using leaching
data to support leaching assessments. LEAF provides a consistent approach to estimate leaching of COPCs
from a wide range of solid materials including as-generated wastes, treated wastes (e.g.,
solidified/stabilized soils and sediments), secondary materials (e.g., blast furnace slags), energy residuals
(e.g., coal fly ash, air pollution control residues), industrial processing residuals (e.g., mining, and mineral
processing wastes) and contaminated soil or sediments. The LEAF test methods consider the effect on
leaching of important leaching factors, such as pH, liquid-to-solid ratio (L/S) and physical form of the
material, that represent a range of plausible field conditions (U.S. EPA, 2010). Thus, a single set of leaching
data can be used to evaluate multiple management options or scenarios.
The LEAF framework provides the flexibility to generate evaluations ranging from screening assessments
to detailed source characterization for site-specific or national assessments. Generally, as used in this
Leaching Key Terms
Chemical Species—Particular forms of a
chemical element or compound (e.g., ions,
molecules, molecule fragments, etc.) that
contribute to the measured concentration
of a constituent in a given liquid or solid
phase.
Constituent—A chemical element, species,
or compound in the liquid or solid phase,
typically chemically analyzed based on
total content of chemical species or
compound.
Constituents of Potential Concern (COPCs) —
Constituents that may be present at
concentrations of regulatory,
environmental, or human health
significance due to their toxicity or other
properties.
Source Term— A numerical or model
based estimate of constituent release used
to represent leaching from material in a
field application and which may also be
used for subsequent fate and transport
modeling.
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document, a screening level assessment means an evaluation based on the laboratory test results using
the LEAF methods alone. A detailed source characterization uses the leach test results in a defined use
scenario, including anticipated environmental conditions. Evaluating leach test results in the context of a
particular scenario provides a more refined and detailed assessment of the likely impact of materials
placement on land and COPC release under the conditions defined in the scenario. Therefore, testing can
be tailored to address particular assessment objectives and the level of information needed to support
decision-making. For some applications, leaching assessments using LEAF may be simple comparisons of
leaching results to relevant benchmarks to evaluate performance of a material in a particular
management scenario or identify COPCs with the potential for adverse impacts to the environment. In
many cases, site-specific factors must be considered, and leaching test results may not directly reflect
concentrations at the point of compliance. More complex assessments may require detailed
characterization of leaching behavior sufficient to support groundwater (or surface runoff) fate and
transport modeling between a source term and a point of compliance (POC), as determined by applicable
state and federal regulations and policies. A number of models are available (U.S. EPA, 2015, 2017a) that
can evaluate the fate and transport of COPCs in the environment using a source term derived from LEAF.
LEAF incorporates a consistent set of standardized testing methods and either generic or application-
specific release models. Free publicly available data management and visualization software, LeachXS™
Lite including Microsoft Excel® templates, is provided to facilitate data management, evaluation, and
reporting as part of LEAF assessments.
1.3.1 Why was LEAF Developed?
Traditionally, the potential for environmental impact through leaching of COPCs from a solid material
disposed or otherwise in contact with the land into ground water or surface water has been estimated
using one or more single-point leaching tests that represent a specific scenario or set of environmental
conditions. For example, the Toxicity Characteristic Leaching Procedure, TCLP (U.S. EPA, 1992), simulates
conditions that may be found within a municipal solid waste landfill while the Synthetic Precipitation
Leaching Procedure, SPLP (U.S. EPA, 1994), mimics contact with a synthetic acidic infiltrate (U.S. EPA,
2010). Other single point test methods also simulate specific scenarios, e.g., ASTM D3987-12 (2012).
Single-point test approaches can be appropriate for screening or classification purposes and TCLP remains
required for specific regulatory applications such as hazardous waste classification under the toxicity
characteristic regulation (40 CFR 261.24) and for many waste treatment regulatory standards. However,
the U.S. EPA desired a flexible leaching characterization framework that can be tailored for use over a
wide range of material types and release scenarios. Broad application of a uniform leaching
characterization approach would enable comparison of leaching behavior between materials or between
release scenarios.
Another approach that is sometimes used to assess constituent release in the environment involves
defining liquid-solid partitioning as constants (Kd values) and modeling the movement of constituents
through groundwater with constant partitioning values to soils and other media. This approach assumes
that partitioning of COPCs from a solid material is proportional to the total COPC concentration (i.e., a
linear partitioning relationship between the total content of the COPC in the material and contacting
water). The Kd approach considers adsorption to mineral surfaces as a primary partitioning mechanism
and may be a reasonable description for leaching or groundwater fate and transport of COPCs under dilute
conditions. However, the partitioning of many constituents between a solid material and a contacting
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liquid is not linear over varying values of pH or L/S and, therefore, has many of the same drawbacks as
single point leach tests. Similarto single point leach tests, a linear partitioning coefficient does not provide
the mechanistic understanding nor represent the important processes and factors that control leaching
(e.g., solubility constraints, available content, or the physical form of the material). Thus, the Kd approach
would not be a reasonable description of leaching when COPC solubility limits leaching, when only a
fraction of the COPC is leachable, or when the available content limits the observed solution concentration
(Thorneloe, Kosson, Sanchez, Garrabrants, & Helms, 2010; U.S. EPA, 2014c).
In 1991 and 1999, the Science Advisory Board (SAB) of the U.S. EPA reviewed the Agency's leaching
evaluation methodology (U.S. EPA, 1991, 1999) and recommended that EPA develop new, flexible
evaluation approaches that consider how environmental parameters may affect the release of COPCs. The
SAB also expressed concern about the over-broad use of theTCLP protocol to assess leaching for scenarios
in which the test conditions were very different from the actual or plausible conditions or in cases where
there was no regulatory requirement to use the test. In addition, the SAB also identified a number of
technical concerns about the design and use of the TCLP (U.S. EPA, 1991).
While not answering all of these SAB concerns, LEAF was developed to provide an approach that
addressed what EPA considered the most critical issues raised. Each method directly addresses one of
three release-controlling factors for inorganic COPCs that may vary under plausible use or disposal
conditions: pH, the L/S of the test material relative to the leaching environment, and whether leaching is
controlled by chemical equilibrium or by mass transport rates (e.g., diffusion). By testing over a range of
values for these release-controlling factors, the LEAF approach allows for flexibility in that a single data
set can be used to evaluate multiple potential management scenarios for a material (e.g., disposal or
beneficial use) under different environmental conditions. The LEAF leaching tests include batch
equilibrium tests, percolation column tests and semi-dynamic leaching tests intended to characterize the
leaching behavior of a solid material under equilibrium or dynamic conditions. The results from these tests
may be interpreted individually or integrated to identify a solid material's characteristic leaching behavior.
Figure 1-1 illustrates the chemical factors influencing leaching estimated by LEAF testing and the
combination of tests utilized by the screening or scenario leaching assessments presented in this
document.
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LEAF Leaching
Analysis
PH
Dependence
L/S Dependence
Percolation
Available Content Screening* I Method 1313*
Equilibrium pH Screening
Equilibrium L/S Screening+
Percolation Scenario
Mass Transport Scenario
Method 1313
Method 1313 I Method 1314
X
Method 1314+
Method 1313
Equilibrium
Method 1316+
Method 1316#
Method 1316#
Mass Transport
Dependence
* Method 1313 only requires pH endpoint 2, 9, and 13 for Available Content Screening
+ Equilibrium L/S Screening can use either Method 1314 or Method 1316
# Optional method for leaching analysis
Figure 1-1. LEAF test methods in leaching evaluations and the chemical factors influencing leaching estimated by each test
method. Leaching analyses presented in this guide(left column) utilize the test methods in the boxes to the right of the analysis.
Methods in grey are optional depending on the specifics of a scenario. A red X indicates the leaching analysis does not use test
for the environmental parameter.
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1.3.2 Why Perform Leaching Tests?
Leaching tests are used to measure the amount of constituent mass that is released from a solid material
into a set volume of water under specified laboratory conditions. The data collected from leaching tests
is not directly representative of field leachates but is used to estimate how a material will leach when
managed in the field. Laboratory testing results can be combined with knowledge of how a material is
managed (or potentially mismanaged) to develop a description of how the COPCs will leach from material
in a defined scenario, often referred to as a source term. The source term can be used to evaluate the
potential for adverse impacts from placement of the material into or onto the land and forms the basis
for a determination of the appropriateness of the material in the proposed management scenario.
Further, the movement of leached COPCs away from the leaching source may be simulated using source
terms in conjunction within several available groundwater fate and transport models.
Laboratory
LEAF Testing
Environment
Figure 1-2. LEAF testing can estimate leaching from a material with varying environmental
factors. A source term to represent leaching in the environment can be developed from LEAF
testing.
1.3.3 When Can LEAF be Used?
The LEAF tests and approach is voluntary and not a requirement under the Resource Conservation and
Recovery Act (RCRA). This guidance provides a general approach that needs to be tailoring to the specific
application or regulation under which it is being used. For example, under RCRA, the TCLP test (EPA
Method 1311) is used for classification of many wastes as hazardous (Subtitle C) or non-hazardous
(Subtitle D) as part of the Toxicity Characteristic regulation (40 CFR 261.24). In addition, many RCRA land
disposal restriction (LDR) treatment standards are based on the results from TCLP testing (40 CFR 268.40).
LEAF is not a regulatory test but may be useful in support of evaluations not designed to meet
requirements under the RCRA regulations. The use of LEAF on a site-specific basis needs to be tailored to
the questions being asked. The usefulness of LEAF testing will depend on how well test results estimate
environmental conditions for a specific application. Using data from ten case studies, comparisons have
been made between LEAF testing and field leaching behavior over a range of materials and conditions
(U.S. EPA, 2014c). Good agreement was found between field and laboratory results except for situations
where redox or carbonation occurred. In these situations, geochemical speciation modeling was
conducted in conjunction with the LEAF results, showing good agreement to what was found in field
leaching behavior. (Garrabrants, Kirkland, Kosson, & van der Sloot, 2009; U.S. EPA, 2003, 2012b, 2014a,
2014b).
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LEAF may also find application in support of cleanup decisions under the Comprehensive Environmental
Response, Compensation and Liability Act (CERCLA) that address specific contaminants on a site-specific
basis. The performance values against which LEAF would be evaluated may differ depending on the
specific regulatory program involved. For example, site-specific data is used to determine whether action
is warranted at a site. Furthermore, under CERCLA as stated in the National Oil and Hazardous Substances
Pollution Contingency Plan, "levels generally should be attained throughout the contaminated plume, or
at and beyond the waste management area when waste is left in place" (55 FR 8753, March 8, 1990).
Decision-makers should consult with the appropriate regulatory agency to ensure compliance when using
LEAF testing in support of an evaluation.
Under CERCLA, cleanup decisions depend on site-specific factors. General guidance on use of LEAF data
that would be applicable to all sites is impractical and beyond the scope of the How-to Guide. As such,
EPA expects to provide additional guidance on the use of LEAF for CERCLA response actions as experience
with LEAF evolves.
1.4 What Topics Are Covered in this Guide?
This document includes a range of topics, from background information on leaching to selecting a leaching
test method and interpreting results. Some users of this guide may benefit from reading this material in
a front to back manner while others may be better served by reviewing a selected section. The How-To
Guide is modular in design but also builds upon previous sections. Specifically, the reader can learn about
the following topics in each section.
Table 1-1. Overview of Topics in the How-To Guide
Section
Topics
Section 1: An Introduction
to LEAF and this Guide
• The purpose of the How-To Guide
• Who can benefit from the How-To Guide
• Why LEAF was developed
• The purpose of leaching tests
Section 2: Understanding
the Leaching Process
• The definition of leaching
• The definition of a source term
• The definition of available content
• An overview of fundamental leaching behavior including
equilibrium control, mass transport control, and factors affecting
leaching in the field
Section 3: An Overview of
LEAF
• A description of analytical test methods and expected results for
Methods 1313, 1314, 1315, and 1316
• The interlaboratory validation of LEAF methods
• The field validation of LEAF methods
• The suggested best practices for an analytical testing program
• Best practices for quality assurance and quality control
• Testing and analytical cost estimates for LEAF tests
• Processing time estimates for LEAF tests
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Table 1-1. Overview of Topics in the How-To Guide
Section
Topics
• Laboratory data management discussion and tools
Section 4: Developing
Leaching Evaluations using
LEAF
• Some potential applications of LEAF
• A general approach to developing an assessment framework
• Assessment ratios and comparing test results to benchmark values
• Developing a screening assessment
• Developing a scenario assessment
• Overview of environmental processes that can influence leaching
• Determining available content
• Interpolating data
• Calculating water contact time
• Identifying solubility and available content-limited leaching
• Mass transport effects on leaching
• Dilution and Attenuation in an Assessment Ratio
• Using source terms from LEAF in environmental modeling
Section 5: Case Studies of
Using LEAF for
Assessments
• Screening Assessment Case Study: Evaluating Coal Combustion Fly
Ash for Use as Structural Fill Material
• Scenario Assessment Case Study: Evaluating Treatment
Effectiveness of a Cement-Based Stabilization/Solidification (SS)
Process
Section 6: Test Your
Knowledge
• Exercises reviewing basic concepts using data from the screening
assessment case study.
• Calculating the available content of a material
• Determining a plausible pH range for environmental conditions
• Interpolating Method 1313 test results to environmental pH
• Solubility versus available content limited leaching behavior
Section 7: Useful
Resources
• A collection of related resources
Section 8: References
• References cited in this document
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2. Understanding the Leaching Process
2.1 What is Leaching?
In an environmental context, leaching is the transfer of chemical species or compounds from a solid
material into contacting water. In the environment, contacting water may result from infiltration of
rainwater through overlying soils or through direct contact of the material with groundwater or surface
water. Constituents that leach into the water have the potential to contaminate adjacent soils or disperse
into groundwater or surface water bodies. The rate and extent of the release of inorganic constituents
from a solid material are controlled by a combination of physical and chemical processes that depend on
the properties of the solid material, the environmental exposure conditions or scenario, and the specific
COPCs contained in the material.
2.2 What is a Source Term?
In leaching assessments, a leaching source term is a numerical description of constituent release from a
material into contacting water under a defined set of environmental conditions. Figure 2-1 illustrates a
variety of scenarios for which leaching from a solid material disposed or otherwise in contact with the
land can be considered a primary source of environmental impact. In each of these scenarios, COPCs are
released from material upon contact with water. This figure shows that these seemingly diverse
applications often result in environmental release facilitated by water. For a chosen material, the leaching
behavior at the source remains relatively constant based on environmental conditions in each of these
scenarios, while the movement to groundwater or transport within groundwater can be significantly
different between scenarios. For example, the POC may be considered at the boundary of the material or
at some point down gradient of the source depending on applicable regulations.
The LEAF assessment approach provides a numerical estimate of COPC release (i.e., a source term) based
on measured leaching data in the context of environmental conditions that a material might encounter in
a chosen application. Leaching assessments typically include a description of the material in the field
scenario, material geometry and placement relative to the groundwater, and ranges or changes to
material properties or leaching conditions over time. While screening-level evaluation may utilize
assumed or default values, detailed information will provide a more precise, and in some cases, more
realistic estimate of release.
The selection of leaching test data to be used as a source term depends on the assessment objectives and
the required level of detail, considering bounding cases and scenario uncertainties. Raw leaching test
results may be used directly to formulate a generic source term that can be directly compared to relevant
benchmarks or thresholds when the POC is at the material boundary. In some applications, LEAF test data
may be compared between materials before and after treatment to evaluate the efficacy of treatment
options (Kosson, van der Sloot, Sanchez, & Garrabrants, 2002). When detailed characterizations are
required, the source term developed from LEAF may be used as an input to simple mass transport models,
or with more-complex fate and transport models, to develop specific source terms for material- and site-
specific applications. In addition, source terms may be developed considering variability as a basis for
regional or national decisions (e.g., through Monte Carlo-based source terms used in fate and transport
modeling for exposure assessment; U.S. EPA, 2014a, 2014b).
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landfill
_T
- ground level
water table
6 point of
compliance
XjX mining \ ^
contaminated
soil
road base
M.
agriculture
industrially
contaminated soil
factory
seepage
basin
treatment development
v . and effectiveness
coastal protection
~
___!!
If '
~
Adapted from van der Sloot, Kosson, and Hjelmar (2003).
Figure 2-1. Various environmental assessment scenarios showing a source term for leaching
with transport to the water table and through the groundwater to a point of compliance.
Note that the point of compliance may be at the unit boundary of the material for some
applications.
2.3 What is the Available Content of a COPC?
Ail materials and wastes contain a number of chemical constituents, some of which may pose
environmental hazards. The fraction of any COPC that is readily released into the environment is
considered the "available content" for that COPC. The available content of a COPC is defined as the
fraction of the total content that is not bound within decomposition-resistant (i.e., recalcitrant) phases,
but that is "available" for release over the domain of leaching conditions. The sum of the recalcitrant and
available fractions of a COPC is equal to the total content of the constituent in the material (U.S. EPA,
2014c). For inorganic constituents, available content is rarely the same as the total content because a
fraction of the total mass may be tightly bound within the solid matrix and is not released under plausible
field conditions. The available content can be determined from leaching tests as the mass release in
milligram of constituent per kilogram of material calculated from the maximum leaching concentration
tested at specific pH values (see Section 4.4.1). Determination of the available content provides a practical
value of the potential release of constituents into the environment that may be used as a bounding
estimate concentration for screening under assumed infinite source terms (see Section 4.2.4) or to place
limits on the extent of leaching for finite source term approaches (see Section 4.2.5).
2.4 How Does Leaching Occur?
Leaching occurs when constituents within a material in the environment solubilize into contacting water.
The leaching process is driven by the principles of mass transport, which defines the movement of
constituents from a solid phase to contacting water to minimize gradients, or differences, in chemical
activity within a phase or across the interface between phases (Bird, Stewart, & Lightfoot, 2001). In
environmental conditions, which often have low ionic strength, gradients in chemical activities can often
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be estimated as concentration gradients. Thus, leaching may be considered the result of gradients in
constituent concentrations between the pore solution of the solid and the contacting water. As leaching
progresses and concentration gradients are minimized, mass transport slows, and the system approaches
a state of chemical equilibrium (i.e., concentrations in the liquid phase are constant).
If the leaching process continues until concentration gradients are minimized and mass transport ceases,
the scenario is considered to have reached chemical equilibrium. Due to slow dissolution of some minerals
and other time-dependent processes, chemical equilibrium may be achieved for some constituents, but
not for all constituents, within a defined duration (such as a short assessment interval or the duration of
some laboratory tests). When chemical equilibrium is achieved, however, the leaching process can have
one of several endpoints with respect to a constituent:
• Available Content Limit: The solid phase becomes depleted of leachable constituent such that the
transferfrom solid to liquid stops. When this endpoint occurs, the extent of leaching is considered
available content-limited because the fraction of the total constituent content that is available for
leaching has been released.
• Solubility Limit: The water phase becomes saturated with respect to the constituent and leaching
stops although there remains a fraction of constituent in the solid available for leaching. For this
case, the extent of leaching is considered solubility-limited because the chemical parameters of
the liquid phase that define the solubility of a constituent constrain the amount that can be
released5.
The identification of leaching behavior as solubility-limited or available content-limited plays an important
role in the estimation of COPC release for environmental purposes. Leaching behavior is interpreted
through evaluation and comparison of equilibrium-based leaching tests results as described in Section
4.4.5. Discussion of relevant adsorption processes associated with sorption-controlled leaching is
provided in Section 4.4.4.
In practical terms, the time that it takes a solid-liquid system to reach an equilibrium endpoint depends
on (i) the geometric size of the material (i.e., particle size for granular materials or the dimension
perpendicular to mass transport for monolithic materials and compacted granular fills), (ii) the L/S (i.e.,
the amount of liquid relative to the amount of solid), (iii) the chemical characteristics of the COPC, and
(iv) the chemical composition of the liquid phase (i.e., pH, oxidation-reduction potential, ionic strength,
composition). For example, when the material is granular (i.e., consists of many particles with relatively
small dimension) and is contacted by a relatively small amount of water, the leaching process reaches an
apparent endpoint within the practical time of bench-scale leaching tests. For these systems, the extent
of leaching (i.e. the COPC mass released) is the practical measure of COPC release because the system is
likely to achieve equilibrium quickly in the environment. The liquid-solid partitioning (LSP) of COPCs
5 While not constrained by the available content or aqueous solubility, a constituent may be distributed between the solid and
water phase by adsorption to mineral or other phases under environmental conditions. Leaching at this endpoint is
considered sorption-controlled because interfacial adsorption/desorption chemistry dictates the concentration of the
constituent in the liquid phase. In basic leaching evaluations, sorption controlled processes are often not easily
distinguishable from solubility-limited leaching and are thus treated similarly in this guide. LEAF data that indicate solubility-
limited leaching, in fact, may reflect or consider the combined effect of solubility and adsorption as controlling processes.
Depending on the surface charge of a granular material, adsorption can result in a constituent concentration in the leachate
much lower than expected based on solubility alone. Chemical speciation modeling may be helpful in determining the
chemical mechanisms that explain leaching concentrations when this level of information is needed.
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between the contacting water and the solid material at equilibrium provides a measure of the extent of
leaching with the available content representing the maximum extent of leaching. Conversely, larger
particles, such as those within monoliths or compacted granular samples, require a longer time to reach
an apparent endpoint to the leaching process. Thus, the rate of leaching becomes the dominant leaching
characteristic that predicts the release of COPCs as measured by the rate of mass transport through the
material to the interface between the material and the contacting water.
Therefore, over a wide range of environmental conditions, mass transport may be considered to control
the rate of leaching while chemical equilibrium controls the extent of leaching. Ideally, comprehensive
leaching assessment would address both the rate and the extent of constituent leaching as applicable
based on the environmental conditions imposed by the combined influences of material and the
management scenario.
2.4.1 The Extent of Leaching Through Liquid-Solid Partitioning (LSP)
LSP is the chemical equilibrium, or near-equilibrium, state that describes the distribution of a constituent
between the solid phase and a contacting liquid. For many materials, LSP concentrations are the combined
result of the available content, aqueous solubility of the various chemical species of the constituent,
adsorption/desorption to (hydr)oxide surfaces and particulate carbon, and chemical reactions in the liquid
phase. Thus, the LSP evaluated through leaching tests is intended to obtain one of the leaching process
endpoints described above and to approximate chemical equilibrium between the aqueous and solid
phases (U.S. EPA, 2010).
Important chemical factors influencing the measured constituent LSP include:
• Eluant or leachate pH that controls aqueous solubility of inorganic COPCs, dissolution of organic
carbon, and sorption or desorption of COPCs to the surface of oxides, clays, minerals, and organic
matter,6
• Liquid-to-solid ratio (L/S) defined as the volume of liquid in contact with a dry mass of solid,
• Reduction/oxidation (redox) conditions that may change the oxidation state of COPCs (e.g., Cr(lll)
to Cr(IV))7 and also the quantity of available surfaces for sorption; e.g. Fe(lll) to Fe(ll) results in a
decrease in sorption to iron (hydr)oxide surfaces,
• Dissolved organic matter that can increase the measured concentration of COPCs through
formation of soluble complexes with dissolved organic carbon (DOC),
• Ionic strength and common ion effects that suppress dissolution of some minerals, and
• Biological activity that result in pH changes or redox changes in the solid-liquid system.
Of these chemical factors, pH and L/S are the two parameters that are most important for the majority of
inorganic constituents with regard to constituent leaching and are the two parameters that can be best
controlled in the laboratory. Information about the other factors can be collected during testing and used
to refine release estimates based on geochemical models when needed, as described in Section 4.4.8.
6 The pH of the eluate or leachate is the combined effect of the acidity or alkalinity of the contacting solution and the
buffering, or acid/base neutralization, capacity of the contacting material.
7 Since a change in the oxidation state of an ion changes solid and aqueous species it can form, oxidation-reduction conditions
also can have an impact on leaching in some cases.
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2.4.1.1 pH-dependence
Typically, the aqueous solubility of many inorganic species, including many COPCs, is a strong function of
solution pH. Figure 2-2 presents a graph of the solubility of metal hydroxides over the pH range from 6 to
14 which may be applicable for some environmental scenarios (e.g., used of solidification/stabilization
with cement as a soil or waste treatment). The figure shows that the solubility of these metals reaches a
minimum value at approximately pH 10 but can vary by several orders-of-magnitude with relatively small
shifts in pH. The pH-dependent behaviors shown in this figure are for simple, single hydroxide minerals in
solution. In comparison, the mineralogy of soil and waste systems is relatively complex with each COPC
potentially present in several different mineral species, each with its own solubility behavior. In the field,
a number of potential mineral species may affect the solubility. Regardless, this figure is helpful as an
illustration of the significant influence that pH can have on the measured LSP of waste and soil systems.
1,000
100
—I
Pb
o
E
E
0.01
Zn
0.001
.Co
Cu
Cd
0.0001
0.00001
6
8
10
12
14
pH
Adapted from Stumm and Morgan (1996).
Figure 2-2. Solubility of metal hydr(oxides) in water as a function of pH.
2.4.1.2 L/S-dependence
The L/S dependence of a constituent allows for estimations of leaching behavior over a range of water
contact rates. A constituent may initially leach as a highly soluble species. However, once a significant
amount of water has contacted the solution and transported the constituent away, the depleted
constituent concentration in the solid material limits further leaching. This transition would be seen in
laboratory experiments at increasing L/S. Alternatively, leaching may be initially limited by the constituent
solubility and a constituent may leach at a relatively constant rate over longer periods.
Figure 2-3 presents an illustration of how changes in L/S can influence the LSP leaching behavior. In this
figure, the five light colored dots represent units of a COPC that are available to leach or have leached
while the five dark colored dots represent units of a COPC that are present in recalcitrant minerals and
are not available to leach. Therefore, the available content of this constituent is 50% of the total content
(i.e., 5 units available out of 10 units). The panels on the left show that, at low L/S (e.g., the L/S associated
with the porewater of a material), constituents in the liquid phase reach a saturation point of 0.1 unit/mL
(i.e., 2 units leached into 20 mL of water) and the leaching behavior is considered solubility-limited. As the
amount of water is doubled from 20 to 40 mL, additional constituent is leached such that the liquid
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concentration remains 0.1 unit/mL. Under solubility-limited release, the measured concentration for
solubility-limited COPCs usually is a weak function of L/S as long as pH does not change significantly and
complexing agents (e.g., DOC) are not present. As the volume of water increases to 60 mL, leaching
continues and all of the available constituent mass is leached from the solid material; thus, the
concentration in the liquid phase decreases to 0.08 unit/mL (5 units in 60 mL) and leaching has become
limited by the available content. At this point, LSP becomes a strong function of L/S because the addition
of water to 80 mL reduces the LSP concentration further to 0.06 units/mL because the same available
mass of the constituent (5 units) is dissolved into a greater volume of water (80 mL).8
—ICDmL
—10flmL
—1G0mL
—lOOmL
Step 1
L/S = x
20 in 20 mL solution
30 in solid
5# not available
solubility-limited
Step 2 Step 3
L/S = 2x L/S = 3x
40 in 40 mL solution 50 in 60 mL solution
lO in solid 00 in solid
5# not available 5 9 rot available
Step 4
L/S = 4x
50 in 80 mL solution
00 in solid
5# not available
solubility-limited
available content-limited available content-limited
Figure 2-3. Illustration of the changes in LSP leaching behavior as the system L/S increases.
For many field scenarios, the L/S may be derived from the information on the rate of infiltration or
groundwater contact and simple physical parameters of the material application. For example, the L/S of
a landfill scenario can be determined by measuring the volume of leachate collected annually from the
landfill and relative to the estimated volume of waste in the landfill or the landfill design capacity. When
scenario-based information about the relative rate of water contact is known, laboratory data at varying
L/S may be considered a surrogate for time that allows for the estimation of leaching as a function of time
under field conditions or the prediction of the time required until constituents are depleted (see Section
4.4.3 for more on calculating L/S). The L/S may also be adjusted to account for the tendency of contacting
water to preferentially flow on or around the material (See Section 4.4.4 for more on interpreting L/S from
LEAF testing). In the laboratory, the L/S in a leaching test is varied by changing the relative proportions of
test material and the leaching solution (i.e. leachant).
8 In addition to the effect on L/S illustrated above, concurrent changes in pH, ionic strength and the presence of other
dissolved species that can also influence solubility. For example, according to the Davies Equation for calculation of activity
coefficients (Stumm & Morgan, 1996) a 0.1 M solution of barium carbonate would result in an ionic strength of 0.4 M and
activity coefficients of 0.292, resulting in solution activity substantially lower than measured solution concentration. An
example of a common ion effect is the lower observed concentration of barium in field leachate compared to laboratory test
results because of lower L/S and presence of higher sulfate concentrations from dissolved calcium sulfate that reduces the
solubility of barium sulfate by Le Chatelier's principle (U.S. EPA, 2014c)
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Understanding the Leaching Process
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2.4.2 The Rate of Leaching (Mass Transport)
Mass transport describes a set of mechanisms (e.g., diffusion, dissolution, adsorption, or complexation)
that collectively control the transfer of constituents from areas of higher concentration to areas of lower
concentration over time. Within a solid material, constituents move via diffusion from areas of higher
concentration to lower concentration and may interact with the minerals and other solid phases
comprising the material through various chemical reactions (e.g., dissolution/precipitation,
adsorption/desorption). The specific rate of diffusion, or the molecular diffusivity, is the speed at which a
constituent travels unhindered by physical or chemical constraints through water, proportional to the
magnitude of the concentration gradient (i.e., diffusion is faster when incremental difference in
concentrations is greater). The observed rate of diffusion for a constituent moving through a porous
material, however, is slowed by the distance that the constituent has to travel, the effective porosity of
the material, the connectivity and tortuosity of the porous network, and chemical reactions that occur
along the diffusion pathway. Often, local chemical equilibrium between the solid material and porewater
is assumed during mass transport, such that all of the chemical parameters that influence LSP also effect
the rate of mass transport.
2.4.3 Leachability of a Material in the Field
The rate and extent that constituents can leach from a material are determined by a number of chemical
and physical factors that can vary between sites and are not likely to remain constant in the field because
the environmental media, including local conditions and the solid materials, change over time. Slight
changes in key factors can have substantial effects on the magnitude of releases by changing either the
rate at which a constituent can be released or the equilibrium water concentration. Some examples of
key factors include:
• Changes to the L/S from increased precipitation that results in a shift between solubility-limited
and available content-limited leaching behavior;
• Changes to the pH that alter the solubility of a constituent in the water (e.g., from acid
precipitation, uptake of atmospheric carbon dioxide, oxidation of reduced minerals or biological
activity);
• Changes to the redox conditions (e.g., reduction from biological activity that alter the oxidation
state of a constituent [e.g., Cr(lll) to Cr(IV)] or oxidation through contact with air);
• Changes to the physical structure of the material (e.g., degradation from internal stress through
freeze/thaw cycles or mechanical erosion that increase the ratio of surface area/volume);
• The tendency for contacting water to preferentially flow over or around material;
• Introduction of DOC from organic material decay; and,
• Changes to the chemical composition of the material (e.g., from co-disposal with other materials).
• Changes to a material from weathering or self-cementation.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Understanding the Leaching Process
-------
3. An Overview of LEAF
LEAF is an integrated framework that uses the results from up to four different laboratory tests to
characterize the leaching behavior of solid materials. Coordinated development of LEAF has occurred
between research laboratories in the U.S. and the European Union to develop and harmonize test
methods to support data comparisons. Test methods analogous to LEAF test methods are available in the
EU with minor differences intended to address the different testing standards (e.g., quality control
requirements, method description requirements, etc., See Appendix A). The four test methods, U.S. EPA
Methods 1313, 1314, 1315 and 1316, are designed to account for the effects of major factors known to
affect leaching behavior of inorganic constituents for most wastes and management scenarios (Kosson et
al., 2002). Because the test methods take into consideration a range of material properties and potential
environmental conditions, the resulting data can provide estimates of constituent leaching behavior that
reflect plausible field conditions and considers the impact of a wide range of material management
scenarios (U.S. EPA, 2014c). The overarching framework provides direction on how to interpret and apply
the data collected based on the complexity and specificity of the evaluation, ranging from a simple and
generalized screening analysis to a complex and site or scenario-specific probabilistic analysis. This section
provides general descriptions of the components of LEAF.
3.1 Analytical Leach Test Methods
For characterization of inorganic constituents, LEAF
includes four distinct leaching test methods. These test
methods directly address one of three most important
factors affecting leaching of inorganics: the final
leachate pH, the amount of water in contact with the
material, and the physical form (i.e., granular vs.
monolithic) of the material (U.S. EPA, 2014c). The test
methods also measure important parameters of the
liquid such as pH, electrical conductivity (EC) and DOC
under the final leaching conditions. Together, these
methods provide information on the available content,
peak leaching concentration, time-dependent release
(Kosson et al., 2002; U.S. EPA, 2010). These methods
can be applied individually or in combination, based on
information needed to characterize the leaching
behavior of the material of interest.
The LEAF tests are conducted under a specified set of
conditions, which provides a standardized basis for
comparison among different samples, materials, leaching tests, and management scenarios. The data can
be used to evaluate a range of environmental conditions that a given material may be exposed to in the
field (U.S. EPA, 2014c). Even when a particular value of interest has not been explicitly measured (e.g.,
leaching at a particular pH or L/S value), it is possible to interpolate between measured concentrations to
more accurately reflect anticipated field conditions. Each of the four test methods have undergone
interlaboratory and field validation for inorganic COPCs (U.S. EPA, 2012c, 2012d, 2014c). A summary of
the parameters for each method is presented in Table 3-1 with a description in the following subsections.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
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LEAF Leaching Tests
Method 1313: Liquid-Solid Partitioning as a
Function of Extract pH using a Parallel
Batch Extraction Procedure (U.S. EPA,
2012f)
Method 1314: Liquid-Solid Partitioning as a
Function of Liquid-to-Solid Ratio for
Constituents in Solid Materials using an Up-
flow Percolation Column Procedure (U.S.
EPA, 2013a)
Method 1315: Mass Transfer Rates of
Constituents in Monolithic and Compacted
Granular Materials using a Semi-Dynamic
Tank Leaching Procedure (U.S. EPA, 2013b)
Method 1316: Liquid-Solid Partitioning as a
Function of Liquid-to-Solid Ratio using a
Parallel Batch Extraction Procedure (U.S.
EPA, 2013c)
-------
A full detailed description of the validated methods can be found on the SW-846 website under validated
methods (U.S. EPA, 2017b).
