United States Science Advisory Board EPA-SAB-EEC-92-003
Environmental Protection (A-101F) -*«*, October 1991
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vvEPA Leachability
Phenomena
Recommendations and
Rationale for Analysis of
Contaminant Release by the
Environmental Engineering
Committee
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
EPA-SAB-EEC-92-003
OFFICE OF
THE ADMINISTRATOR
October 29, 1991
Honorable William K. Reilly
Administrator
U.S. Environmental Protection Agency
401 M Street, 8.W.
Washington, D.C. 20460
Subject: Leachability: Recommendations and Rationale
for Analysis of Contaminant Release
Dear Mr. Reilly:
The Leachability Subcommittee (LS) of the Science Advisory
Board's Environmental Engineering Committee (EEC) has prepared
the attached recommendations and rationale on leachability, an
important release term related to solid wastes and contaminated
soils, for your consideration.
Over the past decade, the EEC has reviewed a number of EPA
issues involving leachability phenomena and noted several
problems relating to this release term that were common to a
variety of EPA offices. The Committee believed that these common
problems would be best called to the Agency's attention through a
general review of leachability phenomena.
Drafts of this report on leachability have been reviewed at
a series of Subcommittee, Committee, and Executive Committee
meetings over the past 18 months. This included both a session
on February 26, 1990, devoted to assessing the Agency's varied
needs on leachability-related information, and a Technical
Workshop on May 9, 1990. The workshop assisted in determining
how leachability phenomena should be used to determine how a
waste will leach when present under various scenarios in the
environment.
The following recommendations have been developed. First,
in regard to leachability test development we recommend:
a) incorporation of research on processes affecting
leachability into EPA's core research program to better define
and understand principal controlling mechanisms,
b) development of a variety of contaminant release tests,
rather than focusing on mimicking a single scenario,
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c) development of improved release and transport-
transformation models of the waste matrix to complement the
leaching tests, and
d) field validation of the tests and models, and
establishment of release-test accuracy and precision before tests
are broadly applied.
Next, in regard to the application of such tests and models,
we recommend:
e) use of a variety of contaminant release tests and test
conditions which incorporate adequate understanding of the
important parameters that affect leaching in order to assess the
potential release of contaminants from sources of concern. A
medical analogy is that no physician would diagnose on the basis
of one test showing only one aspect of the problem,
f) development of a consistent, easily applied, physical,
hydrologic, and geochemical representation for the phenomenon or
waste management scenario of concern,
g) identification and application of appropriate
environmental conditions for tests in order to evaluate long-term
contaminant release potential as required under varying statutes,
and
h) coordination between the Agency's programs which develop
leachability tests with those that develop the environmental
models in which the release terms are used.
Finally, we recommend:
i) establishment by the Agency of an inter-office, inter-
disciplinary task group, including ORD to help implement these
recommendat ions, and
j) development of an Agency-wide protocol for evaluating
release scenarios, tests, procedures, and their applications.
These recommendations are made with the anticipation that an
improved understanding of the fundamental scientific principles
that control contaminant release and transport within a waste
matrix will allow better regulatory and technical decisions to be
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made in cases where the potential exists for leaching of
contaminants into the environment.
We are pleased to be of service to the Agency, and hope that
you will find this effort useful. We look forward to your
response to the recommendations cited above.
Dr. Raymond C. Loehr, Chairman
Executive Committee
Mr. Richard A. Conway, Chairman
Environ. Engineering Committee
Dr. C. H. Ward, Chairman
Leachability Subcommittee
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NOTICE
This report has been written as a part of the activities of
the Science Advisory Board, a public advisory group providing
extramural scientific information and advice to the Administrator
and other officials of the Environmental Protection Agency. The
Board is structured to provide a balanced, expert assessment of
scientific matters related to problems facing the Agency. This
report has not been reviewed for approval by the Agency; hence,
the comments of this report do not necessarily represent the
views and policies of the Environmental Protection Agency or of
other Federal agencies. Any mention of trade names or commercial
products does not constitute endorsement or recommendation for
use.
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ABSTRACT
The Leachability Subcommittee (LS) of tbe Environmental
Engineering Committee (EEC) of the EPA Science Advisory Board
(SAB) conducted a self-initiated study and prepared a report on
the topic of leachability phenomena. The intent of this report
is to provide recommendations and rationale for analysis of
contaminant release to the staff in the various offices of the
Environmental Protection Agency (EPA). The nine recommendations
from the report are highlighted as follows:
1) A variety of contaminant release tests and test condi-
tions which incorporate adequate understanding of the important
parameters that affect leaching should be developed and used to
assess the potential release of contaminants from sources of
concern.
2) Prior to developing or applying any leaching tests or
models, the controlling mechanisms must be defined and
understood.
3) A consistent, replicable and easily applied, physical,
hydrologic, and geochemical representation should be developed
for the waste management scenario of concern.
4) Leach test conditions (stresses) appropriate to the
situations being evaluated should be used for assessing long-term
contaminant release potential.
5) Laboratory leach tests should be field-validated, and
release test accuracy and precision established before tests are
broadly applied.
6) More and improved leach models should be developed and
used to complement laboratory tests.
7) To facilitate the evaluation of risk implications of
environmental releases, the Agency should coordinate the
development of leach tests and the development of models in which
the release terms are used.
8) The Agency should establish an inter-office, inter-
disciplinary task group, including ORD to help implement these
recommendations and devise an Agency-wide protocol for evaluating
release scenarios, tests, procedures, and their applications.
9) Core research on contaminant release and transport within
the waste matrix is needed.
Key Words; leachability, leachability phenomena, leach tests and
methods, leaching chemistry, leaching models
ii
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LEACHABILITY SUBCOMMITTEE
ENVIRONMENTAL ENGINEERING COMMITTEE
Of the
SCIENCE ADVISORY BOARD
Chairman;
Dr. c. Herb Ward, Professor and Chairman/ Department of
Environmental Science and Engineering/ Rice University, Houston/
Texas
Vice-chairman;
Dr. Ishwar P. Murarka, Senior Program Manager/ Land and Water
Quality Studies, Environment Division/ Electric Power Research
Institute/ Palo Alto/ California
Members and consultants;
Dr. Larry I. Bone, Environmental Quality Department, The Dow
Chemical company, Midland, Michigan
Dr. Yoram Cohen, Professor, Department of Chemical Engineering,
University of California at Los Angeles, Los Angeles, California
Mr. Richard A. Conway, Senior Corporate Fellow, Union Carbide
Corporation, South Charleston, West Virginia
Dr. Linda E. Greer, Senior Scientist, Natural Resources Defense
Council, Inc., Washington, D.C.
Dr. J. William Haun, Director of Research & Development,
General Mills, Inc. (retired). Maple Grove, Minnesota
Dr. Wayne M. Kachel, Consultant Manager, Pilko and Associates,
Inc., Houston, Texas
Dr. Raymond C. Loehr, Professor and H.M. Alharthy Centennial
Chair in civil Engineering, University of Texas, Austin, Texas
Dr. Frederick G. Pohland, Professor and Edward R. Weidlein
Chair of Environmental Engineering, University of Pittsburgh,
Pittsburgh, Pennsylvania
Dr. Paul V. Roberts, Professor, Department of Civil
Engineering, Stanford University, Stanford, California
Dr. Walter M. Shaub, Technical Director, Coalition on Resource
Recovery and the Environment, U.S. Conference of Mayors,
Washington, D.C.
Dr. Mitchell J. Small, Professor, Department of civil
Engineering, Carnegie-Mellon University, Pittsburgh, Pennsylvania
iii
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Science Advisory Board Staff*
Mail Address: U.S. Environmental Protection Agency
Science Advisory Board (A101F)
401 M Street, 8.W.
Washington, D.C. 20460
Designated Federal Official
Dr. K. Jack Kooyoomjian
Staff Secretary
Mrs. Marcy Jolly
Assistant Staff Director
Mr. A. Robert Flaak
Director
Dr. Donald G. Barnes
Chairman, Executive
Science Advisory Board
Dr. Raymond C. Loehr
Chairman* Environmental
Mr. Richard A. Conway
iv
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TABLE OF CONTENTS
I. EXECUTIVE SUMMARY 1
II. INTRODUCTION 2
III. WHAT ARE THE NEEDS OF THE AGENCY AND REGULATED
COMMUNITY? 4
IV. ASSESSMENT OF CURRENT PRACTICE 5
V. RECOMMENDATIONS FOR IMPROVED LEACHABILITY
DETERMINATIONS TO FILL GAPS BETWEEN NEEDS AND
CURRENT PRACTICES 7
APPENDIX A - BACKGROUND ON LEACHABILITY AS A
SELF-INITIATED ACTIVITY OF THE
SCIENCE ADVISORY BOARD 33
APPENDIX B - LEACHABILITY WORKSHOP PROGRAM 34
APPENDIX C - LEACHABILITY NEEDS, USES, TESTS,
CONCERNS, AND ISSUES 35
C-l - superfund Remedial and Removal Programs
C-2 - office of Water, Sediment Criteria Program
C-3 - office of Solid Waste
C-4 - Office of Toxic Substances
C-5 - R&D Perspective of the R.s. Kerr Lab,
Ada, oklahoma
C-6 - R&D Perspective of the Office of Modeling,
Monitoring and Quality Assurance,
Washington, D.C.
C-7 - criteria and Objectives of Leaching Tests
and Modeling Considerations for Partitioning
Tests from the Perspective of Regulators
Versus Industry
APPENDIX D - CREDITS AND ACKNOWLEDGEMENTS 46
APPENDIX E - GLOSSARY OF TERMS AND ACRONYMS 49
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LIST OF TABLES
TABLE 1 - EXTRACTION TESTS 20
TABLE 2 - TEST REQUIREMENTS, USES OF TESTS, AND PROGRAMATIC
NEEDS FOR LEACHABILITY TESTS BY THE AGENCY AS
PERCEIVED BY THE SCIENCE ADVISORY BOARD'S
ENVIRONMENTAL ENGINEERING COMMITTEE 25
TABLE 3 - SCIENTIFIC CONSIDERATIONS IN DESIGN AND
INTERPRETATION OF LEACHABILITY TESTS 27
LIST OF FIGURES
FIGURE 1 - CONCEPTUAL VIEW OF LEACHING IN A WASTE UNIT 6
vi
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I. EXECUTIVE SUMMARY
In waste management/ including managing the effects of
spills or other releases which are sources of underground
contamination/ a critical issue is the assessment of the
potential for constituents to leach to the environment. The
Environmental Engineering Committee (EEC) of the Science Advisory
Board (SAB) undertook a study of this issue because it noted
several common problems relating to this release term as it
reviewed/ over the past decade/ various leaching tests and risk
models for several EPA offices. Tests such as the Extraction
Procedure (EP) and the Toxicity Characteristic Leaching Procedure
(TCLP) had, and continue to have/ scientific limitations/ yet
were being inappropriately and in some cases widely used. Often
tests were developed without rigorous review. A self-initiated
study seemed appropriate to define the leachability problem
better and to offer advice on its resolution.
The EEC established a Leachability Subcommittee (LS) that
addressed:
1) Needs of the Agency and regulated communities to
quantify leachability (releases) of contaminants to the
environment.
2) State-of-the-art and science related to fundamental
principles and practice in predicting leaching of constituents
from wastes/ contaminated soils, and other sources.
3) Recommendations to improve the scientific understanding
and application of leaching tests.
Workshops were held, literature was analyzed/ and
findings were discussed over an 18-month period leading to the
preparation of this report.
