A PROCEDURE FOR ESTIMATING MONOFILLED SOLID WASTE LEACHATE COMPOSITION
Technical J&esource Document
SW-924
2nd Edition
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
OFFICE OF SOLID WASTE AND EMERGENCY RESPONSE
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
January 1986
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DISCLAIMER
This document'was prepared by A. Gaskill, Jr., C. C. Allen, and R. S.
Truesdale of Research Triangle Institute and 0. R. Jackson of Battelle
Columbus Laboratories under EPA Contract No. 68-02-3992. Industry reviewers
are thanked for their reviews of the initial version of this document.
Special acknowledgments are extended to M. Houle and D. Long of Dugway Proving
Ground for their timely review comments. The EPA Project Officer was C^I.
Mashni of the Hazardous Waste Engineering Research Laboratory, Cincinnati,
Ohio.
This report has received extensive technical review, but the Agency's
peer and administrative review process has not yet been completed. Therefore
it does not necessarily reflect the views or policies of the Agency. Mention
of trade names or commercial products does not constitute endorsement or
recommendation for use.
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FOREWORD
The Environmental Protection Agency was created because of increasing
public and governmental concern about the dangers of pollution to the health
and welfare of the American people. Noxious air, foul water, and spoiled land
are tragic testimony to the deterioration of our natural environment. The
complexity of the environment and the interplay between its components require
a concentrated and integrated attack on the problem.
The Office of Solid Waste is responsible for issuing regulations and
guidelines on the proper treatment* storage, and disposal of hazardous wastes
to protect human health and the environment from the potential harm associated
with improper management of these wastes. These regulations are supplemented
by guidance manuals, technical guidelines, and technical resource documents,
made available to assist the regulated community and facility designers in
understanding the scope of the regulatory program. Publications like this one
provide facility designers with state-of-the-art information on design and
performance evaluation techniques.
This technical resource document describes a laboratory procedure for
generating aqueous extracts from industrial solid wastes that are candidates
for monofill disposal. Although the extracts produced are not necessarily
representative of leachate that would be produced in a land disposal
environment, the procedure can be used to estimate the quantity of potentially
leachable constituents in a solid waste and potential concentrations of these
constituents in aqueous leachates produced from the waste at a given
solid-to-liquid ratio.
WILLIAM A. CAWLEY
Acting Director
Hazardous Waste
Engineering Research Laboratory
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PREFACE
Subtitle C of the Resource Conservation and Recovery Act (RCRA) requires
the Environmental Protection Agency (EPA) to establish a Federal hazardous
waste management program. This program must ensure that hazardous wastes are
handled safely from generation until final disposition. EPA issued a series
of hazardous waste regulations under Subtitle C of RCRA that are published in
40 Code of Federal Regulations (CFR) through 265 and 122 through 124.
Parts 264 and 265 of 40 CFR contain standards applicable to owners and
operators of all facilities that treat, store, or dispose of hazardous wastes.
Wastes are identified or listed as hazardous under 40 CFR Part 261. The Part
264 standards are implemented through permits Issued by authorized states or
the EPA in accordance with 40 CFR Part 122 and Part 124 regulations. Land
treatment, storage, and disposal (LTSD) regulations in 40 CFR Part 264 issued
on July 26, 1982, establish performance standards for hazardous waste
landfills, surface impoundments, land treatment units,, and wastepiles.
The Environmental Protection Agency is developing three types of
documents for preparers and reviewers of permit applications for hazardous
waste LTSD facilities. These types include RCRA technical guidance documents,
permit guidance manuals, and technical resource documents (TRD's).
The RCRA Technical Guidance Documents present design and operating
specifications or design evaluation techniques that generally comply with or
demonstrate compliance with the design and operating requirements and the
closure and post-closure requirements of Part 264.
The Permit Guidance Manuals are being developed to describe the permit
application information the Agency seeks and to provide guidance to applicants
and permit writers in addressing the information requirements. These manuals
will include a discussion of each step in the permitting process, and a
description of each set of specifications that must be considered for
inclusion in the permit.
The Technical Resource Documents present state-of-the-art summaries of
technologies and evaluation techniques determined by the Agency to constitute
good engineering designs, practices, and procedures. They support the RCRA
Technical Guidance Documents and Permit Guidance Manuals in certain areas
(e.g.,- liners, leachate management, closure covers, water balance) by
describing current technologies and methods for designing hazardous waste
facilities or for evaluating the performance of a facility design. Although
emphasis is given to hazardous waste facilities, the information presented in
these TRD's may be used in designing and operating nonhazardous waste LTSD
facilities as well. Whereas the RCRA Technical Guidance Documents and Permit
Guidance Manuals are directly related to the regulations, the information in
these TRD's covers a broader perspective and should not be used to interpret
the requirements of the regulations.
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This document has undergone review by recognized experts in the technical
areas covered. Their comments, and recommendations for improvement, have been
incorporated whenever possible. The Agency intends to update these TRD's
periodically as warranted. Communications on any of the TRD's should be
addressed to Docket Clerk, Room S-212(A), Office of Solid Waste (WE-562), U.S.
Environmental Protection Agency, 401 M Street, S.W., Washington, D.C. 20460.
The document under discussion should be identified by title and number (i.e.
"A Procedure for Estimating Monofilled Solid Waste Leachate Composition,
SW-924").
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ABSTRACT
The monofilled waste extraction procedure (MWEP) is a laboratory
procedure developed for generating aqueous extracts from Industrial solid
wastes.' The extracts produced by this procedure are not necessarily
representative of the leachate that would be produced in a specific land
disposal environment. However, the procedure can be used to estimate the
quantity of potentially leachable constituents in a given solid waste and to
measure the concentration of these constituents in an extract produced by
extracting the waste at a given solid-to-liquid ratio.
The procedure uses a four-step sequential batch extraction of a waste
sample to produce data that can be used to construct an aqueous extraction
profile of waste constituents. Each step involves extracting the waste with a.
fresh aliquot of extraction medium for 18 hours at a 10:1 liquid-to-solid
ratio. The sequential extractions permit estimation of the total amounts of
specific constituents in a waste that may be released Into aqueous solution.
The procedure is applicable to all solid wastes containing Appendix' VIII
constituents except for those containing volatile organics, and has been
demonstrated on several wastes, including electroplating sludge and polystill
bottoms.
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CONTENTS
Title Page
DISCLAIMER ii
FOREWORD iii
PREFACE .iv
ABSTRACT vi
FIGURES lx
TABLES x
DEFINITIONS OF KEY TERMS * '. xi
1.0 INTRODUCTION 1
1.1 Background 1
1.2 Purpose of Procedure 1
1.3 Limitations of Procedure 2
1.4 Regulatory Significance 3
1.5 Scope of Document 3
2.0 EXPERIMENTAL CONDITIONS 7
2.1 Waste Samples 7
2.2 Contact Area/Particle Size 7
2.3 Extraction Medium 7
2.4 Temperature 9
2.5 Method of Mixing 9
2.6 Time Of Extraction 12
2.7 Number Of Extractions 12
2.8 Liquid-To-Solid Ratio 12
3.0 TEST PROTOCOL 13
3.1 Apparatus And Materials 13
3.1.1 Agitation Apparatus and Extraction Bottles 13
3.1.2 Separation Apparatus 14
3.1.3 General Labware 14
3.2 Reagents '. 14
3.2.1 Extraction Medium '.. 14
3.2.2 Nitric Acid 15
3.3 Sampling 15
3.3.1 Sample Collection and Handling 15
3.3.2 Sample Preservation 15
3.4 Extraction Procedure 15
3.4.1 Extraction 1 15
3.4.2 Extraction 2 18
3.4.3 Extraction 3 19
3.4.4 Extraction 4 19
3.4.5 Further Extractions 19
3.5 Analysis 19
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Title . Page
4.0 QUALITY CONTROL 20
4.1 Procedural Blank 20
4.2 Parallel Extractions 20
4.3 Assessment of Accuracy 20
5.0 CONVERSION AND INTERPRETATION OF EXPERIMENTAL DATA 21
5.1 Data Conversion 21
5.1.1 Concentration and Mass Release Conversions 21
. 5.1.2 Extraction Profile Analysis 23
5.2 Interpretation 31
5.3 Calculation of Time Required for Field Leaching 33
6.0 REFERENCES 36
APPENDICES
Appendix A Generation of Site-Specific Extraction Medium 38
Appendix B Statistical Evaluation of Monofilled Solid Waste Extract
Data 41
Appendix C Suppliers 47
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FIGURES
Number Page
1. NBS-Design Rotary Extractor 10
2. EPRI/Acurex Rotary Extractor 11
3. Schematic Diagram of the Monofill Waste Extraction
Procedure (MWEP) .- 16
4. Extraction Profile for Constituent Data in Table 3 24
5. pH of Extract Versus Liters of Water per 100 g of Waste
for Electroplating Sludge 25
6. Calcium Concentration in Extract Versus Liters of Water per 100 g
of Waste for Electroplating Sludge 26
7. Copper Concentration in Extract Versus Liters of Water per 100 g
of Waste for Electroplating Sludge 27
8. pH of Extract Versus Liters of Water per 100 g of Waste
for Fly Ash 28
9. Aluminum Concentration in Extract Versus Liters of Water per 100 g
Waste for Filter Cake j 29
10. Copper Concentration in Extract Versus Liters of Water per 100 g
Waste for Polystill Bottoms 30
11. Extraction Profile of Cr from Electroplating Sludge 32
A-l Generation of Site-Specific Extraction Medium 39
B-l Comparison of 100Z Landfill Soil and 100Z Chrornate
Waste Profiles 44
B-2 Extraction Profile vith Data for 100Z Chromate Waste 45
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TABLES
Number Page
1. Purpose, Application, Regulatory Status and Conditions of
EP, TCLP and MWEP 5
2. MWEP Test Parameters and Recommended Experimental
Specifications 8
3. Conversion of Experimental Data 22
4. Time Required to Exceed Specific Extraction Sequence for
Selected Cap Infiltration Rates 35
B-l Estimates of the Percent Relative Variation for the Landfill
and 100Z Chromate Wastes 46
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DEFINITIONS OF KEY TERMS
1. Extract—The liquid derived from a laboratory batch extraction
method in which fixed amounts of waste and liquid extraction medium
are mechanically mixed to achieve contact for a specified amount of
time.