Table 3-1. Comparison of Test Parameters for LEAF Leaching Methods
Test
Variable
Method 1313
Method 1314
Method 1315
Method 1316
Test Type
Equilibrium;
pH-dependent
Equilibrium;
percolation
Mass transfer
Equilibrium;
L/S-dependent
Test
Description
Parallel batch
extractions
Column test in up-
flow mode
Tank test with
periodic eluant
renewal
Parallel batch
extractions
Sample Type
and
Dimension
Granular particle
size of 85% by mass
less than 0.3, 2.0 or
5.0 mm
Granular particle
size of 85% by mass
less than 2 mm
with 100% less
than 5 mm
Monolith: cylinder
or cube; 40-mm
minimum
dimension
Compacted
granular: cylinder
with 40 mm
minimum height
Granular particle
size of 85% by mass
less than 0.3, 2.0 or
5.0 mm
Test,
Extraction or
Interval
Duration
Extractions for 24,
48 or 72 hours
based on maximum
particle size
Continuous elution
to L/S 10 mL/g-dry
Estimated test time
of 13 days based
on constant
flowrate of 0.75 L/S
per day
Intervals of 2, 23,
23 hours, 5, 7, 14,
14, 7 and 14 days
Cumulative
leaching time of 63
days
Extractions for 24,
48 or 72 hours
based on maximum
particle size
Eluant
Composition
Reagent water with
additions of HN03
or NaOH
Reagent water or 1
mM CaCI2
Reagent water
Reagent water
pH Range
2 to 13 at specified
targets
As controlled by
material being
tested
As controlled by
material being
tested
As controlled by
material being
tested
Amount of
Solid
Minimum 20 g-dry
per extract;
Approx. 400 g-dry
each for pre-test
and test replicate
(collect 1 kg for
first test; 500 g for
each replicate)
Minimum 300 g;
600-700 g per
column (collect 1
kg per test run)
Monolith: as
specified
Compacted
granular: 500-750
g per test run + 5
pre-test samples
(collect 4 kg for
first test, 1 kg for
each replicate)
Minimum 20 g-dry
per extract;
20 to 400 g-dry
each extract
(collect 1 kg per
test run)
Eluant
Volume
L/S of 10 mL/g-dry
Eluates collected
through cumulative
L/S 10 mL/g-dry
Liquid-surface area
ratio of 9 mL/cm2
L/S of 10,5.0, 2.0,
1.0, and 0.5 mL/g-
dry
Number of
Analytical
Solutions
per Test
9 extractions (10 if
natural pH is
outside target
range)
9 eluate fractions
9 interval solutions
5 extractions
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-------
3.1.1 U.S. EPA Method 1313: pH-Dependent LSP
Method 1313 is designed to evaluate the partitioning of
constituents between liquid and solid phases at near
equilibrium conditions over a wide range of pH values.
The method consists of 9 to 10 parallel batch extractions
of a solid material (Figure 3-1) at various endpoint target
pH values and at an L/S of 10 mL/g-dry. The pH of each
extraction is controlled by additions of a known volume
of dilute acid or base, derived from prior knowledge of
the acid neutralization capacity (ANC) of the material or
from determination of the ANC based on a pre-test
titration step. Parallel extractions provide aqueous
extracts at up to nine target pH values between pH 2 and
13, plus the natural pH of the material (i.e., when
leached with Dl water, and no acid or base is added). To
achieve equilibrium conditions faster and reduce testing
time, particle size reduction of the sample material may
be required (U.S. EPA, 2010). The measured constituent
concentrations and acid/base neutralization capacity
can be plotted as a function of leachate pH. The
measured values can be plotted and graphically
compared to relevant benchmarks to facilitate the
presentation and interpretation of the data. Given that
leachate concentrations can vary by multiple orders of
magnitude over the full pH range, it is recommended
that the graph be log transformed for ease of
presentation.
Total Content—The concentration [mg/kg-
dry] of a constituent in the solid material on
a total dry mass basis.
Available Content—The concentration
[mg/kg-dry] of a constituent in a solid
material on a total dry mass basis that
potentially may leach over a reasonably
near-term timeframe (e.g., 100 years). The
available content is a fraction of the total
content and, thus, less than or equal to the
total content value.
Eluant—Water or aqueous solution used to
contact or extract constituents from a
material during a laboratory test.
Eiuate—The aqueous solution, analyzed as
part of a laboratory leaching test, that
results from contact of an eluant with
tested material.
Leachant—Water or aqueous solution
contacting a material under field conditions
(e.g., infiltrating water, groundwater).
Leachate—An aqueous solution resulting
from leachant contact with a material under
field conditions.
n samples
% *
s.
M
M
Sn
M
D
EJ
...
*
D
chemical
analyses
Adapted from Kosson et al. (2014).
*
0
*
B
Method 1313 consists of 9-10 parallel batch extractions (A through n) of subsamples of a
particulate solid (S) in deionized water with various additions of acid or base intended to
result in specified endpoint target pH values, approximating LSP as a function of pH.
Figure 3-1. Experimental scheme of U.S. EPA Method 1313 as a parallel batch extraction test.
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3-3
-------
Figure 3-2 presents an example of pH-dependent results from Method 1313 for the acid-base titration
curve of a coal combustion fly ash (EaFA) and the LSP curve for chromium presented as eluate
concentration and mass release (Kosson, Garrabrants, DeLapp, & van der Sloot, 2014). For batch
extractions, mass release [mg/kg-dry] is calculated by multiplying eluate concentrations [mg/L] by the
eluate-specific L/S [L/kg-dry], Typically, eluate concentrations are plotted as a function of pH along with
the method detection limit (MDL) and lower limit of quantitation (LLOQ). In Figure 3-2, the data
corresponding to the natural pH extraction (i.e., the extraction where the material dictates the eluate pH)
is indicated by a large circle about the data point.
l
0.5
¦o
i
OI
^ o
"o
E -0.5
u
z
CO -1
u
< -1.5
-2
0 2 4 6 8 10 12 14
PH
Available
Content
0.0001
O 0.01 -
¦C
u
0.001
¦g 0.001
o
k.
¦c
u
0.0001
Figure 3-2. Example results from Method 1313 for leaching from a coal combustion fly ash
(EaFA): Titration curve (top), chromium eluate concentration (lower, left) and chromium release
with available content displayed (lower, right).
Many of the chemical processes that control liquid-solid partitioning are pH-dependent (e.g., solubility,
mineral precipitation, adsorption reactions). Method 1313 provides an equilibrium partitioning curve as
a function of pH that can be used to identify where leaching behavior is sensitive to changes in pH (i.e.,
where solubility may change significantly with a small change in pH). The method can also be used to
estimate the leachable fraction, or available content, of constituents based on the maximum eluate
concentration over the pH range (U.S. EPA, 2014c). LSP and available content information can be used as
input into chemical speciation models to help understand the effects of physical and chemical factors that
are difficult to control for in laboratory tests (e.g., material interactions, reducing conditions, reactions
with atmospheric gases). Table 3-2 provides a summary of the potential applications of Method 1313 data.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
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-------
Table 3-2. Potential Applications of Method 1313 Data
Data Collected
Potential Uses
Acid/base titration curve
• Impact on eluate pH from external sources of acidity or
alkalinity (e.g., from mixing with other materials or from
external sources such as acidic precipitation or ingress of
carbon dioxide)
Equilibrium constituent concentrations at pH
2, 9, and 13
• Available content (i.e., the fraction of total content available
for leaching based on maximum release at these 3 endpoint
target pH values)
Equilibrium constituent concentrations at
natural pH and at pH points within and
bracketing scenario pH domain
• Determination of maximum potential leachate
concentrations over scenario pH domain
• Indication of solubility-limited or available content-limited
leaching
Full suite of constituent concentrations for
all test pH points
• Insights into chemistry controlling leaching
• Comparison of characteristic constituent equilibrium
partitioning as a function of pH between materials
• Input for geochemical speciation modeling
3.1.2 U.S. EPA Method 1314: Percolation Column
Method 1314 is a percolation column
test designed to evaluate constituent
releases from solid materials as a
function of cumulative L/S. The
experimental scheme of Method 1314 is
shown in Figure 3-3. The method
consists of a column packed with
granular material with moderate
compaction to preserve the original
porosity of the material. Particle size
reduction of the sample material may be
required to facilitate testing. Eluant is
introduced through pumping of
deionized water up through the column
to minimize air entrainment and
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Water Contact Key Terms
Percolation—The water contact scenario when
precipitation, infiltrating water or groundwater, moves
through the contiguous voids of a porous material and
leaching occurs at the solid-liquid interface between the
percolating fluid and the solid material.
Washout—A rapid release of constituents resulting from
highly soluble species rapidly dissolving in water
percolating through a material. Washout is usually
indicated during Method 1314 by a decrease in leaching
concentration of approximately one order of magnitude
or more as the liquid to solid ratio increases from L/S = 0.2
mL/g-dry to 2.0 mL/g-dry.
Flow-around—The water contact scenario when
precipitation, infiltrating water, or groundwater flows
around the external surface area of a low-permeability
material (e.g., cement-treated wastes, compacted
material) and release occurs at the interface between the
flowing water and the material.
Mass transport/diffusion-limited leaching—The release from
solid material when leaching is less than equilibrium
liquid-solid partitioning, typically constrained by the rate
of diffusion through the material being leached.
-------
preferential flow.910 The eluant flowrate is slow so that the resulting eluant concentrations approximate
liquid-solid equilibrium within the column. Samples of column eluate are collected over nine specified
cumulative L/S intervals. The eluate pH and specific conductance are measured. The eluate is filtered by
pressure or vacuum in preparation for constituent analysis. Analytical aliquots of the extracts are collected
and preserved accordingly based on the determinative methods to be performed (U.S. EPA, 2012c).
Up-flow percolation column to collect eiuates at specified L/S values, estimating liquid-solid partitioning at
percolation release conditions that approximate chemical equilibrium.
Adapted from Kosson et al. (2014).
Airlock
Luer fitting
N2 or Ar
(optional)
Eluant collection bottle(s)
(sized for fraction volume)
1-cm
sand <
^ fitting 'ayerS\
Eluant
reservoir
Luer shut-off
valve
| End cap
_Subject
material
-4—End cap
Luer skut-off
valve
Figure 3-3. Experimental scheme of U.S. EPA Method 1314 as a percolation column test.
Measured constituent concentrations can be plotted as a function of the cumulative L/S, either as
measured [mg/L] or multiplied by the incremental L/S for that sample and summed into a cumulative
mass release [mg/kg-dry], Eluate concentration and cumulative mass release can be graphed as a function
of cumulative L/S. The measured pH can be plotted against the L/S to determine if early washout of soluble
ions has a substantial impact on leachate pH. Figure 3-4 provides example results from Method 1314 for
a contaminated smelter site soil (CFS).
Data from Method 1314 provide an estimate of pore water concentrations at low L/S (e.g., L/S of 0.2 or
0.5 mL/g-dry) and illustrate how leaching behavior changes as the cumulative L/S ratio increases. As water
percolates through the material, highly soluble salts such as sodium or potassium salts, DOC, and
oxyanions may be washed out, typically with a tenfold reduction in leaching concentration by cumulative
L/S of 2 mL/g-dry.
9 Calcium chloride solution (1 rriM) may be used instead of deionized water in cases where colloid formation is a concern to
prevent defloccuiation of clays and organic matter.
10 The test method uses upflow through the column to minimize flow channeling. However, testing has demonstrated that use
of upflow testing does not have significant impact of the results relative to field behavior (U.S. EPA, 2014c, Lopez et al, 2008)
Leaching Environmental Assessment Framework (LEAF) Flow-To Guide
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10
£ o.i +
0.01
0.001
100
^ 10
E,
I
fD
- 1 -t
£ +
ro
s
0.1
'po OO
~
;
LLOQ
0
2 4 6
L/S (L/kg-dry)
10
o <
o
4
o
¦ r
: f
O
- ¦ ¦ ¦ I
¦ ¦ ¦ 1
¦ ¦ ¦ 1
¦ ¦ ¦ 1
¦ ¦ ¦ 1
1—¦—
4 6 8
L/S (L/kg-dry)
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<>o
-- Oo
o °
—
4
o
I—1—
100
£•
¦o
I
CT
W
E,
u
i/i
IS
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solubility-limited release
/
jf
1—1 ¦ 1 11 III
\
¦ <*
\
\
V
,—
,—
0.1
1 10
L/S (L/kg-dry)
100
Figure 3-4. Example results from Method 1314 for lead as a function of L/S from a
contaminated smelter site soil (CFS): Concentration (top, left), eluate pH (top, right) and
cumulative release on Cartesian axis (lower, left) and logarithmic axis (lower, right).
As infiltrating water percolates through a material, changes in the porewater chemistry can alter the
dissolution of the more stable mineral phases, subsequent pore solutions and leaching of constituents.
The data on concentrations as a function of cumulative L/S from this laboratory test can be used together
with field infiltration rates to estimate leaching as a function of time. Table 3-3 presents a summary of the
potential applications of Method 1314 data.
Table 3-3. Potential Applications of Method 1314 Data
Data Collected
Potential Uses
Constituent concentrations as a function of
incremental and cumulative L/S
• Initial (i.e., porewater) and maximum leaching
concentrations
• Percolation leaching source term
• Co-elution effects of COPC release (e.g., increased leaching of
As after depletion of Ca; Ba and SO4)
Eluate pH and conductivity as a function of
incremental and cumulative L/S
• Estimate of porewater pH (at low L/S), ionic strength
• pH relates Method 1314 results and Method 1313 results
when plotted as a function of pH
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3-7
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3.1.3 U.S. EPA Method 1315: Rates of Mass Transfer
Method 1315 is a semi-dynamic tank leaching procedure used to determine the rate of mass transport
from either monolithic materials (e.g., concrete materials, bricks, tiles) or compacted granular materials
(e.g., soils, sediments, fly ash) as a function of time using deionized water as the leaching solution. The
method consists of leaching of a test sample in a bath with periodic renewal of the leaching solution at
specified cumulative leaching times (Figure 3-5). The volume of leachant used in the test is related to the
surface area exposed to the liquid through a liquid-to-surface area ratio (L/A).
n Leaching
BO
^ analytical
samples
B D
Adapted from Kosson et al. (2014).
1 sample £
r
"
Monolith
compacted
granular
Granu ar
Sequential extraction of a monolith or compacted granular specimen to determine the maximum rate of
release by diffusion and dissolution processes.
Figure 3-5. Experimental scheme of U.S. EPA Method 1315 as a tank leaching test.
Monolithic samples may be cylindrical or rectangular, while granular materials are compacted into
cylindrical molds to a density that approximates the peak field density on a dry basis. At nine specified
time-intervals, samples are transferred to fresh reagent water and the eluate from the previous interval
is analyzed for eluate properties (e.g., pH, EC) and constituent concentrations. Measured constituent
concentrations in mg/L are be plotted as a function of cumulative time and along with an analogous plot
of eluate pH as a function of cumulative leaching time. Eluate concentrations are presented relative to
MDLs and LLOQs to indicate quantitation of measured concentrations. The interval mass flux [mg/m2-s],
or the rate of mass released over an interval, is calculated by multiplying the eluate concentration [mg/L]
by the ratio of the volume of leachate to the surface area of the sample [L/m2] and dividing by the interval-
specific time in seconds [s]. Similarly, the cumulative mass release [mg/m2] is calculated by multiplying
the interval mass flux by the interval specifictime and summing across all previous leaching intervals. Both
interval flux and cumulative mass release are plotted as a function of cumulative leaching time. Figure 3-6
presents example results from Method 1315 for a solidified waste form (U.S. EPA, 2012c, 2012d),
Leaching Environmental Assessment Framework (LEAF) Flow-To Guide
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12
10
11 --
10 --
L4-
"t-
0.01 0.1 1
Time (days)
10
100
oi
E
1
® 0.1
0.01
LLOQ
0.01 0.1 1 10 100
Time (days)
«
N
.E
oi
E,
X
3
Li.
E
10
0.1
0.01
0.001 T
0.0001 -;
0.00001
. ^ Diffusion
10000
0.01
0.1
10
100
OI
E
s.
a
ai
10
1000
100
10
Diffusion
-»*'
, *>•'
*"* n—n
Time (days)
0.01 0.1 1 10 100
Time (days)
Figure 3-6. Example results from Method 1315 for selenium shown as a function of leaching
time from a solidified waste form (SWA): Eluate pH (upper, left), eluate concentration (upper,
right), mean interval flux (lower, left) and cumulative release (lower, right).
Data from Method 1315 indicate the rate of mass transport from the interior of the material to its external
surface (i.e., the interface of the material with the surrounding environment). By maintaining a dilute
eluate solution based on eluant refresh intervals, the boundary conditions for leaching result in a
maximum release rate by diffusion for monolithic and compacted granular materials (U.S. EPA, 2010).
Method 1315 is applicable for cases where water primarily flows around the material, rather than
percolating through it. In the field, however, actual liquid to surface area ratios are often much less than
the test conditions and leaching into the limited contacting liquid can reduce concentration gradients.
Therefore, the rate of leaching in the field can be less than measured in the laboratory and Method 1315
data often are used to estimate the parameters (e.g., observed diffusivity) that control mass transfer for
each constituent (Garrabants, Sanchez, Gervais, Moszkowicz, & Kosson, 2002). The data from Method
1315 may represent mass transport rates over short time durations with the mass transport parameters
used to estimate rates of leaching in the field over longer time durations (U.S. EPA, 2012d). A summary of
the potential applications of Method 1315 data is presented in Table 3-4.
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Table 3-4. Potential Applications of Method 1315 Data
Data Collected Potential Uses
Constituent release rates from monolithic
and compacted granular materials
• Maximum leaching rates under diffusion conditions
• Mass transport-based leaching source term
• Tortuosity and observed diffusivity (diffusion-controlled
release)
Compacted dry density (pre-test for granular
materials)
• Bulk density of compacted granular materials under field
compaction
Eluate pH and conductivity as a function of
cumulative leaching time
• Concentrations graphed as function of pH with Method 1313
results to verify Method 1315 dilute boundary conditions
• pH and total ionic strength domain of anticipated leaching
3.1.4 U.S. EPA Method 1316: L/S-Dependent LSP
Method 1316 is an equilibrium-based leaching test intended to provide eluate solutions over a range of
L/S. This method consists of five parallel batch extractions of a particle-size-reduced solid material in
reagent water over a range of L/S values from 0.5 to 10 mL/g-dry material (Figure 3-7).
samples
% «
' I
* +
n
hemical
inalyses
Adapted from Kosson et al. (2014).
*2
tea
Sn
Ml
0
D
...
K
Parallel batch extractions with varying quantities of deionized water, approximating liquid-solid
partitioning as a function of pH at chemical equilibrium.
Figure 3-7. Experimental scheme of U.S. EPA Method 1316 as a parallel batch extraction test.
At the end of the contact interval, the liquid and solid phases are separated by pressure or vacuum
filtration in preparation for constituent analysis. Extract pH and specific conductance measurements are
taken on an aliquot of the liquid phase. Analytical aliquots of the extracts are collected and preserved
accordingly based on the determinative methods to be performed (U.S. EPA, 2012c). Measured eluate
concentrations are plotted as a function of the L/S along with MDLs and LLOQs to indicate quantitation of
measured concentrations. Method results are presented as eluate concentrations [mg/L] or as mass
release [mg/kg] calculated by multiplying concentrations by the extraction-specific L/S [L/kg-dry]. Often,
the measured eluate pH for each extraction is plotted against the L/S to provide content to pH-dependent
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LSP concentration determined from Method 1313. Figure 3-8 provides example results from Method 1316
for a contaminated smelter site soil (U.S. EPA, 2012c, 2012d).
6.8
6.6 --
6.4
6.2 --
t
r
~ -A
1
4 6
L/S (L/kg-dry)
10
0.1
»
E
0.01
2 o.ooi
o.oooi
~
i
LLOQ
MDL
1 1 1 1
1 1 1
1 1 1
i i i | i i i
•r. o.i -
V
l/l
IS
_0J
a.
n
<
0.01
4 6 8
L/S (L/kg-dry)
10
4 6
L/S (L/kg-dry)
Figure 3-8. Example arsenic results for Method 1316 from a contaminated smelter site soil
(CFS): Eluate pH (top), eluate concentration (lower, left) and release (lower, right).
Data from Method 1316 provides mass release information as a function of L/S similar to Method 1314
data. However, the Method 1316 eluate concentrations are often higher than Method 1314, reflecting
the nature of the batch test where constituents are not sequentially removed from the system at each L/S
as with a flow-through percolating column. The batch method may be useful when characterizing
materials with physical properties that make flow through tests impractical (e.g., low-permeability clay
soil, materials with cementitious properties). A summary of the applications of Method 1316 data is
presented in Table 3-5.
Table 3-5. Potential Applications of Method 1316 Data
Data Collected
Potential Uses
COPC concentrations as a function of L/S
• Estimate porewater concentrations at low L/S
pH and conductivity as a function of L/S
• Porewater pH
COPC mass release as a function of L/S
• Constant mass release as a function of L/S is an indicator of
available content limited leaching
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3.1.5 Validation of LEAF Tests
Extensive method development and refinement occurred in the course of evaluating coal fly ash and other
materials using the LEAF tests (U.S. EPA, 2009, 2010). LEAF has undergone multiple rounds of validation
in the laboratory and in the field to ensure that the data generated is as precise, accurate, and realistic as
possible (U.S. EPA, 2014c). The results of these studies indicate that the data generated by the test
methods are repeatable and provide a good representation of what will occur in the field for inorganic
constituents. The following text describes the results and conclusions of these different validation studies.
3.1.5.1 Interlaboratory Validation
EPA conducted interlaboratory validation studies to determine the repeatability and reproducibility of
each LEAF method (U.S. EPA, 2012c, 2012d). For each method, between seven and ten laboratories
participated in the study, each conducting testing in triplicate for a series of different materials types
including coal fly ash, an analog of a solidified waste, a contaminated smelter site soil and a brass foundry
sand. From eluate concentrations obtained from laboratory testing, method precision was calculated as
the intra-laboratory repeatability relative standard deviation (RSDr) and inter-laboratory reproducibility
relative standard deviation (RSDr). A summary of the interlaboratory validation results are presented in
Table 3-6. For example, Method 1313 results indicate that mean lab precision was 10% of the measured
value within a laboratory and 26% between laboratories. The results of interlaboratory validation provide
the confidence that each method provides the characteristic leaching behavior that is intended by the
LEAF leaching methods with a high degree of precision (U.S. EPA, 2012c, 2012d).
Table 3-6. Precision Data for LEAF Test Methods based on Interlaboratory Validation Studies
Method
Test Output
RSDr
RSDr
Method 1313
Eluate Concentration (average over pH range)
13%
28%
Method 1314
Eluate Concentration (mean at L/S 10 L/kg-dry)
12%
24%
Mass Release (cumulative to L/S=0.5)
7%
18%
Mass Release (cumulative to L/S=10)
5%
14%
Method 1315
Interval Flux (mean excluding wash-off)
12%
30%
Mass Release (cumulative to 7 days)
9%
19%
Mass Release (cumulative to 63 days)
6%
23%
Method 1316
Eluate Concentration (average over L/S range)
8%
19%
3.1.5.2 Field Validation
EPA evaluated the relationship between LEAF test results and leaching of inorganics from a broad range
of materials under disposal and beneficial use scenarios. This evaluation was achieved by defining a
framework for interpretation of laboratory testing results, comparison of laboratory testing on "as
produced" material, laboratory testing of "field aged" material, and results from field leaching studies,
and illustrating the use of chemical speciation modeling as a tool to facilitate evaluation of scenarios
beyond the conditions of laboratory testing. LEAF has been shown to provide effective estimates of
leaching behavior for inorganic constituents (e.g., Al, As, Sb, B, Ca, Cr, Cu, Fe, Pb, K, Mg,, Se, Si, Sr, V, Zn)
for a wide range of materials (the same ones used in inter-laboratory validation) under both disposal and
use conditions (U.S. EPA, 2014c).
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Based on the results of this study, EPA concluded that the combined results from pH-dependent leaching
tests (Method 1313) and percolation column tests (Method 1314) can provide accurate estimates of
maximum field leachate concentrations, extent of leaching and expected leaching responses over time. In
addition, this approach can predict or account for changes in environmental conditions under both
disposal and use scenarios within reasonable bounds. Results from batch testing at low L/S (Method 1316)
can be used in place of column test results when column testing is impractical. Method 1315 should be
used in combination with Method 1313 for scenarios when mass transport from monolithic or compacted
granular materials controls leaching. When field conditions existthat are beyond the domain of laboratory
test conditions (e.g., reduction of oxidized material or introduction of DOC from external sources), consult
with technical experts in geochemical speciation to develop an approach that is as technically robust as
current scientific knowledge allows.
3.1.6 Relationship between LEAF and Single Point Tests (e.g., TCLP, SPLP)
Traditional single-point leaching tests use specified leaching solutions designed to simulate release under
a specific set of environmental and management conditions. For example, the buffered, dilute acetic acid
eluant at an L/S of 20 mL/g (wet basis) used in TCLP (Method 1311) is specified so the eluate
concentrations represent leaching under a plausible mismanagement scenario of industrial waste co-
disposal in a municipal solid waste landfill (U.S. EPA, 1992; U.S. Federal Register, 1986). Although
procedurally analogous to TCLP, the SPLP (Method 1312) uses a blend of dilute inorganic acids to simulate
near-surface exposure of solid material to acidic precipitation (U.S. EPA, 1994).
The LEAF leaching test methods are designed to measure intrinsic leaching properties over a range of
environmentally relevant conditions. Eluate pH, L/S and physical form of the material (i.e., particle size)
are controlled as independent variables to provide measurements of the rate and extent of constituent
release into water contacting the material over a range of test conditions (Kosson et al., 2002)). For
example, Method 1313 varies the final pH at targets between 2 and 14 while maintaining a constant L/S
of 10 mL/g-dry, whereas Method 1316 allows the material to dictate eluate pH at five L/S levels between
0.5 and 10 mL/g-dry.
While typically not done in practice, when the endpoint pH of single point leach tests is recorded such as
in TCLP test reports, the results can be compared to pH-dependent LSP results from LEAF leaching testing
methods. The comparisons in Figure 3-9 illustrate that the results from single-point leaching tests typically
reflect one data point on the LSP curve at equilibrium. However, due to the different L/S values used in
these tests (e.g., TCLP and SPLP at L/S 20 mL/g; Method 1313 at L/S 10 mL/kg-dry), eluate concentrations
from TCLP and SPLP may graph slightly below the LSP curve for Method 1313 data.
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Figure 3-9. Comparison of TCLP (pink square) and SPLP (green triangle) results to pH-
dependent leaching from Method 1313 for a contaminated smelter site soil (CFS; top), a
solidified waste form (SWA; center) and a coal combustion fly ash (EaFA; bottom).
3.2 Building a Testing Program
Developing a testing program includes selection of appropriate leaching tests, target analytes for
evaluation, and analytical methods to sufficiently detect and measure chosen analytes. The testing
program should be specified in a quality assurance project plan (QAPP) that addresses the tests and
conditions to be conducted as well as testing and analytical QA/QC criteria used to support the testing
program. Additional information on development of analytical quality assurance can be found in chapter
one of SW-846 (U.S. EPA, 2014d; available online at https://www.epa.gov/hw-sw846/quality-assurance-
and-hazardous-waste-test-methods).
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3.2.1 Material Collection for Leaching Tests
The goal of material sampling and subsequent material preparation should be to obtain representative
samples and subsamples, or aliquots, of the materials being disposed or reused for use in the selected
leaching tests. Guidance on sampling is available at https://www.epa.gov/hw-sw846/sampling-guidance-
documents-sw-846-compendium. Initial sample collection should account for spatial and temporal
variations in material characteristics through appropriate compositing of individual grab samples. For piles
or accumulated quantities of (what is nominally) a single material, grab samples should be obtained from
different locations and depths within the accumulated material. For a material produced over time,
representative grab samples should be obtained at predefined intervals over the evaluation period.
Individual grab samples should have enough mass to be spatially or temporally representative. The goal
should be to have sufficient sample following preparation to meet the needs of the planned leaching
testing and characterization needs of the project. The information in Table 3-1 (Section 3) includes
recommended sample quantities for carrying out each LEAF leaching test. Depending upon variability in
material composition, replicate testing may be needed. Often-convenient field sample sizes and
containers are 2-liter wide-mouth jars, 1-gallon pails, and 5-gallon pails with tight-fitting re-sealable lids.
The container materials (e.g., high-density polyethylene, glass) must be compatible with the COPCs.
Sample collection systems and subsequent handling should be designed to avoid changes in sample
characteristics that may degrade the representativeness of the samples prior to analysis and can result in
misleading results. For example, oxidation or carbonation of samples during collection and/or handling
can result in changes in pH and constituent speciation and may significantly alter the leaching behavior of
some constituents. Samples should be particle-size reduced and homogenized shortly before sub-
sampling and testing to maximize the representativeness of results. Heterogeneity can result from
variations in the solid material, aging of the cured materials, or by exposure of leaching solutions to the
atmosphere.
3.2.2 Analytical Parameters
As specified in Methods 1313, 1314, 1315, and 1316, all eluates should be analyzed for pH and EC in the
laboratory immediately after contact with the solid. For Method 1313, measurement of EC should be
limited to only the natural pH eluate because of the addition of acid and base in other extractions provides
an artifact in the interpretation of ionic strength. The measurement of oxidation/reduction potential
(ORP) as an indicator of redox conditions is optional based on anticipated scenario conditions and material
properties, but for similar reasons to EC measurements, should be limited to the natural pH test position
for Method 1313 eluates (see 4.3.1 for more on interpreting ORP from LEAF testing).
The selection of COPCs and additional analytes for chemical analysis depends on the intended use of the
results, with assessment-specific COPCs determined based on the requirements of the applicable
regulatory agency, use of a screening list, and/or prior knowledge of the material being evaluated.
• Screening for COPCs - When the assessment objective to identify COPCs that have the potential
to impact the environment, sufficient chemical analysis may include RCRA metals (i.e., Ag, As, Ba,
Cd, Cr, Hg, Pb and Se) and/or inorganic species of the EPA Priority Pollutant List (i.e., Ag, As, Be,
Cd, Cr, Cu, Hg, Pb, Ni, Sb, Se, Tl and Zn). However, additional analytes may need to be included
based on consideration of the specific material being tested.
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• Understanding Basic Leaching Behavior - In addition to the RCRA or EPA Priority Pollutant List,
analyses should be conducted for constituents that can improve understanding of the LEAF test
results based on the predominant chemistry of the final eluate. Because of their ability to increase
eluate concentrations of COPCs, these additional constituents usually include dissolved carbon
from both organic (DOC) and inorganic (e.g., dissolved inorganic carbon, carbonate) forms. Even
minimal amounts of organic matter can dramatically influence the solution equilibrium chemistry
of many important trace species such as copper and lead. Chloride ions can form soluble
complexes with cadmium resulting in elevated measured concentrations of cadmium. In addition,
analysis of dissolved iron is a useful indicator of redox state, where elevated Fe concentrations
are indicative of reducing conditions.
• Detailed Characterization - For full characterization testing, chemical analysis is recommended
to include the above analyses as well as a full suite of major and trace constituents in all leaching
test eluates. Knowledge of the major constituents that control release of the trace constituents
improves understanding of the factors that may affect leaching and allows for calibration of
chemical speciation models. Prior knowledge from testing of analogous materials may reduce the
need for, or extent of, characterization testing.
3.2.3 Suggested Best Practices for Conducting LEAF Tests
As commercial laboratories become more familiar with the LEAF leaching tests, valuable experience will
be gained into the best practices for conducting these tests. Based on experience from developing,
validating, and conducting the LEAF leaching methods, the following best practices are recommended:
3.2.3.1 Reagent Selection and Preparation
• For Method 1313, select a base solution (i.e., NaOH or KOH) compatible with leaching assessment
objectives (i.e., potassium hydroxide should not be used if potassium is likely to be an assessment
constituent). Interlaboratory validation of Method 1313 has shown that KOH may increase eluate
concentrations of thallium and, therefore, NaOH should be used to raise eluate pH whenever
thallium is a COPC (U.S. EPA, 2012c).
• To the extent possible, bulk reagent solutions (i.e., dilute solutions of acid or base used in Method
1313 or the deionized water used in all LEAF tests) should be prepared immediately prior to use.
Storage of bulk solutions over prolonged periods between tests (e.g., > 1 week) should be avoided.
Reagents should be stored in containers compatible with the reagent to avoid contamination of
the solution (e.g., storing strong alkali solutions in borosilicate glass can result in contamination
due to dissolution of boron; U.S. EPA, 2012c).
3.2.3.2 Measurement of Eluate pH
• Meters used for pH measurement should be calibrated with a minimum of two standard pH buffer
solutions that span the range of anticipated pH values. Non-standard pH buffer solutions are
available as special order for calibration of very low pH (pH < 2) and very high pH (pH > 12) as
required for Method 1313. A third, mid-range standard solution (e.g., pH 7) should be used to
verify the two-point calibration.
• When eluate solutions are physically separated from the solid material (e.g., after filtration), the
weakly buffered liquid, especially highly alkaline solutions, may be highly susceptible to reactions
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with air. Thus, eluate pH measurement should be conducted as soon as possible after collection
of eluates to avoid carbonation of alkaline solutions and oxidation that could lead to precipitation
of carbonate and iron species, respectively. However, care should be taken during pH
measurement to ensure that a stable pH is obtained for each eluate.
3.2.3.3 Chemical Analysis
• Unlike single point extraction tests, the multipoint LEAF leaching test methods indicate "trends"
in leaching behavior over a range of conditions. Therefore, eluates from a LEAF test should be
considered a "set" of solutions that should be analyzed at a uniform analytical dilution whenever
practical. However, the measured concentrations over the set of solutions may span several
orders-of-magnitude, especially for Method 1313, and therefore analytical solutions may require
various levels of dilution to complete analysis.
• Major constituents may require dilution that prevents determination of trace constituents, thus
requiring analyses at more than one dilution factor to determine all specified constituents.
• Colloidal formation of DOC-bound analytes in leaching tests eluates can interfere with U.S. EPA
SW-846 analytical methods (e.g., Method 6010 or 6010); however, the influence of colloids can
be minimized by digestion of eluates following U.S. EPA SW-846 Method 3015A. Digestion may
be necessary prior to analysis of Al, As, Be, Cd, Co, Cr, Cu, Fe, P, Pb, Sb, Ti, Tl, U, and Zn in all
eluates with greater than 50 mg/L DOC.
3.2.3.4 Data Review
• Prior to the use of analytical data, the end user should review analytical QA/QC results to ensure
accuracy and consistency in the evaluation of analytical blanks, spike recoveries, and analytical
duplicates.
• Similarly, the results from leaching tests should be reviewed graphically for consistency in trends
within and between test replicates. Abnormal jumps or discontinuities in interrelated data may
indicate potential testing or analytical errors.