The various needs for tests and models to predict leaching
are defined. Tests developed and used in the U.S. and Canada are
summarized. The scientific considerations important in design
and interpretation of leachability tests are presented. This
information/ expert advice and analysis by workshop participants/
and reviews by SAB members/ resulted in guidance which should/ if
progressively implemented, significantly strengthen the Agency's
ability to assess appropriately leaching of contaminants from
hazardous wastes, contaminated soils and other sources.
This guidance, in the form of nine recommendations, is
summarized as follows:
1) A variety of contaminant release tests and test
conditions which incorporate adequate understanding of the
important parameters that affect leaching should be developed
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and used to assess the potential release of contaminants from
sources of concern.
2) Prior to developing or applying any leaching tests or
models, the controlling mechanisms must be defined and
understood.
3) A consistent, replicable and easily applied, physical,
hydrologic, and geochemical representation should be developed
for the waste management scenario of concern.
4) Leach test conditions (stresses) appropriate to the
situations being evaluated should be used for assessing long-term
contaminant release potential.
5) Laboratory leach tests should be field-validated, and
release test accuracy and precision established before tests are
broadly applied.
6) More and improved leach models should be developed and
used to complement laboratory tests.
7) To facilitate the evaluation of risk implications of
environmental releases, the Agency should coordinate the
development of leach tests and the development of models in which
the release terms are used.
8) The Agency should establish an inter-office, inter-
disciplinary task group, including ORD, to help implement these
recommendations and devise an Agency-wide protocol for evaluating
release scenarios, tests, procedures, and their applications.
The task group should also be charged with recommending what the
appropriate focal point(s), responsibilities, and organizational,
budgetary and communication links should be within the Agency for
the most effective, continued and ongoing support and pursuit of
the research, development and utilization of methods and
procedures.
9) Core research on contaminant release and transport within
the waste matrix is needed.
II. INTRODUCTION
In both hazardous and non-hazardous waste management, one of
the most critical issues is the assessment of the potential for
constituents contained in the source material to leach or
otherwise be released to the environment. Approaches to estimate
potential release of organic and inorganic constituents and their
subsequent environmental migration and associated health risks
are important in many situations (e.g., pollution prevention,
risk reduction, restoration-remediation and hazard identi-
fication) .
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This review has been initiated by the Environmental
Engineering Committee of the Science Advisory Board because 1)
the Committee has been reviewing Agency actions which require
definition of the potential for releases from wastes and their
transport to human and environmental receptors where exposure can
occur/ and 2) the Committee has previously reviewed the
scientific and technical basis for two tests for leaching
potential intended for particular uses: the Extraction Procedure
(EP) and the Toxicity Characteristic Leaching Procedure (TCLP)
(See for instance, US EPA, science Advisory Board, Report of the
Environmental Engineering Committee, Report on the Review of EP-
III, A Procedure for Determining the Leaching Potential of
Organic constituents from Solid and Hazardous Wastes. July 19,
1984). In addressing and reviewing Agency proposals, the
Committee has repeatedly observed and commented on the scientific
limitations of the EP and TCLP tests. Many of the proposed uses
for the tests have been inappropriate because the waste
management scenarios of concern were not within the range of
conditions used in the development of the tests themselves.
In most cases of inappropriate use of the EP or TCLP tests,
the justification given was that it is necessary to cite
"standard" or "approved" methods. Even if it is acknowledged
that the tests cannot be applied without significant change in
the test protocol itself, the need to use a previously "approved"
test has been cited.
In a contradictory set of pressures, some offices have
devised new tests to suit particular needs, e.g., the "oily waste
extraction test," when it was considered necessary. Only rarely
have such new or modified leaching tests been subjected to a
rigorous review of their precision, accuracy or technical bases
comparable to that applied to the EP and TCLP tests.
There are many laboratory tests that have been devised to
obtain estimates of the potential for contaminant release. These
tests are generally characterized as either static or dynamic.
In all instances, aqueous solutions have been utilised as the
leaching fluid. Solid-to-liquid ratios of 2:1 to 20:1 have been
prescribed. Leaching times of 18 hours to several days, and in
some tests, years are required. Various tests specify single to
over 20 extractions, and particle sizes from 2 mm to monolith
proportions. Table 1 (page 20), provides a summary of over 30
tests designed to help determine the potential for contaminant
release. Although a wide range of leaching tests exist, a
conceptual framework for their application is generally lacking.
In preparing this report, the Committee has sought the best
technical input available on "state-of-the-art" knowledge of the
leaching phenomenon. It has also sought and received extensive
information on the needs of regulatory and enforcement programs
for reliable leaching predictions and their interpretations.
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Building on its previous experience in technical reviews, on
outside input, and on its own expertise, the Committee offers
advice on ways to resolve the conflict between the need for
"standard" tests and the need for tests better adapted to the
circumstances to which the data are to be applied.
This self-initiated study focused on the following three
questions:
1) What are the needs of the Agency and regulated community
to quantify leachability or release of contaminants to the
environment?
2) what is the state-of-the-art and science dealing with
the fundamental principles that should be considered in
predicting leaching of chemicals from wastes, contaminated soils,
and other sources?
3) What should be or could be done to improve the
scientific understanding and application of leaching tests in
future risk analysis?
III. WHAT ARE THE NEEDS OF THE AGENCY AND REGULATED COMMUNITY?
The Subcommittee convened a one-day session on February 26,
1990, in Washington, D.C., devoted to assessing the Agency's and
other's (private sector and citizen groups) varied needs for
leaching tests and information. The findings are summarized in
Table 2 (page 25) and are detailed in Appendix C (pages 35-45).
Table 2, summarizes the Subcommittee's understanding of the
wants, uses, and needs for leachability tests/data within the
Agency. At least six program offices have expressed interest in
such information. The wants, or what the program offices would
like, are varied. Most focused on a means to predict field
conditions. All offices expressed a desire for a method(s) to
appropriately classify a waste. Given that such a test(s) did
exist, the offices would use it such as to set standards,
primarily through simulating risk. The Office of Toxic
Substances appears to have the broadest uses. Just as the wants
and uses are varied, so too are the needs. Consistently, all
offices see leachability tests as a means of demonstrating
compliance; a use for which most leaching tests were not
originally intended.
The EPA, through mandates of the RCRA, CERCLA, CWA and
associated regulatory programs, has required chemical testing and
other laboratory procedures to predict the possible hazards of
chemicals potentially released into the environment. The intent
of leaching/extraction tests is to reliably estimate the poten-
tial amount and/or rate of contaminant release under worst case
environmental conditions, thus enabling remedial, prevent-ative
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and anticipatory management actions to be taken to protect human
health and the environment.
IV. ASSESSMENT OF CURRENT PRACTICE
The Committee assessed the state-of-the-art in leachability
determinations through several means:
a) Participation in a Workshop on Contaminant Migration
at Rice University on December 15-16, 1989, organized
by the National Center for Ground Water Research
for the EPA Robert s. Kerr Environmental Research
Laboratory in Ada, OK., in cooperation with the
University of Texas at Austin and the Electric Power
Research Institute.
b) Holding a Leachability Workshop under the auspices
of the US Environmental Protection Agency, Science
Advisory Board on May 9, 1990 in Washington, D.C.
The Workshop Program and list of speakers are given
in Appendix B, page 34.
c) Review of key references assessing current leach-
ability tests, e.g., Compend-itim of Waste Leaching
Tests, Wastevater Technology Centre, Environment Canada,
May 27, 1989 (See Table 1, page 20 for summary
of extraction tests).
The findings reported also reflect the personal experiences and
expertise of the members of the Leachability Subcommittee.
The Leachability Workshop was conceived as a vehicle for
knowledgeable scientists, engineers and practitioners in the
field to focus on the scientific principles and issues relating
to leachability. The purpose of the Workshop was to conduct a
review of the scientific principles involved with leachability
phenomena. Various experts discussed relevant topics such as
test methods, their descriptions and capabilities for application
to the leaching of organics and inorganics, the leaching of
stabilized materials, physical-chemical mechanisms, leaching
chemistry of organics and inorganics, and alternative approaches
to laboratory tests.
The Workshop assisted the Leachability Subcommittee in
summarizing the fundamental scientific principles that control
leachability (Appendix B, page 34, and Figure 1 page j6), and
determining how they can be applied to predict the extent to
which contaminants will leach when disposed under various
potential environmental scenarios. The Contaminant Migration
Workshop, the Leachability Workshop, and the review and
assessment of key references, provided the background for
formulation of recommendations on how basic principles can be
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Fluid composition
(e.g.,pH, dissolved
gases) and quantity
Leachates
(a)
(precipitation/
dissolution, adsorption-
desorption, redox, biotic
transformation and
partitioning) reactions
between solids and liquids
t
o
2
8
S
Washing
Dissolution of solubility-
controlling solid
/ Matrix dissolution
\
2
Q>
O
O
Cosolvent
present
/- Microbial
/ degradation
Time or Pore Volumes >
(b)
Depletion *
Aqueous
partitioning
Time or Pore Volumes
(c)
FIRGURE 1. Conceptual View of Leaching in a Waste Unit.
(a) Generation of leachates;
(b) Potential leaching stages for inorganic contaminants;
(c) Generation of organic leachates.
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used on a consistent basis for improving or developing decisions
related to leachability.
A conceptual view and summary of the major processes and
interactions that can occur in leaching of a waste matrix is
presented schematically in Figure 1, page 6. The generation of
leachates is depicted (Figure la) and is the sum of several
geochemical processes involving reactions within a physical
mixture of different forms of the same element. For example/ in
fly ash, an element such as cadmium may occur as simple oxide
salts accumulated on the surface of ash particles, as an element
within the glass matrix, and as a post-combustion product of
aqueous reaction such as Cdco,. Potential leaching stages
areillustrated for an inorganic contaminant in Figure Ib.
Reaction of the readily available and highly soluble fraction,
such as the surface oxide salts, provides high solute
concentration during initial washing or leachate generation.
This stage is followed by considerably decreased concentrations
of solutes as the readily available fractions have been leached
or transformed into less soluble forms (such as the CdCO3).
These transformed solids are referred to as solubility-
controlling solids. Dissolution and depletion of these
solubility controlling solids and the bulk matrix are important
determinants of the temporal change and characteristics in
leachate generation following initial washing.
The generation of organic leachates (Figure Ic) also
involves several biogeochemical processes. For example, the
leachate concentration of an organic compound may be controlled
by its water solubility (aqueous partitioning). However, in the
presence of a cosolvent, the leachate concentration is usually
controlled by the solubility of the constituents in the organic
phase rather than in water and may be substantially increased.
Microbial degradation, abiotic transformations and physical
partitioning to gaseous and solid phases can further alter the
pattern of leachate generation.
V. RECOMMENDATIONS FOR IMPROVED LEACHABILIT.Y DETERMINATIONS TO
FILL GAPS BETWEEN NEEDS AND CURRENT PRACTICES
Based on a broad-ranging review and analysis of needs and
information available on leaching phenomena, the Leachability
Subcommittee has developed the following recommendations:
1) A variety of contaminant release tests and test
conditions which incorporate adequate understanding of the
important parameters that affect leaching should be developed and
used to assess the potential release of contaminants from sources
of concern.
In scientific and technical terms, no "universal" test
procedure is likely to be developed that will always produce
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credible and relevant data for input to all decision making
exercises. There is nothing inherently bad about having a vide
variety of test conditions and methods, to cover the range of
needs, if each is defensible in view of the scientific and
technical understanding of the basic processes involved.
Provisions for adequate margins of safety and varied scenarios
should be made. A wealth of knowledge already exists which can
form the essential basis for quantitative determinations of the
release of contaminants. Appropriate physical, chemical and
biological factors should be selected for a specific test or
model to reliably estimate contaminant releases. Important
information includes: waste characteristics, mobilizing fluid
characteristics, intrinsic behavior of chemicals, and most likely
reactions to occur under varying hydrologic, chemical and
atmospheric conditions (Table 3, page 27).
