SEPA
Leaching Environmental
Assessment Framework
(LEAF) How-To Guide
Understanding the LEAF Approach and
How and When to Use It
SW-846 Update VI
October 2017
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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).
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), and Paul Lemieux
(EPA, Office of Research and Development).
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Notice/Disclaimer & Acknowledgements
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Table of Contents
NOTICE/DISCLAIMER ii
ACKNOWLEDGEMENTS ii
List of Tables vi
List of Figures vii
List of Highlight Boxes ix
Acronyms and Abbreviations x
Abstract xi
Key Definitions xii
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? 1-1
1.3 What is LEAF? 1-2
1.3.1 Why was LEAF Developed? 1-3
1.3.2 Why Perform Leaching Tests? 1-4
1.3.3 When Can LEAF be Used? 1-4
1.4 What Topics Are Covered in this Guide? 1-5
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
3.1.1 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
3.2.4 Quality Assurance/Quality Control 3-17
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Table of Contents (Continued)
3.3 LEAF Data Management Tools 3-21
3.3.1 Laboratory Data and Import Templates 3-21
3.3.2 Data Management with LeachXS™ Lite 3-22
3.3.3 Pre-Existing Leaching Data 3-24
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 4-10
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 4-23
4.3.2 Carbonation of Alkaline Materials 4-26
4.3.3 Microbial Activity 4-27
4.3.4 Complexation with Dissolved Organic Matter 4-27
4.3.5 Co-precipitation of Arsenic with Calcium 4-27
4.3.6 Chemical Interactions 4-28
4.4 Performing Common Analyses in Leaching Assessments 4-31
4.4.1 Determining the Available Content from Method 1313 Data 4-31
4.4.2 Interpolating Method 1313 Data to Endpoint Target pH 4-35
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) 4-36
4.4.4 Interpreting Observed Liquid Solid Partitioning (LSP) Behavior 4-37
4.4.5 Identifying Solubility- and Available Content-Limited Leaching 4-43
4.4.6 Understanding Mass Transport Parameters (Low Permeability Materials) 4-45
4.4.7 Considering Dilution and Attenuation in an Assessment Ratio 4-49
4.4.8 Integrating Source Terms into Models 4-49
5. Case Study of Using LEAF for Screening Assessments 5-1
5.1 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 5-2
5.1.3 Total and Available Content Screening 5-5
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Table of Contents (Continued)
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 Leaching Assessment Considering Dilution and Attenuation 5-11
5.1.7 Consideration of an Alternate Coal Combustion Fly Ash 5-14
6. Useful Resources 6-1
7. References 7-1
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
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List of Tables
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 4-1. Summary of Suggested Test Methods and Analyses for Screening Assessments 4-8
Table 4-2. Summary of Suggested Test Methods and Analyses for Scenario-Based Assessments 4-9
Table 4-3. Summary of Observed pH and Redox Conditions for Field Scenarios 4-19
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) 4-33
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. Dilution and Attenuation Factors (DAFs) based on 10th Percentiles of the National
Distribution for Clay-Lined and Unlined Landfills (U.S. EPA, 2014b) 5-12
Table 5-6. Leaching Assessment Ratios for Coal Combustion Fly Ash EaFA(Left) and Leaching
Assessment Ratios Considering Dilution and Attenuation According to the Example DAF
Values (Right) 5-13
Table 5-7. LEAF Coal Fly Ash CaFA Total Content Analysis and LEAF Leaching Test Results 5-15
Table 5-8. Leaching Assessment Ratios for Alternative Coal Combustion Fly Ash CaFA (Left) and
Leaching Assessment Ratios Considering Dilution and Attenuation According to the Example DAF
Values (Right) 5-16
Leaching Environmental Assessment Framework (LEAF) How-To Guide
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List of Figures
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 and SPLP 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 3-22
Figure 3-11. LeachXS™ Lite program structure showing data inputs, databases and outputs 3-23
Figure 3-12. LeachXS™ Lite interface for comparison of granular materials showing the approach
for comparing pH-dependent arsenic data for three CCR materials 3-24
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. Screening level assessments, test methods and assumed leaching conditions 4-11
Figure 4-3. 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) 4-15
Figure 4-4. Method 1313 LSP results over an applicable pH domain compared to total content,
available content and a reference threshold 4-17
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) 4-17
Figure 4-6. Flowchart for using LEAF for leaching assessments based on water contact 4-21
Leaching Environmental Assessment Framework (LEAF) How-To Guide
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List of Figures (Continued)
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 4-26
Figure 4-8. Method 1314 (left) and Method 1313 (right) for eluate pH, calcium, and arsenic 4-28
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) 4-30
Figure 4-10. Relationship between total content, available content and measured pH-dependent
release for a cationic metal 4-32
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) 4-34
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 4-36
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 4-37
Figure 4-14. LSP patterns for classical pH-dependence leaching behaviors 4-39
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) 4-41
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) 4-42
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) 4.44
Figure 4-18. Comparison of mass transport data (Method 1315) to equilibrium data shown as a
function of pH for a contaminated lead smelter soil (CFS) 4-47
Figure 4-19. Example results from Method 1315 for aluminum shown as a function of leaching
time from a solidified waste form (SWA) 4-48
Figure 5-1. Eluate pH and 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
Leaching Environmental Assessment Framework (LEAF) How-To Guide
List of Figures
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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
Leaching Environmental Assessment Framework (LEAF) How-To Guide
List of Highlight Boxes
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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
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). LEAF is a leaching evaluation framework for estimating constituent release from solid materials,
which consists of four leaching tests (i.e., U.S. EPA Methods 1313, 1314, 1315 and 1316) and data
management tools. The LEAF tests have been designed to consider the effect on leaching of key
environmental conditions and waste properties known to significantly affect constituent release. This
document describes how leach test results can be used alone to develop screening level assessments of
constituent release, or to develop more refined and accurate estimates of release when material is placed
in a defined use or disposal scenario. The four LEAF test methods presented in this document have been
validated 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.
This approach to testing and evaluation 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 is rewarded by increasingly refined estimates of
leaching. LEAF testing can 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. The LEAF tests and evaluation approach may
be useful in evaluations of materials for disposal or beneficial use under varied or site-specific
environmental conditions.