2. Extraction profile—The relative change in concentration of
dissolved waste constituents in extracts (or in mass released into
solution) as a waste sample -is repeatedly extracted. This can be
graphically illustrated by fitting a curve to the concentration
data for the sequential extracts.
3. Extractable quantity—The total mass of a constituent that can be
extracted from a waste using the MWEP.
4. Intensity—The concentration of a constituent in an extract.
5. Leachate—An aqueous mixture of dissolved and/or suspended waste
constituents derived by percolating water through a solid waste.
6. Monofill—A landfill in which only one type of waste is disposed,
e.g., municipal waste incinerator ash, fly ash, and electroplating
sludge, and there is no codisposal with other municipal waste.
xi
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1.0 INTRODUCTION
The proper design and operation of waste management facilities often ;
requires an assessment of leachable chemical constituents of the deposited
waste. This information may be required to determine the compatibility of
liner materials and leachate or to design leachate treatment facilities. In
the absence of information on the composition of a waste leachate obtained
under actual field conditions, a laboratory-generated extract can be used to
simulate this actual leachate. This document describes a laboratory extraction
procedure developed for this purpose.
In this document, the term "monofill" describes the disposal of a
hazardous waste in an environment isolated from co-disposed materials such as
municipal refuse that might alter the leaching chemistry of the primary waste
from that resulting from leaching with natural precipitation. Under current
legislation the term "monofill" has no regulatory meaning with respect to the
disposal of hazardous wastes.
The monofilled waste extraction procedure (MWEP) described in this
document should not be confused with the extraction procedure (EP) or the
toxicity characteristic leaching procedure (TCLP). The EP (1) and TCLP (2)
were developed to assess the potential of a solid industrial waste to produce
a toxic leachate when co-disposed with municipal refuse and each has
regulatory -significance. The MWEP was developed to produce extraction data
that may be used, in conjunction with engineering analysis and judgement, to
assess leachable constituents of a solid waste disposed of in a monofill
facility. The MWEP has no regulatory significance and none is to be implied
by the publication of this document.
1.1 BACKGROUND
Difficulties experienced in the past with disposal of hazardous waste can
be attributed partially to a lack of knowledge concerning the long-term
behavior of various waste forms in various disposal environments. The poor
performance of past disposal practices dictates that factors such as waste
solubility, and compatibility of facility components with wastes or waste
leachates be considered when designing new hazardous waste disposal
facilities. Leachate data from long-term field studies of actual hazardous
waste containment facilities are not available for most wastes. Therefore, to
evaluate waste leachabllity, it is necessary to generate a representative
laboratory extract to approximate field leachate composition.
Several laboratory extraction procedures have been developed for solid
hazardous wastes (3,4). Batch extraction procedures involve the mechanical
mixing of a fixed volume of extracting medium with a fixed mass of hazardous
waste. Advantages of batch extraction procedures over column leaching
procedures include ease of operation and lower experimental variation (5).
1.2 PURPOSE OF PROCEDURE
The MWEP provides a standardized laboratory method for the batch
extraction of chemical constituents from solid waste. The primary purpose of
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the procedure is Co assess maximum leachate concentrations and total
extractable mass of solid waste constituents by producing an extract using
water as the extraction medium. The MWEP specifies a four-step sequential
batch extraction of a waste sample with fresh aliquots of extraction medium.
This is similar to Procedure R of the Standard Leaching Test (SLT) developed
by Ham et al.(6).
The MWEP extract can be used for the following purposes:
o Designing and evaluating the performance of leachate treatment
systems for new and existing hazardous waste facilities.
o Assessing the compatibility of hazardous wastes with earthen and
synthetic liners and with leachate collection system components.
o Assessing potential groundwater contamination fate and transport in
the case of facility failure.
o Evaluating waste stabilization techniques (e.g. admixing lime)
intended to reduce the solubility of hazardous components in the
waste.
MWEP data may be used to construct an aqueous extraction profile of waste
constituents; the profile may be used to assess the waste's capacity for
releasing specific constituents, and to infer the time-release of leachable
constituents if certain conditions are satisfied. Sequential extractions at
realistic liquid-solid ratios are suggested in the procedure for estimating
leachate composition as a function7of time. Guidance is provided for
translating the number of repetitive extractions into leaching time for a
waste in an idealized field environment.
1.3 LIMITATIONS OF PROCEDURE
The production of leachate from a landfilled solid waste is
influenced by numerous variables, such as the amount and chemical composition
of precipitation infiltrating into the waste, permeability within the disposal
facility, interaction of contaminants with one another, the presence and
composition of a common solid waste matrix, and exposure time to the leaching
medium. It is impossible to duplicate these and other variables in the
laboratory and generate a representative leachate for a specific waste site.
This procedure is a compromise intended to produce an aqueous waste extract .
that reflects the maximum level of extractable constituents that could be
leached from the waste. For the MWEP, significant compromises are:
o A batch extraction procedure cannot reproduce slow changes in the
leaching characteristics of waste in a disposal environment.
o Chemical reactions that result from mixing leachate produced in two
or more segregated waste cells within a disposal facility cannot be
accurately simulated by a single component extraction procedure.
However, the extract generated from one waste type can be used as
the extracting medium for a second waste type.
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o A batch extraction procedure does not address physicochemical
changes in the waste initiated by long-term microbiological or
chemical processes.
o The procedure may be unsuitable for oily wastes that produce
extracts having a water-immiscible organic liquid layer. This layer
may influence the precision or accuracy of the procedure.
o The procedure is not applicable to volatile constituents of waste
samples* since the extraction vessels are not headspace free.
o The hydrologic regime of the actual field disposal environment
(e.g., flow channeling) is not addressed by a batch extraction
procedure.
Because of these compromises, analysis of the extract from this laboratory
procedure may not agree with results from field leachate analyses.
This extraction test may be used to obtain data to estimate the long-term
leaching behavior of a waste. However, the procedure does not account for
long-term changes in waste chemistry or physical characteristics (e.g.,
hydraulic conductivity), due to the action of chemical, physical, and
biological processes.
1.4 REGULATORY SIGNIFICANCE
The MWEP has no regulatory significance and none is to be implied by the
publication of this document. Differences between the MWEP and other EPA
waste extraction procedures used for regulatory purposes are summarized in
Table 1. The Extraction Procedure (EP) is currently used to classify waste as
hazardous or non-hazardous as defined in 40 CFR 261.14. The Toxicity
Characteristic Leaching Procedure (TCLP) will replace the EP under recent
legislation in the reauthorization of RCRA.
1.5 SCOPE OF DOCUMENT
This document is designed to be a technical guide describing laboratory
methods for generating data on the quality of leachate from solid waste. The
data can be used in disposal facility design and permit review processes.
The document is designed to be used with the technical resource documents
(TRD's) that have been prepared on various aspects of hazardous waste disposal
for the U.S. EPA-Municipal Environmental Research Laboratory. (MERL). This
series of TRD's provides technical guidance on moisture infiltration, waste
decomposition, waste stabilization,* land treatment, leachate generation,
disposal facility liners leachate transport and collection, and contaminant
transport, migration, and attenuation. The documents in this series are:.
TRD 1 Evaluating Cover Systems for Solid and Hazardous Waste (SW-867).
This document presents a procedure for evaluating design of final
covers on solid and hazardous waste.
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TRD 2 Hydrologic Sinulation of Solid Waste Disposal Sites (SW-868). This
document provides a computer package to aid planners and designers
in predicting runoff, evapo-transpiration, and infiltration through
'landfill covers.
TRD 3 Landfill and Surface Impoundment Performance Evaluation (SW-869).
This document describes how to evaluate the capability of various
liner/drain designs to control leachate release from landfills.
TRD 4 Lining of Waste Impoundment and Disposal Facilities (SW-870). This
document provides information and guidance on the performance,
selection, and installation of specific liners for various disposal
situations.
TRD 5 Management of Hazardous Waste Leachate (SW-871). This document
presents management options for controlling and treating leachate.