Chemical and physical characteristics of a waste are
significant determinants of leachate composition. The nature and
conditions of occurrence of leachable constituents, rather than
the total amounts, often dictate the consequential release of
contaminants from the waste. Moreover, the speciation of
constituents of concern, for example, heavy metals, cannot or has
not in most cases been reliably quantified. This can confound
reliable anticipation of potential contaminant release, further
contributing to uncertainty in contaminant release assessment.
Waste or matrix heterogeneity is another complicating factor.
In addition to waste and matrix characterization, it is
similarly important to characterize the leaching medium (i.e.,the
fluid) which contacts the waste material. Terrestrial
porewaters, including groundwaters, have broadly defined fluid
parameters and show tremendous diversity in those characteristics
which influence solubility and chemical behavior of mobilized
waste chemical constituents. Also, fluid which contacts the
waste can be influenced by the presence of contaminants from
other wastes, such as at a Superfund site where waste oil has
been codisposed with PCBs.
2) Prior to developing or applying any leaching tests or
models, the controlling mechanisms must be defined and
understood.
Contaminant release (and eventual fate) in a field
environment is an extremely complex phenomenon involving multiple
phases and multiple constituents. In order to provide a proper
conceptual framework for a leachability scenario, a recommended
first step in any leaching test or model should be to identify
all significant mechanisms that can ultimately determine release
and environmental fate of the contaminants.
After identifying mechanisms, an understanding of how they
(directly or indirectly) influence release and environmental fate
8
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should be established. Past experience suggests that identifying
the principal controlling mechanisms is often straightforward.
However, anticipating the interrelationships among concurrent and
often competing mechanisms can be much more difficult, yet
critical in the characterization of leachability.
In developing the conceptual framework for a leachability
scenario, attention should be given to accounting for all
significant phenomena be they physical, chemical, or
biological --and their potential interactions. At a minimum, the
following phenomena should be considered: fluid characteristics
and flow dynamics, source matrix morphology and chemistry,
chemical reactions (equilibrium or kinetic), biotic reactions,
and temporal and spatial dependence. These are discussed in
relation to the principles identified throughout this report (see
also Figure 1 and summary Tables l, 2 and 3 for overview
information).
To understand and predict the leaching of organic
constituents of concern, it is important to consider the presence
of organic solubilizers such as solvents and oil in addition to
wastes. Under the conditions of codisposal with solubilizing
agents, the extent of leaching is usually controlled by the
solubility of the constituents in the organic phase rather than
in water. However, dissolved solvents can, to a lesser extent,
affect constituent solubility in the aqueous phase.
Experimental data obtained over the last decade indicate
that the solubilizing effect of some agents can dramatically
increase the concentrations of normally insoluble organic
constituents. In some instances, organ!cs have been shown to
enhance the mobility of inorganic constituents, most likely
through complexation. In these cases, aqueous extractions to
estimate the extent of leachability of the waste may seriously
underestimate the magnitude of release for constituents of
concern.
Biotic reactions are known to be important in some
circumstances and should be considered to fully simulate
leachability. Both inorganic and organic constituents frequently
undergo biological transformations within a source matrix. These
transformations can directly change the chemical environment and
composition of the leachate, and contribute to other secondary
effects such as changing the nature of the leaching fluids and
the setting within which leaching occurs.
The effect of biotransformation has been considered in some
instances. The EP, the TCLP and other tests use an organic acid
in an attempt to simulate codisposal with degradable materials.
The oily waste extraction procedure requires extraction of oil
from the solids prior to leaching, because biodegradation in
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nature will remove the oily film allowing more intimate contact
with the leaching fluid.
It is often difficult to reproduce or simulate in batch
extraction procedures, biotransformations which occur in field
situations, in part because the temporal and spatial
considerations for each are so different. Batch extractions are
designed to evaluate equilibrium processes, while biotrans-
formations are rate-limited. However, biotransformation studies
are not inherently incompatible with column or dynamic leaching
tests, and as such should be incorporated in those cases where
they could be important. In attempting to integrate the
assessment of biotransformation phenomena into a leaching test,
it is critical to consider rate limitations in choosing the
test's duration. The effects of biotransformation should be
considered in interpreting or applying leachability results in
cases where it can occur.
3) A consistent, replicable and easily applied , physical,
hydrologic and geochemical representation should be developed for
the waste management scenario of concern.
Central to devising leaching tests and models is the
development of a sound conceptual framework of the physical
system which is to be simulated. This framework requires proper
and relevant identification of the precipitation-dissolution
reactions by systematically examining the fluid and waste
characteristics as well as the intrinsic chemical behavior of the
constituents. This includes the equilibrium or steady state
conditions as well as the reaction rate representing the dynamics
of the leaching process. Reaction rate is an important, yet
poorly understood, factor.
The complexities of fluid-solid waste interaction dynamics
can occur in "real world" field conditions in which fluid
parameters can change spatially and temporally with corresponding
shifts in constituent release behavior. A constituent may
initially occur in a highly soluble form, but may subsequently be
transformed to highly insoluble precipitates, thereby rendering
it immobile. Similarly, a constituent may be leached at a
greater rate due to the very acidic or very alkaline pH of the
leaching fluid. Dissolution of the protective matrix material may
increase the potential for transport of the leaching fluid and
the release of contaminants.
The Subcommittee believes that rate-limiting chemical and
microbial reactions often play a pivotal role in governing
leaching rate and contaminant fate, consequently, situations can
occur in which equilibrium concepts may not apply to some (and
probably even to the majority) of the contaminant release (and
transport) scenarios. It is expected that, in numerous
instances, equilibrium-based projections of leachate levels can
10
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only provide an asymptotic (e.g./ upper or lower limit) estimate
of leachability that is not experienced at actual disposal sites
during the management period of interest. In addition,
hydrologic conditions and their spatial and temporal variations
can impact on rates of dissolution and precipitation, mass
transfer, and disequilibria. These effects and their impacts are
not well understood, despite their important contributions to
leaching of constituents to the environment. Despite these
limitations, determinations of hazard for various contaminant
release (and transport) scenarios are a necessity in order to
accommodate the realities of statutory requirements and the
attendant regulatory requirements.
If the intent is to match a test to an environmental
situation with respect to contact time, a distinction could be
made between situations where the waste is contained within a
lined landfill (long contact time), or where the waste is
underlain by a very porous medium or is in a flowing surface
water (short contact time). Likewise, the leaching liquid-to-
solid ratio at a waste management site is functionally
(dynamically) related to rainfall, infiltration rates, the
presence or absence of a cap over the waste, the quantity of
waste, and other site-specific factors. Exceptions do occur
based on site-specific factors. For example, if porous media
have been plugged, this would increase contact time. Because of
plugging phenomena, significant retention of waste leachate has
been observed in some municipal landfills (such as in the Long
Island, New York area), despite the fact that they are unlined
and underlain by a very porous medium (sandy soil).
Explicit selection of leachate tests to best match repeated
or continual leaching may require a determination of whether the
particular management scenario involves wastes in a lined and/or
capped landfill, or in more open systems in which greater contact
exists with the surrounding environment. In the former case, the
leachate may only be drained from the waste once. In the latter
case, multiple leaching and contact times can reasonably be
expected to occur. In most cases, multiple leaching can probably
be expected, although contact times, liquid-to-solid ratios, pH
and other environmental factors may vary, not only for different
scenarios, but also for successive leaching events in a given
environmental setting. This variability can be difficult to
predict and simulate.
The nature and influence of physical dimensions (e.g.,
particle size and shape) of the waste matrix is difficult to
predict for test development purposes. As a general principle,
accuracy and reliability should be improved if the waste is
leached in the form that is present in the environment, if it can
be expected and demonstrated that the form of the waste will
remain relatively unchanged with time. In other words, waste
matrix dimensions should simulate what is expected in the
11
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environment over the time period of concern. It also follows
that the dimensions range in test samples should reflect that of
the wastes of concern.
A noteworthy issue is that some wastes in the environment
clearly have dimensions which are too large to be examined with a
particular laboratory test apparatus. Depending on
accommodations to particular requirements of the test apparatus,
this may or may not be a serious problem. If only a modest size
reduction is required, such as reduction of a football-sized
object to an average of one inch diameter, this is likely not to
be a serious problem with respect to the development of
leachability information, because the surface to volume
perturbation is much less severe than had the requirement been to
reduce the football-sized mass to milled wastes of a millimeter
or less size range. The surface-to-volume ratio between large
particles and those of an inch or so in size is not greatly
different. However, diffusion limitations are intimately related
to grain size and matrix uniformity, and the time scale is
proportional to the square of the length scale. Size reduction
may also cause changes in surface chemistry, redox conditions and
availability of reaction sites.
One practical way to limit the size problem in batch tests
is to mill or crumble wastes which do not have strengths
appreciable enough to survive in the environment. Accurate
predictions of leaching potential from wastes with intermediate
strength may be better handled by subjecting them to sequential
leaching accompanied by sequential particle size reduction. At
the other extreme, exceptionally durable materials are best
handled by leaching in an "as is" condition. Column tests,
provided that channel effects are minimized or eliminated, are
more amenable to testing wastes "as is" with respect to waste
matrix size than are batch tests, secondary tests which evaluate
strength in waste management environments include, for example,
the Toxicity Characteristic (TC) structural integrity test,
unconfined compressive strength, freeze-thaw (ASTM Method 4843-
88) and wet-dry (ASTM D4842-89) tests. Most batch leachate tests
require wastes to be tumbled. It has been shown that if wastes
are tumbled "as is", those which are not strong enough to survive
in the environment will, in fact, break up during tumbling, while
only strong materials will survive and remain intact (Bone et al,
"Modification of the TCLP Procedure to Accommodate Monolithic
Wastes," Fifth Annual Waste Testing and Quality Assurance
Symposium, July 24-28, 1989). Additional testing may be
necessary to determine whether the stabilized waste will remain a
monolith under varying environmental conditions. Thus it is
generally best to limit sample size reduction even in batch
tests.
12
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4) Leach test conditions (stresses) appropriate to the
situations being evaluated should be used for assessing long-term
contaminant release potential.
The best way to estimate the extent of contaminant release
from a waste matrix of interest is to have a test that reflects
realistic field conditions (Table 3, page 27). However, the
regulatory and statutory framework for decision makers often
seems to require that estimates be made for the maximum potential
for contaminant release in a specific scenario (Table 2, page
25). This involves testing under extreme conditions or stresses,
employing physical parameters such as fine particle size,
temperature and pH set at high contaminant solubility, high ratio
of leaching fluid to sample, high degree of mixing, and long
fluid/particle contact time. But, while it may seem necessary
from a regulatory and compliance perspective to use maximums in
leach tests, every effort should be made to design realistic
tests which simulate those actual worst case field leaching
conditions that can be reasonably postulated to occur at some
frequency in relevant waste management conditions.
In order to adequately characterize any particular field
scenario for leach tests, the relevant environmental conditions
postulated, and the degree to which they should be applied to
samples undergoing contaminant release testing, should be
carefully established and should take into consideration the
nature of the regulatory decisions that are required. Moreover,
any extrapolation of a set of conditions or stresses appropriate
for one purpose should not be applied for other applications
without reasonable verification of relevance. Extrapolation of
tests designed for one purpose to another purpose should be
scientifically defensible. A suggested approach to development
of an array of leach tests follows:
a) First, identify the set of regulatory decisions that
will be made with the test results.