The purpose of this guide is to provide an understanding of LEAF to facilitate its broader use in
environmental assessment. This document provides background on the LEAF tests and well as information
on how to perform the tests and how to understand the test results. It 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.
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.
Constituent of Potential
Concern (COPC)
A constituent that may be present at concentrations of regulatory, environmental,
or human health significance.
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.
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 leachate contact with a material under field
conditions.
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.
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 limits the leaching process (i.e., the aqueous phase concentration is
at saturation yet available constituent remains in the solid phase).
Sorption-Cont rolled
Leaching
A liquid-solid partitioning endpoint at which neither the solid nor the aqueous phase
limits leaching, but sorption to mineral or organic matter surfaces controls the
concentration measured in the aqueous phase.
Source Term
A numerical or model-based estimate of constituent release used to represent
leaching from material in a field application and that may 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 Agency (U.S. EPA, or the Agency) and, thereby, facilitate its broader use. LEAF
is a leaching evaluation system 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,1 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,2 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.3 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 COPC 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.
1.2 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
1 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.
2 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.
3 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.
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An Introduction to LEAF and this Guide
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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 and reporting graphical and
tabular results, and approaches for using leaching data to support leaching assessments. LEAF provides a
consistent approach estimating leaching of COPCs from a wide range of solid materials including 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
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
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Introduction to LEAF and this Guide
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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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. 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. Freely 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 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
definition of 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
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. Similarly to 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).
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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.
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 on land and to form 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 numerous available groundwater fate and transport models.
1.3.3 When Can LEAF be Used?
This guidance provides a general approach that may need tailoring to the specific application or regulation
under which it is being used. For example, under the Resource Conservation and Recovery Act, 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) standards are based on the results from TCLP testing (40 CFR 268.40).
While not a regulatory test, LEAF testing may nonetheless be useful in support of evaluations for which
TCLP is not technically appropriate (i.e., disposal or reuse under conditions that significantly differ from
co-disposal with municipal solid waste) or not required under RCRA regulations. The LEAF leaching test
methods are intended for situations where an assessment tailored for site-specific conditions is very
useful or necessary or when conditions differ from those simulated by TCLP. As examples, LEAF may be
helpful for supporting LDR variances, determinations of equivalent treatment, hazardous waste delisting,
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beneficial use evaluations, or evaluation of disposal scenarios not subject to the TC regulation
(Garrabrants, Kirkland, Kosson, & van der Sloot, 2013; U.S. EPA, 2003, 2012b, 2014a, 2014b).
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).
For consideration or application of LEAF testing and methodology at Superfund sites, please contact
Schatzi Fitz-James (Fitz-James.Schatzi@epa.gov) in the Office of Superfund Remediation and Technology
Innovation for assistance.
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. Specifically, the reader can learn about the following topics:
• Section 1 - Discover why the LEAF leaching test methods were developed and when leaching
assessment using LEAF may be used to support waste management decisions;
• Section 2 - Understand the basics of the leaching process including the difference between the
extent and rate of leaching;
• Section 3 - Learn about the LEAF leaching tests and data management tools.
• Section 4- Develop an assessment framework using LEAF to assess leaching in evaluations from
simple screenings to more complicated environmental scenarios.;
• Section 5 - See how LEAF data may be used through a specific case study with particular leaching
assessment objectives, and
• Section 6 - Review a list of useful Internet resources for background material and applications for
LEAF.
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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 a
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
1
¦ ground level
¦ water table
point of
compliance
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/ mini"g
I L
contaminated
soil
road base
construction
debris
*1
jh.
agriculture
industrially
contaminated soil
factory
seepage
basin
-jf treatment development
—i and effectiveness
¥
coastal protection
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?
All 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 associated with the maximum concentration 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
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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
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
released4.
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
4 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.
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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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
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 a 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 three 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:
• Eluate or leachate pH that controls aqueous solubility of inorganic COPCs, dissolution of organic
carbon, and sorption of COPCs to mineral surfaces,5
• 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))6 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
5 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.
6 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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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.
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. 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
_l
Pb
o
E
E
(Q
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
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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
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).7
—100mL
—100mL
—lOOmL
—100mL
Step 1
L/S = x
2 O in 20 rnL solution
30 in solid
SO not available
solubility-limited
Step 2 Step 3
L/S = 2 x L/S = 3x
40 iri 40 mL solution SO in 60 mL solution
lO in solid 00 in solid
5# not available 5# not available
Step 4
L/S = 4x
SO 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
7 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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4.4.3 for more on calculating L/S). 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).
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);
• Introduction of DOC from organic material decay; and,
• Changes to the chemical composition of the material (e.g., from co-disposal with other materials).
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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. 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.
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. A full detailed description of the
validated methods can be found on the SW-846 website under validated methods (U.S. EPA, 2017b).
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)
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Table 3-1. Comparison of Test Parameters for LEAF Leaching Methods
.. Method 1313 Method 1314 Method 1315 Method 1316
Variable
Test Type
Equilibrium;
Equilibrium;
Mass transfer
Equilibrium;
pH-dependent
percolation
L/S-dependent
Test
Parallel batch
Column test in up-
Tank test with
Parallel batch
Description
extractions
flow mode
periodic eluant
extractions
renewal
Sample Type
Granular particle
Granular particle
Monolith: cylinder
Granular particle
and
size of 85% by mass
size of 85% by mass
or cube; 40-mm
size of 85% by mass
Dimension
less than 0.3, 2.0 or
less than 2 mm
minimum
less than 0.3, 2.0 or
5.0 mm
with 100% less
dimension
5.0 mm
than 5 mm
Compacted
granular: cylinder
with 40 mm
minimum height
Test,
Extractions for 24,
Continuous elution
Intervals of 2, 23,
Extractions for 24,
Extraction or
48 or 72 hours
to L/S 10 mL/g-dry
23 hours, 5, 7, 14,
48 or 72 hours
Interval
based on maximum
Estimated test time
14, 7 and 14 days
based on maximum
Duration
particle size
of 13 days based
Cumulative
particle size
on constant
leaching time of 63
flowrate of 0.75 L/S
days
per day
Eluant
Reagent water with
Reagent water or 1
Reagent water
Reagent water
Composition
additions of HN03
mM CaCI2
or NaOH
pH Range
2 to 13 at specified
As controlled by
As controlled by
As controlled by
targets
material being
material being
material being
tested
tested
tested
Amount of
Minimum 20 g-dry
Minimum 300 g;
Monolith: as
Minimum 20 g-dry
Solid
per extract;
600-700 g per
specified
per extract;
Approx. 400 g-dry
column (collect 1
Compacted
20 to 400 g-dry
each for pre-test
kg per test run)
granular: 500-750
each extract
and test replicate
g per test run + 5
(collect 1 kg per
(collect 1 kg for
pre-test samples
test run)
first test; 500 g for
(collect 4 kg for
each replicate)
first test, 1 kg for
each replicate)
Eluant
L/S of 10 mL/g-dry
Eluates collected
Liquid-surface area
L/S of 10, 5.0, 2.0,
Volume
through cumulative
ratio of 9 mL/cm2
1.0, and 0.5 mL/g-
L/S 10 mL/g-dry
dry
Number of
9 extractions (10 if
9 eluate fractions
9 interval solutions
5 extractions
Analytical
natural pH is
Solutions
outside target
per Test
range)
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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.