3.2.4 Quality Assurance/Quality Control
Preparing a detailed quality assurance project plan (QAPP) is an important first step in assuring high-
quality information for subsequent decision-making. A QAPP should be tailored to the data quality needs
of the project to ensure efficient use of resources. Minimum quality control for leaching tests should
include use and analysis of method blanks (e.g., extractions conducted without solid material) as specified
in each of the LEAF leaching test methods and appropriate quality control for the chemical analyses
carried out on leaching test eluates (e.g., analytical spike recoveries, repeatability, calibration verification,
etc.). Guidance on development of quality assurance project plans is provided by U.S. EPA (2002) and
further information can be found at https://www.epa.gov/quality.
Quality assurance for leaching tests should consider the following steps:
• Obtaining representative material sample(s) for testing;
• Execution of leaching tests with test-level QA/QC evaluations;
• Chemical analysis of test eluates following accepted methods and QA/QC procedures; and
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• Data management in a manner that minimizes human error and allows for validation relevant to
data quality objectives.
3.2.4.1 QA/QC Samples in LEAF Leaching Tests
The procedure for each of the four LEAF leaching test methods includes steps for collecting QA/QC
solutions (method blanks and eluant blanks) that are used to assess purity of the reagents and equipment
surfaces used in the tests. These solutions include samples of bulk reagents or method blank eluates (i.e.,
extractions without solid material conducted in parallel with test extractions, using the same reagents and
equipment) or samples of bulk reagents:
• Method 1313 - method blanks conducted in deionized water (natural pH), the highest level of
acid addition (pH 2.0 target), and the high level of base addition (pH 13 target);
• Method 1314 - a sample of bulk eluant at the start of the test and when the eluant source is
changed or refreshed;
• Method 1315 - a series of method blanks conducted in parallel with test fractions; and
• Method 1316 - a single method blank using deionized water conducted at the L/S 0.5 test
fraction.
All QA/QC samples should be preserved and analyzed for COPCs in the same manner as test eluates and
reviewed prior to utilization of leaching test results. Test method blanks should be less than the LLOQ or,
if greater than the LLOQ, less than 20% of the minimum measured analyte concentration (U.S. EPA, 2012c,
2012d).
3.2.4.2 Analytical QA/QC
An analytical program, including identification of analytes, setting of quantitation limits and analytical
quality assurance criteria, should be developed by consultation between the end user and the laboratory
conducting the leaching test(s) and, if different, the laboratory conducting chemical analysis. Analytical
data should be reviewed before applying LEAF assessment methodologies to ensure that quality
assurance requirements have been met. Analytical QA/QC should include a selection of the solutions and
evaluations shown in the sidebar to the right as appropriate to ensure adequate precision and accuracy
of measurements. At a minimum, QA/QC should include establishing detection and quantitation limits for
each analytical process and development of initial and continuing calibration.
Chemical analysis of leaching test eluates should include specification of reporting limits that are less than
the applicable threshold values that will be used in subsequent decision-making. Management of values
less than the reporting limits (e.g., less than the LLOQ or MDL) should be reported and used in calculations
in a manner consistent with the relevant regulatory or other applicable evaluation program. Options for
reporting and using values less than the reporting limits include using the reporting limit, one-half the
reporting limit, or one-tenth the reporting limit.11 Applicable U.S. EPA SW-846 analytical methods and
example MDLs and LLOQs for a selection of COPCs are provided in Table 3-7.
11 Further information on the determination and use of the LLOQ and MDL can be found at
https://www.epa.gov/measurements/detection-limitquantitation-limit-summary-table
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Analytical QA/QC Solutions
Although terminology may vary between laboratories, the following is a general list of typical
analytical QA/QC terms that may be used in chemical analyses.
• Method Detection Limit (MDL)-a statistically derived concentration of an analyte indicating that
the analyte concentration is greater than zero with 99% confidence. In practical terms, the MDL
represents the minimum concentration of an analyte for a given analytical technique and sample
matrix.
• Quantitation Limit - a minimum concentration of an analyte that can be measured within
specified limits of precision and accuracy. Although various forms of quantitation limits are
common, the lower limit of quantitation (LLOQ) should be reported for LEAF.
• Reporting Limit-the level at which method, permit, regulatory and client-specific objectives are
met. The reporting limit should be greater than the statistically determined MDL but may be or
may not be greater than quantitation limits.
• Calibration Standard - a certified standard solution containing known concentration of an analyte
measured to establish an initial calibration curve or to verify the validity of the calibration curve
during analysis.
• Calibration Blank - an analyte-free quality control sample prepared in the same manner as
calibration standards and used to establish reagent and system contributions to the analytical
result. Calibration blanks should be less than the quantitation limit.
• Internal Standard - a known amount of a non-interfering substance, different from the analyte,
used to adjust sample concentrations for the substance amount introduced to the instrument.
Internal standards are added to each analytical solution.
• Matrix Spike - an aliquot of sample with known quantities of specified analytes added (spike
amount) and analyzed to estimate interferences.
• Analytical Replicate - an analytical sample that has been split into two equal portions used to
measure precision associated with handling from preparation through analysis.
Commercial analytical laboratories have internal quality assurance/quality control procedures that
comply with their accreditation programs (e.g., National Environmental Laboratory Accreditation
Conference). When contracting with an analytical laboratory for LEAF testing, the user of this guide is
encouraged to review the QA/QC procedures, measured QA/QC solutions and evaluation frequencies with
the contracted analytical laboratory. These quality assurance and quality control procedures should be
considered with respect to the leaching assessment project QAPP and data quality objectives.
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Table 3-7. Example Analytical Method Detection Limit (MDL) and Lower Limit of
Quantitation (LLOQ) Values Compared to U.S. Drinking Water Standards
Symbol
Drinking Water
Standard
[Pg/L]
Analytical
Method
EPA SW-846
Method
MDL [pg/L]
LLOQ [pg/L]
Aluminum
Al
50-200N1
ICP-OES
Method 6010
1
50
Antimony
Sb
6
ICP-MS
Method 6020
0.08
1
Arsenic*
As
10
ICP-MS
Method 6020
0.36
1
Barium
Ba
2,000
ICP-OES
Method 6010
1
10
Beryllium
Be
4
ICP-MS
Method 6020
0.6
1
Boron
B
7,000N2
ICP-OES
Method 6010
4.3
10
Cadmium
Cd
5
ICP-MS
Method 6020
0.08
1
Calcium
Ca
—
ICP-OES
Method 6010
2.6
10
Carbon (Inorganic)
IC
—
TOC
Method 9060A
130
500
Carbon (Organic)
OC
—
TOC
Method 9060A
170
500
Chloride
CI
250,000N1
IC
Method 9056A
6.5
20
Chromium*
Cr
100
ICP-MS
Method 6020
0.44
1
Cobalt
Co
ICP-OES
Method 6010
0.26
1
Copper
Cu
1,300N3
ICP-OES
Method 6010
2.5
10
Iron
Fe
300n1
ICP-OES
Method 6010
1.3
10
Lead
Pb
15mb
ICP-MS
Method 6020
0.062
1
Magnesium
Mg
ICP-OES
Method 6010
1.7
10
Manganese
Mn
1,600N2
ICP-OES
Method 6010
1
10
Mercury
Hg
2
CVAA
Method 7470A
NR
0.025
Molybdenum
Mo
200N2
ICP-OES
Method 6010
0.72
1
Nitrate
N03
10,000
IC
Method 9056A
26
100
Nitrite
N02
1,000
IC
Method 9056A
18
50
Phosphate
P04
IC
Method 9056A
24
100
Phosphorus
P
ICP-OES
Method 6010
4.1
10
Potassium
K
ICP-OES
Method 6010
2.3
10
Selenium
Se
50
ICP-MS
Method 6020
0.54
1
Silicon
Si
ICP-OES
Method 6010
3.1
10
Sodium
Na
ICP-OES
Method 6010
3.7
10
Sulfate
S04
250,000N1
IC
Method 9056A
21
100
Sulfur
S
ICP-OES
Method 6010
4.7
10
Thallium*
Tl
2
ICP-MS
Method 6020
0.53
1
Uranium
U
30
ICP-MS
Method 6020
0.18
1
Vanadium
V
ICP-OES
Method 6010
1.9
10
Zinc
Zn
10M2
ICP-OES
Method 6010
1
10
COPCs indicated in bold red are used in subsequent example cases.
* Method detection limit (MDL) greater than minimum indicator value.
Drinking water standards are the National Primary Drinking Water Regulations (U.S. EPA, 2012a) unless noted:
N1 National secondary drinking water regulations—non-enforceable guideline.
N2 Drinking water equivalent level.
N3 Treatment technique action level.
ICP-MS - Inductively coupled plasma mass spectrometry.
ICP-OES - Inductively coupled plasma optical emission spectrometry.
IC - Ion chromatography.
TOC -Total organic carbon.
CVAA- Cold vapor atomic absorption.
Typically, initial calibration is conducted at the beginning of the analytical process or as recommended by
analytical process or the instrument manufacturer. Continuing calibration is recommended to be
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Overview of LEAF
-------
conducted periodically (e.g., every 20 analytical samples) and assessed relative to the expected value (e.g.,
within 15% of the standard value). For chemical analysis of LEAF eluates, it is recommended that matrix
spikes and analytical replicates be carried out on the following test fractions:
• Method 1313: Eluates corresponding to the natural pH condition, the maximum acid condition
(lowest pH target), and the maximum base condition (highest pH target);
• Method 1314: Eluate collected at cumulative L/S 0.5 and 10 mL/g-dry;
• Method 1315: Eluate from the 1-day cumulative leaching fraction; and
• Method 1316: Eluate conducted at L/S 0.5 mL/g-dry.
Matrix spikes are measured periodically over a set of analyses (e.g., once for each test) and are evaluated
as a percent recovery of a known spike amount (e.g., within 15% of expected value). Analytical replicates
are recommended at regular intervals during an analysis (e.g., once for each test) and are evaluated as a
replicate percent difference between replicate analyses.
3.2.5 Testing and Analytical Costs
Estimated total analytical costs for a single test are anticipated to range from $2,000 to $5,000, which
includes an extensive suite of chemical analyses. Estimated costs for laboratory services are presented in
Table 3-8 through Table 3-11. The method-specific costs in these tables are estimated for single testing
runs on an unknown material with a more complete suite of chemical analytes (e.g. pH, EC, ORP, metals,
anions) than may be applicable for other scenarios. Costs also include the preparation of an electronic
data deliverable for uploading to LeachXS™ Lite for data interpretation. Additional cost information is
available in EPA's Background Information for the Leaching Environmental Assessment Framework (LEAF)
Test Methods (US EPA, 2010). Reductions in costs to laboratories are anticipated as the methods become
commercialized, equipment specific to the test methods is developed, and data interpretation becomes
automated. LEAF may be more economical for significant amounts of material because the potential
analytical costs may be fixed while the quantity of material is scalable. A stepwise approach to testing can
be more economical for smaller material volumes and therefore more broadly feasible (Kosson, van der
Sloot et al., 2002).
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Overview of LEAF
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Table 3-8. Estimated Laboratory Costs for Method 1313
Parameters
Method
Matrix
Unit
Price
Number of
Analytical
Samples2
Single
Sample Cost
LEAF 1313 1
SW846 1313
Solid
$1,650
1
$1,650
PH
SW846 9040C
Water
o
T—1
-c/>
19
$190
Oxidation-reduction potential
SM 2580B
Water
$20
12
$240
Conductivity
SM 2510B
Water
00
T—1
-c/>
12
$216
DOC/DIC
SW846 9060A
Water
$30
12
$360
Metals (19-22)
SW846 6020A
Water
o
00
-c/>
12
$960
Mercury
SW846 7470A
Water
$25
12
$300
Anions (4-7)
SW846 9056A
Water
$75
12
$900
Total:
$4,816
Source: A representative US commercial laboratory (2015)
1 The cost for Method 1313 includes:
A) Sample air-drying to the prescribed >85% total solids.
B) Particle size reduction and sieving of the sample.
C) Nine parallel extractions at the prescribed method pH ranges.
D) Seven pretest extractions used to determine titration curve.
E) Three extraction blanks at low pH, neutral pH, and high pH.
F) A charge for an electronic data deliverable (EDD).
2 Total number of analytical samples includes three method-prescribed blanks. Number of pH samples includes the
seven pre-test samples.
Table 3-9. Estimated Laboratory Costs for Method 1314
Parameters
Method
Matrix
Unit Price
Number of
Analytical
Samples 2
Single Sample
Cost
LEAF 1314 1
SW846 1314
Solid
$1,870
1
$1,870
PH
SW846 9040C
Water
$10
10
$100
Oxidation-reduction potential
SM 2580B
Water
$20
10
$200
Conductivity
SM 2510B
Water
00
T—1
-co-
10
$180
DOC/DIC
SW846 9060A
Water
$30
10
$300
Metals (19-22)
SW846 6020A
Water
$80
10
$800
Mercury
SW846 7470A
Water
$25
10
$250
Anions (4-7)
SW846 9056A
Water
$75
10
$750
Total:
$4,450
Source: A representative US commercial laboratory (2015)
1 Included in the cost for Method 1314 is the following:
A) Sample air-drying to the prescribed >85% total solids.
B) Particle size reduction and sieving of the sample.
C) One extraction blank collected at Time 1.
D) A charge for an EDD.
2 Total number of analytical samples includes one method prescribed blank.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Overview of LEAF
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Table 3-10. Estimated Laboratory Costs for Method 1315
Parameters
Method
Matrix
Unit Price
Number of
Analytical
Samples 2
Single Sample
Cost
LEAF 1315 1
SW846 1315
Solid
$1,100
1
$1,100
PH
SW846 9040C
Water
$10
18
$180
Oxidation-reduction potential
SM 2580B
Water
$20
18
$360
Conductivity
SM 2510B
Water
00
T—1
-co-
18
$324
DOC/DIC
SW846 9060A
Water
$30
18
$540
Metals (19-22)
SW846 6020A
Water
o
00
-co-
18
$1,440
Mercury
SW846 7470A
Water
$25
18
$450
Anions (4-7)
SW846 9056A
Water
$75
18
$1,350
Total:
$5,744
Source: A representative US commercial laboratory (2015)
Table 3-11. Estimated Laboratory Costs for Method 1316
Parameters
Method
Matrix
Unit Price
Number of
Analytical
Samples 2
Single Sample
Cost
LEAF 1316 1
SW846 1316
Solid
$730
1
$730
PH
SW846 9040C
Water
$10
6
$60
Conductivity
SM 2510B
Water
$18
6
$108
Oxidation-reduction potential
SM 2580B
Water
$20
6
$120
DOC/DIC
SW846 9060A
Water
$30
6
$180
Metals (19-22)
SW846 6020A
Water
$80
6
$480
Mercury
SW846 7470A
Water
$25
6
$150
Anions (4-7)
SW846 9056A
Water
$75
6
$450
Total:
$2,278
Source: A representative US commercial laboratory (2015)
1 Included in the cost for the Method 1316 is the following:
A) Sample air-drying to the prescribed >85% total solids.
B) Particle size reduction and sieving of the sample.
C) One extraction blank.
D) A charge for an EDD.
2 Total number of analytical samples includes one method-prescribed blank.
3.2.6 Processing Time
Table 3-12 presents approximate processing times (in days) for conducting LEAF testing and chemical
analysis of eluate after receipt of a material by the laboratory. Actual processing times would need to be
negotiated with contracted laboratories. Accelerated testing may be available, though at least one week
is needed for Method 1313 and 1316 and two weeks are needed for Method 1314. Method 1315 may be
carried out more quickly if not all eluates are required. For a step-by-step breakdown of labor and
processing time in a research laboratory, see the Background Information for the Leaching Environmental
Assessment Framework (LEAF) Test Methods (US EPA, 2010).
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Overview of LEAF
-------
Table 3-12. Processing Time
¦1
Turnaround Time in
Days from Receipt at Laboratory
Method 1313
35
Method 1314
35
Method 1315
84 (63 + 21 for analyses/reporting)
Method 1316
28
Source: US EPA (2010)
3.3 LEAF Data Management Tools
Because LEAF multi-point testing and comprehensive chemical analysis creates a considerably large data
set of inter-related leaching measurements, LEAF includes tools for collecting, managing, and reporting
data. Microsoft Excel® spreadsheets are provided as templates to assist laboratory personnel in
preparation of tests and collection bench and analytical data. These templates import directly into
LeachXS™ Lite, a desktop-based decision support software provided as a free download intended to be
used as a data management tool for LEAF data (see Section 6, "Useful Resources").
3.3.1 Laboratory Data and Import Templates
LEAF and LeachXS™ Lite include a set of method-specific Excel® spreadsheet templates (available at
http://www.vanderbilt.edu/leaching/downloads/test-methods) that laboratories can use to calculate test
parameters, record and document laboratory observations, and archive analytical results. These data
templates, illustrated in Figure 3-10, contain the verified calculations required to conduct each method at
the bench scale. The embedded calculations and upload-ready format help assure data quality by
minimizing errors in calculations and data transfer. Special care is recommended in ensuring that results
are entered into the templates using the parameter units indicated (e.g., eluate concentrations in ng/L)
and that the entered analytical data properly accounts for eluate dilutions for chemical analysis. These
are the two most common errors in using the templates. Populated templates can be uploaded directly
into all versions of the LeachXS™ data management program.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Overview of LEAF
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fi
1
METHOD 1313 LeachXS™ Lite Data Template
2
1
3
4
METHOD 1313 LAB EXTRACTION DATA
Extraction Information
r
5
Code
Test conducted by:
D. McGill
LS Ratio
10
mL/g-dry
6
7
Project
Material
US EPA
KS Fly Ash
Solids Information
Liquid Volume / Extraction
Recommended Bottle Size
200
250
mL
mL
8
Test Replicate
A
Particle Size (85 wt% less than)
0.3
mm
Temperature
21
•c
9
Dry Equivalent Mass
20.00
g-dry
10
Date
Time
Solids Content (default = 1)
0.823
g-dry/g
Reag
ent Information
11
Test Start
11-May-ll
10:00 AM
Mass of "As Tested" Material/Extraction
24.30
g
Acid Type
HN03
*
12
Test End
12-May-ll
9:35 AM
Acid Normality
2.0
meq/mL
13
14
Required Contact Time
23-25
hr
Base Type
Base Normality
KOH
1.0
*
meq/mL
15
16
5
CO
Test Position
Schedule
T01
of Acid and Base Additions
T02 T03 T04
T05
T06
T07
T08
T09
NAT
B01
B02
B03
Amounts Needed
17
"As Tested" Solid [g] (±0.05g)
24.30
24.30
24.30
24.30
24.30
24.30
24.30
24.30
24.30
24.30
no solid
no solid
no solid
243.0 g
18
C
Reagent Water [mL] (±5%)
180.70
194.70
195.40
194.90
193.70
191.70
190.70
155.70
195.70
200.00
160.00
185.00
2238.2 mL
19
E
3
O
u
QJ
TD
SI
c
Acid Volume [mL] (±1%)
0.30
0.80
2.00
4.00
5.00
40.00
40.00
92.1 mL
20
Base Volume [mL] (±1%)
15.00
1.00
15.00
31.0 mL
21
22
Acid Normality [meq/mL]
Base Normality [meq/mL]
1.0
1.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
1.0
23
24
Target pH
13.0+0.5
12.0±0.5
10.5±0.5
9.0±0.5
8.0+0.5
7.0+0.5
5.5±0.5
4.0±0.5
2.0±0.5
NAT
25
Acid Addition [meq/g]
-0.75
-0.05
0.03
0.08
0.2
0.4
0.5
4
0
Water
Acid
Base
26
..
Eluate pH
12.91
12.05
9.31
8.49
7.45
5.87
4.31
2.24
10.47
27
SSISTANCE
Eluate EC [mS/cm]
17.78
0.6621
0.4256
0.9721
1.81
3.52
4.904
22.72
0.1035
28
Eluate ORP [mV]
29
30
31
32
Notes or Remarks
Natural pH
meets 10.5
target
range.
33
Meets pH criteria?
«/
V
*<
V
*
V
~
V
Enter "a" for acceptable or "r" for rejected.
34
<
WW
HBH
........
MAT «.
i ,
Material Classification | Moisture Content | Pre-Test Lab Extractions Lists i ©
Figure 3-10. Example of a Microsoft Excel® data template for recording and archiving
laboratory and analytical information from LEAF tests.
3.3.2 Data Management with LeachXS™ Lite
LeachXS™ Lite is a limited capacity version of LeachXS™12 that provides users with a simplified tool for
comparing leaching data between materials and test types and for exporting tabular and graphical
leaching results. The Microsoft Excel® templates upload LEAF leaching test data directly from the
LeachXS™ Lite interface and output results are exported as Microsoft Excel® workbooks for easy
incorporation into reports and other documents. LeachXS™ Lite can be used to facilitate the process of
compiling data from testing, compare leaching results within and between tests or material replicates and
between different materials, and formulate standardized tables and graphics for data reporting. The
flowchart in Figure 3-11 illustrates the general structure of the LeachXS™ program with the inputs to and
outputs from LeachXS™ Lite.
12 LeachXS™ is licensed software whereby on-going development is supported by annual user fees. The LeachXS™ program was
developed in collaboration between Vanderbilt University, the Energy Research Centre of The Netherlands and Hans van der
Sloot Consultancy. Development of early versions of LeachXS™ also included participation byDHI (Denmark).
Leaching Environmental Assessment Framework (LEAF) Flow-To Guide
An Overview of LEAF
-------
LEAF Scenario
Evaluation Guide
Materials
(Leaching Data, Total Content,
Physical Properties)
Scenarios
(e.g., Fill Characteristics, Geometry,
Infiltration, Hydrologic Properties)
Materials
Database
Scenario
Database
Reference
Threshold
Database
\
*
Excel
Spreadsheets
(Data, Figures)
LeachXS
Lite
Reports
LEAF
Screening
Assessment
Leaching
Source Terms
(Inputs to
groundwater fate
and transport models,
e.g., IWEM, etc.)
IWEM = Industrial Waste Management Evaluation Model
Figure 3-11. LeachXS™ Lite program structure showing data inputs, databases and outputs.
LeachXS™ Lite was created as a collaboration between the LeachXS™ development team and U.S. EPA
with the initial purpose of facilitating data analysis and presentation of leaching potential for CCRs in U.S.
EPA research (U.S. EPA, 2006a, 2008, 2009). Thus, the default materials database included in LeachXS™
Lite contains leaching data on more than 40 constituents found in 70 CCR samples and several other
materials. However, like the LEAF methods, the LeachXS™ Lite program is not specific to any particular
material type and can be used to evaluate any material for which LEAF leaching data has been generated.
A sample screen capture of the primary interface in LeachXS™ for comparison of leaching from granular
materials is presented in Figure 3-12.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Overview of LEAF
-------
Leaching Expert System - LeachXS Lite J
File Help
Welcome to LeachXS Lite
LeachXS Lite'"
constituents _
version of thi
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First, select t
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functions car
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Step 1: Select pH Dependent Data Step 2: Select Percolj
Skp ths step to exciide pH dependent data Sk© ths step to excfcde pe
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0 Add overal poVnomel fit cufve
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Display Units
0 Show pH <-> leading n mg/kg
® Show pH <•> Leachng « mg/L
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0 Show L/S <-> Release (m
0 Show L/S <•> Concentrate
~ Show L/S <•> pH
Composition and Availability
0 Show Total Content, if avaiable
0 Show avatebifcy, if avaiable
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Edit... Select...
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ata
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contxuent at a
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~ Show fitted exponential model values N
weights [wone
Material l ine Scheme
Figure 3-12. LeachXS™ Lite interface for comparison of granular materials showing the
approach for comparing pH-dependent arsenic data for three CCR materials.
3.3.3 Pre-Existing Leaching Data
LeachXS™ Lite contains data on a limited number of samples analyzed through EPA support and other
data that is publicly available. A wider spectrum of leach test results from data collected over several
decades is available in the LeachXS™ database (available at www.vanderbilt.edu/leaching; accessed May
2, 2016). The comprehensive database includes LEAF test results from more than 250 waste types,
secondary materials, contaminated soil, mineral processing slags, sludges, mine tailings, industrial waste
streams (e.g., red mud), fertilizers, municipal solid waste and incineration residues, and construction
products. In addition, users of LEAF and LeachXS™ Lite will generate additional data on materials of
interest as testing continues. Such pre-existing LEAF data for a particular waste material or material type
can be helpful in the understanding of a subject material and useful to inform testing schedules and
possibly reduce testing costs.
For example, the material database contained within LeachXS™ Lite contains the leach test results that
supported the EPA evaluations of CCRs from power plants employing different air pollution control
technologies and burning different types of coal (U.S. EPA, 2006a, 2008, 2009). These materials include a
number of samples of coal combustion fly ash, flue gas desulfurization (FGD) gypsum, and several
combined CCR waste streams. CCR generators can compare LEAF leaching test method results for their
materials to the existing LeachXS™ Lite data to put their materials into perspective of the wider range of
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Overview of LEAF
-------
similar materials and to better understand CCR leaching potential from the interpretation of leaching data
from these EPA evaluations.
For materials that are generated and evaluated on a regular or ongoing basis, pre-existing leaching data
may be helpful for optimizing the assessment process. The scope of a testing program to characterize a
waste can be potentially focused to obtain missing data or to evaluate consistency with previous material
characterizations. Periodic testing of continuous or near-continuous waste streams can inform the
industrial process as the long-term variability of leaching performance is established through time-
dependent sampling and characterization.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Overview of LEAF
-------
4. Developing Leaching Evaluations using LEAF
In general, a leaching assessment can be described as developing a leaching source term by estimating
COPC release to the environment resulting from material contact with infiltrating rain or with
groundwater. One or multiple LEAF tests can be used in an assessment depending on the parameters
needed to represent the material when placed in the environment. The progressive nature of the LEAF
framework tests allows assessment to occur in a stepwise progression with evaluation as to whether the
results at each step are adequate to support a determination that the material is appropriate for the
planned use or disposal. If the results at each step are not adequate, additional testing or more-detailed
evaluations may be conducted to provide assessments that more fully reflect release in the anticipated
placement. For example, a relatively simple screening assessment comparing the results of an individual
LEAF test method directly with COPC target values (e.g., drinking water MCLs) may provide adequate
support in some assessments when no COPC target values are exceeded at any pH value, or over the
plausible range of pH values. However, when screening assessments cannot provide adequate supporting
results, further testing (e.g., Method 1314 and/or Method 1315) and site-specific data may be required
to develop a leaching source term that considers the effects of field conditions for a particular scenario
and the time varying leaching behavior (referred to as a "scenario assessment"). Additionally, leaching
assessments for some cases may utilize empirical or numerical modeling to describe the movement of
COPCs from the source term derived from one or more LEAF test methods to a defined point-of-
compliance.
Using a "source-to-compliance point" approach, the leaching test results are material specific in that they
are only a function of the material leaching performance; the source term accounts for the release under
the environmental conditions of the application scenario; and the source term may be used with dilution
and attenuation factor(s) (DAFs) or as an input to fate and transport models to account for the location-
specific point-of-compliance or source-to-receptor factors (in some cases, the POC may be treated waste
prior to disposal, or the outer edge of contaminated soil that has been treated in-place, without use of
groundwater transport modeling i.e., a DAF with the value 1). Results from this form of evaluation can be
used to back-calculate from thresholds at the point of compliance or to develop threshold values directly
comparable to leaching test results for specific scenarios. In addition, this approach allows for substantial
decoupling of leaching test results, source term models, and location-specific factors to allow greater
generalization of the approach and applicability of leaching test data. This approach allows users to
generate "what if" model simulations to understand likely changes in release/risks for the material under
hypothetical conditions.
This chapter explains how to develop a leaching evaluation utilizing the LEAF test methods. A leaching
evaluation requires determining the appropriate tests and testing parameters and then understanding
how laboratory scale results can be translated to field settings. The appropriate selection of leaching tests
will depend upon both material properties and the anticipated environmental conditions, as well as on
the environmental decision that testing is intended to support. In some cases, a simple evaluation with
minimal testing will provide sufficient results that adequately support environmental decision-making. A
more thorough and complex evaluation may be needed when there is large uncertainty in the leaching of
a material due to possible changing environmental conditions, high waste heterogeneity, or waste
generated in high volumes (where more certainty about release potential may be needed). Alternatively,
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Developing Leaching Evaluations using LEAF
-------
a more thorough leaching evaluation may be warranted when the estimated leaching is close to a
regulatory threshold, where more certainty about the release potential would also be needed.
4.1 Applications of LEAF
LEAF has been used for leaching assessment of CCRs in both disposal and reuse situations, for evaluating
waste treatment effectiveness and in other assessments. These uses illustrate that it can be used to
estimate constituent leaching from a wide range of inorganic materials as-is, or under environmental
scenarios relevant for the beneficial use, treatment, and disposal of waste:
• Materials types for which LEAF is applicable include wastes, treated wastes (e.g., materials treated
by solidification/stabilization), secondary materials potentially being re-used (e.g., blast furnace
slags, bauxite residues), energy residuals (e.g., coal combustion fly ash), contaminated soils and
sediments, and mining and mineral processing wastes.
• Scenarios that can be evaluated using LEAF include, but are not limited to, coal combustion
residue (CCR) disposal units, large or small scale use of secondary materials in concrete or road
construction, management of mining and mineral processing wastes, evaluation of soil
amendments, and evaluation of treatment effectiveness for contaminated soils, sediments, and
wastes.
• LEAF leaching tests provide data that can be used to address a range of assessment objectives
including simple screening assessments to evaluate material acceptability for a selected disposal
or use application, consistency testing during and after treatment of waste or contaminated
materials, and development of detailed leaching source terms for driving more complex fate and
transport models.
The factors addressed by the LEAF leaching tests include the most significant determinants of leaching for
most solid materials under most disposal or use conditions, including wastes and secondary materials
(U.S. EPA, 2014c). The framework recognizes that some factors (e.g., reducing conditions), may be
important for certain materials and field scenarios, but are difficult to evaluate reproducibly in a
laboratory setting. However, their effects on the leaching process may be evaluated using LEAF test results
in conjunction with geochemical speciation modeling. Section 4.3 provides examples of additional factors,
typical COPC leaching behaviors and considerations when developing leaching assessments.
4.1.1 Material Characterization
LEAF was developed for the assessment of a broad range of materials; however, the need to assess CCR
leaching proved to be an opportunity to refine and validate LEAF for inorganic constituents. As a result,
the initial development of LEAF was directed at evaluating and comparing leaching potential of CCRs
generated by facilities burning a range of coal types and utilizing various air pollution control technologies.
LEAF was used to assess the potential leaching of mercury and other metals from CCRs over the range of
field conditions to which CCRs are typically exposed during land disposal and in engineering and
commercial re-use applications (Thorneloe et al., 2010; U.S. EPA, 2006a, 2008, 2009). The LEAF methods
also provided leaching data in support of EPA's assessment of the potential hazards from using coal fly
ash as partial replacement of cement in making concrete (Garrabrants, Kosson, DeLapp, & van der Sloot,
2014; Kosson et al., 2014; U.S. EPA, 2012b, 2012d, 2014a).
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Developing Leaching Evaluations using LEAF
-------
4.1.2 Beneficial Use Evaluation
LEAF has also been applied to leaching assessments estimating the environmental impacts from utilization
of secondary materials, primarily as construction materials. The pH-dependent and L/S-dependent
leaching behavior of contaminated dredged sediments for potential replacement of sand in the
manufacture of controlled low-strength material, or flowable fill, has been characterized using LEAF tests
(Gardner, Tsiatsios, Melton, & Seager, 2007). The LEAF approach has been used to evaluate the reuse of
coal fly ash as road base material and construction of embankments; municipal solid waste incinerator
(MSWI) bottom ash as road base; and secondary materials (e.g., coal fly ash, recycled concrete aggregate,
furnace slags) used as partial substitutes for Portland cement or admixtures in cement and concrete
construction products (U.S. EPA, 2014c). In Europe, leaching procedures analogous to the LEAF methods
(see Appendix A) have been used to evaluate materials such as coal fly ash, recycled concrete aggregate
or municipal solid waste incinerator bottom ash for reuse in road bases and embankments (Engelsen et
al., 2010; Engelsen, Wibetoe, van der Sloot, Lund, & Petkovic, 2012), and use of a byproduct from the
aluminum industry as soil amendment (Carter, van der Sloot, & Cooling, 2009). In China, LEAF methods
have been used to evaluate the environmental safety of use of sewage sludge compost as an agricultural
amendment (Fang, et al., 2017, 2018). Leaching data from LEAF or other relevant leaching tests can be
used in EPA's Methodology for Evaluating Beneficial Uses of Industrial Non-Hazardous Secondary
Materials, which presents a voluntary approach for evaluating potential adverse impacts to human health
and the environment from a wide range of industrial non-hazardous secondary materials and their
associated beneficial uses. Prior to beneficially using secondary materials in any projects, interested
individuals or organizations should consult with the relevant state and federal environmental agencies to
ensure proposed uses are consistent with state and federal requirements.
4.1.3 Treatment Effectiveness
LEAF leaching test methods have also been applied to evaluate treatment effectiveness for remediation
or disposal purposes for industrial wastes such as soil, sludge, and slag using stabilization/solidification
technologies. In these cases, leachability is considered a primary performance parameter used to assess
treatment effectiveness because it indicates the ability of a treatment material to retain or immobilize a
specific set of site contaminants of concern (Pereira, Rodriguez-Pinero, & Vale, 2001). Additional examples
of application of LEAF leaching test methods for treatment effectiveness include evaluation of treatment
process effectiveness for contaminated soils (Sanchez et al., 2002; U.S. EPA, 2003).
4.1.4 Miscellaneous Uses
In Europe, leaching tests analogous to the LEAF methods have been used to develop regulatory criteria
for construction products that may be used on the ground (BMD, 1995; SQD, 2007; Verschoor et al., 2008)
and guidelines for assessment of sustainable landfill in the Netherlands (Brand et al., 2014). Additionally,
leaching tests were used as the basis for evaluation of ecological toxicology (ecotox) testing of soils and
wastes (Postma, van der Sloot, & van Zomeren, 2009). These applications are beyond the scope of this
guide.