TRD 6 Guide to the Disposal of Chemically Stabilized and Solidified Wastes
(SW-872). This document provides basic information on
stabilization/solidification of industrial waste to reduce leaching
and ensure safe burial of waste.
TRD 7 Closure of Hazardous Waste Surface Impoundments (SW-873). This
document describes the methods, tests, and procedures involved in
closing a site to minimize potential environmental hazards.
TRD 8 Hazardous Waste- Land Treatment (SW-874). This document presents and
discusses a comprehensive land, treatment facility design strategy
based on sound environmental protection principles.
This document will complement the TRD series by providing a means for
generating a laboratory extract similar in composition to a waste leachate
generated under field conditions.
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TABLE 1. PURPOSE, APPLICATION, REGULATORY SIGNIFICANCE, AND CONDITIONS OF EP, TCLP, AND MWEP
EP
TCLP
MWEP
Purpose
Classification of wastes
as hazardous or
nonhazardous for 14
specific constituents
based on predetermined
hazard levels.
Classification of
waste as hazardous or
nonhazardous for all
Appendix VIII
constituents,
including volatiles,
based on
predetermined
hazard levels.
Recommended
approach/rationale for
the laboratory batch
extraction of wastes
subject to
monofilllng. All
Appendix VIII
constituents except volatiles
are covered, but no
hazard levels are
assigned.
Application •
Industrial wastes
subject to codisposal
with municipal wastes in
a municipal waste
landfill and/or a
landfill not properly
designed to receive
Industrial waste.
Same as for EP.
Industrial wastes
subject to monofill
disposal In a properly
engineered
facility. Not
applicable to other
types of facilities.
Data could be used in
conjunction with other data
to demonstrate site
suitability for
receiving waste, for
demonstrating liner
compatibility, and for
leachate treament
system design.
(continued)
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TABLE 1. (continued)
EP
TCLP
MWEP
Regulatory 40 CFR 261.24
Significance
Conditions
liquidssolid
ratio 20:1
Extraction
medium 0.5N Acetic Acid
pH control
Contact time
Mixing
technique
Number of
extractions
24 hours
Tumbler
One
To replace EP in
conjunction with ban
on landfilling of
industrial wastes.
20:1
0.1N acetate buffer
None.
18 hours
Tumbler; zero headspace
for volatiles
One"
10:1 per extraction
Distilled/deionlzed water
or other for special site
conditions
None
18 hours per extraction
Tumbler
Four, sequentially
EP = • Extraction procedure.
TCLP = Toxlcity characteristic leaching procedure.
MWEP » Monofllled waste extraction procedure.
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TABLE 2. MWEP TEST PARAMETERS AND RECOMMENDED EXPERIMENTAL CONDITIONS
Extraction test
parameter
Experimental
conditions
Reference section
number
Sample
Contact area/particle size
Extraction medium
Temperature
Method of mixing
Time of extraction
Number of
extractions
Liquid to
solid ratio
Solid waste 2.1
2
Surface 3.1 cm /g or 2.2
sized to pass a 9.5-mm sieve
[unless waste is Monolithic]
Distilled/deionized water
(or other for special site
conditions) 2.3
25±1 °C 2.4
Rotary mixer (tumbler) 2.5
18 hours 2.6
Flexible. Four are recommended. 2.7
10:1 (10 mL liquid to 1 g solid) 2.8
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2.0 EXPERIMENTAL CONDITIONS
Test parameters and experimental conditions for the MWEP are presented in
Table 2. The specifications for this procedure accommodate a variety of waste
types, and address criteria that enable the widespread use of the extraction
procedure for evaluating hazardous waste samples. These criteria include:
o Applicability to wastes containing inorganic and semivolatile organic
constituents.
o Reproducibility, cost-effectiveness, and simplicity.
Experimental parameters specified for the, MWEP are described below.
2.1 WASTE SAMPLES
Samples of the hazardous waste to be evaluated must be collected and
transferred to the laboratory in glass or Teflon® containers. Metal contact
with the waste should be avoided to eliminate possible contamination of the
sample. Methods for obtaining representative samples of waste can be found in
SW-846 (1).
2.2 CONTACT AREA/PARTICLE SIZE
The contact area of the sample must equal 3.1 cm /g unless the solid
waste is monolithic, i.e., composed of. massive solidified material. To
achieve this, the sample may be passed through a 9.5-mm standard sieve as
specified in EPA Method 1310 (1) . The required contact area and particle size
were selected to simulate the conditions likely to be encountered in the field
disposal environment due to mechanical filling operations and weathering. Any
waste passing the structural integrity procedure (1) should be considered to
be monolithic and tested as a whole rather than at a reduced particle size,
as its monolithic character will be retained in a landfill environment. Such
wastes should not have their particle size reduced as this would cause them to
be more leachable than they are under field conditions.
2.3 EXTRACTION MEDIUM
Distilled/deionized water is recommended as the standard extracting
medium to provide for uniform test conditions and to permit the comparison of
data across waste types. The extraction sequence always should be carried out
with this water so that the extractability of different waste types can be
ranked on an equal basis. The water should conform to one of the grades of
reagent water as given in ASTM Method D1193 (7). - -
Method users also have the option of performing the test with a site-
specific medium (in addition to deionized water) that replicates expected
conditions at the disposal site. This medium may be used with or without
first leaching any soil cover material that is to be used on the site.
Suggestions for generating and using a site-specific extraction medium are
presented in Appendix A. Alternatively, the extract obtained from one waste
may be used to extract a second waste if this is likely to occur in the field.
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2.4 TEMPERATURE
To permit comparison of test data across laboratories and waste types, it
is recommended that all extractions be carried out at 25±1 °C. The user has
the option of also conducting the testing at a temperature close to that
expected for the site—specific leachate. The following discussion is presented
as guidance in the selection of a site-specific temperature.
Temperature is known to affect the solubility and reaction rates of many
chemical compounds present in waste. For extractions carried out using site-
specific conditions, the temperature used in the laboratory procedure should
be close to that expected for the site leachate, unless data are available to
show that temperature variances will have little effect on leaching of the
waste being studied. Although ambient air temperatures at land disposal sites
may range from extreme cold (-40 °C) to very high (45 °C), temperatures for
the leachates associated with these sites are likely to be less varied because
overlying cover soil and waste layers have a dampening effect on atmospheric
temperature variations (8). The temperature of the leachate emerging from the
bottom of a disposal site may be that of the waste/soil at the same depth or
may be higher due to chemical reactions within the waste. Seasonal
fluctuations in waste/soil temperature at various depths can be obtained from
historical disposal-site data or may be measured during preliminary site
investigations. Leachate temperatures also may be measured in situ.
2.5 METHOD OF MIXING
A rotary extractor is recommended for this procedure, however, any mixing
device can be used for this procedure that will Impart sufficient agitation to
prevent stratification of the sample suspension and bring the waste solids
into continuous contact with the extraction medium.
Methods of agitating or mixing the sample suspension have been studied to
determine which method performs best in terms of ease of operation and extent
of liquid-solid contact. Several problems have been associated with
mechanical stirrers: (1) binding of the stirring blade by solid particles;
(2) movement of the stirred vessel; (3) stalling of the stirring motor; (4)
uneven blade alignment; and (5) sample grinding (9). However, a mechanical
stirrer has been designed that in many cases eliminates or reduces these
problems (10).
Ham et al. (6) investigated'five methods of mixing: mechanical shaking,
manual shaking, mechanical stirring, swing shaking (180° swing), and variable
pitch rotary mixing. Their study showed comparable results for inorganic
constituents using the various methods. However, their recommendation was to
use a rotary extractor because visual observations indicated that the other
mixing devices occasionally failed to wet the waste uniformly. A study
completed for the U.S. EPA comparing the operation of the stirrer and rotary
extractor (NBS-design tumbler) indicates the rotary extractor produces greater
precision than the stirrer (11). Examples of rotary extractors are shown in
Figures 1 and 2.
Although the reproducibility of test results is enhanced by the mixing
action of the rotary extractor, its use may cause excess particle size
reduction and thus release an unrealistically high level of Appendix VIII
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Rgure 1. NBS - design rotary extractor.
10
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~—-Bonded
\ Foam Liiwr
Rgure 2. EPRI/Acurex rotary extractor.
11
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constituents relative to leacha.te produced in an actual waste monofill.
However, the possible sacrifice in method accuracy is necessary to achieve a
higher precision, a primary criterion for the procedure.
2.6 TIME OF EXTRACTION
The recommended time per extraction is 18 hours. This mixing time was
selected out of consideration for convenience and cost-effectiveness; it
allows samples to be placed on the extractor on an afternoon and removed the
following morning. The reader should be aware that this time is not
necessarily long enough for solute equilibrium to be reached. Equilibrium
times can be expected to vary from waste to waste and from constituent to
constituent due to differences in dissolution rates; thus it is not practical
to try to define unique extraction periods for each waste type or constituent.
If attaining equilibrium is necessary, a series of extractions can be
conducted to determine the optimum extraction time.