LEAF Key Terms
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.
Method 1313 consists of 9-10 parallel batch extractions (A through n) of a subsampies 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,
n samples
% *
S,
n
chemical
analyses
Adapted from Kosson et al. (2014).
D 521
~ f:.
H
mm
*
VP
O
19
D
Figure 3-1. Experimental scheme of U.S. EPA Method 1313 as a parallel batch extraction test.
Leaching Environmental Assessment Framework (LEAF) Flow-To Guide
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-------
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
-0.5
U
z
CO -1
u
< -1.5
-2
0 2 4 6 8 10 12 14
PH
Available
Content
0.0001
10
1
0.1
0.01
0.001
¦g 0.001
o
£ o.oooi
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. 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 preferential flow.8 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
8 Calcium chloride solution (1 mM) may be used instead of deionized water in cases where colloid formation is a concern to
prevent deflocculation of clays and organic matter.
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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.
-------
analysis. Analytical aliquots of the extracts are collected and preserved accordingly based on the
determinative methods to be performed (U.S. EPA, 2012c).
Adapted from Kosson et at. (2014).
Eluant collection bottle(s)
(sized for fraction volume)
1-cm
sand S
Luer shut-off
valve
<-End cap
Subject
N2 or Ar
(optional)
layers \ Sggggt material
fitting
lap
•4h-End cap
Luer shut-off
Eluant Pump valve
reservoir
Up-flow percolation column to collect eluates at specified L/S values, estimating liquid-
solid partitioning at percolation release conditions that approximate chemical equilibrium.
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.
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-------
10
£ o.i +
0.01
0.001
100
^ 10
E,
I
fD
- 1 -t
£ +
ro
s
0.1
4 6 8
L/S (L/kg-dry)
po OO
o y
;
LLOQ
0
2 4 6
L/S (L/kg-dry)
10
o
4
o
O
I
o
" V
: f
O
¦ ¦ ¦ I
¦ ¦ ¦ 1
¦ ¦ ¦ 1
¦ ¦ ¦ 1
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h-¦—
10
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<>o
¦ Oo
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100
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i
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w
E,
-------
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
1 sample At n At At
80 0 0
M0n0lith | J, J, analytical I
Of I _ samples
-------
12
10
11 --
10 --
0.01
0.1
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
o.i
0.01
0.001 T
.2 0.0001 - =
c
a)
10
0.00001
. ^ Diffusion
10000
0.01 0.1 1 10
Time (days)
100
OI
E
2
10
1000
100 ¦:
10
. »¦»
Diffusion
"
0.01 0.1 1 10
Time (days)
100
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
•
Maximum leaching rates under diffusion conditions
and compacted granular materials
•
Mass transport-based leaching source term
•
Tortuosity and observed diffusivity (diffusion-controlled
release)
Compacted dry density (pre-test for granular
•
Bulk density of compacted granular materials under field
materials)
compaction
Eluate pH and conductivity as a function of
•
Concentrations graphed as function of pH with Method 1313
cumulative leaching time
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).
n samples
% *
St
n
chemical
analyses
\
Q
521
n
•••I
D
mm
*
19
mm
A,
19
I
mm
T
0
Adapted from Kosson et al. (2014).
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 --
iv*-_.
Jr
—* -a
4 6
L/S (L/kg-dry)
10
0.1
Ol
E
0.01
2 o.ooi
o.oooi
—~—
1
LLOQ
MDL
—¦ ¦ ¦ i
¦ ¦ ¦ i
¦ ¦ ¦ i
•r. o.i -
V
l/l
IS
_0J
£
n
<
0.01
4 6
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).
Leaching Environmental Assessment Framework (LEAF) How-To Guide ^
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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.
When the endpoint pH of single point leach tests recorded, 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 and SPLP 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 like EC, should be limited to the natural pH test position for Method 1313 eluates.
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.
• 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
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Overview of LEAF
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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
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
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Overview of LEAF
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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 tests 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
• Data management in a manner that minimizes human error and allows for validation relevant to
data quality objectives.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Overview of LEAF
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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 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.9 Applicable U.S. EPA SW-846 analytical methods and
example MDLs and LLOQs for a selection of COPCs are provided in Table 3-7.
9 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
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Overview of LEAF
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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.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Overview of LEAF
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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
[Hg/L]
Analytical
Method
EPA SW-846
Method
MDL [ng/L]
LLOQ [ng/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
15M3
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.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
An Overview of LEAF
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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
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.
3.3 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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wa ntwtw
2 I
9
10
E
METHOD 1313 LaachXS Uta Data Template
METHOD 1313 LAB EXTRACTION DATA
Extraction Information
Project
Material
Test Replicate
US EPA
KS f ly Ash
Test conducted by:
Solids information
Particle Size (85 wt% less than) | 0.3 j mm
Dry Equivalent Mass 20.00 g-dry
IS Ratio
10
ml/g-dry
l iquid Volume / Extraction
200
mL
Recommended Bottle Size
250
mL
Temperature!