4.2 Developing an Assessment Framework
The goal of environmental leaching assessments is to provide an estimate of the leaching potential of
constituents in a material for a plausible management scenario that is as accurate as practical or needed,
but also represents an upper bound that does not underestimate the release of COPCs. LEAF leaching test
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methods can be used effectively to estimate the field leaching behavior of a wide range of materials under
both disposal and use conditions. However, it is important to interpret the leaching test results in the
context of the controlling physical and chemical mechanisms of the field scenario (U.S. EPA, 2014c). The
application of laboratory testing results to environmental decision-making requires comparability of the
laboratory data with threshold or limit values at a defined point of compliance or location. This
comparison may be achieved through (i) screening assessments (i.e., comparisons of bounding leaching
concentrations based directly on test results with threshold values), (ii) scenario-based assessments for
percolation and/or mass transport scenarios, or (iii) subsequent analyses such as the combining of LEAF
source terms with fate and transport or geochemical speciation modeling representing environmental
processes not accounted for by LEAF.
The first step in developing an assessment is to define the objectives of the assessment and the
parameters of the potential material use or disposal scenario. These definitions will support the
subsequent selection of appropriate leaching tests and will provide the basis for interpreting and applying
the resultant leaching data. The assessment scenario is described by a conceptual model of constituent
leaching that considers the physical and leaching characteristics of the material when doing a screening
assessment. When conducting a scenario-based assessment, details about its anticipated placement (i.e.,
quantity, depth or height, footprint, porosity, etc.), the net amount and mode of water contact, the water
quality, would be added to the waste characteristics data.
4.2.1 A Stepwise Assessment Approach
When developing an assessment approach using multiple tests to evaluate leaching in a scenario, the
assessor can consider the information provided by each test in a stepwise fashion. Starting with the
simplest tests and considering the expected results before moving on to more elaborate testing schemes
allows for developing the appropriate leaching evaluation tailored to the environmental scenario. The
LEAF assessment approach can be viewed as a set of progressive steps, whereby each successive step
becomes more accurate by more fully reflecting site conditions present in the environment. However,
each successive step requires an additional level of testing and interpretation. Screening assessments can
provide increasingly refined estimates of the maximum leaching concentration (considered an "infinite
source") for each COPC, while scenario assessments provide estimates of the time varying leaching
concentration and the amount of each COPC that may leach (i.e., a "finite source"). LEAF provides
flexibility in developing an assessment approach because the amount of testing and effort can be tailored
to the assessment, depending upon the objectives of the assessment and the relevant information
regarding the material and the environment. An illustration of the hierarchy in this stepwise approach to
leaching assessment is provided in Figure 4-1. LEAF provides user flexibility in that an evaluation may
utilize one to four methods depending on the assessment objectives and project scope. A LEAF evaluation
may vary from a simple screening estimate using the results of a single test method to a comprehensive
evaluation of leaching behavior of multiple COPCs that encompass the results of all four LEAF methods.
The selection of an evaluation approach will result in differing amounts of material required for testing
and scenario specific information that required to conduct the assessment. Table 4-1 illustrates testing
plans in screening based assessments (described in section 4.2.4). Table 4-2 illustrates testing plans for
use in scenario-based assessments (described in section 4.2.5)
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Testing and Assessment Level
Total Content
(digestion, XRF)
Available Content
(Method 1313)
Equilibrium-pH
(Method 1313)
Equilibrium-L/S
(Method 1314 and/or 1316)
Percolation
(Method 1313 & 1314)
Mass Transport
(Method 1313 & 1315)
Screening Assessments
(Infinite Source)
Scenario Assessments
(Finite Source)
Reactive Transport
Simulations
3
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at
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to
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More Data/Effort
More Refined
Figure adapted from Kosson and van der Sloot (2015).
Figure 4-1. Example assessment hierarchy presenting options for progressively working
from more bounding assessments to less bounding assessments based on levels of leaching
information.
4.2.2 Assessment Objectives
Since the LEAF approach is intended to be flexible and to follow a stepwise methodology, the objectives
for conducting an assessment determine the amount of testing and data analysis required. For example,
a relatively simple screening assessment typically requires less testing and interpretation than a more-
complex "source-to-compliance point" assessment. The objectives of the assessment should address the
decisions anticipated to be made, the nature and physical structure of materials to be tested, the potential
scenarios that may be evaluated, and all applicable regulations or constraints. Definition of these
objectives can follow the Agency's data quality objectives process (U.S. EPA, 2006b) whereby the data
quality objectives or questions to be answered for a specific circumstance (e.g., beneficial use of a
material, site characterization) may influence the decision to use LEAF and the selection of a testing
program.
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One outcome of defining the assessment objectives is the identification of the appropriate leaching
assessment level (e.g., screening assessment vs. detailed characterization) required to meet the
assessment objectives. The extent of information needed as part of the scenario definition increases as
the evaluator seeks to achieve a more detailed and refined (and potentially, site-specific) estimate of
constituent leaching. For example, screening level assessments, which seek to determine the acceptability
of a material for a particular management scenario based on direct comparison of leaching test data to
exposure limit values, such as MCLs, may only require a single test (e.g., Method 1313 or 1314) to provide
an adequate basis for making a scientifically supported decision. Detailed characterization to support a
complex fate and transport model between the leaching source term and a point of compliance will
require integration of leaching data from several leaching tests and incorporation of knowledge of the
environmental scenario. The assumptions used when defining assessment objectives and determining
information needs should be fully described so that results between assessments can be meaningfully
compared.
4.2.3 Comparing Test Results to Threshold Values
4.2.3.1 Direct Comparison of Eluates to Threshold Values
Depending on the defined assessment scenario and the regulatory program, relevant benchmarks may be
derived from drinking water maximum contaminant levels (MCLs), national recommended water quality
criteria, or EPA regional screening levels (RSLs); however, a set of specific benchmarks should be
determined on a case-by-case basis based on assessment objectives and all associate constraints and
limitations. Figure 4-2 illustrates a graphical comparison of leaching results over a range of pH values to
the regulatory limit for a particular constituent, and to the total content of the constituent in the material
that was evaluated. When used to evaluate materials, the LEAF leaching test method results can be used
as the source term for risk assessment to generate estimated risk distributions that can form the basis for
environmental decision-making. This example is for illustrative purposes; users should consult with the
appropriate regulatory body to select appropriate acceptance criteria.
100
Total Content
'Available Content
O)
E
Threshold
0.1
u
E
V
Ifl
L_
0.01
<
LLOQ_
MDL
0.001
0.0001
0
2
6
8
10
12
4
14
PH
Adapted from Kosson et al. (2002).
Figure 4-2. Method 1313 LSP results over an applicable pH domain compared to total
content, available content and a reference threshold.
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When leaching under a plausible range of conditions is demonstrated to be below threshold values for all
COPCs, it may be possibleto conclude thatthe proposed application of the material is acceptable provided
that all regulatory requirements have been met (U.S. EPA, 2012e). However, direct comparison of eluate
concentration to benchmark concentrations (e.g., as illustrated in Figure 4-2) does not always complete
an evaluation. Furthermore, the threshold values used in comparison should be relevant to the type of
testing results being compared. For example, eluate concentrations from Method 1315 results are used
for calculating fluxes and are not reflective of expected maximum leaching concentrations. Thus, Method
1315 eluate concentrations should not be applied to comparisons with threshold concentrations;
whereas, the Method 1315 COPCs flux may be used after consideration of the relative amount of
contacting water to exposed surface area in the assessment scenario. When comparing Method 1313
results to benchmark concentrations, the pH of Method 1313 and the pH of the benchmark may differ.
One approach is to interpolate between two endpoint pH values from Method 1313 (see Section 4.4.2.)
The screening-level assessment of leaching in a particular application can follow the stepwise approach
described in Section 4.2.1. Typically, the threshold criteria against which potential leaching of COPCs is
evaluated (e.g., drinking water MCLs, surface water quality concentrations, etc.) are expressed as
concentrations and, therefore, estimates of COPC leaching should be derived on a similar basis as
concentrations. Screening assessments utilize estimates of maximum leaching concentration, Cieach_max,
derived from a limited dataset of COPC leaching (e.g., from total content analysis or one or more LEAF
tests) which are adjusted to an initial L/S value, (L/S)inmai¦ The initial L/S value can be a default value of
0.5 L/kg-dry, an estimate of porewater L/S based on materials properties,13 or an L/S estimate that reflects
the maximum expected leachate concentration for the specified scenario. For illustrative purposes, the
default value of 0.5 L/kg-dry will be used in all examples of this guide.
For simple screening assessments, the maximum leaching concentration may assume that the total
content of a COPC is leached into an initial L/S, while more-complex screening assessments may utilize
the broader range of leaching behavior (e.g., Method 1313 and Method 1316) to estimate the maximum
leaching concentration over a range of scenario conditions. All screening assessment assumed an infinite
source of leaching based on results obtained from testing the material or treated material14 as it would
be used or disposed.
4.2.3.2 Assessment Ratios
The comparison between the estimated maximum leaching concentration (Cieach_max) and threshold limit
concentrations {Cthes) can be illustrated by a simple ratio of the leaching concentration of a COPC divided
by the target threshold value. For purposes of this document, this is referred to as an assessment ratio
(AR), which considers the maximum leaching estimate and threshold concentrations.
AR Cieach_max /^thres Equation 4-1
13 The lower bound for the porewater L/S of a material can be estimated using the skeletal density, ps [kgSoiid/m3Soiid], and a bulk
porosity, s [m3p0re/m3] as s /(l- e)/ ps *1,000 where 1,000 is a conversion factor for volume (1,000 L/m3).
14 Blending a material with soil or lime would be considered a treatment, and, therefore, the material should be tested "as
used" considering the mixture. Separate testing and modeling can be used to predict the behavior of mixtures of materials;
such testing and modeling is beyond the scope of this document.
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where
AR is the assessment ratio [-];
Cieach_max is the estimated maximum concentration for the COPC [mg/L]; and
Cthres is the threshold value for the COPC [mg/L],
When the assessment ratio for a COPC is less than or equal to 1 (AR < 1), the constituent is not likely to
leach at concentrations greater than the threshold limit concentration under the anticipated scenario
conditions and further evaluation may not be required. An assessment ratio greater than 1 (AR> 1) does
not necessarily indicate that a COPC will leach at a level greater than the threshold limit concentration in
the field but does indicate that further evaluation is required to refine the assessment. For example, a
decision-maker may choose to perform additional leach testing using other LEAF methods to develop a
more refined source term for COPC leaching or may modify the planned use in some way to reduce the
release potential (e.g., a change in the environmental application).15 Additionally, LEAF test results could
be used as an input to groundwater fate and transport modeling to estimate the degree of offsite
migration and potential for groundwater contamination. Additional LEAF leaching test results could result
in a more refined modeling of the potential release. See Section 4.4.7 for consideration of dilution and
attenuation within an Assessment Ratio.
15 In research partially supported by U.S. EPA (e.g., use of 20 percent coal fly ash in making concrete could reduce fivefold the
amount of COPC available to leach; Garrabrants et al., 2014; Kosson et al., 2014; U.S. EPA, 2012b), blending of fly ash into
concrete as a replacement for Portland cement allowed for reuse of a secondary material without significant impact. The
replacement ratio of 20% of the Portland cement fraction reduced the available content for some COPCs fivefold over the
available content in fly ash alone; however, lowering the replacement ratio would further reduce the available content of fly
ash COPCS in the concrete product.
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Table 4-1. Summary of Suggested Test Methods and Analyses for Screening Assessments.
Eluate
Test Methods
Analyses
Assessment Attributes
Step 1 - Total Content Screening (if determined)
Total Content:
COPCs
•
Total content mass release [mg/kg-dry] converted to estimated maximum leaching concentration (Ciench_max) through division
digestion, XRF, etc.
by a scenario L/S value [L/kg-dry].
•
Conversion of total content [mg/kg] to dry mass basis [mg/kg-dry] is necessary using solids content or moisture content (wet
basis).
Step 2 - Available Content Screening
Method 1313:
PH,
•
Basis for infinite source term; assumes available content is maximum cumulative release under field conditions.
pH 2, 9, and 13
EC,1
•
Available content mass release [mg/kg-dry] derived from maximum leachate concentration at Method 1313 endpoint target
COPCs,
pH extractions at 2, 9, and 13. Target pH values in Method 1313 can be reduced to only those demonstrated to achieve
DOC
maximum eluate concentration as used for available content determination.
•
Estimated maximum leaching concentration (Cieach_max); adjusted to initial L/S (default 0.5 L/kg-dry).
Step 3 - Equilibrium-pH Screening
Method 1313:
PH,
•
Basis for infinite source term over applicable scenario pH domain; assumes equilibrium concentrations as an upper bound of
Applicable pH domain2and
EC,1
leaching under field conditions.
pH 2, 9, and 13
COPCs,
•
Available content as indicated above; used to determine solubility-limited vs. available content-limited leaching.
DOC
•
Acid/base neutralization capacity to pH = 7 relevant to evaluation of neutralization due to long-term aging processes (e.g.,
carbonation, acid attack).
•
Estimated maximum leachate concentration (Ciench_max) determined as the maximum eluate concentration over the applicable
pH domain for solubility-limited constituents; adjusted to initial L/S (default at 0.5 L/kg-dry) for available content-limited
COPCs.3
Step 4 - Equilibrium-L/S Screening
Method 1313:
PH,
•
Basis for infinite source term at low L/S; assumes eluate concentrations at low L/S are comparable to porewater.
Applicable pH domain2 and
EC,1
•
Estimated maximum leachate concentration (Ciench_max) for solubility-limited and available content-limited leaching
pH 2, 9, and 13
COPCs,
constituents determined as greater of maximum eluate concentration over the applicable pH domain or maximum eluate
and
DOC
concentration over the L/S range.4
Method 1314 or Method 1316:
•
Supplemental basis for determination of solubility-limited vs. available content limited leaching when evaluated along with
Full set of L/S values
Method 1313 data.
1 Electrical conductivity (EC) measurement in Method 1313 is recommended for natural pH eluate only due to interferences provided by acid/base additions.
2 An applicable pH domain for an assessment scenario is determined by extending the default pH domain (5.5 < pH < 9.0) to include the natural pH of the material and
adjustments required from consideration of the chemical composition of the contacting water, interfaces or commingling with other materials, and long-term changes in pH
due to material aging processes.
3 For many applications, available content-limited species include the Group IA cations (e.g., Na, K) and anions (e.g., Br, CI", F", N03 ). In addition, oxyanions (e.g., As, B, Cr, Se,
Mo, V) may display available content-limited leaching on a case-by-case basis.
4 For some cases, the maximum concentration over the applicable pH domain from Method 1313 may be less than the maximum concentration over the L/S range from
Method 1314 because of aqueous phase complexation by increased concentration of DOC or other constituents at low L/S values in Method 1314. Method 1314 results also
can be used to provide a basis for narrowing the applicable pH domain for evaluation of Method 1313 results to the pH range observed during Method 1314, with 0.5 pH units
added to the maximum pH observed and 0.5 pH units subtracted from the minimum pH observed during Method 1314, unless known aging processes would result in a
broader pH domain (e.g., carbonation of alkali cement materials may result in observed pH values as low as pH 7).
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Table 4-2. Summary of Suggested Test Methods and Analyses for Scenario-Based Assessments.
Test Methods
Eluate Analyses
Assessment Attributes
Percolation Through Permeable Material Scenario Assessment
Method 1313:
Full endpoint target pH
values
and
Method 1314:
Full set of L/S eluates
or
Method 1316:
Full set of L/S eluates
PH,
EC,2
ORP,3
COPCs,
DOC,
DIC,
Major/minor
constituents4
• Basis for infinite source term; assuming LSP with percolating water limited to available mass release.
• Available content mass release [mg/kg-dry] at Method 1313 endpoint target pH values of 2, 9, and 13.
• Acid/base neutralization capacity to pH = 7 relevant to evaluation of neutralization due to long-term aging
processes (e.g., carbonation, acid attack).
• LSP as a function of pH providing a baseline understanding of leaching behavior and speciation assessment.5
• Basis for determination of solubility-limited vs. available content-limited leaching through comparison between
pH- and L/S-dependent leaching.6
• Leachate concentration evolution as a function of L/S for source term development based on test elution curve.
• Basis for verification of chemical speciation modeling at low L/S.
• Supports fate and transport simulations considering sensitivity of field conditions (e.g., infiltration chemistry,
preferential flow, material aging).
Mass Transport Limited Leaching Scenario (Impermeable Material) Assessment
Method 1313:
Full endpoint target pH
values
and
Method 1314:
Full set of L/S eluates
and
Method 1315:
Full set of time intervals
PH,
EC,2
ORP,3
COPCs,
DOC,
DIC,
Major/minor
constituents4
Attributes of Percolation Scenario Assessment plus:
• Estimate of initial porewater concentration (Method 1314 through cumulative L/S 0.2 L/kg-dry).
• Cumulative release and interval flux as a function of leaching time (Method 1315) for saturated and intermittent
wetting conditions.
• Basis for fate and transport model parameters (e.g., diffusivity, tortuosity) for simulation of evolving conditions
(e.g., low liquid-to-surface area, external solution chemistry, carbonation, oxidation, intermittent wetting, etc.).
1 Prior information, such as characterization information from similar materials, may reduce or supplant extent of equilibrium-based assessment for characterization.
2 Electrical conductivity (EC) measurement in Method 1313 is recommended for natural pH eluate only due to interferences provided by acid/base additions.
3 Oxidation reduction potential (ORP) measurement in Method 1313 is recommended for natural pH eluate only due to interferences provided by acid/base additions. ORP
provides useful indications of material properties under abiotic and anoxic conditions, recognizing the sensitivity and uncertainty of ORP measurements.
4 The list of major and minor constituents should include all constituents that are important to the mineralogy and chemical behavior of the material. At minimum, these
constituents would include Al, Ba, Ca, CI, Fe, Si, Mg, Na, P and S for many materials.
5 Speciation assessment refers to evaluations and/or simulations that consider the effects of changes in pH, redox conditions, extent of carbonation, complexation with
dissolved organic carbon, etc. on COPC release. Such assessments may be accomplished heuristically or in combination with geochemical speciation modeling.
6 For many applications, available content-limited species include the Group IA cations (e.g., Na, K) and anions (e.g., Br, CI", F", N03 ). In addition, oxyanions (e.g., As, B, Cr, Se,
Mo, V) may display available content-limited leaching on a case-by-case basis.
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4.2.4 Screening Level Assessments
One approach to a leaching assessment that offsets the level of detail obtained from testing against the
increased effort to provide more refined source terms is a series of screening approaches. These screening
approaches are not required but may be used to determine whether more-detailed assessments (e.g.,
scenario-based assessments) are necessary or whether screening test results alone adequately support
environmental decision-making. In some scenarios, the leaching behavior of COPCs may be screened
against threshold values based on a source term that estimates leachate concentrations for the total
content, available content, and equilibrium LSP (Figure 4-3). The levels of the screening approach allow
for a trade-off between progressive refinement of a bounding estimate of potential leachate
concentration against increased testing and analysis effort. The intent of a screening assessment is to
determine which constituents are relevant to the scenario (i.e., which COPCs are likely to leach in
concentrations presenting a threat to human health and the environment). Screening assessments utilize
results from limited testing and default or minimal assessment scenario information to provide upper
bound estimate of leaching (i.e., "not expected to exceed" concentrations). In the most conservative
estimates, a screening may be based on an "infinite source" leaching assessment16 that can be compared
to threshold values (e.g., the total concentration of a COPC may be less than a threshold value). However,
screening approaches should consider finite sources when possible.
An example of how these testing schemes may estimate environmental leaching is shown below in Figure
4-3. In an example screening application, an assessor may be already aware of or test for the total content
of a COPC in a material. The total content value provides an upper limit on the amount of material that
can be released. A screening use of Method 1313 with pH endpoints of 2, 9 and 13 will provide the assessor
with an estimate of the available content of COPCs within the material. If a more specific pH domain of
the environment is known, the assessor can choose to tailor Method 1313 to provide a better estimate of
equilibrium-controlled leaching. If the assessor is aware that percolation effects will control leaching,
Method 1314 provides additional information on the expected leaching behavior in the environment.
16 An "infinite source" assumes that leaching will continue without change in COPC concentrations over infinite time (i.e., the
COPC will never become depleted from the material). More advanced assessments typically assume a "finite source"
whereby the COPC becomes depleted within the material once the available content has been leached.
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Total Content
(Digestion, XRF)
Assumes total content
leaches into initial L/S.
/ \
Available Content
(Method 1313)
Assumes available
fraction leaches into
initial L/S.
Max. cone at
pH 2,9, or 13
Equilibrium-pH
(Method 1313)
Assumes LSP max conc.
overpH domain
leaches into initial L/S.
Max. conc. over
pH domain
r
Equilibrium-L/S
(Method 1314 or 1316)
Assumes LSP max conc,
over L/S range and pH
domain leaches.
Max. conc. over
L/S range and pH
domain
Increasing Refinement of Bounding Leaching Estimate
Figure 4-3. Screening level assessments, test methods and assumed leaching conditions17.
Screening level assessments may recognize that not all COPCs are present in the material at sufficient
concentration to be of concern and that not all COPCs present will leach under all scenario conditions.
Therefore, the goal of the assessment is to identify and separate material constituents that may leach at
less than or equal to the identified benchmark or threshold values from those COPCs that may be a
concern. Constituents with upper bound leaching estimates less than benchmarks or thresholds would
not require further analysis whereas an evaluation of COPCs with values that exceed benchmarks or
thresholds may benefit from subsequent characterization and analysis.
A screening-based assessment generally assumes limited or partial information regarding the material
and its placement into the environment when developing a leaching assessment. The more information
that is available regarding the material and the environment, the more accurately a testing and analysis
plan can reflect environmental conditions in the field. The flexibility provided by LEAF allows for the
development of a range of assessments from a simple screening-based assessment with limited testing
and limited environmental information to advanced scenario-based assessments with more elaborate
testing and source term model development to evaluate anticipated environmental field conditions. A
screening level assessment can be compared to relevant threshold values to identify and separate COPCs
not likely to adversely impact the environment at threshold levels from COPCs for which further testing is
required. Screening assessments often provide higher estimates of leaching than scenario assessments
due to relying on estimates of maximum leachate concentrations or available content estimates.
17 The max concentrations shown are illustrative and may differ by orders of magnitude depending on the testing and material.
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4.2.4.1 Total Content Screening
Total content is the concentration of a COPC within the solid material [mg/kgdry] that may be derived from
destructive or non-destructive total analysis of the solid material. The total content of COPCs in a material
(mtotal) is obtained through analytical methods such as solid phase digestion (e.g., U.S. EPA Method 3052)
or other total elemental analysis (e.g., X-ray fluorescence). Because this source term does not require any
LEAF methods, it can serve as a useful first step when the bulk content is known from prior knowledge
(e.g., available literature) or testing. This source term assumes that the entire bulk content of a material
is released into the water immediately, resulting in the highest concentration that is physically possible,
albeit unlikely.
The bulk content from digestion methods may be reported on a wet-mass basis [mg/kg], which will result
in an incorrect estimation of releases if not converted into a dry-mass basis. Conversion between wet and
dry bases requires knowledge of the moisture content of the material on a wet mass basis or, alternatively,
the solids content. Equation 4-2 presents the conversion between wet and dry weight:
mtotai,dry— (mtotai,wet) (SC) — (mtotai,wet) (1 MC^ry) Equation 4-2
where
mTotal,dry's Bulk content adjusted to a dry mass [mg/kg-dry]
mTotal,wet's Bulk content reported on a wet mass [mg/kg]
MCdry is Moisture content of the material [kg-H20/kg]
SC is Solids content of the material [kg-dry/kg]
If total content of the COPCs in the material, mtotai, is known from prior knowledge or obtained through a
solid phase digestion method (e.g., U.S. EPA Method 3052) or other total elemental analysis (e.g., X-ray
fluorescence), then the estimated maximum leaching concentration {Cieach_mai) may be calculated by
adjusting the total content on a mass basis for the initial L/S:18
Cleach_max ~ ™total/(.L/S^initial Equation 4-3
where
Cieach_max is the maximum concentration based on total content
mtotai is the total content of a COPC [mg/kg-dry]; and
(L/S)initial is the initial L/S [L/kg-dry],
The calculated concentration is assumed to remain constant in all releases over the timeframe relevant
to the assessment. Since it is likely that only a fraction of the total content is actually available to leach,
use of total content to estimate the maximum leaching concentration should be considered the upper-
18 Evaluation of field L/S values (i.e., Cases 5 and 8 in U.S. EPA, 2014c) demonstrated that an effective porewater L/S of 0.5
L/kg-dry is appropriate for coarse landfilled materials subject to percolation and preferential flow, resulting in a multiplier of
20 to adjust the eluate concentrations measured using Method 1313. L/S may be expressed in equivalent units of L/kg-dry
that are typically used for the scenario scale or units of mL/g-dry that are typically used in laboratory testing (e.g., 10 L/kg-
dry = 10 mL/g-dry).
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most bound on possible concentrations. This maximum concentration is likely to overestimate the actual
leaching of COPCs by a significant margin (i.e., one or more orders of magnitude). However, if total content
data is obtained through either testing or prior knowledge, this initial step in the screening assessment
sequence is easy to execute and may focus subsequent assessment effort on only those COPCs that have
a potential to leach based on a significant presence in the material.
4.2.4.2 Available Content Screening
Following the stepwise approach, the screening assessment based on total content may be refined to
consider only the fraction that is available to leach from the material. As discussed in detail in Section
4.4.1, the eluate concentration associated with available content of a COPC can be determined directly
from Method 1313 extractions conducted at endpoint target pH values of 2, 9 and 13. The pH endpoint
values of 2 and 13 provide a bounding estimate for the amount of leachable material over a broad pH
range.
By test specifications, the available content concentration from Method 1313 data is determined at an
L/S of 10 L/kg-dry. However, the concentration used in the screening assessment should be adjusted to
the initial L/S by multiplying the maximum eluate concentration {Ci3i3(maxph2,9,13)) by the ratio of the
method-specific L/S for Method 1313 [(L/S)i3i3= 10 L/kg-dry] to the initial L/S, (L/S)j„jtiaf.
Cleachjriax ~ ^"l313(max pH 2,9,13)
x (L/S)1313/(L/S)initial Equation 4-4
Based on a default initial L/S value of 0.5 L/kg-dry, the resulting multiplier for the maximum Method 1313
eluate concentration over the pH domain in the equation is 20 (i.e., 10 L/kg-dry divided by 0.5 L/kg-dry):
10
Cleachmax = ^1313(max pH 2,9,13) x jj"j: = 20 X C1313(max 2,9,13)
For cases where available content is known or reported as a mass release [mg/kg-dry] but the underlying
concentrations [mg/L] from Method 1313 are not known, the maximum leaching concentration may be
estimated in the same manner as for the total content.
Cleachjnax ~ Wlavail/initial Equation 4-5
where
iriavaii is the available content of a COPC [mg/kg-dry]; and
(L/S)initial is the initial L/S [L/kg-dry],
One advantage of using the available content in a screening approach is that it requires only three Method
1313 extractions at endpoint target pH values of 2, 9, and 13; however, the estimate may be overly
bounding because it assumes that the entire available content is leached. For COPCs with low solubility in
the near-neutral pH range (e.g., lead, cadmium, chromium, etc.), the estimate of Cieach_maxmay be refined
further by considering only that leaching that may occur over the applicable pH domain through
equilibrium-based screening assessment.
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4.2.4.3 Equilibrium-pH Screening
An equilibrium-based leaching evaluation considers the equilibrium-based partitioning of a constituent
between a liquid and solid phase, LSP, over a range of applicable scenario conditions (i.e., pH domain and
L/S range) as the basis for COPC release. The estimated maximum leaching concentration, Cieach_max, is
based on the maximum concentration from interpolated values of Method 1313 over the applicable
scenario pH domain, Ci3i3(maxPH domain), with consideration for that estimate for available content-limited
COPCs to increase as the L/S decreases to the initial L/S value.
As discussed in Section 4.2.5.1, the applicable scenario pH domain is defined as part of the assessment
scenario definition based on the default pH range of 5.5 < pH < 9. However, the applicable scenario pH
domain may be adapted for specific materials or assessment scenarios. Typically, the definition of a
scenario-specific pH domain considers the natural pH of the material, any established pH values imposed
by scenario conditions, and any anticipated long-term neutralization effects.19 Figure 4-4 presents
examples of Method 1313 eluate concentrations, interpolated Method 1313 data, and the maximum
concentration over the pH domain for cadmium (cation) and selenium (oxyanion) in three materials
matrices - a coal combustion fly ash (CaFA), a contaminated field soil (CFS) and a solidified waste form
(SWA). Note that the applicable pH domain for the assessment changes from the default 5.5 < pH < 9.0
used for the neutral pH soil to 7 < pH < 13 for the cement-based solidified waste form in order to capture
the natural pH of the material and anticipated environmental process (e.g., carbonation) that may occur
over time.
Whether a COPC is availability-content limited or solubility-limited can determine whether the LSP
leaching concentration is a strong function of L/S (see Section 4.4.5 for determining solubility-limited
leaching versus available content-limited leaching). When a COPC is demonstrated to be solubility-limited
over the pH domain (e.g., cadmium for all material and selenium for CFS and CaFA in Figure 4-4,), the LSP
concentration is a weak function of L/S. Therefore, Qeach_max can be assumed bounded by the maximum
concentration in Method 1313 testing of the pH domain, C1313 (maxpH domain-
Cleachjnax ~ ^1313(max pH domain) Equation 4-6
If a COPC exhibits available content-limited leaching over the pH domain (e.g., SWA selenium in Figure
4-4), the maximum concentration measured over the applicable pH domain is likely to be a function of
L/S. The estimated maximum leaching concentration, C]each_ma\-, is derived by adjusting the maximum
Method 1313 concentration over the pH domain, Ci3i3(max ph domain), to the initial L/S, (L/S)inmai, using
Equation 4-7:
Cleachjnax ~ ^1313 (max pH domain) x (L/S)1313/(L/S)initial Equation 4-7
Using the default value of 0.5 L/kg-dry as the initial L/S, Equation 4-6 becomes:
10
Cleach_max ~ ^1313 (max pH domain) *0*5 — ^ * ^1313(maxp// domain)
19 Although the applicable pH domain may be a fraction of the domain covered by Method 1313, it is useful to obtain data
from the entire range of endpoint pH target values to provide definition of the available content (Section 4.4.1) and
identification of available content-limited and solubility-limited leaching (Section 4.4.5).
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CFS
at
E
E
¦o
1000
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0.1
0.01
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pH domain
¦ N.
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LLOQ
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¦ ¦ ¦ 1 ¦ ¦ ¦ 1 ¦ ¦
1 ¦ ¦ ¦ 1 ¦
¦ 1 ¦ ¦ ¦ 1 ¦ ¦ ¦
10 12 14
CFS
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s
L
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¦ ¦¦ i ¦ ¦¦ i ¦¦
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-------
on eluate concentration. Although data from Method 1314 or Method 1316 can be used in this evaluation,
the data provided by Method 1314 should be considered over that from Method 1316 in low L/S
screenings due to the ability of the column test to capture concentrations at very low L/S values (e.g., <
0.5 L/kg-dry) and the nature of the Method 1316 batch test to mask the evolution of competitive
dissolution with L/S (see Section 4.4.4).
The estimated maximum leaching concentration in a full LSP screening, Cieach_max, is the greater value
between the maximum concentration over the applicable pH domain, Ci3i3(maxPH domain), and the maximum
concentration over the L/S range, C(L/s)max-
C,
leach max
MAX [C1313(maxpH domain))
(L/S)max
Equation 4-8
Figure 4-5 presents two examples of data leading to full LSP screening. Barium in solidified waste form
(SWA) shows a solubility-limited leaching in Method 1313 and a relatively weak influence of L/S in both
Method 1314 and Method 1316 data. Thus, the maximum concentration of barium over the applicable
scenario pH domain is significantly greater than maximum eluate concentrations from Method 1314 or
Method 1316. Conversely, the LSP data for boron in the coal combustion fly ash (EaFA) shows available
content-limited leaching and strong influence of L/S. The estimated maximum leaching concentration for
boron used in the full LSP screening assessment would be the greatest concentration at low L/S in Method
1314 (or, alternatively, the highest concentration in Method 1316 in the absence of Method 1314 data).
SWA
Ui
£
o.oi -=
0.001 4
EaFA 1000
100
Max. over pH domain
Max. oyer L/S range
10
1
0.1
0.01
0.001
0.0001
2
4
e
8
pH
10 12 1
i
; Max. over L/S range J
i
i
i
i
Max. over
O V
i
i
i
i
i
i
i
i
i
i
i
i
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i
MDL
10
12
SWA
m
£
_ ________ _ _M^x. over L/S_rangg
0.01 f
0.001
4 6
L/S (L/kg-dry)
EaFA 1000
14
Max j3 v ej_ L£S _r a n ge
O
100 -r
Max. over pH domain
0.01 -r
0.001 -
0.0001
PH
4 6
L/S (L/kg-dry)
-EaFA_1314 -O EaFA_1316 ~ EaFA_1313(interpolated) o Natural pH Indicator
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Figure 4-5. Full LSP screening data showing examples where pH effects dominate LSP
(barium in solidified waste form, SWA) and where L/S-dependence influences maximum LSP
concentration (boron in coal fly ash, EaFA).
4.2.5 Scenario Based Assessments
Screening assessments may provide bounding estimates of leaching in the environment. A scenario
assessment may utilize information and testing that provides a more accurate estimate of leaching in the
environment. Factors contributing to uncertainty in screening estimates can include use of an assumed
"infinite source/' reliance on only a limited amount of leaching data, or utilization of default or estimated
scenario information. An assessor using LEAF may also have additional information regarding their site or
material that can be used in conjunction with data from testing to refine their leaching assessment. These
more-refined leaching estimates may be based on parameters derived from site-specific, generic scenario-
specific20 or national assessments of the leaching potential for a material. A site-specific assessment may
include representative samples of a specific waste, with defined waste management unit designs, local
environmental conditions including metrological and soil data and specific chemical interactions that may
occur within the scenario. For a national assessment, LEAF results from numerous samples representative
of a waste stream type are used in conjunction with the range of waste management unit designs, national
meteorological data, soil types, and other information from numerous units to estimate a national
probability distribution of release (U.S. EPA, 2014b). When such a probabilistic source term is used in
conjunction with a groundwater fate and transport modeling, exposure pathways and toxicity estimates,
a national distribution of risks from disposal or use of the material can be estimated. Similarly, regional
assessments would take the same approach with inputs relevant to a region.
For the purposes of determining the applicability of a material for a scenario with respect to leaching
performance, the flow chart presented in Figure 4-6 shows that the results from the appropriate LEAF
leaching test methods integrate with site- or scenario-specific information to provide an estimated source
term under the assumed release conditions. Scenario assessments rely on Method 1313 pH-dependent
testing data used in conjunction with time or L/S-dependent data from Methods 1314, 1315 or 1316. The
most appropriate method to incorporate with Method 1313 data will depend on the composition of the
material, the mode of water contact, and the specifics of the assessment scenario. Method 1315 is best
suited for flow-around scenarios where water is diverted around a material that is impermeable relative
to the surrounding media. Method 1314 and 1316 are best suited for flow-through scenarios where the
hydraulic conductivity of the material is relatively close to that of the surrounding media (within and
order-of-magnitude) and water percolates through the material.