2.7 NUMBER OF EXTRACTIONS
Four sequential extractions of each waste sample with fresh extraction
media are recommended to determine an extraction profile over a liquid to
solid ratio of 40:1. The solid waste used for the four extractions is
retained pending the analyses of the filtrates and interpretation of the
results. In the event the results warrant further extractions, the extraction
cycle can be resumed with the saved sample and be continued for as many
repetitions as desired.
2.8 LIQUID-TQ-SOLID RATIO
The recommended ratio of liquid to solid used for each sequential
extraction is 10:1 (10 mL/g waste). This ratio should provide both a
sufficient amount of extracting medium to wet the sample and enough excess to
allow sufficient liquid for proper mixing and subsequent analyses. Ham et al.
(6) recommended a 10:1 liquid-to-solid ratio for the standard leaching test
based on extensive comparative studies using liquid to solid ratios ranging
from 5:1 to 20:1.
The solid-to-liquid ratio that a solid waste will experience in situ is
highly site-dependent and very difficult to forecast precisely. In most
cases, the ratio will be one of a large amount of solid per unit volume of
leachate. The ratio specified for this procedure does not truly reflect
likely field conditions; rather it is a workable minimum amount that will ts^
still allow sufficient liquid for proper mixing and constituent analysis. A
2:1 ratio might give excellent information on the concentration (of
constituents) that can be generated by the waste, i.e., the intensity
function, but would probably provide a poor picture of the extractable
quantities of the waste constituents since solubilities of many constituents
might be exceeded early in the extraction. Likewise, a 20:1 or higher ratio
would give less information on intensity and more on extractable quantities.
The 10:1 ratio is an effective compromise ratio that can provide both
intensity (single extractions) and extractable quantity (multiple extractions)
information.
12
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3.0 TEST PROTOCOL
3.1 APPARATUS AND MATERIALS
The apparatus and materials used in the monofill waste extraction
procedure must be free from chemical species that might bias the determination
of extracted constituents. The apparatus and materials used in the procedure
must be selected to avoid potential interactions between the laboratory
equipment and the waste-extract solution. Examples of interactions to be
avoided are:
o Dissolution of the extract vessel or other equipment by the extract,
as might happen with a hydrofluoric acid-containing waste placed in
a glass vessel.
o Preferential sorption of constituents out of the extract by the
sample container or filtration unit, as might happen with some
organic compounds contained in polypropylene vessels.
o Contamination of the extract by constituents leached from the sample
container, as might happen with waste extract to be analyzed for
nickel and chromium contained in stainless steel vessels.
The following discussion suggests appropriate equipment and materials for
use in the procedure. Specification of a particular manufacturer or model is
for purposes of guidance only. Addresses of suppliers referenced in this
section can be found in Appendix C.
3.1.1 Agitation Apparatus and Extraction Bottles
An agitation apparatus must be designed to avoid stratification of the
sample of solid waste and soil and the leaching medium, which would inhibit
adequate contact between the sample and leachate. The type of extraction
apparatus recommended for this procedure is the rotary extractor or tumbler
(Figures 1 and 2). The extractor consists of a rack or box device to hold the
sample containers, which are rotated through 360° at approximately 30
revolutions per minute.
A six-place tumble extractor derived from a design by the National Bureau
of Standards is Illustrated in Figure 1. This equipment may be fabricated by
the investigator or obtained commercially from Associated Design and
Manufacturing Company (Model No. 3740-4-BRE [four-place tumbler] or Model No.
3740-6-BRE [six-place tumbler]). A second type pf six-place tumbler, shown in
Figure 2, may be fabricated by the investigator or obtained commercially from
Acurex Corporation (no model number available).
Extraction bottles sized to fit the tumbling apparatus may be made of
glass, plastic, or Teflon®. Plastic should not be used to extract wastes
containing organic compounds. Heavy-gauge glass bottles are available from
Associated Design and Manufacturing Co. (Cat. N. 37402GB).
13
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3.1.2 Separation Apparatus
Separation of the solid and liquid layers following extraction of the
waste sample can be accomplished by a combination of settling and filtering.
Details on performing these operations can be found in Section 3.4, which
gives step-by-step instructions for the procedure.
Filter Holder
The filter holder must be capable of supporting a 0.45-micrometer ^"
membrane filter and must withstand the pressure needed to accomplish
separation. These units may be simple vacuum units (Millipore model No.
XX10-047-00 Nuclepore model No. 410400 or equivalent). However, units capable
of being pressurized up to 75 psi may be needed for many solid wastes
(Millipore model No. YT30-142-HW, Nuclepore model No. 420800, or equivalent).
Filter Pads
A glass-fiber prefilter, nylon fine-mesh screen spacer, and a membrane
filter are suggested for use in all filtrations of inorganic waste
constituents. Suggested vendors and model numbers are:
o Coarse glass-fiber prefilter pad (Millipore model No. AP 25-042-00
or No. AP 25-127-50 or equivalent)
o Fine-mesh screen spacer (Millipore model AP32-124-50 or equivalent)
o 0.45-micrometer nitrocellulose membrane filter (Millipore model No.
HAWP-047-00 or No. HAWP-142-50 or equivalent)
A 0.6-0.8 inn glass micro fiber filter (Whatman Grade GF/F) should be used in
place of the nitrocellulose membrane filter for filtration of semivolatile
organic waste constituents.
3.1.3 General Labware
Sample Bottles
The sample bottles used for containing wastes or extracts should be of
suitable materials, such as glass or Teflon® for organic analysis or
polypropylene for inorganic analysis should have a screw cap with an inert
liner such as Teflon*.
3.2 REAGENTS
3.2.1 Extraction Medium
The extracting medium selected for general use in the MWEP is reagent
water (9).' This water must be of sufficient quality, that is, free of organic
and inorganic interferences at the minimum levels of interest for the
subsequent extractions and extract analyses.
14
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3.2.2 Nitric Acid
Trace-element-analysis-grade uitric acid (J. T. Baker No. 9598 or
equivalent) should be used to preserve extracts prior to analysis of
inorganics (see Section 3.3.2).
3.3 SAMPLING
3.3.1 Sample Collection and Handling
Samples of the solid wastes and soil cover materials to be tested should
be collected using the methods described in reference (1). It is particularly
Important that the sample be representative of the solid waste as it occurs in
a landfill environment.
A minimum sample of 1 kg should be collected and sent to the laboratory
in a sealed'container or containers. The containers must be of a material
that will not react with the waste (see Section 3.1.3).
3.3.2 Sample Preservation
Preservatives must not be added to waste or soil samples. Samples known
to be stable with regard to biological or chemical change may be shipped and
stored at room temperature. Samples that might undergo significant biological
or chemical change at room temperature must be maintained at 0-5 °C during
shipping and storage. If the stability of the waste or soil is uncertain or
unknown, shipping and storage of the waste at 0-5 °C is recommended.
»
Extraction of samples should be initiated within 1 week of sample
collection to minimize changes in the sample with storage time. Longer
storage times may be used if the waste or soil samples are known to be
chemically and physically stable.
MWEP extracts should be analyzed as soon as possible following
extraction. If they need to be stored, even for a short period of time,
storage must be at 4 °C.
When inorganic constituents are to be determined, trace-metals-analysis-
grade concentrated nitric acid should be added to the extract after separation
until the mixture has a pH of less than 2. This prevents precipitation of
trace metals prior Co analysis.
3.4 EXTRACTION PROCEDURE
The overall flow scheme for the MWEP is shown in Figure 3. Detailed
'laboratory procedures are given below.
3.4.1 Extraction 1
Step 1 Mixture Preparation
Using a separate aliquot of the waste, determine the percent solids
content and compensate for differences in wet weight by extracting an amount
of waste equal to 100 g dry weight of sample. Compensate for the amount of
extraction medium added to maintain a 10:1 liquid-to-solid ratio.
15
-------
Solid Waste
Sample
Addition of
Extracting Medium
(Distilled H2O)
18-hr Extraction^
on Rotary
Extractor
Repeat
Extraction
3 Times
©
Liquid/Filtrate
Fraction
1
Solid/Filter
Cake Fraction
Extraction No. 4
-------
Place a 100-g (dry-weight basis) representative sample of the solid waste
that has been prepared for testing (see comments in Section 2.2) in an
extraction vessel (tumbler bottle or equivalent container). Add 1 L of
extraction medium (Section 2.8) to the extraction vessel. (Note: Different
amounts of waste and extraction medium may be used as long as the 10:1
liquid-to-solid ratio is achieved).
Step 2 Tumbling
Tighten the cap on the vessel and mix by tumbling, using the rotary
extractor. Tumble for 18 (±2) hours at room temperature. Stop the rotary
extractor, remove the extraction vessel, and allow the mixture to settle for
15 minutes.
If a discrete water-immiscible layer is present, withdraw the layer using
a syringe with a wide-bore needle. .Transfer the layer to a tared sample
container of suitable material, such as glass. Determine the mass of the
layer and analyze it separately.
Step 3 Separation
Assemble the filter holder and filter pads following the manufacturer's
instructions. Place the 0.45-micrometer nitrocellulose membrane or the glass
microfiber filter pad on the support screen of the filter holder. Place the
nylon mesh screen and then the coarse.glass fiber prefilter pad on top of the
membrane pad so that the coarse pad will be in contact with the filter cake.