Reagent Information
4>
Test Start
n-Mav-n
30:00 AM
Mass o< "As Tested" Material/fxtraction
24-30
8
Arid Type
HN03
12
Test end
1? M.iy 11
9:35 AM
Acid Normality
2-0
13
Required Contact Time
23-25
hr
BaseType
KOH
14
Base Normality
1.0
15
2
Schedule of Acid an
Base Addition!
16
GO
Test Position
T01
T02
TQ3
T04
TOS
TO 6
T07
TOS
T09
NAT
B01
B02
B03
17
"As Tested" 5olkl [g| (iO.OSg)
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
18
C
E
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
19
Acid Volume [mL] (*!%]
0.30
0.80
2.00
4.00
5.00
40.00
40.00
20
Base Volume [ml J (±1%|
15.00
t.00
15.00
21
u
Acid Normality [meq/ml]
2.0
2.0
2.0
2.0
2X1
2.0
2.0
22
5
lie
c
3
Base Normality [meq/ml|
1.0
1.0
IjG
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
931
8,49
7,45
5,87
4,31
2.24
10.47
Z'l
LU
Eluate EC fms/cml
17,78
0-6621
0.4756
0.9721
1.81
3.52
4.904
22.72
0.1035
28
z
?
t/1
EfuateOKP [mV|
29
30
31
Notes or Remarks
N.il'jral pH
m«
meq/ml
Amounts
243,0
I 2238.2
92.1
31.0
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™10 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.
10 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
(iMttanq 0«U lout Contmt.
PfcytttJi PropctttrU
Scenarios
itq. f* CwKNtntci Gwwn).
tMiitai hupmnl
InJtfrfijH
Qitibil#
ScvfMirio
DtlilMif
r r >r n i: r
Ditibjt#
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) Flow-To Guide
An Overview of LEAF
LEAF
Screening
Msesinwnt
Leaching
Source Terms
Mnpublc
grountfwm* i«»*
and KMHport onodfti
tf. INEHMLl
EaceJ
Spreadsheets
(UtU.ltyjinl
-------
File Help
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tme.
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...\Devetopment CBP database Sept_2013_Saltstone_Ffy3sh_Siag_Test.mdb
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
The complete LeachXS™ Lite database (available at www.vanderbilt.edu/leaching-, accessed May 2, 2016)
contains leach test results from more than 250 waste types, secondary materials, construction materials,
soils, and sediments collected over several decades. 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
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
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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.
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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 method 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 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,
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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).
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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). 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.
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
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
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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 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
Screening Assessments
(Infinite Source)
Less Data/Effort
Less Refined
(large positive bias)
Total Content
(digestion, XRF)
Available Content
(Method 1313)
Equilibrium-pH
(Method 1313)
Equilibrium-L/S
(Method 1314 and/or 1316)
Scenario Assessments
(Finite Source)
Percolation
(Method 1313 & 1314)
Mass Transport
(Method 1313 & 1315)
7
Reactive Transport
Simulations
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.
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
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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.
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 4-4 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.
When leaching under a plausible range of conditions is demonstrated to be below threshold values for all
COPCs, it may be possible to conclude that the 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 4-4) 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.
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, Cleach_maxt
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)initial¦ 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,11 or an L/S estimate that reflects
11 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 [m3pore/m3] as s /(l- e)/ ps *1,000 where 1,000 is a conversion factor for volume (1,000 L/m3).
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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 material12 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
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).13 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
12 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.
13 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.
Test Methods
Eluate
Analyses
Assessment Attributes
Step 1 - Total Content Screening (if determined)
Total Content:
digestion, XRF, etc.
COPCs
• Total content mass release [mg/kg-dry] converted to estimated maximum leaching concentration (Cieach_max)
through division 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 2, 9, and 13
PH,
EC,1
COPCs,
DOC
• Basis for infinite source term; assumes available content is maximum cumulative release under field conditions.
• Available content mass release [mg/kg-dry] derived from maximum leachate concentration at Method 1313
endpoint target pH extractions at 2, 9, and 13. Target pH values in Method 1313 can be reduced to only those
demonstrated to achieve maximum eluate concentration as used for available content determination.
• Estimated maximum leaching concentration (Ciench_max); adjusted to initial L/S (default 0.5 L/kg-dry).
Step 3 - Equilibrium-pH Screening
Method 1313:
Applicable pH domain2 and
pH 2, 9, and 13
PH,
EC,1
COPCs,
DOC
• Basis for infinite source term over applicable scenario pH domain; assumes equilibrium concentrations as an
upper bound of leaching under field conditions.
• Available content as indicated above; used to determine solubility-limited vs. available content-limited leaching.
• 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); 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:
Applicable pH domain2 and
pH 2, 9, and 13
and
Method 1314 or Method 1316:
Full set of L/S values
PH,
EC,1
COPCs,
DOC
• Basis for infinite source term at low L/S; assumes eluate concentrations at low L/S are comparable to porewater.
• Estimated maximum leachate concentration (Cieach_maJ) determined as greater of maximum eluate concentration
over the applicable pH domain or maximum eluate concentration over the L/S range.
• Supplemental basis for determination of solubility-limited vs. available content limited leaching when evaluated
along with 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.
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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 4-2). 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 assessment14 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
4-2. 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
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.
14 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. conc. at
pH 2,9, or 13
Equilibrium-pH
(Method 1313)
Assumes LSP max conc.
over pH domain
leaches into initial L/S.
Max. conc. over
pH domain
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 4-2. Screening level assessments, test methods and assumed leaching conditions.
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 constituent 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.
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
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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:
f total,dry (f total,wet) (SC) (^ntotal,wet
)(l-MCdry)
Equation 4-2
where
mTotal,dry ls
mTotal,wet's
MC
dry
sc
is
is
Bulk content adjusted to a dry mass [mg/kg-dry]
Bulk content reported on a wet mass [mg/kg]
Moisture content of the material [kg-H20/kg]
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 (Cjeac^ma.^ may be calculated by
adjusting the total content on a mass basis for the initial L/S:15
where
C|each_max
total
(L/S) initial
C leach_max ~ Wl total/fS~)initial
is the maximum concentration based on total content
is the total content of a COPC [mg/kg-dry]; and
is the initial L/S [L/kg-dry],
Equation 4-3
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-
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
15 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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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.