A source term developed to represent the estimated COPC release for each chemical of concern in an
environmental application is based upon the testing results considered as whole. The development of the
source term is dependent upon the testing and a description of the scenario chosen to represent the
environmental scenario. Considered together, the results of the testing can be used to identify the
bounding estimate of release as constrained by the anticipated effects of the range of pH, L/S, and mass
transfer considerations.
20 Where a range of materials may be considered for use under a single, bounding application scenario definition.
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4.2.5.1 Determining the Applicable pH Domain
Evaluating the effects of pH plays an important role in almost all leaching assessments. In most scenarios,
the natural pH of the material, the prevailing pH in the proposed application, and long-term pH shifts
associated with material aging or degradation processes should be considered. Inorganic constituents
generally exist in aqueous solution as ionic species, the solubility of which is often dependent upon pH.
As a result, an evaluation of pH dependence on the available content of a material provides important
understanding to almost all leaching evaluations for inorganic constituents (see Section 4.4.1 for details
on calculating available content from Method 1313). The applicable pH domain for a management
scenario may be based on knowledge of material or scenario characteristics, including those anticipated
to evolve overtime. Evolving scenario characteristics may include self-acidification (e.g., via oxidation of
sulfide reactive phases or biodegradation of organic matter), commingling of the material with more
alkaline or acidic materials, and external sources of acidity or alkalinity (e.g., from adjacent materials or
the chemistry of contacting water). Examples of environmental conditions, including pH domains and
special considerations, for several materials and scenarios are presented in Table 4-3.
Because pH-dependent leaching will be evaluated based on the results of Method 1313, which specifies
endpoint target pH values, the applicable pH domain should be based on similar defined pH values. As a
default range, the target pH domain21,22 should include 5.5 < pH < 9.0, but should be expanded as
appropriate to include the natural pH of the material. For example:
• For an alkaline coal fly ash with a natural pH of 10, the applicable pH domain would range from
pH 5.5 (the lower end of the default domain) to pH 10.5 (the upper end extended to correspond
with endpoint target pH values of Method 1313).23
• For an acidic coal fly ash with a natural pH of 4.2, the applicable pH domain would range from pH
4.0 (the lower end extended to correspond with the endpoint target pH values of Method 1313)
to pH 9.0 (the upper end of the default domain).
The applicable pH range may be further refined (expanded or narrowed) based on material-specific or
site-specific scenarios and knowledge of the material's behavior. Changes to the default pH domain should
be supported based on anticipated changes in pH at boundary conditions, as a result of materials aging
(e.g., carbonation), or potential for acid or alkali influx in context with the acid-base neutralization capacity
information from Method 1313. Definition of scenario specific pH domains should be done in consultation
with the appropriate regulatory authority.
21 Although LEAF is applicable to materials other than CCRs, the CCR risk analysis (U.S EPA 2014b) provides useful information
regarding soil pH ranges across the U.S. These results indicate a soil pH distribution of 4.8 (5th percentile), 5.0 (10th
percentile), 6.2 (median/50th percentile), 7.8 (90th percentile), and 8.2 (95th percentile). For ease of use with LEAF data at the
screening level, a default pH domain should correspond with Method 1313 endpoint target pH values of 2, 4, 5.5, 7, 8, 9,
10.5,12, and 13. Thus, the default pH domain is recommended as 5.5 < pH < 9.0 with the pH value of 9.0 roughly
corresponding to the maximum solubility pH observed for many oxyanions of regulatory concern (e.g., As[V], Cr[VI], Se[VI]).
22 The SSURGO database contains information about soil as collected by the National Cooperative Soil Survey over the course
of a century. The information can be displayed in tables or as maps and is available for most areas in the United States and
the Territories, Commonwealths, and Island Nations served by the USDA-NRCS. This database is available online at:
https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey
23 Interpolation of Method 1313 test results within LeachXS™ Lite is currently limited to the target pH values of the test
method. Interpolation to user-defined pH values is a capability currently available within the full version of LeachXS™.
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Table 4 3. Summary of Observed pH and Redox Conditions for Field Scenarios
Case Name (Country)
Leachates
PH
Domain
Special Conditions
Coal fly ash landfill leachate (U.S.)
multiple,
landfills
6-13
oxidizing to reducing
Coal fly ash in large-scale field lysimeters
(Denmark)
lysimeters
11-13
oxidizing to reducing
Landfill of coal combustion fixated
scrubber sludge with lime (U.S.)
landfill
6-12
oxidizing
Coal fly ash used as roadbase and in
embankments (The Netherlands)
road base,
embankment
8-12
oxidizing to reducing
Municipal solid waste incinerator (MSWI)
incinerator bottom ash landfill (Denmark)
landfill
7-11
reducing
MSWI bottom ash used as roadbase
(Sweden)
road base test
section
7-10
oxidizing to reducing
Inorganic industrial waste landfill
(The Netherlands)
lysimeters,
landfill
6-9
oxidizing to reducing
Municipal solid waste landfill (The
Netherlands)
landfill, multiple
landfills
5-9
strongly reducing,
high organic carbon
Stabilized MSWI fly ash disposal (The
Netherlands)
pilot test cells,
landfill
8-13
oxidizing
Portland cement mortars and concrete
(Germany, Norway, and The Netherlands)
8-13
oxidizing,
carbonation
Source: U.S. EPA (2014c).
4.2.5.2 Water Contact and Material Placement in the Environment (Scenario Description)
The placement of material in the environment will have a significant influence on the amount of water
that contacts the material and the mode through which water contacts the material. Direct contact with
groundwater and intermittent rainfall can result in different leaching behavior for constituents. In
addition, physical properties such as soil porosity can influence leaching of constituents. Important
information that should be defined in a leaching scenario includes a description of how the material will
be placed into the environment, the location of the placement relative to the water table (e.g., in the
vadose or saturated zone), the physical dimensions of the placement, and the physical characteristics of
the material.
Aside from the physical parameters of the placement, the most significant factor for the leaching
assessment involves the mode of water contact between the material and infiltrating rainwater or
groundwater. Material may be located: (i) above the ground surface where it is exposed directly to rainfall,
(ii) in the vadose zone where contact is limited to that fraction of rainwater that infiltrates the subsurface,
or (iii) in a saturated environment (e.g., below the water table in the groundwater or surface water
sediments). The physical characteristics of a material and the environment (e.g., density, porosity, and
hydraulic conductivity) may determine whether the contacting water flows through or flows around the
material. When infiltration or groundwater flows through a permeable material at a relatively slow rate,
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equilibrium controls the extent of leaching in what is termed a "percolation scenario." However, when
the flow is fast or predominantly around a material with low hydraulic conductivity or through preferential
flow pathways (Kosson et al., 2002), mass transport through the material to the water boundary controls
the rate of leaching. The LEAF approach defines the applicable water contact mode as either percolation
for materials that are as or more permeable than the surrounding materials or flow-around if the material
performs as a monolith because of significantly lower permeability than the surrounding materials. A
determination that the water contact mode is percolation based allows for evaluating leaching using
Method 1314, while a flow-around scenario may be better represented by Method 1315 results.
Material
Flow-through
Percolation
LEAF Test Results
[Methods 1313 and 1314 (or 1316)]
• Available Content
• LSP as a function of pH
• LSP as a function of L/S
Site Information*
Percolation Assessment Model
Flow-around
Mass Transport
LEAF Test Results
[Methods 1313 and 1315]
• Available Content
• LSP as a function of pH
• Mass transport rate
Site Information*
Mass Transport Assessment Model
Modify
Scenario
Source Term
(Release Estimate)
Scenario and
Regulatory Assessment
Modify
Material
* Default values or site-specific information
Figure adapted from Kosson, Garrabrants et al. (2012).
Leaching < Threshold
Leaching > Threshold
Figure 4-6. Flowchart for using LEAF for leaching assessments based on water contact.
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4.2.5.3 Percolation Scenarios (Permeable Materials)
For management scenarios where water contact is primarily through percolation, Method 1314 results
can be used directly as an estimate of field leaching as a function of the L/S for the management scenario.
In some cases, Method 1316 results can also be used to understand time-dependent releases. In a
percolation scenario, an evaluator may be using knowledge of water infiltration rates or management
timescales to determine relevant L/S for the scenario. However, studies comparing laboratory results to
field leachates indicate that actual field leachate may have significantly lower COPC concentrations
because of preferential flow pathways. These studies suggest that leaching may be over-predicted by
direct leaching test results by an order of magnitude for available content-limited COPCs for many
assessment scenarios (U.S. EPA, 2014c). Solubility limited constituents may have less dependence on
preferential flow and will be less often over-predicted due to preferential flow as a result. In some cases
fate and transport models may be used to examine sensitivity to scenarios beyond laboratory testing
conditions (Dijkstra, Meeussen, van der Sloot, & Comans, 2008; Meima & Comans, 1998).
Materials that could be encountered in percolation scenarios include granular material used as structural
fill or landfilled. These types of materials have a larger surface area that is exposed to water that can result
in equilibrium conditions being reached more quickly. Methods 1314 and 1316 provide data on leachate
concentrations at or near equilibrium as a function of cumulative L/S. The lower L/S provide
measurements of pore water concentrations. These empirical measurements can reflect instances where
only a fraction of COPC mass is limited by available content and instances where solubility limits are
reached before the lowest L/S, which may result in lower concentrations than predicted based on
adjusting Method 1313 data. Conversely, these methods can capture shifts in the pH at low L/S due to the
quick washout of highly soluble ions. This pH shift might result in higher early leachate concentrations
than predicted based on the final fixed pH used in Method 1313. Thus, Methods 1314 and 1316
concentrations may provide a more realistic source term without additional adjustment.
4.2.5.4 Mass Transport Limited Leaching Scenarios (Impermeable Materials)
When the water contact is primarily from flow-around a relatively impermeable fill or monolithic material,
the Fickian diffusion model (Crank, 1975) is commonly used to estimate mass transport of COPCs. Fickian
diffusion assumes that a constituent is initially present throughout the material at a uniform
concentration and that mass transfer takes place in response to concentration gradients in the pore water
solution of the porous material. The Fickian diffusion model is most appropriate for release scenarios for
which highly soluble species are a concern or for which external stresses do not induce sharp internal
chemical gradients (e.g., pH gradients, carbonation, and redox changes) that significantly influence local
LSP within the material (U.S. EPA, 2014c). The amount of water contacting the material also will impact
the amount of a COPC released under a diffusion-controlled scenario.
The mass transport source term for the scenario-based assessment can be bounding because the amount
of a COPC released can be several orders of magnitude less than would be estimated using an infinite bath
assumption in field scenarios when (i) the material is subject to intermittent wetting due to periodic
infiltration (Section 4.4.6), (ii) a portion of the material surface area is obscured from contacting water
due engineering controls or placement in the environment, and (iii) where the amount of water contacting
the material is limited and LSP at a limited L/S controls leaching.
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See Section 4.4.6 for more information on understanding and evaluating mass transport parameters.
Examples of use of empirical mass transport results from Method 1315 as part of scenario assessments
are provided in Section 5.2 (See also U.S. EPA, 2014, Appendix C). Mass transport testing results also may
be incorporated in more detailed reactive transport scenario modeling that integrates geochemical
speciation with diffusion-controlled release.
4.3 Accounting for Environmental Processes That Can Influence Leaching
When defining assessment scenarios, both environmental conditions and the presence of important
environmental processes should be considered. Environmental factors can alter leachability by changing
the chemistry of the material, the concentration of COPCs at equilibrium or the rate of mass transport.
The LEAF leaching tests are designed such that the data reflects the response to one or more of these
factors under controlled laboratory conditions. However, it is important to acknowledge that these factors
do not remain constant in the field as both the environmental media and the solid material under
consideration will change over time. Within the normal range of values, some factors (e.g., temperature)
are unlikely to have a significant effect on leachability whereas slight changes in other factors (e.g., pH)
can have substantial effects on leaching.
Environmental processes may also need to be considered because of their capability to alter leaching
under field conditions from those observed in laboratory testing. The effect of some processes may be
observable from careful evaluation of testing results (e.g., As-Ca interactions) or by conditioning test
materials prior to testing (e.g., carbonated vs non-carbonated materials). Other processes (e.g., evolving
redox conditions) may be best evaluated through geochemical speciation modeling of leaching behavior.
Examples of key phenomena that can influence leaching include:
• Chemical, physical, and biological reactions that may occur on or within the material, including
the change in redox, production of carbon dioxide, organic acids or other products of
biodegradation that may change pH or liquid-solid partitioning of some constituents;
• External stresses (e.g., acids, carbon dioxide, dissolved organic matter) from the surrounding
liquid or gas phases that can change the scenario pH or the sorption capacity of the material;
• Physical degradation of the solid matrix due to erosion or stress-related cracking (e.g.,
freeze/thaw or precipitation reactions);
• Preferential flow through a material that can "short-circuit" the percolation pathway resulting in
leaching concentrations less than estimated by equilibrium-based leaching tests;
• Loss of primary matrix constituents due to the leaching process itself (e.g., calcium, sulfate,
hydroxide, chloride); and
• Changes in the chemistry of the surrounding media (e.g., abiotic, or biotic oxidation/reduction
reactions, and dissolution of atmospheric or biogenic carbon dioxide).
The factors that affect leachability do not act independently of each other and often multiple factors can
result in releases that are synergistically different than would be predicted for each factor. However,
validation of the LEAF approach to field-collected and monitored cases (U.S. EPA, 2014c) indicate that
combined effects either are captured by the test data or can be considered through fate and transport
modeling. In addition, the effects of varying a particular factor will differ for each inorganic constituent.
As a result, understanding how the variability of the different chemical and physical factors (e.g., pH,
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redox, dissolved organic carbon) can affect the leachability of each constituent of concern is key to
understanding how the material will behave from a leaching perspective in an application scenario.
Insights to these affects can be gained both through LEAF testing and geochemical speciation modeling
(U.S EPA 2014c; van der Sloot et al, 2017).
4.3.1 Reducing and Oxidizing Conditions
An assessment scenario should consider the potential for the leaching behavior of COPCs to change due
to anticipated changes in reducing or oxidizing conditions of the management scenario. These changes
may be relevant if the assessment material contains redox-sensitive constituents that can leach more
readily under reducing conditions and whether there is a possibility of oxidizing or reducing conditions
under the planned management scenario. As a consequence of exposure during treatment or placement
in a management scenario, changes in the redox state of a waste or secondary material can affect the
speciation, solubility, and partitioning of multivalent constituents (e.g., Fe, As, Cr). For example, oxidizing
conditions prevail widely in the near-surface environment due to contact with ambient oxygen; however,
biological activity can deplete sources of oxygen over time, resulting in anoxic and reducing conditions.
Biological activity is nearly ubiquitous at near neutral pH (5.0 < pH < 8.5), especially in the presence of
microbial substrates such as organic carbon. Thus, a material initially managed under oxidized conditions
may become reduced as is the case for some fill scenarios, municipal solid waste landfills or sediments
(U.S. EPA, 2014c). The formation of reducing conditions during use or disposal may have adverse
consequences with respect to leaching through the following mechanisms:
• Reduction of iron (hydr)oxides, Fe(lll), which can result in increased dissolution of iron as Fe(ll)
and loss of sorption surfaces responsible for COPC retention (Ghosh, Mukiibi, & Ela, 2004);
• Direct reduction of multivalent species (e.g., arsenic, chromium, selenium, and molybdenum) that
can change the solubility and sorption characteristics of COPCs; and
• Increased dissolution of organic matter that increase dissolved concentrations of some COPCs
(e.g., lead and copper) through formation of soluble complexes with DOC.
For example, the effect of reducing conditions on arsenic is especially significant due to the conversion of
As(V) to As(lll) under moderately reducing conditions which may increase the total solubility of As and
decrease As sorption (Dixit & Hering, 2003; Masscheleyn, Delaune, & Patrick Jr., 1991; Schwartz et al.,
2016; Smedley & Kinniburgh, 2002; Vaca-Escobar, Villalobos, & Ceniceros-Gomez, 2012). However,
strongly reducing conditions can result in the formation of sulfides, which can reduce the solubility of
arsenic and other elements. Similarly, molybdenum and manganese exhibit increased partitioning to the
aqueous phase under reducing conditions, while other COPCs exhibit decreased leaching under reducing
conditions. For example, the partitioning of chromium to the aqueous phase typically is decreased under
reducing conditions because of stronger adsorption and decreased solubility of Cr(lll) compared to Cr(VI)
at neutral pH conditions. Often, the presence of dissolved iron is an indicator of the formation or presence
of reducing conditions.
Reducing conditions may be caused by commingling with other materials that are reducing such as slags
or some mining wastes or the presence of significant amounts of biodegradable organic matter and
barriers to exchange of atmospheric oxygen. In general, laboratory tests are always conducted under
oxidizing conditions unless special precautions are taken (e.g., environmental chambers, anoxic
gloveboxes). Examples of materials that are moderately oxidized include combustion residues and low-
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organic-content soils.24 Oxidizing conditions for initially reduced material can be caused by exposure to
air and oxygenated water (i.e., infiltration). However, materials with high reducing capacities or high levels
of degradable organic matter may remain or become reducing during testing (e.g., Method 1314) or under
field conditions, even if initially oxidized or oxidized only at the surface. Materials that are initially reduced,
or may generate reducing conditions, typically are slags (e.g., blast furnace slag), mining wastes, and high-
organic-matter soils, compost, sewage sludge and sediments. The most common reducing constituents in
waste are organic matter, reduced sulfur species (e.g., sulfides), and reduced Fe(ll) species. In addition,
reduced tin is also often used as a reducing agent in industrially produced materials (e.g., some cements).
Systems may become more oxidized resulting from reaction with atmospheric oxygen. These processes
may result in the precipitation of reduced species (the reverse of reducing conditions) or increased
solubility of some species (e.g., conversion of relatively insoluble Cr(lll) to relatively soluble Cr(VI), i.e.,
formation of chromate (CrC>42") and dichromate (Cr2072 ) anions. Oxidation of sulfides (e.g., pyrites [FeS2])
may result in the release of sulfuric acid.
Within the LEAF testing methods, redox conditions are inferred by measurement of ORP in the test eluate.
Depending on the natural pH of the material, ORP of Method 1313 eluates may be moderately oxidizing
or reducing at mildly acidic to alkaline pH conditions. Unless the material has a high reducing capacity,
oxidizing conditions tend to prevail at strongly acidic pH values because of the use of oxidizing nitric acid
in the test method, along with oxygen exposure during sampling, handling, and testing. In addition, the
presence of iron in solution at pH values above 5 is usually an indicator of reducing conditions because of
the presence of Fe(ll) which is more soluble than Fe(lll) at those pH conditions. In Method 1314, oxidizing
conditions usually prevail unless significant organic carbon and a near-neutral pH is present in the material
being tested, in which case, reducing conditions can occur during the test. Again, the formation of
reducing conditions is typically indicated by the increased leaching of iron. Establishment of reducing
conditions during Method 1314 testing of some materials (e.g., compost-amended soils) has been
observed at or after cumulative L/S of 5 mL/g-dry. For sensitive COPCs or environments, evaluation of
material characteristics and potential changes in redox conditions is critical. Redox potential (Eh),
sometimes referred to as "oxidation-reduction potential" (ORP), measured in solution using units of mV
can be viewed as an electrical potential of the pool of the available free electrons (pE):
pE = — log[e~] = Ehx F/(2. 3 x R x T) Equation 4-9
where
Eh is the redox potential (mV),
F is Faraday's Constant [96.42 kJ/(V eq)],
R is the Universal Gas Constant (8.31 J/(K mol)], and
T is temperature (K).
24 The case studies (Section 5) are limited to oxic or oxidizing scenario conditions. Oxidizing conditions usually result in the
highest extent of leaching for most COPCs. However, notable exceptions include mobilization of precipitated iron Fe(lll)
through reductive conversion to Fe(ll), increased leaching of species (e.g., arsenic) adsorbed to dissolved hydrous iron
oxides, soluble complexes for cations with dissolved organic carbon (e.g., humic, fulvic, or fatty acids), and methylation of
mercury under reducing conditions that results in more toxic Hg speciation.
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The equilibrium constant for redox-sensitive COPCs, K, may be expressed in terms of the concentrations
of reduced species, oxidized species, H+ and e" in the system:
,, \reduced species] _ .. . . _
K = loMl,e*Sp,Cles]x[e-]*[H+1 Equat.on 4-10
Or rearranging,
log K = log [red] — log[ox] — log[e~] — log[f/+] = pH + pE Equation 4-11
Thus, the relative value of (pH + pE) represents the tendency for oxidized species at higher values
(oxidizing conditions) and reduced species at lesser values (reducing conditions). The reduction potentials
of redox half reactions can be compared to the pE of the system to anticipate whether constituents may
oxidize or reduce. Test results may also not reflect environmental conditions if the redox capability of the
leachate does not reflect the redox capabilities of the environment. Additionally, redox reactions can
occur over longer timeframes than bench testing allows for. When reduction or oxidation of COPCs to
more mobile forms is anticipated, the estimated environmental impact may require geochemical
speciation modeling or other considerations. In some cases, oxidizing atmospheres in the laboratory may
underestimate reducing conditions encountered in the field, especially when field conditions do not allow
for infiltration of the atmosphere. The translation of redox behavior from the lab to the field can be seen
in the case studies EPA previously evaluated (U.S. EPA, 2014c).
The concentration of iron in solution as a function of pH is often a useful indicator of the redox state of a
system. Typically, iron is present as Fe(lll) under oxidizing conditions (pH + pE) > 15 and is insoluble at pH
> 4, with solubility increasing with decreasing pH. With progressively more reducing conditions, indicated
by progressively decreasing (pH + pE) and resulting in fractional conversion of Fe3+ to Fe2+, the transition
from insoluble iron to higher iron solubility occurs at greater pH values. The data in Figure 4-7 depicts iron
leaching as a function of pH from municipal solid waste (MSW) as pH-dependent and column leaching test
results. The various lines in the figures show the simulated LSP of iron under different redox conditions
using geochemical speciation modeling (Figure 4.69, U.S. EPA, 2014c, van der Sloot, et al., 2017). Shown
at L/S 10 mL/g-dry of the pH=dependent leaching test and L/S 0.3 mL/g-dry as the lowest L/S in the column
test, the values of (pH + pE) range from (pH + pE) = 13 indicating oxidizing to mildly reducing conditions
to (pH + pE) = 4 indicating strongly reducing conditions. In the pH region anticipated for field applications
(pH > 6), the test data from MSW leachate appear to correspond with (pH + pE) values between 4 and 6,
indicating strongly reducing conditions (van der Sloot et al, 2017). .
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1
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•[Fe] @ L/S 0.3; pH+pe=7
• [Fe] @ L/S 0.3; pH+pe=5.5
Figure 4-7. Comparison of geochemical simulation of iron leaching at various pH/redox
conditions (pH + pE) to laboratory test results for mixed municipal solid waste (MSW)
landfill material.
4.3.2 Carbonation of Alkaline Materials
Alkaline materials, especially those primarily composed of calcium hydroxide and calcium-aluminum-
silicate minerals (e.g., lime and cement-based materials), are likely to react with carbon dioxide when
placed in the environment. The results of the carbonation reaction include reduction of the alkalinity of
the system (i.e., neutralization) and precipitation of relatively insoluble carbonate minerals within the
pore structure of the material. Neutralization of the natural pH from pH > 10 to pH < 9 may concurrently
alter the chemical speciation of COPCs [e.g., lead from soluble Pb(OH)4~2 may precipitate as insoluble
PbC03 or result in Pb sorption to hydrated iron oxide], changes in the mineral distribution (e.g., dissolution
of ettringite) or shifts in the COPC leaching concentration along the LSP curve. Exposure to carbon dioxide
can result from near surface applications where the material is exposed to relatively moderate
concentrations of atmospheric carbon dioxide or from exposure to elevated carbon dioxide in subsurface
scenarios due to microbial respiration. Dissolved carbonates can also compete with other oxyanions for
adsorption to reactive surfaces, e.g., iron (hydr)oxides, and, therefore, increase the leaching
concentrations of oxyanions such as arsenates, chromates, molybdates and selenates.
4.3.3 Microbial Activity
When placed in the environment, the redox conditions of some systems may become more reducing due
to microbial respiration processes that consume available oxygen, nitrate, metal oxides, sulfate, and
carbonate (electron acceptors). These processes are most prevalent and important at pH between 5 and
9 and when significant concentrations of organic carbon are present as substrate (electron donors). As
discussed above, reducing conditions can result in decreased leaching through formation of precipitates
(e.g., sulfides) or can increase leaching through the formation of more soluble reduced species (e.g.,
copper, molybdenum, vanadium).
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4.3.4 Complexation with Dissolved Organic Matter
Dissolved organic matter in the form of humic, fulvic or other analogous polar species as well as organic
acids complex with many dissolved multivalent cations (e.g., Pb, Cu, Mn, Cr(lll)), resulting in increased
apparent solubility because of the presence of both uncomplexed and complexed ions in solution. The
solubility of dissolved organic matter often is a strong function of pH because of
protonation/deprotonation of ionic moieties and alkaline hydrolysis of more complex organic matter. In
addition, organic acids are often formed because of microbial activity.
4.3.5 Co-precipitation of Arsenic with Calcium
Since a COPC may be incorporated into or sorbed onto solid mineral phases, the observed leaching
behavior of a COPC in LEAF tests may be strongly influenced by the release of other constituents. In U.S.
EPA (2014c), a significant increase in arsenic concentration was observed in the latter stages of the column
test due to co-precipitation with calcium minerals. Figure 4-8 shows Method 1314 results for pH, calcium
release and arsenic release from a low calcium fly ash (Sample ID: EaFA). Method 1313 results for each
are shown on the right side of the figure. The graph in the top left shows that the eluate pH released from
the column increases from an initial pH of 4.2 to a near-neutral pH by an L/S value of approximately 2
L/kgdry. The titration curve to right indicates that only a small amount of acid needs be released to result
in this pH increase. At an L/S of 2 L/kgdry, the cumulative release of calcium has reached a plateau;
however, since the LSP of calcium is not a strong function of pH between 4.2 and 7.1, the plateau in the
calcium cumulative release curve must be a result of calcium depletion. The cumulative release of arsenic
remains relatively low until calcium is depleted (i.e. the point at which cumulative calcium plateaus),
beyond which arsenic increases significantly. Geochemical speciation modeling confirmed that arsenic is
co-precipitated with calcium.
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eluate pH in
eluate pH in
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4.3.6 Chemical Interactions
The observed leaching concentrations of specific COPCs can be a result of complex interactions,
prompted, suppressed or enhanced by pH and the leaching of other constituents. For example, in the
presence of calcium-bearing minerals, arsenic leaching may be minimal; however, leaching of arsenic may
increase sharply when calcium concentrations decrease below approximately 100 mg/L because of the
decrease in precipitation of calcium arsenate.
Figure 4-9 shows a comparison of LSP (interpolated from test data) and percolation column data for two
coal combustion fly ash materials - a calcium-rich ash, CaFA, shown in red and a calcium-poor ash, EaFA,
shown in gold. Panels A-H show the titration and pH behavior as well as the leaching data for calcium,
arsenic and chromium. The column test data for calcium (Panel D) illustrates the depletion of calcium for
EaFA prior to an L/S of 5 L/kg-dry (gold vertical line) that is not evident in the higher calcium CaFA ash.
Panel F shows a corresponding increase in arsenic leaching from EaFA starting at approximately L/S 4.5
L/kg-dry, concurrent with the depletion of calcium. In CaFA, however, the leaching of arsenic remains
unchanged consistent with calcium concentrations above 100 mg/L. The leaching of chromium (Panel H)
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may appear at first to be similar to arsenic (i.e., the shape of the column eluate data for EaFA is similar for
chromium and arsenic). However, comparison of chromium pH-dependent behavior (Panel G) with
column concentrations (Panel H) shows that the increase in chromium between L/S 4.5 and 10 L/kg-dry
are a consequence of the change in chromium leaching as a function of pH. Note that the initial eluate pH
in the EaFA column is approximately pH 4 increasing rapidly to a pH of 7 by L/S 2 L/kg-dry (Panel B), while
chromium LSP goes through a minimum leaching concentration at pH 5.5 (Panel G). The observed pH shift
in the column data for EaFA is a consequence of an acidic coating on the fly ash due to sulfuric acid spray
injection. This analysis illustrates the importance of evaluating pH-dependent leaching test results
(Method 1313) in conjunction with percolation column leaching test results (Method 1314) to provide an
improved understanding of complex leaching behavior.
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chromium leaching from low-calcium fly ash (EaFA) and high-calcium fly ash (CaFA).
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4.4 Performing Common Analyses in Leaching Assessments
4.4.1 Determining the Available Content from Method 1313 Data
Within the LEAF approach, the available content is defined as the fraction of the total content that has
the potential to leach under typical environmental conditions. The available content is determined as the
mass release in mg/kg-dry associated with the maximum leaching concentration from Method 1313
conducted at endpoint target pH values of 2, 9, and 13:
mavaii = Cmax(pH2,9,13) x (V^)i3i3 Equation 4-12
where
iriavaii is the available content on a dry mass basis [mg/kg-dry];
Cmax(PH2,9,i3) is the maximum eluate concentration [mg/L] at the endpoint target pH
values of 2, 9, and 13, and;
(L/S)i3i3 is the liquid-to-solid ratio of the Method 1313 eluate (i.e., 10 L/kg-dry).
The relationship between total and available content relative to Method 1313 data is presented Figure
4-10. The figure presents the pH-dependent cumulative mass release of a cationic metal (red solid line) in
comparison to total content (green solid line) and available content (blue dashed line). The total content
is a single mass release value in mg/kg-dry derived from total analysis of the solid material (e.g., from
digestion techniques or non-destructive methods). The total content is comprised of a fraction that is
available for leaching and a fraction that is bound within the mineralogy of the solid material. The available
fraction of the total content is both constituent-dependent (i.e., boron and lead will have different
fractions that are available within a material) and material-dependent (i.e., lead may be primarily
leachable in one material and recalcitrant to leaching in another). Retention is based on the specific
structure of material solid phases (e.g., mineralogy, amorphous/glassy phases) and the potential
substitutions of COPCs within those solid phases. For example, some mineral forms such as quartz are
very stable so that COPCs bound within silicate are not likely to leach. Conversely, hydroxides tend to be
more soluble under environmental pH conditions and COPCs that precipitate as hydroxides are released
when the hydroxide minerals dissolve. As a practical matter, for the timeframes of interest for waste
disposal/use, the fraction of COPCs bound in these stable mineral forms and amorphous phases is unlikely
to be available for leaching (U.S. EPA, 2014c). As the pH changes (i.e., following the LSP curve),
remineralization results in COPCs present in various solid phases being released or retained depending on
the solubility values of individual minerals, sorption characteristics of the solid phases and solution
chemistry.
Determination of available content based on the maximum concentration at end-point eluate pH values
of 2, 9 and 13 is a practical approach because solubility of specific elements is at a maximum at one of
these pH conditions over the Method 1313 test, and therefore release is available-content limited for
most materials. The lowest pH value, pH=2, also results in dissolution of COPCs sorbed to iron (hydr)oxide
surfaces and clays.
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10000
TOTAL CONTENT
2 1000
AVAILABLE CONTENT
100
MEASURED RELEASE
(cationic metal)
0
2
6
8
10
12
4
14
PH
Adapted from Heasman et al. (1997).
Figure 4-10. Relationship between total content, available content and measured pH-
dependent release for a cationic metal.
The reported values for available content using Method 1313 in some cases may be greater than the
reported total content because of uncertainties in the testing methodologies. These uncertainties include:
(i) inherent analytical uncertainty associated with both total content and leaching test chemical analysis,
especially at low extract concentrations, (ii) reliance on very small material quantities used in total content
analyses that may not be representative of the material as a whole, (iii) partial digestion techniques for
total content analysis where recalcitrant minerals (e.g., silicates) are not fully dissolved, and (iv) analytical
dilution of total content digestions from a concentrated but near-dry state to a volume sufficient for
chemical analysis.
Figure 4-11 shows the Method 1313 data for cadmium, boron, molybdenum in each of three materials
including a contaminated smelter site soil (CFS; left), a coal combustion fly ash (EaFA; middle) and a
solidified waste form (SWA; right). Vertical lines in each graph indicate the endpoint target pH values of 2
(blue), 9 (red) and 13 (green) where the maximum concentration values would be expected for various
pH-dependent behaviors. Numerical values for measured concentrations as well as the available content
calculated at the endpoint target pH values are provided in Table 4-4, along with additional COPCs for
comparison. Note that the actual measured concentration for the eluate is used for the calculation of
available content, not the concentration interpolated to the target pH value. In all materials, the maximum
concentration of cadmium occurs at a pH of approximately 2, which is consistent with cationic pH-
dependence. For boron, the pH-dependent leaching is not a strong function of pH and the maximum
concentration occurs at a pH near 2 for CFS and SWA, but at an alkaline pH for EaFA. The maximum
concentration of molybdenum occurs at near pH 9 (SWA) or near 13 (CFS, EaFA). Note that the graphs in
Figure 4-11 show essentially constant concentration at or near the available content for molybdenum
(EaFA, SWA) and boron (EaFA) at pH > 9.
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Table 4-3. Comparison of Method 1313 Eluate Concentrations at pH 2, 9,13 and Reported
Available Content: Contaminated smelter site soil (CFS), coal combustion fly ash (EaFA) and
solidified waste form (SWA).
Cone, at pH 2
Cone, at pH 9
Cone, at pH 13
Available
Target
Target
Target
Content
Max. Cone.
CO PC
Material
[mg/L]
[mg/L]
[mg/L]
[mg/kg-dry]
at pH
Arsenic
CFS
85
0.042
0.23
850
1.9
EaFA
1.6
0.56
9.7
970
13.1
SWA
5.8
0.48
16
160
12.6
Boron
CFS
0.72
0.12
0.056
7.2
1.9
EaFA
3.3
4.5
5.0
50
12.0*
SWA
5.8
1.9
0.78
58
2.5
Cadmium
CFS
47
0.006
0.009
470
1.9
EaFA
0.066
0.015
0.015
0.66
2.1
SWA
0.029
< 0.002
< 0.002
0.29
2.5
Molybdenum
CFS
0.11
0.57
1.3
13
13.1
EaFA
0.33
3.7
3.9
39
13.1
SWA
0.0067
0.15
0.14
1.5
8.9
Selenium
CFS
0.51
0.20
0.29
5.1
1.9
EaFA
0.55
4.0
6.9
69
13.1
SWA
35
130
98
1,300
8.9
Zinc
CFS
170
0.009
5.6
1,700
1.9
EaFA
1.6
< 0.001
0.057
16
2.1
SWA
1.9
0.021
0.017
19
2.5
"<" indicates eluate concentration presented as less than reported MDL value.