After assembling the filtration apparatus, wet the uppermost filter pad
with a small portion of the liquid phase of the extraction mixture. Transfer
the remainder of the extraction liquid to the filtration unit. Take care to
avoid transferring much of the solid from the extraction vessel, because
substantial amounts of solid can clog the filter pads. Apply vacuum or gentle-
pressure (10 to 15 psi) until all liquid passes through the filter.
Stop the filtration when all the liquid has passed through the filter
pads. If this point is not reached under vacuum or using gentle pressure,
then increase the pressure in 10-psi increments to a final may-timim pressure of
75 psi.
If liquid remains above the filter pads after 30 minutes of filtration at
75 psi, halt the filtration by slowly venting the pressurizing gas. Be
certain to follow the manufacturer's instructions for venting a pressurized
filtration apparatus. Some liquid may be trapped in the vent port and may be
released. Care must be taken to direct the vent port away from laboratory
personnel. After venting, decant the liquid above the filter pads into a
suitable container. Place the topmost (coarse) prefilter pad plus any
solid/filter cake into a suitable container, such as the extraction vessel for
use in the next extraction. Replace the filter pads, placing the fresh pads
on the unit in the correct order, and resume filtering the decanted liquid.
Repeat the process of replacing the filter pad as often as necessary
until all of the liquid has been filtered. In each process, retain the
topmost (coarse) prefilter pad along with any solid/filter cake.
17
-------
After completing the filtration, return the unit to atmospheric pressure
by either carefully breaking the vacuum or slowly venting the filtration
apparatus.
Step 4 Solid/Filter Cake
Retain the solid/filter cake after filtration for use in the next
extraction or pending the interpretation of the results obtained from the
procedure. Include the topmost (coarse) prefilter pad from all filtrations,
as stated in Step 3. Use tweezers made of or coated with an inert material to
break apart the filter pads prior to beginning the next extraction.
Step 5 Sample for pH and Inorganic Constituents Analyses
Transfer an aliquot of the liquid/filtrate from Step 4 to a suitable
container, such as a beaker. Determine the pH. If an analysis for inorganic
constituents is needed, add a mirilmum volume of nitric acid (see Section
3.2.2) to lower the pH to less than 2. transfer the acidified sample to a
suitable container, such as a screw-cap polypropylene bottle. Store at room
temperature prior to analysis. Label the sample container including the date,
extraction sequence number, and an appropriate sample identification number.
Step 6 Sample for Semivolatile Organic Constituents Analysis
Transfer an aliquot of the liquid filtrate from Step 4 to be used for
semivolatile organic constituents analysis to a suitable container, such as a
glass bottle with an Teflon® lined screw-cap. Store the sample at 0-5 °C
prior to analysis. Label the sample container properly, including the date,
extraction sequence number, and an appropriate sample identification number.
Step 7 Remainder of Filtrate
Retain any remaining filtrate after samples have been removed for
analysis. After analyses are complete, dispose of the filtrate in accordance
with approved laboratory procedures for disposal of potentially hazardous
liquids.
3.4.2 Extraction 2
Step 8 Mixture Preparation
Place the solid/filter cake from Extraction 1 (Step 5) in an extraction
vessel. Add 1 L of fresh extracting medium to the extraction vessel.
Step 9
Repeat Steps 2 through 8 using the previously extracted solid waste plus
fresh extracting medium mixture.
18
-------
3.4.3 Extraction 3
Step 10 Mixture Preparation
Place the solid/filter cake from Extraction 2 in an extraction vessel.
Add 1 L of fresh extracting medium to the extraction vessel.
Step 11
Repeat Steps 2 through 8 using the previously extracted solid waste plus
fresh extracting medium mixture.
3.4.4 Extraction 4
Step 12 Mixture Preparation
Place the solid/filter cake from Extraction 3 in an extraction vessel.
Add 1 L of fresh extracting medium to the extraction vessel.
Step 13
Repeat Step 2 through 8 using.the previously extracted solid waste plus
fresh extracting medium.
Step 14 Retention of Solid/Filter Cake
Retain the solid/filter cake from Extraction 4 pending a decision on the
need for further extractions.
3.4.5 Further Extractions
The need for further extractions is determined based on interpretation of
the results. Depending on the amount of solid waste that is dissolved during
each extraction, the extraction of the same solid waste sample with fresh
extracting medium can be repeated as many times as needed to satisfy the
objectives of the testing or until solute concentrations of interest are no
longer detectable.
Step 15 Disposal of the Solid/Filter Cake
After all laboratory testing has been completed, the solid/filter cake
be discarded in accordance with approved laboratory procedures for disposal of
potentially hazardous waste.
3.5 ANALYSIS
The samples collected for analysis should be analyzed for the Appendix
VIII constituents of concern by one of the EPA-approved or EPA-proposed
methods. These methods can be found in a variety of references (1,12,13).
The extracts should be analyzed within 7 days after generation.
19
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4.0 QUALITY CONTROL
To ensure that the data generated using the MWEP are of acceptable
quality for the purposes for which they will be used, procedural blanks and
replicate parallel extractions are carried out.
4.1 PROCEDURAL BLANK
The procedural blank extraction is carried out by extracting 1,000 mL of
distilled/deionized water or site-specific extraction medium in an extraction
vessel as if a sample were present. The water that is filtered at the
conclusion of 18 hours of extraction is then analyzed for the Appendix VIII
constituents of interest using the appropriate sample collection,
preservation, preparation, and analysis procedures. The results of the
procedural blank are used to determine if contamination and/or memory effects
are occurring.
Unacceptable contaminant levels are determined bas'ed on the intended use
of the data. If unacceptable levels of Appendix VIII constituents are found
in the final filtered extract of the procedural blank, the individual steps of
the procedure should be investigated to determine the source of the
contamination. For example, prewashing of the prefilters and 0.45-ym filters ^
may be required if contamination from these sources appears to be a problem.
A clean procedural blank must be obtained prior to any waste testing.
A minimum of one procedural blank extraction per five waste sample extractions
per extractor system-per unique extraction medium is to be carried out. If
less than five samples are extracted, then one blank extraction is to be
performed.
4.2 PARALLEL EXTRACTIONS
To assess the extraction precision, three parallel extractions of each
waste are to be carried out. The results are to be reported in terms of the
relative standard deviation (RSD) of the extract levels of the constituents of
interest.
4.3 ASSESSMENT OF ACCURACY
Analyses of each extract for specific constituents should be assessed for /
accuracy by means of standard additions, spiking, and analyses of replicates
as called for in the analytical procedures.
At present, no standard solid waste reference material is available by
which the accuracy of the entire procedure can be assessed. At best, accuracy
can be assessed by extraction of a sample for which a historical data base is
available.
20
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5.0 CONVERSION AND INTERPRETATION OF EXPERIMENTAL DATA
5.1 DATA CONVERSION
Conversion of the experimental data obtained in the extraction
experiments is necessary to estimate the waste extraction characteristics
under laboratory conditions. For interpretative purposes, experimental data
can be converted to concentration and mass of released waste constituents or,
with pertinent assumptions, to constituents released into the extract as a
function of time. Statistical treatment of these data is described in
Appendix B.
5.1.1 Concentration and Mass Release Conversions
The experimental data generated by the MWEP can be converted to (1)
concentration of constituents in the extracts, (2) the mass of constituents
released during each extraction, and (3) the cumulative mass of released
constituents. The following discussion describes methods for converting data
into each of the above forms.
5.1.1.1 Calculation of Concentration in Extract
The data obtained using the MWEP can be used directly in terms of the
concentration of the constituent that was found on analysis of the extract
solution. The general method of calculating this concentration is given in
Equation (1):
C(x)± - C(anal)± x DF (1)
where:
C(x) . = the concentration of constituent x in the extracted
solution from extraction sequence number ±
C(anal). » the concentration of x that was found on analysis
DF = the dilution factor or concentration factor for the
analysis; the dilution factor is the extent to which the
extracted' solution was diluted or concentrated prior to
analysis.
5.1.1.2 Calculation of Mass Per Gram of Waste Released Per Gram of Water Per
Extraction
The mass of the constituent released from the solid waste sample per gram
of waste for each extraction can be calculated by the method given in Equation
(2):
(2)
21
-------
where:
M(x). = the mass of constituent x that was released from the solid
waste sample during extraction sequence number i_ per gram of
waste
S:L = the solid-to-liquid ratio used in the extraction. The volume
in the denominators of both C(x). and S:L must be in the same
units, such as liters or milliliters, that these units will
cancel. The term M(x) . will then have the dimensions of mass
of x released per unit mass of solid waste, such as mg of x per
g of waste.
5.1.1.3 Calculation of Cumulative Mass Released Per Gram of Waste
MWEP data can be used to calculate the cumulative mass of a constituent
released from the solid waste during a series of extractions. The general
method for calculating cumulative mass released is given in Equation (3).
M(x)
CUm
n
Z M(x)
(3)
where:
M(x)
cum
the cumulative mass of constituent x per gm of waste that was
released over the number of extractions (n).
5.1.1.4 . Compilation of Concentration and Mass Release Calculations
A data set of concentration and mass release calculations for a series of
four extractions on one waste sample is presented in Table 3. These data are
representative of data obtained during experimental development of this
procedure.