Cleachjnax ~ ^"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
Cleachjnax = ^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 ~ Travail/(L/S)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.
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
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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.16 Figure 4-3 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 4-3,), the LSP
concentration is a weak function of L/S. Therefore, C/eac/,_mox can be assumed bounded by the maximum
concentration in Method 1313 testing of the pH domain, C1313 (maxpH domain-
Cleach_max ~ ^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
4-3), the maximum concentration measured over the applicable pH domain is likely to be a function of
L/S. The estimated maximum leaching concentration, Cieach_ma\-, is derived by adjusting the maximum
Method 1313 concentration over the pH domain, Ci3i3(maxphdomain), to the initial L/S, (L/S)mitiai, using
Equation 4-7:
Cleach_max ~ ^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
Cleachjnax ~ ^1313 (max pH domain) — 20 X C^13(max pH domain)
16 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 1000
100
10
1
0.1
0.01
0.001
0.0001
CaFA l
oi
E
E
¦c
IS
u
Max. over
pH domain
: c o^,
LLOQ
MDL
- ¦ ¦ ¦ 1 ¦ ¦ ¦ 1 ¦ ¦ 1
1 ¦ ¦ ¦ 1 ¦
¦ 1 ¦ ¦ ¦ 1 ¦ ¦ ¦
10
12
PH
oi
E
E
¦o
0.1
0.01
v o.ooi
0.0001
i
Max. over j
pH domain J
!
\n !
¦
\ i
|_lloq
\ 1
\ | MDL
i
10
12
PH
SWA
0.1
OI
E
E
¦a
is
u
0.01
0.001
0.0001
LLOQ
MDL
Max. over
pH domain
10
12
CFS
o.i -fe
OI
E
0.01
0.0001
¦ _
Max. over J
pH domainij/
i
i
j
L
[ -LLOQ.
! MDL
¦ ¦¦ i ¦ ¦¦ i ¦¦
i
i
i
1 1 1 1 1 1 ' 1 1 1 1 1 1 1 1 1
14
CaFA
oi
E
10
0.1 V
0.01
a
0.001
14
0.0001
SWA iooo
100
oi
E
10
0.1
0.01
_LLOQ_
MDL
14
pH
10
12
14
PH
Max. over
pH domain
V
—
—
LLOQ_
' ' ' 1 ' ' ' 1 ' ' ' 1 ' 1
1 ' 1 ' ' ' 1 ' ' '
MDL
1 1 1
10
12
14
pH
Max. over
pH domain
r======agj].
10
12
14
pH
-Method 1313
O Natural pH Indicator
~ Method 1313 (Interpolated)
Figure 4-3. 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).
4.2.4.4 Full Liquid Solid Partitioning (LSP) Screening
In some evaluations, the material and environmental conditions may be uncertain or vary. LSP results
from Methods 1313 and L/S results from Method 1314 or Method 1316 can be used to develop an upper
estimate under the potential environmental conditions. The LSP screening level assessment builds from
the equilibrium-pH assessment in that it assumes that COPCs leach at a maximum concentration
associated with the greater of the pH effect over the applicable pH domain, or the L/S-dependent effect
on eluate concentration. Although data from Method 1314 or Method 1316 can be used in this evaluation,
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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-
Cleachjnax — MAX [C1313 (max p// domain)* C(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).
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O)
E
c
V
Ifl
Tota Content
Avai ab e Content
Thresho d
0.001
0.0001
PH
Adapted from Kosson et al. (2002).
Figure 4-4. Method 1313 LSP results over an applicable pH domain compared to total
content, available content and a reference threshold.
SWA 10
l
oi
E
is
00
0.1 - r
0.01 -r
0.001
0.0001
EaFA looo
100
o io
l
o.i
o.oi
0.001
0.0001
OI
E
o
00
Max. over
pH domain
[ LLOQ
V
"MDL
PH
Max. over
pH domain
::::
MDL
SWA io
l
oi
E
is
00
0.1 - r
0.01
10 12 14
0.001
0.0001
EaFA looo
100
o io
l
o.i
0.01
0.001
0.0001
¦ Max. overj)H domain
~
o o
r-
-
LLOQ
MDL
0 2
4 6
L/S (L/kg-dry)
10
OI
E
o
CO
i\
-------
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-
specific17 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.
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.
17 Where a range of materials may be considered for use under a single, bounding application scenario definition.
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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 domain1819 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).20
• 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).
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
18 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]).
19 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
20 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
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,
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.
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Material
Flow-through
Flow-around
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
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
X
Assessment
Ratio
<1?
.Yes
Leaching < Threshold
riMo ^
r 1
Leaching > Threshold
* Default values or site-specific information
Figure adapted from Kosson, Garrabrants et al. (2012).
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 is over-predicted by direct
leaching test results by an order of magnitude for available content-limited COPCs and other constituents
for many assessment scenarios (U.S. EPA, 2014c). 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.
See Section 4.4.6 for more information on understanding and evaluating mass transport parameters.
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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 on leachability whereas slight changes in other factors (e.g., pH) can have
substantial effects.
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;
• 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); 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 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.
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
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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, 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-
organic-content soils.21 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-
21 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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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 (Cr042 ) 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 of the material tests, 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).
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:
K = [reduced species] Equation 4-10
[oxidized species\x[e Jx[//+J
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).
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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). 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.
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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 may concurrently alter the chemical
speciation of COPCs [e.g., lead from soluble Pb(OH) may precipitate as insoluble PbCOs], 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
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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).
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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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 similarto arsenic (i.e., the shape of the column eluate data for EaFA is similarfor
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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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
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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 4-4. 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
Cone, at pH
Cone, at pH
Available
Max.
2 Target
9 Target
13 Target
Content
Cone, at
COPC
Material
[mg/L]
[mg/L]
[mg/L]
[mg/kg-dry]
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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10 -r
£
¥
3
E
•a
n
U
0.01 -r
! CFS i
v
[ LLOQ
V i
: MDL
X I
1 1 1 1 1 1 1 1 1 1 1 1 1
¦ »>nr.