"*" pH 13 extraction was not measured for boron due to base storage in dissolution of borosilicate glass (U.S. EPA, 2012c).
Eluate concentrations in bold indicate maximum concentration.
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SWA
SWA
SWA
Figure 4-11. Comparison of eluate concentrations at specified pH values of 2, 9, and 13 used to determine the available content:
Contaminated smelter site soil (CFS; left), coal combustion fly ash (EaFA; middle) and solidified waste form (SWA; right).
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4.4.2 Interpolating Method 1313 Data to Endpoint Target pH
Since the pH-dependent leaching of many COPCs may be sensitive to minor fluctuations in eluate pH, it is
necessary to interpolate Method 1313 test results to the specified endpoint target pH values to provide
reproducible, comparative results to be used in conjunction with comparison the threshold or limit values.
In practice, Method 1313 allows for a tolerance of ±0.5 pH unit for each target pH value recognizing the
experimental error inherent to addition of acid and base and measurement of pH. However, the measured
eluate concentration over the tolerance interval may result in a concentration difference as much as an
order of magnitude. Thus, eluate concentration data to be used to evaluate leaching over a scenario pH
domain should be interpolated to the endpoint target pH values to minimize the bias in eluate
concentrations for highly pH-dependent COPCs. Interpolated eluate concentrations are obtained by
standard linear interpolation of log-transformed data from two neighboring Method 1313 eluates (U.S.
EPA, 2012c).25
logC = logCa + (pH - pHa) x (logCb - logCa)/(pHb - pHa) Equation 4-13
where
logC is the log-transform of the eluate concentration interpolated to the endpoint
target pH value of 2, 9, or 13 in log[mg/L];
pHa is the measured pH value for eluate a;
pHb is the measured pH value of eluate b;
logCa is the log-transform of the measured eluate concentration at pHa in log[mg/L], and;
logCb is the log-transform of the measured eluate concentration at pHb in log[mg/L],
Figure 4-12 shows that the overall result of interpolating measured concentration to Method 1313
endpoint target pH values is not significant except in pH regions where the LSP is highly sensitive (e.g., see
iron near pH 4 or cadmium from pH 5-12).
Although interpolation should be considered carefully or may not be possible for data collected before
the methods were standardized (e.g., Method SR002.1, the predecessor to Method 1313)26 or from single-
point leaching tests, older pH dependent data from the predecessor methods can provide a useful
comparison basis (e.g., see U.S. EPA, 2012b) and be used for more detailed assessments (e.g., see U.S.
EPA, 2014b). Interpolation can be carried out automatically in LeachXS™ Lite upon importing of Method
1313 test results.
25 Interpolation of Method 1313 results to target pH values is achieved automatically using LeachXS™ Lite (see Section 3.3.2).
26 Interpolation is recommended for Method 1313 results within ± 0.5 pH units of endpoint target pH values. However, if
interpolation is conducted at greater intervals, consistency of interpolated values with the trend of the measured eluate
concentration should be evaluated.
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LLOQ
MDL
6 8
PH
Figure 4-12. Comparison of measured Method 1313 eluate data (red dots) for a
contaminated smelter site soil (CFS) with interpolated test results (green squares) using
linear interpolation of log-transformed concentration data.
4.4.3 Calculating Water Contact and Assessment Time: Liquid-Solid Ratio (L/S,
percolation mode) and Liquid-Area Ratio (L/A, flow around mode)
The amount of each COPC that leaches over time in a particular assessment scenario can be estimated
based on the amount of contacting water. In order to evaluate a leaching assessment over time, a liquid
to solid ratio (L/S) can be calculated based on the amount of material in the environment and the expected
amount of water to contact that material over time. L/S is defined as the contacting water per unit mass
of material (i.e., the L/S associated with the annual infiltration or groundwater flow rate) multiplied by
the cumulative leaching time for the assessment. When the assessment is for a material that has a known
geometry volume, per unit mass of the material in the application, LS can be calculated using Equation 4-
14 (Hjelmar, 1990).
(L/S)scenario (Jnf x tyr)/(j) x Hfjjj) x 1000 Equation 4-14
where
Inf is the annual rate of infiltration or groundwater flow [m/year];
tyr is the cumulative leaching time for the scenario [years];
p is the material bulk dry density [kg-dry/m3];
Hfui is the dimension of the fill in the direction of water flow [m]; and
1000 is a units conversion factor (1,000 L = m3).
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Using the above approach, Figure 4-13 illustrates the distribution of time to achieve L/S 2 and 10 L/kg-dry
for a selection of U.S. CCR landfills based on site geometries, material properties and the rates of annual
precipitation or infiltration. These results indicate that only a small fraction of precipitation becomes
infiltration and that achieving even a modest L/S of 2 L/kg-dry can take several decades to centuries
depending on site-specific factors. The time to achieve a higher L/S value like 10 L/kg-dry can take from
about 200 years and up to several millennia. Based on this evaluation at the 10th percentile (i.e., 90% of
the cases in the distribution take longer than the 10th percentile), the cumulative time required to reach
an L/S of 2 and 10 L/kg-dry in a U.S. CCR landfill is approximately 80 and 400 years, respectively.
100,000
10,000
ur
n 1,000
J*
o
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i—
10
1
0 20 40 60 80 100
Percentile
• L/S 2, infiltration O L/S 10, infiltration
—¦--L/S 2, precipitation - ~ L/S 10, precipitation
Data adapted from U.S. EPA (2014b).
Figure 4-13. Statistical distribution of time to reach L/S=2 L/kg-dry or L/S=10 L/kg-dry
based on national distributions of precipitation and infiltration for CCR landfills.
If the material of interest is present in a saturated zone (e.g., within groundwater or surface water
sediments), the amount of water flowing through the material or contacting the external geometric
surface area of a monolithic material can be estimated to determine the annual L/S for percolation cases
or liquid to surface area (L/A) for mass transport cases. L/A is calculated based on the geometry and
resulting surface area of your material that is in contact with water.
4.4.4 Interpreting Observed Liquid Solid Partitioning (LSP) Behavior
The observed leaching behavior of a material (e.g., waste, secondary material, contaminated soil,
sediment, construction material), when exposed to water in the environment, can be viewed as the
combined result of constituent mass transfer and chemical equilibrium between solid, liquid and gas
phases. Chemical equilibrium, often described as liquid-solid partitioning (LSP), is considered the
endpoint, or limit case, for mass transfer when concentration gradients have been minimized. LSP may be
achieved over relatively short duration (e.g., minutes to hours) when water is directly and uniformly in
contact with a representative volume of the solid phase (e.g., in the case of uniform percolation) or over
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long durations (e.g., months to decades, or longer) when water contacts is limited to an external
geometric surface in the case of monolithic or compacted granular materials. Additionally, the approach
to chemical equilibrium is delayed when hydraulic conditions result in significant flow channeling which
reduces the contact time between the liquid and the solid. In scenarios where LSP of a constituent cannot
be assumed, the driving force for mass transport is the difference between the constituent concentration
at equilibrium and the existing concentration in the leachate. Thus, an underlying knowledge of leaching
behavior based on LSP and the rates of mass transport (due to diffusion or other processes) is crucial for
the understanding of observed leaching behavior both in the laboratory and in the field.
The partitioning of constituents between solid and liquid phases at equilibrium is controlled primarily by
the following factors:
• The content of the full set of constituents (COPCs and non-COPC constituents such as calcium,
chloride, sulfate, phosphate and humic/fulvic substances) that can participate in partitioning,
• The system pH which acts as a master variable controlling the solubility and LSP of ionic species
(e.g., most inorganic and many organic constituents),27
• The liquid-to-solid ratio (L/S) in the system defined as the amount of the water present relative
to the equivalent dry mass of solid present in units of [mL/g-dry] at the laboratory scale and [L/kg-
dry] at the field scale,
• The system redox potential which controls the oxidation state of constituents that have multiple
potential valence states, such as Cr(lll) versus Cr(VI), and
• The amount of reactive solid surfaces (e. g., iron (hydr)oxide, clay minerals, natural organic
matter) available for constituent sorption.
Based on these factors, a COPC or other constituent may exist in the liquid phase as a combination of free
and complexed chemical species either at aqueous saturation (maximum liquid concentration at the given
pH, redox and system composition) or at a concentration less than aqueous saturation. The concentration
at aqueous saturation also can be modified by the presence of complexing agents in the water such as
dissolved humic or fulvic substances (often estimated from dissolved organic carbon) or chloride or other
dissolved ionic substances.
As discussed in Section 4.2.4.2 and 4.4.1, the available content is determined as the mass release
associated with the maximum eluate concentration from pH-dependent LSP. In order to provide a uniform
procedure for determining available content, the maximum LSP concentrations from Method 1313 testing
are evaluated at pH values of 2, 9, and 13. The available content represents the fraction of the total
content of a constituent that may leach under environmental conditions. In solution, the available content
may represent an endpoint conditions for leaching (available content-limited leaching) if the available
content in the solid material has been leached into solution at less than aqueous saturation. In addition,
a constituent that is part of the available content (i.e., is leachable under the appropriate conditions) may
exist as the solid in one or more chemical species:
27 The system pH can also be viewed as the available concentration of H+ or OH- ions in the water (i.e., pH = -log[H+] and pOH =
14- pH).
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• Precipitated in one or more mineral forms based on the dissolution/precipitation reactions that
may take place based on the overall system composition,
• Co-precipitated within the mineral phase as by matrix substitution (i.e., a solid solution), or
• Sorbed to a reactive surface (e.g., iron (hydr)oxide, aluminum oxide, clay minerals, natural organic
matter) based on adsorption/desorption or ion exchange reactions.
Many of the above reactions that define the observed LSP may not be well quantified or even well defined.
Research in geochemistry seeks to define and quantify these reactions to the extent possible or practical.
However, even without detailed geochemical knowledge, the leaching behavior is empirically observed
through laboratory testing and field measurements.
In pH-dependent leaching tests, the shape of the observed LSP curve (i.e., relative locations of maxima
and minima) typically has four classic shapes presented schematically in Figure 4-14.
i Hi
ghly Solu
ble
!
Cationic
Amphoteric^ *
Oxyan ionic
f
/
N
/
/
\ /
V
[ V
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V
~
_
\
[
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0 2 4 6 8 10 12 14
Leachate pH
Adapted from Kosson et al. (2002), as cited in U.S. EPA (2012f).
Figure 4-14. LSP patterns for classical pH-dependence leaching behaviors.
Although the shapes in the figure are idealized and seldom are seen as clearly as presented, these trends
provide a basic evaluation of how COPCs may behavior in complex natural systems. Comparing measured
LSP curves obtained through Method 1313 to these idealized shapes may be useful for interpreting broad-
stroke speciation of a constituent. The four classic LSP behaviors as shown in the Figure 4-14 include:
• Highly Soluble Species - The LSP curves for highly soluble species (e.g., B, CI, Na, K, etc.) are
usually a weak function of pH where the measured concentration may vary by up to an order of
magnitude across the entire pH domain. Often, highly soluble species are considered to leach to
the point of depletion of the available content (i.e., no more leachable COC exists in the solid
phase) and re-mineralization due to shifts in pH are minor. Because highly soluble species release
a relatively constant available mass into solution, the concentration of highly soluble species in
solution is typically a strong function of L/S (e.g., halving the amount of liquid doubles the
concentration).
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• Cationic Species - The LSP curves of cationic species (e.g., Ca, Cd, Fe, etc.) show a maximum
concentration in the acidic pH range and a decreasing LSP trend in the alkaline range. Within the
usual alkaline range of pH < 14, the LSP concentration does not increase again. The maximum
concentration value associated with determination of availability content is observed as an
asymptote, typically, at pH < 4.
• Amphoteric Species-The LSP curve for amphoteric species [e.g., Al, As(lll), Pb, Cr(lll), Cu, Zn, etc.]
tend toward a similar shape to that of cationic species; however, concentrations pass through a
minimum in the alkaline pH range and increase in highly alkaline regimes. The increase at high pH
is due to the increasing solubility of hydroxide complexes (e.g., Zn(OH)3_1, Zn(OH)4"2). The pH
associated with the maximum LSP concentration used to determine the available content may be
observed at low pH (pH = 2) or high pH (pH = 13).
• Oxyanionic Species - The LSP curves for oxyanions [e.g., As(V), Cr(VI), Se(VI), Mo(VI), etc.] often
show maxima in the neutral to slightly alkaline range and a decrease in concentration as pH
decreases. Since many metals which make up oxyanions (e.g., Cr in Cr207) may be sensitive to
changes in oxidation-reduction potential, the LSP curve also may show a local maximum at low
pH where more reducing conditions are present.
A more detailed evaluation of constituent speciation may be conducted through geochemical speciation
models that infer the mineral phases, adsorption reactions, and soluble complexes that control the release
of the constituent using Method 1313 data.
Figure 4-15 and Figure 4-16 provide results of Method 1313 testing, as a comparison of observed leaching
behavior of several COPCs for four materials:
• CFS - a lead smelter field soil (U.S. EPA, 2012c, 2012d)
• SWA - a solidified waste analog (U.S. EPA, 2012c, 2012d)
• EaFA - a low calcium coal fly ash (U.S. EPA, 2012c, 2012d)
• CaFA - a high calcium coal fly ash (U.S. EPA, 2009)
Method 1313 results are also provided for several of the key elements that influence the leaching behavior
as discussed above (e.g., calcium, iron, DOC, sulfate, phosphorous).
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and EaFA), smelter site soil (CFS) and solidified waste (SWA).
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Figure 4-16. LSP behavior for different example waste forms: coal combustion fly ash (CaFA
and EaFA), smelter site soil (CFS) and solidified waste (SWA).
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4.4.5 Identifying Solubility- and Available Content-Limited Leaching
Screening-based assessments utilize an upper bounding estimate of the maximum expected leaching
concentration of COPCs in comparisons with relevant thresholds (see Section 4.2.4). When using Method
1313 results to estimate the maximum leaching concentration, it is important to identify if the measured
eluate concentration of each COPC over the scenario pH domain reflects available content-limited
leaching in contrast to solubility-limited leaching.28
• When the LSP determined by Method 1313 reflects solubility limits or adsorption control, the
eluate concentrations are a weak function of L/S and the maximum leaching concentration may
be estimated at the Method 1313 test conditions.
• When LSP leaching reflects available content, however, higher leachate concentrations are
expected a lower L/S values and lower leachate concentrations are expected at higher L/S values
than laboratory test conditions. Thus, Method 1313 results must be adjusted from laboratory test
conditions (i.e., 10 mL/g-dry) to the field scenario L/S to obtain the upper bound concentration
estimate for COPCs.
The simplest way to determine if available content-limited leaching is occurring during Method 1313 is to
compare the measured concentration at each targeted eluate pH to the maximum concentration used to
determine the available content (Section 4.4.1). If leaching is limited by the available content, the
measured concentration should be equal to the maximum concentration used to determine the available
content within the uncertainty of the test method. Based on interlaboratory validation, the mean test
uncertainty for Method 1313 has been determined to be 28% of the measured value shown in Table 3-6.
Thus, leaching is considered available content-limited when evaluating each Method 1313 eluate if the
following condition is met:
Cmax(pH 2,9,13) x[l-0-28] , ,, c .. . ^ c
7 xh+n2«i ~ 1 Equation 4-15
^max(pH domain) XL± + U.ZoJ
where
Cmax(pH2,9,i3) is the maximum eluate concentration used for determination of available
content [mg/L];
Cmax(pHdomain) is the maximum eluate concentration over the applicable scenario pH
domain [mg/L], and;
0.28 is the reproducibility residual standard deviation (RSDr) for concentrations
from the Method 1313 interlaboratory validation study (Table 3-6).
If the fraction in Equation 4-15 is greater than 1, then the LSP behavior is dominated by solubility-limited
or sorption-controlled leaching.
An alternate way to determine whether the environmental leaching is solubility (or sorption)-limited vs.
available content-limited is based on evaluation of Method 1316 results. Graphical presentation of
Method 1316 test results can provide insight into whether the leaching at the natural pH of a material is
28 For some materials, some COPCs may reflect solubility-limited leaching over part of the applicable pH domain, and available
content-limited leaching over another part of the applicable pH domain for the field scenario being evaluated. When this
situation occurs, the maximum concentration estimate based on the available content-limited leaching is used.
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available content-limited or solubility-limited. The Method 1313 and Method 1316 results for boron and
chromium leaching from a coal combustion fly ash (EaFA) are shown in Figure 4-17. The maximum
observed concentration of boron over the applicable pH domain of 5.5 < pH < 9 is 4.97 mg/L is statistically
100% of the maximum concentration of 4.99 mg/L measured at pH 12 for determination of the available
content. In Method 1316, the mass release of boron is a weak function of L/S at values greater than 72%
of the available content and the release at high L/S (where solubility constraints would normally be less)
limited by the available content value. Therefore, boron displays available content-limited leaching
behavior over the pH domain shown in Method 1313 results.
Solubility-limited leaching is indicated by Method 1313 concentrations overthe applicable pH domain that
are significantly less than the maximum concentration used to determine the available content and that
vary strongly with pH values. For solubility-limited release, the mass release Method 1316 usually is a
strong function of L/S (slope of approximately 1 of concentration as a function of L/S), increasing with L/S
to a value that is only a fraction of the available content under laboratory conditions. In contrast, Method
1316 concentration data is a weak function of L/S for solubility-limited release. In Figure 4-17, the
maximum concentration of chromium over the 5.5
o--<
PH
4 6
L/S (L/kg-dry)
10
—•— EaFA_1313 --O- EaFA_1316
Figure 4-17. Available content-limited leaching of boron and solubility-limited leaching of
chromium from a coal combustion fly ash (EaFA) based on the results of Method 1313 (left)
and Method 1316 (right).
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4.4.6 Understanding Mass Transport Parameters (Low Permeability Materials)
Method 1315 is most appropriate for understanding the rate of release under conditions where mass
transport dominates the rate of constituent release (e.g., relatively impermeable materials). If the
material will form, or be incorporated into, a solid monolithic or compacted granular form, it may be
useful to perform Method 1315 to understand the degree to which the reduced surface area exposed to
water contact reduces leaching. Example materials that benefit from mass transport testing include clay-
like soils and sediments, or materials with low permeability due to cementitious or pozzolanic reactions.
Method 1315 is applicable if water is expected to flow around the material, or if fractures in the material
result in diffusion-limited release, based on exposed surface area.
Since the sample material in Method 1315 has contact with water only at the external geometric surface,
COPCs must migrate from the interior of the material before partitioning into the leachate. The tortuous
pathway for migration and chemical interactions with minerals and other constituents that occur along
the pathway within the pore structure of the material reduce the observed rate of leaching. Field
conditions associated with mass transport-controlled leaching are often different from Method 1315
laboratory test conditions:
• Method 1315 conditions are designed to maintain a dilute solution relative to aqueous solubility
(e.g., an "infinite bath" boundary) through specification of a large L/A value and frequent eluant
exchanges. These laboratory conditions ensure that the observed ratio of leaching is limited by
transport through the material and by solubility-limited leaching in the Method 1315 leachate.
The result is the Method 1315 measures a maximum rate of release for a given material. Field
conditions often have a much smaller L/A that results in more cases where LSP at equilibrium
limits leaching (especially for elements with low solubility). However, the range of these field
conditions, which can be highly site-specific, cannot be universally represented in a standardized
leaching test such as Method 1315.
• Method 1315 results represent a case of continuous mass transport over a cumulative leaching
period of 63 days. The continuous liquid contact and eluant exchange intervals of Method 1315
are designed to maintain internal diffusion gradients within the material for the duration of the
test. The peak interval flux measured at the beginning of Method 1315 declines rapidly because
of the established concentration gradient within the material and, eventually, local depletion and
low concentration gradients at the external surface of the material. However, field conditions
often are variable such that a material present at the surface or in the vadose zone is likely to
undergo intermittent water contact (e.g., due to a pattern of rainfall events leading to periodic
infiltration). When a material is not in contact with water (i.e., during drying or storage periods),
the internal concentration gradients established during the previous wetting period relax or
"flatten out," replenishing the low porewater concentration at the material surface. In the
porewater at the material surface, local equilibrium may be established during a drying or storage
period. Thus, the initial release in the next wetting period is greater than would be anticipated by
continuous leaching due to the elevated gradient across the material surface (Garrabants,
Sanchez, & Kosson, 2003; Sanchez, Garrabants, & Kosson, 2003). The greater flux observed for
wetting stages after drying or storage is referred to as a "first flush" phenomena. However, the
cumulative mass release under intermittent wetting conditions typically is significantly less than
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the mass release under continuous leaching conditions (i.e., those imposed by Method 1315)
because material only leaches for a fraction of the total evaluation time.
• Natural aging of the material, leaching of the mineral structure, and exposure to external field
conditions may result in the formation of a surface layer or "rind" that has a different composition
and properties than the material that was tested in the laboratory. For example, exposure to
atmospheric carbon dioxide leads to pore filling and neutralization of porewater pH that may
reduce the observed leaching rate in cementitious materials. Similarly, pore filling may occur after
chemical reaction with constituents present in contacting water (e.g., magnesium carbonate or
sulfate precipitation). Leaching of constituents can result in an increase in porosity resulting from
removal of highly soluble salts when initially present as a large fraction of the material.
• When the hydraulic conductivity of a monolithic or compact granular material is relatively close
(within and order-of-magnitude) of the surround materials, field conditions may allow for a
fraction of the contacting water to percolate through the material such that both percolation and
diffusion processes are present. For these scenarios, the results of Method 1314 (or possibly
Method 1316) at the estimated L/S ratio of the percolation provide a bounding estimate of the
maximum leaching concentration.
Based on the above differences between Method 1315 test conditions and field conditions, the
concentration results from Method 1315 cannot be considered representative of field leachates and
should not be used in comparison to threshold values. However, Method 1315 results may be used in
several different ways to estimate field leaching:
• The flux of COPCs measured during first intervals of Method 1315 testing may be used as a
bounding estimate of initial leaching fluxes or fluxes after drying periods associated with
intermittent wetting. This approach was used in assessing leaching from concrete containing coal
fly ash (U.S. EPA, 2014a).
• The observed diffusivity of COPCs estimated from Method 1315 results applied to a simple Fickian
diffusion model can provide a basis for comparison of relative leaching rates between different
materials potentially used or managed under the same field conditions. For example, observed
diffusivities can be used as a basis of comparison of the effectiveness of different treatment
process for a waste (Sanchez, Kosson, Mattus, & Morris, 2001; Westsik Jr. et al., 2013).
• Method 1315 results may be used to parameterize diffusion processes in simple diffusion models
in cases when physical-chemical conditions do not change (Garrabants et al., 2002) or more
detailed fate and transport model to estimate long-term constituent leaching under a range of
field exposure conditions or scenarios (SRR, 2013, 2014; U.S. EPA, 2014c).
Method 1315 is often conducted in conjunction with Method 1313 to provide information on both the
rate and extent of leaching (Section 2.4). Release calculated from Method 1315 provides a "best estimate"
of leaching rate under mass transport conditions that may be assumed as long as the material maintains
its structural integrity. Method 1313 can provide an upper bounding estimate that may be useful for
understanding leaching as the solid material breaks down over time and ensuring there is not excessive
release. The combined effects of leaching rate and leaching extent were used to evaluate the impact of
coal combustion fly ash substitution for Portland cement in commercial concrete considering under
intermittent wetting conditions based on surface application of concrete exposed to precipitation (U.S.
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EPA, 2014a). Empirical data from Method 1313 estimating available content and Method 1315 estimating
effective diffusivity were used to evaluate applications of MSWI bottom ash scenarios (Kosson, van der
Sloot, & Eighmy, 1996). These approaches can also be used in conjunction with chemical speciation-based
mass transfer models to provide insights into potential changes in leaching that may occur in response to
changing conditions within or on the external surface of the material being evaluated.
Method 1315 results should be accompanied by a careful review to understand controlling mechanisms
during testing and apply appropriate assumptions in extrapolation 1315 results to field scenarios. LEAF
users can determine which process dominates based on comparison of Method 1313 and 1315 results. As
indicated earlier, the test conditions of Method 1315 (i.e., liquid-to-surface area ratio and eluant refresh
schedules) are designed to maintain a dilute eluate with respect to LSP in order to maintain the driving
force for constituent mass transport (e.g., diffusion and dissolution; U.S. EPA, 2010). Thus, Method 1315
concentrations should be significantly less than the corresponding Method 1313 LSP concentration at the
same pH (e.g., arsenic and cadmium in the top of Figure 4-18) for the assumed boundary condition to be
valid. If Method 1315 concentrations for a constituent approach or are equal to the LSP concentrations
(e.g., boron and barium in Figure 4-18), the Method 1315 dilute boundary condition assumption may not
have been maintained throughout the test and the LSP as defined by Method 1313 and 1314 should be
used as the basis for assessment.
I
' MDL
6 8
PH
/
T5
LLOQ
i
/
\
MDL
6 8
PH
Figure 4-18. Comparison of mass transport data (green triangles, Method 1315) to
equilibrium data shown as a function of pH (red circles, Method 1313) for a contaminated
lead smelter soil (CFS).
In describing the leaching process (Section 2.4), mass transport was considered to continue as long as the
concentration gradient was maintained which infers that when eluate concentrations approach
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equilibrium concentrations, Method 1315 data represents equilibrium and not mass transport. As an
internal quality control check, eluate concentrations may be plotted over the LSP data from Method 1313
to verify that the "dilute" boundary condition is met for each constituent.
• Barium eluate concentrations for Method 1315 are essentially the same as the results from
Method 1313. Therefore, the resulting Method 1315 eluates were saturated solutions with
respect to aluminum and did not meet the "dilute" boundary condition. Thus, these barium
results were not mass transfer-controlled, and should not be interpreted as diffusion-controlled
release.
• Arsenic eluate concentrations in Method 1315 are significantly less than the Method 1313 results
at the corresponding eluate pH and greater than the LLOQ. Therefore, Method 1315 eluates were
dilute solutions with respect to arsenic and the arsenic results can be further evaluated to
determine if diffusion-controlled release is a reasonable assumption.
Inspection of the cumulative release and flux as functions of leaching time indicate that release of
selenium initially followed the reference line for idealized Fickian diffusion (i.e., log-linear release with a
slope of Vz with respect to time for cumulative release and -Vz with respect to time for flux). After
approximately 14 days, release declined somewhat which may be indicative of depletion of selenium from
the material. In contrast, the cumulative release and flux of aluminum follow the slopes of Vz and -Vz,
respectively; however, aluminum is not diffusion controlled because the Method 1315 data did not meet
the criteria for maintaining dilute solutions. Furthermore, pH gradients internal to the monolith being
tested result in varying pore solution concentrations of aluminum that cannot be effectively represented
as a constant observed diffusivity in a simple Fickian diffusion-controlled release model.
4.4.7 Considering Dilution and Attenuation in an Assessment Ratio
In some evaluations, it may be appropriate to consider the effect of a relatively small volume of leachate
interacting with a larger groundwater body through use of dilution and attenuation factors. The COPC
concentrations from LEAF test results represent a source term for leaching directly into contacting water.
Upon leaving the source and entering the environment, COPCs may become diluted or immobilized into
the environment before reaching a receptor. A dilution and attenuation factor (DAF) can sometimes be
used to estimate this reduction in concentration of a COPC in the environment. A DAF is COPC specific and
based on existing knowledge of fate and transport for the site of interest. DAFs have a value greater than
or equal to one (DAF > 1), representing the reduction in COPC concentration due to dilution of leachate
from the source into a larger waterbody or the attenuation of COPCs to surrounding materials and
processes, such as sorption to soil.
Constituents can interact with different media in ways that are non-linear with respect to concentration,
pH and other factors. In addition, interactions between different stressors have the potential to affect
fate and transport. As a result, it is important to understand and discuss the basis for a DAF to demonstrate
that the magnitude of reduction identified is applicable to a specific evaluation.
In situations where it is appropriate to apply existing DAF values, the source term from LEAF tests is
divided by DAF values to estimate COPC concentrations at particular points downgradient which can be
compared to threshold values. Alternatively, the Assessment Ratio (see Equation 4-1) can be modified to
account for dilution and attenuation (Equation 4-16).
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ARdaf ~ ~ Cleachjnax/{DAF x C(iires) Equation 4-16
Where
ARdaf is the assessment ratio considering dilution and attenuation [-];
Cieach_max'\s the estimated maximum concentration for the COPC [mg/L] (within the
applicable pH domain when using Method 1313 results or L/S range when using
results from either Method 1314 or Method 1316);
Cthres is the threshold value for the COPC [mg/L]; and
DAF is a COPC-specific dilution and attenuation factor appropriate for a given site[-].
Unless otherwise specified, the Assessment Ratio used in this guide does not consider DAFs.
4.4.8 Integrating Source Terms into Models
Source terms developed using LEAF are dependent upon the level of testing and assessment applied.
Simpler testing and assessments with less information regarding material placement in the environment
result in less defined source terms. The infinite source term assumes that the material will continue to
leach into the future. Infinite source terms developed from LEAF are often based on screening level
assessments. Increased levels of testing and assessment can result in finite-release source terms. A finite
source term representing time dependent leaching will often entail Method 1313 pH dependent data
suited to the scenario pH domain, combined with data from Methods 1314, 1315 or 1316 to evaluate L/S
dependence in the scenario.
The source terms developed from LEAF can be used directly, in conjunction with screening DAF values or
with a bounding deterministic groundwater fate and transport model (e.g., the Industrial Waste
Management Evaluation Model, or IWEM). The use of source terms from LEAF paired with modeling can
provide a more complete understanding of likely releases and resulting risks in contrast to the results from
a single-point leaching test. Sensitivity analysis can be carried out using estimates from LEAF testing of
COPC release over the anticipated pH and other conditions of the landfill or use scenario. Numerical
modeling can allow for consideration of vadose zone and groundwater transport of released constituents,
exposure to humans or animals via drinking water, and the toxicity of the released COPCs. In these models,
leaching data expressed on a concentration basis in mg/L or mass basis in mg/kg-dry represent the source
term for estimating the release of potentially hazardous substances.
Leaching data from LEAF can be used as an input to a sophisticated mass transport model to develop a
more-refined estimate of release for complex environmental conditions. For example, geochemical
speciation modeling software allows for simulation of LSP as a function of pH, L/S, and leachate chemistry
(e.g., redox changes, ionic strength) which can be used directly to inform decision-making or applied
subsequently to several different mass transport models to simulate COPC release in a range of field
leaching scenarios. Tools for geochemical speciation and reactive mass transport modeling include
PHREEQC wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc/), MINTEQA2 (www2.epa.gov/exposure-
assessment-models/minteqa2), LeachXS™ (van der Sloot & Kosson, 2012), and The Geochemist's
Workbench (www.gwb.com).
Reactive mass transport models, including use of geochemical speciation, may be used to examine
sensitivity to scenarios beyond laboratory testing conditions (Dijkstra et al., 2008; Meima & Comans,
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1998). In addition, chemical speciation modeling of pH-dependent and L/S-dependent test data can be
helpful to improve the understanding of the retention mechanisms that control the release of COPCs (e.g.,
mineral phase dissolution, sorption, and aqueous phase complexation phenomena) (van der Sloot, et al.,
2017). Where data are adequate, modeling can be used to estimate the effects of factors that may modify
leaching such as changes in the level of dissolved and particulate organic matter due to biological
degradation, arsenic leaching in the presence of calcium, potential impacts of common ions, and the
impact of constituents that can affect redox conditions (e.g., iron or sulfur), or changes in redox over time
due to microbial processes (i.e., anaerobic biodegradation).
One approach to integrating field scenarios into understanding leaching behavior is to use numeric models
designed to simulate specific release conditions. For example, when the water contact is primarily through
flow-around a relatively impermeable fill, the Fickian diffusion model (Crank, 1975) is commonly used to
estimate mass transport of COPCs. Fickian diffusion assumes that a constituent is initially present
throughout the material at a uniform concentration and that mass transfer takes place in response to
concentration gradients in the pore water solution of the porous material. The Fickian diffusion model is
most appropriate for release scenarios for which highly soluble species are a concern or for which external
stresses do not induce sharp internal chemical gradients (e.g., pH gradients, carbonation, and redox
changes) that significantly influence local LSP within the material (U.S. EPA, 2014c).
The effects of physical parameters can be evaluated through coupling of the results from chemical
speciation models with transport models, or reactive transport models. Chemical speciation and reactive
transport models can be useful tools to evaluate: (i) conditions not practically achievable in the laboratory
on material leaching behavior, (ii) the aging of materials under factors that historically control leaching in
the field, and (iii) integration between laboratory and field leaching data (U.S. EPA, 2014c). ORCHESTRA
can calculate chemical speciation in thermodynamic equilibrium systems using the same thermodynamic
database format as other geochemical speciation programs (e.g., PHREEQC or MINTEQ) and contains
state-of-the-art adsorption models for oxide and organic surfaces as well as solid solutions (U.S. EPA,
2014c).
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5. Case Studies of Using LEAF for Assessments
5.1 Screening Assessment: Evaluating Coal Combustion Fly Ash for Use as
Structural Fill Material
The leaching data used in this illustrative example includes the measured and interpolated results of LEAF
testing conducted on the subject materials and presented in U.S. EPA reports (U.S. EPA, 2009, 2012c,
2012d). The equations cited in the example are found in Section 4.2.4. Full graphical and tabular leaching
data associated with the example are provided in Appendix B. This case study is for illustrative purposes
only and is not intended to be directly applicable to any evaluation. The use of LEAF is voluntary but may
provide information in support of a beneficial use determination.
In this example, a coal combustion fly ash is proposed for beneficial use as construction fill material. LEAF
testing may provide useful information in support of meeting one of the four criteria defined by EPA for
beneficial use of CCR, the environmental demonstration criteria.29 Laboratory leaching test results for the
coal combustion fly ash, EaFA, are used as reported by the U.S. EPA (U.S. EPA, 2012c, 2012d). The
determination as to whether the fly ash material may be appropriate for use from a leaching perspective
is conducted in stages as described by the stepwise screening assessment approach (Section 4.2.1 and
Table 4-1). This evaluation provides an example of a leaching assessment that may be used as one of
several factors within an overall evaluation determining the potential for adverse impacts to human
health and the environmental associated with the proposed beneficial use of a material. EPA's
Methodology for Evaluating Beneficial Uses of Industrial Non-Hazardous Secondary Materials presents a
voluntary approach for evaluating a wide range of industrial non-hazardous secondary materials and their
associated beneficial uses. Prior to beneficially using secondary materials in any projects, interested
individuals or organizations should consult with the relevant state and federal environmental agencies to
ensure proposed uses are consistent with state and federal requirements.