TABLE 3. CONVERSION OF EXPERIMENTAL DATA
Extraction
sequence
number
1
2
3
4
.
C(anal)
(mg/L)1
4.6
3.8
2.8
2.0
DF
2.0
1.0
1.0
0.5
C(x)1
(mg/L)
9.2
3.8
2.8
1.0
M(x)
(mg/g)
0.092
0.038
0.028
0.010
M(x)
cum
(mg/g)
0.092
0.130
0.158
0.168
22
-------
The results calculated above can also be presented graphically showing
the extraction sequence number versus the concentration of constituent in the
extracted solution. Examples of graphed results are shown in Figure 4, which
presents the data from Table 3. The area under the histograms is
approximately equal to the total mass released.
An alternate way of estimating the releasable mass of constituent is to
fit the data to a curve and integrate the area under the curve. For purposes
of illustration, the data in Figure 4 have been connected by a curve. Details
on one approach to mathematical curve fitting of such data are described in
Jackson et al. (14)
The curve-fitted extraction profiles may be used to estimate the
quantities and concentrations of constituent released at higher
liquid-to-solid ratios than used in the MWEP. For example, in Figure 4 the
curve can be extended beyond the fourth extraction sequence to show the
estimated release concentration and quantity of constituent at a 50:1
liquid-to-solid ratio. These estimates are valid only if the extraction at
these higher liquid-to-solid ratios is governed by the same factors as for the
measured extractions.
Similarly, extractable quantity can be estimated by extending the curve
to intersect the x-axis at concentration - 0. This can be useful in allowing
total extractable quantity to be estimated using a minimum number of
extractions.
Note that whereas extrapolation to higher liquid-to-solid ratios is
possible, extrapolation to lower ratios is not, since the MWEP assumes that
all of the concentrations and mass released by lower ratios are integrated
into the first extraction sequence.
5.1.2 Extraction Profile Analysis
Extraction profiles provide an indication of the concentration level of
analyte in the extract as well as an indication of the buffering capacity of
the waste for maintaining a given constituent concentration in the extract.
Examples of extraction profiles are presented in Figures 5 through 10. These
examples are reproduced from Jackson et al. (14).
In this investigation, four wastes were evaluated: electroplating sludge,
fly ash, filter cake, and polystill bottoms. Figure 5 demonstrates the high
buffering capacity of the electroplating waste at an approximate pH of 8.
Figures 6 and 7 illustrate the effect of repetitive leaching on the solubility
of calcium and copper in the electroplating sludge.
Figure 8 shows the neutralization of fly ash extract as sequential
extractions are made. This effect is due to acidifying SO sorbed onto fly
ash surfaces, which results in a relatively low pH in the first extraction.
Subsequent extractions reflect the buffering capacity of calcium and magnesium
oxides and silicates, which are associated with the structure of the fly ash.
Aluminum in an organic filter cake was found to increase in extract
concentrations with repetitive extraction (Figure 9). This effect may be due
23
-------
10
9
8
7
* —
H
O X
•
Ji5
4
3
2
1 .
1
(10:1)
2
(20:1)
3
(30:1)
4
(40:1)
Extraction Sequence Number (IJquidrSolid Ratio)
Figur* 4. Extraction profile for constituent data in Table 3.
24
-------
fl-
85-
8-
75-
7-
e-5-
6-
5-
45-
PH *'
as-
3-
25-
2-
15 -j
05 -j
••=
^^^••M
^•^M^
^^^^^
_-±:
01234
L/lOOg \Vbste
Rgure 5. pH of extract versus liters of water per 100 g of waste
for electroplating sludge.
25
-------
Vf:
Iff:
Irf-
0 1 2 34
L/lOOg Waste
Figure 6. Calcium concentration in extract versus liters of water
per 100 g of waste for electroplating sludge.
26
-------
600-
0.1 2 3 4
L/lOOg Waste
Rgure 7. Copper concentration in extract versus liters of water
per 100 g of waste for electroplating sludge.
27
-------
PH
B-
75-
7-
65-
6-
55-
5-
45-
4-
35-
3-
25-
2-
15-
1-
05-
/
/
/
y
/
/f
rh
01234
L/lOOgWkste
Rgure S. pH of extract versus liters of water per 100 g of waste for fly ash.
28
-------
icf
Mg/1
Irf
ICf
01234
L/lOOg Waste
Rgure 9. Aluminum concentration in extract versus liters of water
per 100 g of waste for filter cake.
29
-------
id
01234
L/lOOg Waste
Rgure 10. Copper concentration in extract versus liters of water
per 100 g waste for polystill bottoms.
30
-------
to the particle size diminution of the material as well as to increased
wetting due to agitation of the waste.
Copper concentrations in extracts of a polystill bottom waste (Figure 10)
illustrate a constituent that is in a relatively high concentration initially,
but does not have high buffering capacity. The copper concentration dropped
approximately an order of magnitude with each succeeding extraction.
5.2 INTERPRETATION
The utilization of extraction profile analysis for estimating the total
extractable quantity of a waste constituent is shown in the data presented in
Figure 11. The results of 10 sequential extractions of a waste are plotted.
The extraction procedure used was not the MWEP but was a similar procedure
developed by EPA in which a synthetic acid rain mixture was used as extractant
(15,16). In this procedure, waste samples that have been previously extracted
according to the extraction procedure toxicity test, EP (Method. 1310), are
sequentially extracted nine times using a synthetic acid rain extraction fluid
(60/40 weight percent sulfuric acid and nitric acid, pH 3.0 ± 0.2). Each
extraction requires 24 hours and is carried out at a liquid-to-solid ratio of
20:1. The extraction sequence and conditions are designed to simulate the
leaching a waste will undergo due to repetitive precipitation of acid rain on
an improperly designed sanitary landfill. The repetitive extractions reveal
the highest concentration and quantity of each constituent that is likely to
leach in a natural environment. If the concentrations of any of the listed
constituents of concern increase from the seventh or eighth extraction to the
ninth extraction, the procedure is repeated until the*concentrations decrease.
A sequence of 10 extractions requires at least 10 days to complete. If
it could be shown from the extraction profile that the extraction of a
particular constituent was following a trend well before the 9th or 10th
extraction, then considerable time and effort could be saved.
The data in Figure 11 are from a delisting petition submitted to EPA by
General Motors Corporation (CMC) for exclusion of the treatment residue
generated from the use of the Chemfix® treatment process on electroplating
operations. The residue was contained in onsite surface impoundments. The
results of the sequential extractions for cadmium, hexavalent chromium, and
nickel indicated that the treatment residue exhibited long-term stability by
extracting nonhazardous levels of these elements after multiple synthetic acid
rain extractions. However, the extraction profile in Figure 11 indicates that
after the 4th extraction, a trend is clearly established that allows
estimation of the total extractable mass of chromium without the need for
performing these additional extractions. While this type profile will not
always be obtained, the user of the MWEP should take advantage of this data
presentation method to minimize the effort required to obtain the needed
extraction information.
The profile illustrated in Figure 4 may be encountered when the
constituent is steadily depleted from the solid waste. Each subsequent
extraction releases more of the constituent, although the mass released per
extraction decreases with each extraction. Other profiles that might be
encountered would show such trends as (1) a steady release where each
extraction releases essentially the same amount and (2) a delayed release.
where initially little or none of the constituent was released, followed by
31
-------
400
300.
c
o
« 200 .
I
o
U
«*
8
«*
x
IU
100 -
466
Extraction No.
8
10
Rgure 11. Extraction profile of Cr from electroplating sludge.
32
-------
large increases in the amount released when alkalinity is leached and pH
decreases, allowing metals to go into solution.
A decision on the need for further extractions will depend on the
profiles obtained for the initial sequence of extractions plus the specific
needs of the research being conducted. The application of the results to
events in a landfill environment depends on site-specific information such as
infiltration rate for rainfall and the density of the waste.
In general, the Interpretation of the results involves comparisons of the
concentration of mass-released profiles of the various constituents that have
been examined. The technical resource documents (TRD's) discussed in Section
1 provide guidance on leachate flow rate calculations (see in particular TRD2,
"Hydrologic Simulation on Solid Waste Disposal Sites [SW-868]," TRD3,
"Landfill and Surface Impoundment Performance Evaluation [SW-869]," and TRD5,
"Management of Hazardous Waste Leachate [SW-871]." These documents plus the
studies on leachate generation by Houle and Long (17, 18) are additional
sources for information on calculations and interpretation of leachate test
data.
5.3 CALCULATION OF-TIME REQUIRED FOR FIELD LEACHING
A simple model was developed to infer a time dimension to the extraction
profile generated by the MWEP. A hypothetical field environment was assumed
for the purpose of determining how many years of constant leaching would be
required for the extractable constituents, as indicated by the MWEP, to be
released into the environment. The model is based on-a "worst-case" scenario
and assumes that the waste constituents in the leachate reflect the same
concentrations as those produced by the sequential leaching of the MWEP.