1 -r
O
Z
0.001 -r
PH
PH
10 12 14
10 12 14
! CFS
i
:lloq
r MDL
10 12 14
10 -r
£
¥
3
E
•a
n
U
0.01 -r
! EaFA
; LLOQ
: MDL
1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1
0.1
O
z
0.001 -
PH
PH
10 12 14
; Ea FA
i LLOQ
MDL
1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1
10 12 14
10 -r
£
¥
3
E
•a
n
U
0.01 -r.
! SWA
[LLOQ
: MDL
—_x_
I ¦ tm
0.1
O
z
0.001 -
PH
PH
10 12 14
\ SWA
i LLOQ
' MDL
1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1
10 12 14
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).22
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)23 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.
22 Interpolation of Method 1313 results to target pH values is achieved automatically using LeachXS™ Lite (see Section 3.3.2).
23 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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0.00001 I ' 11 I ' 11 I ' 11 I ' 11 I ' 11 I ' 11 I ' 11 I
0 2 4 6 8 10 12 14
PH
0.001 I ' ' ' I
0 2
+
4
6 8 10 12 14
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:
/S) scenario ~
(inf
x tyr)/(p x ^fill) 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
is
o
E 100
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 other constituents such as calcium, sulfate
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),24
• 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:
24 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.
(0
u
U)
SI
o
o
'-M
(0
V
U
o
¦ Highly Soli
ble
!
s^Cationic
Amphoteric^ »
Oxyanionic
/
N
/
~
\ /
V
[ V
1 (
A
/
\
N
~
— «*¦
[
[
0
12
14
2 4 6 8 10
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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10
1
u\ 0.1
E
o.oi
0.001
0.0001
0.0001
0.00001 4-
0
E
-------
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).
10000
1000
1000
10
1
0.1
0.01
0.01
0.001
0.001
0.0001
0.01
z 0.001
0.01
0.0001
0.001
10000
1000
—CaFA (fly ash)
-A—CFS (smelter soil)
-~—EaFA (fly ash)
=CHSWA (solidified waste)
O natural pH indicator
1000
100
10
1
0.1
0.01
0.001
0.0001
100
10 -
1 -
E
.2 0.1 -
c
0)
a 0.01
0.001
0.0001
0.01
0.001
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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.
• 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:
c.„'r, X[1-.M] £ t 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
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
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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, 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
-------
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 often are 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)..
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Figure 4-18. Comparison of mass transport data (Method 1315) to equilibrium data shown
as a function of pH 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
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
(see selenium data shown in Figure 3-6 and aluminum data shown in Figure 4-19 ) to verify that the
"dilute" boundary condition is met for each constituent.25
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Concentration of Aluminum as function of pH
Concentration of Aluminum as a function of time
1000
100
I
£ 10
a
I '
I 11 i
0,01
2 4 6 a 10 1? 14
Cumulative release of Aluminum
I imc idnyt)
Flux of Aluminum
L iV-.i
0
Time (days)
Time (djy^>
pH as function of time
Figure 4-19. Example results from Method 1315 for aluminum shown as a function of
leaching time from a solidified waste form (SWA)
• Aluminum 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 aluminum
results were not mass transfer-controlled, and should not be interpreted as diffusion controlled
release.
• Selenium 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 selenium and the selenium 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 Vi with respect to time for cumulative release and -Vt 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 Zz and -Zz,
respectively; however, aluminum is not diffusion controlled because the Method 1315 data did not meet
the criteria for maintaining dilute solutions.
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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. A user of this
guide is encouraged to consult with the appropriate regulatory body to ensure consideration of dilution
and attenuation is appropriate for their evaluation.
An evaluation that considers DAFs may assume that COPC concentrations are reduced by both contact
with groundwater and associated transport toward a down-gradient exposure point. Under these
assumptions, the leaching estimates divided by DAF values are compared to threshold values. The
assessor is responsible for ensuring that the use of dilution and attenuation is scientifically appropriate
and meets any regulatory requirements. The source term information developed using the LEAF test
methods can also be used with other groundwater fate and transport models to estimate receptor
exposures at any defined compliance point. When this is the case, the Assessment Ratio (see Equation
4-1) can be modified to account for dilution and attenuation (Equation 4-16).
AR
ARdaf ~ ~oXf ~ ^leachjnax/(DAF x Cfhres) Equation 4-16
Where
ARdaf is the assessment ratio considering dilution and attenuation [-];
Cieach_max is the estimated maximum concentration for the COPC [mg/L];
Cthres is the threshold value for the COPC [mg/L]; and
DAF is a COPC-specific dilution and attenuation factor [-].
In the assessment ratio equation that considers dilution and attenuation (Equation 4-16), the DAF has a
value greater than or equal to one (DAF > 1) that represents 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. When applicable, the value of DAF may be based on
default values, established from regional or national DAF distributions, or developed from site-specific
analyses. 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
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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,
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). Where data are
adequate, modeling can be used to estimate the effects of factors that may modify leaching such as
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
external factors (such as anaerobic bacteria).
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
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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 Study of Using LEAF for Screening Assessments
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.
5.1 Evaluating Coal Combustion Fly Ash for Use as Structural Fill Material
In this example, a coal combustion fly ash is proposed for beneficial use as construction fill material.26
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 stages of the screening assessment, 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.
26 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 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 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.
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.
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
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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
COPC
Total
Content
[mg/kg-dry]
LEAF Leaching Test Results
Method 1313
Method 1314
Available
Content -
Max Cone.
pH 2, 9,13
[mg/L]
pH for
Available
Content
Max Cone.
pH Domain
5.5 < pH < 9
[mg/L]
pH at Max
Cone.
LSP Limit
Max Cone.
Over L/S
Range
[mg/L]
iys at Max
Cone.
[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 ~ Wl 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:
< r ( mg \ I 1 (kg-dry\ _ (mg\
'leach max - A. a ykg_dry)\ 0.5 V L )~ * U\L )
The Qeach_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:
Cleach max = ^1313 (max pH 2,9,13) x (i/S)Mtial = ^0 x ^ 1313 (max pH 2,9,13)
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:
Cleachjnax ~ ^0 X C-L3-L3(max pjj 2,9,13) — ^0 X 0. 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
Available Content
Cleach_max [mg/L]
Assessment
Ratio
(AR)
Cleach_max [mg/L]
Assessment
Ratio
(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.27 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:
Cleachjnax ~ ^ 1313 (max pH domain)
27 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:
Cleach_max ~ ^1313 (max pH domain)
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 Ci213(maxpH domciiri)
Clench max = 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, a COPC with
a relatively high threshold of 2 mg/L, is 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
COPC
Threshold
Value
[mg/L]
Method 1313
Equil-pH Assessment
Max Cone.