The decision set could include (but is not limited to): (1)
a decision whether or not a waste should be classified as
hazardous; (2) the extent of leaching from a large volume waste
in order to determine suitability for waste utilization or
alternative management with or without restriction; (3) a
determination of release potential to support an estimate of risk
to human health or the environment; (4) a determination of
solidification/stabilization effectiveness to provide a basis for
a containment design; and, (5) selection of containment,
treatment or remediation technologies.
b) Convene a panel of individuals that represent a cross-
section of the regulatory community, the regulated community,
academia, and environmental/public interest groups for the
13
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purpose of defining the array of conditions for each type of
test.
Inputs should be sought from the broad technical (expert)
community/ for example, ASTM committee D-34 on Waste Management
and other technically credible groups of scientists, engineers
and practitioners in the field. Consideration should be given to
obvious stress factors such as: the appropriateness of sample
size reduction, leaching fluid pH and buffering capacity,
leaching temperature, waste-to-leaching fluid ratio, number and
sequence of leaching steps, contact time, agitation mode,
biological action, and exposure to freeze/thaw as well as wet/dry
cycles.
c) Develop a hierarchial framework for reasonable stresses.
The set of possible stresses can be ranked from moderate to
severe, and identified with appropriate regulatory decisions,
depending on the conditions to which they are applied and the
importance of the decisions.
Using the above rationale, as the need for a new decision is
identified, its placement within and relevance to the decision-
making framework of prescribed stresses (and extant leach tests)
should be clear. While some procedures must be developed to make
decisions in direct compliance with regulations, and require
either site-by-site or type of application assessments, this
recommended exercise could help to avoid the inappropriate
application of a leach test or related test that has been
developed for another purpose.
5) Laboratory leach tests should be field-validated, and
release test accuracy and precision established before tests are
broadly applied.
Numerous tests have been developed by the EPA, ASTM and
others in order to estimate contaminant release and subsequent
transport through soil matrices (Table 1, page 20 and Appendix C,
page 35). Some of the test methods have been subjected to
extensive precision studies involving multiple laboratory samples
and analysis, while other tests have clearly only been subjected
to minimal or very limited evaluation, as in single laboratory
precision studies. Furthermore, the accuracy of leaching test
results has not been, for the most part, subjected to field
verification. Anecdotal evidence suggests that the accuracy and
reliability of laboratory test results for field application are
questionable, primarily due to the simplifications or
approximations utilized. In principle, the accuracy and
precision of contaminant release predictions can be improved by
matching the controllable test variables more closely to the
environmental conditions that actually are encountered under
field conditions. But it is questionable whether many leaching
14
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tests are adequately predictive of some reasonable worst case
scenarios.
The number and types of analytes for which the tests have
been evaluated and applied are likely to evolve continuously.
Currently/ all of the tests are designed for metals/ semi-
volatile, and non-volatile organics, and only a few are valid for
volatile organics. Consequently, there are considerable data to
determine the precision of the tests for metals. This is
fortunate, since metals leachability is much more sensitive to
factors which are difficult to control, such as pH, ionic
strength and particle size. Thus, in view of current knowledge
about metals leachability, much can be inferred about the
fundamental processes involved in leaching of inorganic
constituents from wastes.
As was suggested in the SAB EEC Leachability Workshop and
technical briefing of Hay 9, 1990, review of the reliability and
precision of metals leachability test results leads the
Subcommittee to conclude that test precision is probably
satisfactory, particularly in comparison to the reliability of
test methods and variables associated with other factors which
are used in conjunction with leachability to arrive at
environmental risk assessments. Although the precision of any
test used for regulatory decisions or environmental risk
assessments should always be evaluated, test accuracy is more
important than test precision.
The state of scientific capability for leaching test
interpretation indicates that, in order to provide a realistic
estimate of the leachability of a specific waste in a given
environment, site-specific conditions must be fully considered.
Consideration must be given to all factors that have the
potential to impact leachability in either a positive or a
negative fashion. For example, cosolvent effects can greatly
facilitate the movement of contaminants out of the waste matrix,
while biological activity can increase or decrease the release of
contaminants as well as transform contaminants prior to their
release into the environment.
Therefore, the Subcommittee recommends that, through the
Office of Research and Development, EPA carry out a comprehensive
"field validation" of leaching tests and establish laboratory
accuracy and precision. The results should then be factored into
guidance for the improvement of leaching tests.
6. More and improved leach models should be developed and
used to complement laboratory tests.
Unlike the advances in models for transport and fate
predictions, development of mathematical models to predict
contaminant leaching is in its infancy. Only a small number of
15
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"leachate generation" models are proposed (e.g./ HELP, FOWL,
UNIFAC), and to date these have had limited use.
While various laboratory tests can, in principle, be used to
physically "model" a contaminant release scenario, more and
improved "mathematical" models for leaching predictions should be
developed and employed to complement laboratory tests.
Simple equilibrium (or as warranted, more comprehensive
dynamic) models could be utilized to analyze data obtained from
various leaching tests. These investigations could then be used
to evaluate the applicability of such models as a leach test
adjunct, or in more direct application, as an approach to
estimating field leachability.
Contaminant release and transport models currently play an
important role in the Agency's regulatory decision-making
process. For example, the HELP model is used in the delisting
regulation to project hydraulic flux through landfills. Further,
the HELP model, in conjunction with the EPACML, is used to
predict the dilution attenuation of contaminants from the bottom
of a landfill to the nearest well. This and other models hold
the promise of significant utility if: (l) they are sufficiently
comprehensive and reliable for predicting the transport and fate
of contaminants of concern; and (2) the data base necessary
(including leachate composition) for model use is adequate and
reliable. These criteria limit the conditions under which a
model can be applied.
Potential pitfalls in the use of models should be examined
prior to their application, to ensure that their results are
reliable (Refer to the SAB Resolution on Use of Mathematical
Models by EPA for Regulatory Assessment and Decision-Making (EPA-
SAB-EEC-89-012), January 1989). Generally, such a review can
proceed consistent with principles outlined in prior SAB
deliberations on the generic use of models. Examples of concern
to be addressed include: Agency over-reliance on models to the
exclusion of the acquisition of needed data; the extent to which
models are based on a fundamental representation of the relevant
physical, chemical and biological processes that can affect
environmental systems; the extent to which models have been
validated with laboratory and field data; the analysis of
sensitivity and uncertainty impacts on models and model
predictions; and, the need to ensure adequate peer review of
model development and utilization. In circumstances where
laboratory and field data fail to confirm the adequacy of a
model, it is inappropriate to use the model for decision making
until improvements of an acceptable nature can be implemented.
Laboratory and field tests should be utilized to establish
the conditions under which model simulations can be used to
extrapolate laboratory and field data. A model should not be
16
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used to predict leachability or transport in scenarios that are
outside the scope of the model applicability.
The sensitivity of a model to specific input data parameters
should be established; this indicates the level of effort needed
in the determination of the parameters for model evaluation.
Pertinent questions include: How accurate should the input data
be? Can input data be estimated by analogy rather than obtained
from actual field measurements? Following these judgments, an
appropriate data base can be developed for a model input.
Analysis should attempt to identify whether a different
outcome might have been realized had more representative data
been available, i.e., the expected model outcomes associated with
varying degrees of data uncertainty should be established.
Consistent with input data requirements, a model can then be used
to predict leachability behavior in a specified field scenario.
7) To facilitate the evaluation of risk implications of
environmental releases, the Agency should coordinate the
development of leach tests and the development of models in which
the release terms are used.
Leaching tests characterize the "source terms" for transport
and fate models. Yet almost all transport and fate models assume
that leachates are of constant concentration and of infinite
duration and quantity. In reality, source terms (leachates) are
a function of time, space, waste properties, and leaching fluid
characteristics.
Numerous models presently are available to describe the
transport of chemicals through porous material, including both
the saturated and unsaturated zones. The hydrologic or fluid
flow models (such as EPACML, HELP) could be improved to consider
the chemistry and microbiology of contaminant release within the
source waste matrix. The resulting leaching predictions would
then be dynamically included in the transport analysis. The
Subcommittee recommends that models used by the Agency be
modified to couple source leaching masses with the transport and
fate predictions. Such linked models would more accurately and
precisely predict environmental concentrations to quantitatively
evaluate risk implications, albeit at the cost of greater
computational and data collection effort.
8) The Agency should establish an inter-office, inter-
disciplinary task group, including ORD to help implement these
recommendations and devise an Agency-wide protocol for evaluating
release scenarios, tests, procedures, and their applications.
The task group should also be charged with recommending what the
appropriate focal point(s), responsibilities, and organizational,
budgetary and communication links should be within the Agency for
the most effective, continued and ongoing support and pursuit of
17
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tbe research, development and utilization of methods and
procedures.
The Subcommittee's discussions on Agency "needs" with the
various program offices pointed out that a variety of
applications and regulatory decisions depend on appropriate
"release" tests and waste matrix transport and fate analyses
(Table 2, page 25 and Appendix C, page 35). Therefore, it is
recommended that an inter-office, inter-disciplinary task group
be established to aggressively formulate implementation plans for
the development of scientifically defensible leaching tests and
models for the many contaminants and applications. This task
group should include experts in the field of hydrology, soil
science, analytical chemistry, environmental chemistry and
biology, mathematical modeling and environmental engineering.
9) Core research on contaminant release and transport
within the waste matrix is needed.
Consonant with the underlying concept of EPA's core research
initiative and its intent to provide and sustain knowledge and
expertise responsive to both current and future risks to human
health and the environment, it is apparent from the preceding
discussions that issues associated with leachability, and
specifically methods to adequately measure and predict leaching
from an assortment of waste matrices, are and should remain a
priority focus.
Unfortunately, consensus with respect to the use of
leachability testing protocols has yet to be attained. It
appears that methods currently advocated neither fully satisfy
short-term or long-term needs, nor do they withstand the rigors
of scientific scrutiny to an extent that scientifically
supportable management decisions can be made.
Therefore, the present state-of-knowledge concerning
leaching phenomena under a broad range of waste management
scenarios of regulatory and scientific interest should be fully
analyzed and reported. Based on the outcome of this task, an
integrated, active program of research, including exploration of
potential and actual risks associated with leaching of
constituents, should be developed.
The core research program regarding leachability should
embrace, to the maximum extent feasible, all underlying issues
pertinent to leachability. This should include, but not be
limited to the following: basic mechanisms, potential test
procedures, analytical methods, predictive model development,
performance standards, and regulatory initiatives. Accord-
ingly, a complementary understanding of the scientific and
operational issues of various waste management options, as well
as the intricacies of the associated environmental settings, is
18
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required. For instance, a possible approach may be to develop a
waste management matrix which defines both current and potential
future treatment, storage, use or disposal practices and
associated environmental circumstances, and then develop
companion testing protocols to simulate each situation. These
tests should consider the operational phase as well as the pre-
installation and post-closure periods.
Such an approach as recommended above should provide
better correspondence between the results of testing protocols
intended to simulate actual conditions under both short-term and
long-term conditions. Whether these objectives can be
accomplished with laboratory, pilot or field-scale simulations
would be part of the challenge of the core research initiative.
However, it could be anticipated that both short-term or
accelerated screening and long-term field-scale simulations may
need to be developed as an essential adjunct to each selected
waste management alternative. The ultimate goal would be to
provide operational as well as regulatory (and remedial) control,
thereby enhancing the potential for more meaningful assessments
of environmental and health risks.