The amount of time required in the field to collect a volume of leachate
comparable to that in each extraction sequence can be computed from the
experimental data assuming the .following:
o Primary leachate volume in the waste is disregarded. This
assumption is necessary because primary leachate is mixed with the
extraction media in the first sequential extraction of the MWEP.
o Depth of waste is fixed and known.
o The concentration of solutes in the waste is assumed to follow the
extraction profile produced by the MWEP as the waste is leached over
time.
o Waste is a monofill and is saturated with water at the time of
disposal. This assumption was made to simplify the analytical
solution of the model.
Some wastes, as disposed, contain interstitial liquids having high
concentrations of solutes that may be displaced as .undiluted leachates early
in the leaching process. This leachate has been classified as primary in
contrast to secondary, which is reflective of solutes dissolved in percolating
water of external origin, such as precipitation (19).
33
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Based on these assumptions* the equation for calculating the time
corresponding to each leaching fraction is presented below:
LT - (DW . p . LSR (I . Pwafcfir) (4)
where:
LT • Leaching time (years to exceed extraction sequence, i.e.,
to exceed 1:10, 1:20, 1:30 ratio, etc.)
DW - Depth of fill (cm)
„ * t i 3«
p - Density of waste (g/cm )
waste
LSR - Liquid-to-solid ratio of MWEP
I = Infiltration rate (cm/s)
3
p - Density of water (g/cm )
A representative case has been devised to illustrate use of this
equation. Let:
DW - 610 cm
"waste - L3 g/cm3
LSR =10:1
I - 1 x 10~7 cm/s
Pwater = 1'° *lca?
LT - (610 cm * 1.3 g/cm3 * 10)/(I x 10~7cm/s * 1.0 g/cm3)
= 2,517 years
Thus, the leaching time in the field corresponding to the first leaching
sequence is 2,517 years using the 1 x 10~ cm/s infiltration rate.
The usefulness of this computation is illustrated in Table 4.
Calculations are presented for four leaching sequences and five infiltration
rates. For example, the time corresponding to the first extraction sequence
ranges from 25 years to 250,000 for infiltration rates of 10~ cm/s and 10~
cm/s, respectively, at a depth of waste fill of 6.1 m. The results of these
time calculations, as shown in Table 4, demonstrate the extremely long time
(in terms of landfill life) associated with each extraction sequence. In most
cases, the initial extraction sequence will provide an estimate of the
leachate fraction of prime interest. These calculations presume that the
infiltration rate determines the flow of leachate through the fill.
34
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TABLE 4. TIME REQUIRED TO EXCEED SPECIFIC EXTRACTION SEQUENCE
FOR SELECTED CAP INFILTRATION RATES (DEPTH OF WASTE = .610 cm)
Extraction Time corresponding to sequence at selected infiltration rates (years)
sequence _5 _, _? _.
number 10 cm/s 10 cm/3 10 cm/s 10 cm/s 10 on/s
1
2
3
4
25
50
75
100
250
500
750
1,000
2,500
5,000
7,500
10,000
25,000
50,000
75,000
100,000
250,000
500,000
750,000
1,000,000
35
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6.0 REFERENCES
1. U. S. Environmental Protection Agency. Office of Solid Waste,
Washington, D. C. July 1982. Test Methods for Evaluating Solid Wastes,
SW-846, Method 1310 Second Edition.
2. Federal Register, Vol. 51., No. 9, Tuesday, January 14, 1986. 1750-1758,
40 CFR Parts 260, 261, 262, 264, 265, 268, 270, 271. Hazardous Waste
Management System: Land Disposal Restrictions: Appendix T- Toxicity
Characteristic Leaching Procedure (TCLP).
3. Perket, C. L. and W. C. Webster. Literature review of batch laboratory
leaching and extraction procedures. In: Hazardous Solid Waste Testing:
First Conference, ASTM STP 760. R. A. Conway and B. C. Malloy, Eds.,
American Society For Testing and Materials, 1981. pp. 7-27.
4. Cote, P. A proposed procedure for the development of a Canadian data
base on waste leachability. Environment Canada, Burlington, Ontario, pp
1-24. 1981.
5. Lowenbach, W. Compilation and evaluation of leaching test methods.'
EPA-600/2-78-095, U. S. Environmental Protection Agency, Cincinnati, Ohio,
1978. Ill pp.
6. Ham, R., M. A. Anderson, R. Stegmann, and R. Stanforth. Background
study on the development of a standard leaching test. EPA-600/2-78-109,
U. S. Environmental Protection Agency, Cincinnati, Ohio, 1979. 274 pp.
7. American Society for Testing Materials. 1984 Annual Book of Standards,
Volume 11.01: Water. ASTM D1193-77 (83). Philadelphia, Pennsylvania.
8. Fluker, B. J. Soil temperature. Soil Sci. 86:35-46, 1958.
9. Epler, J. L., et al. Toxicity of leachates. IAG No.
DOE-IAG-40-646-77/EPA-IAG-78-D-X0372. Interim Progress Report to U. S.
Environmental Protection Agency, Oak Ridge National Laboratory, Oak Ridge,
Tennessee, 1979.
10. Epler, J. L., et al. Toxicity of leachates. EPA-600/2-80-057, U. S.
Environmental Protection Agency, Cincinnati, Ohio, 1980. 142 pp.
11. Warner, J. S., B. J. Hidey, G. A. Jungclaus, M. M. McKown, M. P. Miller,
and R. M. Riggin. Determining the leachability of organic compounds from
solid wastes. In: Hazardous Solid Waste Testing: First Conference,
ASTM STP 760. R. A. Conway and B. C. Malloy, Eds., American Society for
Testing and Materials, 1981. pp. 40-60.
12. Federal Register, Vo. 49., No. 290, Friday, October 26, 1984, 43234, 40
CFR Part 136, Guidelines Establishing Test Procedures for the Analysis of
Pollutants Under the Clean Water Act.
36
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13. 0. S. Environmental Protection Agency. March 1983. Methods for chemical
analysis of water and wastes. EPA-600/4-79-020.
14. Jackson, D. R., B. C. Garrett, and T. A. Bishop. Comparison of batch and
column methods for assessing leachability of hazardous waste. Environ.
Sci. Technol. 18:668-673. 1984.
15. U. S. Environmental Protection Agency. 1984. Multiple Extraction
Procedure. Proposed sampling and analytical methodologies for addition
to test methods for evaluating solid vaste: Physical/Chemical methods
(SW-846, Method 1320, 2nd Edition) p. 209-210.
16. Federal Register, Vol. 50., No. 229, Wednesday, November 27, 1985.
k48911-48926, 40CFR Part 261, Hazardous Waste Management System;
• Identification and Listing of Hazardous Waste, Proposed Rule and Request
for Comments.
17. Houle, M. J., and D. E. Long. Accelerated testing of waste leachability
and contaminant movement in soils. In: Land Disposal of Hazardous
Wastes: Proceedings of the Fourth Annual Research Symposium, at San
Antonio, Texas, March 6-8, 1978. EPA-600/9-78-016, 0. S. Environmental
Protection Agency, Cincinnati, Ohio, 1978. pp 152-168.
• •
18. Houle, M. J., and D. E. Long. Interpreting results from serial batch
extraction tests of wastes and soils. In: Disposal of Hazardous Waste:
Proceedings of the Sixth Annual Research Symposium, at Chicago, Illinois,
March 17-20, 1980. EPA-600/9-80-010. 0. S. Environmental Protection
Agency, Cincinnati, Ohio, 1980. pp 60-81.
19. Brown, K. W., and D. Anderson. Effect of organic chemicals on clay liner
permeability. In: Disposal of -Hazardous Waste: Proceedings of the
Sixth Annual Research Symposium, EPA-600/9-80-010, U. S. Environmental
Protection Agency, Cincinnati, Ohio, 1980. pp 123-124.
37
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APPENDIX A
GENERATION OF SITE-SPECIFIC EXTRACTION MEDIUM
Objective - Co generate a site-specific extraction medium.
The approach used in generation of the site specific extraction medium is
shown in Figure A-l.
The primary extraction medium should simulate the typical precipitation
falling on the site. Rainfall collected at the site is inappropriate for this
purpose. It is likely to be unrepresentative of the long-term rainfall (over
a period of years). For example, although brief rainstorms may produce little
rain, the rain that is produced may be much more acidic then storms of longer
duration which would dissolve and rain out the same ions but in a much greater
volume of water.
A synthetic precipitation mixture should be prepared based on historical
data, which can be obtained from the EPA Acid Deposition System, a
computerized data base of acid precipitation data from several long-term
monitoring networks (1). The synthetic precipitation sample can be prepared
by dissolving high-purity salts and acids in high-purity distilled/deionized
water as described by Deardorff et al. (2). This mixture will contain the
average levels of cations and anions reported in the historical monitoring
data for the general area around the proposed landfill. The mixture will also
have a pH based on these data. It is likely that only the acidity of the
synthetic precipitation sample will have a significant impact on the leaching
of the waste, and this may be minimal if the soil cover that is leached first
has a buffer capacity sufficient to neutralize the precipitation acidity. If
soil is to be used in the fill as cover material, it is extracted first and
the extract used as the solution to carry out the first extraction of the
waste. If layers of soil are placed on the waste intermittently, waste
extracts should be used to extract the soil in a sequence that simulates the
field situations.