Over pH
Domain
[mg/L]
LSP limit
Cleach_max
[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.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Case Study of Using LEAF for Screening Assessments
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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 ~ MAX [C1313(max pH 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.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Case Study of Using LEAF for Screening Assessments
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7 ¦¦
6 ¦¦
5 ¦¦
Ol
E
« 0.1 ¦:
0.01
4 6
L/S (L/kg-dry)
L/S (L/kg-dry)
4 ,
I 1 1 1 I 1 1 1 I 1 1 1 I 1 1 1 I
10
Max. over pH domain
Ol
E
E
¦c
IS
u
0.0001
1000
100
10
1
0.1
0.01
0.001
0.0001
Max. over pH domain
0.01 -r
0.001 -r-
4 6
L/S (L/kg-dry)
Max. over pH
4 6
L/S (L/kg-dry)
LLOQ
MDL
10
—A—EaFA_1314 — O EaFA_1316 ¦ EaFA_1313(interpolated) O Natural pH Indicator
Figure 5-1. Eluate pH and 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.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Case Study of Using LEAF for Screening Assessments
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Table 5-4. Full LSP Screening Assessment of EaFA Fly Ash Fill Material
EaFA
COPC
Threshold
Value
(mg/L)
Method 1313
Method 1314
Full LSP Assessment
Max Cone.
pH Domain
5.5
-------
5.1.6 Leaching Assessment Considering Dilution and Attenuation
In some scenarios, 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 (DAFs). In this
hypothetical case study, COPC estimates already evaluated using LEAF can be further evaluated by
considering dilution and attenuation when allowed by the appropriate regulatory body. This evaluation
assumes that COPC concentrations are reduced by both contact with groundwater and associated
transport toward a down-gradient exposure point. Under these assumptions, the leaching estimates
divided by DAF values are compared to threshold values. The constituent-specific national values from
the CCR regulation risk assessment are used within the assessment ratio considering DAFS equation
(Equation 4-16) as an example in lieu of site-specific DAFs (U.S. EPA, 2014a, 2014b).
ARDAF ~ Cleach_max/(DAF X Cihres)
The assessor is responsible for ensuring that the use of dilution and attenuation is scientifically
appropriate and meets any regulatory requirements. The source term information developed using the
LEAF test methods can also be used with other groundwater fate and transport models to estimate
receptor exposures at any defined compliance point. The impact of considering dilution and attenuation
within the assessment approach above is presented in the comparisons in Table 5-6. In this table, the
stepwise assessment ratios without consideration of dilution and attenuation are shown to the left while
parallel analysis incorporating the example DAF values at the 10th percentile are shown to the right. The
comparison shows that the inclusion of DAF values decreases the assessment ratios significantly;
however, not all COPCs estimates fall below the threshold values.
When no dilution or attenuation is considered, the results show that all COPCs, with the exception of
barium, may be a concern under full LSP assessment with estimated leaching concentrations in excess of
threshold values. However, when example DAFs are considered (Table 3-7), chromium, molybdenum and
selenium are filtered from subsequent consideration at the total content screening level, while barium
and boron are filtered during available content screening. Following the filtration process, the equilibrium-
pH screening assessment indicates that cadmium and lead are likely to leach at concentrations less than
threshold values over the applicable scenario pH domain. However, when considering the full LSP over
the pH domain and the L/S range, the leaching of antimony, arsenic, cadmium and thallium remain above
threshold values; thus, this level of assessment does not support the conclusion that EaFA fly ash is
appropriate as a fill material for construction applications.
Table 5-5 shows the DAF values used in this example. These DAFs were derived at the 10th percentile of
the national distribution of DAF values reported in the U.S. EPA 2014 CCR Risk Assessment (U.S. EPA,
2014b).28
28 Selection of the 10th percentile DAF value for individual COPCs is considered a bounding assumption whereby the DAFs for
individual COPCs in 90% of the cases on a national basis will be greater than the selected values. Lower DAF estimates infer
less dilution and attenuation than higher DAFs and, thereby, result in higher concentrations at the point of compliance.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Case Study of Using LEAF for Screening Assessments
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Table 5-5. Dilution and Attenuation Factors (DAFs) based on 10th Percentiles of the National
Distribution for Clay-Lined and Unlined Landfills (U.S. EPA, 2014b).
DAF
DAF
COPC
Symbol
(Unlined)
(Lined)
Antimony
Sb
6
19
Arsenic(lll)
As [III]
4
9
Arsenic(V)
As[V]
25
114
Boron
B
29
55
Cadmium
Cd
17
89
Chromium(lll)
Cr[lll]
100,000
100,000
Chromium(VI)
Cr[VI]
9
23
Cobalt
Co
16
71
Mercury
Hg
5
14
Molybdenum
Mo
1,163
43,676
Selenium(IV)
Se[IV]
100,000
100,000
Selenium(VI)
Se[VI]
9
25
Thallium
Tl
7
18
Vanadium
V
8,478
100,000
A DAF value of 10 was assumed for anions and oxyanions, and 100 was assumed for
cations when CCR risk assessment values were not available (US EPA, 2014).
A maximum of 100,000 is indicated when the calculated value exceeded this amount.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Case Study of Using LEAF for Screening Assessments
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Table 5-6. Leaching Assessment Ratios for Coal Combustion Fly Ash EaFA(Left) and Leaching Assessment Ratios Considering
Dilution and Attenuation According to the Example DAF Values(Right)
EaFA
COPC
Threshold
Value
[mg/L]
Assessment Ratio (AR)
Example
DAF
Values
Assessment Ratio Considering Example DAFs (ARdaf)
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)
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
500
600
500
64
12
83
100
42
5.3
Arsenic (As)
0.01
13,000
19,000
46
240
25
500
780
1.8
9.5
Barium (Ba)
2
830
8.8
0.24
1.0
200
4.2
0.044
0.0012
0.006
Boron (B)
7
400
28
0.71
22
29
14
0.97
0.025
0.77
Cadmium (Cd)
0.005
1,400
220
5.6
280
17
82
13
0.33
17
Chromium (Cr)
0.1
2,400
400
2.0
53
100,000
0.024
0.0040
<0.001
<0.001
Lead (Pb)
0.015
5,200
350
0.10
1.8
100
52
3.5
0.001
0.018
Molybdenum (Mo)
0.2
150
390
370
110
1,163
0.13
0.34
0.32
0.10
Selenium (Se)
0.05
960
2,800
66
140
100,000
0.010
0.028
<0.001
0.0014
Thallium (Tl)
0.002
910
2,600
15
260
7
130
370
2.1
37
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.