19
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24
-------
TABLE 2 - TEST REQUIREMENTS, USES OF TESTS, AMD PROGRAMATIC
BEDS FOR LBACHABILITY TESTS BT THE AGENCY
AS PERCEIVED BT THE SCIENCE ADVI8(
ENVIRONMENTAL ENGINEERING COMMIT
PROGRAM OFF
TEST REQUIREMENTS 8F BC O8W OTS
Simple method O X X O
Field Analoa
Model Source Term
Predict Leaching
Method Validation
TIE Compatible
Surface Water Interface
Mismanagement Predictor
Waste Classification
"No Reasonable Risk"
Determination
USES OF TESTS
Demonstrate Federal/
State Compliance
Simulate Risk
Set Standards
Compare waste
Management strategies
Compliance/
Clean-Up Goals
Examine "Worst Case"
ADDIV to Human Health
Identify Toxicants
New Product Information
Establish "Equivalency"
To Thermal Destruction
Evaluate Lined and
unlined Units
X X O
X O X
X X
X X
X
X X 0
XXX
XXX
XXX
XXX
X 0 X
X 0 X
X O O
x x
O X O
O X X
X X
O
O
O
O
X
X
X
X
X
X
O
O
O
X
X
X
O
)RY BOARI
TEE
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O
O
X
X
X
O
X
X
O
O
X
O
O
O
X
O
X
O
D'S
OMMQA
X
O
X
X
X
O
X
X
O
X
X
O
X
X
x
O
X
0
0
O
25
-------
TABLE 2 - (Continued)
PROGRAMATIC MEEDS FOR TESTS 8F BC OSW OT8
Flexibility X X o
Multiple Tests
Standardized Protocols
Compliance
Remedial Design
Biological Response
Matrix Data
EP/TCLP
Acid Rain Leachina
Multiple Extraction
Oily Waste Extract
Equivalent Tests
Non-Destructive Tests
X X
X
X X
X 0
0 X
X X
X
0 O
0 0
0 0
0 0
o
X 0
X X
o o
0 0
X O
X O
X
X X
X X
X
0
RSKERL
o
X
o
X
X
o
X
X
X
X
X
o
OMMQA
O
X
o
X
o
o
X
o
o
X
X
o
o
* SF = Super fund Program, us EPA
SC = Office of Water, Sediment Critria Program, US EPA
OSW = Office of Solid Waste, US EPA
OTS = Office of Toxic Substances, US EPA
RSKERL = R.S. Kerr Environmental Research Lab, US EPA
OMMQA = ORD/Office of Modeling, Monitoring, and Quality
Assurance, US EPA
X = Yes, a Blank Signifies No
0 = Sometimes or Occasionally
26
-------
TABLE 3 - SCIENTIFIC CONSIDERATIONS IN DESIGN AND
INTERPRETATION OF LBACHABILITY TESTS
1.
PROPERTIES/CHARACTERISTICS
Source Matrix ProDerti.es
Matrix properties affect availability
and accessibility of contaminants.
Chemical composition (functional Relates to containment and leaching
groups/ carbon content/ etc.) environment.
Morphological structure
(amorphous vs. crystalline)
Surface area (surface-to-
volume ratio)
Surface physics (e.g./ charge,
tension)
Matrix heterogeneity
Pore structure (volume/
distribution)
Pore liquid volume (degree
of saturation)
Pore liquid composition
Permeability
Ease of saturation (time/
pressure required)
Pooling (micro- and macro-
reservoirs, field capacity)
Biodegradability
Toxicity
Affects access and containment.
Determines interface for sorption;
can affect pH.
Controls access and flow in the
pores matrix.
Creates morphological and chemical
differences.
Constricts flow, retains gas/
serves as "small" reactor.
Contributes to effective leachate
volume.
Modifies leachate composition.
Affects flow regime and residence
time.
Leachant/waste interface may be
limited by the rate and extent of
saturation.
Extracting fluid ("leachant") and
leachate retention; provides in
situ reaction opportunity.
Matrix can change properties due
to biodegradaton.
May limit biodegradation of the
contaminants or matrix property
changes.
27
-------
TABLE 3 (continued)
PROPERTIES/CHARACTERISTICS
Buffer capacity
Chemical composition
Concentration
Toxicity
Biodegradability
Heterogeneity
Diffusivity
Solubility
Volatility (boiling point,
Henry's constant)
3. Leach?Tit Properties
Initial chemical composition
Aqueous/non-aqueous
Availability of buffer capacity
affects leachability and diffusion,
and regulates efficiency and
nature of biodegradation.
Leachability is a function of the
nature of the contaminants.
Different chemicals or the same
contaminant in a different
physical or chemical form
exhibit distinct differences
in leachability.
Concentration gradients affect
leaching rate and equilibria.
Reduces efficiency of concurrent
biotransformation.
Compound structure and environmental
conditions affect biodegradability.
Affects containment and availability
for reaction and/or leaching.
Determines transport via diffusion.
May affect mass transport and limit
removal and/or reaction.
Controls liquid/vapor phase transport
and loss of contaminants during
leaching and analysis.
Leachant properties control
solubilization/dissolution and mass
transport processes.
Could contain contaminants, may be
aggressive, may change as the
leaching process proceeds.
Normally water (distilled, tap, or
site) as modified by test protocol.
28
-------
TABLE 3 (continued)
PROPERTIES/CHARACTERISTICS IMPORTANT
TEST RAMIFICATIONS
Hydrophobi c-hydroph i1ic
nature **
Gas (oxygen, carbon dioxide
content, etc.)
Density
Buffer capacity
viscosity
pH
Flow gradient
Flow regime (laminar vs.
turbulent)
Surfactants or hydrophobia solvents
could enhance leaching.
Affects pH and nature of biological,
physical and chemical interactions.
Contributes to hydraulic gradient
effects and hydraulic conductivity.
Controls pH change.
Affects flow regime, saturation, and
hydraulic conductivity.
May or may not control the leaching
process.
Fluid dynamics in a given system
dictate contact time and opportunity,
which affect reaction extent and mass
transfer. Fluid dynamics have
important ramifications to the
selection of leaching mode, e.g.,
continuous column, batch, sequential
batch; equilibrium (intended to
represent specific, worst case
scenarios), non-equilibrium; dynamic
(mixed), static.
Affects transport of contaminants by
dispersion, convection, and
advection. Also affects mechanism of
mass transport. Agitation may be
used to generate a maximum gradient.
Flow path could lead around or
through the waste, cracks or inter-
connected pores would short-circuit
flow.
Affects contaminant transport and
gradient. Restricts the applica-
bility of Darcy's Law.
** NOTE: This is also a contaminant characteristic which determines
affinity to leach or to be bound in a matrix.
29
-------
TABLE 3 (continued)
PROPERTIES/CHARACTERISTICS
Flow pattern (intermittent vs
continuous)
5. System Properties
Precipitation/dissolution/
reprecipitation
Solubilization (capacity,
limits)
IMPORTANCE AMD TEST
Could weather and/or disintegrate
waste matrix. Impacts on the
concentration gradient and
transport.
Operationally determined by the
leachant/waste interaction.
Potential removal/release process,
Ability to remove contaminants by
dissolution.
other chemical reaction and
reversibility
Complexation
Sorption/desorption
Partitioning
Cosolvency
Common ion effect
Redox environment
pH
Temperature
Mass transfer or equilibrium
limitations
May change contaminant behavior
and/or structure.
Affects transport, solubilization
and possible surficial binding
of metals and organometallic
compounds.
Contributes to the retention or
removal of solutes.
Affects equilibrium opportunity and
spatial and temporal distribution.
Enhanced removal by solvent
mixtures, affects distribution
of solutes.
Could delay the removal of contamin-
ants associated with more than one
anion.
Could affect opportunity for biolog-
ical or chemical transformations
and reactivity.
Major influence on biological,
physical and chemical transformation
processes.
Affects reaction rates, solubility,
pore pressure, etc.
Need to determine which dominates.
30
-------
TABLE 3 (continued)
)PERTIE8/CHARACTERISTIC8 IMPOI
6. Temporal/Spatial Dependence
Contaminant recharge
Temporal and spatial limitations may
accelerate or retard leaching.
Important element of tests involving
site-specific simulations.
Aging dynamics
Weathering effects (dis-
solution surface washing,
vet/dry, freeze/thaw)
Physical and chemical properties may
change in time.
Long-term humidity and temperature
changes affect matrix integrity.
Biodegradability
Barometric fluctuation
Leachant volumes (contact
time)
7. Monitoring methods
Precision/accuracy (overall)
Environmental sampling,
sample preservation/holding
time (environmental samples
and leachate test samples)
Leaching test
Leachate preservation/storage
Aerobic and anaerobic transformation
of and within the matrix.
Impact gradients, dispersion,
and groundwater movement, and
behavior of gases and volatiles.
Major consideration when selecting
the leachant/waste (or source
matrix) ratios. Leachant/source-
matrix interface over an extended
period of time could result in the
depletion of the contaminant or in
the erosion of the matrix.
Method of monitoring could influence
the test and their results.
To be defined by the data quality
objectives.
Affects results; plans and standards
may be available.
Selected in accordance with
objectives. Considers time,
environmental conditions, and
site specifity.
Sample components change with time.
31
-------
TABLE 3 (continued)
PROPERTIES/CHARACTERISTICS
Analytical (sample preparation
and test method)
Testing schedule (time)
Reproducible, specific, and efficient
methods are available. Analytical
procedures need to be appended with
appropriate protocols.
Could affect reproducibility,
interpretation, and comparability
of data.
8. Physical Modeling
Comparability with scenario
to be simulated
Congruence with scenario
Similar in form and arrangement.
Governs applicability of results,
32
-------
APPENDIX A - BACKGROUND ON LEACHABILITY AS A
SELF-INITIATED ACTIVITY OP THE
SCIENCE ADVISORY BOARD
Over the past decade, the Environmental Engineering Committee
(EEC) of the Science Advisory Board (SAB) has reviewed a number of EPA
subjects and issues involving leachability phenomena either as a major
or minor factor in the review. In these various reviews, the Committee
has noted a number of problems and issues, relating to leachability
phenomena that were common to a variety of programs, rules and Agency
procedures. The Committee believed that these common problems and
issues, would be best called to the Agency's attention through a
general set of recommendations on leachability phenomena, rather than
in the specific, individual reviews.
Believing that the scientific principles of contaminant
leachability need broader understanding and exposition, the EEC has
undertaken the initiative, with the concurrence of the Executive
Committee, to conduct this self-initiated review to:
1) Consider the fundamental scientific principles that can
reliably describe contaminant release/transport. In particular, to
consider the controlling characteristics of the source, the leaching
media and the importance of dynamic considerations; and
2) Suggest how the scientific principles can be applied to
determine how a waste will leach when present in the environment,
according to a prescribed scenario.
The Leachability Subcommittee (LS) was formed by the EEC. The
group convened a project scoping and planning session in Houston, Texas
on December 15-16, 1989, immediately following a Workshop related to
this topic. The LS then followed this with a one-day session in EPA's
Headquarters Office in Washington, D.C. on February 26, 1990, devoted
to assessing the Agency's varied needs for leachability-related
information. The day's activities and findings were then discussed
with the full EEC on February 27, 1990. This was followed by a
Workshop on Leachability on May 9, 1990 in Washington, D.C. The
Workshop was conceived as a vehicle for distinguished scientists,
engineers and practitioners in the field to focus on the scientific
principles and issues relating to leachability phenomena. The Workshop
was video taped, so that those unable to attend from EPA or any other
interested parties could have the benefit of this exchange of
information.
The Leachability Workshop assisted the LS of the SAB's EEC to
better define the fundamental scientific principles that control
leachability. Further, the workshop assisted the SAB and the attendees
in ascertaining how leachability phenomena and tests can be applied on
an appropriate and consistent basis to determine how a waste will leach
when present under various scenarios in the environment.