This soil should be of the same type and be present in the same
proportion as that encountered at the disposal site. The ability of soils to
alter the mobility of species in leachates is well known and has been studied
extensively for various types of soils and wastes. For example, the extent to
which trace inorganic constituents of leachates are attenuated is related to
the amounts and types of clay and iron and manganese hydrous oxides in the
soil (3, 4); and attenuation of organic compounds such as PCB's is directly
related to the organic carbon content of the soil (5). Furthermore, soil type
influences complexing agents and colloidal constituents present in & leachate
and soil mixture. Where soil is to be mixed with the waste and not used to
cover it forming distinct layers, then this admixture should be extracted.
Where the solid waste disposal plan precludes the use of soil during active
filling, no soil is used in the extraction procedure. Where appropriate,
both the intermittent cover material and the material proposed for site
closure can be tested along with the waste.
38
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SOIL COVER MATERIAL,
100
EXTRACT FOR 18 HOURS WITH SITE-
SPECIFIC PRECIPITATION MIXTURE,
1,000 wL
LIQUID/SOLID SEPARATION
0.6-0.8 um
GLASS FIBER FILTERS
DISCARD- SOLIDj
LIQUID USED
TO EXTRACT WASTE
Figure A-1. Generation of site-specific extraction medium.
39
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REFERENCES
1. Watson, C. R., and A. R. (XLsen, Acid deposition system (ADS) for
statistical reporting—system design and users code manual.
EPA-600/8-84-023. September 1984.
2. Deardorff, E. R., T.C. Rains, and W. F. Koch. Simulated precipitation
reference materials, III. Prepared by NBS for USEPA and USGS,
NBSIR-1953. September 1980. 21 pp.
3. Fuller, W. H. Investigation of landfill leachate pollutant attenuation
by soils, EPA-600/2-78-158, U. S. Environmental Protection Agency,
Cincinnati, Ohio, 1978. 239 pp.
4. Griffin, R. A., and N. F. Shrimp. Attenuation of pollutants in municipal
landfill leachate by clay minerals. EPA-600/2-78-157, U. S. Environmental
Protection Agency, Cincinnati, Ohio, 1978. 157 pp.
5. Griffin, R. A., and E. S. K. Chian. Attenuation of water-soluble
polychlorinated biphenyls by earth materials. EPA-600/2-80-027, U. S.
Environmental Protection Agency, Cincinnati, Ohio, 1980. 101 pp.
40
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APPENDIX B
STATISTICAL EVALUATION OF MONOFILLED SOLID WASTE EXTRACT DATA
A statistical evaluation of data generated from the MWEP is needed to
ensure the quality of interpretive information obtained from this procedure.
As part of the development of the MWEP, a statistical model was developed for
the purpose of analyzing the various components of error associated with the
procedure.
Central to the concept of statistical evaluation of a leachate generation
method is the analysis of an extraction "profile." It is likely that leachate
produced from a waste disposal site changes in composition over time. This
process is a function representing the concentration of a chemical species.
The MWEP was designed to produce this profile, which would take several years
in the field environment, by accelerating the release of chemical species as a
function of repetitive extractions with distilled water. Thus, in the
laboratory procedure the extraction profile consists of a plot of constituent
concentration versus liquid-to-solid ratio or the number of repetitive
extractions.
An extraction profile is characterized using the MWEP based on a series
of batch extractions. This laboratory extraction procedure involves
subsampling from a -grab sample obtained from the waste, extracting the sample
of waste, filtering to obtain a liquid filtrate and a solid filter cake, and
finally analyzing the concentration of important analytes'in the filtrate.
The leaching process is repeated several times using the filter cake obtained
from the previous trial to obtain a characteristic extraction profile for a
given waste sample.
There are several important sources of experimental variation that can
affect the results of this type of leachate generation method. Significant
variation may be associated with (1) subsampling the grab sample of the waste,
(2) the extraction procedure, and (3) the chemical analysis process. Sampling
of the original waste is recognized as probably being the major source of
experimental variation. However, for the purpose of this discussion, it will
be assumed that a representative grab sample of the waste was collected. The
grab sample usually can be carefully mixed so that sub-sampling variance is
small.
Objectives of the statistical analysis of data collected from an
extraction method include:
o Estimating the extraction profile function;
o Comparing the extraction* profile functions across different types of
waste;
o Estimating components of variation associated with waste sampling
and extraction and chemical analysis.
41
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These objectives can be accomplished through the use of a statistical
model that characterizes the data generated by the extraction experiments.
The statistical model is based on the assumption that a function B(k) exists
that, apart from uncontrollable experimental variation, estimates the amount
of analyte extracted from a sample with each successive extraction (k) .
The function jJ(k) describes only the deterministic mechanism affecting
the leaching process at successive extraction number k. The complete
statistical model would also include the error structure describing the
important sources of experimental variability, such as subsampling,
extractions, and chemical analysis. The level of detail required to
completely describe the development of the appropriate form for S(k) and the
error structure is too complex to describe in this appendix.
A simplified version of the complete statistical model is a mixture of
fixed and random effects and is given by:
where
Xikn ' 8(k) + Si + Yik + eikn
X,. « the observation recorded for the nth analysis for the kth
extraction of the ith subsample of the waste
S. = the random error due to subsampling
Y.. = the random error due to extraction
e . =• the random error due to chemical analysis.
The usual distribution assumptions for the random model components are:
S± * N (0, (Jg)
Yik * N (°' aL)
and
eikn * N (°* V
2
where X *• N (u, a ) indicates a random variable distributed normally with mean
v and variance a2.
Standard statistical techniques can be used to estimate the profile .
222
function 6(k) and the variance components o OT a . Because the total
o w £
42
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variance of the observed data vlto is given by:
2 2' + a2 + o2 ,
aY = °S L e
the relative percent contribution of each source of variability to the total
variability in Y can be estimated. For example, the percent relative
contribution of subsampling to-the total variation is given by:
RV (Subsampling) - 0* /a* x 10
Figure B-l and Table B-l provide examples of the type of information
that is obtained from the statistical analysis of a leaching method. Figure
B—1 displays data obtained on the level of chromium contained in the leachate
obtained from a 100-percent chromate waste for six successive extractions.
The smooth curve superimposed on the data is the estimated extraction profile
function 6(k).
Figure B-2 compares the leachate profiles for the analyte chromium
extracted from a landfill soil and a chromate waste. Table B-l presents the
estimates for the variance components and their relative contribution to the .
total variability for the two types of waste and for eight constituents.
43
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240
180-
Chromium (fig/I)
120-
60-
\
TWO OR MORE DATA POINTS
l ONE DATA POINT
I I
2 4
Extraction Number
I
6
Figure B-1. Extraction profile with data for 100% chromate waste.
44
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300
770-
Extract ion Numbtr
Figure B-2. Comparison of 100% landfill soil
and 100% chromate waste profiles.
45
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TABLE B-l. ESTIMATES OF THE PERCENT RELATIVE VARIATION FOR THE
LANDFILL AND 100Z CHROMATE WASTES
100Z Landfill Soil
100% Chrornate Waste
Analyte
Boron
Barium
Calcium
Chromium
Magnesium
Sodium
Strontium
Zinc
Mean
PRV
0
4
0
9
0
4
0
0
2
PRV_
L>
58
95
91
47
97
61
97
78
78
PRVE
42
1
9
44
3
35
3
22
20
PRV
3
6
0
37
4
38
0
36
0
15
PRVL
43
100
*
62
56
61
81
. 61
78
68
PRVE
51
0
1
40
1
19
4
22
17.
PRV = percent relative variation due to laboratory subsampling
PRV
PRV,
percent relative variation due to laboratory analyses
percent relative variation due to extraction
This information is valuable in making comparisons between waste types
and analytes. For example, from Figure B-2 it is clear that the extraction
profiles for the landfill soil and chromate wastes have similar shapes, but
the level of chromium extracted from the landfill soil is much, less than from
the chromate waste. Results in Table B-l indicate that the greatest source of
variability is the extraction procedure for both landfill soil and chromate
waste. This result may be due to the potential error associated with
performance of the sequential extractions, such as filtering and mixing of the
waste. In addition, the contribution of the subsampling to the total
variation in the data appears to be greater for the chromate waste than for
the landfill soil, indicating the soil is more uniformly mixed.
Specific comparisons can also be made. For example, results shown in
Table B-l indicate th.at the percent relative variation associated with the
chemical analysis (a e) for boron in the chromate waste is significantly
greater (51 percent on a relative basis) than that for calcium (1 percent on a
relative basis).
46
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APPENDIX C
Item
SUPPLIERS
Suppliers
1. NBS Tumbler
2. Membrane Filters
3. Glass Fiber Filters
Associated Design and Manufacturing Company
814 North Henry Street
Alexandria, VA 22314
(703) 549-5999
Millipore Corporation
Asbby Road
Bedford. MA 01730
(800) 225-1380
Nuclepore Corporation
7035 Commerce Circle
Pleasanton, CA 94566
(415) 462-2230
Gelman Sciences, Inc.
600 South Wagner Road
Ann Arbor, MI 48106
47
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