The simplest stage of the screening assessment is estimated maximum leaching concentration derived
from total and available content of COPCs in the material. These estimated leaching concentrations are
compared directly to relevant thresholds values based on requirements for beneficial use of a material,
other applicable use criteria and the regulatory program. In this example, the criteria for beneficial use is
assumed the compliance of estimated leaching concentrations for all COPCs with drinking water MCLs. If
all COPC release estimate concentrations fall below the applicable regulatory threshold values, the
beneficial use may be considered appropriate on this basis. The comparison between estimated leachate
concentrations and threshold concentrations is made through calculation of an assessment ratio using
Equation 4-1:
AR — C leachmax / C Hires
For the screening assessment in this case study, it is assumed that the assessment is conducted at the
boundary of the fly ash fill.
29 For coal combustion residuals (CCR), the Agency's April 2015 CCR Disposal Final Rule promulgated a definition for beneficial
use (40 CFR 257.53). This definition identifies four criteria that distinguish beneficial use from disposal (21349 FR 80). Those
considering beneficial use for CCR should consult both this definition and the relevant state authorities to identify all the
requirements that would apply.
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5.1.1 Definition of the Assessment Scenario
Following the workflow discussed in Section 4.2, the application scenario is defined as a 3-meter thick
structural fill of fly ash material compacted in place to a dry density of 1,500 kg-dry/m3 that is used as a
permeable construction fill. The construction fill is covered by a layer of clean sandy loam with a natural
pH of 6.0 and a permeability that allows infiltrating water to percolate through to the fill material at a rate
of 25 cm per year.
The objective of this leaching assessment is to determine if the leaching of COPCs from the EaFA fly ash
when used as construction fill is appropriate from a leaching perspective (i.e., to meet the environmental
demonstration criteria within the definition of beneficial use of CCR material). Many of the scenario-based
assumptions and parameters used in this hypothetical case study were chosen for purely illustrative
purposes and were not intended to represent typical or default values to be used in similar assessments.
For example, the U.S. national drinking water regulations were selected as thresholds in this hypothetical
example to illustrate how LEAF leaching results may be evaluated relative to applicable benchmarks. The
appropriate regulatory thresholds for actual scenarios will be dependent upon the rules and guidance of
the applicable regulatory agency, but the methodology for evaluation will be essentially the same. Other
potential thresholds could include site-specific performance values or surface or ambient water quality
limits (e.g., U.S. EPA National Recommended Water Quality Criteria). Since this case study focuses on the
leaching performance related to evaluation of coal combustion fly ash for construction applications, all
other aspects of the application (e.g., geotechnical, etc.) are assumed not to preclude use of fly ash as
construction fill.
Key Attributes of the Beneficial Use Case Study
Problem Statement - Will leaching concentrations of COPCs exceed or fall below the leaching
thresholds designated at the point of compliance?
Assumed Field Conditions - A sandy loam soil with a natural pH of 6.0 is used as a cover over a
3-meter thick layer of construction fill. The soil offers negligible acidity to the infiltrating water
that percolates through the soil at a net infiltration rate of 25 cm/year into the underlying
construction fill material. The construction fill is compacted in place to a density of
approximately 1,500 kg-dry/m3.
Material Composition - The properties of a coal combustion fly ash material (EaFA) are as
reported by U.S. EPA (2012c) and include total content analysis, Method 1313 and Method 1316
test results.
Assumed Threshold Values - For this hypothetical case study, it is assumed that the state
environmental regulatory agency has determined the relevant COPCs to be antimony (Sb),
arsenic (As), barium (Ba), boron (B), cadmium (Cd), lead (Pb), molybdenum (Mo), selenium (Se)
and thallium (Tl) and that the applicable threshold values are the national drinking water
regulations.
Assumed Point of Compliance - In consultation with the state environmental agency, the point
of compliance is determined to be 100 m hydraulically downgradient from the proposed fill.
Surface water quality threshold are not considered because the nearest surface water body is
greater than 100 m from the source.
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5.1.2 Testing Program and Results
Since the overlying soil is a sandy loam with a natural pH of 6.0 and an insignificant amount of acidity, the
natural pH of the fly ash fill will dominate the leachate pH. Therefore, Method 1313, Method 1316 and
Method 1314 are the most appropriate LEAF tests to characterize leaching for this scenario and the
leaching assessment should follow the screening approach in Figure 4-1 through the equilibrium-based
and percolation-based leaching steps. Table 5-1 presents the total content by digestion and LEAF leaching
data that were used to support the assessments in this case study. Because Method 1314 is preferred
over Method 1316 data when both are available (see Section 4.2.4.4), Method 1314 data is used in the
assessment presented here. Only the LEAF results that are relevant to the various assessment stage (i.e.,
leaching of the available content, maximum leaching over the application pH domain, maximum over the
L/S range) are presented in Table 5-1; however, all leaching data, including data from Method 1316, are
presented in graphical and tabular form in Appendix B.
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Table 5-1. Total Content and LEAF Testing Results for EaFA Coal Combustion Fly Ash
EaFA LEAF Leaching Test Results
Method 1313 Method 1314
Max Cone. pH 2, 9,
Total 13 Used to pHofMax Max Cone. pH Max Cone.
Content Calculate Available Cone, used Domain OverL/S L/SatMax
[mg/kg-
Content
for Available
5.5 < pH <9
pH at Max
Range
Cone.
COPC
dry]
[mg/L]
Content
[mg/L]
Cone.
LSP Limit
[mg/L]
[mL/g-dry]
Antimony (Sb)
1.5
0.18
13
0.15
7
Avail. Cont.
0.38
2
Arsenic (As)
63
9.7
13
0.46
9
Solubility
2.4
10
Barium (Ba)
830
0.88
2
0.48
9
Solubility
2.2
5
Boron (B)
1,400
9.8
13
5.0
5.5
Solubility
160
0.2
Cadmium (Cd)
3.5
0.056
2
0.028
5.5
Solubility
1.4
0.2
Chromium (Cr)
120
2.0
2
0.20
9
Solubility
5.3
0.2
Lead (Pb)
39
0.26
2
0.0015
5.5
Solubility
0.028
0.2
Molybdenum (Mo)
15
3.9
13
3.7
9
Avail. Cont.
22
0.5
Selenium (Se)
24
6.9
13
3.3
9
Solubility
6.9
2
Thallium (Tl)
0.91
0.26
2
0.03
5.5
Solubility
0.51
0.2
Source: U.S. EPA (2012c, 2012d).
Reported values of total content by digestion may be less than available content by Method 1313 because of uncertainty associated with testing (see Section 4.4.1)
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5.1.3 Total and Available Content Screening
Screening based on total content is an assessment level that requires testing data outside of the scope of
the LEAF test methods; therefore, it may not be practical for all assessments. Typically, total content data
is provided through digestion of the solid material or through non-destructive testing. When total content
data is available, estimates of maximum leaching concentration (Cieach_ma.\-) based on total content may be
calculated for the default initial L/S value of 0.5 L/kg-dry using Equation 4-3.
C leach_max ~ total/fS~)initial
Using the testing and characterization data for the EaFA fly ash shown in Table 5-1, the total content for
antimony is 1.5 mg/kg-dry and, therefore, Equation 4-3 becomes:
3.0(S)
The Cieach_maxvalue based on the total content assumes that the full amount of a COPC in a solid material
leaches into a liquid at the default initial L/S.
The available content data in Table 5-1 is reported directly from Method 1313 as the maximum eluate
concentration of the three available content pH extractions at endpoint target pH values of 2, 9 and 13.
Therefore, the estimated maximum leaching concentration for available content is calculated using
Equation 4-4:
r r v (£/*£) 1313 of* v y-
Lleach_max ~ L1313(maxptf 2,9,13) x (L/S)initial ~ L1313(maxpH2,9,13)
Since, the L/S for Method 1313, (L/S)i3i3, is defined as 10 L/kg-dry in the test method (U.S. EPA, 2012f),
the multiplier for the maximum leaching concentration, Ci3i3(maxpH 2,913), is 20 (i.e., 10 L/kg-dry divided by
0.5 L/kg-dry). From Table 5-1, the available content of antimony was determined to be 0.17 mg/kg-dry
measured at a pH of 13. Therefore, the estimated maximum leaching concentration for the available
content assessment is:
Cleach_max= 20 x ^1313(maxpH2,9,13) = 20 x0.18 = 3-6
Note that the estimated leachate concentration based on available content is greater than that estimated
by total content. Section 4.4.1 discusses the uncertainties regarding total content analysis that may result
in an available content greater than a total content.
Table 5-2 provides the threshold concentration for each COPC in EaFA, the estimated maximum leaching
concentration and assessment ratio value for the total content and available content screening levels.
Assessment ratio values less than or equal to one (AR< 1) indicate COPCs where the maximum leaching
concentrations does not exceed threshold values and, therefore, are not likely to be a concern. For COPCs
where the assessment ratio is greater than one (AR> 1), additional refinement of the assessment, either
through further leaching evaluation orthrough alteration of the reuse scenario, is indicated. For all COPCs,
the assessment ratios in Table 5-2 indicate that estimated leaching concentrations based on both total
content and available content exceed threshold values by 1 to 4 orders of magnitude. However, this
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screening level approach is highly bounding in that it assumes the complete release of the total or
available content of all COPCs under field conditions. Thus, this assessment alone cannot support a
conclusion that the proposed use of EaFA as a construction fill is acceptable and a more-refined
assessment is required to account for environmental processes not considered in this initial screening.
Table 5-2. Initial Screening Values for EaFA Fly Ash Using LEAF Leaching Estimates
EaFA
COPC
Threshold Value
[mg/L]
Total Content
Assessment
Cleach_max Ratio
[mg/L] (AR)
Available Content
Assessment
Cleach_max Ratio
[mg/L] (AR)
Antimony (Sb)
0.006
3.0
500
3.6
600
Arsenic (As)
0.01
130
13,000
190
19,000
Barium (Ba)
2
1700
830
18
8.8
Boron (B)
7
2800
400
200
28
Cadmium (Cd)
0.005
7.0
1,400
1.1
220
Chromium (Cr)
0.1
240
2,400
40
400
Lead (Pb)
0.015
78
5,200
5.2
350
Molybdenum (Mo)
0.2
30
150
78
390
Selenium (Se)
0.05
48
960
140
2,800
Thallium (Tl)
0.002
1.8
910
5.2
2,600
Assessment ratios shown in bold red indicate COPCs where the maximum estimated leaching concentration for the assessment
exceeds the indicated comparative threshold.
Threshold values are the National Primary Drinking Water Regulations (U.S. EPA, 2012a) unless otherwise noted in Table 3-7.
5.1.4 Equilibrium-pH Screening (Method 1313)
In addition to available content, Method 1313 provides eluate concentration data across a broad pH range
that may be focused to estimate the maximum leaching of COPCs over an applicable pH domain for the
application scenario. The maximum concentration over an applicable pH domain provides a bounding
estimate of potential leaching under field conditions that may be more accurate for COPCs with LSP
behaviors that are a strong function of pH (e.g., heavy metals, radionuclides).
The selection and modification of an applicable scenario pH domain are discussed in Section 4.2.5.1 of the
guide. For this case study, the default pH domain of 5.5 < pH < 9.0 was selected since the natural pH of
EaFA (pH = 6.8) falls within this interval.30 For COPCs where solubility-limited leaching dictates the
concentration over the pH domain, the estimated maximum concentration is derived from the maximum
concentration of the pH domain, Ci3i3(maspHdomain), using Equation 4-6:
Cleach_max ~ ^ 1313 (max pH domain)
30 As discussed in Section 4.2.5.1, the pH domain applicable to many scenarios should include the natural pH of the material
and should consider the prevailing pH in proposed application and the pH effects associated with any aging or degradation
processes to which the material might be exposed.
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If a COPC has been demonstrated to be available content-limited over the entire applicable scenario pH
domain, the estimated maximum leachate concentration will be a strong function of L/S and requires
adjustment to the default initial L/S value of 0.5 L/kg-dry using Equation 4-4:
f _ f v (L/S) 1313
c leachjnax c 1313(maxpH domain) A (j,/s)- t- (
Based on the Method 1313 testing data provided in Table 5-1, the maximum concentration of antimony
over the default pH domain, 5.5 < pH < 9.0, is 0.15 mg/L measured at the natural pH of 6.8. Since antimony
was determined to be available content limited over this pH domain, Equation 4-4 is used to estimate the
maximum leachate concentration at the default L/S:
Cleachjnax ~ 20 X domain)
C leachjnax = 20 X 0. 15 (^) = 3. 0 (^)
Table 5-3 provides a summary of the test results and estimated maximum leachate concentrations for the
equilibrium-pH leaching assessment of EaFA fly ash. For each COPC, Method 1313 test data includes the
maximum eluate concentration measured over the applicable pH domain and the identified LSP limit (i.e.,
available content- or solubility-limited leaching). The assessment columns show the corresponding
Cieach_max value and the assessment ratio value based on the equilibrium-pH assessment. The assessment
ratio results show that the maximum estimated field concentration for most COPCs in the EaFA fly ash
exceed threshold values for the equilibrium-based assessment. Only the leaching of barium, boron and
lead are acceptable based on this leaching assessment. Therefore, a more-detailed leaching source term,
such as that provided by percolation leaching assessment using Method 1314, may be used to further
refine the leaching assessment.
Table 5-3. Equilibrium-pH Assessment of Fly Ash
EaFA
Method 1313
Equil-pH Assessment
Max Cone. Over
Threshold Value
pH Domain
Cleach_max
COPC
[mg/L]
[mg/L] LSP limit
[mg/L] AR
Antimony (Sb)
0.006
0.15
Available
Content
3.0
500
Arsenic (As)
0.01
0.46
Solubility
0.46
46
Barium (Ba)
2
0.48
Solubility
0.48
0.24
Boron (B)
7
5.0
Solubility
5.0
0.71
Cadmium (Cd)
0.005
0.028
Solubility
0.028
5.6
Chromium (Cr)
0.1
0.20
Solubility
0.2
2.0
Lead (Pb)
0.015
0.0015
Solubility
0.0015
0.10
Molybdenum (Mo)
0.2
3.7
Available
Content
74
370
Selenium (Se)
0.05
3.3
Solubility
3.3
66
Thallium (Tl)
0.002
0.03
Solubility
0.03
15
Assessment ratios shown in bold red indicate COPCs where the maximum estimated leaching concentration for the assessment
exceeds the indicated comparative threshold.
Threshold values are the National Primary Drinking Water Regulations (U.S. EPA, 2012a) unless otherwise noted in Table 3-7.
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5.1.5 Full LSP Screening (Method 1313 and Method 1314)
For the scenario presented in this illustrative example, a granular material is contacted with infiltration
such that the mode of water contact may be considered percolation of infiltrating water through a relative
permeable bed (Section 4.2.5.3). Therefore, the inclusion of L/S-dependent leaching data (e.g., from
Method 1314 or Method 1316) in the screening assessment may provide increased refinement of the
bounding estimate of leaching offered through equilibrium-pH screening.
The estimated maximum leachate concentration is the greater of the maximum eluate concentration over
the applicable pH domain (i.e., Ci3i3(maxpHdomain) from the equilibrium-pH screening) and the maximum
eluate concentration as a function of L/S as shown in Equation 4-8:
Cleachjnax ~ ^AX ^maXpH domain)'^(L/S),max^
An illustration of the improved understanding provided by Method 1314 is presented in Figure 5-1 by
comparisons of EaFA eluate pH and COPC concentrations for Method 1314 (blue triangles), Method 1316
(orange diamonds) and the natural pH from Method 1313 (red dot with indicator circle). In the column
test (Method 1314), the eluate pH data from the column indicates an initial eluate pH of 4.2 with
increasing pH to near-neutral values an L/S of 2 L/kg-dry. Thereafter, the eluate pH in the column
remained approximately pH 7, consistent with the pH in the batch style leaching tests (Method 1313 and
Method 1316). The initially acidic pH that is obvious in the Method 1314 data is not indicated by the eluate
pH in Method 1316 or the natural pH in Method 1313 due to the differences between batch tests and
column elution tests. For this coal combustion ash, the cause of the initially low pH is a process operation
where sulfuric acid is sprayed into the effluent stream to aid in electrostatic precipitator collection of fly
ash resulting in an acidic surface coating on the EaFA sample.
The full results of Method 1314 testing of EaFA fly ash presented in Appendix B show the impact of the
evolution in eluate pH in the column on the LSP behavior of each COPC as a function of pH (e.g., as
characterized by Method 1313). As a result of the pH increase from pH 4.2 to pH 7, COPC concentrations
in column eluates initially may be high when solubility is increased under acidic conditions only to
decrease as pH becomes more neutral (e.g., cadmium). Alternatively, initial concentrations of a COPC in
column eluates may be low because of lower solubility at acidic pH than at neutral pH (e.g., selenium).
COPCs may rapidly wash out or are depleted after the pH reaches an available content-limited domain
(e.g., boron). The arsenic and chromium represent special cases where increased eluate concentration
reflect solubility-limited leaching at acidic and neutral pH but pass through a minimum solubility point at
approximately pH 5.
Table 5-4 presents the maximum eluate concentrations for each COPC derived from Method 1314 testing
of EaFA fly ash, along with the corresponding L/S at which the maximum occurred. The table also provides
assessment ratio for the equilibrium-L/S assessment calculated as the maximum for each COPC in a
percolation assessment step, calculated by dividing the maximum concentration over the L/S by the
threshold value. The conclusions of the percolation assessment are consistent with those in previous steps
indicating that most or all of the COPCs leach at concentrations above threshold value. Therefore, the only
conclusion that can be reached based on this stepwise leaching assessment is that EaFA is not appropriate
for the proposed permeable construction fill scenario.
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w
E
o
CO
EaFA 1000
100
10
1
0.1
0.01
0.001
0.0001
EaFA 10
l
: Max. over L/S range
----------
Max. over
pH domain
~
3—tj
MDL
10 12 14
PH
oi
E
1—¦
E
3
1
¦o
IS
u
0.1
0.01
0.001
0.0001
! Max. over L/S range
.
pH domain
LLOQ_
MDL
PH
EaFA100
w
E
1 - :
V
W 0.1
0.01
¦ Max. over L/S range
Max. over r
T ~D~ "
pH domf
LLOQ
MDL
PH
EaFA 1000
Max jDver L/S_ran j>e
O
Max. over pH domain
0.001
0.0001
L/S (L/kg-dry)
EaFA 10
l
Ol
E
0.1
0.01
0.001
0.0001
¦ Max. over L/S range
Max.
over pH domain
O
" LLOQ
: MDL
10 12 14
10
L/S (L/kg-dry)
EaFA
100
01
E
1—¦
E 1
2
E
V
W 0.1
0.01
Max. over L/S range
1 r — — ~
4
! -J Max. over
~ A ^
jH domain
LLOQ
MDL
- 1 1 1 1
1 1 1 1 1
1 1 1 1 1
1 1 1 1 1
1 ' ' ' M
10 12 14
10
L/S (L/kg-dry)
—±—EaFA_1314 — O EaFA_1316 ¦ EaFA_1313(interpolated) O Natural pH Indicator
Figure 5-1. COPC concentrations as a function of pH (left) and L/S (right) for a coal
combustion fly ash (EaFA) for full LSP screening assessment: Method 1313 interpolated),
Method 1314, and Method 1316.
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Table 5-4. Full LSP Screening Assessment of EaFA Fly Ash Fill Material
EaFA
COPC
Threshold
Value
(mg/L)
Max Cone.
pH Domain
5.5
-------
5.1.6 Consideration of an Alternate Coal Combustion Fly Ash
In parallel to evaluation of EaFA, an alternate coal combustion fly ash, CaFA, was evaluated for use in the
same scenario. The evaluation of this alternative material is one of many ways in which leaching
assessments may vary. Results from LEAF testing of CaFA are provided in Table 5-7 while the associated
assessment results are provided in Table 5-8.
The assessment for the alternative CaFA material was conducted in the same manner as described for
EaFA fly ash with the exceptions that the upper bound of scenario pH domain was expanded from the
default value 9.0 to a value of 12.0. Therefore, the applicable pH domain used in equilibrium-based
assessment of Method 1313 data (5.5 < pH < 12.0) captured the natural pH of the CaFA material.
The results of the leaching assessment of CaFA provided in Table 5-8 indicate that the CaFA material is
similarly not appropriate for use as a construction fill under the assumption of no dilution and attenuation.
Although both CaFA and EaFa are coal combustion fly ash materials, the contrast between assessment
results illustrates the importance of careful consideration of scenario parameters in accordance with
existing regulatory requirements.
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Table 5-5. LEAF Coal Fly Ash CaFATotal Content Analysis and LEAF LeachingTest Results
CaFA
COPC
Total
Content
[mg/kg-dry]
Available
Content
[mg/L]
pH for
Available
Content
LEAF Leaching Test Results
Method 1313
Max Cone. Available
pH Domain content- or
7 < pH < 12 pH at Max Solubility-
[mg/L] Cone. limited
Method 1314
Max Cone.
Over L/S L/S at Max
Range Cone.
[mg/L] [mL/g-dry]
Antimony (Sb)
6.2
0.68
2
0.070
10.5
Solubility
0.039
10
Arsenic (As)
22
4.9
2
0.097
9
Solubility
0.018
10
Barium (Ba)
960
8.3
2
2.7
12
Solubility
400
0.2
Boron (B)
NA
63
2
41
7
Avail. Cont.
21
5
Cadmium (Cd)
1.7
0.21
2
0.058
7
Solubility
<0.00067
-
Chromium (Cr)
88
9.4
2
0.63
12
Solubility
0.31
10
Lead (Pb)
56
1.3
2
0.0026
7
Solubility
0.015
1
Molybdenum (Mo)
19
3.7
2
2.0
12
Solubility
4.7
9.5
Selenium (Se)
8.6
4.6
2
0.49
10.5
Solubility
0.83
2
Thallium (Tl)
1.5
0.10
2
0.0115
7
Solubility
<0.005
-
Reported values of total content by digestion may be less than available content by Method 1313 because of uncertainty associated with testing (see Section 4.4.1)
NA = boron total content not available because of metaborate addition.
"<" indicates all eluate values less than the reported MDL concentration.
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Table 5-6. Leaching Assessment Ratios for Alternative Coal Combustion Fly Ash CaFA
CaFA
Assessment Ratio (AR)
COPC
Threshold Value
[mg/L]
Total Content
(total content
leaches)
Available
Content
(available content
leaches)
Equil-pH
(max. conc. over
pH domain)
Full LSP
(max. conc. over
pH domain and
L/S range)
Antimony (Sb)
0.006
2,100
2,300
12
12
Arsenic (As)
0.01
4,400
9,800
10
10
Barium (Ba)
2
960
83
1.4
200
Boron (B)
7
NA
180
120
5.8
Cadmium (Cd)
0.005
680
840
12
12
Chromium (Cr)
0.1
1,800
1,900
6.3
6.3
Lead (Pb)
0.015
7,500
1,700
0.17
1.0
Molybdenum (Mo)
0.2
190
370
10
24
Selenium (Se)
0.05
340
1,800
10
17
Thallium (Tl)
0.002
1,500
1,000
5.8
5.8
NA indicates data or assessment ratios that are "not available."
Assessment ratios shown in bold red indicate COPCs where the maximum estimated leaching concentration for the assessment
exceeds the indicated comparative threshold.
Assessment ratios shown as "<0.001" (see chromium and selenium) indicate values calculated at less than 0.001.
Threshold values are the National Primary Drinking Water Regulations (U.S. EPA, 2012a) unless otherwise noted in Table 3-7.
5.2 Scenario Assessment: Evaluating Treatment Effectiveness of a Cement-
Based Stabilization/Solidification (SS) Process
In this example, the potential effectiveness of onsite treatment using a cement-based
Stabilization/Solidification (S/S) process is evaluated for contaminated soil at a copper and lead smelter.
This evaluation provides an example of a leaching assessment for determining treatment effectiveness
based on data from (Garrabrants et al. Pending Publication a, b). This case study is for illustrative purposes
only and is not intended to be directly applicable to any evaluation. The use of LEAF is voluntary but may
provide information in support of a treatment effectiveness study. A number of other tests or criteria may
also be appropriate or required when determining treatment effectiveness.
The leaching of COPCs from contaminated foundry soil subject to Stabilization/Solidification (S/S-CFS)
follows a mass transport leaching scenario. Infiltrating water flows around the exposed surface area of
the monolith and COPCs must diffuse toward the exposed surface to leach. The rate of diffusion is driven
by the internal concentration gradient between the concentration in the porewater at the core of the
material and the concentration at the monolith surface. For permanently submerged materials in the
water table, COPCs that diffuse to the material surface are leached into a continuous surrounding liquid
phase; however, a continuous liquid phase does not exist in the vadose zone during the interval between
infiltration events. Internal concentration gradients within the material relax by diffusion and the initial
conditions within the monolith are restored for the beginning of the next infiltration event.
The methodology for estimating leaching concentrations under a mass transport scenario is based on the
approach used to estimate COPC release from cement pavements containing coal combustion fly ash [US
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EPA 2014a], An effective leaching concentration is calculated for both 1-day and 2-day infiltration events
as the estimated COPC mass released from the monolith dissolved in the volume of contacting water. The
average leaching concentration over the assessment interval is determined as the weighted average of
isolated and extended infiltration events (see 2.4.1.).
5.2.1 Definition of the Assessment Scenario
It has been determined that contaminated soil surrounding a copper and lead smelter is in need of
remediation. The impact is localized to a 400 m2 plan-view area (20 m by 20 m), starting at grade level to
a depth of 5 m. The total volume of impacted material is 2,000 m3. The soil is a loamy sand with an
assumed bulk porosity of 0.4 cm3p0res/cm3, density of 1,700 kg/m3, and field capacity of 0.24
cm3Water/cm3p0re based on the negligible drainage flux approach of Meyer and Gee (Meyer & Gee, 1999).
The water table is sufficiently deep that it is not a concern for leaching of constituents at the unit boundary
of the site.
The objective of this assessment is to determine if the release of COPCs from treated soil is acceptable
from a leaching perspective. Many of the scenario-based assumptions and parameters used in this
hypothetical case study were chosen for purely illustrative purposes and were not intended to represent
typical or default values to be used in similar assessments. For example, the U.S. national drinking water
regulations were selected as thresholds in this hypothetical example to illustrate how LEAF leaching
results may be evaluated relative to applicable benchmarks. The appropriate regulatory thresholds for
actual scenarios will be dependent upon the rules and guidance of the applicable regulatory agency, but
the methodology for evaluation will be essentially the same. Other potential thresholds could include site-
specific performance values or surface or ambient water quality limits (e.g., U.S. EPA National
Recommended Water Quality Criteria). Since this case study focuses on the leaching performance related
to evaluation of coal combustion fly ash for construction applications, all other aspects of the application
(e.g., geotechnical, etc.) are assumed not to preclude use of fly ash as construction fill.
A portion of contaminated field soil (CFS) was treated for analysis of the treatment effectiveness at the
laboratory bench scale. The proposed S/S remedy called for mixing the soil with Portland cement (12%
dry mass basis) to create a monolithic material (S/S-CFS). The final water/binder ratio was 2:1 which is
higher than typical cement blends; however, much of the added water was absorbed by the air-dried soil
so that the effective water/binder ratio was estimated to be 0.65:1. The moisture content of the S/S-CFS
was 26% (wet basis). The S/S-CFS material was cast into 5-cm diameter by 10-cm long cylindrical molds
and cured in a humid environment (>95% relative humidity) for a minimum cure time of 90 days. Prior to
testing using Method 1313 and 1314 (both of which use granular or particle-size reduced material), the
S/S-CFS material was crushed with a hammer and fed through a parallel plate grinder until >85% of the
mass passed a No. 10 (2-mm) sieve. Cast materials used for Method 1315 were dry cut in half to create 5-
cm diameter by 5-cm long monolithic samples.
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Key Attributes of the Treatment Effectiveness Case Study
Problem Statement - Will leaching concentrations of COPCs exceed or fall below the thresholds
designated at the point of compliance?
Assumed Field Conditions-The soil contamination is across a 400 m2 plan-view area (20 m by
20 m), starting at grade level to a depth of 5 m. The total volume of impacted material is 2,000
m3. The soil is a loamy sand with an assumed bulk porosity of 0.4 cm3Pores/cm3, density of 1,700
kg/m3, and field capacity of 0.24 cm3Water/cm3Pore based on the negligible drainage flux approach
of Meyer and Gee [Meyer and Gee, 1999], The water table is sufficiently deep that it is not a
concern for leaching of constituents at the unit boundary of the site.
Material Composition - Total content analysis of soil indicate concentrations of aluminum (Al),
cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), and zinc (Zn) in excess of 1000
mg/kg. Other COPCs include arsenic (As), barium (Ba), beryllium (Be), chloride (CI ), fluoride (F ),
nitrate (NO3), antimony (Sb), selenium (Se), sulfate (SO4) and thallium (Tl).
Assumed Threshold Values - For this hypothetical case study, it is assumed that the state
environmental regulatory agency has determined the relevant COPCs to be antimony (Sb),
arsenic (As), barium (Ba), boron (B), cadmium (Cd), lead (Pb), molybdenum (Mo), selenium (Se)
and thallium (Tl) and that the applicable threshold values are the national drinking water
regulations.
Assumed Point of Compliance - The point of compliance is at the edge of the unit boundary of
contaminated soil.
5.2.2 Testing Plan
The selection of appropriate leaching tests depends on the environmental factors that drive leaching in
the field. In this scenario the use of Portland cement to solidify and stabilize the CFS material is expected
to raise the pH and to limit leaching due to mass transfer. In order to estimate the effects of these two
parameters, Methods 1313, 1314, and 1315 are chosen. Method 1315 is selected for this testing plan as
it provides leaching data under mass transfer limited scenarios (e.g., leaching from a monolithic sample
of S/S-CFS). Method 1313 is selected to serve two purposes in this testing plan. The first purpose of
Method 1313 in this testing plan is to estimate the anticipated environmental pH (e.g., alkaline Portland
cement will raise the pH of the material, See Figure 5-2). The second purpose of Method 1313 is to provide
pH dependent equilibrium values for leaching of particle size reduced SS-CFS to compare against the mass
transport limited results from Method 1315 (at L/S = 10). The use of Method 1313 is important because
the test results from Method 1315 are a function of time and L/A ratio (comparable to L/S by considering
sample geometry) while Method 1313 is a function of pH and fixed at an L/S of 10. The pH of the leachate
in Method 1315 may change during testing and an understanding of the possible effects on equilibrium
from Method 1313 data assists the evaluator in making the appropriate estimate on leachability in the
field. Further characterization of potential leaching could rely on Methods 1314 or 1316. Both methods
provide equilibrium leaching results for particle size reduced SS-CFR at L/S increments similar to the L/A
increments used in Method 1315. In this case, Method 1314 is selected as the test method is an open
system, potentially providing information on co-constituent dependent leaching behavior.
5.2.3 Material Characterization and Environmental Conditions
The total content analysis of a representative sample of contaminated soil indicated concentrations of
aluminum (Al), cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), and zinc (Zn) in excess of
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1000 mg/kg. Other COPCs include arsenic (As), barium (Ba), beryllium (Be), chloride (CI"), fluoride (F ),
nitrate (N03), antimony (Sb), selenium (Se), sulfate (S04) and thallium (Tl) (See Table 5-9). This indicates
the primary constituents of concern in the sample are inorganics, several of which are known to display
pH dependent behavior (e.g., lead, and arsenic.)
Table 5-7. Total Content Analysis of Contaminated Field Soil (CFS) and Monolithic Material
(S/S-CFS)
Material
Total Content
(mg/kg)
-
CFS
S/S-CFS
Aluminum
26,000
25,000
Antimony
460
440
Arsenic
360
250
Barium
530
520
Beryllium
0.34
0.38
Cadmium
14,000
13,000
Chloride
NA
NA
Chromium
1,200
550
Copper
15,000
16,000
Fluoride
NA
NA
Iron
17,000
49,000
Lead
3,400
3,100
Nitrate
NA
NA
Selenium
32
32
Sulfate
NA
NA
Thallium
35
24
Zinc
12,000
11,000
Note: "NA" indicates that contents CI, F, NO3 and SO4 of UBO2 digests were not analyzed.
The change in pH of the CFS material due to stabilization/solidification was determined using HN03 and
KOH additions in Method 1313 extract. Additions of KOH were used to raise the eluent pH above the
natural pH of the material. Relative to the titration of CFS, the titration curve for S/S-CFS is shifted toward
higher acid addition values, indicating more buffering capacity than the untreated soil (Figure 5-2). The
differences in the natural pH of the materials (CFS pHnat= 6.9 and S/S-CFS pHnat= 12.8) and the shift in
buffering capacity are a direct result of the addition of Portland cement during S/S treatment. The strong
shift in pH of the material upon stabilization highlights the importance of leach testing for pH dependence
as well as for testing for mass transfer limitations. The anticipated pH of the scenario needs to consider
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the strong shift in pH to a highly alkaline environment and whether that alkalinity is sufficiently buffered
to represent environmental conditions. An anticipated environmental pH for the untreated material (pH
=6.9) would be 5.9 < pH < 7.9. For the treated material in this scenario, a more plausible range is 8 < pH <
13.3.
14
12
10
8
X
a
6
4
2
0
-3 -2 -1 0 1 2 3 4 5
Acid Added (mol/kg)
14
12
10
8
X
a
6
4
2
0
0 2 4 6 8 10 12
L/S (L/kg-dry)
: o—
Q
¦ S/S-CFS
; pHNat=12.3
¦
¦
CFS
4i
~
;
HNat=6.
E
n
rO
S/S-CFS pHNat=12.3
~ ~
~ C
S®-0-£^
Q
CFS pHNat=6.9
""~iF
O CFS_Rep-A
O CFS_Rep-B
O CFS Natural pH
CFS_M ean
~ SS-CFS_Rep-A
~ SS-CFS_Rep-B
SS-CFS Natural pH
SS-CFS_Mean
Figure 5-2. pH characterization of contaminated field soil (CFS) and monolithic material
(S/S-CFS)
The volume of contacting water, or anticipated L/S, in the environment can be determined based on the
infiltration rate of water. This illustrative scenario uses U.S. EPA meteorological data [14] for Nashville, TN
(Table 5-8.) The EPA datasets included daily precipitation, evaporation, evapotranspiration, and other
data collected over a 30-year period from 1961-1990. For days with recorded precipitation greater than
zero, daily net infiltration was calculated as the balance of the daily precipitation (P), the pan evaporation
(Epan), and the evapotranspiration (ET0) data:
Inf = P- Epan - ET0
Summary statistics for the relevant precipitation data and infiltration data for this environmental setting
are shown in Table 5-8.