Example DAF values are hypothetical values for illustration purposes only.
Threshold values are the National Primary Drinking Water Regulations (U.S. EPA, 2012a) unless otherwise noted in Table 3-7.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Case Study of Using LEAF for Screening Assessments
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5.1.7 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.
However, when the effects of dilution and attenuation using the example DAF values were considered,
the leaching assessment conducted for percolation using Method 1314 results supportthe conclusion that
CaFA may be acceptable when compared against the alternative scenario requirements. 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.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Case Study of Using LEAF for Screening Assessments
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Table 5-7. LEAF Coal Fly Ash CaFATotal Content Analysis and LEAF LeachingTest Results
CaFA
COPC
Total
Content
[mg/kg-dry]
LEAF Leaching Test Results
Method 1313
Method 1314
Available
Content
[mg/L]
pH for
Available
Content
Max Cone.
pH Domain
7 < pH < 12
[mg/L]
pH at Max
Cone.
Available
content- or
Solubility-
limited
Max Cone.
Over iys
Range
[mg/L]
L/S at Max
Cone.
[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.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Case Study of Using LEAF for Screening Assessments
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Table 5-8. Leaching Assessment Ratios for Alternative Coal Combustion Fly Ash CaFA (Left) and Leaching Assessment Ratios
Considering Dilution and Attenuation According to the Example DAF Values (Right)
CaFA
COPC
Threshold
Value
[mg/L]
Assessment Ratio (AR)
Example
DAF
Values
Assessment Ratio Considering Example DAFs (ARdaf)
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)
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
12
170
190
1.0
1.0
Arsenic (As)
0.01
4,400
9,800
10
10
25
180
390
0.39
0.39
Barium (Ba)
2
960
83
1.4
200
200
4.8
0.41
0.0068
0.99
Boron (B)
7
NA
180
120
5.8
29
NA
6.2
4.0
0.33
Cadmium (Cd)
0.005
680
840
12
12
17
40
49
0.68
0.68
Chromium (Cr)
0.1
1,800
1,900
6.3
6.3
100,000
0.018
0.019
<0.001
<0.001
Lead (Pb)
0.015
7,500
1,700
0.17
1.0
100
75
17
0.0017
0.010
Molybdenum (Mo)
0.2
190
370
10
24
1,163
0.16
0.32
0.0086
0.02
Selenium (Se)
0.05
340
1,800
10
17
100,000
0.0034
0.018
<0.001
<0.001
Thallium (Tl)
0.002
1,500
1,000
5.8
5.8
7
210
140
0.8
0.8
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.
Example DAF values are hypothetical values for illustration purposes only.
Threshold values are the National Primary Drinking Water Regulations (U.S. EPA, 2012a) unless otherwise noted in Table 3-7.
Leaching Environmental Assessment Framework (LEAF) How-To Guide
Case Study of Using LEAF for Screening Assessments
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6. Useful Resources
Resource
Available Online1
LeachXS and LeachXS Lite
www. vanderbilt. edu/leaching/leach-xs-lite/
www. leachxs. com/lxsdll. h tml
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 ://orch estra. meeussen. n 1/
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/ZyPURLcgi?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
-------
7. References
ASTM. (2012). D3987-12 Standard Practice for Shake Extraction of Solid Waste with Water. ASTM
International, West Conshohocken, PA.
Bird, R. B., Stewart, W. E., & Lightfoot, E. N. (2001). Transport Phenomena (2nd ed.). John Wiley & Sons,
New York. ISBN 0-471-41077-2.
BMD. (1995). Dutch Building Materials Decree.
Brand, E., de Nijs, T., Claessens, J., Dijkstra, J. J., Comans, R. N. J., & Lieste, R. (2014). Development of
emission testing values to assess sustainable landfill management on pilot landfills, Phase 2: Proposals
for testing values. RIVM report 607710002/2014. National Institute for Public Health and the
Environment, Bilthoven, The Netherlands.
Carter, C. M., van der Sloot, H. A., & Cooling, D. (2009). pH dependent extraction of soils and soil
amendments to understand the factors controlling element mobility - New approach to assess soil and
soil amendments. European Journal of Soil Science, 60, 622-637.
Crank, J. (1975). The Mathematics of Diffusion (2nd ed.). Oxford: Clarendon Press.
Dijkstra, J. J., Meeussen, J. C. L., van der Sloot, H. A., & Comans, R. N. J. (2008). A consistent geochemical
modelling approach for the leaching and reactive transport of major and trace elements in MSWI
bottom ash. Applied Geometry, 23(6), 1544-1562.
Dixit, S., & Hering, J. G. (2003). Comparison of arsenic (V) and arsenic (III) sorption onto iron oxide
minerals: implications for arsenic mobility. Environmental Science & Technology, 37, 4182-4189.
Engelsen, C. J., van der Sloot, H. A., Wibetoe, G., Justnes, H., Lund, W., & Stoltenberg-Hansson, E. (2010).
Leaching characterisation and geochemical modelling of minor and trace elements released from
recycled concrete aggregates. Cement and Concrete Research, 40, 1639-1649.
Engelsen, C. J., Wibetoe, G., van der Sloot, H. A., Lund, W., & Petkovic, G. (2012). Field site leaching from
recycled concrete aggregates applied as sub-base material in road construction. Science of the Total
Environment, 427-428, 86-97.
EPA, U. (2016). Methodology for Evaluating Beneficial Uses of Industrial Non-Hazardous Secondary
Materials.
Gardner, K. H., Tsiatsios, C. J., Melton, J., & Seager, T. P. (2007). Leaching behavior of estuarine
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