33
-------
APPENDIX B
LEACHABILITY WORKSHOP PROGRAM
May 9, 1990
Welcome and Administrative Remarks Dr. C.H. Ward
Mr. Richard A. Conway
Statement of Issues and Needs Dr. Raymond C. Loehr
Test Methods: Descriptions, Dr. Pierre C6te'
Capabilities, Organics-Inorganics
Leaching of Stabilized Materials Dr. Paul Bishop
Physical-Chemical Mechanisms: Dr. Marvin Dudas
Concepts on Interactions of Solids-
Liquids, Liquid-Liquid, Solids-
Liquids-Gases
Technical Problems and Challenges Mr. Robert L. Huddleston
for Regulators and the Regulated
Leaching Chemistry of Inorganics Dr. John M. Zachara
Leaching Chemistry of Organics Dr. P. Suresh Rao
Alternative Approaches to Dr. Carl Enfield
Laboratory Tests (Modeling)
Concluding Remarks Dr. C.H. Ward
Dr. Ishuar P. Murarka
CONVENERS AND SPEAKERS
Dr. C.H. Ward, Chairman, Leachability Subcommittee, Rice University, Houston, Texas
Dr. Ishwar P. Murarka, Vice-chairman, Leachability Subcommittee, Electric Power Research Institute, Palo Alto, California
Mr. Richard A. Conway, Chairman, Environmental Engineering Committee, Union Carbide Corporation, South Charleston,
West Virginia
Dr. Raymond C. Loehr, Chairman, Science Advisory Board, University of Texas, Austin, Texas
Dr. K. Jack Kooyoomjian, Designated Federal Official, US EPA, Science Advisory Board
Dr. Donald G. Barnes, Director, US EPA, Science Advisory Board
Mr. A. Robert Flaak, Assistant Staff Director, US EPA, Science Advisory Board
Dr. Pierre Cote1, Zenon Environmental, Inc., Burlington, Ontario, Canada
Dr. Paul Bishop, University of Cincinnati, Cincinnati, Ohio
Dr. Marvin Dudas, The University of Alberta, Edmonton, Alberta, Canada
Mr. Robert L. Huddleston, Conoco, Inc., Ponca City, Oklahoma
Dr. John M. Zachara, Battelle Pacific Northwest Laboratories, Richland, Washington
Dr. P. Suresh Chandra Rao, University of Florida, Gainesville, Florida
Dr. Carl Enfield, R.S. Kerr Environmental Research Laboratory, Ada, Oklahoma
34
-------
APPENDIX C - LEACHABILITY HEEDS, USES, TESTS. CONCERNS, AND ISSUES
C-1 - SUPERFUND REMEDIAL AND REMOVAL PROGRAMS
MEED FOR USE OF LEACHING TESTS USES OF LEACHABILITY AND LEACH TESTS
Need to comply with Federal and State laws that are
applicable, or relevant and appropriate (e.g.,
RCRA)
- Need to approximate real world conditions
- Need for methods which provide input to groundwater
modeling
- Need for standardization of Leaching methods
(including Kj for specific applications and data uses
Need for methods development for predicting long-term
Leaching potential
- Need for validation of Leaching methods
- Leaching, extraction and other chemical test are
typically needed to provide a variety of data on
either untreated or solidification/stabilization
(S/S)-treated wastes for the following purposes:
- To identify principal threats which indicate
mobility of contaminants (e.g., in untreated
or S/S-treated waste) when they are in the
environment (e.g., in contact with leaching
medium and each other)
- Determine compliance with regulations, such as
CERCLA, RCRA (e.g., if Land ban BOAT has been met)
- To show that reduction in mobility of the hazardous
components has been achieved between untreated and
treated wastes, or that treated waste is protective
(i.e., that it meets National Contingency Plan
expectations, such as passing a specific test, such
as the TC test)
- To assess the effectiveness of a technology (e.g.,
S/S technology)
- To estimate source terms and/or boundary conditions
for ground-water modeling
- To look for "hot-spots," and in many cases, locate
with model instead of acquiring (sometimes
extensive) data
- To demonstrate compliance with Federal and State
Laws (e.g., RCRA, TSCA, etc.)
- To model risk to:
- Assess potential for groundwater and surface
water contamination
- Establish clean-up standards
- Selection of Remedy:
- To differentiate among various waste management
regimes for modeling and assessing risk
- In situ management/disposal (modeling)
- Delisting
- To ensure that waste management alternatives
address environmental concerns
- To predict long-term environmental behavior (e.g.,
such as for "mixed11 waste, radioactive, RCRA
hazardous waste, debris and/or large objects)
- To determine chemical characteristics of wastes
- To identify possible interference with treatment
(e.g., immobilization)
- To evaluate treatment (e.g., treatment residuals)
compliance with clean-up goals
- Input data to modeling, such as fluxes into
saturated zone (e.g., ANSI 16.1)
- For organics, such as immoble constituents. Low
concentrations to examine:
- "Worst case" Leaching
- Total waste extraction
- Non-polar solvents for PCB's
35
-------
C-1 - SUPERFUND REMEDIAL AND REMOVAL PROGRAMS (Continued)
TYPES OF DATA REQUIRED, SPECIAL CONCERNS, ISSUES AND
CONSTRAINTS (e.g.. variables that can affect test
results.)
- Super-fund allows flexibility in choice of
teachability test based on site specific
conditions and needs
- National Contingency Plan (NCP) outlines program
goals and expectations which drive the remedy
selection process. Some of the expectations are:
- EPA expects to use treatment to address principle
threat wastes (e.g., highly toxic, mobile, etc.)
- EPA expects to use engineering controls (e.g.,
containment) to address wastes which pose a
relatively low long-term threat or where
treatment is impracticable
- EPA expects to return usable ground waters to
their beneficial uses whenever practicable
- Parameters that can affect test results include:
- Sample heterogeneity
- Curing time
- Liquid-to-solid ratio
- Extraction time, number and frequency
- Leaching medium
- Superfund is unique in that the program can use
flexibility on a site-by-site and case-by-case
technical basis for selection of remedy:
- Additional goals in the NCP aim to treat waste
that are the principal threat (e.g., highly
mobile, toxic, etc.)
Probably will not excavate and treat non-mobile
wastes which are not the principal threat
- Generally, there is an expectation goal to
reduce toxicity, mobility and volume of the
waste by 90X to 99X (whether or not this
presumption is valid)
- Superfund may use multiple tests. Various leach
tests (e.g., 18 hours versus 90 days or more) are
employed. There is a large variety, depending on
the waste and the disposal scenario:
- The more agreement and consensus on appropriate-
ness of tests, the more important are the tests
to the program (e.g., decisions in New Jersey
and California should be consistent.)
Superfund waste removal activities have more
flexibility than remedial activities. However,
the science and technical decisions must withstand
scrutiny.
- For Superfund, RCRA protocols may not be
appropriate because:
- The Superfund application is a different
purpose than for what the RCRA protocol
was originally devised.
- Lack of standardized protocols in Superfund
- Many methods exist with a lot of variability
- Technical uncertainty on making sense of the
varied forms of data to make a decision.
TYPE OF TESTS
- Note that all treated wastes (not just solidified/
stabilized (S/S) treated wastes) need to be evaluated
to determine how protective they are in specific
management scenarios
While Superfund program must comply with Federal
and State regulatory requirements (e.g., RCRA TCLP
methodology), other tests may be utilized to
approximate real world conditions. Single or multiple
methods may apply to a site. Additional methods may
include the following listed below:
- Short-term extraction tests (hours to days)
- Leaching tests (weeks to years)
- Column Leach Test
- EP (Method 1310) (was used in the past, but is
superseded by the TCLP)
- TCLP (Method 1311)
- TCLP with cage modification (This has never been
promulgated and appears to have reproducibility
problems)
- California Waste Extraction Test (Cal WET)
- Multiple Extraction Procedure (MEP)
- Synthetic Acid Precipitation Leach Test
- Hoooffiled Waste Extraction Procedure
(Method 1312} (MWEP)
- Materials Characterization Center Static
Leach Test
- American Nuclear Society Leach Test
- Dynamic Leach Test (DLT)
- Shake Extraction Test
- Others
36
-------
C-2 - OFFICE OF WATER. SEDIMENT CRITERIA PROGRAM
HEEDS FOR USE OF LEACHING OR OTHER TESTS
Simple methods that can be simply used by field
people for all types of sediment and water
environments to address the toxicity of sediment:
- Need for an in-the-field practical method where
each method is not turned into a "research project"
- The AET (Apparent Effects Threshold) method uses
a preponderance of evidence approach
- The AET method has no relevance to sediments
that are exposed to leaching conditions
- Addresses the toxicity of in-place sediments
Methods to provide sediment criteria decisions to
evaluate the following:
- Most likely scenario
- Methods to be applicable to human health, aquatic
life or wildlife protection
Ability to generate numerical criteria for
specific chemicals
Toxicity Identification Evaluation (TIE) procedures
to identify and quantify chemical components
responsible for sediment toxicity, such as:
- Techniques for the identification of toxic
compounds in aqueous samples containing
mixtures of chemicals
- Interstitial water toxicity method TIE procedures
are implemented in three phases to evaluate:
- Pore water toxicity,
- Identify the suggested toxicant, and
- Confirm toxicant identification.
USES OF LEACHABILITY AND LEACH TESTS
- Sediment criteria decisions for:
- Applicability of method to human health, aquatic
life or wildlife protection
- Predicting effects on different organisms
- Suitability for in-place pollutant control
- Suitability for source control
- Suitability for disposal actions
- Suitability for different sediment types
- Suitability for different chemicals or classes
- Ability to generate numerical criteria for
specific chemicals
- Toxicity Identification Evaluation (TIE) potential
uses:
- Use of pore water as a fraction to assess
sediment toxicity
- In conjunction with TIE procedures, can provide
data concerning specific compounds responsible
for toxicity in contaminated sediments
- Ability to identify specific toxicants
responsible for acute toxicity in contaminated
sediments
37
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C-2 - OFFICE OF UATER. SEDIMENT CRITERIA PROGRAM (Continued)
TYPES OF DATA REQUIRED, SPECIAL CONCERNS. ISSUES AND
CONSTRAINTS (e.g., variables that can affect test
results.)