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Table 5-8. Precipitation data for Nashville, TN
Units
Dry
City, State
Nashville, TN
Annual Precipitation
cm/y
120
Days with Precipitation
d/y
118
Annual Net Infiltration
cm/y
82
Infiltration Events l-day (N2)
events/y
13
Net Infiltration of Events l-day (P2)
cm/event
3.5
Infiltration Events >2-days
%
6.7%
After each infiltration event, soils in the subsurface drain to a relative pore saturation at field capacity [8],
The volume of water-filled pores at any saturation can be expressed in terms of L/S31 as:
/r / c\ e-9-V]r>e£/-l,000
{L/S)e ~ ^
The capacity for water uptake (i.e., volume of empty pores at the beginning of an infiltration event) is the
difference between the L/S at water saturation (9sat = 1) and the L/S at field capacity (9f = 0.24). For the
CFS bed, the L/S at water saturation and field capacity is 0.25 L/kg-dry and 0.15 L/kg-dry, respectively,
indicating that the empty pore volume at the start of each infiltration event is 0.1 L/kg-dry. Converted to
an L/S basis for the defined field scenarios, the annual net infiltration represents an L/S of 0.1 L/kg per
year.
5.2.4 Mass Transport Assessment
In the mass transport scenario, L/S cannot be directly compared to lab results. Instead, daily infiltration
events were separated into "isolated events" (one-day) based
infiltration during consecutive days. The average duration of extended events was 2.5 days. Given that
infiltration is not likely to occur over the entirety of an extended infiltration event, the mass release over
a 2-day cumulative leaching interval, which can be provided directly by Method 1315, was a good
approximation for release over extended infiltration events. The annual average number of infiltration
events (N1 and N2) and water volumes per event (PI and P2) over the 30-year dataset were determined
and considered constant for each assessment interval. These data are used to estimate effective leaching
concentrations for one- and two-day infiltration events. An average concentration for the assessment
interval, I, can then be calculated based on the effective concentrations of the one- and two-day
infiltration events.
31 Where e is the bulk porosity, [m3p0re/m3]; 0 is water saturation, Vbed is the volume of material, and rrid is the dry
mass.
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The effective concentration for a one-day event is estimated using data points on the Method 1315
cumulative release curve (Figure 5-3). From the Method 1315 interval concentration data (q1315), the
cumulative mass release per area at the end of a test interval J (Rj) is calculated using the volume of eluate
collected (vj1315) and the exposed surface area (Aexp1315) of the test sample as:
ZRj = ^Cj
1315 T/1315'
j j
The mass released for the one-day interval is represented by the difference in cumulative release between
the first leaching interval at cumulative leaching time of 0.08 days) and second leaching interval
(2R2> at cumulative leaching of 1.1 days).32 The average volume of infiltration for a 1 day event (PI) is
dependent upon the ratio of the infiltrated area (Ainf) to the exposed surface area (Aexp) of the SS-CFS
material. The effective concentration of a COPC for a one-day event may be estimated as:
Ml (XR2~ER±)-AeXp
VI PlAinf 1,000
An analogous equation for a two-day infiltration event uses (1R3 - ZRi) to represent the mass release and
P2 to represent the average volume of infiltration over a 2-day interval:
£2 (Ei?3—Effi)-AeXp
V2 P2Ainf 1,000
An average concentration for an assessment interval, /', may be calculated as a weighted average
concentration over the series of one- and two-day infiltration events: This average leaching concentration
is the effective leaching concentration over the assessment interval.
cr=[
N1-C1+N2-C2
}
Ol
E
is
_4)
01
cc
01
(A
k.
<
100
10
o.i
0.01
Method 1315
. -"¦*
——
>*•
LLOQ -
MDL *"
0.01
0.1
10
100
Ol
E
IS
_0)
01
a
01
M
100
10
0.1
0.01
0.001
: Method 1315
0
m
B
LLOQ -J- * *
MDL -
0.01
0.1
10
100
Time (days)
Time (days)
O CFS_Rep-A
O CFS_Rep-B
O CFS Natural pH
CFS_M ean
~ SS-CFS_Rep-A
~ SS-CFS_Rep-B
SS-CFS Natural pH
SS-CFS_Mean
Figure 5-3. Method 1315 test results for arsenic and selenium release
32 The concentration measured in the first interval of Method 1315 is often biased by surface dissolution and sample
preparation (e.g., washing off of cutting swarf). Therefore, the mass released this first interval at 0.08 days is not used in
calculations as it is not representative of the mass transport leaching behavior of the bulk material.
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5.2.5 LSP Considerations
The suggested effective leaching concentrations for one and two-day infiltration events are based on
Method 1315 data where a relatively small sample is exposed to a large bath of water to maintain the
interval concentration gradients that drive mass transport. However, these conditions are not indicative
of the majority of field conditions where, typically, a small volume of water contacts a relatively large
surface area. Thus, the effective concentration calculations can numerically exceed the thermodynamic
bounds of chemical equilibrium represented by the Method 1313 data. If the effective leaching
concentration for any one- or two-day event is greater than the measured Method 1313 solubility-
controlled eluate concentration, the effective concentration should be set to the Method 1313 maximum
concentration over the pH domain:
if CI (or C2) > Cmax d0maini then CI (or C2) — Cmax p# domain
The results of Method 1313 and 1314 testing for arsenic and selenium before and after treatment can be
seen in Figure 5-4. Method 1313 shows that both COPCs have pH dependent solubility behavior above
the regulatory thresholds and that the stabilization process (i.e., increased alkalinity) effects the leachate
concentrations.
The arsenic behavior seen in Methods 1313 and 1314 (Figure 5-4) suggests that arsenic is solubility
controlled as Method 1313 results show a strong dependence of solubility on pH while Method 1314
results show weak dependence on L/S. The selenium behavior appears to be available content limited as
there is a strong dependence of concentration on L/S and a weak dependence on pH. In comparison, the
Method 1315 test results (Figure 5-3) show an initial concentration likely representative of pore water
values and surface effects before a more gradual increase in leaching with time. The grey dashed line
indicates the expected Fickian diffusion that would occur if no other mass transport limitations were in
place. Both arsenic and selenium show less leaching than predicted by Fickian diffusion in Method 1315.
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100
oi
E
U
"E
v
w
b.
<
0.001
H
Method
1313
~
~ °
D JirOu
lyD U-l
§)lloq
Thresholc
1 1 1
1 1 1
¦ 1 1
¦ ¦ ¦ 1
—1—1—1—1
1 1 1
MDL
1 1 1
0 2 4
PH
10 12 14
O)
E
E
3
E
«
«
w
10
1
o.i -t
0.01 -r
0.001 -E
0.0001
0.00001
Method 1313
CD
LLOQ
_| i i i | i i i | i i i | i i i | i i i |
0 2 4
10 12 14
PH
oi
E
w
n
l.
<
0.1
0.001
Method 1314
¦n
<
rocs
LLOq
Th resho
~
n
D-C
MDL
10
10 12
L/S (L/kg-dry)
oi
E
w
Ifl
0.01
0.00001
ir
Method 1314
~_.
Threshold
LLOQ
MDL
—¦—¦—1—i
I 1 1 1 I
1 1 1 I
1 1 1 I
1 1 1 I
1 1 1 1
2 4 6 8 10 12
L/S (L/kg-dry)
O CFS_Rep-A
O CFS_Rep-B
O CFS Natural pH
CFS_M ean
~ SS-CFS_Rep-A
~ SS-CFS_Rep-B
O SS-CFS Natural pH
SS-CFS_Mean
Figure 5-4. Method 1313 and 1314 test results for CFS and SS-CFS
The available content for arsenic and selenium can be determined from Method 1313 as the highest
leachate concentration at a pH of 2, 9 and 13.
Cleachjnax ~ ^1313(max pH 2,9,13)
Method 1313 also shows an increase in arsenic concentrations after treatment that directly overlaps with
the scenario pH of 8 < pH < 13.3. The LSP limited concentration for arsenic is the maximum concentration
within the pH range (including interpolation to endpoints of the pH range if necessary):
Cleachjnax ~ ^ 13 13 S />// 13 3
The mass transport scenario has the restriction that the total mass released cannot exceed the available
content for a COPC. The interval mass release for an assessment interval i is calculated as:
(NlClPlA;„r1000) (N2C2P2A;„r1000)
M: = Ml + M2 = - ^ - + ^ -
md md
The available content at the end of an assessment interval is estimated as previous available content
minus the mass released over the assessment interval. If the available content for any assessment interval
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Case Studies of Using LEAF for Assessments
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is less than zero, the COPC has depleted and the interval mass release is limited to the previous available
content:
if (AC)i < 0; then (AC)i = 0 and Mt = (AC)^
The average leaching concentration should be adjusted to match the mass released over the assessment
interval. ARs may be calculated for the mass transport scenario based on the estimated leaching
concentration for an assessment interval or an averaged value for an assessment period.
5.2.6 Treatment Effectiveness
The cumulative release of selected COPCs for untreated CFS and cement-treated S/S-CFS over a 30-year
timescale is shown in Figure 5-5. In each figure, the available content is the upper limit of mass release
and the CFS mass release was normalized to the exposed surface area of S/S-CFS monolith. The
comparison between the original material and the treated material illustrates the effectiveness of
treatment for different constituents. In this case, treatment of the S/S-CFS material would be expected to
significantly reduce the rate of leaching for cadmium, selenium, and lead. Arsenic leaching was reduced
to a lesser amount while chloride and nitrate releases were only significantly reduced by treatment over
shorter timescales than 30 years.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
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Ui
E
w
(0
Q)
Q)
Ot
u
l.E+07
S/S Soil A vail ableCo n te n t
Soil Available Coiitent
l.E+06
l.E+05
l.E+04
l.E+03
l.E+02
l.E+01
5S CFS
1.E+00
j i i i i i i i i i i i i i i i i i i i i i i i i i i i i
10 15 20
Time (year)
is
s.
E
¦o
IS
(J
l.E+07
l.E+06
l.E+05
l.E+04
l.E+03
l.E+02
l.E+01
1.E+00
l.E-01
- [S/S Soil Available Content
iSoil Available Content
SS-CFS
10 15 20
Time (year)
l.E+06
E
oi 1.
E+05
w
(/>
IS
«
s.
¦a
is
V
l.E+04
l.E+03
l.E+02
l.E+01
s/s son Available content Soil Available Content
SS-CFS
10 15 20
Time (year)
l.E+05
rM
E
oi l.E+04
:S/S Soil Available Content
Soil Available Content
l.E+03
l.E+02
« l.E+01
SS-CFS
1.E+00
10 15 20
Time (year)
oi
E
V
W
(0
0)
£
0)
-a
l.E+07
l.E+06 -
l.E+05
l.E+04
S/S Soil Available Content
Son Avai ab e Content
ss CFS
l.E+06
10 15 20
Time (year)
l.E+05 -f
I ,E+M
cc
w
¦S l.E+03
l.E+02
S/S Soil Available Content
Son Avai ab e Content
SS-CFS
10 15 20
Time (year)
Figure 5-5. Mass transport limited leaching of arsenic, cadmium, lead, selenium, chloride,
and nitrate.
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5-23
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5.2.7 Comparison to Reference Thresholds
The assessment ratio for COPCs can be calculated using the average concentrations for an assessment
interval and the threshold values for this example, the U.S. EPA National Primary Drinking Water
Regulations. In this scenario the point of compliance is at the unit boundary of the contaminated soil,
meaning the leachate concentrations are directly compared to the threshold values with no consideration
of dilution or attenuation. Table 5-9 below shows assessment ratios for 1, 5, and 30 year assessments.
While the stabilization process was effective at reducing the mobility of the majority of the COPCs,
Arsenic, lead and thallium remain above the threshold values. The proposed remedy for this site of in-situ
stabilization with Portland cement is not appropriate based on LEAF testing results and the assumptions
made in the assessment to estimate leaching in the field.
All leaching assessments make simplifying assumptions when developing estimates of leaching. This
example provided estimates of leaching in the field assuming that LEAF test results from short timescales
can represent long term behavior, and also relied on net infiltration parameters derived from 30 years of
meteorological data to anticipate field conditions. In cases where leaching of COPCs exhibits time
dependent behavior (e.g., one or more constituents becomes depleted), an average value for an
assessment interval may not appropriately reflect the environmental conditions. Users of LEAF testing
should work closely with the appropriate regulatory body when developing a leaching evaluation to meet
regulatory requirements.
Table 5-9. Comparison of leaching assessment results to reference thresholds
1-Year Assessment
5-Year Assessment
30-Year Assessment
COPC
Threshold
(mg/L)
Cav
(mg/L)
AR
(-)
Cav
(mg/L)
AR
(-)
Cav
(mg/L)
AR
(-)
Antimony
0.006
0.0022
0.4
0.0022
0.4
0.0022
0.4
Arsenic
0.01
0.018
1.8
0.018
1.8
0.018
1.8
Cadmium
0.005
0.0014
0.3
0.0014
0.3
0.0014
0.3
Chloride
250*
36
0.1
36
0.1
36
0.1
Chromium
0.1
0.014
0.1
0.014
0.1
0.014
0.1
Copper
1.3
0.070
0.05
0.070
0.05
0.070
0.05
Fluoride
4
0.019
<0.01
0.019
<0.01
0.019
<0.01
Lead
0.015
0.20
14
0.20
14
0.20
14
Nitrate
44
2.7
0.06
2.7
0.06
2.7
0.06
Selenium
0.05
0.014
0.3
0.014
0.3
0.014
0.3
Sulfate
250*
140
0.6
140
0.6
140
0.6
Thallium
0.002
0.17
87
0.17
87
0.17
87
Zinc
5*
0.018
<0.01
0.018
<0.01
0.018
<0.01
Notes: Orange italic text indicates ARs <1 (i.e., no further assessment is required).
Threshold values based on U.S. EPA National Primary Drinking Water Regulations (U.S. EPA 2009) with * indicating
secondary drinking water criteria.
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6. Test Your Knowledge
The below exercises are based on the data used in the screening assessment case study above in Section
5.1. The calculations and concepts used below are explained in Section 4, This example is for illustrative
purposes and is not intended to be directly applied to an evaluation. The actual use of LEAF testing must
be tailored to a given purpose and site-specific conditions that may occur.
6.1 Paula's First Assignment
Paula the program manager is a new employee at a state environmental agency. Paula is working on a
team to determine whether fly ash can be used as structural fill in a local project. The team assigns Paula
to study the potential effects of the fly ash material on groundwater. The potential for leaching of
constituents of concern to groundwater had been overlooked to this point by the team and Paula is
starting from the beginning. Paula is eager to impress her new supervisor and coworkers, and she knows
that she needs to start with a good testing plan to characterize the material. After talking to the analytical
chemist in the Agency's testing lab, Paula realizes that she needs to understand her material and the
environment to choose the right leaching tests.
Question 1: What does Paula need to know about her material and the environment before she can
develop a leaching evaluation?
(See next page for answer)
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Answer 1: What does Paula need to know about her material and the environment before she can
develop a leaching evaluation?
• Paula needs to know the composition of her material and which constituents of concern are
present.
• Paula also needs to know what the anticipated field conditions (now and over time) are in order
to estimate leaching under the right conditions. For example, many inorganic constituents have
pH dependent leaching behavior. Additionally, the amount, frequency, and mode of water
contacting the material needs to be understood or estimated. Testing of soil at a site or
consultation with databases for rainfall or soil data can provide valuable information.
• Paula will also need threshold values to compare her leaching estimates to. In some cases, the
total content of constituents of concern may be so high or so low, testing will not provide value.
For example, if leaching tests (or total content) show that leaching values will not exceed the
relevant thresholds, then no further analysis may be needed. If there is uncertainty in the
estimated leaching, further testing may determine a material is or is not appropriate for use.
6.2 Characterizing the Fly Ash
Paula checks back in with her analytical lab and learns that she is in luck. The total content analysis of a
representative sample of fly ash has already been completed using acid digestion (EPA Method 3052)
followed by ICP-OES (EPA Method 6010). The total content testing (shown below) indicates that the
constituents of concern are primarily inorganic. The pH of the fly ash material is 6.8 and the pH of the soil
the fly ash will be adjacent to is 6.0. Paula expects the fly ash material pH to control the pH of the leachate
as the soil has no significant buffering capacity. Paula decides the default pH range suggested in the LEAF
How-To Guide (Section 4.2.5.1) of 5.5 < pH < 9.0 could be used here to estimate the anticipated pH of the
fly ash and to estimate behavior if the pH were to change overtime. Paula checks her notes from the team
meeting to remind herself that the infiltration rate is expected to be 25 cm per year and the fly ash
material will be compacted to 1,500 kg-dry/m3. Before investing resources into testing, Paula compares
the total content of her material against standards set by EPA drinking water regulations. She notes that
the total concentrations of arsenic, chromium, and other inorganics appear high and warrant further
testing before a decision is made on the appropriateness of the fly ash as structural fill.
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Total Content
Drinking Water Standard
COPC
[mg/kg-dry]
[mg/L
Antimony (Sb)
1.5
0.006N1
Arsenic (As)
63
0.01
Barium (Ba)
830
2
Boron (B)
1,400
jN2
Cadmium (Cd)
3.5
0.005
Chromium (Cr)
120
0.1
Lead (Pb)
39
0.015N3
Molybdenum (Mo)
15
0.2N2
Selenium (Se)
24
0.05
Thallium (Tl)
0.91
0.002
Source: U.S. EPA (2012c, 2012d)
Drinking water standards are the National Primary Drinking Water Regulations (U.S. EPA, 2012a) unless noted:
N1 National secondary drinking water regulations—non-enforceable guideline.
N2 Drinking water equivalent level.
N3 Treatment technique action level.
Question 2: Which constituents listed in the table above are of potential concern to Paula based on
total content analysis?
(See next page for answer)
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Answer 2: Which constituents are of potential concern to Paula based on total content analysis?
In this scenario Paula is comparing constituents against drinking water standards. All of the
constituents listed in the table are above the drinking water standards and therefore are of concern
to Paula.
In real applications, the standards against which a constituent is compared should be carefully
considered. Consultation with the appropriate regulatory body may be needed.
Part 3: Paula's Proposed Testing Plan
Armed with knowledge of the material and the anticipated environmental conditions, Paula knows she
needs to determine what tests are appropriate to estimate leaching from the fly ash. She knows that there
are a variety of tests that may help her predict leaching in the environment, but she is specifically looking
for testing that applies to inorganic constituents such as lead, arsenic, and chromium. This helps her
narrow down the list, removing tests focused on organics or designed to simulate specific scenarios that
do not adequately represent structural fill. She decides to then check with her coworkers, and the state's
analytical laboratory to see what existing testing capabilities are available. Finally, before spending time
and resources on testing, Paula checks in with technical consultant hired onto the project, who just
happens to be you.
14
H
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6-4
Question 3: What leaching tests should Paula employ in her evaluation?
(See next page for answer)
-------
Answer 3: What leaching tests should Paula employ in her evaluation?
• Paula knows there are a variety of leaching tests available for inorganics, such as the EPA
Methods; TCLP, SPLP, or LEAF Methods 1313, 1314, 1315, or 1316; ASTM Standards D-3897 or D-
4874; and European methods such as EN 14429, NEN 7373, or EN 15863.
• The TCLP (EPA Method 1311) employs buffered solutions of acetic acid (either pH of 4.93 or 2.88)
to simulate conditions in municipal solid waste landfills. TCLP is likely not the best choice for
Paula as there is no acetic acid in her anticipated environment or in the waste and Paula is
interested in evaluating pH dependent leaching closer to a pH of 6.
• The SPLP (EPA Method 1312) is designed to simulate leaching of organic or inorganic constituents
in soils and employs a leachant consisting of a mixture of sulfuric and nitric acid with a pH of 4.2
or 5 depending on whether the soil is east or west of the Mississippi River. SPLP is not likely to be
the most appropriate test for Paula's anticipated environmental conditions.
• EPA Method 1313 will allow Paula to estimate leaching in the field within a window of pH
endpoints. Equilibrium data from this test alone will provide an estimate of the upper bound, or
available content, that a constituent that may leach at a given pH. EPA Method 1313 is generally
applicable to most scenarios with inorganics that have pH dependent solubility.
• EPA Method 1314 or EPA Method 1316 will allow Paula to estimate L/S dependent leaching
behavior of the fly ash. The L/S dependent leaching results from either test will provide
information on whether the material is solubility or availability controlled. EPA Method 1314
estimates percolation-based leaching in an open system, which may also provide insight into
percolation-based effects or preferential flow. Method 1316 estimates equilibrium results from
batch testing. In some cases, both tests may provide useful and complimentary results. However,
testing from one of these two methods is often sufficient.
• EPA Method 1315 estimates mass transport limited leaching from densely compacted or
stabilized material. The fly ash is not solidified into a bound matrix or otherwise densely
compacted. As a result, this test method will provide minimal value to Paula's evaluation.
Note: This question does not have one right answer. A variety of other tests to estimate leaching are
available that may or may not be suitable. LEAF testing is chosen for the purposes of this guide. See
the Appendix for a comparison of LEAF testing to analogous European standards.
6.3 Preliminary Available Content Evaluation
Paula knows that she is interested in evaluating pH dependent behavior of her fly ash and selects EPA
Method 1313 to do so. She also knows that L/S can be used as a surrogate for leaching over time and
elects to choose EPA Method 1314 to evaluate this parameter (Note: Paula could have also chosen
Method 1316 to evaluate L/S and it is not necessarily wrong to choose one or both methods for this
purpose.) The analytical lab completes Method 1313 and 1314 testing and sends the test results to Paula.
Paula is particularly worried about the high concentrations of arsenic in the leachate. Before proceeding
to evaluate the solubility within the pH range of interest, Paula checks the available content for arsenic
using Method 1313 results.
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Question 4: Can you determine the available content for arsenic from the Method 1313 lab results
(next page)? Hint: Paula recalls from reading the LEAF How-To Guide that available content is
calculated from the highest concentrations in the leachate at pH 2, 9 or 13 (see Section 4.4.1).
Leaching Environmental Assessment Framework (LEAF) How-To Guide
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EPA Method 1313
Sample: EaFA(P,l,l)
Concentration in mg/L
Fraction
9
8
7
6
5
4
3
2
1
PH
2.08
3.85
5.40
6.99
7.97
9.26
10.4
12.0
13.1
Al
128
32.0
0.335
0,202
1.21
17.7
27.1
33.8
37.0
As
1.55
0.0900
0.0417
0.0784
0.199
0.560
1.05
1.01
9.69
B
3.25
3.82
4.98
4,62
4.38
4.50
4.64
4.99
9.77
Ba
0.876
0.220
0.281
0.260
0.256
0.562
0.903
0.921
0.659
Be
0.441
0.142
0.00258
(0.000320)
(0.000320)
(0.000320)
(0.000320)
(0.000320)
(0.000320)
6r"
(0.00871)
0.668
0.687
0,515
0.598
0.700
0.652
0.722
0.827
Ca
141
140
167
155
135
111
87.3
40.9
9,20
Cd
0.0555
0.0427
0.0311
0.00580
0,00470
0,00460
0.00461
0.00505
0.00540
cr
1.64
1.57
1.25
1.30
1.28
1.30
1.26
1.30
4.19
Co
0.419
0.214
0.252
0.0261
0.00430
0.00140
0.00118
0.000726
(0.000207)
Cr
1.96
0.175
(0.000249)
0.0422
0.134
0.223
0.248
0.306
0.392
Cs
0.0642
0.0239
0.0172
0.0130
0.0148
0.0188
0.0218
0.0282
0.0336
Cu
3.16
1.91
0.0894
0.000900
(0.000351)
(0.000351)
0.000900
0.00192
0.0179
DIC
0.138
0.150
0.154
(0.0650)
(0.0650)
0.653
1.93
7.95
29.2
DOC
1.69
1.04
1.06
1.15
1.21
1.83
3.19
9.66
142
F"
0.0945
3.34
0.409
1.70
2.05
3.13
3.62
3.91
9.38
Fe
33.9
0.419
(0.00100)
(0.00100)
(0.00100)
(0.00100)
(0.00100)
0.0202
0,0339
K
22.1
18.6
26.1
25.0
55,3
135
190
441
1719
Li
1.51
2.12
3.26
3.24
2.97
2.70
2.56
2.23
1.56
Mg
14.0
7.69
8.90
7,49
5.10
2.86
0.111
(0.000500)
(0.000500)
Mn
1.84
1.17
0.982
0.268
0.0324
(0.000171)
(0.000171)
(0.000171)
(0.000171)
Mo
0.334
0.108
0.552
3,32
3.49
3.70
3.83
3.77
3.92
Report Date: 25-Jan-2017 page 3
See next page for answer
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Answer 4: Can you determine the available content for arsenic from the lab results?
Paula knows that the available content will be determined by the highest leaching concentration at a
pH of 2, 9, or 13. For arsenic, the highest concentration in the leachate is 9.69 mg/L at a pH of 13.1.
However, Paula needs to interpolate to estimate the concentration of arsenic at a pH of 13. In this
case the pH endpoints of 13.1 and 12.0 are used to interpolate. Using Equation 4-13 from section
4.4.2, the concentration of arsenic in the leachate is found to be 7.9 mg/L at a pH of 13.
logCAs = logCa + (pH - pHJ x (logCb - logCa)/(j)Hb - pHa)
logCAs = log(9. 69) + (13 - 13.1) x (log(l. 01) - log(9. 69))/(12 - 13.1)
me
Cas = 7.9-^
Now that Paula has the concentration of arsenic in the leachate at a pH of 13, she needs to account
for the liquid to solid ratio in Method 1313 using Equation 4-12 (See section 4.4.1)
mavail = Cmax(pH 2,9,13) x (L/S)1313
mg L
m-avail = 7 ¦ 9 - X 10
L Kg —dry
mg
m-avail ~ 79 ,
kg - dry
Available content can be reported as mg/kg-dry, however, Paula wants to be able to compare the
available content to a leachate concentration that may represent her environmental scenario. Paula
uses the initial L/S value of 0.5 to estimate the maximum potential for leaching when the material is
initially placed as structural fill, based on available content.
ill (L/S) initial
me
mavail = 79 ,/0- 5-
LKg — dry Kg — dry
mg
mavail — I58 —
6.4 Paula's Plausible Range of pH Dependent Leaching
Paula is not relieved to see her available content estimate for arsenic is considerably higher than the
regulatory thresholds for drinking water. However, Paula knows that her anticipated environment
considers a pH between 5.5 and 9. Using the same data from Method 1313, Paula can calculate the
maximum concentration of arsenic in the leachate within her anticipated conditions. What concentrations
of arsenic can Paula expect to see in her leachate when she considers the applicable pH range?
Leaching Environmental Assessment Framework (LEAF) How-To Guide
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Question 5: What is the maximum concentration of arsenic in the anticipated pH range? (Hint: Use
the Method 1313 data from the table provided in Question 4.)
See next page for answer
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Test Your Knowledge
-------
Answer 5: What is the maximum concentration of arsenic in the anticipated pH range?
The maximum concentration of arsenic in the anticipated pH range is 0.46 mg/L. The Method 1313
data shows an arsenic concentration of 0.56 mg/L at a pH of 9.26 and 0.199mg/L at a pH of 7.97. The
arsenic solubility is increasing with increasing pH and the highest pH in the anticipated pH range is 9.
Paula therefore needs to interpolate an arsenic concentration value at pH 9 using the data at a pH of
9.26 and a pH of 7.97.
logCAs = logCa + (pH - pHa) x (logCb - logCa)/(pHb - pHa)
logCAs = log(0. 56) + (9 - 9. 26) x (log(0.199) - log(0. 56))/(7.97 - 9. 26)
me
CAs = 0.46-^
6.5 Confirming Solubility Limited Leaching
Paula reviewed the Method 1313 results and suspects that the leaching behavior of arsenic in her
anticipated environment is solubility limited. She noticed that the leachate concentration controlling her
available content, 7.9 mg/L at pH 12, is significantly higher than the maximum leaching concentrations
within the anticipated environmental window, 5.5 < pH < 9.0, of 0.46 mg/L at pH 9. Paula would like to
confirm the solubility limited behavior with the Method 1314 results.
Question 6: How can Paula confirm that arsenic is solubility limited using her Method 1314 data
below? Hint: Paula realizes in reviewing her data that the L/S behavior of arsenic below an L/S ratio
of 2 is controlled by interactions between calcium and arsenic. The calcium has washed out of the
column at an L/S ratio greater than 2.
L/S (L/kg-dry)
See next page for answer
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-------
Answer 6: How can Paula confirm that arsenic is solubility-limited using the 1314 data below?
• Paula can tell that the arsenic leaching is solubility controlled because the cumulative release of
arsenic is a strong function of L/S (right figure).
• The method 1314 data in the left figure shows the concentration of arsenic is dependent on L/S
below an L/S of 2 (L/Kg-dry). Solubility controlled leaching does not often show a strong
dependence of concentration on L/S. However, Paula realized from looking at her other
constituents that the solubility of arsenic at low L/S values was likely controlled by calcium, which
washed out of the system at an L/S close to 2 (L/kg-dry).
• Paula can also compare the cumulative arsenic release at an L/S of 10 (mg/kg-dry) to the available
content of 79 (mg/kg-dry). The release of only 14% of the available arsenic by an L/S ratio of 10
indicates the leaching is limited by solubility. Available-content limited leaching would have been
expected to leach almost all of the available arsenic by or before L/S 10.
• A slope close to 1 on a logarithmic plot of cumulative constituent release versus L/S is often an
indicator of solubility-limited leaching. Available-content limited leaching will often show a more
rapid release of the constituent (e.g., an exponential curve).
6.6 Conclusions on Use for Structural Fill
While Paula has learned a great deal about the potential behavior of the arsenic in the fly ash, her analysis
has not concluded that the fly ash is suitable for use as a structural fill. The estimated leaching
concentration from Method 1313 results within the anticipated pH range of 0.46 mg/L is above Paula's
threshold of the 0.01 mg/L drinking water standard. In addition, analysis of the 1314 data indicates that
arsenic levels will reach 2.4 mg/L at an L/S of 10. The higher concentrations of arsenic at high L/S are a
result of the initially acidic nature of the fly ash (likely from acid washing) changing over time to a more
alkaline pH that better solubilizes (and therefore mobilizes) arsenic. At the same time, constituents such
as calcium lower arsenic solubility while present but eventually wash out of the method 1314 column test.
Paula returns to her supervisor with her results and to discuss considering alternative materials for
structural fill in the project.
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7. Useful Resources
Resource
Available Online1
LeachXS and LeachXS Lite
www. vanderbilt. edu/leaching/leach-xs-lite/
www. leachxs. com/lxsdll.html
LeachXS Lite data templates
www. vanderbilt. edu/leaching/downloads/test-
methods/
LEAF leaching test methods
https://www.epa.gov/hw-sw846/validated-test-
methods-recommended-waste-testing
TCLP leaching test method
https://www.epa.gov/hw-sw846/sw-846-test-method-
1311-toxicity-characteristic-leaching-procedure
SPLP leaching test method
https://www.epa.gov/hw-sw846/sw-846-test-method-
1312-synthetic-precipitation-leaching-procedure
EPA test methods: frequently asked questions
https://www.epa.gov/hw-sw846/frequent-questions-
about-sw-846-compendium-and-related-documents
ORCHESTRA: geochemical speciation and reactive transport code
http://orchestra.meeussen.nl/
PHREEQC: computer program for speciation, batch-reaction, one-
dimensional transport, and inverse geochemical calculations
wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc
MINTEQA2: geochemical equilibrium speciation model
www2.epa.gov/exposure-assessment-models/minteqa2
The Geochemist's Workbench: geochemical modeling software
www.gwb.com
IWEM: deterministic groundwater fate and transport model
https://www.epa.gov/smm/industrial-waste-
management-evaluation-model-version-31
EPA's Leaching Test Relationships, Laboratory-to-Field
Comparisons and Recommendations for Leaching Evaluation
using the Leaching Environmental Assessment Framework
(EPA/600/R-14/061)
www. vanderbilt. edu/leaching/wordpress/wp-
content/uploads/600rl4061-Lab-to-Field-LEAFl.pdf
EPA's Background Information for the Leaching Environmental
Assessment Framework (LEAF) Test Methods (EPA/600/R-10/170)
https://cfpub.epa.gov/si/si_public_record_report.cfm7d
irEn trylD=231332
EPA's Interlaboratory Validation of the Leaching Environmental
Assessment Framework (LEAF) Method 1313 and Method 1316
(EPA/600/R/12/623)
https://cfpub.epa. gov/si/si_public_record_Report.cfm ?
dirEn trylD=307273
EPA's Interlaboratory Validation of the Leaching Environmental
Assessment Framework (LEAF) Method 1314 and Method 1315
(EPA 600/R-12/624)
nepis.epa.gov/Exe/ZyPURL.cgi ?Dockey=P100FAFC.TXT
EPA's Characterization of Mercury-Enriched Coal Combustion
Residues from Electric Utilities Using Enhanced Sorbents for
Mercury Control (EPA/600/R-06/008)
https://cfpub.epa. gov/si/si_public_record_Report.cfm ?
dirEn trylD=147063
EPA's Characterization of Coal Combustion Residues from Electric
Utilities Using Wet Scrubbers for Multi-Pollutant Control
(EPA/600/R-08/077)
nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100EEGL.txt
EPA's Characterization of Coal Combustion Residues from Electric
Utilities—Leaching and Characterization Data (EPA/600/R-
09/151)
nepis.epa.gov/Adobe/PDF/P1007JBD.pdf
EPA's Leaching Behavior of "AGREMAX" Collected from a Coal-
Fired Power Plant in Puerto Rico (EPA/600/R-12/724)
nepis.epa.gov/Adobe/PDF/P100G02B.pdf
EPA's The Impact of Coal Combustion Fly Ash Used as a
Supplemental Cementitious Material on the Leaching
Constituents from Cements and Concretes (EPA/600/R-12/704)
nepis.epa.gov/Adobe/PDF/P100FBS5.pdf
EPA's Final Report for Sampling and Analysis Project—Beneficial
Use of Red and Brown Mud and Phosphogypsum as Alternative
Construction Materials
nepis.epa.gov/Adobe/PDF/P100BMWU.pdf
EPA's Composite Model for Leachate Migration with
Transformation Products (EPACMTP)
www.epa.gov/epawaste/nonhaz/industrial/tools/cmtp/
index.htm
1 All websites accessed 2 May 2016.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Useful Resources
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8. References
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