- Types of data required:
- Biological response data (either acute or
chronic)
- Choice of Test Organism
- Practical concerns of method choices:
- Ease of use
- Relative cost
- Tendency to be conservative
- Level of acceptance
- Ability to be implemented by laboratories with
available/typical equipment and handling facilities
- Degree to which results lend themselves to the
following:
- Interpretation
- Environmental applicability
- Accuracy and precision
- Concern for leaching of hazardous substances or
hazardous materials to food, plants, groundwater
and sediment
- Concern for monofilling and impacts on groundwater:
- There are differences in sorptive capacity
(reductions) observed in monofill versus an
increase in sorptive capacity in well-aerated soil
(plow zone)
- Groundwater to surface water issues
- All current sediment criteria development efforts
address the toxicity of in-place sediments. As a
result, research activities have not focused on what
happens to sediment-bound chemicals when exposed to
leaching conditions:
- Some research suggests that for non-ionic organic
contaminants, the presence of organic carbon in
leaching materials may be responsible for some
binding of contaminants, as well as mobility
- For metals, it is possible that the leaching
conditions might provide for the release of
significant levels of metals, because of the
expected reduction of the acid volatile sulfide
(AVS) content of many sediments
- AVS binds up significant levels of metals and
is lost when exposed to oxidizing conditions
TYPE OF TESTS
Aeration tests
Bioassays
Equilibrium Partitioning Approach
Solid phase extraction tests
Graduated pH test
Filtration tests
Reversed phase, Solid Phase Extraction
(SPE) tests
Oxidant reduction test
EDTA addition test (The EDTA - Ethylene
diamine tetraacetic acid test)
Hollow block with a semi-permeable
membrane, which is inserted into the
sediments
38
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C-3 - OFFICE OF SOLID IUSTE
NEEDS FOR USE OF LEACHING TESTS:
Statutory requirement of RCRA to look at
reasonable worst-case mismanagement and
maintenance scenarios to assess:
- Landfill scenarios (sanitary and monofill)
- Maintenance scenarios
- "Mismanagement" scenarios
- Acid leaching scenarios
- Pump and treat systems
- Effect of covers
- Effect of Liners
To characterize the leachate source term, such as:
- Finite versus infinite source of waste
- Effect on leachate quantity
- Effect on leachate quality
To determine if a waste is hazardous or non-
hazardous. (Such determinations are built into
RCRA.):
To determine how a particular material needs to be
managed:
- Need a decision-making tool to evaluate
teachability
- Need to examine various scenarios and their
validity
USES OF LEACHABILITY AND LEACH TESTS:
To model and simulate risks
To assess risks
To direct regulatory decisions
To come to grips with the complexities of
teachability phenomena (i.e., the source term itself
is very difficult and complex)
To answer questions pertaining to what kind of
contaminant levels are appropriate to be left in the
soil or removal from the soil (e.g., clean closure)
TYPES OF DATA REQUIRED. SPECIAL CONCERNS,
ISSUES AND CONSTRAINTS (That is, variables
that can affect test results.):
- Factors affecting teachability include, but
are not necessarily limited to the following:
- Size of materials
- Permeability of solid
- Time dependency of leaching
- Contact time (a crucial issue_
- Type of contact (tumbling versus stirring)
- Ratio of leaching fluid to waste (i.e.,
solubility versus mass-limited; also,
infinite source versus finite source)
- Changes in the waste itself (e.g., due to
biodegradation, chemical changes, anaerobic
versus aerobic, hydrology, and climate
changes)
- Issue of scenarios where organics may be
bound better under acid, rather than neutral
or basic circumstances (Many industrial
landfills are highly on the basic side)
TYPE OF TESTS
- EP (Extraction Procedure) (Method 1310)
- TCLP (Toxicity Characteristic Leaching
Procedure) (Method 1311)
- TCLP with cage modification
- Acid rain leaching tests for large volume
wastes (Method 1312)
- Multiple Extraction Procedures (MEP) for
delisting
- Oily Waste Extraction Procedure (OWEP) for
delisting
39
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C-4 - OFFICE OF TOXIC SUBSTANCES
NEEDS FOR USE OF LEACHING TESTS
-TSCA is a "No Unreasonable Risk" Statute
- The only alternative technologies acceptable, for
instance for PCB's, must demonstrate that they are
equivalent to thermal destruction of PCB's (e.g.,
solidification of PCB's would cause a problem under
these TSCA criteria.)
- TSCA is also a cost-benefit statute:
- Possible use of waivers by EPA Regional
Administrators
- With this (cost-benefit) constraint, there
could be a problem between what the Superfund
and the Office of Toxic Substances programs
says are "low" and/or acceptable concentrations
- Need some tests to determine the long-term
effectiveness of these problems
USES OF LEACHABILITY AND LEACH TESTS
- Particularly interested in teachability data,
especially for new product information in the PMN
(Pre-Hanufacturing Notification) program for new and
existing chemicals
- OTS is in need of information on teachability for
establishing the equivalent comparison in a chemical
waste landfill, which is the only non-destructive
method that is authorized (that is not to say that
treatment processes that are non-destructive
would not be examined)
TYPES OF DATA REQUIRED, SPECIAL CONCERNS,
ISSUES AND CONSTRAINTS (This is. variables
that can affect test results.)
- Equivalency test data, for alternative
technologies to thermal destruction
- Cost-benefit data on alternative
technologies to incineration:
- The Office of Toxic Substances is in
need of information that examines the
alternative technologies to incineration
- The alternative technologies to incineration
must demonstrate equivalency
- Need to know what kind of teachability
criteria would be needed to obtain
a revised equivalent to incineration
- Also, need to know what kind of laboratory
testing should be required to give results
equivalent to incineration
- R&D is needed to answer above.
TYPE OF TESTS
- Equivalency tests (as compared to the
incineration alternative) need to be developed
- At present, disposal of waste in chemical
waste landfill is the only non-destructive
method that is authorized
- Other treatment processes that are non-
destructive could be possible, but to date,
no research has occurred to develop such
non-destructive tests which demonstrate the
equivalence to incineration
- Need some tests to look at the long-term
effectiveness of these problems
40
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C-S - UD PERSPECTIVE OF THE R.S. KERB LAB. IN ADA, OKLAHOMA
MEEDS FOR USE OF LEACHIMG TESTS
The RCRA statute requires development and use of
teachability data and tests
Mission of the Lab. and the technical support center
is to further understanding of subsurface media to:
- Remediate contaminated vadose and saturated zones
- Provide a technical support bridge between the
Lab. and the EPA regional and state regulators
- R.S. Kerr Lab. is primarily a user and not a
developer of different Leaching test methods
and alternative procedures:
- EPA ORD, EPA OSU, ASTM, NRC and others develop
leaching tests
USES OF LEACHABILITY AND LEACH TESTS
To answer questions pertaining to what kind of
contaminant levels are appropriate to be left in the
soil, so that there will not be a problem later
(i.e., so that leachate through the soil will be
protective of groundwater). Hence, this leads to
the following questions:
- What kind of leaching test can be used to
develop criteria for "safe levels?"
- What site specific processes must be considered
in the criteria development process?
- What kind of vadose zone models should be used?
TYPES OF DATA REQUIRED, SPECIAL CONCERNS.
ISSUES AND CONSTRAINTS (That is variables
that can affect test results.)
- To develop a "family of procedures" and to
determine when it is appropriate to use each
procedure to answer site-specific questions
- Ability to get source term in model is a
problem
- Need to act conservatively, particularly *'
with organics, but need to use "common
sense"
- There is considerable competition between
different tests
- To date no evaluation has been made as to what,
in fact, are the reasonable stresses, such as:
- When to grind or not to grind a waste
- When to apply acid and at what strength
and duration
- Issues with appropriate tests for
radionuclides and mixed wastes:
- What kind of test will be applicable to
low-level radioactive material?
- Is EP Tox. or TCLP appropriate? Under
what circumstances?
- There are no "standard" R&D leaching tests
or migration potential evaluation protocols
for Superfund on-site remedies
- For the combustion residue area, the
following issues illustrate special concerns
and constraints:
- The ability to get the appropriate source
term is usually a basic problem
- The R*D program uses a lot of different
procedures to develop a credible data base
- In this context, ORD is primarily a user.
and not a developer of methods for leaching
tests
- The RCD staff are using a lot of different
procedures to develop a credible data base
TYPE OF TESTS
- EP (Method 1310)
- TCLP (Method 1311)
41
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C-6 - RID PERSPECTIVE OF THE OFFICE OF MODELING.
MONITORING. AND QUALITY ASSURANCE. 1MSHINGTOH. D.C.
USES OF LEACHING TESTS
- Determining regulatory status of waste
- Determining effectiveness of treatment
processes which are designed to reduce
teachability
- Determining leachability of waste under
different management scenarios
TYPES OF TESTS HEEDED (SCENARIOS TO BE
MODELED)
- Sanitary Landfill co-disposal:
- Lined unit
- Unlined unit
- Monowaste disposal
- Dedicated, mixed waste unit
- Uncontrolled contaminated soil
USES OF TRANSPORT TESTS
- Predicting transport through media as input to
fate and transport nodeIs (i.e., serve as the
source ten* for the models)
TYPES OF TESTS NEEDED (ENVIRONMENTS TO BE
MODELED)
- Vadose Zone:
- Moist
- Dry
- Saturated Zone:
- Sandy
- Clay
- Loam
- Calcarious
- Acidic
- Effect of waste on LeachabiIity/transport
of material from other wastes
42
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C-7 - CRITERIA AMD OBJECTIVES OF LEACHING TESTS AND MODELING CONSIDERATIONS FOR PARTITIONING TESTS FROM THE
PERSPECTIVE OF REGULATORS VERSUS INDUSTRY
INDUSTRY VIEW OF THE PERSPECTIVE
OF THE REGULATORS
- Simplicity (e.g., simplicity of test protocol)
- Reproducibility
- Conservatism, if realism is not practical
- One/few tests to fit most wastes
- Use to delineate "non-hazardous" versus "hazardous"
wastes (e.g., differentiating between wastes needing
RCRA "C" standards management and wastes that only
need "D" controls.)
[NOTE: The above is in contrast to a large part of
the Agency's response, particularly
Superfund and the Kerr Lab.]
PERSPECTIVE OF INDUSTRY
- Simplicity only where appropriate,
- Reproducibility
- Realism in approximating site and waste specific
conditions
- Test variations to account for waste differences
- Suitable for differentiating between different
disposal conditions
- Use to define acceptable disposal conditions
TYPICAL CURRENT PRACTICES OF INDUSTRY IN LEACHATE
TESTING
- Determine regulatory status of waste, such as
hazardous waste e.g.. Subtitle C which is subject to
land ban), EP, TCLP and SPLP (e.g., Method 1312)
- Determine reasonable worst-case releases from waste
residual oils, and contaminated media
- Determine effectiveness of waste treatment process
(e.g., solidification/stabilization)
- Provide basis for landfill design
- Account for biological activity (rarely) in soil
column effects
- Deal primarily with large volume, mono-filled
wastes
DISTINCTIONS TO BE HADE BETWEEN LEACHING
TESTS AND MODELING CONSIDERATIONS FOR
REGULATORS AND INDUSTRY
- There is a distinction between leaching
tests and partitioning tests:
- Current leaching tests are
standardized regulatory tests
not requiring site-specific
analyses (e.g., modeling)
- Partitioning tests are used for data
input into mathematical models for site-
specific subsurface migration analysis
- Leaching tests are not for site-specific
analysis of contaminant transport
- Regulators and Industry do not want to
spend time, money and resources applying
leaching tests which are not:
- Applicable for given conditions
- Realistic, given site specific conditions
type and strength
- Cannot be used to identify prudent waste
management and disposal activities
- "False positives" and "false negatives" are
costly from both the regulator and industry
point-of-view
PERSPECTIVE OF PUBLIC
- Desire for conservatism
- Tests subject to public review
- Reflective of reasonable worst-case
environmental transformation
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C-7 - CRITERIA AID OBJECTIVES OF LEACHING TESTS AND MODELING CONSIDERATIONS FOR PARTITIONING TESTS FROM THE
PERSPECTIVE OF REGULATORS VERSUS INDUSTRY (Continued)
BASIC NEEDS
o A Rational Construct of the Leaching Phenomenon
- Avoid regulatory expediency, conservatism)
- Aim for well founded approach
o Understand and Clearly Define the Role of Basic Mechanisms
- Heathering, Dissolution
- Desorption
- Diffusion, Permeation
- Mechanics/Chemistry of
Stabilization/Solidification
o Develop a Leachate Test/Model Interface
- Tests representative of important phenomena
- Test results usable in diffusion, flow models
o Validate Model Results through Field Studies
- Realistic Test Cells
- Actual Disposal Situations
BASIC BELIEFS
o All Materials Leach
o Our Goal Should be an Acceptable Rate of Release To
The Environment
o Leachate Tests Provide a Useful Measure of
Environmental Availability
- Excellent predictor of water borne contamination
- Of Secondary value for volatile emissions
o Leachate Tests Should Fairly Represent the Actual
Mechanics in the Field
o Properly Constructed Leachate Experiments Coupled
With Technically Sound Analysis of Flow Phenomena Can:
- Provide environmentally acceptable disposal
- Define risks posed by contaminated media
44
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C-7 - CRITERIA AND OBJECTIVES OF LEACHING TESTS AND MODELING CONSIDERATIONS FOR PARTITIONING TESTS FROM THE
PERSPECTIVE OF REGULATORS VERSUS INDUSTRY (Continued)
EFFECTS OF SQK LEACHATE TEST PARAMETERS
o Waste/Liquid Ratio
- Most allow equilibrium/saturation
- Worst case for total dissolved materials
Saturation night suppress relative solubility of
some constituents
o Leaching Time
- Most approach equilibrium
- No residence time/advection relationship unless a
column test
o Number of Extractions
- Single extractions tell little of leaching phenomena
- Multiple extractions can provide more information
o Surface Effects
o Diffusional Fluxes
o Compositional Changes
o Particle Size
- Size reduction provides rapid equilibrium, most
conservative, but unrealistic results
o Ignores permeation, diffusion rate
o Defeats solidification/stabilization mechanisms
o Leaching Medium (Eluant) Composition
- Organic acids represent specialized case
o To simulate municipal co-disposal
o To provide buffered system, stable Ph
o Acetates, citrates preferentially extract metals
o May confuse analysis
- Inorganic acids to represent "acid rain"
o More realistic for mono-wastes
- Total acidity
o Often high to counteract high alkalinity wastes
o Overestimates rate and amount of neutralization
o Agitation
- Speeds Equilibrium
- Not representative of actual conditions
45
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APPENDIX D - CREDITS AND ACKNOWLEDGEMENTS
The Leachability Subcommittee (LS) of the Science Advisory
Board's (SAB) Environmental Engineering Committee (EEC) wishes to
acknowledge the many people and offices for their numerous
contributions to this self-initiated study to arrive at
recommendations and rationale for analysis of contaminant
release. While listing names provokes the opportunity to miss
contributors by omission, we believe that the following
contributors to the efforts of the LS and its parent EEC deserve
a special "thank-you" and acknowledgement for their time,
energies and efforts toward improving this product and the
perspective of the SAB members and consultants in this very
complex area.
With respect to an information gathering session conducted
on February 26, 1990 in which the LS attempted to assess the
varied needs of the Agency, the following persons are recognized
for their participation in this exercise, as well as
participation in the follow-up activities after this session:
Mr. Harry Allen, EPA, Office of Emergency and Remedial
Response (OERR), Emergency Response Division (ERD), Edison, New
Jersey
Ms. Robin Anderson, EPA, OERR, Hazardous Site Control
Division (HSCD), Washington, D.C.
Ms. Joan Blake, EPA, Office of Toxic Substances (OTS),
Exposure Evaluation Division (BED), Washington, D.C.
Mr. David Friedman, EPA, Office of Research and Development
(ORD), Modeling, Monitoring Systems and Quality Assurance Office,
Washington, D.C. (Formerly with the Office of Solid Waste (OSW),
Characterization and Assessment Division (CAD))
Ms. Gail Hansen, EPA, OSW, CAD, Washington, D.C.
Mr. Alexander C. McBride, Chief, Technical Assessment
Branch, EPA, OSW, CAD, Washnigton, D.C.
Ms. Lynnann Kitchens, EPA, ORD, Office of Environmental
Engineering and Technology Demonstration (OEETD), Washington,
D.C. (Now with ORD's Waste Minimization, Destruction and Disposal
Research Division (WMDDRD) within the Risk Reduction Engineering
Laboratory (RREL), Cincinnati, Ohio)
Mr. M. R. Scalf, EPA, ORD, R.S. Kerr Environmental Research
Laboratory, Ada, Oklahoma
Mr. Carlton Wiles, Chief, Stabilization Section of the
Municipal Solid Waste Residuals Branch,WMDDRD, RREL, ORD, EPA
Cincinnati, Ohio.
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Mr. Christopher Zarba, EPA, Criteria and Standards Division
(CSD), Office of Water Regulations and Standards (Now known as
the Health and Ecological Criteria Division, Office of Science
and Technology ), Washnigton, D.C.
Dr. Linda E. Greer, Natural Resources Defense Council,
Washington, D.C. (At the time she was with the Hazardous Waste
Treatment Council (HWTC), but represented herself at the meeting,
and not the HWTC)
Mr. Phillip A. Palmer, E. I. duPont DeNemours & Co.,
Engineering Department, Newark, Delaware
The above participants in the February 26, 1990 information
gathering session deserve special recognition for helping develop
Appendix B which summarizes the various uses and needs of
leaching tests. Dr. K. Jack Kooyoomjian of the SAB Staff and
Designated Federal Official to the EEC and its LS deserves
particular recognition for synthesizing the above information.
Additionally, Mr. Samuel Rondberg's assistance in setting up
Appendix B and assisting in the numerous and often tedious edits
is greatly appreciated.
With respect to the reachability Workshop and Technical
Briefing which the LS held on May 9, 1990, the following persons
are recognized for their contributions as participants in
briefing the LS members and consultants:
Dr. Paul Bishop, Department of Civil and Environmental
Engineering, University of Cincinnati, Cincinnati, Ohio
Dr. Pierre Cote, ZENON Environmental, Inc., Ontario, Canada
Dr. Marvin Dudas, Department of Soil Science, The University
of Alberta, Edmonton, Alberta, Canada
Dr. Carl Enfield, R.S. Kerr Environmental Research
Laboratory, Ada, Oklahoma
Dr. Robert Huddleston, Conoco, Inc., Ponca City, Oklahoma
Dr. P. Suresh Chandra Rao, Institute of Food and
Agricultural Sciences, Soil Science Department, University of
Florida, Gainesville, Florida
Dr. John Zachara, Battelle Pacific Northwest Laboratories,
Geochemistry Section, Richland, Washington
With respect to Figure 1 in the text which depicts a
conceptual view of leaching in a waste unit, the following person
deserves recognition:
Dr. Ishwar Murarka, Program manager for Land and Water
Studies, EPRI, Palo Alto, California
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With respect to the development of information on Extraction
Tests (Table 1), the following persons deserve particular
recognition:
Dr. Larry I. Bone, Environmental Quality, Dow Chemical,
Midland, Michigan
Ms. Gail Hansen, EPA, OSW, Characterization and Assessment
Division, Washington, D.C.
With respect to the development of Table 3 which lists the
scientific considerations in design and interpretation of
leachability tests, the following persons deserve particular
recognition:
Mr. Richard Conway, Senior Corporate Fellow, Union Carbide
Corporation, South Charleston, West Virginia
Mr. Peter Hannak, Union Carbide Chemicals and Plastics
Company, Inc., South Charleston, West Virginia (Formerly of
Alberta Environmental Centre)
And last, but not least, we would like to offer a special
thanks to Mrs. Marcy Jolly, Secretary to the Leachability
Subcommittee, for typing and retyping the numerous drafts of this
report.
Of course, this report would never have materialized without
the perseverance of the LS and the EEC after the need for a self-
initiated report on leachability was recognized. Special
recognition is made to Dr. Ward, Chairman of the LS and to Dr.
Murarka, Vice-Chair of the LS for guiding the report to a
successful conclusion.
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APPENDIX E - GLOSSARY OF TERMS AND ACRONYMS
AET
ANS
ANSI
ARARSs
ASTM
AVS
BOAT
C
CERCLA
CWA -
DI
DLT
EDTA
EEC
EP
EPA
EPACML
FOWL
HELP
IAEA
ISO
MCC
MEP
MEQ/G -
MIN
ML
MM
MWEP
OMMQA -
N
N/A
NCP
NRC
OMMQA -
ORD
OSW
OTS
OSW
OTS
OWEP
PCB's -
pH -
PMN
R&D
RCRA
RSKERL
APPARENT EFFECTS THRESHOLD
AMERICAN NUCLEAR SOCIETY
AMERICAN NATIONAL STANDARDS INSTITUTE
APPLICABLE OR RELEVANT AND APPROPRIATE
AMERICAN SOCIETY OF TESTING MATERIALS
ACID VOLATILE SULFIDE
BEST DEMONSTRATED ACHIEVABLE TECHNOLOGY
CENTIGRADE
COMPREHENSIVE ENVIRONMENTAL RESPONSE, COMPENSATION
AND LIABILITY ACT (ALSO KNOWN AS "SUPERFUND")
CLEAN WATER ACT
DEIONIZED
DYNAMIC LEACH TEST
ETHYLENE DIAMINE TETRAACETIC ACID
ENVIRONMENTAL ENGINEERING COMMITTEE (SAB/EPA)
EXTRACTION PROCEDURE TOXICITY
U.S. ENVIRONMENTAL PROTECTION AGENCY (US EPA, or
"THE AGENCY")
EPA COMPOSITE MODEL FOR LANDFILLS
FOSSIL FUEL COMBUSTION WASTE LEACHING
HYDROLOGIC EVALUATION OF LANDFILL PERFORMANCE
INTERNATIONAL ATOMIC ENERGY AGENCY
INTERNATIONAL STANDARDS ORGANIZATION
DISTRIBUTION COEFFICIENT
LEACHABILITY SUBCOMMITTEE (EEC/SAB/EPA)
MOLE (MOLARITY)
MATERIAL CHARACTERISTIC CENTER
MULTIPLE EXTRACTION PROCEDURE
MILLI EQUIVALENT PER GRAM
MINUTE
MILLILITER
MILLIMETER
MONOFILL WASTE EXTRACTION PROCEDURE
ORD/OFFICE OF MODELING, MONITORING, AND QUALITY
ASSURANCE, US EPA
NORMAL (NORMALITY)
NOT APPLICABLE
NATIONAL CONTINGENCY PLAN
NUCLEAR REGULATORY COMMISSION
OFFICE OF MODELING MONITORING AND QUALITY ASSURANCE,
ORD/EPA
OFFICE OF RESEARCH AND DEVELOPMENT, US EPA
OFFICE OF SOLID WASTE, US EPA
OFFICE OF TOXIC SUBSTANCES, US EPA
OFFICE OF SOLID WASTE, US EPA
OFFICE OF TOXIC SUBSTANCES, US EPA
OILY WASTE EXTRACTION PROCEDURE
POLYCHLORINATED BIPHENYLS
NEGATIVE LOG OF HYDROGEN ION CONCENTRATION
PRE-MANUFACTURING NOTIFICATION
RESEARCH AND DEVELOPMENT
RESOURCE CONSERVATION AND RECOVERY ACT
R.S. KERR ENVIRONMENTAL RESEARCH LABORATORY, US EPA
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APPENDIX E- GLOSSARY OF TERMS AND ACRONYMS - Continuation
SAB SCIENCE ADVISORY BOARD (EPA)
SC OFFICE OF WATER, SEDIMENT CRITERIA PROGRAM, US EPA
SF SUPERFUND PROGRAM, US EPA
SPE SOLID PHASE EXTRACTION
SPLP SYNTHETIC PRECIPITATION LEACHING PROCEDURE
S/S SOLIDIFICATION/STABILIZATION
SYN SYNTHETIC (IN REFERENCE TO SYNTHETIC LANDFILL LEACHATE)
TC TOXICITY CHARACTERISTIC
TCLP TOXICITY CHARACTERISTIC LEACHING PROCEDURE
THF TETRAHYDROFURAN
TIE TOXICITY IDENTIFICATION EVALUATION
TSCA TOXIC SUBSTANCES CONTROL ACT
JAM MICRO MOLES
UNIFAC UNIVERSAL FUNCTIONAL ACTIVITY COEFFICIENT MODEL
WET WASTE EXTRACTION JEST
50
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